Effects of fluorine addition on the structure and optical properties of SiO2 films formed by plasma-enhanced chemical vapor deposition

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Abstract
In order to elucidate the effects of fluorine addition on the structure and optical properties of SiO2 films formed by plasma-enhanced chemical vapor deposition of tetraethoxysilane, photoluminescence and optical absorption characteristics were studied using synchrotron radiation as an excitation photon source. Luminescence appears at 4.4 eV in both fluorine-doped and nondoped films when excited by 7.6 eV photons, indicating that the oxygen vacancies exist in both films. The decay profile of the 4.4 eV luminescence deviates from a single-exponential curve, indicating that the microscopic structure is not uniform in the sample. This deviation becomes smaller by the fluorine addition. Infrared absorption spectra indicate that the width of the distribution of bond angle ∠SiOSi becomes smaller with an increase in the fluorine content. From these results, it is considered that the distribution of the bond angle decreases by the addition of fluorine. The optical gap energy was found to increase with the increase in the fluorine content. Presumably, this is also due to the homogeneous structure with a uniform bond angle caused by the fluorine addition.

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