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.

Experiments and Modeling of Si-Ge Interdiffusion with Partial Strain Relaxation in Epitaxial SiGe Heterostructures

“…The edges of all the SIMS Ge peaks were flatter and went farther than the edges of the simulated Ge peaks, and the Ge peaks did not get steeper as Equation 10 predicted. This issue can be explained by the dislocation-mediated interdiffusion, which is not included in Equation 10. Equation 10 only accounts for the point-defect mediated interdiffusion (lattice diffusion), and the interdiffusivity associated with that isD lattice .…”

“…One can imagine that if R (t) is well characterized with a fine time step, then the degree of relaxation R can be approximated to be constant in a small enough time interval. Therefore, interdiffusion can be roughly estimated with theD lattice term using Equation 10. For other advanced thermal annealing, such as spike rapid thermal annealing with much faster ramp rates, the characterization of R (t) can be very challenging.…”

“…≡D lattice [10] ) unless CC License in place (see abstract In Equation 10, the degree of relaxation R appears in two places, (1 − R) 2 in the large parenthesis for the driving force change and (1 − R) in the exponent term for the interdiffusivity change. When the R value equals 1, we can see that the apparent interdiffusivity equalsD relax , where there is no strain impact.…”

“…As the biaxial compressive strain reduces to ε 0 (1 − R), correspondingly, the strain enhancement of interdiffusion decreases, which is consistent with the SIMS results in Figure 3. According to the model for interdiffusion with partially relaxed compressive strain in Equation 10, at 800…”

“…This interdiffusion increases exponentially with Ge concentration and compressive stress, and also increases with ion implantation damage. 10,11 Si-Ge interdiffusion is generally undesirable as it degrades MOSFET performance by reducing strain and carrier confinement and increasing alloy scattering. 12 It also decreases photodetector efficiency, 13 and delays the lasing of Ge/Si lasers.…”