Comprehensive Thin Film Analysis:XRD vs Ellipsometry and Raman

Welcome

Uwe PreckwinkelWebinar Host

Today’s TopicsIntroduction to X-ray Diffraction (XRD)Comparison of XRD with other Metrology MethodsSemiconductor Application Examples

Guest SpeakersMike Lyubchenko – Applications Scientist, XRD, Madison, WIDr. Assunta Vigliante – Head of Business Development, Semiconductor Industry, Karlsruhe, Germany

IntroductionWhat Can XRD “See”?

When x-rays are scattered from nanoscale structures –such as atoms, molecules, films, grains or pores –a diffraction pattern will appear that carries information about the structure and morphology of the illuminated sample volume

X-ray Applications for Materials in the Semiconductor Field

XRD Thickness, Profiling

Phase, Composition, Crystallinity

Orientation, Texture, Mis-cut

Stress, Strain,

RelaxationDensity

Grain Size, Porosity,

RoughnessMetal layers

Diffusion stop layers

Low-k layers

Substrate

Silicides

High-k materials

Channel materials

D8 DISCOVER

Advanced Technology Platform

X-ray Source

4-bounce Monochromator Ge 022 asym.D8 Goniometer

Detector

SecondaryOptics

Göbel Mirror

KECEulerianCradle

D8 DISCOVER for Thin Film Analysis

Detectors for XRDD

imen

sion

CapabilitiesGain factor 3

GF >150 GF >500

GF >1000 GF >1500

XRD3 – Diffraction Space Viewer

LEPTOSMaterial Database

IntroductionXRD in the Semiconductor Field

Advanced sources, optics and detectors, as well as goniometers and software, allow straightforward analysis of:

small sample features and thin films

in high, medium and low resolution

for high-end research and fully integrated metrology

During this webinar, we will compare XRD to other analytical techniques and show application examples related to thin films

Semiconductor MetrologyMethods & Applications

Mike Lyubchenko

Semiconductor Applications

Metal layers: Cu, Al-Cu, WThickness, phase, orientation, stress

Barrier layers: Ta/TaN, Ti/TiN, W/WNThickness, density, phase

Low-k layers: Black Diamond, SiLKThickness, porosity

Silicide: WSi, TiSi, CoSi, NiSiThickness, phase

Gate oxide / High-k: SiO2, SiNO, Ta2O5, HfO2Thickness, phase, crystallinity

Channel: epi-SiGe, strained SiThickness, composition, relaxation

Substrate: Si, SOI, sSOIOxide thickness / depth, Ge profile, mis-cut angle

Metrology Techniques for Thin Films

Film Thickness MeasurementTransmission Electron Microscopy (TEM)Spectroscopic Ellipsometry (SE)X-ray Reflectivity (XRR)X-ray Fluorescence (XRF)X-ray Diffraction (XRD)Secondary Ion Mass Spectrometry (SIMS)Auger Electron Spectrometry (AES)Rutherford Backscattering Spectrometry (RBS)

Elemental CompositionX-ray Fluorescence (XRF)X-ray Diffraction (XRD)Auger Electron SpectrometrySpectroscopic Ellipsometry (SE)Secondary Ion Mass Spectrometry (SIMS)Rutherford Backscattering Spectrometry (RBS)Energy Dispersive Spectroscopy (EDS/TEM)

Metrology Techniques for Thin Films

Lattice Strain CharacterizationX-ray Diffraction (XRD)UV Raman SpectroscopyHigh Resolution Lattice Image (HRTEM)

Surface/Interface RoughnessX-ray Reflectivity (XRR)Atomic Force Microscopy (AFM)Transmission Electron Microscopy (TEM)

Use your mouse to answer the question on the right of your screen:

What methods do you currently use for thin films analysis? (Check all that apply):

Transmission Electron MicroscopySpectroscopic EllipsometryRaman SpectroscopyX-ray Reflectivity X-ray FluorescenceX-ray DiffractionOther

And the results are...

