Soft x-ray photoemission studies of Hf oxidation

Soft x-ray photoemission spectroscopy has been applied to determine the binding energy shifts and the valance band offset of HfO2 grown on Hf metal. Charging of oxide films upon x-ray exposure is found to be very severe and special care is taken to eliminate it. Photoemission results show the presence of metallic Hf (from the substrate) with a 4f7/2 binding energy of 14.22 eV, fully oxidized Hf (from HfO2) with a 4f7/2 binding energy of 18.16 eV, and at least one clearly defined suboxide peak. The position of the valence band of HfO2 with respect to the Hf(metal) Fermi level is 4.23 eV.