Influence of the unipolar or bipolar pulse mode in reactive magnetron sputtering on the deposition and properties of optical films

Recently, FEP developed a new family of flange mounted magnetron sources together with pulsed powering and process control. This system can be applied either as single magnetrons powered in unipolar pulse mode, e. g. with a pulsed dc voltage, or can be applied as a pair of magnetrons powered in bipolar mode, e. g. with an alternating pulsed voltage between both magnetrons that act alternately as the anode and cathode of the discharge. The pulse unit can be switched between the two pulse modes. This allows to investigate directly the influence of the pulse mode and pulse parameters using the same magnetron configuration and the same type of pulse power supply. Experimental results of the reactive deposition of SiO2, Si3N4 and TiO2 demonstrate the specifics of both process modes. There are effects of the pulse mode observed for all this materials that are independent on the target material. Furthermore we observed effects of the duty cycle, i. e. the ratio of the pulse-on-time to the cycle time of the rectangular current or voltage pulses. The deposition rate and thermal substrate load exhibit a pronounced dependence on the pulse parameters. The values of film properties like refractive index and internal stress will be discussed for the materials SiO2, Si3N4 and TiO2. The flexibility of the pulse sputtering system with free choice of pulse mode allows the universal use either for basic research or in production. The investigations made with this system demonstrate the new possibility to use the pulse parameters to influence film properties.