Optical inspection of a specimen using multi-channel responses from the specimen using bright and darkfield detection

• US 5,822,055 A
• Filed: 06/27/1997
• Issued: 10/13/1998
• Est. Priority Date: 06/06/1995
• Status: Expired due to Term

• Current Assignee: KLA Instruments, Corporation (KLA Corporation)
• Original Assignee: KLA Instruments, Corporation (KLA Corporation)
• Inventors: Tsai, Bin-Ming Benjamin, Pon, Russell M.
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): VIERRA EISENBERG, JASON D
• Application Number:
  US08/884,467
• Time in Patent Office: 473 Days
• Field of Search: 356/237, 356/239, 356/394, 356/390, 250/559.39, 250/559.4, 250/559.41, 250/559.44, 250/559.45, 250/559.46
• US Class Current: 356/237.1
• CPC Class Codes: G01N 2021/8825 Separate detection of dark field and bright field
• CPC Class Codes: G01N 21/8806 Specially adapted optical and illumination features
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/95607 using a comparative method

Abstract

A method and inspection system to inspect a first pattern on a specimen for defects against a second pattern that is intended to be the same where the second pattern has known responses to at least one probe. The inspection is performed by applying at least one probe to a point of the first pattern on the specimen to generate at least two responses from the specimen. Then the first and second responses are detected from the first pattern, and each of those responses is then compared with the corresponding response from the same point of the second pattern to develop first and second response difference signals. Those first and second response difference signals are then processed together to unilaterally determine a first pattern defect list.

Claims

1. A method of inspection of a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern has known reflected darkfield and brightfield images at each point of interest, said method comprising the steps of:

a. illuminating said first pattern on said specimen with both darkfield and brightfield illumination;

b. detecting a reflected darkfield image from said first pattern at said each point of interest independent of a brightfield image at said each point of interest;

c. detecting a reflected brightfield image from said first pattern at said each point of interest independent of a darkfield image at said each point of interest;

d. comparing said reflected darkfield image of step b. against said reflected darkfield image from said second pattern to develop a reflected darkfield difference signal at each corresponding point of interest in each of said first and second patterns;

e. comparing said reflected brightfield image of step c. against said reflected brightfield image from said second pattern to develop a reflected brightfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

f. utilizing both of said reflected darkfield and brightfield difference signals from steps d. and e. together at said each point of interest as coordinates of a combined reflected pattern defect map.

2. A method of inspection as in claim 1 further including the step of:

g. post processing said combined reflected pattern defect map of step f. to identify and remove known non-performance degrading surface features from said combined reflected pattern defect map.

3. A method of inspection as in claim 1 wherein step a. includes the steps of:

g. illuminating said first pattern area with illumination from a darkfield illumination source; and

h. illuminating said first pattern area with illumination from a brightfield illumination source.

4. A method of inspection as in claim 3 wherein said darkfield and brightfield illumination sources of steps g. and h. provide illumination of different frequencies.

5. A method of inspection as in claim 4 wherein:

said darkfield illumination source provides narrow band illumination; and

step b. includes the step of;

i. passing said reflected darkfield image through a spatial filter to enhance defect detection.

6. A method of inspection as in claim 1 wherein:

said specimen is optically transmissive and said second pattern has known transmitted darkfield and brightfield images;

said method further includes the steps of;

g. detecting a transmitted darkfield image from said first pattern at said each point of interest independent of a brightfield image at said each point of interest;

h. separately detecting a transmitted brightfield image from said first pattern at said each point of interest independent of a darkfield image at said each point of interest;

i. comparing said transmitted darkfield image of step g. against said transmitted darkfield image from said second pattern to develop a transmitted darkfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

j. comparing said transmitted brightfield image of step h. against said transmitted brightfield image from said second pattern to develop a transmitted brightfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

step f. includes the step of;

k. utilizing both of said transmitted darkfield and brightfield difference signals of steps i. and j. at said each point of interest as coordinates to determine a combined transmitted pattern defect map.

