Study of boron effects on the reaction of Co and Si1-xGex at various temperatures

Abstract

The effects of boron on Co and Si1-xGex interfacial reaction were studied. Undoped and ill situ boron-doped strained Si0.91Ge0.09 and Si0.86Ge0.14 layers prepared at 550 degrees C by an ultrahigh vacuum chemical vapor deposition system were subjected to Co silicidation at various rapid thermal annealing (RTA) temperatures ranging from 500 to 1000 degrees C. The resulting films were characterized by a sheet resistance measurement, Auger electron spectroscopy, x-ray diffractometry (XRD), high resolution x-ray diffractometry, secondary ion mass spectroscopy, scanning electron microscopy, and transmission electron microscopy. Seen from XRD spectroscopy, a Co(Si1-yGey) cubic structure was formed with RTAs ranging from 500 to 700 degrees C. For boron-doped samples, the CoGe fraction in Co(Si1-yGey) was less than that in undoped samples, indicating that baron atoms retarded the incorporation of Ge into the Co(Si1-yGey) ternary phase. It also led to a large Ge pileup at the interface between the Co-rich and silicidation regions. On the other hand, from the high resolution x-ray spectra, the presence of boron led to less relaxation of the strained Si1-xGex lattice. It is the first time that small boron atoms inhibiting the relaxation of the Si1-xGex layer during silicidation was observed. Furthermore, from the sheet resistance measurement, the formation of CoSi2 was found to be slightly retarded in boron-doped samples, due probably to the decrease of Co or Si diffusivities as a result of boron accumulation at the Co/SiGe reaction interface. At temperatures above 800 degrees C, CoSi2 formed and Ge segregated to the silicide boundaries and the upper reaction region was discovered. These phenomena caused by B dopants are explained in detail. (C) 2000 American Vacuum Society. [S0734-2101(00)04604-2].