EUROMAT 2013 - Tutorial on Helium Ion Microscopy

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EUROMAT 2013 - Tutorial on Helium Ion Microscopy

  1. 1. Helium Ion Microscopy – Extending the Frontiers of Nanotechnology Giulio Lamedica Assing SpA / Zeiss Microscopy
  2. 2. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFab Technology• Conclusions• Introduction• More Applications•
  3. 3. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFAab technology• Conclusions• Introduction• More Applications•
  4. 4. 4 As the beam is raster scanned across the sample, secondary electrons are generated which are detected by ET Detector …. Image Formation HIM Image
  5. 5. BS PB SE1 SE2 SE3 Pole piece Resolution in CPM BSP  Probe Size  Interaction VolumeSE1/SE2)
  6. 6. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFAab technology• Conclusions• Introduction• More Applications•
  7. 7. 7 Superposition of the aberration discs 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Resolution and Probe Size – Electron Beam Probe Size: 3 5.0 iSS Cd Spherical aberration: iCC U U Cd   Chromatic aberration: i dd   6.0Diffraction Error: Demagnified source: gSo dMd  i i [mrad] dp[nm]   2222 dCSgP ddddMd 
  8. 8. 07.10.2013 Page 8 Carl Zeiss NTS, Peter Gnauck 1,00E-06 1,00E-04 1,00E-02 1,00E+00 1 10 100 1000 U [kV] Wavelength[nm] Resolution and Probe Size He+ Ga+ e-
  9. 9. 9 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 Resolution and Probe Size – Helium Ion Beam Probe Size:   2222 dCSgP ddddMd  3 5.0 iSS Cd Spherical aberration: iCC U U Cd   Chromatic aberration: i dd   6.0Diffraction Error: Demagnified source: gSo dMd   i [mrad]dp[nm] •The Helium Ion Microscope has a half angle (/2) of 0.5mrad compared to a typical SEM of 5-10mrad • The Helium Ion Microscope has a theoretical probe size of 0.2nm and a demonstrated probe size of 0.24nm (product specification <0.35nm)
  10. 10. No diffraction limitations (MHe/Me = 7289) Helium ions are more particle-like in nature due to higher mass (compared to electrons) 1 Key Attributes of Helium Ion Microscopy 10 He ions have extremely little diffraction effects Imaging of small aperture with He ions Imaging of small aperture with He ions Diffraction limited image No diffraction limitations Wavelength ~ 0.01 nm Wavelength ~ 0.0001 nm MHe/Me = 7289 80X smaller at all energies 2 2 1 1 2 cm eUeUm h He He  
  11. 11. Key Attributes of Helium Ion Microscopy 11 Spot size = 0.8 nm Electrons Very high lateral resolution in images Sub-nm probe size and very narrow interaction volume 2 He ions Silicon Sample30 nm 1 keV e-beam into Silicon: Image suffers from large interaction volume at the surface. Many SE’s are really SE2. 30 keV Helium into Silicon: Beam is well collimated beyond the SE escape depth. Recoil contribution is negligible. Spot size = 0.35 nm
  12. 12. Key Attributes of Helium Ion Microscopy 12 Surface sensitive imaging Secondary electrons get generated from within 3-5 nm of the sample surface 3 Electrons He ions Silicon Sample30 nm 1 keV e-beam into Silicon: Image suffers from large interaction volume at the surface. Many SE’s are really SE2. 30 keV Helium into Silicon: Beam is well collimated beyond the SE escape depth. Recoil contribution is negligible. Secondaryelectron escapedepth Volume from which SE’s are generated Volume from which SE’s are generated
  13. 13. High SE yield means low ion doses can generate excellent images Helium ions generate many secondary electrons per ion 4 Key Attributes of Helium Ion Microscopy 13 Electrons He ions Silicon Sample30 nm He ions product 4-7 times as many secondary electrons 30 keV Helium into Silicon: Beam is well collimated beyond the SE escape depth. Recoil contribution is negligible.
