We investigated the etch rate of indium gallium zinc oxide (IGZO) thin films and the selectivity of IGZO for SiO2 and Si in an inductively coupled plasma. The maximum etch rate of the IGZO thin film was 158 nm/min in BCl3/Ar (10: 10 sccm) plasma, and the selectivity of IGZO for SiO2 and Si was 0.7 and 2.2, respectively. We analyzed the chemical reaction on the surface of the IGZO thin film via XPS analysis. Numerous byproducts, including GaxCly, InClx, and ZnClx, were generated in BCl3/Ar plasma during the etching of the IGZO thin film, and the non-volatile byproducts from the surface of the etched IGZO thin film were removed by Ar bombardment. Consequently, the etching mechanism of the IGZO thin film can be explained as a chemical reaction with the ion-assistance of Ar sputtering. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.034204jes] All rights reserved.