Coma aberration automatic measuring mark and measuring method

Abstract

Two coma aberration automatic measuring marks M,and M,of a first-order diffraction grating are each composed of a plurality of elongated isosceles triangle patterns which are so arranged that the axis of symmetry passing on the center of each elongated isosceles triangle is parallel to one another, that a half P,, P,, and P,of the elongated isosceles triangle patterns have the widths thereof which extend in a direction opposite to that of the remaining half P,, P,and P,of the elongated isosceles triangle patterns, and the elongated isosceles triangle patterns are located separately from one another, in a direction perpendicular to the axis of symmetry passing on the center of each elongated isosceles triangle, and at a pitch diffracting a measuring coherent light. The two first-order diffraction gratings M,and M,are located separately from each other in a direction of the axis of symmetry passing on the center of the elongated isosceles triangle, in such a manner that the elongated isosceles triangle patterns included in the two first-order diffraction gratings are in symmetry to each other, in connection with a line positioned between the two first-order diffraction gratings and which is perpendicular to the axis of symmetry passing on the center of the elongated isosceles triangle. The two first-order diffraction gratings are scanned by the measuring coherent light, and a relative distance R,between diffraction lights generated by the two first-order diffraction gratings, is measured and compared with a distance R between the two first-order diffraction gratings.