US3790280A
Expired / Lapsed
US
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Spatial filtering system utilizing compensating elements
Assignee: AT&T Inc
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Filing: 1972-05-03
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Granted: 1974-02-05
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Expires: 1992-05-03
Abstract
Abstract A spatial filtering system for inspecting integrated circuit photomasks, and the like. The system includes a spatial filter comprising a matrix-like array of opaque regions on a transparent field, as well as one pair of opaque compensating elements for each element edge orientation in the photomask to be inspected. The opaque regions block the d.c. and lower spatial frequencies of the periodic photomask feature information, while the compensating elements block the corresponding higher spatial frequencies (i.e., the edge information). Use of the system significantly improves the signal-to-noise ratio of the filtered image.
Inventors
- 👤 R Heinz
- 👤 R Oehrle
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 19:34
CPC Classifications
G; G03; G03F; G03F1/00; G03F1/68; G03F1/82; G03F1/84; G02; G02B; G02B27/00; G02B27/42; G02B27/46; G03F7/00; G03F7/70; G03F7/70483; G03F7/70605; G03F7/70616; G03F7/7065
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
266 words
A method of isolating non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually spaced apart by a predetermined distance, along at least one axis, which comprises the steps of: directing a spatially coherent beam of light at the pattern to diffract the light; focusing the diffracted light on a filter consisting of a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, and at least one pair of opaque compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the spacing of said substantially equally sized opaque regions, along at least one axis of the filter being uniform and defined by the equation: x n lambda f/d where, x the distance of the nth region from the origin, lambda the wavelength of the light forming said image, n the order of the spatial harmonic, f the focal length of the Fourier-transform lens, d the step-and-repeat distance of the workpiece, to spatially modulate the light; and then reimaging the spatially modulated light to form an image exhibiting the non-periodic errors in the pattern, the periodic information in said image, and said at least one pair of compensating regions blocking the higher spatial frequencies corresponding to the edge information of the polygonal elements of the feature pattern.
Claim 2
Independent Claim
266 words
A method of isolating non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually spaced apart by a predetermined distance, along at least one axis, which comprises the steps of: directing a spatially coherent beam of light at the pattern to diffract the light; focusing the diffracted light on a filter consisting of a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, and at least one pair of opaque compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the spacing of said substantially equally sized opaque regions, along at least one axis of the filter being uniform and defined by the equation: x n lambda f/d where, x the distance of the nth region from the origin, lambda the wavelength of the light forming said image, n the order of the spatial harmonic, f the focal length of the Fourier-transform lens, d the step-and-repeat distance of the workpiece, to spatially modulate the light; and then reimaging the spatially modulated light to form an image exhibiting the non-periodic errors in the pattern, the periodic information in said image, and said at least one pair of compensating regions blocking the higher spatial frequencies corresponding to the edge information of the polygonal elements of the feature pattern.
Claim 3
Independent Claim
278 words
A method of isolating non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually spaced apart by a predetermined distance, along at least one axis, which comprises the steps of: directing a spatially coherent beam of light at the pattern to diffract the light; focusing the diffracted light on a filter consisting of a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, and at least one pair of opaque compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the spacing of said substantially equally sized opaque regions, along at least one axis of the filter being uniform and greater than the spacing dictated by the equation: x n lambda f/d where, x the distance of the nth region from the origin, lambda the wavelength of the light forming said image, n the order of the spatial harmonic, f the focal length of the Fourier-transform lens, d the step-and-repeat distance of the workpiece, to spatially modulate the light; and then reimaging the spatially modulated light to form an image exhibiting the non-periodic errors in the pattern, the discrete regions in said filter blocking essentially all periodic information in said image, and said at least one pair of compensating regions blocking the higher spatial frequencies corresponding to the edge information of the polygonal elements of the feature pattern.
Claim 4
Independent Claim
278 words
A method of isolating non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually spaced apart by a predetermined distance, along at least one axis, which comprises the steps of: directing a spatially coherent beam of light at the pattern to diffract the light; focusing the diffracted light on a filter consisting of a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, and at least one pair of opaque compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the spacing of said substantially equally sized opaque regions, along at least one axis of the filter being uniform and greater than the spacing dictated by the equation: x n lambda f/d where, x the distance of the nth region from the origin, lambda the wavelength of the light forming said image, n the order of the spatial harmonic, f the focal length of the Fourier-transform lens, d the step-and-repeat distance of the workpiece, to spatially modulate the light; and then reimaging the spatially modulated light to form an image exhibiting the non-periodic errors in the pattern, the discrete regions in said filter blocking essentially all periodic information in said image, and said at least one pair of compensating regions blocking the higher spatial frequencies corresponding to the edge information of the polygonal elements of the feature pattern.
