Si/SiO₂_ MOSFET reliability physics: From four-state model to all-state model

As implemented in the commercialized device modeling software, the four-state nonradiative multi-phonon model has attracted intensive attention in the past decade for describing the physics in negative bias temperature instability (NBTI) and other reliability issues of Si/SiO₂ MOSFET devices. It was proposed initially based on the assumption that the oxygen vacancy defects (V_O) in the SiO₂ dielectric layer are bistable in the Si-dimer and back-projected structures during carrier capture and emission. Through high-throughput first-principles structural search, we found V_O on non-equivalent O sites in amorphous SiO₂ can take 4 types of structural configurations in neutral state and 7 types of configurations in +1 charged state after capturing holes, which produce a wide range of charge-state transition levels for trapping holes. The finding contrasts with the structural bi-stability assumption and makes the four-state model invalid for most of the O sites. To describe the reliability physics accurately, we propose an all-state model to consider all these structural configurations as well as all the carrier capture/emission transitions and thermal transitions between them. With the all-state model, we show that the V_O defects play important roles in causing NBTI, which challenges the recent studies that discarded V_O as a possible hole trap in NBTI. Our systematical calculations on the diversified V_O properties and the all-state model provide the microscopic foundation for describing the reliability physics of MOSFETs and other transistors accurately.