Thin film analysis - S. N. Bose National Centre for Basic ...xrdsnb11/ThinFilm_XRD.pdf · Thin film analysis Advanced X-ray ... •residual stress •epitaxial relationship Grazing

Thin film analysis

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

Innovation with Integrity

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 FilmsSamples 1

Advanced X-ray Workshop

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 FilmsSamples 2


14-15/12/2011 4

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

• Thin films can have different degree of crystallinity: from amorphous to single crystal.

Thin Film Characteristics

Organic monolayer

Nanoparticlesin matrix

Back-end (Semi.)

Front-endSiGe

OxydeSemi.

1 µm100 nm10 nm1 nm Layer thickness

Low-k oxides

Degree of order

AmorphousPolycrytal.Single crystal

CoatingsMagn. storage

LEDs


Thin Film XRD MethodsParameters 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




High-Resolution

X-Ray Diffraction


X-Ray Reflectometry


Reciprocal Space

Mapping


Stress and Texture


Grazing incidence

Diffraction (GIXRD)


In-Plane GIXRD



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

Analytical tasks

Lateral structure

Layer thickness ChemicalComposition

(electron density)

Roughness

Specular XRR Diffuse

14-15/12/2011 Advanced X-ray Workshop 8

The specular XRR scattering geometry

9

Wavevector transfer has a non-zero component perpendicular to the sample surface

For Cu-Kα (λ=1.54Å)

XRR probes the laterally averaged electron density

yxzyxz

,),,()( ρρ =

q=(0,0,q )z

ki kf

θ θ

z

x

θsin2kqz =

22)exp()()( ∫∝ dzziqzqS zz ρ

][140/2 1−= nmqz θ


The reflectivity from a substrate

10

0 z

ρ( )z

exp(iqz)

R exp(-iqz)

T exp(iQz)

ρπ erqQ 162 −=2

2)()(Qq

QqqRqr FF +

−==

Fresnel reflectivity

with


• The higher the electron density ρ(z) of a material the higher the critical angle

• The higher the electron density, the more intensity is scattered at higher angles

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

Density dependency of the reflectivity

11

ρθ ∝c

4

2

≈θ

θcr


12

• small inclinations of the surface normal on a large scale of some 100 nm

• broadening of the specular reflected beam

• The broadening of the specular reflected beam decreases thereflected intensity

• It does not contains any information about internal sample structure

• Samples should have a flat surface

Influence of RoughnessWaviness

waviness


13

• large inclinations of the surface normal on an atomic scale of a few nanometers

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

Influence of RoughnessMicroscopic Roughness

waviness

microscopicroughness


Influence of Roughness

• Roughness decreases the reflected intensity dramatically

• XRR is highly sensitive to roughness

• Roughness causes diffuse scattering

• The interface roughness should not be larger than 2-3 nm.


XRR from single layer on substrate: Thickness fringes

15

• The interference of the waves reflected from the interfaces causes oscillations of period

• The minimal observable thickness is limited by the maximal measurable range

• The maximal observable thickness is limited by the instrumental resolution

• The sample should have thicknesses observable with the instrumental setup.

dqz /2π=∆


Thickness fringesAmplitude

16

• Amplitude of the thick-ness fringes increases with increasing density contrast

• XRR is quite sensitive to variations of the electron density

• The sample should have a good contrast in the electron density.


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 Ag60 nm Au

Si - substrat

Ref

lect

ivity

Incidence angle [°]


X-ray Reflectometry in PractiseDemands on Sample Properties

18

Golden Rule:

You should be able to see your reflection on the surface of the

sample!

• Flat and lateral homogeneous - not structured

• Sample roughness < 5nm

• Good contrast in electron density for layered samples

• Length of at least 3-5 mm in beam direction


19

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

Simplest Setup for XRR


20

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

Principle of the Göbel Mirror

Parabola

X-ray source

Goebel mirror

Sample


21

• 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


22

• Use slits to balance flux and resolution

Reflectometry with different slitsIn

t. [c

ps]

100

1000

1e4

1e5

1e6

1e7

2θ/ω[°]

0 1 2 3 4 5 6 7

with 0.6 mm slitwith 0.1 mm slit

~ 5 min

~ 6.5 h

Int.

[cps

]

100

1000

1e4

1e5

1e6

1e7

2θ/ω[°]

0 1 2 3 4 5 6 7


23

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

XRR setup for very thin layers


Limits of X-Ray Reflectometry Thin layers Example: LaZrO on Si

24

2θ [°]1412108642

Inte

nsity

[au]

-81*10

-71*10

-61*10

-51*10

-41*10

-31*10

-21*10

-11*10

01*10

Si (111)

6.7 nm LaZrO


25

• Analyzer crystal separates Kα1, suppresses diffuse scattering and fluorescence

• 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)


26

• Monochromator cystals provide highly parallel and monochromatic beam

• 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


Limits of X-ray Reflectometry Thick layers example: SiO2 on Si

27

Int.

