Hydrogen-containing carbon nitride films produced by the combined hot filament–plasma CVD technique

Carbon nitride films were prepared by combined hot filament (HF) and radiofrequency (RF) plasma enhanced chemical vapor deposition techniques from three mixtures, C2H6–N2–Ar, C2H4–N2–Ar and C2H2–N2–Ar, denominated M1, M2 and M3, respectively. Depositions were carried out in a vacuum chamber fitted with two parallel-plate electrodes driven by a 40-MHz generator and a Ta filament resistively heated by an AC power supply. The deposition rates, composition and structural properties were compared for films deposited using the same flow rates of the hydrocarbon, nitrogen and argon mixture fed to the vacuum chamber, and the same radiofrequency and filament power. The deposition rate, R, was determined by dividing the film height, obtained using a profilemeter, by the deposition time. Reflection infrared and Raman spectroscopies were used to investigate the molecular structure while Rutherford backscattering spectroscopy was used to determine the elemental composition. Using combined RF and HF excitation: (i) R increased from mixture M1 to mixture M3; (ii) the concentration of CC bonds was higher in the films deposited in the M3 mixture; and (iii) the incorporation of nitrogen, determined by the nitrogen to carbon atomic ratio, increased from mixture M1 to M3. For the mixture M3, a comparison of the film structure and deposition rate of films produced using HF, RF and combined HF–RF excitation, was made. Both R and the concentration of C–H bonds were higher when HF excitation alone was used. An interpretation of the role of the plasma in the decrease in R is suggested. The influence of the degree of saturation of the hydrocarbon molecules in each mixture on R and on the film structure is highlighted. The Raman spectroscopy results revealed that diamond-like carbon is formed under HF excitation while the use of RF, alone or combined with HF, eliminates the diamond phases.