XPS Studies of Structure-Induced Radiation Effects at the Si/SiO2 Interface

The interfacial structures of radiation hard and soft oxides grown by both dry and wet processes on <100> silicon substrates are examined using high resolution x-ray photoelectron spectroscopy (XPS). Substantial differences are observed in the relative concentration of strained Si-O-Si bridging bonds in the interfacial region and in the distribution of intermediate oxidation states of silicon at the abrupt Si/SiO2 chemical interface. Thin thermal SiO2 films (<80 Å) grown on Si <100> substrates are irradiated with electrons having kinetic energies of 0 to 20 eV during in situ XPS measurements. Straightforward field-effect behavior is observed for electron kinetic energies below 6 eV. Both oxide/vacuum surface states and Si(+3) species at the Si/SiO2 interface are generated and allowed to relax during the course of the measurements. These results are correlated with the presence of a strained layer of SiO2 (~20 Å) at the interface that we had previously reported. A structural model for hole and electron trap generation by ionizing radiation is developed to interpret these results and our previous observations.