Toward accurate radial velocities with the fiber-fed GIRAFFE multi-object VLT spectrograph

A mask alignment method of the reduction-projection type comprising the steps of illuminating only regions of alignment patterns formed on a mask and a wafer, before a circuit pattern formed on the mask is projected onto the chips of the wafer through a reduction-projection lens, and aligning the mask and the wafer with each other by detecting the reflected images of both the alignment patterns. The alignment pattern region is illuminated by the light having the same wavelength as the exposure light. In addition, a mask alignment apparatus of the reduction-projection type comprising an illumination device for illuminating the mask. The mask is disposed at a distance from the wafer. The illumination light includes g-line or h-line or a combination of g-line and h-line. The projection lens is interposed between the mask and the wafer so that the circuit pattern formed on the mask is projected on the chips of the wafer on a reduced scale thereby to give the optical printing of the circuit pattern to the wafer. A field diaphragm device is disposed in the vicinity of the mask in order to prevent the exposure of the circuit pattern during the alignment operation. The field diaphragm device is provided with an opaque base plate of the size corresponding to the circuit pattern region and a transparent window of the size corresponding to the alignment pattern. The mirror or the semi-transparent mirror is disposed for reflecting optical images of the alignment patterns of the mask and the wafer in a direction toward a detecting system for displacement. The relative displacement between the mask and the wafer is detected by the detecting system thereby to align the mask and the wafer with each other by moving one of them.