Properties and structures of diamond-like carbon film deposited using He, Ne, Ar/methane mixture by plasma enhanced chemical vapor deposition

Diamond-like carbon (DLC) films have been deposited by a magnetically enhanced plasma (MEP) chemical vapor deposition (CVD) system. The properties and structures of DLC films deposited by MEP-CVD using various gases (methane, He/methane, Ne/methane, and Ar/methane) were studied. The mechanical properties in terms of hardness, Young's modulus and stress, and optical properties in terms of optical band gap and refractive index were enhanced by adding inert gas in methane plasma. The magnitude of the effects on the properties for various inert gases was found as Ne, Ar, and He, on the surface roughness was found as Ar, Ne, and He. The Raman characteristic shows a dependence of the bias voltage and inert-gas/methane ratio, as well as the inert gases dilution. The Raman spectroscopy analysis indicates that the changes of properties of the DLC films are due to the structural changes, such as sp² and sp³ content in the films prepared under various deposition conditions. The films deposited in Ne/methane show the lowest disordered (D) peak to graphitic (G) peak intensity ratio, the D and G peak positions; highest stress, hardness, Young's modulus, optical band gap, and lowest reflective index. The films deposited in Ar/methane show the lowest surface roughness. This was proposed due to the optimum balance in the inert gas ionization potential and atomic mass.