Silicide formation and silicide-mediated crystallization of nickel-implanted amorphous silicon thin films

Abstract

The nucleation and growth of isolated nickel disilicide precipitates in Ni-implanted amorphous Si thin films and the subsequent low-temperature silicide-mediated crystallization of Si was studied using in situ transmission electron microscopy. Analysis of the spatial distribution of the NiSi 2 precipitates strongly suggested the occurrence of site saturation during nucleation. NiSi2 precipitates were observed in situ to migrate through the amorphous Si thin films leaving a trail of crystalline Si at temperatures as low as ∼484°C. Initially, a thin region of epitaxial Si formed on {111} faces of the octahedral NiSi2 precipitates with a coherent interface which was shown by high-resolution electron microscopy to be Type A. Migration of the NiSi2 precipitates led to the growth of needles of Si which were parallel to 〈111〉 directions. The growth rate of the crystalline Si was limited by diffusion through the NiSi2 precipitates, and an effective diffusivity was determined at 507 and 660°C. A mechanism for the enhanced growth rate of crystalline Si is proposed.