Laser irradiation device

摘要

In annealing a non-single crystal silicon film through the use of a linear laser beam emitted by a YAG laser of a light source, it is the object of the present invention to prevent heterogeneity in energy caused by an optical interference produced in the linear laser beam from having an effect on the silicon film. The laser beam is divided by a mirror 604 shaped like steps into laser beams which have an optical path difference larger than the coherence length of the laser beam between them. The divided laser beams are converged on an irradiate surface 611 by the action of a cylindrical lens array 605 and a cylindrical tens 606 to homogenize the energy of the laser beam in the length direction and to determine the length of the linear laser beam. On the other hand, the laser beams divided by a cylindrical lens array 607 are converged on the irradiate surface 611 by a cylindrical lens 608 and a doublet cylindrical lens 609 to homogenize the energy in the width direction of the laser beam and to determine the width of the linear laser beam. Interference fringes parallel to the width direction of the linear laser beam disappears in the linear laser beam by the action of a mirror 604 shaped like steps. If the silicon film is annealed by the linear laser beam while the linear laser beam is being shifted in the width direction of the linear laser beam, the silicon film is remarkably homogenized as compared with a conventional silicon film.