Determining the Optical Determining the Optical Constants of EUV Constants of EUV

ReflectorsReflectorsJedediah JohnsonJedediah Johnson

Dr. David AllredDr. David Allred

Talk OutlineTalk Outline

Background physics/applicationsBackground physics/applications

Project MotivationProject Motivation

Previous measurement techniquesPrevious measurement techniques

Current sputtered diode researchCurrent sputtered diode research

Reflectors in EUV rangeReflectors in EUV range

EUV range is about EUV range is about 100-1000Å100-1000Å

General Challenges:General Challenges:- hydrocarbon - hydrocarbon buildupbuildup- absorption- absorption- high vacuum - high vacuum neededneeded

Complex index of Complex index of refraction: refraction: ñ=n+ik

EUV ReflectorsEUV Reflectors

Light interacts Light interacts principally with principally with electrons.electrons.

More electrons = More electrons = higher the higher the theoretical theoretical reflectance. reflectance.

High density High density desired.desired.

Applications of EUV RadiationApplications of EUV RadiationEUV Lithography

Images from www.schott.com/magazine/english/info99/ and www.lbl.gov/Science-Articles/Archive/xray-inside-cells.html.

Soft X-ray Microscopes

Thin Film or Multilayer Mirrors

EUV Astronomy

The Earth’s magnetosphere in the EUV

Optical ConstantsOptical Constants Precise optical constant data allows scientists to Precise optical constant data allows scientists to

engineer reflectors for specific projects. engineer reflectors for specific projects. R+T+A=1R+T+A=1

Reflectance, S polarization at 10 degrees of various materials

0

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0.9

0 100 200 300 400 500 600

Energy in eV

Re

fle

cta

nc

e

Au Ni ThO2 UO2

Optical Constant Optical Constant Determination from Determination from

Transmission MeasurementsTransmission Measurements•CXRO has compiled optical constants which were usually measured from transmission measurements and Kramers-Kronig analysis

Kramers-Kronig AnalysisKramers-Kronig Analysis)()()( 21 i

0 222

1

)(21)(

dP

)()()()( 212 iN

)()()( inN •Integral evaluated from zero to infinity (approximations introduced)

•Numerical methods or complex analysis required

Computer and Measured Computer and Measured Reflectance vs. WavelengthReflectance vs. Wavelength

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0 5 10 15 20 25 30 35 40Wavelength (nm)

Ref

lect

ance

2.16-2.8 nm 2.7-4.8 nm 4.4-6.8 nm 6.6-8.8 nm8.4-11.6 nm 11.0-14.0 nm 12.4-18.8 nm 17.2-25.022.5-32.5 calc. AFM CXRO S polarized

Differences in the measured reflectance of thorium and the reflectance computed from CXRO constants call into question the accuracy of currently published data.

Simultaneous Reflection and Simultaneous Reflection and Transmission MeasurementsTransmission Measurements

First data acquired with new First data acquired with new diodesdiodes

ThO2 Transmission at normal incidence

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2 7 12 17 22

wavelength (nm)

tran

smis

sio

n

11-14 nm

12.4-18.8 nm

8.8-11.6 nm

6.6-8.8 nm

4.4 - 6.8 nm

2.7 - 4.8 nm

Comparison with previous Comparison with previous transmission window datatransmission window data

Normalized ThO2 transmission at 90 degrees

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wavelength (nm)

tran

smis

sio

n 124-188

123-133

172-250

110-140

84-116

66-88

44-68

28-48

172-250 redo

ConclusionsConclusions

We believe our methods will provide We believe our methods will provide the most accurate optical constant the most accurate optical constant measurements in the EUV.measurements in the EUV.

Remainder of data taken in March Remainder of data taken in March 2005 must be analyzed and fit.2005 must be analyzed and fit.

Acknowledgments Acknowledgments

BYU XUV Research Group colleaguesBYU XUV Research Group colleagues Dr. David D. Allred Dr. David D. Allred Dr. R. Steven TurleyDr. R. Steven Turley BYU Physics Department Research BYU Physics Department Research

FundingFunding