Apparatus and methods for generating an inspection reference pattern

• US 6,691,052 B1
• Filed: 01/30/2002
• Issued: 02/10/2004
• Est. Priority Date: 01/30/2002
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation
• Original Assignee: KLA-Tencor Corporation
• Inventors: Maurer, Wilhelm
• Primary Examiner(s): Bui, Bryan
• Assistant Examiner(s): PRETLOW, DEMETRIUS R
• Application Number:
  US10/061,632
• Time in Patent Office: 741 Days
• Field of Search: 702/81, 702/85, 702/108, 382/144, 382/145, 716/19, 716/21, 250/311, 250/307, 250/310, 356/511, 356/904, 356/451, 700/117, 700/121, 316/237, 316/237.4, 316/237.5
• US Class Current: 702/81
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G03F 7/70616 Monitoring the printed patterns

Abstract

Disclosed are methods and apparatus for generating reference images to reduce the number of false defects found when comparing a reference image to a corresponding target image of a reticle or mask (or integrated circuit). In one specific implementation, parameters that characterize the reticle making process are collected from a representative reticle or reticle. These parameters are collected (e.g., measured) from a reticle prior to inspection of the reticle. The collected parameters are then used to simulate process effects on the reference images of the design data. After the layout data is altered to simulate process effects and represent a “real” layout after it has been fabricated into a mask, this “real” layout data is then altered again to simulate imaging effects. The resulting reference images now include both processing and imaging effects and may then be used during an inspection of a corresponding reticle or integrated circuit.

Claims

1. A method of generating a reference image for an inspection tool, the method comprising:

collecting a plurality of parameters that characterize a process for fabricating a sample;

providing a first reference representation that is designed to be used to fabricate a target structure on the sample;

altering the first reference representation based on the collected parameters so as to produce a second reference representation that simulates process effects from fabricating the sample sufficiently well so as to reduce detection of false defects during a subsequent inspection of the sample using the first reference representation; and

altering the second reference representation so as to simulate imaging effect from imaging the second reference representation with the inspection tool,

wherein altering the first and second reference representations to simulate process and imaging effects, respectively, results in a simulated reference image that may be compared against the target structure to determine whether the target structure has any defects.

2. A method as recited in claim 1, wherein the first reference representation is altered to simulate process effects by inputting the first reference representation and the collected parameters that characterize a process for fabricating a sample into a process simulation tool which thereafter simulates the process effects by altering the first reference representation.

3. A method as recited in claim 1, further comprising performing an inspection by:

imaging the target structure to obtain a target image;

comparing the simulated reference image to the target image; and

when there is a difference between the simulated reference image and the target image, determining that there is a defect present within the target structure.

4. A method as recited in claim 3, wherein the collection of the parameters is performed independently of the comparison.

5. A method as recited in claim 4, wherein the collection of the parameters is performed with a scanning electron microscope and the imaging of the target structure is performed with an optical inspection tool.

6. A method as recited in claim 3, further comprising:

determining whether the collected parameters are within specification;

performing inspection when the collected parameters are within specification and

not performing inspection when the collected parameters are not within specification.

7. A method as recited in claim 6, further comprising adjusting the process for fabricating the sample when the collected parameters are not within specification.

8. A method as recited in claim 1, wherein the process effects include feature tapering, corner rounding, and feature shrinkage.

9. A method as recited in claim 8, wherein the process effects further include feature warping and edge roughening.

10. A method as recited in claim 1, wherein the imaging effects are based on one or more imaging parameters selected from a group consisting of numerical aperture of the inspection tool'"'"'s lens, magnification of the inspection tool'"'"'s lens, and coherence of the inspection tool'"'"'s illumination.

11. A method as recited in claim 1, wherein the inspection tool is an optical inspection tool designed to measure and/or inspect samples.

12. A method as recited in claim 1, wherein the sample is selected from a group consisting of a reticle and an integrated circuit and the target structure is selected from a group consisting of an integrated circuit structure, a resist pattern structure utilizable for fabricating an integrated circuit structure, a reticle structure, and a resist pattern structure utilizable for fabricating a reticle structure.

13. A computer system operable generate a reference image for an inspection tool, the computer system comprising:

one or more processors;

one or more memory, wherein at least one of the processors and memory are adapted to;

collect a plurality of parameters that characterize a process for fabricating a sample;

provide a first reference representation that is designed to be used to fabricate a target structure on the sample;

alter the first reference representation based on the collected parameters so as to produce a second reference representation that simulates process effects from fabricating the sample sufficiently well so as to reduce detection of false defects during a subsequent inspection of the sample using the first reference representation; and

alter the second reference representation so as to simulate imaging effect from imaging the second reference representation with the inspection tool,

wherein altering the first and second reference representations to simulate process and imaging effects, respectively, results in a simulated reference image that may be compared against the target structure to determine whether the target structure has any defects.

