Polysilicon film having smooth surface and method of forming the same

A method for forming a polysilicon layer, comprising the steps of:

• (a) forming an amorphous silicon layer on a substrate;
• (b) irradiating a first irradiation area of the substrate by a first laser shot with sufficient energy to melt the amorphous silicon in the first irradiation area, whereupon the melted amorphous silicon crystallizes to form polysilicon;
• (c) moving the substrate a step of distance d, and irradiating a second irradiation area of the substrate by a second laser shot with sufficient energy to melt the amorphous silicon in the second irradiation area and a portion of the polysilicon in the first irradiation area overlapping the second irradiation area, whereupon the melted amorphous silicon and melted polysilicon crystallize and re-crystallize, respectively;
• and
• (d) repeating step (c) until the amorphous silicon layer on the substrate is transformed completely into a polysilicon layer,
• wherein in steps (b) and (c), the first and second laser shots each have a laser energy intensity profile in a direction of said moving that increases in said direction from 10% of the respective first and second laser shot's maximum energy intensity to 90% of the respective first and second laser shot's maximum laser energy intensity such that the laser energy intensity over a lateral distance, the lateral distance being larger than the distance d of movement of the substrate in said step (c).