Reticle inspection system

• US 4,926,489 A
• Filed: 10/05/1987
• Issued: 05/15/1990
• Est. Priority Date: 03/11/1983
• Status: Expired due to Term

• Current Assignee: KLA Instruments, Corporation (KLA Corporation)
• Original Assignee: KLA Instruments, Corporation (KLA Corporation)
• Inventors: Joseph, David A., Danielson, Donald L., Wihl, Mark J.
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): Couso, Jose L.
• Application Number:
  US07/104,740
• Time in Patent Office: 953 Days
• Field of Search: 356/390, 356/394, 356/398, 356/399, 356/400, 356/401, 358/106, 358/107, 382/8, 382/30, 382/34
• US Class Current: 382/144
• CPC Class Codes: G01N 2021/95676 Masks, reticles, shadow masks
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G06F 18/00 Pattern recognition
• CPC Class Codes: G06T 2207/30148 Semiconductor; IC; Wafer
• CPC Class Codes: G06T 7/001 using an image reference approach
• CPC Class Codes: G06T 7/30 Determination of transform parameters for the alignment of images, i.e. image registration
• CPC Class Codes: G06V 2201/06 Recognition of objects for industrial automation

Abstract

An automatic inspection system including an illuminator for illuminating a reticle or photomask to be inspected, while optically projecting a magnified image of the reticle or photomask onto a plurality of detector elements. A carriage assembly moves the object at a constant velocity to allow the detector elements to sequentially view the entire surface to be inspected. The detector elements are responsive to the intensity of light incident thereupon and are periodically scanned to obtain a two-dimensional measured representation of the object. A database adaptor formulates a two-dimensional representation from the design database description corresponding to the scanned object simultaneously and in synchronism with the scanning of the photomask or reticle. The measured and database adapted representation of the scanned object are input to a signal processor for alignment and defect detection. While the representations are shifted through a memory, an alignment circuit dynamically measures and corrects for misalignment between the representations, so that a defect detector can effectively compare the representations for defects. Additional correction of misalignment between the representations is obtained by modulating the size of the measured representation as detected by the detector elements. At the operator'"'"'s option, a second measured image of a multi-cell reticle or photomask may be used for comparison as a substitute for the database representation.

Claims

1. Optical inspection apparatus for scanning a patterned object and comparing it to information contained in an electronic data base, comprising:

optical scanning means responsive to a first timing control signal and operative to scan the patterned object and to develop a first data signal including a sampled and quantitized electronic representation of the patterned object;

data base means responsive to a second timing control signal and operative to generate a second data signal corresponding to a design database description of the patterned object scanning by said scanning means, said second data signal having a variable time relationship to said first data signal;

data alignment means for comparing said first data signal to said second data signal and for developing an excess alignment signal which corresponds to any misalignment of said second data signal exceeding a predetermined limit, and for adjusting said time relationship between said first data signal and said second data signal to provided aligned first and second data signals which are time coincident with each other;

timing control means responsive to said excess alignment signal and operative to develop said first and second timing control signals, said first and second timing control signals being used to adjust the relative output data signal rates of said optical scanning means and said data base means for the purpose of maintaining the alignment of said first and second data signals within predetermined limits; and

defect detector means for comparing said aligned first data signal and said aligned second data signal and for developing defect data signals corresponding to differences therebetween having predetermined characteristics.

2. Optical inspection apparatus as recited in claim 1 wherein said database means includes:

electronic storage means for storing said design database description;

pattern memory means for receiving a selected portion of said design database description stored in said storage means;

pattern generating means for converting said selected portion into bit mapped data;

bit map memory means for storing said bit mapped data; and

scan converter means for converting the stored bit mapped data into said second data signal.

3. Optical inspection apparatus as recited in claim 2 wherein said pattern memory means is a double-buffered memory and said bit map memory is a double-buffered memory.

4. Optical inspection apparatus as recited in claim 3 wherein said data alignment means includes:

an alignment memory for receiving and storing said first and second data signals and for responding to alignment error correction signals to develop said aligned first and second data signals; and

alignment error detection means for comparing portions of said first and second data signals stored in said alignment memory and developing said alignment error correction signals.

