Abstract

Immersion lithography has become attractive since it can reduce critical dimensions by increasing numerical aperture (NA) beyond unity. Among all the candidates for immersion fluids, those with higher refractive indices and low absorbance are desired. Characterization of the refractive indices and absorbance of various inorganic fluid candidates has been performed. To measure the refractive indices of these fluids, a prism deviation angle method was developed. Several candidates have been identified for 193  nm application with refractive indices near 1.55, which is approximately 0.1 higher than that of water at this wavelength. Cauchy parameters of these fluids were generated and approaches were investigated to tailor the fluid absorption edges to be close to 193  nm. The effects of these fluids on photoresist performance were also examined with 193  nm immersion lithography exposure at various NAs. Half-pitch 32  nm lines were obtained with phosphoric acid as the immersion medium at 1.5  NA. These fluids are potential candidates for immersion lithography technology.

© 2006 Optical Society of America

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References

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  1. M. S. Hibbs, "System overview of optical steppers and scanners," in Microlithography Science and Technology, J.R.Sheats and B.W.Smith, eds. (Marcel Dekker, 1998), pp. 1-108.
  2. B. W. Smith, A. Bourov, Y. Fan, L. Zavyalova, N. Lafferty, and F. Cropanese, "Approaching the numerical aperture of water immersion lithography at 193-nm," in Optical Microlithography XVII, B.W.Smith, ed., Proc. SPIE 5377, 273-284 (2004).
  3. S. Peng, R. H. French, W. Qiu, R. C. Wheland, M. Yang, M. F. Lemon, and M. K. Crawford, "Second generation fluids for 193 nm immersion lithography," in Optical Microlithography XVIII, B.W.Smith, ed., Proc. SPIE 5754, 427-434 (2005).
  4. B. Budhlall, G. Parris, P. Zhang, X. Gao, Z. Zarkov, and B. Ross, "High refractive index immersion fluids for 193 nm immersion lithography," in Optical Microlithography XVIII, B.W.Smith, ed. Proc. SPIE 5754, 622-629 (2005).
  5. G. Gauglitz and D. Moore, "Nomenclature, symbols, units, and their usage in spectrochemical analysis-XII. Laser-based molecular spectrometer for chemical analysis: absorption," Pure Appl. Chem. 71, 2189-2204 (1999).
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    [CrossRef]
  7. R. Gupta, J. H. Burnett, U. Gnesmann, and M. Waihout, "Absolute refractive indices and thermal coefficients of fused silica and calcium fluoride near 193 nm," Appl. Opt. 37, 5964-5968 (1998).
  8. J. Burnett and S. Kaplan, "Measurement of refractive index and thermo-optic coefficient of water near 193 nm," in Optical Microlithography XVI, A.Yen, ed., Proc. SPIE 5040, 1742-1749 (2003).
  9. H.-J. Eichler, "Dispersion and absorption of light," in Optics of Waves and Particles, H.Niedrig, ed. (de Gruyter, 1999), pp. 187-280.
  10. W. Hinsberg, F. A. Houle, J. Hoffnagle, M. Sanchez, G. Wallraff, M. Morrison, and S. Frank, "Deep-ultraviolet interferometric lithography as a tool for assessment of chemically amplified photoresist performance," J. Vac. Sci. Technol. B 16, 3689-3694 (1998).
    [CrossRef]
  11. T. A. Savas, S. N. Shah, M. L. Schattenburg, J. M. Carter, and H. I. Smith, "Achromatic interferometric lithography for 100-nm-period gratings and grids," J. Vac. Sci. Technol. B 13, 2732-2735 (1995).
    [CrossRef]
  12. Y. Fan, A. Bourov, L. Zavyalova, J. Zhou, A. Estroff, N. Lafferty, and B. W. Smith, "ILSim, a compact simulation tool for interferometric lithography," in Optical Microlithography XVIII, B.W.Smith, ed., Proc. SPIE 5754, 1805-1816 (2005).

1999 (1)

G. Gauglitz and D. Moore, "Nomenclature, symbols, units, and their usage in spectrochemical analysis-XII. Laser-based molecular spectrometer for chemical analysis: absorption," Pure Appl. Chem. 71, 2189-2204 (1999).

1998 (2)

W. Hinsberg, F. A. Houle, J. Hoffnagle, M. Sanchez, G. Wallraff, M. Morrison, and S. Frank, "Deep-ultraviolet interferometric lithography as a tool for assessment of chemically amplified photoresist performance," J. Vac. Sci. Technol. B 16, 3689-3694 (1998).
[CrossRef]

R. Gupta, J. H. Burnett, U. Gnesmann, and M. Waihout, "Absolute refractive indices and thermal coefficients of fused silica and calcium fluoride near 193 nm," Appl. Opt. 37, 5964-5968 (1998).

