Segregation of O defects in Si:HfO$_{2}$ heterojunctions: A first principles investigation.

Driven by a need for device miniaturization in the microelectronic industry, Hf-based high-permittivity materials, such as HfO$_{2}$, have gained interest for their potential application as gate dielectrics. However, undesirable interfacial phases such as Hf silicides and SiO$_{x}$ are known to form and degrade the performance of devices. It has been postulated that these interfacial phases are related to the segregation of O defects (vacancy or interstitial) to the interface. In this work, we examine the thermodynamic and kinetic driving forces for the segregation of isolated and clustered O defects (vacancies and interstitials) to the Si:HfO$_{2}$ interface. Using first principles density functional theory calculations, we have determined the formation and migration energies per O defect within bulk HfO$_{2}$ and at the Si:HfO$_{2}$ interface. Our results indicate that isolated as well as a distribution of point defects display large driving forces for interface segregation, allowing for the formation of silicides and silicates. Thus, while an abrupt Si:HfO$_{2}$ interface may be stable in the absence of O defects, such an interface is unstable to the formation of other phases in the presence of O defects.