Effect of Mixture Ratio of Ar Gas and C₂H₂ Gas on Gas-Injection Pulsed Plasma CVD Method for Ultra-High-Rate DLC Deposition

Diamond-like carbon (DLC) films have been used as a surface protective film. To use the DLC films in a wide range of applications, a faster DLC formation method than the conventional method is required. In this study, the effect of the mixture ratio of Ar gas and C₂H₂ gas on the DLC films prepared using a pulsed plasma CVD with the injection of the mixed gas is investigated.

DLC films were formed on a Si substrate using the gas-injection pulsed plasma CVD method. Ar and C₂H₂ mixed gas was injected into a chamber. A pulsed voltage of -500 V was applied to a substrate stage as a discharge electrode.

The DLC film deposition rate was the fastest in approximately 0.4–0.6 of the ratio of the Ar flow rate to the C₂H₂ flow rate and improved with the increase of the total gas flow rate. It is considered that the relationship between the Ar-gas-flow-rate ratio and the DLC film deposition rate depended on the effects of the C₂H₂ decomposition and the sputtering to the film with Ar ion collision. A DLC film with a nanoindentation hardness of 18 GPa was formed at a deposition rate of 2.8 μm/min under the condition of an Ar ratio of 0.71 and a total gas flow rate of 1750 sccm.