Plasma dynamics of HiPIMS discharges investigated by high-speed camera*

Plasma in magnetron sputtering discharges is concentrated in azimuthally dense regions called spokes. These structures form periodic or quasi-periodic patterns, typically exhibit triangular shape and rotate with velocities of several km/s. Such self-organization was observed in classical DC magnetron sputtering [1], high power impulse magnetron sputtering (HiPIMS) [2] and RF magnetron sputtering [3] discharges.

In this work, we investigated the dynamics of HiPIMS plasma using a high-speed camera. The dynamics was analyzed for a range of Ar pressures (0.25-2 Pa) and peak currents (10-400 A). Experiments demonstrate that plasma self-organization evolves through several stages with increasing discharge current. From the initiation of the pulse to 25-50 A, plasma forms spoke patterns comparable to those in DCMS  ­– ­spokes rotate with velocities up to 15 km/s in -E×B direction. This stage is followed by a plasma reorganization with the formation of irregular patterns and complex spoke propagation. After this stage a regular spoke patterns with a well-defined triangular shape form ­– spokes rotate in E×B direction with velocities in 6-9 km/s range. If the current is increased further, spokes become larger, and at the highest currents (close to 400 A) plasma becomes azimuthally homogenous.