Production of high performance optical spatial filters
First Claim
1. A method of producing an optical spatial filter corresponding to a subject disposed within a subject plane, comprising the steps of:
- directing a first coherent beam of light at said subject such that said light is diffracted and/or reflected thereby, whereafter said light contains optical information regarding said subject;
focusing said light containing said subject information so as to define a Fourier transform plane;
disposing a first optical recording means at said Fourier transform plane and exposing said recording means with said light containing said subject information;
recording upon said first recording means at least partially opaque areas corresponding to at least a portion of said subject information as said information appears within said transform plane;
attenuating at least a portion of said subject information by directing said light containing said information through said first recording means located within said transform plane;
directing a second coherent beam of light, through a holographic recording plane located beyond said transform plane, from a first direction so as to form an interference pattern in said recording plane with said light containing said subject information minus said information partially attenuated by said first recording means;
recording at said recording plane a first hologram of said partially attenuated subject information;
removing said first beam;
removing said first recording means from said transform plane;
disposing a second optical recording means at said transform plane;
redirecting said second beam through said hologram at said recording plane from a second direction opposite said first direction, whereby said second recording means is exposed with light from said second beam containing optical information from said hologram; and
recording upon said second recording means at least partially opaque areas corresponding to at least a portion of said hologram information as said information appears within said transform plane.
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Accused Products
Abstract
High performance optical spatial filters are produced photographically with an apparatus that directs a coherent beam of light through or off a subject and into a lens. The lens focuses the diffracted and/or reflected light to define a Fourier transform of the subject information. A filter is produced by exposing a photographic plate at the Fourier transform plane, processing the plate, and repositioning it. A hologram is recorded through the processed plate with the apparatus, which directs a reference beam to a holographic recording plane. A second photographic plate is placed at the transform plane and exposed with light directed through the hologram from a direction conjugate to the reference beam. The second plate is then processed. Successive generations of filters may also be produced. A method of using the filters for isolating nonperiodic defects in IC photomasks and wafers is also disclosed.
81 Citations
18 Claims
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1. A method of producing an optical spatial filter corresponding to a subject disposed within a subject plane, comprising the steps of:
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directing a first coherent beam of light at said subject such that said light is diffracted and/or reflected thereby, whereafter said light contains optical information regarding said subject; focusing said light containing said subject information so as to define a Fourier transform plane; disposing a first optical recording means at said Fourier transform plane and exposing said recording means with said light containing said subject information; recording upon said first recording means at least partially opaque areas corresponding to at least a portion of said subject information as said information appears within said transform plane; attenuating at least a portion of said subject information by directing said light containing said information through said first recording means located within said transform plane; directing a second coherent beam of light, through a holographic recording plane located beyond said transform plane, from a first direction so as to form an interference pattern in said recording plane with said light containing said subject information minus said information partially attenuated by said first recording means; recording at said recording plane a first hologram of said partially attenuated subject information; removing said first beam; removing said first recording means from said transform plane; disposing a second optical recording means at said transform plane; redirecting said second beam through said hologram at said recording plane from a second direction opposite said first direction, whereby said second recording means is exposed with light from said second beam containing optical information from said hologram; and recording upon said second recording means at least partially opaque areas corresponding to at least a portion of said hologram information as said information appears within said transform plane. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A high performance multi-generation optical spatial filter, comprising the product resulting from the process including the steps of:
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positioning a subject within a subject plane; directing a first coherent beam of light at said subject such that said light is diffracted and/or reflected thereby, whereafter said light contains optical information regarding said subject; focusing said light containing said subject information so as to define a Fourier transform plane; disposing a first optical recording means at said Fourier transform plane and exposing said recording means with said light containing said subject information; recording upon said first recording means at least partially opaque areas corresponding to at least a portion of said subject information as said information appears within said transform plane; attenuating at least a portion of said subject information by directing said light containing said information through said first recording means located within said transform plane; directing a second coherent beam of light, through a holographic recording plane located beyond said transform plane, from a first direction so as to form an interference pattern in said recording plane with said light containing said subject information minus said information partially attenuated by said first recording means; recording at said recording plane a first hologram of said partially attenuated subject information; removing said first beam; removing said first recording means from said transform plane; disposing a second optical recording means at said transform plane; redirecting said second beam through said hologram at said recording plane from a second direction opposite said first direction, whereby said second recording means is exposed with light from said second beam containing optical information from said hologram; and recording upon said second recording means at least partially opaque areas corresponding to at least a portion of said hologram information as said information appears within said transform plane. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of producing an optical spatial filter corresponding to a subject or subjects similar thereto, said subject being disposed within a subject plane, comprising the steps of:
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directing a first coherent beam of light from a source toward said subject such that said light is diffracted and/or reflected thereby, whereby said light contains optical information regarding said subject; focusing said light containing said subject information so as to define a Fourier transform plane; placing a first photographic plate at said Fourier transform plane and exposing said plate with said light containing said subject information for a time sufficient to record only high intensity regions within said transform plane; developing said first plate to produce darkened portions thereon corresponding to said high intensity regions, said plate thereafter being located in its original position in said transform plane to attenuate high intensity light directed into said transform plane; directing a second coherent beam of light from said source through a holographic recording plane beyond said transform plane from a first direction, while continuing to direct said first beam toward said subject, so as to form an interference pattern in said recording plane with said second beam and said light containing said subject information minus said information attenuated by said first plate; recording at said recording plane a first hologram of said partially attenuated subject information; removing said first beam; removing said first plate from said transform plane; placing a second photographic plate at said transform plane; redirecting said second beam through said hologram at said recording plane from a second direction opposite said first direction, whereby said second plate is exposed with light from said second beam for a time sufficient to record both regions of intensity within said transform plane lower than those recorded on said first photographic plate, and originally high regions of intensity attenuated by said first plate during recording of said first hologram; and developing said second plate to produce darkened portions thereon corresponding to said lower regions of intensity and said originally high regions of intensity. - View Dependent Claims (17, 18)
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Specification