Scanning Electron Microscope & Surface Analysis. Wageningen EM Centre Marcel Giesbers

Transcription

1 Scanning Electron Microscope & Surface Analysis Wageningen EM Centre Marcel Giesbers

2 Scanning Electron Microscope & Surface Analysis SEM vs Light Microscope and Transmission EM Secondary Electron Imaging Backscatter Imaging Energy Dispersive X-ray Spectrometry (EDX / EDS) Layer thickness determination By EDX By cross section Summary 2

3 Light Microscope & Transmission Electron Microscope Light microscope Transmission Electron Microscope (TEM) 3

4 The Scanning Electron Microscope (SEM) 4

5 Information from the electron specimen interactions 5

6 Different signals from different regions in the specimen. Interaction volume 15kV electrons travel ~1 μ into sample Sampling volume volume from which a particular signal (e.g. X-rays) originates 6

7 Regular SEM imaging of secondary electrons 7

8 The SEM image is a 2D intensity map The SEM image is a 2D intensity map Beam scans the sample Sample surface The scanning on the computer screen is synchronized with the electron-probe scan. Brightness variations, depends on the number of the secondary electrons collected, forms the SEM image 8

9 Backscatter imaging The incoming electrons are reflected back out of the sample 9

10 Backscatter imaging In Backscatter imaging, the signal is dependent on the atomic number. 10

11 Energy Dispersive X-ray Spectrometry (EDX or EDS) 11

12 X-ray spectrum is acquired Elements are identified and labelled. The higher the peak, the higher the concentration of that element Transistor 12

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17 EDX analysis in SEM output Element Line Wt% Wt% Type Sigma C K series O K series P K series Qualitative elemental analysis Ca K series Fe K series W M series Total: Quantitative analysis Sensitivities to 0.1 wt. % Depending on matrix and composition 17

18 EDX analysis in SEM Linescans Pointspectra Elemental composition along a line Elemental maps 18

19 Thin film Thickness Measurements by SEM Question: Silicon Nitride layer on Silicon How thick is this layer? Methods in SEM 1) EDX analysis 2) Cross section image of the sample 19

20 Thin film Thickness Measurements by EDX EDX Can also be used to calculate the composition and thickness of the individual layers beneath the surface. X-rays overlayer X-rays Bulk material X-ray spectrum Bulk material Overlayer thickness can be calculated from the attenuation of the X-rays. 20

21 Layer thickness determination by EDX Siliconnitride layer on silicon Define a model in the software ->composition, density and layers Choose analysis conditions Acquire spectrum Software fits the data calculates layers 21

22 Layer thickness and composition characterization using EDX Calculating the composition and thickness of the individual layers beneath the surface non-destructive high-resolution Characterises features down to 200 nm wide Suitable for metallic layers Usefull for coatings thin film deposition processes oxide layer formation 22

23 Layer thickness determination by cross section imaging Shell particles cross-section of solar cell Cross Section Polisher 23

24 Silicon nitride layer on Silicon EDX Imaging the Cross Section Layer thickness by EDX: Layer thickness by EDX 95.0nm Layer thickness by cross section 96.5nm 24

25 Silicon oxide layer EDX Imaging the Cross Section Layer thickness by EDX 37.5nm Layer thickness by cross section 36.5nm 25

26 Summary SEM uses a high energy beam of electrons to create images of a surface. Usually secondary electrons are used for this imaging. SEM is capable of more: Backscatter imaging can be used to differentiate contrasts in a material comprising of different chemical compositions. EDS in SEM (X-rays) can be used to identify the composing elements of materials surface. EDX does not reveal chemical bonding information. qualitative & quantitative elemental analysis elemental mapping, linescans, point spectra works on conductive and non-conductive samples. EDS can be used for layer thickness characterization. non-destructive analysis of layers high-resolution. thickness range nm 26

27 Thank you for your attention WEMC is here: RADIX, building nr. 107 nl