Plasma dynamics as a key to successful upscaling of pulsed plasma processes

In order to produce homogeneous hard coatings, e.g. titanium nitride, using the pulsed direct current plasma-assisted chemical vapour deposition technique, it is necessary to achieve a temporally and a spatially uniform plasma. In unipolar operation mode of the power supply, the spreading of the discharge is too slow under certain loading conditions. While the presence of this phenomenon is revealed by an oscillographic observation of the discharge current, a high-speed video camera is applied to investigate it in more detail. The problem can be remedied in a variety of way, e.g. by inserting additional anodes or by superimposing short high voltage pulses onto the normal discharge pulse. An attractive option supported by most commercially available power supplies is the use of additional pulses of reversed (positive) polarity, i.e. bipolar mode. Therefore, we investigated the effect of additional positive pulses on the dynamics of the discharge (bipolar operation mode). Our experiments show a clear improvement of the ignition and spreading behaviour of the discharge by the use of bipolar voltage pulses.