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