Diffusion-reaction mechanisms of nitriding species in SiO2

TL;DR

This study uses first-principles calculations to analyze how different nitriding species diffuse and react in SiO2 during thermal nitridation, revealing charge state effects and temperature-dependent diffusivities.

Contribution

It provides detailed insights into the diffusion-reaction mechanisms of nitriding species in SiO2, highlighting the role of charge states and temperature effects, which was not previously well understood.

Findings

Neutral species do not react and diffuse through SiO2.

Charged species are trapped and react within the SiO2 network.

NH and atomic N diffusivities increase with temperature.

Abstract

We study using first-principles total-energy calculations, diffusion-reaction processes involved in the thermal nitridation of SiO2. We consider NO, NH, N2 and atomic N in different charge states as the nitriding species in alpha-quartz. Our results show that none of neutral species react with the SiO2 network remaining at interstitial sites. Therefore, they are likely to diffuse through the oxide, incorporating nitrogen at near-interface (Si/SiO2) regions. Whereas, charged species are trapped by the network, nitriding bulk SiO2. For the diffusing species, we find that NH and atomic N show increasing diffusivities with temperatures, whereas for NO and N2 they are relatively constant. This result agree well with the finding of higher N concentration at the Si/SiO2 interface obtained by thermal processing of SiO2 in NH3 as compared with those obtained in N2O. Finally, we discuss spin-dependent incorporation reaction mechanisms of NH and atomic N with the SiO2 network.