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:
Jul. 13, 1999
Filed:
Apr. 25, 1995
Michael William Cresswell, Frederick, MD (US);
Loren Wendell Linholm, Ijamsville, MD (US);
Richard A Allen, Germantown, MD (US);
Other;
Abstract
Imaging instruments for inspecting products, such as semiconductor chips, are calibrated by providing a reference test structure having features which can be located by optical measurements not subject to tool-induced shift and wafer-induced shift experienced by the imaging instrument, thereby enbabling self correction of the imaging instrument. The reference test structure, which has a plurality of target units formed therein, is first qualified using the optical measurements, and is then used to calibrate the imaging instrument. The optical measurements may be made by a supplementary alternative imaging-sensor means which can be integrated into existing imaging instrument architecture. A series of test structure elements may be fabricated with one component of each being spaced at progressively greater distances from an arbitrary baseline, such that a zero overlay element may be identified by the alternative imaging sensor means.