1. Eliminating organic contamination on oxidized Si surfaces using atomic oxygen Liz Strein, David Allred, R. Steven Turley, and the EUV/thin films group

2. Outline Motivation Techniques/Methods Results

3. J. Tveekrem, “Contamination effects on EUV optics,” NASA Technical Report TP-1999-209264, 1999. Used with permission.

4. Calculated reflectance for 41.3nm (30 eV) light on silicon SiO 2 Si organic incident light reflected light E. Gullikson, X-Ray Interactions with Matter, http://henke.lbl.gov/optical_constants Accessed 27 Feb 2008. (calculated with the bilayer program) reflectance

5. Instrumentation X-ray Photoelectron Spectrometer (XPS) Ellipsometer Excimer UV lamp (cleans samples) Evactron Plasma Cleaner (cleans XPS antechamber)

6. Excimer Lamp Cleaning technique The excimer lamp creates ozone and oxygen radicals by exposing oxygen to 172nm photons. These products oxidize the adventitious carbon on the samples thus freeing the sample of its organic contamination Adapted from http://ecl.web.psi.ch/NanoKat/Ni_Al2O3_ethanol_1.jpg O SiO 2 organic

7. Ellipsometry Looks at how polarized light changes when it reflects from a surface. Used to determine the relative change in thickness for the “apparent oxide” on a sample Adapted from http://users.aber.ac.uk/tej/ellipso5.gif SiO 2 Si Substrate organic “apparent oxide” layer

8. X-ray Photoelectron Spectroscopy (XPS) Detects the speed of electrons ripped off from a sample’s surface by x rays. Used to determine the chemical composition of a sample. http://www.almaden.ibm.com/st/scientific_services/materials_analysis/xps/XPS.gif

9. Need for Evactron: Deposition rate on the samples exposed to the XPS antechamber

10. Evactron C DeContaminator Plasma clean the XPS chamber http://www.evactron.com/63193/image2.gif

11. Before excimer lamp After excimer lamp Si 2p

12. Correlation between characterization methods

13. how the “apparent oxide” thickness decreases with exposure time

14. Conclusions 5 min under lamp cleans off most of the last couple of angstroms of AC Correlation between characterization techniques (there are big problems when the characterization instruments change the nature of a sample) Cleanliness is important

15. Acknowledgements Amy Grigg Mike Keenlyside at Surface Physics Resonance LTD for the excimer lamp Gabe Morgan and Ron Vane for their loan of the Evactron C De-Contamination System Dr. Matt Linford Lei Pei The department of Physical and Mathematical Sciences for funding

16. Storage data Storage time: 10 min to 19 days Most samples began with an apparent oxide layer ≤ 1.83nm