The effect Of Cl-2 addition into CF4/Ar plasma on etching of CeO2 thin film was studied in terms of etch rate and selectivity. We obtained the maximum etch rate of 250 Angstrom/min at 10% Cl-2 addition into CF4/Ar gas mixing ratio of 20%. The maximum etch rate may be explained by the variation of volume density for Cl atoms and by the concurrence of two etching mechanisms such as physical sputtering and chemical reaction with formation of low-volatile products, which can be desorbed only by ion bombardment. In addition, the roles of ion bombardment include destruction of Ce-O bonds to facilitate the chemical interaction of Ce with chlorine and fluorine atoms. The variation of volume density for Cl, F, and Ar atoms are measured by optical emission spectroscopy. The chemical states of CeO2 thin films before and after etching are investigated with x-ray photoelectron spectroscopy. (C) 2003 American Vacuum Society.