Threshold Ion Energies and Cleaning of Etch Residues During Inductively Coupled Etching of NiO/Ga2O3 in BCl3

Abstract

BCl3 is an attractive plasma etchant for oxides because it is a Lewis acid used to scavenge native oxides on many semiconductors due to the strong B–O bonding. We investigated BCl3-based dry etching of the NiO/Ga2O3 heterojunction system. BCl3/Ar Inductively Coupled Plasmas produced maximum etch rates for NiO up to 300 Å.min−1 and 800 Å.min−1 for β-Ga2O3 under moderate plasma power conditions suitable for low damage pattern transfer. The selectivity for NiO: Ga2O3 was <1 under all conditions. The ion energy threshold for initiation of etching of NiO was between 35–60 eV, depending on the condition 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. By sharp contrast, the etching of Ga2O3 had a stronger chemical component, without a well-defined ion energy threshold. The as-etched NiO and Ga2O3 surfaces show chlorine residues, which can be removed on both materials by the standard 1NH4OH: 10H2O or 1HCl: 10H2O rinses used for native oxide removal. According to the location of the Cl 2p3/2 peak, the Cl is ionically bonded.