A crystallization method is disclosed. In one embodiment, the method includes providing a substrate having an amorphous silicon layer, wherein the substate has first and second sides opposing each other and irradiating a laser beam onto the substrate so as to have an inclined angle with respect to the first and second sides of the substrate. The method further includes relatively moving one of the laser beam and the substate with respect to the other i) in a first direction from the first side to the second side of the substate and ii) in a second direction which crosses the first direction.