We have investigated chemical states and charge density in HfSiON films as a function of depth using x-ray irradiation time-dependent photoemission spectroscopy. N 1s core-level photoemission spectra deconvoluted into three components depend on HfSiON thickness, indicating the component, which is attributed to the N atoms bonded to Hf atoms, has peak near the surface. On the other hand, charge density estimated from band bending in Si from Si 2p photoemission spectra is also distributed mainly near the surface. These results indicate that the origin of the negative charge trapping can be directly related to the presence of Hf-N bonds.
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