Claim 5
Dependent Claim
79 words
The method according to claim 2 wherein at least one of said regions is positioned in coincidence with a location dictated by the equation: x f tan (sin1 (n lambda /d)) where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic and is greater than one; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 6
Dependent Claim
27 words
The method according to claim 3 wherein said point of coincidence lies approximately halfway between the centermost filter region and the corresponding one of said compensating regions.
Claim 7
Independent Claim
280 words
A method of isolating non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually spaced apart by a predetermined distance, along at least one axis, which comprises the steps of: directing a spatially coherent beam of light at the pattern to diffract the light; focusing the diffracted light on a filter consisting of a matrix-like array of discrete substantially equally sized opaque regions on a transparent field and at least one pair of opaque compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the spacing of said substantially equally sized opaque regions, along at least one axis thereof, increases outwardly from the centermost region, according to the formula: x f tan (sin 1 (n lambda /d) ) where, x the distance of the nth region from the origin, lambda the wavelength of the light forming said image, n the order of the spatial harmonic, d the step-and-repeat distance of the workpiece, f the focal length of the Fourier-transform lens, to spatially modulate the light; and the reimaging the spatially modulated light to form an image exhibiting the non-periodic errors in the pattern, the discrete regions in said filter blocking essentially all periodic information in said image, and said at least one pair of compensating regions blocking the higher spatial frequencies corresponding to the edge information of said polygonal elements of the feature pattern.
Claim 8
Independent Claim
280 words
A method of isolating non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually spaced apart by a predetermined distance, along at least one axis, which comprises the steps of: directing a spatially coherent beam of light at the pattern to diffract the light; focusing the diffracted light on a filter consisting of a matrix-like array of discrete substantially equally sized opaque regions on a transparent field and at least one pair of opaque compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the spacing of said substantially equally sized opaque regions, along at least one axis thereof, increases outwardly from the centermost region, according to the formula: x f tan (sin 1 (n lambda /d) ) where, x the distance of the nth region from the origin, lambda the wavelength of the light forming said image, n the order of the spatial harmonic, d the step-and-repeat distance of the workpiece, f the focal length of the Fourier-transform lens, to spatially modulate the light; and the reimaging the spatially modulated light to form an image exhibiting the non-periodic errors in the pattern, the discrete regions in said filter blocking essentially all periodic information in said image, and said at least one pair of compensating regions blocking the higher spatial frequencies corresponding to the edge information of said polygonal elements of the feature pattern.
Claim 9
Dependent Claim
211 words
Apparatus for inspecting non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually arranged in a planar periodic array, which Comprises: means for directing a spatially coherent beam of light at the plane of the pattern so that the light is diffracted thereby; a first lens positioned to focus the light diffracted by the pattern; a planar optical filter consisting of an array of discrete substantially equally sized opaque regions on a transparent field, and at least one pair of compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding feature edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the filter being positioned at the focal plane of the first lens for spatially modulating the intensity of the light focused thereon by the first lens; a second lens positioned to reimage the light transmitted by the filter to form a visual image of the non-periodic errors in the pattern of the image-display means; and means for projecting the visual image onto the image-display means.
Claim 10
Dependent Claim
211 words
Apparatus for inspecting non-periodic errors in a matrix-like array of nominally identical features, each feature comprising a pattern of lines and other polygonal elements, said features being mutually arranged in a planar periodic array, which Comprises: means for directing a spatially coherent beam of light at the plane of the pattern so that the light is diffracted thereby; a first lens positioned to focus the light diffracted by the pattern; a planar optical filter consisting of an array of discrete substantially equally sized opaque regions on a transparent field, and at least one pair of compensating regions for each element edge orientation located symmetrically about and spaced from the center of the filter, on an axis orthogonal to the corresponding feature edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions the filter being positioned at the focal plane of the first lens for spatially modulating the intensity of the light focused thereon by the first lens; a second lens positioned to reimage the light transmitted by the filter to form a visual image of the non-periodic errors in the pattern of the image-display means; and means for projecting the visual image onto the image-display means.
