Method of crystallizing amorphous silicon and device fabricated using the same

1. A method of crystallizing amorphous silicon, comprising:

forming an amorphous silicon film over a substrate;

crystallizing the amorphous silicon film to form a polycrystalline silicon film using a sequential lateral solidification crystallization method, wherein the sequential lateral solidification crystallization method includes at least a first application of a first laser beam having a first energy density that completely melts a first uncrystallized portion of the amorphous silicon film and melts a first crystallized portion of the amorphous silicon film,

wherein the first application of the first laser beam forms a plurality of seeds along first border regions between solid and liquid phases of the amorphous silicon film,

wherein the first uncrystallized portion of the amorphous silicon film is crystallized within a second region along a direction from the first border regions toward a center portion of the first uncrystallized portion using the plurality of seeds as nucleation cites during the first application of the first laser beam,

wherein the second region includes a plurality of first sub-grains having a first size and a plurality of first sub-grain boundaries,

wherein the sequential lateral solidification crystallization method includes at least a second application of the first laser beam that grows the first sub-grains to form a plurality of second sub-grains having a second size greater than the first size,

wherein a first group of the second sub-grains grow along a first direction to contact a second group of the second sub-grains that grow along a second direction substantially opposite to the first direction, and wherein the first and second groups of second sub-grains form a second sub-grain boundary,

wherein the plurality of first sub-grain boundaries are disposed among the plurality of first sub-grains and among the plurality of second sub-grains, and wherein the plurality of first sub-grain boundaries and the second sub-grain boundary include a plurality of microscopic defect particles; and

performing a surface treatment to the polycrystalline silicon film, wherein the surface treatment includes application of a second laser beam having a second energy density that has a partial melting energy density to melt defect sites in the polycrystalline silicon film,

wherein the application of the second laser beam partially melts and re-crystallizes the polycrystalline silicon film and removes the plurality of microscopic defect particles to smoothen the surface of the polycrystalline silicon film.

2. The method according to claim 1 , wherein the surface treatment maintains polycrystalline characteristics of the plurality of second sub-grains.

3. The method according to claim 2 , wherein the surface treatment forms a new grain boundary within a region where the first and second groups of second sub-grains directly contacts each other.

4. The method according to claim 1 , wherein the first laser beam has a beam width of about 2 to 3 micrometers.

5. The method according to claim 1 , wherein the surface treatment is performed within a vacuum chamber.

6. The method according to claim 5 , wherein the vacuum chamber includes inert gas.

7. The method according to claim 5 , wherein the vacuum chamber includes a dielectric window on a top portion of the vacuum chamber and a stage within an interior of the vacuum chamber.

8. The method according to claim 7 , wherein the dielectric window provides an air/vacuum tight seal with the vacuum chamber, and the substrate is disposed on the stage.

9. The method according to claim 5 , further comprising:

disposing the polycrystalline silicon film formed by the first laser beam over the stage of the vacuum chamber; and

applying the second laser beam along an entire surface of the polycrystalline silicon film disposed in the vacuum chamber.

10. The method according to claim 9 , wherein the application of the second laser beam is through the dielectric window of the vacuum chamber.