In this work, the authors investigated the etching characteristics of TaN and HfO2 layers for gate stack patterning in BCl3/Ar and BCl3/C4F8/Ar inductively coupled plasmas and the effects of C4F8 addition on the etch selectivity of the TaN to the HfO2 layer. Addition of C4F8 gas to the BCl3/Ar chemistry improved the TaN/HfO2 etch selectivity because adding the C4F8 gas enhances the formation of the CFxCly passivation layer on HfO2 surface and decreased the HfO2 etch rate more rapidly than the TaN etch rate in a disproportionate way. Reduction in the etch time for HfO2 layer also increases the TaN/HfO2 etch selectivity because the etch time gets closer to the initiation time for HfO2 etching. (c) 2007 American Vacuum Society.