Preparation and characterization of hydrogenated diamond-like carbon films in a dual DC-RF plasma system

A dual direct current and radio frequency (DC-RF) plasma system was used to deposit hydrogenated diamond-like carbon (DLC) films from methane plasma. It has the advantages of separately controlling ion density and ion energy by RF power and DC bias, respectively, over conventional simply capacitive-coupled radio frequency plasma enhanced chemical vapour deposition system. Thus, the hydrogenated DLC films were obtained at different RF powers and DC biases, using CH4 plus Ar as the feedstock. The effects of RF power and DC bias on the structure and properties of the films were investigated by means of Fourier transformation infrared spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and nano-indentation. The results were as follows: the sp3 content, hardness, and Young's modulus of the DLC films increased with increasing RF power at a constant DC bias of −200 V and reached the maximum values at an RF power of 300 W, after which they decreased with further increase of the RF power. The DC bias had a similar but greater effect on the structure and properties of the films, owing to a greater influence of the ion energy on the characteristics of the films than the ion current density. The film deposited at an RF power of 300 W and DC bias of −200 V has the most diamond-like characteristics with maximum hardness, Young's modulus, and sp3 content. Since both the ion current density and ion energy greatly affect the structure and characteristics of the DLC films, it is imperative to select proper processing parameters to obtain high quality DLC films.