Introduction to SEM Characterization.pptx

Introduction to SEM Characterization
A scanning electron microscope is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample.

1. Scanning electron microscopy 1

2. Why electron microscopy? 2

3. Motivation for electron microscopy 3

4. Electron microscopy H is Planck’s constant. P is the momentum of electrons. 4

5. Comparing Microscopes 5

6. Optical vs. Scanning Electron Microscopy 25m m OM SEM Small depth of field Low resolution Large depth of field High resolution radiolarian 6

7. Principles 7

8. WORKING PRINCIPLE 8

9. Electron-atom interactions 9

10. Electron-atom interactions 10

11. SEM Setup Electron/Specimen Interactions When the electron beam strikes a sample, both photon and electron signals are emitted. Incident Beam Specimen X-rays Through thickness composition info Auger electrons Surface sensitive compositional Primary backscattered electrons Atomic number and topographical Cathodoluminescence Electrical Secondary electrons Topographical Specimen Current Electrical 11

12. 12

13. How are these rays generated? 13

14. Effect of Atomic Number, Z, on BSE and SE Yield 14

15. Elastic vs. inelastic scattering 15

16. Electron energy distribution 16

17. Escape volumes of various signals Primary Signals: - Secondary Electrons - Backscattered Electrons - X-rays 17

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22. 22

23. Technology 23

24. 24

25. Electron Gun e - beam  25

26. COMPONENTS Electron gun Electromagnetic lenses Scanning Detectors Sample stage Vacuum system 26

27. SAMPLE CHAMBER 27

28. Electron Detectors and Sample Stage Objective lens Sample stage 28

29. Electron gun 29

30. ELECTRON GUN 30

31. TECHNOLOGY: 31

32. Electron beam Source W or LaB 6 Filament Thermionic or Field Emission Gun 32

33. Thermionic Emission Gun - + 33

34. Field Emission Gun 34

35. Comparison 35

36. Magnetic lenses 36

37. Electromagnetic Lenses soft iron pole piece electrical coil 37

38. The Objective Lens 38

39. The Objective Lens - Focusing 39

40. The Objective Lens – The Aperture Electron beam Objective lens Wide aperture Narrow aperture Wide disc of least confusion Narrow disc of least confusion Large beam diameter striking specimen Small beam diameter striking specimen 40

41. The Scan Coil and Raster Pattern X-direction scanning coil y-direction scanning coil specimen Objective lens Holizontal line scan Blanking 41

42. Image Formation in SEM 42

43. beam e - A A Detector Amplifier 10cm 10cm Image Formation in SEM M = c/x c-length of CRT scan x-length of e - beam scan 43

44. Magnification 44

45. Magnification Low M Large x 40 m m High M small x 7 m m 2500x 15000x 1.2 m m e - x 45

46. 46

47. Depth of Field D = (  m) AM 4x10 5 W Depth of Field 47

48. Image Contrast Image contrast, C is defined by S A -S B C= ________ S A SE Images 48

49. SE Images - Topographic Contrast The debris shown here is an oxide fiber got stuck at a semiconductor device detected by SEM 1 m m Defect in a semiconductor device Molybdenum trioxide crystals 49

50. BSE Image – Atomic Number Contrast BSE atomic number contrast image showing a niobium-rich intermetallic phase (bright contrast) dispersed in an alumina matrix (dark contrast). Z (Nb) = 41, Z (Al) = 13 and Z(O) = 8 Alumina-Al 2 O 3 2  m 50

51. Voltage contrast 500  m +U -U 51

52. Sample preparation 52

53. Sputter coating 53