Structural modifications of silicon-doped carbon nitride films during post-deposition annealing

Abstract

The incorporation of silicon in the composition of carbon nitride coatings has been demonstrated to improve their tribological behaviour by diminishing the negative influence of ambient moisture [1]. In this work, a detailed study by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) concerning the thermal stability of these silicon-containing amorphous carbon nitride films (SiCN x ) is presented. Such films are grown at room temperature by reactive direct current magnetron sputtering of a graphite target in a nitrogen discharge while a volatile silicon precursor is added. The structural and compositional modifications induced upon heating in air and vacuum environments are followed by XPS and in situ EELS measurements, respectively. The thermal stability is not observed to be improved by incorporation of silicon in the CN network compared to similar treatments on free-silicon CN x films [2]. Annealing in ambient air led to the loss of nitrogen for temperatures above 350 °C and partial oxidation of carbon and silicon species. TEM observation combined with EDX nanoprobe analysis revealed the formation of separate morphological domains with different chemical composition. A strong differential charge effect in XPS core level spectra of Si 2p and O 1s confirmed this phase segregation. The stability in vacuum is much higher, showing a significant decrease of the nitrogen content above 700 °C and a partial reduction of oxidised silicon species.