1. Uranium Oxide as a Highly Reflective Coating from 2.7 to 11.6 Nanometers Richard L. Sandberg Thanks to Advisors: David D. Allred, R. Steven Turley Fellow EUV Members: Jed E. Johnson, Luke J. Bissel, William R. Evans, and others from EUV Group Funding: BYU Physics Dept. Funding, ORCA Scholarship, SPIE Scholarship BYU EUV Optics October 25, 2003

2. Why Uranium and Thorium? In the EUV, uranium and thorium have many electrons to interact with photons (light) and is more dense than many materials, causing them to interact with high energy EUV photons. We study different compounds of uranium and thorium, such as uranium-oxide (UO 2 ), uranium-nitride (UN), and thorium-oxide (ThO 2 ) in search of compounds with the best optical constants and that do not react with air. BYU EUV Optics October 10, 2003

3. 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 4.48nm BYU EUV Optics October 25, 2003

4. Reflectance computed using the CXRO Website: http://www-cxro.lbl.gov/optical_constants/mirror2.html BYU EUV Optics October 10, 2003

5. Schematic of DC magnetron sputtering system at BYU. Sample Preparation The 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 Sputtering The 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/Au Resistive Thermal Evaporation Evaporated Ni wire/Au beads from a resistively heated tungsten boat (RD Mathis Co.) in a large, cryopumped, stainless steel “bell jar” coater. XRD Sample Thickness -UO 2 30.0 nm (ρ=10.97 g/cm 3 ) -NiO 49.7 nm (ρ=6.67 g/cm3) -Au 28.5 nm (ρ=19.3 g/cm3) BYU EUV Optics October 25, 2003

6. 5 Studying Our Samples Images courtesy of www.weizmann.ac.il/surflab/peter/afmworks, www.mos.org/sln/SEM/works/ http://volta.byu.edu/adamson03.pdf, and http://www.swt.edu/~wg06/manuals/Gaertner117/ellipsometerHome.htm. Ellipsometry X-ray Photoelectron Spectroscope (XPS) Scanning /Tunneling Electron Microscopes (SEM/TEM) Atomic Force Microscopy (AFM) BYU EUV Optics October 10, 2003

7. Inage courtesy of http:// www.lbl.gov / BYU EUV Optics October 10, 2003 Taking Reflectance Measurements at the ALS (Advance Light Source) Sample of Data from the ALS Beamline 6.3.2 Reflectometer Bright synchrotron radiation 1-24.8 nm range High spectral purity Energy/wavelength or θ-2θ scan capability BYU EUV Optics October 25, 2003 Small Discrepancies arise from one region to another with the use of different filters. Normalization given by R=(I detector -I dark )/(I beam -I dark )

8. BYU EUV Optics October 10, 2003

9. BYU EUV Optics October 10, 2003

10. BYU EUV Optics October 10, 2003

11. Measured Data compared with CXRO Atomic Scattering Factor Model Assumption: condensed matter may be modeled as a collection of non- interacting atoms. In the higher energy EUV, chemical bonds shouldn’t contribute. **This is a bad assumption for the EUV where most electron resonances reside. Photons are scattered principally off electrons. More electrons = higher reflection.

12. [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. BYU EUV Optics October 10, 2003

13. BYU EUV Optics October 25, 2003 Conclusions UO 2 reflects significantly better than Ni and Au, the current materials with highest reflectance, between 4 and 11 nm. UO 2 reflectance differs from the reflectance predicted by the atomic scattering factor model (ASF). Reflectances of naturally oxidized uranium (UO 2 ) matches reactively sputtered UO 2 –Thus the material can be made in a number of different ways and is stable enough for practical use. Goals Determine why UO 2 measured reflectance does not agree with ASF Determine the optical properties of UO 2 below Shannon’s data (4.5 nm). Publish results, finish thesis, and graduate! Successes Presented at 2004 SPIE Annual Meeting in San Diego, CA and published research in Proceedings of the SPIE Presented at 2004 SRI Meeting in San Fransisco, CA and published research in Proceedings of the SRI THANK YOU!!