DEPOSITION OF DIAMOND-LIKE CARBON-FILM IN CH4-HE RF PLASMA

The deposition of diamond-like carbon (DLC) film for surface hard coatings was carried out in a CH4-He r.f (13.56 MHz) plasma. Mass spectrometry measurements were performed to study the film deposition mechanism. The film deposition rates and properties were measured as functions of gas pressure and CH4 composition ratio in the CH4-He mixture gas. The deposition rate shows an abrupt increase at about 5% CH4 composition ratio and then increases monotonically with increasing CH4 volume. At this critical condition, higher hydrocarbon ions generated by secondary reactions also increase markedly, which suggests that these secondary hydrocarbon ions contribute more to the film formation than do the primary CH3+ and CH4+ ions. The Knoop film hardness and internal film stress as functions of CH4 composition ratio and gas pressure were examined. The hydrocarbon ions enhanced by Penning ionization with excited He atoms influence these film properties.