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Encyclopedia of materials characterization

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ENCYCLOPEDIA OF MATERIALS CHARACTERIZATION C. Richard Brundle Charles A. Evans, Jr. Shaun Wilson a MAT E R I A L S CHARACTER S E R I E S S U R F A C E S , I N T E R F A C E S , T H I N F I L M S +
ENCYCLOPEDIA OF MATERIALS CHARACTERIZATION
MATERIALS CHARACTERIZATION SERIES Surfaces, Interfaces,Thin Films SeriesEditors: C. Richard Brundleand CharlesA. Evans,Jr. SeriesTitles Encyclopedia of Materiah Characterization, C. Richard Brundle, CharacterizationofMekth andAlloys,Paul.H. Hollowayand P. N. Characterizationof Ceramics,Ronald E. Loehman CharacterimtionofPobmers, Ned J. Chou, Stephen P. Kowalczyk, Characterizationin SiliconProcessing,Yale Strausser Characterizationin CompoundSemiconductorProcessing, Yale Strausser CharacterizationofIntegraedCircuitPackagingMateriah, ThomasM. Moore and Robert G. McKenna CharacterizationofCadyticMateriah,IsraelE. Wachs Characterizationof CompositeMateriah,Hatsuo Ishida Characterizationof OpticalMateriah,Gregory J. Exarhos Characterizationof TribologicalMateriah,William A. Glaeser Characterizationof Organic ThinFilms,Abraham Ulman Charlesk Evans,Jr., and ShaunWilson Vaidyanathan Ravi Sard, and Ho-Ming Tong
ENCYCLOPEDIA OF MLATERIALS CHARACTERIZATION Surfaces, Interfaces, Thin Films EDITORS C Ricbard Brundle CharlesA. Evans,Jr. SbaunWihon MANAGINGEDITOR LeeE. Fitzpatrick BUTTERWORTH-HEINEMANN Boston London Oxford Singapore Sydney Toronto Wellington MANNING Greenwich
Thisbookwas acquired, developed,andproducedbyManningPublicationsCo. CopyrightQ 1992byButxetworch-Heinemann,adivisionofReedPublishingCUSA) Inc Au rightsr a d Noparcofthispublicarionmay be reproduced,scoredinaretriedsystem, ortransmitted, in anyform orbymeans. electronic, mechanical,photocopying, ororherwise, without prior writtenpermissionofthe publisher. Recognizingthe importanceof preservingwhat has beenwritten,it is thepolicyof Butterworth-Heinemannand ofManningto have the bookstheypublishprintedon acid-free paper, and weexertour best &m to that end. LibraryofCongressCataloging-in-Publication Data Brundle, C. R. Encyclopediaofmaterialscharacterization:surfaces,interfaces,thin films/C. Richard Brundle, CharlesA. Evans, Jr., ShamWilson. p. un.--(Materials characterizationseries) Indudesbibliographicalrefrrenoaand index. ISBN CL7506-9168-9 1.Surfaces(Tedmoology)-Tes~ I. Evans,Charlak 11.Wilson,Shaun. 111.Title. IV.Series. TA418.7.B73 I992 92-14999 620’.4Pdc20 CIP Butterworth-Heinemann 80MontvaleAvenue Stoneham,MA02180 ManningPublications Co. 3h i s Street Greenwich,CT 06830 1 0 9 8 7 6 5 4 3 Printedin the Unired StatesofAmerica
Contents Prefaceto Series ix Preface x Acronyms Glossary xi Contributors xvi INTRODUCTIONAND SUMMARIES 1.0 Introduction I Technique Summaries 7-56 IMAGING TECHNIQUES(MICROSCOPY) 2.0 Introduction 57 2.1 Light Microscopy 60 2.2 ScanningElectron Microscopy, SEM 70 2.3 ScanningTunneling Microscopyand 2.4 TransmissionElectron Microscopy,TEM 99 ScanningForce Microscopy, STM and SFM 85 ELECTRONBEAM INSTRUMENTS 3.0 Introduction 117 3.1 Energy-DispersiveX-Ray Spectroscopy,EDS 120 3.2 Electron Energy-Loss Spectroscopyin the Transmission Electron Microscope,EELS 135 3.3 Cathodoluminescence, CL 149 3.4 ScanningTransmission Electron Microscopy, STEM 161 3.5 Electron Probe X-Ray Microanalysis,EPMA 175 V
STRUCTUREDETERMINATIONBY DIFFRACTIONAND SCATTERING 4.0 Introduction 193 4.1 X-Ray Diffraction, XRD 198 4.2 ExtendedX-Ray Absorption Fine Structure,EXAFS 214 4.3 Su&ce ExtendedX-Ray Absorption Fine Structureand Near EdgeX-Ray Absorption Fine Structure,SEXAFS/NEXAFS Auger Electron Difiction, XPD and AED 227 4.4 X-Ray Photoelectron and 4.5 Low-Energy Electron Diffraction, LEED 252 4.6 Reflection High-EnergyElectron Diffraction,WEED 264 240 ELECTRONEMISSIONSPECTROSCOPIES 5.0 Introduction 279 5.1 X-Ray Photoelectron Spectroscopy,XPS 282 5.2 Ultraviolet Photoelectron Spectroscopy,UPS 300 5.3 Auger Electron Spectroscopy,AES 310 5.4 ReflectedElectron Energy-loss Spectroscopy, REELS 324 X-RAYEMISION TECHNIQUES 6.0 Introduction 335 6.1 X-Ray Fluorescence,XRF 338 6.2 Total Reflection X-Ray FluorescenceAnalysis, TXRF 349 6.3 Particle-InducedX-Ray Emission, PIXE 357 VISIBLE/W EMISSION, REFLECTION,AND ABSORPTION 7.0 Introduction 371 7.1 Photoluminescence,PL 373 7.2 Modulation Spectroscopy385 7.3 VariableAngle SpectroscopicEllipsometry, VASE 401 VIBRATIONALSPECTROSCOPIESAND NMR 8.0 Introduction 413 8.1 Fourier Transform Infrared Spectroscopy,FTIR 416 8.2 RamanSpectroscopy 428 8.3 High-Resolution Electron Energy Loss Spectroscopy,HREELS 4-42 8.4 Solid State Nuclear Magnetic Resonance, NMR 460 vi Contents
ION SCATTERINGTECHNIQUFS 9.0 Introduction 473 9.1 Rutherford BackscatteringSpectrometry,RBS 476 9.2 Elastic Recoil Spectrometry,ERS 488 9.3 Medium-EnergyIon Scatteringwith Channelingand Blocking,MEIS 502 9.4 Ion scattering Spectroscopy,Iss 514 MASSAND OPTICALSPECTROSCOPIES 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 Introduction 527 Dynamic SecondaryIon MassSpectrometry,Dynamic SIMS StaticSecondaryIon Mass Spectrometry,StaticSIMS 549 SurficeAnalysis by h e r Ionization, SAL1 SputteredNeutral Mass Spectrometry,SNMS Laser Ionization Mass Spectrometry,LIMS SparkSourceMass Spectrometry,SSMS 598 Glow-DischargeMass Spectrometry,GDMS 609 InductivelyCoupled Plasma Mass Spectrometry,ICPMS InductivelyCoupled Plasma-Optical Emission Spectroscopy,ICP-OES 633 532 559 586 571 624 NEUTRONANDNUCLEARTECHNIQUES 1'1.0 Introduction 645 11.I Neutron Diffraction 648 11.2 Neutron Reflectivity 660 11.3 Neutron ActivationAnalysis, NAA 671 11.4 Nuclear ReactionAnalysis, NRA 680 PHYSICALAND MAGNETICPROPERTIES 12.0 Introduction 695 12.1 SurfaceRoughness:Measurement, Formation by Sputtering,Impact on Depth Profiling 698 12.2 Optical Scatterometry 711 12.3 Magneto-optic Kerr Rotation, MOJSE 723 12.4 Physical and ChemicalAdsorption Measurement of Solid SurfaceAreas 736 Contents vii
Prefaceto Series This Materialj CharacterizationSeries attempts to address the needs of the practi- cal materials user, with an emphasis on the newer areas of surfice, interface, and thin film microcharacterization. The Series is composed of the leading volume, Enychpedia of Materialj Characterization,and a set of about 10 subsequent vol- umes concentratingon characterizationof individualmaterials classes. In the Encyclopedia, 50 brief articles (each 10-18 pages in length) are presented in a standard format designed for ease of reader access, with straightforward technique descriptionsand examples of their practical use. In addition to the arti- cles, there are one-page summaries for every technique, introductory summaries to groupings of related techniques, a complete glossary of acronyms, and a tabu- lar comparisonof the major features of all 50techniques. The 10volumes in the Series on characterizationof particular materials classes include volumes on silicon processing, metals and alloys, catalytic materials, integrated circuit packaging, etc. Characterization is approached from the mate- rials user’s point of view. Thus, in general, the format is based on properties, pro- cessing steps, materials classification, etc., rather than on a technique. The emphasis of all volumes is on surfaces, interfaces, and thin films, but the emphasis varies depending on the relative importance of these areas for the materials class concerned. Appendixes in each volume reproduce the relevant one-page summa- ries from the Encyclopedia and provide longer summaries for any techniques referred to that are not coveredin the Envcbpedia The concept for the Seriescame firom discussionwith Marjan Bace of Manning Publications Comparly. A gap exists between the way materials characterization is often presented and the needs of a large segment of the audience-the materials user, process engineer, manager, or student. In our experience,when, at the end of talks or courses on analytical techniques, a question is asked on how a particular material (or processing) characterization problem can be addressed the answer often is that the speaker is “an expert on the technique, not the materials aspects, and does not have experience with that particular situation.” This Series is an attempt to bridge this gap by approaching characterization problems from the sideof the materials user rather than from that of the analyticaltechniquesexpert. We would like to thank Marjan Bace for putting forward the original concept, Shaun Wilson of Charles Evans and Associates and Yale Strausser of Surface Sci- ence Laboratories fbr help in hrther defining the Series, and the Editors of all the individual volumes for their efforts to produce practical, materials user based volumes. C R Brundle C.A.Evans,Jr. ix
This volume contains 50 articles describing analytical techniques for the charac- terization of solid materials, with emphasis on surfaces, intedices, thin films, and microanalyticalapproaches. It is part of the Materzah CharacterizationSeries, copublishedby Buttenvorth-Heinemann and Manning. Thisvolumecan serveasa stand-alone reference as well as a companion to the other volumes in the Series which deal with individual materials classes. Though authored by professional characterization experts the articles are written to be easily accessible to the materialsuser, the processengineer,the manager, the student-in shortto all those who arenot (andprobablydon’t intend to be) expertsbut who need to understand the potential applications of the techniques to materials problems. Too often, techniquedescriptions arewritten for the techniquespecialist. With 50 articles, organization of the book was difficult; certain techniques could equally well have appeared in more than one place. The organizational intent of the Editors was to group techniques that have a similarphysical basis, or that provide similar types of information. This is not the traditional organiza- tion of an encyclopedia,where articles are ordered alphabetically.Such ordering seemedless useful here, in part because many of the techniqueshave multiple pos- sible acronyms(anAcronym Glossavyis provided to help the reader). The articles follow a standard format for each technique: A clear description of the technique, the range of information it provides, the range of materials to which it is applicable, a few typical examples, and some comparison to other related techniques. Each technique has a “quickreference,” one-page summary in Chapter 1,consistingof a descriptiveparagraph and a tabular summary. Some of the techniques included apply more broadly than just to surhces, interhces, or thin films; for example X-Ray Diffraction and Infrared Spectros- copy, which have been used for half a century in bulk solid and liquid analysis, respectively.They are included here because they have by now been developed to also apply to surfaces. A fay techniques that are applied almost entirely to bulk materials (e.g., Neutron Diffraction) are included because they give complemen- tary information to other methods or because they are referred to significantlyin the 10 materials volumes in the Series. Some techniques were left out because they were consideredto be too restricted to specificapplicationsor materials. We wish to thank all the many contributorsfor their efforts, and their patience and restraint in dealing with the Editors who took a hirly demanding approach to establishingthe format, length, style, and content of the articles. We hope the readers will consider our efforts worthwhile. Finally, we would like to thank Lee Fitzpatrick of Manning Publications Co. for her professional help as Managing Editor. C.R.Brund. CA.Evans,/r. S.Mhon
Acronyms Glossary This glossary lists all the acronyms referred to in the encyclopedia together with their meanings. The major technique acronyms are listed alphabetically. Alter- natives to these acronyms are listed immediately below each of these entries, if they exist. Related acronyms (variations or subsets of techniques; terminology used within the technique area) are grouped together below the major acronym and indented to the right. Most, but not all, of the techniques listed here are the subject of individual articlesin this volume. AAS AA VPD-AAS GFAA FAA AES Auger S A M SAM AED ADAM K.E CMA AIS BET BSDF BRDF BTDF CL CLSM EDS EDX EDAX EELS HEELS REELS REELM EELS AtomicAbsorption Spectroscopy AtomicAbsorption Vapor Phase Decomposition-AtomicAbsorption Spectroscopy GraphiteFurnaceAtomicAbsorption Flame AtomicAbsorption Auger ElectronSpectroscopy Auger Electron Spectroscopy ScanningAuger Microscopy ScanningAuger Microprobe Auger Electron Diffraction Angular DistributionAuger Microscopy KineticEnergy CylindricalMirror Analyzer Atom InelasticScattering Brunauer, Emmett, andTeller equation BidirectionalScatteringDistribution Function BidirectionalReflective Distribution Function BidirectionalTransmissionDistribution Function Cathodluminescence ConfocalScanningLaser Microscope Energy Dispersive(X-Ray) Spectroscopy Energy DispersiveX-Ray Spectroscopy CompanysellingEDX equipment Electron EnergyLossSpectroscopy High-ResolutionElectronEnergy-Loss Spectroscopy ReflectedElectronEnergy-Loss Spectroscopy ReflectionElectronEnergy-Loss Microscopy Low-Energy Electron-LossSpectroscopy xi
PEELS EXELFS EELFS CEELS VEELS EPMA ElectronProbe ERS HFS HRS FRS ERDA ERD PRD EXAFS SEXAFS NEXAFS XANES XAFS FMR FTIR FT Raman HREELS HRTEM GDMS GDQMS Gloquad ICP-MS ICP LA-ICP-MS ICP-Optical ICP IETS IR FTIR GC-FTIR TGA-FTIR ATR Parallel (Detection)ElectronEnergy-LossSpectrscopy ExtendedEnergy-Loss Fine Structure ElectronEnergy-Loss FineStructure CoreElectronEnergy-Loss Spectroscopy ValenceElectronEnergy-Loss Spectroscopy Electron ProbeMicroanalysis ElectronProbeMicroanalysis ElasticRecoil Spectrometry HydrogenForwardScattering Hydrogen Recoil Spectrometry ForwardRecoil Spectrometry ElasticRecoil DetectionAnalysis ElasticRecoilDetection ParticleRecoilDetection ExtendedX-RayAbsorptionFine Structure SurfaceExtendedX-RayAbsorptionFine Structure Near-EdgeX-RayAbsorptionFine Structure X-Ray AbsorptionNear-Edge Structure X-RayAbsorptionFine Structure FerromagneticResonance See IR SeeRaman See EELS SeeTEM Glow DischargeMass Spectrometry Glow DischargeMassSpectrometryusing a QuadrupleMassAnalyser Manufacturername InductivelyCoupledPlasma Mass Spectrometry InductivelyCoupled Plasma Laser Ablation ICP-MS InductivelyCoupledPlasma OpticalEmission InductivelyCoupledPlasma InelasticElectronTunnelingSpectroscopy Infrared(Spectroscopy) FourierTransformInfra-Red (Spectroscopy) Gas ChromatographyFTIR Thermo GravimetricAnalysisFTIR ArtenuatedTotalReflection xii Acronyms Glossary
RA IRAS ISS LEIS RCE LEED LIMS LAMMA LAMMS LIMA NRMPI MEISS MEIS MOKE SMOKE NAA INAA NEXAFS XANES NIS NMR MAS NRA OES PAS PIXE HIXE PL PLE PR EBER RDS Raman FT Raman RS RRS CARS ReflectionAbsorption (Spectroscopy) Infrared ReflectionAbsorption Spectroscopy Ion ScatteringSpectrometry Low-Energy Ion Scattering ResonanceChargeExchange Low-Energy Electron Diffraction Laser Ionization Mass Spectrometry Laser MicroprobeMass Analysis Laser MicroprobeMass Spectrometry Laser Ionization MassAnalysis Nonresonant Multi-Photon Ionization Medium-EnergyIon ScatteringSpectrometry Medium-EnergyIon Scattering Magneto-optic Kerr Rotation SurfaceMagneto-optic Kerr Rotation Neutron ActivationAnalysis InstrumentalNeutron ActivationAnalysis Near EdgeX-RayAbsorption Fine Structure X-Ray Absorption Near EdgeStructure Neutron InelasticScattering Nuclear MagneticResonance Magic-Angle Spinning Nuclear ReactionAnalysis Optical Emission Spectroscopy PhotoacousticSpectroscopy Particle InducedX-Ray Emission Hydrogen/HeliumInducedX-ray Emission Photoluminescence PhotoluminescenceExcitation Photoreflectance ElectronBeam Electroreflectance ReflectionDifferenceSpectroscopy Raman Spectroscopy FourierTransform Raman Spectroscopy Raman Scattering ResonantRaman Scattering CoherentAnti-Stokes Raman Scattering Acronyms Glossary xiii
SERS SurfaceEnhancedRaman Spectroscopy RutherfordBackscatteringSpectrometry High-EnergyIon Scattering Reflected High Energy Electron Diffraction ScanningReflectionElectronMicroscopy SurficeAnalysisby h e r Ionization Post-IonizationSecondaryIon Mass Spectrometry Multi-Photon Nonresonant Post Ionization MultiphotonResonant Post Ionization ResonantPost Ionization Multi-PhotonIonization Single-PhotonIonization Sputter-InitiatedResonance IonizationSpectroscopy SurfaceAnalysii by ResonantIonizationSpectroscopy Time-of-FlightMass Spectrometer SeeAES ScanningElectronMicroscopy ScanningElectronMicroprobe SecondaryElectron Miscroscopy SecondaryElectron Backscattered Electron SecondaryElectronMicroscopywith PolarizationAnalysis ScanningForce Microscopy ScanningForceMicroscope AtomicForceMicroscopy ScanningProbeMicroscopy SecondaryIon MassSpectrometry DynamicSecondaryIon Mass Spectrometry StaticSecondaryIon Mass Spectrometry SIMSusing a QuadrupleMassSpectrometer SIMSusing a MagneticSectorMassSpectrometer SeeMagneticSIMS SIMSusingTune-of-FlightMass Spectrometer Post IonizationSIMS SputteredNeutralsMass Spectrometry SecondaryNeutralsMass Spectrometry Direct BombardmentElectronGasSNMS SparkSourceMass Spectrometry SparkSourceMass Spectrometry SeeTEM ScanningTunnelingMicroscopy RBS HEIS WEED SREM SAL1 PISIMS MPNRPI MRRPI RPI MPI SPI SINS SARIS TOFMS SAM SEM SE BSE SEMPA SFM AFM SPM SIMS DynamicSIMS StaticSIMS MagneticSIMS SectorSIMS TOF-SIMS PISIMS Q-SIMS SNMS SNMSd SSMS SparkSource STEM STM xiv Acronyms Glossary
SPM ScanningTunnelingMicroscope ScanningProbeMicroscopy Thermal EnergyAtom Scattering TransmissionElectron Microscopy TransmissionElectron Microscope ConventionalTransmission Electron Microscopy ScanningTransmission Electron Microscopy High ResolutionTransmission Electron Microscopy SelectedArea Diffraction AnalyticalElectron Microscopy ConvergentBeam Electron Diffraction LorentzTransmissionElectron Microscopy Thin Layer Chromatography Tandem ScanningReflected-LightMicroscope Tandem ScanningReflected-LightMicroscope SeeXRF TEAS TEM CTEM STEM HRTEM SAD AEM CBED LTEM TLC TSRLM TSM TXRF UPS MPS VASE WDS WDX XAS X P S ESCA XPD PHD KE XRD GIXD GIXRD DCD XRF XFS TXRF TRXFR VPD-TXRF Ultraviolet PhotoelectronSpectroscopy Ultraviolet PhotoemissionSpectroscopy MolecularPhotoelectronSpectroscopy VariableAngle SpectroscopicEllipsometry WavelengthDispersive &-Ray) Spectroscopy Wavelength DispersiveX-Ray Spectroscopy X-Ray Absorption Spectroscopy X-Ray Photoelectron Spectroscopy X-Ray PhotoemissionSpectroscopy Electron Spectroscopyfor ChemicalAnalysis X-Ray PhotoelectronDiffraction PhotoelectronDiffraction KineticEnergy X-RayDiffraction GrazingIncidenceX-Ray Diffraction GrazingIncidenceX-Ray Diffraction Double CrystalDiffractometer X-Ray Fluorescence X-Ray FluorescenceSpectroscopy Total ReflectionX-Ray Fluorescence Total ReflectionX-Ray Fluorescence Vapor Phase DecompositionTotalX-Ray Fluorescence Acronyms Glossan/ xv
MarkR Antonio BP Research International Cleveland, OH J. E. E. Bagh IBMAlrnaden ResearchCenter SanJose, CA ScottBaumann CharlesEvans &Associates Redwood City, CA ChristopherH. Becker SRIInternational MenloPark, CA AlbertJ. Bevolo Ames Laboratory, Iowa StateUniversity Ames, IA J. B. Bindell AT&T BellLaboratories Allentown, PA FilippoRadicati diBrozolo CharlesEvans&Associates Redwood City, CA C. R Brundle IBMAlmaden ResearchCenter SanJose, CA DanieleCherniak Rennsselaer PolytechnicInstitute Troy,NY Paul Chu CharlesEvans &Associates RedwoodCity,CA Carl Colvard CharlesEvans&Assoociates RedwoodCity, CA J. Neal Cox INTEL,ComponentsResearch SantaClara, CA John Gustav Delly McCroneResearch Institute Chicago, IL ExtendedX-RayAbsorptionFine Structure ElasticRecoil Spectrometry RutherfordBackscatteringSpectrometry SurfaceAnalysisby Laser Ionization ReflectedElectron Energy-LossSpectro~copy ScanningElectron Microscopy Laser Ionizarion Mass Spectrometry X-Ray Photoelectron Spectroscopy; Ultraviolet PhotoelectronSpectroscopy Nuclear ReactionAnalysis DynamicSecondaryIon MassSpectrometry Photoluminescence FourierTransformInfraredSpectroscopy Light Microscopy xvi
Hellmut F.ckert UniversityofCalifornia, SantaBarbara SantaBarbara, CA Peter Eichinger GeMeTecAnalysis Munich P. Fenter RutgersUniversity Piscataway,NJ David E. Fowler IBM Almaden Research Center SanJose, CA S. M. Gaspar University ofNew Mexico Albuquerque,NM ROYH. Geiss IBMAlmaden Research Center SanJose, CA TorgnyGustafsson RutgersUniversity Piscataway,NJ William L. Harrington EvansFast Plainsboro, NJ BrentD. Hermsmeier IBMAlmaden ResearchCenter SanJose,CA K.C. Hidunan University ofNewMexico Albuquerque,NM Tim Z. Hossain CornellUniversity Ithica,NY Rebecca S. Howland ParkScientificInstruments Sunnyvale,CA JohnC.Huneke CharlesEvans&Assodates RedwoodCity, CA TingC. Huang IBMAlmadenResearch Center SanJose, CA William Katz EvansCentral Minnetonka,MN MichaelD. Kirk Park ScientificInstruments Sunnyvale,CA SolidStateNuclearMagneticResonance TotalReflectionX-Ray Fluorescence Medium-Energy Ion Scatteringwith ChannelingandBlocking Magneto-optic Kerr Rotation OpticalScatterometry Energy-DispersiveX-Ray Spectroscopy Medium-EnergyIon ScattefmgWith Channelingand Blocking SparkSourceMassSpectromeuy X-Ray PhotoelectronandAuger Electron Diffraction OpticalScatterometry NeutronActivationAnalysis ScanningTunnelingMicroscopy and ScanningForce Microscorn SputteredNeutralMassSpectrometry, Glow-DischargeMass Spectrometry X-Ray Fluorescence StaticSecondaryIonMassSpectrometry ScanningTunnelingMicroscopy and ScanningForce Microscopy Contributors xvii
BruceE. Koel UniversityofSouthernCalifornia LosAngles, CA Max G. Lagally UniversityofWmnsin, Madison, WI W. A. Lanford StateUniversityofNewYork, Albany, NY CharlesE. Lyman Lehigh University Bethlehem, PA SusanMacKay Perkin Elmer Eden Prairie, MN John R McNeil Universityof New Mexico Albuquerque,NM Ronald G. Musket LawrenceLivermoreNationalLaboratory Livermore,(=A S. S.H. Naqvi Universiy of New Mexico Albuquerque,NM DaleE. Newbury NationalInstitutesof Scienceand Technology Gairhersburg, MD David Norman SERCDaresbury Laboratory Daresbury, Cheshire John W. Olesik Ohio StateUniversity Columbus,OH Fred H. Pollak BrooklynCollege,CUNY NewYork, NY ThomasP. Russell IBMA l d e n ResearchCenter SanJose, CA Donald E. Savage UniversityofWisconsin Madison, WI Kurt E. Si& LosAlamosNationalLaboratory LosAlamos,NM Paul G. Snyder Universityof Nebraska Lincoln, NE High-ResolutionElectron Energy Loss Spectrometry Low-EnergyElectron Diffraction Nudear ReactionAnalysis ScanningTransmission Electron Microscopy Surface Analysisby LaserIonization OpticalScatterometry Partide-InducedX-Ray Emission OpticalScatterometry Electron ProbeX-RayMicroanalysis SurfaceExtended X-Ray Absorption FineStructure,Near EdgeX-Ray AbsorptionFine Structure InductivelyCoupledPlasma-Optical Emission Spectroscopy Modulation spectroscopy Neutron Reflectivity ReflectionHigh-EnergyElectron Diffraction Transmission E l m n Microscopy VariableAngle SpectroscopicEllipsometry xviii Contributors
Gene Sparrow AdvancedR&D St. Paul, MN Fred A. Stevie AT&T Bell Laboratories Allentown,PA Yale E. Strausser SurfaceScienceLaboratories Mountainview,CA BarryJ. Streusand AppliedAnalytical Austin,TX Raymond G. Teller BP Research International Cleveland,OH Michael F. Toney IBM AlmadenResearch Center SanJose, CA WojciechViech CharlesEvans &Assoociates RedwoodCity, CA William B. White PennsylvaniaSkateUniVeI'Siq' UniversityPark, PA S.R Wilson Universityof New Mexico Albuquerque,NM JohnA. Woollam Universityof Nebraska Lincoln,NE Ben G. Yacobi Universityof Californiaat LosAngeles LosAngeles, CA DavidJ. C. Yates Consultant Poway, CA Nestor J. Zaluzec ArgonneNational Laboratory Argonne, IL Ion ScatteringSpectroscopy SurfaceRoughness:Measurement, Formation by Sputtering, Impact on Depth Profiling AugerElectron Spectroscopy InductivelyCoupled Plasma Mass Spectrometry Neutron Diffraction X-Ray Diffraction Glow-DischargeMassSpectrometry Raman Spectroscopy Optical Scatterometry VariableAngleSpectroscopicEllipsometry Cathodoluminescence Physical and ChemicalAdsorption for the Measurementof SolidSurfaceAreas ElectronEnergy-Loss Spectroscopyin the TransmissionElectronMicroscope Contributors xix
