Use of the ring gap plasmatron for high rate sputtering

Abstract

The application of ring gas plasmatron discharges for high rate sputtering using a model PPS-5 planar plasmatron sputter source is discussed. Characteristic sputter rates of the order of 0.1 g min -1 kW -1, i.e. rates similar to those of electron beam evaporators with water-cooled crucibles, are obtained. The working pressure giving the highest sputter rates is 0.5 Pa but discharge pressure levels down to about 0.07 Pa are possible. Any damage to the substrates is prevented by the underlying discharge mechanism, especially by the low energy charge carriers in the plasma and the concentration of the latter on the target. In addition, carrier impingement on the substrates can be avoided without difficulty. When using the plasmatron for sputtering, the specific energy expended is about three times lower than that expended with conventional sputtering techniques, e.g. with diode sputtering. With bias sputtering, the PPS-5 planar plasmatron sputter source (at a discharge power of 5 kW) gives a bias current of approximately 1 A even at a substrate bias voltage of only a few volts. Typical performance parameters of the high rate sputter source are a discharge voltage of 500 V, a discharge current of 10 A, a sputter rate for copper in argon of 0.7 g min -1 and, at a distance of 50 mm, a condensation rate of 25 000 Å min -1.