Influence of oxygen on the thermal stability of amorphous hydrogenated carbon films

Influence of oxygen on the thermal stability of amorphous hydrogenated carbon (a-C:H) films is investigated by annealing the films at 520, 610, and 670 K in vacuum and in O2 flow, respectively. The a-C:H films used for this study were deposited using microwave plasma from a mixture of 10 sccm pure methane and 100 sccm hydrogen in an electron cyclotron resonance chemical vapor deposition system. It is found that the anneals in O2 gas flow lead to much more prominent variation in film thickness, optical band gap, and IR absorption related to C–H stretching vibration than the anneals in vacuum. Raman scattering and optical absorption indicate that O2 greatly promotes the transformation from polymeric to graphitic microstructure with increasing annealing temperature. Possible conversion of bond structure and the role of O2 in the stability of the films are discussed.