Redeposition of etch products on sidewalls during SiO_2 etching in a fluorocarbon plasma. Ⅱ. Effects of source power and bias voltage in a CF_4 plasma

摘要

Variations in the properties of sidewalls due to the redeposition of etch products emitted from the bottom during SiO_2 etching in a CF_4 plasma were studied under different conditions of source power and bias voltage, in the range of 100 and 500 V, and 0 and 400 W, respectively. A Faraday cage and a step-shaped SiO_2 pattern located in a transformer coupled plasma etcher permitted the control of the incident angle of ions, thus permitting the redeposition phenomenon to be observed on a macroscopic scale. Under all process conditions, the deposition rate on sidewall (A), affected by the redeposition of particles emitted from the bottom, was larger than that on sidewall (B), which was unaffected by the redeposition, because particle redeposition induced the formation of a sidewall passivation layer on sidewall (A). It was indirectly confirmed that the amount and the kinetic energy of particles sputtered from the bottom were closely related to the formation "of the sidewall passivation layer. The redop-effect, which indicates the extent to which the redeposition contributes to the deposition rate on the sidewall, increased with bias voltage and source power. The extent of etching of the SiO_2 underlayer of sidewall (B) increased with both the source power and bias voltage, in contrast to the case of sidewall (A). On sidewall (A), the extent of SiO_2 etching increased continuously with source power, but only increased with bias voltage when the latter was under 300 V. The etching decreased at higher bias voltages.