Plasma drift and non-uniformity effects in plasma immersion ion implantation

Summary form only given. Plasma immersion ion implantation (PIII) is a technology used to modify material surface properties. By repetitively applying negative high-voltage bias pulses to the substrate, ions are extracted from the plasma, accelerated across the high voltage sheath and implanted into the substrate. The accumulated ion implantation dose for this technique depends upon the ion current drawn by the substrate, which is determined by the sheath expansion during the pulse. We have carried out some measurements of ion saturation current in PIII using a filtered vacuum arc metal plasma source. The vacuum arc plasma jet is characterized by its spatial non-uniformity and high ion drift velocity. In order to investigate these effects we have placed the substrate at various distances from the source exit plane and various angles with respect to the jet streaming direction. The bias pulse was up to -8 kV. We found that the ion saturation current increases with applied voltage. We have also measured the dependence of ion saturation current on the angular target position with respect to the plasma stream. A model was developed for the sheath expansion in a non-uniform plasma with substantial drift velocity. We find that generally the nonuniformity and high drift velocity lead to a decrease in the sheath thickness. In a non-uniform plasma, the ion saturation current increases with applied voltage. Predictions of our model were found to be in agreement with experiment.