Effects of an unbalanced magnetron in a unique dual-cathode, high rate reactive sputtering system

In the last few years a number of investigators have studied various"unbalanced" magnetron geometries, as a means of obtaining higher ion current densities at the substrate during deposition of hard coatings; however, previous discussions have been limited to single-cathode systems. Presented here for the first time are simple plasma and magnetic field measurements that illustrate the unique opportunities afforded by using unbalanced magnetrons in a dual-cathode system. The system studied employs a pair of opposed cathodes, 38 cm × 13 cm, placed 27.5 cm apart, to coat specimens mounted on a rotational substrate holder. Comparisons are drawn between the original "balanced" magnetron and several unbalanced configurations in terms of field strengths, deposition rates, etching characteristics, and substrate ion current densities for the growth of TiN films. Plasma probe and magnetic field studies were performed under a variety of. conditions in order to understand better the effects of "unbalancing" on the nature of the plasma within the three-dimensional geometry of the deposition chamber. All the unbalanced configurations examined provided enhanced ion bombardment at the surface of the growing film; however, the closed-field or opposed magnet geometry resulted in a threefold or greater increase in current density when compared with that obtained utilizing the corresponding mirrored geometry under the same conditions.