US3879131A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Photomask inspection by real time diffraction pattern analysis
Assignee: AT&T Inc
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Filing: 1974-02-06
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Granted: 1975-04-22
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Expires: 1994-02-06
Abstract
Abstract A focused beam of laser light producing a spot smaller than the minimum size of any valid feature of the photomask pattern is swept in a raster over the pattern being inspected. The light transmitted and diffracted by the locally illuminated pattern is collected and presented as a stationary but time-varying diffraction pattern to a detector array. The electrical output signals from the detectors are processed to distinguish diffraction patterns which are produced by edges of valid features from patterns produced by edges of defects. This photodetector analysis may involve several types of photodetector arrangements and may further involve analog, digital or hybrid computers.
Inventors
- 👤 John David Cuthbert
- 👤 Delmer Lee Fehrs
- 👤 David Farnham Munro
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 23:09
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/84; G01N21/88; G01N21/95; G01N21/956
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
91 words
A method for detecting defects in a photomask having a substantially straight edge pattern thereon comprising the steps of a. scanning the photomask with a light spot from a beam of coherent light which illuminates no more than two edges comprising a corner of the pattern at a time, b. collecting the light transmitted and diffracted by illuminated portions of the photomask, c. presenting the collected light to a photodetector array, and d. processing the electrical signals from the photodetector array to derive an indication that a defect has been scanned.
Claim 2
Independent Claim
91 words
A method for detecting defects in a photomask having a substantially straight edge pattern thereon comprising the steps of a. scanning the photomask with a light spot from a beam of coherent light which illuminates no more than two edges comprising a corner of the pattern at a time, b. collecting the light transmitted and diffracted by illuminated portions of the photomask, c. presenting the collected light to a photodetector array, and d. processing the electrical signals from the photodetector array to derive an indication that a defect has been scanned.
Claim 3
Dependent Claim
29 words
The method in accordance with claim 1 in which the step of processing the electrical signals includes comparing the magnitude of signals from different portions of the photodetector array.
Claim 4
Dependent Claim
25 words
The method in accordance with claim 1 in which the step of presenting the collected light includes dividing and separating the collected light into portions.
Claim 5
Dependent Claim
23 words
The method in accordance with claim 3 in which the step of dividing produces a central portion and at least two annular portions.
Claim 6
Dependent Claim
27 words
The method in accordance with claim 4 in which the step of dividing includes separating the outermost annular portion of the collected light into separate, equal segments.
Claim 7
Dependent Claim
35 words
The method in accordance with claim 5 in which the step of processing the electrical signals includes comparing the magnitude of the maximum and minimum signals produced by the segmental portions of said collected light.
Claim 8
Dependent Claim
87 words
Apparatus for detecting defects in a photomask having a substantially straight edgE pattern thereon comprising: a. a source of a beam of coherent light having a spot size which illuminates no more than two edges comprising a corner of the pattern at a time, b. means for scanning the beam over said photomask, c. means for collecting the light transmitted and diffracted by said photomask, and d. photodetecting means for translating the collected light into signals indicating the presence or absence of a defect in said photomask.
Claim 9
Dependent Claim
87 words
Apparatus for detecting defects in a photomask having a substantially straight edgE pattern thereon comprising: a. a source of a beam of coherent light having a spot size which illuminates no more than two edges comprising a corner of the pattern at a time, b. means for scanning the beam over said photomask, c. means for collecting the light transmitted and diffracted by said photomask, and d. photodetecting means for translating the collected light into signals indicating the presence or absence of a defect in said photomask.
Claim 10
Dependent Claim
87 words
Apparatus for detecting defects in a photomask having a substantially straight edgE pattern thereon comprising: a. a source of a beam of coherent light having a spot size which illuminates no more than two edges comprising a corner of the pattern at a time, b. means for scanning the beam over said photomask, c. means for collecting the light transmitted and diffracted by said photomask, and d. photodetecting means for translating the collected light into signals indicating the presence or absence of a defect in said photomask.
Claim 11
Dependent Claim
87 words
Apparatus for detecting defects in a photomask having a substantially straight edgE pattern thereon comprising: a. a source of a beam of coherent light having a spot size which illuminates no more than two edges comprising a corner of the pattern at a time, b. means for scanning the beam over said photomask, c. means for collecting the light transmitted and diffracted by said photomask, and d. photodetecting means for translating the collected light into signals indicating the presence or absence of a defect in said photomask.
Claim 12
Dependent Claim
25 words
Apparatus in accordance with claim 7 including means for dividing and separating the collected light beam into separate portions for presentation to the photodetecting means.
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) | 1978-04-21 | 1978-10-21 | 1979-04-22 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-04-21 | 1982-10-21 | 1983-04-22 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-04-21 | 1986-10-21 | 1987-04-22 | $7700.00 | Window Closed / Lapsed |