A mask for crystallization of amorphous silicon to polysilicon is provided. The mask includes a plurality of slit patterns for defining regions to be illuminated. The plurality of slit patterns are formed along a longitudinal first direction and the mask moves along a longitudinal second direction. The first longitudinal direction is substantially perpendicular to the second longitudinal direction. Each of the split patterns is deviated apart by substantially a same distance from another. Thus, the polysilicon using the mask are grown to be isotropic with respect to the horizontal and vertical directions.