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

Publication Type:

Journal Article


Journal of Applied Physics, Volume vol. 101, p.044901 (2007)


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 10 at. %. 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 4.66 eV and 310 cm2/s,
respectively, for the temperature and Ge fraction ranges of this study. Threading dislocation
densities on the order of 107 cm−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.

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