Claims
- 1. An apparatus for detecting defects in a pattern having linear straight line features and nonlinear defects comprising:
- (a) a coherent light source for radiating coherent light;
- (b) a collimator for collimating the coherent light radiated from said coherent light source into a light beam with a predetermined diameter and for directing it to said pattern;
- (c) a transform lens for transforming the intensity distribution of transmitted or reflected light from said pattern into a Fourier-transformed pattern; and
- (d) a spatial filter placed in the Fourier-transform plane of said transform lens which prevents transmission of the coherent light containing information of said linear straight line features of said pattern, said filter having a light intercepting area including a plurality of arm sections extending in the horizontal and vertical directions from a common point of intersection corresponding to the linear straight line features of said subject pattern and a portion lying between the two adjacent arm sections being of a circular shape protruding toward the center of said filter wherein the coherent light intercepting area of said spatial filter is defined according to the following four equations ##EQU3## where X and Y indicate the X-axis and Y-axis of said filter respectively, said X- and Y-axes corresponding to the respective axes of the arm sections of said filter extending in the horizontal and vertical directions, X=Y=0 is indicative of the center of said filter and, in the situation where the effective pupil is circular, 9.sqroot.2/32 L.times.0.85.ltoreq.R.ltoreq.9.sqroot.2/32 L.times.1.05 where L is a diameter of an effective pupil of the lens or in the situation where the effective pupil is square .sqroot.2/4 L.times.0.85.ltoreq.R.ltoreq..sqroot.2/4 L.times.1.05 where L is a length of each side of an effective pupil of the lens.
- 2. An apparatus according to claim 1 which further comprises an incoherent light source radiating an incoherent light and means for directing the incoherent light from the light source to said pattern in compliance with the optical axis of said coherent light.
- 3. An apparatus according to claim 2 wherein said coherent light source is a Helium-Neon laser and said incoherent light source is an uncandescent lamp.
- 4. An apparatus according to claim 3 which further comprises a color filter located across the optical path of the incoherent light radiated from said incoherent light source.
- 5. An apparatus according to claim 4 wherein said color filter is a blue or green, gelatin filter.
- 6. An apparatus according to claim 1 which further comprises control means for chopping, intermittently, the coherent light radiated from said coherent light source.
- 7. An apparatus according to claim 6 wherein said control means includes a beam chopper with a plurality of holes therein, placed adjacent to said coherent light source, and driving means for rotating said beam chopper.
- 8. An apparatus according to claim 7 wherein said control means includes a liquid crystal plate placed adjacent to said coherent light source, a lens system for collimating the coherent light transmitted through said liquid crystal plate, and a plate with a pinhole arranged in said lens system.
- 9. An apparatus for detecting defects in a pattern having linear straight line features and nonlinear defects comprising:
- (a) a coherent light source for radiating coherent light;
- (b) a collimator for collimating the coherent light radiated from said coherent light source into a light beam with a predetermined diameter and for directing it to said pattern;
- (d) a transform lens for transforming the intensity distribution of transmitted or reflected light from said pattern into a Fourier-transformed pattern; and
- (d) a spatial filter placed in the Fourier-transform plane of said transform lens which prevents transmission of the coherent light containing information of said linear straight line features of said pattern, said filter having a light intercepting area including a plurality of arm sections extending in the horizontal and vertical directions from a common point of intersection corresponding to the linear straight line features of said subject pattern and a portion lying between the two adjacent arm sections being of an elliptical-shape protruding toward the center of said filter wherein the coherent light intercepting area of said spatial filter is defined according to the following four equations ##EQU4## where X and Y indicate the X-axis and Y-axis of said filter respectively, said X- and Y-axes corresponding to the respective axes of the arm sections of said filter extending in the horizontal and vertical directions and, in the situation where the effective pupil is circular 21.2/64 L.times.0.85.ltoreq.r.sub.1 .ltoreq.21.2/64 L.times.1.05 and 25.5/64 L.times.0.85=r.sub.2 .ltoreq.25.5/64 L.times.1.05
- where L is a diameter of an effective pupil of the lens or in the situation where the effective pupil is square 20.9/64 L.times.0.85.ltoreq.r.sub.1 20.9/64 L.times.1.05 and 22.6/64 L.times.0.85.ltoreq.r.sub.2 .ltoreq.22.6/64 L.times.1.05 where L is a length of each side of an effective pupil of the lens.
- 10. An apparatus according to claim 9 which further comprises an incoherent light source radiating an incoherent light and means for directing the incoherent light from the light source to said pattern in compliance with the optical axis of said coherent light.
- 11. An apparatus according to claim 10 wherein said coherent light source is a Helium-Neon laser and said coherent light source is an incandescent lamp.
- 12. An apparatus according to claim 11 which further comprises a color filter located across the optical path of the incoherent light radiated from said incoherent light source.
- 13. An apparatus according to claim 12 wherein said color filter is a blue or green, gelatin filter.
- 14. An apparatus according to claim 9 which further comprises control means for chopping, intermittently, the coherent light radiated from said coherent light source.
- 15. An apparatus according to claim 14 wherein said control means includes a laser beam chopper with a plurality of holes therein, placed adjacent to said coherent light source, and driving means for rotating said beam chopper.
- 16. An apparatus according to claim 15 wherein said control means includes a liquid crystal plate placed adjacent to said coherent light source, a lens system for collimating the coherent light transmitted through said liquid crystal plate, and a plate with a pinhole arranged in said lens system.
Priority Claims (1)
Number |
Date |
Country |
Kind |
50/151951 |
Dec 1975 |
JPX |
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CROSS-REFERENCE TO THE RELATED APPLICATION
This is a continuation-in-part application of United States Patent Application Ser. No. 752,984 filed Dec. 21, 1976, now U.S. Pat. No. 4,153,336.
US Referenced Citations (6)
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
752984 |
Dec 1976 |
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