Optical properties of non-stoichiometric SiO 2 as a function of excess silicon content and thermal treatments

Abstract

The infrared (IR) absorption spectra and the behavior of the refraction index of a two-phase non-stoichiometric SiO 2 film with excess Si have been studied as a function of the excess of Si and post-deposition thermal treatment. The oxides were deposited by low-pressure chemical vapor deposition using SiH 4 and N 2O as reactant gases at a substrate temperature in the range of 650 to 750 °C. Some of the films were given a final annealing treatment at temperatures ranging from 700 to 1100 °C in N 2 for 30 min. Both annealed and as-deposited oxides have IR absorption peaks associated with the bending, rocking and stretching modes of the Si-O-Si bonds in SiO 2, although the exact location of these peaks is different for different contents of excess silicon and it also depend on the post-deposition thermal treatment given to the oxides. Unannealed samples present a shift of the stretching peak towards low wavenumbers as the excess of Si is increased. The samples annealed at 1000 °C on the other hand do not present this shift. Unannealed samples with large content of Si also present an absorption peak at 890 cm −1 that could be associated with partially oxidized Si. It is suggested that at least part of the excess Si in the as-deposited samples is present in the form of an SiO x phase while in the annealed samples a clear separation occurs between a Si and a SiO 2 phase. The behavior of the refraction index is similar for both types of sample, increasing as the excess silicon is increased.