In this study, high density plasma reactive ion etching of CoFeB magnetic thin films was investigated using CH4/Ar and CH4/O-2/Ar gas mixes. The etch rate, etch selectivity and etch profile of CoFeB thin films were obtained as a function of gas concentration and etch parameters. The etch rate of CoFeB thin films and Ti hard mask gradually decreased with increasing CH4 or O-2 concentrations. As the CH4 gas was added to Ar gas, the etch profile of the CoFeB thin films improved. The addition of O-2 gas into the CH4/Ar gas mix also led to anisotropic etching of the CoFeB thin films. With an increase in the dc-bias voltage supplied to the substrate and a decrease in gas pressure, the etch rates increased and the etch profile became vertical without any redepositions or etch residues. Based on the etch characteristics and surface analysis of the etched films by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of CoFeB thin films in CH4/Ar and CH4/O-2/Ar plasmas does not follow the reactive ion etch mechanism but rather a chemically assisted physical sputtering mechanism. (C) 2011 Elsevier B. V. All rights reserved.