Time-resolved triple probe investigations of a pulsed magnetron discharge

Abstract

Time-resolved measurements of the electron temperature Te and density ne at the centerline of a bipolar pulsed dc magnetron argon discharge were obtained using a triple probe. Two electron temperature spikes at the pulse transients were observed and are interpreted as being due to the presence of energetic electrons generated during these periods. During the off time the observed rapid decay of Te and gradual decay of ne are shown to be a consequence of enhanced plasma retention due to the magnetized electrons. The rapid rise in ne during the on time was observed to reach a maximum, coinciding with a minimum in Te (with Te decaying rapidly), probably due to enhanced ionization by the energetic electrons. Throughout the rest of the pulse period Te increased slightly whereas ne decreased due to global collisional heating of electrons with an additional energetic electron group formed during the on time. The results also show that the electron temperature and plasma density increase with decreasing duty cycle. The plasma density increased linearly with the total energy input per pulse E and increases with pressure. The electron temperature decreases towards the higher pressures and was found to be approximately independent of E. The calculated ion power flux density to a floating substrate (averaged over one pulse cycle and being proportional to the ion-to-atom arrival ratio) was found to be higher by a factor between 2 and 4 than during dc at the same discharge conditions. The power flux was also found to increase linearly with time-averaged power with the steepest rise at the lowest duty cycle. Decreasing the duty cycle and increasing the time-averaged power will lead to the rise in the ion-to-atom arrival ratio and generally improve the quality of the deposited thin films. Finally, these results show the triple probe to be a reliable and efficient method to measure the temporal evolution of the plasma parameters in the pulsed magnetron.