Degradation mechanism of dielectric properties of HfO due to interaction of oxygen composition and strain

This paper reports on a quantum chemical molecular dynamics analysis for HfO₂ film with different amount of oxygen in order to make clear the effect of the strain and intrinsic defects in the film on the dielectric characteristic of the hafnium dioxide film. When an oxygen vacancy or a carbon atom as the impurity is introduced in HfO₂ film, a donor site is formed locally around the vacancy or carbon atom. On the other hand, it has been found that an acceptor site is formed when an excess oxygen atom is added to the film. The magnitude of the band gap of the HfO_2plusmnx decreases drastically from 5.6 eV to about 0.1 eV. Uni-axial strain causes anisotropic change of the band structure of HfO₂. The change rate of the band gap due to the uni-axial strain is about 10% /10%-strain.