INFLUENCE OF AXISYMMETRIC MAGNETIC FIELD ON CATHODE SPOTS MOVEMENT IN ARC ION PLATING

Abstract

Arc ion plating(AIP) has been widely utilized in the deposition of various kinds of thin solid films due to the excellent characteristics of the arc plasma produced from an active cathode spot that emits ions of cathode material,as well as electrons.In AIP process,the cathode spot is usually steered by an external magnetic field.Cathode spot motion is the key factor because it affects the physical characteristics of the vacuum arc plasma,the utilization of the cathode material, the emission of macroparticles(MPs) and the quality of subsequent films containing these MPs. Therefore,cathode spot dynamics should be understood practically under a compound external magnetic field,such as in axisymmetric magnetic field(AMF),for industrial applications.An AMF produced by using an adjustable electromagnetic coil associated with a concentric magnetic flux guider was applied to the cathode surface to investigate the influence of the AMF on the arc cathode spot motion.The distribution of the magnetic field was simulated by the finite element method (FEM) software.The magnetic field intensity was measured by an SHT-V magnetometer and the distributions of magnetic field with different intensities were analyzed.Based on the results of FEM simulation and the physical mechanism of the arc cathode spot discharge,the effects of magnetic-field components and AMF on the cathode spot movement were discussed.The results showed that increasing the AMF intensity can strongly influence cathode spot movement.In the case of a weak AMF, the cathode spot moves randomly on the cathode surface.With increasing AMF,there is an increasing tendency for the cathode spot to rotate and drift toward the cathode target edge.The increase in the transverse magnetic field(TMF) intensity,B_T,can accelerate the rotational velocity of the cathode spot,increase the arc voltage and decrease the arc current.With a relatively strong AMF(B_T≈30 Gs), the cathode spot rotates near the edge of the cathode surface and is confined to a circular trajectory. A new arc cathode spot is ignited,splits,and is extinguished repeatedly on the cathode surface,which can be observed at intervals of about 0.5 s,while there is an obvious erosion track left at the bottom of the cathode edge.