I INTRODUCTION AND SUMMARIES 1.0 INTRODUCTION Though a wide range of analytical techniques is covered in this volume there are certain traits common to many of them. Most involve eitherelectrons,photons, or ions as a probe beam strikingthe materialto be analyzed.The beaminteractswith the materialin someway, and in someof the techniquesthe changesinducedin the beam (energy, intensity, and angular distribution) are monitored after the inter- action, and analytical information is derived from the observation of these changes. In other techniques the information used for analysis comes from elec- trons, photons, or ions that are ejected from the sample under the stimulation of the probe beam. In many situationsseveral connectedprocesses may be going on more or less simultaneously, with a particular analytical technique picking out only one aspect, e.g., the extent of absorption of incident light, or the kinetic energydistributionof ejectedelectrons. The rangeof informationprovidedby the techniquesdiscussed hereisas0wide, but again there are common themes. What types of information are provided by these techniques?Elemental composition is perhaps the most basic information, followed by chemical state information, phase identification, and the determina- tion ofstructure(atomicsites, bond lengths,and angles). One might need to know howthesevaryas a functionof depth into the material,or spatiallyacrossthe mate- rial, and many techniquesspecializein addressingthesequestionsdown to very fine dimensions.For su&s, interfaces,and thin filmsthere is ofienverylittlematerial at all to analyze, hence the presence of many microanalyticalmethods in this vol- ume. Within thisfield (microanalysis)it iso b necessaryto identifytracecompo- nents down to extremelylow concentration (partsper trillion in some cases) and a number of techniquesspecializein this aspect. In other cases a high degreeof accu- racy in measuringthe presence of major components might be the issue. Usually the techniques that are good fbr trace identificationare not the sameones used to accurately quantifymajor components. Most complete analyses require the use of 1
multiple techniques, the selection of which depends on the nature of the sample and the desiredinformation. Thisfirst chaptercontainsonepage summariesofeachof the 50techniquescov- ered in the followingchapters.All summarieshave the same format to alloweasy comparisonand quick accessto the information.Further comparativeinformation is provided in the introductions to the chapters. Finally, a table is provided at the endofthis introduction,inwhichmanyoftheimportantparametersdescribingthe capabilitiesforall 50techniquesarelisted. The subtitleof this Series is “Su&m, Interfices, and Thin Films.” The defi- nition of a “surface”or of a “thinfilm”varies considerablyh m person to person and with application area. The academic discipline of ‘‘Surfice Science” is largely concerned with chemistry and physics at the atomic monolayer level, whereas the “surfaceregion” in an engineeringor applicationssense can be much more extensive. The same is true for interfaces between materials. The practical consideration in distinguishing“sudace” from “bulk” or “thin” from “thick” is usually connected to the property of interest in the application. Thus, fbr a cata- lytic reaction the presence of haf a monolayer of extraneoussulfur atoms in the top atomic layer of the catalyst material might be critical, whereas for a corro- sion protection layer (for example, Cr segregation to the surface region in steels) the important region ofdepth may be several hundred 8,. For interfaces the epi- taxial relationship between he last atomic layer of a single crystal material and the first layer of the adjoining material may be critical for the electrical proper- ties of a device, whereas diffusion barrier interfaces elsewhere in the same device may be 1000A thick. In thin-film technologyrequirements can range from layers pm thick, which for the majority ofanalytical techniquesdiscussed in this volume constitute bulk material, to layers as thin as 50 8, or so in thin-film magnetic recording technology. Because of these different perceptions of “thick” and “thin,”actual numbers are used whenever discussingthe depth an analytical tech- nique examines.Thus in Ion ScatteringSpectroscopythe signalsused in the anal- ysis are generated fiom only the top atomic monolayer of material exposed to a vacuum, whereas in X-ray photoemission up to 1008,is probed, and in X-ray flu- orescencethe signal can come from integrateddepths ranging up to 10 pm. Note that in these three examples, two are quoted as having rangesofdepths.For many ofthe techniques it is impossible to assign unique values because the depth from which a signal originates may depend both on the particular manner in which the technique is used, and on the nature ofthe material being examined.Perfbrming measurements at grazing angles ofincidence of the probe beain, or grazing exit angles fbr the detected signal, will usually make the technique more surfacesensi- tive. For techniques where X-ray, electron, or high-energy ion scattering is the critical Factor in determining the depth analyzed, materials consisting of light elements are always probed more deeply than materials consisting of heavy ele- ments. 2 INTRODUCTIONAND SUMMARIES Chapter 1
Another confusingissue is that of “depth resolution.” It is a measurementof the technique’s ability to clearly distinguish a property as a function of depth. For example a depth resolution of 20 A, quoted in an elemental composition analysis, means that the compositionat one depth can be distinguishedfrom that at another depth if there is at least 20 A depth profile is a record of the variationof a property (suchascomposition)as a function of depth. Some of the techniques in this volume have essentially no intrinsicdepth profiling capabilities;the signalis representativeof the materialinte- grated over a fived probing depth. Most, however, can vary the depth probed by varying the condition of analysis,or by removing the surface, layer by layer, while collectingdata. By varying the angle of incidence, the X-ray, electron, or ion beam energy, etc. many techniques are capable of acquiringdepth profiles. Those profiles are gener- ated by combining several measurements, each representative of a different inte- grated depth. The higher energy ion scattering techniques (Medium Energy Ion Scattering, MEIS,and Rutherford Backscattering, RBS), however, are unique in that the natural output of the methods is compositionasa function of depth. By far the most common way of depth profilingis the destructivemethod of removingthe surface, layer by layer, while also taking data. For the mass spectrometry-based techniques of Chapter 10, removal of surface material is intrinsic to the sputtering and ionizationprocess. Other methods, suchasAuger Electron Spectroscopy,AES, or X-Ray Photoemission,XPS, use an ancillaryion beam to remove material while constantly ionizing the newly exposed surface. Under the most favorable condi- tions depth resolutionsof around 20Acan be achievedthisway, but there are many artifacts to be aware of and the depth resolution usually degrades rapidly with depth. Someaspectsof sputterdepth profilingaretouched upon in the article“Sur- face Roughness”in Chapter 12, but for a more completediscussionof the capabil- ities and limitations of sputter depth profiling the reader is referred to a paper by D. Marton and J. Fine in Thin Solid Films, 185, 79, 1990 and to other articles cited there. between them. 3
Compilationof Comparative Informationonthe AnalyticalTechniques DiscussedinThisVolume Maininformation Article Technique No. 2.1 2.2 2.3 2.3 2.4 3.1 3.2 XI 0 3.3 0 3.4 C 0 4.1zrn P 4.2 0 4.3 C 4.3 4.4 5E !E Firn 4.6 3 2 3.5 v) % 4.5 5.1 5.2 5.3 8PI R 4d Light Microscopy SEM STM SFM TEM EDS EELS Gthodo- 1umin&cence STEM EPMA XRD EXAFS SEXAFS NEXAFS XPD LEED WEED XPS U P S AES Depth probed ( w i d ) Variable m e subpm m m m subA m e m subA 200 nm* 1pm m e e 20 nm* e e m e e . e 10nm-pm 100nm* e lpm 10Cun e e Bulk* e e lnm e . . . e . . e . 1nm m . 3nm 1 nm m m l n m m e 3nm m e e 1nm e . 2 nm T p ofsolidsample (typical) 0.2 pn 10 nm i A 1Ml 5 nm 0.5 pn 1 nm 1Cun lnm 0.5 pm mm mm mm mm 150prn 0.1 mrn 0.02 mm 150pm mm 100nrn 500 ppm Few% PPm - 100ppm 3% Few% Few % Few% 1% - - 1% 0.1% - All Cond,coatedins. Conductors All All;e200 nm thick AU;Z>5 All;e30 nm thick All; sunicond. usually All; e200 nm thick All; flat best Crystalline All Surfaceand adsorbate Surfaceandadsorbate Singlecrystal Singlecrystal Singlecrysml All All All, inorganic usually N 1 Y 2 N 2 N 2 Y 3 Y 2 Y 2 Y 1 Y 3 Y 3 N 2 YIN - Y - Y - Y 3 Y - Y - Y 3 Y - Y 3 1 Y 1 Y 3 Y 2 Y 2 Y 2 Y 3 N 3 N 3 N 2 Y 1 Y 3 N 3 N 3 N 3 N 2 N 2 N 1 Y 3 N 1 Y
Compilationof ComparativeInformationonthe AnalyticalTechniquesDiscussedinThisVolume Maininformation Article Technique No. 5.4 6.1 6.2 6.3 7.1 7.2 7.3 8.1 8.2 8.3 8.4 9.1 9.2 9.3 9.4 10.1 10.2 10.3 VI REELS XRF TXRF PKE Photo- luminescence Modulation VASE FTIR Raman Scattering HREELS NMR RBS ERS MEIS ISS Dynamic SIMS static SIMS SALI spectrosmpy 1Pm lw a a a m a a Fewpm a a F e w p a a 2 nm a m Bulk a a m To 2 pn 1 P n 0 3A 0 0 . 1nm 0 2 nm o m a 3 A a m 3 A 100nm rnm un 100pn FewPn 100pm 20 pm llrm un mm 1oow 100 nrn PPrn - Variable Variable 1% 0.01-10% 0.01% 0.1%-10% 50 ppm-1% PPb-PPm Few % PPb-PPrn All All Trace heavy metals All All, semicond. usually All, semicond. usually Flat thin h All All AU;flatcond. best All; not all elements All H containing All; usuallysinglecrystal All All, mostly sernicond. All, mostly polymer AU,mostlyinorg. Y - 3 N N 2 1 Y Y 3 3 Y Y 3 3 Y N 1 2 N N 2 3 N N 2 3 Y N 2 1 Y N 2 2 Y Y 3 3 N N 3 3 N Y l N 3 2 Y Y - 3 N Y 3 3 N Y - 3 Y Y 3 1 Y Y 3 2 Y Y 3 3 N
Compilationof ComparativeInformationon the AnalyticalTechniques DiscussedinThis Volume Depth Width (typical) (typical) (typical) 0, 6. Maill ~ n l l a t i ~ TkCe Types ofsolid sample (typical) ArrideTechnique probed probed capability No. 10.4 SNMS . 1.5 nm un 50 PPm Flat conductors Y 2 2 Y 10.5 LIMS * . 10.6 SSMS 0 10.7 GDMS 0 10.8 ICPMS .10.9 ICPOES 0 ll.' ; E 2 0 l l 5 11.2 ;l;g;v 11.3 NAA 11.4 NRA 20 0 C Optical 0 : 12.2 scatternmetryz v) 12.3 MOU P 12.4 Adsorption U .. * . 100nm 2pm 1-100ppm All Y 3 2 Y 3 P cm 0.05 ppm Samplef o r m s e l d e Y - 2 Y 5w mm PPt All Y 2 1 Y 5 P mm PPb All Y 1 1 Y 100nm cm ppt-ppb Sampleformselecd y 3 2 Y Bulk I Crystalline N - 3 N uptomm - - Flatpolymerfilms N - 3 N Bulk - PPt-PPm Trace metals N 2 3 Y 10-1OOnm l o p 10-lOOppm All:z<21 Y - 3 Y 0 - mm - Flatsmoothfilms N 1 3 Y 30nm 0 . 5 ~ - Magnetic films N 1 2 N Outeratoms - - LargesurFacearea Y - 2 N v) Notes Tbitable shouldbeuscdasa"quickreference" guideody. CommnrialZnmMuntcThesemtypical costs;large ranges dependingon sophistication andaccessories: 1 means < $50k2 means $50-300k; 3 means >$300k."-" meansno mmplcrecommerciainstrument. Usup:Numbersreferto usage for anaylsisofsolidmaterials. 1 means Extensive;2 means medium;3 means not common. Timcapz6iliy:Guideonly. Oftenvery material/wnditions dependent. "-" meansnot used for trace components. !ix % *Measuredin transmission. iii v) 0 5 'E! m,-I
Light Microscopy 1.2.1 The light microscope uses the visible or near visible portion of the electromagnetic spectrum; light microscopy is the interpretive use of the light microscope. This technique, which is much older than other characterization instruments, can trace its origin to the 17th century. Modern analytical and characterization methods began about 150years ago when thin sections of rocks and minerals, and the first polished metal and metal-alloy specimens were prepared and viewed with the intention of correlating their structures with their properties. The technique involves,at itsvery basiclevel,the simple, directvisual observationof a samplewith white-light resolution to 0.2 pm. The morphology, color, opacity, and optical propertiesare often sufficient to characterizeand identifl a material. Range of samples characterized Destructive Quantification Detection limits Resolvingpower Imagingcapabilities Main use Instrument cost Size Almost unlimited for solidsand liquid crystals Usually nondestructive; sample preparation may involve material removal Via calibrated eyepiece micrometers and image analysis To sub-ng 0.2 pm with white light YeS Direct visual observation; preliminary observation for final characterization, or preparative for other instrumentation $2,500-$50,000 or more Pocket to large table 7
ScanningElectronMicroscopy(SEM) 1.2.2 The Scanning Electron Microscope (SEM) is often the first analytical instrument used when a "quick look" at a material is required and the light microscope no longerprovides adequateresolution. In the SEMan electron beam is focusedinto a fine probe and subsequently raster scanned over a small rectangular area. As the beam interactswith the sampleit createsvarioussignals(secondaryelectrons,inter- nal currents, photon emission, etc.), all of which can be appropriately detected. These signals are highly localized to the area directly under the beam. By using these signals to modulate the brightness of a cathode ray tube, which is raster scanned in synchronismwith the electronbeam, an image is formed on the screen. This image is highly magnified and usually has the U 1 ~ ~ k "of a traditional micro- scopic image but with a much greater depth of field. With ancillary detectors, the instrument is capableof elementalanalysis. Main use High magnification imaging and composition (elemental) mapping No, some electron beam damage 10~-300,000~;5000~-100,000~is the typical operating range 500eV-50 keV; typically,20-30 keV conducting film; must be vacuum compatible Less thanO.lmm, up to 10cm or more 1-50 nm in secondaryelectron mode Varies from a few nm to a few pm, depending upon the acceleratingvoltageand the mode of analysis Destructive Magnification range Beam energy range Samplerequirements Minimal, occasionally must be coated with a Samplesize Lateralresolution Depth sampled Bonding information No Depth profiling Only indirect capabilities Instrument cost $100,000-$300,000is typical Size Electronicsconsole3ft. x 5 fi.;electron beam column 3 ft. x 3 ft. 8 INTRODUCTIONAND SUMMARIES Chapter 1
Scanning Tunneling Microscopy and Scanning Force Microscopy (STMand SFM) 1.2.3 In ScanningTunneling Microscopy(STM) or Scanning Force Microscopy(SFM), a solid specimenin air, liquid or vacuum is scanned by a sharp tip locatedwithin a few A of the surface. In STM, a quantum-mechanical tunneling current flows between atoms on the surface and those on the tip. In SFM, also known as Atomic Force Microscopy(AFM), interatomic forcesbetween the atoms on the surfaceand those on the tip cause the deflection of a microfabricated cantilever. Because the magnitude of the tunneling current or cantileverdeflectiondepends stronglyupon the separation between the surfaceand tip atoms, they can be used to map out sur- facetopography with atomic resolution in all three dimensions.The tunneling cur- rent in STM is also a function of local electronic structure so that atomic-scale spectroscopyis possible. Both STM and SFM are unsurpassed as high-resolution, three-dimensional profilometers. Parametersmeasured Surface topography (SFM and STM); local electronic Destructive No Vertical resolution Lateral resolution Quantification Yes; three-dimensional Accuracy Imaging/mapping Yes Field of view From atoms to > 250 pm Samplerequirements STM-solid conductorsand semiconductors,conductive coating required for insulators; SFM-solid conductors, semiconductorsand insulators structure (STM) STM, 0.01 8;SFM, 0.1 A STM, atomic; SFM, atomic to 1nm Better than 10%in distance Main uses Real-space three-dimensional imaging in air, vacuum, or solution with unsurpassed resolu- tion; high-resolution profilometry; imaging of nonconductors (SFM). Instrument cost Size $65,000 (ambient) to $200,000 (ultrahigh vacuum) Table-top (ambient), 2.27-12 inch bolt-on flange (ultrahighvacuum) 9
Transmission Electron Microscopy (TEM) 1.2.4 In Transmission Electron Microscopy (TEM) a thin solid specimen (5 200 nm thick) is bombarded in vacuumwith a highly-focused,monoenergeticbeam of elec- trons. The beam is of sufficient energyto propagate through the specimen.A series of electromagneticlensesthen magnifies this transmitted electron signal. Diffracted electrons are observed in the form of a diffraction pattern beneath the specimen. This information is used to determine the atomic structure of the material in the sample. Transmitted electrons form images from small regions of samplethat con- tain contrast, due to several scattering mechanisms associated with interactions between electronsand the atomic constituents of the sample.Analysis of transmit- ted electron images yields information both about atomic structure and about defects present in the material. Range of elements Destructive Chemical bonding information Quantification Accuracy Detection limits Depth resolution Lateral resolution Imaging/mapping TEM does not specificallyidentifyelements measured Yes, during specimen preparation Sometimes, indirectlyfrom diffractionand image simulation Yes, atomic structures by diffraction;defect character- ization by systematicimage analysis Lattice parameters to four significant figures using convergentbeam diffraction One monolayer for relativelyhigh-Zmaterials None, except there are techniques that measure sample thickness Better than 0.2 nm on some instruments Yes Samplerequirements Solid conductors and coated insulators. Typically 3-mm diameter, c 200-nm thick in the center Main uses Atomic structure and Microstructural analysisof solid materials, providinghigh lateral resolution Instrument cost $300,000-$1,500,000 Size 100 fL2to a major lab 10 INTRODUCTION AND SUMMARIES Chapter 1
Energy-Dispersive X-Ray Spectroscopy (EDS) 1.3.1 When the atomsin a materialareionizedbya high-energyradiation they emit char- acteristicX rays. EDS is an acronym describinga technique of X-ray spectroscopy that is based on the collection and energy dispersion of characteristic X rays. An EDS system consistsofa sourceofhigh-energy radiation, usually electrons; a sam- ple; a solid state detector, usually made from lithium-drifted silicon, Si (Li); and signal processing electronics. EDS spectrometersare most frequently attached to electron column instruments. X rays that enter the Si (Li) detector are converted into signalswhich can be processed by the electronics into an X-ray energy histo- gram. This X-ray spectrum consists of a series of peaks representative of the type and relative amount ofeach element in the sample. The number of counts in each peak may be furtherconvertedinto elementalweight concentration either by com- parison with standardsor by standardlesscalculations. Range of elements Destructive Chemical bonding information Quantification Detection limits Lateralresolution Depth sampled Imaging/mapping Boron to uranium No Not readilyavailable Best with standards, although standardless methods arewidelyused Nominally P5%, relative, for concentrations > 5yo wt. 100-200 ppm for isolated peaks in elements with Z>11,1-2% wt. for low-Zand overlappedpeaks -5-1 pm for bulk samples; as small as 1 nm for thin samplesin STEM 0.02 to pm, depending on Z and keV In SEM, EPMA, and STEM Samplerequirements Solids, powders, and composites; size limited only by the stage in SEM, EPMA and XRF; liquids in XRF; 3 mm diameter thin foils in TEM To add analytical capability to SEM, EPMA and TEM $25,000-$100,000, depending on accessories (not including the electron microscope) Main use cost 11
ElectronEnergy-LossSpectroscopyinthe TransmissionElectron Microscope(EELS) 1.3.2 In Electron Energy-Loss Spectroscopy (EELS) a nearly monochromatic beam of electrons is directed through an ultrathin specimen, usually in a Transmission (TEM) or ScanningTransmission (STEM) Electron Microscope. As the electron beam propagates through the specimen, it experiences both elastic and inelastic scatteringwith the constituent atoms,which modifies its energydistribution. Each atomic speciesin the analyzed volume causes a characteristicchange in the energy of the incident beam; the changesareanalyzedby meansofa electronspectrometer and counted by a suitabledetectorsystem.The intensityofthe measured signalcan be used to determine quantitatively the local specimen concentration, the elec- tronic and chemical structure,and the nearest neighbor atomic spacings. Range of elements Destructive Chemical bonding information Depth profiling Quantification Detection limits Depth probed Lateral resolution ImagingCapabilities Lithium to uranium; hydrogen and helium are some- times possible No Yes, in the near-edgestructure of edge profiles information None, the specimenis alreadythin capabilities Without standards+fl0-20% at.; with standards -1-2% at. -lo-21 g Thickness of specimen (I2000A) 1 nm-10 pm, depending on the diameter of the inci- dent electronprobe and the thicknessof the specimen Yes Samplerequirements Solids;specimensmust be transparentto electronsand -100-2000 athick Main use Light element spectroscopy for concentration, electronic, and chemical structure andysis at ultra- high lateral resolution in a TEM or STEM As an accessory to a TEM or STEM: $50,000- $150,000 (doesnot include electron microscope cost) cost 12 INTRODUCTIONAND SUMMARIES Chapter 1
Cathodoluminescence(CL) 1.3.3 In Cathodoluminescence (CL) analysis, electron-beam bombardment of a solid placed in vacuum causes emission of photons (in the ultraviolet, visible, and near- infrared ranges) due to the recombination of electron-hole pairs generated by the incident energetic electrons. The signal provides a means for CL microscopy (i.e., CL images are displayed on a CRT) and spectroscopy (i.e., luminescence spectra from selected areas of the sample are obtained) analysis of luminescent materials using electron probe instruments. CL microscopycan be used for uniformity char- acterization (e.g., mapping of defects and impurity segregation studies), whereas CLspectroscopyprovidesinformation on variouselectronicpropertiesof materials. Range of elements Chemical bonding information Nondestructive Detection limits Depth profding Lateralresolution Imaging/mapping Not element specific Sometimes Yes; caution-in certain cases electron bombardment may ionizeor create defects In favorable cases, dopant concentrations down to 1014atoms/cm3 Yes, by varying the range of electron penetration (between about 10 nm and several pm), which depends on the electron-beam energy ( I 4 0kev). On the order of 1 pm; down to about 0.1 pm in special cases Yes Samplerequirements Solid, vacuum compatible Quantification Difficult, standardsneeded Main use Nondestructivequalitativeand quantitativeanalysisof impuritiesand defects, and their distributions in lumi- nescent materials Instrument cost $25,000-$250,000 Size Smalladd-on item to SEM,TEM 13
ScanningTransmission Electron Microscopy (STEM) 1.3.4 In Scanning Transmission Electron Microscopy (STEM) a solid specimen, 5- 500 nm thick, is bombarded in vacuum by a beam (0.3-50 nm in diameter) of monoenergeticelectrons. STEM imagesare formedby scanningthis beam in a ras- ter acrossthe specimenand collectingthe transmitted or scattered electrons.Com- pared to the TEM an advantageof the STEM is that manysignalsmay be collected simultaneously:bright- and dark-field images;Convergent Beam Electron Diffrac- tion (CBED) patterns fbr structure analysis; and energy-dispersive X-Ray Spec- trometry (EDS) and Electron Energy-Loss Spectrometry (EELS) signals for compositional analysis. Taken together, these analysis techniques are termed Ana- lyticalElectron Microscopy (AEM).STEM provides about 100times better spatial resolution of analysis than conventionalTEM. When electronsscattered into high angles are collected, extremely high-resolution images of atomic planes and even individual heavy atomsmay be obtained. Range of elements Destructive Chemical bonding information Quantification Accuracy Detection limits Lateral resolution Imaging/mapping capabilities Lithium to uranium Yes, during specimenpreparation Sometimes,from EELS Quantitative cornpositional analysis from EDS or EELS, and crystal structure analysis from CBED 5-10% relativefor EDS and EELS 0.1-3.0% wt. for EDS and EELS Imaging,0.2-10 nm; EELS, 0.5-10 nm; EDS, 3-30 nm Yes, lateralresolution down to < 5 nm Samplerequirements Solidconductorsand coated insulatorstypically 3 mm in diameter and c 200 nm thick at the analysis point b r imaging and EDS, but < 50 nm thick for EELS Microstructural,crystallographic,and compositionalanal- ysis; highspatial resolution with @elemental detection and accuracyjuniquestructural analysiswithCBED Main uses Instrument cost $500,000-$2,000,000 Size 3 m x 4 m x 3 m 14 INTRODUCTIONAND SUMMARIES Chapter 1
