To determine energy band gaps of ultrathin gate oxides, the onset of energy loss signals of O1s photoelectrons has often been measured. However, for Hf-based oxides, it is imperative that Hf4s signals are subtracted accurately from the measured spectrum in the lower kinetic energy side of primary O1s photoelectrons to obtain true energy loss signals, and the O1s spectral analysis in consideration of a mixture of different chemical bonding features is also needed for the accurate calibration of the loss energy. Similarly, for Ge oxides, the overlapping of Ge LMM Auger signals and O1s energy loss signals makes it difficult to determine the onset of the true energy loss signals.
In this work, we have demonstrated that the energy loss spectra of core lines of cationic elements rather than O1s photoelectrons (Si2p3/2 for Hf-silicates and Ge3d5/2 for GeO2) are practically useful for energy band gap measurements. Also, the determination of the energy band alignment for a high-k dielectric stack on Ge(100), in which a ultrathin TaOx layer was inserted in between HfO2 and Ge(100) to control interfacial reactions, has been shown in combination of valence band offsets determined from the analysis of valence band spectra and energy band gaps from the analysis of energy loss spectra of core lines.