Time evolution of electron energy distribution function and plasma parameters in pulsed and unbalanced magnetron argon discharge

The temporal behavior of the electron energy distribution function and plasma parameters in the vicinity of the substrate have been investigated in detail by performing time-resolved probe measurements in a pulsed and unbalanced magnetron argon discharge. A $20-kHz$ midfrequency unipolar dc pulse with an on-time average power of $160W$ and a duty cycle of 50% was applied to the metallic cathode target. It was found that the high-energy electrons with energies higher than the sheath potential energy are generated within a few microseconds after the dc pulse is turned on and the electron energy distribution functions during the pulse-on period show a bi-Maxwellian distribution with the high-energy electron group. In the afterglow after the dc pulse is turned off, the initial fast decay of the high-energy electrons and the subsequent diffusive slower decay of the low-energy electrons were observed. This temporal behavior of the electron energy distribution function reflected two-fold decay characteristics of electron density and electron temperature when approximated by a biexponential function with two characteristic decay times and an initial fast decay time of less than a few microseconds and a subsequent slower decay time of few tens of microseconds were observed. The temporal behavior of the other plasma parameters were presented and these results were explained in view of electron heating by deeply penetrating the high-voltage cathode sheath and electron transport.