Plasma energy transport to an electrically biased surface

Abstract

The total energy flux, including ion and electron energy fluxes, transport to a biased surface in contact with a plasma is systematically and analytically investigated in this study. Micro-electro-mechanical systems (MEMS), semiconductor technology, plasma etching, spray deposition, sputtering, cutting and surface treatment, etc. are usually controlled by energy transfer from the plasma to workpiece. In this work, the plasma is composed of a collisionless presheath and sheath on an electrically negative biased workpiece partially reflecting and secondly emitting ions and electrons. The presheath is an ionization region that continuously produces ions to supply ion loss to the surface, while the sheath is a space-charge region that accelerates ions and retards electrons toward the surface. Based on the kinetic analysis, the predicted ion density, velocity and energy transmission factor on the surface are found to agree well with experimental data. The effects of dimensionless ion recombination and electron absorption energies, reflectivities and second emissivities of the ions and electrons on the wall, ion-to-electron mass ratio, charge number, electron-to-ion source temperature ratio at the presheath edge, and net current density on energy fluxes across the sheath are obtained. Energies released from recombination of the ions and electrons on the surface play the most important role in energy transfer to the workpiece. The sheath should be accounted for predicting energy transport to a biased surface.