Features of changes in optical response within the surface oxide layer in Si and GaAs

Abstract

In this paper, the angular ellipsometric studies of natural oxidized surface layer on silicon and gallium arsenide are carried out. The mean wavelength of probe radiation beam was λ = 625 nm, with FWHM = 10 nm. Angular dependencies of ellipsometric parameters ψ and Δ (azimuth of restored linear polarization and phase shift between p- and s- components of reflected radiation) were recorded. The combined approach for their analysis, which consists in sectioning the investigated medium near-surface area into 500 ultrathin layers interconnected by the dielectric permittivity function and determining the ellipsometric parameters of the medium by applying matrix methods for calculating the amplitudes and phases of the reflected waves from such a system in two polarizations, was used. The depth of the optical response profile was determined by the method of differential evolution by varying optical constants in accordance with the chosen theoretical model to achieve a minimum deviation (MSE, Mean Squared Error) between the calculated and measured ellipsometric parameters. Optical response profiles corresponding to the models of half-infinite medium, a homogeneous layer, as well as the linear and exponential profiles are analyzed.