Consequences of three-dimensional physical and electromagnetic structures on dust particle trapping in high plasma density material processing discharges

Abstract

Plasma processing discharges are typically designed with the goal of having uniform reactant fluxes to the substrate and a minimum of dust particle contamination of the wafer. It is not uncommon, however, that reactors have three-dimensional (3D) structures such as antennas (or coils), gas injection nozzles, sub- or super-wafer topography and single-sided pump ports. These structures can contribute to azimuthal asymmetries in reactant fluxes. These structures may also produce dust particle traps. In this paper, a 3D plasma equipment model is applied to investigate the impact of these structures on reactant fluxes and their influence on dust particle trapping in inductively coupled radio frequency discharges under conditions where trapping is not typically obtained. We find that 3D structures, such as injection nozzles, perturb the plasma potential and ion fluxes to distances well beyond their geometrical boundaries. These perturbations are sufficient to create dust particle traps. Electromagnetic asymmetries caused by coils which have poor impedance matching may also produce sufficient azimuthal asymmetries in ion fluxes that dust particle traps are generated.