CoSi2/Si1−xGex/Si(001) heterostructures formed through different reaction routes: Silicidation-induced strain relaxation, defect formation, and interlayer diffusion

The microstructure and microchemistry of CoSi2/Si1−xGex/Si(001) heterostructures, in which the Si1−xGex layers were grown by molecular-beam epitaxy (MBE) and the silicides formed by different postdeposition reaction paths, were investigated using a combination of high-resolution cross-sectional transmission electron microscopy, high-resolution x-ray diffraction, and secondary-ion-mass spectrometry. In two of the three sample configurations investigated, Co was deposited either (S1) directly on a strained Si1−xGex layer or (S2) on a sacrificial MBE Si overlayer on Si0.9Ge0.1. In the third sample configuration (S3) Si1−xGex was grown on a Si(001) substrate containing a buried ion-implanted CoSi2 layer. Only in sample configuration S2 was it possible to obtain a fully strained nearly defect-free CoSi2/Si0.9Ge0.1 structure. A high density of threading dislocations, corresponding to ≊60% relaxation at the Si0.9Ge0.1/Si interface, was observed in S1 while S3, in addition to the dislocations, exhibited a pronounced faceting at the CoSi2/Si interface.