Compositional and structural modifications of amorphous carbon nitride films induced by thermal annealing

Amorphous carbon nitride films deposited by rf magnetron sputtering were annealed up to 900degreesC in vacuum for 1 h. The variations of composition and bonding structure of the films were investigated by Fourier transformation infrared, Raman spectroscopy and x-ray photoelectron spectroscopy. The results showed that a great loss of N content was induced by annealing in the films surface, which dropped abruptly from 26.4 to 1.5 at.% with annealing temperature rising to 900degreesC. In addition, it was found that annealing led to disruptions of most C-N bonds and the conversion from sp(3) C to sp(2) C. As a result, graphitization occurred and a large fraction of sp(2) C bonds was formed in the CNx films surface. Surface etching of post-annealed films was carried out to study the change in the film interior layer. Approximately 7 at.% nitrogen atoms were found to still remain in the film interior layer at the annealing temperature 900degreesC. These remaining N atoms were mainly bound to sp(3) C in CNx films instead of N-sp(2) C bonds, which indicates the N-sp(3) C bonds have higher thermal stability than N-sp(2) C bonds.