Oxide Thin Film Growth on Silicon Carbide Surfaces

The most recent investigations into the atomic scale understanding of silicon carbide surface oxidation and subsequent initial oxide/SiC interface formation are reviewed for the 6H and 4H hexagonal polytypes. These studies are conducted using advanced experimental techniques primarily based on core level photoemission spectroscopy using synchrotron radiation at NSRRC in Hsinchu. The results indicate a very high reactivity to oxygen of the Si-rich 6H-4H-SiC(0001) 3×3 surface reconstruction (≈ 3 orders of magnitude larger than for Si surfaces). Oxygen atom insertion is taking place below the surface close to the first carbon atomic plane, leaving the Si ad-atoms unaffected. By low temperature (500°C) oxidation of a predeposited Si overlayer onto the 6H-SiC(0001) 3×3 surface, a carbon free SiO₂ ultrathin film (≈ 10 Å) could be grown, leading to the formation of an abrupt SiO₂/6H-SiC interface. However, the two 6H and 4H polytypes have significantly different behaviors with larger amounts of oxide products having higher oxidation states for the 6H-SiC(0001) 3×3 surface, while mixed oxides including carbon species (Si-O-C) are the dominant oxidation products for the 4H polytype surface. The oxidation rate is improved at increased surface temperatures. In all cases, the oxygen uptake remains significantly larger for the 6H polytype when compared to the 4H one. The very different behavior of the 6H and 4H polytypes seems to originate, at least in part, from the presence of two domains in the bulk for the 4H polytype (as evidenced by two bulk components in the Si 2p core level spectrum) which limits the oxygen insertion into the 4H-SiC lattice. These findings show that a "gentle" oxidation could be a promising approach to SiC surface passivation.