Structural changes of fluorinated amorphous carbon films by nitrogen incorporation

In this work, the effects of nitrogen addition on the properties of a-C:H:F films produced by radio-frequency plasma enhanced chemical vapor deposition at different temperatures are reported. The structural and optical properties were investigated by X-ray photoelectron spectroscopy, Raman spectroscopy, UV–VIS transmittance and ellipsometry measurements. The main effect of progressive nitrogen incorporation is a decrease of transmittance of the optical band gap of the samples grown at room temperature and at 4001C. Raman spectra evidence that for films deposited at 4001C a sudden loss of sp3 carbon bonding occurs. In particular, at fixed plasma composition the decrease of the optical band gap is interpreted as a clustering of the existing sp2 carbon sites. Ellipsometry characterization indicates that films deposited at 4001C are characterized by a reduction of the refractive index. In particular, the increase in the deposition temperature produces an increase in the size of the graphitic clusters.