Challenges in the industrial deposition of transparent conductive oxide materials by reactive magnetron sputtering from rotatable targets

Reactive magnetron sputter deposition of transparent conductive oxides (TCOs) is a cost effective deposition technique due to low target costs compared to ceramic processes. Rotatable tube targets are used in industries because of their high material reservoir and a high target utilization (approx. factor 2 compared to planar targets). Another advantage for reactive sputtering is the absence of erosion groves. However, the reactive sputter process is highly complex because nearly any process parameter has strong impact on the properties of the growing film. Thus, the variation of the working point along the tube target may cause serious problems, in particular because conductivity, transparency, and thickness have to be optimized over a large substrate area at the same time. The most commonly sputtered TCO materials are aluminium doped zinc oxide and indium tin oxide. The respective reactive sputter processes are very distinct. This concerns among others the possible process control mechanisms as well as the dependence of the film properties on the reactive working point. The reliable industrial application of the reactive TCO sputter processes is still a big challenge for large area substrates. There are different possibilities to control the sputter process as well as the film properties in situ.