Fluorination induced etching selectivity of boron nitride phases

Selective etching by hydrogen for different carbon phases is pivotal in enabling the synthesis of diamond using low-pressure chemical vapor deposition (CVD). However, this is not the case in the CVD synthesis of cubic boron nitride (c-BN). Here, by carrying out a systematic atomic-level study using the frontier orbital theory based on ab initio calculations, we show that, upon fluorination at the boron site, the etching selectivity of both hydrogen and fluorine for different boron nitride phases is significantly enhanced. By examining the electronic structural change, we found that the etching selectivity enhancement relates to the boundary saturation improvement upon fluorination. Moreover, fluorination also enhances the structural stability, particularly at the surface layers, providing a suitable environment for maintaining a proper charge transfer between boron and nitrogen atoms, which is the key factor for determining reactivity and stability. The enhanced etching selectivity would facilitate the CVD synthesis of high-quality cubic boron nitride films.