[au]

5

10

100

1000

1e4

2θ [°]

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


28

• For Cu-Kα radiation: λ ≈ 1.54 Å• Values for ∆θ were obtained by scanning the direct beam• Obtained from the rough estimation

Resolution of differents setups

θλ ∆≈ 2/d

Tube side Detector side ∆θ [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


29

• Footprint of the beam on surface:

• Beam matches the sample size at:

• Below θB the intensity is reduced by:

Geometrical corrections –The footprint

)/arcsin( LdB =θ)sin(/)sin( BB θθ=

θsin/dD =

d : beam widthL : sample length || beamD : illuminated area

L

d

θ

D


30

• Sample size reduces the reflected intensity at small angles • Sample must be sufficiently large for XRR

Geometrical corrections –The footprint

Beamsize : 200 µm


31

• 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 footprintThe Knife Edge Collimator


Controlling the footprintThe Knife Edge Collimator

32

• Measurement with KEC must be performed up to at least 2θB

• The high-angle measurement without KEC must have an overlap with the KEC – measurement to rescale the data properly

0,0 0,5 1,0 1,5 2,0104

105

106

107

108

with KECwithout KEC

Inte

nsity

2θ [deg]


Evaluation of SampleFitting Procedure

Sample Model parameterized by {p1,…pN}

Tolerance

XRR Simulation

Comparison with Experiment, χ2 cost function

Minimization of χ2 using Genetic Algorithm, Levenberg-Marquardt, Simplex,Simulated Annealing, etc. in view of {p1..pN}


Amorphous HfO2 film – Ultra thin films

34

θ [degees]


XRR on MEMS – Ru/SiN film


GMR Heterostructure – 8 Layers

36

Sample courtesy of Dr. Schug, IBM Mainz




High-Resolution

X-Ray Diffraction


X-Ray Reflectometry


Reciprocal Space

Mapping


Stress and Texture


Grazing incidence

Diffraction (GIXRD)


In-Plane GIXRD



14-15/12/2011 38

• For coatings (few microns down to sub-micron range), the Bragg-Brentano geometry (BB) is still the best configuration. This is basically the classical powder 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 analysis or microstructure investigation (size/strain) are quite easy to perform.

• Limitations of the BB set-up: If the substrate is a single crystal, the huge intensity from the substrate peak will emphasize all minor peaks originating from the energy spectrum of the tube and other aberrations (Kβ, tube tails, Ni absorption edge, W lines,…) with the consequence that a significant part of the scan won’t be usable.

Remarks for Coatings


14-15/12/2011 39

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

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

• The confinement of the grains into a limited volume very often causes preferred orientation and the quantitative phase analysis might become impossible.

• The grain interaction during growth can also induce residual stress.

• A composition gradient through the layer may also appear during the growth.

Polycrystalline Thin FilmsConstrains


Grazing Incidence X-Ray DiffractionInstrumental Set-up Requirements

14-15/12/2011 40

• 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 the

sample 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)


Lin

(Co

unts

)

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 90

14-15/12/2011 41

• Bragg-Brentano geometry • Grazing incidence geometry

Lin

(Co

unts

)

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 90

Grazing incidence diffractionAg2Te thin film on glass

GIXRD emphasizes the signal of the Ag2Te nanocrystallites,and the glass substrate signal is reduced


14-15/12/2011 42

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 density and the expected penetration depth, an incident angle is chosen and remains fixed during the data collection.

GIXRDThe Footprint

42

d : beam widthL : sample length || beamD : illuminated area

L

d

θD


14-15/12/2011 43

• A detector scan (or 2θ scan) is performed. The use of a Sollerplates collimator maintains a good resolution in 2θ (given by the acceptance of the Soller plates) while getting diffraction signal from the whole footprint on the sample.

GIXRDData collection

43

θ θ2

Soller plates collimator defines the instrumental resolution!

Available: 0,1°, 0,2°, 0,3°, 0,4°


14-15/12/2011 44

Incident angle Theta=0.2 to few degrees

Göbel mirror

Equatorial soller

LYNXEYE 0D

XYZ stage

Grazing Incidence DiffractionPhase ID depth profile


14-15/12/2011 45

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

• At higher incident angle, the YH2 layer is reached and starts to diffract.

Grazing Incidence DiffractionPhase ID depth profile


14-15/12/2011 46

• Standard GIXRD or so-called coplanar geometry

• In-plane GIXRD or so-called non-coplanar geometry

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

Combination of GIXRD with IP-GIXRD


ULTRA-GIDCoplanar 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 @ 90°ααααiααααf

θθθθi

θθθθD

2θθθθIP-GID

XRR on Si/SiO2/Si

14-15/12/2011 48

LEPTOS results

100,3 nm SiO214,7 nm Si


Coplanar GIXRD on Si/SiO2/Si

14-15/12/2011 49

TOPAS results

Cubic Si a=5.41285 A9 nm normal crystallite size


Non-coplanar GIXRD on Si/SiO2/Si

14-15/12/2011 50

TOPAS results

Cubic Si a=5.41285 A14 nm lateral crystallite size


XRR on ZrO2/Si

14-15/12/2011 51

LEPTOS results

3,2 nm ZrO2


Coplanar GIXRD on ZrO2

14-15/12/2011 52

TOPAS results

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


Non-coplanar GIXRD on ZrO2

14-15/12/2011 53

TOPAS results

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




High-Resolution

X-Ray Diffraction


X-Ray Reflectometry


Reciprocal Space

Mapping


Stress and Texture


Grazing incidence

Diffraction (GIXRD)


In-Plane GIXRD



14-15/12/2011 55

• The conventional sin2Ψ 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 diffractedintensity.

