Comparison of the large-area reactive sputter processes of ZnO:Al and ITO using industrial size rotatable targets

• The ITO and ZnO:Al reactive sputter processes of an 1.7 m tube target are reported.
• The ITO and the ZnO:Al processes require unique feedback controls.
• The ZnO:Al process can be controlled globally by power supply parameters.
• The ITO process requires also an emission line or a partial pressure for control.
• The film property dependence on the global working-point parameter is discussed.

The most commonly sputtered transparent conductive oxide (TCO) materials are aluminum doped zinc oxide (ZnO:Al) and indium tin oxide (ITO). The deposition of these TCO materials is complex as it involves optimizing conductivity, transparency, and thickness over a large substrate area. Although compound ceramic sputter targets are the standard in the Solar and Display industries, exploring reactive sputtering from metallic targets is interesting in that it may substantially reduce the target cost. This paper compares the reactive sputter deposition of ZnO:Al and ITO from an industrial scale rotatable single magnetron (RSM) with a tube length of 1.7 m. It will be shown that both processes are very distinct and thus different control mechanisms have to be chosen in order to control the working point of the reactive process. Whereas the global working point of the reactive ZnO:Al process can be controlled by parameters of the power supply only, this is not possible for the reactive ITO process. Here, the partial pressures or optical emissions have to be controlled as well. Suitable tools for the basic characterization of the reactive processes are the well-known hysteresis and voltage–current characteristics at different reactive gas flows. The properties of the deposited thin films will be linked to the chosen control parameters.