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.

Automated summary

Using first-principles calculation, the study explores the diffusion path of Si emission from the interface into the Si oxide surface during the Si oxidation process, assuming Si emission primarily consists of SiO interstitial diffusion. The diffusion path was successfully found and the energy profile of the diffusion path can be evaluated. Only three elementary processes were considered, namely O vacancy transfer, coordination number conversion of Si, and ACBD bond order conversion. The results confirm that SiO interstitial moves in the oxide by kicking neighboring Si and O, while absorbed Si and O become part of the oxide and kicked-out Si and O become new SiO interstitials. Comparisons with similar diffusion path in bulk SiO2 crystal showed that the Si oxide layer is relatively flexible, the oxide surface is much more flexible, and the oxide layer near the interface is less flexible due to the rigid Si substrate. These findings indicate the fair assumption of Si emission and the inevitable SiO interstitial diffusion in the oxide film to reduce the impact of volume expansion at the interface.