Laser annealing method, laser annealing apparatus, and manufacturing process for thin film transistor

A laser annealing method for irradiating laser light to an amorphous silicon thin film deposited on gate electrodes formed in a matrix at regular array pitches on a substrate so as to crystallize the amorphous silicon thin film into polysilicon as semiconductor layers on the gate electrodes,

• the method comprising:
• the step of multiply irradiating the laser light while changing an irradiation area of the laser light on the amorphous silicon thin film to achieve such a grain size distribution that a crystal grain size of the polysilicon decreases from a central portion to a side edge portion at least along a center line of the irradiation area of the laser light, wherein
• the step of multiply irradiating the laser light is performed
• by using a photo mask having a plurality of apertures formed in a matrix at the array pitches of the gate electrodes, the matrix having rows each including apertures of the same size and extending in a direction crossing a conveyance direction of the substrate and columns each including apertures of different sizes and extending in the conveyance direction, and
• by irradiating the laser light sequentially through the rows of apertures by moving the substrate stepwise so that the laser light is irradiated through the apertures of different sizes in the photo mask and an irradiation width of the laser light changes in stages.