Monroe Lee King

Enhanced ionization freeman ion source

Abstract We developed modifications to a standard Freeman ion source which increased the plasma electron temperature and density by minimum factors of 1.5 and 1.1, respectively. The improvement in these fundamental plasma parameters resulted in a greater than 40% increase in B+ currents from boron trifluoride gas and substantial usable beam current increases in B2+, P2+, and As2+. A large increase in triple charge currents was also present in the extracted beam. Ion source lifetime tests were performed at 1 mA scanned B+ wafer current with a 125 mm aperture on an Eaton NV-6200 Ion Implanter. Filament lifetime was observed to be in excess of 50 h. Further, erosion was more uniformly distributed along the filament length and tests indicate that the extracted ion beam uniformity was increased along the extraction slit. Therefore, we conclude that our modifications to the standard Freeman ion source also increased discharge uniformity.