Ion flux characteristics and efficiency of the deposition processes in high power impulse magnetron sputtering of zirconium

Abstract

High power impulse magnetron sputtering of zirconium was investigated at the average target power density of up to 2.22 kW cm−2 in a pulse. The depositions were performed using a strongly unbalanced magnetron with a planar zirconium target of 100 mm diameter at the argon pressure of 1 Pa. The repetition frequency was 500 Hz at duty cycles ranging from 4% to 10%. Time-averaged mass spectroscopy was carried out at the substrate positions of 100 and 200 mm from the target. The increase in the average target power density from 0.97 kW cm−2 to 2.22 kW cm−2 in shortened voltage pulses (from 200 to 80 μs) at an average target power density of 100 W cm−2 in a period led to high fractions (21%–32%) of doubly charged zirconium ions in total ion fluxes onto the substrate located 100 mm from the target. However, the respective fractions of singly charged zirconium ions decreased from 23% to 3%. It was observed that ion energy distributions were extended to high energies (up to 100 eV relative to the ground potential) under these conditions. The increased target power densities during the shortened voltage pulses resulted in a reduced deposition rate of films from 590 to 440 nm/min and in a weakly decreasing ionized fraction (from 55% to 49%) of the sputtered zirconium atoms in the flux onto the substrate. The doubly charged zirconium ions became strongly predominant (up to 63%) in the total ion flux onto the substrate at the distance of 200 mm from the target. Model calculations were carried out to explain the complicated deposition processes.