Application of XPS time-dependent measurement to the analysis of charge trapping phenomena in HfAlO _x films

We found that the Si 2p photoelectron peak binding energy of a Si substrate covered with a 3 nm thick HfAlO _X film increased to a saturation value during X-ray irradiation. This shift towards a higher binding energy indicates an increase in the amount of positive charges in the film, and the density of hole traps is estimated to be significantly higher than that in a SiO ₂ film. Before X-ray irradiation, the interface Fermi level coincided with the valence-band maximum of the Si substrate, which indicates that the Si surface band bends upward. This means that there were negative charges already in the film before X-ray irradiation. Investigating the effects of the interlayer beneath the HfAlO _x film on these trapped charges reveals that the observed hole trapping and initial electron trapping are intrinsic to the HfAlO _x film.