Total dose dependence of radiation-induced leakage current in ultra-thin gate oxides

Radiation-induced leakage current (RILC) has been studied on ultra-thin gate oxides (4 and 6 nm) irradiated with 8 MeV electrons. Both RILC and stress-induced leakage current (SILC) have been fitted with the same FowlerNordheim law, suggesting that RILC and SILC have similar conduction mechanisms. The RILC dependence from total dose during irradiation has been analysed and compared with the SILC dependence from the cumulative injected charge. Different growth laws of RILC and SILC have been found in the two cases. The intensity of positive and negative RILC also depends on the applied gate bias voltage during irradiation, probably reflecting different distributions of the oxide traps mediating the trap assisted tunnelling. Finally, we have presented the first evidence of a quasi-breakdown phenomenon due to ionizing radiation.