Large-Scale Atomistic Modeling of Thermally Grown SiO₂ on Si(111) Substrate

Large-scale SiO₂/Si(111) models were constructed by introducing oxygen atoms in c-Si models in an atom-by-atom manner. Molecular dynamics calculation at a constant temperature was repeatedly carried out for the growing oxide model. By comparing the oxidation simulation of Si(111) substrate with that of Si(001) substrate performed previously, the influence of substrate orientation on the oxide structure was discussed. Owing to the significant feature of bonding arrangement within a Si bilayer in the Si(111) substrate, the inherent stress induced at the SiO₂/Si interface by oxygen insertions is originally higher for the Si(111) oxidation than for the Si(001) oxidation, resulting in frequent changes in the bonding network. The resulting structure of bulk SiO₂ on Si(111) has less strain and a lower density than that on Si(001), but involves a larger number of dangling bonds. The X-ray diffraction pattern calculated for the SiO₂/Si(111) model exhibits a diffraction peak with a Laue-function-like profile on each of the crystal-truncation-rods from the 111 and 111 points, agreeing well with experimental results. These diffraction peaks indicate that the thermally grown SiO₂ retains the residual order emanating from the {111} atomic planes in the original c-Si. Because of differences in the angles between the surface and the {111} atomic planes, the residual order within the SiO ₂ differs depending on the substrate orientation.