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Auger Electron Spectroscopy Overview

Also known as: AES, Auger, SAM

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Auger Electron Spectroscopy

EKLL = EK - EL - EL’

2p

1s

2s1/2

3/2

Ef

K

LI

LII

LIII

Incident Beam

AugerElectron

EKLL

0 500 1000 1500 2000 2500 3000Kinetic Energy (eV)

E N(E)

E N(E) x 5

EdN(E)/dE

Cu LMMCu MNN

AES Spectra of Cu

Note that Auger peaks are typically superimposed on a large background (see red and magenta spectra).For this reason Auger spectra are typically displayed in a differentiated mode as shown in the green spectrum.Detection limits for AES are approximately 0.1 atomic percent.

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Auger Electron and X-ray Emission

IncidentBeam

Auger Electron

X-ray

Photon

Energy Dispersive X-ray Spectroscopy (EDX) Auger Electron Emission

Incident Beam Incident Beam

Auger Electron

X-ray

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AES and EDX

Primary Electron Beam

Auger Electrons

Particulate defects

Auger Analysis Volume (5-75 Å)

Primary Electron Beam

Characteristic X-rays

EDX Analysis Volume (<1 - 5 µm)

AES Provides Superior Nanovolume Analysis Capabilities

EDX minimum analysis area > 1 µm

710 AES minimum analysis area 8 nm

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AES Analysis Depth

Mean Free Path: Mean distance electrons travel before undergoing inelastic scattering

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Analysis Depth – “Universal” Curve

1 10 100 1000Energy (eV)

1

10

100

1000

λ(m

onol

ayer

s)

nm analysis depth

Typical Auger electron energies

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Auger Electron Spectroscopy� Auger Electron Spectroscopy is an analytical technique that

provides compositional information from the top few monolayers of a material

� Detect all elements above He

� Detection limits: 0.1 – 1 atomic %

� Surface sensitive: top 5-75 Å

� Spatial resolution: < 60 Å probe size (PHI 710)

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What Information Does Auger Provide ?� Surface composition at high spatial resolution

– Secondary Electron Imaging• Provides high magnification visualization of the sample

– Elemental analysis (spectra)• Determines what elements are present & their quantity

– Elemental imaging (mapping)• Illustrates two-dimensional elemental distributions

– High energy resolution spectra, imaging and depth profiling• Chemical state analysis for some materials

� Sputter depth profiling– Reveals thin film and interfacial composition

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PHI 710 Scanning Auger NanoProbe

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PHI 710: Analytical Capabilities

�Nanoscale image resolution

�Image registration for high sensitivity

�Constant sensitivity for all geometries

�Constant sensitivity with tilt for insulators

�Nano-volume depth profiling

�Chemical state analysis

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PHI 710: High Spatial Resolution

Locations for Line Scans

Area Analyzed 4 nm Al LineAlGaAs Line Width (nm)

AugerLine

Scans

Sample provided by Federal Institute

for Materials Research and Testing (BAM)

Berlin, Germany

1

2

3

4

24 hour stability test demonstrating exceptional image registry

BAM-L200 Standard Sample

Ga Map 25 kV - 1 nA 256x256 pixels Al Map 25 kV - 1 nA 256x256 pixels

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PHI 710: High Spatial Resolution

4 nm Al Line

0 0.05 0.10 0.15 0.20 0.25 0.30 0.35Distance (µm)

Inte

nsity

Ga

Al (X3)

BAM-L200 Standard Sample Line Scan #4

24 hour stability test demonstrating exceptional image registry

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PHI 710: Constant Sensitivity for All GeometriesPHI 710

Coaxial Analyzer & Electron Gun Geometry

0200400600800

1,0001,2001,4001,6001,8002,000

-90 -75 -60 -45 -30 -15 0 15 30 45 60 75 90Tilt Angle (degrees)

Sen

sitiv

ity (

kcps

)

Sensitivity vs. Sample Tilt Angle

Coaxial (CMA)

Non-Coaxial (SCA)

The CMA with coaxial electron gun provides high sensitivity at all sample tilt angles which is essential for insulator analysis and samples with topography

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PHI 710: CMA with Coaxial Geometry

Secondary Electron Image Ni Map In Map

No shadowing• Every pixel can be identified as part of a Ni sphere or as

part of the In substrate.• The Ni particles are complete spheres and the substrate

fills in around the particles.• Variations in In and Ni intensity provide meaningful

compositional information.

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Non-Coaxial Geometry

Secondary Electron Image Ni Map In Map

Shadowing• Many pixels are of unknown composition, apparently

neither Ni balls nor In substrate. • The Ni particles are not observed as complete spheres

and very little of the substrate is seen.• Variations in In and Ni intensity do not provide

meaningful compositional information.

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PHI 710 High Energy Resolution Mode� How does the high energy resolution mode work?

