Abstract

The role of Mo/Si reflective coatings in the imaging performance of an extreme-ultraviolet projection lithography system under polychromatic illumination has been theoretically examined. Using a thin-film computer model, we have explored various multilayer design criteria. Optimum operating conditions, leading to the maximum system transmittance, were found for a tuned multilayer system operating at λ = 12.7 nm. In this configuration, Mo/Si coatings have been shown to be nondetrimental to the imaging performance of our system with the introduction of only minor modifications to the propagating wave front, which can be adequately described by a simple tilt and defocus term.

© 1998 Optical Society of America

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References

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  1. T. Jewell, J. M. Rodgers, K. P. Thompson, “Reflective systems design study for soft-x-ray projection lithography,” J. Vac. Technol. B 8, 1519–1523 (1990).
    [CrossRef]
  2. N. J. Duddles, “Optical performance of Mo/Si multilayer coatings in the EUV: implications for EUV imaging,” submitted to Appl. Opt. (1997).
  3. H. Yamanashi, M. Ito, “Image simulation of extreme ultraviolet lithography optics: effect of multilayer coatings,” Jpn. J. Appl. Phys. 35, 6475–6479 (1996).
    [CrossRef]
  4. B. Lai, F. Cerrina, J. H. Underwood, “Image formation in multilayers optics: the Schwartzschild objective,” in Applications of Thin Film Multilayered Structures to Figured X-Ray Optics, G. F. Marshall, ed., Proc. SPIE563, 174–179 (1985).
    [CrossRef]
  5. W. C. Sweatt, “Condenser for illuminating a ring field,” U.S. patent5,361,292 (1November1994).
  6. Optical constants compiled by B. L. Henke, E. M. Gullickson, J. C. Davis and held at the Center for X-ray Optics (CXRO), Lawrence Berkley National Laboratory. Accessed through http://www-cxro.lbl.gov/optical constants (1997).
  7. The computer program code v is available commercially from Optical Research Associates, Pasadena, Calif.
  8. D. G. Stearns, R. S. Rosen, S. P. Vernon, “Multilayer mirror technology for soft-x-ray projection lithography,” Appl. Opt. 32, 6952–6960 (1993).
    [CrossRef] [PubMed]

1996 (1)

H. Yamanashi, M. Ito, “Image simulation of extreme ultraviolet lithography optics: effect of multilayer coatings,” Jpn. J. Appl. Phys. 35, 6475–6479 (1996).
[CrossRef]

1993 (1)

1990 (1)

T. Jewell, J. M. Rodgers, K. P. Thompson, “Reflective systems design study for soft-x-ray projection lithography,” J. Vac. Technol. B 8, 1519–1523 (1990).
[CrossRef]

Cerrina, F.

B. Lai, F. Cerrina, J. H. Underwood, “Image formation in multilayers optics: the Schwartzschild objective,” in Applications of Thin Film Multilayered Structures to Figured X-Ray Optics, G. F. Marshall, ed., Proc. SPIE563, 174–179 (1985).
[CrossRef]

Duddles, N. J.

N. J. Duddles, “Optical performance of Mo/Si multilayer coatings in the EUV: implications for EUV imaging,” submitted to Appl. Opt. (1997).

Ito, M.

H. Yamanashi, M. Ito, “Image simulation of extreme ultraviolet lithography optics: effect of multilayer coatings,” Jpn. J. Appl. Phys. 35, 6475–6479 (1996).
[CrossRef]

Jewell, T.

T. Jewell, J. M. Rodgers, K. P. Thompson, “Reflective systems design study for soft-x-ray projection lithography,” J. Vac. Technol. B 8, 1519–1523 (1990).
[CrossRef]

Lai, B.

B. Lai, F. Cerrina, J. H. Underwood, “Image formation in multilayers optics: the Schwartzschild objective,” in Applications of Thin Film Multilayered Structures to Figured X-Ray Optics, G. F. Marshall, ed., Proc. SPIE563, 174–179 (1985).
[CrossRef]

Rodgers, J. M.

