Effects of nitrogen incorporation on structural properties of fluorinated amorphous carbon films

Nitrogen-incorporated fluorinated amorphous carbon (a-C:F:N) films were prepared by plasma chemical vapor deposition at room temperature using a CF4, CH4 and N2 gas mixture. Structural, optical and defect properties of these films were investigated by infrared (IR) absorption, X-ray photoelectron spectroscopy, ultraviolet visible absorption, ellipsometry, and electron spin resonance measurements. Carbon, fluorine and nitrogen concentrations, respectively, of the a-C:F:N films ranged from (33, 67, 0) to (41, 46, 13) with an increase in nitrogen gas flow rate. The dielectric constant of these films estimated by ellipsometry was less than 2.5. From IR measurements an intensity ratio of CF2 to CF for a-C:F:N films was comparable to that for a-C:F film with larger fluorine concentrations. Furthermore, the IR band known as the Raman D band was observed, whereas no IR signal due to Raman G band was observed. Based on these results, we suggest that a-C:F:N films have a low-dimensional structure without crystalline regions. The dangling bond density decreased and the optical band gap was approximately constant with increasing nitrogen concentration.