High-density remote plasma sputtering of high-dielectric-constant amorphous hafnium oxide films

Authors

  • Flora M. Li,

    1. Electrical Engineering Division, Engineering Department, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, UK
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  • Bernhard C. Bayer,

    1. Electrical Engineering Division, Engineering Department, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, UK
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  • Stephan Hofmann,

    1. Electrical Engineering Division, Engineering Department, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, UK
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  • Stuart P. Speakman,

    1. Electrical Engineering Division, Engineering Department, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, UK
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  • Caterina Ducati,

    1. Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge CB2 3QZ, UK
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  • William I. Milne,

    1. Electrical Engineering Division, Engineering Department, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, UK
    2. Kyung Hee University, Display Research Laboratory, Department of Information Display, Seoul 130701, South Korea
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  • Andrew J. Flewitt

    Corresponding author
    1. Electrical Engineering Division, Engineering Department, Cambridge University, J J Thomson Avenue, Cambridge CB3 0FA, UK
    • Phone: +44 1223 748332, Fax: +44 1223 748348
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Abstract

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Hafnium oxide (HfOx) is a high dielectric constant (k) oxide which has been identified as being suitable for use as the gate dielectric in thin film transistors (TFTs). Amorphous materials are preferred for a gate dielectric, but it has been an ongoing challenge to produce amorphous HfOx while maintaining a high dielectric constant. A technique called high target utilization sputtering (HiTUS) is demonstrated to be capable of depositing high-k amorphous HfOx thin films at room temperature. The plasma is generated in a remote chamber, allowing higher rate deposition of films with minimal ion damage. Compared to a conventional sputtering system, the HiTUS technique allows finer control of the thin film microstructure. Using a conventional reactive rf magnetron sputtering technique, monoclinic nanocrystalline HfOx thin films have been deposited at a rate of ∼1.6 nm min−1 at room temperature, with a resistivity of 1013 Ω cm, a breakdown strength of 3.5 MV cm−1 and a dielectric constant of ∼18.2. By comparison, using the HiTUS process, amorphous HfOx (x = 2.1) thin films which appear to have a cubic-like short-range order have been deposited at a high deposition rate of ∼25 nm min−1 with a high resistivity of 1014 Ω cm, a breakdown strength of 3 MV cm−1 and a high dielectric constant of ∼30. Two key conditions must be satisfied in the HiTUS system for high-k HfOx to be produced. Firstly, the correct oxygen flow rate is required for a given sputtering rate from the metallic target. Secondly, there must be an absence of energetic oxygen ion bombardment to maintain an amorphous microstructure and a high flux of medium energy species emitted from the metallic sputtering target to induce a cubic-like short range order. This HfOx is very attractive as a dielectric material for large-area electronic applications on flexible substrates.

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