Optical Film Thickness Monitoring

Abstract

Experiments and theoretical calculations are carried out to determine the accuracy attainable by intensity modulation and wavelength modulation optical monitoring techniques used to specify film thickness. Experimental results show that film thickness errors of 5% are typical in deposition thickness monitoring based on intensity modulation techniques. It is demonstrated by calculation that an appreciable improvement of film thickness accuracy can be obtained by wavelength modulation techniques, and that variable wavelength dielectric filters may conveniently be used as spectral filters for wavelength modulation devices to provide a film thickness accuracy between 0.5 and 1%. Results obtained may be used for the design of optical thickness monitoring systems.