We have investigated the thermal stability of TiN/HfSiON gate stack structures using synchrotron-radiation photoemission spectroscopy. Spectral intensities of the Si-oxide components in Si 2p core-level spectra systematically increase with annealing temperature, which strongly depends on thickness of the TiN metal gate layer. Changes brought by annealing procedures in in-depth profiles indicate segregation of Si atoms at the TiN surface. Furthermore, chemical-states-resolved in-depth analyses by angle-resolved photoemission spectroscopy suggest formation of TiSix and HfNy components, due to chemical bond breaking in the HfSiON layer during TiN film growth. This can be related to the degradation of thermal stability.
