Selective Wet and Dry Etching of NiO over β-Ga2O3

Abstract

Patterning of NiO/Ga2O3 heterojunctions requires the development of selective wet and dry etch processes. Solutions of 1:4 HNO3 :H2O exhibited measurable etch rates for NiO above 40 °C and activation energy for wet etching of 172.9 kJ.mol-1 (41.3 kCal.mol-1, 1.8 eV/atom), which is firmly in the reaction-limited regime. The selectivity over β-Ga2O3 was infinite for temperatures up to 55°C. The strong negative enthalpy for producing the etch product Ga(OH)4 suggests that HNO3-based wet etching of NiO occurs via the formation and dissolution of hydroxides. For dry etching, Cl2/Ar Inductively Coupled Plasmas produced etch rates for NiO up to 800Å.min-1, with maximum selectivities of < 1 over β-Ga2O3. The ion energy threshold for initiation of the etching of NiO was ~55 eV and the etch mechanism was ion-driven, as determined by the linear dependence of etch rate on the square root of ion energy incident on the surface.