Design of a fast in situ infrared diagnostic tool

Abstract

Conventional Fourier transform infrared (FTIR) spectroscopes cannot be used to perform real time in situ infrared reflection absorption spectroscopy at monolayer sensitivity for high deposition rates (a couple of tens to hundreds of nm/s) which can be obtained when using an expanding thermal deposition plasma. Therefore a new analysis tool has been developed. The tool is based on a fast optical scanner in combination with conventional grating technology. This results in a loss of spectral range with respect to FTIR spectroscopes, but a significant gain is obtained in time resolution. For the combination used this makes it possible to measure at time resolution as low as 1.3 ms and resolution of 24 cm−1 at 1000 cm−1. The absorption sensitivity for single reflection at the best time resolution is approximately 10−2, but can be improved by using signal enhancement techniques. Here attenuated total reflection is used and the best sensitivity obtained is approximately 10−3, which is close to monolayer sensitivity for various absorption bands in the infrared spectrum of silicon oxide films. Monolayer sensitivity can be obtained by averaging multiple spectra, however this will cause the time resolution to decrease.