Abstract

We have built an adaptive system capable of detecting submicrometer defects in periodic structures by using real-time holography in photorefractive crystals. We summarize the design and optimization of the defect-enhancement system. We present representative results of 0.2- to 0.5-μm diameter defect detection on two different periodic substrates: chrome-on-glass masks and patterned silicon wafers. On patterned silicon we detect 94% of the 0.5-μm diameter defects with three false positives, while inspecting an area greater than 1 mm2 in 20 s or less. The throughput on the glass masks is somewhat less. To the best of our knowledge, these defects have an area 100 times smaller than those previously detected with any real-time holographic technique.

© 1994 Optical Society of America

Full Article  |  PDF Article

References

  • View by:
  • |
  • |
  • |

  1. B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
    [CrossRef]
  2. R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).
  3. E. Ochoa, J. W. Goodman, L. Hesselink, “Real-time enhancement of defects in a periodic mask using photorefractive Bi12SiO20,” Opt. Lett. 10, 430–432 (1985).
    [CrossRef] [PubMed]
  4. J. O. White, A. Yariv, “Real-time image processing via four-wave mixing in a photorefractive medium,” Appl. Phys. Lett. 37, 5–7 (1980).
    [CrossRef]
  5. L. Pichon, J. P. Huignard, “Dynamic joint-Fourier-transform correlator by Bragg diffraction in photorefractive B12SiO20 crystals,” Opt. Commun. 36, 277–280 (1981).
    [CrossRef]
  6. M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).
  7. L. H. Lin, D. L. Cavan, R. B. Howe, R. E. Graves, “A holographic photomask defect inspection system,” in Optical Microlithography IV, H. L. Stover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.538, 110–116 (1985).
  8. D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
    [CrossRef]
  9. A. P. Ghosh, R. R. Dube, “Real-time defect inspection of periodic patterns using self-pumped barium titanate crystal,” Opt. Commun. 77, 135–138 (1990).
    [CrossRef]
  10. C. J. Gaeta, P. V. Mitchell, D. M. Pepper, “Real-time defect enhancement diagnostic system using a spatial light modulator and a phase-conjugate mirror,” in OSA Annual Meeting, Vol. 17 of 1991 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1991), paper THI6.
  11. C. Uhrich, L. Hesselink, “Optical surface inspection using real time Fourier transform holography in photorefractives,” Appl. Opt. 27, 4497–4503 (1988).
    [CrossRef] [PubMed]
  12. M. A. Taubenblatt, J. B. Batchelder, “Patterned wafer inspection using spatial filtering for the cluster environment,” Appl. Opt. 31, 3354–3362 (1992).
    [CrossRef] [PubMed]
  13. C. Uhrich, L. Hesselink, “Submicrometer defect enhancement in periodic structures by using photorefractive holography,” Opt. Lett. 17, 1087–1089 (1992).
    [CrossRef] [PubMed]
  14. T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
    [CrossRef]
  15. N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
    [CrossRef]
  16. H. Kogelnik, “Coupled wave theory for thick hologram gratings,” Bell Syst. Tech. J. 48, 2909–2947 (1969).
  17. F. Vachss, L. Hesselink, “Holographic beam coupling in anisotropic photorefractive media,” J. Opt. Soc. Am. A 4, 325–339 (1987).
    [CrossRef]
  18. A. Marrakchi, R. V. Johnson, A. R. Tanguary, “Polarization properties of photorefractive diffraction in electrooptic and optically active sillenite crystals (Bragg regime),” J. Opt. Soc. Am. B 3, 321–336 (1986).
    [CrossRef]
  19. J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, San Francisco, Calif.1968), pp. 77–90.
  20. R. N. Bracewell, Fourier Transform and Its Applications (McGraw-Hill, New York, 1986), p. 214.
  21. M. Born, E. Wolf, Principles of Optics, 6th ed., (Pergamon, Oxford, 1980), p. 441.
  22. G. Videen, “Light scattering from a sphere on or near a surface,” J. Opt. Soc. Am. A 8, 483–489 (1991); J. Opt. Soc. Am. A 9, 844–845 (1991).
    [CrossRef]
  23. G. L. Wojcik, D. K. Vaughan, L. K. Galbraith, “Calculation of light scatter from structures on silicon surfaces,” in Lasers in Microlithography, J. S. Batchelder, D. J. Ehrlich, J. Y. Tsao, eds., Proc. Soc. Photo-Opt. Instrum. Eng.774, 21–31 (1987).

