US3604808A
Expired / Lapsed
US
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Detection of cumulative registration errors on photomasks using optical interference fringes
Assignee: AT&T Inc
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Filing: 1969-10-31
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Granted: 1971-09-14
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Expires: 1989-10-31
Abstract
Abstract A fringe pattern generated by a pair of intersecting light beams of the same wavelength is employed in a spatial filtering technique to detect cumulative positional errors along a superposed linear test array of identical elements having a nominally fixed pitch between corresponding border edges, as in a row of repetitive images on an array-type photomask. The angle between the beams is adjusted so that the spatial period between points of equal intensity on the fringe pattern is an integral submultiple of the nominal spacing between corresponding edges of adjacent elements of the test array. The fringe pattern is spatially modulated by the test array and its diffraction pattern focused on a low-pass optical filter, which suppresses the spatial period of the fringe pattern. The light passed by the filter is reimaged to form a visual replica of the gross features (i.e., the edges) of the array elements, such edges having a cyclic variation of illumination because of the superposed portions of the fringe pattern. The period of the cyclic variation is inversely proportional to the magnitude of the cumulative positional error along the test array.
Inventors
- 👤 Laurence S Watkins
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 10:33
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/70; G03F7/70483; G03F7/70605; G03F7/70616; G03F7/70633; G02; G02B; G02B27/00; G02B27/42; G02B27/46; G03F7/70591; H; H10; H10P; H10P95/00
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
123 words
A method of measuring a cumulative positional error along a linear array of repetitive regions which are nominally spaced apart by a predetermined distance, which comprises the steps of: illuminating the successive regions in the array with a superposed optical fringe pattern; and adjusting the spatial period of the fringe pattern to a value less than half the predetermined distance to cyclically vary the intensity of illumination of the successive regions with a period inversely proportional to the magnitude of the cumulative positional error along the array, whereby a variation of intensity from a maximum to a minimum between a pair of spaced regions of the array is indicative of a cumulative positional error therebetween of one-half the spatial period of the pattern.
Claim 2
Independent Claim
123 words
A method of measuring a cumulative positional error along a linear array of repetitive regions which are nominally spaced apart by a predetermined distance, which comprises the steps of: illuminating the successive regions in the array with a superposed optical fringe pattern; and adjusting the spatial period of the fringe pattern to a value less than half the predetermined distance to cyclically vary the intensity of illumination of the successive regions with a period inversely proportional to the magnitude of the cumulative positional error along the array, whereby a variation of intensity from a maximum to a minimum between a pair of spaced regions of the array is indicative of a cumulative positional error therebetween of one-half the spatial period of the pattern.
Claim 3
Dependent Claim
26 words
A method as defined in claim 1, in which the spatial period of the fringe pattern is adjusted to an integral submultiple of the predetermined distance.
Claim 4
Independent Claim
177 words
A method of measuring a cumulative positional error along a linear array of identical elements having corresponding border edges that are nominally spaced apart by a predetermined distance, which comprises the steps of: directing, through the array, an aligned fringe pattern of light whose spatial period is less than half the predetermined distance to spatially modulate the light; focusing the spatially modulated light on a low-pass optical filter which transmits spatial wavelengths longer than half the predetermined distance but stops spatial wavelengths shorter than half the predetermined distance; and reimaging the light passed by the filter to define a visual replica of the border edges of the array, the resulting intensity of illumination of successive edges in the replica array by the modulated light varying cyclically with a period inversely proportional to the magnitude of the cumulative positional error; whereby a variation in intensity from a maximum to a minimum between a pair of spaced edges on the replica array is indicative of a cumulative positional error therebetween of one-half the spatial period of the fringe pattern.
Claim 5
Independent Claim
177 words
A method of measuring a cumulative positional error along a linear array of identical elements having corresponding border edges that are nominally spaced apart by a predetermined distance, which comprises the steps of: directing, through the array, an aligned fringe pattern of light whose spatial period is less than half the predetermined distance to spatially modulate the light; focusing the spatially modulated light on a low-pass optical filter which transmits spatial wavelengths longer than half the predetermined distance but stops spatial wavelengths shorter than half the predetermined distance; and reimaging the light passed by the filter to define a visual replica of the border edges of the array, the resulting intensity of illumination of successive edges in the replica array by the modulated light varying cyclically with a period inversely proportional to the magnitude of the cumulative positional error; whereby a variation in intensity from a maximum to a minimum between a pair of spaced edges on the replica array is indicative of a cumulative positional error therebetween of one-half the spatial period of the fringe pattern.
