Abstract

Conjugate wave-front generation by degenerate four-wave mixing has been employed to project images with submicrometer features onto photoresist-coated substrates. The developed patterns demonstrate a resolution of >800 line pairs per millimeter for 413-nm illumination, consistent with theoretical expectations. The patterns are not degraded by speckle or edge enhancement, and the magnification is within 0.1% of unity. Focusing is accomplished by a novel interferometric procedure.

© 1981 Optical Society of America

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References

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  1. For an up-to-date review, see the special issue of IEEE Trans. Electron Devices ED-27, 1319–1725 (August1980).
  2. B. J. Lin, “Optical methods for fine line lithography,” in Fine Line Lithography, R. Newman, ed. (North-Holland, Amsterdam, 1980), pp. 107–230.
  3. G. R. Brewer, “Electron beam technology in microelectronic fabrication” (Academic, New York, 1980).
  4. R. W. Hellwarth, “Generation of time reversed wave fronts by nonlinear refraction,” J. Opt. Soc. Am. 67, 1–3 (1977).
    [Crossref]
  5. D. M. Bloom and G. C. Bjorklund, “Conjugate wave front generation and image reconstruction by four wave mixing,” Appl. Phys. Lett. 31, 592–594 (1977).
    [Crossref]
  6. A. Yariv, “Phase conjugate optics and real time holography,” IEEE J. Quantum Electron. QE-14650–660 (1978); also IEEE J. Quantum Electron. QE-15, 524 (1979) and references therein.
    [Crossref]
  7. M. D. Levenson, “High resolution imaging by wavefront conjugation,” Opt. Lett. 5, 182–184 (1980).
    [Crossref]
  8. J. Feinberg, “Real-time edge enhancement using the photorefractive effect,” Opt. Lett. 5, 330–332 (1980).
    [Crossref] [PubMed]
  9. F. A. Hopf and A. Tomita, “Optical distortion due to self-focusing by degenerate four wave mixing in silicon,” J. Opt. Soc. Am. 70, 54A (1980).
  10. L. H. Enloe, “Noise-like structure in the image of diffusely reflecting objects in coherent illumination,” Bell Syst. Tech. J. 46, 1474–1489 (1967). Also see J. W. Goodman, J. Opt. Soc. Am. 66, 1145–1149 (1976).
    [Crossref]
  11. J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, New York, 1968), Chap. 7.
  12. J. O. White and A. Yariv, “Real time image processing via four wave mixing in a photorefractive medium,” Appl. Phys. Lett. 37, 5–7 (1980).
    [Crossref]
  13. J. D. Cuthbert, Solid State Technol. 20, 59–69 (1977).
  14. J. J. Amodei, W. Phillips, and D. L. Staebler, “Improved electrooptic materials and fixing techniques for holographic recording,” App. Opt. 11, 390–396 (1972).
    [Crossref]
  15. A. Krumins and P. Günter, “Diffraction efficiency and energy transfer during hologram formation in reduced KNbO3,” Appl. Phys. 19, 153–163 (1979).
    [Crossref]
  16. J. P. Huignard and et al., “Speckle free imaging in four wave mixing experiments with Bi12SiO20 crystals,” Opt. Lett. 5, 436–437 (1980).
    [Crossref] [PubMed]

1980 (6)

M. D. Levenson, “High resolution imaging by wavefront conjugation,” Opt. Lett. 5, 182–184 (1980).
[Crossref]

J. Feinberg, “Real-time edge enhancement using the photorefractive effect,” Opt. Lett. 5, 330–332 (1980).
[Crossref] [PubMed]

F. A. Hopf and A. Tomita, “Optical distortion due to self-focusing by degenerate four wave mixing in silicon,” J. Opt. Soc. Am. 70, 54A (1980).

For an up-to-date review, see the special issue of IEEE Trans. Electron Devices ED-27, 1319–1725 (August1980).

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

J. P. Huignard and et al., “Speckle free imaging in four wave mixing experiments with Bi12SiO20 crystals,” Opt. Lett. 5, 436–437 (1980).
[Crossref] [PubMed]

1979 (1)

A. Krumins and P. Günter, “Diffraction efficiency and energy transfer during hologram formation in reduced KNbO3,” Appl. Phys. 19, 153–163 (1979).
[Crossref]

1978 (1)

A. Yariv, “Phase conjugate optics and real time holography,” IEEE J. Quantum Electron. QE-14650–660 (1978); also IEEE J. Quantum Electron. QE-15, 524 (1979) and references therein.
[Crossref]

1977 (3)

J. D. Cuthbert, Solid State Technol. 20, 59–69 (1977).

R. W. Hellwarth, “Generation of time reversed wave fronts by nonlinear refraction,” J. Opt. Soc. Am. 67, 1–3 (1977).
[Crossref]

D. M. Bloom and G. C. Bjorklund, “Conjugate wave front generation and image reconstruction by four wave mixing,” Appl. Phys. Lett. 31, 592–594 (1977).
[Crossref]

1972 (1)

J. J. Amodei, W. Phillips, and D. L. Staebler, “Improved electrooptic materials and fixing techniques for holographic recording,” App. Opt. 11, 390–396 (1972).
[Crossref]

1967 (1)

L. H. Enloe, “Noise-like structure in the image of diffusely reflecting objects in coherent illumination,” Bell Syst. Tech. J. 46, 1474–1489 (1967). Also see J. W. Goodman, J. Opt. Soc. Am. 66, 1145–1149 (1976).
[Crossref]

Amodei, J. J.

