Method for aligning photomasks
AssigneesAmerican Telephone and Telegraph Company, AT&T Bell Laboratories, American Telephone and Telegraph Company
InventorsGeorge T. Harvey, Laurence S. Watkins
Life of this patent
Estimating the term…
Abstract
Photomasks (11, 12) are aligned on opposite sides of a wafer by directing light beams through zone plates (13 A-C) in one photomask and through aligned transparent slits (14 A-C) on the other photomask. Simulantaneous detection of the beams by photodetectors (18 A-C) indicates alignment. A method for obtaining precise centering by scanning the slits with the beams, sampling light transmitted through the slits, and fitting the samples to a parabola by the use of a computer (27) is also described.
Claims8
A method for aligning first and second planar members, comprising the step of forming first and second light confining elements in the first planar member, forming first and second transparent openings, each of smaller width than length, in the second member so as to be approximately aligned, respectively, with the first and second light confining elements, locating first and second photodetectors, respectively, adjacent the first and second openings and opposite the first planar member, directing a first light beam through the first light confining member toward the second planar member, direction a second light beam through the second light confining member toward the second member, causing the first beam to scan the first opening in a direction traverse to the width of the first opening, causing the second beam to scan the second opening in a direction traverse to the width of the second opening, and causing movement of the second member relative to the first member until the first beam is transmitted through the first opening and is detected by the first light detector and the second light beam is simultaneously transmitted through the second opening and detected by the second detector.
A method for aligning first and second members comprising the step of forming at least a first zone plate in a first planar member, forming at least a first transparent opening in the second member so as to be aligned with the first zone plate, locating at least a first photodetector adjacent the first opening and opposite the first planar member, directing at least a first light beam through the first zone plate toward the second member, moving the second member relative to the first member so as to cause the first light beam to scan the width of the first opening, making three equally-spaced measurements of light intensity through the first opening, after each scan changing the location of the initiation of the successive scan until two of the three measurements are substantially equal and the three measurements of light intensity vs. distance each substantially describe a parabola, and the parabola is used to center the first opening on the first beam.
A method for aligning first and second planar members comprising the steps of forming first and second zone plates in the first planar member, forming first and second transparent openings in the second member so as to be approximately aligned, respectively, with the first and second zone plates, locating first and second photodetectors, respectively, adjacent the first and second openings and opposite the first planar member, directing a first light beam through the first zone plate toward the second planar member, directing a second light beam through the second zone plate toward the second member, causing the first and second light beams to make a plurality of scans of the widths of the first and second openings, making three equally-spaced measurements of light intensity through each opening, after each scan, changing the location of the initiation of the successive scan and the angular orientation of the second planar member until two of the three measurements are substantially equal and the three measurements of light intensity vs. distance each substantially describe a parabola, and using the parabolas to center, respectively, the first opening on the first beam and the second opening on the second beam.
Dependencies are inferred from the claim text.