Claim 11
Dependent Claim
71 words
The apparatus according to claim 6 wherein the region-to-region spacing in said array, along at least one axis thereof, is given by the equation: x n lambda f/d where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 12
Dependent Claim
76 words
The apparatus according to claim 6 wherein the region-to-region spacing in said array, along at least one axis thereof, is greater than the spacing dictated by the equation: x n lambda f/d where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n + the order of the spatial harmonic; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 13
Dependent Claim
80 words
The apparatus according to claim 8 wherein at least one of said regions is positioned in coincidence with a location dictated by the equation: x f tan (sin 1 (n lambda /d)) where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic and is greater than one; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 14
Dependent Claim
27 words
The apparatus according to claim 9 wherein said point of coincidence lies approximately halfway between the centermost filter region and the corresponding one of said compensating regions.
Claim 15
Dependent Claim
80 words
The apparatus according to claim 6 wherein the region-to-region spacing in said array, along at least one axis thereof, increases outwardly from the centermost region, according to the formula: x f tan (sin 1 (n lambda /d)) where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 16
Dependent Claim
69 words
Apparatus according to claim 6 wherein said image-display means and said projecting means comprises: a television camera focused on said visual image; control means, connected to said camera, for supplying deflection signals and power to said camera, said camera scanning across said visual image to detect said non-periodic errors; and counting means, connected to the video output of said camera, for counting the number of non-periodic errors so detected.
Claim 17
Dependent Claim
134 words
A spatial filter for filtering the Fourier transform of the image of a workpiece, said workpiece comprising a matrix-like array of nominally identical features, containing polygonal elements, which consists of: a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, said regions inhibiting further transmission of substantially all periodic information in said transform; and at least one pair of opaque compensating regions for each element edge orientation, located symmetrically about the center of said filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions to inhibit further transmission of the higher spatial frequencies corresponding to the edge information of the polygonal elements of the feature pattern.
Claim 18
Dependent Claim
134 words
A spatial filter for filtering the Fourier transform of the image of a workpiece, said workpiece comprising a matrix-like array of nominally identical features, containing polygonal elements, which consists of: a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, said regions inhibiting further transmission of substantially all periodic information in said transform; and at least one pair of opaque compensating regions for each element edge orientation, located symmetrically about the center of said filter, on an axis orthogonal to the corresponding element edge, such that a substantial number of said substantially equally sized opaque regions are disposed between the individual regions of each pair of compensating regions to inhibit further transmission of the higher spatial frequencies corresponding to the edge information of the polygonal elements of the feature pattern.
Claim 19
Dependent Claim
73 words
The spatial filter according to claim 13 wherein, the region-to-region spacing in said array, along at least one axis thereof, is given by the equation: x n lambda lambda f/d where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 20
Dependent Claim
76 words
The spatial filter according to claim 13 wherein the region-to-region spacing in said array, along at least one axis thereof, is greater than the spacing distated by the equation: x n lambda f/d where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 21
Dependent Claim
81 words
The spatial filter according to claim 15 wherein at least one of said regions is positioned in coincidence with a location dictated by the equation: x f tan (sin 1 (n lambda /d)) where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic and is greater than one; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
Claim 22
Dependent Claim
28 words
The spatial filter according to claim 16 wherein said point of coincidence lies approximately halfway between the centermost filter region and the corresponding one of said compensating regions.
Claim 23
Dependent Claim
81 words
The spatial filter according to claim 13 wherein the region-to-region spacing in said array, along at least one axis thereof, increases outwardly from the centermost region, according to the equation: x f tan (sin 1 (n lambda /d)) where, x the distance of the nth region from the origin; lambda the wavelength of the light forming said image; n the order of the spatial harmonic; d the step-and-repeat distance of the workpiece; and f the focal length of the Fourier-transform lens.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-02-04 | 1977-08-06 | 1978-02-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-02-04 | 1981-08-06 | 1982-02-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-02-04 | 1985-08-06 | 1986-02-05 | $7700.00 | Window Closed / Lapsed |