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

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 mu s and peak powers up to 6 kW are measured by energy-resolved ion mass spectrometry with a temporal resolution of 2 mu s. 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 mu s after ignition in the magnetic trap in front of the target. They require long transport times of a few 100 mu s 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.