Control of Spokes in Magnetron Discharges*

Magnetron Sputtering is a Plasma Vapour Deposition (PVD) process widely used in industry and scientific communities. HiPIMS produces plasma pulses of very high density of the order of 10¹⁹ m⁻³ without overheating the target. The plasma shows localised zones of high brightness rotating in the E x B direction when observed with an ICCD camera with exposure times below 1μs. These local ionization zones, also called 'spokes' are assumed to play a role in the transport of particles and energy away from the target. This anomalous transport results in an enhanced deposition rate by counteracting the return effect. The primary objective of this project is to control spoke frequency in HiPIMS in-order to study its influence on the IEDF and metal ion flux from the target. DCMS was chosen for the development of spoke control as an initial test object since the spokes in DC regime are more uniform compared to HiPIMS. Amplified rectangular signals are applied to multiple probes to draw electron current from the plasma at the highest gradients in the E x B direction. The responses of the spoke frequency and intensity to the applied signal are measured with a flat probe. The metal ion flux from the target surface is measured time and energy resolved with a mass spectrometer.