Correlation of thermal stability of the mechanical and optical properties of diamond-like carbon films

Abstract

The aim of the present contribution is the study of the influence of the annealing on the mechanical and optical properties of the plasma deposited diamond-like carbon (DLC) films. The DLC films were prepared for different values of hydrogen content from the mixture of methane and hydrogen in capacitively coupled PECVD reactor. Thermal stability of the films was investigated using sample annealing. The optical properties of the as deposited and annealed DLC films were studied ex situ using variable angle spectroscopic ellipsometry and spectroscopic reflectometry applied within the near-UV, visible and near-IR regions. For optical constants our dispersion model based on parameterization of the densities of electronic states was used. The dependence of the hardness and the elastic modulus on the hydrogen content in the deposition feed was determined using depth sensing indentation technique. It was found that with increasing temperature the sp 3-to-sp 2 ratio, atomic fraction of hydrogen, hardness and elastic modulus decreased. For the samples prepared with relatively high hydrogen flow rate the annealing helped to minimize the film intrinsic stress. Moreover, these films exhibited free-carrier anisotropy. This fact was respected by including the Drude absorption term into the dispersion model.