Abstract

Transmittance of fluoride films prepared by various kinds of deposition methods is not sufficient for a vacuum-ultraviolet (VUV) stepper application. Moreover, moisture penetrates into fluoride films because of porous structures. Then the moisture reacts with the fluoride chemically, and the photoabsorption of the films increases with elapsed time. Postfluorination treatment, in which F-poor areas of fluoride films are sufficiently fluorinated and the film structures are modified to be denser, has been developed. The postfluorination treatment was performed at 0.1MPa of diluted F2 gas in a special apparatus made of nickel. This treatment reduces photoabsorption of fluoride films and prevents photoabsorption from increasing again with elapsed time. In a long-time F2 laser irradiation test, the transmittance of as-deposited fluoride films remarkably degraded with irradiation. On the other hand, there is no tendency of transmittance degradation in the case of postfluorinated fluoride films. The postfluorination is able to improve the optical performance of fluoride films, promising the highest coating level for VUV lithography.

© 2006 Optical Society of America

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References

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  1. S. Niisaka, T. Saito, J. Saito, A. Tanaka, A. Matsumoto, M. Otani, R. Biro, C. Ouchi, M. Hasegawa, Y. Suzuki, and K. Sone, 'Development of optical coatings for 157-nm lithography. I. Coating materials,' Appl. Opt. 41, 3242-3247 (2002).
    [CrossRef] [PubMed]
  2. Y. Taki, 'Film structure and optical constants of magnetron-sputtered fluoride films for deep ultraviolet lithography,' Vacuum 74, 431-435 (2004).
    [CrossRef]
  3. Y. Taki and K. Muramatsu, 'Hetero-epitaxial growth and optical properties of LaF3 on CaF2,' Thin Solid Films 420-421, 30-37 (2002).
    [CrossRef]

2004 (1)

Y. Taki, 'Film structure and optical constants of magnetron-sputtered fluoride films for deep ultraviolet lithography,' Vacuum 74, 431-435 (2004).
[CrossRef]

2002 (2)

Biro, R.

Hasegawa, M.

Matsumoto, A.

Muramatsu, K.

Y. Taki and K. Muramatsu, 'Hetero-epitaxial growth and optical properties of LaF3 on CaF2,' Thin Solid Films 420-421, 30-37 (2002).
[CrossRef]

Niisaka, S.

Otani, M.

Ouchi, C.

Saito, J.

Saito, T.

Sone, K.

Suzuki, Y.

Taki, Y.

Y. Taki, 'Film structure and optical constants of magnetron-sputtered fluoride films for deep ultraviolet lithography,' Vacuum 74, 431-435 (2004).
[CrossRef]

Y. Taki and K. Muramatsu, 'Hetero-epitaxial growth and optical properties of LaF3 on CaF2,' Thin Solid Films 420-421, 30-37 (2002).
[CrossRef]

Tanaka, A.

Appl. Opt. (1)

Thin Solid Films (1)

Y. Taki and K. Muramatsu, 'Hetero-epitaxial growth and optical properties of LaF3 on CaF2,' Thin Solid Films 420-421, 30-37 (2002).
[CrossRef]

Vacuum (1)

Y. Taki, 'Film structure and optical constants of magnetron-sputtered fluoride films for deep ultraviolet lithography,' Vacuum 74, 431-435 (2004).
[CrossRef]

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Figures (11)

Fig. 1
Fig. 1

Illustrations of transmittance and reflectance measurements of (a) a bare substrate and (b) an AR-coated substrate.

Fig. 2
Fig. 2

Long-time irradiation system with a F 2 excimer laser.

Fig. 3
Fig. 3

Photograph of the postfluorination apparatus.

Fig. 4
Fig. 4

Illustrations of cross-sectional structures of (a) as-deposited fluoride film and (b) postfluorinated fluoride film.

Fig. 5
Fig. 5

Cross-sectional SEM images of MgF 2 , AlF 3 , and LaF 3 films.

Fig. 6
Fig. 6

Depth profiles of O and OH concentrations in MgF 2 films investigated with SIMS. CPS, counts per second.

Fig. 7
Fig. 7

Changes in the transmittance and reflectance spectra of narrow-AR coatings for 157 nm on a parallel CaF 2 ( 111 ) substrate. The sample was left in an environment at a temperature of 23 °C and a humidity of 40%–50%. The sample was cleaned before each measurement.

Fig. 8
Fig. 8

Elapsed time dependence of optical losses of narrow- and wide-AR coatings for 157 nm on parallel CaF 2 ( 111 ) substrates. The samples were left in an environment at a temperature of 23 °C and a humidity of 40%–50%. The samples were cleaned before each measurement.

Fig. 9
Fig. 9

Transmittance changes of the set of five wide-AR coatings on both sides of parallel CaF 2 ( 111 ) substrates during long-time F 2 laser irradiation.

Fig. 10
Fig. 10

Photograph of a finely finished CaF 2 ( 111 ) bulk that is 50 mm thick and 150 mm in diameter that is set on a lens holder in the postfluorination apparatus.

Fig. 11
Fig. 11

Interferometric analysis with Zernike polynomials on the deviations of the wavefront of a finely finished CaF 2 ( 111 ) bulk before and after the postfluorination.

Tables (1)

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Table 1 Comparison between As-Deposited Fluoride Films and Postfluorinated Fluoride Films

Equations (2)

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L sub ( % ) = 90.89 % - T sub ( % ) .
L coat ( % ) = ( 100 - T 1 - R 1 - L sub ) / 2.

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