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.