Three-step decay of the plasma density near the substrate in pulsed-dc magnetron sputtering discharge

Abstract

The plasma density near the substrate in a pulsed-dc magnetron sputtering source was measured using a time-resolved, wave-cutoff probe method. The decay of the plasma density during the off-phase had three periods with different decay times. In this paper, this type of decay is referred to as 'three-step decay'. The three-step decay characteristics were examined under various conditions. From deduction using a number of references and the experimental results of tests done as part of this study, the spatial reversal of the plasma potential is assumed to cause three-step decay of the plasma density. In addition, the density decay time varied with the change in the magnetic field. This result indicates the existence of the magnetic field confinement effect on the plasma near the substrate during the off-phase. The average electron density and the average substrate ion current increased with the pulse frequency and decreased with the duty cycle. This can be explained in terms of the changes in the overall plasma loss according to the pulse conditions. In particular, in a pulsed-dc magnetron sputtering source, magnetic field confinement and plasma potential reversal are thought to be two important factors changing the plasma loss.