Your Turn…

Metrology Techniques - TEM

Capabilities

Multi-layer thickness capabilityExcellent defect detectionElemental composition (with EDS)

Advantages

Provides accurate film thicknessExcellent contrast between filmsProvides film interface informationProvides information on crystallinityHigh resolution (higher than SEM)

Disadvantages

Destructive; samples need thinning, down to <50 μmSpecimen preparation is time and labor intensive (2-3 hrs typical)Image artifacts require expert interpretation of micrographsSamples may be sensitive to electron beam damageSample may not be representative

Spectroscopic Ellipsometry

Ellipsometry is an optical technique used to analyze thin transparent layers. As the light shining on the sample passes through and bounces out, it undergoes some changes in its amplitude and phase. These two parameters are analyzed to derive information about the layers, such as their refractive indices and thicknesses.

Metrology Techniques - SE

CapabilitiesUses polarized light for stacked film optical thickness (refractive index)Elemental composition, roughness, thickness, optical constants

AdvantagesRapidNon-destructiveInsensitive to light intensity fluctuations & lossesMany in-line systems availableSmall spot size (25 μm) for features

DisadvantagesRequires transparent filmsDoes not measure quantities directlyQuantifiable only with standardsAnalysis can be difficultDifficult for thin conformal Si layer on rough relaxed SiGeProblems with fits when substrate stress is different from model stress

Optical constants change as a function of strain.

Raman – Principles

When a photon strikes a molecule, it can interact with it in many different ways. The two main ones are:

1. Rayleigh scattering - The photon bounces off of the molecule without any energy exchange

2. Raman scattering - The photon strikes the molecule, gets absorbed exciting the molecule. The molecule then relaxes to one of the lower energy states by emitting another photon of energy different from the incident one. The energy of the re-emitted photon can be either higher or lower than the original depending on a chemical state of he molecule.

Metrology Techniques – UV Raman

CapabilitiesComposition, crystallinity, strain/stressPhonon frequency shift in Si used todetermine strain in Si channelPeak broadening related to defects:dislocations, disorder, Ge out-diffusion, strain, nonuniformity

AdvantagesNon-destructive, no sample preparationRapid (364 nm Ar-ion laser resonance Raman 10X faster than 325 nm He-Cd laser non-resonance Raman)Small spot size (0.4 μm)Not affected much by roughnessControl of penetration depth (325nm <10 nm)

DisadvantagesNo in-line monitoring tools available for patterned wafersRequires complex data interpretationGe composition variation (out-diffusion) affects accuracy of derived strain value.

Metrology Techniques - XRFCapabilities

Multi-element compositionGood precisionFluorescence intensity is proportional to atomic densityThickness measurements

AdvantagesSpot size (40-50μm)ppm capability in a few cases; more commonly, 0.01% detection limitsSimple spectra – No fitting or models requiredHigh Throughput (~10 sec per site)Whole wafer analysisNon-destructive

DisadvantagesCalibration standards requiredSome elements (e.g. Ge) have low fluorescence yield (long acquisition times)Matrix effects (fluorescence absorption and enhancement) must be compensatedOnly elements beyond O detectableInterference (different element, same peak)Diffraction background depends on substrate type

Metrology Techniques –High Resolution X-ray Diffraction

Capabilities

Strain/stressFilm thicknessComposition

Advantages

In-line monitoring tools availableNon-destructiveRapidHigh-accuracy

Disadvantages

Strain measurement straight-forward only on bulk Si wafersStrain measurement on SOI wafers is time-consumingRequires triple-axis reciprocal space maps

What Can Be Measured with X-rays?Thin Film Real Structure

Analytical TasksX-ray Reflectometry

RoughnessLayer thickness

A C

A B

A BxC1-x

Chemical Composition

Lateral structure

X-ray ReflectometryGeneral Remarks

Based on reflection of X-rays at interfaces – no crystal lattices needed

Non-destructive method for the investigation of the near surface region of different sample systems

• single crystalline, polycrystalline and amorphous samples

• polymers, organic samples (Langmuir Blodgett, etc.), fluids

Specular reflection of X-rays

• film thickness of single- and multilayer systems (0.1nm → 1000nm)

• density profiles of near surface regions (~1%)

• roughness of surfaces and interfaces (0.1nm → 5nm)

Diffuse scattering of X-rays

• roughness structure of surfaces and interfaces

• morphology, correlation length, fractal parameters

XRR – X-ray Reflectometry

thickness

density

Slope = roughness

A technique which utilizes the effect of total external reflection of X-rays. The measurements are done around a “critical angle” (an angle of total reflection). Below the critical angle, the X-rays don’t penetrate the sample surface. Above it, the penetration rises quickly with an angle. At every interface, a portion of X-rays is reflected. Interference of these partially reflected X-ray beams creates a reflectometry pattern.

