Laser irradiation method and laser irradiation apparatus

#1. Field of the Invention

#The present invention relates to a laser irradiation method and a laser irradiation apparatus which are suitable, for example, for crystallizing an amorphous semiconductor film and which can project a linear laser beam having homogeneous intensity distribution to an irradiation surface. More specifically, the present invention relates to a laser irradiation method and apparatus using a cylindrical lens which can form a laser beam having homogeneous intensity distribution and which can project the linear laser beam having homogeneous intensity distribution onto an irradiation surface without causing the linear laser beam to have bias in its intensity distribution in reflection of intensity distribution of an original beam.

#2. Description of the Related Art

#In the accompanying drawings:

#FIGS. 1A to 1C are drawings showing energy intensity distribution of a laser beam in the case where a linear laser beam is formed by a concave cylindrical lens array in a major-axis direction;

#FIGS. 2A to 2C are drawings showing energy intensity distribution of a laser beam in the case where a linear laser beam is formed by a convex cylindrical lens array in a major-axis direction;

#An embodiment mode and an embodiment are hereinafter described with reference to the drawings. However, the present invention is not limited to the description of the following embodiment mode and embodiment, and is specified by the description of the scope of the claims. In the present invention, a laser beam emitted from a laser oscillator is divided by two kinds of cylindrical lens arrays into a plurality of beams with their energy intensity distribution inverted. Therefore, the bias in the energy intensity distribution is offset, and a linear laser beam with high homogeneity can be formed on the irradiation surface. A configuration, a function, a characteristic, usage, and the like of these cylindrical lenses are hereinafter described.

#In order to homogenize the laser beam with the cylindrical lens, a concave or convex cylindrical lens is usually used. FIGS. 1A to 1C illustrate a step of shaping a linear laser beam in a major-axis direction by a concave cylindrical lens array 101 using concave cylindrical lenses. FIG. 1A illustrates the energy intensity distribution of the original laser beam before transmitting through the cylindrical lens array, FIG. 1B schematically illustrates the laser beam after transmitting through the cylindrical lens array, and FIG. 1C illustrates the energy intensity distribution of the laser beam on the irradiation surface. The linear laser beam is formed on the irradiation surface 103 in such a way that after the laser beam is divided by the concave cylindrical lens array 101 into a plurality of beams, they are combined by a condensing lens 102 on the irradiation surface 103. When a linear laser beam is formed by dividing the original beam having energy distribution 104 with bias in one direction by the array 101, energy distribution 105 with bias in one direction is formed on the irradiation surface 103.

#On the other hand, FIGS. 2A to 2C illustrate a step of shaping a linear laser beam in a major-axis direction by a convex cylindrical lens array 201 using convex cylindrical lenses. FIG. 2A illustrates the energy intensity distribution of the original laser beam before being incident into the cylindrical lens array, FIG. 2B schematically illustrates the laser beam after transmitting through the cylindrical lens array 201, and FIG. 2C illustrates the energy intensity distribution of the laser beam on an irradiation surface 203. When the original beam has biased energy distribution 204, the beams divided by the convex cylindrical lens array 201 also has the energy distribution with the bias in the same manner as the distribution formed by the concave cylindrical lens array 101. However, since the laser beam transmitted through the convex cylindrical lens expands after being condensed once, energy distribution 205 formed on the irradiation surface 203 is inverted from the energy distribution 105 formed by the concave cylindrical lens array 101.