Intrinsic Paramagnetic Defects in Zirconium and Hafnium Oxide Films
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Intrinsic Paramagnetic Defects in Zirconium and Hafnium Oxide Films Robert N. Schwartz,1,2 Heinrich G. Muller,1 Paul M. Adams,1 James D. Barrie,1 and Ronald C. Lacoe1 1 2
Electronics and Photonics Laboratory, The Aerospace Corporation, El Segundo, CA 90245, U.S.A. Department of Electrical Engineering, University of California, Los Angeles, Los Angeles, CA 90024, U.S.A.
ABSTRACT Thin films of zirconium oxide (ZrOx) and hafnium oxide (HfOx) were rf sputtered onto fused silica substrates in an oxygen rich argon environment. Pure zirconium and hafnium targets were used, and the oxygen partial pressure was varied to control the oxygen stoichiometry. Measurement of the EPR characteristics of the ZrOx films indicated two peaks corresponding to two orientations of the magnetic field. This anisotropic response suggested the films were polycrystalline with a preferred orientation. This was confirmed by XRD pole figures. The measured g-values for the ZrOx films were less than the free-spin g-value, indicating the defects corresponded to electron traps. It was further shown that the lower the oxygen partial pressure during deposition, the larger the EPR response, strongly suggesting the traps correspond to oxygen vacancies in ZrOx. Hafnium oxide thin films were also characterized by EPR. The EPR measurements indicated the presence of a single resonance peak, suggesting these films were polycrystalline without a preferred orientation or amorphous. XRD measurements confirmed that the HfOx films were amorphous. The g-value for these films was greater than that the freespin value, indicating the presence of possibly self-trapped oxygen hole centers. These results will be discussed in the context of prior experimental and theoretical work on these systems. INTRODUCTION The scaling of complementary metal-oxide-semiconductor (CMOS) transistors requires the replacement of SiO2 gate oxide by higher dielectric constant materials in order to avoid excessive gate leakage currents [1]. High-κ gate dielectrics, such as ZrO2 and HfO2 and their alloys with SiO2, are currently considered as a practical solution for integrating high-κ materials in future electronic devices [2]-[5]. It is well established that intrinsic point defects, such as oxygen vacancies [3],[4],[6],[7], play an important role in the reliability of high-κ dielectrics and pose one of the fundamental limits for use of high-κ dielectrics in silicon metal – oxide semiconductor field effect transistors [8],[9]. These materials are also used for fabricating antireflective dielectric coatings for solar panels used in space-craft applications. The density of defects in these new materials is much greater than found in SiO2. The challenge is to understand the nature of defects in these materials and to evaluate their impact on device performance and reliability. In recent years, oxides of Group IVA transition metals, Ti, Zr, and Hf have become some of the most investigated materials. It is well established that material properties are strongly influenced by the presence of intrinsi
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