Analysis of Polymer Formation during SiO2 Microwave Plasma Etching

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.