Analysis of x-ray irradiation effect in high-k gate dielectrics by time-dependent photoemission spectroscopy using synchrotron radiation

We have developed a method to precisely determine the band offsets for hafnium oxide (HfO₂), hafnium silicate (HfSiO) and nitrided hafnium silicate (HfSiON) films on Si by elimination of x-ray irradiation effects with time-dependent photoemission spectroscopy (PES) and x-ray absorption spectroscopy. The core-level PES spectra shift during PES measurements, which is explained as the dielectric films charging due to photoemission by the x-ray irradiation. For elimination of the x-ray irradiation effect on the determination of the band offsets, time-dependent photoemission spectroscopy was performed. The precisely determined valence band offsets for HfO₂, HfSiO and HfSiON are 3.2, 3.4, and 1.9 eV, respectively. On the other hand, the conduction band offsets are almost the same values of about 1.3 eV. Thus, the elimination of x-ray irradiation effect enables to precisely determine the band offsets, leading to the accurate estimation of gate leakage current.