  Silicon carbide (SiC) is an attractive semiconductor material for
applications in power electronic devices. However, fabrication of a
high-quality SiC/SiO${}_2$ interface has been a challenge. It is well-known
that there is a great difference in oxidation rate between the Si-face and
C-face, and that the quality of oxide on the Si-face is greater than that on
the C-face. However, the atomistic mechanism of the thermal oxidation of SiC
remains to be solved. In this paper, a new Si-C-O interatomic potential was
developed to reproduce the kinetics of the thermal oxidation of SiC. Using this
newly developed potential, large-scale SiC oxidation simulations at various
temperature were performed. The results showed that the activation energy of
the Si-face is much larger than that of the C-face. In the case of the Si-face,
a flat and aligned interface structure including Si${}^{1+}$ was created. Based
on the estimated activation energies of the intermediate oxide states, it is
proposed that the stability of the flat interface structure is the origin of
the high activation energy of the oxidation of the Si-face. In contrast, in the
case of the C-face, it is found that the Si atom at the interface are easily
pulled up by the O atoms. This process generates the disordered interface and
decreases the activation energy of the oxidation. It is also proposed that many
excess C atoms are created in the case of the C-face.
