16 August 200616 August 2006

Using Simultaneous Reflection and Using Simultaneous Reflection and Transmission MeasurementsTransmission Measurements

of Oxide to Help Determine Optical of Oxide to Help Determine Optical Constants in the EUVConstants in the EUV

D. D. Allred, G. A. Acosta, N. Farnsworth- D. D. Allred, G. A. Acosta, N. Farnsworth- Brimhall, J.E Johnson and R. S. Turley,Brimhall, J.E Johnson and R. S. Turley,

Brigham Young University,Brigham Young University,Provo, UTProvo, UT

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Outline of TalkOutline 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.

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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 (Th) ThO2 & Sc2O3 (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

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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

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U/Si ML coating for EUV instrument 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

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

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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

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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?

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

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But reflectance is a problemBut reflectance is a problem

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

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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 signals from various coated diodes with identical capping layers.

• JOSA 21(2) 298-305 (2004).

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Our group’s 1Our group’s 1stst approach 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.

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Fitting T(Fitting T() to get dead layer thickness ) to get dead layer thickness (6-7nm) on bare AXUV diode (6-7nm) on bare AXUV diode

@@=13.5nm=13.5nm

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Focusing on the high reflectance & Focusing on the high reflectance & transmission had a problemtransmission had a problem

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

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Our recent group’s approachOur 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).

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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

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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

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

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

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

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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

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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.

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““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.

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AcknowledgementsAcknowledgements• 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

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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.

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Important info 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