IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Dielectrics Monday Sessions
       Session DI1-MoP

Paper DI1-MoP5
Annealing Effects on Optical Properties of Hafnium Oxide Films Observed by Spectroscopic Ellipsometry

Monday, October 29, 2001, 5:30 pm, Room 134/135

Session: High K Dielectrics Poster Session
Presenter: Y.J. Cho, National Institute of Standards and Technology
Authors: Y.J. Cho, National Institute of Standards and Technology
N.V. Nguyen, National Institute of Standards and Technology
C.A. Richter, National Institute of Standards and Technology
J.R. Ehrstein, National Institute of Standards and Technology
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We have applied spectroscopic ellipsometry (SE) to investigate a set of HfO@sub 2@ films and correlate their optical properties with fabrication processes, in particular, with high temperature annealing. Among the many proposed high-k dielectrics such as HfO@sub 2@, Ta@sub 2@O@sub 5@, TiO@sub 2@, and ZrO@sub 2@, the use of HfO@sub 2@ films as the replacement for SiO@sub 2@ as the gate dielectric in CMOS devices has received much attention recently due to its high dielectric constant, low leakage current, good thermal stability, and interface characteristics comparable to silicon dioxide/silicon interface. In spite of these promising properties, little is known about the optical properties of HfO@sub 2@. Thin HfO@sub 2@ films were grown on Si substrate by dc magnetron sputtering and then annealed at high temperatures. SE measurements were performed on a high-accuracy custom-made spectroscopic ellipsometer. The dielectric functions of these films were determined by inversions of SE data and compared with the results with those obtained by using a Tauc-Lorentz (TL) dispersion function. It will be shown that, in the near-IR-visible-UV spectral range, TL can be used to effectively describe the optical properties of HfO@sub 2@. From the characteristics found in the pseudo-dielectric functions or the TL dispersions, when the annealing temperatures increase from 500 to 700 °C, we observed that, for the HfO@sub 2@ films, the optical band gap increases. In addition, for samples annealed at 600 °C and above, new optical features, which are not present at lower temperature, are clearly seen in their dielectric functions. These features are the signature of poly-crystallization in the film attributable to the annealing. As a result, we conclude that SE can easily and quickly identify the onset or the existence of crystalline HfO@sub 2@ films without employing a more elaborate and destructive method such as a transmission-electron microscope (TEM).