Dynamics of pulsed d.c. discharges used for PACVD – effect of additional high voltage pulses

Plasma-assisted chemical vapor deposition (PACVD) of titanium nitride is mostly performed with pulsed d.c. glow discharges using titanium tetrachloride as a component of the feed stock gas. Recent investigations of the dynamics of such discharges have shown that, in large reactors under certain loading conditions, the spreading of the discharge is slow, reaching some parts of the reactor with substantial delay. The result is a non-uniform plasma power density in front of the substrates as well as a spatially varying exposure time of the surface to the plasma. The present study investigates the possibility of improving the ignition and spreading behavior of the discharge by the use of additional synchronized short high voltage pulses. The position of the high voltage pulse was varied between 2 μs before and 15 μs after the leading edge of the conventional pulse. Peak voltages up to −1600 V with a duration of 440 ns were used. It turned out that the superposition of short high voltage pulses with a peak voltage of −1300 V at the beginning of the conventional pulses (independent of the exact position) enabled an immediate ignition and spreading of the discharge across the reactor, ensuring time-independent and uniform discharge conditions.