Spectroscopic investigation of vacuum arc anode plasmas for thin film deposition

A vacuum arc plasma source has been designed and tested for fabrication of thin films clear of droplets. In order to avoid these droplets, the source has been optimized to produce pulsed plasmas generated by the anode, and to screen the anodic region against the plasma streaming away from the cathode spot. We present here spectroscopic measurements and analyses carried out in order to characterize the electron population of such anode plasmas. The vacuum arc was first operated with a carbon anode of diameter 0.5 mm and an arc current of 192 A. The visible and near infrared spectra were recorded with various resolutions, in direct view of the anode spot, with an intensified CCD camera. Several dominant lines were identified as C⁺ and C²⁺ Lines. The relative intensities corresponding to transitions between meaningful multiplets show that the local thermal equilibrium is reached, and this allows a straightforward determination of the electron temperature and of the electron density. The values are about 3.2 eV and 2.5 10¹⁷ cm^-3. The study has been extended to lower currents of 140, 92 and 65 A. The temperature and the density are regularly decreasing down to about 2 eV and 1.5 10¹⁵ cm^-3