Abstract

We have observed a dramatic dependence of the extreme ultraviolet (EUV) reflectivity of Mo/Y multilayers on the oxygen content of yttrium. This is explained as being due to a change in the microstructure and an increase in roughness of the yttrium layers and not just to an increase in absorption owing to the amount of oxygen within the yttrium layers. We found that the best reflectivity of 38.4% was achieved with an oxygen content of 25%, which was reduced to 32.6% and 29.6% for multilayers manufactured from oxygen-free yttrium and 39%-oxygen yttrium, respectively. These results highlight the importance of including experimentally determined optical constants as well as interface roughness in multilayer calculations. In addition, the lifetime stability of Mo/Y multilayers with different capping layers was monitored for 1 year. The molybdenum- and palladium-capped samples exhibited low surface roughness and ∼4% relative reflectivity loss in 1 year. The relative reflectivity loss of the yttrium-capped sample (yttrium with 39% oxygen) was ∼8%. However, the reflectivity loss in all three capping layers occurred within the first 100 days after the deposition, and the reflectivity remained stable afterward.

© 2004 Optical Society of America

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References

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  1. See http://sdo.gsfc.nasa.gov/ for more details about the Solar Dynamics Observatory mission.
  2. C. Montcalm, P. A. Kearney, J. M. Slaughter, B. T. Sullivan, M. Chaker, H. Pépin, C. M. Falco, “Survey of Ti-, B-, and Y-based soft x-ray extreme ultraviolet multilayer mirrors for the 2- to 12-nm wavelength region,” Appl. Opt. 35, 5134–5147 (1996).
    [CrossRef] [PubMed]
  3. B. Sae-Lao, S. Bajt, C. Montcalm, J. F. Seely, “Performance of normal-incidence molybdenum-yttrium multilayer-coated diffraction grating at a wavelength of 9 nm,” Appl. Opt. 41, 2394–2400 (2002).
    [CrossRef] [PubMed]
  4. R. Soufli, E. M. Gullikson, “Absolute photoabsorption measurements of molybdenum in the range 60–930 eV for optical constant determination,” Appl. Opt. 37, 1713–1719 (1998).
    [CrossRef]
  5. B. Sae-Lao, R. Soufli, “Measurements of the refractive index of yttrium in the 50–1300-eV energy region,” Appl. Opt. 41, 7309–7316 (2002).
    [CrossRef] [PubMed]
  6. R. C. Weast, M. J. Astle, eds., CRC Handbook of Chemistry and Physics, 63rd ed. (CRC Press, Boca Raton, Fla., 1982); see also http://www.webelements.com .
  7. B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
    [CrossRef]
  8. E. M. Gullikson, S. Mrowka, B. B. Kaufmann, “Recent developments in the EUV reflectometry at the Advanced Light Source,” in Emerging Lithographic Technologies V, E. A. Dobisz, eds., Proc. SPIE4343, 363–373 (2001).
    [CrossRef]
  9. D. L. Windt, “IMD: software for modeling the optical properties of multilayer films,” Comput. Phys.12, 360–370 (1998). The software can be downloaded at http://cletus.phys.columbia.edu/∼windt/imd/ .
  10. F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

2002 (2)

1998 (1)

1996 (1)

1986 (1)

B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
[CrossRef]

Bajt, S.

Boom, R.

F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

Chaker, M.

de Boer, F. R.

F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

Falco, C. M.

Gullikson, E. M.

R. Soufli, E. M. Gullikson, “Absolute photoabsorption measurements of molybdenum in the range 60–930 eV for optical constant determination,” Appl. Opt. 37, 1713–1719 (1998).
[CrossRef]

E. M. Gullikson, S. Mrowka, B. B. Kaufmann, “Recent developments in the EUV reflectometry at the Advanced Light Source,” in Emerging Lithographic Technologies V, E. A. Dobisz, eds., Proc. SPIE4343, 363–373 (2001).
[CrossRef]

Henke, B. L.

B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
[CrossRef]

Kaufmann, B. B.

E. M. Gullikson, S. Mrowka, B. B. Kaufmann, “Recent developments in the EUV reflectometry at the Advanced Light Source,” in Emerging Lithographic Technologies V, E. A. Dobisz, eds., Proc. SPIE4343, 363–373 (2001).
[CrossRef]

Kearney, P. A.

Mattens, W. C. M.

F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

Miedema, A. R.

F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

Montcalm, C.

Mrowka, S.

E. M. Gullikson, S. Mrowka, B. B. Kaufmann, “Recent developments in the EUV reflectometry at the Advanced Light Source,” in Emerging Lithographic Technologies V, E. A. Dobisz, eds., Proc. SPIE4343, 363–373 (2001).
[CrossRef]

Niessen, A. K.

