ARXPS studies of SiO₂-SiC interfaces and oxidation of 6H SiC single crystal Si-(001) and C-(001) surfaces

The main puzzle in oxidation of hexagonal SiC is the slower rate of the Si-terminated surface as compared to the C-terminated surface, which is blamed on an unknown interface compound. ARXPS is a unique method to identify minor amounts of interface compounds, especially for smooth surfaces. Our ARXPS analysis of oxidized Si-(001) and C-(001) surfaces of 6H SiC reveals the interface oxide Si₄C_4−xO₂ (x < 2), likely a reaction product of a peroxidic O₂-bond to a SiC double layer. Si₄C_4−xO₂ occurs in larger thickness (≃1 nm) at the slowly oxidizing Si-(001) surface, whereas the C-(001) surface shows smaller amounts, diminishing fast with oxidation above 1000 K. Evidence is presented that with increasing amount of Si₄C_4−xO₂ the oxidation of SiC to SiO₂ is reduced. ARXPS is consistent with a layer of SiO₂ containing less than 3% Si₄C₄O₄ being an oxidation product of Si₄C_4−xO₂. At the surface of SiO₂, graphite and some Si₄C₄O₄ exist, aside from standard adsorbates.