Lecture 13:Introduction to Thin Film

Characterization: Surface Analysis (XPS, AES, SIMS, RBS)

Block Diagram of SIMS Technique

Dynamic SIMS: Magnetic Sector Mass Spectrometer

Effect of Primary Beam on Secondary Ion YieldsEffect of Primary Beam on Secondary Ion Yields

Oxygen bombardmentWhen sputtering with an oxygen beam, the concentration of oxygen increases in the surface layer and metal-oxygen bonds are present in an oxygen-rich zone. When the bonds break during the bombardment-secondary ion emission process, oxygen becomes negatively charged because of its high electron affinityand the metal is left with the positive charge. Elements in yellow analyzed with oxygen bombardment, positivesecondary ions for best sensitivity.Cesium bombardmentWhen sputtering with a cesium beam, cesium is implanted into the sample surface which reduces the workfunction allowing more secondary electrons to be excited over the surface potential barrier. With the increasedavailability of electrons, there is more negative ion formation. Elements in green analyzed with cesium, negativesecondary ions for best sensitivity.

Graphics courtesy of Charles Evans & Associates web sitehttp://www.cea.com

QUANTITATIVE DEPTH PROFILES to study correlation of unintentional hydrogen passivation of acceptors in heavily C-doped GaAs by ambient conditions during cool down following growth by MOCVD

Detects hydrogenLarge dynamic range

Depth Profile Application with HydrogenDepth Profile Application with Hydrogen

Ion Imaging with Dynamic SIMSIon Imaging with Dynamic SIMS

CROSS-SECTIONAL ION IMAGES GENERATED FROM SEQUENTIAL IMAGES IN DEPTH PROFILE

Two Dimensional Imaging with Dynamic SIMSTwo Dimensional Imaging with Dynamic SIMS

Comparison of Static and Dynamic SIMS

TECHNIQUE

STATIC

DYNAMIC

Flux

<1013 ions/cm2

(per experiment)

~1017 ions/cm2

(minimum dose density) Information

Chemical

Elemental

Sensitivity

.01%

<1 ppm

(ppb for some elements) Type of Analysis

Surface Mass Spectrum

Surface Ion Image

Depth Profile Mass Spectrum

Ion Image Image Depth Profile Quantitative Analysis

Sampling Depth (monolayers)

2

10

Spatial Resolution

~0.1 µm

Best: 20 nm (Ga Source) Cameca ims 5f:

Probe Mode: 200 nm Microscope Mode: 1µ

Sample Damage

Minimal

Destructive in analyzed area—

up to 500µ per area

The PHI TRIFT III TOF SIMS is a time-of-flight secondary ion mass spectrometer which employs three hemispherical electrostatic analyzers. It is equipped with Ga and Au analysis ion guns and Cs and O2 sputtering ion guns. The instrument is used for static and dynamic SIMS with high mass resolution up to 15,000 m/∆m. The mass range is 1-5000 amu. The instrument has a cooling stage

Time-of-Flight Secondary Ion Mass Spectrometry

TRIFT Secondary Ion Trajectories

Ga+

Cs+

Pre-SpectrometerBlanker

SED

Detector

ContrastDiaphragm

ESA 1

ESA 2ESA 3

EnergySlitPost-

SpectrometerBlanker

Sam

ple

In+ Linescans of Quantum Dots

µm0 0.5 1.0 1.5 2.0

0

5

10

15

20

µm0 0.5 1.0 1.5

0

5

10

15

µm0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

5

10

15

20

25

Cts: 550893; Max: 36; Scale: 1µm

InAs/GaAs Quantum Dots

GaAs/AlGaAs

Al

Ga

Analysis beam: 15kV Ga+

Sputter Beam: 300V O2+ with oxygen flood

Trace Analysis of GaAs

85.85 85.90 85.95 86.00Mass [m/z]

0

5000

10000

15000

20000

Cou

nts

GaOH

71GaNH3

m/∆m = 11,600

Trace analysis of Si Wafer

38.94 38.96 38.98 39.00 39.02 39.04Mass [m/z]

010

110

210

310

410

510

610

Cou

nts

K

C3H3

C2HN

No sputtering to remove organics on surface.Large C3H3 peak does not have a tail to lower mass which would obscure C2HN and K.

