Structural evolution of a-C:F:H film prepared by microwave ECR CVD

The a-C:F:H films were prepared with the mixture of CH4 and CHF3 gases by the microwave ECR chemical vapor deposition method. The deposition rate of the film first increases and then decreases with variable flow ratios R {[CHF3]/([CHF3]+[CH4])}. The results from Fourier transform infrared transmission spectroscopy for these films have shown that a structural evolution of the a-C:F:H film occurs with the variable gas flow ratios R. The main structure of the film presents a DLC-like characteristic as R<64%, while the film takes on a PTFE-like structure as R>64%, where the films consist mainly of –CF2– chains. It seems that this structural evolution also exerts an influence on the optical band gap. The optical band gap decreases with the increase of flow ratios R in the DLC-like region, while it increases in the PTFE-like region. Hydrogen and fluorine concentrations of these films from FTIR are also discussed.