1 uranium oxide as a highly reflective coating from 2.7 to 11.6 nanometers william r. evans, richard...
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Uranium Oxide as a Highly Reflective Coating from 2.7 to 11.6 Nanometers
William R. Evans, Richard L. Sandberg, David D. Allred*, Jed E. Johnson, R. Steven Turley
Department of Physics and AstronomyBrigham Young University
*allred@byu.edu; phone 1 801 422-3489; fax 1 801 422-0553; xuv.byu.edu
BYU EUV Optics
October 25, 2003
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Overview• RESULTS
1. Uranium reflects more than nickel, the current metal of choice for soft X-Ray applications, between 4 and 11 nm.
2. The atomic scattering factor model (ASF) needs revision for compounds. Oxidized uranium reflectance differs from that predicted by ASF.
3. Reflectance of air-oxidized uranium (UO2) matches reactively sputtered UO2.
• OUTLINE– Why EUV and soft X-
Rays?– Why uranium?– What do the current
models predict?– Methods.
• Sample preparation• Reflectance measurement
– Results. – Conclusions.
BYU EUV Optics
October 25, 2003
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BYU EUV Optics
October 25, 2003
Why Extreme Ultraviolet (EUV) and Soft X-Rays?
Images from www.schott.com/magazine/english/info99/ and www.lbl.gov/Science-Articles/Archive/xray-inside-cells.html.
EUV Lithography(making really small computer chips)
Thin Film or Multilayer Mirrors
EUV Astronomy
The Earth’s magnetosphere in the EUV
Soft X-Ray Microscopes
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Why Uranium?• Uranium has many electrons to interact with photons (light) and is more dense
than many materials, causing them to interact with high energy EUV photons.
• High Theoretical Reflectivity: Low absorption and high index of refraction
• Previous Success: IMAGE Satellite Mirror Project (Launched March 25, 2000)
BYU EUV Optics
October 25, 2003
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Note: Nickel and its neighboring 3d elements are the nearest to uranium in this area.
Delta vs. beta plot for several elements at 4.48 nm
kn
iikn
,1
1ñ r
4.48nm
BYU EUV Optics
October 25, 2003
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Computed Reflectance, ASF model, CXRO
0
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0.9
2 3 4 5 6 7 8 9 10 11 12
Wavelength (nm)
Ref
lect
ance
Ni NiO U UO2
Reflectances for Ni, NiO, U, and UO2 predicted by the atomic scattering factor model from the Center for
X-Ray Optics (CXRO) website (www-cxro.lbl.gov).
BYU EUV Optics
October 25, 2003
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Schematic of DC magnetron sputtering system at BYU.
Sample PreparationThe uranium oxide and nickel samples were deposited on pieces polished silicon test wafers (100 orientation). Quartz crystal monitors were used to measure the sputtering and evaporation rates.
•U DC Magnetron SputteringThe uranium sputter targets used here were of depleted uranium metal (less than 0.2% U-235). After sputtering, the uranium was allowed to oxidize naturally in laboratory air.
•Ni Resistive Thermal EvaporationEvaporated Ni wire from a resistively heated tungsten boat (RD Mathis Co.) in a large, cryopumped, stainless steel “bell jar” coater.
BYU EUV Optics
October 25, 2003
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Taking Reflectance Measurements at the Advanced Light Source (ALS) Beamline 6.3.2
Schematic of ALS beamline 6.3.2 courtesy of http://www-cxro.lbl.gov/ALS6.3.2/.
Beamline 6.3.2 Reflectometer• Bright synchrotron radiation• 1-24.8 nm range• High spectral purity• Energy/wavelength or θ-2θ scan capability
ALS Reflectance Measurements• UOx means UO2, U most abundant natural oxide• NiO on Ni means Ni sample on Si oxidized by UV cleaning lamp• Ni on quartz means Ni on quartz slide* Discrepancies in data appear between wavelength scans because samples were removed and from chamber and then re-measured.
