Stochastic charge trapping in oxides: From random telegraph noise to bias temperature instabilities

Charge trapping at oxide defects fundamentally affects the reliability of MOS transistors. In particular, charge trapping has long been made responsible for random telegraph and 1/f noise. Recently, it has been identified as a significant contributor to bias temperature instabilities. Conventional defect models assume that the defect has two states, one of them neutral and the other charged. The transition rates between the two states are calculated using some extended Shockley-Read-Hall theory, which neglects the configurational changes occurring at the defect site following a charge trapping or emission event. In order to capture these changes, multiphonon models have been in use for many decades but have not found their way into the mainstream of reliability modeling yet. Furthermore, recent experimental results demonstrate that defects have more states than the two assumed in the conventional model. These additional states together with multiphonon charge transfer mechanisms are essential for the understanding of the complex defect dynamics. The present review summarizes the basic principles of how to model stochastic defect transitions with a particular focus on multi-state defects. After discussing the limitations of Shockley-Read-Hall theory, the relatively simple semiclassical approximation of multiphonon theory is introduced which already provides a much better description. Finally, the transition rates for multi-state defects are estimated using multiphonon theory, which gives a very accurate description of the latest experimental data. (C) 2011 Elsevier Ltd. All rights reserved.