First-principles study on silicon emission from interface into oxide during silicon thermal oxidation

Using the first-principles calculation, the diffusion path is explored in the Si emission from the interface into the Si oxide surface during the Si oxidation process, by assuming that the Si emission dominantly consists of a SiO interstitial diffusion. Searching for the diffusion path was succeeded and the energy profile of diffusion path can be evaluated. At this time, only three elementary processes, such as O vacancy transfer, coordination number conversion of Si, and ACBD bond order conversion, were just considered. It has been confirmed that the SiO interstitial moves in the oxide with sequentially kicking the neighboring Si and O like a billiards, and that the kicked-out Si and O become a new SiO interstitial, while Si and O belonging to the old SiO interstitial are absorbed as a part of the oxide. Furthermore, the energy profile of similar diffusion path in bulk SiO2 crystal is also compared. It is revealed that the Si oxide layer is relatively flexible against structural deformation, and that the oxide surface is much more flexible, but that the oxide layer near the interface is less flexible due to the influence of the rather rigid Si substrate. The results indicate that our assumption on the Si emission in the Si oxidation process is fair, and that the SiO interstitial diffusion in the oxide film is inevitable in order to reduce the impact of volume expansion that occurs at the interface.