Single and dual-mode plasma enhanced chemical vapor deposition of fluorinated diamond-like carbon films

Abstract

Fluorinated diamond-like carbon (F-DLC) films were deposited on glass and polycarbonate (PC) substrates by radio frequency (RF) and radio frequency/microwave (RF & MW) plasma enhanced chemical vapor deposition, which are called single and dual-mode systems, respectively. A mixture of acetylene (C2H2) and carbon tetra fluoride (CF4) was used for the deposition of the films. The effects of RF and MW powers on the fluorine concentration, micro structure, surface morphology, deposition rate, contact angle, surface energy and optical properties of the films as well as the plasma produced chemical species were investigated. The energy dispersive X-ray analysis (EDX) revealed that the fluorine (F) concentration grew from 12.47 to 16.53at.% with increasing RF power from 50 to 200W. However, the atomic F content began to decrease unexpectedly as the MW plasma was added in the dual-mode system. The Raman spectra showed that by increasing RF power, the G peak position shifted toward higher frequencies and the ID/IG ratio increased. The same trend was almost preserved with increasing MW power. The contact angle measurements revealed that the surface of the films became more hydrophobic as the F content increased. The surface energy decreased from 47.2 to 41.8mN/m by increasing the RF power and then started to reach 50.6mN/m with increasing the MW power. The surface roughness of the films was found to increase with growing concentration of fluorine. Also the deposition rate increased with increasing the RF and MW power. The direct band gap of the films reduced with increasing the RF and MW power as the sp2 cluster size increased in the film structure. In addition the optical emission spectroscopy (OES) data showed the correlation between the chemical species produced in the plasma medium and the F content of the films.