Heavy ion irradiation of thin gate oxides

We have studied the gate leakage current after heavy ion irradiation of MOS capacitors with thin gate oxides. In 3-nm and 4-nm oxides radiation-induce d soft breakdown (RSB) occurs even after ion fluences as small as 100 ion h its on the device surface. The RSB conductive paths likely reproduce the io n hit distribution: some of them can drive a substantial fraction of the wh ole gate leakage current. The bias applied during irradiation enhances the RSB current intensity but no critical field exists to ignite the RSB, which is observed also under nat-band. The irradiated 3-nm oxides show smaller c urrent variations and random telegraph signal CRTS) noise than the 4-nm oxi des, owing to the higher current driven in fresh devices by direct tunnelin g conduction. The RTS noise increases with the radiation dose; it can be de scribed successfully neither by a Levy nor by a Gaussian distribution. In 6 .5-nm and IO-nm thick oxides the defect clusters generated by heavy ion irr adiation can produce RSB and RILC (radiation induced leakage current), whic h have not been observed after low LET irradiation, or electrical stresses.