Atomic scale characterization of oxidized 6H–SiC(1 1 2̄ 0) surfaces

The initial oxidation of the 6H–SiC(1 1 2̄ 0) surface was studied by high-resolution medium energy ion scattering (MEIS) combined with photoelectron spectroscopy induced by synchrotron-radiation-light (SR-PES). The oxygen coverage is saturated at 0.35 ± 0.04 ML (1 ML=1.49 × 1015 atoms/cm2) with O2-exposure of 5000 L at room temperature. The oxidation rate and the saturated oxygen coverage are considerably low and small compared with those for the α-SiC(0 0 0 1)-3×3 and α-SiC(0 0 0 1)-3 × 3 surfaces. The Si-2p core level analysis shows that the primary components come from the Si+ and Si2+ states and the ratio of the Si2+ state relative to the Si+ state is almost 1/2. The above MEIS and PES results suggest that an O atom is preferentially adsorbed to a corner bridge site of Si-adatoms and side by side another O atom is inserted into the backbond of the one of the corner adatoms connected to a second-layer-Si atom. In the thermal oxidation under O2-pressure of 1.0 × 10−4 Torr, the oxygen coverage is linearly increased with elevating oxidation temperature and an ultra-thin SiO2 layer is formed at temperatures higher than 500 °C. The present MEIS analysis has also revealed the fact that a maximum compressive strain of 2% is induced by thermal oxidation (700 °C) at the SiC substrate just below the oxide layer and the strain decreases gradually down to a depth about 1.5 nm from the surface.