A Model for NBTI in Nitrided Oxide MOSFETs Which Does Not Involve Hydrogen or Diffusion

The negative bias temperature instability (NBTI) is, arguably, the single most important reliability problem in present day metal-oxide-silicon field-effect transistor (MOSFET) technology. This paper presents a model for the NBTI which is radically different from the quite widely utilized reaction diffusion models which dominate the current day NBTI literature. The proposed model is relevant to technologically important nitrided oxide pMOSFETs. The model is clearly not, at least in its entirety, relevant to pure silicon dioxide gate pMOSFETs. The reaction diffusion models involve hydrogen/silicon bond breaking events at the silicon/silicon dioxide interface initiated by the presence of an interface hole, followed by the diffusion of a hydrogenic species from the interface as well as the potential rebonding of hydrogen and interface trap defect centers. This model does not invoke hydrogen in any form whatsoever but does simply account for the observed NBTI power law response with a reasonable, at least very plausible, assumption about defect distribution and provides a reasonably accurate value for this exponent. (Without making any assumption about defect distribution, the model still provides a time response semiquantitatively consistent with the observations, reasonable agreement considering the simplifying assumptions in the calculations.) The model also provides a reasonable explanation for the recovery which includes a simple explanation for the extremely rapid rate of recovery at short times. In addition, the model provides a very simple explanation why the introduction of nitrogen greatly enhances the NBTI. The model, as presented in this paper, should be viewed as a first-order approximation; it contains several simplifying assumptions. Finally, the model is consistent with recent electron paramagnetic resonance studies of NBTI defect chemistry in nitrided oxide pMOSFETs.