Position sensor having double focuses and utilizing a chromatic

Details Position sensor having double focuses and utilizing a chromatic Position sensor having double focuses and utilizing a chromatic

1989-04-27

1990-04-17

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

350316, G02B 522, H01J 314, H01J 516

Patent

active

049183010

ABSTRACT:
An apparatus having double focuses and utilizing a chromatic aberration senses the positions observed in the direction perpendicular to a common optical axis of first and second objects separated from each other by a very small distance on the order of several microns to several tens of microns, such as the distance between a mask and a wafer in an X-ray exposure system. The apparatus is provided with a lens system for imaging the marks of the two objects in an identical plane by axial spherical visible light having two different wavelengths, and is also provided with a filter for cancelling blurring caused by chromatic aberration. The images of the respective marks are optically processed. Thus, the positional relationship observed in the direction perpendicular to a common optical axis of the two objects can be sensed by a single lens and thereby the small distance between the objects can be accurately set.

REFERENCES:
patent: 3990789 (1976-11-01), White
patent: 4650983 (1987-03-01), Suwa
patent: 4733062 (1988-03-01), Horikawa et al.
patent: 4734570 (1988-03-01), Horikawa et al.
patent: 4769530 (1988-09-01), Miyahara
patent: 4856905 (1989-08-01), Nishi
European Search Report-Application Number EP 88 10 5743 listing documents No. DE-A-No. 3 413 374 and U.S. Pat. No. 3,990,798.

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