Effect of additive gases on the selective etching of ZrOx film using inductively coupled BCl3-based plasmas

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 dc bias voltage, the ZrOx etch rate of about 535 Å/min could be obtained with infinite etch selectivity to Si.