X-ray absorption spectra for transition metal high-κ dielectrics: Final state differences for intra- and inter-atomic transitions

Abstract

This article applies x-ray absorption spectroscopy to a study of the electronic structure of the high-k gate dielectrics, TiO2, ZrO2, and HfO2. Qualitative and quantitative differences are identified between intra-atomic transitions such as the Zr 3p-state, M2,3 core state absorptions which terminate in TM 4d*- and 5s*-states, and inter-atomic transitions such as the Zr 1s- and O 1s-state K1 absorptions which terminate in Zr 4d*- and 5s*-states that are mixed with O atom 2p* states through nearest neighbor bonding interactions. Differences between the spectral peak energies of the lowest d*-features in the O K1 spectra are demonstrated to scale with optical band gap differences for TiO2, ZrO2, and HfO2, providing important information relevant to applications of TM oxides as high-κ gate dielectrics in advanced Si devices. This is demonstrated through additional scaling relationships between (i) conduction band offset energies between Si and the respective dielectrics, and the optical band gaps, and (ii) the conduction band offset energies, and the electron tunneling masses as well.

Conduction band-edge States associated with the removal of d-state degeneracies by the Jahn-Teller effect

“…Qualitatively similar spectra have been obtained for the corresponding TM p-state and O atom core level absorption spectra in TiO and HfO [6]. These include the Ti L and Hf N The relative intensities of features that terminate in empty dand s-states, respectively, in Ti L , Zr M and Hf N spectra are consistent with the intra-atomic character of these transitions.…”

“…XAS measurements were performed at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory (BNL), and at the Stanford Synchrotron Radiation Laboratories (SSRL) at the Stanford Linear Accelerator Center (SLAC) using total photo-electron yield to determine the relative absorption strength of the spectral features associated with transitions from TM, RE, and O-atom core level states to empty conduction band-states [6]. Thin film samples of ZrO and HfO and their respective silicate alloys were prepared by remote plasma enhanced chemical vapor deposition (RPECVD) [7].…”

“…Differences Between Intra-and Inter-Atomic Spectra Fig. 2(a) and (b) presents Zr M and O K spectra for thin film nanocrystalline ZrO [6]. The Zr M spectrum in Fig.…”

X-ray reflection spectroscopy of the HfO2/SiO2/Si system in the region of the O–K absorption edge

“…The values obtained agree well with experimental values of D(d* 1,2 ) = 4.3 eV and D(d* 1 , s*) = 9.0 eV for HfO 2 from Refs. [24,27].…”

“…[23,24] the ab initio results are presented for relatively small clusters that include the Hf atom at the center with eight O-atom neighbors. According to these calculations, the anti-bonding O 2p* states are hybridized with the anti-bonding Hf 5d* and Hf 6s* states.…”