Relationship of aluminum grain size to the grain size of polycrystalline silicon produced by the aluminum induced crystallization of amorphous silicon

The aluminum-induced crystallization and layer exchange process shows great promise for converting a-Si into large-grained poly-Si for solar cell applications. To investigate the relationship between the grain size of Al and the final grain size of poly-Si, a series of samples were deposited by RF magnetron sputtering 165 nm of Al onto SiN/SiO₂ coated (100) silicon substrates. The Al grain size was varied by vacuum annealing prior to the deposition of 195 nm of a-Si. Completion of the layer exchange process resulted in poly-Si films which were then characterized with plan view TEM. The average Si grain size was found to increase as a function of increasing Al grain size, consistent with the grain-boundary nucleation model for this process. The largest average Si grain size of 4.9 ± 1.92 ¿m corresponded to the Al sample which was annealed for 24 hours at 550°C. The microstructure of the poly-Si film can therefore be manipulated by altering the properties of the as-deposited Al layer with an isothermal anneal.