Structural analysis of amorphous carbon films by BEMA theory based on spectroscopic ellipsometry measurement

Abstract

The structural analysis of amorphous carbon films is imperative for the application of their unique properties into industrial fields. Density is one of the most fundamental properties of amorphous carbon films, and directly related to their structures. In the present study, thirteen amorphous carbon film samples with different sp3/(sp3+sp2) ratios and hydrogen contents were deposited by various physical and chemical vapor deposition techniques. All these films were analyzed by spectroscopic ellipsometry and simulated using Bruggeman effective medium approximation (BEMA) theory. In this simulation analysis, ten types of optical models were proposed based on the selected five kinds of standard materials (diamond, highly oriented pyrolytic graphite, glassy carbon, polyethylene, and void) with considering a feasibility of each model. The comparisons of the X-ray reflectivity density and BEMA calculated density, as well as those of the sp3/(sp3+sp2) ratios obtained from BEMA simulation and the near-edge X-ray absorption fine-structure analysis were carried out for the individual samples. Thus, using BEMA theory, it was established that the suitable optical models should be applied to make a detailed structural analysis of the individual types of amorphous carbon films.