On the connection between the self-sputter yield and deposition rate in high power impulse magnetron sputtering

The magnetron sputtering discharge is utilized in a wide range of industries [1]. When driven by high power unipolar pulses of low repetition frequency and low duty cycle, it is referred to as high power impulse magnetron sputtering (HiPIMS) [2]. Operation with high power pulses results in increased ionization of the sputtered species and lower deposition rate than in dc operation, when operated at the same average power. In the HiPIMS discharge the fraction of ionized sputtered material can be significant. Therefore, at least some fraction, often a significant fraction, of the ions involved in the sputter process are ions of the target material. This also implies that a large fraction of the ions of the sputtered species can be attracted back to the target and is not deposited onto the substrate to form a film or coating. Self-sputtering and the self-sputter yield are therefore expected to play a significant role in HiPIMS operation, and to have a decisive impact on the film deposition rate, at least for metal targets. We have applied the ionization region model (IRM) to model HiPIMS discharges in argon with a number of different target materials [3,4,5], to study various processes, such as working gas rarefaction and refill processes [6], the electron heating mechanisms, the ionization probability and the back-attraction of the sputtered species, and recycling mechanisms. It will be discussed how these processes depend on the mass and ionization potential of the target atom, the discharge current density, and maybe most importantly the self-sputter yield of the target material.