Secondary ion mass spectrometry (SIMS) is an analytical technique that bombards a sample surface with a primary ion beam, causing charged secondary ions to emit. These secondary ions are then analyzed using mass spectrometry to determine their mass-to-charge ratios. SIMS has high sensitivity and can detect elements down to parts-per-million or parts-per-billion levels. It provides both elemental and molecular composition of solid surfaces with good depth resolution and lateral resolution in the 2-5 nm and 20 nm to 1 μm range, respectively. SIMS finds applications in composition analysis, depth profiling, trace detection in semiconductors, and imaging of surfaces.

1. By
Dhivyaprasath. K
413117057
Research scholar
Department of Physics
NITT
Secondary Ion Mass
Spectroscopy (SIMS)

2. Outline
o Introduction
o Basic principle
o Basic overview
o Ion gun
o Energy and Mass Analyzer
o Ion Detectors
o Advantages and limitations
o Applications

3. Mass Spectroscopy
Mass spectrometry (MS) is an analytical technique that measures mass to
Charge ratio of charged particles.
Secondary ion mass spectrometry
Secondary ion mass spectrometry (SIMS) is based on the observation of
charged particles (Secondary Ions) are ejected from a sample surface when
bombarded by a primary beam of heavy particles.
Introduction

4. o Bombardment of a sample surface with a primary
ion beam (Ip) followed by mass spectrometry of
the emitted secondary ions (Is) constitutes
secondary ion mass spectrometry.
o SIMS is a surface analysis technique used to
characterize the surface and sub-surface region
of materials
o It has used in two modes Static SIMS mode and
Dynamic SIMS mode
Basic Principle

5. SIMS Basic overview
Basic overview

6. Ion Gun
o Electrons into a vacuum chamber.
o Small amount of argon gas , It become
ionized by interacting with free
electron and forming a plasma.
o The plasma is then accelerated
through a series of at least two highly
charged grids, and becomes an ion
beam, moving at fairly high speed
from the aperture of the device.
o O2
+, O-, Cs+, Ar+, Xe+, Ga+, etc
o Beam angle : 0 - 60 deg.
o Beam energy : 0.5 - 20 keV
o Beam diameter : typical 10 ~ 100 µm, extreme 0.1 µm

7. o It has other two types for liquid and
solid ion sources
o For Cesium atoms vaporize through a
porous tungsten plug and are ionized
during evaporation
o For Liquid Metal Ion Gun (LMIG),
operates with metals or metallic
alloys
Other ion Gun

8. o Ions has different
energy
o Electrostatic energy
analyzer
o Low energy strongly
deflected than High
energy Ions
o Movable energy slit
used to selected
energy ions
Ion Energy Analyzer

9. Ion Mass Analyzer
o BS ion pass though Magnetic
field
o Ions are acted force on
right angle to magnetic
field and ion beam direction
o Deflection of ion species is
given by the equation
o Magnetic field measured by Semiconductor Hall probe

10. Ion Detector
Modern mass spectroscopy has more than one detector.
There are four types of detectors.
o Electron Multiplexer
o Faraday Cup
o Micro-Channel Plate
o RAE Image Detector

11. Electron Multiplexer
o It has series of Dynodes
o Each dynode is connected to a resistor
chain
o The first dynode is at ground potential,
so that both positive or negative ions may
be detected. The last dynode can be b/w
+1500 to +3500 V depending on the age
and type of multiplier.
o When a BS Ion strikes the first dynode it
may produce a few (1, 2 or 3) secondary
ions. These secondary electrons are
accelerated to the second dynode that is
held at a slightly higher positive potential.
o Finally these ions are pass to counting
system

12. Faraday Cup
o The Faraday cup detector consists of a
hollow conducting electrode connected
to ground via a high resistance.
o The ions hitting the collector cause a
flow of electrons from ground through
the resistor.
o The resulting potential drop across the
resistor is amplified. A plate held at
about -80 V in front of the collector,
prevents any ejected secondary
electrons from escaping and causing
an anomalous reading.

13. Micro-Channel Plate
o It has ion image plate consists of an array
of miniature electron multipliers composed
of lead glass.
o Typically the ion multipliers or channels,
are about 10 µm in diameter, 400 µm long
and about 7O from the perpendicular to
the plate face.
o They are located about 12 µm between
centers and number up to 2000 in a 25 m
m array. The front face of the plate is held
at ground potential, while the back plate
may be between +1000 to +2000V.
o Rest of the things just like electron
multiplexer

14. RAE Image Detectors
o The resistive anode encoder is a
position-sensitive detector, it is used
to digitally record ion images.
o The resulting ions pulse strikes a
resistive plate comprising a thick
resistive film, deposited on a ceramic
plate. The geometry of the detector
designed to avoid image distortion.
o The charge pulse is partitioned off
to four electrodes at the corners of
the plate.
o where the X and Y position is
calculated by the equations

15. SIMS-Spectra
m/z Mass to charge ratio
NoofionsCounts/s

17. Advantages and Limitations
Advantages
o All elements detectable and isotopes can be distinguished.
o Detection limits of ppm for most elements and ppb for favorable elements.
o Good depth resolution (2~5 nm) and lateral resolution (20 nm ~ 1 µm)
Insulator analyzable
o Chemical information obtained from relative molecular ion abundances.
Limitations
o Mass interferences.
o Secondary ion yields are often matrix dependent.
o Numerous secondary standards are required to quantify data.
o Flat surface required for best depth resolution and for ion microscopy.
o Destructive analysis.

18. o Composition of solid surfaces
o Surface analysis
o Ion mapping
o Depth Profile
o Trace detection in semiconductors
o Analysis and depth profiling of thin layers
o Imaging of surfaces
Applications of SIMS

19. o SIMS can be used to analyze the composition of organic and
inorganic solids.
o SIMS can generate spatial or depth profiles of elemental or
molecular concentrations.
o To detect impurities or trace elements, especially in semiconductors
and thin filaments.
o Secondary ion images have spatial resolution on the order of
0.5 to 5 μm. The depth resolution is around 2 to 5 nm.
o Detection limits for trace elements range between 1012 to
1016 atoms/cm3. That is around ppb ~ ppm.
o SIMS is the most sensitive elemental and isotopic surface
microanalysis technique. However, very expensive.
Summary

20. o Secondary Ion Mass Spectrometry – A Practical Handbook f
or Depth Profiling and Bulk Impurity Analysis, by R. G. Wilso
n, F. A. Stevie, and C. W. Magee, Wiley- Interscience, 1989
o Precise and fast secondary ion mass spectrometry depth pr
ofiling of polymer materials with large Ar cluster ion beams,
by S. Ninomiya
Reference