wageningen em centre marcel giesbers · 2018-02-13 · scanning electron microscope & surface...

Scanning Electron Microscope & Surface Analysis

Wageningen EM Centre

Marcel Giesbers

Scanning Electron Microscope & Surface Analysis

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SEM vs Light Microscope and Transmission EM

Secondary Electron ImagingBackscatter Imaging

Energy Dispersive X-ray Spectrometry (EDX / EDS)

Layer thickness determination By EDXBy cross section

Summary

Light Microscope & Transmission Electron Microscope

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Transmission Electron Microscope (TEM)Light microscope

The Scanning Electron Microscope (SEM)

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Information from the electron specimen interactions

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Different signals from different regions in the specimen.

Sampling volume volume from which a particular signal (e.g. X-rays) originates

Interaction volume 15kV electrons travel ~1 μ into sample

Regular SEM imaging of secondary electrons

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The SEM image is a 2D intensity map

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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

The SEM image is a 2D intensity map

Sample surface

Beam scans the sample

Backscatter imaging

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The incoming electrons are “reflected” back out of the sample

Backscatter imaging

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

Energy Dispersive X-ray Spectrometry (EDX or EDS)

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12Transistor

X-ray spectrum is acquiredElements are identified and labelled.The higher the peak, the higher the concentration of that element

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EDX analysis in SEM output

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Element Line Type

Wt% Wt% Sigma

C K series 60.72 0.28

O K series 25.22 0.25

P K series 0.56 0.04

Ca K series 0.65 0.05

Fe K series 8.72 0.18

W M series 4.13 0.16

Total: 100.00

Quantitative analysisSensitivities to 0.1 wt. %Depending on matrix and composition

Qualitative elemental analysis

EDX analysis in SEM

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Linescans Pointspectra

Elemental composition along a line

Elemental maps

Thin film Thickness Measurements by SEM

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Question:Silicon Nitride layer on SiliconHow thick is this layer?

Methods in SEM

1) EDX analysis

2) Cross section image of the sample

Thin film Thickness Measurements by EDX

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EDX Can also be used to calculate the composition and thickness of the individual layers beneath the surface.

X-rays

Bulk material

X-rays

Bulk material

overlayer

Overlayer thickness can be calculated from the attenuation of the X-rays.

X-ray spectrum

Layer thickness determination by EDX

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Define a model in the software->composition, density and layers

Choose analysis conditions

Acquire spectrum

Siliconnitride layer on silicon

Software fits the datacalculates layers

Layer thickness and composition characterization using EDX

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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

Layer thickness determination by cross section imaging

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Cross Section Polisher

Shell particles cross-section of solar cell

Silicon nitride layer on Silicon

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Layer thickness by EDX:

EDX Imaging the Cross Section

Layer thickness by EDX95.0nm

Layer thickness by cross section96.5nm

Silicon oxide layer

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Layer thickness by EDX37.5nm

EDX Imaging the Cross Section

Layer thickness by cross section36.5nm

Summary

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• 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 1-2000nm

Thank you for your attention

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WEMC is here:RADIX, building nr. 107marcel.giesbers@wur.nlwww.wemc.wur.nl0317483292