Infrared study of oxygen precipitate composition in silicon

High spatial resolution Fourier transform absorption measurements were performed with polarized light on oxygen precipitates grown in silicon samples briefly annealed. We demonstrate that the wave-number position and intensity of the 1230-${\mathrm{cm}}^{\mathrm{-}1}$ absorption band, directly related to the precipitates, give information regarding stoichiometry of the oxide constituting such precipitates and their density. In particular, the precipitates in our samples are made of amorphous suboxides, mainly ${\mathrm{SiO}}_{1.8}$, with 5 ppm local concentration. Moreover, our conclusions give evidence that disk-shaped precipitates in silicon have the same optical properties of thermal oxide films with comparable thickness grown on silicon.