Polarity dependence in Cl₂-based plasma etching of GaN, AlGaN and AlN

This work compares Cl₂-based inductively-coupled plasma (ICP) etching of N-polar and III-polar Al_xGa_1-xN, including GaN and AlN. For the etch processes of this study, etch rates of Al_xGa_1-xN decreased with increasing Al:Ga alloy ratio. A 750 W ICP power, 175 W platen power Cl₂/Ar ICP process exhibited etch rates in the range 160–450 nm/min for Al_xGa_1-xN with the precise rate depending on alloy composition and material polarity, and etch rate selectivity between AlN and GaN of 3.0 for III-polar material and 1.6 for N-polar material. Cl₂/Ar/O₂ processes with 650 W ICP power and 50 W platen power showed an overall reduction in etch rate in the range 2–360 nm/min for Al_xGa_1-xN with precise rate depending on alloy composition and material polarity. These O₂ containing chemistries demonstrated significantly greater etch rate selectivity for N-polar materials (8–80) compared to III-polar materials (1.8–1.9). A correlation between GaN etch rate, surface roughening and selectivity was observed, and the possible reasons behind the polarity dependence of etch rate selectivity are discussed.