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 Lithography Absorber 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

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

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