Optics: measuring and testing – By alignment in lateral direction – With light detector
Patent
1988-11-21
1990-02-27
Evans, F. L.
Optics: measuring and testing
By alignment in lateral direction
With light detector
250548, G01B 1100
Patent
active
049040871
ABSTRACT:
Photomasks (11, 12) are aligned on opposite sides of a wafer by directing light beams through zone plates (13 A-C) in one photomask and through aligned transparent slits (14 A-C) on the other photomask. Simulantaneous detection of the beams by photodetectors (18 A-C) indicates alignment. A method for obtaining precise centering by scanning the slits with the beams, sampling light transmitted through the slits, and fitting the samples to a parabola by the use of a computer (27) is also described.
REFERENCES:
patent: 4037969 (1977-07-01), Feldman et al.
patent: 4761561 (1988-08-01), Fujiwara et al.
Harvey George T.
Watkins Laurence S.
American Telephone & Telegraph Co., AT&T Bell Laboratories
American Telephone & Telegraph Company
Anderson Roderick B.
Evans F. L.
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