Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Patent
1997-08-28
2000-10-10
Hantis, K. P.
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
G01B 1100
Patent
active
061307505
ABSTRACT:
A metrology apparatus for determining bias or overlay error in a substrate formed by a lithographic process includes an aperture between the objective lens and the image plane adapted to set the effective numerical aperture of the apparatus. The aperture is adjustable to vary the effective numerical aperture of the apparatus and the aperture may be non-circular, for example, rectangular, to individually vary the effective numerical aperture of the apparatus in horizontal and vertical directions. To determine bias or overlay error there is provided a target having an array of elements on a substrate, the array comprising a plurality of spaced, substantially parallel elements having a length and a width, the sum of the width of an element and the spacing of adjacent elements defining a pitch of the elements, edges of the elements being aligned along a line forming opposite array edges, the distance between array edges comprising the array width. The numerical aperture is adjusted such that the pitch of the elements is less than or approximately equal to the ratio of the wavelength of the light source to the numerical aperture value of the optical metrology tool in the direction of the array edges, and the edges of the array are resolved with the optical metrology tool and the width of the array are measured to determine bias or overlay error in the substrate. A camera may be adapted to create a digital image of a target and the components of the digital image in the direction of the pitch of the elements, normal to the length of the elements, may be suppressed to resolve the edges of the array and measure the width of the array. Preferably, the means for suppressing components of the digital image comprises a microprocessor adapted to perform a fast Fourier transform on the digital image to convert image intensity to a spatial frequency domain and a filter to suppress high spatial frequency components of the image in the direction of the pitch of the elements.
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Ausschnitt Christopher P.
Brunner Timothy A.
Hantis K. P.
International Business Machines - Corporation
Townsend Tiffany L.
Ziegler, Jr. Geza C.
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