Electron ProbeX-Ray Microanalysis(EPMA) 1.3.5 Electron Probe X-Ray Microanalysis (EPMA) is an elemental analysis technique based upon bombarding a specimen with a focused beam of energetic electrons (beam energy 5-30 kev) to induce emission of characteristicX rays (energy range 0.1-15 kev). The X rays are measured by Energy-Dispersive (EDS) or Wave- length-Dispersive(WDS) X-ray spectrometers.Quantitativematrix (interelement) correction procedures based upon first principles physical models provide great flexibility in attacking unknown samples of arbitrary composition; the standards suite can be as simple as pure elementsor binary compounds. Typical error distri- butions are such that relative concentration errorslie within &4% for 95% of cases when the analysis is performed with pure element standards. Spatial distributions of elemental constituents can be visualized qualitativelyby X-ray area scans (dot maps) and quantitativelyby digital compositionalmaps. Range of elements Beryllium to the actinides Destructive No, except for electronbeam damage Chemical bonding In rare cases: from light-elementX-ray peak shifts Depth profiling Rarely, by changingincident beam energy Quantification Standardlessor;pure element standards Accuracy &4% relative in 95% of cases;flat, polished samples Detection limits WDS, 100ppm; EDS, 1000ppm Samplingdepth Energy and matrix dependent, 100nm-5 pm Lateral resolution Energy and matrix dependent, 100 nm-5 pm Imaging/mapping Yes, compositionalmapping and SEM imaging Samplerequirements Solid conductors and insulators;typically,e 2.5 cm in diameter, and e 1 cm thick, polished flat; particles, rough surfldces,and thin films Major uses Accurate, nondestructive quantitative analysis of major, minor, and trace constituents of materials Instrument cost $300,000-$800,000 Size 3 m x 1.5 m x 2 m high 15
X-Ray Diffraction(XRD) 1.4.1 In X-Ray Diffraction(XRD)a collimatedbeam ofX rays,withwavelengthh- 0.5- 2 8,is incidenton a specimenand isdiffractedby the crystallinephasesin thespec- imen accordingto Bragg's law (h = 2dsin0, where dis the spacingbetween atomic planes in the crystallinephase).The intensityof the diffractedX rays is measuredas a hnction of the diffractionangle 28 and the specimen'sorientation. This diffrac- tion pattern is used to identifythe specimen'scrystallinephases and to measure its structuralproperties, includingstrain (which is measuredwith great accuracy),epi- taxy,andthesizeand orientationof crystallites(smallcrystallineregions).XRDcan also determineconcentration profiles, film thicknesses, and atomic arrangements in amorphousmaterialsand multilayers. It as0can characterized&ts. Toobtain this structural and physical information ftom thin films, XRD instruments and techniquesare designedto maximizethe diffractedX-ray intensities, since the dif- fractingpower of thin filmsis small. Rangeof elements Probingdepth Detection Limits Destructive Depth profiling All, but not element specific. Low-Zelementsmay be difficult to detect Typically a few pm but material dependent; mono- layer sensitivitywith synchrotronradiation Material dependent,but -3%in a two phase mixture; with synchrotronradiationcan be -0.1% No, for most materials Normallyno; but thiscanbe achieved. Samplerequirements Any material, greater than -0.5 an,althoughsmaller Lateral resolution Normallynone; although 10pmwith microfbcus Main use with microfocus Identification of crystalline phases; determination of strain, and crystallite orientation and size; accurate determination of atomicarrangements Defect imaging and characterization; atomic arrange- ments in amorphous materials and multilayers; con- centration profiles with depth; film thickness measurements Specializeduses Instrumentcost $70,000-$200,000 Size Varieswith instrument,greaterthan -70 fc.2 16 INTRODUCTIONAND SUMMARIES Chapter 1
ExtendedX-Ray Absorption FineStructure (EXAFS) 1.4.2 An EXAFS experimentinvolvesthe irradiation of a samplewith a tunable sourceof monochromatic X rays from a synchrotron radiation facility.As the X-ray energyis scanned from just below to well above the binding energy of a core-shell electron (e.g., K or L) of a selected element, the X-ray photoabsorption process is moni- tored. When the energy of the incident X-rays is equal to the electron binding energy, X-ray absorption occurs and a steeply rising absorption edge is observed. For energies greater than the binding energy, oscillations of the absorption with incident X-ray energy (i.e., EXAFS) are observed. EXAFS data are characteristicof the structural distribution of atoms in the immediate vicinity (-5 A) of the X-ray absorbing element. The frequency of the E M S is related to the interatomic dis- tance between the absorbingand neighboringatoms. The amplitude of the EXAFS is related to the number, type, and order of neighboringatoms. Range of elements Destructive No Bonding information Accuracy Detection limits Depth probed Depth profiling Lateralresolution Not yet developed Imaging/mapping Not yet developed Sample requirements Virtually any material;solids,liquids,gas Main use Instrument cost Lithium through uranium Yes,interatomicdistances,coordinationnumbers, atom types, and structural disorder;oxidationstate by inference 1-2% for interatomic distances; 10-25% for coordi- nation numbers Surface,monolayer sensitivity;bulk, > 100ppm Variable, from8,to pm Yes,with glancing incidence angles;electron-and ion-yield detection Local atomic environmentsof elements in materials Laboratory Facility, c $300,000; synchrotron beam line, > $1,000,000 Smallattachment to synchrotron beam lineSize 17
Surface ExtendedX-Ray Absorption Fine Structure and Near EdgeX-Ray Absorption FineStructure (SEXAFS/NEXAFS) 1.4.3 In Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Absorption Fine Structure (SEXAFS/NEXAFS) a solid sample, usually placed in ultrahigh vacuum, is exposed to a tunable beam of X rays from a synchrotron radi- ation source.Aspectrumis collectedbyvaryingthe photon energyof theX rays and measuringthe yield of emitted electronsor fluorescentX rays. Analysis of the wig- gles in the observed spectrum (the SEXAFS features) gives information on nearest neighbor bond lengths and coordination numbers for atoms at or near the surface. Features near an absorption edge (NEXAFS) are often characteristic of the local coordination (octahedral,tetrahedral, etc.) or oxidation state. For adsorbed mole- cules, NEXAFS resonances characterizethe type of bonding. On a flat surface, the angular variation of intensity of the resonances gives the orientation of the mole- cule. Range of elements Destructive No Chemical bonding Yes, through NEXAFS information Accuracy In nearest neighbor distance,M.01 with care Surfacesensitivity Top few monolayers Detection limits 0.05 monolayer Lateral resolution -0.5 mm Imaging/mapping No Samplerequirements Vacuum-compatiblesolids Main use of SEXAFS Main use of NEXAFS Instrument cost Size Almost all, from C to U Adsorbatesubstrate bond lengths Orientation of molecular adsorbates $400,000, plus cost of synchrotron Small attachment to synchrotron beam line 18 INTRODUCTIONAND SUMMARIES Chapter 1
X-Ray Photoelectronand Auger ElectronDiffraction (XPDandAED) 1.4.4 In X-Ray Photoelectron Diffraction (XPD) and Auger Electron Diffraction (AED), a single crystalor a textured polycrystallinesample is struck by photons or electrons to produce outgoing electrons that contain surface chemical and struc- tural information. The focus of XPD and AED is structural information, which originates from interference effects as the outbound electrons from a particular atom are scattered by neighboringatomsin the solid. The electron-atom scattering processstronglyincreasesthe electron intensityin the forward direction, leadingto the simpleobservation that intensity maxima occur in directionscorrespondingto rows of atoms. An energy dispersive angle-resolved analyzer is used to map the intensity distribution as a function of anglefor elements of interest. Range of elements Destructive Element specific Chemicalstate specific Accuracy Sitesymmetry Depth Probed Depth profiling Detection limits Lateral resolution Imaging/ mapping All except H and He XPD no; AED may cause e-beam damage YeS Yes,XPD is better than AED Bond angles to within lo; atomic positions to within 0.05 A Yes, and usually quickly 5-50 A Yes, to 30A beneath the surface 0.2 at.% 150A (AED), 150pm (XPD) Yes Samplerequirements Primarily single crystals,but also textured samples Main use To determine adsorption sites and thin-film growth modes in a chemicallyspecificmanner Instrument cost $300,000-$600,000 Size 4 m x 4 m x 3 m 19
Low-EnergyElectron Diffraction (LEED) 1.4.5 In Low-EnergyElectron Diffraction (LEED)a collimated monoenergetic beam of electrons in the energy range 10-1000 eV (A = 0.4-4.0 A) is diffracted by a speci- men surface. In this energy range, the mean free path of electrons is only a few A, leading to surface sensitivity. The diffraction pattern can be analyzed for the exist- ence of a clean surface or an ordered overlayer structure. Intensities of diffracted beams can be analyzed to determine the positions of surfaceatoms relative to each other and to underlying layers. The shapesof diffracted beams in anglecan be ana- lyzed to provide information about surfacedisorder. Various phenomena related to surface crystallography and microstructure can be investigated. This technique requires a vacuum. Range of elements Destructive Depth probed Detection limits Resolvingpower Lateral resolution Imaging capability All elements, but not element specific No, except in specialcasesof electron-beamdamage 4-20 A 0.1 monolayer; any ordered phase can be detected; atomic positions to 0.1 step heights to 0.1 A; sur- facedisorder down to -10%of surfacesites Maximum resolvable distance for detecting disorder: typically200 A;best systems, 5 pm Typical beam sizes,0.1 mm; best systems, -10 pm Typically, no; with specialized instruments (e.g., low- energy electron microscopy), 150A Samplerequirements Single crystals of conductors and semiconductors; insulators and polycrystalline samples under special circumstances;0.25 cm2or larger, smallerwith special effort Main uses cost Size Analysis of surface crystallography and microstruc- ture; surfacecleanliness 1$75,000;can be home built cheaply Generallypart of other systems;if self-standingY-8m2 20 INTRODUCTIONAND SUMMARIES Chapter 1
ReflectionHigh-Energy Electron Diffraction (RHEED) 1.4.6 In Reflection High-Energy Electron Diffraction (RHEED), a beam of high-energy electrons (typically5-50 kev), is acceleratedtoward the surfaceof a conducting or semiconducting crystal, which is held at ground potential. The primary beam strikesthe sampleat a grazingangle (+1-5") and is subsequentlyscattered.Some of the electronsscatterelastically. Sincetheir wavelengthsare shorter than interatomic separations, these electrons can diffract off ordered rows of atoms on the surface, concentrating scattered electrons into particular directions, that depend on row separations. Beams of scattered electrons whose trajectories intersect a phosphor screenplaced oppositethe electron gun will excitethe phosphor. The light from the phosphor screen is called the RHEED pattern and can be recorded with a photo- graph, television camera, or by some other method. The symmetry and spacing of the bright features in the RHEED pattern give information on the surfacesymme- try, lattice constant, and degreeof perfection, i.e., the crystal structure. Range of elements Destructive All, but not chemicalspecific No, Except for electron-sensitivematerials Depth probed 2-100 A Depth profiling No Lateral resolution Structural information sensitiveto structural defects Samplerequirements Usually single crystal conductor or semiconductor surfaces Main use Monitoring surface structures, especially during thin- film epitaxial growth; can distinguish two-and three- dimensional defects Instrument cost $50,000-$200,000 Size 200 pm x 4 mm, in specialcases 0.3 nm x G nm Measuressurfacecrystal structure parameters, +25 sq. ft., larger if incorporated with an MBE chamber 21
X-Ray PhotoelectronSpectroscopy (XPS) 1.5.1 In X-Ray Photoelectron Spectroscopy(XPS) monoenergeticsofiX rays bombard a sample material, causing electrons to be ejected. Identification of the elements present in the samplecan be made directlyfrom the kineticenergiesof theseejected photoelectrons. On a finer scale it is also possible to identify the chemical state of the elementspresent from small variations in the determinedkineticenergies. The relative concentrationsof elements can be determined from the measured photo- electronintensities.For a solid,XPS probes2-20 atomiclayers deep, dependingon the material, the energy of the photoelectron concerned, and the angle (with respect to the surface) of the measurement. The particular strengths of XPS are semiquantitative elemental analysis of surfaces without standards, and chemical state analysis, for materials as diverse as biological to metallurgical. X P S also is known as electronspectroscopyfor chemicalanalysis (ESCA). Range of elements Destructive Elementalanalysis Chemicalstate Yes information Depth probed 5-50 A Depth profiling Yes, over the top 50 A; greater depths require sputter profiling Depth resolution A fewto severaltens ofA, dependingon conditions Lateral resolution 5 mm to 75 pm; down to 5 pm in specialinstruments Sample requirements All vacuum-compatible materials; flat samples best; sizeaccepted depends on particular instrument Main uses Determinations of elemental and chemical state wm- positions in the top 30A $200,000-$1,000,000,dependingon capabilities 10fi. x 12fi. All except hydrogen and helium No, somebeam damageto X-ray sensitivematerials Yes, semiquantitative without standards; quantitative with standards. Not a trace element method. Instrument cost Size 22 INTRODUCTION AND SUMMARIES Chapter 1
Ultraviolet PhotoelectronSpectroscopy (UPS) 1.5.2 If monoenergeticphotons in the 10-100 eV energy range strike a samplematerial, photoelectrons from the valence levels and low-lying core levels (i.e., having lower binding energy than the photon energy) are ejected. Measurement of the kinetic energy distribution of the ejected electrons is known as Ultraviolet Photoelectron Spectroscopy(UPS).The physics of the technique is the sameasXPS, the only dif- ferencesbeing that much lower photon energiesare used and the primary emphasis is on examining the valence electron levels, rather than core levels. Owing to this emphasis, the primary use, when investigatingsolidsurfaces,is for electronicstruc- ture studiesin surfacephysicsrather than for materialsanalysis.There are,however, a number of situationswhere UPS offers advantagesover XPS for materialssurface analysis. Elemental analysis Destructive Chemicalstate information levels as for XPS Not usually, sometimesfrom availablecore levels No, somebeam damageto radiation-sensitivematerial Yes, but complicated usingvalence levels;for core Depth probed 2-1 00 A Depth profiling Yes, over the depth probed; deeper profiling requires sputter profiling Lateral resolution Generally none (mm size), but photoelectron micro- scopeswith capabilitiesdown to the 1-pm range exist Samplerequirements Vacuum-compatible material; flat samples best; size accepteddepends on instrumentation Main use Electronic structure studies of free molecules (gas phase), well-defined solid surfaces, and adsorbates on solidsurfaces No commercial instruments specificallyfor UPS; usu- ally an add-on to XPS (incrementalcost +$30,000)or done using a synchrotron ficility as the photon source 10 ft. x 10ft. for a stand-alonesystem Instrument cost Size 23
Auger Electron Spectroscopy (AES) 1.5.3 Auger Electron Spectroscopy(AES) uses a focusedelectron beam to createsecond- ary electronsnear the surfaceof a solid sample. Some of these (theAuger electrons) have energies characteristic of the elements and, in many cases, of the chemical bonding of the atoms from which they are released. Because of their characteristic energies and the shallowdepth from which they escapewithout energy loss, Auger electrons are able to characterize the elemental composition and, at times, the chemistryof the surfaces of samples.When used in combination with ion sputter- ing to gradually remove the surface, Auger spectroscopy can similarly characterize the samplein depth. The high spacial resolution of the electron beam and the pro- cessallowsmicroanalysisofthree-dimensionalregionsofsolidsamples.AEShas the attributes of high lateral resolution, relatively high sensitivity, standardless semi- quantitative analysis, and chemical bonding information in somecases. Range of elements Destructive All except H and He No, except to electron beam-sensitive materials and during depth profiling Yes, semiquantitative without standards; quantitative with standards 100ppm for most elements,depending on the matrix Yes, in many materials ElementalAnalysis Absolutesensitivity Chemicalstate information? Depth probed 5-1 00 a Depth profiling Lateral resolution Imaging/mapping Samplerequirements Vacuum-compatiblematerials Main use Instrument cost $100,000-$800,000 Size Yes, in combination with ion-beam sputtering 300A forAuger analysis, even less for imaging Yes, called ScanningAuger Microscopy, S A M Elementalcomposition of inorganicmaterials 10ft. x 15 ft. 24 INTRODUCTIONAND SUMMARIES Chapter 1
ReflectedElectron Energy-Loss Spectroscopy (REELS) 1.5.4 In Reflected ElectronEnergy-LossSpectroscopy(REELS)a solid specimen, placed in avacuum, is irradiatedwith a narrowbeam of electronsthat are sufficientlyener- getic to induce electron excitations with atoms or clusters of atoms. Some of the incident electrons reemerge from the sample having lost a specific amount of energyrelative to the well-definedenergyI$,of the incident electron. The number, direction k,and energy of the emitted electrons can be measured by an electron energy analyzer. Composition, crystal structure, and chemical bonding informa- tion can be obtained about the sample’ssurfacefrom the intensityandline shapeof the emitted electron energy-lossspectra by comparisonto standards. Range of elements Destructive Chemical band information Depth profiling Quantification Accuracy Detection limits Probing depth Lateral resolution Imaging/mapping Hydrogen to uranium; no isotopes No Yes; energeticsand orientation Yes; tilting or ion sputtering Standards required Few percent to tens of percent Few tenths of a percent 0.07-3.0 nm 100 nm-50 pm; sample independent; not limited by redifised primaries Yes, called REELM Sample requirements Solids; liquids; vacuum compatible; typically < 2.5 cm-diameter, < 1.5 cm-thickness Main use Few-monolayerthin-film analysis,e.%.,adsorbate and very thin-film reactions;submicron detection of metal hydrides $0-$700,000, free on any type of electron-excited Auger spectrometer None extra overAuger spectrometer Instrument cost Size 25
X-Ray Fluorescence(XRF) 1.6.1 In X-Ray Fluorescence (XRF), an X-ray beam is used to irradiatea specimen, and the emitted fluorescentX rays are analyzedwith a crystal spectrometer and scintil- lation or proportional counter. The fluorescentradiation normallyis diffractedby a crystalat differentanglesto separatetheX-raywavelengthsand thereforeto identify the elements; concentrations are determined from the peak intensities. For thin filmsXRF intensity-composition-thickness equationsderivedfrom first principles are used for the precision determination of compositionand thickness. This can be done also for each individuallayer of multiple-layerfilms. Range of elements All but low-Zelements: H, He, and Li Accuracy kl%for composition, 3%for thickness Destructive No Depth sampled Depth profiling Detection limits Sensitivity Lateral resolution Chemical bond information spectra Samplerequirements 15.0 cm in diameter Main use Identification of elements; determination of composition and thickness Instrument cost $50,000-$300,000 Size Normally in the 10-pm range, but can be a fewtens of A in the total-reflection range Normally no, but possible using variable-inci- dence X rays Normally 0.1% in concentration. 10-1 O5 A in thickness can be examined Normally none, but down to 10 pm using a microbeam Normally no, but can be obtained from softX-ray 5 ft. x 8 fi. 26 INTRODUCTIONAND SUMMARIES Chapter 1
Total ReflectionX-Ray Fluorescence Analysis (TXRF) 1.6.2 In Total Reflection X-Ray Fluorescence Analysis (TXRF), the surface of a solid specimenis exposed to an X-ray beam in grazinggeometry. The angle of incidence is kept below the critical anglefor total reflection,which is determined by the elec- tron density in the specimen surfacelayer, and is on the order of mrad. With total reflection,only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristicX-ray fluorescence radiation. The energy spectrum recordedby the detector contains quantitative information about the ele- mental composition and, especially, the trace impurity content of the surface,e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. Range of elements Destructive Chemical bonding information Depth probed Depth profiling capability Quantification Accuracy Detection limits Lateral resolution Sodium to uranium No Not usually Typically 1-5 nm Limited (variationof angleof incidence) Yes 1-20% 10"-1 oi4at/cm2 Limited, typically 10mm Samplerequirements Specular surhce, typically12.5-cm diameter Main use Multielement analysis, excellent detection limits for heavy metals; quantitative measurement of heavy- metal trace contamination on silicon wafers Instrument cost $300,000-$600,000 27
Particle-InducedX-Ray Emission (PIXE) 1.6.3 Particle-Induced X-Ray Emission (PIXE) is a quantitative, nondestructiveanalysis technique that relies on the spectrometry of characteristicX rays emitted during irradiation of a specimen with high-energy ionic particles (-0.3-10 MeV). The processis analogousto the emissionof characteristicX raysunder electron and pho- ton bombardment of a specimen (seethe articleson EDS, EMPA, and XRF).With appropriate corrections, X-ray yields (X rays per particle) can be converted to ele- mental concentrations.The background X-ray radiationfor PIXE is much less than that for electron excitation;thus, the detection limits fortraceelementsusing PIXE is orders of magnitude better. PIXE is best for the analysis of thin samples, suhce layers, and sampleswith limited amounts of materials, while photon bombardment (XRF)is better for bulk analysis and thick specimens. Using wavelength-dispersive detectors, PIXE,EMPA, and XRF can provide identificationof the chemicalbond- ing of elements. Although EMPA and EDS require that the specimen be in vac- uum, PIXE and XRF can be performed with the specimen in vacuum or at atmosphericpressure. Range of elements Chemical bonding information Depth probed Depth profiling Detection limits Accuracy Lateral resolution Imaging/mapping Lithium to uranium Yes, when spectralresolution is high I 1 0 p n Yes, by varying angle of incidence or particleenergy. Thin, freestanding foil, 0.1-1 0 ppm; d c e layers on thick specimens, 10'3-5x10'5 at/cm2; Bulk speci- mens, 1-100 ppm -2-1 O%, with standards -5 pm-2 mm Yes Samplerequirements Solids,liquids, and gases Main use Systemcost Systemsize Fast analysis for many elements, in all materials, simultaneously -$ 1,000,000,includingsrnall ionaccelerator(2-MeV H+) -100sq. ft. floor space 28 INTRODUCTIONAND SUMMARIES Chapter 1
Photoluminescence(PL) 1.7.1 In photoluminescence one measures physical and chemical properties of materials by using photons to induce excitedelectronicstatesin the materialsystemand ana- lyzing the optical emission as these statesrelax. Typically,light is directed onto the sample for excitation, and the emitted luminescence is collected by a lens and passed through an optical spectrometer onto a photodetector. The spectral distri- bution and time dependence of the emission are related to electronic transition probabilitieswithin the sample, and can be used to provide qualitativeand, some- times, quantitative information about chemical composition, structure (bonding, disorder, interfaces, quantum wells), impurities, kinetic processes, and energy transfer. Destructiveness Nondestructive Depth probed 0.1-3 pm; limited by light penetration depth and car- rier diffusion length Lateral resolution Down to 1-2 pm Quantitative abilities Intensity-based impurity quantification to several percent possible; energy quantification very precise Sensitivity Down to parts-per-trillion level, depending on impu- rity speciesand host Imaging/mapping Yes Samplerequirements Liquid or solid having optical transitions; probe size 2 pm to a few cm Main uses Band gaps of semiconductors; carrier lifetimes; shal- low impurity or defect detection; sample quality and structure Less than $10,000to over $200,000 Table top to small room Instrument cost Size 29
