auger electron spectroscopy overview · 2017. 8. 29. · auger electron spectroscopy ekll = ek - el...
TRANSCRIPT
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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
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2
3
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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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