Two-dimensional simulation of plasma-based ion implantation

A particle-in-cell simulation is used to study the time-dependent evolution of the potential and the electrical field surrounding two-dimensional objects during a high voltage pulse in the context of plasma immersion ion implantation. The numerical procedure is based on the solution of Poisson's equation on a grid and the determination of the movement of the particles through the grid. Ion current density, implanted concentration, average impact energy, and impact angle of the ions were calculated using this method for two geometrical shapes, a square and an L-shaped object. The nonuniformity of the sheath potential near convex and concave corners is shown. The divergence of the electrical field in the vicinity of corners leads to dramatically reduced concentration of the incident ions. The simulation also shows that a large ion flux hits the surface during the rise time of the pulse. Directly after the rise time, more than 40% of the whole concentration is implanted. Hence, the average impact energy of the ions is reduced during the rise time of the pulse. In the vicinity of corners the incident ions strike the surface under oblique angles. The interior sides of the objects are characterized by smaller average impact angles than the exterior sides. In addition, the dependence of the impact angle and the energy distribution on the pulse time is presented. The influence of the shape of the objects on the average energy of the ions turns out to be slight for both geometries. The results of the particle-in-cell simulation are in good agreement with the published measurements. (C) 1999 American Institute of Physics. [S0021-8979(99)08002-0].