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 - PowerPoint PPT Presentation

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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

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

3 5 7 9 11 13 15 17

Wavelength (nm)

Ref

lect

ance

Measured Reflectance of Th02 at 5 degrees

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

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

0.3

0.4

0.5

0.6

0.7

0.8

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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