Method and apparatus for using an alignment target with designed in offset

• US 6,982,793 B1
• Filed: 04/04/2002
• Issued: 01/03/2006
• Est. Priority Date: 04/04/2002
• Status: Expired due to Term

• Current Assignee: Onto Innovation Inc.
• Original Assignee: Nanometrics Incorporated (Onto Innovation Inc.)
• Inventors: Yang, Weidong, Li, Guoguang, Lowe-Webb, Roger R., Heaton, John D.
• Primary Examiner(s): Smith, Zandra V
• Assistant Examiner(s): Stock, Jr., Gordon J.
• Application Number:
  US10/116,863
• Time in Patent Office: 1,370 Days
• Field of Search: 356399-401, 356/614, 356/620, 250/548, 355/53, 355/55, 430/5, 430/22, 430/30
• US Class Current: 356/401
• CPC Class Codes: G03F 7/70633 Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching
• CPC Class Codes: G03F 9/7076 Mark details, e.g. phase grating mark, temporary mark
• CPC Class Codes: H01L 21/681 using optical controlling means

Abstract

An alignment target includes periodic patterns on two elements. The alignment target includes two locations, at least one of which has a designed in offset. In one embodiment, both measurement locations have a designed in offset of the same magnitude but opposite directions. For example, two separate overlay patterns that are mirror images of each other may be used. Alternatively, the magnitudes and/or directions may vary between the measurement locations. The radiation that interacts with the measurement locations is compared. The calculated difference is extremely sensitive to any alignment error. If the difference between the patterns is approximately zero, the elements are properly aligned. When an alignment error is introduced, however, calculated difference can be used to determine the error. In one embodiment, the alignment target is modeled to determine the alignment error. In another embodiment, additional overlay patterns with additional reference offsets are used to determine the alignment error.

Claims

1. A method of determining the alignment of a first element with respect to a second element, said method comprising:

providing an alignment target on said first element and said second element, the alignment target having a first overlay pattern, a second overlay pattern, and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude, said third overlay pattern having a third designed in offset between the periodic pattern of said first and second elements, said third designed in offset having a magnitude that is different than said first magnitude;

illuminating said first overlay pattern, said second overlay pattern, and said third overlay pattern on said alignment target with incident radiation that reacts with said alignment target;

detecting the radiation that is diffracted from said first overlay pattern, said second overlay pattern, and said third overlay pattern; and

calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said second overlay pattern to produce a first measured difference;

calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said third overlay pattern to produce a second measured difference, and

determining the approximate alignment error based on said first measured difference and said second measured difference.

2. The method of claim 1, wherein said periodic patterns are diffraction gratings.

3. The method of claim 1, wherein at least one of said periodic patterns has periodicities in two directions.

4. The method of claim 1, wherein said first element is first pattern produced on a first layer on a substrate and said second element is a second pattern produced on said first layer on said substrate.

5. The method of claim 1, wherein at least one of said periodic patterns on said first element and said second element of said first overlay pattern, said second overlay pattern, and said third overlay pattern are continuous periodic patterns.

6. The method of claim 1, wherein detecting the radiation comprises:

receiving light diffracted by said first overlay pattern, said second overlay pattern, and said third overlay pattern on two dimensional array detector that receives said diffracted light with the spectra dispersed along one dimension of said detector and the spectra associated with different locations on said alignment target separated along the direction perpendicular to the direction of the spectral dispersion.

7. The method of claim 1, wherein said second overlay pattern has a second designed in offset of a second magnitude.

8. The method of claim 7, wherein said first magnitude is the same as said second magnitude, wherein said first overlay pattern has a designed in offset in a first direction and said second overlay pattern has a designed in offset in a second direction opposite said first direction.

9. The method of claim 7, wherein said first magnitude and said second magnitude are different, wherein said first overlay pattern has a designed in offset in a first direction and said second overlay pattern has a designed in offset in a second direction that is non-parallel with said first direction.

10. The method of claim 7, wherein said first designed in offset having a first magnitude is in a first direction, said second designed in offset between the periodic pattern on said first and second elements is in a second direction opposite said first direction, and third designed in offset has a third magnitude in said first direction, said third magnitude being equal to said first magnitude plus a first reference offset.

11. The method of claim 10, wherein said alignment target includes a fourth overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said fourth overlay pattern having a fourth designed in offset between the periodic pattern on said first and second elements, said fourth designed in offset having said third magnitude in said second direction.

12. The method of claim 10, wherein said alignment target includes a fourth overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said fourth overlay pattern having a fourth designed in offset between the periodic pattern on said first and second elements, said fourth designed in offset having a fourth magnitude.

