Neutral gas simulation on the influence of rotating spokes on gas rarefaction in high‐power impulse magnetron sputtering

Abstract

High‐power impulse magnetron sputtering (HiPIMS) relies on electrical power deposition constricted to very short time intervals for the generation of intense plasmas. Typically, this leads to a substantial “background gas” rarefaction immanent to the harsh discharge conditions. Experimental observations, in addition, suggest the presence of localized ionization zones rotating in an azimuthal direction, with typical angular frequencies of ωsp ≥ 100 kHz, for example, observed for discharges using small laboratory targets. To understand the gas dynamics within these discharges, a three‐dimensional kinetic neutral particle model, building on the direct simulation Monte Carlo (DSMC) method, is utilized. By considering solely neutral particles, the influence of accompanying plasma phenomena (e.g., depletion due to ionization) is neglected. For a generic discharge setup, the rarefaction and relaxation dynamics of sputtered aluminium and “background” argon is investigated. Subsequently, the implications of a localized rotating sputtering pattern onto the respective transport dynamics are considered. With sole regards to neutral particles, it is found that the presence of fast spoke‐like dynamics is of subordinate relevance due to the inherent collisional and transport time scales. These results present only approximate solutions compared to the case when plasma dynamics are comprehensively considered. The latter scenario, however, is presently inaccessible in terms of three‐dimensional kinetic simulations.