  14. 14. Key Attributes of Helium Ion Microscopy 14 Electrons 5X-10X greater depth of focus in the images Helium ion beam has 5X lower convergence angle than FESEM 5 He ions Silicon Sample30 nm Convergence Angle = 0.020  Best Focus Best Focus
  15. 15. Key Attributes of Helium Ion Microscopy 15 Extremely easy to get high resolution images of insulating samples without complex preparation Insulating samples are only positively charged under helium ion beam 6 The sample interaction volumes and the positive and negative charge distributions (+,-) arising from imaging with the SEM and with the HIM. SE1 are secondary electrons created from the primary beam. SE2 are secondary electrons created from backscattered electrons (BSE) 0 nm 10 nm 300 nm Helium @ 30 kVSEM @ 0.5 kV - SE2 SE2 SE1 BSE - -- ++++ + + SE1 SE1 +++ ++ -- - - - Bulk Charging Surface Charging Positive surface charging only - easily neutralized by electron flood gun! Electrons He ions
  16. 16. Why Helium Ion Microscopy? Very high lateral resolution in images Sub-nm probe size and very narrow interaction volume 1 No diffraction limitations Helium ions are more particle-like nature due to higher mass (compared to electrons) 2 Surface sensitive imaging Secondary electrons get generated from within 3-5 nm of the sample surface 3 High SE yield means low ion doses can generate excellent images Helium ions generate many secondary electrons per ion 4 5X-10X greater depth of focus in the images Helium ion beam has 5X lower convergence angle than FESEM 5 16 Extremely easy to get high resolution images of insulating samples without complex preparation Insulating samples are only positively charged under helium ion beam 6
  17. 17. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFAab technology• Conclusions• Introduction• More Applications•
  18. 18. What is Ion Beam Milling? 18 Schematic showing material being sputtered away by helium beam Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008 Helium ion beam can remove material … (1) … at a controlled rate (2) … with high fidelity (3) … from within 5 nm of beam impact point Complex shapes and arrays of shapes can be milled using patterning engine. APPLICATION AREAS (1) Nanopore fabrication in thin films (2) Precision milling of thin films (3) Optical and magnetic metamaterial research Ion beam milling utilizes the sputtering capability of ion beam to remove material
  19. 19. Why is Helium Ion Beam Suitable for Nanofabrication? Remove material by sputtering Helium ions are much more massive than electrons 1 Remove material at a controlled rate Helium ions are less massive than gallium ions 2 Remove material locally Helium ions sputter material from within 5 nm radius of beam impact point 3 Chemically enhanced etching and deposition at length scales not achievable with Gallium FIB Helium ions can induce etching and deposition reactions at surface with precursor gases 4 No proximity effect in helium ion beam lithography Helium ions scattering profile in resists is narrow conical with low backscatter 5 High sensitivity, better contrast than e-beam lithography Helium ions can expose resists in 5X smaller doses 6 19
  20. 20. Ion Beam Milling Comparison between Helium and Gallium FIB 20 1 10 20 30 100 nm Ga FIBHe FIB Helium FIB Type of Ion Source Gas Field Ion Source Minimum feature size Spot size (30 kV) Diameter of sputtered region in gold (spot) 1 nm 0.35 nm 2.6 nm Gallium FIB Liquid Metal Ion Source 25 nm 5 nm 20 nm Suitable for milling Small structures Large structures
  21. 21. Nanofabrication Examples … 21 Graphene Photonics DNA Sequencing Nanopores Lithography Nanopillars
  22. 22. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFAab technology• Conclusions• Introduction• More Applications•