5. Optical inspection apparatus as recited in claim 4 wherein said alignment memory includes:

a memory address control means responsive to said alignment error correction signal and operative to develop first and second data select signals;

a left pixel memory for storing a quantity of said first data signal and responsive to said first data select signal to output a portion thereof as said aligned first data signal; and

a right pixel memory for storing a quantity of said second data signal and responsive to said second data select signal to output a portion thereof as said aligned second data signal.

6. Optical inspection apparatus as recited in claim 4 wherein said alignment error detection means includes:

two-dimensional phase detection means which compares portions of said first and second data signals and develops error signals corresponding to the instantaneous magnitude and direction of misalignment therebetween; and

alignment processor means responsive to said error signals and operative to generate said alignment error correction signals and said excess alignment signal.

7. Optical inspection apparatus as recited in claim 6 wherein said two-dimensional phase detection means includes:

X-direction error detection means responsive to portions of said first and second data signals and operative to generate X-components of said error signals; and

Y-direction error detection means responsive to portions of said first and second data signals and operative to generate Y-components of said error signals.

8. Optical inspection apparatus as recited in claim 6 wherein said alignment error detection means further includes goodness logic means responsive to portions of said first and second data signals and operative to generate goodness signals qualifying said error signals for input to said alignment processor means.

9. Optical inspection apparatus as recited in claim 4 wherein said timing control means includes a controllable phase locked oscillator means responsive to a scan position signal developed by said optical sensing means and to said excess alignment signal and operative to generate said first and second timing control signals.

10. Optical inspection apparatus as recited in claim 9 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

11. Optical inspection apparatus as recited in claim 9 wherein said timing control means further includes a scale compensation means for generating a scale compensation signal, and wherein said phase locked oscillator means is further responsive to said scale compensation signal and operative to modify at least one of said first and second timing signals to compensate for known scale errors in the patterned object.

12. Optical inspection apparatus as recited in claim 11 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

13. Optical inspection apparatus as recited in claim 3 wherein said timing control means includes a controllable phase locked oscillator means responsive to a scan position signal developed by said optical sensing means and to said excess alignment signal and operative to generate said first and second timing control signals.

14. Optical inspection apparatus as recited in claim 13 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

15. Optical inspection apparatus as recited in claim 13 wherein said timing control means further includes a scale compensation means for generating a scale compensation signal, and wherein said phase locked oscillator means is further responsive to said scale compensation signal and operative to modify at least one of said first and second timing signals to compensate for known scale errors in the patterned object.

16. Optical inspection apparatus as recited in claim 15 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

17. Optical inspection apparatus as recited in claim 2 wherein said data alignment means includes:

an alignment memory for receiving and storing said first and second data signals and for responding to alignment error correction signals to develop said aligned first and second data signals; and

alignment error detection means for comparing portions of said first and second data signals stored in said alignment memory and developing said alignment error correction signals.

18. Optical inspection apparatus as recited in claim 17 wherein said alignment memory includes:

a memory address control means responsive to said alignment error correction signal and operative to develop first and second data select signals;

a left pixel memory for storing a quantity of said first data signal and responsive to said first data select signal to output a portion thereof as said aligned first data signal; and

a right pixel memory for storing a quantity of said second data signal and responsive to said second data select signal to output a portion thereof as said aligned second data signal.

19. Optical inspection apparatus as recited in claim 17 wherein said alignment error detection means includes:

two-dimensional phase detection means which compares portions of said first and second data signals and develops error signals corresponding to the instantaneous magnitude and direction of misalignment therebetween; and

alignment processor means responsive to said error signals and operative to generate said alignment error correction signals and said excess alignment signal.

20. Optical inspection apparatus as recited in claim 19 wherein said two-dimensional phase detection means includes:

x-direction error detection means responsive to portions of said first and second data signals and operative to generate X-components of said error signals; and

y-direction error detection means responsive to portions of said first and second data signals and operative to generate Y-components of said error signals.

21. Optical inspection apparatus as recited in claim 19 wherein said alignment error detection means further includes goodness logic means responsive to portions of said first and second data signals and operative to generate goodness signals qualifying said error signals for input to said alignment processor means.

22. Optical inspection apparatus as recited in claim 17 wherein said timing control means includes a controllable phase locked oscillator means responsive to a scan position signal developed by said optical sensing means and to said excess alignment signal and operative to generate said first and second timing control signals.