ModulationSpectroscopy 1.7.2 Modulation spectroscopy is a powerful experimental method for measuring the energy of transitions between the filled and empty electronic states in the bulk (band gaps) or at surfaces of semiconductor materials over a wide range of experi- mental conditions (temperature, ambients, etc.). By taking the derivative of the reflectance(or transmittance)of a material in an analogmanner, it producesa series of sharp, derivative-likespectralfeaturescorrespondingto the photon energyof the transitions.These energiesaresensitiveto a number of internal and externalparam- eters such as chemical composition, temperature, strain, and electricand magnetic fields. The line widths of these spectral features are a function of the quality of the material. Destructiveness Depth probed Lateral resolution Image/mapping Sensitivity Main uses Instrument cost Size Somemethods are nondestructive For bulk applications 0.1-1 pm; for surface applica- tions one monolayer is possible Down to 100pm Yes Alloy composition (e.g., Gal-,&&) Ax = 0.005; car- rier concentration 1015-1019cm-3 Contactless, nondestructive monitoring of band gaps in semiconductors; Wide range of temperatures and ambients (air, ultrahigh vacuum); in-situ monitoring of semiconductor growth $30,000-$100,000 For most methods about 2 x 3ft. 30 INTRODUCTIONAND SUMMARIES Chapter 1
Variable-AngleSpectroscopic Ellipsometry (VASE) 1.7.3 In Variable-AngleSpectroscopicEllipsometry(VA!5E),polarized light strikesa sur- fa.= and the polarization of the reflected light is analyzed using a second polarizer. The light beam is highly collimated and monochromatic, and is incident on the material at an oblique angle. For each angle of incidence and wavelength, the reflectedlight intensityis measured asa function of polarizationangle, allowingthe important ellipsometric parameter to be determined. An optimum set of angle of incidenceand wavelength combinationsis used to maximizemeasurementsensitiv- ity and information obtained. Physical quantities derivable from the measured parameter includethe opticalconstantsof bulk or filmed media, the thicknessesof films (from 1to a fewhundred nm), and the microstructuralcompositionofa mul- ticonstituent thin film. In general only materials with parallel interfaces, and with structural or chemical inhomogeneities on a scale less than about 1/ 10 the wave- length of the incident light, can be studied by ellipsometry. Main use Optical range Samplerequirements Planar materials and interfaces Destructive No, operation in any transparent ambient, including vacuum, gases, liquids, and air Depth probed Light penetration of the material (tensof nm to pm) Lateral resolution mm normally, 100pm under specialconditions Image/mapping No Instrument cost $50,000-$150,000 Size 0.5 rnx 1m Film thicknesses, microstructure, and optical proper- ties Near ultraviolet to mid infrared 31
FourierTransform InfraredSpectroscopy (IFTIR) 1.8.1 The vibrational motions of the chemicallybound constituents of matter have fre- quencies in the infrared regime. The oscillations induced by certain vibrational modes provide a means for matter to couple with an impinging beam of infrared electromagneticradiation and to exchange energywith it when the frequenciesare in resonance. In the infrared experiment, the intensity of a beam of infrared radia- tion is measured before (10)and after (I)it interactswith the sampleas a hnction of light frequency, {wi}.A plot of 1/10 versus frequency is the “infrared spectrum.” The identities, surrounding environments, and concentrations of the chemical bonds that are present can be determined. Information Element Range Destructive Chemical bonding information Depth profiling Depth Probed Detection limits Quantification Reproducibility Lateralresolution Imaging/mapping Vibrationalfrequenciesof chemicalbonds All, but not element specific No Yes, identificationof hnctional groups No, not under standard conditions Sampledependent, from pm’s to 10nm Ranges from undetectable to e lOI3 bonds/cc. Sub- monolayer sometimes Standards usually needed 0.1%variation over months 0.5 cm to 20 pm Available,but not routinely used Samplerequirements Solid, liquid, or gas in all forms; vacuum not required Main use Qualitative and quantitative determination of chemical species, both trace and bulk, for solids and thin films. Stress, structural inhomogeneity $50,000-$150,000 for FTIR; $20,000 or more for non-FT spectrophotometers Ranges from desktop to (2 x 2 m) Instrument cost Instrument size 32 INTRODUCTIONAND SUMMARIES Chapter 1
Raman Spectroscopy 1.8.2 Raman spectroscopy is the measurement, as a function of wavenumber, of the inelastic light scattering that results from the excitation of vibrations in molecular and crystalline materials. The excitation source is a single line of a continuous gas laser,which permits optical microscope optics to be used for measurement of sam- ples down to a few pm. Raman spectroscopyis sensitive to molecular and crystal structure; applications include chemical fingerprinting, examination of single grains in ceramics and rocks, single-crystal measurements, speciation of aqueous solutions, identification of compounds in bubbles and fluid inclusions, investiga- tions of structure and strain states in polycrystalline ceramics, glasses, fibers, gels, and thin and thick films. Information Element range Destructive Lateral resolution Depth profiling Depth probed Detection limits Quantitative Imaging Vibrational Frequencies of chemical bonds All, but not element specific No, unless sampleis susceptibleto laser damage 1 pm with microfocus instruments Limited to transparent materials Few pm to mm, depending on material 1000A normally, submonolayerin specialcases With difficulty;usuallyqualitativeonly Usually no, although imaging instruments have been built Samplerequirements Very flexible: liquids, gases, crystals, polycrystalline solids, powders, and thin films Main use Identification of unknown compounds in solutions, liquids, and crystalline materials; characterization of structural order, and phase transitions Instrument cost $150,00O-$250,000 Size 1.5 m x 2.5 m 33
High-ResolutionElectron Energy LossSpectroscopy (HREELS) 1.8.3 In High-Resolution Electron Energy Loss Spectroscopy (HREELS), a highly monoenergeticbeam of low energy (1-10 eV) electrons is focused onto a sample’s surface, and the scatteredelectronsare analyzed with high resolution of the scatter- ing energy and angle. Some of the scattered electrons suffer small characteristic energylossesdue to vibrational excitation of surface atoms and molecules.A vibra- tional spectrum can be obtained by counting the number of electrons versus the electron energy loss relative to the elastically scattered (no energy loss) electron beam. This spectrum is used mainly to identify chemical species (functional groups) in the first layer of the surface. Often this layer contains adsorbed species on a solid. Information Main use Range of elements Bonding Detection limits Quantification Depth probed Lateral resolution Molecularvibrational frequencies Nondestructive identification of the molecular hnc- tional groupspresent at surfaces Not element specific Any chemical bonds that have vibrations in the range 50-4000 cm-l 0.1% monolayer for strong vibrational bands Difficult, possible with standards 2 nm 1 mm2 Samplerequirements Single-crystal samples of conductors best; other solid samples are suitable, including polycrystalline metals, polymeric materials, semiconductors, and insulators, ultrahigh vacuum compatible;typically2 5mm diam- eter, 1-3 mm thick Instrument cost $100,000 plus associated techniques and vacuum system Size Attaches to vacuum chamber by 8-14 inch diameter flange. 34 INTRODUCTIONAND SUMMARIES Chapter 1
Solid State Nuclear MagneticResonance (NMR) 1.8.4 Solidstate Nuclear MagneticResonance (NMR) exploitsthe interaction of nuclear magnetic moments with electromagneticwaves in the radio frequency region. In the experiment, a solid specimen (crystallineor amorphous, aligned or randomly oriented) is placed in a strong external magnetic field (typically 1-14 Tesla) and irradiated with intense radio frequency pulses over a frequency range required to excite a specific atomic nucleus from the ground magnetic (spin) state to another higher state. As the nucleus releases back to its ground state the sample re-emits a radio signal at the excitation frequency, which is detected by electromagnetic induction and Fourier transformed to yield a plot of intensity versus frequency. The spectrum thus obtained identifiesthe presenceof the atom and its relativecon- centration (with standards) and is a sensitive indicator of structural and chemical bonding properties. It can servefor phase identificationaswell as for the character- ization of local bonding environments in disorderedmaterials. Elementsdetected Detection limit Surfacesensitivity Typicalsamplesize Measurement conditions Sampleform Main use Instrument cost Spacerequirement All elementspossessingan isotopewith a suitablemag- netic dipole moment (about half the elements in the periodic table) On the order of 1018 atoms of the nuclear isotope studied Not intrinsically surface sensitive: Surface areas > 10m2/g required or desirablefor surfacestudies 10-500 mg, varies greatly with the nucleus studied; samplelength, 0.5-5 cm; width, 0.5-2 cm Usuallyat ambient temperature and pressure Powder, single crystal, randomly oriented, or aligned film Element-selectivephase identification and quantifica- tion, structural characterization of disorderedstates $200,000-$1,200,000, depending mostly on the field strength desired 300 ft.2 35
RutherfordBackscatteringSpectrometry (RBS) 1.9.1 Rutherford BackscatteringSpectrometry(RBS) analysisis performed by bombard- ing a sample target with a monoenergetic beam of high-energy particles, typically helium, with an energyof a few MeV. A fraction of the incident atomsscatterback- wards from heavier atoms in the near-surface region of the target material,and usu- ally are detected with a solid state detector that measures their energy. The energy of a backscatteredparticle is related to the depth and mass of the target atom, while the number of backscattered particles detected from any given element is propor- tional to concentration. This relationship is used to generate a quantitative depth profile of the upper 1-2 pm of the sample. Alignment of the ion beam with the crystallographic axes of a sample permits crystal damage and lattice locations of impurities to be quantitativelymeasured and depth profiled. The primary applica- tions of RBS are the quantitative depth profilingof thin-film structures, crystailin- ity, dopants, and impurities. Range of elements Destructive Chemical bonding information Quantification Detection limits Lateralresolution Depth profiling Depth resolution Maximum depth Imaging/mapping Lithium to uranium + 10l3 He atomsimplanted;radiationdamage. No Yes, standardless;accuracy5-20% 1012-1016 atoms/cm2; 1-10 at.% for 1ow-z ele- ments; 0-100 ppm for high-Zelements 1 4 mm, 1pm in specialized equipment Yes and nondestructive 2-30 nm -2 pn, 20 pm with H+ Under development Samplerequirements Solid,vacuum compatible Main use Instrument cost $450,000-$1,000,000 Size 2 m x 7 m Nondestructive depth profiling of thin films, crystal damage information 36 INTRODUCTIONAND SUMMARIES Chapter 1
ElasticRecoilSpectrometry (ERS) 1.9.2 Energetic recoil ions, 'H+and 2H+,are produced when 4He+ions having energies in the MeV range undergo elasticnucleus-nucleus collisionswithin a hydrogen- or deuterium-containingsolidsample.Energyspectrometryof the recoilingions iden- tifiestheir mass and depth of origin. The total hydrogen content of a thin layer may be determined directly from the recoil fluence. In combination with Rutherford Backscattering(RBS)analysisof the samesample,elasticrecoilspectraprovidecon- centration profiles and complete compositional analysis of near-surface regions of the sample material. ERS requires equipment common to RES analysis. It is the simplestion beam techniqueforhydrogenprofiling,sinceion backscattering(RBS) from hydrogen is not possible. Range of elements Destructive Chemical bonding information Quantitation Sensitivity Depth probed Depth profiles Depth resolution Lateral resolution Unique selectionof 'H, 2H Radiationdamage may releaseH in polymers None Absolute atoms/cm2 f2% typically 5 x 1013atom/cm2 or 0.01at.% (typically) 5 1pm typically Yes; concentration profile to f 1% relative Varies with depth; 300-600 8,at depth 1000Ain Si 1-4 mm typically Samplerequirements Solid,vacuum compatible,dimensions2 5mm Main use Determination of H concentrations in thin fdms; rapid; matrix-independent Instrument cost As for RBS; MeV accelerator ($1,000,000- $1,500,000);servicesavailable Size Requires laboratory 2 20 ft. x 50 ft., depending on instrument 37
Medium-Energy Ion Scatteringwith Channeling and Blocking (MEIS) 1.9.3 Medium-Energy Ion Scattering (MEIS)with channeling and blocking is a quanti- tative, real space,nondestructivetechnique for studyingthe composition and struc- ture of surfices and interfacesburied up to a fav atomic layers below the surface. Single-crystal or epitaxial samples are required for the structural determinations. The basic quantities measured are the energyand angulardistribution of backscat- tered ions in the 50-400 keV range. The technique has elemental and depth sensi- tivity. The ion angular distributions are characterized by minima (dips) in intensity, the positions of which are closely connected to the relative positions of atoms in the surface layer. MEIS is more surfice sensitive, and more complex instrumentally than other surfice ion spectroscopies, though interpretation is straightforward. The technique is useful for the analysis of all ultrahigh vacuum compatiblesolids, and in particularmetals, semiconductors,and overlayerson such suhces (submonolayer adsorbateconcentrations, thin filmsof silicides,etc.). Elementsdetected Elementalsensitivity Chemicalsensitivity Depth probed Depth resolution Quantification Lateralresolution Destructive Samplerequirements Main uses Accuracy cost Size all elements Scales as the square of nuclear charge; best for heavy elements(e 1 0 4 monolayer); poor for hydrogen None Typically4-5 atomiclayers,but up to 200A in special cases Optimally on a monolayer level Absolute technique for elementalconcentrations None Not inherently Ultrahigh vacuum compatibility;practical size -1 cm in diameter Determination of structural parameters of surfices and interfaces;very high resolutiondepth profiling > 1% (structural parameters); element dependent (composition) $1,000,000-$2,000,000 - 7 m x 3 m 38 INTRODUCTIONAND SUMMARIES Chapter 1
Ion Scattering Spectroscopy (ISS) 1.9.4 In Ion Scattering Spectroscopy(ISS) a low-energy monoenergetic beam of ions is focusedonto a solidsurfaceand the energyof the scatteredions ismeasuredat some fixed angle.The collision of the inert ion beam, usually3He+,4He+,or 20Ne+,fol- lows the simple laws of conservation of momentum for a binary elastic collision with an atom in the outer surface ofthe solid. The energy loss thus identifies the atom struck. Inelasticcollisionsand ions that penetrate deeper than the first atomic layer normallydo not yield a sharp, discretepeak. Neighboring atoms do not affect the signal because the kinetics of the collision are much shorter than bond vibra- tions. A spectrum is obtained by measuring the number of ions scattered from the surficeas a function of their energyby passingthe scatteredions through an energy analyzer. The spectrum is normally plotted as a ratio of the number of ions of energy Eversus the energy of the primary beam 4.This can be directly converted to a plot of relative concentration versus atomic number, 2. Extremely detailed information regardingthe changesin elementalcomposition from the outer mono- layer to depths of 50A or more are routinely obtained by continuously monitoring the spectrum while slowlysputtering away the surface. Range of elements Samplerequirements Any solidvacuum-compatible material All but helium; hydrogen indirectly Sensitivity Quantitation Speed Depth of analysis Lateral resolution Imaging Sampledamage Main uses Instrument cost Size c 0.01 monolayer, 0.5% for C to 50 ppm for heavy metals Relative; 0.5-20% Singlespectrum, 0.1s; nominal 100-Aprofile, 30 min Outermost monatomic layer to any sputtered depth 150pm Yes, limited Only if done with sputter profiling Exclusive detection of outer most monatomic layer and very detailed depth profilesof the top 100A $25,000-$150,000 10ft. x 10fi. 39
DynamicSecondary Ion Mass Spectrometry (DynamicSIMS) 1.10.1 In Secondary Ion Mass Spectrometry (SIMS), a solid specimen, placed in a vac- uum, is bombarded with a narrow beam of ions, called primary ions, that are suffi- cientlyenergeticto cause ejection (sputtering)of atoms and small clusters of atoms from the bombarded region. Some of the atoms and atomic clusters are ejected as ions, called secondary ions. The secondary ions are subsequentlyaccelerated into a massspectrometer,wherethey areseparated accordingto their mass-to-chargeratio and counted. The relative quantities of the measured secondaryions are converted to concentrations, by comparison with standards, to reveal the composition and trace impurity content of the specimen as a function of sputteringtime (depth). Range of elements Destructive Chemical bonding information Quantification Accuracy Detection limits Depth probed Depth profiling Lateral resolution Imaging/mapping H to U; all isotopes Yes, material removed during sputtering In rare cases,from molecular clusters, but see StaticSIMS Standardsusuallyneeded 2% to factor of 2 for concentrations 10'~-10'~atoms/cm3 (ppb-ppm) 2 nm-100 pm (depends on sputter rate and data col- lection time) Yes, by the sputteringprocess; resolution 2-30 nm 50 nm-2 pm; 10nm in specialcases Yes Samplerequirements Solid conductorsand insulators, typicallyI2.5 cm in diameter, I 6 mm thick, vacuum compatible Main use Measurement of composition and of trace-level impu- rities in solid materials a hnction of depth, excellent detection limits, good depth resolution Instrument cost $500,000-$1,500,000 Size 10fi. x 15fi. 40 INTRODUCTIONAND SUMMARIES Chapter 1
Static Secondary Ion Mass Spectrometry (StaticSIMS) 1.10.2 Static SecondaryIon Mass Spectrometry (SIMS) involves the bombardment of a sample with an energetic (typically 1-10 kev) beam of particles, which may be either ions or neutrals.As a result of the interaction of these primary particles with the sample, species are ejected that have become ionized. These ejected species, known as secondaryions, are the analyticalsignal in SIMS. In static SIMS, the use of a low dose of incident particles (typically less than 5 x 10l2atoms/cm2) is critical to maintain the chemical integrity of the sample surface during analysis. A mass spectrometer sorts the secondary ions with respect to their specificcharge-to-massratio, therebyproviding a mass spectrum composed of fragment ions of the varioushnctional groups or compounds on the samplesur- face. The interpretation of these characteristicfragmentation patterns results in a chemicalanalysisof the outer few monolayers.The abilityto obtain surfacechemi- cal information is the key feature distinguishing static SIMS from dynamic SIMS, which profilesrapidlyinto the sample,destroyingthe chemicalintegrityof the sam- ple. Range of elements Destructive Chemical bonding information Depth probed Lateral resolution Imaging/mapping Quantification Massrange H to U; aI1isotopes Yes, if sputtered long enough Yes Outer 1or 2 monolayers Down to -100pm Yes Possiblewith appropriate standards Typically, up to 1000 amu (quadrupole), or up to 10,000amu (time of flight) Samplerequirements Solids, liquids (dispersed or evaporated on a sub- strate), or powders; must be vacuum compatible Main use Surface chemical analysis, particularly organics, poly- mers Instrument cost $500,000-$750,000 Size 4 ft. x 8 ft. 41
Surface Analysis by Laser Ionization (SALI) 1.10.3 In SurfaceAnalysis by Laser Ionization (SALI),a probe beam such as an ion beam, electron beam, or laser is directed onto a surfaceto removea sampleof material.An untuned, high-intensity laser beam passes parallel and close to but above the sur- face. The laser has sufficient intensity to induce a high degreeof nonresonant, and hence nonselective,photoionization of the vaporizedsampleof material within the laser beam. The nonselectively ionized sample is then subjected to mass spectral analysis to determine the nature of the unknown species. SALI spectra accurately reflect the surface composition, and the use of time-of-flight mass spectrometers provides fast, efficientand extremelysensitiveanalysis. Range of elements Destructive Post ionization approaches Information Detection limit Quantification Dynamic range Probing depth Lateralresolution Mass range Hydrogen to Uranium Yes,surfacelayers removed during analysis Multiphoton ionization (MPI), single-photon ionization (SPI) Elementalsurfaceanalysis (MPI);molecularsurface analysis (SPI) PPm to PPb -10%usingstandards Depth profile mode -1O4 2-5 down to 60 nm 1-10,000 amu or greater (to several pm in profilingmode) Samplerequirements Solid,vacuum compatible, anyshape Main uses Instrument cost $600,000-$1,000,000 Quantitative depth profiling, molecular analysisusing SPI mode; imaging Size Approximately45 sq. fi. 42 INTRODUCTION AND SUMMARIES Chapter 1
Sputtered NeutralMass Spectrometry (SNMS) 1.10.4 Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejectedfrom a solidsurfaceby energeticion bombardment. The sputtered atoms are ionized for mass spectrometricanalysis by a mechanism sepa- rate from the sputtering atomization.Assuch,SNMS is complementaryto Second- ary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms.Theforte of SNMS analysis, com- pared to SIMS, is the accurate measurement of concentration depth profiles through chemicallycomplex thin-film structures, including inte&ces, with excel- lent depth resolution and to trace concentration levels. Genericallyboth SAL1and GDMS are specific examplesof SNMS. In this articlewe concentrate on post ion- ization only by electron impact. Range of elements Li to U Destructive Yes, surfacematerial sputtered Chemical bonding None information Quantification Detection limits 10-100 ppm Depth probed Depth profiling Yes, by sputtering Lateral resolution Yes, accuracy x 3 without standards; 5-10% with analogousstandard; 30%with dissimilarstandard 15A (to many pm when profiling) A few mm in direct plasma sputtering; 0.1-10 pn using separate,focusedprimary ion-beam sputtering Imaging/mapping Yes, with separate, focusedprimary ion-beam Samplerequirements Solid conducting material, vacuum compatible; flat wafer up to 5-mm diameter;insulatoranalysispossible Main use Complete elemental analysis of complex thin-film structures to several pm depth, with excellent depth resolution cost $200,000-$450,000 Size 2.5 ft. x 5 ft. 43
Laser Ionization Mass Spectrometry (LIMS) 1.10.5 In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatiblesolid sample is irradiated with short pulses (+lons) of ultravioletlaser light. The laser pulse vaporizesa microvolume of material,and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquiresa completemass spectrum, typically coveringthe range 0- 250 atomic mass units (amu), with each laser pulse. A survey analysisof the mate- rial is performed in thisway. The relative intensitiesof the signalscan be converted to concentrations with the use of appropriate standards, and quantitative or semi- quantitative analysesare possible with the use of such standards. Range of elements Destructive Chemical bonding information Quantification Standards needed Detection limits Depth probed Depth profiling Lateralresolution 3-5 pm Mapping capabilities No Samplerequirements Vacuum-compatible solids; must be able to absorb ultraviolet radiation Main use Survey capability with ppm detection limits, not affected by surfacechargingeffects; complete elemen- tal coverage; survey microanalysis of contaminated areas, chemicalfailure analysis Instrument cost $400,000 Size 9 fi. x 5 fi. Hydrogen to uranium; all isotopes Yes, on a scaleof fewmicrometersdepth Yes, depending on the laser irradiance 10'~-10'~at/cm3 (ppm to 100ppm) variablewith material and laser power Yes, repeated laser shots sampleprogressivelydeeper layers; depth resolution 50-100 nm 44 INTRODUCTIONAND SUMMARIES Chapter 1
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Encyclopedia of materials characterization

  • 1. ENCYCLOPEDIA OF MATERIALS CHARACTERIZATION C. Richard Brundle Charles A. Evans, Jr. Shaun Wilson a MAT E R I A L S CHARACTER S E R I E S S U R F A C E S , I N T E R F A C E S , T H I N F I L M S +
  • 2.
  • 3.
