Recent advances in vacuum arc ion sources

Intense beams of metal ions can be formed from a vacuum arc ion source. This kind of source works well for most of the solid metals of the Periodic Table, and because the ions are, in general, multiply stripped with charge states as high as 4+ to 6+ , the mean energy of the ion beam produced can be 100–200 keV for an extractor voltage in the comfortable range of about 50–75 kV. Broad-beam extraction is convenient, and the time-averaged ion beam current delivered downstream can readily be in the tens of milliamperes range. The vacuum arc ion source has, for these reasons, found good application for metallurgical surface modification: it provides relatively simple and inexpensive access to high dose metal ion implantation. Several important source developments have been demonstrated recently, including very-broad-beam operation, macroparticle removal, charge state enhancement and the formation of gaseous beams. We have made a very-broad-beam source embodiment with beam formation electrodes 50 cm in diameter (area, 2000 cm 2 ), producing a beam with a width of approximately 35 cm for a nominal beam area of about 1000 cm 2 , and a pulsed Ti beam current of about 7 A was formed at a mean ion energy of approximately 100 keV. Separately, we have developed a high efficiency macroparticle-removing magnetic filter and have incorporated such a filter into a vacuum arc ion source so as to form macroparticle-free ion beams. Jointly with researchers at the High Current Electronics Institute, Tomsk, Russia and the Gesellschaft fur Schwerionenforschung, Darmstadt, Germany, we have developed a compact technique for increasing the charge states of ions produced in the vacuum arc plasma, thus providing a simple means of increasing the ion energy at fixed extractor voltage. Finally, operation with mixed metal and gaseous ion species has been demonstrated. In this paper, we briefly review the operation of vacuum arc ion sources and the typical beam and implantation parameters that can be obtained, and describe these source advances and their bearing on metal ion implantation applications.