Structure of pyrolytic and sputtered SiO2 films by X-ray Fourier analysis

Structures of pyrolytic and sputtered SiO2 films have been obtained by X-ray Fourier analysis method. The electron radial distribution function was calculated from experimental X-ray spectra. Both pyrolytic and sputtered SiO2 films have slightly oxygen deficient SiO4 tetrahedral structures. Sputtered SiO2 has a structure more similar to that of fused silica than pyrolytic oxide. The pyrolytic SiO2 consists of SiO4 tetrahedral units randomly stacked and packed. The SiOSi angles are distributed in such a way in the pyrolytic oxide that no ordering exists beyond a given tetrahedral unit, i.e. ≈︁ 3 Å. Therefore, pyrolytic oxide has a less compact structure or lower specific density, a larger amount of vacancies and pinholes, and, consequently, higher susceptibility to water absorption and higher etching rate than fused silica or sputtered SiO2.