Methods and Scatterometers, Lithographic Systems, and Lithographic Processing Cells

• US 20110027704A1
• Filed: 07/29/2010
• Published: 02/03/2011
• Est. Priority Date: 07/31/2009
• Status: Active Grant

• Current Assignee: ASML Netherlands BV (ASML Holding NV)
• Original Assignee: ASML Netherlands BV (ASML Holding NV)
• Inventors: Kubis, Michael, Schellekens, Andrianus Johannes Hendrikus, Megens, Henricus Johannes Lambertus, Den Boef, Arie Jeffrey, Cramer, Hugo Augustinus Joseph, Smilde, Hendrik Jan Hidde
• Granted Patent: US 9,081,303 B2
• Time in Patent Office: Days
• US Class Current: 430/30
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G01B 11/22 for measuring depth
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures
• CPC Class Codes: G01B 11/30 for measuring roughness or irregularity of surfaces
• CPC Class Codes: G01N 21/47 Scattering, i.e. diffuse reflection G01N21/25, G01N21/41 take precedence G01N21/55 takes precedence
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination
• CPC Class Codes: G03F 7/70608 Monitoring the unpatterned workpiece, e.g. measuring thickness, reflectivity or effects of immersion liquid on resist
• CPC Class Codes: G03F 7/70625 Dimensions, e.g. line width, critical dimension [CD], profile, sidewall angle or edge roughness
• 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 7/70641 Focus
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects

Abstract

In a method of determining the focus of a lithographic apparatus used in a lithographic process on a substrate, the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has an asymmetry in the printed profile which varies as a function of the focus of the lithographic apparatus on the substrate. A first image of the periodic structure is formed and detected while illuminating the structure with a first beam of radiation. The first image is formed using a first part of non-zero order diffracted radiation. A second image of the periodic structure is foamed and detected while illuminating the structure with a second beam of radiation. The second image is formed using a second part of the non-zero order diffracted radiation which is symmetrically opposite to the first part in a diffraction spectrum. The ratio of the intensities of the measured first and second portions of the spectra is determined and used to determine the asymmetry in the profile of the periodic structure and/or to provide an indication of the focus on the substrate. In the same instrument, an intensity variation across the detected portion is determined as a measure of process-induced variation across the structure. A region of the structure with unwanted process variation can be identified and excluded from a measurement of the structure.

Claims

1. A method of determining the focus of a lithographic apparatus used in a lithographic process on a substrate, the method comprising:

using the lithographic process to form a structure on the substrate, the structure having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic apparatus on the substrate;

a first measurement comprising forming and detecting a first image of the periodic structure while illuminating the structure with a first beam of radiation, the first image being formed using a first part of non-zero order diffracted radiation while excluding zero order diffracted radiation;

a second measurement comprising forming and detecting a second image of the periodic structure while illuminating the structure with a second beam of radiation, the second image being formed using a second part of the non-zero order diffracted radiation which is symmetrically opposite to the first part in a diffraction spectrum; and

using the first and second images detected in the first and second measurements to determine the asymmetry in the profile of the periodic structure and/or to provide an indication of the focus on the substrate.

2. The method according to claim 1, in which the first and second parts of the non-zero diffraction orders are different ones of at least a portion of each of the +1st and −

1st orders.

3. The method according to claim 1, in which the asymmetry is determined by measuring the intensity of selected portions of the first and second images.

4. The method according to claim 1, wherein the area of the structure is less than the area of the beam of radiation on the substrate.

5. The method according to claim 1, wherein the first and second measurements are repeated a plurality of times for structures formed by the lithographic apparatus using different focus values, the structures each having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic apparatus on the substrate;

and the images detected in the repeated first and second measurements are used in the determination of a relationship between the asymmetry and the focus on the substrate.

6. The method according to claim 5, wherein lithographic simulations are used in the determination of the relationship between the asymmetry and the focus on the substrate.

7. The method according to claim 1, wherein the first and second measurements are repeated a plurality of times for structures formed by the lithographic apparatus using different focus values, the structures each having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic apparatus on the substrate;

and the images detected in the repeated first and second measurements are used in the determination of a relationship between the intensity of the selected portions of the images and the focus on the substrate.

8. The method according to claim 7, wherein lithographic simulations are used in the determination of the relationship between the intensity of the selected portions and the focus on the substrate.

9. The method according to claim 1, wherein the first and second symmetrically opposed parts of non-zero order diffracted radiation comprise substantially the +1 and −

1 order diffracted radiation.

10. The method according to claim 1, wherein, in an optical system used in the measurements, the first and second beams of radiation have angles of incidence on the periodic structure which are symmetrically off-axis with respect to the optical system, and the first and second images are formed and detected using that radiation which is diffracted by the periodic structure into a narrower range of angles centered on the optical axis.

