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The objective of this paper is to study the effect of magnetic field strength on spoke behaviour in a high power impulse magnetron sputtering discharge. In three magnetic field configurations, a broad range of experimental conditions was investigated by high-speed camera imaging. The dual image feature of the employed camera enabled us to determine the shape and spoke mode number, as well as the velocity of the spokes. Five distinct spoke shapes were detected. For each magnetic field, a map was created relating the occurrence of the spoke shape with the discharge conditions. Similarly, the spoke mode number, as well as the spoke velocity, was found to be strongly dependent on the discharge conditions. Based on the optical emission results, it was proposed that the trailing edge of the triangular spoke is related to the production of secondary electrons created by argon ions on the spoke edges, while in the case of a round spoke shape, the secondary electrons are mainly created by multiple charged titanium ions in the centre of the spoke.

A detailed experimental study of high power impulse magnetron sputtering processes is performed by time-resolved imaging of the ground state sputtered particles. New details related to the behavior of both neutral and singly ionized atoms are shown, as a result of separate treatment of the plasma-on and plasma-off time phases. In Paper I, the ion/neutral density redistribution in the ionization zone during sputtering is analyzed; the role of main discharge parameters, such as pulse repetition rate, pulse energy, etc., is discussed systematically. The time-resolved evolution of the ground state levels population for both sputtered neutrals and ions is also considered. In addition, propagation of the sputtered particles is analyzed using 2D density gradient diagrams calculated based on the measured particle density distributions. The results of this work are compared, when possible, to the data obtained previously [Britun et al., J. Appl. Phys. 117, 163302 (2015)].

This paper is focused on experimental studies of a high power pulsed magnetron discharge stabilized by low current pre-ionization. Time resolved studies were performed for a Cu target by optical emission spectroscopy and electrical measurements for different pressures of Ar buffer gas. Due to the elimination of the statistical delay time and a fast discharge current rise the quasi-stationary state was reached in 6 µs. The quasi-stationary state is characterized by an extremely high and pressure independent discharge current density of ∼10 A cm −2 and stable Cu + and Cu ++ emissions. Such fast discharge dynamics permits the magnetron cathode current to be driven with a pulse of duration of the order of a few µs, significantly shorter than in other devices. During this short time, the plasma does not have time to undergo the transition from the glow to the arc discharge even at the extremely high cathode loads met in our case. Different stages of the fast discharge development are identified and the composition of the magnetized plasma as a function of the pressure is discussed in detail.