Influence of nitrogen incorporation in ultrathin SiO on the 2 structure and electronic states of the SiO rSi 100/ interface

The vibrational and electronic structures of N2O-annealed SiO2layers on Si 100. have been studied by infrared absorption and photoemission measurements in comparison with those of as-grown SiO2rSi 100.without N2O annealing. The analysis of N1s core spectrum as a function of the distance from the SiO2rSi interface shows that nitrogen atoms pile up in the SiO2 network within ;2 nm from the interface. The frequency change in the LO-phonon mode for N2O-annealed SiO2 indicates that three-coordinate nitrogen atoms, whose concentration is a few atomic percent in the interfacial region, relax built-in compressive stress in the oxide network near the interface. The energy loss spectra of O1s photoelectrons and the valence band spectra exhibit no changes in the oxide bandgap and the valence band offset, respectively, being consistent with a theoretical prediction for compressed SiO2 glass. On the other hand, the gap state density above midgap in Si bandgap is significantly decreased by nitrogen incorporation with such a low level, which might be involved with the structural relaxation near the interface. q2000 Published by Elsevier Science B.V.