This study compared the formation of nickel silicide or germanosilicide layers on various SiGe based heterostructures as well as the effects of the different annealing schemes (one-step versus two-step annealing) on the morphological, structural, and electrical properties. Uniform nickel silicide or germanosilicide layers were first formed by rapid thermal annealing of various heterostructures. The two-step annealing process of the samples first at 400 degrees C (T-A1) and subsequently at between 600 and 800 degrees C (T-A2) led to an increase in the sheet resistance, which was attributed to the formation of a high-resistivity NiSi2 phase, the agglomeration of the silicide or germanosilicide layers, and the formation of an amorphous interlayer between the silicide or germanosilicide layers. The lower sheet resistance of the silicide or germanosilicide layers formed on the relaxed-Si1-xGex (x=0.15)/Si(001) substrates by two-step annealing compared with that of the samples formed on the strained Si/relaxed SiGe/Si(001) and Si(001) was attributed to the suppression of the high-resistivity NiSi2 phase as well as the superior thermal stability of the germanosilicide layer formed on the relaxed Si1-xGex (x=0.15)/Si(001). The amorphous interlayers formed in the samples annealed using two-step procedure appeared to suppress interface roughening between the silicide or germanosilicide and the SiGe layer presumably due to the reduced Ni and Ge diffusion rate. Here, an amorphous interlayer was formed, which was attributed to the large negative heat of mixing in Ni-Si-Ge systems during the phase transformation and grain growth. (c) 2006 American Vacuum Society.