Patent ID: 7828894

Claim:
A crystallization method, comprising: forming an amorphous silicon layer on a substrate; performing a first crystallization process by irradiating the amorphous silicon layer with a first laser beam having an asymmetrical upper cross sectional energy density profile of a ramp shape that descends in a scanning direction to form a first lateral crystallization region, wherein the asymmetrical upper cross sectional energy density profile is not flat, and wherein the first crystallization process is performed by a sequential lateral crystallization method; and performing a second crystallization process with the laser beam by moving a second laser beam to a predetermined length in a scanning direction so as to be partially overlapped with the first lateral crystallization region formed by the first crystallization process, wherein the second crystallization process is performed by irradiating the amorphous silicon layer with the laser beam having an asymmetrical upper cross sectional energy density profile of a ramp shape that descends in a scanning direction to form a second lateral crystallization region, and wherein the second crystallization process is performed by a sequential lateral crystallization method, wherein the second crystallization process overlaps with the first lateral crystallization region, and the first lateral crystallization region irradiated with the first laser beam has a larger grain size than the second lateral crystallization region irradiated with the second laser beam having a lower peak than that of the first laser beam, and a crystallization region comprises the first and second crystallization regions, wherein the first lateral crystallization region and the second lateral crystallization region are formed by a first laser pulse so the lateral crystallization occurs in a direction towards the center by using the amorphous silicon at the sides as seeds for crystal growth, and a grain boundary is formed to the right of center of the first laser pulse, to accomplish sequential lateral solidification, and wherein the first lateral crystallization region is relatively larger than the second lateral crystallization region; and a second laser pulse is irradiated after moving a laser generator to a predetermined length less than a length of the first lateral crystallization region so that some parts of the first lateral crystallization region are overlapped, to accomplish crystallization again, wherein the crystallization is performed subsequent to the first lateral crystallization region as the first lateral crystallization region acts as seeds, to form a bigger grain.