PURPOSE: To enable a high precision alignment by selectively transmitting the diffracted light beams from a reference grating by an optical system for lighting, irradiating said diffracted light beams from a specified direction defined by the NA of the optical system for lighting to the reference grating to be aligned, and extracting optical beat signals using two light beams having slightly different frequencies and planes of polarization orthogonal with each other, thereby improving the S/N of the detected signal.
CONSTITUTION: After passing through an optical system for lighting, the 0, ± primary diffracted lights 1W3 from a reference grating 12 are irradiated onto a second grating 15 and a third grating 17 at an angle defined by the NA(Numeral Aperture) of the optical system for lighting with any one diffracted light being cut. And the diffracted light beams from the reference grating are separated again at the second and third gratings into 0, ±primary, ± secondary... diffracted light beams. Of these, by synthesizing the diffracted light of a particular degree, the amount of the positional shifts of the second and third diffraction gratings with respect to the reference grating 12 and the amount of the relative positional shift of the third grating with respect to the second grating can equivalently detected as the phase difference of optical beat signals. By moving a mask 19 and a wafer 20 mounting stages based on the phase difference detected from the optical beat signals, alignment is performed.
AOKI SHINICHIRO
YAMAGUCHI KATSUMASA
KANEKO TADASHI
NOMURA NOBORU
KOGA KEISUKE
YAMASHITA KAZUHIRO