• For layer thicknesses around 20 nm, the only geometry were intensity issignificant enough for further analysis is GIXRD. Using small angle α ofincidence the effective sampling volume is confined in the surface regionresulting higher diffracted intensities than conventional diffraction methods.

• By measuring lattice strain using different hkl reflections (the incidenceangle α is kept constant while the detector is moved along the 2θ circle) thedirection of the diffraction vector can be varied without tilting the specimenphysically: under such conditions the inclination angle is equal to Ψhkl = θhkl- α

Residual stress analysis on thin TiN layerThe multiple (hkl) approach


Experiments with D8 ADVANCE –Configuration of the diffractometer

14-15/12/2011 56

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

Goniometer D8 ADVANCE Theta/Theta

Measurementcircle

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 filmsGIXRD scan on a 25 nm TiN layer

14-15/12/2011 57

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: ImportCommander 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

(C

ps)

10

2030

4050

6070

8090

100110

120130

140150

160

170180

190200

210220

230240

250260

270

280290

300310

320330

340350

360370

2-Theta - Scale

30 40 50 60 70 80 90 100 110 120 130 140 150

[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


14-15/12/2011 58

• The refraction of the incident beam α and diffracted beam αi at the surface of the specimen causes a positive shift between the measured peak position 2θ and the true Bragg angle 2 θBrhkl:

• ∆2 θhkl = 2θ – 2 θBrhkl, where 2θBrhkl = αt- αi

Measuring geometry in GIXRD experiment: α — the angle of incidence, αt — the refraction angle, αi — the incidence angle of the diffracted beam

Ψhkl

QhklSurf. normal

Residual stress analysis on thin filmsThe refraction effect


14-15/12/2011 59

θC= 0.311 °

From Leptos fit: 25 nm TiN layer

Residual stress analysis on thin filmsXRR scan for critical angle determination


14-15/12/2011 60

Evaluation of the peak Kα1position

Residual Stress Analysis on Thin FilmsData Treatment LEPTOS


14-15/12/2011 61

Peak shift due to the refraction effect

n=1-δ-iβ, where sin2αc=2δ

and β=(λ/4π) µ



14-15/12/2011 62

-4,7 ± 0.5 GPa



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 + 15.0 mm - File: TiCrN_2.75deg.raw - Type: Detector Scan - Start: 30.000 ° - End: 150.000 ° - Step: 0.050 ° - Step time: 60. s - Theta: 2.750 °Y + 10.0 mm - File: TiCrN_2.00deg.raw - Type: Detector Scan - Start: 30.000 ° - End: 150.000 ° - Step: 0.050 ° - Step time: 60. s - Theta: 2.000 °

Y + 5.0 mm - File: TiCrN_1.25deg.raw - Type: Detector Scan - Start: 30.000 ° - End: 150.000 ° - Step: 0.050 ° - Step time: 60. s - Theta: 1.250 °File: TiCrN_0.50deg.raw - Type: 2Th alone - Start: 30.000 ° - End: 150.000 ° - Step: 0.050 ° - Step t i me: 60. s - Theta: 0.500 °

Sqr

t (C

ps)

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 90 100 110 120 130 140 150

14-15/12/2011 63

• Incident angle from 0,5° to 3,5°

1,2µm TiCrN on Fe

Detector scan

Q(hkl)

Ψ(hkl)

Stress GradientMultiple (hkl) Approach


14-15/12/2011 64

• Incident angle from 0,5° to 3,5°

1,2µm TiCrN on Fe � Higher stress at the surface

Stress GradientMultiple (hkl) Approach


14-15/12/2011 65

• 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

Texture analysis on thin films

min min min maxmaxmax

The fiber texture is apparent

Simulation using MULTEX softwareAdvanced X-ray Workshop

14-15/12/2011 66

As measured Simulated Residual

(220)

(422)

(111)

TiN pole figure simulation using MULTEX

Point focus, POLYCAP andscintillation counter

Texture analysis on thin films


Innovation with Integrity

© Copyright Bruker Corporation. All rights reserved.14-15/12/2011 6715. Dezember 2011 67© Copyright Bruker Corporation. All rights reserved

Documents

Thin film analysis - S. N. Bose National Centre for Basic ...xrdsnb11/ThinFilm_XRD.pdf · Thin film analysis Advanced X-ray ... •residual stress •epitaxial relationship Grazing