Origin of the energetic ions at the substrate generated during high power pulsed magnetron sputtering of titanium

Abstract

Abstract. High power impulse magnetron sputtering (HiPIMS) plasmas generate energetic metal ions at the substrate as a major difference to conventional direct current magnetron sputtering (dcMS). The origin of these very energetic ions in HiPIMS is still an open issue, which is unraveled by using two fast diagnostics: time resolved mass spectrometry with a temporal resolution of 2 µs and phase resolved optical emission spectroscopy with a temporal resolution of 1 µs. A power scan from dcMS-like to HiPIMS plasmas was performed, with a 2-inch magnetron and a titanium target as sputter source and argon as working gas. Clear differences in the transport as well in the energetic properties of Ar + , Ar 2+ , Ti + and Ti 2+ were observed. For discharges with highest peak power densities a high energetic group of Ti + and Ti 2+ could be identified with energies of approximately 25 eV and of 50 eV, respectively. A cold group of ions is always present. It is found that hot ions are observed only, when the plasma enters the spokes regime, which can be monitored by oscillations in the IV-characteristics in the MHz range that are picked up by the used VI-probes. These oscillations are correlated with the spokes phenomenon and are explained as an amplification of the Hall current inside the spokes as hot ionization zones. To explain the presence of energetic ions, we propose a double layer (DL) confining the hot plasma inside a spoke: if an atom becomes ionized inside the spokes region it is accelerated because of the DL to higher energies whereas its energy remains unchanged if it is ionized outside. In applying this DL model to our measurements the observed phenomena as well as several measurements from other groups can be explained. Only if spokes and a double layer are present the confined particles can gain enough energy to leave the magnetic trap. We conclude from our findings that the spoke phenomenon represents the essence of HiPIMS plasmas, explaining their good performance for material synthesis applications. ‡

A comparative study of direct current magnetron sputtering and high power impulse magnetron sputtering processes for CNx thin film growth with different inert gases

“…This is commonly observed when DCMS and HiPIMS discharges are compared [12,31,32]. The origin of high energetic ions in HiPIMS processes is a matter of discussion in literature [33]. However, the here presented results are in agreement with the study performed by Hecimovic et al [28], attributing the high energetic ions to increased peak target currents.…”

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

“…At the moment of peak current, the maximum number of metal ions with the highest possible ion energies is achieved [18,24,25]. Compared to other investigations of ion distributions in Argon HPPMS-plasma with Ti and Al, where current and power densities were similar to those in this study, it can be assumed that the plasma at all selected pulse-frequencies consists of single-and multiple-charged Ti and Al ions [24,26]. After the maximum peak current is achieved, the gasrarefaction generally becomes dominating and the current decreases as the number of sputtering ions decreases due to lower degree of ionization.…”

“…Apart from this, no overshoots after the pulse-off were generated. More details to plasma instabilities during HPPMS deposition are discussed by, for example, Sarakinos et al [13], Maszl et al [26], or Breilmann et al [27]. Subsequent to this instable phase, the discharge at a pulse-frequency of 200-500 Hz passes into a plateau phase where self-sputtering processes sustain the discharge for a few s. This constant current density (plateau phase) occurs when a significant fraction of ions with high potential energy generates fast secondary electrons which can sustain the impact ionization [17].…”

Benefits of the controlled reactive high-power impulse magnetron sputtering of stoichiometric ZrO2 films

“…which are driven by energetic drifting electrons in front of the sputtered target, can contribute to this effect [51][52][53]. However, the main contribution is probably given by a backscattering In Table 3, we give the backscattering probability of atoms, B, and the mean energy of backscattered atoms at the target surface, E b , calculated for Ar, Zr and O atoms backscattered from Zr and ZrO 2 targets after their bombardment by the respective Ar + , Zr + and O + ions.…”