Chemical Bonding Composition and Growth Mechanism of a-CNx Thin Films by Low-Temperature rf-PECVD Technique

In this study, amorphous carbon nitride (a-CNx) thin films were deposited using radio frequency plasma enhanced chemical vapor deposition (rf-PECVD) technique. Samples were prepared at different substrate temperatures of 80, 100, 120, 150, and 180 degrees C and the effect on morphology, deposition rate and chemical bonding composition were studied. Next, the growth mechanism of a-CNx thin films using acetylene (C2H2) and nitrogen (N) as gas precursor. Film thickness and morphology of a-CNx thin film were characterized using field emission scanning electron microscopy, (FESEM). while the chemical bonding composition was obtained using Fourier transform infrared spectroscopy (FTIR). The morphology of the a-CNx thin film looks like a uniform structural shape of a cauliflower. Whereas samples deposited at 100 and 180 degrees C show nanosize granular structure on the entire surface of the film. Maximum deposition rate of a-CNx thin films at deposition temperature of 120 degrees C and minimum at 180 degrees C. Overall, all samples show the presence of C-N, C = C, C = N, C, N, C-H and N-H /O-H bonds, which are the corresponding bonds present in a-CNx thin films. In this study, the growth mechanism of a-CNx thin films discusses the formation of C-H, C-N and HCN by-products resulting from the decomposition of C2H2 and N-2 gas. The growth of a-CNx films was also due to the kinetic reactions during the deposition process: the adsorption of carbon and nitrogen species on the surface of the film growth and the desorption of saturated nitride species, caused by energetic species, and the high mobility of the species on the growth surface. Thus, the chemical bonding composition and deposition rate of the film is influenced by the equilibrium between the CN molecules and the C and N atoms reaching the film growth surface.