On physical models for gate oxide breakdown

Electrical breakdown of thin (32-nm) SiO
2
films subjected to constant-current stressing is studied. By studying the effects of reversing the polarity of the constant-current bias and the effects of thermal annealing on the charge-to-breakdown it is determined that electrical breakdown of SiO
2
is not caused by the widely-cited accumulation of trapped electrons. Rather it is caused by the buildup of positive charges near the cathode at localized areas. The positive charges are not mobile ions but exhibit many characteristics of trapped holes. We conclude that electrical breakdown in SiO
2
is caused by the accumulation of holes, generated by impact ionization in the oxide.