Oxidation of SiC investigated by ellipsometry and Rutherford backscattering spectrometry

Abstract

Oxidation of SiC was performed in Ar–O2 mixture of atmospheric pressure at 1100 °C and compared with that of Si. The partial pressure of O2 varied from 100 to 1000 mbar, while the oxidation time ranged from 0.5 to 45 h. The thickness of the oxide films was determined by spectroscopic ellipsometry and Rutherford backscattering spectrometry. The time and the pressure dependence of the oxidation kinetics of SiC are well described by the modified Deal–Grove model. In the diffusion-limited region, even for the faster case, the oxidation kinetics of the C-terminated face of SiC is not clearly limited by oxygen indiffusion, as for pure silicon. To interpret the ellipsometry spectra, two models of possible structure were used. In the case of the one-layer model, for layer thicknesses above 30 nm, the refractive index of the oxide layers is identical to that of thermally oxidized Si, and it increases rapidly with decreasing thickness below about 15 nm. This increase is significantly larger for C-terminated than for Si-terminated faces, and this difference can be explained by a transition layer introduced into the two-layer model. This model contains a pure SiO2 layer and a transition layer modeled by a mixture of 50 % SiO2 and 50 % SiC. The transition layer is thicker on the C-terminated surface than on the Si-terminated one. The thickness ratio of the transition layers is slightly larger than the surface roughness ratio on the two different sides determined by atomic force microscopy. The density of the oxide films, which can be determined from the backscattering and spectroscopic ellipsometry spectra, decreases with decreasing thickness below about 30 nm. For thicker films, the density of the oxide is equal to the bulk density of SiO2.