Plasma molding over surface topography: Simulation of ion flow, and energy and angular distributions over steps in RF high-density plasmas

A two-dimensional fluid/Monte Carlo (MC) simulation model was developed to study plasma "molding" over surface topography. The radio frequency (RF) sheath potential evolution, ion density, and flux profiles over the surface were predicted with a self-consistent fluid simulation. The trajectories of ions and energetic neutrals (resulting by ion neutralization on surfaces or charge exchange collisions in the gas phase) were then followed with a MC simulation. In this paper, ion flow, energy and angular distributions of ions, and energetic neutrals bombarding an otherwise planar surface with a step are reported. The step height was comparable to the sheath thickness for the RF high-density plasma considered. As one approaches the step sidewall, the ion flux decreases, the ion energy distribution narrows, and the ion impact angle increases drastically. The ion impact angle at the foot of the step scales with the ratio of sheath thickness to step height. The energetic neutral flux is found to be comparable to the ion flux on the horizontal surface near the step sidewall. Simulation results are in good agreement with experimental data on ion flux and ion energy and angular distributions near the step.