Abstract

Two basic types of interferometer, a point diffraction interferometer (PDI) and a lateral shearing interferometer (LSI) suitable for operation in the extreme-ultraviolet (EUV) wavelength region, are described. To address the challenges of wavefront measurement with an accuracy of 0.1  nm rms, we present a calibration method for the PDI that places a mask with two large windows at the image plane of the illumination point light source and a general approach to deriving the phase-shift algorithm series that eliminates the undesired zeroth-order effect in the LSI. These approaches to improving the measurement accuracy were experimentally verified by the wavefront measurements of a Schwarzschild-type EUV projection lens.

© 2007 Optical Society of America

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References

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  1. K. A. Goldberg, P. Naulleau, S. H. Lee, C. Chang, C. Bresloff, R. Gaughan, H. N. Chapman, J. Goldsmith, and J. Bokor, "Direct comparison of EUV and visible-light interferometries," Proc. SPIE 3676, 635-642 (1999).
    [CrossRef]
  2. K. A. Goldberg, P. Naulleau, P. Denham, S. B. Rekawa, K. Jackson, J. A. Liddle, and E. H. Anderson, "EUV interferometric testing and alignment of the 0.3 NA MET optic," Proc. SPIE 5374, 64-73 (2004).
    [CrossRef]
  3. S. Kato, C. Ouchi, M. Hasegawa, A. Suzuki, T. Hasegawa, K. Sugisaki, M. Okada, Y. Zhu, K. Murakami, J. Saito, M. Niibe, and M. Takeda, "Comparison of EUV interferometry methods in EUVA project," Proc. SPIE 5751, 110-117 (2005).
    [CrossRef]
  4. Z. Liu, K. Sugisaki, Y. Zhu, M. Ishii, K. Murakami, J. Saito, A. Suzuki, and M. Hasegawa, "Double-grating lateral shearing interferometer for extreme ultraviolet lithography," Jpn. J. Appl. Phys. 43, 3718-3721 (2004).
    [CrossRef]
  5. M. Takeda and S. Kobayashi, "Lateral aberration measurements with a digital Talbot interferometer," Appl. Opt. 23, 1760-1764 (1984).
    [CrossRef] [PubMed]
  6. P. P. Naulleau, K. A. Goldberg, and J. Bokor, "Extreme ultraviolet carrier-frequency shearing interferometry of a lithographic four-mirror optical system," J. Vacuum Sci. Technol. B 18, 2939-2943 (2000).
    [CrossRef]
  7. M. Hasegawa, C. Ouchi, T. Hasegawa, S. Kato, A. Ohkubo, A. Suzuki, K. Sugisaki, M. Okada, K. Otaki, K. Murakami, J. Saito, M. Niibe, and M. Takeda, "Recent progress of EUV wavefront metrology in EUVA," Proc. SPIE 5533, 27-36 (2004).
    [CrossRef]
  8. K. A. Goldberg, "EUV interferometry," Ph.D. dissertation (Univ. of California, Berkeley, 1997).
  9. Y. Zhu and T. Gemma, "Method for designing error-compensating phase-calculation algorithms for phase-shifting interferometry," Appl. Opt. 40, 4540-4546 (2001).
    [CrossRef]
  10. Y. Zhu, K. Sugisaki, K. Murakami, K. Ota, H. Kondo, M. Ishii, J. Kawakami, T. Oshino, J. Saito, A. Suzuki, M. Hasegawa, Y. Sekine, S. Takeuchi, C. Ouchi, O. Kakuchi, and Y. Watanabe, "Shearing interferometry for at wavelength wavefront measurement of extreme-ultraviolet lithography projection optics," Jpn. J. Appl. Phys. Part 1 42, 5844-5847 (2003).
    [CrossRef]

2005

S. Kato, C. Ouchi, M. Hasegawa, A. Suzuki, T. Hasegawa, K. Sugisaki, M. Okada, Y. Zhu, K. Murakami, J. Saito, M. Niibe, and M. Takeda, "Comparison of EUV interferometry methods in EUVA project," Proc. SPIE 5751, 110-117 (2005).
[CrossRef]

2004

Z. Liu, K. Sugisaki, Y. Zhu, M. Ishii, K. Murakami, J. Saito, A. Suzuki, and M. Hasegawa, "Double-grating lateral shearing interferometer for extreme ultraviolet lithography," Jpn. J. Appl. Phys. 43, 3718-3721 (2004).
[CrossRef]

K. A. Goldberg, P. Naulleau, P. Denham, S. B. Rekawa, K. Jackson, J. A. Liddle, and E. H. Anderson, "EUV interferometric testing and alignment of the 0.3 NA MET optic," Proc. SPIE 5374, 64-73 (2004).
[CrossRef]

M. Hasegawa, C. Ouchi, T. Hasegawa, S. Kato, A. Ohkubo, A. Suzuki, K. Sugisaki, M. Okada, K. Otaki, K. Murakami, J. Saito, M. Niibe, and M. Takeda, "Recent progress of EUV wavefront metrology in EUVA," Proc. SPIE 5533, 27-36 (2004).
[CrossRef]

