| 摘要 |
PURPOSE:To correct various chromatic aberrations which are developed by an optical system of projection when conditions of projected plane are observed by means of an observation optical system through the projection optical system with the aid or wave lengths which are different from those used for projection and obtain favorable obsevations by arranging plural parallel plates at a part of optical path of the observation optical system after inclining the plates to optical axes of the observation optical system each other. CONSTITUTION:A first object, for example, a reticle 1 is projected on a second object, for example, a wafer 2 by a projection optical system 3 and plural parallel plates are arranged at a part of optical path of an observation optical system 100 which is observed by wave lengths different from those of projection on a face of the second object 2 after inclining the plates to optical axes of the projection optical system 100 each other. For example, the above plural parallel plates consist of three parallel plates 6, 7, and 7' and one plate of them is arranged to have an inclination to meridional beams of the projection optical system 3 and the rest of two plates 7 and 7' are arranged to have the inclination each other to the parallel plate 6 in a face intersecting at right angles to a face tilted by the plate 6. Accordingly, coma aberration to an observation wavelength of the projection optical system is corrected by the parallel plate 6 and then, astigmatism of all the systems is corrected by means of two parallel plates 7 and 7'. |
