Spectroscopic ellipsometry of silicon-containing diamond-like carbon (DLC-Si) films

To clarify optical properties of DLC-Si film, we have studied the change in optical constants of the DLC-Si films as a function of the Si content using spectroscopic ellipsometry. Using the 4 layered structure model (substrate/interface/film/surface roughness/ adsorbed water/ air), the thickness of each layer and the parameters of the Tauc-Lorentz oscillator of the film were estimated. The calculated spectra agreed well with the measured one using the layered model with adsorbed water on the DLC-Si films, compared to the model without water. The thickness of the adsorbed water was in the range from 1nm to 4nm on the DLC-Si films. However, there was no adsorbed water on the DLC film. This fact is consistent with the larger content of silanol (Si-OH) measured by the derivatization-XPS of the DLC-Si films, compared to that of the DLC film. We have clarified that the refractive index increased at the broad range of 200-850 nm, the extinction coefficient at the broad range of 200-1700 nm decreased with an increase in the Si content of the DLC-Si films.