The hydrogenated hard carbon films were deposited at elevated temperature in planar rf CH4 plasmas. The deposition rate and mechanical properties of the carbon films deposited at substrate temperature between room temperature and 400 degrees C were examined. The behavior of the film deposition rate indicated the negative temperature slope, and activation energies of around 0.04-0.05 eV at gas pressures of 40-100 mTorr were obtained from the Arrhenius plots of the deposition rates. Both the temperature behavior and the value of the activation energy suggest that the spontaneous incorporation of physisorbed CH3 precursor into the growing film is negligible, and the chemical reaction between the CH3 molecules and hydrocarbon ions bombarding the film surface is most probable in the present deposition process. The dense carbon films having film densities up to 2.7 g/cm(3) were obtained at 40 mTorr.