Mechanism for the reduction of threading dislocation densities in Si{sub}0.82Ge{sub}0.18 films on silicon on insulator substrates

摘要

We have made an extensive study of Si{sub}0.82Ge{sub}0.18 film relaxation on silicon on insulator (SOT) substrates having a top Si layer 40, 70, 330nm, and 10μm thick. SiGe films were deposited with a thickness up to 1.2μm in an ultrahigh vacuum chemical vapor deposition system at 630°C. Following growth, films were characterized by X-ray diffraction and a dislocation revealing etch. The same level of relaxation is reached for each thickness of SiGe film independent of the substrate structure. Accompanying the film relaxation is the development of a tetragonal tensile strain in the thin Si layer of the SOT substrates. This strain reached 0.22% for the 1.2μm film on the 40nm SOT and decreases with SOT thickness. The Si thickness of the SOT substrate also effected the threading dislocation density. For 85% relaxed films the density fell from 7×10{sup}6 pits/cm{sup}2 on bulk Si to 10{sup}3pits/cm{sup}2 for the 40, 70, and 330nm SOI substrates. The buried amorphous layer of the SOT substrate alters the dislocation dynamics by allowing dislocation core spreading or dislocation dissociation. The reduced strain field of these dislocations reduces dislocation interactions and the pinning that results. Without the dislocation pinning, the misfit dislocations can extend longer distances yielding a greatly reduced threading dislocation density.