Characterizing crystalline polymorph transitions in $HfO2$ by extended x-ray absorption fine-structure spectroscopy

Atomic layer deposited $HfO2$ films on Si(100) substrates have been measured by extended x-ray absorption fine-structure (EXAFS), pre- and postanneal processing. Analysis of the second coordination shell indicates an increase in atomic order with increasing film thickness for each anneal temperature and with increasing anneal temperature for each film thickness. Fourier transformed EXAFS spectra fit with $HfO2$ reference phases have identified orthorhombic to tetragonal to monoclinic transformations. Evidence for greater retention of the higher permittivity metastable tetragonal phase corresponding to thinner $HfO2$ films is consistent with a surface energy effect giving rise to the critical grain size phenomenon.