Microscopic mechanisms of hydrogen depassivation at amorphous SiO2/Si interfaces

Abstract

Hydrogen is widely employed to passivate the dangling bonds formed during the thermal oxidation of silicon, thereby improving the electronic quality of the SiO2/Si interface. However, such hydrogen-related passivation can also compromise device reliability, as ionizing radiation or bias stress may generate mobile protons that migrate to the interface and depassivate the Si dangling bonds. In this work, we investigate the microscopic mechanisms of hydrogen depassivation at amorphous SiO2/Si interfaces. Two representative interface defects, Pb1 and Pb0, are examined to reveal the energetics and reaction pathways associated with proton-induced depassivation. For the Pb1 center, the depassivation proceeds through proton detachment from oxygen followed by H2 formation at the Si dangling bond, with a forward activation barrier of ∼0.4 eV and an overall energy release of 0.85 eV. In contrast, the depassivation of Pb0 defects is more complex due to the local structural disorder and variable proton capture sites. The proton may transiently form metastable configurations, such as a threefold-coordinated oxygen or an Si–H+–Si bridge, resulting in reaction intermediates that compete kinetically with direct H2 formation. Our results provide a unified microscopic picture of hydrogen depassivation at SiO2/Si interfaces and highlight the critical role of local bonding topology and charge-state transitions in determining the interfacial reliability of Si-based devices.