XPS time-dependent measurement of SiO2/Si and HfAlOx/Si interfaces

We measure the binding energy Eb of the Si 2p core-level for Si substrates covered with thin (∼1 nm) SiO2 films as a function of X-ray irradiation time (XPS time-dependent measurement). We find that Eb, which correlates with band bending at the SiO2/Si interface, either increases or decreases as the X-ray irradiation time increases. We attribute this change to the trapping of carriers generated by photoelectron emission in the SiO2 films. We demonstrate that we can evaluate not only the number of traps but also the type of traps in SiO2 films by the XPS time-dependent measurement. We also discuss the nature of carrier-trapping centers in SiO2 films on the basis of the complex changes in Eb observed during long-time X-ray irradiation. The measurement is utilized to evaluate a HfAlOx/Si system with unknown carrier-trapping centers of much larger quantity, which has been extensively studied as an alternative gate-dielectric structure in advanced metal-oxide-semiconductor field-effect transistors (MOSFETs).