RF Models for Plasma-Surface Interactions

Plasma sheaths near metallic and dielectric surfaces in the presence of oscillating electric fields impart physics effects of critical significance for fusion experiments and industrial plasma processing applications. In magnetic fusion research, thin sheaths form near radiofrequency (RF) antenna structures and induce ion sputtering from antenna surfaces; the sputtered ions contaminate and cool the core plasma and reduce fusion power output. Industrial processes for semiconductor manufacturing (etching, thin-film deposition, etc.) require precise knowledge and control of the plasma steady-state in order to ensure proper fabrication, but these equilibrium parameters are sensitive to sheath parameters which vary on much shorter timescales. To enable the numerical optimization of fusion reactor antennas and plasma processing reactors, development of rapid, accurate simulation methods which model sheath effects on larger spatial and slower temporal scales are needed. Sub-grid models to mimic the faster timescales and smaller length scales of the sheath physics at plasma-wall interfaces are developed and verified. These models are incorporated into the VSim commercial software package. Capacitive lumped-circuit element sub grid sheath models were generalized for plasma in contact with dielectric walls, and the model was successfully benchmarked in first-principles particle-in- cell simulations. Test particle behavior was augmented to account for the sheath voltage increment when passing through a sheath, and accurate surface deposition fields were added for charge and energy. New test particle features from the Phase I will be deployed to provide accurate electron and ion energy distributions and sputtering/impurity-production predictions for industrial and fusion plasma applications. Plasma chemistry tools and self-consistent steady-state initializations will be added. The sheath sub grid model will be augmented to include improvements to the DC-rectified potential, magnetic field effects, and effects arising from multispecies plasmas. Fusion antennas and industrial processing reactor operations will be modeled. Commercial Applications and OtherBenefits: The proposed VSim development enables its use as a design tool for plasma-etch-based semiconductor manufacturing equipment, filling a need in the industrial plasma processing community for computational kinetic and fluid models which make effective use of parallel computing clusters. Industrial plasma processing customers can use the software to more rapidly design and optimize equipment to carry out increasingly complex manufacturing processes. Additionally, by studying the optimization of RF antennas in the International Thermonuclear Experimental Reactor (ITER) device, we will be able to improve the efficiency, and perhaps even enable the success, of a $10B fusion experiment.