Oxygen species in HfO2 films:: An in situ x-ray photoelectron spectroscopy study

The chemical bonding of O atoms in HfO2 films on Si was investigated by in situ x-ray photoelectron spectroscopy in the O 1s spectral region. In addition to trivial O forming only O-Hf bonds, O 1s signals corresponding to nontrivial secondary O (O-sec) were also observed. By ruling out possible roles of impurities as well as by comparing O 1s signals for different thermochemical processing routes, O-sec chemical origins were inferred. Moreover, angle-resolved photoelectron analysis was employed to quantitatively separate surface and bulk O-sec contributions. Surface O-sec was assigned to surface O-H groups generated either by room temperature water vapor exposure or by 600 degrees C H-2 annealing. Bulk O-sec was assigned to O-O or O-H bonds and, as indicated by thermodynamic calculations and complementary structural analysis, is located in HfO2 amorphous regions and grain boundaries. This bulk O-sec can be partly removed by annealing in reducing atmospheres. For some of the processing routes employed here, we observed additional, water-induced bulk O-sec, which was attributed to dissociative water absorption in HfO2 amorphous regions and O-depleted grain boundaries. (c) 2007 American Institute of Physics.