ThinFilm_XRD

7/22/2019 ThinFilm_XRD

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Thin film analysis

Advanced X-ray Workshop, S.N. Bose National Centre

Innovation with Integrity


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14-15/12/2011 2

Metal conductor paths (Cu, Al, AlSiCu) Insulators (SiO2, HfO2) in semiconductors Diffusion barriers (Si3N4, Ti/TiN) Semiconductors (SiGe, GaAs, InP) Active zones in lasers and LEDs (InGaN, AlGaAs, GaN) Hard coatings (TiN) Solar cells a.k.a photovoltaics (CuInSe2,CdS, CdTe, organic) Magnetic active layers (CoPtCr) Piezoelectrics(PMN-PT, PZT, PLZT, PbTiO3) Optical coatings Electro-optics (PLZT, PMN-PT) Magnetostrictives (FeGa) Fuel cells (YSZ, Gd-CeO2) Superconductors (MgB2, YBa2Cu3O7)

Thin Films

Samples 1

Advanced X-ray Workshop


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14-15/12/2011 3

Electrolytes in batteries (LiPO3) Oxide electrodes (SrRuO3) Catalysts (MOFs, CeO2) Coatings (bathroom fixtures, corrosion prevention) Communication/band gap tuning (HEMTs...quantum wells) Thermoelectrics (Pb0.5Sn0.5Te) Energy storage (ultracapacitors using metal carbides) Energy harvesting/ energy conversion

Thin Films

Samples 2



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A thin film is a layer of material ranging from fractions ofnanometers (monolayer) to several micrometers in thickness.

Thin films can have different degree of crystallinity: fromamorphous to single crystal.

Thin Film Characteristics

Organicmonolayer

Nanoparticlesin matrix

Back-end(Semi.)

Front-endSiGe

OxydeSemi.

1 m100 nm10 nm1 nm Layer thickness

Low-k oxides

Degree of order

Amorphous

Poly

crytal.Singlecrystal

CoatingsMagn. storage

LEDs



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Thin Film XRD Methods

Parameters of Interest

14-15/12/2011 5Bruker Confidential

High-Resolution

X-Ray Diffraction

thickness lattice parameter

lattice mismatch composition strain & relaxation lateral structure mosaicity (crystallinity)

defects

X-Ray Reflectometry

layer thickness composition roughness density porosity

Reciprocal Space

Mapping

lattice parameter lattice mismatch

composition orientation relaxation lateral structure

Stress and Texture

orientation distribution orientation quantification residual stress epitaxial relationship

Grazing incidence

Diffraction (GIXRD)

depth dependent information phase identification lattice parameter microstructure (size/strain) residual stress

In-Plane GIXRD

IP-lattice parameter IP-crystallite size IP-orientation

epitaxial relation



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High-Resolution

X-Ray Diffraction



defects

X-Ray Reflectometry

layer thickness composition roughness density porosity

Reciprocal Space

Mapping



Stress and Texture

orientation distribution orientation quantification residual stress epitaxial relationship

Grazing incidence

Diffraction (GIXRD)


In-Plane GIXRD


epitaxial relation



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7

A surface-sensitive X-ray scattering technique

Non-destructive method Wavelength probes on nanometer scale Works for crystalline and amorphous materials

What does XRR provide?

Layer thickness 0.1 nm 1000 nm Material density < 1-2% Roughness of surfaces and interfaces < 3-5 nm

What is X-ray Reflectometry (XRR)?

14-15/12/2011 Advanced X-ray Workshop


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Analytical tasks

Lateralstructure

Layer thickness ChemicalComposition

(electron density)

Roughness

Specular XRR Diffuse

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The specularXRR scattering geometry

9

Wavevector transfer hasa non-zero component

perpendicular to thesample surface

For Cu-K (=1.54)

XRR probes the laterally averagedelectron density

yxzyxz

,),,()( =

q=(0,0,q )z

ki kf

z

x

sin2kqz=

22)exp()()( dzziqzqS zz

][140/2 1= nmqz



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The reflectivity from a substrate

10

0 z

( )z

exp(iqz)

R exp(-iqz)

