In this study, the effect of BCl3/C4F8 gas mixture on the ZrOx etch rates and the etch selectivities of ZrOx/Si were investigated and its etch mechanism was studied. The increase of C4F8 in BCl3/C4F8 decreased the silicon etch rate significantly and finally deposition instead of etching occurred by mixing C4F8 more than 3%. In the case of ZrOx, the etch rate remained similar until 4% of C4F8 was mixed, however, the further increase of C4F8 percentage finally decreased the ZrOx etch rate and deposition instead of etching occurred by mixing more than 6%. Therefore, by mixing 3-4% of C4F8 to BCl3, infinite etch selectivity of ZrOx/Si could be obtained while maintaining the similar ZrOx etch rate. The differences in the etch behaviors of ZrOx and Si were related to the different thickness of C-F polymer formed on the surfaces. The thickness of the C-F polymer on the ZrOx surface was smaller due to the removal of carbon incident on the surface by forming COx with oxygen in ZrOx. Using 12 mTorr BCl3/C4F8 (4%), 700 W of rf power, and -80 V of de bias voltage, the ZrOx etch rate of about 535 angstrom/min could be obtained with infinite etch selectivity to Si. (c) 2006 Elsevier B.V. All rights reserved.