Spoke behaviour in reactive HiPIMS

Plasma in high-power impulse magnetron sputtering discharge, similarly to other discharges utilising E x B field (Hall thrusters, homopolar devices), undergoes self-organisation into the ionisation zones predominantly rotating in the E x B direction, called spokes. Many studies were conducted focussing on the characterisation of their appearance, mode number, rotational velocity, merging and splitting events in different experimental conditions. Nevertheless, only very little research has been conducted in the case of reactive sputtering, where only the general spoke characteristics were evaluated. A dual-image fast camera screening was utilised to capture plasma emission on 3 '' Nb target in a reactive mixture of nitrogen and argon. Spoke characteristics were evaluated while overall pressure and supplied power was kept constant and the content of nitrogen in N-2/Ar mixture was varied. The shape, velocity and spoke mode number were significantly affected by the higher content of N-2 in the mixture. To distinguish between the effects of the modified target surface state and reactive gas present in the plasma volume on spokes experiments with compound NbN target were also performed. Surprisingly, no real differences of spoke behaviour between Nb and NbN targets were observed.

Automated summary

In high-power impulse magnetron sputtering discharge, plasma self-organizes into ionization zones rotating in the E x B direction, known as spokes. Research shows that increasing nitrogen content in the reactive mixture significantly affects the shape, velocity, and mode number of the spokes. Surprisingly, experiments with different targets showed no real differences in spoke behavior.