XRR – X-ray Reflectometry

CapabilitiesStacked film thickness, density, surface/interface roughnessMost accurate in-line thin film metrology

AdvantagesCan accurately determine thickness, roughness, density of layersAny type of material can be analyzed (amorphous, crystalline, opaque) Complex multilayer structures can be measuredDoesn’t require a prior knowledge of material composition

DisadvantagesModeling can be difficultFairly slowSpot size, 80μm x ~3mm Ge diffusion reduces density contrastDoesn’t work well with very rough interfacesThere is an upper limit on thickness (<0.5 μm)

XRR – X-ray ReflectometryTypical Experimental Setup

Comparison of X-ray and Optical Analytical Techniques

ThicknessXRR is a direct methodXRR is material independentCan resolve complex layer stacks

CrystallinityXRD is the ideal technique to probe crystal structure

StrainHRXRD can determine strain and concentration independently with precision <1%HRXRD analysis is simple and can be automated

Semiconductor Industrial Applications

Assunta Vigliante

Bruker AXSD8 FABLINE with UMC300 STAGE

Industrial ApplicationsMeasurement Schemes

High-Resolution X-ray Diffraction (HRXRD)

• Single-crystal / epitaxial layer structure

• Composition, thickness, relaxation

X-ray Reflectivity (XRR)

• Polycrystalline, amorphous, single-crystal film structure

• Thickness, density, surface / interface roughness

Grazing Incidence Diffraction (GID)

• Polycrystalline thin film

• Crystallinity phase, grain size

Use your mouse to answer the question on the right of your screen:

What is your biggest challenge in analyzing semiconductor or thin film samples? Choose one:

Integrating analysis instruments into my fabrication processesDetermining the best measurement method for my applicationBeing able to apply multiple analytical methods with one instrumentLogistical and environmental constraints of placing an instrument in my facility

Please Tell Us…

And the results are…

Limits of X-ray Reflectometry Thick LayersExample: SiO2 on Si

Int. [a

u]

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

Limits of X-ray Reflectometry Thin LayersExample: LaZrO on Si

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

X-ray ReflectometryExample of Sensitivity to Layer Thickness

0,0 0,5 1,0 1,5 2,0 2,5 3,010-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

5x10x

InPInPInGaAsInPInP50nm

5nm3,5nm4,5nm

InPInPInGaAsInPInP

4nm4nm5nm50nm

10x 5x

Refle

ctiv

ity

Incidence angle [o]

Metal / Barrier Layers (Cu Process)30 nm Cu/10 nm Ta/Si

2θ (degrees)1 2 3 4 5

Rel

ativ

e in

tens

ity

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

experimental simulation

Material Thickness(nm)

Roughness(nm)

Density(g cm-3)

Cu2O 2.20 ± 0.57 0.80 ± 0.47 2.38 ± 1.70

Cu 29.14 ± 0.56 1.91 ± 0.93 9.00 ± 0.55

Ta 8.23 ± 0.05 0.35 ± 0.09 16.62 ± 0.55

Si --- 0.48 ± 0.04 2.33

Silicide LayersTiSi / TiN / Si

Detected Phases: TiSi2, Ti5Si3, TiN

VLR40077.05

00-038-1420 (*) - Osbornite, syn - TiN - Y: 50.00 % - d x by00-029-1362 (*) - Titanium Silicon - Ti5Si3 - Y: 18.75 % - d

00-035-0785 (*) - Titanium Silicon - alpha-TiSi2 - Y: 12.50 Operations: Background 0.000,1.000 | ImportFile: VLR40077-05.raw - Type: 2Th alone - Start: 20.000 ° -Operations: ImportFile: VLR40077-05.raw - Type: 2Th alone - Start: 20.000 ° -

