Ion current distribution in a filtered vacuum arc deposition system

Abstract

The ion current distribution produced by a filtered vacuum arc deposition system consisting of a 90-mm diameter cathode, 122-mm internal diameter anode, and a 240-mm major radius / 80-mm minor radius quarter-torus duct macroparticle filter was measured with a nine-element multi-probe, and the total ion current was measured with a 130-mm diameter probe. Arcs were sustained on Ti and Sn cathodes, with currents of 300–340 and 160–175 A, respectively. Radial magnetic fields of up to 3 mT were imposed on the cathode surface for cathode spot rotation, and fields of up to 20 mT generally parallel to the duct were imposed for plasma guiding. In general, the plasma distribution function exiting from the duct was approximately Gaussian, but with an offset from the center of the duct. At the torus exit, the Ti plasma beam was offset 12 mm towards the outside of the torus at B = 4 mT, while with increasing toroidal field the beam center moved towards the center of the duct, and reached the center at B = 8 mT. The beam was offset towards the inside of the torus for B > 8 mT, reaching a displacement of up to 5 mm for B = 12 mT. The Sn beam, by contrast, was shifted towards the inside of the torus, and the displacement from the center was as much as 15 mm. In addition, for both cases an offset in the (B × g) direction was observed, where B is the duct magnetic field vector and g is a vector pointing outward from the toroidal center of curvature. The displacements from the center were stronger for Sn plasma (up to 16 mm) than for Ti plasma (up to 7 mm). The displacement from the center in both directions grew with the distance from the exit of the torus. A beam steering coil, whose axis was normal to the axis of plasma duct, was used to shift the plasma beam center towards the chamber axis.