Microscopic structure of the SiO2/Si interface

Abstract

The bonding of Si atoms at the SiO2/Si interface is determined via high-resolution core-level spectroscopy with use of synchrotron radiation. All four oxidation states of Si are resolved, and their distribution is measured for Si(100) and Si(111) substrates. For oxides grown in pure O2, the density of Si atoms in intermediate oxidation states is (1.5 0.5)×1015 cm-2. This value is obtained by measuring the core-level intensity, the escape depth in Si and SiO2, and the relative Si 2p photoionization cross section for different oxidation states. From the density and distribution of intermediate-oxidation states, models of the interface structure are obtained. The interface is not abrupt, as evidenced by the high density of intermediate-oxidation states (about two monolayers of Si) and by their nonideal distribution. The finite width of the interface is explained by the bond-density mismatch between SiO2 and Si. The electrical properties of the interface (band lineup, Fermi, and vacuum level) are determined. Annealing in H2 is found to influence the electrical parameters by removing the Pb centers that pin the Fermi level. The distribution of oxidation states is not affected. © 1988 The American Physical Society.