High Selectivity, Low Damage ICP Etching of -GaN over AlGaN for Normally-off -GaN HEMTs Application.

A systematic study of the selective etching of -GaN over AlGaN was carried out using a BCl/SF inductively coupled plasma (ICP) process. Compared to similar chemistry, a record high etch selectivity of 41:1 with a -GaN etch rate of 3.4 nm/min was realized by optimizing the SF concentration, chamber pressure, ICP and bias power. The surface morphology after -GaN etching was characterized by AFM for both selective and nonselective processes, showing the exposed AlGaN surface RMS values of 0.43 nm and 0.99 nm, respectively. MIS-capacitor devices fabricated on the AlGaN surface with ALD-AlO as the gate dielectric after -GaN etch showed the significant benefit of BCl/SF selective etch process.