Diamond-like carbon films were deposited using electron cyclotron resonance chemical vapor deposition system under various process pressure conditions. The electron cyclotron resonance plasma was characterized using a Langmuir probe and optical emission spectroscopy. The film properties were characterized using Raman and Fourier transform infrared spectroscopy, hardness and optical gap measurements. It was found that the ion density and all peaks in the optical emission spectrum decreased monotonously following the increase in process pressure. Raman spectra and optical gap measurements suggest that the films become more diamond-like and contain a lower sp(2) content following the increase in process pressure. Infrared spectroscopy measurements showed a significant increase in hydrogen content as the process pressure increased from 4 to 12 mtorr, and only a slight increase as the pressure increased from 12 to 20 mtorr. A deposition mechanism is described which involved ion bombardment and hydrogen-surface interactions. The deposition rate is correlated to the ion density and CH3 density.