Ultrahigh GaN:SiO2 etch selectivity by in situ surface modification of SiO2 in a Cl2-Ar plasma

Abstract

The realization of vertical GaN devices requires deep plasma etching and is contingent on high mask selectivity. In this work, we show that SiO₂ can be an effective mask material for deep etching GaN with GaN:SiO₂ selectivities greater than 40—higher than the conventionally reported 15 for metal hard masks such as nickel. Ultrahigh SiO₂ selectivities were achieved by introducing Al and AlCl into the Cl₂-Ar inductively coupled plasma, which reacts with the SiO₂ mask surface to form an etch-resistant aluminum silicate surface layer. This mechanism provides a low-contamination pathway to etch deep GaN microdevices.