Dry etching of NiO thin films masked with a photoresist was performed in a Cl-2/Ar gas mix. The etch rate of NiO films decreased as Cl-2 concentration increased. The surface morphology etched at high Cl-2 concentration was smoother than that etched at low Cl-2 concentration. The etch profiles were improved with increasing coil radio-frequency (rf) power and dc-bias voltage. An X-ray photoelectron spectroscopy analysis confirms the formation of NiCl2 compound due to a chemical reaction with chlorine radicals. These results indicate that the etching of NiO films is governed by a physical sputtering etching mechanism with a surface chemical reaction. (c) 2007 The Electrochemical Society.