Although gate stack structures with high-k materials have been extensively investigated, there are some issues to be solved for the formation of high quality gate stack structures. In the present study, we employed hard x-ray photoelectron spectroscopy in operating devices. This method allows us to investigate bias dependent electronic states, while keeping device structures intact. Using this method, we have investigated electronic states and potential distribution in gate metal/HfO2gate stack structures under device operation. Analysis of the core levels shifts as a function of the bias voltage indicated that a potential drop occurred at the Pt/HfO2interface for a Pt/HfO2gate structure, while a potential gradient was not observed at the Ru/HfO2interface for a Ru/HfO2gate structure. Angle resolved photoelectron spectroscopy revealed that a thicker SiO2layer was formed at the Pt/HfO2interface, indicating that the origin of potential drop at Pt/HfO2interface is formation of the thick SiO2layer at the interface. The formation of the thick SiO2layer at the metal/high-k interface might concern the Fermi level pinning, which is observed in metal/high-k gate stack structures.
ASJC Scopus subject areas
- Physics and Astronomy(all)