  23. 23. He Ion Beam Milling Graphene Research Research Area Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials. It has extraordinary properties: (1) Electronic (2) Optical (3) Thermal (4) Mechanical 2010 Nobel Prize in Physics awarded for groundbreaking experiments with graphene Research Applications Nanoribbons Transistors Optical modulators Integrated circuit Transparent electrodes Ultracapacitor Chemical and electrical sensors Structure
  24. 24. Helium Ion Microscopy Imaging of Graphene 24 Material Science Challenge How do you see graphene CVD growth? Zeiss Solution Helium Ion Microscopy: highly surface sensitive imaging The grain boundaries of the graphene can be identified as ridges on the surface. CVD grown graphene monolayer on copper. Sample Courtesy: University of Houston Research
  25. 25. Helium Ion Microscopy Imaging of Graphene Material Science Challenge How do you see quality of Graphene trasferred on Silicon ? Zeiss Solution Helium Ion Microscopy: highly surface sensitive imaging Research
  26. 26. University of Bielefeld (D) Helium Ion Microscopy Imaging of Graphene
  27. 27. Graphene Machining for Quantum Confinement The bandgap in a graphene ribbon increases as the ribbon width decreases In order to increase bandgap above room temperature thermal energy (25 meV), confinement of ribbon to less than 20 nm is desired. M. Han, B. Özyilmaz , Y. Zhang., P Kim, Phys; Phys. Rev. Lett. 98 (2007) 206805 Graphene nanoribbons bandgaps can be modulated
  28. 28. Current Solutions • Lithographic patterning has been applied, but resist deposition and then removal can alter graphene electronic properties. • Ga FIB milling produces too much damage to be useful (image) • E-beam bond damage, followed by chemical etch, cannot produce sufficiently sharp feature edges. • Need: low damage, precise, method that does not touch graphene intended for pattern. Gierak et al., Microscopy Today (2009)
  29. 29. FOV 500 nm 1.86 E18 1.99 E18 * All units in Ions/cm2 2.39 E18 2.13 E18 2.53 E18 2.93 E18 2.26 E18 2.63 E18 2.79 E18 5-6 nm width Direct Patterning of Graphene: 5 nm Features Graphene created by the exfoliation method (1-3 layers thick) Created on SiO2 over cylindrical holes on surface. Ion milling carried out on the suspended area. FOV 100 nm 2.79 E18 Dr. Dan Pickard, National University of Singapore
  30. 30. 4.8 E18 2.9 E18 4.8 E18 Dose (ions/cm2) 5nm width 10nm width 20nm width Vertical FOV 700nm Direct Patterning of Graphene: Ribbon Width Control • Pattern generator (Nabity ) used to define milling structures • External control of column • 700 nm vertical field of view • Milling proceeded simultaneously down both sides of ribbon to maintain strength Dr. Dan Pickard, National University of Singapore
  31. 31. 10nm wide ribbon 3.5 microns long 20nm wide ribbon 3 microns long Direct Patterning of Graphene • 20 nm and 10 nm wide suspended ribbons • 4 µm field of view • Aspect ratio up to 350X FOV 4 µm Dr. Dan Pickard, National University of Singapore
  32. 32. • Graphene layer (could be multiple layers) on SiO2 substrate • Goal: creation of a quadrupole quantum dots structure • 4 dots, with 4 electrodes to control the occupancy of dots • Created by bitmap imported into Orion patterning interface • 10 nm gaps have been created • Next required step: pattern electrodes to the device for electrical testing (using beam chemistry!) Graphene Milling on a Substrate Creation of features with high machining precision Graphene on SiO2 Courtesy of Stuart Boden, University of Southampton
  33. 33. Graphene Nanoribbons Why Helium Ion Milling over other methods? • Fast • Non-destructive • Contamination free • Extends limitations (down to 5-6 nm width) • Capable of complex geometries • External control of column
  34. 34. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFAab technology• Conclusions• Introduction• More Applications…•
