1 / 18

Determining Ruthenium’s Optical Constants in the Extreme Ultraviolet

This study focuses on determining the optical constants of ruthenium in the extreme ultraviolet range for potential applications in multilayer mirrors for lithography. Measurement methods, sample preparation, and data analysis are discussed.

kelty
Download Presentation

Determining Ruthenium’s Optical Constants in the Extreme Ultraviolet

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Determining Ruthenium’s Optical Constants in the Extreme Ultraviolet Luke J. Bissell, David D. Allred, R. Steven Turley, William R. Evans, Jed E. Johnson

  2. Multilayer mirrors for EUV lithography • Goal is to get a mirror that has maximum • reflectance in the range of 11-14 nm • Multilayers maximize the constructive • interference of thin films by repetition of • high index/low index materials • Molybdenum/silicon multilayers have been • made which reflect 70% at 13.5 nm at 5° • from normal incidence [2] [1]

  3. Why ruthenium? • Ru is the closest neighbour to Mo that has a similar absorption coefficient (f2) and doesn’t oxidize • Ru f2 of 2.89 at 13.5 nm, compared to 1.23 for Mo at the same wavelength [2]. • Ru capped multilayers have better long-term reflectance than older design [3]. • Long Term Goal: study the reflectance of a Mo/Si multilayer capped with a Ru-Mo alloy.

  4. Survey of reported Ru index of refraction 1 – d + ib

  5. Short term goal: getting d & b • The absorption coefficient (b) can be extracted from *transmission data • We can use Fresnel’s equations to fit the complex index of refraction to reflectance data • Interested in wavelengths between 11 and 14 nm. • Used Ru thin films *where T is the transmission after correction is made for reflection

  6. Experimental details • Three films were prepared during two depositions via RF magnetron sputtering at a base pressure < 8 E -7 torr. • Films were deposited on: • polished Si (100) substrates • transparent polyimide window from Moxtek, Inc. • Reflectance and transmission measurements were made at the Advanced Light Source at LBNL

  7. Characterization • To fit d and b to reflectance data, we need an accurate model of our sample: • SiO2 thickness determined by ellipsometry prior to • deposition • Ru thickness determined by fitting x-ray reflectance at • 0.154 nm and at 11-14 nm • Our previous research indicates • Ru oxide thickness is negligible Ru thin film (not to scale) Ru Si02 Si substrate

  8. Determining Ru thickness

  9. a b Reflectance Reflectance Reflectance Reflectance l l l l = 13 nm = 13 nm = 11.5 nm = 11.5 nm theta theta theta theta Reflectance vs. Incidence Angle • Fitting done with JFIT 1st deposition 2nd deposition

  10. coated uncoated Lambert’s law • used T = TRu=Tcoated/Tuncoated • d = 21.32 nm • assumed (1) both polyimide films were the same thickness (2) same thickness for samples B and C • R = ¼(d2 + b2)

  11. sample B sample A Issues relative to fitting reflectance data

  12. (■) this study, weighted average (Δ) Windt et al. (●) the ASF values (Henke et al.) (▲) Windt (unpublished)

  13. (■) this study, weighted average (Δ) Windt et al. (●) the ASF (Henke et al.) (▲) Windt (unpublished)

  14. Summary • We have measured the complex index of refraction for Ru from 11-14 nm. • Comparison with other sources shows differences as great as 20% between our measured d and b values and those reported by other authors • We will deposit a Mo-Ru alloy and study its stability

  15. SPIE BYU V. Dean and Alice J. Allred Marathon Oil Acknowledgments Work suported by: Special thanks to Eric Gullikson and Andy Aquila at ALS Beamline 6.3.2 for their help in data interpretation, reduction, and analysis.

  16. References [1] Atwood, David. Soft X-Rays and Extreme Ultraviolet Radiation. Cambridge 1999. p. 113 [2] “X-ray Properties of the Elements,” http://www-cxro.lbl.gov/optical_constants [3] S. Bajt, J.B. Alameda, T.W. Barbee Jr., W.M. Clift, J.A. Folta, B. Kaufmann, E.A. Spiller, “Improved Reflectance and Stability of Mo-Si multilayers,” Opt. Eng.41, 1797-1804 (2002). [4] D. L. Windt, W. C. Cash, M. Scott, P. Arendt, B. Newman, R. F. Fisher, A. B. Swartzlander, “Optical constants for thin films of Ti, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Os, Pt, and Au from 24 Å to 1216 Å,” 27 (2), 246-278 (1988). [5] B.L. Henke, E.M. Gullikson, J.C. Davis. “X-ray interactions: photoabsorption, scattering, transmission, and reflection at E=50-30000 eV, Z=1-92,” Atomic Data and Nuclear Data Tables, 54 (2), 181-342 (1993).

More Related