Thickness of the SiO2/Si interface and composition of silicon oxide thin films: Effect of wafer cleaning procedures

We determined the areal density of Si atoms constituting the oxide-silicon interface and the stoichiometry of ultra-thin silicon oxide films, thermally grown on Si(001) in dry O-18(2) atmospheres, using the channeling of alpha-particles along the (001) axis of the Si substrates associated with grazing angle detection of the scattered particles. The amount of O-18 atoms in the films was determined independently using the O-18(p,alpha)N-15 nuclear reaction at 730 keV. The Si wafers were submitted to different cleaning procedures before oxidation in O-18(2), namely: standard RCA cleaning, HF etching followed by a rinse in ethanol and rapid thermal cleaning (RTC) under high vacuum. The stoichiometry of all oxide films having thicknesses between 2 and 13 nm could be fitted assuming a ratio O/Si = 2, that is, the films were constituted by silicon dioxide. By comparing the results for samples cleaned in different ways, however, we noticed a pronounced change in the number of atoms in the non-registered Si layers at the SiO2/Si interface and so in the thickness of these interfaces.