High rate electron cyclotron resonance etching of GaN, InN, and AlN

Abstract

Electron cyclotron resonance etch rates of GaN, InN, and AlN are reported as a function of pressure, microwave power, and radio-frequency (rf) power in a Cl2/H2/CH4/Ar plasma at 170 °C. The etch rates for GaN and InN increase as a function of rf power. At 275 W, the etch rates reach maximum values of 2850 and 3840 Å/min, respectively. These are the highest etch rates reported for these materials. As a function of pressure, the etch rates reach a maximum value at 2 mTorr and then decrease as the pressure is increased to 10 mTorr. The GaN and AlN etch rates increase less than a factor of 2 as the microwave power is increased from 125 to 850 W whereas the InN etch rate increases by more than a factor of 3.5. The maximum etch rate for AlN obtained in this study is 1245 Å/min at a microwave power of 850 W, 1 mTorr pressure, and 225 W rf power. Atomic force microscopy is used to determine root-mean-square roughness as a function of etch conditions for GaN and InN and, while very smooth pattern transfer can be obtained for a wide range of plasma conditions for GaN, the smoothness of the etched InN surface is more sensitive to rf power, microwave power, and process pressure. The surface composition of the GaN is characterized using Auger spectroscopy and has shown that the Ga:N ratio increases with increasing rf power or microwave power.