AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS-TuM

Paper PS-TuM9
Coulomb Crystals in Plasma Processing Reactors@footnote 1@

Tuesday, November 5, 2002, 11:00 am, Room C-103

Session: Atmospheric Pressure and Other Emerging Plasma Applications
Presenter: V. Vyas, University of Illinois at Urbana-Champaign
Authors: V. Vyas, University of Illinois at Urbana-Champaign
M.J. Kushner, University of Illinois at Urbana-Champaign
Correspondent: Click to Email
Many plasma deposition systems operate in regimes whereby large densities of small particles are nucleated in the gas phase. Given sufficient densities of these particles, they can exhibit collective behavior and form Coulomb solids. These structures typically form at moderate gas pressures, small particle sizes and lower powers in capacitively coupled, radio frequency discharges. Lattices having different radial structure functions [g(r)], non-ideality factors and geometrical shapes can be formed given somewhat subtle changes in discharge properties. Having scaling laws for their behavior would be desirable to minimize unwanted feedback to the plasma or film properites. To address these phenomena, a 3-dimensional dust transport simulation has been developed and incorporated into a plasma equipment model. The forces included in the dust transport model are electrostatic, ion-drag, thermophoretic, fluid-drag by neutrals, gravity and particle-particle Coulomb interactions. We will discuss formation of plasma crystals as function of operating conditions in rf discharges and, in particular, the formation of voids in the plasma crystal at high substrate biases. The negative ion fluxes in electronegative gas mixtures alter the ion drag force acting on the dust particle leading to qualitatively different crystal morphologies than those found in electropositive plasmas. For example, addition of electronegative gases such as Cl@sub 2@ and O@sub 2@ to Ar causes voids in the plasma crystals to close. The effect of ion streaming on dust particle motion will be discussed, as will the effect of surface topology on radial compression of the plasma crystal producing changes in interparticle spacing and g(r). @FootnoteText@ @footnote 1@ Work was supported by Sandia National Laboratory and the National Science Foundation.