Contactless analysis of electric dipoles at high-k/SiO2 interfaces by surface-charge-switched electron spectroscopy

Abstract

The continuous development of silicon devices has been supported by fundamental understanding of the two interfaces that predict the device properties: high-dielectric oxide (high-k)/SiO2 and SiO2/Si. In the absence of metal electrode fabrication, it is challenging to use spectroscopic approaches to deduce the electric dipoles in these interfaces for the prediction of electrical characteristics such as the leakage current and threshold voltage. Here, we propose a method to analyze the permanent dipole at the high-k/SiO2 interface by surface-charge-switched electron spectroscopy (SuCSES). An electron flood gun was used to switch the electrical polarity at the insulating surface to extract the interface-dipole contribution from the macroscopic dielectric polarization in the high-k/SiO2/Si stack structure. TaO3− nanosheet (TaNS) crystallites, which are a family of high-k tantalate materials deposited on the SiO2/Si substrates, were annealed to prepare a nanoscale model interface. The properties of this interface were examined as a function of annealing temperature across the crystalline-to-amorphous transition. Macroscopic dielectric polarization of the TaNS/SiO2/Si gate stack was found to exhibit a gradual decay that depended upon the quantum tunneling processes of induced carriers at the SiO2/Si interface. Additionally, the dipole at the high-k/thin-SiO2 interface abruptly changed by ∼0.4 eV before and after annealing at 400 °C, which may be the result of a decrease in conduction-band offsets at the high-k/Si interface. Thus, SuCSES can aid in determining the inherent valence-band offsets in dielectric interfaces by using X-ray photoelectron spectroscopy with high accuracy and precision. Furthermore, SuCSES can determine whether dielectric polarization, including the interfacial dipole, affects the experimental value of the band offsets.