Structural disorders in an amorphousHfO2film probed by x-ray absorption fine structure analysis

Abstract

The local structural order of amorphous ${\text{HfO}}_{2}$ films $(a{\text{-HfO}}_{2})$ was examined using $\text{Hf}\text{ }{L}_{3}$-edge x-ray absorption spectroscopy and fine structure analyses. The fine structure simulation successfully reproduced the spectral evolution of the crystalline-to-amorphous phase transition by reducing the characteristic radius for atomic ordering to $\ensuremath{\sim}3.5\text{ }\text{\AA{}}$. Detailed path-by-path analyses further showed that the vibrational displacement of oxygen atoms in $a{\text{-HfO}}_{2}$ films is highly anisotropic showing mainly lateral dispersion perpendicular to a Hf-O bond. This anisotropic structural disorder is responsible for enhancing the dielectric constant accompanying phonon mode softening in the $a{\text{-HfO}}_{2}$ film.