Plasma etching of ZrO2 and HfO2 was studied in BCl3/Cl2 plasmas, as functions of the ion energy, chamber pressure, microwave power, and gas compositions. MClx is found to be the major etching product in Cl2 plasmas while MBxCly is the major etching product in BCl3 plasmas. The etching selectivity to Si is increased at lower ion energies and higher electron temperatures. Increasing microwave powers and reducing chamber pressures in BCl3/Cl2 plasmas increased the Cl and BCl2+ densities in the gas phase and consequently increased the metal oxide etch rate. A phenomenological model that takes into account the Cl density, BCl2+ density, and metal oxygen bond strength is proposed to describe the etch rate of ZrO2 and HfO2 in pure BCl3 plasmas as functions of the ion energy, microwave power, and chamber pressure. More accurate Cl flux measurement is needed to improve the model predictions. © 2004 American Vacuum Society.