CNx Films Prepared Alternative Irradiation of 12C+ and 14N+ Ion Beams

Carbon nitride(CNx) films were deposited on Si(100) wafers by means of alternative irradiation of mass-separated low energy 12C+ and 14N+ ion beams at the ultra-high vacuum pressure 10-7 Pa. The influence of substrate temperature during deposition on the structure, composition, and chemical bonds of the films was investigated. The ion energy of both ion species was 50 eV. The Si substrate was kept at room temperature (RT), 460, 800, or 1130 K during deposition. The films were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron energy-loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). The carbon and CNx film prepared at rt was amorphous. The amorphous carbon films changed to a graphite-like one with the random crystal orientations when the substrate temperature is increased. The amorphous CN film prepared at rt consisted of sp2 C-N, sp3 C-N, sp2 C-C, and sp3 C-C bonds, whose bond angles were distorted. This distortion of the chemical bonds decreased, and the structure of the CNx film changed to a graphite-like one on increasing the growth temperature. The graphite-like CN(x) film has a highly preferential crystal orientation, and the c-axis of the graphite basal plane is parallel to the film growth surface. The basal plane is also curved and interlinked because of the presence of in-plane sp2 C-N and three-dimensional sp3 C-N bonds.