Spatial and temporal investigation of high power pulsed magnetron discharges by optical 2D-imaging

Optical 2D-imaging in combination with Abel inversion was used to study the spatial and temporal evolution of the plasma-induced emission of HIPIMS discharges. A titanium target, as well as an aluminium-doped zinc target was sputtered in an argon atmosphere of pressures 0.53 Pa and 1.33 Pa and an average power of 650 W and 400 W, respectively. The discharge was observed optically employing various wavelength filters to investigate the development of selected species, namely argon and titanium neutrals, as well as argon and zinc neutrals and ions.The argon neutral emission did not only differ substantially from the DC case but also underwent a significant development during the pulse ‘on’-time, showing a structure similar to an ion acoustic wave travelling away from the target, as well as rarefaction of the working gas while sputtering with high discharge peak currents. In addition, the intensity profile of argon and zinc ions revealed an increased width in front of the target which is then reflected by a wider sputter distribution of the target material. Indeed, it was found that the width of the metal neutral emission increased with increasing discharge current. Their emission revealed two distinct maxima and the loss of intensity in between these maxima could be explained by an increased ionisation of the sputtered metal flux.