Ocean Optics NanoCalc - Manual (Page 68)

Ocean Optics Germany GmbH Thin Film Metrology
67
10.2 How to measure very thin films
It depends very much of the type of layers whether it is difficult to measure very thin films or not. As we have
seen in the first section it is necessary to expand the spectral measurement range as wide as it is possible
with this system. See chapter 6.2.3 Frequency Limits.
1st example: 20 nm SiO
2
on Si
This is difficult to measure because the intensities and the spectral information of the signals with and
without the SiO
2
-layer do not differ very much. The problem reduces more or less to an intensity
measurement.
This means that you should use a light source with a extremely high stability and measure the reference
signal immediately before measuring the SiO
2
sample to avoid any drifts. (You should use a UV/VIS/NIR
System with a large spectral range (and a suitable lamp as well).
2nd example: 5 nm Si on BK7-glass
You can see that it is rather easy to measure such a thin film.
Si
20nm SiO
2
on Si
BK7
5nm Si on BK7