Microscopic evidence of C40 and C54 in (Ti,Ta)Si-2: Template mechanism

The formation of C54 TiSi2 with a thin Ta layer deposited between Si and Ti is investigated at atomic scale level using transmission electron microsco py. When the Si/Ta/Ti structure is annealed at 650 degrees C for 30 a, both C40 and C54 (Ti,Ta)Si-2 are found at the Si/silicide interface. The Ta-to- Ti ratio in such C40 or C54 grains changes rapidly from 0.11-0.12 at the in terface to 0 at a distance about 35 nm away from the interface. The observa tion of C40 TiSi2 and C54 (Ti0.89Ta0.11)Si-2, is a consequence of epitaxial growth at low temperatures. After annealing at 750 degrees C, the C40 phas e is not detectable by electron or x-ray diffraction. These results verify, from a microscopic point of view, the template mechanism suggested earlier for the enhanced formation of C54 TiSi2 in the presence of Mo, Nh, or Ta, based on the macroscopic analysis results. In addition, the high-Ta content s in the C54 phase induce a high concentration of stacking faults in the (0 10) direction along which epitaxy of C54 (Ti,Ta)Si-2 on C40 (Ti;Ta)Si-2 tak es place.