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, which are clear of droplets. In order to avoid these droplets, the source has been designed to produce pulsed plasmas generated by the anode, and to screen the substrate 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 this anode plasma. 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. Dominant C⁺ and C²⁺ lines were identified and the plasma parameters deduced from their relative intensities showed that local thermal equilibrium was reached, giving an electron temperature about 3.2 eV and an electron density around 2.5×10¹⁷ cm^-3. The study was extended to lower currents of 140, 92 and 65 A. The temperature and the density monotonically decreased down to about 2 eV and 1.5×10¹⁵ cm^-3.