7 april 2006 simultaneous reflection and transmission measurements of scandium oxide thin films in...

7 April 20067 April 2006

Simultaneous Reflection and Simultaneous Reflection and Transmission MeasurementsTransmission Measurements

of Scandium Oxide Thin Films in of Scandium Oxide Thin Films in the Extreme Ultravioletthe Extreme Ultraviolet

G. A. Acosta, G. A. Acosta, D. D. AllredD. D. Allred, D. Muhlestein, , D. Muhlestein, N. Farnsworth- Brimhall, and R. S. N. Farnsworth- Brimhall, and R. S. Turley,Brigham Young University,Turley,Brigham Young University,

Provo, UTProvo, UT

7 April 20067 April 2006 22

OverviewOverview• 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 ThO2 &Sc2O3 (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. $$

7 April 20067 April 2006 33

Important info 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

7 April 20067 April 2006 44

EUV ApplicationsEUV Applications• Extreme Ultraviolet Optics has

many applications. • These Include:

– EUV Lithography- α & β- 2008– EUV Astronomy– Soft X-ray Microscopes

• A Better Understanding ofmaterials for EUV applications is needed.

EUV Lithography

EUV Astronomy

The Earth’s magnetosphere in the EUV

Soft X-ray Microscopes

7 April 20067 April 2006 55

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

7 April 20067 April 2006 66

Optics like n-IR, visible, & n-UV?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 April 20067 April 2006 77

TransmissionTransmissionkk??

• T = (Corrections) exp (-αd);

• Corrections are due to R and can be small

• At normal incidence R goes as [2 + β2]/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?

7 April 20067 April 2006 88

Transmission thru a film on PI Transmission thru a film on PI

7 April 20067 April 2006 99

But reflectance is a problemBut reflectance is a problem

7 April 20067 April 2006 1010

The problem is waviness of The problem is waviness of substrate. Sample on Si does fine.substrate. Sample on Si does fine.

7 April 20067 April 2006 1111

The Solution: Deposit the film The Solution: Deposit the film on the detectoron 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)

7 April 20067 April 2006 1212

Our group’s improvementsOur 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).

7 April 20067 April 2006 1313

Comments Comments 1. Either T or R have n and k data, but2. Transmission has very little n data when d is

small (the EUV).3. Reflection n, k and when interference

fringes are seen, and4. It has thickness (z) data.

What follows shows how we confirmed thickness for air-oxidized Sc sputter-coated AXUV diodes.

7 April 20067 April 2006 1414

Fitting T(Fitting T() to get dead layer thickness ) to get dead layer thickness (6nm) on bare AXUV diode @(6nm) on bare AXUV diode @=13.5nm=13.5nm

7 April 20067 April 2006 1515

Interference in R (50<Interference in R (50<φφ<70<7000) ) z zfitfit=19.8 nm @=19.8 nm @ =4.7 nm =4.7 nm

7 April 20067 April 2006 1616

The complete set of R data The complete set of R data (6<(6<θθ<20<2000) z) zfit fit =28.1 nm =28.1 nm @@ =4.7 nm =4.7 nm

7 April 20067 April 2006 1717

We might gone with z= 24 nm, butWe might gone with z= 24 nm, but

7 April 20067 April 2006 1818

We looked at another We looked at another = 7.7nm; = 7.7nm; needs z=29 nmneeds z=29 nm

7 April 20067 April 2006 1919

And the And the =4.7nm data is OK=4.7nm data is OK

7 April 20067 April 2006 2020

Reflectance and transmittance of a ThOReflectance and transmittance of a ThO22-coated -coated

diode at 15 nm fitted simultaneously to obtain n&kdiode 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

7 April 20067 April 2006 2121

R &T of a ThOR &T of a ThO22-coated diode at 12.6 nm fitted -coated diode at 12.6 nm fitted

simultaneously to obtain optical constants.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.

7 April 20067 April 2006 2222

““Conclusions”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.

7 April 20067 April 2006 2323

AcknowledgementsAcknowledgements• 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

7 April 20067 April 2006 2424

Not shown in talkNot 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.