1992

1991

1990

A. P. Ghosh, R. R. Dube, “Real-time defect inspection of periodic patterns using self-pumped barium titanate crystal,” Opt. Commun. 77, 135–138 (1990).
[CrossRef]

1988

C. Uhrich, L. Hesselink, “Optical surface inspection using real time Fourier transform holography in photorefractives,” Appl. Opt. 27, 4497–4503 (1988).
[CrossRef] [PubMed]

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

1987

F. Vachss, L. Hesselink, “Holographic beam coupling in anisotropic photorefractive media,” J. Opt. Soc. Am. A 4, 325–339 (1987).
[CrossRef]

M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).

1986

1985

T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
[CrossRef]

R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).

E. Ochoa, J. W. Goodman, L. Hesselink, “Real-time enhancement of defects in a periodic mask using photorefractive Bi12SiO20,” Opt. Lett. 10, 430–432 (1985).
[CrossRef] [PubMed]

1981

L. Pichon, J. P. Huignard, “Dynamic joint-Fourier-transform correlator by Bragg diffraction in photorefractive B12SiO20 crystals,” Opt. Commun. 36, 277–280 (1981).
[CrossRef]

1980

J. O. White, A. Yariv, “Real-time image processing via four-wave mixing in a photorefractive medium,” Appl. Phys. Lett. 37, 5–7 (1980).
[CrossRef]

1979

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

1969

H. Kogelnik, “Coupled wave theory for thick hologram gratings,” Bell Syst. Tech. J. 48, 2909–2947 (1969).

Batchelder, J. B.

Batchelder, J. S.

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

Bonner, R.

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

Born, M.

M. Born, E. Wolf, Principles of Optics, 6th ed., (Pergamon, Oxford, 1980), p. 441.

Bracewell, R. N.

R. N. Bracewell, Fourier Transform and Its Applications (McGraw-Hill, New York, 1986), p. 214.

Brecher, V. H.

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

Cavan, D. L.

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

L. H. Lin, D. L. Cavan, R. B. Howe, R. E. Graves, “A holographic photomask defect inspection system,” in Optical Microlithography IV, H. L. Stover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.538, 110–116 (1985).

Connors, L. M.

T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
[CrossRef]

Cooper, I. R.

M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).

Dom, B. E.

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

Dube, R. R.

A. P. Ghosh, R. R. Dube, “Real-time defect inspection of periodic patterns using self-pumped barium titanate crystal,” Opt. Commun. 77, 135–138 (1990).
[CrossRef]

Foote, P. D.

T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
[CrossRef]

Fusek, R. L.

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).

Gaeta, C. J.

C. J. Gaeta, P. V. Mitchell, D. M. Pepper, “Real-time defect enhancement diagnostic system using a spatial light modulator and a phase-conjugate mirror,” in OSA Annual Meeting, Vol. 17 of 1991 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1991), paper THI6.

Galbraith, L. K.

G. L. Wojcik, D. K. Vaughan, L. K. Galbraith, “Calculation of light scatter from structures on silicon surfaces,” in Lasers in Microlithography, J. S. Batchelder, D. J. Ehrlich, J. Y. Tsao, eds., Proc. Soc. Photo-Opt. Instrum. Eng.774, 21–31 (1987).

Ghosh, A. P.

A. P. Ghosh, R. R. Dube, “Real-time defect inspection of periodic patterns using self-pumped barium titanate crystal,” Opt. Commun. 77, 135–138 (1990).
[CrossRef]

Gibbons, G. G.

M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).

Goodman, J. W.

Graves, R. E.

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

L. H. Lin, D. L. Cavan, R. B. Howe, R. E. Graves, “A holographic photomask defect inspection system,” in Optical Microlithography IV, H. L. Stover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.538, 110–116 (1985).

Gustafson, S.

R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).

Hall, T. J.

T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
[CrossRef]

Harding, K.

R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).

Hesselink, L.

Howe, R. B.

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

L. H. Lin, D. L. Cavan, R. B. Howe, R. E. Graves, “A holographic photomask defect inspection system,” in Optical Microlithography IV, H. L. Stover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.538, 110–116 (1985).

Huignard, J. P.

L. Pichon, J. P. Huignard, “Dynamic joint-Fourier-transform correlator by Bragg diffraction in photorefractive B12SiO20 crystals,” Opt. Commun. 36, 277–280 (1981).
[CrossRef]

Jaffe, R. S.

