Oxygen species in HfO_2 films: An in situ x-ray photoelectron spectroscopy study

摘要

The chemical bonding of O atoms in HfO_2 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℃ 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 HfO_2 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 HfO_2 amorphous regions and O-depleted grain boundaries.