Controlled glow to arc transition in sputtering for high rate deposition of carbon films

We achieve control over the transition from a magnetically confined (magnetron) glow discharge to an arc discharge operating on a carbon cathode by applying constant voltage square wave pulses. A power supply with rapid turn off at a chosen current set point is used to produce a mode with a high current magnetron discharge and no arc (the high power impulse magnetron sputtering or HIPIMS mode) or a high current magnetron discharge that includes a short lived cathodic arc with very high but controlled current density (mixed HIPIMS arc mode). The deposition rate in the mixed HIPIMS arc mode at a duty factor of less than 1% was found to be greater than for conventional r.f. sputtering. We have studied the properties of carbon films deposited using both modes. In the mixed mode, the films contain graphitic nanoclusters with a number density and a morphology that depends on the bias applied to the substrate. The nanoclusters in the films prepared with bias have a flattened shape with graphitic layers approximately parallel to the surface, consistent with energetic impact of a spherical cluster of graphitic material. The matrix of the films has a sp3 content of approximately 50%, significantly greater than that for a conventionally sputtered film, but with a much higher instantaneous deposition rate. For negative substrate bias values of greater than 80 V, the surface is smooth enough to make films of interest as wear resistant coatings.

Research Highlights▶ Formation and properties of carbon composite thin films are reported. ▶ They (the films) are deposited at high rate and contain nanometer-sized graphitic clusters. ▶ The clusters are formed in the dense and hot plasma of a new type of mixed pulsed arc sputtering mode. ▶ The clusters are charged and their shape when embedded in the film depends on the applied substrate bias. ▶ The films have a high sp3 content significantly greater compared to conventionally sputtered films.