  • 4. ENCYCLOPEDIA OF MATERIALS CHARACTERIZATION
  • 5. MATERIALS CHARACTERIZATION SERIES Surfaces, Interfaces,Thin Films SeriesEditors: C. Richard Brundleand CharlesA. Evans,Jr. SeriesTitles Encyclopedia of Materiah Characterization, C. Richard Brundle, CharacterizationofMekth andAlloys,Paul.H. Hollowayand P. N. Characterizationof Ceramics,Ronald E. Loehman CharacterimtionofPobmers, Ned J. Chou, Stephen P. Kowalczyk, Characterizationin SiliconProcessing,Yale Strausser Characterizationin CompoundSemiconductorProcessing, Yale Strausser CharacterizationofIntegraedCircuitPackagingMateriah, ThomasM. Moore and Robert G. McKenna CharacterizationofCadyticMateriah,IsraelE. Wachs Characterizationof CompositeMateriah,Hatsuo Ishida Characterizationof OpticalMateriah,Gregory J. Exarhos Characterizationof TribologicalMateriah,William A. Glaeser Characterizationof Organic ThinFilms,Abraham Ulman Charlesk Evans,Jr., and ShaunWilson Vaidyanathan Ravi Sard, and Ho-Ming Tong
  • 6. ENCYCLOPEDIA OF MLATERIALS CHARACTERIZATION Surfaces, Interfaces, Thin Films EDITORS C Ricbard Brundle CharlesA. Evans,Jr. SbaunWihon MANAGINGEDITOR LeeE. Fitzpatrick BUTTERWORTH-HEINEMANN Boston London Oxford Singapore Sydney Toronto Wellington MANNING Greenwich
  • 7. Thisbookwas acquired, developed,andproducedbyManningPublicationsCo. CopyrightQ 1992byButxetworch-Heinemann,adivisionofReedPublishingCUSA) Inc Au rightsr a d Noparcofthispublicarionmay be reproduced,scoredinaretriedsystem, ortransmitted, in anyform orbymeans. electronic, mechanical,photocopying, ororherwise, without prior writtenpermissionofthe publisher. Recognizingthe importanceof preservingwhat has beenwritten,it is thepolicyof Butterworth-Heinemannand ofManningto have the bookstheypublishprintedon acid-free paper, and weexertour best &m to that end. LibraryofCongressCataloging-in-Publication Data Brundle, C. R. Encyclopediaofmaterialscharacterization:surfaces,interfaces,thin films/C. Richard Brundle, CharlesA. Evans, Jr., ShamWilson. p. un.--(Materials characterizationseries) Indudesbibliographicalrefrrenoaand index. ISBN CL7506-9168-9 1.Surfaces(Tedmoology)-Tes~ I. Evans,Charlak 11.Wilson,Shaun. 111.Title. IV.Series. TA418.7.B73 I992 92-14999 620’.4Pdc20 CIP Butterworth-Heinemann 80MontvaleAvenue Stoneham,MA02180 ManningPublications Co. 3h i s Street Greenwich,CT 06830 1 0 9 8 7 6 5 4 3 Printedin the Unired StatesofAmerica
  • 8. Contents Prefaceto Series ix Preface x Acronyms Glossary xi Contributors xvi INTRODUCTIONAND SUMMARIES 1.0 Introduction I Technique Summaries 7-56 IMAGING TECHNIQUES(MICROSCOPY) 2.0 Introduction 57 2.1 Light Microscopy 60 2.2 ScanningElectron Microscopy, SEM 70 2.3 ScanningTunneling Microscopyand 2.4 TransmissionElectron Microscopy,TEM 99 ScanningForce Microscopy, STM and SFM 85 ELECTRONBEAM INSTRUMENTS 3.0 Introduction 117 3.1 Energy-DispersiveX-Ray Spectroscopy,EDS 120 3.2 Electron Energy-Loss Spectroscopyin the Transmission Electron Microscope,EELS 135 3.3 Cathodoluminescence, CL 149 3.4 ScanningTransmission Electron Microscopy, STEM 161 3.5 Electron Probe X-Ray Microanalysis,EPMA 175 V
  • 9. STRUCTUREDETERMINATIONBY DIFFRACTIONAND SCATTERING 4.0 Introduction 193 4.1 X-Ray Diffraction, XRD 198 4.2 ExtendedX-Ray Absorption Fine Structure,EXAFS 214 4.3 Su&ce ExtendedX-Ray Absorption Fine Structureand Near EdgeX-Ray Absorption Fine Structure,SEXAFS/NEXAFS Auger Electron Difiction, XPD and AED 227 4.4 X-Ray Photoelectron and 4.5 Low-Energy Electron Diffraction, LEED 252 4.6 Reflection High-EnergyElectron Diffraction,WEED 264 240 ELECTRONEMISSIONSPECTROSCOPIES 5.0 Introduction 279 5.1 X-Ray Photoelectron Spectroscopy,XPS 282 5.2 Ultraviolet Photoelectron Spectroscopy,UPS 300 5.3 Auger Electron Spectroscopy,AES 310 5.4 ReflectedElectron Energy-loss Spectroscopy, REELS 324 X-RAYEMISION TECHNIQUES 6.0 Introduction 335 6.1 X-Ray Fluorescence,XRF 338 6.2 Total Reflection X-Ray FluorescenceAnalysis, TXRF 349 6.3 Particle-InducedX-Ray Emission, PIXE 357 VISIBLE/W EMISSION, REFLECTION,AND ABSORPTION 7.0 Introduction 371 7.1 Photoluminescence,PL 373 7.2 Modulation Spectroscopy385 7.3 VariableAngle SpectroscopicEllipsometry, VASE 401 VIBRATIONALSPECTROSCOPIESAND NMR 8.0 Introduction 413 8.1 Fourier Transform Infrared Spectroscopy,FTIR 416 8.2 RamanSpectroscopy 428 8.3 High-Resolution Electron Energy Loss Spectroscopy,HREELS 4-42 8.4 Solid State Nuclear Magnetic Resonance, NMR 460 vi Contents
  • 10. ION SCATTERINGTECHNIQUFS 9.0 Introduction 473 9.1 Rutherford BackscatteringSpectrometry,RBS 476 9.2 Elastic Recoil Spectrometry,ERS 488 9.3 Medium-EnergyIon Scatteringwith Channelingand Blocking,MEIS 502 9.4 Ion scattering Spectroscopy,Iss 514 MASSAND OPTICALSPECTROSCOPIES 10.0 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 Introduction 527 Dynamic SecondaryIon MassSpectrometry,Dynamic SIMS StaticSecondaryIon Mass Spectrometry,StaticSIMS 549 SurficeAnalysis by h e r Ionization, SAL1 SputteredNeutral Mass Spectrometry,SNMS Laser Ionization Mass Spectrometry,LIMS SparkSourceMass Spectrometry,SSMS 598 Glow-DischargeMass Spectrometry,GDMS 609 InductivelyCoupled Plasma Mass Spectrometry,ICPMS InductivelyCoupled Plasma-Optical Emission Spectroscopy,ICP-OES 633 532 559 586 571 624 NEUTRONANDNUCLEARTECHNIQUES 1'1.0 Introduction 645 11.I Neutron Diffraction 648 11.2 Neutron Reflectivity 660 11.3 Neutron ActivationAnalysis, NAA 671 11.4 Nuclear ReactionAnalysis, NRA 680 PHYSICALAND MAGNETICPROPERTIES 12.0 Introduction 695 12.1 SurfaceRoughness:Measurement, Formation by Sputtering,Impact on Depth Profiling 698 12.2 Optical Scatterometry 711 12.3 Magneto-optic Kerr Rotation, MOJSE 723 12.4 Physical and ChemicalAdsorption Measurement of Solid SurfaceAreas 736 Contents vii
  • 11.
  • 12. Prefaceto Series This Materialj CharacterizationSeries attempts to address the needs of the practi- cal materials user, with an emphasis on the newer areas of surfice, interface, and thin film microcharacterization. The Series is composed of the leading volume, Enychpedia of Materialj Characterization,and a set of about 10 subsequent vol- umes concentratingon characterizationof individualmaterials classes. In the Encyclopedia, 50 brief articles (each 10-18 pages in length) are presented in a standard format designed for ease of reader access, with straightforward technique descriptionsand examples of their practical use. In addition to the arti- cles, there are one-page summaries for every technique, introductory summaries to groupings of related techniques, a complete glossary of acronyms, and a tabu- lar comparisonof the major features of all 50techniques. The 10volumes in the Series on characterizationof particular materials classes include volumes on silicon processing, metals and alloys, catalytic materials, integrated circuit packaging, etc. Characterization is approached from the mate- rials user’s point of view. Thus, in general, the format is based on properties, pro- cessing steps, materials classification, etc., rather than on a technique. The emphasis of all volumes is on surfaces, interfaces, and thin films, but the emphasis varies depending on the relative importance of these areas for the materials class concerned. Appendixes in each volume reproduce the relevant one-page summa- ries from the Encyclopedia and provide longer summaries for any techniques referred to that are not coveredin the Envcbpedia The concept for the Seriescame firom discussionwith Marjan Bace of Manning Publications Comparly. A gap exists between the way materials characterization is often presented and the needs of a large segment of the audience-the materials user, process engineer, manager, or student. In our experience,when, at the end of talks or courses on analytical techniques, a question is asked on how a particular material (or processing) characterization problem can be addressed the answer often is that the speaker is “an expert on the technique, not the materials aspects, and does not have experience with that particular situation.” This Series is an attempt to bridge this gap by approaching characterization problems from the sideof the materials user rather than from that of the analyticaltechniquesexpert. We would like to thank Marjan Bace for putting forward the original concept, Shaun Wilson of Charles Evans and Associates and Yale Strausser of Surface Sci- ence Laboratories fbr help in hrther defining the Series, and the Editors of all the individual volumes for their efforts to produce practical, materials user based volumes. C R Brundle C.A.Evans,Jr. ix
  • 13. This volume contains 50 articles describing analytical techniques for the charac- terization of solid materials, with emphasis on surfaces, intedices, thin films, and microanalyticalapproaches. It is part of the Materzah CharacterizationSeries, copublishedby Buttenvorth-Heinemann and Manning. Thisvolumecan serveasa stand-alone reference as well as a companion to the other volumes in the Series which deal with individual materials classes. Though authored by professional characterization experts the articles are written to be easily accessible to the materialsuser, the processengineer,the manager, the student-in shortto all those who arenot (andprobablydon’t intend to be) expertsbut who need to understand the potential applications of the techniques to materials problems. Too often, techniquedescriptions arewritten for the techniquespecialist. With 50 articles, organization of the book was difficult; certain techniques could equally well have appeared in more than one place. The organizational intent of the Editors was to group techniques that have a similarphysical basis, or that provide similar types of information. This is not the traditional organiza- tion of an encyclopedia,where articles are ordered alphabetically.Such ordering seemedless useful here, in part because many of the techniqueshave multiple pos- sible acronyms(anAcronym Glossavyis provided to help the reader). The articles follow a standard format for each technique: A clear description of the technique, the range of information it provides, the range of materials to which it is applicable, a few typical examples, and some comparison to other related techniques. Each technique has a “quickreference,” one-page summary in Chapter 1,consistingof a descriptiveparagraph and a tabular summary. Some of the techniques included apply more broadly than just to surhces, interhces, or thin films; for example X-Ray Diffraction and Infrared Spectros- copy, which have been used for half a century in bulk solid and liquid analysis, respectively.They are included here because they have by now been developed to also apply to surfaces. A fay techniques that are applied almost entirely to bulk materials (e.g., Neutron Diffraction) are included because they give complemen- tary information to other methods or because they are referred to significantlyin the 10 materials volumes in the Series. Some techniques were left out because they were consideredto be too restricted to specificapplicationsor materials. We wish to thank all the many contributorsfor their efforts, and their patience and restraint in dealing with the Editors who took a hirly demanding approach to establishingthe format, length, style, and content of the articles. We hope the readers will consider our efforts worthwhile. Finally, we would like to thank Lee Fitzpatrick of Manning Publications Co. for her professional help as Managing Editor. C.R.Brund. CA.Evans,/r. S.Mhon
  • 14. Acronyms Glossary This glossary lists all the acronyms referred to in the encyclopedia together with their meanings. The major technique acronyms are listed alphabetically. Alter- natives to these acronyms are listed immediately below each of these entries, if they exist. Related acronyms (variations or subsets of techniques; terminology used within the technique area) are grouped together below the major acronym and indented to the right. Most, but not all, of the techniques listed here are the subject of individual articlesin this volume. AAS AA VPD-AAS GFAA FAA AES Auger S A M SAM AED ADAM K.E CMA AIS BET BSDF BRDF BTDF CL CLSM EDS EDX EDAX EELS HEELS REELS REELM EELS AtomicAbsorption Spectroscopy AtomicAbsorption Vapor Phase Decomposition-AtomicAbsorption Spectroscopy GraphiteFurnaceAtomicAbsorption Flame AtomicAbsorption Auger ElectronSpectroscopy Auger Electron Spectroscopy ScanningAuger Microscopy ScanningAuger Microprobe Auger Electron Diffraction Angular DistributionAuger Microscopy KineticEnergy CylindricalMirror Analyzer Atom InelasticScattering Brunauer, Emmett, andTeller equation BidirectionalScatteringDistribution Function BidirectionalReflective Distribution Function BidirectionalTransmissionDistribution Function Cathodluminescence ConfocalScanningLaser Microscope Energy Dispersive(X-Ray) Spectroscopy Energy DispersiveX-Ray Spectroscopy CompanysellingEDX equipment Electron EnergyLossSpectroscopy High-ResolutionElectronEnergy-Loss Spectroscopy ReflectedElectronEnergy-Loss Spectroscopy ReflectionElectronEnergy-Loss Microscopy Low-Energy Electron-LossSpectroscopy xi
  • 15. PEELS EXELFS EELFS CEELS VEELS EPMA ElectronProbe ERS HFS HRS FRS ERDA ERD PRD EXAFS SEXAFS NEXAFS XANES XAFS FMR FTIR FT Raman HREELS HRTEM GDMS GDQMS Gloquad ICP-MS ICP LA-ICP-MS ICP-Optical ICP IETS IR FTIR GC-FTIR TGA-FTIR ATR Parallel (Detection)ElectronEnergy-LossSpectrscopy ExtendedEnergy-Loss Fine Structure ElectronEnergy-Loss FineStructure CoreElectronEnergy-Loss Spectroscopy ValenceElectronEnergy-Loss Spectroscopy Electron ProbeMicroanalysis ElectronProbeMicroanalysis ElasticRecoil Spectrometry HydrogenForwardScattering Hydrogen Recoil Spectrometry ForwardRecoil Spectrometry ElasticRecoil DetectionAnalysis ElasticRecoilDetection ParticleRecoilDetection ExtendedX-RayAbsorptionFine Structure SurfaceExtendedX-RayAbsorptionFine Structure Near-EdgeX-RayAbsorptionFine Structure X-Ray AbsorptionNear-Edge Structure X-RayAbsorptionFine Structure FerromagneticResonance See IR SeeRaman See EELS SeeTEM Glow DischargeMass Spectrometry Glow DischargeMassSpectrometryusing a QuadrupleMassAnalyser Manufacturername InductivelyCoupledPlasma Mass Spectrometry InductivelyCoupled Plasma Laser Ablation ICP-MS InductivelyCoupledPlasma OpticalEmission InductivelyCoupledPlasma InelasticElectronTunnelingSpectroscopy Infrared(Spectroscopy) FourierTransformInfra-Red (Spectroscopy) Gas ChromatographyFTIR Thermo GravimetricAnalysisFTIR ArtenuatedTotalReflection xii Acronyms Glossary
  • 16. RA IRAS ISS LEIS RCE LEED LIMS LAMMA LAMMS LIMA NRMPI MEISS MEIS MOKE SMOKE NAA INAA NEXAFS XANES NIS NMR MAS NRA OES PAS PIXE HIXE PL PLE PR EBER RDS Raman FT Raman RS RRS CARS ReflectionAbsorption (Spectroscopy) Infrared ReflectionAbsorption Spectroscopy Ion ScatteringSpectrometry Low-Energy Ion Scattering ResonanceChargeExchange Low-Energy Electron Diffraction Laser Ionization Mass Spectrometry Laser MicroprobeMass Analysis Laser MicroprobeMass Spectrometry Laser Ionization MassAnalysis Nonresonant Multi-Photon Ionization Medium-EnergyIon ScatteringSpectrometry Medium-EnergyIon Scattering Magneto-optic Kerr Rotation SurfaceMagneto-optic Kerr Rotation Neutron ActivationAnalysis InstrumentalNeutron ActivationAnalysis Near EdgeX-RayAbsorption Fine Structure X-Ray Absorption Near EdgeStructure Neutron InelasticScattering Nuclear MagneticResonance Magic-Angle Spinning Nuclear ReactionAnalysis Optical Emission Spectroscopy PhotoacousticSpectroscopy Particle InducedX-Ray Emission Hydrogen/HeliumInducedX-ray Emission Photoluminescence PhotoluminescenceExcitation Photoreflectance ElectronBeam Electroreflectance ReflectionDifferenceSpectroscopy Raman Spectroscopy FourierTransform Raman Spectroscopy Raman Scattering ResonantRaman Scattering CoherentAnti-Stokes Raman Scattering Acronyms Glossary xiii
  • 17. SERS SurfaceEnhancedRaman Spectroscopy RutherfordBackscatteringSpectrometry High-EnergyIon Scattering Reflected High Energy Electron Diffraction ScanningReflectionElectronMicroscopy SurficeAnalysisby h e r Ionization Post-IonizationSecondaryIon Mass Spectrometry Multi-Photon Nonresonant Post Ionization MultiphotonResonant Post Ionization ResonantPost Ionization Multi-PhotonIonization Single-PhotonIonization Sputter-InitiatedResonance IonizationSpectroscopy SurfaceAnalysii by ResonantIonizationSpectroscopy Time-of-FlightMass Spectrometer SeeAES ScanningElectronMicroscopy ScanningElectronMicroprobe SecondaryElectron Miscroscopy SecondaryElectron Backscattered Electron SecondaryElectronMicroscopywith PolarizationAnalysis ScanningForce Microscopy ScanningForceMicroscope AtomicForceMicroscopy ScanningProbeMicroscopy SecondaryIon MassSpectrometry DynamicSecondaryIon Mass Spectrometry StaticSecondaryIon Mass Spectrometry SIMSusing a QuadrupleMassSpectrometer SIMSusing a MagneticSectorMassSpectrometer SeeMagneticSIMS SIMSusingTune-of-FlightMass Spectrometer Post IonizationSIMS SputteredNeutralsMass Spectrometry SecondaryNeutralsMass Spectrometry Direct BombardmentElectronGasSNMS SparkSourceMass Spectrometry SparkSourceMass Spectrometry SeeTEM ScanningTunnelingMicroscopy RBS HEIS WEED SREM SAL1 PISIMS MPNRPI MRRPI RPI MPI SPI SINS SARIS TOFMS SAM SEM SE BSE SEMPA SFM AFM SPM SIMS DynamicSIMS StaticSIMS MagneticSIMS SectorSIMS TOF-SIMS PISIMS Q-SIMS SNMS SNMSd SSMS SparkSource STEM STM xiv Acronyms Glossary
  • 18. SPM ScanningTunnelingMicroscope ScanningProbeMicroscopy Thermal EnergyAtom Scattering TransmissionElectron Microscopy TransmissionElectron Microscope ConventionalTransmission Electron Microscopy ScanningTransmission Electron Microscopy High ResolutionTransmission Electron Microscopy SelectedArea Diffraction AnalyticalElectron Microscopy ConvergentBeam Electron Diffraction LorentzTransmissionElectron Microscopy Thin Layer Chromatography Tandem ScanningReflected-LightMicroscope Tandem ScanningReflected-LightMicroscope SeeXRF TEAS TEM CTEM STEM HRTEM SAD AEM CBED LTEM TLC TSRLM TSM TXRF UPS MPS VASE WDS WDX XAS X P S ESCA XPD PHD KE XRD GIXD GIXRD DCD XRF XFS TXRF TRXFR VPD-TXRF Ultraviolet PhotoelectronSpectroscopy Ultraviolet PhotoemissionSpectroscopy MolecularPhotoelectronSpectroscopy VariableAngle SpectroscopicEllipsometry WavelengthDispersive &-Ray) Spectroscopy Wavelength DispersiveX-Ray Spectroscopy X-Ray Absorption Spectroscopy X-Ray Photoelectron Spectroscopy X-Ray PhotoemissionSpectroscopy Electron Spectroscopyfor ChemicalAnalysis X-Ray PhotoelectronDiffraction PhotoelectronDiffraction KineticEnergy X-RayDiffraction GrazingIncidenceX-Ray Diffraction GrazingIncidenceX-Ray Diffraction Double CrystalDiffractometer X-Ray Fluorescence X-Ray FluorescenceSpectroscopy Total ReflectionX-Ray Fluorescence Total ReflectionX-Ray Fluorescence Vapor Phase DecompositionTotalX-Ray Fluorescence Acronyms Glossan/ xv
  • 19. MarkR Antonio BP Research International Cleveland, OH J. E. E. Bagh IBMAlrnaden ResearchCenter SanJose, CA ScottBaumann CharlesEvans &Associates Redwood City, CA ChristopherH. Becker SRIInternational MenloPark, CA AlbertJ. Bevolo Ames Laboratory, Iowa StateUniversity Ames, IA J. B. Bindell AT&T BellLaboratories Allentown, PA FilippoRadicati diBrozolo CharlesEvans&Associates Redwood City, CA C. R Brundle IBMAlmaden ResearchCenter SanJose, CA DanieleCherniak Rennsselaer PolytechnicInstitute Troy,NY Paul Chu CharlesEvans &Associates RedwoodCity,CA Carl Colvard CharlesEvans&Assoociates RedwoodCity, CA J. Neal Cox INTEL,ComponentsResearch SantaClara, CA John Gustav Delly McCroneResearch Institute Chicago, IL ExtendedX-RayAbsorptionFine Structure ElasticRecoil Spectrometry RutherfordBackscatteringSpectrometry SurfaceAnalysisby Laser Ionization ReflectedElectron Energy-LossSpectro~copy ScanningElectron Microscopy Laser Ionizarion Mass Spectrometry X-Ray Photoelectron Spectroscopy; Ultraviolet PhotoelectronSpectroscopy Nuclear ReactionAnalysis DynamicSecondaryIon MassSpectrometry Photoluminescence FourierTransformInfraredSpectroscopy Light Microscopy xvi
  • 20. Hellmut F.ckert UniversityofCalifornia, SantaBarbara SantaBarbara, CA Peter Eichinger GeMeTecAnalysis Munich P. Fenter RutgersUniversity Piscataway,NJ David E. Fowler IBM Almaden Research Center SanJose, CA S. M. Gaspar University ofNew Mexico Albuquerque,NM ROYH. Geiss IBMAlmaden Research Center SanJose, CA TorgnyGustafsson RutgersUniversity Piscataway,NJ William L. Harrington EvansFast Plainsboro, NJ BrentD. Hermsmeier IBMAlmaden ResearchCenter SanJose,CA K.C. Hidunan University ofNewMexico Albuquerque,NM Tim Z. Hossain CornellUniversity Ithica,NY Rebecca S. Howland ParkScientificInstruments Sunnyvale,CA JohnC.Huneke CharlesEvans&Assodates RedwoodCity, CA TingC. Huang IBMAlmadenResearch Center SanJose, CA William Katz EvansCentral Minnetonka,MN MichaelD. Kirk Park ScientificInstruments Sunnyvale,CA SolidStateNuclearMagneticResonance TotalReflectionX-Ray Fluorescence Medium-Energy Ion Scatteringwith ChannelingandBlocking Magneto-optic Kerr Rotation OpticalScatterometry Energy-DispersiveX-Ray Spectroscopy Medium-EnergyIon ScattefmgWith Channelingand Blocking SparkSourceMassSpectromeuy X-Ray PhotoelectronandAuger Electron Diffraction OpticalScatterometry NeutronActivationAnalysis ScanningTunnelingMicroscopy and ScanningForce Microscorn SputteredNeutralMassSpectrometry, Glow-DischargeMass Spectrometry X-Ray Fluorescence StaticSecondaryIonMassSpectrometry ScanningTunnelingMicroscopy and ScanningForce Microscopy Contributors xvii
  • 21. BruceE. Koel UniversityofSouthernCalifornia LosAngles, CA Max G. Lagally UniversityofWmnsin, Madison, WI W. A. Lanford StateUniversityofNewYork, Albany, NY CharlesE. Lyman Lehigh University Bethlehem, PA SusanMacKay Perkin Elmer Eden Prairie, MN John R McNeil Universityof New Mexico Albuquerque,NM Ronald G. Musket LawrenceLivermoreNationalLaboratory Livermore,(=A S. S.H. Naqvi Universiy of New Mexico Albuquerque,NM DaleE. Newbury NationalInstitutesof Scienceand Technology Gairhersburg, MD David Norman SERCDaresbury Laboratory Daresbury, Cheshire John W. Olesik Ohio StateUniversity Columbus,OH Fred H. Pollak BrooklynCollege,CUNY NewYork, NY ThomasP. Russell IBMA l d e n ResearchCenter SanJose, CA Donald E. Savage UniversityofWisconsin Madison, WI Kurt E. Si& LosAlamosNationalLaboratory LosAlamos,NM Paul G. Snyder Universityof Nebraska Lincoln, NE High-ResolutionElectron Energy Loss Spectrometry Low-EnergyElectron Diffraction Nudear ReactionAnalysis ScanningTransmission Electron Microscopy Surface Analysisby LaserIonization OpticalScatterometry Partide-InducedX-Ray Emission OpticalScatterometry Electron ProbeX-RayMicroanalysis SurfaceExtended X-Ray Absorption FineStructure,Near EdgeX-Ray AbsorptionFine Structure InductivelyCoupledPlasma-Optical Emission Spectroscopy Modulation spectroscopy Neutron Reflectivity ReflectionHigh-EnergyElectron Diffraction Transmission E l m n Microscopy VariableAngle SpectroscopicEllipsometry xviii Contributors
  • 22. Gene Sparrow AdvancedR&D St. Paul, MN Fred A. Stevie AT&T Bell Laboratories Allentown,PA Yale E. Strausser SurfaceScienceLaboratories Mountainview,CA BarryJ. Streusand AppliedAnalytical Austin,TX Raymond G. Teller BP Research International Cleveland,OH Michael F. Toney IBM AlmadenResearch Center SanJose, CA WojciechViech CharlesEvans &Assoociates RedwoodCity, CA William B. White PennsylvaniaSkateUniVeI'Siq' UniversityPark, PA S.R Wilson Universityof New Mexico Albuquerque,NM JohnA. Woollam Universityof Nebraska Lincoln,NE Ben G. Yacobi Universityof Californiaat LosAngeles LosAngeles, CA DavidJ. C. Yates Consultant Poway, CA Nestor J. Zaluzec ArgonneNational Laboratory Argonne, IL Ion ScatteringSpectroscopy SurfaceRoughness:Measurement, Formation by Sputtering, Impact on Depth Profiling AugerElectron Spectroscopy InductivelyCoupled Plasma Mass Spectrometry Neutron Diffraction X-Ray Diffraction Glow-DischargeMassSpectrometry Raman Spectroscopy Optical Scatterometry VariableAngleSpectroscopicEllipsometry Cathodoluminescence Physical and ChemicalAdsorption for the Measurementof SolidSurfaceAreas ElectronEnergy-Loss Spectroscopyin the TransmissionElectronMicroscope Contributors xix
  • 23.
