1. 16 August 2006 Using Simultaneous Reflection and Transmission Measurements of Oxide to Help Determine Optical Constants in the EUV D. D. Allred, G. A. Acosta, N. Farnsworth- Brimhall, J.E Johnson and R. S. Turley, Brigham Young University, Provo, UT

2. 16 August 20062 Outline of Talk EUV overview BYU Group involvement in EUV –Past projects Image Spacecraft –What does UG research look like? The importance of O. The need to contribute. An account of the campaign to understand two oxides.

3. 16 August 20063 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 (Th) ThO 2 & Sc 2 O 3 (scandia) Our 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. IRD

4. 16 August 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. 16 August 20065 U/Si ML coating for EUV instrument Picture (41 eV) is from EUV imager on the IMAGE Spacecraft. He (II) in magnetosphere This was student powered project 1997-98 Designed: needed 7 degree width off normal, 7.5 layer U/Si ML with UOx cap- peak R 25% Coated & Tested Launched 2000 March 25

6. 16 August 20066 Optics like n-IR, visible, & n- UV? First you need a light.

7. 16 August 20067 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

8. 16 August 20068 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?

9. 16 August 20069 Transmission thru a film on PI

10. 16 August 200610 But reflectance is a problem

11. 16 August 200611 The problem is waviness of substrate. Sample on Si does fine.

12. 16 August 200612 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 signals from various coated diodes with identical capping layers. JOSA 21(2) 298-305 (2004).

13. 16 August 200613 Our group’s 1 st approach 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 and T data to check ellipsometry of witness.

14. 16 August 200614 Fitting T(  ) to get dead layer thickness (6-7nm) on bare AXUV diode @ =13.5nm

15. 16 August 200615 Focusing on the high reflectance & transmission had a problem

16. 16 August 200616 Comments 1.Either T or R have n and k data, but 2.Transmission has very little n data when δ 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.

17. 16 August 200617 Our recent group’s approach 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).

18. 16 August 200618 Interference in R (50<φ<70 0 )  z fit =19.8 nm @ =4.7 nm

19. 16 August 200619 The complete set of R data (6<θ<20 0 ) z fit =28.1 nm @ =4.7 nm

20. 16 August 200620 We might gone with z= 24 nm, but

21. 16 August 200621 We looked at another = 7.7nm; needs z=29 nm

22. 16 August 200622 And the =4.7nm data is OK

23. 16 August 200623 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

24. 16 August 200624 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.

25. 16 August 200625 “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.

26. 16 August 200626 Acknowledgements The BYU EUV Thin Film Optics Group, past and present. ALS for beam time under funded proposals. Robert Lawton 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

27. 16 August 200627 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.

28. 16 August 200628 Important info The EUV offers special challenges –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