Micro-structural analysis of carbon nitride (CN_x) film prepared by ion beam assisted magnetron sputtering

The growth and structural evolution of carbon nitride (CN_x) films, deposited by nitrogen ion beam assisted magnetron sputtering, were studied. The deposition rate, composition ([N]/[C] ratio), structure, and mechanical properties of CN_x films were investigated as a function of nitrogen ion energy in the range of 30 eV-1 keV. For the ion energy below 200 eV, the increasing fraction of curved structure as revealed by transmission electron microscopy and sp³ hybridized bonding were attributed to structural transition and improved mechanical properties of CN_x films. However, when increasing nitrogen ion energy above 200 eV, the [N]/[C] ratio in film was inversely proportional to the nitrogen ion energy and preferential distribution of nitrogen in sp² hybridized site induced the retransition from curved structure to planar structure. From these results, it was found that CN_x films exhibit two different structural and bonding characteristics with ion energy and this transition of film characteristics is closely related to the nitrogen content in the film.