Nanoscale Characterization of High-K/IL Gate Stack TDDB Distributions After High-Field Prestress Pulses

The effect of single nondestructive pulsed voltage prestresses on the time to breakdown distributions of a SiON/HfSiON bilayer gate stack is investigated at nanometric scale using an atomic force microscope in conduction mode under ultrahigh vacuum. The results are compared with the degradation due to a voltage pulse of the SiON layer alone. It is found that only the shape parameters of the distributions are affected by the prestress pulses. This effect is then discussed in terms of a progressive degradation starting at the Si/SiON interface, and an extrapolation formula is given to predict the decrease of the time to breakdown of the bilayer gate stack as a function of the prestress pulse parameters.