Dynamic model and electrical characteristics for rf-biased electronegative plasma sheath

Abstract

The dynamic model for the sheath of an RF-biased electronegative plasma is developed. The low-pressure high-density plasma conditions are assumed and considered as an electric-field-free boundary. The Bohm criterion for collisionless sheath is assumed to be valid and the presheath region is separately considered in calculating the sheath properties. The electron density n/sub e/ and the electronegativity /spl alpha/ /spl equiv/ n/sub -//n/sub e/ are taken to be determined independently of the sheath dynamics. The time-resolved wave forms of the sheath potential and thickness are obtained. The characteristics for the RF power dissipation mechanisms are also investigated. The RF bias power is assumed to be dissipated through two power loss channels - the first is due to ion acceleration in the sheath and the second is due to the electron heating at the plasma-sheath boundary. From the power loss point of view, the equivalent circuit model is developed and the sheath impedance is calculated. The electronegativity, as well as the current and RF bias frequency, is found to be an important factor in determining the electrical characteristics for the RF-biased electronegative plasma sheath.