Nickel distribution in crystalline and amorphous silicon during solid phase epitaxy of amorphous silicon

Solid phase epitaxy of nickel-doped amorphous silicon (a-Si) films on crystalline silicon (c-Si) substrates has been investigated. The crystallization mode of the a-Si films depends strongly on the nickel concentration. Below ∼5×1018 Ni/cm3, redistribution of nickel into the c-Si substrate occurs and the regrowth process is controlled by an “ordinary” thermally activated solid phase epitaxial crystallization (SPEC) process. In contrast, above 5×1018 Ni/cm3 segregation of Ni in the a-Si films is observed and the silicon crystallization is driven by impurity enhanced SPEC and/or silicide mediated crystallization in the bulk of the amorphous film. The redistribution of Ni during crystallization can be described in terms of an effective distribution coefficient accounting for the actual crystallization rate of a-Si and the Ni diffusivity in a-Si. Further, dissolution of implantation-induced (311) defects is observed in the samples exhibiting Ni diffusion into the crystalline phase during ordinary SPEC. This indicates annealing and /or suppression of the (311) defects due to nickel accumulating in the region of end-of-range defects.