High density plasma etching of GaN films in Cl₂/Ar discharges with a low-frequency-excited DC bias

Gallium nitride films (undoped, n-type and p-type GaN) were etched in inductively coupled Cl₂/Ar plasmas. To control the ion energy, we applied a dc bias voltage excited by low frequency of 100 kHz to the susceptor electrode. Etch rates were strongly affected by the inductively coupled plasma (ICP) source power, the rf chuck power, the reactor pressure and the etch gas concentration. Fast etch rates of 5300 ∼ 9300 Å/min, depending on materials, were obtained at 700 W ICP, 150 W rf, 40 mTorr and 25 % Cl₂. The surface roughness was relatively independent of the chuck power up to 200 W and showed quite smooth morphology (rms roughness of 1.1 ∼ 1.3 nm). The stoichiometry was maintained at the etched surfaces of the undoped and the p-type GaN films, but the n-type GaN showed some depletion of nitrogen from the surface.