Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1988-03-14
1989-05-16
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
356400, G01B 1127
Patent
active
048312720
ABSTRACT:
An apparatus for projecting a pattern formed on a reticle onto a substrate through a projection optical system and detecting the positional relation between a first alignment mark of the reticle and a second alignment mark formed on the substrate includes a radiation source for applying radiation to the first alignment mark of the reticle, the radiation passed through the reticle being directed to the second alignment mark of the substrate by the projection optical system, photoelectric detectors for detecting the radiation reflected by the first alignment mark and the second alignment mark, the photoelectric detectors disposed at a position optically substantially conjugate with the entrance pupil of the projection optical system between the radiation source and the reticle, the photoelectric detectors disposed outside a predetermined area of the optic axis relative to the optic axis so that the radiation from the radiation source can pass through the predetermined area of the optic axis, and displacement apparatus responsive to the output of the photoelectric detectors to impart relative displacement between the reticle and the substrate.
REFERENCES:
patent: 4362385 (1982-12-01), Lobach
patent: 4717257 (1988-01-01), Kaneta et al.
patent: 4780615 (1988-10-01), Suzuki
Nikon Corporation
Westin Edward P.
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