Dependence of microstructure and nanomechanical properties of amorphous carbon nitride thin films on vacuum annealing

Three kinds of ultrathin amorphous carbon nitride films (α-CN x ) with different internal stress were deposited on silicon (111) substrates by an ion beam assisted deposition method. The as-deposited α-CN x was post-annealed to eliminate the internal stress. The microstructure and nanomechanical properties of both as-deposited and annealed α-CN x were studied by using micro Raman spectroscopy, nanoindentation measurement, and nanoscratch test in atomic force microscopy. The Raman spectra of as-deposited and annealed film show that the ratio of intensities of the D band to G band increased after vacuum annealing. Nanoscratch tests showed that the elimination of compressive internal stress due to annealing resulted in reduced scratch resistance, while elimination of tensile internal stress due to annealing resulted in enhanced scratch resistance. Nanoscratch test results were in good agreement with the results of nanoindentation measurement. Experimental results indicate that the effect of internal stress on scratch resistance is stronger than that of microstructure evolution due to post-annealing. Nanoscratch tests show that suitable compressive internal stress is beneficial for enhancement of nanoscratch resistance of the thin α-CN x film.