7. A method of inspection as in claim 6 further including the step of:

l. post processing said combined transmitted pattern defect map of step k. to identify and remove known non-performance degrading surface features from said combined transmitted pattern defect map.

8. A method of inspection as in claim 6 wherein step a. includes the steps of:

l. illuminating said first pattern with illumination from a darkfield illumination source; and

m. illuminating said first pattern with illumination from a brightfield illumination source.

9. A method of inspection as in claim 8 wherein said darkfield and brightfield illumination sources of steps l. and m. provide illumination of different frequencies.

10. A method of inspection as in claim 9 wherein:

said darkfield illumination source provides narrow band illumination;

step b. includes the step of;

n. spatial filtering said reflected darkfield image to enhance defect detection; and

step g. includes the step of;

o. spatial filtering said transmitted darkfield image to enhance defect detection.

11. A method of inspection as in claim 6 further including the step of:

l. overlaying said reflected and transmitted pattern defect maps of steps f. and k, respectively, to produce a combined reflected and transmitted pattern defect map.

12. A method of inspection as in claim 11 further including the step of:

m. post processing said combined reflected and transmitted pattern defect map of step l to identify and remove known non-performance degrading surface features from said combined reflected and transmitted pattern defect map.

13. An inspection system to inspect a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern has known reflected darkfield and brightfield images at each point of interest, said inspection system comprising:

a darkfield and brightfield illumination system to illuminate said first pattern on said specimen;

a reflected darkfield image detector positioned to detect a reflected darkfield image from said each point of interest on said first pattern on said specimen independent of a brightfield image at said each point of interest;

a reflected brightfield image detector positioned to detect a reflected brightfield image from said each point of interest on said first pattern on said specimen independent of a darkfield image at said each point of interest;

a reflected darkfield comparator coupled to said darkfield detector to generate a darkfield difference signal at said each point of interest by comparing said reflected darkfield image from said darkfield image detector and said reflected darkfield image from said second pattern to develop a reflected darkfield difference signal at each corresponding point of interest in each of said first and second patterns;

a reflected brightfield comparator coupled to said brightfield detector to generate a brightfield difference signal at said each point of interest by comparing said reflected brightfield image from said brightfield image detector and said reflected brightfield image from said second pattern to develop a reflected brightfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

a processor coupled to said darkfield and brightfield comparators to utilize both of said reflected darkfield and brightfield difference signals at said each point of interest as coordinates of a reflected pattern defect map.

14. An inspection system as in claim 13 further including a post processor coupled to said processor to receive said reflected pattern defect map to identify known non-performance degrading surface features and to delete them from said reflected pattern defect map.

15. An inspection system as in claim 13 wherein said darkfield and brightfield illumination system includes:

a darkfield illumination subsystem; and

a brightfield illumination subsystem.

16. An inspection system as in claim 15 wherein said darkfield and brightfield illumination subsystems provide illumination of different frequencies from each other.

17. An inspection system as in claim 16 wherein:

said darkfield illumination subsystem provides narrow band illumination; and

said darkfield image detector includes a spatial filter through which said reflected darkfield image is passed to enhance defect detection.

18. An inspection system as in claim 13 wherein:

said specimen is optically transmissive and said second pattern has known transmitted darkfield and brightfield images;

said inspection system further includes;

a transmitted darkfield image detector positioned to detect a transmitted darkfield image from said first pattern and said specimen at said each point of interest independent of a brightfield image at said each point of interest;

a transmitted brightfield image detector positioned to detect a transmitted brightfield image from said first pattern and said specimen at said each point of interest independent of a darkfield image at said each point of interest;

a transmitted darkfield comparator coupled to said transmitted darkfield detector to generate a transmitted darkfield difference signal by comparing said transmitted darkfield image from said transmitted darkfield image detector and said transmitted darkfield image from said second pattern to develop a transmitted darkfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

a transmitted brightfield comparator coupled to said transmitted brightfield detector to generate a transmitted brightfield difference signal by comparing said transmitted brightfield image from said transmitted brightfield image detector and said transmitted brightfield image from said second pattern to develop a transmitted brightfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

said processor is also coupled to said transmitted darkfield and brightfield comparators to also receive said transmitted darkfield and brightfield difference signals at said each point of interest as coordinates of a combined transmitted pattern defect map.

