Common origin for enhanced low-dose-rate sensitivity and bias temperature instability under negative bias

Degradation due to irradiation is known to be associated with the presence of hydrogen in the bulk of the gate oxide, in bulk Si, and at the Si/SiO₂ interface. Previous studies have shown that the migration of protons in the oxide for positive applied gate bias and their reactions at the interface can account for the time and dose-rate dependence of the degradation. Recent experiments, however, have shown that interfacial degradation can occur even in the presence of strong negative gate bias that prevents the arrival of protons at the interface from the oxide side. This result suggests that mechanisms in addition to proton drift in SiO₂ can lead to radiation-induced interface-trap formation. Since previous work on modeling the enhanced low-dose-rate sensitivity (ELDRS) of irradiated bipolar devices was based on formation of an electrostatic barrier that hinders proton transport to the interface at high dose rates, this effect also must be examined in more detail. In this work we use results from first-principles calculations to demonstrate that hydrogen can also be released easily in bulk Si, and especially in the near interfacial area. This hydrogen moves readily to the interface under negative bias. Typical hydrogen precursors in Si are identified as H-dopant complexes. ELDRS shares thus a common origin with another critical reliability phenomenon, the negative bias-temperature instability.