Optical emission study of CH4+CHF3 ECR plasma and properties of a-C:F:H films

a-C:F:H films were prepared with a mixture of CH4 and CHF3 gases by microwave electron cyclotron resonance chemical vapor deposition method. An actinometer optical emission spectroscopy was used to reveal the trend in the concentration of some species (H, F, C2, CH etc.) as a function of flow ratio R {[CHF3]/([CHF3]+[CH4])}. The results from Fourier transform infrared transmission spectroscopy showed the structural evolution of a-C:F:H films with variable gas flow ratios R. This structural evolution had an influence on the film optical band gap. The optical band gap decreased with the increasing flow ratios R in the polymer-like region, while it increased in the PTFE-like region. The correlation between the C2 species density and the properties of a-C:F:H films is also discussed.