11. An angularly resolved scatterometer configured to determine the focus of a lithographic apparatus used in a lithographic process on a substrate, wherein the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic apparatus on the substrate, the scatterometer comprising:

an illumination arrangement operable to deliver first and second beams of radiation to the substrate for use in first and second measurements;

a detection arrangement operable during the first and second measurements to form and detect respective first and second images of the substrate using radiation diffracted from the substrate; and

a stop arrangement within the detection arrangement, wherein the illumination arrangement and stop arrangement together are effective to stop zero order diffracted radiation contributing to the first and second images, while the first and second images are formed using first and second parts respectively of the non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation; and

a computational arrangement operable to determine the profile asymmetry for the feature from the first and second images and/or to use the determined asymmetry and the relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate.

12. The scatterometer according to claim 11, in which, when the structure has a certain periodicity, the detection arrangement is adapted to measure the +1st and −

1st orders as the first and second parts of the diffracted radiation.

13. The scatterometer according to claim 11, in which the asymmetry is determined from measuring the intensity of the first and second images of the structure.

14. The scatterometer according to claim 11, wherein the computational arrangement is operable to compare selected portions of the first and second images, when an area of the structure is less than the area of the substrate represented in the first and second images.

15. The scatterometer according to claim 11, wherein the computational arrangement is configured to select and compare respective portions of the first and second images for each of a plurality of structures formed using different focus values, each structure having at least one feature having a profile which has an asymmetry which depends on the focus of the lithographic apparatus and to use the selected portions of the images in the determination of a relationship between the asymmetry and the focus on the substrate.

16. The scatterometer according to claim 15, wherein lithographic simulations are used in the determination of the relationship between the asymmetry and the focus on the substrate.

17. The scatterometer according to claim 11, wherein the computational arrangement is configured to select and compare respective portions of the first and second images for each of a plurality of structures formed using different focus values, each structure having at least one feature having a profile which has an asymmetry which depends on the focus of the lithographic apparatus and to use the selected portions of the images in the determination of a relationship between the intensity of the detected portions and the focus on the substrate.

18. The scatterometer according to claim 17, wherein lithographic simulations are used in the determination of the relationship between the intensity of the detected portions and the focus on the substrate.

19. The scatterometer according to claim 11, wherein the first and second symmetrically opposed parts of non-zero order diffracted radiation comprise substantially the +1 and −

1 order radiation.

20. The scatterometer according to claim 11, wherein, in an optical system used in the measurements, the first and second beams of radiation have angles of incidence on the periodic structure which are symmetrically off-axis with respect to the optical system, and the first and second images are formed and detected using that radiation which is diffracted by the periodic structure into a narrower range of angles centered on the optical axis.

21. A lithographic system comprising:

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 on to a substrate; and

an angularly resolved scatterometer configured to determine the focus of the lithographic system used in a lithographic process on the substrate, wherein the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic system on the substrate, the scatterometer comprising;

an illumination arrangement operable to deliver first and second beams of radiation to the substrate for use in first and second measurements;

a detection arrangement operable during the first and second measurements to form and detect respective first and second images of the substrate using radiation diffracted from the substrate; and

a stop arrangement within the detection arrangement,

wherein the illumination arrangement and stop arrangement together are effective to stop zero order diffracted radiation contributing to the first and second images, while the first and second images are formed using first and second parts respectively of the non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation; and

a computational arrangement operable to determine the profile asymmetry for the feature from the first and second images and/or to use the determined asymmetry and the relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate.

22. A lithographic cell comprising:

a coater arranged to coat substrates with a radiation sensitive layer;

a lithographic apparatus arranged to expose images onto the radiation sensitive layer of substrates coated by the coater;

a developer arranged to develop images exposed by the lithographic apparatus; and

an angularly resolved scatterometer configured to determine the focus of the lithographic apparatus used in a lithographic process on the substrate, wherein the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic apparatus on the substrate, the scatterometer comprising;

an illumination arrangement operable to deliver first and second beams of radiation to the substrate for use in first and second measurements;

a detection arrangement operable during the first and second measurements to form and detect respective first and second images of the substrate using radiation diffracted from the substrate; and

a stop arrangement within the detection arrangement,

wherein the illumination arrangement and stop arrangement together are effective to stop zero order diffracted radiation contributing to the first and second images, while the first and second images are formed using first and second parts respectively of the non-zero order diffracted radiation, the first and second parts being symmetrically opposite one another in a diffraction spectrum of the diffracted radiation; and

a computational arrangement operable to determine the profile asymmetry for the feature from the first and second images and/or to use the determined asymmetry and the relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate.

