Optical Bandgaps and Composition Dependence of Hafnium Aluminate Thin Films grown by Atomic Layer Chemical Vapor Deposition

Published

November 17, 2005

Author(s)

Nhan V. Nguyen, Safak Sayan, Igor Levin, James R. Ehrstein, I.J.R. Baumvol, C. Driemeier, L Wielunski, Pui-Yee Hung, Alain C. Diebold

Abstract

Hafnium-aluminate (HfAlO) films grown on Si by Atomic Layer Chemical Vapor Deposition (ALCVD) of different aluminum contents were investigated in this article. Vacuum Ultra-Violet Spectroscopic Ellipsometry (VUV-SE), high Resolution Transmission Electron Microscopy (HRTEM), Channeling Rutherford Backscattering Spectrometry (RBS), and Resonant Nuclear Reaction Analysis (NRA) were employed to characterize these films. In the analyses of ellipsometry data, a double Tauc-Lorentz dispersion produces a best fit to the experimental VUV-SE data. As a result, the determined complex pseudo-dielectric <e> functions of the films clearly exhibit a dependency on the aluminum densities measured by RBS and NRA. We will show that the optical fundamental bandgap Eg shifts from 5.56 ¿ 0.05 eV for HfO2 to 5.92 ¿ 0.05 eV for HfAlO. The latter was grown using equal (1:1) ratio of HfO2 and Al2O3 precursors pulsed in each deposition cycle. The shift of Eg to the higher photon energies with increasing aluminum content indicates that intermixing of HfO2 and Al2O3 occurred during the ALCVD growth process. We found that Eg varies linearly with the mole fraction x of Al2O3 in the alloy (HfO2)x(Al2O3)1-x, but has a parabolic dependency with the aluminum density. The <e> magnitudes of higher concentrations of Al2O3 used during the growth of Hf-aluminate films are lower than those of HfO2 as expected. Furthermore, the absence of the ~ 5.7 eV peak in the <e> spectrum which was previously reported for polycrystalline HfO2 films concludes that the films are amorphous, and were confirmed by their HRTEM images

Citation

Journal of Vacuum Science and Technology A

Volume

23

Issue

6

Pub Type

Journals

Keywords

Bandgaps, Hf-Aluminates, HfO2, Highh-k dielectric thin films, Nuclear Reaction Analysis, Optical Properties, Rutherford Backscattering, Transmission Electron Microscopy, Vacuum Ultraviolet Spectroscopic Ellipsometry

Citation

Nguyen, N. , Sayan, S. , Levin, I. , Ehrstein, J. , Baumvol, I. , Driemeier, C. , Wielunski, L. , Hung, P. and Diebold, A. (2005), Optical Bandgaps and Composition Dependence of Hafnium Aluminate Thin Films grown by Atomic Layer Chemical Vapor Deposition, Journal of Vacuum Science and Technology A (Accessed April 18, 2024)