Deposition of amorphous CN, thin films on silicon by electron cyclotron resonance plasma-enhanced chemical vapor deposition is investigated. The use of neon instead of argon to form the plasma promotes species activation and leads to deposition on silicon substrates. The influence of precursor flow ratio. addition of hydrogen, and radio frequency power was studied. Optical emission spectroscopy has been used for the diagnosis of active species involved in the deposition process and neither nitrogen nor carbon atomic species were detected. Fourier transform infrared spectroscopy measurements showed as main bands those related to C-N and C=N bonds. Dielectric constants of the films were obtained by spectroscopic ellipsometry: samples grown with the highest methane flow ratios showed absorption throughout all the measured energy range, probably due to free carriers. Present results suggest that CN, layers consist mainly of C-N and C=N bonds in an amorphous matrix, besides C=C bonds probably in the form of small graphitic clusters.