T exp(iQz)

erqQ 162 =

2

2)()(Qq

QqqRqr FF

+

==

Fresnel reflectivity

with



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The higher the electron density(z) of a material the higher the

critical angle

The higher the electron density,

the more intensity is scattered athigher angles

This limits the accessible angularrange for light materials like soft-matter films

Density dependency of the reflectivity

11

c

4

2

c

r



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small inclinations of the surface normal on a large scale of some100 nm

broadening of the specular reflected beam The broadening of the specular reflected beam decreases the

reflected intensity

It does not contains any information about internal sample

structure Samples should have a flat surface

Influence of Roughness

Waviness

waviness



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large inclinations of the surface normal on an atomic scale of a fewnanometers

leads to diffuse reflection of the incident beam the intensity of the specular reflected beam decreases


Microscopic Roughness

waviness

microscopicroughness



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Roughness decreases thereflected intensity dramatically

XRR is highly sensitive toroughness

Roughness causes diffuse

scattering

The interface roughness shouldnot be larger than 2-3 nm.



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XRR from single layer on substrate:

Thickness fringes

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The interference of the wavesreflected from the interfacescauses oscillations of period

The minimal observablethickness is limited by themaximal measurable range

The maximal observablethickness is limited by the

instrumental resolution

The sample should havethicknesses observable withthe instrumental setup.

dqz /2=



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Thickness fringes

Amplitude

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Amplitude of the thick-ness fringes increases

with increasing densitycontrast

XRR is quite sensitive tovariations of the electron

density

The sample should have agood contrast in the

electron density.



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XRR from multilayers

0,0 0,5 1,0 1,5 2,0 2,5 3,010-6

10-5

10-4

10-3

10-2

10-1

100

2 - layer system

10 nm Ag

60 nm Au

Si - substrat

Reflectivity

Incidence angle []



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X-ray Reflectometry in Practise

Demands on Sample Properties

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Golden Rule:

You should be able to see yourreflection on the surface of the

sample!

Flat and lateral homogeneous - notstructured

Sample roughness < 5nm

Good contrast in electron density forlayered samples

Length of at least 3-5 mm in beamdirection



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Reasonable resolution requires slit of 50-100 m Intensity is on the order of 107 cps Full energy spectrum creates high background

Simplest Setup for XRR



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Mirror converts 0.35 into a parallel beam of 1.2 mm Integrated intensity >109 cps Mainly K-radiation is reflected

Principle of the Gbel Mirror

Parabola

X-ray source

Goebel mirror

Sample



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Slits can be easily exchanged to tune resolution A reasonable resolution requires a slit size of 0.1 0.2 mm Integrated intensity 2x108 cps

The standard XRR setup for thin films



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Use slits to balance flux and resolution

Reflectometry with different slits

Int

.[cps]

100

1000

1e4

1e5

1e6

1e7

2/

0 1 2 3 4 5 6 7

with 0.6 mm slit

with 0.1 mm slit

~ 5 min

~ 6.5 h

Int

.[cps]

100

1000

1e4

1e5

1e6

1e7

2/

0 1 2 3 4 5 6 7



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Full beam on primary side Soller with resolution down to 0.1 Integrated intensity 8x108 cps

XRR setup for very thin layers



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Limits of X-Ray Reflectometry

Thin layers Example: LaZrO on Si

24

2 []

1412108642

Intens

ity[au]

-81*10

-7

1*10

-61*10

-51*10

-4

1*10

-31*10

-21*10

-11*10

01*10

Si (111)

6.7 nm LaZrO



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Analyzer crystal separates K1, suppresses diffuse scattering andfluorescence

Crystal can accept the full incident beam Integrated intensity 3x107 cps (for a 3-bounce analyzer)

XRR with an analyzer crystal

Analyzer crystal

improves the resolution:

1-bounce Ge(220)

3-bounce Ge(220)



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Monochromator cystals provide highly parallel and monochromaticbeam

Crystals can accept the full incident beam Integrated intensity 105 - 106 cps

XRR setup for thick layers

Analyzer crystal:

1-bounce Ge(220s)

3-bounce Ge(220s)

Monochromator crystal:

4-bounce Ge



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Limits of X-ray Reflectometry

Thick layers example: SiO2 on Si

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Int.[au]

5

10

100

1000

1e4

2 []