13. The method of claim 12, wherein said fourth magnitude is equal to said first magnitude minus a second reference offset and wherein:

detecting radiation comprises detecting light diffracted by said first overlay pattern, said second overlay pattern, said third overlay pattern, and said fourth overlay pattern; and

said method further comprising;

calculating the difference between the diffracted light from said first overlay pattern and the diffracted light from said fourth overlay pattern to produce a third measured difference.

14. The method of claim 13, wherein the first reference offset is equal to the second reference offset, the method further comprising determining the approximate alignment error based on the ratio of said first measured difference and the sum of said second measured difference and said third measured difference.

15. The method of claim 12, wherein said fourth magnitude is equal to said second magnitude and a second reference offset in said second direction and wherein:

detecting radiation comprises detecting light diffracted by said first overlay pattern, said second overlay pattern, said third overlay pattern, and said fourth overlay pattern; and

said method further comprising;

calculating the difference between the diffracted light from said third overlay pattern and the diffracted light from said fourth overlay pattern to produce a third measured difference;

calculating the difference between the diffracted light from said fourth overlay pattern and the diffracted light from said second overlay pattern to produce a fourth measured difference; and

determining the approximate alignment error based on the first measured difference, the second measured difference, the third measured difference and the fourth measured difference.

16. The method of claim 15, wherein the first magnitude is equal to the second magnitude and said first reference offset is equal to said second reference offset and wherein determining the approximate alignment error is based on the ratio of the sum of said first measured difference summed with said third measured difference and the sum of said second measured difference with said fourth measured difference and multiplying said ratio by one half of said first reference offset.

17. The method of claim 1, wherein said radiation is light that is diffracted from said first overlay pattern, said second overlay pattern, and said third overlay pattern.

18. The method of claim 17, said method further comprising:

modeling at least two of said first overlay pattern, said second overlay pattern, and said third overlay pattern of said alignment target including modeling the diffracted light;

calculating the difference between the modeled diffracted light from said first overlay pattern and said second overlay pattern to produce a modeled difference;

comparing said first measured difference with said modeled difference to determine if said measured difference and said modeled difference have an acceptable fit.

19. The method of claim 18, said method further comprising:

remodeling at least two said first overlay pattern, said second overlay pattern, and said third overlay pattern of said alignment target with a different alignment offset including remodeling diffracted light;

calculating the difference between the remodeled diffracted light from said at least two of said first overlay pattern, said second overlay pattern, and said third overlay pattern to produce a remodeled difference;

comparing said measured difference with said remodeled difference, to determine if said measured difference and said remodeled difference have an acceptable fit; and

repeating the acts of remodeling, calculating the remodeled difference, and comparing until an acceptable fit is found.

20. The method of claim 18, wherein at least one of the model of the locations and the modeled difference is stored in a library.

21. A method of determining the alignment of a first element with respect to a second element, said method comprising:

providing an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target having at least two locations at least one of which having a designed in offset between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element;

illuminating said at least two locations on said alignment target with incident radiation that reacts with said alignment target, wherein said radiation is light that is diffracted diffracted from said at least two locations;

detecting the radiation from said at least two locations after reacting with said alignment target; and

calculating the difference between the light diffracted from one location and the light diffracted from a second location;

modeling said two locations of said alignment target including modeling the light diffracted from said two locations;

comparing said modeled light from said two locations with the measured light from said two locations;

determining if said modeled light is an acceptable fit for said measured light for each location;

remodeling either location until said modeled light is an acceptable fit for said measured light for each location; and

averaging the modeled offset for the periodic patterns on said first element and said second element for each of said modeled location to determine the alignment of said first element with respect to said second element.

22. A method of determining the alignment of a first element with respect to a second element, said method comprising:

providing an alignment target on said first element and said second element, the alignment target having a first overlay pattern, a second overlay pattern, and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude, said third overlay pattern having a third designed in offset between the periodic pattern of said first and second elements, said third designed in offset having a magnitude that is different than said first magnitude;

illuminating said first overlay pattern, said second overlay pattern, and said third overlay pattern on said alignment target with incident radiation that reacts with said alignment target;

detecting the radiation that is different from said first overlay pattern, said second overlay pattern, and said third overlay pattern; and

calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said second overlay pattern to produce a first measured difference;

calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said third overlay pattern to produce a second measured difference; and

determining the approximate alignment error based on said first measured difference and said second measured difference, wherein determining the approximate alignment error is based on the ratio of said first measured difference and said second measured difference.

23. The method of claim 22, wherein determining the approximate alignment error comprises calculating the product of said ratio and one half of said first magnitude to determine the approximate alignment error.

