Magnetron sputtering is commonly used vapor deposition technique for the preparation of thin films and coatings. Until recently it was believed that magnetron plasma is homogeneously distributed in a ring-shaped region above the cathode. Investigations by ICCD cameras and other time-resolved techniques changed this view. Namely, plasma is concentrated in dense regions that are called "ionization zones" or "spokes". Ionization zones were first observed in pulsed discharges (i.e., HiPIMS) [1] and later in continuously run discharges (i.e., DCMS) [2]. They are usually organized in semi-periodic patterns and exhibit an arrowhead-like shape. In general, ionization zones in DCMS have a longer azimuthal length, whereas in HiPIMS they are more numerous and azimuthally shorter. Dynamics of zones strongly depends on the discharge conditions. In a low-current DCMS discharges zones move in the -E×B direction, while in a high-current DCMS or HiPIMS discharges they move in the E×B direction [3].In the talk we will present our understanding of the ionization zone phenomenon. The formation, sustainability, organization and dynamics of ionization zones will be reviewed [4]. Measurements of the plasma potential by emissive probe show highly non-uniform potential distribution with strong electric fields at the edge of the ionization zone. Such fields strongly affect motion and energy of charged particles. A self-sustaining feedback loop exists between the potential structure, electron heating and ionization processes as electrons drift in the magnetic trap of the magnetron. We suggest that a moving double layer plays a crucial role in the energization of electrons and is in large part responsible for sustaining the discharge [5]. (References: [1] A. Anders
et al.,
J. Appl. Phys. 111 (2012) 053304; [2] M. Panjan
et al.,
Plasma Sources Sci. Technol. 24 (2015) 065010; [3] Y. Yang
et al.,
Appl. Phys. Lett. 105 (2014) 254101; [4] M. Panjan
et al.,
Plasma Sources Sci. Technol. 23 (2014) 025007; [5] M. Panjan and A. Anders,
J. Appl. Phys. accepted for publication)
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