0.11 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

Si

1014 nm SiO2:H



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For Cu-K radiation: 1.54 Values for were obtained by scanning the direct beam

Obtained from the rough estimation

Resolution of differents setups

2/d

Tube side Detector side [deg] dmax [nm]

GM + 1.2mm 0.2 soller 0.06 73

GM + 0.2mm 0.2mm slits 0.029 150

2xGe(220a) 0.2mm slits 0.026 170

GM 3xGe(220s) 0.013 340

2xGe(220a) 3xGe(220s) 0.01 440

4xGe(220s) 3xGe(220s) 0.006 735

4xGe(440s) 3xGe(220s) < 0.006 > 735



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Footprint of the beam on surface: Beam matches the sample size at:

Below B the intensity is reduced by:

Geometrical corrections

The footprint

)/arcsin( LdB=

)sin(/)sin( BB =

sin/dD=

d : beam width

L : sample length || beam

D : illuminated area

L

d

D



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Sample size reduces the reflected intensity at small angles

Sample must be sufficiently large for XRR

Geometrical corrections

The footprint

Beamsize : 200 m



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The KEC allows the removal of the footprint effect by making the probedarea smaller than the sample size

For higher angles, the KEC needs to be lifted from the surface to gain flux

The measurement with KEC will be upscaled to the curve without KEC

Controlling the footprint

The Knife Edge Collimator



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Controlling the footprint

The Knife Edge Collimator

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Measurement with KEC mustbe performed up to at least2B

The high-anglemeasurement without KECmust have an overlap withthe KEC measurement torescale the data properly

0,0 0,5 1,0 1,5 2,0

104

105

106

107

108

with KEC

without KEC

Inte

nsity

2 [deg]



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Evaluation of SampleFitting Procedure

Sample Model parameterized by {p1,pN}

Tolerance

XRR Simulation

Comparison with Experiment, 2 cost function

Minimization of 2 using Genetic Algorithm,

Levenberg-Marquardt, Simplex,

Simulated Annealing, etc. in view of {p1..pN}



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Amorphous HfO2 film Ultra thin films

34

[degees]



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XRR on MEMS Ru/SiN film



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GMR Heterostructure 8 Layers

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Sample courtesy of Dr. Schug, IBM Mainz



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High-Resolution

X-Ray Diffraction



defects

X-Ray Reflectometry

layer thickness

composition roughness density porosity

Reciprocal Space

Mapping



Stress and Texture

orientation distribution

orientation quantification residual stress epitaxial relationship

Grazing incidence

Diffraction (GIXRD)


In-Plane GIXRD


epitaxial relation



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For coatings (few microns down to sub-micron range), the Bragg-Brentanogeometry (BB) is still the best configuration. This is basically the classicalpowder diffraction case and BB will offer the best grain statistic and the

easiest instrumental function characterization.

Providing that the preferred orientation is weak, quantitative phase analysisor microstructure investigation (size/strain) are quite easy to perform.

Limitations of the BB set-up: If the substrate is a single crystal, the hugeintensity from the substrate peak will emphasize all minor peaks originatingfrom the energy spectrum of the tube and other aberrations (K, tube tails,Ni absorption edge, W lines,) with the consequence that a significant partof the scan wont be usable.

Remarks for Coatings



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Even if a layer is polycrystalline, several characteristics differentiate apolycrystalline thin film with a loosed powder:

Due to the limited layer thickness, the grain statistics is limited. Theclassical BB geometry might fail in providing necessary peak intensity forfurther analysis. An alternative is then to go for GIXRD.

The confinement of the grains into a limited volume very often causespreferred orientation and the quantitative phase analysis might becomeimpossible.

The grain interaction during growth can also induce residual stress.

A composition gradient through the layer may also appear during thegrowth.