T. Jewell, J. M. Rodgers, K. P. Thompson, “Reflective systems design study for soft-x-ray projection lithography,” J. Vac. Technol. B 8, 1519–1523 (1990).
[CrossRef]

Rosen, R. S.

Stearns, D. G.

Sweatt, W. C.

W. C. Sweatt, “Condenser for illuminating a ring field,” U.S. patent5,361,292 (1November1994).

Thompson, K. P.

T. Jewell, J. M. Rodgers, K. P. Thompson, “Reflective systems design study for soft-x-ray projection lithography,” J. Vac. Technol. B 8, 1519–1523 (1990).
[CrossRef]

Underwood, J. H.

B. Lai, F. Cerrina, J. H. Underwood, “Image formation in multilayers optics: the Schwartzschild objective,” in Applications of Thin Film Multilayered Structures to Figured X-Ray Optics, G. F. Marshall, ed., Proc. SPIE563, 174–179 (1985).
[CrossRef]

Vernon, S. P.

Yamanashi, H.

H. Yamanashi, M. Ito, “Image simulation of extreme ultraviolet lithography optics: effect of multilayer coatings,” Jpn. J. Appl. Phys. 35, 6475–6479 (1996).
[CrossRef]

Appl. Opt. (1)

J. Vac. Technol. B (1)

T. Jewell, J. M. Rodgers, K. P. Thompson, “Reflective systems design study for soft-x-ray projection lithography,” J. Vac. Technol. B 8, 1519–1523 (1990).
[CrossRef]

Jpn. J. Appl. Phys. (1)

H. Yamanashi, M. Ito, “Image simulation of extreme ultraviolet lithography optics: effect of multilayer coatings,” Jpn. J. Appl. Phys. 35, 6475–6479 (1996).
[CrossRef]

Other (5)

B. Lai, F. Cerrina, J. H. Underwood, “Image formation in multilayers optics: the Schwartzschild objective,” in Applications of Thin Film Multilayered Structures to Figured X-Ray Optics, G. F. Marshall, ed., Proc. SPIE563, 174–179 (1985).
[CrossRef]

W. C. Sweatt, “Condenser for illuminating a ring field,” U.S. patent5,361,292 (1November1994).

Optical constants compiled by B. L. Henke, E. M. Gullickson, J. C. Davis and held at the Center for X-ray Optics (CXRO), Lawrence Berkley National Laboratory. Accessed through http://www-cxro.lbl.gov/optical constants (1997).

The computer program code v is available commercially from Optical Research Associates, Pasadena, Calif.

N. J. Duddles, “Optical performance of Mo/Si multilayer coatings in the EUV: implications for EUV imaging,” submitted to Appl. Opt. (1997).

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Figures (6)

Fig. 1
Fig. 1

Schematic diagram showing the imaging optics of the EUVL system.

Fig. 2
Fig. 2

Spectral response of a common and tuned ML system after propagating through the primary and the imaging optics. Both systems have been optimized for maximum transmittance at λ p = 12.7 nm.

Fig. 3
Fig. 3

Transmittance of chief ray f 2 through the primary and the imaging optics as a function of wavelength of operation λ p . Results are shown for both (a) peak and (b) integrated transmittance for both tuned and common ML systems.

Fig. 4
Fig. 4

Phase map of the exit pupil f 1 at 12.7 nm for (a) the bare system and (b) the tuned ML system with λ p = 12.7 nm. Phase is expressed here in units of wavelength, and pupil dimensions are given as relative coordinates.

Fig. 5
Fig. 5

Comparison between the distortion in the image field for the tuned ML system and a system assuming perfectly reflecting mirrors (╍) calculated at various wavelengths bounded by the transmittance curve (——). Results are shown from exit pupils derived from tracing both y-(┅) and x-(——) polarized light.

Fig. 6
Fig. 6

Calculated MTF [at f 1, f 2, and f 3 in (a), (b), and (c), respectively] for both the bare and the tuned ML systems. In the former case solid and dotted curves represent meridional and sagittal MTF’s, respectively. Meridional and sagittal MTF’s for the tuned ML system (λ p = 12.7 nm) are represented by ◯ and +, respectively.

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