Dynamic of the growth flux at the substrate during high-power pulsed magnetron sputtering (HiPIMS) of titanium

Abstract

The temporal distribution of the incident fluxes of argon and titanium ions on the substrate during an argon HiPIMS pulse to sputter titanium with pulse lengths between 50 to 400 µs and peak powers up to 6 kW are measured by energy-resolved ion mass spectrometry with a temporal resolution of 2 µs. The data are correlated with time-resolved growth rates and with phase-resolved optical emission spectra. Four ion contributions impinging on the substrate at different times and energies are identified: (i) an initial argon ion burst after ignition, (ii) a titanium and argon ion flux in phase with the plasma current due to ionized neutrals in front of the target, (iii) a small energetic burst of ions after plasma shut off, and (iv) cold ions impinging on the substrate in the late afterglow showing a pronounced maximum in current. The last contribution originates from ions generated during the plasma current maximum at 50 µs after ignition in the magnetic trap in front of the target. They require long transport times of a few 100 µs to reach the substrate. All energy distributions can be very well fitted with a shifted Maxwellian indicating an efficient thermalization of the energetic species on their travel from target to substrate. The energy of titanium is higher than that of argon, because they originate from energetic neutrals of the sputter process. The determination of the temporal sequence of species, energies and fluxes in HiPIMS may lead to design rules for the targeted generation of these discharges and for synchronized biasing concepts to further improve the capabilities of high-power impulse magnetron sputtering (HiPIMS) processes.

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

“…All ions see this identical potential difference and are accelerated towards the chamber walls and the substrate. This effect has be discussed in detail in [26].…”

“…All measured signals are proportional to the mass/charge ratio and the energy/charge ratio, respectively. A more detailed description of the setup is given elsewhere [26]. Simultaneously with the EQP measurements, the optical emission of the plasma is monitored by an intensified CCD camera (ICCD).…”

“…The ions in the afterglow are slightly more energetic (V). These are ions being de-trapped from the racetrack [26].…”

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

“…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].…”

Control of High Power Pulsed Magnetron Discharge by Monitoring the Current Voltage Characteristics

“…The number of spokes decreases with increasing current and increases with pressure in the system [3][4][5][6]; (iii) the appearance of spokes coincides with the observation of an energetic group of ions of typically few tens of eV in the growth flux on the substrate. The hypothesis holds that their creation occurs inside the spokes, which are believed to be regions of higher electrical potential [7][8][9]; (iv) the confinement in HiPIMS plasmas is much smaller compared to conventional dc-magnetron plasmas as can be judged from the ratio between the Hall current along the plasma torus and the discharge current towards the target. This effect is most likely associated to internal electrical fields leading to anomalous cross B-field transport [10]; (v) the spoke pattern undergoes a complex transition from a homogeneous plasma torus at low currents, to a spoke regime at intermediate currents, to a homogeneous plasma torus again at very high currents [11].…”