2003

Y. Zhu, K. Sugisaki, K. Murakami, K. Ota, H. Kondo, M. Ishii, J. Kawakami, T. Oshino, J. Saito, A. Suzuki, M. Hasegawa, Y. Sekine, S. Takeuchi, C. Ouchi, O. Kakuchi, and Y. Watanabe, "Shearing interferometry for at wavelength wavefront measurement of extreme-ultraviolet lithography projection optics," Jpn. J. Appl. Phys. Part 1 42, 5844-5847 (2003).
[CrossRef]

2001

2000

P. P. Naulleau, K. A. Goldberg, and J. Bokor, "Extreme ultraviolet carrier-frequency shearing interferometry of a lithographic four-mirror optical system," J. Vacuum Sci. Technol. B 18, 2939-2943 (2000).
[CrossRef]

1999

K. A. Goldberg, P. Naulleau, S. H. Lee, C. Chang, C. Bresloff, R. Gaughan, H. N. Chapman, J. Goldsmith, and J. Bokor, "Direct comparison of EUV and visible-light interferometries," Proc. SPIE 3676, 635-642 (1999).
[CrossRef]

1984

Appl. Opt.

J. Vacuum Sci. Technol. B

P. P. Naulleau, K. A. Goldberg, and J. Bokor, "Extreme ultraviolet carrier-frequency shearing interferometry of a lithographic four-mirror optical system," J. Vacuum Sci. Technol. B 18, 2939-2943 (2000).
[CrossRef]

Jpn. J. Appl. Phys.

Z. Liu, K. Sugisaki, Y. Zhu, M. Ishii, K. Murakami, J. Saito, A. Suzuki, and M. Hasegawa, "Double-grating lateral shearing interferometer for extreme ultraviolet lithography," Jpn. J. Appl. Phys. 43, 3718-3721 (2004).
[CrossRef]

Jpn. J. Appl. Phys. Part 1

Y. Zhu, K. Sugisaki, K. Murakami, K. Ota, H. Kondo, M. Ishii, J. Kawakami, T. Oshino, J. Saito, A. Suzuki, M. Hasegawa, Y. Sekine, S. Takeuchi, C. Ouchi, O. Kakuchi, and Y. Watanabe, "Shearing interferometry for at wavelength wavefront measurement of extreme-ultraviolet lithography projection optics," Jpn. J. Appl. Phys. Part 1 42, 5844-5847 (2003).
[CrossRef]

Proc. SPIE

K. A. Goldberg, P. Naulleau, S. H. Lee, C. Chang, C. Bresloff, R. Gaughan, H. N. Chapman, J. Goldsmith, and J. Bokor, "Direct comparison of EUV and visible-light interferometries," Proc. SPIE 3676, 635-642 (1999).
[CrossRef]

K. A. Goldberg, P. Naulleau, P. Denham, S. B. Rekawa, K. Jackson, J. A. Liddle, and E. H. Anderson, "EUV interferometric testing and alignment of the 0.3 NA MET optic," Proc. SPIE 5374, 64-73 (2004).
[CrossRef]

S. Kato, C. Ouchi, M. Hasegawa, A. Suzuki, T. Hasegawa, K. Sugisaki, M. Okada, Y. Zhu, K. Murakami, J. Saito, M. Niibe, and M. Takeda, "Comparison of EUV interferometry methods in EUVA project," Proc. SPIE 5751, 110-117 (2005).
[CrossRef]

M. Hasegawa, C. Ouchi, T. Hasegawa, S. Kato, A. Ohkubo, A. Suzuki, K. Sugisaki, M. Okada, K. Otaki, K. Murakami, J. Saito, M. Niibe, and M. Takeda, "Recent progress of EUV wavefront metrology in EUVA," Proc. SPIE 5533, 27-36 (2004).
[CrossRef]

Other

K. A. Goldberg, "EUV interferometry," Ph.D. dissertation (Univ. of California, Berkeley, 1997).

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Figures (9)

Fig. 1
Fig. 1

Configurations of our experimental systems. (a) PDI: The second window transmits the first-order beam containing aberrations caused by the test optics and the second pinhole diffracts the zeroth-order beam and generates a spherical wavefront, which is used as a reference wavefront in the PDI. (b) LSI: The two windows on the mask transmit ± 1 st -order diffracted waves. Both of them carry the aberration information of the test optics but laterally shifted by a small amount. The original and the displaced test wavefronts produced the interference pattern in lateral shearing interferometry.

Fig. 2
Fig. 2

Illustration of the calibration principle for the PDI: Two measurements were carried out by using two different mask patterns. Subtracting one measurement from the other, the result is the direct comparison between the wavefront aberration of the test optics and the ideal wavefront diffracted from the small pinhole.

Fig. 3
Fig. 3

Illustrating that, although the order-selective window is designed to only pass the test beam, i.e., the 1st- (or the 1 st -) order diffraction beam, the 0th-order noise beam could spread and pass through the order-selective window, too; therefore it interferes with the test beam and as a result it reduces the measurement accuracy.

