Basic Principles of X-ray Reflectivity in Thin Films - Felix Jimenez-Villacorta [Compatibility Mode].pdf

7/28/2019 Basic Principles of X-ray Reflectivity in Thin Films - Felix Jimenez-Villacorta [Compatibility Mode].pdf

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BasicPrinciples

of

X

ray

ReflectivityinThinFilms

FlixJimnezVillacorta

02-24-2011


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Outline

Xraydiffraction

Xraydiffractioninthinfilms:highanglevslowangle

XRR

as

structural

characterization Diffusescattering:specularvsoffspecular

reflectivity

Summary


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William Lawrence Bragg

William Henry Bragg


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Xray

diffraction

Bragg slaw:anglewhere

constructiveinterferenceofscatteredXraysproducesadiffractionpeak:

n =BC+CD=2dhklsinwhered

hklisthevectordrawnfrom

theoriginoftheunitcelltointersectthecrystallographicplane.


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Highangle

vs

Low

angleProbing ranges in x-ray

diffraction on thin filmsn = 2dsin = 2dhklsin n = 2tsin

~ 1/d

2=

k i k fQ

2=

k i k fQ

k (incident)

k(diffracted)

Q

d

High (high Q) = Lowd Low (lowQ) = High d


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Xray

Reflectivity

0 1 2 3 41E-6

1E-4

0,01

1

2c

2

m2

Log(Reflectivity)

Grazing incidence (degree)

8 nm

15 nm

0 20 40 60 80

0,000

0,001

0,002

W (8 nm) // Si

(/2d)2

2

222

2

=

dmc

44

22 116)(

zyx

z

el

qqq

qQR =

Reflectivity

(background)

Ateveryinterface,aportionofxraysisreflected.Interferenceofthesepartialyreflectedxraybeamscreatesareflectometrypattern.

Kiessigfringes


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Xray

Reflectivity

0 1 2 3 4

1E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

Grazing incidence angle (degree)

Log(Reflectivity)

CoSi2(15 nm) // Si

* Flat surface Vacuum/CoSi2

=0

* Rough interface CoSi

2/Si

no roughness

5A

10 A

Xrayreflectivitycanbeusedfor: Layerthicknessofthinfilmsandmultilayers. Surfaceandinterfaceroughness. Surfacedensitygradientsandlayerdensity.


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Xray

Reflectivity

Special case: bilayers and multilayers

Bilayer:2oscillationfrequenciesareevidenced

0 1 2 3

1E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

Grazing incidence (degree)

Log(Reflectivit

y)

CuO2 (5,5 nm) // Cu (45 nm) // Si

Cu

thickness

CuO2thickness

Multilayer:n1Kiessigfringesbetween2BraggPeaks

1 2 310

100

1000

10000

100000

Intensity(c.p.s.)

2-Theta

CoSN2


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Diffusescattering

Specular vs off-specular reflectivity

Specularcontributionofthediffusescattering Sameoscillationsthanreflectivitycurve

Longitudinaldiffusescattering


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Diffusescattering

0 1 2 3 4 5

10

100

1000

10000

100000

1000000

Intensity

2 theta ()

XRR specular

long. diff (=0.05)

long. diff (=0.1)

Off Specular XRR - (s2 - Au Cold)

0 1 2 3 4 5

10

100

1000

10000

100000

1000000

Off Specular XRR - (s6 - Au Hot)

Intensity

2 theta

XRR specular

long. diff. (=0.05)

long. diff. (=0.1)

Longitudinaldiffusescattering

FeRhthinfilms+cap

Um+1(x,y)

Um (x,y)

Um (x,y)hm

ideal

zm+1

zm

Q qzQ = qz


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Diffusescattering

Transversediffusescan(rockingcurve)

0 1 2

Log[

Intensity

(arb.

units)]

scan

=7000 A=2000 A=500 A

Yoneda Wingsc c

Specular

Various : Large lateral correlation at interfaceSpecular peak

Yoneda wings : each time iorf=c


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Summary

Ateveryinterface,aportionofxraysisreflected.Interferenceofthesepartialyreflectedxraybeamscreatesareflectometrypattern.

Xrayreflectivityisausefultechinqueforstructural

characterization

of

thin

films.

Information

about

the

thickness

andtheroughnessofsuchsamplescanbeobtained.

Diffusescatteringofxraysgivealsoinformationabouttheroughness,correlationlength(fractalparameters)insurfaces

andinterfaces.

Documents

Basic Principles of X-ray Reflectivity in Thin Films - Felix Jimenez-Villacorta [Compatibility Mode].pdf