Optical Constants ofOptical Constants ofUranium Nitride Thin FilmsUranium Nitride Thin Films

in the EUV (80-182 eV)in the EUV (80-182 eV)

Marie K. UrryMarie K. Urry

EUV Thin Film GroupEUV Thin Film Group

Brigham Young UniversityBrigham Young University

AcknowledgementsAcknowledgements

Thanks to:Thanks to:

Dr. David D. AllredDr. David D. AllredDr. R. Steven TurleyDr. R. Steven TurleyKristi R. AdamsonKristi R. Adamson

Luke J. BissellLuke J. BissellJennie GuzmanJennie Guzman

Elke JacksonElke JacksonWinston LarsenWinston Larsen

Mindy TonksMindy TonksDepartment FundingDepartment Funding

OutlineOutline

Why We Do What We DoWhy We Do What We Do

Making Thin FilmsMaking Thin Films

Studying Thin FilmsStudying Thin Films

Finding Optical ConstantsFinding Optical Constants ReflectometerReflectometer

Why Extreme Ultraviolet (EUV)?Why Extreme Ultraviolet (EUV)?

AstronomyAstronomy Our IMAGE Satellite Our IMAGE Satellite

Mirror ProjectMirror Project

LithographyLithography Projection ImaginingProjection Imagining Scheduled for 2009Scheduled for 2009

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

In EUV, In EUV, n n ≈ ≈ 1 and 1 and kk is huge. is huge. n n = 1 - = 1 -

kk = =

High High and low and low for maximum reflection for maximum reflection for multilayersfor multilayers..

→→

Delta-Beta Scatter Plot at 220 eVDelta-Beta Scatter Plot at 220 eV

ββ

Why Uranium Nitride?Why Uranium Nitride?

UraniumUranium High theoretical reflectivity due to high High theoretical reflectivity due to high

Problem: OxidationProblem: Oxidation NitrideNitride

Little effect on reflectivityLittle effect on reflectivity Prevents oxidationPrevents 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

0 50 100 150 200 250 300 350 400 450Photon Energy (eV)

Refle

ctan

ce

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

50 70 90 110 130 150 170 190 210 230 250Photon Energy (eV)

Ref

lecta

nce

ThO2 UO2 UN U

Reflectance computed using the CXRO Website: http://www-cxro.lbl.gov/optical_constants/mirror2.html

Delta-Beta Scatter Plot at 220 eVDelta-Beta Scatter Plot at 220 eV

ββ

Making Thin FilmsMaking Thin Films SputteringSputtering

Bombard target, uranium, Bombard target, uranium, with argon ionswith argon ions

Uranium atoms leave Uranium atoms leave target due to collisionstarget due to collisions

Nitrogen partial pressure in Nitrogen partial pressure in plasma introduces N atomsplasma introduces N atoms

U and UN molecules U and UN molecules deposit on our samplesdeposit on our samples

Making Thin FilmsMaking Thin Films 10-30 nm thick10-30 nm thick

Deposited on:Deposited on: silicon waferssilicon wafers quartz slidesquartz slides polyimide filmspolyimide films SiN membranesSiN membranes carbon coated TEM gridscarbon coated TEM grids

Low pressure sputteringLow pressure sputtering smooth, dense, low stress filmssmooth, dense, low stress films

Side Note for ClarificationSide Note for Clarification

Samples 002 – 005Samples 002 – 005 002 and 003 are U002 and 003 are U22NN33

004 and 005 are UN004 and 005 are UN• 005 is new and unmeasured005 is new and unmeasured

Making Thin FilmsMaking Thin Films

Partial pressure Partial pressure determines determines stoichiometrystoichiometry

Our system Our system couldn’t control couldn’t control partial pressures in partial pressures in the critical rangethe critical range

N2 Partial Pressure vs N/U RatioN2 Partial Pressure vs N/U Ratio

Image courtesy of L. Black, et al., Journal of Alloys and Compounds, 315 (2001) 36-41.

Learning About the SamplesLearning About the Samples

CompositionComposition Depends on partial pressure in systemDepends on partial pressure in system

ThicknessThickness Crystal monitor is to the side of the film and Crystal monitor is to the side of the film and

gets less accurate with timegets less accurate with time RoughnessRoughness

Optical ConstantsOptical Constants

X-Ray Photoelectron Spectroscopy X-Ray Photoelectron Spectroscopy (XPS)(XPS)

Uses photoelectric Uses photoelectric effect to find effect to find compositioncomposition

Images courtesy of http://volta.byu.edu/adamson03.pdf .

