EFFECT OF TUNNELING ELECTRONS IN FOWLER-NORDHEIM REGIME ON THE CURRENT-VOLTAGE CHARACTERISTICS AND MODEL OF DEGRADATION OF METAL-OXIDE-SEMICONDUCTOR CAPACITORS

The evolution of the shift of current-voltage characteristics after Fowler-Nordheim stress has been investigated. In some cases, a diminution of the slope of current-voltage characteristics was observed. It has been studied and discussed with respect to the mode of the injection of carriers in the oxide, the type of carrier trapping, and the generation of defects. The variation of the slopes of current-voltage characteristics after high-electric-field stress is due to a nonuniformity of the field in the oxide and mainly depends on the cathode field. The variation of the cathode field is basically related to the location of the oxide charge (positive or negative) near the substrate-Si/SiO2 and gate/SiO2 interfaces which modify the shape of the tunneling barrier. A model of degradation of the metal-oxide-semiconductor structures has been deduced from a qualitative analysis of voltage shifts of current-voltage characteristics depending on the magnitude of electric field stress, on the stress mode with a positively or negatively biased gate, and on the injected charge density. The degradation of the oxide is consistent with both mechanisms of trap creation and/or impact ionization.