Permittivity of Oxidized Ultra-Thin Silicon Films From Atomistic Simulations

We establish the dependence of the permittivity of oxidized ultra-thin silicon films on the film thickness by means of atomistic simulations within the density-functional-based tight-binding (DFTB) theory. This is of utmost importance for modeling ultra-thin and extremely thin silicon-on-insulator MOSFETs, and for evaluating their scaling potential. We demonstrate that electronic contribution to the dielectric response naturally emerges from the DFTB Hamiltonian when coupled to Poisson equation solved in vacuum, without phenomenological parameters, and obtain good agreement with the available experimental data. Comparison with calculations of H-passivated Si films reveals much weaker dependence of permittivity on film thickness for the SiO₂-passivated Si, with less than 18% reduction in the case of 0.9-nm silicon-on-insulator.