| 摘要 |
<p>PROBLEM TO BE SOLVED: To increase the moving distance of a wafer stage by vertically setting the wafer stage, bending a laser beam through a pentaprism and directing the laser beam towards a plurality of interferometers on the wafer stage via a plurality of beam splitters and field mirrors. SOLUTION: Four interferometer laser beams are aligned with a wafer plane in a nominally parallel plane. Alignment information from laser gages, i.e., interferometers, is all referred to with respect to a plane in parallel with the wafer plane. In order to satisfy the requirements for overlay alignment which is extremely important in microlithography, a wafer requires micro-motion control and alignment of six degrees of freedom, i.e., three degrees of freedom on the wafer plane and three degrees of freedom in the directions perpendicular thereto. A wafer stage 10 can move over a relatively long distance, or it can move freely in X-Y direction, so long as the interferometer laser beams enter into reference mirrors 30, 32.</p> |
