Optical Constants of Uranium Nitride Thin Films in the EUV (7-15 nm) Marie K. Urry EUV Thin Film...
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Transcript of Optical Constants of Uranium Nitride Thin Films in the EUV (7-15 nm) Marie K. Urry EUV Thin Film...
Optical Constants ofOptical Constants ofUranium Nitride Thin FilmsUranium Nitride Thin Films
in the EUV (7-15 nm)in the EUV (7-15 nm)
Marie K. UrryMarie K. Urry
EUV Thin Film GroupEUV Thin Film Group
Brigham Young UniversityBrigham Young University
Why Extreme Ultraviolet (EUV)?Why Extreme Ultraviolet (EUV)?
AstronomyAstronomy Energetic ObjectsEnergetic Objects IMAGE Satellite Mirror IMAGE Satellite Mirror
ProjectProject
LithographyLithography Projection ImaginingProjection Imagining
MedicineMedicine High Resolution High Resolution
Imaging MicroscopesImaging Microscopes
Images courtesy of http://euv.lpl.arizona.edu/euv/, www.schott.com/magazine/english/info99/ and www.schott.com/magazine/english/info99/.
Optical ConstantsOptical Constants
Index of refraction:Index of refraction:N = N = n n + + i ki k , ,
where where nn is the real part of the index of is the real part of the index of refraction and refraction and k k , the imaginary part, is , the imaginary part, is called the coefficient of absorption.called the coefficient of absorption.
For maximum reflection for multilayers, we For maximum reflection for multilayers, we want high change in want high change in nn and low and low k .k .
For a given material, optical constants are For a given material, optical constants are different for different wavelengths.different for different wavelengths.
Why Uranium?Why Uranium?
Most things, including air, are highly Most things, including air, are highly absorptive (big absorptive (big kk) in the EUV.) in the EUV.
Uranium has high theoretical reflectivity for Uranium has high theoretical reflectivity for the wavelengths of interest.the wavelengths of interest.
Problem: OxidationProblem: Oxidation
Computed Reflectance at 10 degrees of various materials
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
2 4 6 8 10 12 14 16 18 20Wavelength (nm)
Ref
lect
ance
Au Ni U
Reflectance computed using the CXRO Website: http://www-cxro.lbl.gov/optical_constants/mirror2.html
Computed Reflectance at 10 degrees of various materials
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
2 4 6 8 10 12Wavelength (nm)
Ref
lect
ance
ThO2 UO2 UN U
Reflectance computed using the CXRO Website: http://www-cxro.lbl.gov/optical_constants/mirror2.html
Making Thin FilmsMaking Thin Films SputteringSputtering
Bombard target, a large Bombard target, a large piece of uranium, with piece of uranium, with argon ions from glow argon ions from glow dischargedischarge
Uranium atoms leave Uranium atoms leave target due to collisionstarget due to collisions
Nitrogen partial pressure in Nitrogen partial pressure in plasma creates N atomsplasma creates N atoms
U and UN molecules U and UN molecules deposit on our samplesdeposit on our samples
Making Thin FilmsMaking Thin Films
SamplesSamples Samples deposited on silicon wafers, quartz Samples deposited on silicon wafers, quartz
slides, polyimide films, SiN membranes, and slides, polyimide films, SiN membranes, and carbon coated TEM gridscarbon coated TEM grids
UNUNxx films 10-30 nm thick films 10-30 nm thick Low pressure sputtering allows for smooth, Low pressure sputtering allows for smooth,
dense, low stress films because of the dense, low stress films because of the increased mean free path U atomsincreased mean free path U atoms
Making Thin FilmsMaking Thin Films
PressuresPressures Different partial pressures result in different Different partial pressures result in different
compounds.*compounds.* Above 1x10Above 1x10-4-4 torr partial pressure N torr partial pressure N22, we create , we create
UU22NN33. With lower pressures we can make UN.. With lower pressures we can make UN. Our system can’t measure partial pressures in Our system can’t measure partial pressures in
this range, so we don’t know which we made.this range, so we don’t know which we made.
L. Black, et al., Journal of Alloys and Compounds, L. Black, et al., Journal of Alloys and Compounds, 315315 (2001) 36-41. (2001) 36-41.
NN22 Partial Pressure vs. N/U Ratio Partial Pressure vs. N/U Ratio
Learning About the SamplesLearning About the Samples
X-Ray Photoelecton X-Ray Photoelecton Spectroscopy (XPS)Spectroscopy (XPS) To find compositionTo find composition
X-Ray Diffraction X-Ray Diffraction (XRD)(XRD) To find thicknessTo find thickness mλ = 2d sinθ
Atomic Force Atomic Force Microscopy (AFM)Microscopy (AFM) To measure roughnessTo measure roughness
Images courtesy of http://www.weizmann.ac.il/surflab/peter/afmworks/, and http://volta.byu.edu/adamson03.pdf .
Finding Optical ConstantsFinding Optical Constants
EllipsometryEllipsometry Optical constants are Optical constants are
different for different different for different polarizations of lightpolarizations of light
Advanced Light Advanced Light Source at BerkeleySource at Berkeley Measures reflectance Measures reflectance
at different angles and at different angles and wavelengthswavelengths
Images courtesy of http://www.lbl.gov/ and http://www.swt.edu/~wg06/manuals/Gaertner117/ellipsometerHome.htm.
Problem!!Problem!!
Is it really UN or is it UNIs it really UN or is it UN2-x2-x??
Our samples change with time.Our samples change with time. The peaks seen in XRD move.The peaks seen in XRD move.
Continuing research in this area.Continuing research in this area.
XRD DataXRD Data
TEM DataTEM Data
TEM DataTEM Data
SAMPLES UN002 UN003 UN004
N2 Pressure >1e-4 torr >1e-4 torr ~1e-5 torr
Suspected Phase U2N3 U2N3 UN
Lattice Size (nm) (Lit.) 0.534 0.534 0.489
XRD (nm) (Lattice Size) 50 40
Thickness Change
1% in 10 days
TEM (nm) (Thickness) 0.546 0.498
Ratio (measured/lit) 1.022 1.018
AcknowledgementsAcknowledgements
Thanks to:Thanks to:
Dr. David D. AllredDr. David D. Allred
Dr. R. Steven TurleyDr. R. Steven Turley
Kristi R. AdamsonKristi R. Adamson
Luke J. BissellLuke J. Bissell
Winston LarsenWinston Larsen
Richard L. SandbergRichard L. Sandberg
Mindy TonksMindy Tonks