Assessment of capture cross sections and effective density of electron traps generated in silicon dioxides

Abstract

Generation of acceptor-like electron traps in gate oxides is an important source for device instability. Despite previous efforts, capture cross sections are not unambiguously determined, and there is confusion on how many capture cross sections genuinely exist. Neither is the dependence of trap density for a given capture cross section on stress level clear. The objective of this paper is to fill this knowledge gap by investigating electron-trapping kinetics. There are a number of obstacles for such an investigation including the simultaneous occurrence of trapping and trap generation, stability of trapping, and effects of positive charges. Through careful selection of experimental conditions and testing samples, the authors have been able to overcome these obstacles. In particular, their recent work in this area has allowed them to develop a new method for correcting the effect of positive charges. After removing all uncertainties, the authors are able to identify a capture cross section as large as 10/sup -13/-10/sup -14/ cm/sup 2/ for the generated acceptorlike trap. It will be shown that electron trapping follows the first-order model, and there is also a smaller capture cross section in the region of 10/sup -15/-10/sup -16/ cm/sup 2/. To the best of their knowledge, for the first time, the authors will show that the density of the larger trap increases with stress, but the density of the smaller trap clearly saturates.