The effects of a positive voltage pulse following a negative voltage pulse in the high-power impulse magnetron sputtering (HiPIMS) pulse are becoming very popular and almost every HiPIMS power supply in the market is equipped with BiPolar power supplies.
Prof. David Ruzic is the first one to propose the idea of using a "kick-pulse" which he means a positive voltage pulse following the conventional negative HiPIMS pulse, which is termed as “Bipolar HiPIMS pulsing”.
We all know that HiPIMS coating technology generates large amounts of depositing ions in addition to the sputter gas ions, widened the options for “self-sputtering” resulting in even better film properties such as increased density and enhanced mechanical properties.
The detailed atomistic reason for the improvement of the functional and physical properties of the HiPIMS coatings are still under diagnostics as they are more complex owing to the combination of several factors, including a matching of mass of bombarding and surface species, a higher intrinsic ion energy of bombarding particle and a reduction in sputter gas incorporation in the growing film thanks to the significant increase in the metal-ion-flux in relation to the noble-gas-ion flux in the plasma.
Prof. David Ruzic and his group, followed by Dr. Ivan Fernandez applied "kick-pulses" positively biased voltage pulses to the target immediately after the negative HiPIMS voltage pulses to raise the plasma potential and subsequently accelerate ions towards the depositing layers.
The improved coating properties are caused due to the high ion-flux bombarding the growing layers by the positive pulse as the ions near the target are “kicked” accelerated to the substrate.
Prof. David Ruzic and his group reported that the discharge ions undergo significant acceleration towards the substrate. Ivan Fernandez and his collaborators have proved through their hidden mass-energy spectrometer studies that the ions are well-thermalized not only in perpendicular to that direction but also sideways.
The above picture shows the plasma during TriPack with a Cu target in operation
(a) no discharge
(d) Modified HiPIMS with 50 V (100 μs) kick pulse.
The color of plasma is
deep blue and purple in DCMS operation
green in HiPIMS operation
and green appearing dimmer in the modified HiPIMS