Selection of wavelengths for integrated circuit optical metrology

• US 20030225535A1
• Filed: 06/03/2002
• Published: 12/04/2003
• Est. Priority Date: 06/03/2002
• Status: Active Grant

• Current Assignee: Tokyo Electron America Incorporated (Tokyo Electron Limited)
• Original Assignee: Timbre Technologies Incorporated (Tokyo Electron Limited)
• Inventors: Vuong, Vi, Bao, Junwei, Drege, Emmanuel, Jakatdar, Nickhil, Doddi, Srinivas, Lane, Lawrence, Laughery, Mike, Barry, Kelly
• Granted Patent: US 7,216,045 B2
• Time in Patent Office: Days
• US Class Current: 702/76
• CPC Class Codes: G01B 11/00 Measuring arrangements characterised by the use of optical techniques

Abstract

Specific wavelengths to use in optical metrology of an integrated circuit can be selected using one or more selection criteria and termination criteria. Wavelengths are selected using the selection criteria, and the selection of wavelengths is iterated until the termination criteria are met.

Claims

1. A method of selecting wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile, the method comprising:

determining one or more termination criteria;

determining one or more selection criteria;

selecting wavelengths using one or more input diffraction spectra for the integrated circuit structure and the selection criteria; and

performing the selecting step until the termination criteria are met.

2. The method of claim 1 wherein:

the termination criteria for the selection process includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

3. The method of claim 1 wherein:

the termination criteria for the selection process includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to one of the one or more input diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

4. The method of claim 1 wherein:

the termination criteria for the selection process includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

5. The method of claim 1 wherein:

the termination criteria for the selection process includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to one of the one or more input diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

6. The method of claim 1 wherein the criteria for selecting wavelengths include one or more feature selection algorithms.

7. The method of claim 6 wherein the one or more feature selection algorithms include set cover feature selection, Eigen covariance analysis, and single value decomposition.

8. The method of claim 1 wherein the one or more input diffraction spectra comprises measured diffraction spectra off at least one site in a wafer.

9. The method of claim 1 wherein the one or more input diffraction spectra comprises simulated diffraction spectra off at least one hypothetical site in a hypothetical wafer.

10. The method claim 1 wherein setting the criteria for selection of wavelengths further comprises:

setting noise level criteria for selecting wavelengths.

11. The method of claim 10 wherein performing the selection of wavelengths further comprises:

calculating one or more mean values of measured diffraction spectra off the same site in a wafer; and

selecting wavelengths with measured diffraction spectra off the same site in the wafer that are within a preset range of the one or more mean values of measured diffraction spectra.

12. The method of claim 10 wherein the performing a selection of wavelengths further comprises:

calculating one or more mean values of measured diffraction spectra off the same site in a wafer; and

excluding wavelengths with measured diffraction spectra exceeding a preset number of sigma standard deviation of all the measured diffraction spectra off the same site in the wafer.

13. The method of claim 1 further comprising:

saving the selected wavelengths, selection process information, and structure identification information,

wherein the selection process information includes the termination criteria and the selection criteria.

14. A method of selecting wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile, the method comprising:

determining one or more termination criteria;

determining one or more selection criteria;

creating a correlation matrix for a set of diffraction spectra measured at optical metrology measurement points, the measurement points corresponding to specified wavelengths, the correlation matrix having as matrix members correlation coefficients corresponding to the measurement points;

selecting wavelengths using the set of diffraction spectra for the integrated circuit structure, the selection criteria, and a wavelength selection algorithm; and

performing the selecting step until the termination criteria are met.

15. The method of claim 14 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum, wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

16. The method of claim 14 wherein:

the termination criteria for the selection process includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to one of the set of diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

17. The method of claim 15 wherein:

the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

18. The method of claim 15 wherein:

the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to one of the set of diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

19. The method of claim 14 wherein the performing the selecting step until the termination criteria are met includes:

creating a symmetric binary matrix derived from the correlation matrix, the symmetric binary matrix having members with values of one or zero,

wherein the correlation matrix member is set to one if the correlation coefficient is equal to or greater than a correlation threshold, and

wherein the correlation matrix member is set to zero if the correlation coefficient is less than the correlation threshold; and

performing at least one iteration of selecting a wavelength corresponding to a row with the most number of one'"'"'s in the symmetric binary matrix and setting the row and a corresponding column of the symmetric binary matrix to zeros, the row and column corresponding to the wavelength selected, the iterations of selecting a wavelength continuing until the symmetric binary matrix members are all zeros.

