METHOD OF AND APPARATUS FOR ANALYSING PATTERNS AND INSPECTING OBJECTS

• US 3,814,943 A
• Filed: 06/12/1973
• Issued: 06/04/1974
• Est. Priority Date: 08/26/1969
• Status: Expired due to Term

• Current Assignee: Lionel Richard Baker, Patricia Ann West, Peter Robert Archer
• Original Assignee: Lionel Richard Baker, Patricia Ann West, Peter Robert Archer
• Inventors: Baker, Lionel Richard, Archer, Peter Robert, West, Patricia Ann
• Primary Examiner(s): Borchelt, Archie R.
• Assistant Examiner(s): Nelms, D. C.
• Application Number:
  US05/369,334
• Time in Patent Office: 357 Days
• Field of Search: 250/550,556,559,223,237,233 350/162R,162SF,3.5 356/106,107,109,111,156,163,167,71
• US Class Current: 250/550
• CPC Class Codes: G01N 21/956 Inspecting patterns on the surface of objects contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G06E 3/001 Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements optical elements per se G02B; devices consisting of a plurality of solid state components, including light sensitive semiconductor components, formed in or on a common substrate H01L27/14; electro-, magneto- or acousto-optics, non-linear optics G02F1/00; graph reading G06K11/00
• CPC Class Codes: G06V 10/993 Evaluation of the quality of the acquired pattern
• CPC Class Codes: G07D 7/12 Visible light, infrared or ultraviolet radiation
• CPC Class Codes: G07D 7/20 Testing patterns thereon G07D7/004, G07D7/005 take precedence

Abstract

A method and apparatus for analysing two-dimensional patterns, particularly printed matter carried on sheet-like objects, and for inspecting such sheet-like objects to locate defects therein. The invention performs such analysis of inspection by subjecting the moving pattern or sheet to light which may be incoherent and scanning the light beam to periodically vary its intensity at some stage in the process. The spatial frequency of scanning (cycles/mm) is preferably variable and the scanned light as affected by the pattern or sheet is used to produce an electrical test signal as a function of the fourier transform thereof. The test signal is subsequently compared with a reference signal or stored data to evaluate the characteristics of the pattern or to determine the presence of defect-indicative information.

Claims

1. A method of analyzing a two-dimensional test pattern;

said method comprising the steps of;

a. scanning a beam of electromagnetic radiation with a moving attenuation pattern which is cyclic along a path of movement of the attenuation pattern to provide a modified beam of radiation;

b. subjecting the test pattern to be analyzed to said modified beam of radiation;

c. collecting radiation derived from said modified beam and subjected to the influence of a part of the test pattern and to the influence of a part of the attenuation pattern extending over a plurality of cycles thereof exerted simultaneously by the whole of said part of the attenuation pattern;

d. producing an electrical test signal from the collected radiation and representing part of a defined Fourier transform of said part of the test pattern; and

e. comparing said test signal with a reference.

2. A method according to claim 1, and further comprising splitting the beam into two components after the scanning operation, directing one component at the pattern under test and directing the other component at a reference pattern, collecting further radiation subjected to the influence of said part of the attenuation pattern and to the influence of a part of the reference pattern corresponding to said part of the test pattern, producing from said further collected radiation an electrical reference signal which represents part of a defined Fourier transform of the said part of the reference pattern, said reference signal constituting said reference and the comparison being effected between the test and reference signals.

3. A method according to claim 1, wherein the test pattern is moved so that said part of the test pattern changes.

4. A method according to claim 1, wherein the characteristic spatial frequency produced by the scanning operation is varied.

5. A method according to claim 1, wherein the test signal is used to provide a data record and this data record is automatically compared with another record constituting said reference.

6. A method of analyzing a two-dimensional test pattern, said method comprising the steps of:

a. subjecting the test pattern to be analyzed to a beam of electromagnetic radiation;

b. scanning the radiation influenced by the presence of the test pattern with a moving attenuation pattern which is cyclic along a path of movement of the attenuation pattern;

c. collecting radiation subjected to the influence of a part of the test pattern and to the influence of a part of the attenuation pattern, extending over a plurality of cycles thereof, exerted simultaneously by the whole of said part of the attenuation pattern;

d. producing an electrical test signal from the collected radiation and representing part of a defined Fourier transform of said part of the test pattern; and

e. comparing said test signal with a reference.

7. A method according to claim 6, wherein the test pattern is moved so that said part of the test pattern changes.

8. A method according to claim 2, wherein the test and reference patterns are moved in synchronism so that said parts of the test and reference patterns change.

9. A method according to claim 6, wherein the characteristic spatial frequency produced by the scanning operation is varied.

10. A method according to claim 6, wherein the test signal is used to provide a data record and this data record is automatically compared with another record constituting said reference.

11. An apparatus for use in analyzing or inspecting an object;

said apparatus comprising;

a. conveying means for moving the object in a direction;

b. means for producing a beam of electromagnetic radiation;

c. means for scanning said beam of radiatioN with a moving attenuation pattern which is cyclic along a path of movement of the attenuation pattern to provide a modified beam of radiation for direction at the object under test;

d. means for collecting radiation derived from said beam which has been subjected firstly to the influence of a movable part of the object under test and secondly to the influence of a part of the attenuation pattern, extending over a plurality of cycles thereof, exerted simultaneously by the whole of said part of the attenuation pattern;

e. means for defining said part of the object under test so that said part extends generally laterally of said direction; and

f. means for producing from the collected radiation an electrical test signal which represents part of a defined Fourier transform of said part of the object under test.

