Influence of ion and neutral flux on the properties of diamond-like carbon from pulsed glow discharges of acetylene

The deposition rates, composition and mechanical properties of diamond-like carbon (DLC) coatings deposited using pulsed glow discharges of acetylene (C2H2) have been studied as a function of deposition bias and gas pressure. The data show that a −4-kV bias is one order of magnitude more efficient than a bias of −8 kV for depositing DLC via plasma immersion ion processing (PIIP). Sputtering is the suspected cause for the reduced deposition efficiency at −8 kV. A methodology for comparing the magnitude of the ion and neutral flux is used to show that neutrals dominate the deposition process under all conditions tested. The necessary data are shown to prove that the coating hardness is independent of gas pressure when the ion flux, Ji, is less than 10% of the total flux, Jd. If Ji/Jd is greater than 10%, then increasing the gas pressure reduces the coating hardness to levels below 15 GPa. The implications of these results regarding sheath thickness, deposition rates and throughputs for large-area processing (many m2) are discussed.