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

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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;
Title: Optical Bandgaps and Composition Dependence of Hafnium Aluminate Thin Films grown by Atomic Layer Chemical Vapor Deposition
Published: November 17, 2005
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
Pages: pp. 1706 - 1713
Keywords: Bandgaps;Hf-Aluminates;HfO2;Highh-k dielectric thin films;Nuclear Reaction Analysis;Optical Properties;Rutherford Backscattering;Transmission Electron Microscopy;Vacuum Ultraviolet Spectroscopic Ellipsometry
Research Areas: Semiconductors