Patent ID: 7833349

Claim:
A laser anneal apparatus which irradiates a semiconductor thin film with a luminous flux having a regular light intensity distribution to crystallize the semiconductor thin film, the apparatus comprising: a laser light source; an illumination system which converges laser light emitted from the laser light source onto a focal point; a phase shifter disposed in the focal point of the illumination system; and an image-forming optical system disposed between the phase shifter and the semiconductor thin film; the phase shifter comprising: a first transparent layer having a first refractive index in a wavelength of the laser light for use; a second transparent layer disposed on the first transparent layer and having a second refractive index which is different from the first refractive index in the wavelength of the laser light for use; a third transparent layer disposed on the second transparent layer and having the first refractive index in the wavelength of the laser light for use; and a spacer which is disposed between the first transparent layer and the third transparent layer along peripheral edge portions of the first and third transparent layers and which blocks the second transparent layer from the outside so as to prevent particles from entering between the first transparent layer and the third transparent layer, wherein a two-dimensional pattern of fine stepped portions is formed in at least one of an interface between the first transparent layer and the second transparent layer and an interface between the second layer and the third transparent layer, whereby a phase difference is made between the laser light passed through the stepped portion and the laser light passed through a portion other than the stepped portion, and wherein a thickness of the second transparent layer is selected so as to prevent interference of the laser light while the laser light passes through the second transparent layer.