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Reflectometry-Theory
This kind of non-destructive, optical thin film measurement technique analysis the light-interference caused by thin layers.
The reflection at the layer surface and layer-substrate interface results in constructive and destructive interference depending
on the wavelength of the light.
As the layer thickness cannot be calculated out of these refection spectra directly, a special best-fit-algorithm is used to determine the layer thickness. In this way not only single layers but also multi-layer stacks with known optical data (n,k) can be measured easily and very fast.
The following prerequisites are necessary for the existance of this type of thin layer interference:
1. The layers and the substrate must have a difference in refractive index to get any refection at the interface at all.
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2. The layers must be transparent or at least semi-transparent in the used spectral range to let the light through. E.g.
100µm hick silicon membrane can be measured very well as silicon itself gets transparent above 900nm wavelength.
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3. The substrate and the layer surface must be smooth enough to get enough directly reflected light back. E.g. layers on
standard white paper are not measurable because of the highly diffuse reflection of the paper surface, while e.g. layers
on rough aluminium plates can still be measured perfectly. |
The NanoCalc Software also allows a simulation of any defined layer stack to see if it is measurable theoretically, even before having a real sample prepared.
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- Mapping
transparent samples
