Analysis of Polymer Formation during SiO2 Microwave Plasma Etching

Abstract

The mechanism of C _x F _y fluorocarbon deposition during SiO₂ etching is analyzed using a test sample with an overhang mask. For C₄F₈, CHF₃, and CH₂F₂, only C _x F _y deposition was observed at 0 W of substrate-bias rf power, and the deposition profiles were similar. At a higher rf power, reaction phenomena changed to those of SiO₂ etching. The standard deviation σ of the etching-ion incident angle was measured as less than 2°. On the other hand, σ _{d e p o} measured from the deposition profile was about 20°. This difference may be caused by surface migration. This migration is thought to be a key factor in excess deposition at the bottom of a high-aspect-ratio hole. Etching rates of the deposit increased in the order of C₄F₈>CHF₃>CH₂F₂. Therefore, SiO₂-etching gases, such as C₄F₈, which form easily removable deposits, reduce RIE lags for contact hole patterning.