The evolution of the He-implantation induced defect structure in SiGe/ Si heterostructures is observed during in situ annealing at 650 and 800°C within a transmission electron microscope. The He implantation and annealing results in the formation of He precipitates below the SiGe/ Si interface, which at first show a platelike shape and subsequently decay into spherical bubbles. The coarsening mechanism of the He bubbles is revealed as coalescence via movement of entire bubbles. The nucleation of dislocation loops at overpressurized He platelets and their propagation into the heterostructure could be observed as well. We found distinctly different velocities of the dislocations which we attribute to glide and climb processes. The in situ experiments clearly show that the He platelets act as internal dislocation sources and play a key role in the relaxation of SiGe layers. Since strained silicon is generally realized by epitaxial deposition of Si on relaxed SiGe layers, relaxed buffers in an adequate quality are required. Efficient relaxation of thin SiGe films with a thickness of 100-200 nm and Ge contents of up to 30% was demonstrated by ion implantation of H or He and subsequent annealing.2-7 Its mechanism, however, is still under debate. Recently, Schwarz 8 simulated for a similar model system the dislocation dynamics during strain relaxation by assuming solely dislocation glide processes. Here, we follow an analytical model proposed by Trinkaus et al. 9 where H / He implantation and annealing induces the formation of dislocation loops created at overpressurized He precipitates located underneath the SiGe/ Si heterointerface. These loops glide to the interface where subsequently one part unlaces up to the surface and creates two threading segments, whereas the lagging part in the interface forms a strain-relieving misfit dislocation segment. Driven by the misfit strain the two threading segments move apart and eventually annihilate with threading dislocations of opposite Burgers vector. As a consequence, efficient and "healthy" strain relaxation is observed. Measurements of the pressure within the platelike shaped He precipitates, which represent the initial stage of He precipitates, 10,11 revealed the shear stress to reach the critical value of dislocation formation. 12This indicates that He platelets may be capable to emit dislocations. In order to gain deeper insight into the relaxation mechanism of SiGe layers, we studied the evolution of the helium bubble structure as well as its interplay with nucleation and growth of dislocation loops utilizing in situ annealing investigations by transmission electron microscopy ͑TEM͒.Si 81 Ge 19 layers with a thickness of 170 nm were deposited onto Si ͑001͒ substrates by chemical vapor deposition. Helium was implanted with an energy of 37 keV at a dose of 1 ϫ 10 16 cm −2 resulting in a helium concentration profile with its maximum in a depth about double the layer thickness. These implant conditions are optimum with respect to high degree of relaxation and low th...

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Thin relaxed SiGe buffer layers with Ge contents of 23at% and 26at% and thicknesses between 150 to 180 nm on Si(100) terminated with 6 nm Si were made by He ion implantation and annealing. Subsequent overgrowth of the thin buffers with thin strained Si cap layers with SiGe and strained Si reduced the threading dislocation and pile-up densities significantly. Best results were achieved for high temperature SiGe overgrowth with a thickness of 200nm and Ge contents lower than the effective Ge content of the buffer. Threading dislocation densities as low as 1x105 cm-2 and dislocation pile-up densities of 10 cm-1 were determined. Strained silicon on insulator wafers were produced by wafer bonding. Wafer splitting was done by H ion implantation and annealing. The strain of the layers was measured by Raman spectroscopy revealing a strain of 0.66% in the tensile strained Si on the partially relaxed Si0.77Ge0.23 buffers.