12. An apparatus according to claim 11, wherein the scanning means is in the form of a rotatable radiation-transmissive disc having radial grating lines thereon, the axis of rotation of said disc being displaceable to thereby vary the characteristic spatial frequency produced by the scanning operation.

13. An apparatus according to claim 11, wherein there is provided a beam splitter which splits said beam into two components after the scanning operation, one component being directed at the object to be tested to produce said test signal, and the other component being directed at a reference object, there being further provided means for collecting further radiation which has been subjected firstly to the influence of a part of the reference object and secondly to the influence of a part of the attenuation pattern extending over a plurality of cycles thereof, exerted simultaneously by the whole of said part of the attenuation pattern;

means for producing from the collected further radiation an electrical reference signal which represents part of a defined Fourier transform of said reference object, said reference signal being comparable with said test signal as a basis for the analysis of the test object.

14. An apparatus according to claim 11 and further comprising means for comparing said test signal with a reference.

15. An apparatus according to claim 11 and further comprising means for determining the presence of defect-indicative information in said test signal.

16. An apparatus according to claim 11, wherein said defining means also defines said part of the attenuation pattern.

17. An apparatus according to claim 16, wherein said defining means is in the form of a slit with a dimension extending substantially in the direction of movement of the attenuation pattern.

18. An apparatus according to claim 17, wherein there is provided means for focussing an image of the attenuation pattern onto said slit.

19. An apparatus for use in analyzing or inspecting an object;

said apparatus comprising;

a. conveying means for moving the object in a direction;

b. means for producing and directing a beam of electromagnetic radiation at the object under test;

c. means for scanning the radiation influenced by the presence of the test object with a moving attenuation pattern which is cyclic along a path of movement of the attenuation pattern;

d. means for collecting radiation subjected firstly to the influence of a part of the test pattern and secondly to the influence of a part of the attenuation pattern extending over a plurality of cycles thereof, exerted simultaneously by the whole of said part of the attenuation pattern;

e. means for defining said part of the object under test so that said part extends generally laterally of said direction;

an f. means for producing from the collected radiation an electrical test signal which represents part of a defined Fourier transform of said part of the object under test.

20. An apparatus according to claim 19, wherein said defining means also defines said part of the attenuation pattern.

21. An apparatus according to claim 20, wherein said defining means is in the form of a slit with a dimension extending substantially in the direction of movement of the attenuation pattern.

22. An apparatus according to claim 21, wherein there is provided means for forming an image of the slit which image is scanned by the scanning means.

23. An apparatus according to claim 19, and further comprising means for comparing said test signal with a reference.

24. An apparatus according to claim 19 and further comprising means for determining the presence of defect-indicative information in said test signal.

25. An apparatus according to claim 19, wherein the defining means is a slit which defines an image of the radiation influenced by said part of the object which image is scanned by the scanning means, and a photo-electric device is provided for receiving the scanned radiation.

26. A method of inspecting an object to determine the presence of defects, said method comprising the steps of:

a. subjecting the object to be tested to a beam of electromagnetic radiation to establish a distribution of radiation influenced by the object;

b. scanning radiation influenced by the object with a moving attenuation pattern which is cyclic along a path of movement of the attenuation pattern;

c. collecting radiation subjected to the influence firstly of a part of the object and secondly to the influence of a part of the attenuation pattern, extending over a plurality of cycles thereof, exerted simultaneously by the whole of said part of the attenuation pattern;

d. producing an electrical test signal from the collected radiation and representing part of a defined Fourier transform of said part of the object; and

e. comparing said test signal with a reference, in the form of a preset electrical value, to determine the presence of defect-indicative information in said test signal.

27. A method according to claim 26, wherein the scanning operation involves simultaneous scanning at two or more different spatial frequencies and the components of the test signal related to said different spatial frequencies are separately processed.

28. A method of inspecting an object to determine the presence of defects, said method comprising the steps of:

a. scanning a beam of electromagnetic radiation with a moving attenuation pattern which is cyclic along a path of movement of the attenuation pattern to provide a modified beam;

b. subjecting the object to be tested to said modified beam of radiation;

c. collecting radiation subjected to the influence firstly of a part of the object and secondly to the influence of a part of the attenuation pattern, extending over a plurality of cycles thereof, exerted simultaneously by the whole of said part of the attentuation pattern;

d. producing an electrical test signal from the collected radiation and representing part of a defined Fourier transform of said part of the object; and

e. comparing said test signal with a reference to determine the presence of a defect-indicative information in said test signal.

29. A method according to claim 28, wherein scanned radiation reflected by an outer surface of the object in a diffuse manner is collected and converted into said test signal.

30. A method according to claim 28, where scanned radiation reflected by an outer surface of the object in a specular manner is collected and converted into said test signal.

31. A method according to claim 28, wherein scanned radiation transmitted through the object is collected and converted in said test signal.

32. A method according to claim 28, wherein scanned radiation is scattered by an outer surface of the object and the radiation scattered in a pre-selected direction is collected and converted into said test signal.

33. A method according to claim 28, wherein the scanning operation involves simultaneous scanning at two or more different spatial frequencies and the components of the test signal related to said different spatial frequencies are separately processed.