Electronic properties of ultrathin (HfO2)x(SiO2)1−x dielectrics on Si (100)

Abstract

Electronic properties of 6 nm (HfO2)x(SiO2)1−x dielectric thin films, deposited on Si(100) by atomic layer deposition with x equal to 0.75 and 0.25, were studied by means of x-ray photoelectron spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS). XPS measurements confirmed the formation of a silicate structure, and showed shifts of the Hf 4f and Si 2p peaks with varying Hf concentrations; these shifts are believed to be caused by changes in the amount of charge transfer and by the substitution of Si by Hf as second-nearest-neighbors. The band gap, Eg, was estimated from REELS. It increased from 5.52 eV for Hf silicate with a Hf/Si ratio of 3:1 to 6.61 eV for Hf silicate with a Hf/Si ratio of 1:3. For Hf silicate dielectrics, the band gap is mainly determined by Hf 5d conduction-band and O 2p valence-band states, and the increase with increasing Si concentration is due to mixing with the Si 3s electrons. By quantitative analysis of REELS spectra, the dielectric functions of the thin films were also determined and expressed as a sum of oscillators. The position, strength, and width of the oscillators were determined quantitatively for the different dielectric films.

Dielectric and optical properties of Zr silicate thin films grown on Si(100) by atomic layer deposition

“…The values of the momentum dispersion coefficient ␣ i are related to the effective mass, e.g., ␣ i Ϸ 0 for insulator and ␣ i Ϸ 1 for metals. 5,8,10 In accordance with this, we found that good fits were obtained with ␣ i = 0.02 for all oscillators. The ELF Im͑−1 / ͒ and the surface ELF ͑SELF͒ Im͓−1 / ͑1+͔͒ for Zr silicates obtained by using these parameters are shown in Fig.…”

“…5,8,10,[12][13][14] The model used in this software takes into account the inelastic scattering of electrons as they travel through the vacuum above the surface, the surface region, and the bulk region of a solid, and it also takes into account the interference effects between these excitations. 14 In this model, all excitations are described by the dielectric function ͑k , ͒ of the material, which is the only input in the theoretical calculation of inelastic scattering cross section.…”

“…1͒ as described in our previous paper. 5,7,8 The experimental inelastic cross sections after background subtraction were fitted with fitting parameters of the A i , ␥ i , ប i , and ␣ i , until good agreement with the calculated inelastic cross section at several primary electron energies. The ELF Im͑−1 / ͒ is adjusted to make sure that it fulfills the well-established Kramers-Kronig sum rule, [14][15][16] …”

“…2 As a consequence of arduous search for materials satisfying the above criteria, transition metal oxides such as HfO 2 ͑Refs. 2-5͒ and ZrO 2 , 5,6 and their compound with SiO 2 have been proposed as the most promising high-k dielectrics. In fact, the Zr based dielectrics are vigorously studied as one of the promising candidates for high-k gate dielectrics.…”

Energy loss function for Si determined from reflection electron energy loss spectra with factor analysis method

“…[3 -6] REELS is a useful technique in surface and interface analysis because the backscattered electrons provide information on electron-solid inelastic interactions and can give a nondestructive analysis of nanostructures when used at low primary electron energies. [6,7] However, the REELS spectrum is a complicated convolution of separate physical phenomena including bulk and surface plasmon excitations, interband transitions, multiple scattering and momentum transfer. [8,9] In particular, losses due to surface excitations significantly affect REELS experimental data, especially at low primary electron energies less than 500 eV.…”