Lin

(Cou

nts)

0

1000

2000

3000

4000

5000

6000

2-Theta - Scale20 30 40 50 60 70 80 90

Θ=0.3°

Pattern or Product Wafers

HeterostructuresRelaxation Degree RExample: Si1-xGex - Si structure

R = 0R = 1

SL ad ≠||

partially relaxed layer completely relaxed layerpseudomorphic layer

0||

≠Δdd

LLL add ==⊥ ||

aa

dd

dd Δ

=Δ

=Δ

⊥||

relaadd

Δ

Δ

= ||R

Measurement Scheme (I)High-Resolution X-ray Diffractometry (HRXRD)

Applicable semiconductor processes

• SiGe and SiCepitaxial thin film

• Strained Si film

• SOI and sSOI

Analysis parameters

• Composition

• Thickness

• RelaxationSim Curve Raw Curve

2theta / omega (degree)69.869.669.469.26968.868.668.468.26867.867.667.467.2

Inte

nsity

-51*10

-41*10

-31*10

-21*10

-11*10

01*10

Pattern Recognition

Cognex Pattern Recognition

Autofocus function

7 zoom factors

Laser video system

SiGe on Si

Operations: ImportFile: PatternedSiGe_VS0i1_HS0i2_SiGe004_06.raw - Type: Rocking curve - Start: 33.600 ° - End: 34.600 ° - Step: 0.002 ° - Step time: 2.1 s - Temp.: 25 °C (Room) - Time Started: 1074 s - 2-Theta: 68.

Log

(Cps

)

1

2

10

3456

100

1000

1e4

2e4

Theta - Scale33.6 33.7 33.8 33.9 34.0 34.1 34.2 34.3 34.4 34.5 34

Counts

1 10 100 1000 1e41 10 100 1000 1e4

[001] - File: m224+ [001].raw - Type: General Scan - Start: 1.

l [00

1]

3.915

3.92

3.93

3.94

3.95

3.96

3.97

3.98

3.99

4.00

4.01

4.02

4.03

h [110]1.986 1.99 2.00 2.0

Cps

1 10 100 1000 1e41 10 100 1000 1e4

[001] - File: m004 [001].raw - Type: General Scan - Start: -0

l [00

1]

3.915

3.92

3.93

3.94

3.95

3.96

3.97

3.98

3.99

4.00

4.01

4.02

4.03

h [110]0

(-0,0018; 3,9436) (1,9975; 3,9457)(0; 3,9436)

(1,9994; 3,9437)

Miscut=0,038 deg)

SiGe on SOI

SOI

200μm collimeter, about 400 seconds per point

DIFFRACplus LEPTOS 3Automatic FittingExtended Genetic Algorithm

Measurement tasks automated using Visual Basic scriptsAutomatic alignment for reflectometry and Bragg reflectionsFirst task - analytic profile fitting - TOPAS BBQ • Choice of profile shape function: Pseudo-Voigt and

Pearson VII• Crystallite size determination by Scherrer method

Second task - simulation & fitting- LEPTOS • unified program for XRR &HRXRD• script automation

D8 FABLINEAutomated Operation and Analysis

Texture Measurements on Cu Lines

Beam spot 100μmTexture measurement can be done in 15 min(111) and (200) Cu reflections are collected simultaneously

Stress Measurements on Cu Lines

Beam spot 100 μmStress measurement can be done in 2 hrs(331) and (420) Cu reflections are collected simultaneously

Stress Measurements on Cu Lines

Industrial Applications

High-Resolution X-ray Diffraction (HRXRD)

X-ray Reflectivity (XRR)

Grazing Incidence Diffraction (GID)

Grazing Incidence Small Angle Scattering (GI-SAXS)

In-Plane Grazing Incidence Diffraction (IP-GID)

Texture

Stress

All in one instrument!

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www.bruker-axs.com

See us at:International Conference on Crystal Growth (ICCG-15)

August 12-17, 2007Salt Lake City, UT