Physics of high power impulse magnetron sputtering discharges

The most striking difference between HiPIMS and other magnetron sputtering discharges, in terms of the plasma process itself, lies in the high-power discharge pulses applied and the large discharge currents generated. We therefore start this chapter on the physics of HiPIMS by exploring the current composition at the target surface and the physical and chemical mechanisms operating at different stages of the discharge pulse and afterglow, which give rise to large discharge currents. Of particular interest is how internal process features such as gas rarefaction, ionization of the sputtered species, self-sputter recycling, and working gas recycling can be influenced by (as well as influence) the choice of pulse length, repetition frequency, applied power density, magnetic field strength and topology, target material, working gas, and so on. Using our understanding of the physics behind the discharge pulse, we then turn to discussing several key aspects in non-reactive and reactive HiPIMS, which includes dealing with the much debated issues of deposition rate as well as loss and transport of charged particles. The latter topic will, by necessity, also address plasma instabilities in HiPIMS.