A semi-analytic collisionless sheath model for multicomponent plasmas and ion energy and angular distributions at rf-biased electrodes

Abstract

The ion energy and angular distributions (IEADs) arriving at substrates strongly affect the etching rates in plasma etching processes. In order to determine the IEADs accurately, it is important to obtain the characteristics of radio frequency (rf) sheaths with multicomponent plasmas. However, very few studies have been conducted on an rf sheath model for multiple ion species including negative ions over the past few decades. Therefore, in this work, we extended previous semi-analytic collisionless rf sheath models for electronegative plasmas. The extended model was based on the previously developed models, and an equivalent circuit model was used to determine the sheath characteristics. Also, we obtained the IEADs using the rf sheath model and an analytic model for evaluation of the ion angular distribution functions. We observed that the developed model was in good agreement with the experimental results and the one-dimensional dynamics model. Also, we found that negative ion species could affect the characteristics of rf sheaths, hence negative ion species should be considered to obtain more accurate IEADs.