Si–Ge interdiffusivity in epitaxial strained Si∕Si1−yGey/strained Si/relaxed Si1−x0Gex0 heterostructures is extracted for Ge fractions between 0 and 0.56 over the temperature range of 770–920°C. Boltzmann-Matano analysis is applied to determine interdiffusivity from diffused Ge profiles in strained Si/relaxed Si1−x0Gex0 heterostructures [L. Boltzmann, Wiedemanns Ann. Phys. 53, 959 (1894) and C. Matano, Jpn. J. Phys. 8, 109 (1933)]. A model for the interdiffusivity suitable for use in the process simulator TSUPREM-4 is constructed. Si–Ge interdiffusivity increases by 2.2 times for every 10% increase in Ge fraction for interdiffusion in strained Si/relaxed Si1−x0Gex0 samples. Significantly enhanced Si–Ge interdiffusion is observed for Si1−yGey layers under biaxial compressive strain. Si–Ge interdiffusivity is found to increase by 4.4 times for every 0.42% increase in the magnitude of biaxial compressive strain in the Si1−yGey, which is equivalent to a decrease in the Ge percentage in the substrate by 10at.%. These results are incorporated into an interdiffusion model that successfully predicts experimental interdiffusion in various SiGe heterostructures. The extracted activation energy and prefactor for the interdiffusivity are 4.66eV and 310cm2∕s, respectively, for the temperature and Ge fraction ranges of this study. Threading dislocation densities on the order of 107cm−2 are shown to have negligible effect on Si–Ge interdiffusion in Si∕Si0.69Ge0.31 structures. Substituting the strained Si layers surrounding the Si1−yGey peak layer with SiGe layers is shown to have little effect on the Si–Ge interdiffusivity. The implications of these findings for the design and process integration of enhanced mobility strained Si/strained SiGe metal-oxide-semiconductor field-effect transistors are discussed.
In this study, the authors investigated the addition of zirconium (Zr) into HfO2 to improve its dielectric properties. HfxZr1−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. HfxZr1−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. HfxZr1−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 HfxZr1−xO2∕Si interface and no Zr silicide formation. Significant improvement in device properties such as lower electrical thickness (higher permittivities), lower threshold voltage (Vt) shift after stress (improved reliability), and higher mobilities are observed with Zr addition into HfO2. All of these results show HfxZr1−xO2 to be a promising candidate for SiO2 replacement.
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