Methods and patterning devices for measuring phase aberration
A method of measuring a phase difference between two regions in an aberration function: Reference structures are produced on a substrate using illumination that minimizes effects of phase aberration. A grating is produced on the substrate using a phase-shift grating reticle to produce, in the exit pupil, a pair of diffracted non-zero orders, while forbidding other diffracted orders and produces interference fringes formed by interference between the pair. The interference contributes to a first grating on the substrate. Overlay error is measured between the grating and the reference structure using diffraction-based or image-based overlay measurements. A phase aberration function for the exit pupil of the lithographic apparatus can then be determined from the measured overlay errors.
1. A method comprising:
producing, using a lithographic apparatus, a first reference structure on a substrate;
producing, using the lithographic apparatus, a first grating on the substrate by illuminating a reticle with radiation, the reticle comprising an area with a phase-shift grating periodic in first and second directions and configured to produce:
in an exit pupil of the lithographic apparatus, a pair of diffracted orders of the radiation other than the zeroth order, while forbidding other diffracted orders of the radiation in the exit pupil; and
interference fringes formed by interference between the pair of diffracted orders of the radiation, the interference fringes contributing to the definition of the first grating on the substrate; and
measuring overlay error between the first grating and the first reference structure.
2. The method of claim 1 , wherein the interference fringes together with the interferences between the zeroth order and each of the pair of diffracted orders define the first grating on the substrate.
3. The method of claim 1 , wherein the first and second directions are at an oblique angle to each other.
4. The method of claim 1 , wherein the measuring the overlay error is performed by an angular resolved scatterometer making a diffraction based overlay (DBO) measurement.
5. The method of claim 4 , wherein the measuring the overlay error by the angular resolved scatterometer is performed using a combination of measurement wavelength and numerical aperture at which interference fringes formed by interference between any of the pair of diffracted orders of the radiation and zeroth order non-diffracted radiation are not resolved within the numerical aperture.
6. The method of claim 1 , wherein the measuring the overlay error is produces an image-based overlay (IBO) measurement.
7. The method of claim 6 , wherein the first reference structure and the first grating are produced by a double exposure of the same resist layer.
8. The method of claim 1 , wherein the first reference structure and the first grating are produced by separate exposure steps of different respective resist layers.
9. The method of claim 1 , further comprising determining, from the measured overlay error, a phase difference between regions in the exit pupil of the lithographic apparatus sampled by the respective interfering orders.
10. The method of claim 1 , wherein the producing and measuring are repeated for multiple pitches of the first grating in either the first direction or the second direction with correspondingly adapted multiple first reference structures and further comprises determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
11. The method of claim 10 , wherein the phase aberration function is determined using a Zernike polynomial expansion to estimate the phase aberration function.
12. The method of claim 1 , wherein the producing and measuring are repeated for multiple orientations of the first grating with correspondingly adapted multiple first reference structures and further comprises the determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
13. The method of claim 1 , wherein the producing and measuring are repeated for multiple illumination modes of the lithographic apparatus with correspondingly adapted multiple first reference structures and further comprises the determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
14. The method of claim 1 , wherein the first reference structure is produced by an illumination mode of the lithographic apparatus configured to minimize effects of phase aberration of the lithographic apparatus.
15. A method comprising:
producing, by a lithographic apparatus, a first reference structure on a substrate;
producing, by the lithographic apparatus, a first grating on the substrate by illuminating a reticle with radiation, the reticle comprising an area with a phase-shift grating configured to produce:
in an exit pupil of the lithographic apparatus an allowed diffracted first order of the radiation while forbidding diffraction of another first order and both second orders of the radiation in the exit pupil; and
interference fringes formed by interference between a zeroth order of the radiation and the allowed diffracted first order of the radiation, the interference fringes defining the second grating on the substrate; and
measuring an overlay error between the second grating and the second reference structure.
16. The method of claim 15 , wherein the phase-shift grating comprises regions of subsegmentation with different phase shift interleaved with a spacing small enough so that any non-zero diffracted orders arising from the interleaving fall outside the exit pupil of the lithographic apparatus.
17. The method of claim 16 , wherein the regions of different phase shift combine to produce an average transmission of 1+i.
18. The method of claim 15 , wherein the phase-shift grating comprises a periodic transmission comprising the transmissions 1, 1+i, i, 0 or their inversion.
19. The method of claim 15 , wherein the phase-shift grating comprises a periodic transmission comprising a cyclic permutation of transmissions 1, 1+i, i, 0 or their inversion.
20. The method of claim 15 , wherein the measuring the overlay error is performed by an angular resolved scatterometer making a diffraction based overlay (DBO) measurement.
21. The method of claim 15 , wherein the measuring the overlay error produces an image-based overlay (IBO) measurement.
22. The method of claim 21 , wherein the first reference structure and the first grating are produced by a double exposure of the same resist layer.
23. The method of claim 15 , wherein the first reference structure and the first grating are produced by separate exposure steps of different respective resist layers.
24. The method of claim 15 , further comprising the determining, from the measured overlay error, a phase difference between regions in the exit pupil of the lithographic apparatus sampled by the respective interfering orders.
