Cubic HfO2 Doped with Y2O3 for Advanced Gate Dielectrics by MBE.

High $\kappa $ HfO$_{2}$ ($\kappa $ =20) is currently employed as an alternative gate dielectric replacing SiO$_{2}$ in CMOS scaling. There are three known crystal structures of HfO$_{2}$, monoclinic, cubic, and tetragonal with varying dielectric constants [1]. Recently we showed HfO$_{2}$ films epitaxially grown on GaAs(100) formed the stable monoclinic phase ($\alpha =\gamma $ = 90° and $\beta \quad \sim $ 99°) with the $a$ and $b$ axes aligned with the in-plane GaAs{\{}100{\}}axes resulting in four equivalent domains. This work demonstrates the successful alteration of the crystal structure of HfO$_{2 }$from the lower $\kappa $ monoclinic phase to the higher $\kappa $ ($\kappa $ =30) cubic phase stabilized through epitaxy on GaAs(100) and Si(100) with the aid of Y$_{2}$O$_{3}$ doping ($\sim $ 20{\%} based on XPS). X-ray diffraction scans on these films clearly indicated the cubic symmetry. Doping Y$_{2}$O$_{3}$ is also to enhance the thermal stability of amorphous HfO$_{2}$. Y$_{2}$O$_{3 }$doping was shown to help raise the re-crystallization temperature of HfO$_{2 }$to be$_{ }$compatible with high temperature processing. [1] X. Zhao et al, PRB \textbf{65}, 233106, (2002).