Phase separation in hafnium silicates for alternative gate dielectrics - Influence on the unoccupied states

We have used X-ray absorption near-edge fine-structure (XANES) analysis of oxygen K-edges in combination with high-resolution transmission electron microscopy to investigate phase separation in Hf-silicate thin films subjected to high temperature anneals. We show that the oxygen K-edge fine structures can, in a first approximation, be interpreted as an overlap of features from amorphous silica and crystalline hafnia phases in the phase separated microstructures. Increasing amounts of silica in the samples resulted in an increase of bulk silica-like features in the oxygen K-edges. The lowest conduction band levels are determined by the Hf d states of hafnia for all compositions investigated. XANES was not able to detect silicate-type bonding that is expected to be present in some of the films. (C) 2003 The Electrochemical Society.