Reactive sputtering of dielectric layers on large scale substrates using an AC twin magnetron cathode

Abstract

The source of instabilities in the reactive sputter process of SiO 2 is discussed. It is argued that arcing is mainly initiated by: (i) disappearance of the anode caused by covering with a dielectric layer and (ii) by electrical breakdown of the insulating layer growing on the sputtering cathode. The ways to avoid these effects are considered. New equipment for reactive sputtering of highly insulating SiO 2 layers with unusual process stability was achieved combining a twin cathode arrangement with a mid frequency power supply and a special surrounding. The long term stability was proved for 300 h and measured arc rate was lower than 1 arc/2 h. During this time transparent SiO 2 layers were produced on glass substrates moving in front of the cathode. The obtained film thicknesses were greater than 50 nm at a substrate speed of lm/min. This value is nearly 10 times higher than that obtained for conventional sputter arrangement. The discussed arrangement was successfully applied for large area coating with cathode lengths of up to 2650 mm in mass production coaters. The index of refraction of the produced SiO 2 layers could be controlled by the oxygen amount in the sputter chamber in the range from 1.45 to 1.6. Therefore it was possible to apply these layers as Na tight barriers for the industrial mass production of LCD flat panels. The layers with the lowest index of refraction are used for the production of antireflective coatings. Such machines are realized for large scale architectural glass and foil substrates. The values of flim thicknesses for Si 3N 4, Al 2O 3 and Ta 2O 5 measured at transport speed of lm/min were 40 nm, 35 nm and 100 nm, respectively.