Chemically assisted ion beam etching of gallium nitride

Chemically assisted ion beam etching of gallium nitride (GaN) grown by metalorganic chemical vapor deposition has been characterized using an Ar ion beam and Cl₂gas. The etch rate of GaN was found to increase linearly with Ar ion beam current density, increase linearly then saturate with Ar ion beam energy, vary slightly with Cl₂ flow rate, and lastly, increase moderately with substrate temperature. Etch rates as high as 330 nm/min were obtained at high beam energies and 210 nm/min at a more nominal level of 500 eV. The anisotropy of etched profiles improved in the presence of Cl₂ in comparison to those etched by Ar ion milling only. Elevated substrate temperatures further enhanced the anisotropy to obtain near-vertical profiles for fairly deep-etched structures. Auger electron spectroscopy was used to investigate etch-induced surface changes. Oxygen contamination was observed on the as-etched surface but a dilute HC1 treatment restored the stoichiometry of the material to its unetched state.