Intensity spatial filter having uniformly spaced filter elements

Claim 3

The method according to claim 1 wherein said point of coincidence lies approximately halfway between the centerMost filter regions and the edge of said filter.

Claim 4

Apparatus for inspecting non-periodic errors in a two-dimensional pattern containing a plurality of nominally identical and regular spaced regions 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 a distribution of discrete substantially equally sized opaque regions on a transparent field, the spacing between adjacent regions, along at least one axis of the filter being uniform and greater than the spacing dictated by the formula: x n lambda f/d where, x the distance of the nth region from the centermost region (origin), lambda the wavelength of said beam of light, n the order of the spatial harmonic, d the step-and-repeat distance of said regular array of regions, f the focal length of said focusing lens, 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 centermost region (origin); lambda the wavelength of said beam of light; n the order of the spatial harmonic and is greater than one; d the step-and-repeat distance of said regular array of regions; f the focal length of said focusing lens; 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; and means for projecting the visual image onto the image display means.

Claim 5

Apparatus for inspecting non-periodic errors in a two-dimensional pattern containing a plurality of nominally identical and regular spaced regions 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 a distribution of discrete substantially equally sized opaque regions on a transparent field, the spacing between adjacent regions, along at least one axis of the filter being uniform and greater than the spacing dictated by the formula: x n lambda f/d where, x the distance of the nth region from the centermost region (origin), lambda the wavelength of said beam of light, n the order of the spatial harmonic, d the step-and-repeat distance of said regular array of regions, f the focal length of said focusing lens, 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 centermost region (origin); lambda the wavelength of said beam of light; n the order of the spatial harmonic and is greater than one; d the step-and-repeat distance of said regular array of regions; f the focal length of said focusing lens; 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; and means for projecting the visual image onto the image display means.

Claim 6

Apparatus according to claim 3 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 7

A spatial filter for filtering the Fourier transform of the image of a workpiece comprising a matrix-like array of nominally identical features, which consists of: a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, the spacing between adjacent regions, along at least one axis of said array, 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 centermost region (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; wherein at least one of said regions is positioned in coicidence 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 centermost region (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; f the focal length of the Fourier transform lens; whereby said opaque regions inhibit further transmission of substantially all periodic information In said transform.

Claim 8

A spatial filter for filtering the Fourier transform of the image of a workpiece comprising a matrix-like array of nominally identical features, which consists of: a matrix-like array of discrete substantially equally sized opaque regions on a transparent field, the spacing between adjacent regions, along at least one axis of said array, 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 centermost region (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; wherein at least one of said regions is positioned in coicidence 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 centermost region (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; f the focal length of the Fourier transform lens; whereby said opaque regions inhibit further transmission of substantially all periodic information In said transform.

Claim 9

The filter according to claim 5 wherein said point of coincidence lies approximately halfway between the centermost filter region and the edge of said filter.