Determining the Optical
Constants of EUV Reflectors
Jedediah Johnson
Dr. David Allred
Talk Outline

Background physics/applications

Project Motivation
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Previous measurement techniques

Current sputtered diode research
Reflectors in EUV range



EUV range is about
100-1000Å
General Challenges:
- hydrocarbon buildup
- absorption
- high vacuum needed
Complex index of
refraction: ñ=n+ik
EUV Reflectors



Light interacts
principally with
electrons.
More electrons =
higher the theoretical
reflectance.
High density desired.
Applications of EUV Radiation
Thin Film or Multilayer Mirrors
EUV Lithography
EUV Astronomy
Soft X-ray Microscopes
The Earth’s magnetosphere in the EUV
Images from www.schott.com/magazine/english/info99/ and www.lbl.gov/Science-Articles/Archive/xray-inside-cells.html.
Optical Constants

Precise optical constant data allows scientists to
engineer reflectors for specific projects.
R+T+A=1
Reflectance, S polarization at 10 degrees of various materials
0.9
0.8
0.7
Reflectance

0.6
0.5
0.4
0.3
0.2
0.1
0
0
100
200
300
400
Energy in eV
Au
Ni
ThO2
UO2
500
600
Optical Constant Determination
from Transmission Measurements
•CXRO has compiled optical constants which were usually
measured from transmission measurements and Kramers-Kronig
analysis
Kramers-Kronig Analysis
 ()   1 ()  i 2 ()
  2 ( )
 1 ( )  1  P 
d 
2
2
 0   
2
N ( )   ( )   1 ( )  i 2 ( )
2

N ( )  n( )  i ( )
•Integral evaluated from zero to infinity (approximations introduced)
•Numerical methods or complex analysis required
Computer and Measured
Reflectance vs. Wavelength
Differences in the measured reflectance of thorium and the reflectance
computed from CXRO constants call into question the accuracy of currently
published data.
0.9
0.8
Reflectance
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
5
2.16-2.8 nm
8.4-11.6 nm
22.5-32.5
10
15
20
25
Wavelength (nm)
2.7-4.8 nm
11.0-14.0 nm
calc. AFM CXRO S polarized
4.4-6.8 nm
12.4-18.8 nm
30
35
6.6-8.8 nm
17.2-25.0
40
Simultaneous Reflection and
Transmission Measurements
First data acquired with new diodes
ThO2 Transmission at normal incidence
0.9
0.8
transmission
0.7
0.6
11-14 nm
12.4-18.8 nm
0.5
8.8-11.6 nm
6.6-8.8 nm
0.4
4.4 - 6.8 nm
2.7 - 4.8 nm
0.3
0.2
0.1
0
2
7
12
17
wavelength (nm)
22
Comparison with previous
transmission window data
Normalized ThO2 transmission at 90 degrees
1
0.9
transmission
0.8
0.7
124-188
0.6
172-250
123-133
110-140
0.5
84-116
66-88
0.4
44-68
28-48
0.3
172-250 redo
0.2
0.1
0
0
5
10
wavelength (nm)
15
20
Conclusions
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We believe our methods will provide the
most accurate optical constant
measurements in the EUV.
Remainder of data taken in March 2005
must be analyzed and fit.
Acknowledgments
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BYU XUV Research Group colleagues
Dr. David D. Allred
Dr. R. Steven Turley
BYU Physics Department Research
Funding