19. An inspection system as in claim 18 further including a post processor coupled to said processor to receive said combined transmitted pattern defect map to identify known non-performance degrading surface features and to delete them from said transmitted pattern defect map.

20. An inspection system as in claim 18 wherein said darkfield and brightfield illumination system includes:

a darkfield illumination subsystem; and

a brightfield illumination subsystem.

21. An inspection system as in claim 20 wherein said darkfield and brightfield illumination subsystems provide illumination of different frequencies from each other.

22. An inspection system as in claim 21 wherein:

said reflected darkfield illumination subsystem provides narrow band illumination;

said darkfield image detector includes a first spatial filter through which said reflected darkfield image is passed to enhance defect detection; and

said transmitted darkfield image detector includes a second spatial filter through which said transmitted darkfield image is passed to enhance defect detection.

23. An inspection system as in claim 18 wherein said processor overlays said reflected and transmitted pattern defect maps to produce a combined reflected and transmitted pattern defect map.

24. An inspection system as in claim 23 wherein said processor further identifies and removes known non-performance degrading surface features from said combined reflected and transmitted pattern defect map.

25. An inspection system as in claim 13 wherein:

said darkfield and brightfield illumination system includes;

a single laser illumination source;

a beamsplitter positioned to reflect illumination from said laser toward said specimen; and

a condenser lens intermediate said beamsplitter and said specimen to direct said illumination to said specimen;

said reflected darkfield image detector is placed at a low angle to said specimen to receive said reflected darkfield image; and

said reflected brightfield detector is placed above the point being inspected on said specimen to received said reflected brightfield image through said condenser lens and beamsplitter of said darkfield and brightfield illumination system.

26. An inspection system as in claim 25 wherein:

said specimen permits transmitted illumination to pass therethrough; and

said inspection system further includes;

a transmitted darkfield image detector placed at a low angle to said specimen on the side thereof away from said illumination sources to receive a transmitted darkfield image from said specimen; and

a transmitted brightfield detector is placed directly opposite the point being illuminated on said specimen and on the side of said specimen away from said illumination sources to receive a transmitted brightfield image from said specimen.

27. An inspection system as in claim 13 wherein:

said darkfield and brightfield illumination system includes;

a narrow band laser illumination source of a selected frequency placed at a low angle to said specimen to provide darkfield illumination;

a mercury arc lamp;

a first condenser lens to receive illumination from said mercury arc lamp;

a first beamsplitter positioned to reflect brightfield illumination from said first condenser lens toward said specimen; and

a second condenser lens intermediate said first beamsplitter and said specimen to direct said brightfield illumination from said first beamsplitter to said specimen at the same point on said specimen to which said darkfield illumination is directed;

said reflected darkfield image detector includes;

a second beamsplitter positioned on the side of said first beamsplitter away from said specimen to receive reflected illumination from said specimen through said second condenser lens and said first beamsplitter, said second beamsplitter having a dichroic coating selected to reflect darkfield image illumination originating from said laser source and permitting other illumination to pass therethrough, said second beamsplitter further positioned at an angle to reflect said darkfield image out of the path defined by said second condenser lens and first and second beamsplitters;

a third lens to focus said reflected darkfield image from said second beamsplitter; and

a reflected darkfield illumination detector placed to receive said reflected darkfield image from said third lens; and

said reflected brightfield detector includes;

a fourth lens positioned on the side of said second beamsplitter away from said specimen and in line with said second condenser lens and said first and second beamsplitters to focus the brightfield image received from said second beamsplitter; and

a reflected brightfield illumination detector placed directly on the side of said fourth lens away from said specimen to received said reflected brightfield image from said specimen.

