Numerical optimization of non-equilibrium plasma source for surface processing of materials

Abstract

Over the years, non-equilibrium plasma sources have emerged as a promising technology in surface processing of materials. Various strategies have been employed to make significant advancement in the technology. However, the process optimization is found to depend on different factors like power supply frequency, gas species and gas pressure. In order to control material processing outcome, it is necessary to control plasma parameters as per requirement. In the present work, a surface microwave generated non-equilibrium plasma source is proposed for material processing applications. The source comprises of rectangular waveguide system and a quartz tube, whose dimensions are optimized based on the electric field profile obtained within the plasma tube in the presence of the microwave (f = 2.45 GHz). Argon gas is allowed to flow through the discharge tube at a velocity of 10 m/s keeping its pressure at 1 torr. The microwave electric field within the discharge tube ionizes the argon gas medium resulting into plasma state whose properties are investigated using commercially available COMSOL Multiphysics® software. The inner surface of the discharge tube is then filled with dielectric beads (radius = 2 mm) and the effect of the dielectric constant on the plasma properties are studied. An investigation of ion flux at different positions in the plasma tube suggests that in the absence of dielectric beads, remote contact mode of operation can be preferred while in the presence of dielectric beads, direct contact mode of operation can be implemented. These results are of significance for direct as well as remote mode of surface processing of materials.