Numerical Simulation of Plasma-Immersion Ion Implantation on Insulators

In plasma immersion ion implantation (PIII), a high voltage pulsed bias is applied to a substrate to accelerate ions from a surrounding plasma for implantation beneath the surface. This technique is often used to modify the surface properties of materials. For example, the intrinsic stress of thin films can be lowered, resulting in improved adhesion. For conducting samples, the energy of the incoming ions is directly related to the bias voltage applied. However, PIII of insulators is known to lead to a reduced bias potential due to surface charging. Previous work has attempted to measure the time-dependent charging of an insulating surface both directly and by measuring sheath collapse. In this paper, the sheath collapse near a circular insulating sample on a conducting stage is modeled by a hybrid particle-in-cell simulation. As a result of surface charging, the sheath is observed to collapse earlier at the center of the sample than at the edge. This has important implications for dose uniformity in implantation depth for insulating samples. We will present results showing the distribution of implanted ion fluence, energy and angle.