Ultrahigh-Speed Coating of DLC at Over 100 $\mu{\rm m}/{\rm h}$ by Using Microwave-Excited High-Density Near Plasma

Abstract

In this paper, ultrahigh-speed deposition of diamond-like carbon (DLC) at deposition rates over 100 m/h is investigated. DLC coatings to steel substrates are conducted by using a plasma CVD apparatus employing new-type high-density plasma, which is sustained by microwaves propagating as surface waves along plasma–sheath interface. For plasma generation during coating in a mixture gas of Ar, methane, and tetra-methyl-silane (TMS), injection of 2.45-GHz microwave and application of substrate bias are conducted in a pulsed manner at a frequency of 500 Hz. DLC coatings with a microwave peak power of 1000 W, and a bias voltage of ${-}{200}~{\rm V}$ show that the deposition rate and hardness of DLC are increased and decreased, respectively, with increasing duty ratio from 6% to 50% for pulsed plasma generation. The hardness of DLC is increased by increasing the gas flow rate of TMS from 10 to 20 sccm. In addition, the hardness of DLC is increased almost linearly with increasing substrate current averaged over coating time. As an example of DLC coating in this paper, the deposition rate and hardness of DLC are 188 $\mu{\rm m/h}$ and 12.9 GPa, respectively, where plasma is generated at a duty ratio of 50% with the gas flow rates of 40, 200, and 20 sccm in Ar, methane, and TMS, respectively.