  35. 35. Carbon Nanotubes – Large Depth of Focus 200nm Research Single walled Carbon nanotubes on Si-Ge catalyst imaged with a 70 tilt Challenge study of the growth dynamics that progress parallel to the substrate in this case Zeiss Solution long depth of focus allows the CNT attachment to the catalyst to be imaged deep into the background Contrast for low atomic weight material at high resolution Sample courtesy Prof. H.N.Rutt, Univ. of Southampton
  36. 36. Helium Ion Microscopy Carbon Nanotubes Research CNT with Sn and Pd nanoparticles Challenge How do you evaluate nanoparticle distribution? Zeiss Solution Helium Ion Microscopy: Topographical and Material contrast
  37. 37. Nanowires – Strong Materials Contrast 100 nm Sample courtesy Princeton University Research Nanowires in the beginning of growth phase Catalyst array in substrate Challenge Study the dynamics of the growth in this system with greater detail Zeiss Solution Strong material contrast clearly delineates the nanowires but without saturation of the image
  38. 38. Helium Ion Microscopy SAM Modification Research Nitro-biphenyl-thiol (NBPT) self-assembled monolayer on gold, Electron beam patterning via stencil mask converted terminal nitro group to amine Challenge How to identify chemical changes? Zeiss Solution Helium Ion Microscopy: Topographical and Material contrast possible studies of this chemical lithography which otherwise requires AFM, which has throughput limitations
  39. 39. Helium Ion Microscopy Imaging of Uncoated Polymers 39 200 nm 200 nm SEM HIM Research Bioengineering (PLLA/hydroxyapatite composites for large bone defect healing) Challenge How do you visualize biomineral growth on sensitive polymer surfaces? Zeiss Solution Helium Ion Microscopy: damage –free imaging Hydroxyapatite crystal on PLLA Charging and sample damage
  40. 40. Research Material Science Challenge How do you visualize at high magnification low weight materials ? Zeiss Solution HeIM: Good contrast for low weight materials @ over 1MX (0.29 nm res) Helium Ion Microscopy Carbon Black
  41. 41. Helium Ion Microscopy Imaging of Inner Ear Tectorial Membrane 41 Bioscience Challenge How do you see the complex morphology of tissue nanostructures? Zeiss Solution Helium Ion Microscopy: charge neutralization technology allows clear view Sample Courtesy: NIH Research
  42. 42. Ion Beam Milling Metamaterial Research 42 Research Area Metamaterials are engineered materials with properties that are not found in natural materials. Also known as “left-handed” media, “Negative refractive index” media Metamaterials gain their properties from structure rather than composition, using small periodic (1D, 2D or 3D) inclusions (holes, lines, space etc.) in bulk material to create effective macroscopic property. Electromagnetic Waves Visible light Infrared Terahertz Microwaves Radiowaves Research Applications Terahertz materials Photonic materials Plasmonic materials Metamaterial antennas Nonlinear materials Metamaterial absorber Superlens Cloaking devices Working Principle The objective is to create a “structured” metamaterial that will exhibit desired properties when electromagnetic waves interact with respect to (1) Propagation (3) Absorption (2) Transmission (4) Reflection Metamaterial
  43. 43. Ion Beam Milling Metamaterial Research 43 Traditional Methods  Lithography  Layer by Layer or Self-assembly based methods Zeiss Ion Beam Milling Solution Drawbacks Multi-step – have to rely on success of multiple steps Tedious – numerous iteration of process development steps Structure is big enough to make with Ga FIB 20 nm Gold (evaporated) 5 nm ITO Glass Substrate Zeiss Ga FIB Solution: Array fabricated in 20 minutes Source: “Focused-Ion-Beam Nanofabrication of Near-Infrared Magnetic Metamaterials”, Adv. Mater. 2005, 17, 2547–2549
