Improved high-temperature stability of Si incorporated a-C:H films

The temperature stability of silicon incorporated hydrogenated amorphous carbon films (a-C(1-x)Si(x):H) is investigated. Elastic recoil hydrogen detection measurements showed that films with x greater than or equal to 0.15 have an improved hydrogen stability when compared with those with smaller silicon contents. This result is consistent with the gas effusion experiments, which showed that silicon incorporation induces a shift of the hydrogen effusion peak to higher temperatures and a strong reduction in the effusion of methane molecules. The Raman spectra of samples annealed at 500 degrees C clearly evidenced the graphitization process of the low silicon content samples. As x is increased, the graphitization process becomes less clear, and for samples with silicon contents larger than 15 at.%, no evidence of graphitization could be found. Similarly, electron spin resonance (ESR) measurements showed a strong reduction of the ESR linewidth upon annealing in the case of low silicon content samples, indicating the growth of sp(2) islands with unpaired spins. This effect is also inhibited by silicon incorporation. Based on these observations, the improved thermal stability of silicon incorporated samples is associated with an increased disorder of these films, which inhibits the carbonisation of the material that, consequently, presents a reduced graphitization. (C) 1998 Elsevier Science S.A.