| 摘要 |
A unit magnification, achromatic, anastigmatic optical projection system, more particularly for microlithography on semi-conductor wafers, comprises a concave mirror (52), an achromatic lens (56) including a meniscus lens (53), a plano-convex lens (55) and two reflecting prisms (56, 57), all with appropriate refraction indices. Light which has passed through a recticle (R) is reflected by prism (56), then by mirror (52) and thereafter by prism (57) toward a wafer (W). Mirror (52) has an aperture (58) through which a beam of light is directed towards a photomultiplier tube (66) which is thus used to align wafer (W) with respect to reticle (R). |
