Inductively coupled Cl2/Ar/O2 plasma etching of GaN, InGaN, and AlGaN

The etch selectivities of GaN and In0.12Ga0.88N over Al0.1Ga0.9N were investigated using an inductively coupled Cl-2/Ar/O-2 plasma and the results were as high as 24 and 32, respectively. An X-ray photoelectron spectroscopic (XPS) analysis of the etched surface showed that an Al-O bond was formed on the AlGaN surface during the Cl-2/Ar/O-2 plasma etching, so the high selectivity thus obtained could be attributed tot eh etch-resistant oxido layer. This oxide layer could be easily etched off by using an HF-based solution during the mask removal process. The atomic force microscopic image of the surface morphology showed the presence of an Al/Ga droplet-like structure on the nitride surfaces, that had been etched by oxygen-free plasma while those that had been etched using an oxygen-containing plasma showed a droplet-free smooth surface. A gallium oxynitride layer, which prevented the preferential sputtering of nitrogen on the nitride surface, was also observed by XPS.