A time-dependent plasma discharge model has been developed for the ionization region in a high-power impulse magnetron sputtering (HiPIMS) discharge. It provides a flexible modeling tool to explore, e.g., the temporal variations of the ionized fractions of the working gas and the sputtered vapor, the electron density and temperature, and the gas rarefaction and refill processes. A separation is made between aspects that can be followed with a certain precision, based on known data, such as excitation rates, sputtering and secondary emission yield, and aspects that need to be treated as uncertain and defined by assumptions. The input parameters in the model can be changed to fit different specific applications. Examples of such changes are the gas and target material, the electric pulse forms of current and voltage, and the device geometry. A basic version, ionization region model I, using a thermal electron population, singly charged ions, and ion losses by isotropic diffusion is described here. It is fitted to the experimental data from a HiPIMS discharge in argon operated with 100 µs long pulses and a 15 cm diameter aluminum target. Already this basic version gives a close fit to the experimentally observed current waveform, and values of electron density n e , the electron temperature T e , the degree of gas rarefaction, and the degree of ionization of the sputtered metal that are consistent with experimental data. We take some selected examples to illustrate how the model can be used to throw light on the internal workings of these discharges: the effect of varying power efficiency, the gas rarefaction and refill during a HiPIMS pulse, and the mechanisms determining the electron temperature.

In this paper we present a study of how the magnetic field of a circular planar magnetron is affected when it is exposed to a pulsed high current discharge. Spatially resolved magnetic field measurements are presented and the magnetic disturbance is quantified for different process parameters. The magnetic field is severely deformed by the discharge and we record changes of several millitesla, depending on the spatial location of the measurement. The shape of the deformation reveals the presence of azimuthally drifting electrons close to the target surface. Time resolved measurements show a transition between two types of magnetic perturbations. There is an early stage that is in phase with the axial discharge current and a late stage that is not in phase with the discharge current. The later part of the magnetic field deformation is seen as a travelling magnetic wave. We explain the magnetic perturbations by a combination of E × B drifting electrons and currents driven by plasma pressure gradients and the shape of the magnetic field. A plasma pressure wave is also recorded by a single tip Langmuir probe and the velocity (∼10 3 m s −1 ) of the expanding plasma agrees well with the observed velocity of the magnetic wave. We note that the axial (discharge) current density is much too high compared to the azimuthal current density to be explained by classical collision terms, and an anomalous charge transport mechanism is required.

A plasma discharge model has been developed for the bulk plasma (also called the extended presheath) in sputtering magnetrons. It can be used both for high power impulse magnetron sputtering (HIPIMS) and conventional dc sputtering magnetrons. Demonstration calculations are made for the parameters of the HIPIMS sputtering magnetron at Linköping University (LiU), and also bench-marked against results in the literature on dc magnetrons.New insight is obtained regarding the structure and time development of the currents, the electric fields, and the potential profiles. The transverse resistivity η ⊥ has been identified as having fundamental importance both for the potentials profiles and for the motion of ionized target material through the bulk plasma. New findings are that in the HIPIMS mode, as a consequence of a high value of η ⊥ , (1) there can be an electric field reversal that in our case extends 0.01-0.04 m from the target, (2) the electric field in the bulk plasma is typically an order of magnitude weaker than in dc magnetrons, (3) in the region of electric field reversal the azimuthal current is diamagnetic in nature, i.e., mainly driven by the electron pressure gradient, and actually somewhat reduced by the electron Hall current which here has a reversed direction, and (4) the azimuthal current above the racetrack can, through resistive friction, significantly influence the motion of the ionized fraction of the sputtered material and deflect it sideways, away from the target and towards the walls of the magnetron.

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The bifurcation structure of periodically driven current oscillations in the central chamber of a magnetized triple plasma device is investigated experimentally. The target chamber of the triple plasma device is positively biased with respect to the source chamber and the bias voltage mainly drops in a strong double layer formed in the central chamber. At the low potential side of the double layer, a variable negative potential forms that gives rise to a region of negative resistance in the static current-voltage characteristic of the device. In this regime, if a sufficiently high inductance is added to the external circuit, strong nonlinear low-frequency oscillations both in the plasma current and the voltage drop over the plasma occur. These oscillations are interpreted as the periodically repeated exchange between magnetic energy and particle motion in the double layer. The dynamics of the current circuit is described by a van der Pol-type equation where the nonlinearity is given by the derivative of the current-voltage characteristic of the plasma. An additional periodic driver signal, added to the bias voltage, gives rise to a considerably enriched dynamical behaviour as predicted by the theory of driven nonlinear oscillators, including frequency entrainment, quasiperiodicity, periodic pulling and period doubling bifurcations. The experimental observations are well explained by means of the known bifurcation structure of the the periodically driven van der Pol oscillator model.