winston larson american vacuum society conference
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Determining Physical and Chemical Constants of Sputtered Uranium and
Thorium as Thin Film Reflectors Within the Extreme Ultraviolet (EUV)
Winston Larson
American Vacuum Society Conference
Overview
• Practical applications and importance of research
• Experiments
• Results
• Conclusions
• Discussion of Conclusions
Why EUV?
• EUV Lithography– 10 Ghz by 2007
– 32 nm nodes
• EUV Astronomy– Earth’s Magnetosphere
– Background Imaging
EUV LithographyAbsorber Pattern
Reflective Mask
Wafer to record 32 nm or smaller features
λ = 4 nm
Reduction optics
Uranium and Thorium
• Uranium and Thorium are very dense and are highly reflective in the EUV range.
• Uranium oxide, uranium nitride, thorium metal, and thorium dioxide were studied.
Structure
• The structure will affect the reflectance:– Compound– Relative Density– Lattice Structure– Roughness
TEM and AFM Experimentation
• Samples made on TEM grids and silicon wafers using RF Magnetron sputtering
• The TEM was used to obtain diffraction patterns.– Analyzed for compound, relative density, and
lattice structure.
• The AFM was used to obtain roughness data.– RMS roughness used to find change in
reflectance.– Power Spectral Density
TEM Analysis
• Bragg’s Law used to analyze diffraction patterns and find lattice parameters.– Lattice Parameters used to find
compound, lattice structure, and relative density.
– Lattice Parameters found for thorium, uranium nitride and uranium oxide.
Uranium nitride diffraction pattern taken at 160 keV and 130 cm.
TEM Conclusions
• Thorium lattice parameters were around 5.08 Å, representing thorium metal.
• Uranium oxide lattice parameters were around 5.47 Å, representing uranium dioxide.
• Uranium nitride lattice parameters were around 4.98 Å, representing uranium mononitride.
• All compounds had a face-centered cubic structure.
1
2
Smooth Surface
Rough Surface
AFM Roughness Analysis
• Debye-Waller method used, which overestimates effect on reflectance.
• Nevot-Croce method also used, which underestimates effect on reflectance.
• Results from both methods averaged to find a good estimate of change in reflectance.
The surface of uranium oxide at 100 nm by 100 nm.
Detector
High Frequency Roughness
Detector
Low Frequency Roughness
Power Spectral Density
• Shows high frequency roughness and low frequency roughness.
• All samples were mostly high frequency roughness with little low frequency roughness.
AFM Conclusions
• Change in thorium reflectance was about 20%.
• Change in uranium oxide reflectance was about 40%.
• Change in uranium nitride relfectance was about 10%.
Combined Conclusions
• Thorium– Second highest density– Second lowest roughness– Second best reflectance
• Uranium Dioxide– Lowest density– Highest roughness– Worst reflector
• Uranium Mononitride– Highest Density– Lowest roughness– Best reflector
Measured Reflectance of Uranium Oxide at 5 deg.
0
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3 5 7 9 11 13 15 17
Wavelength (nm)
Ref
lect
ance
Measured Reflectance of Th02 at 5 degrees
0
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0 5 10 15 20 25 30 35
Wavelength (nm)
Ref
lect
ance
2.06-2.21 nm 2.16-2.8 nm 2.7-4.8 nm 4.4-6.8 nm 6.6-8.8 nm 8.4-11.6 nm 11.0-14.0 nm 12.4-18.8 nm
17.2-25.0 nm 22.5-32.5
UN004 at 5 degrees
0
0.1
0.2
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0.4
0.5
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0.9
1
1 6 11 16 21 26 31 36
Wavelength (nm)
Ref
lect
ance
Series1
Series2
Series3
Series4
Series5
Series6
Series7
Series8
Series9
Series10
Series11
Why This is Important
• Again, the many practical applications.• Structure greatly affects the reflectance
of thorium and uranium.• Good basis for more sophisticated
research in the future.• A good estimate of the reflectance can
be made when a sample is sputtered.
Review
• Practical applications and importance of research
• Experiments
• Results
• Conclusions
• Practical Applications
Acknowledgements
• Thanks to – Dr. Allred– Dr. Turley– Niki Farnsworth– Richard Sandberg– Jed Johnson– Luke Bissell– Mom and Dad– Everyone else who so
kindly helped me– Santa, because I believe
The End!
• Any questions, comments, cares, concerns, feelings, other appropriate emotions, or otherwise important things that need to be expressed to our happy group while we are here together in such a pleasant setting?
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