Characterisation studies of the pulsed dual cathode magnetron sputtering process for oxide films

Pulsed magnetron sputtering has become the leading industrial production process for large area thin film deposition due to its versatility, low environmental impact and ability to provide uniform coatings across large substrate areas. Such applications commonly employ oxides, including silica (SiO2), alumina (Al2O3) and titania (TiO2). Although all of these materials can be produced by reactive DC-magnetron sputtering, until recently the deposition process was highly problematic. The industrial exploitation of the pulsing process is impeded by the fact that, during long-term deposition runs, eventually all surfaces will be covered with the insulator. Once the chamber and anode are covered with insulating material, there can be no average (DC) current flowing to the power supply leads. Moreover, if the anode/chamber becomes covered with the dielectric film it will cease to operate as an effective ground (anode). A more viable approach is to use two magnetrons in a dual bipolar arrangement (dual cathode). In this arrangement each magnetron acts alternatively as an anode and a cathode. The broad aim of this study is to investigate the inter-relationship between 'global' parameters, pulse parameters, plasma parameters and in particular, film properties in relation to the dual cathode system. The spatial distribution of measured parameters will be considered. This paper describes the production of Al2O3 films by dual cathode unbalanced reactive magnetron sputtering, in particular, the effects of spatial distribution and pulse frequency on coating properties. In general, it was observed that, once hard arcs have been removed, all coating structures, coating surfaces and hardness show little variation. However, more variation was observed in critical loads during scratch adhesion testing for coatings deposited at different pulse frequencies. (C) 2001 Elsevier Science B.V. All rights reserved.