Analysis of native oxide growth process on an atomically flattened and hydrogen terminated Si (111) surface in pure water using Fourier transformed infrared reflection absorption spectroscopy

Abstract

Early stages of native oxide growth on an atomically flat and hydrogen terminated Si (111) surface in pure water was discussed on the basis of Fourier transform infrared reflection absorption spectroscopy (FT-IR-RAS) spectra of the oxide. To explain the RAS spectra change with oxidation time, we calculated the RAS spectra theoretically using a model that we named a precipitate model. In the model, we assumed that the shape of oxides formed at the surface was ellipsoid with axes of a1, a2, and a3. Oblateness of the ellipsoid was represented by a depolarization factor (L1, L2, and L3) relating to the reciprocal numbers of each axis of the ellipsoid; L1+L2+L3=1 and L1:L2:L3=1/a1:1/a2:1/a3. Thus, if L1=1, a2 and a3 are infinite, then the ellipsoid is a layer stretching toward direction of a2 and a3, and when L1=L2=L3=1/3, the oxide shape is spherical. The dielectric constant of a surface layer containing the ellipsoidal oxides was calculated using the effective media approximation. Calculated spectra were well fitted to the measured spectra. However, the depolarization factor (L1) calculated from the IR-RAS spectra did not become 1 even after 1×105 minutes oxidation, though the native oxide after 100 220 min oxidation contained more Si–O bonds than that formed by a sulfuric acid and hydrogen peroxide (SPM) solution (H2SO4/H2O2). FT-IR-RAS spectra of thermally grown oxide and chemical oxide formed in the SPM have similar shape to the calculated spectra at L1=1. Thus native oxide grew insularly and not through a layer-by-layer process in the early stages of oxidation.