1. 7 April 2006 Simultaneous Reflection and Transmission Measurements of Scandium Oxide Thin Films in the Extreme Ultraviolet G. A. Acosta, D. D. Allred, D. Muhlestein, N. Farnsworth- Brimhall, and R. S. Turley,Brigham Young University, Provo, UT

2. 7 April 20062 Overview Our goal is a better understanding of the optical properties of materials in the EUV. EUV Astronomy The Earth’s magnetosphere in the EUV The materials we have been studying most recently are ThO 2 & Sc 2 O 3 (scandia) GAA’s project was to see if we could get n as well as k from samples set up to measure transmission in the EUV. The films were deposited DIRECTLY on Absolute EUV silicon photodiodes. $$

3. 7 April 20063 Important info The EUV offers special challenges –Where in the EM spectrum is EUV? 1895 Roentgen discovers ~10 keV 20 years later understood ~ –What is between UV (3-7 eV) & x-rays? VUV, EUV & soft x-rays about 10 to 100 energy of UV –High absorption k = β = αλ/(4π) –Refractive index ~ <1; n = 1-  EUV Astronomy The Earth’s magnetosphere in the EUV

4. 7 April 20064 EUV Applications Extreme Ultraviolet Optics has many applications. These Include: –EUV Lithography- α & β- 2008 –EUV Astronomy –Soft X-ray Microscopes A Better Understanding of materials for EUV applications is needed. EUV Lithography EUV Astronomy The Earth’s magnetosphere in the EUV Soft X-ray Microscopes

5. 7 April 20065 Optics like n-IR, visible, & n- UV? First you need a light.

6. 7 April 20066 Optics like n-IR, visible, & n-UV? How to manipulate light? Lens? Prisms? Mirrors? Diff Gratings? ML interference coatings? We need to have optical constants; How to get in EUV? –Kramers-Kronig equations n ( )  k ( ) –Variable angle of reflection measurements, –Real samples aren’t good enough. Roughness

7. 7 April 20067 Transmission  k? T = (Corrections) exp (-αd); Corrections are due to R and can be small At normal incidence R goes as [  2 + β 2 ]/4 If film is close to detector scattering due to roughness etc. is less important. But how to get an even, thin film? –A very thin membrane?

8. 7 April 20068 Transmission thru a film on PI

9. 7 April 20069 But reflectance is a problem

10. 7 April 200610 The problem is waviness of substrate. Sample on Si does fine.

11. 7 April 200611 The Solution: Deposit the film on the detector Uspenskii, Sealy and Korde showed that you could deposit a film sample directly onto an AXUV100 silicon photodiode. (IRD) and determine the films transmission ( by ) from the ratio of the signal of the coated diode to an uncoated diode. SPIE proc. (2002)

12. 7 April 200612 Our group’s improvements 1.Measure the reflectance of the coated diode at the same time I am measuring the transmission. And 2.Measure both as a function of angle. And 3.Get the film thickness from the (R) interference fringes (@ high angles).

13. 7 April 200613 Comments 1.Either T or R have n and k data, but 2.Transmission has very little n data when d is small (the EUV). 3.Reflection  n, k and when interference fringes are seen, and 4.It has thickness (z) data. What follows shows how we confirmed thickness for air-oxidized Sc sputter- coated AXUV diodes.

14. 7 April 200614 Fitting T(  ) to get dead layer thickness (6nm) on bare AXUV diode @ =13.5nm

15. 7 April 200615 Interference in R (50<φ<70 0 )  z fit =19.8 nm @ =4.7 nm

16. 7 April 200616 The complete set of R data (6<θ<20 0 ) z fit =28.1 nm @ =4.7 nm

17. 7 April 200617 We might gone with z= 24 nm, but

18. 7 April 200618 We looked at another = 7.7nm; needs z=29 nm

19. 7 April 200619 And the =4.7nm data is OK

20. 7 April 200620 Reflectance and transmittance of a ThO 2 -coated diode at 15 nm fitted simultaneously to obtain n&k Green (blue) shows reflectance (transmission) as a function of grazing angle (  )* Noted the interference fringes at higher angles in R. *  is always from grazing incidence

21. 7 April 200621 R &T of a ThO 2 -coated diode at 12.6 nm fitted simultaneously to obtain optical constants. The fits were not very good at wavelengths where the transmission was lower than 4%. All of these fits were trying to make the fit of transmission narrower than the data was.

22. 7 April 200622 “Conclusions” Thin films of scandium oxide, 15-30 nm thick, were deposited on silicon photodiodes by –Sputtering Sc from a target & letting it air oxidize OR – reactively sputtering scandium in an oxygen environment. R and T Measured using synchrotron radiation at the als (Beamline 6.3.2), at LBNL –over wavelengths from 2.5-40 nm at variable –angles, were taken simultaneously.

23. 7 April 200623 Acknowledgements The BYU EUV Thin Film Optics Group, past and present. ALS for beam time under funded proposals. BYU Department of Physics and Astronomy, including support staff: Wes Lifferth, W. Scott Daniel and John E. Ellsworth. BYU Office of Research and Creative Activities, and Rocky Mountain NASA Space Grant Consortium for support and funding. SVC for scholarship support for Guillermo Acosta when this work was begun. Alice & V. Dean Allred (with matching contributions from Marathan Oil Company), ALS for beam time under funded proposals

24. 7 April 200624 Not shown in talk Data collected revealed the positions of electron transitions, which are displaced from the positions predicted by standard methods of calculation. Analysis of the data has provided optical constants for scandium oxide thin films, which have potential for use as a barrier or capping layer to prevent oxidation of sensitive optical coatings.