The role of nitrogen-related defects in high-k dielectric oxides: Density-functional studies

Abstract

Using ab initio density-functional total energy and molecular-dynamics simulations, we study the effects of various forms of nitrogen postdeposition anneal(PDA) on the electric properties of hafnia in the context of its application as a gate dielectric in field-effect transistors. We consider the atomic structure and energetics of nitrogen-containing defects which can be formed during PDA in various N -based ambients: N 2 , N 2 + , N , NH 3 , NO , and N 2 O . We analyze the role of such defects in fixed charge accumulation, electron trapping, and in the growth of the interface SiO 2 layer. We find that nitrogen anneal of the oxides leads to an effective immobilization of native defects such as oxygen vacancies and interstitial oxygen ions, which may inhibit the growth of a silica layer. However, nitrogen in any form is unlikely to significantly reduce the fixed charge in the dielectric.