Effects of the Plasma Conditions on the Bonding Type in Carbon Nitride Thin Films

Carbon nitride thin films have been prepared by plasma enhanced chemical vapour deposition of CH4 and N2 gas mixtures, by chemical transport from a hollow graphite cathode and by reactive sputtering of a high purity graphite target. The vibrational properties of the films have been studied by Fourier transform infrared spectroscopy (FTIR) and Raman microprobe spectroscopy. Optical emission studies from the plasmas were obtained in the range between 275 and 800 nm. Single, double and triple carbon nitrogen bonds were detected in the FTIR spectra by bands at 1230 cm-1, 1600 cm-1 and 2150 cm-1; their relative intensity being a function of the temperature of the species and the energy supplied to the plasma. A correlation was found between the nitrogen concentration in the films and the existance of strong emission lines of CN and N2+. In the sputtered samples, the substrate temperature and the amount of ion bombardment determined when the films were hard; i.e. Vicker's hardness values above 2500 HV. In the case of the sputtered samples, a temperature window was found which resulted in hard films.