Abstract

Substrates intended for use as extreme-ultraviolet (EUV) optics have extremely stringent requirements in terms of finish. These requirements can dramatically increase the cost and fabrication time, especially when nonconventional shapes, such as toroids, are required. Here we present a spin-on-glass resist process capable of generating superpolished parts from inexpensive substrates. The method has been used to render diamond-turned substrates compatible for use as EUV optics. Toroidal diamond-turned optics with starting rms roughness in the 3.33.7  nm range have been smoothed to the 0.40.6nm range. EUV reflectometry characterization of these optics has demonstrated reflectivities of approximately 65%.

© 2006 Optical Society of America

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References

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  1. R. Stulen and D. Sweeney, "Extreme ultraviolet lithography," IEEE J. Quantum Electron. 35, 694-699 (1999).
    [CrossRef]
  2. H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).
  3. K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).
  4. R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).
  5. F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
    [CrossRef]
  6. P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
    [CrossRef]
  7. P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
    [CrossRef]
  8. P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
    [CrossRef]
  9. The copper diamond-turned optic was manufactured by RPM Opto Electronics, Santa Rosa, Calif.
  10. The aluminum diamond-turned optic was manufactured by Nu-Tek Precision Optical Corporation, Aberdeen, Md.
  11. J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).
  12. ZYGO Corporation, Middlefield, Conn.

2004 (1)

P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
[CrossRef]

2003 (1)

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

2001 (1)

P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
[CrossRef]

2000 (1)

F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
[CrossRef]

1999 (1)

R. Stulen and D. Sweeney, "Extreme ultraviolet lithography," IEEE J. Quantum Electron. 35, 694-699 (1999).
[CrossRef]

1996 (1)

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Anderson, E.

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
[CrossRef]

Baker, S.

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Batson, P. J.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Benschop, J.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Bokor, J.

P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
[CrossRef]

Denham, P.

P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
[CrossRef]

Denham, P. E.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Franck, K. D.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Geyl, R.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Gullikson, E.

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
[CrossRef]

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Gullikson, E. M.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Hada, H.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Hamamoto, K.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Harned, N.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Hartman, R.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Hoef, B.

P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
[CrossRef]

Hoghoj, P.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Johnson, M.

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Kinoshita, H.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Kishimura, S.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Koike, M.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Komano, H.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Kürz, P.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Liddle, J.

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

Meiling, H.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

Mirkarimi, P.

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

Naulleau, P.

P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
[CrossRef]

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
[CrossRef]

Okazaki, S.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Ratti, S.

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Rekawa, S.

P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
[CrossRef]

Robbinson, J.

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Romijn, H.

F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
[CrossRef]

Salmassi, F.

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

Schmidt, M.

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Soufli, R.

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Spiller, E.

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

Steele, W. F.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Stulen, R.

R. Stulen and D. Sweeney, "Extreme ultraviolet lithography," IEEE J. Quantum Electron. 35, 694-699 (1999).
[CrossRef]

Sweeney, D.

R. Stulen and D. Sweeney, "Extreme ultraviolet lithography," IEEE J. Quantum Electron. 35, 694-699 (1999).
[CrossRef]

Tackaberry, R. E.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Underwood, J. H.

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

van Delft, F.

F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
[CrossRef]

van Langen-Suurling, A.

F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
[CrossRef]

Watanabe, T.

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

Weterings, J.

F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
[CrossRef]

IEEE J. Quantum Electron. (1)

R. Stulen and D. Sweeney, "Extreme ultraviolet lithography," IEEE J. Quantum Electron. 35, 694-699 (1999).
[CrossRef]

J. Vac. Sci. Technol. B (1)

F. van Delft, J. Weterings, A. van Langen-Suurling, and H. Romijn, "Hydrogen silsesquioxane/novolak bilayer resist for high aspect ratio nanoscale electron-beam lithography," J. Vac. Sci. Technol. B 18, 3419-3423 (2000).
[CrossRef]

Opt. Commun. (3)

P. Naulleau, E. Anderson, E. Gullikson, and J. Bokor, "Fabrication of high-efficiency multilayer-coated binary blazed gratings in the EUV regime," Opt. Commun. 200, 27-34 (2001).
[CrossRef]

P. Naulleau, J. Liddle, E. Anderson, E. Gullikson, P. Mirkarimi, F. Salmassi, and E. Spiller, "Fabrication of high-efficiency multilayer-coated gratings for the EUV regime using e-beam patterned substrates," Opt. Commun. 229, 109-116 (2003).
[CrossRef]

P. Naulleau, P. Denham, B. Hoef, and S. Rekawa, "A design study for synchrotron-based high-numerical-aperture scanning illuminators," Opt. Commun. 234, 53-62 (2004).
[CrossRef]

Rev. Sci. Instrum. (1)

J. H. Underwood, E. M. Gullikson, M. Koike, P. J. Batson, P. E. Denham, K. D. Franck, R. E. Tackaberry, and W. F. Steele, Rev. Sci. Instrum. 9, 1-5 (1996).

Other (6)

ZYGO Corporation, Middlefield, Conn.

The copper diamond-turned optic was manufactured by RPM Opto Electronics, Santa Rosa, Calif.

The aluminum diamond-turned optic was manufactured by Nu-Tek Precision Optical Corporation, Aberdeen, Md.

H. Meiling, J. Benschop, R. Hartman, P. Kürz, P. Hoghoj, R. Geyl, and N. Harned, "EXSTATIC: ASML's a-tool development for EUVL," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 1-10 (2002).

K. Hamamoto, T. Watanabe, H. Hada, H. Komano, S. Kishimura, S. Okazaki, and H. Kinoshita, "Fine pattern replication on 10 × 10-mm exposure area using the ETS-1 laboratory tool in HIT," in Emerging Lithographic Technologies VI, R.L.Engelstad, ed., Proc. SPIE 4688, 664-671 (2002).

R. Soufli, E. Spiller, M. Schmidt, J. Robbinson, S. Baker, S. Ratti, M. Johnson, and E. Gullikson, "Smoothing of diamond-turned substrates for extreme ultraviolet lithography illuminators," in Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications, A.M.Khounsary, U.Dinger, and K.Ota, eds., Proc. SPIE 5193, 98-104 (2004).

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Figures (4)

Fig. 1
Fig. 1

Atomic-force microscope (AFM) images of diamond-turned toroidal optics before and after HSQ-based smoothing. (a), (b) Aluminum and copper optics, respectively, before smoothing. (c), (d) The same aluminum and copper optics, respectively, after smoothing. (e) The same AFM image as in (c) but rescaled to accentuate the surface features.

Fig. 2
Fig. 2

Power spectral density (PSD) of the roughness before and after smoothing for the (a) aluminum and (b) copper optics.

Fig. 3
Fig. 3

Frequency-dependent smoothing factor (or transfer function) for the aluminum and copper optics. In both cases the smoothing efficiency starts to roll off at an approximately 25 μm period; however, the smoothing is observed to be more effective on aluminum in the period range 25–1 μm.

Fig. 4
Fig. 4

Interferometric figure-error test results. (a), (b) Measured surface figure of the spherical test optic before and after smoothing, respectively. The large bumps common to (a) and (b) are alignment fiducials. (b) The smoothed optic additionally shows a series of imperfections arising from particulate contamination. (c) Direct point-by-point difference between (a) and (b). (d) low-pass filtered version of the difference, eliminating the effect of the contamination while preserving as many as ∼6 cycles across the optic. The added figure error is 2.7 nm, and the maximum slope error is 4.3 μrad.

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