Method and apparatus for detecting focal plane

Details Method and apparatus for detecting focal plane Method and apparatus for detecting focal plane

1991-04-22

1992-10-06

Brinich, Stephen

Image analysis

Histogram processing

For setting a threshold

382 54, 382 65, G06K 913

Patent

active

051539160

ABSTRACT:
A method and apparatus measures an image plane of a test pattern projected onto a surface of a sample disposed on a stage to precisely detect the image plane to thereby obtain a precise alignment therebetween for subsequent exposure. The test pattern is provided on a member having a conjugate surface with an upper surface of an illumination detecting unit having at least three optical sensors at different positions thereof and disposed on the stage. The upper surface of the illumination detecting unit has an analogous pattern to the test pattern on each optical sensor and, by moving the stage three dimensionally, outputs of the optical sensors are processed to obtain amounts of light and peak values thereof from which the image plane is obtained.

REFERENCES:
patent: 3882462 (1975-05-01), McMahon
patent: 3891968 (1975-06-01), McMahon
patent: 3968476 (1976-07-01), McMahon
patent: 4029944 (1977-06-01), Trenkamp
patent: 4164788 (1979-08-01), Jain
patent: 4540277 (1985-09-01), Mayer et al.
patent: 4711567 (1987-12-01), Tanimoto

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