A plasma doping system including a plasma doping chamber, a platen mounted in the plasma doping chamber for supporting a workpiece, a source of ionizable gas coupled to the chamber, the ionizable gas containing a desired dopant for implantation into the workpiece, a plasma source for producing a plasma having a plasma sheath in a vicinity of the workpiece, the plasma containing positive ions of the ionizable gas, and accelerating said positive ions across the plasma sheath toward the platen for implantation into the workpiece, a shield ring surrounding the platen and adapted to extend the plasma sheath beyond an edge of the workpiece, and a cover ring disposed on top of the shield ring and adapted to mitigate sputtering of the shield ring, wherein the cover ring comprises a crystalline base layer and a non-crystalline top layer.