Effect of oxidation temperature on the inhomogeneity of chemical composition and density in nanometric SiO2 films grown on 4H-SiC

Abstract

State-of-the-art secondary ion mass spectrometry (SIMS), X-ray reflectivity (XRR) and atomic force microscopy (AFM) have been used to determine the effect of oxidation temperature on the inhomogeneity of chemical composition and density in nanometric SiO₂ films grown on n-type 4H-SiC by thermal oxidation in dry oxygen. Within the films grown at 1000–1100 °C with thicknesses of 7.6–21.1 nm, we have revealed three regions with various distributions of the Si, O and C concentrations: the transition region, adjacent to the substrate surface, where the O concentration steeply rises and the Si and C concentrations go down, the middle region, where the O, Si and C concentrations are nearly constant, and the near-surface region, adjacent to the outer surface of the oxide film, where the O concentration increases towards the surface. Based on the images of the two-dimensional distributions of the O and C concentrations and the density profiles in the oxide films, we postulate that in the transition and middle regions the density depends on the ratio of the volume of SiO_xC_y and SiO₂ phases. In the near-surface regions, the density is mainly determined by SiO₂ porosity.