Metrology method and apparatus, lithographic apparatus, device manufacturing method and substrate

• US 8,411,287 B2
• Filed: 08/12/2010
• Issued: 04/02/2013
• Est. Priority Date: 08/24/2009
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Smilde, Hendrik Jan Hidde, Bleeker, Arno Jan, Den Boef, Arie Jeffrey, Koolen, Armand Eugene Albert, Pellemans, Henricus Petrus Maria, Plug, Reinder Teun, Coene, Willem Marie Julia Marcel
• Primary Examiner(s): STAFIRA, MICHAEL PATRICK
• Application Number:
  US12/855,394
• Publication Number:
  US 20110043791A1
• Time in Patent Office: 964 Days
• Field of Search: 356399-401, 356/620
• US Class Current: 356/620
• CPC Class Codes: G03F 7/70616 Monitoring the printed patterns
• 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

Abstract

A metrology apparatus is arranged to illuminate a plurality of targets with an off-axis illumination mode. Images of the targets are obtained using only one first order diffracted beam. Where the target is a composite grating, overlay measurements can be obtained from the intensities of the images of the different gratings. Overlay measurements can be corrected for errors caused by variations in the position of the gratings in an image field.

Claims

1. An apparatus comprising:

an objective lens configured to direct a beam of radiation onto targets on a substrate and to collect radiation diffracted by the targets;

a sensor configured to detect an image of the targets; and

an image processor configured to identify separate images of respective ones of the targets in the image detected by the sensor,

wherein the source, the objective lens, and the sensor are arranged so that the beam substantially simultaneously illuminates the targets and so that the image of the targets that is detected by the sensor is formed by one first order diffracted beam.

2. The apparatus of claim 1, wherein the image processor comprises a pattern recognizer.

3. The apparatus of claim 2, wherein the pattern recognizer is configured to recognize an array of four or more separate images.

4. The apparatus of claim 1, further comprising a controller configured to determine an intensity value from each of the separate images.

5. The apparatus of claim 4, wherein the controller is further configured to determine an overlay error between layers of the substrate in which parts of the target are formed from the determined intensity values.

6. The apparatus of claim 5, wherein the controller is configured to determine overlay on based on:

7. The apparatus according to claim 4, wherein the controller is further configured to determine the position of said target images within an image field of the sensor, and to apply a correction in the determined intensity or overlay value by reference to the determined position.

8. The apparatus of claim 1, wherein the source and the objective lens are arranged to illuminate the targets in an off-axis illumination mode.

9. The apparatus of claim 8, wherein the off-axis illumination mode consists essentially of a single pole.

10. The apparatus of claim 8, wherein the off-axis illumination mode consists essentially of a first pole and a second pole.

11. The apparatus of claim 10, wherein the first pole is located on a first axis of the pupil plane and the second pole is located on a second axis of the pupil plane, the first and second axes being orthogonal.

12. The apparatus of claim 10, wherein the targets comprise at least one grating having lines perpendicular to the first axis and at least one grating having lines perpendicular to the second axis.

13. The apparatus of claim 1, wherein the targets include a first grating having a first bias and a second grating having a second bias, the second bias being different from the first bias.

14. The apparatus of claim 1, further comprising an aperture stop between the objective lens and the sensor, the aperture stop being configured to block the zeroth order of radiation diffracted by the targets.

15. The apparatus of claim 14, wherein the aperture stop is configured to pass substantially only one first order of radiation diffracted by the targets.

16. A lithographic apparatus comprising:

an illumination optical system arranged to illuminate a pattern;

a projection optical system arranged to project an image of the pattern onto a substrate; and

a metrology device comprising,

an objective lens configured to direct a beam of radiation onto targets on the substrate and to collect radiation diffracted by the targets;

a sensor configured to detect an image of the targets; and

an image processor configured to identify separate images of respective ones of the targets in the image detected by the sensor,

wherein the source, the objective lens, and the sensor are arranged so that the beam substantially simultaneously illuminates the targets and so that the image of the targets that is detected by the sensor is formed by one first order diffracted beam.

17. The apparatus of claim 16, further comprising:

an exposure station;

a measurement station; and

a substrate table moveable between the exposure station and the measurement station,

wherein the metrology device is positioned at the measurement station.

18. A lithographic cell comprising:

a lithographic apparatus;

at least one process device;

a substrate handler; and

a metrology device comprising,

an objective lens configured to direct a beam of radiation onto targets on a substrate and to collect radiation diffracted by the targets;

a sensor configured to detect an image of the targets; and

an image processor configured to identify separate images of respective ones of the targets in the image detected by the sensor,

wherein the source, the objective lens, and the sensor are arranged so that the beam substantially simultaneously illuminates the targets and so that the image of the targets that is detected by the sensor is formed by one first order diffracted beam.

19. A method comprising:

directing an illumination beam as a measurement beam onto targets using an objective lens so that the measurement beam substantially simultaneously illuminates the targets;

collecting radiation diffracted by the targets using the objective lens;

detecting an image of the targets, the image being formed by only one first order diffracted beam; and

identifying separate images of respective ones of the targets in the detected image.

20. The method of claim 19, wherein the identifying is performed by a pattern recognizer.

21. The method of claim 20, wherein the pattern recognizer is configured to recognize an array of four or more separate images.

22. The method of claim 19, further comprising determining an intensity value from each of the separate images.

23. The method of claim 22, further comprising determining an overlay error between layers of the substrate in which parts of the target are formed from the determined intensity values.

24. The method of claim 23, wherein the determining an overlay error is based on:

25. The method according to claim 22, wherein a correction is applied in the determined intensity or overlay value in accordance with the position of each target image within the detected image.

26. The method of claim 19, wherein the illumination beam is directed onto the targets in an off-axis illumination mode.

27. The method of claim 26, wherein the off-axis illumination mode consists essentially of a single pole.

28. The method of claim 26, wherein the off-axis illumination mode consists essentially of a first pole and a second pole.

29. The method of claim 28, wherein the first pole is located on a first axis of the pupil plane and the second pole is located on a second axis of the pupil plane, the first and second axes being orthogonal.

30. The method of claim 29, wherein the targets comprise at least one grating having lines perpendicular to the first axis and at least one grating having lines perpendicular to the second axis.

31. The method of claim 19, wherein the targets include a first grating having a first bias and a second grating having a second bias, the second bias being different from the first bias.

32. The method of claim 19, further comprising blocking the zeroth order of radiation diffracted by the targets between the objective lens and a sensor used to detect the image.

33. The method of claim 19, further comprising allowing substantially only one first order of radiation diffracted by the targets to reach a sensor used to detect the image.