Polycrystalline Thin Films

Constrains



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Grazing Incidence X-Ray Diffraction

Instrumental Set-up Requirements

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GIXRD requires a parallel-beam set-up

A parallel beam Goebel mirror (mostly

Cu radiation is used)

A small slit would also work, at the

cost of intensity

A stage able to precisely adjust thesample height (z-alignment)

A parallel beam attachement on

secondary side (Soller plate collimator,

defining the instrumental resolution) A 0-D detector (e.g. scintillation

counter or LYNXEYE in 0-D mode)



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Lin(Counts)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

2-Theta - Scale

5 10 20 30 40 50 60 70 80 9

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Bragg-Brentano geometry Grazing incidence geometry

Lin(Counts)

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

2-Theta - Scale

5 10 20 30 40 50 60 70 80 9

Grazing incidence diffraction

Ag2Te thin film on glass

GIXRD emphasizes the signal of the Ag2Te nanocrystallites,

and the glass substrate signal is reduced



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Footprint of the beam on surface: The all idea of GIXRD is to increase the number of diffracting crystallites

(low incident angle) and increase the flux density (Goebel mirror).

Depending on the sample length, the layer densityand the expectedpenetration depth, an incident angle is chosen and remains fixed during thedata collection.

GIXRD

The Footprint

42

d : beam widthL : sample length || beam

D : illuminated area

L

d

D



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A detector scan (or 2 scan) is performed. The use of a Sollerplates collimator maintains a good resolution in 2 (given by the

acceptance of the Soller plates) while getting diffraction signal fromthe whole footprint on the sample.

GIXRD

Data collection

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2

Soller plates collimator defines the

instrumental resolution!Available: 0,1, 0,2, 0,3, 0,4



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Incident angle

Theta=0.2 to few degrees

Gbelmirror

Equatorialsoller

LYNXEYE 0D

XYZ stage

Grazing Incidence Diffraction

Phase ID depth profile



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At 0,2 deg incident angle,only Mo layer is detected.

At higher incident angle,the YH2 layer is reachedand starts to diffract.

Grazing Incidence Diffraction

Phase ID depth profile



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Standard GIXRD or so-called coplanar geometry In-plane GIXRD or so-callednon-coplanar geometry

The idea remains the same:optimizing the grain statistic when looking at different grain orientations

Combination of GIXRD with IP-GIXRD



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ULTRA-GID

Coplanar vs. Non-Coplanar Diffraction

14-15/12/2011 47Advanced X-ray Workshop

Coplanar diffraction

(hkl) // sample surface

ULTRA-GID @ 0

Non-coplanar diffraction

In-Plane GID (hkl) sample surface

ULTRA-GID @ 90if

i

D

2IP-GID


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XRR on Si/SiO2/Si

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LEPTOS results

100,3 nm SiO214,7 nm Si



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Coplanar GIXRD on Si/SiO2/Si

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TOPAS results

Cubic Si

a=5.41285 A9 nm normal crystallite size



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Non-coplanar GIXRD on Si/SiO2/Si

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TOPAS results

Cubic Si

a=5.41285 A14 nm lateral crystallite size



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XRR on ZrO2/Si

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LEPTOS results

3,2 nm ZrO2



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Coplanar GIXRD on ZrO2

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TOPAS results

Tetragonal ZrO2a=3,5658 Ac=5,1614 A3,4 nm normal crystallite size



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Non-coplanar GIXRD on ZrO2

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TOPAS results

Tetragonal ZrO2a=3,5994 Ac=5,18424 A30,4 nm lateral crystallite size




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High-Resolution

X-Ray Diffraction


lattice mismatch composition strain & relaxation lateral structure mosaicity (crystallinity) defects

X-Ray Reflectometry

layer thickness

composition roughness density porosity

Reciprocal Space

Mapping



Stress and Texture

orientation distribution

orientation quantification residual stress epitaxial relationship

Grazing incidence

Diffraction (GIXRD)


In-Plane GIXRD

IP-lattice parameter IP-crystallite size IP-orientation epitaxial relation


Residual stress analysis on thin TiN layer


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The conventional sin2 method using (i) a unique (hkl) Bragg condition and(ii) different sample orientations with respect to the incident beam (iso- orside-inclination mode) has not been successful due to the weak diffracted

intensity.

For layer thicknesses around 20 nm, the only geometry were intensity issignificant enough for further analysis is GIXRD. Using small angle ofincidence the effective sampling volume is confined in the surface region

resulting higher diffracted intensities than conventional diffraction methods.

