Novel Optical Method for Widening Process Window of Phase-Modulated Excimer Laser Crystallization

A wide process window has been achieved for "the phase-modulated excimer-laser annealing" method of Si thin films. Ordinary and extraordinary light rays resulting from the birefringence effects of a crystal quartz plate, which is newly introduced within the optical path of the annealing system, generate a pair of projected images of a phase modulator. By adjusting their separation to be half the modulator pattern pitch, undesirable deformations, which appear in pair images owing to defocus, cancel each other out, resulting in a stable superposed image (light intensity profile) on the sample surface. It is shown by optical simulation and experiment that this "double-image method" widens the depth of focus from less than 2 µm to as wide as about ±6 µm.