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. 03, 2001
Filed:
Oct. 06, 1998
Fuyuhiko Inoue, San Mateo, CA (US);
Nikon Corporation, Tokyo, JP;
Abstract
An autofocus system for use for instance in a photolithography machine (but not so limited) uses oblique incident optics which transform a defocus of the plane of the wafer whose location is being detected to a lateral shear of the beam. A common path interferometer measures the lateral shear. The common path interferometer is for instance a triangular path interferometer. Since both the signal (object) light beam and the reference light beams transverse almost exactly the same optical path, the system is thereby independent of mechanical vibration or other environmental influence such as temperature variations. Compensation is provided for refractive effects caused by local atmospheric heating immediately above the wafer surface.