Effects of increasing nitrogen concentration on the structure of carbon nitride films deposited by ion beam assisted deposition

Amorphous carbon nitride films containing increasing concentrations of nitrogen were deposited by ion beam assisted deposition at a substrate temperature of 150 degrees C. The relationship between the deposition conditions and the chemical bonding structure was investigated by x-ray photoelectron, ultraviolet photoelectron, infrared, and Raman spectroscopies. Film properties were examined by ultraviolet-vis spectroscopy, conductivity, hardness, density, and internal stress measurements. The experimental results confirm a pronounced change of the structure and properties at a nitrogen concentration of about 20 at. %. After reaching a maximum at this concentration, properties like hardness, conductivity, and density show a strong decrease up to a nitrogen content of 35 at. %. In order to identify the formed microstructure and better understand the cause of the structural transformation a statistical model is introduced and the results are compared with the intensities of the deconvoluted spectral features obtained by photoelectron spectroscopy. On the basis of the obtained correlation between independent experiments it is demonstrated that below 20 at. % N an increasing number of nonaromatic CN bonds is formed inducing a localization of nitrogen lone pair electrons and thus stressing the former planar aromatic structures. The addition of more N causes a further reduction of aromatic configurations and a relaxation of the strained network due to the formation of isocyanide structures (C=N-), aliphatic CN bonds, and terminating nitrile groups (-C=N). The nitrogen induced rearrangement of the bonding structure accounts for the lower intrinsic stress values and higher optical gap of these films. Structural information from both Raman and infrared spectra support these findings. (C) 2000 American Vacuum Society. [S0734-2101(00)00505-4].