Cl_2/Ar based Inductively Coupled Plasma Etching of GaN/AlGaN Structure

摘要

Cl_2/Ar based inductively coupled plasma etching of GaN/AlGaN is investigated using photoresist mask in a restricted domain of pressure < 10mTorr and RF power <100W, for selective mesa etching. The etch characteristics and root-mean-square surface roughness are studied as a function of process parameters viz. process pressure, CI_2 percentage in total flow rate ratio, and RF bias at a constant ICP power, to achieve moderately high GaN etch rate with anisotropic profiles and smooth surface morphology. The etch rate and resultant rms roughness of etched surface increased with pressure mainly due to dominant reactant limited etch regime. The etch rate also increased with increasing Cl_2 % as a result of increased chlorine radicals that enhances chemical etching. The etch rate and rms roughness showed strong dependence on RF power with former increasing and later decreasing with applied RF power up to 80W. The process etch yield variation with applied RF bias is also reported. Negligible etch selectivity was observed between GaN and AlGaN up to 25% aluminum concentration with etch rate ~120nm/min. The studied etch parameters resulted in highly anisotropic mesa structures with Ga rich etched surface.