Oxygen species in HfO/sub 2/ films : an in situ x-ray photoelectron spectroscopy study

Abstract

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 (Osec) were also observed. By ruling out possible roles of impurities as well as by comparing O 1s signals for different thermochemical processing routes, Osec chemical origins were inferred. Moreover, angle-resolved photoelectron analysis was employed to quantitatively separate surface and bulk Osec contributions. Surface Osec was assigned to surface O-H groups generated either by room temperature water vapor exposure or by 600 °C H2 annealing. Bulk Osec 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 Osec can be partly removed by annealing in reducing atmospheres. For some of the processing routes employed here, we observed additional, water-induced bulk Osec, which was attributed to dissociative water absorption in HfO2 amorphous regions and O-depleted grain boundaries.