Annealing-time dependence in interfacial reaction between poly-Si electrode and HfO₂/Si gate stack studied by synchrotron radiation photoemission and x-ray absorption spectroscopy

We have investigated annealing-time dependence in interfacial reactions between polycrystalline-Si (poly-Si) electrodes and HfO₂/Si gate stacks using synchrotron radiation photoemission and x-ray absorption spectroscopy. From photoemission core-level spectra, we found that silicidation started at the upper interface between poly-Si electrodes and HfO₂ gate dielectrics under the conditions of 700 °C and 3 min in ultrahigh vacuum. Before silicidation, we observed nonstoichiometric silicon oxide at the upper interface, suggesting the formation of oxygen vacancies which may cause Fermi level pinning. The interface layer between HfO₂ gate dielectrics and Si substrates was changed into silicide by further annealing. In addition, from valence-band photoemission and O K-edge absorption spectra, we have found that the crystallization of HfO₂ gate dielectrics is independent of silicidation.