IONIZING-RADIATION INDUCED LEAKAGE CURRENT ON ULTRA-THIN GATE OXIDES

MOS capacitors with a 4.4 nm thick gate oxide have been exposed to gam ma radiation from a Co-60 source. As a result, we have measured a stab le leakage current at fields lower than those required for Fowler-Nord heim tunneling. This Radiation Induced Leakage Current (RILC) is simil ar to the usual Stress Induced Leakage Currents (SILC) observed after electrical stresses of MOS devices. We have verified that these two cu rrents share the same dependence on the oxide field, and the RILC cont ribution can be normalized to an equivalent injected charge for Consta nt Current Stresses. We have also considered the dependence of the RIL C from the cumulative radiation dose, and from the applied bias during irradiation, suggesting a correlation between RILC and the distributi on of trapped holes and neutral levels in the oxide layer.