Secondary Ion Mass Spectroscopy (SIMS) PPT

Basics about secondary ion mass spectroscopy. ion Mass spectroscopy

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

2. Outline Introduction Basic principle Basic overview Ion gun Energy and Mass Analyzer Ion Detectors Advantages and limitations 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. 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. SIMS is a surface analysis technique used to characterize the surface and sub-surface region of materials It has used in two modes Static SIMS mode and Dynamic SIMS mode Basic Principle

5. SIMS Basic overview Basic overview

6. Ion Gun Electrons into a vacuum chamber . Small amount of a rgon gas , It become ionized by interacting with free electron and forming a plasma. 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 2 + , O - , Cs + , Ar + , Xe + , Ga + , etc Beam angle : 0 - 60 deg. Beam energy : 0.5 - 20 keV Beam diameter : typical 10 ~ 100 µm , extreme 0.1 µm

7. It has other two types for liquid and solid ion sources For Cesium atoms vaporize through a porous tungsten plug and are ionized during evaporation For L iquid M etal I on G un (LMIG), operates with metals or metallic alloys Other ion Gun

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

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

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

11. Electron Multiplexer It has series of Dynodes Each dynode is connected to a resistor chain 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 . 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 . F inally these ions are pass to counting system

12. Faraday Cup The Faraday cup detector consists of a hollow conducting electrode connected to ground via a high resistance . The ions hitting the collector cause a flow of electrons from ground through the resistor. 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 It has ion image plate consists of an array of miniature electron multipliers composed of lead glass . Typically the ion multipliers or channels, are about 10 µ m in diameter, 400 µm long and about 7 O from the perpendicular to the plate face. They are located about 12 µ m between centers and number up to 2000 in a 25 mm array. The front face of the plate is held at ground potential, while the back plate may be between +1000 to + 2000V. Rest of the things just like electron multiplexer

14. RAE Image Detectors The resistive anode encoder is a position-sensitive detector, it is used to digitally record ion images. 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. The charge pulse is partitioned off to four electrodes at the corners of the plate. where the X and Y position is calculated by the equations

15. SIMS-Spectra m/z Mass to charge ratio No of ions Counts/s

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

17. Composition of solid surfaces Surface analysis Ion mapping Depth Profile T race detection in semiconductors A nalysis and depth profiling of thin layers Imaging of surfaces Applications of SIM S

18. SIMS can be used to analyze the composition of organic and inorganic solids. SIMS can generate spatial or depth profiles of elemental or molecular concentrations. To detect impurities or trace elements, especially in semiconductors and thin filaments. Secondary ion images have spatial resolution on the order of 0.5 to 5 μm . The depth resolution is around 2 to 5 nm. Detection limits for trace elements range between 10 12 to 10 16 atoms/cm 3 . That is around ppb ~ ppm. SIMS is the most sensitive elemental and isotopic surface microanalysis technique. However, very expensive . Summary

19. Secondary Ion Mass Spectrometry – A Practical Handbook for Depth Profiling and Bulk Impurity Analysis, by R. G. Wilson, F. A. Stevie, and C. W. Magee, Wiley- Interscience , 1989 Precise and fast secondary ion mass spectrometry depth profiling of polymer materials with large Ar cluster ion beams,by S. Ninomiya Reference

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