| 摘要 |
PURPOSE:To improve the precision in detection of a position and to reduce the cost by constructing an optical system wherein both of an illumination light illuminating the surface of a wafer and an illumination light illuminating the surface of a reticle pass through a first lens. CONSTITUTION:An S-polarized illumination light 20 illuminating the surface of a wafer 32 is passed through an illuminating lens 21, a mirror 22 and a beam splitter 23, converted into a circular polarized light by a lambda/4 phase plate 24, passed through a first lens 25 and a mirror 26 and reflected by a reflecting part of an alignment mark 28 of a reticle 27, and illuminates the part of an alignment mark of the wafer 32 through a reducing lens 31. A detection light 33 diffracted from this alignment mark at a diffraction angle of psi follows an optical path indicated by a dotted line and forms an image of the alignment mark of the wafer 32 in an imaging spot 43. The detection light 33 converted into a P-polarized light by the phase plate 24 and transmitted through the beam splitter 23 is detected by a sensor 39 through the intermediary of a second lens 34, a third lens 35, first and second cylindrical lenses 36 and 37 and a polarizing plate 38. |
