Direct evaluation of electrical dipole moment and oxygen density ratio at high-kdielectrics/SiO₂interface by X-ray photoelectron spectroscopy analysis

Abstract

The electrical dipole moment at an ultrathin high-k (HfO 2 , Al 2 O 3 , TiO 2 , Y 2 O 3 , and SrO)/SiO 2 interface and its correlation with the oxygen density ratio at the interface have been directly evaluated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. The electrical dipole moment at the high-k/SiO 2 interface has been measured from the change in the cut-off energy of secondary photoelectrons. Moreover, the oxygen density ratio at the interface between high-k and SiO 2 has been estimated from cation core-line signals, such as Hf 4f, Al 2p, Y 3d, Ti 2p, Sr 3d, and Si 2p. We have experimentally clarified the relationship between the measured electrical dipole moment and the oxygen density ratio at the high-k/SiO 2 interface.

Dependence of the Metal–Insulator–Semiconductor Schottky Barrier Height on Insulator Composition

“…This hypothesis is supported by a report on the correlation of XPSmeasured electrical dipoles at SiO x /high-κ interfaces to the XPS-derived oxygen density ratios of the oxides. 20 Calculations by Lin and Robertson instead indicated that dipoles originate from the parent metal work functions/group electronegativities as long as there was a sufficient difference in the dielectric constant κ between the layers. 21 They argue that dipoles exist along the metal−oxygen bonds on both sides of the oxide interface with dipole strengths related to the parent metal work functions.…”

“…In this case, bond relaxation would be achieved when negatively charged oxygen ions move from the higher-OAD to the lower-OAD side of the interface, forming Frenkel-type defects and inducing a dipole with a positive charge in the high-OAD side and negative charge in the low-OAD side. This hypothesis is supported by a report on the correlation of XPS-measured electrical dipoles at SiO x /high-κ interfaces to the XPS-derived oxygen density ratios of the oxides …”

Dipole Formation and Electrical Properties According to SiO2 Layer Thickness at an Al2O3/SiO2 Interface

“…Therefore, several studies using the SiO 2 buffer layer have been performed. , It has been reported that interfacial dipole is generated between the SiO 2 and high-k material formed at this time, and interfacial dipole affects the movement of the flat-band voltage ( V FB ). − Several mechanisms for dipole formation have been suggested, including electronegativity difference model, dielectric constant-induced gap states (DCIGS) model, fermi level pinning model, and oxygen density model. − Among them, the oxygen density difference model asserts that the dipole is formed by the oxygen density difference between high-k and SiO 2. Recently, dipole studies according to the high-k difference are being conducted through the oxygen density difference model …”

“…22 Recently, dipole studies according to the high-k difference are being conducted through the oxygen density difference model. 23 In the MOS structure, the SiO 2 buffer layer plays an important role in thermal stability and interfacial characteristics. Also, it has been reported that the barrier height changes depending on the thickness of existing SiO 2 or electrical characteristics change significantly, which affects device characteristics.…”

Energy band diagram for SiO2/Si system as evaluated from UPS analysis under vacuum ultraviolet with variable incident photon energy

“…Photoemission spectroscopy such as ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) is a powerful tool used to evaluate such an energy band structure at the solid-state surface. [12][13][14][15][16][17] UPS measurements have been often used to investigate the valence band structure, work function, and electron affinity of the sample surface. [18][19][20] Since the UPS measurements under HeI (21.2 eV) and HeII (40.8 eV) are the surface sensitive analysis as long as a few nm from the surface, 21,22) evaluation of the electronic states at the interface is not so easy, and the removal of the surface contaminants is one of the key issues to measure the electronic states precisely.…”