F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

Pépin, H.

Sae-Lao, B.

Seely, J. F.

Slaughter, J. M.

Soufli, R.

Sullivan, B. T.

Tackaberry, R. T.

B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
[CrossRef]

Uejid, J. Y.

B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
[CrossRef]

Yamada, H. T.

B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
[CrossRef]

Appl. Opt. (4)

Opt. Eng. (1)

B. L. Henke, J. Y. Uejid, H. T. Yamada, R. T. Tackaberry, “Characterization of multilayer x-ray analysers: model and measurements,” Opt. Eng. 25, 937–947 (1986).
[CrossRef]

Other (5)

E. M. Gullikson, S. Mrowka, B. B. Kaufmann, “Recent developments in the EUV reflectometry at the Advanced Light Source,” in Emerging Lithographic Technologies V, E. A. Dobisz, eds., Proc. SPIE4343, 363–373 (2001).
[CrossRef]

D. L. Windt, “IMD: software for modeling the optical properties of multilayer films,” Comput. Phys.12, 360–370 (1998). The software can be downloaded at http://cletus.phys.columbia.edu/∼windt/imd/ .

F. R. de Boer, R. Boom, W. C. M. Mattens, A. R. Miedema, A. K. Niessen, Cohesion in Metals: Transition Metal Alloys, Vol. 1 of the Cohesion and Structure Series (North-Holland, Amsterdam, 1988).

See http://sdo.gsfc.nasa.gov/ for more details about the Solar Dynamics Observatory mission.

R. C. Weast, M. J. Astle, eds., CRC Handbook of Chemistry and Physics, 63rd ed. (CRC Press, Boca Raton, Fla., 1982); see also http://www.webelements.com .

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Figures (10)

Fig. 1
Fig. 1

EUV reflectance of three representative multilayers, A, B, and C, which were fabricated from yttrium targets from ACI Alloys, Plasmaterial, Inc., and Research and PVD Materials Corporation, respectively. The reflectance measurements were performed at a 3° normal-incidence angle.

Fig. 2
Fig. 2

Calculated EUV reflectance of three Mo/Y multilayers, A, B, and C, which have <3%, 25%, and 39% atomic oxygen in their yttrium layers, respectively.

Fig. 3
Fig. 3

Measured XRD spectra of three representative Mo/Y multilayers, A (<3% oxygen), B (25% oxygen), and C (39% oxygen), showing up Bragg reflection up to the sixth order.

Fig. 4
Fig. 4

First- and second-order rocking curves of multilayers A (<3% oxygen), B (25% oxygen), and C (39% oxygen). The intensities away from the Bragg peaks drop rapidly because the input beam or the detector was shadowed by the sample.

Fig. 5
Fig. 5

Best fits to the XRD data (symbols) of multilayers A (<3% oxygen), B (25% oxygen), and C (39% oxygen). The yttrium optical constants at copper K α energy were adjusted according to the yttrium compositions and densities obtained from the RBS measurements.

Fig. 6
Fig. 6

Comparison of measured (open symbols) and calculated (filled symbols) EUV reflectance on linear (top) and log (bottom) scales of three representative Mo/Y multilayer samples, A (circles), B (squares), and C (diamonds), for the structure parameters that were determined from the fits to their XRD data.

Fig. 7
Fig. 7

Comparison of large-angle XRD spectra of Mo/Y multilayer samples A (<3% oxygen), B (25% oxygen), and C (39% oxygen).

Fig. 8
Fig. 8

TEM images of top, Mo/Y sample A (<3% oxygen) and bottom, Mo/Y sample C (39% oxygen). A thicker sample or a higher-Z material will scatter more electrons than a thinner sample or a lower-Z material. Therefore the originally thicker sample A has better contrast than sample C, and the higher-Z material (molybdenum, Z = 42) appears darker than the lighter-Z material (yttrium, Z = 39). A few examples of large yttrium crystallites in the direction normal to the multilayer growth owing to the presence of a high amount of oxygen are outlined in sample C.

Fig. 9
Fig. 9

Measured (points) and calculated (curve) EUV reflectance as a function of thickness of palladium capping for five Mo/Y multilayers. The palladium capping is coated on top of a molybdenum-terminated Mo/Y multilayer.

Fig. 10
Fig. 10

Measured EUV reflectance (R) of molybdenum-, yttrium-, and palladium-capped Mo/Y multilayers (symbols) normalized to their initial reflectance values (R0, obtained immediately after deposition) as a function of time for a period of 1 year. The curves are interpolations of the measured points.

Tables (1)

Tables Icon

Table 1 Fitted Parameters for the XRD Data of Three Representative Mo/Y Multilayers: A (<3% oxygen), B (25% oxygen), and C (39% oxygen)

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