Reactive magnetron sputter deposited CNx: Effects of N2 pressure and growth temperature on film composition, bonding, and microstructure

Abstract

The effects of growth processes on the chemical bond structure, microstructure, and mechanical properties of carbon–nitride (CNx) thin films, deposited by reactive magnetron sputtering in a pure N2 discharge, are reported. The film deposition rate RD increases with increasing N2 pressure PN2 while N/C ratios remain constant. The maximum N concentration was ∼35 at. %. RD was found to be dependent upon the film growth temperature Ts. For a given PN2, RD decreased slightly as Ts was increased from 100 to 600 °C. The variations in RD with both PN2 and Ts can be explained by ion-induced desorption of cyano radicals CNx from both the target and growth surfaces during deposition. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy (FTIR) analyses showed that N atoms in films grown at Ts≳350 °C with low nitrogen partial pressures PN2, ∼2.5 mTorr, were bound to C atoms through hybridized sp2 and sp3 configurations. For low Ts=100 °C and higher PN2, 10 mTorr, triple-bonded C≡N was detected by FTIR. Two types of microstructures were observed by high-resolution transmission electron microscopy, depending on Ts: an amorphous phase, containing crystalline clusters for films deposited at Ts=100 °C, while a turbostraticlike or fullerenelike phase was observed for films deposited at Ts≳200 °C CNx films deposited a higher Ts and lower PN2 were found to have higher hardness and elastic modulus.