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

Jaura, R.

T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
[CrossRef]

Johnson, R. V.

Kogelnik, H.

H. Kogelnik, “Coupled wave theory for thick hologram gratings,” Bell Syst. Tech. J. 48, 2909–2947 (1969).

Kukhtarev, N. V.

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

Lin, L. H.

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).

L. H. Lin, D. L. Cavan, R. B. Howe, R. E. Graves, “A holographic photomask defect inspection system,” in Optical Microlithography IV, H. L. Stover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.538, 110–116 (1985).

Markov, V. B.

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

Marrakchi, A.

Mitchell, P. V.

C. J. Gaeta, P. V. Mitchell, D. M. Pepper, “Real-time defect enhancement diagnostic system using a spatial light modulator and a phase-conjugate mirror,” in OSA Annual Meeting, Vol. 17 of 1991 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1991), paper THI6.

Nicholson, M. G.

M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).

Ochoa, E.

Odulov, S. G.

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

Pepper, D. M.

C. J. Gaeta, P. V. Mitchell, D. M. Pepper, “Real-time defect enhancement diagnostic system using a spatial light modulator and a phase-conjugate mirror,” in OSA Annual Meeting, Vol. 17 of 1991 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1991), paper THI6.

Petts, C. R.

M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).

Pichon, L.

L. Pichon, J. P. Huignard, “Dynamic joint-Fourier-transform correlator by Bragg diffraction in photorefractive B12SiO20 crystals,” Opt. Commun. 36, 277–280 (1981).
[CrossRef]

Soskin, M. S.

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

Tanguary, A. R.

Taubenblatt, M. A.

Uhrich, C.

Vachss, F.

Vaughan, D. K.

G. L. Wojcik, D. K. Vaughan, L. K. Galbraith, “Calculation of light scatter from structures on silicon surfaces,” in Lasers in Microlithography, J. S. Batchelder, D. J. Ehrlich, J. Y. Tsao, eds., Proc. Soc. Photo-Opt. Instrum. Eng.774, 21–31 (1987).

Videen, G.

Vinetskii, V. L.

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

White, J. O.

J. O. White, A. Yariv, “Real-time image processing via four-wave mixing in a photorefractive medium,” Appl. Phys. Lett. 37, 5–7 (1980).
[CrossRef]

Wojcik, G. L.

G. L. Wojcik, D. K. Vaughan, L. K. Galbraith, “Calculation of light scatter from structures on silicon surfaces,” in Lasers in Microlithography, J. S. Batchelder, D. J. Ehrlich, J. Y. Tsao, eds., Proc. Soc. Photo-Opt. Instrum. Eng.774, 21–31 (1987).

Wolf, E.

M. Born, E. Wolf, Principles of Optics, 6th ed., (Pergamon, Oxford, 1980), p. 441.

Yariv, A.

J. O. White, A. Yariv, “Real-time image processing via four-wave mixing in a photorefractive medium,” Appl. Phys. Lett. 37, 5–7 (1980).
[CrossRef]

Appl. Opt.

Appl. Phys. Lett.

J. O. White, A. Yariv, “Real-time image processing via four-wave mixing in a photorefractive medium,” Appl. Phys. Lett. 37, 5–7 (1980).
[CrossRef]

Bell Syst. Tech. J.

H. Kogelnik, “Coupled wave theory for thick hologram gratings,” Bell Syst. Tech. J. 48, 2909–2947 (1969).

Ferroelectrics

N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, V. L. Vinetskii, “Holographic storage in electrooptic crystals I. Steady state,” Ferroelectrics 22, 949–960 (1979).
[CrossRef]

J. Opt. Soc. Am. A

J. Opt. Soc. Am. B

J. Vac. Sci. Technol. B

D. L. Cavan, L. H. Lin, R. B. Howe, R. E. Graves, R. L. Fusek, “Patterned wafer inspection using laser holography and spatial frequency filtering.” J. Vac. Sci. Technol. B 6, 1934–1939 (1988).
[CrossRef]

Mach. Vis. Appl.

B. E. Dom, V. H. Brecher, R. Bonner, J. S. Batchelder, R. S. Jaffe, “The P300: a system for automatic patterned wafer inspection,” Mach. Vis. Appl. 1, 205–211 (1988).
[CrossRef]

Opt. Commun.

