Changes in the density of ultrathin silicon oxide films related to excess Si atoms near the oxide–Si(100) interface

Abstract

To clarify the considerable changes in the (volumetric) density ρox of 3.5–8.0-nm-thick silicon oxide films on Si(100) oxidized at 800–950 °C, which were confirmed by our previous work, ρoxs and (areal) number densities of the 700–750 °C oxidation films were investigated. The ρoxs and number densities of Si and O atoms were determined by charged-particle activation analysis and Rutherford backscattering spectrometry, respectively. It was confirmed again that excess Si atoms relative to the stoichiometric SiO2 composition exist near the oxide–Si substrate interface and the number densities of them NSi(excess)s were changed with oxidation temperature. The ρoxs were also changed with oxidation temperature but the changes in ρox were diametrically contrasted with those in NSi(excess). For the 2.0–8.0-nm-thick films oxidized at 700–950 °C, the ρox characteristics exhibited a maximum at 850 °C but the NSi(excess) ones exhibited a minimum at 850 °C. It is, therefore, believed that this ρox change is governed mainly by microscopic changes in the atomic arrangement structure due to the NSi(excess) difference.