Determination of optical constants and thickness of diamond-like carbon films by a multiple sample method

Using the glow discharge technology with acetylene reactive gas, the diamond-like carbon films with different nominal thicknesses are deposited on Si substrate with the identical process. Variable angle spectroscopic ellipsometry (VASE) is used to characterize the film optical constants at the wavelength range of 380~1700 nm. Given the various selected film thickness, the different optical constants of refractive index and extinction coefficient of sbsorbing films, showing good consistency between the calculated and experimental data, could be obtained based on single sample ellipsometric fitting method. This result indicates that it is generally rather difficult to determine the refractive index and extinction coefficient of absorbing films accurately and rapidly due to the strong correlations between thickness and optical constants. A new multiple sample analysis method is put forwarded to solve this problem. Assume that the optical properties are same for the used three samples of DLC films with various deposition time, the accurate optical constants and related thickness of each sample could be determined rapidly even without any predicted dispersion models. Meanwhile, this new method can be used both for the transparent substrate and non-transparent substrate with absorbing films.