23. An angularly resolved scatterometer configured to determine the focus of a lithographic apparatus used in a lithographic process on a substrate, wherein the lithographic process is used to form a structure on the substrate, the structure having at least one feature which has a profile which has an asymmetry which depends on the focus of the lithographic apparatus on the substrate, the scatterometer comprising:

an illumination device effective to produce a beam of radiation;

a masking device arranged such that a beam of radiation produced by the illumination device and directed onto the substrate through the masking device will illuminate the structure within a first range of angles;

a detection device configured to detect radiation diffracted from the substrate;

a stop device between the substrate and the detection device, the masking device and stop device together being effective to stop zero order diffracted radiation and a part of the higher order diffracted radiation from being detected;

a rotation device operative to rotate the masking device and the substrate relative to each other about their respective optical axes such that after the relative rotation the structure is illuminated within a second range of angles, the second range being diametrically opposed to the first range within the cross section of the illuminating beam;

wherein the detection device is effective to measure different portions of the image produced by the diffracted radiation produced by directing the beam of radiation onto the periodic structure through the stop device before and after the rotation of the masking device and the substrate relative to each other about their respective optical axes; and

a computational device operative to determine the profile asymmetry for the feature from the measured spectra measured before and after the rotation of the masking device and the substrate device relative to each other or to use the determined asymmetry and the relationship between the focus and the asymmetry for each feature to provide an indication of the focus on the substrate.

24. The scatterometer according to claim 23, wherein:

the detection device is configured to measure different portions of the image produced by the diffracted radiation produced by directing the beam of radiation onto the periodic structure through the stop device before and after the rotation of the masking device and the substrate relative to each other about their respective optical axes for each of a plurality of structures formed by the lithographic apparatus using different focus values, each structure having at least one feature having a profile which has an asymmetry which depends on the focus of the lithographic apparatus; and

the computational device is configured to use the detected portions of the images in the determination of a relationship between the intensity of the detected portions and the focus on the substrate.

25. A method of detecting process variation in a structure on a substrate, the method comprising:

directing a beam of radiation onto the substrate so as to illuminate the structure;

forming an image of the structure using only one selected diffraction order of radiation diffracted by the substrate;

detecting a portion of the formed image;

determining an intensity variation across the detected portion, corresponding to variation in diffraction efficiency across the structure; and

identifying process-induced variation in the structure using the determined intensity variation.

26. The method according to claim 25, wherein the image is formed by spatial frequency filtering in a spectral plane to prevent diffraction orders other than the selected order from being detected.

27. The method according to claim 25, wherein the area of the structure is less than the area of the beam of radiation on the substrate.

28. The method according to claim 25, further comprising selecting a region of interest of the detected portion excluding an unwanted region of the detected portion corresponding to a region of the structure with unwanted process variation.

29. The method according to claim 28, further comprising using the selected region of interest of the detected portion for a measurement of the structure, while excluding the unwanted region.

30. An angularly resolved scatterometer configured to determine process-induced variation in a structure on a substrate, the angularly resolved scatterometer comprising:

an illumination device operable to produce a beam of radiation;

a directing device configured to direct the beam of radiation onto the substrate to illuminate the structure;

a detection device configured to form and detect an image of the structure using radiation diffracted from the substrate;

a stop device configured to stop all except one order of diffracted radiation from being detected by the detection device; and

a computational arrangement operative to determine an intensity variation across the detected radiation, corresponding to variation in diffraction efficiency across the structure; and

to identify process-induced variation in the structure using the determined intensity variation.

31. The angularly resolved scatterometer according to claim 30, wherein the portion of the image is a spectral image in a spatially filtered image plane and all except one order of diffracted radiation is prevented by the stop device by spatial frequency filtering from being detected.

32. The angularly resolved scatterometer according to claim 30, wherein the area of the structure is less than the area of the beam of radiation on the substrate.

33. The angularly resolved scatterometer according to claim 30, wherein the computational arrangement is further operative to select a region of interest of the detected portion excluding an unwanted region of the detected portion corresponding to a region of the structure with unwanted process variation.

34. The angularly resolved scatterometer according to claim 33, wherein the computational arrangement is further operative to use the selected region of interest of the detected portion for a measurement of the structure, while excluding the unwanted region.

35. A lithographic system comprising:

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 on to a substrate; and

an angularly resolved spectrometer comprising;

an illumination device operable to produce a beam of radiation;

a directing device configured to direct the beam of radiation onto the substrate to illuminate the structure;

a detection device configured to detect radiation diffracted from the substrate and to form an image;

a stop device between the substrate and the detection device, the stop device being configured to stop all except one order of diffracted radiation from being detected by the detection device; and

a computational arrangement operative to determine an intensity variation across the detected image, corresponding to variation in diffraction efficiency across the structure, and to identify process-induced variation in the structure using the determined intensity variation.

36. A lithographic cell comprising:

a coater arranged to coat substrates with a radiation sensitive layer;

a lithographic apparatus arranged to expose images onto the radiation sensitive layer of substrates coated by the coater;

a developer arranged to develop images exposed by the lithographic apparatus; and

an angularly resolved spectrometer comprising;

an illumination device operable to produce a beam of radiation;

a directing device configured to direct the beam of radiation onto the substrate to illuminate the structure;

a detection device configured to detect radiation diffracted from the substrate and to form an image;

a stop device between the substrate and the detection device, the stop device being configured to stop all except one order of diffracted radiation from being detected by the detection device; and

a computational arrangement operative to determine an intensity variation across the detected image, corresponding to variation in diffraction efficiency across the structure, and to identify process-induced variation in the structure using the determined intensity variation.