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:
Jan. 04, 1994
Filed:
Oct. 31, 1991
Alexander Starikov, Fishkill, NY (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
A method and apparatus is provided for estimating the centerline of an alignment/overlay measurement target by means of projecting light from a tunable, variable wavelength the illumination source onto the target, then performing optical observation of the measurement mark and providing an output signal representing the quantity measured in the observation, computing from the output signal a criterion of signal asymmetry to provide an output product, and tuning the tunable illumination source as a function of the output product. As a result tuning adjustment of the wavelength of illumination is employed to expose an observed feature, and the illumination source is tuned until the criterion is minimized, thus improving the accuracy of the estimated centerline.