Challenges and progress toward a 250 kV, 100 kW plasma ion implantation facility

Abstract

Plasma ion implantation (PII) is a large-scale cost-effective technique for modifying the surface properties of materials via omnidirectional ion implantation. The implantation voltage and ion species define the energy-to-ion ratio which, together with the ion dose, determines the effectiveness of an implant in achieving successful tribological improvements in materials. For most metal treatment applications of PII, modest energy-to-ion ratios and high ion doses are required to achieve respectable improvements in hardness and wear life. For example, implantation of N2+ ions into metal tools and dies via PII at 100 kV (energy-to-ion ratio of 50 keV per N+ ion) at a dose of 3×1017 N+ cm−2 can result in an increase of wear life by a factor of -8. In contrast with metals, polymers require high energy-to-ion ratios and low doses to achieve significant improvements in hardness and wear life. For example, ion beam implantation of N+ ions into Kapton at 300 kV (energy-to-ion ratio of 300 keV per N+ ion) and a dose of 3×1015 N+ cm−2 can increase hardness by a factor of 13. This energy-to-ion ratio is six times higher than that achievable using present PII technology. A provocative question to ask is how this can be achieved in a PII system. Work is under way at the Hughes Research Laboratories (HRL) to address this issue. The approach being used involves first scaling PII voltage technology from 100 to 250 kV, and then implanting doubly and triply charged atomic nitrogen ions at 250 kV to achieve an energy-to-ion ratio range of 500–750 keV per N+ ion. To date single-pulse ion implants have been conducted at 250 kV in the HRL PII facility. A plasma source has been built for the production of multiply charged nitrogen ions. A technique for treating non-conducting objects in a PII facility has been developed, and a method of reducing X-ray production in a PII system operating at 250 kV has been investigated.