Growth of amorphous silicide during Ti/Si interfacial reactions in multilayer thin films

We have monitored the amorphization reaction in alternating layers of vacuum-deposited Ti and Si using transmission electron microscopy and compositional profiling. The concentration difference across the thickening amorphous interlayer was observed to decrease with the growth of the silicide. This change in interfacial compositions is proposed as a possible reason for the slowing down and eventual stagnation of the amorphous silicide growth observed in this system. Possible reasons for this behavior are discussed. Such a low-temperature process forming metastable alloys upon controlled annealing is contrasted with the formation of equilibrium silicides in a self-propagating exothermic reaction, which results in very high local temperatures in multilayers in an explosive fashion. These examples also serve to demonstrate the range of interesting phenomena that can occur due to the nanometer length scales in thin-film diffusion couples.