20. The method of claim 14 further comprising:

saving the selected wavelengths, selection process information, and structure identification information,

wherein the selection process information includes termination criteria for the selection of wavelengths and wavelength selection criteria.

21. A method of selecting wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile, the method comprising:

determining one or more termination criteria;

setting one or more sensitivity criteria for selection of wavelengths, the sensitivity criteria including at least one measure of change of the diffraction spectrum induced by a change in the structure profile;

selecting wavelengths using one or more input diffraction spectra for the integrated circuit structure and the selection criteria; and

performing the selecting step until the termination criteria are met.

22. A method of selecting wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile, the method comprising:

determining one or more termination criteria;

creating a covariance matrix for a set of input diffraction spectra, an input diffraction spectrum comprising diffraction data at metrology measurement points, the measurement points corresponding to specified wavelengths, the covariance matrix having rows and columns, each row including a covariance of diffraction data for a measurement point assigned to the row relative to diffraction data for a measurement point assigned to the column;

selecting wavelengths using the set of input diffraction spectra for the integrated circuit structure and the covariance matrix; and

performing the selecting step until the termination criteria are met.

23. The method of claim 22 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

24. The method of claim 22 wherein:

the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

25. The method of claim 22 wherein selecting wavelengths step includes:

selecting measurement points meeting a covariance threshold; and

converting the selected measurement points to corresponding selected wavelengths.

26. The method of claim 22 further comprising:

saving the selected wavelengths, selection process information, and structure identification information,

wherein the selection process information includes termination criteria for the selection of wavelengths and wavelength selection criteria.

27. A method of selecting wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile, the method comprising:

determining one or more termination criteria;

determining two or more criteria for selection of wavelengths;

selecting wavelengths using a set of input diffraction spectra for the integrated circuit structure and the two more criteria for selection of wavelengths; and

performing the selecting step until the termination criteria are met.

28. The method of claim 27 wherein performing the selecting step comprises:

activating a wavelength selection algorithm based on selecting wavelengths meeting a noise selection criteria;

activating a wavelength selection algorithm based on selecting wavelengths meeting a correlation coefficient criteria;

activating a wavelength selection algorithm based on selecting wavelengths meeting a signal sensitivity criteria;

making a final selection of wavelengths based on one or more selection criteria;

testing the final selection of wavelengths against the termination criteria; and

adjusting one or more wavelength selection criteria.

29. The method of claim 28 further comprising:

saving the selected wavelengths, selection process information, and structure identification information,

wherein the selection process information includes termination criteria for the selection of wavelengths and wavelength selection criteria.

30. A method of selecting wavelengths and using the selected wavelengths for optical metrology of integrated circuit structures having a nominal profile, the method comprising:

selecting wavelengths for optical metrology, the selection based on one or more selection criteria, the selection optimized to meet a termination criteria;

extracting measured diffraction spectrum corresponding to the selected wavelengths, the diffraction spectra measured off an integrated circuit structure; and

determining one or more critical dimensions of the integrated circuit structure using the extracted measured diffraction spectrum corresponding to the selected wavelengths, the determination of one of more critical dimensions utilizing one or more regression techniques.

31. The method of claim 30 wherein selecting wavelengths for optical metrology comprises selecting one or more wavelength selection algorithm;

wherein the selection algorithm includes selecting wavelengths meeting noise selection criteria, selecting wavelengths meeting correlation coefficient criteria, and selecting wavelengths meeting signal sensitivity criteria.

32. A method of selecting wavelengths and using the selected wavelengths for optical metrology of integrated circuit structures having a nominal profile, the method comprising:

selecting wavelengths for optical metrology of integrated circuit structures, the selection based on one or more selection criteria and termination criteria;

creating a library of simulated diffraction spectra and associated profiles, the simulated diffraction spectra calculated utilizing the selected wavelengths;

extracting measured diffraction spectra corresponding to the selected wavelengths, the diffraction spectra measured off integrated circuit structures;

selecting a best match library diffraction spectrum from the library of simulated diffraction spectra and associated profiles to a measured diffraction spectra; and

accessing profile data of associated profiles of the best match library diffraction spectrum.