28. An inspection system as in claim 26 wherein:

said specimen permits transmitted illumination to pass therethrough; and

said inspection system further includes;

a fifth condenser lens on the side of said specimen away from said illumination sources to condense transmitted illumination from said specimen;

a transmitted darkfield image detector including;

a third beamsplitter positioned on the side of said fifth condenser lens away from said specimen to receive transmitted illumination from said specimen through said fifth condenser lens, said third beamsplitter having a dichroic coating selected to reflect transmitted darkfield image illumination originating from said laser source and permitting other illumination to pass therethrough, said second beamsplitter at an angle to reflect said transmitted darkfield image out of the path defined by said fifth condenser lens;

a sixth lens to focus said transmitted darkfield image from said third beamsplitter; and

a transmitted darkfield illumination detector placed to receive said transmitted darkfield image from said sixth lens; and

a transmitted brightfield detector including;

a seventh lens positioned on the side of said third beamsplitter away from said specimen and in line with said fifth condenser lens to focus the transmitted brightfield image received from said third beamsplitter; and

a transmitted brightfield illumination detector placed on the side of said seventh lens away from said specimen to received said transmitted brightfield image from said specimen.

29. A method of inspection of a first pattern on a specimen for defects against a second pattern that is intended to be the same, said second pattern has known first and second responses to at least one probe, said method comprising the steps of:

a. applying said at least one probe to each point of said first pattern on said specimen to generate at least two responses from said each point of said first pattern;

b. detecting a first response from said each point of said first pattern;

c. detecting a second response from said each point of said first pattern;

d. comparing said first response of step b. against said first response from the same point of said second pattern to develop a first response difference signal at said each point;

e. comparing said second response of step c. against said second response from the same point of said second pattern to develop a second response difference signal at said each point; and

f. processing said first and second response difference signals from steps d. and e. together as coordinates to unilaterally determine a first pattern defect map.

30. An inspection system to inspect a first pattern on a specimen for defects against a second pattern that is intended to be the same, said second pattern has known first and second responses to at least one probe, said inspection system comprising:

at least one probe to each point of said first pattern on said specimen to generate at least two responses from said each point of said first pattern on said specimen;

a first response detector positioned to detect said first response from said each point of said first pattern on said specimen;

a second response detector positioned to detect said second response from said each point of said first pattern on said specimen;

a first response comparator coupled to said first response detector to generate a first response difference signal by comparing the output from said first response detector and said first response from the same point of said second pattern to develop a first response difference signal at said each point;

a second response comparator coupled to said second response detector to generate a second response difference signal by comparing the output from said second response detector and said second response from the same point of said second pattern to develop a second response difference signal at said each point; and

a processor coupled to said first and second response comparators to process said first and second response difference signals together as coordinates to unilaterally determine a first pattern defect map.

31. A method of inspection of a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern having known reflected darkfield and brightfield images each resulting from different selected frequencies of illumination at each point of interest, said method comprising the steps of:

a. illuminating said first pattern on said specimen with brightfield illumination from a single brightfield illumination source, and darkfield illumination from a plurality of darkfield illumination sources, each brightfield and darkfield illumination source having a different illumination frequency, the different illumination frequencies resulting in distinguishable darkfield and brightfield images of said first pattern;

b. separately detecting a plurality of reflected darkfield images from said first pattern resulting from each of said plurality of darkfield illumination sources at said each point of interest independent of a brightfield image at said each point of interest;

c. detecting a reflected brightfield image from said first pattern at said each point of interest independent of a darkfield image at said each point of interest;

d. comparing said reflected darkfield images of step b. against said reflected darkfield image from corresponding illumination frequencies from said second pattern to develop a plurality of reflected darkfield difference signals at said each corresponding point of interest in each of said first and second patterns;

e. comparing said reflected brightfield image of step c. against said reflected brightfield image from said second pattern to develop a reflected brightfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

f. utilizing said reflected darkfield and brightfield difference signals of steps d. and e. together at said each point of interest as coordinates of a combined pattern reflected defect map.

