An optical characterization of native oxides and thin thermal oxides on silicon

Vacuum ultraviolet reflectance spectroscopy is used to characterize native oxides and thin thermal oxides on silicon. The reflectance of 0–50 Å thick layers of noncrystalline SiO2,SiOx(X∼1.5), SiO, and Si on crystalline Si substrates are calculated for the photon energy range 8.5–12 eV using known optical data for these materials. Reflectance data for native oxide growths and thin thermal oxides are compared to these curves calculated for the ellipsometrically measured layer thickness. Native oxides contain little, if any, SiO2 but can be fitted to curves for SiO or composite SiO-SiOX layers while thermal oxides are essentially all SiO2 exclusive of a thin interfacial layer ∼5 Å in thickness which may exist between Si and SiO2. The technique of vacuum ultraviolet spectroscopy which clearly delineates SiO2 from other silicon-oxygen materials such as SiOX and SiO is capable of extreme precision in the characterization of these layers.