A study of the interface-trap activation kinetics in the Negative Bias Temperature Instability

Abstract

Experiments on a silicon p-channel MOS FET with heated gate electrode have provided evidence that the increase of the interface-trap density observed upon homogeneous negative bias temperature stress can be modelled as the unbalance of two reaction-limited activation and deactivation processes. The variation of the measured trap density with the stress time shows saturating trends, with bias-dependent saturation level. This feature is explained as the dynamic balance of a field-dependent forward reaction and a field-independent backward reaction. The rate constants of both reactions appear to be Arrhenius-like, with distributed activation energy. The activation energy of the forward reaction, which is identified as the depassivation of native Si/SiO2 (near-) interface defects, turns out to be a nearly square root function of the electric field in the oxide. By analogy with the early Frenkel’s theory of electron transport in dielectric materials we discuss whether this field dependence can be considered as the first evidence that the defect depassivation would proceed through a stage where a positively charged hydrogen specie escapes from negatively charged defect.