24. A method of determining the alignment of a first element with respect to a second element, said method comprising:

illuminating at least three locations of an alignment target on said first element and said second element, wherein said at least three locations are a first overlay pattern and a second overlay pattern and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second embodiment that have the same pitch, at least two of said at least three locations of said alignment target having a designed in offset between the periodic pattern on said first element and said periodic pattern on said second element;

detecting light diffracted from said at least three locations;

comparing the detected light diffracted from said at least three locations by calculating the difference between the light diffracted from a first location and the light diffracted from a second location to produce a first measured difference and calculating the difference between the light diffracted from said first location and the light from a third location to produce a second measured difference; and

using said first measured difference with said second measured difference to determine the approximate alignment error between said first element and said second element.

25. The method of claim 24, wherein said periodic patterns are diffraction gratings.

26. The method of claim 24, wherein at least one of said periodic patterns has periodicities in two directions.

27. The method of claim 24, wherein detecting light diffracted from said at least three locations comprises:

receiving light diffracted by said at least three locations on a two dimensional array detector that receives said diffracted light with the spectra dispersed along one dimension of said detector and the spectra associated with different locations on said alignment target separated along the direction perpendicular to the direction of the spectral dispersion.

28. The method of claim 24, wherein a first of said at least three locations has a designed in offset of a first magnitude and a second of said at least three locations has a designed in offset of a second magnitude and a third of said at least three locations has a designed in offset of a third magnitude.

29. The method of claim 28, wherein said first magnitude is the same as said second magnitude, wherein said first of said at least locations has a designed in offset in a first direction and said second of said at least three locations has a designed in offset in a second direction opposite said first direction.

30. The method of claim 28, wherein said first magnitude and said second magnitude are different, wherein said first of said at least three locations has a designed in offset in a first direction and second of said at least three locations has a designed in offset in a second direction that is non-parallel with said first direction.

31. The method of claim 24, wherein said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude in a first direction, said second overlay pattern having a second designed in offset between the periodic pattern on said first and second elements, said third overlay pattern having a third designed in offset between the periodic pattern on said first and second elements, said third designed in offset having a second magnitude in said first direction, said second magnitude being equal to said first magnitude plus a reference offset.

32. The method of claim 31, wherein said second designed in offset is of said first magnitude in a second direction opposite said first direction and wherein determining the approximate alignment error comprises calculating the ratio of said first measured difference and said second measured difference and calculating the product of said ratio and one half of said first magnitude.

33. The method of claim 31, wherein said alignment target includes a fourth overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said fourth overlay pattern having a fourth designed in offset between the periodic pattern on said first and second elements, said fourth designed in offset having a third magnitude in said first direction, said third magnitude being equal to said first magnitude minus said reference offset.

34. The method of claim 33, wherein said second designed in offset is of said first magnitude in a second direction opposite said first direction and wherein detecting light diffracted from said at least three locations further comprises detecting light diffracted by said fourth overlay pattern, said method further comprising:

calculating the difference between the diffracted light from said first overlay pattern and the diffracted light from said fourth overlay pattern to produce a third measured difference; and

determining the approximate alignment error based on the ratio of said first measured difference and the sum of said second measured difference and said third measured difference multiplied by said first magnitude.

35. The method of claim 31, wherein said alignment target includes a fourth overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said fourth overlay pattern having a fourth designed in offset between the periodic pattern on said first and second elements, said fourth designed in offset having said second magnitude in said second direction.

36. The method of claim 35, wherein said second designed in offset is of said first magnitude in a second direction opposite said first direction and wherein detecting light diffracted from said at least three locations further comprises detecting light diffracted by said fourth overlay pattern, said method further comprising:

calculating the difference between the diffracted light from said third overlay pattern and the diffracted light from said fourth overlay pattern to produce a third measured difference;

calculating the difference between the diffracted light from said fourth overlay pattern and the diffracted light from said second overlay pattern to produce a fourth measured difference; and

determining the approximate alignment error based on the ratio of the sum of said first measured difference summed with said third measured difference and the sum of said second measured difference with said fourth measured difference multiplied, and multiplying said ratio by one half of said reference offset.

37. A apparatus for determining the alignment of a first element with a second element by way of an alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target including at least three locations at least two of which having a designed in offset between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element such that when said first element and said second element are aligned there is an offset of different magnitudes between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element at the two locations having a designed in offset, said apparatus comprising:

a radiation source for producing radiation to be incident on said at least three locations of said alignment target;

a detector for detecting radiation after it interacts with said at least three locations of said alignment target; and

a computer and a computer-usable medium having computer-readable program code embodied therein for causing said computer to calculate the difference between the detected radiation from said at least three locations by;

calculating the difference between the detected radiation from a first location and detected radiation from a second location to produce a first measured difference;

calculating the difference between the detected radiation from said first location and the detected radiation from a third location to produce a second measured difference; and

using said first measured difference and said second measured difference to determine if the first element and the second element are aligned.

