High rate deposition of hard a-C:H films using microwave excited plasma enhanced CVD

High rate deposition processes for hydrogenated diamond-like carbon films (a-C:H) were developed using microwave plasma enhanced CVD (PECVD) techniques. Basic investigations were carried out in a laboratory scale deposition apparatus (0.04 m³ chamber) and after that the processes were transferred to an industrial scale PECVD machine (1 m³) and optimized therein. The application of an asymmetric bipolar pulsed mid-frequency substrate bias allowed controlling the ion fluxes to the growing films independently of the generation of film forming species (radicals and ions) by the microwave plasma source. After preliminary experiments using five different hydrocarbon precursors, more thorough investigations were done with the selected precursors acetylene (C₂H₂) and isobutene (C₄H₈; isobutylene, 2-Methyl-1-propene). The a-C:H films were characterised with respect to deposition rates, hardness, abrasive wear rates, internal stresses and topography.Wear resistant, atomically smooth a-C:H films with a hardness above 25 GPa were deposited at a very high rate of 15 μm/h. The combination of high rate and high hardness values should be promising for industrial applications, even for in-line technologies. For the both mentioned precursors C₂H₂ and C₄H₈ some differences in hardness–rate relations were observed.