A PARTICLE-IN-CELL SIMULATION OF DUST CHARGING AND SHIELDING IN LOW-PRESSURE GLOW-DISCHARGES

The transport of particles (''dust'') in low pressure electrical glow discharges is being studied in regard to its role in contaminating sil icon wafers during plasma etching and deposition. Particles (10s nm-mu m) negatively charge in glow discharges and, to first order, appear to be massively large negative ions around which sheaths develop. The fo rces on particles in plasmas include electrostatic (drift of charged p articles in electric fields) and viscous ion drag. The latter force is momentum transfer from ions to particles by either collisions or orbi tal motion. This force critically depends on the charge on the particl e and the shape of the sheath surrounding the particle. In this work, we report on a Pseudoparticle-in-Cell (PIC) simulation of the transpor t of electrons and ions in the vicinity of dust particles in low press ure glow discharges. The simulation produces the electrical charge on the dust particle, the sheath structure around the dust particle and t he orbital dynamics of the ions. A companion molecular dynamics simula tion uses these parameters to produce ion-dust and electron-dust parti cle cross sections for momentum transfer and collection. Results will be discussed for charge, sheath thickness, cross sections and viscous ion drag forces on dust particles as a function of radius and plasma p arameters.