Crystalline carbon nitride films have been synthesized in a rf plasma assisted hot filament chemical vapor deposition system. Large crystalline grains up to ∼10 &mgr;m in size as well as film‐like regions are observed in the morphology of the films. &bgr;‐C3N4with two groups of lattice parameters (one is consistent with the theoretical value and the other is ∼3% smaller) in the deposited films on polycrystalline Ni substrate has been revealed by x‐ray diffraction spectrum (XRD). No Raman shift peaks have been found by Raman scattering measurement, but some presently unknown diffraction peaks appeared in the XRD spectrum. It is proposed that there are possible unknown structures of crystalline C‐N in the films. ©1996 American Institute of Physics.