Study of the optical constants determination of thin films: Dependence on theoretical assumptions

We present a critical study of the known reflectance (R) and transmittance (T) method to extract the optical constants of thin film–substrate systems. In order to study the effect of the usual assumptions (homogeneous layers, semi-infinite substrate, normal incidence angle for reflectance measurement, etc.) in the loss of solution during the numerical inversion process, we have developed a theoretical model that overcomes these approximations. Simulated film–substrate systems as well as RT measurements from a ZnSe film onto a CaF2 substrate have been used to show how accurate film thickness and optical constants can be obtained using a more complete optical model.