Observation of HfO2 thin films by deep UV spectroscopic ellipsometry

Deep UV spectroscopic ellipsometry (SE) is used for structure change observations in thin hafnia (HfO2) layers deposited by p-MOCVD on silicon substrate. The absorption edge E-g and most of the critical point transitions in HfO2 are above 6 eV, which makes the extension to Deep UV SE (5-9 eV) very suitable. The phase mixture changes as function of thickness and deposition process temperature, deduced from SE correspond well to XRD and Angle Resolved (AR)-XPS spectroscopy observations. From the absorption spectra at 4.5 eV, defects such as oxygen vacancies are detected, whereas from XPS spectra the estimation of the O/Hf ratio follows the same trend. Deep UV SE reveals differences in the dielectric function with orthorhombic/monoclinic phase mixtures essentially with peaks at 7.5 and 8.5 eV. Quantum confinement originated from the grain size of the films and the excitonic origin of the 6 eV feature are discussed. (c) 2007 Elsevier B.V. All rights reserved.