Si–Ge interdiffusion in strained Si/strained SiGe heterostructures and implications for enhanced mobility metal-oxide-semiconductor field-effect transistors

Abstract

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.