In this work, an experimental analysis of gate disturbance degradation with
negative bias stress caused by nitridation of flash, tunnel oxide has been
performed. Nitrided tunnel oxide successfully suppresses gate disturbance
with positive bias stress, however, it enhances gate disturbance with negat
ive bias stress. A similar gate polarity dependence has been observed in ch
arge-to-breakdown and gate voltage shifts during Fowler-Nordheim stress. We
propose the following dual-quality-layer model, which can explain all the
polarity results. A poor-quality layer compared with base oxide is concurre
ntly formed at the region where nitrogen atoms do not exist during nitridat
ion. Subsequent to program/erase stress, more hole traps are created at the
surface of tunnel oxide and modulate the energy band at the surface of tun
nel oxide. Therefore, electrons can easily tunnel through the oxide with a
negative bias stress because of the reduced barrier height at the surface o
f tunnel oxide.