33. The method of claim 32 wherein the selecting wavelengths for optical metrology comprises:

determining termination criteria;

determining selection criteria;

selecting wavelengths using one or more input diffraction spectra for the integrated circuit structure and the selection criteria; and

performing the selecting step until the termination criteria are met.

34. The method of claim 33 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

35. The method of claim 33 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength cost function value is less than or equal to a preset cost function value, the selected-wavelength cost function value calculated by comparing a selected-wavelength spectrum to an input diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

36. The method of claim 33 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to a full-wavelength spectrum,

wherein the selected-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for a metrology device, the simulated diffraction spectrum determined using only the selected wavelengths, and

wherein the full-wavelength spectrum is a simulated diffraction spectrum of the nominal profile of the integrated circuit structure for the metrology device, the simulated diffraction spectrum determined using wavelengths used for the metrology device.

37. The method of claim 33 wherein the termination criteria for the selection of wavelengths includes testing if a selected-wavelength goodness of fit value is equal to or greater than a preset goodness of fit value, the selected-wavelength goodness of fit value calculated by comparing a selected-wavelength spectrum to an input diffraction spectra,

wherein the selected-wavelength spectrum is a best match diffraction spectrum from a library of diffraction spectra created for the integrated circuit structure, the selected-wavelength spectrum best match determined using only the selected wavelengths.

38. A system for selecting wavelengths for optical metrology of integrated circuit structures, the system comprising:

a diffraction spectra source configured to provide one or more input diffraction spectra; and

a wavelength selector configured to determine one or more termination criteria and one or more selection criteria, and configured to select wavelengths using one or more input diffraction spectra for the integrated circuit structure and the selection criteria until the termination criteria are met.

39. The system of claim 38 wherein the diffraction spectra source is an optical metrology simulator configured to simulate a diffraction spectrum from a specified structure profile.

40. The system of claim 38 further comprising:

a data store configured to store selected wavelengths, selection process information, and structure identification information,

wherein the selection process information includes termination criteria for the selection of wavelengths and wavelength selection criteria.

41. The system of claim 38 further comprising:

an input device configured to communicate the wavelength selection termination criteria, selection process information, and structure identification information to the wavelength selector.

42. A system for real-time determination of profile data of integrated circuit structures using optical metrology, the system comprising:

an optical metrology system configured to measure diffraction spectrum off integrated circuit structures;

a data store configured to store selected wavelengths, selection process information, and structure identification information;

an extractor configured to access the data store and retrieve stored selected wavelengths and to extract diffraction spectra data corresponding to the selected wavelengths; and

a profilometric estimator configured to utilize extracted diffraction spectra data and determine a critical dimension of the integrated circuit structure.

43. The system of claim 42 further comprising:

an input device configured to communicate selection process information and integrated circuit structure identification information to the extractor.

44. A system for creating and using a library utilizing selected wavelengths for use in optical metrology of integrated circuit structures, the system comprising:

a data store configured to store selected wavelengths, selection process information, and integrated circuit structure identification information;

an optical metrology simulator configured to simulate the diffraction spectra from hypothetical profiles of integrated circuit structures and to create a library of diffraction spectra and associated profiles;

a library configured to contain the library of diffraction spectra and associated profiles;

an optical metrology system configured to measure diffraction spectrum off integrated circuit structures; and

an extractor configured to access the data store and to extract diffraction spectra data corresponding to selected wavelengths from the data communicated from the optical metrology system.

45. The system of claim 44 further comprising:

a profile application server configured to match the extracted diffraction spectra from the extractor and obtain a best match from the library and to determine the critical dimension, profile, and underlying film thickness of the integrated circuit structure.

