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

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.