Cathode current distributions in an unbalanced magnetron

Abstract

The planar magnetron is extensively used as a sputtering source for a wide variety of target materials. Unfortunately, in some configurations, the target may have to be replaced when as little as 30% of its material had been sputtered [S. Schiller, U. Heisig, K. Goedicke, Thin Solid Films, 40 (1977) 327–334]. This is due to the non-uniform distribution of bombarding ions across the face of the target, which leads to the formation of an erosion profile that peaks beneath the ‘racetrack’. A better understanding of this process could lead to a number of benefits including improved target utilization in sputtering processes. The arrival of ions and the emission of electrons from a target can be measured as a current, and it is the variation of this current with position that is the focus of this paper. To measure how the current varies a number of probes were constructed to suit a circular unbalanced magnetron. The target was sputtered in DC mode at over a range of pressures and discharge currents, in both argon and argon/oxygen atmospheres. Results indicate that the width of a Gaussian distribution function, fitted to the data, increases with discharge current, and also that pressure has a negligible effect on the shape of the distribution. The introduction of oxygen appeared to have no discernable effect, within experimental error, on the current distribution over the range of parameters tested.