BYU EUV Optics
October 25, 2003
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Measured reflectances of UOx, NiO on Ni, and Ni on quartz at 5 degrees from 2.7-11.6 nm
00.10.20.30.40.50.60.70.8
4.4 4.9 5.4 5.9 6.4Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
00.10.20.30.40.50.60.70.8
2.5 3 3.5 4 4.5 5Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
0
0.1
0.2
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0.4
0.5
0.6
0.7
0.8
6.6 7.1 7.6 8.1 8.6Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
00.10.20.30.40.50.60.70.8
8.4 8.9 9.4 9.9 10.4 10.9 11.4Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
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Measured reflectance at 10 degrees of UO2, NiO on Ni, Ni on Quartz from 2.7-11.6 nm
00.10.20.30.40.50.60.70.8
4.4 4.9 5.4 5.9 6.4
Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
00.10.20.30.40.50.60.70.8
2.7 3.2 3.7 4.2 4.7
Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
0
0.1
0.2
0.3
0.4
0.5
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0.7
0.8
6.6 7.1 7.6 8.1 8.6
Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
00.10.20.30.40.50.60.70.8
8.4 9.4 10.4 11.4
Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
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Measured reflectance at 15 degrees of UO2, NiO on Ni, and Ni on Quartz from 2.7-11.6 nm.
00.10.20.30.40.50.60.70.8
4.4 4.9 5.4 5.9 6.4
Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
00.10.20.30.40.50.60.70.8
2.5 3 3.5 4 4.5 5
Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
0
0.1
0.2
0.3
0.4
0.5
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0.7
0.8
6.6 7.1 7.6 8.1 8.6Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
0
0.1
0.2
0.3
0.4
0.5
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0.7
0.8
8.4 8.9 9.4 9.9 10.4 10.9 11.4Wavelength (nm)
Ref
lect
ance
UOx NiO on Ni Ni on Quartz
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Reflectance of Naturally Oxidized and Reactively Sputtered UO2
00.10.20.30.40.50.60.70.80.9
1
3 5 7 9 11 13 15 17Wavelength (nm)
Ref
lect
ance
UO18-Naturally oxidized UO2 [i]Lunt UOx on UO2-Reactively Sputtered [ii]
[i] Sandberg et a., Advances in Mirror Technology for X-Ray, EUV Lithography, Laser, and Other Applications , Ali M. Khounsary, Udo Dinger, Kazuya Ota, Editors, Proc. SPIE 5193, SPIE, Bellingham, WA, 2003. [ii] Shannon Lunt, Determining the Indices of Refraction of Reactively Sputtered Uranium Dioxide Thing Films from 46 to 584 Angstroms, Masters Thesis, Dept. of Physics and Astronomy, BYU, Provo, UT 2002.
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October 25, 2003
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Reflectance of Measured UO2 and Computed Models
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2 3 4 5 6 7 8 9 10 11 12
Wavelength (nm)
Ref
lect
ance
Measured UOx
BYU EUV Optics
October 25, 2003
Reflectance of Measured UO2 and Computed Models
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Wavelength (nm)
Ref
lect
ance
Measured UOx Computed UOx (d=30 nm)
Reflectance of Measured UO2 and Computed Models
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Wavelength (nm)
Ref
lect
ance
Measured UOx Computed UOx (d=30 nm)
Computed UOx with 0.5 nm C on top Computed UOx with C(density=1.5g/cc) 3 nm
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BYU EUV Optics
October 25, 2003
AcknowledgementsHollilyn Drury and Megan Rowberry (Provo High
School) aided in sputtering the uranium films studied. An SPIE scholarship and department funding aided
Richard Sandberg in the research. We also acknowledge gratefully the financial
contributions of V. Dean and Alice J. Allred and Marathon Oil Company (US Steel) and Nan Ellen Ah You for gifts to Brigham Young University for thin film research.
We would also like to thank the ALS for the beamtime used to make the optical measurements.
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BYU EUV Optics
October 25, 2003
Conclusions1. Uranium oxide reflects significantly better than nickel, the current
material with highest reflectance, between 4 and 11 nm. 2. Uranium oxide reflectance differs from the reflectance predicted
by the atomic scattering factor model (ASF).
3. Reflectances of naturally oxidized uranium (UO2) matches reactively sputtered UO2 –Thus the material can be made in a number of different ways and is stable enough for practical use.
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