A method to extract absorption coefficient of thin films from transmission spectra of the films on thick substrates

Abstract

In this paper we present a method that allows extraction of the absorption coefficient of a thin film from transmittance spectrum of the film on a silicon substrate. The method essentially removes all “optical effects,” such as interference fringes, reflectance losses, substrate absorption, etc. The method requires that the refractive index of the film is known at one wavelength and that the thickness of the film is approximately known, both of which are generally available from ellipsometric measurements. As a by-product of the procedure, the method also extracts optical constants of the film over the entire spectral range of interest and provides improved values of thickness and refractive index over those provided by ellipsometry.