Crystallization of a-Si thin film using an ultra thin n+ poly-Si seed layer for solar cell applications

New results on the crystallization of the a-Si thin film using the low thermal budget pulsed rapid thermal annealing process and the SiO₂ sacrificial layer are reported. The intrinsic a-Si thin film was transformed into the poly-Si thin film with a 30 nm thick n⁺ poly-Si seed layer. Process parameters, such as the number of the pulsed rapid thermal annealing cycles, affected the grain structure of the n⁺ film on the glass/Mo/Ni surface. Material properties, such as the crystal size and the volume fraction of the crystalline phase, of the intrinsic poly-Si thin films were influenced by the grain structure of the n⁺ seed layer. The multi-step pulsed rapid thermal annealing process can reduce the Ni residue in the crystallized Si film. Therefore, in addition to the thermal budget, the material property of the seed layer is critical to the final poly-Si properties. The poly-Si film´s structure and impurity content are important to the solar cell performance.