Compensation for errors in off-axis interferometric measurements

• US 20050162664A1
• Filed: 11/03/2004
• Published: 07/28/2005
• Est. Priority Date: 07/29/2002
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Zygo Corporation (Ametek Incorporated)
• Inventors: Hill, Henry A.
• Granted Patent: US 7,262,860 B2
• Time in Patent Office: Days
• US Class Current: 356/508
• CPC Class Codes: G01B 11/022 by means of tv-camera scanning
• CPC Class Codes: G01B 11/2441 using interferometry
• CPC Class Codes: G01B 11/306 for measuring evenness
• CPC Class Codes: G01B 2290/45 Multiple detectors for detecting interferometer signals
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02027 Two or more interferometric channels or interferometers
• CPC Class Codes: G03F 7/70775 Position control, e.g. interferometers or encoders for determining the stage position

Abstract

In general, in a first aspect, the invention features a method for determining the location of an alignment mark on a stage, which includes directing a measurement beam along a path between an interferometer and a mirror, wherein at least the interferometer or the mirror is mounted on the stage, combining the measurement beam with another beam to produce an output beam comprising information about the location of the stage, measuring from the output beam a location, x₁, of the stage along a first measurement axis, measuring a location, x₂, of the stage along a second measurement axis substantially parallel to the first measurement axis, calculating a correction term, ψ₃, from predetermined information characterizing surface variations of the mirror for different spatial frequencies, wherein contributions to the correction term from different spatial frequencies are weighted differently, and determining a location of the alignment mark along a third axis parallel to the first measurement axis based on x₁, x₂, and the correction term.

Claims

1. A method for determining the location of an alignment mark on a stage, the method comprising:

directing a measurement beam along a path between an interferometer and a mirror, wherein at least the interferometer or the mirror is mounted on the stage;

combining the measurement beam with another beam to produce an output beam comprising information about the location of the stage;

measuring from the output beam a location, x₁, of the stage along a first measurement axis;

measuring a location, x₂, of the stage along a second measurement axis substantially parallel to the first measurement axis;

calculating a correction term, ψ

₃, from predetermined information characterizing surface variations of the mirror for different spatial frequencies, wherein contributions to the correction term from different spatial frequencies are weighted differently; and

determining a location of the alignment mark along a third axis parallel to the first measurement axis based on x₁, x₂, and the correction term.

2. The method of claim 1, wherein x₁ and x₂ correspond to the location of the mirror at the first and second measurement axes, respectively.

3. The method of claim 1, wherein the correction term, ψ

₃, is related to departures of the mirror surface at the first measurement axis from a straight line.

4. The method of claim 1, wherein the correction term, ψ

₃, is related to an integral transform of X₂−

X₁, wherein X₂ and X₁ correspond to x₂ and x₁ monitored while scanning the stage in a direction substantially orthogonal to the first and second measurement axes.

5. The method of claim 4, wherein the integral transform is a Fourier transform.

6. The method of claim 4, wherein contributions to ψ

₃ from different spatial frequency components of variations of the mirror surface are weighted to increase the sensitivity of ψ

₃ to spatial frequency components near K_d and harmonics of K_d, wherein K_d corresponds to the 2π

/d where d is a separation between the first and second measurement axes.

7. The method of claim 3, wherein the alignment mark location is related to a location, x₃, on the third axis given by

x₃=x₁+η

(x₂−

x₁)−

ψ

₃,

wherein η

is related to a separation between first measurement axis and the third axis.

8. The method of claim 1, wherein the predetermined information is compiled by monitoring x₁ and x₂ while scanning the stage in a direction substantially orthogonal to the first and second measurement axes.

9. The method of claim 1, further comprising monitoring the location of the stage along a y-axis substantially orthogonal to the first measurement axis.

10. The method of claim 9, wherein the location of the alignment mark along the third axis depends on the location of the stage along the y-axis.

11. The method of claim 1, wherein the measurement beam reflects from the mirror more than once.

12. A method comprising:

correcting measurements of a degree of freedom of a mirror relative to a first axis made using an interferometry system based on information that accounts for surface variations of the mirror for different spatial frequencies, wherein contributions to the correction from the different spatial frequencies are weighted differently.

