DYNAMICS OF COLLISIONLESS RF PLASMA SHEATHS

The behavior of rf plasma sheaths has been the subject of much scienti fic study and also is technologically important for plasma etching and deposition in the manufacture of integrated circuits. This paper pres ents a semianalytic model of rf sheaths and describes an experiment th at tested the model. An approximation to the first integral of the Poi sson equation allows solving for the response of plasma sheaths to an imposed rf bias voltage. This approximation enables the plasma sheaths to be included within an electrical model of the plasma and external rf circuit components, and affords a prediction of the ion energy dist ributions impacting the electrodes, which are in contact with the plas ma. The model is a significant advance beyond previous sheath models b ecause it has no restriction on the ratio of the rf period to the ion transit time across the sheath. The model is applicable to those high- density, low-pressure plasmas in which the Debye length is a small fra ction of the ion mean-free path, which itself is a small fraction of t he plasma dimension. The experimental test of the model was conducted by comparing the predicted and measured rf potential, current, and pow er at the sheath adjacent to a capacitively coupled, rf-biased electro de in a plasma reactor with argon discharges sustained by an inductive ly coupled plasma source. The comparisons included both linear and non linear components of the rf electrical parameters. Results of the expe riment were in substantial agreement with model predictions. (C) 1997 American Institute of Physics.