Simulation of time-dependent tunneling characteristics of MOS structures

Abstract

A detailed model has been developed to simulate the Fowler-Nordheim tunneling and degradation characteristics of thermal oxides on silicon incorporating geometry effects, trapping at pre-stress and post-stress trap sites, and field dependent charge to breakdown. For the first time, the effect of gate edge on the time-dependent tunneling characteristics has been quantitatively analyzed, using the Schwarz-Christoffel transformation method. It is found that gate edge region can enhance the tunneling current significantly and also accelerate oxide degradation and breakdown. One application of this model is to remove geometry effects in the oxide parameters extracted using ramp-stress measurements. Another application is to use the asymmetry in gate and substrate injections to electrically characterize the gate geometry and obtain an effective edge curvature.