Molecular dynamics simulations on the oxidation of Si(100)/SiO2 interface: Emissions and incorporations of Si-related species into the SiO2 and substrate

摘要

Si(100)-oxidation processes at the Si/SiO2 interface and in the SiO2 region are investigated focusing on the dynamics of Si and SiO emissions from the interface and the following incorporation into the substrate and/or SiO2. To clarify these atomic processes, classical molecular dynamics (MD) simulations with variable charge interatomic potentials are performed. By incorporating oxygen atoms, twofold coordinated (twofolded) Si atoms are formed after structural relaxation at the interface. The energy changes of the twofolded Si emissions into the substrate and SiO2 are estimated to be 2.97-7.81 eV. The energy barrier of the twofolded Si emission as SiO molecule is estimated to be 1.20 eV on the basis of the enthalpy change in an MD simulation. The emitted SiO molecule is incorporated into the SiO2 network through a Si-O rebonding process with leaving local deficiency of oxygen, i.e., generating an oxygen vacancy. The energy barrier of the SiO incorporation is estimated to be 0.79-0.81 eV. The elementary process of oxygen vacancy diffusion leading to the complete SiO incorporation are also simulated, and the energy barriers are found to be relatively small, 0.71-0.79 eV. The energy changes of Si emissions into the substrate and SiO2 are larger than the energy barrier of the SiO emission, which suggests that, at the ideally flat Si/SiO2 interface with relatively small oxidation stress, the SiO emission into the SiO2 region occurs prior to the Si emission. This result is consistent with previous theoretical and experimental studies. The above-mentioned typical atomic processes are successfully extracted from some (or one) of MD simulations among many trials in which a statistical procedure is partly employed. Our results give a unified understanding of Si oxidation processes from an atomistic point of view. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim