Influence of inert gases on ionized magnetron plasma deposition of carbon nitride thin films

Abstract

Carbon nitride films were deposited by ionized magnetron sputtering in gas mixtures containing helium, neon, argon or krypton plus nitrogen. Sputtering voltages and deposition rates were measured, and the films were characterized by Fourier transform infrared (FTIR) spectroscopy, Rutherford back-scattering and nano-indentation. Application of an inductive plasma decreased the sputtering voltage, suggesting a decrease in the impedance of the discharge. A stable discharge was only obtained at pressures above 8 Pa in helium/nitrogen mixtures. The deposition rates increased with nitrogen content in neon, argon or krypton mixtures, both with and without an inductive plasma. The deposition rates with an inductive plasma in krypton/nitrogen were much higher than those in argon/nitrogen and neon/nitrogen mixtures with the same nitrogen contents. IR absorption bands at 1250, 1500 and 2200 cm −1 indicated the presence of disordered sp 2 hybridized carbon, graphite-like sp 2 carbon, and nitrile/isocyanate groups, respectively. In addition, amide-like vibration between 2800 and 3700 cm −1 was pronounced on application of the inductive plasma. FTIR results suggest that less dense films were synthesized with the inductive plasma. The N:C ratio was <0.3 in films deposited with no inductive plasma in the different inert gas mixtures, and increased with the inductive plasma in helium or argon mixtures. The film deposited in neon/nitrogen showed a low hardness (4.5 GPa) but high modulus (100.6 GPa). Deposition in argon/nitrogen with an inductive plasma produced the highest hardness.