The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Apr. 18, 1995
Filed:
Jan. 11, 1994
Shigeru Hirukawa, Kashiwa, JP;
Eiji Takane, Tokyo, JP;
Nikon Corporation, Tokyo, JP;
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.