Optimizing the deposition rate and ionized flux fraction of a high power impulse magnetron sputtering discharge

High power impulse magnetron sputtering (HiPIMS) is a physical vapor deposition technique with a high probability of target species ionization in the ionization region. Some of these ions escape the ionization region towards a substrate, where they supply additional energy and momentum to a growing film. However, most of the ions of the target species are back-attracted onto the target by an electric field in the ionization region. The loss in deposition rate in HiPIMS discharges compared to direct current magnetron sputtering discharges, at equal average power, can largely be explained by this effect. As only ions respond to the electric field, the ionization rate is usually closely linked to the loss in deposition rate. Here, we present an optimization scheme to maximize the deposition rate for a certain ionized flux fraction to the substrate. The scheme uses externally adjustable parameters, peak discharge current, pulse length, magnetic field strength and working gas pressure to manipulate internal discharge parameters, the probabilities of target species ionization and target ion back-attraction. The benefit of the optimization scheme can be quantified by the energy cost per target ion on the substrate, which for a well optimized discharge can be less than half of the cost for a non-optimized discharge.