Structural and mechanical properties of facing-target sputtered amorphous CNx films

Structural and mechanical properties of carbon nitride films, deposited using a DC facing-target reactive sputtering system at various N2 fractions (PN) in the gas mixture, were studied systematically. XPS analyses indicate that N concentration is not directly proportional to PN, and it rises quickly to a saturation value of ∼ 33 at.% at a PN of 20%. The ratio of N–C(sp2)/N–C(sp3) increases with the rise of PN from 0% to 20%, and then decreases with further rising PN. However, the number and size of disordered sp2-hybridized C clusters continue to increase over the whole range of PN, which is consistent with the Raman and high-resolution transmission electron microscopy measurements. Nanoindenter measurements show that the hardness of the films continuously decreases from ∼ 17.5 to ∼ 5.6 GPa with the increasing PN from 0% to 100%, due to the conversion from sp3 C to sp2 C and the clustering of sp2 C structure.