The growth of carbon films with random atomic structure from ion impact damage in a hydrocarbon plasma

• Published in: Thin solid films 1979-01, Vol.58 (1), p.107-116
• Main Authors: Holland, L., Ojha, S.M.
• Format: Article
• Language: English
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/0040-6090(79)90219-0

Initially procedures for preparing insulating carbon films of exceptional hardness by ion beam deposition and ion impact growth in hydrocarbon plasmas are reviewed; for completeness reference is also made to thermally cracked carbon films grown on diamond. We described experiments on the coating of germanium targets on a water-cooled electrode in a butane r.f. plasma (13.56 MHz) with the electrode capacitively coupled to the supply to provide a negative bias to enhance ion impact. Films prepared at a low power input-to-pressure ratio of 1–2 W cm -2Torr -1 were polymers with some oxygen contamination as shown by their infrared absorption bands. Raising the ratio to 40 W cm -2 Torr -1 produced carbon films without absorption in the measured region λ = 2–20 μm. The films were amorphous with a refractive index of 1.9–2.0 and a resistivity of 10 12 Ω cm. At higher power-to-pressure ratios or target temperatures the film resistivity fell with loss of the infrared transparency. A critical ratio exists at which energetic ion impact is sufficient to rupture all CH bonded species reaching the target and to damage any structure ordering which may otherwise arise. At high ratios the target cooling is considered to be insufficient to prevent the film temperature rising and resulting in a transition from a metastable to a graphitic form. In conclusion the properties of vacuum-deposited carbon and the nature of some reported defects in diamond are considered in relation to the characteristics of ion impact films.