In this study, we investigated how fluorine implantation affects the crystallization of amorphous silicon (a-Si) prepared by low-pressure chemical vapor deposition. Fluorine and silicon ions were implanted at the center of the a-Si and a-Si/SiO2 interface to identify whether the effect is caused by implantation damage or fluorine incorporation into the thin film. Two-dimensional Monte-Carlo simulation was performed to clarify crystallization mechanisms. The microstructures obtained experimentally were reproduced by the simulation. Experimental and simulation results indicate that damage caused by fluorine implanted at the a-Si/SiO2 interface increased the energy barrier to stable nuclei formation, causing a significant reduction in the nucleation rate. Fluorine incorporation into the a-Si film reduced the growth rate as fluorine was implanted at the film center.