Searching for the starting approximation when solving inverse problems in ellipsometry and spectrophotometry

Abstract

This paper discusses an approach to the search for the starting approximations when inverse optical problems are to be solved to determine the refractive indices and thicknesses of dielectric films on substrates. It is proposed to use reflection spectra obtained at different angles of incidence of light on the sample, from which the refractive indices and thickness of the film are computed from the location of the intensity extrema. In monochromatic null ellipsometry, the measurement of the polarization parameters of light at different angles of incidence makes it possible to determine the refractive index and ellipsometric thickness for each angle. The starting approximation for the thickness for solving the inverse problem in ellipsometry, based on the data for all the angles of incidence used for light on the sample, is obtained from the optical thickness of the film, determined from the reflection spectra at small angles of incidence.