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

Abstract

The vibrational and electronic structures of N 2O-annealed SiO 2 layers on Si(100) have been studied by infrared absorption and photoemission measurements in comparison with those of as-grown SiO 2/Si(100) without N 2O annealing. The analysis of N1s core spectrum as a function of the distance from the SiO 2/Si interface shows that nitrogen atoms pile up in the SiO 2 network within ∼2 nm from the interface. The frequency change in the LO-phonon mode for N 2O-annealed SiO 2 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 SiO 2 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.