*Jon Tomas Gudmundsson^1,2, Hamidreza Hajihoseini^1,3, Martin Rudolph⁴. Tiberiu M. Minea³, Michael A. Raadu², Nils Brenning^2,3,5, Daniel Lundin^3,5
1University of Iceland, Reykjavik, Iceland; ²KTH Royal Institute of Technology, Stockholm, Sweden; ³Université Paris Saclay, Orsay, France; ⁴Leibniz Institute of Surface Engineering (IOM), Leipzig, Germany; ⁵Linköping University, Linköping, Sweden
The main drawback of the high power impulse magnetron sputtering (HiPIMS) technique is the low deposition rate. The deposition rate in HiPIMS operation is typically in the range of 30-85 % of the dcMS rates, depending on target material. This is mainly due to the back-attraction of ions of the sputtered species to the cathode target, while some other mechanisms have also been suggested as well. This includes the nonlinear sputter yield effect, guiding effect of the magnetic field, the increased density of the deposited film, the effect of different ion species on the sputter yield and that the sputtered material is being transported radially outward in the vicinity of the cathode. We discuss how the magnetic field strength |B| and geometry (degree of balancing) influences the deposition rate and ionized flux fraction F_flux in dcMS and HiPIMS operation both axially and radially. We then relate the deposition rate and the ionized flux fraction to the internal parameters that describe ionization probability α_t and the back attraction probability of the sputtered species β_t. We conclude that the reduction in the (axial) deposition rate in HiPIMS compared to dcMS is not due to an increase in sideways material transport in HiPIMS. We discuss the trade off between a high ionized flux fraction of the sputtered species and a high deposition rate referred to as the HiPIMS compromise, and other approaches to optimize the sputter process such as shortening the pulse length.