23. Optical inspection apparatus as recited in claim 22 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

24. Optical inspection apparatus as recited in claim 22 wherein said timing control means further includes a scale compensation means for generating a scale compensation signal, and wherein said phase locked oscillator means is further responsive to said scale compensation signal and operative to modify at least one of said first and second timing signals to compensate for known scale errors in the patterned object.

25. Optical inspection apparatus as recited in claim 24 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

26. Optical inspection apparatus as recited in claim 2 wherein said timing control means includes a controllable phase locked oscillator means responsive to a scan position signal developed by said optical sensing means and to said excess alignment signal and operative to generate said first and second timing control signals.

27. Optical inspection apparatus as recited in claim 26 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

28. Optical inspection apparatus as recited in claim 26 wherein said timing control means further includes a scale compensation means for generating a scale compensation signal, and wherein said phase locked oscillator means is further responsive to said scale compensation signal and operative to modify at least one of said first and second timing signals to compensate for known scale errors in the patterned object.

29. Optical inspection apparatus as recited in claim 28 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

30. Optical inspection apparatus as recited in claim 1 wherein said data alignment means includes:

an alignment memory for receiving and storing said first and second data signals and for responding to alignment error correction signals to develop said aligned first and second data signals; and

alignment error detection means for comparing portions of said first and second data signals stored in said alignment memory and developing said alignment error corresponding signals.

31. Optical inspection apparatus as recited in claim 30 wherein said alignment memory includes:

a memory address control means responsive to said alignment error correction signal and operative to develop first and second data select signals;

a left pixel memory for storing a quantity of said first data signal and responsive to said first data select signal to output a portion thereof as said aligned first data signal; and

a right pixel memory for storing a quantity of said second data signal and responsive to said second data select signal to output a portion thereof as said aligned second data signal.

32. Optical inspection apparatus as recited in claim 30 wherein said alignment error detection means includes:

two-dimensional phase detection means which compares portions of said first and second data signals and develops error signals corresponding to the phase instantaneous magnitude and direction of misalignment therebetween; and

alignment processor means responsive to said error signals and operative to generate said alignment error correction signals and said excess alignment signal.

33. Optical inspection apparatus as recited in claim 32 wherein said two-dimensional phase detection means includes:

X-direction error detection means responsive to portions of said first and second data signals and operative to generate X-components of said error signals; and

Y-direction error detection means responsive to portions of said first and second data signals and operative to generate Y-components of said error signals.

34. Optical inspection apparatus as recited in claim 32 wherein said alignment error detection means further includes goodness logic means responsive to portions of said first and second data signals and operative to generate goodness signals qualifying said error signals for input to said alignment processor means.

35. Optical inspection apparatus as recited in claim 30 wherein said timing control means includes a controllable phase locked oscillator means responsive to a scan position signal developed by said optical sensing means and to said excess alignment signal and operative to generate said first and second timing control signals.

36. Optical inspection apparatus as recited in claim 35 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

37. Optical inspection apparatus as recited in claim 35 wherein said timing control means further includes a scale compensation means for generating a scale compensation signal, and wherein said phase locked oscillator means is further responsive to said scale compensation signal and operative to modify at least one of said first and second timing signals to compensate for known scale errors in the patterned object.

38. Optical inspection apparatus as recited in claim 37 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

39. Optical inspection apparatus as recited in claim 1 wherein said timing control means includes a controllable phase locked oscillator means responsive to a scan position signal developing by said optical sensing means and to said excess alignment signal and operative to generate said first and second timing control signals.

40. Optical inspection apparatus as recited in claim 39 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.

41. Optical inspection apparatus as recited in claim 39 wherein said timing control means further includes a scale compensation means for generating a scale compensation signal, and wherein said phase locked oscillator means is further responsive to said scale compensation signal and operative to modify at least one of said first and second timing signals to compensate for known scale errors in the patterned object.

42. Optical inspection apparatus as recited in claim 41 wherein said timing control means is further responsive to an input pixel size select signal developed by said optical scanning means and operative to modify certain characteristics of said first and second timing control signals so as to cause said optical scanning means to scan at a speed such that it has a resolution corresponding to said input pixel size select signal, and operative to cause said database means to generate said second data signal at a resolution likewise corresponding to said input pixel size select signal.