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:
Oct. 18, 1988
Filed:
Apr. 13, 1987
Guenter Makosch, Sindelfingen, DE;
International Business Machines Corporation, Armonk, NY (US);
Abstract
To align a grating on a mask with respect to an equivalent grating of a wafer in a photolithographic system where the mask is imaged by an imaging system onto the wafer, symmetrical diffraction orders (u.degree..sub.+1, u.degree..sub.-1) are focussed on the wafer grating and diffracted a second time to return colinear with the optical axis and to be deflected by a beam splitter to a photo detector. The intensity of the superimposed outbeams depends on the relative phase differences of the diffracted beams, and, hence, on the displacements of the mask and wafer gratings. The phase of the electrical output signal is determined by introducing periodic phase differences in the diffracted beams of the mask grating by a wobbling parallel glass plate. For simultaneous X-, Y- alignment, crossed gratings are used that operate on two pairs of diffracted beams. The polarization direction of one of these pairs is rotated by 90.degree. before impinging on the second grating so that each pair of diffracted beams can be fed to a separate photodetector. In a step-and-repeat photolithographic system, optical fine alignment can be performed by adjusting a fixed tilt angle of the glass plate after having determined the amount of misalignment.