A crystallization method, a method of manufacturing a thin-film transistor, and a method of manufacturing a display device are provided. The crystallization method includes: forming a backup amorphous silicon layer on a substrate, forming nickel particles on the backup amorphous silicon layer, converting the backup amorphous silicon layer into an amorphous silicon layer by thermally processing the backup amorphous silicon layer so as to diffuse the nickel particles throughout said backup amorphous silicon layer; and irradiating the amorphous silicon layer with energy from a laser.