1995 (1)

T. A. Savas, S. N. Shah, M. L. Schattenburg, J. M. Carter, and H. I. Smith, "Achromatic interferometric lithography for 100-nm-period gratings and grids," J. Vac. Sci. Technol. B 13, 2732-2735 (1995).
[CrossRef]

1970 (1)

M. J. Blandamer and M. F. Fox, "Theory and applications of charge-transfer-to-solvent Spectra," Chem. Rev. 70, 59-93 (1970).
[CrossRef]

Appl. Opt. (1)

Chem. Rev. (1)

M. J. Blandamer and M. F. Fox, "Theory and applications of charge-transfer-to-solvent Spectra," Chem. Rev. 70, 59-93 (1970).
[CrossRef]

J. Vac. Sci. Technol. B (2)

W. Hinsberg, F. A. Houle, J. Hoffnagle, M. Sanchez, G. Wallraff, M. Morrison, and S. Frank, "Deep-ultraviolet interferometric lithography as a tool for assessment of chemically amplified photoresist performance," J. Vac. Sci. Technol. B 16, 3689-3694 (1998).
[CrossRef]

T. A. Savas, S. N. Shah, M. L. Schattenburg, J. M. Carter, and H. I. Smith, "Achromatic interferometric lithography for 100-nm-period gratings and grids," J. Vac. Sci. Technol. B 13, 2732-2735 (1995).
[CrossRef]

Pure Appl. Chem. (1)

G. Gauglitz and D. Moore, "Nomenclature, symbols, units, and their usage in spectrochemical analysis-XII. Laser-based molecular spectrometer for chemical analysis: absorption," Pure Appl. Chem. 71, 2189-2204 (1999).

Other (7)

Y. Fan, A. Bourov, L. Zavyalova, J. Zhou, A. Estroff, N. Lafferty, and B. W. Smith, "ILSim, a compact simulation tool for interferometric lithography," in Optical Microlithography XVIII, B.W.Smith, ed., Proc. SPIE 5754, 1805-1816 (2005).

J. Burnett and S. Kaplan, "Measurement of refractive index and thermo-optic coefficient of water near 193 nm," in Optical Microlithography XVI, A.Yen, ed., Proc. SPIE 5040, 1742-1749 (2003).

H.-J. Eichler, "Dispersion and absorption of light," in Optics of Waves and Particles, H.Niedrig, ed. (de Gruyter, 1999), pp. 187-280.

M. S. Hibbs, "System overview of optical steppers and scanners," in Microlithography Science and Technology, J.R.Sheats and B.W.Smith, eds. (Marcel Dekker, 1998), pp. 1-108.

B. W. Smith, A. Bourov, Y. Fan, L. Zavyalova, N. Lafferty, and F. Cropanese, "Approaching the numerical aperture of water immersion lithography at 193-nm," in Optical Microlithography XVII, B.W.Smith, ed., Proc. SPIE 5377, 273-284 (2004).

S. Peng, R. H. French, W. Qiu, R. C. Wheland, M. Yang, M. F. Lemon, and M. K. Crawford, "Second generation fluids for 193 nm immersion lithography," in Optical Microlithography XVIII, B.W.Smith, ed., Proc. SPIE 5754, 427-434 (2005).

B. Budhlall, G. Parris, P. Zhang, X. Gao, Z. Zarkov, and B. Ross, "High refractive index immersion fluids for 193 nm immersion lithography," in Optical Microlithography XVIII, B.W.Smith, ed. Proc. SPIE 5754, 622-629 (2005).

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Figures (7)

Fig. 1
Fig. 1

Different diffraction orders have different optical paths. This will cause the transmission to be different.

Fig. 2
Fig. 2

Absorbance spectrum of 85% H3PO4 aqueous solution and the absorption onset wavelength λ0.

Fig. 3
Fig. 3

Experimental setup for refractive index measurement. (a) Modified Woollam variable angle spectroscopic ellipsometer. (b) Top view of optical path (not to scale).

Fig. 4
Fig. 4

Refractive index of 85% phosphoric acid and the Cauchy curve fit.

Fig. 5
Fig. 5

Schematic diagram of the 193 nm interferometric immersion lithography system.

Fig. 6
Fig. 6

SEM images of immersion interferometric lithography using 85% H3PO4 as immersion media. (a) 1.42 NA, 34 nm half pitch; (b) 1.5 NA, 32 nm half pitch.

Fig. 7
Fig. 7

SEM images of immersion interferometric lithography using AlCl3 and Na2SO4 aqueous solutions as immersion media at 0.6 NA, 75 nm half pitch. (a) AlCl3 · 6H2O 50%, n = 1.584; (b) Na2SO4 30%, n = 1.479.

Tables (4)

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Table 1 Absorption Peak Caused by Different Anions in Water

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Table 2 Absorbance of Various Inorganic Aqueous Solutions at 193 and 248 nm ( e based) and Absorption Onset Wavelength. Absorbance Greater Than 1.9 mm−1 was Not Measurable

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Table 3 Uncertainties of Refractive Index Measurement

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Table 4 Fluid Refractive Indices and Cauchy Parameters

Equations (4)

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α = A 2 A 1 t 2 t 1 ,
n liquid = n air sin α / sin θ 1 .
n liquid sin θ 2 = n air sin ( A α + β ) ,
n liquid = n air { 2 sin 2 ( A α + β ) + [ sin α + cos A sin ( A α + β ) sin A ] 2 } 1 / 2 .

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