Ralf Bandorf, Holger Gerdes, Günter Bräuer, Fraunhofer Institute for Surface Engineering and Thin Films IST, Braunschweig, Germany
Besides conventional unipolar High Power Impulse Magnetron Sputtering (HIPIMS), dual cathode operation is offering additional degrees of freedom, especially in case of reactive sputtering. For oxides improvement of process stability and coating quality is reported using dual cathode mode over single cathode operation.
This paper investigates the influence of the used pulse arrangement on the resulting voltage-current response at the target. Furthermore, the ion current and floating potential at substrate site correlated with the chosen pulse pattern is discussed. For this basic investigation of dual cathode HIPIMS titanium targets in non-reactive mode were investigated. The pulse on-time on both cathodes of the dual arrangement was kept constant at 100 µs for all investigations. The off-time between following pulses at the two cathodes was varied to study the influence on the I-V behaviour and the ionization, i.e. floating potential and ion current at the substrate. From a symmetric arrangement of 100 µs on-time pulses and an off-time of 4900 µs the off-time was modified. The off-time was cut down to 20 µs between the pulses. To compensate and keep the average frequency constant the off-time in the following bipolar sequence was in same matter extended up to 9780 µs.
Reducing the off-time between two pulses on different cathodes at fixed charging voltage leads to a significant increase of the peak current in the second pulse. Correlated with this increase the floating potential stays at the level of the first pulse nearly without decaying between the pulses. The ion current also stays nearly constant for the two subsequent pulses without an initial build up phase in the second pulse. This arrangement can be used to tailor the ionization in a bipolar HIPIMS process.