New Developments in Metal Ion Implantation by Vacuum Arc Ion Sources and Metal Plasma Immersion
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Berkeley National Laboratory, University of California, Berkeley, CA 94720. tHigh Current Electronics Institute, Russian Academy of Sciences, Tomsk 634050, Russia. tPresent address: Applied Materials Corp., 3225 Oakmead Village Dr., Santa Clara, CA 95054. ABSTRACT Ion implantation by intense beams of metal ions can be accomplished using the dense metal plasma formed in a vacuum arc discharge embodied either in a vacuum arc ion source or in a tmetal plasma immersion' configuration. In the former case high energy metal ion beams are formed and implantation is done in a more-or-less conventional way, and in the latter case the substrate is immersed in the plasma and repetitively pulse-biased so as to accelerate the ions at the high voltage plasma sheath formed at the substrate. A number of advances have been made in the last few years, both in plasma technology and in the surface modification procedures, that enhance the effectiveness and versatility of the methods, including for example: controlled increase of the ion charge states produced; operation in a dual metal-gaseous ion species mode; very large area beam formation; macroparticle filtering; and the development of processing regimes for optimizing adhesion, morphology and structure. These complementary ion processing techniques provide the plasma tools for doing ion surface modification over a very wide parameter regime, from 'pure' ion implantation at energies approaching the MeV level, through ion mixing at energies in the -1 to -100 keV range, to IBAD-like processing at energies from a few tens of eV to a few keV. Here we review the methods, describe a number of recent developments, and outline some of the surface modification applications to which the methods have been put. INTRODUCTION Many different kinds of plasma and ion beam techniques have been developed for the modification of material surfaces and the tailoring of surface properties [1-6]. At the high energy end of the spectrum, ion implantation is used to inject ions to depths of hundreds or thousands of Angstroms below the surface, and non-equilibrium alloys can be formed that are difficult or impossible to form in other ways. At lower energies, thin films of a great variety of elements and compounds can be deposited using a low energy plasma stream incident upon the surface. Hybrids and other related methods have also been investigated, such as ion beam mixing [7] and ion beam assisted deposition (IBAD) [8]. For example a condensible species (eg, metallic) deposited at low energy can be driven into the substrate material by knock-on collisions by energetic ions; this is called recoil implantation, and much progress has been made in a number of means of implementation of this technique. In conventional ion implantation [9] a beam of energetic ions is directed onto the material to be implanted using an appropriate ion source to form and accelerate the ion beam; additional post-extraction acceleration of the beam may also be applied. The ion source, the beam and the target are located within a high
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