A CoFeB thin film composing a magnetic tunneling junction of CoFeB/MgO/CoFeB was etched in an inductively coupled plasma (ICP) etching system using CO/NH3 gas mixtures, and its etch characteristics were compared with those of the CoFeB thin film etched using Cl-2/Ar. When Cl-2/Ar was used to etch the CoFeB thin film, even though its etch rate was faster than that of the CoFeB thin film etched using CO/NH3, a rough CoFeB surface could be observed due to the corrosion of the CoFeB surface during exposure to the air in addition to the significant change of surface composition. On the other hand, no corrosion of the CoFeB thin film was observed after the etching using CO/NH3. When the ratio of CO/NH3 was varied, the highest etch rate of 12 nm/min could be observed at the ratio of 1: 3 compared to about 4 nm/min for CO or NH3 at the ICP source power of 700 W, bias power of 300 W, and 5 mTorr of operating pressure. The highest etch rate was related to the formation of volatile metal carbonyls between metal and CO, where NH3 appeared to assist the easier formation of metal carbonyl by preventing the dissociation of CO into C and CO2. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3505295] All rights reserved.