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-sil icon interface and the stoichiometry of ultra-thin silicon oxide films , thermally grown on Si(001) in dry O-18(2) atmospheres, using the cha nneling of alpha-particles along the (001) axis of the Si substrates a ssociated 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 eth anol and rapid thermal cleaning (RTC) under high vacuum. The stoichiom etry of all oxide films having thicknesses between 2 and 13 nm could b e fitted assuming a ratio O/Si = 2, that is, the films were constitute d 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.