Thin Film Measurements by Scanning Ellipsometry

A method is presented whereby the thickness and complex refractive index of a very think, partially absorbing film, on an absorbing substrate, may be determined with the ellipsometer. This is accomplished by indirectly measuring the ratio of the intensity reflectance of the film-coated substrate to that of the bare substrate.This information is then combined with the quantities D and Y from normal ellipsometer measurements to determine the physical parameters of the film. The accuracy with which the reflectance ration must be measured for a prescribed accuracy in determining the film thickness is found to vary greatly depending on the film properties. Equations are developed to show what requirements must be placed on the measurement system and to evaluate the existing system. Finally, a number of methods for measuring the reflectance ration are described and the results of measurements on thin films of violan-throne on a gold substrate are presented. Although an error analysis, using values of uncertainty in the measured quantities typical of the equipment used, shows that the film thickness should be measurable to within a few per cent, an actual group of measurements on the same sample at different wavelengths shows a much wider variation than this. The possible reasons for this are discussed and suggestions are made for improving the measurement conditions. Advisor: N. M. Bashar