Oxygen defects and Fermi level location in metal-hafnium oxide-silicon structures

We describe an in situ method for measuring the band bending of Si substrates in complex metal-oxide-semiconductor systems using femtosecond pump-probe photoelectron spectroscopy. Following deposition of metal layers (Pt, Re, or Re oxide) on the high-k dielectric HfO2, measurement of the band bending in the underlying Si provides a direct determination of the location of the Fermi level within the Si band gap at the Si-dielectric interface. Changes in the Fermi level with post-deposition anneals and oxygen exposure were correlated with valence and core photoelectron spectroscopy as well as capacitance-voltage measurements. These studies illuminate the roles that gate metal work function, modified by metal induced gap states and defects within the oxide, such as oxygen vacancies, play in defining the location of the Fermi level in metal-oxide-semiconductor structures.