Ocean Optics NanoCalc - Manual (Page 69)

Ocean Optics Germany GmbH Thin Film Metrology
68
10.3 How to measure very thick films
Here you see a (simulated) example of 11µm resist on silicon
If the film thickness increases above 5 - 10 micrometers it gets more and more difficult to get good results
because the numbers of extrema in your spectrum increases. This is in conflict with the spectral resolution of
your spectrometer and the thickness of the fiber.
You get the best results (concerning spectral resolution) if you are using a system with a narrow slit. This
means that you probably do not get enough intensity. To avoid problems with signal-to-noise-ratio try the
following:
- adjust your lamp intensity to maximum
- minimize distance fiber – wafer
- adjust integration time (menu options)
- be careful in your choice of extraction and plot limits
- try manual measurement mode instead of automatic mode
Quite often thick resists are inhomogeneous or have a rough surface. This may destroy the signal completely
or reduce the amplitude compared to theory.