  44. 44. Ion Beam Milling Metamaterial Research 44 Going Smaller By making the shapes in the array smaller, one can modulate the frequency response of the metamaterial. Example: As array element is made smaller, transmission of shorter wavelengths is suppressed. Long wavelengths blocked Medium wavelengths blocked Short wavelengths blocked How does one make smaller structures? Helium Ion Beam Milling, (Neon Ion Beam Milling)
  45. 45. Ion Beam Milling Complex Shapes for Plasmonics 45 Research Area Plasmonics, Photonics, Sensors Challenge How does one make small enough structure in metal film that will exhibit plasmon- enhanced transmission at desired wavelength? Zeiss Solution Helium Ion Beam Milling Theory: Fractal shapes enhance plasmon-assisted transmission* *Source: “Fractal extensions of near-field aperture shapes for enhanced transmission and resolution”, Optics Express, 2005, 13, 636-647 ** Courtesy: Dan Pickard, NUS First fractal iteration based on Hilbert Curve Second Fractal iteration based on Hilbert Curve 50 nm Helium ion beam milling can make complex structures Au Al Ag **
  46. 46. Ion Beam Milling Technology Comparison • Ga FIB vs. Helium Ion Beam 46 1 10 20 30 100 nm Ga FIBHe FIB * Courtesy: Dan Pickard, NUS
  47. 47. What is Ion Beam Induced Etching? 47 Schematic showing material being etched away by He beam in the presence of precursor gas molecules Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008 When an etch gas (such as XeF2) adsorbs on a surface, enhanced etching/material removal will occur if the surface is scanned by helium ion beam. APPLICATION AREAS (1) Photomask repair (2) Removal of excessive amounts of material Material removal in the scanned region He+
  48. 48. Ion Beam Induced Etching Photomask Repair 48 Area Photomasks for lithography Challenge How do you increase throughput in EUV photomask repair? Zeiss Solution Helium Ion Beam Induced Etching TaN Absorber Layer No XeF2 XeF2 Present TaN Absorber Layer  12 nm wide lines at 25 nm pitch  Etching speed significantly enhanced by XeF2 precursor  Same exposure conditions (areal dose / scan repeats etc.)Introduce XeF2 100 nm Source: Diederik Maas, TNO
  49. 49. What is Ion Beam Induced Deposition? 49 Schematic showing material being deposited by He beam in the presence of precursor gas molecules Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008 When a deposition precursor gas adsorbs on a surface, material will be deposited if the surface is scanned by helium ion beam. APPLICATION AREAS (1) Deposition of conductive lines and pads (2) Failure analysis of integrated chips Material deposition in the scanned region He+
  50. 50. Ion Beam Induced Deposition Application • Vertical Nanopillars 50 Area AFM probes tips, Hard mask for lithography Challenge How does one create vertical nanopillars? Zeiss Solution Helium Ion Beam Induced Deposition Platinum Nanopillars (a) At low currents (b) Blow-up of the enclosed pillar, the yellow ellipse is the estimated pillar bottom (c) At high currents Source: Nanotechnology 21 (2010) 455302 (7pp)
  51. 51. What is Ion Beam Lithography? 51 When resists such as HSQ and PMMA are exposed to ion beams, their solubility changes and can be used for patterning. Just like electron beams, ion beams can be used for lithography He+ He+ Develop Develop
  52. 52. Ion Beam Lithography Sub-10 nm Lithography 52 Research Area There is an interest in making smaller and smaller lines at a tighter pitch using lithography to keep up with Moore’s law. State-of-the-art E-Beam Litho Best results : 6 nm lines at 12 nm pitch Half-pitch = 5 nm Dose = 4000 e-/nm Half-pitch = 6 nm Dose = 4400 e-/nm Half-pitch = 8 nm Dose = 5000 e-/nm Half-pitch = 10 nm Dose = 6300 e-/nm Source: Karl Berggren, MIT Reaching limits of EBL ….
