Structure and optical properties of Si incorporated diamond-like carbon ®lms deposited by r.f. plasma-assisted chemical vapor deposition

Silicon incorporated diamond-like carbon (Si-DLC) ®lms were deposited by 13.56 MHz r.f. plasma assisted chemical vapor deposition (RF-PACVD), and the optical properties of the ®lms were examined by spectroscopic ellipsometry analysis. In particular, the dispersion model developed by Jellison and Modine was used to determine the optical constants by ®tting the measured ellipsometric spectra in the 300± 1200 nm range. Various mixtures of benzene and diluted silane (SiH4:H2 10:90) were used as reaction gases, and the Si concentration in the ®lm was found to increase monotonically up to 17 at. % as the diluted silane fraction in the reaction gas was increased from 0 to 95%. However, the variation of the optical gap exhibited distinctive silicon-concentration dependence; the minimum optical gap was found from the ®lm with 5 at. % silicon concentration. The observed changes of the optical properties were attributed to the modi®cation of the atomic bonding structures induced by silicon incorporation. In particular, the change in SP2-bonded carbon cluster sizes and the interlinking betwee