Amorphous-to-polycrystalline Phase Transformations in Sn-implanted Silicon

An amorphous-to-fine-grain-polycrystalline phase transformation has been observed during annealing of Sn-implanted Si when the peak Sn concentration exceeds about 2 at.%. At lower Sn concentrations, epitaxial growth is retarded in (100) Si but proceeds to completion with a large fraction of Sn residing on substitutional lattice sites. As the Sn concentration is increased, epitaxy is pre-empted by the sudden transformation of the near-surface Sn-doped region into polycrystalline Si. The time required to initiate the transformation is temperature dependent and is characterized by an activation energy of ~1.7 eV. Rapid redistribution of Sn has been observed to accompany the transformation. Our observations are shown to be consistent with a melt-mediated crystallization process which is rate limited by Sn diffusion and precipitation in amorphous Si.