Selective Wet and Dry Etching of NiO over β-Ga2O3

Abstract

Patterning of NiO/Ga2O3 heterojunctions requires 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−1), 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 HNO3-based wet etching of NiO occurs via formation and dissolution of hydroxides. For dry etching, Cl2/Ar Inductively Coupled Plasmas produced etch rates for NiO up to 800 Å.min−1, with maximum selectivities of <1 over β-Ga2O3. The ion energy threshold for initiation of etching of NiO was ∼55 eV and the etch mechanism was ion-driven, as determined the linear dependence of etch rate on the square root of ion energy incident on the surface.