Spectroscopic ellipsometry characterization of diamond-like carbon films formed by filtered arc deposition

Abstract

The properties of diamond-like carbon (DLC) films can vary widely from graphite (sp 2 local bonding) to diamond (sp 3 local bonding), strongly depending on the film preparation conditions. As the optical constants ( n, k) of sp 3 bonded carbon are quite different from those of sp 2 bonded carbon over the visible and near-infrared (VIS–NIR) spectral range, it is possible to provide precise quantitative information on sp 3 C (sp 2 C) fractions using optical characterization methods. In the present work, spectroscopic ellipsometry (SE) using multiple sample analysis method has been applied to study a series of DLC films on silicon substrates prepared by filtered arc deposition (FAD) technique. In contrast to most reported SE studies, the DLC film was simulated by a mixture of sp 3 C, sp 2 C and void constituents instead of treating it as a whole. From the interpretation of SE spectra, the film thickness and the volume fractions of sp 3 C, sp 2 C and void have been derived, respectively. In addition, comparison between SE results and Rutherford backscattering spectroscopy (RBS) and electron energy loss spectroscopy (EELS) results will be given. This work shows that SE using multiple sample analysis method is a very useful optical method to determine sp 3 C fractions in DLC films.