25. The method of claim 15 , wherein the producing and measuring are repeated for multiple pitches of the first grating in either the first direction or the second direction with correspondingly adapted multiple first reference structures and further comprises determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
26. The method of claim 25 , wherein the phase aberration function is determined using a Zernike polynomial expansion to estimate the phase aberration function.
27. The method of claim 15 , wherein the producing and measuring are repeated for multiple orientations of the first grating with correspondingly adapted multiple first reference structures and further comprises the determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
28. The method of claim 15 , wherein the producing and measuring are repeated for multiple illumination modes of the lithographic apparatus with correspondingly adapted multiple first reference structures and further comprises the determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
29. The method of claim 15 , wherein the first reference structure is produced by an illumination mode of the lithographic apparatus configured to minimize effects of phase aberration of the lithographic apparatus.
30. A method comprising:
producing by, a lithographic apparatus, a first reference structure on a substrate;
producing by, the lithographic apparatus, a second reference structure on the substrate;
producing by, the lithographic apparatus a first grating on the substrate by illuminating a reticle with radiation, the reticle comprising an first area with a first phase-shift grating periodic in first and second directions and configured to produce in an exit pupil of the lithographic apparatus:
a pair of diffracted orders of the radiation other than the zeroth order, while forbidding other diffracted orders of the radiation in the exit pupil; and
interference fringes formed by interference between the pair of diffracted orders of the radiation, the interference fringes contributing to the definition of the first grating on the substrate;
producing by, the lithographic apparatus a second grating on the substrate by illuminating the reticle with radiation, the reticle comprising an second area with a second phase-shift grating configured to produce in the exit pupil of the lithographic apparatus:
an allowed diffracted first order of the radiation, while forbidding diffraction of another first order and both second orders of the radiation in the exit pupil and
interference fringes formed by interference between a zeroth order of the radiation and the allowed diffracted first order of the radiation, the interference fringes defining the second grating on the substrate;
measuring the overlay error between the first grating and the first reference structure; and
measuring the overlay error between the second grating and the second reference structure.
31. The method claim 30 , wherein the producing and measuring are repeated for multiple pitches of the first grating in one or more of the first and second directions with correspondingly adapted multiple first reference structures and further comprising determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
32. The method claim 31 , wherein the phase aberration function is determined using a Zernike polynomial expansion to estimate the phase aberration function.
33. The method claim 30 , wherein the producing and measuring are repeated for multiple orientations of the first grating with correspondingly adapted multiple first reference structures and further comprising determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
34. The method claim 30 , wherein the producing and measuring are repeated for multiple illumination modes of the lithographic apparatus with correspondingly adapted multiple first reference structures and further comprising determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
35. The method claim 30 , wherein the producing and measuring are repeated for multiple pitches of the second grating with correspondingly adapted multiple second reference structures and wherein the method comprises the determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
36. The method claim 30 , wherein the producing and measuring are repeated for multiple orientations of the second grating with correspondingly adapted multiple second reference structures and further comprising determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
37. The method claim 30 , wherein steps of claim 30 are repeated for multiple illumination modes of the lithographic apparatus with correspondingly adapted multiple second reference structures and further comprising determining, from the measured overlay errors, a phase aberration function for the exit pupil of the lithographic apparatus.
38. The method claim 30 , wherein the first and second reference structures are produced by an illumination mode of the lithographic apparatus configured to minimize effects of phase aberration of the lithographic apparatus.
39. A lithographic apparatus comprising:
a patterning device configured to produce a first grating on a substrate by illuminating the patterning device with radiation, the patterning device comprising:
an area with a phase-shift grating periodic in first and second directions and configured to produce in the exit pupil of the lithographic apparatus:
a pair of diffracted orders of the radiation other than the zeroth order, while forbidding any other diffracted orders of the radiation in the exit pupil and
interference fringes formed by interference between the pair of diffracted orders of the radiation, the interference fringes contributing to the definition of the first grating on the substrate.
40. A lithographic apparatus comprising:
a patterning device configured to produce a first grating on a substrate by illuminating the patterning device with radiation, the patterning device comprising:
an area with a phase-shift grating periodic in first and second directions and configured to produce in the exit pupil of the lithographic apparatus:
an allowed diffracted first order of the radiation while forbidding diffraction of another first order and both second orders of the radiation in the exit pupil and
interference fringes formed by interference between a zeroth order of the radiation and the allowed diffracted first order of the radiation, the interference fringes defining the second grating on the substrate.
41. A lithographic apparatus comprising:
a patterning device configured to produce a first grating and a second grating on a substrate by illuminating the patterning device with radiation, the patterning device comprising:
a first area with a first phase-shift grating periodic in first and second directions and configured to produce in the exit pupil of the lithographic apparatus:
a pair of diffracted orders of the radiation other than the zeroth order, while forbidding any other diffracted orders of the radiation in the exit pupil and
interference fringes formed by interference between the pair of diffracted orders of the radiation, the interference fringes contributing to the definition of the first grating on the substrate;
a second area with a second phase-shift grating configured to produce in the exit pupil of the lithographic apparatus:
an allowed diffracted first order of the radiation while forbidding diffraction of another first order and both second orders of the radiation in the exit pupil and
interference fringes formed by interference between a zeroth order of the radiation and the allowed diffracted first order of the radiation, the interference fringes defining the second grating on the substrate.