A novel interatomic potential energy function is proposed for condensed systems composed of silicon and oxygen atoms, from SiO2 to Si crystal. The potential function is an extension of the Stillinger-Weber potential, which was originally designed for pure Si systems. All parameters in the potential function were determined based on ab initio molecular orbital calculations of small clusters. Without any adjustment to empirical data, the order of stability of five silica polymorphs is correctly reproduced. This potential realizes a large-scale modeling of SiO2/Si interface structures on average workstation computers.

We propose a new oxidation rate equation for silicon supposing only a diffusion of oxidizing species but not including any rate-limiting step by interfacial reaction. It is supposed that diffusivity is suppressed in a strained oxide region near SiO(2)/Si the interface. The expression of a parabolic constant in the new equation is the same as that of the Deal-Grove model, while a linear constant makes a clear distinction with that of the model. The estimated thickness using the new expression is close to 1 nm, which compares well with the thickness of the structural transition layers.

We have performed three-dimensional molecular dynamics simulations to investigate strain and stress distributions in silicon nanostructures covered with thermal oxide films, by using our original molecular force field for Si, O mixed systems. We have modeled a wire-shaped nanostructure by carving a Si(001) substrate, and then an oxide film with a uniform thickness was formed by inserting oxygen atom into Si-Si bonds from the surface. The simulation results show that a compressive stress is concentrated on the oxide region in the vicinity of the side SiO 2 /Si interface of the nanowire. At the top interface, there is also a compressive stress in the [110] direction, whereas the [001] component of the normal stress tensor is almost relaxed. These results suggest that the oxidation is strongly suppressed at the side faces of the silicon nanowire.