Carbon nitride thin films deposited by reactive plasma beam sputtering

Carbon nitride thin films have been deposited on silicon substrates by reactive sputtering of a pure graphite target. In this process, argon plasma, generated by a hot cathode discharge, diffuses through a diaphragm into a deposition chamber towards the target which is biased at −300 V. The current density on the target is about 30 mA cm−2. Nitrogen gas is injected into the deposition chamber during the sputtering. Evolution of the deposition rate is measured versus the partial N2 pressure. The films are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infra-red spectroscopy (FTIR) and Raman spectroscopy. The atomic ratios of N and C in films are evaluated by XPS. At high N2 partial pressure, the atomic fraction saturates at a value of 38 at.%. The curve fitting of the C 1s and N 1s XPS peak spectra indicates that C and N atoms in films exhibit two different chemical states, representative of different CN chemical bonds. These XPS results, combined with FTIR and Raman analysis, suggest the existence of two amorphous carbon nitride phases in films, one with a stoichiometry similar to C3N4 and the other with an increasing fraction of nitrogen as the total N content in the films increases. These two carbon nitride phases seem to be present as soon as nitrogen is incorporated in films, even at low atomic concentration of nitrogen.