AVS 51st International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM10
Process Parameter - Film Structure/Optical Property Study of Reactive Sputter Deposited Hafnium Dioxide

Thursday, November 18, 2004, 11:20 am, Room 303C

Session: Modeling & Fundamentals in Thin Film Deposition
Presenter: E. Hoppe, University of Wisconsin-Milwaukee
Authors: E. Hoppe, University of Wisconsin-Milwaukee
C.R. Aita, University of Wisconsin-Milwaukee
Correspondent: Click to Email
HfO@sub 2@ is a refractory material that has gained importance in thin films for high k, high n, wide band gap applications. Here, we deposited HfO@sub 2@ films by sputtering a Hf target in rf-excited Ar/O@sub 2@ discharges. 150-nm thick films were grown at room temperature on <100> Si and fused SiO@sub 2@ substrates. Nine combinations of cathode voltage (500 to 1000 V) and O@sub 2@ gas content (10 to 40%) were used. Our goal was to determine the relationship between deposition process parameters and the films atomic structure (long and short range order) and near ultraviolet-visible-infrared absorption and reflection behavior. X-ray diffraction showed the following results: (1) All films were nanocrystalline with monoclinic (m) HfO@sub 2@, the STP phase, predominant. (2) For a fixed cathode voltage, m-HfO@sub 2@ orientation with respect to the substrate was strongly dependent upon the gas O@sub 2@ content. Specifically at high gas O@sub 2@ content, a preferred m(11-1) orientation, the lowest energy growth orientation, was observed. Other orientations of m-HfO@sub 2@ became strong at low gas O@sub 2@ content and low cathode voltage, including a preferred m(111) orientation. (3) A trace amount of tetragonal (t) HfO@sub 2@, a high temperature phase, was observed in some films. This phase was possibly stabilized by a finite crystal size effect, analogous t-ZrO@sub 2@. However, the tetragonal phase occurs in significant amounts in ZrO@sub 2@ but in trace amounts in HfO@sub 2@ films grown under similar conditions, suggesting that the critical radius above which t transforms to m is smaller in HfO@sub 2@ than in ZrO@sub 2@ films, consistent with a lower t-to-m transformation temperature in bulk ZrO@sub 2@. All films are highly transparent. Transmission v. wavelength curves yielded an optical band gap of ~6.4 eV. Optical absorption edge characteristics were independent of film nanocrystal orientation, consistent with this property depending chiefly upon short-range order in wide band gap oxides.