J. J. Amodei, W. Phillips, and D. L. Staebler, “Improved electrooptic materials and fixing techniques for holographic recording,” App. Opt. 11, 390–396 (1972).
[Crossref]

Bjorklund, G. C.

D. M. Bloom and G. C. Bjorklund, “Conjugate wave front generation and image reconstruction by four wave mixing,” Appl. Phys. Lett. 31, 592–594 (1977).
[Crossref]

Bloom, D. M.

D. M. Bloom and G. C. Bjorklund, “Conjugate wave front generation and image reconstruction by four wave mixing,” Appl. Phys. Lett. 31, 592–594 (1977).
[Crossref]

Brewer, G. R.

G. R. Brewer, “Electron beam technology in microelectronic fabrication” (Academic, New York, 1980).

Cuthbert, J. D.

J. D. Cuthbert, Solid State Technol. 20, 59–69 (1977).

Enloe, L. H.

L. H. Enloe, “Noise-like structure in the image of diffusely reflecting objects in coherent illumination,” Bell Syst. Tech. J. 46, 1474–1489 (1967). Also see J. W. Goodman, J. Opt. Soc. Am. 66, 1145–1149 (1976).
[Crossref]

Feinberg, J.

Goodman, J. W.

J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, New York, 1968), Chap. 7.

Günter, P.

A. Krumins and P. Günter, “Diffraction efficiency and energy transfer during hologram formation in reduced KNbO3,” Appl. Phys. 19, 153–163 (1979).
[Crossref]

Hellwarth, R. W.

Hopf, F. A.

F. A. Hopf and A. Tomita, “Optical distortion due to self-focusing by degenerate four wave mixing in silicon,” J. Opt. Soc. Am. 70, 54A (1980).

Huignard, J. P.

Krumins, A.

A. Krumins and P. Günter, “Diffraction efficiency and energy transfer during hologram formation in reduced KNbO3,” Appl. Phys. 19, 153–163 (1979).
[Crossref]

Levenson, M. D.

Lin, B. J.

B. J. Lin, “Optical methods for fine line lithography,” in Fine Line Lithography, R. Newman, ed. (North-Holland, Amsterdam, 1980), pp. 107–230.

Phillips, W.

J. J. Amodei, W. Phillips, and D. L. Staebler, “Improved electrooptic materials and fixing techniques for holographic recording,” App. Opt. 11, 390–396 (1972).
[Crossref]

Staebler, D. L.

J. J. Amodei, W. Phillips, and D. L. Staebler, “Improved electrooptic materials and fixing techniques for holographic recording,” App. Opt. 11, 390–396 (1972).
[Crossref]

Tomita, A.

F. A. Hopf and A. Tomita, “Optical distortion due to self-focusing by degenerate four wave mixing in silicon,” J. Opt. Soc. Am. 70, 54A (1980).

White, J. O.

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

Yariv, A.

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

A. Yariv, “Phase conjugate optics and real time holography,” IEEE J. Quantum Electron. QE-14650–660 (1978); also IEEE J. Quantum Electron. QE-15, 524 (1979) and references therein.
[Crossref]

App. Opt. (1)

J. J. Amodei, W. Phillips, and D. L. Staebler, “Improved electrooptic materials and fixing techniques for holographic recording,” App. Opt. 11, 390–396 (1972).
[Crossref]

Appl. Phys. (1)

A. Krumins and P. Günter, “Diffraction efficiency and energy transfer during hologram formation in reduced KNbO3,” Appl. Phys. 19, 153–163 (1979).
[Crossref]

Appl. Phys. Lett. (2)

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

D. M. Bloom and G. C. Bjorklund, “Conjugate wave front generation and image reconstruction by four wave mixing,” Appl. Phys. Lett. 31, 592–594 (1977).
[Crossref]

Bell Syst. Tech. J. (1)

L. H. Enloe, “Noise-like structure in the image of diffusely reflecting objects in coherent illumination,” Bell Syst. Tech. J. 46, 1474–1489 (1967). Also see J. W. Goodman, J. Opt. Soc. Am. 66, 1145–1149 (1976).
[Crossref]

IEEE J. Quantum Electron. (1)

A. Yariv, “Phase conjugate optics and real time holography,” IEEE J. Quantum Electron. QE-14650–660 (1978); also IEEE J. Quantum Electron. QE-15, 524 (1979) and references therein.
[Crossref]

IEEE Trans. Electron Devices (1)

For an up-to-date review, see the special issue of IEEE Trans. Electron Devices ED-27, 1319–1725 (August1980).

