Physical modelling of non-invasive silicon temperature measurement by infrared absorption

It has recently been shown that the temperature of silicon wafers can be measured in situ in rapid thermal processing reactors by monitoring the infrared absorption of the substrate at specific wavelengths. In the present work, a physical model of infrared absorption in silicon is used to determine the dominant absorption mechanisms in the relevant temperature and wavelength ranges. The model is then used to predict the ultimate temperature ranges of applicability of the technique and to show the effects of heavy doping. Since free carrier absorption dominates at wavelengths over 1.55 mu m, approximately 850 degrees C may be estimated as an upper limit for the technique of silicon temperature measurement by infrared transmission. Because bandgap absorption dominates at short wavelengths, the technique may be extended to temperatures as low as 77 K.<>