INFLUENCE OF AN EXTERNAL MAGNETIC-FIELD ON CATHODE SPOT MOTION AND COATING DEPOSITION USING FILTERED VACUUM-ARC EVAPORATION

Arcs were established on a Ti cathode in a filtered vacuum are deposition system in vacuum and in a low pressure (0.1-0.67 Pa) nitrogen atmosphere. External magnetic fields of up to 25 mT were applied with a radial component in the vicinity of the are cathode in order to drive the cathode spots in an azimuthal motion on the front surface of the cathode, and with an axial component parallel to the walls of the plasma ducts leading from the cathode region to the substrate in order to collimate the plasma beam. Cathode spot motion was observed by means of a television camera and VCR via a window installed at the substrate holder flange, and a mirror located in the quarter-torus. Ion current convected by the plasma beam was measured with a negatively biased probe. It was shown that the magnetic field coils located on the plasma ducts have a strong influence on cathode spot behaviour. If their field is stronger than 4 mT at the cathode, the spots move off the cathode surface, and the probability of their return is slight. The are voltage increases, and the are becomes unstable, and tends to extinguish. Location of the cathode spots on the side of the cathode, which becomes increasingly likely with increasing duct coil current, results in a decrease in the plasma flux through the plasma duct, leading to an optimal field current for optimizing the plasma output flux.