Thyratron Modulators in Plasma Source Ion Implantation

Plasma Source Ion Implantation (PSII) is an emerging technology which can be used to harden metal surfaces in a conformal manner. North Star Research Corp. (NSRC) is building a unique implanter system for Empire Hard Chrome which will be the first truly commercial implanter of this type. The choice of pulsed power technology for this application is important from the standpoint of both reliability and compatibility with the basic plasma processes under consideration. In this paper, we will evaluate the various possible pulsed power system choices including thyratron modulators, hard tube modulators, and crossatron modulators in the context of compatibility with the plasma and implantation process. Currents in the hundreds of amperes at 80100 kV are clearly found to be desirable based on the requirements of the process. This leads to the logical choice of thyratron/transformer modulators at lower average powers, or Crossatron modulators at higher average powers. We also discuss PFN design for thyratron modulators for the universal PSII-type waveform. A thyratron modulator was selected for the Empire implanter due to the requirements for low cost and high peak current. 1. 0 Introduction and Basics of PSII Ion implantation has the potential to improve the wear and corrosion properties of a wide variety of components, and it is in common use reducing corrosion and wear in parts such as artificial hip joints. This technology has more significant applications in the area of wear reduction in metal and plastic forming tooling. There have been a number of extensive reviews of ion implantation effects in the literature••• Reductions in the rate of wear of up to a factor of 40 in EN40B steel have been observed, probably due to the presence of interstitial nitrogen in the lattice. Ion implantation differs from most other surface modification processes in that it is intrinsically a non-equilibrium process, and is therefore not limited by the physics of equilibrium processes. Both non-equilibrium states and amorphous states can be produced through implantation. A number of organizations have significant programs in ion implantation. 5 Conventional implanters produce a unidirectional beam which strikes the whole surface at normal incidence only for flat surfaces. In positions where the beam is at an angle (say at an angle e) to the surface, the depth of implantation varies as cose, and the flux varies as 1/cose. The process of surface thinning due to sputtering also has a rate which varies as 1/cose. Since