Synthesis and tribological properties of DLC film by RF PACVD: Effect of processing parameters

Diamond-like carbon (DLC) films, have gained grounds in many industries ranging from automobile and oil and gas to electronics and bio fields due to their low friction and wear rate, chemical inertness and high hardness. Radio Frequency (RF) plasma discharge has been widely used to produce amorphous carbon films, because this method can be applied not only for etching but also for deposition on insulators. The advantage of RF plasma discharge is the application for wide area and the stability as compared with direct current (DC) plasma. The properties of DLC films deposited by RF plasma-assisted chemical vapor deposition (PACVD) strongly depend on deposition conditions such as total gas pressure, input power supplied from a generator, gas flow rate and also substrate material.;In the present study, DLC films were synthesized utilizing low power RF PACVD in a CH4/Ar glow discharge. First, the effect of processing parameters namely: RF power, chamber pressure, gas flow rate and Ar dilution on the DLC film deposition and hardness was studied to identify parameters that produce quality films. Following the initial study, nanoindentation and tribological experiments were conducted to characterize hardness, friction and wear resistance of the films. Nanoindentation experiments showed that higher hardness can be obtained with a moderate increase in RF power (35 W - 40 W) after which delamination of the film occurs. With decreasing pressure, the hardness of the film increases. This behavior was attributed to higher sp3 content of the films as the power increases or pressure decreases. Also, it was found that the flow rate and Ar dilution in the range of 17% - 30% Ar has no significant effect on the hardness of the film. Combination of different parameters affect the friction coefficient and wear resistance of the DLC films and three groups of tribological behavior were identified; (i) low friction and low wear resistance, characteristic of films with high graphitic content; (ii) low friction and high wear resistance for films with a good balance of graphite-like and diamond-like content; and (iii) moderate friction (with a coefficient of friction between 0.12 and 0.22) and ultra high wear resistance (<10-8 mm3/Nm). The results show that compared to DC PACVD, low power RF PACVD can produce quality DLC films with comparable if not better tribological behavior. This is attributed to better plasma uniformity produced by RF compared to DC PECVD.