14. A computer system as recited in claim 13, wherein the first reference representation is altered to simulate process effects by inputting the first reference representation and the collected parameters that characterize a process for fabricating a sample into a process simulation tool which thereafter simulates the process effects by altering the first reference representation.

15. A computer system as recited in claim 13, wherein the one or more memory, wherein at least one of the processors and memory are further adapted to:

image the target structure to obtain a target image;

compare the simulated reference image to the target image; and

when there is a difference between the simulated reference image and the target image, determine that there is a defect present within the target structure.

16. A computer system as recited in claim 15, wherein the collection of the parameters is performed independently of the comparison.

17. A computer system as recited in claim 16, wherein the collection of the parameters is performed with a scanning electron microscope and the imaging of the target structure is performed with an optical inspection tool.

18. A computer system as recited in claim 15, wherein the one or more memory, wherein at least one of the processors and memory are further adapted to:

determine whether the collected parameters are within specification;

perform inspection when the collected parameters are within specification and not perform inspection when the collected para meters are not within specification.

19. A computer system as recited in claim 18, wherein the one or more memory, wherein at least one of the processors and memory are further adapted to adjust the process for fabricating the sample when the collected parameters are not within specification.

20. A computer system as recited in claim 19, wherein the inspection tool is an optical inspection tool designed to measure and/or inspect samples selected from a group consisting of a reticle and an integrated circuit and the structures are selected from a group consisting of integrated circuit structures, resist pattern structures utilizable for fabricating integrated circuit structures, reticle structures, and resist pattern structures utilizable for fabricating reticle structures.

21. A computer system as recited in claim 19, wherein locating the structures on the sample is accomplished by a pixel based search.

22. A computer system as recited in claim 19, wherein locating the structures on the sample is accomplished by finding a first structure on the sample that is significantly correlated with a first one of the second reference images.

23. A computer system as recited in claim 13, wherein the process effects include feature tapering, corner rounding, and feature shrinkage.

24. A computer system as recited in claim 23, wherein the process effects further include feature warping and edge roughening.

25. A computer system as recited in claim 24, wherein the imaging effects are based on one or more imaging parameters selected from a group consisting of numerical aperture of the inspection tool'"'"'s lens, magnification of the inspection tool'"'"'s lens, and coherence of the inspection tool'"'"'s illumination.

26. A computer system as recited in claim 13, wherein the imaging effects are based on one or more imaging parameters selected from a group consisting of numerical aperture of the inspection tool'"'"'s lens, magnification of the inspection tool'"'"'s lens, and coherence of the inspection tool'"'"'s illumination.

27. A computer system as recited in claim 13 that forms part of an optical inspection tool designed to measure and/or inspect samples.

28. A computer system as recited in claim 13, wherein the sample is selected from a group consisting of a reticle and an integrated circuit and the target structure is selected from a group consisting of an integrated circuit structure, a resist pattern structure utilizable for fabricating an integrated circuit structure, a reticle structure, and a resist pattern structure utilizable for fabricating a reticle structure.

29. An inspection system for inspecting a sample, comprising:

an imaging system arranged to generate a target image of the sample; and

a computer system as recited in claim 13, wherein the one or more memory, wherein at least one of the processors and memory are further adapted to cause the imaging system to generate the target image of the sample.

30. A computer program product for generating a reference image for an inspection tool, the computer program product comprising:

at least one computer readable medium;

computer program instructions stored within the at least one computer readable product configured to;

collect a plurality of parameters that characterize a process for fabricating a sample;

provide a first reference representation that is designed to be used to fabricate a target structure on the sample;

alter the first reference representation based on the collected parameters so as to produce a second reference representation that simulates process effects from fabricating the sample sufficiently well so as to reduce detection of false defects during a subsequent inspection of the sample using the first reference representation; and

alter the second reference representation so as to simulate imaging effect from imaging the second reference representation with the inspection tool,

wherein altering the first and second reference representations to simulate process and imaging effects, respectively, results in a simulated reference image that may be compared against the target structure to determine whether the target structure has any defects.

31. A computer program product as recited in claim 30, wherein the first reference representation is altered to simulate process effects by inputting the first reference representation and the collected parameters that characterize a process for fabricating a sample into a process simulation tool which thereafter simulates the process effects by altering the first reference representation.

32. A computer program product as recited in claim 30, the computer program instructions stored within the at least one computer readable product being further configured to perform an inspection by:

imaging the target structure to obtain a target image;

comparing the simulated reference image to the target image; and

when there is a difference between the simulated reference image and the target image, determining that there is a defect present within the target structure.

33. A computer program product as recited in claim 32, the computer program instructions stored within the at least one computer readable product being further configured to:

determine whether the collected parameters are within specification;

perform inspection when the collected parameters are within specification and

not perform inspection when the collected parameters are not within specification.

34. A computer program product as recited in claim 33, the computer program instructions stored within the at least one computer readable product being further configured to adjust the process for fabricating the sample when the collected parameters are not within specification.