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 ZrO_x etch rates and the etch selectivities of ZrO_x/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 ZrO_x, the etch rate remained similar until 4% of C₄F₈ was mixed, however, the further increase of C₄F₈ percentage finally decreased the ZrO_x 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 ZrO_x/Si could be obtained while maintaining the similar ZrO_x etch rate. The differences in the etch behaviors of ZrO_x 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 ZrO_x surface was smaller due to the removal of carbon incident on the surface by forming CO_x with oxygen in ZrO_x. Using 12 mTorr BCl₃/C₄F₈ (4%), 700 W of rf power, and − 80 V of dc bias voltage, the ZrO_x etch rate of about 535 Å/min could be obtained with infinite etch selectivity to Si.