Quantum-mechanical study of nitrogen bonding configurations at the nitrided Si-SiO2 interface via model molecules

High-level self-consistent-held calculations for a set of nitrogen-containing model molecules are carried out to study the influence on the N(1s) binding energy of first-, second-, and third-nearest neighbors, stress (bond angles), and conformation. These calculations are directed to account for the N(1s) peak structure (generally fit with two Gaussian functions whose centers are separated by 0.7-0.9 eV) as seen by x-ray photoemission spectroscopy at the nitrided Si-SiO2 interface. Using a nonlinear extrapolation method to determine the core energy levels in large molecules, we have ascribed the Gaussian peak centered on (398.3+/-0.2) eV to nitrogen bonded to otherwise fully oxidized silicon in "bulk" SiO2 and the Gaussian peak shifted by 0.7-0.9 eV toward lower binding energy to the interfacial species N[Si(-)Si)(3-y)(O-)(y)](3) with y similar or equal to 1. Not only can the observed peak be resolved in those two components, but also there is no other choice involving only nitrogen, silicon, and oxygen, which allows for the observed spectrum.