Determining factor of effective work function in metal/bi-layer high-k gate stack structure studied by photoemission spectroscopy

摘要

We have demonstrated the determining factor of effective work function in TiN/HfO2/Al2O3/SiO2 gate stack structures by photoemission spectroscopy with synchrotron radiation. Difference in depth profiles indicate that the Si layer inserted at the HfO2/Al2O3 interface suppresses diffusion of Al atoms into the HfO2 layer after annealing, resulting in keeping magnitude of the high-k/SiO2 interface dipole. However, it is found that the increase of the effective work function cannot be explained only by the interface dipole model. We suggest that oxidation of the TiN metal electrode due to oxygen diffusion from the HfO2 layer is one of the most important factors.