| 摘要 |
PURPOSE:To enable any optical aberration to be corrected compactly at low cost by a method wherein a plurality of rear reflection type mirrors each parallel surfaces on both sides are arranged at part of an optical path of a detection optical system, mutually inclining to the optical axis of the detection optical system. CONSTITUTION:Various aberrations caused by a projection optical system must be corrected properly. At this time, if the correcting optical system is constituted of a transmission type system, the system is subjected to the defect of larger size. Therefore, a plurality of rear reflection type mirrors are arranged mutually inclining to the optical axis to constitute an aberration correcting optical system. The reflected light from a wafer mark (MK1Y, etc.) enters into a mirror M11 through the intermediary of a projection optical system PO. At this time, the mirror M11 as a parallel flat back surface reflection type mirror inclines to meridional luminous flux of the projection optical system. The luminous flux enters into mirrors M12, M13. The mirrors M12, M13 are back surface reflection type similar to the mirror M11 but orthogonal to the mirror M11. In such a constitution, the light flux passing through the mirror 13 is reflected in the surface reflection type mirror M14 to form image on a reference mask BM. |
