HYDROGEN AT THE Si/SiO2 INTERFACE: FROM ATOMIC-SCALE CALCULATIONS TO ENGINEERING MODELS

Abstract

Two contrasting behaviors have been observed for H in Si / SiO 2 structures: a) Radiation experiments established that protons released in SiO 2 migrate to the Si / SiO 2 interface where they induce new defects; b) For oxides exposed first to high-temperature annealing and then to molecular hydrogen, mobile positive charge believed to be protons can be cycled to and from the interface by reversing the oxide electric field. First-principles density functional calculations identify the atomic-scale mechanisms for the two types of behavior and conditions that are necessary for each. Using the results of the atomic-scale calculations we develop a model for enhanced interface-trap formation at low dose rates due to space charge effects in the base oxides of bipolar devices. We find that the hole trapping in the oxide cannot be responsible for all the Enhanced Low-Dose-Rate Sensitivity (ELDRS) effects in SiO 2, and the contribution of protons is also essential. The dynamics of interface-trap formation are defined by the relation between the proton mobility (transport time of the protons across the oxide) and the time required for positive-charge buildup near the interface due to trapped holes. The analytically estimated and numerically calculated interface-trap densities are found to be in very good agreement with available experimental data.