– The CMA energy resolution is given as:– ΔE / E = 0.5%– An optics element placed between the sample surface and the entrance to

the standard CMA retards the Auger electrons, reducing their energy, E– From the energy resolution equation, if E is reduced, ΔE is also reduced

and so is the Auger peak width; energy resolution is improved– The CMA is not modified in any way and retains a 360º coaxial view of the

sample relative to the axis of the electron gun– US Patent 12 / 705,261

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PHI 710 High Energy Resolution Mode

710 Energy Resolution Specification

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0 500 1000 1500 2000 2500Auger Peak Kinetic Energy (eV)

ΔE

/ E

(%

)

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PHI 710 High Energy Resolution Mode

1360 1370 1380 1390 1400 1410-50

0

50

100

150

200

250

300

350

1393.4 eV (Al metal)(Al oxide) 1386.9 eV

Kinetic Energy (eV)

N(E

) cp

s

Al KLL Spectra of Native Oxide on Al Foil

EnergyResolution

0.5 %

0.1 %

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PHI 710 High Energy Resolution Mode

Zn oxide Zn metal

970 980 990 1000 1010 1020 10300 surface

5

10th sputter cycle

8.4

8.6

8.8

9.0

9.2

9.4

9.6

9.8x 105

Kinetic Energy (eV)

c/s

Depth Profile of Zn Oxide on Zn

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PHI 710: Spectral Window ImagingB

C

Si Metal

SilicideSi Oxynitride

Si KLL Basis Spectra

1608 1612 1616 1620Kinetic Energy (eV)

Inte

nsity

A Composite Si KLL

1605 1615 1625Kinetic Energy (eV)

Inte

nsity

Panel A shows the Si KLL spectrum from the sum of all pixel spectra in the Si KLL Auger image shown in panel B. Panel B shows the three Regions Of Interest (ROI) selected for creation of the basis spectra for Linear Least Squares (LLS) fitting of the Si KLL image data set. Panel C shows the three basis spectra with their corresponding chemical state identifications.

Si KLL image with ROI areas

20 µm

20 µ

m

In the spectral window imaging mode, a Si KLLspectrum is collected and stored for each image pixel.

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PHI 710: Spectral Window ImagingA SEI

20 µm20

µm

B Si KLL (all Si)

20 µm

20 µ

m

SilicideC

20 µm

20 µ

m

D Si Metal

20 µm

20 µ

m

E Si Oxynitride

20 µm20

µm

Panel A shows a 200 µm FOV SEI of a semiconductor bond pad. Panel B shows the Si KLL peak area image from the area of panel A. Panels C, D and E show the chemical state images of silicide, elemental Si and Si oxynitride respectively. Panel F shows a color overlay of elemental silicon, silicide and silicon oxynitride images.

F Si Chemical States

20 µm

20 µ

m

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PHI 710: Thin Film Analysis

�World’s best Auger sputter depth profiling

– Floating column ion gun for high current, low voltage sputter depth profiling

– Compucentric Zalar Rotation™ minimizes sputtering artifacts and maximizes depth resolution

– Image registration maintains field-of-view

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PHI 710: Low Voltage Depth Profiling

0 10 20 30Sputter Time (min)

Inte

nsity

As

Ga

Al

500 eV Depth Profile

0 200 400 600 800Sputter Time (min)

Inte

nsity

As

Al

Ga

100 eV Depth Profile

Improved Interface Definition with use of Ultra Low Ion Energies

AlAs/GaAs Super Lattice Thin Film Structure

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PHI 710: Nanoscale Depth Profiling

FOV: 2.0 µm

Φ

0.5 µm

1

P from the growth gas is detected on the surface of a Si nanowire

60 nm Diameter Si Nanowire

20 kV, 10 nA, 12 nm Beam

100 300 500 700Kinetic Energy (eV)

Inte

nsity

O

CSi

P

Surface Spectrum of NanowireSEI

Atom %Si 97.5P 2.5

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PHI 710: Nanoscale Depth Profiling

� 500 V Ar sputter depth profiling shows a non-homogeneous radial P distribution

� The data suggests Vapor-Solid incorporation of P rather than Vapor-Liquid-Solid P incorporation

0

0.5

1

1.5

2

2.5

3

0 2 4 6

Pho

spho

rous

(at

om %

)

Sputter Depth (nm)

Depth Profile of the Si Nanowire

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PHI 710: Compucentric Zalar Rotation

Zalar rotation is used to reduce or eliminate sputtering artifacts that can occur when sputtering at a fixed angle.

Compucentric Zalar rotation depth

profiling defines the selected analysis point as the center of rotation. This is accomplished by moving the sample in X and Y while rotating, all under software control.

Micro-area Zalar depth profiling is possible on features as small as 10 µm with the 710’s automated sample stage.

