D. H. Triyoso, R. I. Hegde, J. K. Schaeffer, R. Gregory, X.-D. Wang, M. Canonico, D. Roan, E. A. Hebert, K. Kim, J. Jiang, R. Rai, V. Kaushik, S. B. Samavedam, N. Rochat

Characteristics of atomic-layer-deposited thin Hf_xZr_1-xO₂ gate dielectrics

Journal of Vacuum Science and Technology B 25 (2007) 845–852

In this study, the authors investigated the addition of zirconium (Zr) into HfO₂ to improve its dielectric properties. Hf_xZr_1-xO₂ films were deposited by atomic-layer deposition at 200–350 °C and annealed in a nitrogen ambient environment at 1000 °C. Extensive physical characterization of the impact of alloying Zr into HfO₂ is studied using vacuum ultraviolet spectroscopy ellipsometry, attenuated total reflectance Fourier transform infrared spectroscopy, secondary-ion mass spectrometry, transmission electron microscopy, atomic force microscopy, x-ray diffraction, Rutherford backscattering spectrometry, and x-ray reflectometry. Hf_xZr_1-xO₂ transistors are fabricated to characterize the impact of Zr addition on electrical thickness, mobility, and reliability. Zr addition into HfO₂ leads to changes in film microstructure and grain-size distribution. Hf_xZr_1-xO₂ films have smaller and more uniform grain size compared to HfO₂ for all deposition temperatures explored here. As Zr content and deposition temperature are increased, stabilization of the tetragonal phase is observed. A monotonic decrease in band gap is observed as ZrO₂ content is increased. The chlorine impurity in the films is strongly dependent on deposition temperature and independent of film composition. TEM images of transistors showed excellent thermal stability as revealed by a sharp Hf_xZr_1-xO₂/Si interface and no Zr silicide formation. Significant improvement in device properties such as lower electrical thickness (higher permittivities), lower threshold voltage (V_t) shift after stress (improved reliability), and higher mobilities are observed with Zr addition into HfO₂. All of these results show Hf_xZr_1-xO₂ to be a promising candidate for SiO₂ replacement.

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Cited Articles

1. Franta D., Ohlídal I.,
   Optical characterization of inhomogeneous thin films of ZrO₂ by spectroscopic ellipsometry and spectroscopic reflectometry,
   Surface and Interface Analysis 30 (2000) 574–579