46. A system for selecting wavelengths to use in optical metrology processing and simulation, the system comprising:

a wavelength selector configured to determine one or more termination criteria for selection of wavelengths, to set selection one or more criteria for selection of wavelengths; and

to perform one or more iterations of selection of wavelengths, the iterations of the selection of wavelengths continuing until the termination criteria for selection of wavelengths are met, each iteration of the selection of wavelengths using one or more input diffraction spectra for the integrated circuit structure and the criteria for selection of wavelength; and

one or more wavelength selection engines coupled to the wavelength selector, the one or more wavelength selection engines configured to optimize the selection of wavelengths meeting one or more selection criteria.

47. The system of claim 46 wherein:

the one or more wavelength selection engines include an engine utilizing a set cover feature selection algorithm, Eigen Covariance Analysis algorithm, singular value decomposition algorithm, or other feature selection algorithm.

48. A computer-readable storage medium containing computer executable code to select wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile by instructing a computer to operate as follows:

determining one or more termination criteria;

determining one or more selection criteria;

selecting wavelengths using one or more input diffraction spectra for the integrated circuit structure and the selection criteria; and

performing the selecting step until the termination criteria are met.

49. A computer-readable storage medium containing computer executable code to select wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile by instructing a computer to operate as follows:

determining one or more termination criteria;

determining one or more selection criteria;

creating a correlation matrix for a set of diffraction spectra measured at optical metrology measurement points, the measurement points corresponding to specified wavelengths, the correlation matrix having as matrix members correlation coefficients corresponding to the measurement points;

selecting wavelengths using the set of diffraction spectra for the integrated circuit structure, the selection criteria, and a wavelength selection algorithm; and

performing the selecting step until the termination criteria are met.

50. A computer-readable storage medium containing computer executable code to select wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile by instructing a computer to operate as follows:

determining one or more termination criteria;

setting a sensitivity criteria for selection of wavelengths, the sensitivity criteria including at least one measure of change of the diffraction spectrum induced by a change in the structure profile;

selecting wavelengths using one or more input diffraction spectra for the integrated circuit structure and the sensitivity criteria; and

performing the selecting step until the termination criteria are met.

51. A computer-readable storage medium containing computer executable code to select wavelengths for use in optical metrology of an integrated circuit structure having a nominal profile by instructing a computer to operate as follows:

determining one or more termination criteria;

creating a covariance matrix for a set of input diffraction spectra, an input diffraction spectrum comprising diffraction data at metrology measurement points, the measurement points corresponding to specified wavelengths, the covariance matrix having rows and columns, each row including a covariance of diffraction data for a measurement point assigned to the row relative to diffraction data for a measurement point assigned to the column;

selecting wavelengths using the set of input diffraction spectra for the integrated circuit structure and the covariance matrix; and

performing the selecting step until the termination criteria are met.

52. A computer-readable storage medium containing computer executable code to select wavelengths and use selected wavelengths in optical metrology of an integrated circuit structure having a nominal profile by instructing a computer to operate as follows:

selecting wavelengths for optical metrology, the selection based on one or more selection criteria, the selection optimized to meet one or more termination criteria;

extracting measured diffraction spectrum corresponding to the selected wavelengths, the diffraction spectra measured off an integrated circuit structure; and

determining one or more critical dimensions of the integrated circuit structure using the extracted measured diffraction spectrum corresponding to the selected wavelengths, the determination of one of more critical dimensions utilizing one or more regression techniques.

53. A computer-readable storage medium containing computer executable code to select wavelengths and use selected wavelengths for optical metrology of integrated circuit structures by instructing a computer to operate as follows:

selecting wavelengths for optical metrology of integrated circuit structures, the selection based on one or more selection criteria and termination criteria;

creating a library of simulated diffraction spectra and associated profiles, the simulated diffraction spectra calculated utilizing the selected wavelengths;

extracting measured diffraction spectra corresponding to the selected wavelengths, the diffraction spectra measured off integrated circuit structures;

selecting a best match library diffraction spectrum from the library of simulated diffraction spectra and associated profiles to a measured diffraction spectra; and

accessing profile data of associated profiles of the best match library diffraction spectrum.

54. A computer-readable storage medium containing stored data including:

identification information pertaining to the fabrication process, wafer, site, and metrology device; and

one or more set of selected wavelengths for use in integrated circuit optical metrology,

wherein each set of selected wavelengths is associated with one or more termination criteria and wavelength selection criteria.