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M. Fink, J. Laimer, H. Störi:
"On the dynamics of unipolar and bipolar pulsed dc discharges used for plasma CVD ";
Vacuum, 71 (2003), 219 - 223.

Investigations of the development of discharges relevant for the production of titanium nitride (TiN) coatings using titanium tetrachloride (TiCl₄) as a feedstock gas have shown that under certain loading conditions the spreading of the discharge during the pulse is too slow. Recently, we have demonstrated that the ignition and spreading behaviour can be very much improved by the stuperposition of short high voltage pulses at the beginning of each conventional pulse. However, an extra high voltage power supply is needed.
In the present work we investigate another possibility to get a better performance of the ignition and spreading behaviour of the discharge, the bipolar operation of the voltage power supply. Discharge current measurements and video observations reveal for this operation mode a very much improved ignition and spreading behaviour during the negative voltage pulses for durations of the positive voltage pulses of at least 50 μs. The reason might be that at the end of the pulse-off time which follows after the more powerful positive pulse more charge carriers remain and hence, the density of charge carriers should be high enough to allow a better ignition of the discharge at the beginning of the negative pulse.

Keywords: Plasma CVD; Plasnia dynamics, Unipolar discharge; Bipolar discharge