An interdiffusivity model was established for SiGe interdiffusion under tensile or relaxed strain over the full Ge content (xGe) range (0 ≤ xGe ≤ 1), which is based on the correlations between self-diffusivity, intrinsic diffusivity, and interdiffusivity. It unifies available interdiffusivity models over the full Ge range and applies to a wider temperature range up to 1270 °C at the xGe = 0 end and to 900 °C at the high xGe = 1 end. Interdiffusion experiments under soak and spike rapid thermal annealing conditions were conducted to verify the model. Literature interdiffusion data under furnace annealing conditions were also used for the same purpose. The interdiffusivity model of this work has been implemented in major process simulation tools, and the simulation results showed good agreement with experimental data under furnace annealing and soak and spike rapid thermal annealing conditions. This work demonstrated a new approach in studying SiGe interdiffusion, which has the advantage of studying interdiffusion under non-isothermal annealing conditions.
The role of compressive strain on Si-Ge interdiffusion in epitaxial SiGe heterostructures was systematically investigated both by experiments and by theoretical analysis. The Ge fraction x Ge range (0.36-0.75) studied in this work extended to a wider Ge regime. With x-ray diffraction and Raman spectroscopy measurements, it was demonstrated that the epitaxial SiGe structures were kept pseudomorphic during the annealing. Complete theoretical analysis was presented to address the strain impact on the interdiffusion driving force, the interdiffusivity prefactor and the activation energy. The strain derivative of the interdiffusivity q , was shown to be temperature dependent. q was quantitatively extracted from the experimental data in the Ge content range (0.36-0.75) and the temperature range (720-880 • C), and is shown to have the form of q = (−0.081T + 110) eV/unit strain, where T is temperature in Kelvin.
Si-Ge interdiffusion with different P doping configurations was investigated. Significant interdiffusion happened when the Ge layers were doped with P in high 10 18 cm −3 range, which resulted in a SiGe alloy region thicker than 150 nm after defect annealing cycles. With high P doped Ge, Si-Ge interdiffusivity is enhanced by 10-20 times in the x Ge > 0.7 region compared with the control sample without P doping. We attribute this phenomenon to the much faster P transport towards the Ge seeding layers from the Ge side during the Ge layer growth, which increases the negatively charged vacancy concentrations and thus the interdiffusivity due to the Fermi effect in Si-Ge interdiffusion. This work is relevant to Ge-on-Si type device design, especially Ge-on-Si lasers.
We demonstrate for the first time, asymmetrically strained Ge, high-κ/metal gate nanowire (NW) trigate p-MOSFETs with record hole mobility of 1490 cm 2 /Vs. This mobility is 2× above on-chip, biaxially strained Ge planar FETs and ~15×above Si universal mobility. The fabrication approach features: (1) a new strained Si/strained Ge/HfO 2 NW channel materials stack, with HfO 2 dielectric at the bottom which acts as an excellent etch stop for top-down NW formation, and also unpins the back Ge-dielectric interface, (2) large compressive biaxial strain (~2.5%) that is built into the channel material prior to layer transfer, and (3) lateral strain relaxation by nanoscale patterning of the channel. The resulting asymmetric strain distribution dramatically reduces the conductivity effective mass. 6×6 k.p quantum mechanical simulations predict an increase in the Ge NW average inverse effective mass by a factor of 1.6 relative to planar biaxially strained Ge, consistent with the measured 2× mobility enhancement.
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