Investigation of multilayer samples of porous silicon with periodic structure by spectroscopic ellipsometry

In this article, multilayer samples of porous silicon (PS) with a periodic structure, fabricated by electrochemical etching, are studied before and after air annealing. The experimental dependences of the parameters ψ, Δ, and the p-component intensity of the reflected light component at different angles of incidence on the wavelength before and after annealing were obtained by spectroscopic ellipsometry. The samples differ in the thickness of the periodic layers and their porosity. Using the Complete EASE software, theoretical models were created that well describe the experimental dependencies. The total thickness and optical characteristics of the samples before and after annealing were determined using the theoretical models. It was found that after annealing, the structure, chemical composition, and refractive index n of both samples of pitted silicon change. It has been shown that as a result of the applied heat treatment, the refractive index of all layers in multilayer samples decreases, which is associated with the oxidation of PS. Although after annealing the fraction of silicon and porosity in all layers decreases, their complete oxidation does not occur. All layers remain porous and contain silicon and silicon oxide. The overall thickness of the multilayer PS increases slightly after annealing.