Mechanism of SiC formation by Si surface carbonization using CO gas

SiC thin films formed by Si surface carbonization can be used as buffer layers for the heteroepitaxial growth of nitride semiconductors. We propose a Si surface carbonization method using CO gas. In this study, we investigate the dependence on CO activity (a_CO) of the carbonization of Si(100), Si(110), and Si(111). The Si surface reacts with the CO molecules to form SiC nuclei during the initial carbonization stage. Following nucleation, carbonization proceeded based on the thermodynamic carbonization driving force. At a lower a_CO with a larger driving force but smaller nucleation density, a thicker SiC film comprising larger grains with higher crystal coherency was formed, whereas the roughness of the SiC surface and SiC/Si interface is larger. Furthermore, voids with larger sizes and densities were formed at the SiC/Si interface. The thickness, grain size, and crystal coherency of the SiC film were on Si(110)≳Si(111)≫Si(100). All the SiC films were singly oriented. The SiC films were oriented to Si(100) and Si(111), regardless of carbonization conditions. In contrast, SiC(111) or SiC(110) was formed on Si(110) carbonized at lower and higher a_CO, respectively, as determined by the SiC formation rate, structural stability of the plane, and lattice mismatch.