Plasma drift and nonuniformity effects in plasma immersion ion implantation

Measurements of the ion current collected by a substrate biased to high vol tage have been carried out in plasma immersion ion implantation with a filt ered vacuum arc plasma source. We have found that the ion saturation curren t increases with applied voltage and that this effect depends upon the angl e of the normal to the substrate with respect to the plasma stream and on t he distance of the substrate from the plasma duct exit. We also found that the ion current increases with increasing angle of the normal to the substr ate with respect to the plasma stream. A model was developed for the sheath expansion in a nonuniform plasma with substantial ion drift velocity. We f ind that nonuniformity and high drift velocity lead to a decrease in sheath thickness. In a nonuniform plasma, the ion saturation current increases wi th applied voltage. The predictions of the model were found to be in good a greement with experiment. (C) 2000 American Institute of Physics. [S0003-69 51(00)05421-8].