To examine the mechanism of film deposition in a planar rf CH4discharge plasma, measurements were made of the spatial distributions of the deposition rate and optical emission intensity along the discharge axis between parallel electrodes. Optical‐absorption properties of the deposited carbon films were also measured over both the infrared and visible regions. To measure the spatial deposition rates, the substrate surface was elevated from the cathode electrode with the use of quartz glass plates. It was found that the spatial properties of films, which were deposited in both the ion‐sheath and bulk‐plasma regions, differ markedly from each other. The carbon films obtained from within the ion‐sheath region were found to be extremely hard, while those obtained in the bulk‐plasma region were polymerlike soft films. This disparity was thought to be due to the difference in the kinetic energy of the ions bombarding the substrate surface; that is, the substrate surface potential could be changed by elevating the substrate surface. These results were incorporated in the discussion of the deposition mechanism, with emphasis on the contribution of ion bombardment to the film‐deposition process. It was tentatively concluded that the film‐deposition rate was predominantly dependent on the product of the ion kinetic energy and ion flux density that reached the substrate surface.