Infrared spectroscopy study of the thermal stability of fluorinated SiO2 thin films

Fluorinated SiO2 (SiOF) films containing up to about 4 atom % of F and prepared by plasma enhanced chemical vapor deposition from SiH4, N2O, and CF4 precursors have been analyzed by infrared (LR) spectroscopy and X-ray photoelectron spectroscopy to extract chemical and structural information. LR data have demonstrated that the F insertion in the SiO2 network induces a deep structural modification of the film, mainly consisting in the increase of the Si-O-Si bond angle and in the decrease of the angle value dispersion. Also, the polarizability of the system results are significantly affected. Thermal annealing processes in the 400-600 degreesC range induce a marked F loss from the films. This phenomenon does not appreciably affect the peculiar structural properties of the SiOF films, because in all cases, the bond angles relative to the annealed films are equal or higher than those relative to the as deposited ones, while the polarizability of the system, sensitive to the E presence, is modified.