Vacuum arc metal plasma production and the transition of processing mode from metal ion beam to dc metal plasma immersion

Abstract

The vacuum arc provides a straightforward method for the efficient production of dense metal plasma. The plasma so formed can be utilized more-or-less ‘as-is’, or with macroparticle filtering, for the deposition of films of many different kinds. More advanced techniques involve substrate pulse-biasing to achieve a metal plasma immersion processing mode, or the vacuum arc plasma source can be embodied within an ion source configuration for the formation of energetic metal ion beams for carrying out ion implantation. Not inconsequentially, the vacuum arc metal plasma has an innate high ion drift velocity (ion drift speed greater than the ion sound speed), a plasma feature that leads to some novel and important consequences — a negatively-biased substrate located in the plasma stream can maintain unexpectedly high voltages on an essentially dc basis, and an ion source with ‘conventionally poor’ extractor design can provide a kind of plasma immersion ion implantation mode of operation. As the ion source operating parameters are varied, there can in fact be a smooth transition between these two modes — a plasma immersion processing mode and an energetic ion beam processing mode. The metal ion beam mode of operation and the plasma immersion mode of operation are closely related because of the plasma drift. Here, vacuum arc generation of metal plasma is summarized, and a brief review of ion source and plasma immersion modes presented. The significance of high plasma drift as a mechanism that can lead to a dc (or, at least, long-pulse) mode of plasma immersion ion implantation is outlined.