PVD for decorative applications Lesson 2: The cathodic arc evaporation PVD process

In the first stage of cathodic arc evaporation (CAE), an electrical arc is ignited on a round or rectangular cathode in a high vacuum. The cathode is made of a conductive material (mostly called the ‘target’) that will later become part of the coating, connected with a grounded wire. As in arc welding, the arc is maintained on the target surface and either moves randomly or is magnetically guided over the target surface. As long as a significant proportion of the conductive plasma consists of ionized cathode material, a stable, self-maintaining arc can form in a vacuum, even without ionizable gas particles like argon.

In the cathode spot, where the arc meets the cathode, the target material melts and is vaporized. In this process, ions, neutral particles and droplets (bigger macro-particles) are emitted. The ions speed away from the cathode surface and hit the substrate, where they form the thin film as we described in the first lesson. The droplets, too, are deposited in the growing layer during the coating process. This is one of the drawbacks of CAE, leading to a higher roughness of the coating plus some defect formation. Although it is possible to install a filter of magnetic systems or shutters to reduce the incorporation of droplets, this also reduces the deposition rate.