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RasteredIon Beam

Compucentric Zalar RotationAxis of Rotation at the Analysis Area

Sample

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PHI 710: Compucentric Zalar Rotation

Sputter Time (min)0 50 100 150 200 250 300

0

20

40

60

80

100

Ato

mic

Con

cent

ratio

n (%

)

O

Al (oxide)

Al (metal)Si

Compucentric Zalar Depth Profile of 10 µm Via Contact

Secondary Electron Image(Before Sputtering)

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PHI 710: Compucentric Zalar RotationDepth Profile Comparison With and Without Zalar Rotation

Without Zalar RotationWith Zalar Rotation

Sputter Time (min)0 50 100 150 200 250 300

0

20

40

60

80

100

Ato

mic

Con

cent

ratio

n (%

) Al (metal)

O

Al (oxide)

Si

Sputter Time (min)0 50 100 150 200 250 300

0

20

40

60

80

100

Ato

mic

Con

cent

ratio

n (%

)

O

Al (oxide)

Al (metal)Si

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PHI 710: Compucentric Zalar Rotation

Without RotationWith Rotation

SE Images of 10 µm Via Contacts after Depth Profiling

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PHI 710: Chemical State Depth Profiling

Sample:Ni deposited on Si substrateAnnealed at 425°C

Analysis Conditions:As Received0.1% Energy Resolution10 kV-10 nA20 µm Area Average

Sputter Conditions:500 V Argon1 x 0.5 mm raster

No Zalar Rotation10° Sample Tilt

Chemical State of Si ? Chemical State of Ni ?

0 10 20 30 40 50 600

100

200

300

Sputter Time (min)

Inte

nsity

(kc

ps)

Ni LMM

Si KLL

Large Area Elemental Depth Profile

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PHI 710: Chemical State Depth Profiling

Si from Ni layer

Si from substrate

0 10 20 30 40 50 60

0

100

200

Sputter Time (min)

Inte

nsity

(kc

ps)

Si KLL

FromNi layer1617.2 eV(silicide)

From Si Substrate1616.5 eV(metal)

1610 1615 1620 1625Kinetic Energy (eV)

Nor

mal

ized

Inte

nsity

Si KLL

Large area Si chemical state depth profilescreated with Linear Least Squares (LLS) fitting

0.1% Energy Resolution

Si basis spectra extracted from depth profile data set

nickel silicide

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PHI 710: Chemical State Depth Profiling

0.1% Energy Resolution

Ni fromNi layer

Ni fromSi substrate

0 10 20 30 40 50 60

0

100

200

300

Sputter Time (min)

Inte

nsity

(kc

ps)

Ni LMMNi fromNi layer846.2 eV(Ni-metal)

Ni fromSi substrate844.8 eV(Ni-silicide)

830 840 850 860Kinetic Energy (eV)

Nor

mal

ized

Inte

nsity

Ni LMM

Large area Ni chemical state depth profilescreated with LLS fitting

Ni basis spectra extracted from depth profile data set

nickel silicide

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PHI 710: Chemical State Depth Profiling

FOV: 5.0 µm 20.000 keV

Fe3C 2/16/2010Φ

1.0 µm

1

2

SEM 20kV - 1nA 500 1000 1500

1.0

1.5

2.0

2.5

Kinetic Energy (eV)

Inte

nsity

(M

cps)

Si

Ni

Si

Si

Si

C

C

Ni

Point 1

Point 2

22 nm beam size

Point 2Si fromSubstrate1616.5 eV(metal)

Point 1Si fromMicrostructure1617.2 eV(silicide)

1610 1615 1620 1625Kinetic Energy (eV)

Nor

mal

ized

Inte

nsity

Si KLL Spectra

Microstructure observed in SEM image after depth profile Survey Spectra

0.1% Energy Resolution

Nano-area spectra from selected areas showing islands of nickel silicide

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PHI 710: Chemical State Depth Profiling

FOV: 5.0 µm 20.000 keV

Ni/Si 425C 3/30/2010Φ

1.0 µm

1

2

1

2

SEM 20 kV - 10 nA Auger Image Color Overlay 20 kV - 10 nA

New area on Ni/Si sample with 12 nm removed – microstructures visible

Nano-areas selected for analysis Compositional images show presence of silicide microstructures

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PHI 710: Chemical State Depth Profiling

� Ni/Si film chemical state depth profiling summary:

– The large area depth profiles unknowingly included heterogeneous distributions of nickel silicide microstructures that grew through imperfections in the Ni film

– The nano-area depth profile on the Ni film (off microstructures) shows nickel silicide only at the nickel / silicon interface

Chemical state depth profile frompoint #1 - on film (off microstructure)

Created with LLS fitting in PHI MultiPak

0 20 40 60 80 100 120 140 160 180 2000

100

200

Sputter Depth (nm)

Inte

nsity

(kc

ps)

Si metal

Si silicide

Ni metal

Ni silicide

10 kV – 10 nA 22 nm beam size 35

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PHI 710 Scanning Auger Nanoprobe

�Multi-Technique options

– Energy Dispersive Spectroscopy (EDS or EDX)

– Backscatter Electron Detector (BSE)

– Electron Backscatter Diffraction (EBSD)

– Focused Ion Beam (FIB)

The Complete Auger Solution

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PHI 710 Chamber Layout for Options

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PHI 710 Scanning Auger NanoProbe

Complete Auger Compositional Analysisfor Nanotechnology, Semiconductors,

Advanced Metallurgy and Advanced Materials

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