  • 24. I INTRODUCTION AND SUMMARIES 1.0 INTRODUCTION Though a wide range of analytical techniques is covered in this volume there are certain traits common to many of them. Most involve eitherelectrons,photons, or ions as a probe beam strikingthe materialto be analyzed.The beaminteractswith the materialin someway, and in someof the techniquesthe changesinducedin the beam (energy, intensity, and angular distribution) are monitored after the inter- action, and analytical information is derived from the observation of these changes. In other techniques the information used for analysis comes from elec- trons, photons, or ions that are ejected from the sample under the stimulation of the probe beam. In many situationsseveral connectedprocesses may be going on more or less simultaneously, with a particular analytical technique picking out only one aspect, e.g., the extent of absorption of incident light, or the kinetic energydistributionof ejectedelectrons. The rangeof informationprovidedby the techniquesdiscussed hereisas0wide, but again there are common themes. What types of information are provided by these techniques?Elemental composition is perhaps the most basic information, followed by chemical state information, phase identification, and the determina- tion ofstructure(atomicsites, bond lengths,and angles). One might need to know howthesevaryas a functionof depth into the material,or spatiallyacrossthe mate- rial, and many techniquesspecializein addressingthesequestionsdown to very fine dimensions.For su&s, interfaces,and thin filmsthere is ofienverylittlematerial at all to analyze, hence the presence of many microanalyticalmethods in this vol- ume. Within thisfield (microanalysis)it iso b necessaryto identifytracecompo- nents down to extremelylow concentration (partsper trillion in some cases) and a number of techniquesspecializein this aspect. In other cases a high degreeof accu- racy in measuringthe presence of major components might be the issue. Usually the techniques that are good fbr trace identificationare not the sameones used to accurately quantifymajor components. Most complete analyses require the use of 1
  • 25. multiple techniques, the selection of which depends on the nature of the sample and the desiredinformation. Thisfirst chaptercontainsonepage summariesofeachof the 50techniquescov- ered in the followingchapters.All summarieshave the same format to alloweasy comparisonand quick accessto the information.Further comparativeinformation is provided in the introductions to the chapters. Finally, a table is provided at the endofthis introduction,inwhichmanyoftheimportantparametersdescribingthe capabilitiesforall 50techniquesarelisted. The subtitleof this Series is “Su&m, Interfices, and Thin Films.” The defi- nition of a “surface”or of a “thinfilm”varies considerablyh m person to person and with application area. The academic discipline of ‘‘Surfice Science” is largely concerned with chemistry and physics at the atomic monolayer level, whereas the “surfaceregion” in an engineeringor applicationssense can be much more extensive. The same is true for interfaces between materials. The practical consideration in distinguishing“sudace” from “bulk” or “thin” from “thick” is usually connected to the property of interest in the application. Thus, fbr a cata- lytic reaction the presence of haf a monolayer of extraneoussulfur atoms in the top atomic layer of the catalyst material might be critical, whereas for a corro- sion protection layer (for example, Cr segregation to the surface region in steels) the important region ofdepth may be several hundred 8,. For interfaces the epi- taxial relationship between he last atomic layer of a single crystal material and the first layer of the adjoining material may be critical for the electrical proper- ties of a device, whereas diffusion barrier interfaces elsewhere in the same device may be 1000A thick. In thin-film technologyrequirements can range from layers pm thick, which for the majority ofanalytical techniquesdiscussed in this volume constitute bulk material, to layers as thin as 50 8, or so in thin-film magnetic recording technology. Because of these different perceptions of “thick” and “thin,”actual numbers are used whenever discussingthe depth an analytical tech- nique examines.Thus in Ion ScatteringSpectroscopythe signalsused in the anal- ysis are generated fiom only the top atomic monolayer of material exposed to a vacuum, whereas in X-ray photoemission up to 1008,is probed, and in X-ray flu- orescencethe signal can come from integrateddepths ranging up to 10 pm. Note that in these three examples, two are quoted as having rangesofdepths.For many ofthe techniques it is impossible to assign unique values because the depth from which a signal originates may depend both on the particular manner in which the technique is used, and on the nature ofthe material being examined.Perfbrming measurements at grazing angles ofincidence of the probe beain, or grazing exit angles fbr the detected signal, will usually make the technique more surfacesensi- tive. For techniques where X-ray, electron, or high-energy ion scattering is the critical Factor in determining the depth analyzed, materials consisting of light elements are always probed more deeply than materials consisting of heavy ele- ments. 2 INTRODUCTIONAND SUMMARIES Chapter 1
  • 26. Another confusingissue is that of “depth resolution.” It is a measurementof the technique’s ability to clearly distinguish a property as a function of depth. For example a depth resolution of 20 A, quoted in an elemental composition analysis, means that the compositionat one depth can be distinguishedfrom that at another depth if there is at least 20 A depth profile is a record of the variationof a property (suchascomposition)as a function of depth. Some of the techniques in this volume have essentially no intrinsicdepth profiling capabilities;the signalis representativeof the materialinte- grated over a fived probing depth. Most, however, can vary the depth probed by varying the condition of analysis,or by removing the surface, layer by layer, while collectingdata. By varying the angle of incidence, the X-ray, electron, or ion beam energy, etc. many techniques are capable of acquiringdepth profiles. Those profiles are gener- ated by combining several measurements, each representative of a different inte- grated depth. The higher energy ion scattering techniques (Medium Energy Ion Scattering, MEIS,and Rutherford Backscattering, RBS), however, are unique in that the natural output of the methods is compositionasa function of depth. By far the most common way of depth profilingis the destructivemethod of removingthe surface, layer by layer, while also taking data. For the mass spectrometry-based techniques of Chapter 10, removal of surface material is intrinsic to the sputtering and ionizationprocess. Other methods, suchasAuger Electron Spectroscopy,AES, or X-Ray Photoemission,XPS, use an ancillaryion beam to remove material while constantly ionizing the newly exposed surface. Under the most favorable condi- tions depth resolutionsof around 20Acan be achievedthisway, but there are many artifacts to be aware of and the depth resolution usually degrades rapidly with depth. Someaspectsof sputterdepth profilingaretouched upon in the article“Sur- face Roughness”in Chapter 12, but for a more completediscussionof the capabil- ities and limitations of sputter depth profiling the reader is referred to a paper by D. Marton and J. Fine in Thin Solid Films, 185, 79, 1990 and to other articles cited there. between them. 3
  • 27. Compilationof Comparative Informationonthe AnalyticalTechniques DiscussedinThisVolume Maininformation Article Technique No. 2.1 2.2 2.3 2.3 2.4 3.1 3.2 XI 0 3.3 0 3.4 C 0 4.1zrn P 4.2 0 4.3 C 4.3 4.4 5E !E Firn 4.6 3 2 3.5 v) % 4.5 5.1 5.2 5.3 8PI R 4d Light Microscopy SEM STM SFM TEM EDS EELS Gthodo- 1umin&cence STEM EPMA XRD EXAFS SEXAFS NEXAFS XPD LEED WEED XPS U P S AES Depth probed ( w i d ) Variable m e subpm m m m subA m e m subA 200 nm* 1pm m e e 20 nm* e e m e e . e 10nm-pm 100nm* e lpm 10Cun e e Bulk* e e lnm e . . . e . . e . 1nm m . 3nm 1 nm m m l n m m e 3nm m e e 1nm e . 2 nm T p ofsolidsample (typical) 0.2 pn 10 nm i A 1Ml 5 nm 0.5 pn 1 nm 1Cun lnm 0.5 pm mm mm mm mm 150prn 0.1 mrn 0.02 mm 150pm mm 100nrn 500 ppm Few% PPm - 100ppm 3% Few% Few % Few% 1% - - 1% 0.1% - All Cond,coatedins. Conductors All All;e200 nm thick AU;Z>5 All;e30 nm thick All; sunicond. usually All; e200 nm thick All; flat best Crystalline All Surfaceand adsorbate Surfaceandadsorbate Singlecrystal Singlecrystal Singlecrysml All All All, inorganic usually N 1 Y 2 N 2 N 2 Y 3 Y 2 Y 2 Y 1 Y 3 Y 3 N 2 YIN - Y - Y - Y 3 Y - Y - Y 3 Y - Y 3 1 Y 1 Y 3 Y 2 Y 2 Y 2 Y 3 N 3 N 3 N 2 Y 1 Y 3 N 3 N 3 N 3 N 2 N 2 N 1 Y 3 N 1 Y
  • 28. Compilationof ComparativeInformationonthe AnalyticalTechniquesDiscussedinThisVolume Maininformation Article Technique No. 5.4 6.1 6.2 6.3 7.1 7.2 7.3 8.1 8.2 8.3 8.4 9.1 9.2 9.3 9.4 10.1 10.2 10.3 VI REELS XRF TXRF PKE Photo- luminescence Modulation VASE FTIR Raman Scattering HREELS NMR RBS ERS MEIS ISS Dynamic SIMS static SIMS SALI spectrosmpy 1Pm lw a a a m a a Fewpm a a F e w p a a 2 nm a m Bulk a a m To 2 pn 1 P n 0 3A 0 0 . 1nm 0 2 nm o m a 3 A a m 3 A 100nm rnm un 100pn FewPn 100pm 20 pm llrm un mm 1oow 100 nrn PPrn - Variable Variable 1% 0.01-10% 0.01% 0.1%-10% 50 ppm-1% PPb-PPm Few % PPb-PPrn All All Trace heavy metals All All, semicond. usually All, semicond. usually Flat thin h All All AU;flatcond. best All; not all elements All H containing All; usuallysinglecrystal All All, mostly sernicond. All, mostly polymer AU,mostlyinorg. Y - 3 N N 2 1 Y Y 3 3 Y Y 3 3 Y N 1 2 N N 2 3 N N 2 3 Y N 2 1 Y N 2 2 Y Y 3 3 N N 3 3 N Y l N 3 2 Y Y - 3 N Y 3 3 N Y - 3 Y Y 3 1 Y Y 3 2 Y Y 3 3 N
  • 29. Compilationof ComparativeInformationon the AnalyticalTechniques DiscussedinThis Volume Depth Width (typical) (typical) (typical) 0, 6. Maill ~ n l l a t i ~ TkCe Types ofsolid sample (typical) ArrideTechnique probed probed capability No. 10.4 SNMS . 1.5 nm un 50 PPm Flat conductors Y 2 2 Y 10.5 LIMS * . 10.6 SSMS 0 10.7 GDMS 0 10.8 ICPMS .10.9 ICPOES 0 ll.' ; E 2 0 l l 5 11.2 ;l;g;v 11.3 NAA 11.4 NRA 20 0 C Optical 0 : 12.2 scatternmetryz v) 12.3 MOU P 12.4 Adsorption U .. * . 100nm 2pm 1-100ppm All Y 3 2 Y 3 P cm 0.05 ppm Samplef o r m s e l d e Y - 2 Y 5w mm PPt All Y 2 1 Y 5 P mm PPb All Y 1 1 Y 100nm cm ppt-ppb Sampleformselecd y 3 2 Y Bulk I Crystalline N - 3 N uptomm - - Flatpolymerfilms N - 3 N Bulk - PPt-PPm Trace metals N 2 3 Y 10-1OOnm l o p 10-lOOppm All:z<21 Y - 3 Y 0 - mm - Flatsmoothfilms N 1 3 Y 30nm 0 . 5 ~ - Magnetic films N 1 2 N Outeratoms - - LargesurFacearea Y - 2 N v) Notes Tbitable shouldbeuscdasa"quickreference" guideody. CommnrialZnmMuntcThesemtypical costs;large ranges dependingon sophistication andaccessories: 1 means < $50k2 means $50-300k; 3 means >$300k."-" meansno mmplcrecommerciainstrument. Usup:Numbersreferto usage for anaylsisofsolidmaterials. 1 means Extensive;2 means medium;3 means not common. Timcapz6iliy:Guideonly. Oftenvery material/wnditions dependent. "-" meansnot used for trace components. !ix % *Measuredin transmission. iii v) 0 5 'E! m,-I
  • 30. Light Microscopy 1.2.1 The light microscope uses the visible or near visible portion of the electromagnetic spectrum; light microscopy is the interpretive use of the light microscope. This technique, which is much older than other characterization instruments, can trace its origin to the 17th century. Modern analytical and characterization methods began about 150years ago when thin sections of rocks and minerals, and the first polished metal and metal-alloy specimens were prepared and viewed with the intention of correlating their structures with their properties. The technique involves,at itsvery basiclevel,the simple, directvisual observationof a samplewith white-light resolution to 0.2 pm. The morphology, color, opacity, and optical propertiesare often sufficient to characterizeand identifl a material. Range of samples characterized Destructive Quantification Detection limits Resolvingpower Imagingcapabilities Main use Instrument cost Size Almost unlimited for solidsand liquid crystals Usually nondestructive; sample preparation may involve material removal Via calibrated eyepiece micrometers and image analysis To sub-ng 0.2 pm with white light YeS Direct visual observation; preliminary observation for final characterization, or preparative for other instrumentation $2,500-$50,000 or more Pocket to large table 7
  • 31. ScanningElectronMicroscopy(SEM) 1.2.2 The Scanning Electron Microscope (SEM) is often the first analytical instrument used when a "quick look" at a material is required and the light microscope no longerprovides adequateresolution. In the SEMan electron beam is focusedinto a fine probe and subsequently raster scanned over a small rectangular area. As the beam interactswith the sampleit createsvarioussignals(secondaryelectrons,inter- nal currents, photon emission, etc.), all of which can be appropriately detected. These signals are highly localized to the area directly under the beam. By using these signals to modulate the brightness of a cathode ray tube, which is raster scanned in synchronismwith the electronbeam, an image is formed on the screen. This image is highly magnified and usually has the U 1 ~ ~ k "of a traditional micro- scopic image but with a much greater depth of field. With ancillary detectors, the instrument is capableof elementalanalysis. Main use High magnification imaging and composition (elemental) mapping No, some electron beam damage 10~-300,000~;5000~-100,000~is the typical operating range 500eV-50 keV; typically,20-30 keV conducting film; must be vacuum compatible Less thanO.lmm, up to 10cm or more 1-50 nm in secondaryelectron mode Varies from a few nm to a few pm, depending upon the acceleratingvoltageand the mode of analysis Destructive Magnification range Beam energy range Samplerequirements Minimal, occasionally must be coated with a Samplesize Lateralresolution Depth sampled Bonding information No Depth profiling Only indirect capabilities Instrument cost $100,000-$300,000is typical Size Electronicsconsole3ft. x 5 fi.;electron beam column 3 ft. x 3 ft. 8 INTRODUCTIONAND SUMMARIES Chapter 1
  • 32. Scanning Tunneling Microscopy and Scanning Force Microscopy (STMand SFM) 1.2.3 In ScanningTunneling Microscopy(STM) or Scanning Force Microscopy(SFM), a solid specimenin air, liquid or vacuum is scanned by a sharp tip locatedwithin a few A of the surface. In STM, a quantum-mechanical tunneling current flows between atoms on the surface and those on the tip. In SFM, also known as Atomic Force Microscopy(AFM), interatomic forcesbetween the atoms on the surfaceand those on the tip cause the deflection of a microfabricated cantilever. Because the magnitude of the tunneling current or cantileverdeflectiondepends stronglyupon the separation between the surfaceand tip atoms, they can be used to map out sur- facetopography with atomic resolution in all three dimensions.The tunneling cur- rent in STM is also a function of local electronic structure so that atomic-scale spectroscopyis possible. Both STM and SFM are unsurpassed as high-resolution, three-dimensional profilometers. Parametersmeasured Surface topography (SFM and STM); local electronic Destructive No Vertical resolution Lateral resolution Quantification Yes; three-dimensional Accuracy Imaging/mapping Yes Field of view From atoms to > 250 pm Samplerequirements STM-solid conductorsand semiconductors,conductive coating required for insulators; SFM-solid conductors, semiconductorsand insulators structure (STM) STM, 0.01 8;SFM, 0.1 A STM, atomic; SFM, atomic to 1nm Better than 10%in distance Main uses Real-space three-dimensional imaging in air, vacuum, or solution with unsurpassed resolu- tion; high-resolution profilometry; imaging of nonconductors (SFM). Instrument cost Size $65,000 (ambient) to $200,000 (ultrahigh vacuum) Table-top (ambient), 2.27-12 inch bolt-on flange (ultrahighvacuum) 9
  • 33. Transmission Electron Microscopy (TEM) 1.2.4 In Transmission Electron Microscopy (TEM) a thin solid specimen (5 200 nm thick) is bombarded in vacuumwith a highly-focused,monoenergeticbeam of elec- trons. The beam is of sufficient energyto propagate through the specimen.A series of electromagneticlensesthen magnifies this transmitted electron signal. Diffracted electrons are observed in the form of a diffraction pattern beneath the specimen. This information is used to determine the atomic structure of the material in the sample. Transmitted electrons form images from small regions of samplethat con- tain contrast, due to several scattering mechanisms associated with interactions between electronsand the atomic constituents of the sample.Analysis of transmit- ted electron images yields information both about atomic structure and about defects present in the material. Range of elements Destructive Chemical bonding information Quantification Accuracy Detection limits Depth resolution Lateral resolution Imaging/mapping TEM does not specificallyidentifyelements measured Yes, during specimen preparation Sometimes, indirectlyfrom diffractionand image simulation Yes, atomic structures by diffraction;defect character- ization by systematicimage analysis Lattice parameters to four significant figures using convergentbeam diffraction One monolayer for relativelyhigh-Zmaterials None, except there are techniques that measure sample thickness Better than 0.2 nm on some instruments Yes Samplerequirements Solid conductors and coated insulators. Typically 3-mm diameter, c 200-nm thick in the center Main uses Atomic structure and Microstructural analysisof solid materials, providinghigh lateral resolution Instrument cost $300,000-$1,500,000 Size 100 fL2to a major lab 10 INTRODUCTION AND SUMMARIES Chapter 1
  • 34. Energy-Dispersive X-Ray Spectroscopy (EDS) 1.3.1 When the atomsin a materialareionizedbya high-energyradiation they emit char- acteristicX rays. EDS is an acronym describinga technique of X-ray spectroscopy that is based on the collection and energy dispersion of characteristic X rays. An EDS system consistsofa sourceofhigh-energy radiation, usually electrons; a sam- ple; a solid state detector, usually made from lithium-drifted silicon, Si (Li); and signal processing electronics. EDS spectrometersare most frequently attached to electron column instruments. X rays that enter the Si (Li) detector are converted into signalswhich can be processed by the electronics into an X-ray energy histo- gram. This X-ray spectrum consists of a series of peaks representative of the type and relative amount ofeach element in the sample. The number of counts in each peak may be furtherconvertedinto elementalweight concentration either by com- parison with standardsor by standardlesscalculations. Range of elements Destructive Chemical bonding information Quantification Detection limits Lateralresolution Depth sampled Imaging/mapping Boron to uranium No Not readilyavailable Best with standards, although standardless methods arewidelyused Nominally P5%, relative, for concentrations > 5yo wt. 100-200 ppm for isolated peaks in elements with Z>11,1-2% wt. for low-Zand overlappedpeaks -5-1 pm for bulk samples; as small as 1 nm for thin samplesin STEM 0.02 to pm, depending on Z and keV In SEM, EPMA, and STEM Samplerequirements Solids, powders, and composites; size limited only by the stage in SEM, EPMA and XRF; liquids in XRF; 3 mm diameter thin foils in TEM To add analytical capability to SEM, EPMA and TEM $25,000-$100,000, depending on accessories (not including the electron microscope) Main use cost 11
  • 35. ElectronEnergy-LossSpectroscopyinthe TransmissionElectron Microscope(EELS) 1.3.2 In Electron Energy-Loss Spectroscopy (EELS) a nearly monochromatic beam of electrons is directed through an ultrathin specimen, usually in a Transmission (TEM) or ScanningTransmission (STEM) Electron Microscope. As the electron beam propagates through the specimen, it experiences both elastic and inelastic scatteringwith the constituent atoms,which modifies its energydistribution. Each atomic speciesin the analyzed volume causes a characteristicchange in the energy of the incident beam; the changesareanalyzedby meansofa electronspectrometer and counted by a suitabledetectorsystem.The intensityofthe measured signalcan be used to determine quantitatively the local specimen concentration, the elec- tronic and chemical structure,and the nearest neighbor atomic spacings. Range of elements Destructive Chemical bonding information Depth profiling Quantification Detection limits Depth probed Lateral resolution ImagingCapabilities Lithium to uranium; hydrogen and helium are some- times possible No Yes, in the near-edgestructure of edge profiles information None, the specimenis alreadythin capabilities Without standards+fl0-20% at.; with standards -1-2% at. -lo-21 g Thickness of specimen (I2000A) 1 nm-10 pm, depending on the diameter of the inci- dent electronprobe and the thicknessof the specimen Yes Samplerequirements Solids;specimensmust be transparentto electronsand -100-2000 athick Main use Light element spectroscopy for concentration, electronic, and chemical structure andysis at ultra- high lateral resolution in a TEM or STEM As an accessory to a TEM or STEM: $50,000- $150,000 (doesnot include electron microscope cost) cost 12 INTRODUCTIONAND SUMMARIES Chapter 1
  • 36. Cathodoluminescence(CL) 1.3.3 In Cathodoluminescence (CL) analysis, electron-beam bombardment of a solid placed in vacuum causes emission of photons (in the ultraviolet, visible, and near- infrared ranges) due to the recombination of electron-hole pairs generated by the incident energetic electrons. The signal provides a means for CL microscopy (i.e., CL images are displayed on a CRT) and spectroscopy (i.e., luminescence spectra from selected areas of the sample are obtained) analysis of luminescent materials using electron probe instruments. CL microscopycan be used for uniformity char- acterization (e.g., mapping of defects and impurity segregation studies), whereas CLspectroscopyprovidesinformation on variouselectronicpropertiesof materials. Range of elements Chemical bonding information Nondestructive Detection limits Depth profding Lateralresolution Imaging/mapping Not element specific Sometimes Yes; caution-in certain cases electron bombardment may ionizeor create defects In favorable cases, dopant concentrations down to 1014atoms/cm3 Yes, by varying the range of electron penetration (between about 10 nm and several pm), which depends on the electron-beam energy ( I 4 0kev). On the order of 1 pm; down to about 0.1 pm in special cases Yes Samplerequirements Solid, vacuum compatible Quantification Difficult, standardsneeded Main use Nondestructivequalitativeand quantitativeanalysisof impuritiesand defects, and their distributions in lumi- nescent materials Instrument cost $25,000-$250,000 Size Smalladd-on item to SEM,TEM 13
  • 37. ScanningTransmission Electron Microscopy (STEM) 1.3.4 In Scanning Transmission Electron Microscopy (STEM) a solid specimen, 5- 500 nm thick, is bombarded in vacuum by a beam (0.3-50 nm in diameter) of monoenergeticelectrons. STEM imagesare formedby scanningthis beam in a ras- ter acrossthe specimenand collectingthe transmitted or scattered electrons.Com- pared to the TEM an advantageof the STEM is that manysignalsmay be collected simultaneously:bright- and dark-field images;Convergent Beam Electron Diffrac- tion (CBED) patterns fbr structure analysis; and energy-dispersive X-Ray Spec- trometry (EDS) and Electron Energy-Loss Spectrometry (EELS) signals for compositional analysis. Taken together, these analysis techniques are termed Ana- lyticalElectron Microscopy (AEM).STEM provides about 100times better spatial resolution of analysis than conventionalTEM. When electronsscattered into high angles are collected, extremely high-resolution images of atomic planes and even individual heavy atomsmay be obtained. Range of elements Destructive Chemical bonding information Quantification Accuracy Detection limits Lateral resolution Imaging/mapping capabilities Lithium to uranium Yes, during specimenpreparation Sometimes,from EELS Quantitative cornpositional analysis from EDS or EELS, and crystal structure analysis from CBED 5-10% relativefor EDS and EELS 0.1-3.0% wt. for EDS and EELS Imaging,0.2-10 nm; EELS, 0.5-10 nm; EDS, 3-30 nm Yes, lateralresolution down to < 5 nm Samplerequirements Solidconductorsand coated insulatorstypically 3 mm in diameter and c 200 nm thick at the analysis point b r imaging and EDS, but < 50 nm thick for EELS Microstructural,crystallographic,and compositionalanal- ysis; highspatial resolution with @elemental detection and accuracyjuniquestructural analysiswithCBED Main uses Instrument cost $500,000-$2,000,000 Size 3 m x 4 m x 3 m 14 INTRODUCTIONAND SUMMARIES Chapter 1
