Diamondlike carbon films were prepared by electron cyclotron resonance chemical vapor deposition. Structures of the carbon films were characterized by Raman spectroscopy and Fourier‐transform infrared spectroscopy. The relationship between the properties of films and growth conditions has been examined. High‐energy ion species extracted from a discharge of methane in the electron cyclotron resonance cavity, which is positively‐biased electrically against the earthed substrate, have an important role in the growth behavior of hard diamondlike carbon films.