The plasma of a high power impulse magnetron sputtering (HiPIMS) system has been investigated using a time-of-flight (TOF) spectrometer. The target materials included high sputter yield materials (Cu, Ag), transition metals (Nb, Cr, Ti), and carbon (graphite); the sputtering gases were argon, krypton and nitrogen, and two different target thicknesses were selected to consider the role of the magnetic field strength. Measurements for selected combinations of those parameters give quantitative information on the transition from gas-dominated to metal-dominated (self-sputtering) plasma, on the fractions of ion charge states, and in the case of molecular gases, on the fraction of atomic and molecular ions.

Metal and gas ion species and their charge state distributions were measured for pulsed copper cathodic arcs in argon background gas in the presence of an axial magnetic field. It was found that changing the cathode position relative to anode and ion extraction system as well as increasing the gas pressure did not much affect the arc burning voltage and the related power dissipation. However, the burning voltage and power dissipation greatly increased as the magnetic field strength was increased. The fraction of metal ions and the mean ion charge state were reduced as the discharge length was increased. The observations can be explained by the combination of charge exchange collisions and electron impact ionization. They confirm that previously published data on characteristic material-dependent charge state distributions (e.g., Anders and Yushkov, J. Appl. Phys., Vol. 91, pp. 4824-4832, 2002) are not universal but valid for high vacuum conditions and the specifics of the applied magnetic fields.

The evolution of copper ion species and charge state distributions is measured for a long vacuum arc discharge plasma operated in the presence of a longitudinal magnetic field of several 10 mT and working gas (Ar). It was found that changing the cathode-anode distance within 20 cm as well as increasing the gas pressure did not affect the arc burning voltage and power dissipation by much. In contrast, burning voltage and power dissipation were greatly increased as the magnetic field was increased. The longer the discharge gap the greater was the fraction of gaseous ions and the lower the fraction of metal ions, while the mean ion charge state was reduced. It is argued that the results are affected by charge exchange collisions and electron impact ionization.

The self-sputtering mode in high power pulsed magnetron discharges opens the possibility of generating plasma that contains mainly singly charged metal ions of the target (cathode) material. The main idea of a self-sputtering magnetron ion source is to utilize the dense plasma to extract ions from it and thus to form a beam of accelerated, purely singly charged metal ions. Such kind of metal ion source based on a planar magnetron has been reported in our previous, recent publication. The present paper describes the special features observed for the self-sputtering mode of an "inverted" cylindrical magnetron configuration formed by two coaxial cylindrical electrodes. This geometry appears attractive for a novel ion source design and its applications.

Current fluctuations of cathodic arcs were recorded with high analog bandwidth (up to 1 GHz) and fast digital sampling (up to 5 Gsamples/sec). The power spectral density of the arc current was determined by fast Fourier transform clearly showing material dependent, non-linear features in the frequency domain. These features can be associated with the non-linear impedance of the conducting channel between cathode and anode, driven by the explosive nature of electron emission and plasma formation. The characteristic times of less than 100 ns can be associated with individual explosive processes, "ectons," and therefore represent the short-time physical cutoff for the fractal model of cathodic arcs.

A new metal ion source is presented based on sustained self-sputtering plasma in a magnetron discharge. Metals exhibiting high self-sputtering yield like Cu, Ag, Zn, and Bi can be used in a high-power impulse magnetron sputtering (HIPIMS) discharge such that the plasma almost exclusively contains singly charged metal ions of the target material. The plasma and extracted ion beam are quiescent. The ion beams consist mostly of singly charged ions with a space-charge limited current density which reached about 10 mA/cm2 at an extraction voltage of 45 kV and a first gap spacing of 12 mm.

The paper reviews the results of vacuum arc experimental investigations made collaboratively by research groups from Berkeley and Tomsk over the last two years, i.e. since the last ISDEIV in 2006. Vacuum arc plasma of various metals was produced in pulses of a few hundred microseconds duration, and the research focussed on three topics: (i) the energy distribution functions for different ion charge states, (ii) the temporal development of the ion charge state distribution, and (iii) the evolution of the mean directed ion velocities during plasma expansion. A combined quadruple mass-to-charge and energy ana-lyzer (EQP by HIDEN Ltd) and a time-of-flight spectrometer were employed. Cross-checking data by those complimen-tary techniques helped to avoid possible pitfalls in interpre-tation. It was found that the ion energy distribution func-tions in the plasma were independent of the ion charge state, which implies that the energy distribution on a substrate are not equal to due to acceleration in the substrate's sheath. In pulsed arc mode, the individual ion charge states fractions showed changes leading to a decrease of the mean charge state toward a steady-state value. This decrease can be re-duced by lower arc current, higher pulse repetition rate and reduced length of the discharge gap. It was also found that the directed ion velocity slightly decreased as the plasma expanded into vacuum.

There are divergent results in the literature on the (in)dependence of the ion velocity distribution functions on the ion charge states. Apparently, most time-of-flight methods of measurements indicate independence whereas most measurements with electrostatic analyzers state the opposite. It is shown here that this grouping is coincidental with investigations of pulsed and continuous arcs. All results can be consolidated by taking ion-neutral interaction into account, especially charge exchange collisions with the metal neutrals produced by the arc itself. The velocity distribution functions are independent of charge state when produced at cathode spots but become charge-state dependent when the plasma interacts with neutrals.