  53. 53. Ion Beam Lithography Sub-10 nm Lithography 55
  54. 54. Ion Beam Lithography Neon Beam Lithography 56
  55. 55. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFab Technology• Conclusions• Introduction• More Applications•
  56. 56. 58 Orion Plus
  57. 57. He – Ne Gas Field Ion Source (GFIS) Single column – dual source concept  Probe Size; Probe Current:  He – 0.5 nm; 0.1 - 5 pA  Ne – 1.9 nm; 0.1 - 2.5 pA  Accelerating Voltage • 10 – 35 kV  Switching time between gases ET Detector Electron Flood Gun Sample SE Helium + Neon Target Specs.  Higher sputter yield (30% greater than helium)  Shallower penetration depth  Higher SE yield compared to He - 3X faster resist exposure than He  Improved deposit quality – Metal deposit resistivity equivalent to Ga Neon Beam Benefits High resolution imaging using He combined with High fidelity nanostructuring using Ne 59
  58. 58. 9/20/2012 PageCarl Zeiss NTS LLC , Bernhard Goetze Cryogen ic Cooling Gas InletHigh Voltage High Speed Camera Phospho r Screen Gas Field Ion Source
  59. 59. 61 The Technology Behind It Individual atoms are stripped away from the source until an atomic pyramid is created with just three atoms at the very end of the source tip – a configuration called the trimer. Once the trimer is formed, the tip is maintained under high vacuum and cryogenic temperatures with helium or neon gas flowing over it. The helium or neon atoms are attracted to the energized tip where they are ionized. With ionization happening in the vicinity of a single atom, the resulting ion beam appears to be emanating from a region that is less than an angstrom in size.
  60. 60.  FIM tip created via chemical etching  ALIS tip formed with additional reshaping  3 atom shelf called the “trimer” created through field evaporation  Single atom selected to form the final probe  Results in a sub-angstrom virtual source with high brightness (4x109 A/(cm2 sr)) and low energy spread (<1eV) The Atomic Level Ion Source 62
  61. 61. ORION NanoFab– The Column 9/20/2012
  62. 62. Bulk Milling with Ga Multi-ion Beam Machining in ORION NanoFab Intermediate Milling with NeFinal Milling with He Sample: Gold film on Glass substrate Ga Milling He Milling Ne Milling 64
  63. 63. Nanofabrication Why He ions for Imaging? HeiM on Graphene Summary • • • Orion NanoFAab technology• Conclusions• Introduction• More Applications•
  64. 64. The ORION NanoFab Platform • Configurable architecture to address specific imaging and nanofabrication applications. • High Resolution Imaging on insulating samples – ideal for life science and polymer imaging applications. • 3D Nanofabrication of sub-10nm structures. • Precise Machining with He/Ne beams and Rapid Prototyping with Ga beam – only platform offering unique combination of three different ion beams. Sample Helium + Neon Ga XRE
  65. 65. Stereocilia 9/20/2012 67 Carl Zeiss NTS LLC , Bernhard Goetze 200 nm HIM: Unsurpassed Resolution 0,24nm
  66. 66. Carbon Nanotubes(Provided by Prof. Brendan Griffin Univ. W. Australia) CNT HIM: Low Damaging Effect
  67. 67. MEMS HIM: High Depth of Field
  68. 68. Collagene HIM: Effective Charge Compensation
  69. 69. (Provided by Prof. Brendan Griffin Univ. W. Australia) CNT HIM: Surface Details
  70. 70. 9/20/2012 72Carl Zeiss NTS LLC , Bernhard Goetze Collecting Duct HIM: High Resolution and Elevated Surface Details
  71. 71. 500nm Catalyst: Pd on ZnO nanowires 73 HIM: High Depth of Field
  72. 72. Bacteria 9/20/2012 74Carl Zeiss NTS LLC , Bernhard Goetze 200 nm HIM: Minimal Sample Preparation
  73. 73. HIM: Nanofabricaation with Ga ions 75 TEM lamella S/C
  74. 74. 200nm 76 Al bump su Silicio HIM: Nanofabricaation with Neon ions
  75. 75. 100nm ~4nm gap TEM Image 77 Plasmonic Devices HIM: Nanofabricaation with He ions
  76. 76. Bulk Milling with Ga Multi-ion Beam Machining in ORION NanoFab Intermediate Milling with NeFinal Milling with He Sample: Gold film on Glass substrate Ga Milling He Milling Ne Milling 78 HIM: Nanofabricaation with Multiple Beam Plasmonic Devices
  77. 77. 79

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