Two-dimensional Si crystal growth during thermal annealing of Au/polycrystalline-Si bilayers

Interactions between Au and polysilicon (where polysilicon denotes polycrystalline Si) thin films during thermal annealing at temperatures below 300 °C produce large-grain Si crystals (c-Si). Si is transported from the fine-grain polysilicon laterally through the Au layer to form large (400-μ${\mathrm{m}}^2$) plate-like-shaped single crystals of Si of thickness equal to that of the Au layer. The Si crystals displace the Au in the original Au layer and at the same time the Au penetrates into the polysilicon. X-ray diffraction data indicate that the Si crystals have the same preferred orientation (110) as the initial polysilicon film. The driving force for this transformation is the reduction of the interface energy at the grain boundaries of the polysilicon. It is concluded that the large grains from the polysilicon layer grow at the expense of the smaller grains.