Method of measuring the best focus position having a plurality o

Details Method of measuring the best focus position having a plurality o Method of measuring the best focus position having a plurality o

1994-01-11

1995-04-18

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Photocell controls its own optical systems

355 53, G01J 120

Patent

active

054080835

ABSTRACT:
Disclosed is a method of calculating the best focus position of a projection optical system by arranging a photosensitive substrate in the best focus position of a projection optical system, projecting measuring mark images in a plurality of focus positions on the photosensitive substrate in an optical-axis direction of the projection optical system to projection-expose mask patterns and thus obtaining the best focus position from a relationship between each of the focus positions and the measuring mark image corresponding thereto. The method comprises a first step of approximating a size of the measuring mark image with an nth-order or larger (n is an integer of 2 or larger) function relative to the focus position by a statistical operation. The method also comprises a second step of obtaining a tentative best focus position from the approximated function and a third step of calculating a weight corresponding to each of the plurality of measuring mark images on the basis of a difference between the tentative best focus position and each of the plurality of focus positions. The method further comprises a fourth step of approximating a size of the measuring mark image with an nth-order or smaller function relative to the focus position by a statistical operation to minimize a sum, relative to the focus position, of product of the weight obtained in the third step by a square of a difference between the nth-order or smaller function relative to the focus position and the size of the measuring mark image corresponding thereto and a fifth step of obtaining the best focus position of the projection optical system from the nth-order or smaller function obtained in the fourth step.

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patent: 5286963 (1994-02-01), Torigoe
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