Selective dry etching of GaN over AlGaN in BCl3/SF6 mixtures

Inductively coupled plasma (ICP) etching of GaN with high selectivity over Al_0.22Ga_0.78N in BCl₃/SF₆ mixtures has been studied. Selectivity and surface morphology were investigated over a wide range of pressures (3.75-37.5mTorr), RF powers (30-120 W), ICP powers (100-400 W), and SF₆/BCl₃ ratios (0.1-0.7). Higher pressures, lower dc biases, and higher SF₆/BCl₃ ratios increased the GaN to AlGaN selectivity. Selectivities up to 25 were measured by laser interferometry. A root mean square (rms) surface roughness of 0.67 nm was measured by atomic force microscopy (AFM) after removal of 0.5 μm from a GaN template (process selectivity: 15, as-grown rms surface roughness: 0.56 nm). A degradation in surface morphology, with the gradual formation of pits, was observed for selectivities above 10.