By measuring lattice strain using different hkl reflections (the incidenceangle is kept constant while the detector is moved along the 2 circle) thedirection of the diffraction vector can be varied without tilting the specimen

physically: under such conditions the inclination angle is equal to hkl= hkl-

Residual stress analysis on thin TiN layer

The multiple (hkl) approach


Experiments with D8 ADVANCE


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Experiments with D8 ADVANCE

Configuration of the diffractometer

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(*) A focusing Goebel mirror gives a lower penetration depth resolution,but a higher flux on the sample surface. If the customer has a focusingmirror for capillary measurements, he can definitely use it for GIXRD.

Goniometer D8 ADVANCE Theta/Theta

Measurement

circle

560 mm

Tube 2.2 kW Cu long fine focus

Tube power 40 kV / 40 mA

Primary opticsFocusing Goebel mirror (*)

0,4 mm exit slit

Sample stage XYZ stage with vacuum chuck

Secondary optics 0,4 deg equatorial Soller slit

DetectorScintillation counter or

LYNXEYE in 0D mode


Residual stress analysis on thin films


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GIXRD scan on a 25 nm TiN layer

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GIXRD on Sample 1A : phase ID

03-065-4085 (I) - Osbornite, syn - TiN0.98 - Y: 99.90 % - d x by: 1. - WL: 1.5406 - Cubic - a 4.24190 - b 4.24190 - c 4.24190 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centered - Fm-3m (225)

Operations: Import

Commander Sample ID - File: GID@0,3245.raw - Type: Detector Scan - Start: 30.000000 - End: 146.00000 0 - Step: 0.100000 - Step time: 40. s - Temp.: 25 C (Room) - Time Started: 0 s - 2-Theta:

Lin(Cps)

10

20

30

4050

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250

260

270

280

290

300

310

320

330

340

350

360

370

2-Theta - Scale

30 40 50 60 70 80 90 100 110 120 130 140 1

[1,

1,

1]

[2,0,0

]

[2,

2,

0]

[3,

1,

1]

[2,2,2

]

[4,0,0

]

[3,3,1

]

[4,2,0

]

[4,2,2

]

[5,1,1

]

TiN osbornite




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The refraction of the incident beam and diffracted beam i at the surfaceof the specimen causes a positive shift between the measured peak position2 and the true Bragg angle 2 Brhkl:

2 hkl = 2 2 Brhkl, where 2Brhkl = t- i

Measuring geometry in GIXRD experiment: the angle of incidence, t the refraction angle,

i the incidence angle of the diffracted beam

hkl

QhklSurf.

normal


The refraction effect




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C= 0.311

From Leptos fit: 25 nm TiN layer


XRR scan for critical angle determination


Residual Stress Analysis on Thin Films


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Evaluation of the peak K1position


Data Treatment LEPTOS




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Peak shift due to the refraction effect

n=1--i, where sin2c=2

and =(/4)






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-4,7 0.5 GPa

y



Stress Gradient


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Y + 20.0 mm - File: TiCrN_3.50deg.raw - Type: Detector Scan - Start: 30. 000 - End: 150.000 - Step: 0.050 - Step time: 60. s - Theta: 3.500



Y + 5.0 mm - File: T iCrN_1.25deg.raw - Type: Detector Scan - Start: 30.0 00 - End: 150.000 - Step: 0.050 - Step time: 60. s - Theta: 1.2 50

File: TiCrN_0.50deg.raw - Type: 2Th alone - Start: 30.000 - End: 150.000 - Step: 0.050 - Step ti me: 60. s - Theta: 0.500

Sqrt(Cps)

0

10

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

2-Theta - Scale

31 40 50 60 70 80 90 100 110 120 130 140 1

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Incident angle from 0,5 to 3,5

1,2m TiCrN on Fe

Detector scan

Q(hkl)

(hkl)

Multiple (hkl) Approach


Stress Gradient


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Incident angle from 0,5 to 3,5

1,2m TiCrN on Fe Higher stress at the surface

Multiple (hkl) Approach


Texture analysis on thin films


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Pt layer on Si Point focus, Polycap and scintillation counter (311) texture of platinum recorded at 81.6 using a 7 grid

30 min measurement time


min min min maxmaxmax

The fiber texture is apparent

Simulation using MULTEX softwareAdvanced X-ray Workshop



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As measured SimulatedResidual

(220)

(422)

(111)

TiN pole figure simulationusing MULTEX

Point focus, POLYCAP andscintillation counter



ThinFilm_XRD

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