32. A method of inspection of a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern having known reflected darkfield and brightfield images each resulting from different selected frequencies of illumination at each point of interest, said method comprising the steps of:

a. illuminating said first pattern on said specimen with darkfield illumination from a single darkfield illumination source, and brightfield illumination from a plurality of brightfield illumination sources, each brightfield and darkfield illumination source having a different illumination frequency, the different illumination frequencies resulting in distinguishable darkfield and brightfield images of said first pattern;

b. separately detecting a plurality of reflected brightfield images from said first pattern resulting from each of said plurality of brightfield illumination sources at said each point of interest independent of a darkfield image at said each point of interest;

c. detecting a reflected darkfield image from said first pattern at said each point of interest independent of a brightfield image at said each point of interest;

d. comparing said reflected darkfield image of step c. against said reflected darkfield image from said second pattern to develop a reflected darkfield difference signal at said each corresponding point of interest in each of said first and second patterns;

e. comparing said reflected brightfield images of step b. against said reflected brightfield images from corresponding illumination frequencies from said second pattern to develop a plurality of reflected brightfield difference signals at said each corresponding point of interest in each of said first and second patterns; and

f. utilizing said reflected darkfield and brightfield difference signals of steps d. and e. together at said each point of interest as coordinates of a combined pattern reflected defect map.

33. A method of inspection of a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern having known reflected darkfield and brightfield images each resulting from different selected frequencies of illumination at each point of interest, said method comprising the steps of:

a. illuminating said first pattern on said specimen with darkfield illumination from a plurality of darkfield illumination sources, and brightfield illumination from a plurality of brightfield illumination sources, each of said brightfield and darkfield illumination sources having a different illumination frequency, the different illumination frequencies resulting in distinguishable darkfield and brightfield images of said first pattern;

b. separately detecting a plurality of reflected brightfield images from said first pattern resulting from each of said plurality of brightfield illumination sources at said each point of interest independent of a darkfield image at said each point of interest;

c. separately detecting a plurality of reflected darkfield images from said first pattern resulting from said plurality of darkfield illumination sources at said each point of interest independent of a brightfield image at said each point of interest;

d. comparing said reflected darkfield images of step c. against said reflected darkfield images from corresponding illumination frequencies from said second pattern to develop a plurality of reflected darkfield difference signals at said each corresponding point of interest in each of said first and second patterns;

e. comparing said reflected brightfield images of step b. against said reflected brightfield images from corresponding illumination frequencies from said second pattern to develop a plurality reflected brightfield difference signals at said each corresponding point of interest in each of said first and second patterns; and

f. utilizing said reflected darkfield and brightfield difference signals of steps d. and e. together at said each point of interest as coordinates of a combined pattern reflected defect map.

34. An inspection system to inspect a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern has known reflected darkfield and brightfield images each resulting from different selected frequencies of illumination at each point of interest, said inspection system comprising:

an illumination system including;

a brightfield illumination subsystem having a single brightfield illumination source to illuminate said first pattern on said specimen; and

a darkfield illumination subsystem having a plurality of darkfield illumination sources to illuminate said first pattern on said specimen;

with each of said brightfield and darkfield illumination sources having a different illumination frequency resulting in distinguishable reflected brightfield and darkfield images on said first pattern;

a darkfield image detector positioned to individually detect reflected darkfield images from said each point of interest on said first pattern on said specimen resulting from each of said plurality of darkfield illumination sources independent of a brightfield image at said each point of interest;

a brightfield image detector positioned to detect a reflected brightfield image from said each point of interest on said first pattern on said specimen independent of a darkfield image at said each point of interest;

a darkfield comparator coupled to said darkfield image detector to generate a plurality of darkfield difference signals by comparing said reflected darkfield image from said darkfield image detector and said reflected darkfield images from corresponding illumination frequencies from said second pattern to develop a plurality of reflected darkfield difference signals at said each corresponding point of interest in each of said first and second patterns;

a brightfield comparator coupled to said brightfield detector to generate a brightfield difference signal by comparing said reflected brightfield image from said brightfield image detector and said reflected brightfield image from said second pattern to develop a reflected brightfield difference signal at said each corresponding point of interest in each of said first and second patterns; and

a processor coupled to said darkfield and brightfield comparators to utilize said reflected darkfield and brightfield difference signals together at said each point of interest as coordinates of a first pattern reflected defect map.