A. P. Ghosh, R. R. Dube, “Real-time defect inspection of periodic patterns using self-pumped barium titanate crystal,” Opt. Commun. 77, 135–138 (1990).
[CrossRef]

L. Pichon, J. P. Huignard, “Dynamic joint-Fourier-transform correlator by Bragg diffraction in photorefractive B12SiO20 crystals,” Opt. Commun. 36, 277–280 (1981).
[CrossRef]

Opt. Eng.

M. G. Nicholson, I. R. Cooper, G. G. Gibbons, C. R. Petts, “Optimization of an updatable optical image correlator,” Opt. Eng. 26, 445–452 (1987).

R. L. Fusek, L. H. Lin, K. Harding, S. Gustafson, “Holographic optical processing for submicrometer defect detection,” Opt. Eng. 24, 731–734 (1985).

Opt. Lett.

Prog. Quantum Electron.

T. J. Hall, R. Jaura, L. M. Connors, P. D. Foote, “The photorefractive effect—a review,” Prog. Quantum Electron. 10, 77–146 (1985).
[CrossRef]

Other

J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, San Francisco, Calif.1968), pp. 77–90.

R. N. Bracewell, Fourier Transform and Its Applications (McGraw-Hill, New York, 1986), p. 214.

M. Born, E. Wolf, Principles of Optics, 6th ed., (Pergamon, Oxford, 1980), p. 441.

C. J. Gaeta, P. V. Mitchell, D. M. Pepper, “Real-time defect enhancement diagnostic system using a spatial light modulator and a phase-conjugate mirror,” in OSA Annual Meeting, Vol. 17 of 1991 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1991), paper THI6.

L. H. Lin, D. L. Cavan, R. B. Howe, R. E. Graves, “A holographic photomask defect inspection system,” in Optical Microlithography IV, H. L. Stover, ed., Proc. Soc. Photo-Opt. Instrum. Eng.538, 110–116 (1985).

G. L. Wojcik, D. K. Vaughan, L. K. Galbraith, “Calculation of light scatter from structures on silicon surfaces,” in Lasers in Microlithography, J. S. Batchelder, D. J. Ehrlich, J. Y. Tsao, eds., Proc. Soc. Photo-Opt. Instrum. Eng.774, 21–31 (1987).

Cited By

OSA participates in CrossRef's Cited-By Linking service. Citing articles from OSA journals and other participating publishers are listed here.

Alert me when this article is cited.


Figures (17)

Fig. 1
Fig. 1

Schematic representation of the basic photorefractive defect-enhancement system. A transparent object is shown for simplicity.

Fig. 2
Fig. 2

Modulation depth versus recording-beam ratio inside the crystal.

Fig. 3
Fig. 3

Space charge field amplitude (solid curve and left axis) and exposure factor (dashed curve and right axis) for BSO crystal. Bottom axes indicate the magnitude of the grating vector and the grating period (on a log scale). The top axis indicates the half-angle (in air) between 514.5-nm writing beams, assuming they are incident symmetrically about the crystal face normal.

Fig. 4
Fig. 4

Relative diffraction efficiency versus angular detuning for 11-mm-thick BSO crystal: A; linear polarized readout in the absence of optical activity; B, linear polarized readout with optical activity of 36°/mm; C, circularly polarized readout with optical activity of 36°/mm.

Fig. 5
Fig. 5

Defect-enhanced image of a 2 mm by 2 mm periodic region showing reconstruction of the sidelobes of each periodic pattern spike as evident by the bright edges of the periodic region. Defects shown have areas of 6 μm2 and 2 μm2; the vertical lines are also errors in the periodic pattern.

Fig. 6
Fig. 6

Plot of defect signal (calculated by integrating m2 over the crystal face) versus fFT.

Fig. 7
Fig. 7

Expanded view of the important components in the defect-enhancement system. In practice the object is as close to the Fourier-transform lens as possible. Small letters (H, V, L, R) indicate the polarization of each ray. FTL, Fourier-transform lens; MO, microscope objective; BSO, Bi12SiO20 crystal.

Fig. 8
Fig. 8

Schematic representation of the offset position of the photorefractive crystal to avoid scattered light noise and diffracted light from rectangular features on the object.

Fig. 9
Fig. 9

Schematic of the actual experimental setup used for defect enhancement, not drawn to scale: SF, spatial filter; CL, collimating lens; HWP, half-wave plate; LP, linear polarizer; FTL, Fourier-transform lens; MO, 63× microscope objective; S, shutter; AP, square aperture.

