Dynamic modeling of Si(100) thermal oxidation: Oxidation mechanisms and realistic amorphous interface generation

Silicon and its native oxide SiO2 have been utilized in semiconductor technology since the 1950s and are still crucial for the development of novel device technologies today. Recent theoretical and experimental studies show that the fabrication of high-quality interfacial layers becomes critical for reliable operation of modern nanoscale devices. This paper presents a first-principles based approach to theoretically assess the thermal oxidation process of the technologically relevant Si(100) surface in the ultra-thin layer regime below 2 nm. The oxidation process is dynamically modeled by means of ab-initio molecular dynamics and density functional based tight binding simulations. We qualitatively explain the experimentally well-known but poorly understood decrease of oxidation rate in the initial oxidation stage as a complex interplay between various oxidation mechanisms such as fast O2 dissociation at the surface, slower oxygen integration mediated by molecular precursor states and O2 diffusion through the oxide. Our model combines previously reported experimental insights into a comprehensive picture of Si oxide growth. Strong evidence for an immediate amorphization of the oxide surface layer was found and identified as a direct consequence of lattice vibrations. Furthermore, our modeling method is a novel approach for the generation of realistic, amorphous interface structures that is based on the stepwise oxidation of the crystalline Si surface and could be extended to other materials systems as well.