13. The method of claim 12, wherein the interferometry system monitors a degree of freedom of the mirror along a second axis and a third axis, wherein the second and third axes are parallel to and offset from the first axis.

14. The method of claim 13, wherein contributions to the correction from different spatial frequency components of variations of the mirror surface are weighted to increase the sensitivity of the correction to spatial frequency components near K_d and harmonics of K_d, wherein K_d corresponds to the 2π

/d where d is a separation between the second and third axes.

23. A lithography method for use in fabricating integrated circuits on a wafer, the method comprising:

supporting the wafer on a moveable stage;

imaging spatially patterned radiation onto the wafer;

adjusting the position of the stage; and

monitoring the position of the stage using the method of claim 12.

24. A lithography method for use in the fabrication of integrated circuits comprising:

directing input radiation through a mask to produce spatially patterned radiation;

positioning the mask relative to the input radiation;

monitoring the position of the mask relative to the input radiation using the method of claim 12;

and

imaging the spatially patterned radiation onto a wafer.

25. A lithography method for fabricating integrated circuits on a wafer comprising:

positioning a first component of a lithography system relative to a second component of a lithography system to expose the wafer to spatially patterned radiation; and

monitoring the position of the first component relative to the second component using the method of claim 12.

26. A method for fabricating integrated circuits, the method comprising the lithography method of claim 23.

27. A method for fabricating integrated circuits, the method comprising the lithography method of claim 24.

28. A method for fabricating integrated circuits, the method comprising the lithography method of claim 25.

31. A method for fabricating a lithography mask, the method comprising:

directing a write beam to a substrate to pattern the substrate;

positioning the substrate relative to the write beam; and

monitoring the position of the substrate relative to the write beam using the method of claim 12.

15. A method comprising:

interferometrically monitoring locations X₁ and X₂ of a mirror surface relative to respective parallel axes while translating the mirror surface along a path substantially orthogonal to the parallel axes; and

determining from the monitored mirror locations contributions from different spatial frequencies to surface imperfections of the mirror.

16. An apparatus comprising:

an interferometer configured to produce an output beam comprising a phase related to an optical path difference between two beam paths, at least one of which contacts a mirror surface; and

an electronic controller coupled to the interferometer, wherein during operation the electronic controller determines a position, x₁, of the mirror with respect to a first measurement axis based on information derived from the output beam and an error correction term that accounts for surface variations of the mirror for different spatial frequencies, wherein contributions to the error correction term from the different spatial frequencies are weighted differently.

17. The apparatus of claim 16, further comprising a second interferometer configured to produce a second output beam comprising a phase related to an optical path difference between two beam paths, at least one of which contacts the mirror surface, wherein during operation the electronic controller determines a position, x₂, of the mirror with respect to a second measurement axis based on information derived from the output beam.

18. The apparatus of claim 16, wherein the first measurement axis is parallel to the second measurement axis.

19. The apparatus of claim 18, wherein during operation the electronic controller determines a position, x₃, of a mark with respect to a third axis based on x₁, x₂, and the error correction term, wherein the third axis is parallel to and offset from the first and second measurement axes.

20. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising:

a stage for supporting the wafer;

an illumination system for imaging spatially patterned radiation onto the wafer;

a positioning system for adjusting the position of the stage relative to the imaged radiation; and

the apparatus of claim 16 for monitoring the position of the wafer relative to the imaged radiation.

21. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising:

a stage for supporting the wafer; and

an illumination system including a radiation source, a mask, a positioning system, a lens assembly, and the apparatus of claim 16,

wherein during operation the source directs radiation through the mask to produce spatially patterned radiation, the positioning system adjusts the position of the mask relative to the radiation from the source, the lens assembly images the spatially patterned radiation onto the wafer, and the apparatus monitors the position of the mask relative to the radiation from the source.

22. A beam writing system for use in fabricating a lithography mask, the system comprising:

a source providing a write beam to pattern a substrate;

a stage supporting the substrate;

a beam directing assembly for delivering the write beam to the substrate;

a positioning system for positioning the stage and beam directing assembly relative one another; and

the apparatus of claim 16 for monitoring the position of the stage relative to the beam directing assembly.

29. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 20.

30. A method for fabricating integrated circuits, the method comprising using the lithography system of claim 21.