Laser annealing method

1. A laser annealing method comprising:

preparing a substrate having an amorphous semiconductor film formed on a surface thereof; and

forming a plurality of polycrystalline regions by irradiating the amorphous semiconductor film with laser light a plurality of times through a mask having a plurality of openings, an irradiation energy density of the laser light and a time duration and number of times of the irradiating being set so that the amorphous semiconductor film is not heated to or above a melting point of polycrystalline, while moving the substrate relative to the mask so as to partially melt-crystallize the amorphous semiconductor film,

wherein the plurality of polycrystalline regions include a first polycrystalline region that has a shape elongated in a first direction with an aspect ratio of three or more and symmetrical with respect to a first center line parallel to the first direction, and two second polycrystalline regions that are adjacent to the first polycrystalline region in a direction perpendicular to the first direction, that have congruent shapes to each other, and that are arranged symmetrically with respect to the first center line, and

the forming includes simultaneously forming two molten regions to be the two second polycrystalline regions.

2. The laser annealing method of claim 1 , wherein the forming includes, after forming the first polycrystalline region, irradiating a region of the amorphous semiconductor film including the first polycrystalline region with the laser light so as to simultaneously form the two molten regions to be the two second polycrystalline regions.

3. The laser annealing method of claim 1 , wherein the forming includes, after forming the first polycrystalline region, irradiating two regions of the amorphous semiconductor film, each of which partially overlaps the first polycrystalline region and that are arranged symmetrically with respect to the first center line, with the laser light so as to simultaneously form the two molten regions to be the two second polycrystalline regions.

4. The laser annealing method of claim 1 , wherein the forming includes, after forming the two second polycrystalline regions, a step of irradiating a region of the amorphous semiconductor film, which partially includes both of the two second polycrystalline regions, with the laser light as to form a first molten region to be the first polycrystalline region that is adjacent to the two second polycrystalline regions.

5. The laser annealing method of claim 1 , wherein the plurality of polycrystalline regions include a third polycrystalline region that has a shape elongated in a second direction perpendicular to the first direction and symmetrical with respect to a second center line parallel to the second direction, and two fourth polycrystalline regions that are adjacent to the third polycrystalline region, the two fourth polycrystalline regions having congruent shapes to each other, and the two fourth polycrystalline regions being arranged symmetrically with respect to the second center line, and

wherein the forming includes simultaneously forming two fourth molten regions to be the two fourth polycrystalline regions.

6. The laser annealing method of claim 1 , wherein the plurality of polycrystalline regions include a third polycrystalline region that has a shape elongated in the first direction and symmetrical with respect to the first center line, and that is spaced from the first polycrystalline region, and

the forming includes irradiating a molten region to be the third polycrystalline region with the laser light a plurality of times.

7. The laser annealing method of claim 1 , wherein the substrate is moved relative to the mask in the first direction.