LARGE-SCALE MODELING OF SiO_2/Si(001) INTERFACE STRUCTURES BY USING A NOVEL INTER-ATOMIC INTERACTION MODEL

摘要

Large-scale modeling (up to 3904 atoms) of ultrathin SiO_2 films on Si(001) surfaces has been performed using our original inter-atomic potential energy function for Si, O mixed systems. The SiO_2 film was formed by layer-by-layer insertion of O atoms into Si-Si bonds in a Si wafer from the surface. The obtained oxide films show the presence of a structural transition region about 0.9 nm in thickness, where the average Si-O-Si bond angle for each layer becomes smaller in the region closer to the interface. The peak of Si-O-Si bond angle distribution in the oxide film is shifted toward narrower angle from the equilibrium angle of 144 degrees. The SiO_2/Si models show the thin distorted region of two atomic layers on the Si crystal side. These structural features agree well with many experimental measurements. In addition, SiO_2/Si(001) model including step and terrace configurations was made in the same manner. Just after backbond oxidation of the 2X1-dimer structure, a clear difference in the oxide structures appeared between type-A and B terraces. It was also found that the oxide film near the step preferentially became amorphous. These results suggest a possibility that the structure of thin oxide film can be controlled by the initial Si surface preparation.