Automatic photomask and reticle inspection method and apparatus including improved defect detector and alignment sub-systems
DCFirst Claim
1. A method of detecting defects in objects such as photomasks, reticles, wafers, printed circuit boards, and the like, comprising the steps of:
- inspecting a selected surface area of an object and generating a first stream of data having signal values representing the image content of each pixel thereof;
generating a second stream of data having signal values representing the image content of each pixel of said second stream of data;
storing corresponding portions of the first and second streams of data in memory;
detecting with a resolution to a fraction of a pixel any misalignment between the stored portions of said first and second streams of data;
aligning the stored first and second portions of data using subpixel interpolation to correct any detected misalignment therebetween; and
comparing corresponding subportions of the stored and aligned first and second portions of data to detect differences therebetween, and upon detecting a difference, indicating the presence of a defect at a particular pixel location on the inspected object.
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Abstract
A photomask and reticle inspection method and apparatus wherein a selected surface area of an object is inspected and a first stream of data having signal values representing the image content of each pixel thereof is generated, a second stream of data having signal values representing the intended image content of each pixel of the first stream of data is generated, corresponding portions of the first and second streams of data are stored in memory, any misalignment between the stored portions of the first and second streams of data is detected, the misaligned first and second portions of data are then aligned using shifts of an integral number of pixels and/or subpixel interpolation to correct the detected misalignment therebetween, corresponding subportions of the stored and aligned first and second portions of data are then compared to detect difference therebetween, and upon detecting a difference exceeding a predetermined threshold, the presence of a defect at a particular pixel location on the inspected object is indicated.
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Citations
52 Claims
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1. A method of detecting defects in objects such as photomasks, reticles, wafers, printed circuit boards, and the like, comprising the steps of:
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inspecting a selected surface area of an object and generating a first stream of data having signal values representing the image content of each pixel thereof; generating a second stream of data having signal values representing the image content of each pixel of said second stream of data; storing corresponding portions of the first and second streams of data in memory; detecting with a resolution to a fraction of a pixel any misalignment between the stored portions of said first and second streams of data; aligning the stored first and second portions of data using subpixel interpolation to correct any detected misalignment therebetween; and comparing corresponding subportions of the stored and aligned first and second portions of data to detect differences therebetween, and upon detecting a difference, indicating the presence of a defect at a particular pixel location on the inspected object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. An Apparatus for inspecting objects such as photomasks and the like for defects, comprising:
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means for inspecting a selected surface area of an object and for generating a first stream of data having signal values representing the image content of each pixel thereof; means for generating a second stream of data having signal values representing the image content of each pixel of said second stream of data; memory means for storing corresponding portions of said first and second streams of data; detector means for detecting with resolution to a fraction of a pixel any misalignment between the stored first and second portions of data; alignment means using subpixel interpolation to correct any detected misalignment in the stored first and second portions of data; and detector means for comparing corresponding subportions of the aligned first and second portions of data to detect any difference therebetween, and upon detecting such difference, for indicating the presence of a defect at a particular pixel location on the inspected object. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50)
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51. A method of detecting defects in objects such as photomasks, reticles, wafers, printed circuit boards, and the like, comprising the steps of:
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inspecting a selected surface area of an object and generating a first stream of data having signal values representing the image content of each pixel thereof; generating a second stream of data having signal values representing the image content of each pixel of said second stream of data; storing corresponding portions of the first and second streams of data in memory; detecting with a resolution to an integer pixel any misalignment between the stored portions of said first and second streams of data; aligning the stored first and second portions of data to the closest integer pixel to correct any detected misalignment therebetween; and comparing corresponding subportions of the stored and aligned first and second portions of data to detect differences therebetween by correlating data corresponding to a particular pxp array of pixel data from said aligned first portion of data to a plurality of p×
p arrays of shifted data derived from a corresponding p×
p array of pixel data from said aligned second portion of data, each said shifted pxp array being shifted a different subpixel increment relative to said corresponding p×
p array and developing corresponding correlation values, and then comparing said correlation values to a predetermined threshold to detect the presence of a defect.
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52. A method of detecting defects in objects such as photomasks, reticles, wafers, printed circuit boards, and the like, comprising the steps of:
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using a first electro-optical system to inspect a first selected surface area of an object and to generate a first stream of data having signals values representing the image content of each pixel thereof; using a second electro-optical system to inspect a second surface area of said object and to generate a second stream of data having signal values representing the image content of each pixel of said second stream of data; storing corresponding portions of the first and second streams of data in memory; detecting with a resolution to a fraction of a pixel any misalignment between the stored portions of said first and second streams of data; aligning the stored first and second portions of data using subpixel interpolation to correct any detected misalignment therebetween; and comparing corresponding subportions of the stored and aligned first and second portions of data to detect differences therebetween by correlating data corresponding to a particular p×
p array of pixel data from said aligned first portion of data to a plurality of p×
p arrays of shifted data derived from a corresponding p×
p array of pixel data from said aligned second portion of data, each said shifted p×
p array being shifted a different subpixel increment relative to said corresponding p×
p array and developing corresponding correlation values, and then comparing said correlation values to a predetermined threshold to detect the presence of a defect.
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Specification