38. The apparatus of claim 37, wherein said first element is a first layer on a substrate and said second element is a second layer on said substrate.

39. The apparatus of claim 37, wherein said first element is a first pattern produced on a first layer on a substrate and said second element is a second pattern produced on said first layer on said substrate.

40. The apparatus of claim 37, wherein each location includes a diffraction grating on said first element and a diffraction grating on said second element, the diffraction gratings of said at least three locations being oriented in the same direction.

41. The apparatus of claim 40, wherein said computer-readable program code embodied in said computer-usable medium causes said computer to perform the steps of

comparing the calculated difference with a library of differences of detected radiation to determine alignment error.

42. The apparatus of claim 37, wherein said first location and said second location have a designed in offset of a first magnitude in opposite directions, said at least one periodic pattern at said third location having a designed in offset of a second magnitude in the same direction as said first location, said second magnitude being equal to said first magnitude plus a reference offset.

43. The apparatus of claim 42, wherein said computer-readable program code embodied in said computer-usable medium causes said computer to:

determining the approximate alignment error based on the ratio of said first measured difference and said second measured difference multiplied by one half of the reference offset.

44. The apparatus of claim 42, wherein said at least one periodic pattern at said first, said second, and said third locations are diffraction gratings, wherein said alignment target includes a fourth location including a diffraction grating on said first element and a diffraction grating on said second element, the diffraction gratings being oriented in the same direction as the diffraction gratings of said first, second, and third locations, said fourth location having a designed in offset of a third magnitude in the same direction as said first location, said third magnitude being equal to said first magnitude minus said reference offset.

45. The apparatus of claim 44, wherein said computer-readable program code embodied in said computer-usable medium causes said computer to:

calculating the difference between the detected radiation from said first location and the detected radiation from said fourth location to produce a third measured difference; and

determining the approximate alignment error based on the ratio of said first measured difference and the sum of said second measured difference on said third measured difference multiplied by said reference offset.

46. The apparatus of claim 42, wherein said at least one periodic pattern at said first, said second, and said third locations are diffraction gratings, wherein said alignment target includes a fourth location including a diffraction grating on said first element and a diffraction grating on said second element, the diffraction gratings being oriented in the same direction as the diffraction gratings of said first, second, and third locations, said fourth having a designed in offset of said second magnitude in the same direction as said second location.

47. The apparatus of claim 46, wherein said computer-readable program code embodied in said computer-usable causes said computer to:

calculating the difference between the detected radiation from said third location and the detected radiation from said fourth location to produce a third measured difference;

calculating the difference between the detected radiation from said fourth location and the detected radiation from said second location to produce a fourth measured difference; and

determining the approximate alignment error based on the ratio of the sum of said first measured difference summed with said third measured difference and the sum of said second measured difference with said fourth measured difference multiplied, and multiplying said ratio by one half of said reference offset.

48. An apparatus for determining the alignment of a first element with a second element by way of an alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target including at least three locations at least two of which having a designed in offset between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element such that when said first element and said second element are aligned there is an offset of different magnitudes between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element at the two locations having a designed in offset, said apparatus comprising

a radiation source for producing radiation to be incident on said at least three locations of said alignment target, wherein said radiation source produces light that is simultaneously incident on said at least three locations of said alignment target;

an imaging spectrometer grating that receives diffracted light from said at three locations and focuses said diffraction light;

a detector for detecting said focused diffracted light from said imaging spectrometer, wherein said light detector is a two dimensional array detector that receives said diffracted light with the spectra dispersed along one dimension of said detector and the spectra associated with different locations of said alignment target separated along the direction perpendicular to the direction of the spectral dispersion; and

a computer and a computer-usable medium having computer-readable program code embodied therein for causing said computer to calculate the difference between the detected radiation from said at least three locations by;

calculating the difference between the detected radiation from a first location and detected radiation from a second location to produce a first measured difference;

calculating the difference between the detected radiation from said first location and the detected radiation from a third location to produce a second measured difference; and

using said first measured difference and said second measured difference to determine if the first element and the second element are aligned.

49. A method of determining the alignment of a first element with respect to a second element, said method comprising:

providing an alignment target on said first element and said second element, said alignment target having at least four locations, wherein said at least four locations are a first overlay pattern, a second overlay pattern, a third overlay pattern, and a fourth overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element that have the same pitch and a plurality of which have a designed in offset between the periodic pattern on said first element and said periodic pattern on said second element;

illuminating said at least four locations on said alignment target with incident radiation that reacts with said alignment target;

detecting the radiation from said at least four locations after reacting with said alignment target; and

solving a polynomial equation using the detected radiation to determine the alignment of said first element with respect to said second element.