ION ENERGY-DISTRIBUTION IN PLASMA IMMERSION ION-IMPLANTATION

In plasma immersion ion implantation the ions are accelerated from the plasma to the target. The total current, as delivered by the high vol tage pulse generator, is only a qualitative reading of the ion flux de nsity on the target. The main reason for this is a large secondary ele ctron coefficient, which is strongly dependent on the ion energy and t he surface composition. In this work direct time-resolved ion flux mea surements are presented. High voltage pulses of eU(0)=5, 10, 15 and 20 kV were applied to a spherical target with a small orifice. The ions were collected in the high vacuum region behind this orifice and their energy distribution was determined with a Faraday cup. The measured i on energy distribution function exhibits a sharp peak at the nominal e nergy eU(0) with the height decreasing during the voltage pulse, in ag reement with the theoretical predictions for a collisionless transit t hrough the plasma sheath. (C) 1997 Elsevier Science S.A.