Claim 6
Dependent Claim
33 words
A method as defined in claim 3, comprising the further step of aligning a first one of the edges in the replica array with a point of maximum illumination of the modulated light.
Claim 7
Independent Claim
180 words
A method of measuring a cumulative positional error along a row of elements on a photomask transparency wherein successive elements have corresponding border edges that are nominally spaced apart by a predetermined distance, which comprises the steps of: directing, through the row of elements, an aligned fringe pattern of light whose spatial period is an integral submultiple of the predetermined distance to spatially modulate the light; focusing the spatially modulated light on a low-pass optical filter which transmits spatial wavelengths longer than half the predetermined distance but stops spatial wavelengths shorter than half the predetermined distance; and reimaging the light passed by the filter to define a visual replica of the border edges of the successive elements, the resulting intensity of illumination of successive replica edges by the modulated light varying cyclically with a period inversely proportional to the magnitude of the cumulative positional error; whereby a variation in intensity from a maximum to a minimum between a pair of spaced replica edges is indicative of a cumulative positional error therebetween of one-half the spatial period of the fringe pattern.
Claim 8
Independent Claim
180 words
A method of measuring a cumulative positional error along a row of elements on a photomask transparency wherein successive elements have corresponding border edges that are nominally spaced apart by a predetermined distance, which comprises the steps of: directing, through the row of elements, an aligned fringe pattern of light whose spatial period is an integral submultiple of the predetermined distance to spatially modulate the light; focusing the spatially modulated light on a low-pass optical filter which transmits spatial wavelengths longer than half the predetermined distance but stops spatial wavelengths shorter than half the predetermined distance; and reimaging the light passed by the filter to define a visual replica of the border edges of the successive elements, the resulting intensity of illumination of successive replica edges by the modulated light varying cyclically with a period inversely proportional to the magnitude of the cumulative positional error; whereby a variation in intensity from a maximum to a minimum between a pair of spaced replica edges is indicative of a cumulative positional error therebetween of one-half the spatial period of the fringe pattern.
Claim 9
Dependent Claim
168 words
In an apparatus for measuring cumulative positional errors in a linear array of repetitive elements having corresponding border edges that are nominally spaced apart by a predetermined distance: means for directing a pair of beams of coherent light through the array at an adjustable intersecting angle to generate an optical fringe pattern that is spatially modulated by the array; means for adjusting the angle of intersection to vary the spatial period of the fringe pattern; a low-pass optical filter for passing spatial wavelengths longer than half the predetermined distance and for blocking spatial wavelengths shorter than half the predetermined distance; means for focusing the light spatially modulated by the array on the filter; and means for reimaging the portion of the focused light passed by the filter to define a visual replica of the border edges of the array, the intensity of illumination of successive edges in the replica by the modulated fringe pattern varying cyclically with a period determined by the magnitude of the cumulative positional errors.
Claim 10
Dependent Claim
168 words
In an apparatus for measuring cumulative positional errors in a linear array of repetitive elements having corresponding border edges that are nominally spaced apart by a predetermined distance: means for directing a pair of beams of coherent light through the array at an adjustable intersecting angle to generate an optical fringe pattern that is spatially modulated by the array; means for adjusting the angle of intersection to vary the spatial period of the fringe pattern; a low-pass optical filter for passing spatial wavelengths longer than half the predetermined distance and for blocking spatial wavelengths shorter than half the predetermined distance; means for focusing the light spatially modulated by the array on the filter; and means for reimaging the portion of the focused light passed by the filter to define a visual replica of the border edges of the array, the intensity of illumination of successive edges in the replica by the modulated fringe pattern varying cyclically with a period determined by the magnitude of the cumulative positional errors.
References Cited (Backward Citations)
US3544197A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-09-13 | 1975-03-15 | 1975-09-14 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-09-13 | 1979-03-15 | 1979-09-14 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-09-13 | 1983-03-15 | 1983-09-14 | $7700.00 | Window Closed / Lapsed |