Effects of nitrogen addition on methane-based ECR plasma etching of gallium nitride

The effects of nitrogen addition on methane-based ECR plasma etching of GaN were studied. The etch rate 30 nm/min and r.m.s. roughness 2.6 nm were obtained when the GaN sample was etched by a methane-based gas mixture without N2. The addition of N2 gas resulted in a decrease of etch rate and a smoother etched surface. The r.m.s. roughness became less than 0.4 nm even only 1.5 sccm N2 gas was added to the mixture. In situ XPS measurements showed that, without N2, heavy N-depletion took place on the etched surface, resulting in appearance of Ga metal on the surface. In contrast, the loss of N was compensated when the N2 gas was added, and the etched surface approached the stoichiometric one with the increase of N2 gas flow. This suppression of preferential loss of N was considered to be the main reason that improved the etched surface morphology.