Atomic level simulation of permittivity of oxidised ultra-thin Si channels

Abstract

We use density-functional-based tight binding theory, coupled to a Poisson solver to investigate the dielectric response in oxidized ultra-thin Si films with thickness in the range of 0.8 to 10.0 nm. Building on our recent work on the electronic structure of such Si films using the same formalism, we demonstrate that the electronic contribution to the permittivity of Si and of SiO2 is modeled with good accuracy. The simulations of oxidized Si films agree well with available experimental data and show appreciable degradation of permittivity by nearly 18% at 0.8nm. Notable is however that simulations with hydrogenated Si substantially overestimate the degradation of permittivity. Beyond clarifying the quantitative trend of permittivity versus Si thickness, which is very relevant e.g. for fully-depleted Si-on-insulator MOSFETs, the present work is a cornerstone towards delivering an atomistic modelling approach that is free of material- or device-related phenomenological parameters.