Comparative study of GaN mesa etch characteristics in Cl2 based inductively coupled plasma with Ar and BCl3 as additive gases

GaN thin film etching is investigated and compared for mesa formation in inductively coupled plasma (ICP) of Cl2 with Ar and BCl3 gas additives using photoresist mask. Etch characteristics are studied as a function of ICP process parameters, viz., ICP power, radio frequency (RF) power, and chamber pressure at fixed total flow rate. The etch rate at each ICP/RF power is 0.1–0.2 μm/min higher for Cl2/Ar mixture mainly due to higher Cl dissociation efficiency of Ar additive that readily provides Cl ion/radical for reaction in comparison to Cl2/BCl3 mixture. Cl2/Ar mixture also leads to better photoresist mask selectivity. The etch-induced roughness is investigated using atomic force microscopy. Cl2/Ar etching has resulted in lower root-mean-square roughness of GaN etched surface in comparison to Cl2/BCl3 etching due to increased Ar ion energy and flux with ICP/RF power that enhances the sputter removal of etch product. The GaN surface damage after etching is also evaluated using room temperature photoluminescence and found to be increasing with ICP/RF power for both the etch chemistries with higher degree of damage in Cl2/BCl3 etching under same condition