Internal current measurements in high power impulse magnetron sputtering

Abstract

The transport of charged particles in a high power impulse magnetron sputtering (HiPIMS) discharge is of considerable interest when optimizing this promising deposition technique with respect to deposition rate and control of the ion acceleration. In this study the internal current densities Jφ (azimuthal direction) and Jz (axial direction) have therefore been spatially and temporally resolved in the bulk plasma region above a cylindrical magnetron using Rogowski coils. From the measurements a phenomenological model has been constructed describing the evolution of the current density in this pulsed plasma. The core of the model is based on three different types of current systems, which characterize the operating transport mechanisms, such as current transport along and across magnetic field lines. There is a gradual change between these current systems during the initiation, build-up and steady state of a HiPIMS plasma. Furthermore, the data also show that there are spatial and temporal variations of the key transport parameter Jφ/Jz, governing the cross-B resistivity and also the energy of the charged particles. The previously reported faster-than-Bohm cross-B electron transport is verified here, but not for all locations. These results on the plasma dynamics are essential input when modeling the axial electric field, governing the back-attraction of ionized sputtered material, and might furthermore provide a link between the different resistivities reported in HiPIMS, pulsed-DC, and DC magnetron discharges.

High power impulse magnetron sputtering discharge

“…The discharge will likely ignite as a localized glow discharge at the target substrate in the vicinity of the anode ring, where the vacuum electric field is the strongest, which thus leads to a rather small current in the radial direction in the case of a circular magnetron. 265 Time resolved tunable diode-laser absorption spectroscopy measurements by Vitelaru et al 247 show that there is a very strong increase in the emission from the metastable working gas atoms (Ar m ) during phase 1, which is seen in Fig. 15.…”

“…(z) have been measured by a Rogowski coil. 265 These measurements indicate a variation of the transport parameter J e;/ =J d? over time and space.…”

Drifting localization of ionization runaway: Unraveling the nature of anomalous transport in high power impulse magnetron sputtering

“…To improve film quality for numerous applications, attempts have been made to ionize sputtered atoms, e.g., by adding a radio-frequency discharge 1 or by using very high magnetron power levels in a pulsed manner. 2 This contribution deals with the latter approach, often labeled high power impulse magnetron sputtering (HiPIMS), [3][4][5][6][7][8][9][10] among other names.…”

Effect of HPPMS Pulse-Frequency on Plasma Discharge and Deposited AlTiN Coating Properties

“…Generally, every pulse starts with an ignition phase when the negative voltage is applied to the target and the ionization of the working gas begins. The discharge will likely ignite as a localized glow discharge at the target in the vicinity of the anode ring, where the vacuum electric field is strongest [20]. This improves the ionization of the working gas species and the number of charge carriers increases.…”

“…After bulk plasma breakdown, the discharge current increases rapidly until a current maximum is reached combined with a decrease in voltage. In this current rise phase, a dense plasma torus is developed above the target race track [20] and the metal atom density builds up due to sputtering of the working gas ions. With increasing number of metal atoms, Penning ionization of the sputtered vapour atoms as well as electron impact ionization of neutral gas atoms increases [21].…”