Noise characteristics of radiation-induced soft breakdown current in ultrathin gate oxides

We have investigated new aspects of the gate leakage current due to radiation-induced soft breakdown (RSB) of thin oxides subjected to heavy-ion irradiation. Temperature and noise characteristics of RSB on MOS capacitors with 3- and 4- nm MOS oxides have been experimentally investigated. We have developed an empirical law to describe quantitatively the temperature dependence of the RSB current. A small activation energy has been found by using an Arrhenius relation, in agreement with the RSB tunneling conduction mechanism. The RSB variation at high temperature has been only estimated, as measurements of RSB oxides easily produced catastrophic breakdown. We have studied the RSB noise and identified different contributions to the characteristic random telegraph noise, correlated with the trapping and conduction characteristics of the RSB spots. An original model has been developed that successfully describes the different probability distributions of the current fluctuations that cannot be simulated by using previous models, such as those based on Levy or Gaussian distributions. Finally, a correlation was established between the shape of the fluctuation distribution and the degradation level of the oxide.

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