1000 900 800 700 600 500 400 300 200 100 0

1.8K

1.6K

1.4K

1.2K

1K

800

600

400

200

X-Ray Photoelectron Spectroscopy X-Ray Photoelectron Spectroscopy (XPS)(XPS)

Counts

Energy (eV)

Survey Scan of SurfaceIdentifying Peaks:

100eV – U 5d5/2280eV – C1s380eV – U4f7/2390eV – U4f5/2398eV – N1s530eV – O1s740eV – U4d5/2780eV – U4d3/2980eV – Auger O

X-Ray Photoelectron Spectroscopy X-Ray Photoelectron Spectroscopy (XPS)(XPS)

409.9 404.9 399.9 394.9 389.9 384.9 379.9 374.9

360340320300

280260240220200180

1601401201008060

4020

Uranium Energy Peaks

Counts

Energy (eV)

X-Ray Photoelectron Spectroscopy X-Ray Photoelectron Spectroscopy (XPS)(XPS)

399.9 398.9 397.9 396.9

180

175

170

165

160

155

150

145

140

135

130

Nitrogen Energy Peaks

Counts

Energy (eV)

X-Ray Diffraction (XRD)X-Ray Diffraction (XRD)

To find thicknessTo find thickness m λ = 2d sin θ

UNx004d1

0

500

1000

1500

2000

2500

3 3.5 4 4.5 5 5.5 6Degrees

Co

un

tsUNx003l

100110021003100410051006100710081009100

10100

1.6 2.1 2.6 3.1 3.6Degrees

Co

un

ts

XRD DataXRD Data

Change in theta between 8 peaks minima around theta=1.5 for UO2

XRD DataXRD Data

Atomic Force Microscopy (AFM)Atomic Force Microscopy (AFM)

To Measure To Measure RoughnessRoughness

Result: RMS Result: RMS roughnessroughness

Images courtesy of http://www.weizmann.ac.il/surflab/peter/afmworks/.

Length Scale vs. RMSLength Scale vs. RMSRMS and length scale in nm

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.5 1.7 1.9 2.1 2.3 2.5

log [1/(length scale )]

log

(R

MS

)

Y= -0.5666 x +1.677

Transmission Electron Microscope Transmission Electron Microscope (TEM)(TEM)

Transmission Electron Microscope Transmission Electron Microscope (TEM)(TEM)

 SAMPLES UN002 UN003 UN004N2 Pressure >1e-4 torr >1e-4 torr ~1e-5 torr

Suspected Phase U2N3 U2N3 UN

Lattice Size

Literature (Å) 5.34 5.34 4.89

XRD (Å)   5.0 4.0

TEM (Å) 5.46   4.98

Ratio (measured/lit) 1.022   1.018

EllipsometryEllipsometry

Optical constants are Optical constants are different for different different for different polarizations of lightpolarizations of light

If we know the If we know the substance and a substance and a model for the optical model for the optical constants, we can constants, we can find thickness and find thickness and optical constants in optical constants in UVUV

Images courtesy of http://www.swt.edu/~wg06/manuals/Gaertner117/ellipsometerHome.htm.

Finding Optical ConstantsFinding Optical Constants

Advanced Light Advanced Light Source at BerkeleySource at Berkeley

Light created by Light created by synchrotronsynchrotron

Measures reflectance Measures reflectance at different angles and at different angles and wavelengthswavelengths

Image courtesy of http://www.lbl.gov/.

ReflectometerReflectometer Reassembled and alignedReassembled and aligned

Hollow Cathode Light SourceHollow Cathode Light Source

Plasma with H or HePlasma with H or He 700 V DC700 V DC Spectral Lines from Spectral Lines from

HeHe 304 Angstroms304 Angstroms

• 2p->1s2p->1s 584 Angstroms584 Angstroms

• 1s2p->1s1s2p->1s22

Found leaksFound leaks Replace plexi-glassReplace plexi-glass

ReflectometerReflectometer Replaced CEMReplaced CEM Purchased stages Purchased stages

and stepper motorsand stepper motors

ElectronMultiplierTube

ReflectometerReflectometer

Lab VIEW Program Lab VIEW Program for Centering Detectorfor Centering Detector Assumed a GaussianAssumed a Gaussian Theta/2*theta Theta/2*theta

misalignmentmisalignment

ReflectometerReflectometer

Other ImprovementsOther Improvements Circuit diagramsCircuit diagrams SOP’sSOP’s

Still workingStill working Fixing virus problemsFixing virus problems

On to Berkeley!On to Berkeley!

OutlineOutline

Background (9 minutes)Background (9 minutes) Why EUV? Why EUV? Optical ConstantsOptical Constants Why Uranium?Why Uranium?

Making & Studying Thin Making & Studying Thin Films (13 minutes)Films (13 minutes)

SputteringSputtering XPSXPS XRDXRD AFMAFM TEMTEM EllipsometryEllipsometry

Finding Optical Constants Finding Optical Constants (10 minutes)(10 minutes)

What we want to knowWhat we want to know ALSALS Reflectometer/ Reflectometer/

MonochromatorMonochromator Results/Continuing Results/Continuing

Research (8 minutes)Research (8 minutes) Acknowledgements (1 Acknowledgements (1

minute)minute)

To DoTo Do

Learn about light source (internet)Learn about light source (internet) Ellipsometry stuff (Dr. Allred)Ellipsometry stuff (Dr. Allred) Update “Problem!!” and data slides (Dr. Update “Problem!!” and data slides (Dr.

Allred)Allred)

IMDIMD

Written by David WendtWritten by David Wendt Computes reflectivities of materials based Computes reflectivities of materials based

on their optical constantson their optical constants We used UO model because of similar We used UO model because of similar

densitiesdensities (Insert graph here)(Insert graph here)

Problem!!Problem!!

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.