Negative-bias temperature instability (NBTI) of nitrided gate oxides prepared with different nitridation processes was characterized and the NBTI results can be well described by an analytical reaction-dispersive-diffusion model in the diffusion-limited regime. The activation energies were recalculated by eliminating the non-Arrhenius part, and this confirms that both the interfacial nitrogen concentration and the nitrogen depth profile in the nitrided oxides play important roles in the nitrogen-enhanced NBTI. Furthermore, first-principles calculations were carried out to examine the effects of nitrogen as either the reaction site or the neighboring atoms at the interface. Lower reaction energies due to the incorporation of nitrogen suggest that nitrogen is a more effective hydrogen-originated hole-trapping center than oxygen and hence enhances NBTI. It was also found that hydrogenoriginated hole trapping at vacancy defects has the strongest dependence on the nitrogen neighboring effect. Moreover, the role of nitrogen in NBTI was also investigated in terms of its influence on the electronegativity and atomic-charge distribution. (c) 2007 The Electrochemical Society.