The diamond-like carbon thin films were deposited by RF ion source which can control ion energy and flux incident on the substrate without applying substrate bias voltage at room temperature. The film depositions are performed using a mixture of methane and hydrogen and changing the DC self bias voltage via RF power applied to ion accelerating grid electrode in order to control the energy and flux of ions bombarding the substrate. The structure and optical properties of the films are evaluated by ellipsometer, UV-VIS spectrometer, and Raman spectroscopy. The refractive index of the deposited films increases from 1.89 to 2.35 as DC self bias voltage is increased from -50V to -300V. The optical bandgap decreases from 2.35 to 1.35 and the ratio of I_D/I_G obtained from Raman spectroscopy increases from 0.79 to 4.48, respectively, with increasing DC self bias voltage from -100V to -300V. From this results it is concluded that at low DC self bias voltage(<-50V), soft, polymer-like films are formed while at moderately high DC self bias voltage (-100V to -200V), diamond-like carbon(DLC) films are formed, and at high DC self bias voltage (>-300V), graphite-like carbon films are formed due to high ion bombardment.