CHARGE GENERATION IN THIN SIO2 POLYSILICON-GATE MOS CAPACITORS

Charge generation in the bulk of thin oxides (10-33 nm) during high-field (Fowler-Nordheim) stress is investigated on polysilicon-gate MOS capacitors using constant current injection and high frequency C-V measurements. Our data show that initially positive charges are generated in the bulk of the oxide, followed by negative ones. The mechanisms that govern the creation of these different charges are investigated. A qualitative physical model is presented. We propose that positive charges are created by electron detrapping. Negative charges are due to electron trapping at preexistent and, possibly, newly created trap sites in the region of the oxide where the injected electrons have low kinetic energy. This model helps us understand the wear-out and breakdown of thin oxides.