Electron energy distributions and plasma parameters in high-power pulsed magnetron sputtering discharges

We report on the results obtained using time-resolved Langmuir probe measurements in high-power pulsed dc magnetron sputtering discharges. Time evolutions of the electron energy distribution and the local plasma parameters were investigated at a substrate position of 100 mm from a planar target of 100 mm diameter during a high-rate deposition of copper films. The average target power density in a pulse was 500 W cm-2 at a repetition frequency of 1 kHz, a voltage pulse duration of 200 μs and an argon pressure of 1 Pa. The electron energy distributions with two energy groups and sharply truncated high-energy tails were observed during a pulse. After a fast rise in a 50 μs initial stage of the pulse, the kinetic temperature of electrons, defined using the mean electron energy, remained in the range from 10 500 to 12 200 K till the pulse termination. The temperature of weakly populated hot electrons decreased rapidly in the initial stage of the pulse approaching the kinetic temperature approximately 100 μs after a pulse initiation. High plasma densities, being in the range 1 x 1012-2 x 1012 cm-3 for 100 μs, were achieved at the substrate position with a 50 μs delay after establishing the 125 μs steady-state discharge regime with the target power density of 650-680 W cm-2 during a pulse. The plasma potential slowly increased from 0.5 to 3.5 V during the pulse and 25 μs after its termination.