35. An inspection system to inspect a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern has known reflected darkfield and brightfield images each resulting from different selected frequencies of illumination at each point of interest, said inspection system comprising:

an illumination system including;

a darkfield illumination subsystem having a single darkfield illumination source to illuminate said first pattern on said specimen; and

a brightfield illumination subsystem having a plurality of brightfield illumination sources to illuminate said first pattern on said specimen;

with each of said brightfield and darkfield illumination sources having a different illumination frequency resulting in distinguishable reflected brightfield and darkfield images on said first pattern;

a brightfield image detector positioned to individually detect reflected brightfield images from said each point of interest on said first pattern on said specimen resulting from each of said plurality of brightfield illumination sources independent of a darkfield image at said each point of interest;

a darkfield image detector positioned to detect a reflected darkfield image from said each point of interest on said first pattern on said specimen independent of a brightfield image at said each point of interest;

a brightfield comparator coupled to said brightfield image detector to generate a plurality of brightfield difference signals by comparing said reflected brightfield images from said brightfield image detector and said reflected brightfield images from corresponding illumination frequencies from said second pattern to develop a plurality of reflected brightfield difference signals at said each corresponding point of interest in each of said first and second patterns;

a darkfield comparator coupled to said darkfield detector to generate a darkfield difference signal by comparing said reflected darkfield image from said darkfield image detector and said reflected darkfield image from said second pattern to develop a reflected darkfield difference signal at each said corresponding point of interest in each of said first and second patterns; and

a processor coupled to said darkfield and brightfield comparators to utilize said reflected darkfield and brightfield difference signals together at said each point of interest as coordinates of a first pattern reflected defect map.

36. An inspection system to inspect a first pattern on a specimen for defects to be compared against a second pattern that is intended to be the same, said second pattern has known reflected darkfield and brightfield images each resulting from different selected frequencies of illumination at each point of interest, said inspection system comprising:

an illumination system including;

a darkfield illumination subsystem having a plurality of darkfield illumination sources to illuminate said first pattern on said specimen; and

a brightfield illumination subsystem having a plurality of brightfield illumination sources to illuminate said first pattern on said specimen;

with each of said brightfield and darkfield illumination sources having a different illumination frequency resulting in distinguishable reflected brightfield and darkfield images on said first pattern;

a brightfield image detector positioned to individually detect reflected brightfield images from said each point of interest on said first pattern on said specimen resulting from each of said plurality of brightfield illumination sources independent of a darkfield image at said each point of interest;

a darkfield image detector positioned to individually detect a plurality of reflected darkfield images from said each point of interest on said first pattern on said specimen resulting from each of said plurality of darkfield illumination sources independent of a brightfield image at said each point of interest;

a brightfield comparator coupled to said brightfield image detector to generate a plurality of brightfield difference signals by comparing said reflected brightfield images from said brightfield image detector and said reflected brightfield images from corresponding illumination frequencies from said second pattern to develop a plurality of reflected brightfield difference signals at said each corresponding point of interest in each of said first and second patterns;

a darkfield comparator coupled to said darkfield detector to generate a plurality of darkfield difference signals by comparing said reflected darkfield images from said darkfield image detector and said reflected darkfield images from corresponding illumination frequencies from said second pattern to develop a plurality of reflected darkfield difference signals at said each corresponding point of interest in each of said first and second patterns; and

a processor coupled to said darkfield and brightfield comparators to utilize said reflected darkfield and brightfield difference signals together at said each point of interest as coordinates of a first pattern reflected defect map.