J. Opt. Soc. Am. (2)

R. W. Hellwarth, “Generation of time reversed wave fronts by nonlinear refraction,” J. Opt. Soc. Am. 67, 1–3 (1977).
[Crossref]

F. A. Hopf and A. Tomita, “Optical distortion due to self-focusing by degenerate four wave mixing in silicon,” J. Opt. Soc. Am. 70, 54A (1980).

Opt. Lett. (3)

Solid State Technol. (1)

J. D. Cuthbert, Solid State Technol. 20, 59–69 (1977).

Other (3)

J. W. Goodman, Introduction to Fourier Optics (McGraw-Hill, New York, 1968), Chap. 7.

B. J. Lin, “Optical methods for fine line lithography,” in Fine Line Lithography, R. Newman, ed. (North-Holland, Amsterdam, 1980), pp. 107–230.

G. R. Brewer, “Electron beam technology in microelectronic fabrication” (Academic, New York, 1980).

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Figures (9)

Fig. 1
Fig. 1

Ray paths in an idealized wave-front conjugation projection system. The index of refraction of the beam-splitter cube is assumed to be 1.5. Rays scattered from an object point in the direction of the dashed lines are reflected into the conjugator crystal at top. The wave generated in the crystal propagates back along the same lines but is transmitted through the diagonal surface, ultimately converging on the image point. The solid lines indicate ray paths that enter the conjugator medium after one total internal reflection at surfaces of the beam-splitter cube. The conjugate waves corresponding to these rays would also converge to the image point if the beam splitter were a perfect cube. The pump waves are indicated by heavy arrows.

Fig. 2
Fig. 2

Schematic of our actual projection exposure tool. The beam-splitter cube was 15 mm on a side, whereas the LiNbO3 conjugator crystal was 25 mm × 25 mm and 5 mm thick. The optical axis of the crystal was in the plane of the diagram, parallel to the long crystal face. All polarizations were in the plane of the diagram. The mask and photoresist-coated substrate were 0.5 mm away from the face of the beam splitter, whereas the conjugator crystal was displaced by 5 mm. White-light fringes could be observed through the beam-splitter surface at the bottom of the diagram when the back of the conjugator crystal was diffusely illuminated. The intensity monitor collected the light transmitted through the glass substrate.

Fig. 3
Fig. 3

Typical variation of the image intensity with time. At t = 0 the shutter that blocks the laser beam was opened, and an image stored from a previous exposure was incident upon the substrate. As the beam paths changed owing to expansion of our Newport Research Corporation table, a new image was formed that initially interfered destructively with the old, reducing the intensity. Later, the image intensity rose, oscillated, and vanished when the shutter was closed.

Fig. 4
Fig. 4

A low-power-light micrograph of the pattern produced in an exposure of the entire resolution test mask. The individual square chips are 0.8 mm on a side with a center-to-center distance of 2 mm. Later tests of the conjugator resolution employed a chip at one corner of this pattern.

Fig. 5
Fig. 5

Scanning electron micrograph of a portion of a typical developed substrate. The lines at the top are 2 μm wide, and those at the bottom are 0.75 μm. The separation of the lines at the right is 4 μm, and those at the left are separated by 0.75 μm. Pits in the glass substrate simulate wafer topography. Letters identifying each subpattern are illegible.

Fig. 6
Fig. 6

Portions of developed patterns due to five 1.0-μm lines separated by 1.0-μm gaps: (a) tips of the lines, (b) close-up of one vertical wall between overexposed lines. The wall height is 1.5 μm, as determined by counting standing wave nodes. The irregularities of the pattern are comparable with those on the mask.

Fig. 7
Fig. 7

Scanning electron micrograph of a developed substrate exposed to light scattered by a ground-glass screen. The screen was 1 cm away from the substrate and was illuminated with two 1.5-cm-diameter spots of 413-nm radiation separated by 1 cm. The rugged topography is typical of that produced by speckle. Standing wave patterns are absent because the substrate was baked briefly after development.

Fig. 8
Fig. 8

Developed patterns of 0.75-μm lines: (a) five such lines separated by 0.75-μm gaps, (b) pattern with 4-μm gaps. The resolution in the direction parallel to the lines is not so great as that in the perpendicular direction. The resist film was 0.6 μm thick.

Fig. 9
Fig. 9

Pattern formed by five 0.75-μm lines with 0.50-μm gaps in AZ1350B photoresist.

Equations (4)

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Λ = 2 π λ N . A . = 0.39 μ m
r ( z ) = Λ 2 [ 1 + 1 1 - ( 2 λ / π Λ ) 2 ( 4 π λ z Λ 2 ) 2 ] 1 / 2 .
2 r ( z ) - Λ 0.30 Λ .
z F = 0.64 Λ 2 λ [ 1 - ( 2 λ / π Λ ) 2 ] 1 / 2 ,