Plasma source ion implantation: A new, cost-effective, non-line-of-sight technique for ion implantation of materials

Surface modification by ion bombardment is a well-established technique for improving the hardness, friction, wear resistance and corrosion resistance of materials. Surface modification of materials by conventional ion implantation is a line-of-sight process in which a directed beam of energetic ions is rastered across a target. If the target is three dimensional, the process generally requires target manipulation to achieve uniform implantation over the entire surface of the object. This target manipulation requirement can seriously limit the cost effectiveness of ion implantation relative to more conventional surface treatments, especially for large and/or heavy targets. We are developing a new technique, plasma source ion implantation (PSII), which circumvents the line-of-sight restriction of conventional ion implantation. In PSII, targets to be implanted are placed directly in a plasma source chamber and are then pulse biased to high negative voltage (10 – 100 kV in our experiments). A thick, ion matrix sheath forms around the target, and ions accelerate through the sheath drop and bombard the target from all sides simultaneously without the necessity of target manipulation. Although the PSII process bears a superficial resemblance to existing techniques such as “ion plating”, “ion coating” or “plasma nitriding”, PSII produces a deposition profile characteristic of high energy ion implantation. Our experiments have demonstrated that PSII (1) efficiently implants ions to the concentrations and depths required for surface modification, (2) produces material with improved microhardness and wear properties and (3) dramatically improves the life of manufacturing tools in actual industrial applications. For example, in recent industrial field tests the tool life of M-2 pierce punches used to produce holes in mild steel plate has been increased by a factor of 70 – 80. In this paper we describe (1) the latest results from a series of ongoing field tests, (2) extensions of the PSII process to ion beam mixing and ion beam enhanced deposition modes of operation, and implantation of molecular ions, and (3) the comparative economics of surface modification by PSII relative to conventional ion implantation.