Fig. 10
Fig. 10

Reverse contrast images of the photorefractive crystal in phase-conjugate light to show where in the crystal the phase conjugation is occurring: (a) No HOE. Reading beam is optimally focused (slightly diverging) to compensate for the slight curvature of the crystal surface. (b) HOE in the writing beam compensates for crystal aberrations and improves the overlap of the pump beams.

Fig. 11
Fig. 11

Sequence of images showing how periodic pattern suppression fails if the unit cell of the pattern is too large: Boxes drawn on (a) and (b) indicate the rectangles in the pattern. (a) 4 μm × 6 μm squares on 6 μm × 8 μm centers; (b) 12 μm × 18 μm squares on 20 μm × 26 μm centers; (c) 60 μm × 90 μm squares on 85 μm × 115 μm centers; (d) same as (c) except Fourier axes are blocked at the crystal to remove the light from the rectangle edges.

Fig. 12
Fig. 12

(a) Dark-field microscopic image of a patterned silicon wafer. Arrows indicate the position of microspheres that are not visible in the image because of strong scatter from the rough surface of the patterned features. (b) Defect-enhanced image of the same scene; additional submicrometer pattern defects appear (A, C, and D). The other dots in the image are incompletely suppressed periodic pattern features. (c) Improved suppression of the periodic features by using a spatially nonuniform erase before readout. Defects, A, B, C, E, and F are clearly visible. See discussion in text.

Fig. 13
Fig. 13

(a) Chrome-on-glass mask: dark-field microscope image, (b) defect-enhanced image. Each square is 3.5 μm wide. Defects B, D, F–L, M, P, and R are 0.2–0.5 mm wide; D, F, G, I, J, M, and R are 0.5-μm-diameter polystyrene spheres.

Fig. 14
Fig. 14

Pattern defects in a chrome-on-glass mask: (a) dark-field microscope image, (b) defect-enhanced image. A is a 2-μm square and B–H are unintentional defects that range from submicrometer to over 1 μm in size.

Fig. 15
Fig. 15

Half-micrometer microspheres on a patterned silicon wafer: (a) dark-field image, (b) defect-enhanced image.

Fig. 16
Fig. 16

Half-micrometer microspheres on a patterned silicon wafer: (a) dark-field image, (b) defect-enhanced image.

Fig. 17
Fig. 17

Binary defect map created from thresholded defect-enhanced image. Dashed box shows area from Fig. 13.

Equations (24)

Equations on this page are rendered with MathJax. Learn more.

η ( t , k G ) = η 0 ( k G ) m 2 ( { 1 - exp [ - t τ ( k G , I 0 ) ] } ) 2 ,
m = 2 ( I obj I ref ) 1 / 2 I 0 ( e ^ ref * · e ^ obj ) ,
= 2 R 1 + R ( e ^ ref * · e ^ obj ) ,
τ ( I 0 , k G ) = U ( k G ) / I 0 .
k G = 4 π λ sin ( θ ) = 2 π Λ ,
η 0 ( k G ) κ [ E M ( k G ) ] 2 ,
S = η I read .
ρ = S I obj .
ρ 4 WM 4 I ref I read ( I obj + I ref + I read ) 2 ,
ρ 1 ,             I obj I ref ,
ρ ( 2 I ref I obj ) 2 ,             I obj I ref .
k read + k G = k obj ,
m = 2 ( E obj + E noise ) * E ref E obj + E noise 2 + E ref 2 .
m = 2 E obj * E ref E obj + E noise 2 + E ref 2 .
ρ 2 WM 4 I ref I read ( I obj + I ref ) 2 .
ρ 2 WM ρ 4 WM ~ 4 I read I ref .
I ref , opt 2 WM = 5 U 4 t w .
Δ z = ± 2 n λ 0 ( f FT / a ) 2 ,
E defect ( x x , y x ) = E inc ( d 2 λ f FT ) sinc ( x x d λ f FT ) sinc ( y x d λ f FT ) ,
S ( f FT ) xtal m 2 ( x x , y x , d , f FT , R ) d x x d y x ,
f FT , optimum = 3 d W xtal 2 λ .
B ( θ ) 0.02 I inc exp ( - 0.2 θ ) ,
I noise ( θ ) B ( θ ) a 2 / f FT 2 ,
RSNR 2 WM ( t ) = I def I spike [ 1 - exp ( - t I ref / U ) ] 2 I ref 2 [ 1 - exp ( - t I spike / U ) ] 2 .

Metrics