closed-field unbalanced magnetron sputtering. Despite the benefits offered by unbalanced magnet rons, it is still difficult to uniformly coat complex components at acceptable rates from a single source. Therefore, in order to commercially exploit this technology, multiple magnetron systems have been introduced. In a multiple magnetron system, the magnetic arrays in adjacent magnetrons can be configured with either identical, or opposite magnetic polarities. In the former case the configuration is described as"mirrored' and in the latter case closed field', and both configurations are shown in Fig. 3. In the mirrored case, the field lines are directed towards the chamber walls. Secondary electrons following these lines are lost, resulting in a low plasma density in the substrate region. Conversely, in the closed lon Current Density Current Density