Simulation of a surface-reflection neutral stream source

We have developed a computational model to optimize the design of a surface reflection neutralization source of hyperthermal neutrals for charge-free processing. For the deployment of this technique to production (≥8 in. wafers) processing, a system design study has been completed. A Monte Carlo model is used to determine the energy and angular distributions of reflected hyperthermal neutrals at the surface of a wafer, as well as flux uniformity. A simple form for the plasma profile is chosen to allow simulation of various profiles reported in the literature. Neutrals are launched from the reflector consistent with the relative plasma density at each position on the reflector with angular and energy distributions consistent with experimental observations. These neutrals are then followed through interactions with thermal background atoms and the plasma. Charge exchange, ionization, and elastic scattering processes are considered for argon as the main feedstock gas. The results show the trade off between a high density plasma for substantial wafer neutral flux and losses of the neutral stream due to ionization and charge exchange in the plasma stream.