Spatially-resolved optical emission from a bi-polar pulsed DC magnetron discharge

Using optical emission spectroscopy we have observed the origins of short bursts of visible light radiation from the bulk plasma in a pulsed magnetron discharge. These bursts occur during the fast transients in the driving bi-polar voltage waveform. In an extension to the work reported in Swindells et al. [I. Swindells, P.J. Kelly and J.W. Bradley, New J. Phys. 8 No 4 (2006) 47], we have made new spatially-resolved measurements of the light intensity from transitions in Ar(I) at 750.4 nm and 811.5 nm and from Ti(I) at 398.2 nm. The results indicate that energetic electrons (> 13.5 eV) are generated both at the target during off-on phase of the pulse and at a grounded substrate during the on-off phase and penetrate deep into the plasma. The presence of fast electrons during the on-off transition of the bi-polar pulse is correlated directly with positive exertions in the plasma potential relative to the grounded substrate, while the energetic electrons observed during the off-on voltage swings are believed to those accelerated by the advancing cathode sheath.