Effect of ion neutral collisions on the ion and neutral velocity distribution on negatively biased electrodes

Abstract

In the present work, a model is proposed that can estimate ion and neutral energy distributions at negatively biased electrodes (substrates), assuming charge exchange as the dominant ion neutral collision. The model is applicable over a wide pressure range, and can be used to compute the ratio of ion flux to neutral flux, net momentum transfer from plasma to substrate, etc. The ratio of the sheath thickness to the collision mean free path is a crucial parameter determining the ion and neutral velocity distribution The model predicts that at high pressure (∼few Torr), neutral flux and momentum transfer is dominant for negative electrode bias (∼1 kV). The model can be used for plasma nitriding, plasma immersion ion implantation, plasma etching, etc., to predict ion and neutral bombardment effects on the electrode surface.