  • 38. Electron ProbeX-Ray Microanalysis(EPMA) 1.3.5 Electron Probe X-Ray Microanalysis (EPMA) is an elemental analysis technique based upon bombarding a specimen with a focused beam of energetic electrons (beam energy 5-30 kev) to induce emission of characteristicX rays (energy range 0.1-15 kev). The X rays are measured by Energy-Dispersive (EDS) or Wave- length-Dispersive(WDS) X-ray spectrometers.Quantitativematrix (interelement) correction procedures based upon first principles physical models provide great flexibility in attacking unknown samples of arbitrary composition; the standards suite can be as simple as pure elementsor binary compounds. Typical error distri- butions are such that relative concentration errorslie within &4% for 95% of cases when the analysis is performed with pure element standards. Spatial distributions of elemental constituents can be visualized qualitativelyby X-ray area scans (dot maps) and quantitativelyby digital compositionalmaps. Range of elements Beryllium to the actinides Destructive No, except for electronbeam damage Chemical bonding In rare cases: from light-elementX-ray peak shifts Depth profiling Rarely, by changingincident beam energy Quantification Standardlessor;pure element standards Accuracy &4% relative in 95% of cases;flat, polished samples Detection limits WDS, 100ppm; EDS, 1000ppm Samplingdepth Energy and matrix dependent, 100nm-5 pm Lateral resolution Energy and matrix dependent, 100 nm-5 pm Imaging/mapping Yes, compositionalmapping and SEM imaging Samplerequirements Solid conductors and insulators;typically,e 2.5 cm in diameter, and e 1 cm thick, polished flat; particles, rough surfldces,and thin films Major uses Accurate, nondestructive quantitative analysis of major, minor, and trace constituents of materials Instrument cost $300,000-$800,000 Size 3 m x 1.5 m x 2 m high 15
  • 39. X-Ray Diffraction(XRD) 1.4.1 In X-Ray Diffraction(XRD)a collimatedbeam ofX rays,withwavelengthh- 0.5- 2 8,is incidenton a specimenand isdiffractedby the crystallinephasesin thespec- imen accordingto Bragg's law (h = 2dsin0, where dis the spacingbetween atomic planes in the crystallinephase).The intensityof the diffractedX rays is measuredas a hnction of the diffractionangle 28 and the specimen'sorientation. This diffrac- tion pattern is used to identifythe specimen'scrystallinephases and to measure its structuralproperties, includingstrain (which is measuredwith great accuracy),epi- taxy,andthesizeand orientationof crystallites(smallcrystallineregions).XRDcan also determineconcentration profiles, film thicknesses, and atomic arrangements in amorphousmaterialsand multilayers. It as0can characterized&ts. Toobtain this structural and physical information ftom thin films, XRD instruments and techniquesare designedto maximizethe diffractedX-ray intensities, since the dif- fractingpower of thin filmsis small. Rangeof elements Probingdepth Detection Limits Destructive Depth profiling All, but not element specific. Low-Zelementsmay be difficult to detect Typically a few pm but material dependent; mono- layer sensitivitywith synchrotronradiation Material dependent,but -3%in a two phase mixture; with synchrotronradiationcan be -0.1% No, for most materials Normallyno; but thiscanbe achieved. Samplerequirements Any material, greater than -0.5 an,althoughsmaller Lateral resolution Normallynone; although 10pmwith microfbcus Main use with microfocus Identification of crystalline phases; determination of strain, and crystallite orientation and size; accurate determination of atomicarrangements Defect imaging and characterization; atomic arrange- ments in amorphous materials and multilayers; con- centration profiles with depth; film thickness measurements Specializeduses Instrumentcost $70,000-$200,000 Size Varieswith instrument,greaterthan -70 fc.2 16 INTRODUCTIONAND SUMMARIES Chapter 1
  • 40. ExtendedX-Ray Absorption FineStructure (EXAFS) 1.4.2 An EXAFS experimentinvolvesthe irradiation of a samplewith a tunable sourceof monochromatic X rays from a synchrotron radiation facility.As the X-ray energyis scanned from just below to well above the binding energy of a core-shell electron (e.g., K or L) of a selected element, the X-ray photoabsorption process is moni- tored. When the energy of the incident X-rays is equal to the electron binding energy, X-ray absorption occurs and a steeply rising absorption edge is observed. For energies greater than the binding energy, oscillations of the absorption with incident X-ray energy (i.e., EXAFS) are observed. EXAFS data are characteristicof the structural distribution of atoms in the immediate vicinity (-5 A) of the X-ray absorbing element. The frequency of the E M S is related to the interatomic dis- tance between the absorbingand neighboringatoms. The amplitude of the EXAFS is related to the number, type, and order of neighboringatoms. Range of elements Destructive No Bonding information Accuracy Detection limits Depth probed Depth profiling Lateralresolution Not yet developed Imaging/mapping Not yet developed Sample requirements Virtually any material;solids,liquids,gas Main use Instrument cost Lithium through uranium Yes,interatomicdistances,coordinationnumbers, atom types, and structural disorder;oxidationstate by inference 1-2% for interatomic distances; 10-25% for coordi- nation numbers Surface,monolayer sensitivity;bulk, > 100ppm Variable, from8,to pm Yes,with glancing incidence angles;electron-and ion-yield detection Local atomic environmentsof elements in materials Laboratory Facility, c $300,000; synchrotron beam line, > $1,000,000 Smallattachment to synchrotron beam lineSize 17
  • 41. Surface ExtendedX-Ray Absorption Fine Structure and Near EdgeX-Ray Absorption FineStructure (SEXAFS/NEXAFS) 1.4.3 In Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Absorption Fine Structure (SEXAFS/NEXAFS) a solid sample, usually placed in ultrahigh vacuum, is exposed to a tunable beam of X rays from a synchrotron radi- ation source.Aspectrumis collectedbyvaryingthe photon energyof theX rays and measuringthe yield of emitted electronsor fluorescentX rays. Analysis of the wig- gles in the observed spectrum (the SEXAFS features) gives information on nearest neighbor bond lengths and coordination numbers for atoms at or near the surface. Features near an absorption edge (NEXAFS) are often characteristic of the local coordination (octahedral,tetrahedral, etc.) or oxidation state. For adsorbed mole- cules, NEXAFS resonances characterizethe type of bonding. On a flat surface, the angular variation of intensity of the resonances gives the orientation of the mole- cule. Range of elements Destructive No Chemical bonding Yes, through NEXAFS information Accuracy In nearest neighbor distance,M.01 with care Surfacesensitivity Top few monolayers Detection limits 0.05 monolayer Lateral resolution -0.5 mm Imaging/mapping No Samplerequirements Vacuum-compatiblesolids Main use of SEXAFS Main use of NEXAFS Instrument cost Size Almost all, from C to U Adsorbatesubstrate bond lengths Orientation of molecular adsorbates $400,000, plus cost of synchrotron Small attachment to synchrotron beam line 18 INTRODUCTIONAND SUMMARIES Chapter 1
  • 42. X-Ray Photoelectronand Auger ElectronDiffraction (XPDandAED) 1.4.4 In X-Ray Photoelectron Diffraction (XPD) and Auger Electron Diffraction (AED), a single crystalor a textured polycrystallinesample is struck by photons or electrons to produce outgoing electrons that contain surface chemical and struc- tural information. The focus of XPD and AED is structural information, which originates from interference effects as the outbound electrons from a particular atom are scattered by neighboringatomsin the solid. The electron-atom scattering processstronglyincreasesthe electron intensityin the forward direction, leadingto the simpleobservation that intensity maxima occur in directionscorrespondingto rows of atoms. An energy dispersive angle-resolved analyzer is used to map the intensity distribution as a function of anglefor elements of interest. Range of elements Destructive Element specific Chemicalstate specific Accuracy Sitesymmetry Depth Probed Depth profiling Detection limits Lateral resolution Imaging/ mapping All except H and He XPD no; AED may cause e-beam damage YeS Yes,XPD is better than AED Bond angles to within lo; atomic positions to within 0.05 A Yes, and usually quickly 5-50 A Yes, to 30A beneath the surface 0.2 at.% 150A (AED), 150pm (XPD) Yes Samplerequirements Primarily single crystals,but also textured samples Main use To determine adsorption sites and thin-film growth modes in a chemicallyspecificmanner Instrument cost $300,000-$600,000 Size 4 m x 4 m x 3 m 19
  • 43. Low-EnergyElectron Diffraction (LEED) 1.4.5 In Low-EnergyElectron Diffraction (LEED)a collimated monoenergetic beam of electrons in the energy range 10-1000 eV (A = 0.4-4.0 A) is diffracted by a speci- men surface. In this energy range, the mean free path of electrons is only a few A, leading to surface sensitivity. The diffraction pattern can be analyzed for the exist- ence of a clean surface or an ordered overlayer structure. Intensities of diffracted beams can be analyzed to determine the positions of surfaceatoms relative to each other and to underlying layers. The shapesof diffracted beams in anglecan be ana- lyzed to provide information about surfacedisorder. Various phenomena related to surface crystallography and microstructure can be investigated. This technique requires a vacuum. Range of elements Destructive Depth probed Detection limits Resolvingpower Lateral resolution Imaging capability All elements, but not element specific No, except in specialcasesof electron-beamdamage 4-20 A 0.1 monolayer; any ordered phase can be detected; atomic positions to 0.1 step heights to 0.1 A; sur- facedisorder down to -10%of surfacesites Maximum resolvable distance for detecting disorder: typically200 A;best systems, 5 pm Typical beam sizes,0.1 mm; best systems, -10 pm Typically, no; with specialized instruments (e.g., low- energy electron microscopy), 150A Samplerequirements Single crystals of conductors and semiconductors; insulators and polycrystalline samples under special circumstances;0.25 cm2or larger, smallerwith special effort Main uses cost Size Analysis of surface crystallography and microstruc- ture; surfacecleanliness 1$75,000;can be home built cheaply Generallypart of other systems;if self-standingY-8m2 20 INTRODUCTIONAND SUMMARIES Chapter 1
  • 44. ReflectionHigh-Energy Electron Diffraction (RHEED) 1.4.6 In Reflection High-Energy Electron Diffraction (RHEED), a beam of high-energy electrons (typically5-50 kev), is acceleratedtoward the surfaceof a conducting or semiconducting crystal, which is held at ground potential. The primary beam strikesthe sampleat a grazingangle (+1-5") and is subsequentlyscattered.Some of the electronsscatterelastically. Sincetheir wavelengthsare shorter than interatomic separations, these electrons can diffract off ordered rows of atoms on the surface, concentrating scattered electrons into particular directions, that depend on row separations. Beams of scattered electrons whose trajectories intersect a phosphor screenplaced oppositethe electron gun will excitethe phosphor. The light from the phosphor screen is called the RHEED pattern and can be recorded with a photo- graph, television camera, or by some other method. The symmetry and spacing of the bright features in the RHEED pattern give information on the surfacesymme- try, lattice constant, and degreeof perfection, i.e., the crystal structure. Range of elements Destructive All, but not chemicalspecific No, Except for electron-sensitivematerials Depth probed 2-100 A Depth profiling No Lateral resolution Structural information sensitiveto structural defects Samplerequirements Usually single crystal conductor or semiconductor surfaces Main use Monitoring surface structures, especially during thin- film epitaxial growth; can distinguish two-and three- dimensional defects Instrument cost $50,000-$200,000 Size 200 pm x 4 mm, in specialcases 0.3 nm x G nm Measuressurfacecrystal structure parameters, +25 sq. ft., larger if incorporated with an MBE chamber 21
  • 45. X-Ray PhotoelectronSpectroscopy (XPS) 1.5.1 In X-Ray Photoelectron Spectroscopy(XPS) monoenergeticsofiX rays bombard a sample material, causing electrons to be ejected. Identification of the elements present in the samplecan be made directlyfrom the kineticenergiesof theseejected photoelectrons. On a finer scale it is also possible to identify the chemical state of the elementspresent from small variations in the determinedkineticenergies. The relative concentrationsof elements can be determined from the measured photo- electronintensities.For a solid,XPS probes2-20 atomiclayers deep, dependingon the material, the energy of the photoelectron concerned, and the angle (with respect to the surface) of the measurement. The particular strengths of XPS are semiquantitative elemental analysis of surfaces without standards, and chemical state analysis, for materials as diverse as biological to metallurgical. X P S also is known as electronspectroscopyfor chemicalanalysis (ESCA). Range of elements Destructive Elementalanalysis Chemicalstate Yes information Depth probed 5-50 A Depth profiling Yes, over the top 50 A; greater depths require sputter profiling Depth resolution A fewto severaltens ofA, dependingon conditions Lateral resolution 5 mm to 75 pm; down to 5 pm in specialinstruments Sample requirements All vacuum-compatible materials; flat samples best; sizeaccepted depends on particular instrument Main uses Determinations of elemental and chemical state wm- positions in the top 30A $200,000-$1,000,000,dependingon capabilities 10fi. x 12fi. All except hydrogen and helium No, somebeam damageto X-ray sensitivematerials Yes, semiquantitative without standards; quantitative with standards. Not a trace element method. Instrument cost Size 22 INTRODUCTION AND SUMMARIES Chapter 1
  • 46. Ultraviolet PhotoelectronSpectroscopy (UPS) 1.5.2 If monoenergeticphotons in the 10-100 eV energy range strike a samplematerial, photoelectrons from the valence levels and low-lying core levels (i.e., having lower binding energy than the photon energy) are ejected. Measurement of the kinetic energy distribution of the ejected electrons is known as Ultraviolet Photoelectron Spectroscopy(UPS).The physics of the technique is the sameasXPS, the only dif- ferencesbeing that much lower photon energiesare used and the primary emphasis is on examining the valence electron levels, rather than core levels. Owing to this emphasis, the primary use, when investigatingsolidsurfaces,is for electronicstruc- ture studiesin surfacephysicsrather than for materialsanalysis.There are,however, a number of situationswhere UPS offers advantagesover XPS for materialssurface analysis. Elemental analysis Destructive Chemicalstate information levels as for XPS Not usually, sometimesfrom availablecore levels No, somebeam damageto radiation-sensitivematerial Yes, but complicated usingvalence levels;for core Depth probed 2-1 00 A Depth profiling Yes, over the depth probed; deeper profiling requires sputter profiling Lateral resolution Generally none (mm size), but photoelectron micro- scopeswith capabilitiesdown to the 1-pm range exist Samplerequirements Vacuum-compatible material; flat samples best; size accepteddepends on instrumentation Main use Electronic structure studies of free molecules (gas phase), well-defined solid surfaces, and adsorbates on solidsurfaces No commercial instruments specificallyfor UPS; usu- ally an add-on to XPS (incrementalcost +$30,000)or done using a synchrotron ficility as the photon source 10 ft. x 10ft. for a stand-alonesystem Instrument cost Size 23
  • 47. Auger Electron Spectroscopy (AES) 1.5.3 Auger Electron Spectroscopy(AES) uses a focusedelectron beam to createsecond- ary electronsnear the surfaceof a solid sample. Some of these (theAuger electrons) have energies characteristic of the elements and, in many cases, of the chemical bonding of the atoms from which they are released. Because of their characteristic energies and the shallowdepth from which they escapewithout energy loss, Auger electrons are able to characterize the elemental composition and, at times, the chemistryof the surfaces of samples.When used in combination with ion sputter- ing to gradually remove the surface, Auger spectroscopy can similarly characterize the samplein depth. The high spacial resolution of the electron beam and the pro- cessallowsmicroanalysisofthree-dimensionalregionsofsolidsamples.AEShas the attributes of high lateral resolution, relatively high sensitivity, standardless semi- quantitative analysis, and chemical bonding information in somecases. Range of elements Destructive All except H and He No, except to electron beam-sensitive materials and during depth profiling Yes, semiquantitative without standards; quantitative with standards 100ppm for most elements,depending on the matrix Yes, in many materials ElementalAnalysis Absolutesensitivity Chemicalstate information? Depth probed 5-1 00 a Depth profiling Lateral resolution Imaging/mapping Samplerequirements Vacuum-compatiblematerials Main use Instrument cost $100,000-$800,000 Size Yes, in combination with ion-beam sputtering 300A forAuger analysis, even less for imaging Yes, called ScanningAuger Microscopy, S A M Elementalcomposition of inorganicmaterials 10ft. x 15 ft. 24 INTRODUCTIONAND SUMMARIES Chapter 1
  • 48. ReflectedElectron Energy-Loss Spectroscopy (REELS) 1.5.4 In Reflected ElectronEnergy-LossSpectroscopy(REELS)a solid specimen, placed in avacuum, is irradiatedwith a narrowbeam of electronsthat are sufficientlyener- getic to induce electron excitations with atoms or clusters of atoms. Some of the incident electrons reemerge from the sample having lost a specific amount of energyrelative to the well-definedenergyI$,of the incident electron. The number, direction k,and energy of the emitted electrons can be measured by an electron energy analyzer. Composition, crystal structure, and chemical bonding informa- tion can be obtained about the sample’ssurfacefrom the intensityandline shapeof the emitted electron energy-lossspectra by comparisonto standards. Range of elements Destructive Chemical band information Depth profiling Quantification Accuracy Detection limits Probing depth Lateral resolution Imaging/mapping Hydrogen to uranium; no isotopes No Yes; energeticsand orientation Yes; tilting or ion sputtering Standards required Few percent to tens of percent Few tenths of a percent 0.07-3.0 nm 100 nm-50 pm; sample independent; not limited by redifised primaries Yes, called REELM Sample requirements Solids; liquids; vacuum compatible; typically < 2.5 cm-diameter, < 1.5 cm-thickness Main use Few-monolayerthin-film analysis,e.%.,adsorbate and very thin-film reactions;submicron detection of metal hydrides $0-$700,000, free on any type of electron-excited Auger spectrometer None extra overAuger spectrometer Instrument cost Size 25
  • 49. X-Ray Fluorescence(XRF) 1.6.1 In X-Ray Fluorescence (XRF), an X-ray beam is used to irradiatea specimen, and the emitted fluorescentX rays are analyzedwith a crystal spectrometer and scintil- lation or proportional counter. The fluorescentradiation normallyis diffractedby a crystalat differentanglesto separatetheX-raywavelengthsand thereforeto identify the elements; concentrations are determined from the peak intensities. For thin filmsXRF intensity-composition-thickness equationsderivedfrom first principles are used for the precision determination of compositionand thickness. This can be done also for each individuallayer of multiple-layerfilms. Range of elements All but low-Zelements: H, He, and Li Accuracy kl%for composition, 3%for thickness Destructive No Depth sampled Depth profiling Detection limits Sensitivity Lateral resolution Chemical bond information spectra Samplerequirements 15.0 cm in diameter Main use Identification of elements; determination of composition and thickness Instrument cost $50,000-$300,000 Size Normally in the 10-pm range, but can be a fewtens of A in the total-reflection range Normally no, but possible using variable-inci- dence X rays Normally 0.1% in concentration. 10-1 O5 A in thickness can be examined Normally none, but down to 10 pm using a microbeam Normally no, but can be obtained from softX-ray 5 ft. x 8 fi. 26 INTRODUCTIONAND SUMMARIES Chapter 1
  • 50. Total ReflectionX-Ray Fluorescence Analysis (TXRF) 1.6.2 In Total Reflection X-Ray Fluorescence Analysis (TXRF), the surface of a solid specimenis exposed to an X-ray beam in grazinggeometry. The angle of incidence is kept below the critical anglefor total reflection,which is determined by the elec- tron density in the specimen surfacelayer, and is on the order of mrad. With total reflection,only a few nm of the surface layer are penetrated by the X rays, and the surface is excited to emit characteristicX-ray fluorescence radiation. The energy spectrum recordedby the detector contains quantitative information about the ele- mental composition and, especially, the trace impurity content of the surface,e.g., semiconductor wafers. TXRF requires a specular surface of the specimen with regard to the primary X-ray light. Range of elements Destructive Chemical bonding information Depth probed Depth profiling capability Quantification Accuracy Detection limits Lateral resolution Sodium to uranium No Not usually Typically 1-5 nm Limited (variationof angleof incidence) Yes 1-20% 10"-1 oi4at/cm2 Limited, typically 10mm Samplerequirements Specular surhce, typically12.5-cm diameter Main use Multielement analysis, excellent detection limits for heavy metals; quantitative measurement of heavy- metal trace contamination on silicon wafers Instrument cost $300,000-$600,000 27
  • 51. Particle-InducedX-Ray Emission (PIXE) 1.6.3 Particle-Induced X-Ray Emission (PIXE) is a quantitative, nondestructiveanalysis technique that relies on the spectrometry of characteristicX rays emitted during irradiation of a specimen with high-energy ionic particles (-0.3-10 MeV). The processis analogousto the emissionof characteristicX raysunder electron and pho- ton bombardment of a specimen (seethe articleson EDS, EMPA, and XRF).With appropriate corrections, X-ray yields (X rays per particle) can be converted to ele- mental concentrations.The background X-ray radiationfor PIXE is much less than that for electron excitation;thus, the detection limits fortraceelementsusing PIXE is orders of magnitude better. PIXE is best for the analysis of thin samples, suhce layers, and sampleswith limited amounts of materials, while photon bombardment (XRF)is better for bulk analysis and thick specimens. Using wavelength-dispersive detectors, PIXE,EMPA, and XRF can provide identificationof the chemicalbond- ing of elements. Although EMPA and EDS require that the specimen be in vac- uum, PIXE and XRF can be performed with the specimen in vacuum or at atmosphericpressure. Range of elements Chemical bonding information Depth probed Depth profiling Detection limits Accuracy Lateral resolution Imaging/mapping Lithium to uranium Yes, when spectralresolution is high I 1 0 p n Yes, by varying angle of incidence or particleenergy. Thin, freestanding foil, 0.1-1 0 ppm; d c e layers on thick specimens, 10'3-5x10'5 at/cm2; Bulk speci- mens, 1-100 ppm -2-1 O%, with standards -5 pm-2 mm Yes Samplerequirements Solids,liquids, and gases Main use Systemcost Systemsize Fast analysis for many elements, in all materials, simultaneously -$ 1,000,000,includingsrnall ionaccelerator(2-MeV H+) -100sq. ft. floor space 28 INTRODUCTIONAND SUMMARIES Chapter 1
  • 52. Photoluminescence(PL) 1.7.1 In photoluminescence one measures physical and chemical properties of materials by using photons to induce excitedelectronicstatesin the materialsystemand ana- lyzing the optical emission as these statesrelax. Typically,light is directed onto the sample for excitation, and the emitted luminescence is collected by a lens and passed through an optical spectrometer onto a photodetector. The spectral distri- bution and time dependence of the emission are related to electronic transition probabilitieswithin the sample, and can be used to provide qualitativeand, some- times, quantitative information about chemical composition, structure (bonding, disorder, interfaces, quantum wells), impurities, kinetic processes, and energy transfer. Destructiveness Nondestructive Depth probed 0.1-3 pm; limited by light penetration depth and car- rier diffusion length Lateral resolution Down to 1-2 pm Quantitative abilities Intensity-based impurity quantification to several percent possible; energy quantification very precise Sensitivity Down to parts-per-trillion level, depending on impu- rity speciesand host Imaging/mapping Yes Samplerequirements Liquid or solid having optical transitions; probe size 2 pm to a few cm Main uses Band gaps of semiconductors; carrier lifetimes; shal- low impurity or defect detection; sample quality and structure Less than $10,000to over $200,000 Table top to small room Instrument cost Size 29
