The effect of sheath on plasma momentum transport to an electrically biased surface

Abstract

Ion and electron momentum fluxes transport to a biased workpiece surface in contact with a plasma are systematically and kinetically investigated in this study. Micro-electro-mechanical systems (MEMS), semiconductor technology, plasma etching, spray deposition, sputtering, cutting and surface treatment, etc. are strongly affected by momentum transfer from the plasma to workpiece. In this work, the plasma is composed of a collisionless presheath and sheath on an electrically negative biased surface that partially reflects or secondly emits ions and electrons. The presheath is an ionization region that continuously produces ions to maintain ion loss to the workpiece, while the sheath is a space-charge region that accelerates ions and retards electrons to the negative biased surface. The predicted total momentum flux at the wall including that of the ions and electrons as a function of negative electrically biased voltage is found to agree well with experimental data. The effects of the sheath and plasma parameters such as net current density, ion and electron reflectivities of the wall, ion-to-electron mass ratio, charge number, electron-to-ion source temperature ratio at the presheath edge, on the total momentum flux, ion and electron momentum fluxes, and their components through the sheath to the surface are obtained.