Fig. 4
Fig. 4

Experimental setup: The beam coming from the undulator is focused on the first pinhole mask placed at the object plane of the test optic by a Schwarzschild-type illuminator. The EEI has five piezostages for precise alignment of optical components such as pinhole masks and gratings. Each mask and grating contains many different patterns and gratings for the different types of interferometer.

Fig. 5
Fig. 5

Comparisons between two different calibration methods: The agreement between these two different methods confirmed our proposed calibration principle experimentally as the rotation method is generally considered one with high accuracy and reliability. The 9th, 16th, and 25th Zernike orders are not compared due to their axial symmetry. The 17th, 18th, 28th, and 29th orders are not compared due to the choice of rotation angle of 90°. (a) Systematic aberration errors expressed in Zernike polynomials measured by the two different calibration methods (sys-rot: obtained by the rotation method; sys-w-w: obtained by the proposed method in this paper). (b) Differences between the systematic errors in the PDI measured by these two different calibration methods.

Fig. 6
Fig. 6

Larger deviations among the measurements before calibration are considered mainly due to the different systematic errors in the different PDI structure. The consistency in the results after employing our proposed calibration method indicates the achievable calibration accuracy experimentally. (a) Measured wavefronts on an EEI based on the configuration of the Fig. 1(a) PDI before calibration. (b) Measured wavefronts on an EEI based on the configuration of the Fig. 2 PDI after calibration.

Fig. 7
Fig. 7

Measured wavefronts on an EEI to illustrate the principle of the calibration method described in Section 3. Some of the wavefronts expressed in Zernike coefficients have appeared in Figs. 6(a) and 6(b).

Fig. 8
Fig. 8

Measured interferometric fringes of the LSI on an EEI used in the comparisons of different algorithms to verify that Eq. (10) itself is sufficient to eliminate the zeroth-order beam effect as its principle implied. (a) Example of the measured fringe of the LSI [Fig. 1(b)] with the zeroth-order noise beam effect remaining. (b) Example of the measured fringe of the LSI where the zeroth-order noise beam was partially removed by the Fourier transform method for comparison.

Fig. 9
Fig. 9

Measured wavefront differences obtained from two sets of interferograms shown in Figs. 8(a) and 8(b) using Eqs. (10) and (16), respectively. The difference when Eq. (10) was applied was much smaller than the case when Eq. (16) was applied. It experimentally indicated that the measurement accuracy was less affected by the zeroth-order noise beam when Eq. (10) was applied.

Equations (16)

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T 1 = ( W T 1 + W R 1 ) + W S Y S 1 W R 0 ,
T 2 = ( W T 1 + W R 1 ) + W S Y S 1 ( W T 0 + W R 0 ) ,
W 3 = T 1 T 2 = W T 0 .
W 3 Δ = W T 0 1 = W T 1 .
W 4 = T 1 W 3 Δ = W S Y S 1 + ( W R 1 W R 0 ) .
g 0 = a 0 2 + a 1 2 + a 1 2 + 2 a 0 a 1   cos [ k ( W 1 W 0 ) ] + 2 a 0 a 1   cos [ k ( W 0 W 1 ) ] + 2 a 1 a 1  cos [ k ( W 1 W 1 ) ] ,
Δ ϕ = 2 π m Δ x / p ,
( g 3 g 3 ) ( g 1 g 1 ) = 8 a 1 a 1   sin [ k ( W 1 W 1 ) ] ,
( g 4 + g 4 ) / 2 ( g 2 + g 2 ) + g 0 = 8 a 1 a 1   cos [ k ( W 1 W 1 ) ] ,
k ( W 1 W 1 ) = tan 1 [ 2 ( g 3 g 3 ) 2 ( g 1 g 1 ) ( g 4 + g 4 ) 2 ( g 2 + g 2 ) + 2 g 0 ] .
k ( W 1 W 1 ) = tan 1 [ m = 0 N [ 2 ( g 4 m + 3 g ( 4 m + 3 ) ) 2 ( g 4 m + 1 g ( 4 m + 1 ) ) ] m = 0 N [ ( g 4 m + 4 + g ( 4 m + 4 ) ) 2 ( g 4 m + 2 + g ( 4 m + 2 ) ) + ( g 4 m + g 4 m ) ] ] ,
T 2 R = ( W T 1 R + W R 1 ) + W S Y S 1 W R 0 ,
W 5 = ( W T 1 + W R 1 R ) + W S Y S 1 R W R 0 R
T 1 W 5 = ( W S Y S 1 W S Y S 1 R ) + ( W R 1 W R 0 ) ( W R 1 R W R 0 R ) .
W 6 = W S Y S 1 + ( W R 1 W R 0 ) .
k ( W 1 W 1 ) = tan 1 [ 26 ( g 1 g 1 ) 6 ( g 3 g 3 ) 16 ( g 2 + g 2 ) ( g 4 + g 4 ) 30 g 0 ] .

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