Transmission electron microscopy studies of metal-induced crystallization of amorphous silicon

The metal-induced crystallization of a-Si films in contact with Ni, Pd, Al, and Au was studied by cross-sectional transmission electron microscopy after rapid thermal annealing. In no case did crystallite nucleation initiate at the initial Si-metal interface and growth progress toward the substrate; in all cases the microstructures were equiaxed rather than columnar. Interfacial silicides were not found for the Ni or Pd cases, although palladium silicide was detected in the bulk of the film. The microstructures of the Al and Au catalyzed samples were comparable to the microstructure of a sample crystallized by an excimer laser pulse, suggesting the possibility of an explosive-type crystallization process in which a crystallization front is initiated at the metal-Si interface and propagates through the Si at a rate greater than that possible for solid-state epitaxial grain growth.