Temperature-dependent Cl2/Ar plasma etching of bulk single-crystal ZnO

The etch rate of bulk ZnO in Cl2/Ar high density plasmas was found to be thermally activated with an activation energy of ∼0.31 eV at <300 °C. The rate-limiting step appears to be the ion-assisted desorption of the ZnClX etch products. The threshold ion energy for etching ZnO at 150 °C in Cl2/Ar is ∼170 eV, obtained by fitting to a model of ion-enhanced sputtering by a collision-cascade process. The amount of residual chlorine on the ZnO surface decreases with increasing etch temperature, but there is a tendency for the surface to become Zn-rich and roughen at elevated temperatures (>200 °C).