| 摘要 |
PURPOSE:To precisely detect the positional displacement of a mask and a wafer by a method wherein a laser light is emitted to a linear Fresnel zone plate on the mask, and a diffracted light reflected from a linear diffraction grating on the wafer is detected. CONSTITUTION:A mask 1 and a wafer 2 are placed confronting to each other. A linear Fresnel zone plate 3 is provided on the mask 1 to change the focal length continuously. A linear diffraction grating 4 is provided on the wafer 2. The positional displacement between the mask 1 and wafer 2 can be detected by detecting a reflected diffraction light 6 from the grating 4 when a laser beam 5 is irradiated to the plate 3. The beam 5 emitted to the plate 3 passes through the plate 3 and forms a spot on the wafer 2. When the spot overlaps with the grating 4, the beam 5 is reflected and diffracted. This reflected diffraction light 6 is a cylindrical wave which is parallel only in an elongated direction of the grating 4, but becomes a plane wave again after passing through the plate 3. In this manner, the positional displacement between the mask 1 and wafer 2 can be detected precisely. |
