The influence of the thermal annealing treatments on the microstructure and optical properties of a-C:H films prepared by PECVD method

Abstract

In this work, hydrogenated amorphous carbon (a-C:H) films were prepared by using a radio frequency (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) method at 220 °C. The influence of the annealing treatments on the microstructure and optical properties of the a-C:H films has been investigated. Raman and X-ray photo electron spectroscopy (XPS) results showed that the sp2 carbon fraction and sp2/sp3 ratio increase and sp3 carbon fraction decrease with increasing the annealing temperature. However, with increasing annealing temperature, the D and G peak positions and the G peak FWHM have no obvious changes. The spectroscopic ellipsometry suggested that the density, refractive index n and the extinction coefficient k of the as-deposited film and the films annealed at 300 and 400 °C are not affected obviously by thermal annealing treatments. However, when the annealing temperature is higher than 400 °C, the films become high-density and opaque, meanwhile, the film thickness decrease significantly. The UV-VIS spectroscopy measurement indicated that the increase of sp2 fraction and graphitization features of the a-C: H films result in the decrease of the films transmission and optical band gap.