Theoretical and experimental investigation of ultrathin oxynitrides and the role of nitrogen at the Si-SiO₂ interface

A combination of state of the art experimental techniques with the theoretical analysis using a first-principles density functional method is used to investigate the microscopic structure and electronic properties of ultrathin oxynitrides. Results show that nitrogen prefers to localize at the interface, where its presence results in the structural improvement of the interfacial oxide layer and the strain reduction. This strain reduction is possibly responsible for the lowering of the free energy that stabilizes the oxynitried layer. Calculations of the vibrational density of states reveal a localized nitrogen related mode at 809 cm^-1.