MUTUAL SHIELDING OF CLOSELY SPACED DUST PARTICLES IN LOW-PRESSURE PLASMAS

The transport of particles (''dust'') in low pressure electrical glow discharges is of interest as a result of their role in contaminating w afers during plasma etching and deposition of semiconductors. Particle s (10s nm to many micrometers) negatively charge in glow discharges an d, to first order, appear to be massively large negative ions around w hich sheaths develop. The electrical and fluid forces acting on dust p articles in plasma processing discharges may cause the interparticle s pacing to be less than the shielding distance around particles. The mu tual shielding of dust particles is therefore of interest. In this art icle, we report on results from a pseudoparticle-in-cell simulation of the mutual shielding of two adjacent dust particles. Results will be discussed for charge, potential, and electrostatic forces on dust part icles as a function of particle size and separation distance between t wo particles. We found that two closely spaced particles not only shie ld each other but can shadow their partner, thereby resulting in asymm etric charging of otherwise identical particles.