Characterization of Carbon Nitride Thin Films Deposited by Reactive d.c. Magnetron Sputtering on Various Substrate Materials

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The effects of substrate material on structure, composition and mechanical properties of carbon nitride thin films, deposited by reactive d.c. magnetron sputtering in N2 discharge, have been studied. CNx films, with a nitrogen concentration between 15 and 30 at.%, were deposited at two different N2 partial pressures (2.5mTorr and 10mTorr) on to a number of different substrate materials, SiO2, Si3N4, TiN, Ni and high-speed steel, kept at temperatures between ambient and 500 °C. The results show that the adhesion of CNx films to Ni and steel substrates was very poor, especially at elevated temperatures, whereas in the case of SiO2, Si3N4, and TiN substrates, the adhesion was generally good. The variation in growth rate was also found to be different depending on which substrate was used. Atomic force microscopy (AFM) revealed that the films grown at a lower pressure were very smooth with an rms roughness between 0.2 and 0.3 nm, whereas the roughness was more than one order of magnitude higher (2–10 nm) for films grown at 10 mTorr. Nanoindentation measurements showed that the films grown at the low pressure and above 200 °C were both hard and elastic as expected, based on previous results. The films grown at temperatures below 200 °C were much softer and less elastic.