Can I use the In-Situ 4000 Process Monitor on transparent substrates?
It is possible under limited circumstances to use substrates which are transparent at 950 nm. The conditions which permit proper measurement are: – The back surface of the substrate must be coated with an opaque material. In this case it is the backside surface coating which is being measured for radiation rather than the front surface. – The back surface of the substrate must be left rough or unpolished (i.e. single sided polish only). This requirement ensures only the front surface of the substrate contributes to a reflectance measurement. In theory, a polished backside might work, but the reflectance of a metal coated backside is often much higher than the front surface and makes a proper front surface reflectance impractical. In our application laboratory, we have successfully used the In-Situ 4000 Process Monitor to measure the temperature and growth rate of GaN films on transparent sapphire substrates. We used a thin film of a high temperature refractory metal on the unpolished b
