Dry etch selectivity of Gd2O3 to GaN and AlN

Gd2O3 is a promising gate dielectric for GaN, but little is known of its dr y etching characteristics. We achieved Gd2O3 etch rates up to similar to 60 0 Angstrom . min(-1) in high density Cl2-based discharges, with maximum sel ectivities of similar to 15 over GaN and similar to 4 over AlN. Pure Cl-2 d ischarges produced reverse selectivities for both Gd2O3/GaN and Gd2O3/AlN, with typical values between 0.1-0.4. When a rare gas additive such as Ar or Xe was added to the plasma chemistry, the nitrides etched faster than the oxide. This indicates that volatile etch products (GaCl3, AlCl3, N-2) form in Cl-2- based plasmas once the GaN or AlN bonds are broken by ion bombardm ent, but that GdClx species are not volatile. In conjunction with the low e fficiency for Gd2O3 bond-breaking at low ion energies, this leads to low se lectivity.