Vacuum arc plasma beam produced from an erbium cathode

An Er plasma was produced by a vacuum arc source with a truncated cone-shaped Er cathode and an annular copper anode. The plasma beam was injected into a cylindrical magnetic duct through the annular anode aperture and flowed towards the substrate or an electrostatic ion current probe positioned on the duct axis, in vacuum or in a low-pressure oxygen background. The cathode spot operation, transport of the plasma beam in the duct, and coating deposition rate were studied as a function of arc current, axial magnetic field and oxygen pressure. Favorable conditions for arcing were obtained with relatively low arc current (I_arc=30-50 A) and an axial magnetic field of 12 mT, which confined the spot motion on the cathode apex. Under such conditions, the arc operated stably, and the cathode erosion (~235 mug/C) and coating deposition rates (2-5 mum/min) were very high. With higher I_arc (150-175 A), the cathode spots tended to move on the circumference of the large cone base, eroding a deep groove, which significantly decreased the cathode life.