Property Control of Diamond-Like Carbon Coatings by Selection of Precursor, Bias, and Dilutant

Diamond-like carbon (DLC) films characterized by high wear resistance, low friction coefficients, and chemically inertness are most often deposited by RF, PACVD, but DC PACVD can also be used with electrically conductive substrates. The deposition has to be performed under negative bias in order obtain DLC properties. In studies performed with acetylene and cyclohexane, it was found that the wear resistance and physical properties of the DLC films are affected by precursor and substrate bias. The minimum substrate bias required to achieve diamond-like properties was found to be precursor dependent and films deposited at a substrate bias below the threshold value have been found to have polymer-like characteristics. Diluting the precursors with inert gas enhanced the diamond-like properties of films deposited below the threshold bias and the effect increased with increasing dilution. At sufficiently high dilution of the precursor, wear resistant DLC films deposited at a bias below the threshold level could be obtained. Similarly, the wear resistance of fluorinated DLC films deposited from hexafluorobenzene could be enhanced by sufficiently high dilution of the fluorinated precursor with hydrogen. The possible mechanisms responsible for the variation in the properties of the DLC films as affected by precursors and dilutants will be discussed. The effect of ion bombardment, controlled by negative substrate bias and by enhanced ionization in the plasmas containing inert dilutants, and the chemcial effects, in plasmas containing chemically active species, on the formation of the diamond-like structure will be addressed and related to the observed properties.