  • 53. ModulationSpectroscopy 1.7.2 Modulation spectroscopy is a powerful experimental method for measuring the energy of transitions between the filled and empty electronic states in the bulk (band gaps) or at surfaces of semiconductor materials over a wide range of experi- mental conditions (temperature, ambients, etc.). By taking the derivative of the reflectance(or transmittance)of a material in an analogmanner, it producesa series of sharp, derivative-likespectralfeaturescorrespondingto the photon energyof the transitions.These energiesaresensitiveto a number of internal and externalparam- eters such as chemical composition, temperature, strain, and electricand magnetic fields. The line widths of these spectral features are a function of the quality of the material. Destructiveness Depth probed Lateral resolution Image/mapping Sensitivity Main uses Instrument cost Size Somemethods are nondestructive For bulk applications 0.1-1 pm; for surface applica- tions one monolayer is possible Down to 100pm Yes Alloy composition (e.g., Gal-,&&) Ax = 0.005; car- rier concentration 1015-1019cm-3 Contactless, nondestructive monitoring of band gaps in semiconductors; Wide range of temperatures and ambients (air, ultrahigh vacuum); in-situ monitoring of semiconductor growth $30,000-$100,000 For most methods about 2 x 3ft. 30 INTRODUCTIONAND SUMMARIES Chapter 1
  • 54. Variable-AngleSpectroscopic Ellipsometry (VASE) 1.7.3 In Variable-AngleSpectroscopicEllipsometry(VA!5E),polarized light strikesa sur- fa.= and the polarization of the reflected light is analyzed using a second polarizer. The light beam is highly collimated and monochromatic, and is incident on the material at an oblique angle. For each angle of incidence and wavelength, the reflectedlight intensityis measured asa function of polarizationangle, allowingthe important ellipsometric parameter to be determined. An optimum set of angle of incidenceand wavelength combinationsis used to maximizemeasurementsensitiv- ity and information obtained. Physical quantities derivable from the measured parameter includethe opticalconstantsof bulk or filmed media, the thicknessesof films (from 1to a fewhundred nm), and the microstructuralcompositionofa mul- ticonstituent thin film. In general only materials with parallel interfaces, and with structural or chemical inhomogeneities on a scale less than about 1/ 10 the wave- length of the incident light, can be studied by ellipsometry. Main use Optical range Samplerequirements Planar materials and interfaces Destructive No, operation in any transparent ambient, including vacuum, gases, liquids, and air Depth probed Light penetration of the material (tensof nm to pm) Lateral resolution mm normally, 100pm under specialconditions Image/mapping No Instrument cost $50,000-$150,000 Size 0.5 rnx 1m Film thicknesses, microstructure, and optical proper- ties Near ultraviolet to mid infrared 31
  • 55. FourierTransform InfraredSpectroscopy (IFTIR) 1.8.1 The vibrational motions of the chemicallybound constituents of matter have fre- quencies in the infrared regime. The oscillations induced by certain vibrational modes provide a means for matter to couple with an impinging beam of infrared electromagneticradiation and to exchange energywith it when the frequenciesare in resonance. In the infrared experiment, the intensity of a beam of infrared radia- tion is measured before (10)and after (I)it interactswith the sampleas a hnction of light frequency, {wi}.A plot of 1/10 versus frequency is the “infrared spectrum.” The identities, surrounding environments, and concentrations of the chemical bonds that are present can be determined. Information Element Range Destructive Chemical bonding information Depth profiling Depth Probed Detection limits Quantification Reproducibility Lateralresolution Imaging/mapping Vibrationalfrequenciesof chemicalbonds All, but not element specific No Yes, identificationof hnctional groups No, not under standard conditions Sampledependent, from pm’s to 10nm Ranges from undetectable to e lOI3 bonds/cc. Sub- monolayer sometimes Standards usually needed 0.1%variation over months 0.5 cm to 20 pm Available,but not routinely used Samplerequirements Solid, liquid, or gas in all forms; vacuum not required Main use Qualitative and quantitative determination of chemical species, both trace and bulk, for solids and thin films. Stress, structural inhomogeneity $50,000-$150,000 for FTIR; $20,000 or more for non-FT spectrophotometers Ranges from desktop to (2 x 2 m) Instrument cost Instrument size 32 INTRODUCTIONAND SUMMARIES Chapter 1
  • 56. Raman Spectroscopy 1.8.2 Raman spectroscopy is the measurement, as a function of wavenumber, of the inelastic light scattering that results from the excitation of vibrations in molecular and crystalline materials. The excitation source is a single line of a continuous gas laser,which permits optical microscope optics to be used for measurement of sam- ples down to a few pm. Raman spectroscopyis sensitive to molecular and crystal structure; applications include chemical fingerprinting, examination of single grains in ceramics and rocks, single-crystal measurements, speciation of aqueous solutions, identification of compounds in bubbles and fluid inclusions, investiga- tions of structure and strain states in polycrystalline ceramics, glasses, fibers, gels, and thin and thick films. Information Element range Destructive Lateral resolution Depth profiling Depth probed Detection limits Quantitative Imaging Vibrational Frequencies of chemical bonds All, but not element specific No, unless sampleis susceptibleto laser damage 1 pm with microfocus instruments Limited to transparent materials Few pm to mm, depending on material 1000A normally, submonolayerin specialcases With difficulty;usuallyqualitativeonly Usually no, although imaging instruments have been built Samplerequirements Very flexible: liquids, gases, crystals, polycrystalline solids, powders, and thin films Main use Identification of unknown compounds in solutions, liquids, and crystalline materials; characterization of structural order, and phase transitions Instrument cost $150,00O-$250,000 Size 1.5 m x 2.5 m 33
  • 57. High-ResolutionElectron Energy LossSpectroscopy (HREELS) 1.8.3 In High-Resolution Electron Energy Loss Spectroscopy (HREELS), a highly monoenergeticbeam of low energy (1-10 eV) electrons is focused onto a sample’s surface, and the scatteredelectronsare analyzed with high resolution of the scatter- ing energy and angle. Some of the scattered electrons suffer small characteristic energylossesdue to vibrational excitation of surface atoms and molecules.A vibra- tional spectrum can be obtained by counting the number of electrons versus the electron energy loss relative to the elastically scattered (no energy loss) electron beam. This spectrum is used mainly to identify chemical species (functional groups) in the first layer of the surface. Often this layer contains adsorbed species on a solid. Information Main use Range of elements Bonding Detection limits Quantification Depth probed Lateral resolution Molecularvibrational frequencies Nondestructive identification of the molecular hnc- tional groupspresent at surfaces Not element specific Any chemical bonds that have vibrations in the range 50-4000 cm-l 0.1% monolayer for strong vibrational bands Difficult, possible with standards 2 nm 1 mm2 Samplerequirements Single-crystal samples of conductors best; other solid samples are suitable, including polycrystalline metals, polymeric materials, semiconductors, and insulators, ultrahigh vacuum compatible;typically2 5mm diam- eter, 1-3 mm thick Instrument cost $100,000 plus associated techniques and vacuum system Size Attaches to vacuum chamber by 8-14 inch diameter flange. 34 INTRODUCTIONAND SUMMARIES Chapter 1
  • 58. Solid State Nuclear MagneticResonance (NMR) 1.8.4 Solidstate Nuclear MagneticResonance (NMR) exploitsthe interaction of nuclear magnetic moments with electromagneticwaves in the radio frequency region. In the experiment, a solid specimen (crystallineor amorphous, aligned or randomly oriented) is placed in a strong external magnetic field (typically 1-14 Tesla) and irradiated with intense radio frequency pulses over a frequency range required to excite a specific atomic nucleus from the ground magnetic (spin) state to another higher state. As the nucleus releases back to its ground state the sample re-emits a radio signal at the excitation frequency, which is detected by electromagnetic induction and Fourier transformed to yield a plot of intensity versus frequency. The spectrum thus obtained identifiesthe presenceof the atom and its relativecon- centration (with standards) and is a sensitive indicator of structural and chemical bonding properties. It can servefor phase identificationaswell as for the character- ization of local bonding environments in disorderedmaterials. Elementsdetected Detection limit Surfacesensitivity Typicalsamplesize Measurement conditions Sampleform Main use Instrument cost Spacerequirement All elementspossessingan isotopewith a suitablemag- netic dipole moment (about half the elements in the periodic table) On the order of 1018 atoms of the nuclear isotope studied Not intrinsically surface sensitive: Surface areas > 10m2/g required or desirablefor surfacestudies 10-500 mg, varies greatly with the nucleus studied; samplelength, 0.5-5 cm; width, 0.5-2 cm Usuallyat ambient temperature and pressure Powder, single crystal, randomly oriented, or aligned film Element-selectivephase identification and quantifica- tion, structural characterization of disorderedstates $200,000-$1,200,000, depending mostly on the field strength desired 300 ft.2 35
  • 59. RutherfordBackscatteringSpectrometry (RBS) 1.9.1 Rutherford BackscatteringSpectrometry(RBS) analysisis performed by bombard- ing a sample target with a monoenergetic beam of high-energy particles, typically helium, with an energyof a few MeV. A fraction of the incident atomsscatterback- wards from heavier atoms in the near-surface region of the target material,and usu- ally are detected with a solid state detector that measures their energy. The energy of a backscatteredparticle is related to the depth and mass of the target atom, while the number of backscattered particles detected from any given element is propor- tional to concentration. This relationship is used to generate a quantitative depth profile of the upper 1-2 pm of the sample. Alignment of the ion beam with the crystallographic axes of a sample permits crystal damage and lattice locations of impurities to be quantitativelymeasured and depth profiled. The primary applica- tions of RBS are the quantitative depth profilingof thin-film structures, crystailin- ity, dopants, and impurities. Range of elements Destructive Chemical bonding information Quantification Detection limits Lateralresolution Depth profiling Depth resolution Maximum depth Imaging/mapping Lithium to uranium + 10l3 He atomsimplanted;radiationdamage. No Yes, standardless;accuracy5-20% 1012-1016 atoms/cm2; 1-10 at.% for 1ow-z ele- ments; 0-100 ppm for high-Zelements 1 4 mm, 1pm in specialized equipment Yes and nondestructive 2-30 nm -2 pn, 20 pm with H+ Under development Samplerequirements Solid,vacuum compatible Main use Instrument cost $450,000-$1,000,000 Size 2 m x 7 m Nondestructive depth profiling of thin films, crystal damage information 36 INTRODUCTIONAND SUMMARIES Chapter 1
  • 60. ElasticRecoilSpectrometry (ERS) 1.9.2 Energetic recoil ions, 'H+and 2H+,are produced when 4He+ions having energies in the MeV range undergo elasticnucleus-nucleus collisionswithin a hydrogen- or deuterium-containingsolidsample.Energyspectrometryof the recoilingions iden- tifiestheir mass and depth of origin. The total hydrogen content of a thin layer may be determined directly from the recoil fluence. In combination with Rutherford Backscattering(RBS)analysisof the samesample,elasticrecoilspectraprovidecon- centration profiles and complete compositional analysis of near-surface regions of the sample material. ERS requires equipment common to RES analysis. It is the simplestion beam techniqueforhydrogenprofiling,sinceion backscattering(RBS) from hydrogen is not possible. Range of elements Destructive Chemical bonding information Quantitation Sensitivity Depth probed Depth profiles Depth resolution Lateral resolution Unique selectionof 'H, 2H Radiationdamage may releaseH in polymers None Absolute atoms/cm2 f2% typically 5 x 1013atom/cm2 or 0.01at.% (typically) 5 1pm typically Yes; concentration profile to f 1% relative Varies with depth; 300-600 8,at depth 1000Ain Si 1-4 mm typically Samplerequirements Solid,vacuum compatible,dimensions2 5mm Main use Determination of H concentrations in thin fdms; rapid; matrix-independent Instrument cost As for RBS; MeV accelerator ($1,000,000- $1,500,000);servicesavailable Size Requires laboratory 2 20 ft. x 50 ft., depending on instrument 37
  • 61. Medium-Energy Ion Scatteringwith Channeling and Blocking (MEIS) 1.9.3 Medium-Energy Ion Scattering (MEIS)with channeling and blocking is a quanti- tative, real space,nondestructivetechnique for studyingthe composition and struc- ture of surfices and interfacesburied up to a fav atomic layers below the surface. Single-crystal or epitaxial samples are required for the structural determinations. The basic quantities measured are the energyand angulardistribution of backscat- tered ions in the 50-400 keV range. The technique has elemental and depth sensi- tivity. The ion angular distributions are characterized by minima (dips) in intensity, the positions of which are closely connected to the relative positions of atoms in the surface layer. MEIS is more surfice sensitive, and more complex instrumentally than other surfice ion spectroscopies, though interpretation is straightforward. The technique is useful for the analysis of all ultrahigh vacuum compatiblesolids, and in particularmetals, semiconductors,and overlayerson such suhces (submonolayer adsorbateconcentrations, thin filmsof silicides,etc.). Elementsdetected Elementalsensitivity Chemicalsensitivity Depth probed Depth resolution Quantification Lateralresolution Destructive Samplerequirements Main uses Accuracy cost Size all elements Scales as the square of nuclear charge; best for heavy elements(e 1 0 4 monolayer); poor for hydrogen None Typically4-5 atomiclayers,but up to 200A in special cases Optimally on a monolayer level Absolute technique for elementalconcentrations None Not inherently Ultrahigh vacuum compatibility;practical size -1 cm in diameter Determination of structural parameters of surfices and interfaces;very high resolutiondepth profiling > 1% (structural parameters); element dependent (composition) $1,000,000-$2,000,000 - 7 m x 3 m 38 INTRODUCTIONAND SUMMARIES Chapter 1
  • 62. Ion Scattering Spectroscopy (ISS) 1.9.4 In Ion Scattering Spectroscopy(ISS) a low-energy monoenergetic beam of ions is focusedonto a solidsurfaceand the energyof the scatteredions ismeasuredat some fixed angle.The collision of the inert ion beam, usually3He+,4He+,or 20Ne+,fol- lows the simple laws of conservation of momentum for a binary elastic collision with an atom in the outer surface ofthe solid. The energy loss thus identifies the atom struck. Inelasticcollisionsand ions that penetrate deeper than the first atomic layer normallydo not yield a sharp, discretepeak. Neighboring atoms do not affect the signal because the kinetics of the collision are much shorter than bond vibra- tions. A spectrum is obtained by measuring the number of ions scattered from the surficeas a function of their energyby passingthe scatteredions through an energy analyzer. The spectrum is normally plotted as a ratio of the number of ions of energy Eversus the energy of the primary beam 4.This can be directly converted to a plot of relative concentration versus atomic number, 2. Extremely detailed information regardingthe changesin elementalcomposition from the outer mono- layer to depths of 50A or more are routinely obtained by continuously monitoring the spectrum while slowlysputtering away the surface. Range of elements Samplerequirements Any solidvacuum-compatible material All but helium; hydrogen indirectly Sensitivity Quantitation Speed Depth of analysis Lateral resolution Imaging Sampledamage Main uses Instrument cost Size c 0.01 monolayer, 0.5% for C to 50 ppm for heavy metals Relative; 0.5-20% Singlespectrum, 0.1s; nominal 100-Aprofile, 30 min Outermost monatomic layer to any sputtered depth 150pm Yes, limited Only if done with sputter profiling Exclusive detection of outer most monatomic layer and very detailed depth profilesof the top 100A $25,000-$150,000 10ft. x 10fi. 39
  • 63. DynamicSecondary Ion Mass Spectrometry (DynamicSIMS) 1.10.1 In Secondary Ion Mass Spectrometry (SIMS), a solid specimen, placed in a vac- uum, is bombarded with a narrow beam of ions, called primary ions, that are suffi- cientlyenergeticto cause ejection (sputtering)of atoms and small clusters of atoms from the bombarded region. Some of the atoms and atomic clusters are ejected as ions, called secondary ions. The secondary ions are subsequentlyaccelerated into a massspectrometer,wherethey areseparated accordingto their mass-to-chargeratio and counted. The relative quantities of the measured secondaryions are converted to concentrations, by comparison with standards, to reveal the composition and trace impurity content of the specimen as a function of sputteringtime (depth). Range of elements Destructive Chemical bonding information Quantification Accuracy Detection limits Depth probed Depth profiling Lateral resolution Imaging/mapping H to U; all isotopes Yes, material removed during sputtering In rare cases,from molecular clusters, but see StaticSIMS Standardsusuallyneeded 2% to factor of 2 for concentrations 10'~-10'~atoms/cm3 (ppb-ppm) 2 nm-100 pm (depends on sputter rate and data col- lection time) Yes, by the sputteringprocess; resolution 2-30 nm 50 nm-2 pm; 10nm in specialcases Yes Samplerequirements Solid conductorsand insulators, typicallyI2.5 cm in diameter, I 6 mm thick, vacuum compatible Main use Measurement of composition and of trace-level impu- rities in solid materials a hnction of depth, excellent detection limits, good depth resolution Instrument cost $500,000-$1,500,000 Size 10fi. x 15fi. 40 INTRODUCTIONAND SUMMARIES Chapter 1
  • 64. Static Secondary Ion Mass Spectrometry (StaticSIMS) 1.10.2 Static SecondaryIon Mass Spectrometry (SIMS) involves the bombardment of a sample with an energetic (typically 1-10 kev) beam of particles, which may be either ions or neutrals.As a result of the interaction of these primary particles with the sample, species are ejected that have become ionized. These ejected species, known as secondaryions, are the analyticalsignal in SIMS. In static SIMS, the use of a low dose of incident particles (typically less than 5 x 10l2atoms/cm2) is critical to maintain the chemical integrity of the sample surface during analysis. A mass spectrometer sorts the secondary ions with respect to their specificcharge-to-massratio, therebyproviding a mass spectrum composed of fragment ions of the varioushnctional groups or compounds on the samplesur- face. The interpretation of these characteristicfragmentation patterns results in a chemicalanalysisof the outer few monolayers.The abilityto obtain surfacechemi- cal information is the key feature distinguishing static SIMS from dynamic SIMS, which profilesrapidlyinto the sample,destroyingthe chemicalintegrityof the sam- ple. Range of elements Destructive Chemical bonding information Depth probed Lateral resolution Imaging/mapping Quantification Massrange H to U; aI1isotopes Yes, if sputtered long enough Yes Outer 1or 2 monolayers Down to -100pm Yes Possiblewith appropriate standards Typically, up to 1000 amu (quadrupole), or up to 10,000amu (time of flight) Samplerequirements Solids, liquids (dispersed or evaporated on a sub- strate), or powders; must be vacuum compatible Main use Surface chemical analysis, particularly organics, poly- mers Instrument cost $500,000-$750,000 Size 4 ft. x 8 ft. 41
  • 65. Surface Analysis by Laser Ionization (SALI) 1.10.3 In SurfaceAnalysis by Laser Ionization (SALI),a probe beam such as an ion beam, electron beam, or laser is directed onto a surfaceto removea sampleof material.An untuned, high-intensity laser beam passes parallel and close to but above the sur- face. The laser has sufficient intensity to induce a high degreeof nonresonant, and hence nonselective,photoionization of the vaporizedsampleof material within the laser beam. The nonselectively ionized sample is then subjected to mass spectral analysis to determine the nature of the unknown species. SALI spectra accurately reflect the surface composition, and the use of time-of-flight mass spectrometers provides fast, efficientand extremelysensitiveanalysis. Range of elements Destructive Post ionization approaches Information Detection limit Quantification Dynamic range Probing depth Lateralresolution Mass range Hydrogen to Uranium Yes,surfacelayers removed during analysis Multiphoton ionization (MPI), single-photon ionization (SPI) Elementalsurfaceanalysis (MPI);molecularsurface analysis (SPI) PPm to PPb -10%usingstandards Depth profile mode -1O4 2-5 down to 60 nm 1-10,000 amu or greater (to several pm in profilingmode) Samplerequirements Solid,vacuum compatible, anyshape Main uses Instrument cost $600,000-$1,000,000 Quantitative depth profiling, molecular analysisusing SPI mode; imaging Size Approximately45 sq. fi. 42 INTRODUCTION AND SUMMARIES Chapter 1
  • 66. Sputtered NeutralMass Spectrometry (SNMS) 1.10.4 Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejectedfrom a solidsurfaceby energeticion bombardment. The sputtered atoms are ionized for mass spectrometricanalysis by a mechanism sepa- rate from the sputtering atomization.Assuch,SNMS is complementaryto Second- ary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms.Theforte of SNMS analysis, com- pared to SIMS, is the accurate measurement of concentration depth profiles through chemicallycomplex thin-film structures, including inte&ces, with excel- lent depth resolution and to trace concentration levels. Genericallyboth SAL1and GDMS are specific examplesof SNMS. In this articlewe concentrate on post ion- ization only by electron impact. Range of elements Li to U Destructive Yes, surfacematerial sputtered Chemical bonding None information Quantification Detection limits 10-100 ppm Depth probed Depth profiling Yes, by sputtering Lateral resolution Yes, accuracy x 3 without standards; 5-10% with analogousstandard; 30%with dissimilarstandard 15A (to many pm when profiling) A few mm in direct plasma sputtering; 0.1-10 pn using separate,focusedprimary ion-beam sputtering Imaging/mapping Yes, with separate, focusedprimary ion-beam Samplerequirements Solid conducting material, vacuum compatible; flat wafer up to 5-mm diameter;insulatoranalysispossible Main use Complete elemental analysis of complex thin-film structures to several pm depth, with excellent depth resolution cost $200,000-$450,000 Size 2.5 ft. x 5 ft. 43
  • 67. Laser Ionization Mass Spectrometry (LIMS) 1.10.5 In Laser Ionization Mass Spectrometry (LIMS, also LAMMA, LAMMS, and LIMA), a vacuum-compatiblesolid sample is irradiated with short pulses (+lons) of ultravioletlaser light. The laser pulse vaporizesa microvolume of material,and a fraction of the vaporized species are ionized and accelerated into a time-of-flight mass spectrometer which measures the signal intensity of the mass-separated ions. The instrument acquiresa completemass spectrum, typically coveringthe range 0- 250 atomic mass units (amu), with each laser pulse. A survey analysisof the mate- rial is performed in thisway. The relative intensitiesof the signalscan be converted to concentrations with the use of appropriate standards, and quantitative or semi- quantitative analysesare possible with the use of such standards. Range of elements Destructive Chemical bonding information Quantification Standards needed Detection limits Depth probed Depth profiling Lateralresolution 3-5 pm Mapping capabilities No Samplerequirements Vacuum-compatible solids; must be able to absorb ultraviolet radiation Main use Survey capability with ppm detection limits, not affected by surfacechargingeffects; complete elemen- tal coverage; survey microanalysis of contaminated areas, chemicalfailure analysis Instrument cost $400,000 Size 9 fi. x 5 fi. Hydrogen to uranium; all isotopes Yes, on a scaleof fewmicrometersdepth Yes, depending on the laser irradiance 10'~-10'~at/cm3 (ppm to 100ppm) variablewith material and laser power Yes, repeated laser shots sampleprogressivelydeeper layers; depth resolution 50-100 nm 44 INTRODUCTIONAND SUMMARIES Chapter 1