No Pre-Sputter to remove organics

Polymer sample

300 350 400 450Mass [m/z]

0100200300400500600

Cou

nts

PEO_2000_900C_P.TDC

373 405331 361317 449 493433 477345 389

500 600 700 800 900Mass [m/z]

0100200300400500600

Cou

nts

PEO_2000_900C_P.TDC

829581 669625653537 741697609565521

1000 1200 1400 1600 1800Mass [m/z]

050

100150200250300

Cou

nts

PEO_2000_900C_P.TDC

150713741270113811831094

1050

Auger Electron SpectroscopyAuger Electron Spectroscopy

Primary beam = 3-20KeV electronsSampling distance = 2 to 4 nmDetection sensitivity =~ 1 atomic %Elements = Li and above Schematic of Auger system with

Cylindrical Mirror Analyzer (CMA)

Auger energy is specific to element

AES is a technique which uses an electronprobe to generate Auger electrons at thesample surface.

Relative Probabilities of RelaxationRelative Probabilities of Relaxationof a K Shell Core Holeof a K Shell Core Hole

5

B Ne P Ca Mn Zn Br Zr

10 15 20 25 30 35 40 Atomic Number

Elemental Symbol

0

0.2

0.4

0.6

0.8

1.0

Pro

babi

lity

Note: The lightNote: The lightelements have aelements have alow cross sectionlow cross sectionfor X-rayfor X-rayemission.emission.

Auger ElectronAuger ElectronEmissionEmission

X-ray PhotonX-ray PhotonEmissionEmission

INCIDENTELECTRON

STEP 2L electron fallsto fill vacancy

K

L1

L2

L3

FERMILEVEL

FREEELECTRONLEVEL

CONDUCTION BAND

VALENCE BAND

1s

2s

2p

STEP 1Ejected electron

STEP 3KLL Auger electronemitted to conserveenergy released instep 2

STEP 3 (alternative)an x-ray is emittedto conserve energyreleased in step 2

THE AUGER PROCESS

The emitted Auger electron is designated the (core hole) (step 2 level) (step 3 level) transition ie. (KLL) transition.

The kinetic energy of the emitted Auger electron is : E(Auger) = E(K) - E(L2) - E(L3).

The energy of the emitted X-ray is : E(X-ray) = E(K) - E(L2).

-or-

Ref: Charles Evans & Assoc. web page tutorial by Ron Flleming http://www.cea.com

INCIDENTELECTRON

EJECTED CORE ELECTRON

EJECTED AUGER ELECTRON

AES Imaging and ProfilingAES Imaging and Profiling

SPUTTER TIME (MIN.)

PEA

K-TO

-PE

AK

Fracture surface of Carbon fibers in BN matrix - analysis area outlined in black

Depth profile on fiber to determine point of fracture. Variations in fracture surfaceinterface for different sample treatments will be reflected in depth profile.

From research by C. Cofer/J. Economy, Materials Science Dept.

50 100 150 200 250 300 350 400 450 500 550-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1x 104

Kinetic Energy (eV)

c/s

COFER73.SPE

Si

BAr

C O

N

Survey on Fiber surface at 1 min. in profile

Electron Beam in combination withan SED detector allows for imagingof the sample to select the area for analysis.

0 200 400 600

O

C

Cr

Cr

VV

Ti

Ti

V VV

Cr

Cr

Ti

Cr

TiTiN

KL 2,

3L2,

3

Sc M

1M4M

4

Sc M

2,3M

4M4

Cou

nts

(arb

. uni

ts) N K

L 2,3L

2,3

Sc L

3M2,

3M2,

3

Sc L

3M2,

3M4,

5

Sc L

3M4,

5M4,

5

3 keV spectra - as deposited

Kinetic energy (eV)0 200 400 600

Cr Cr Cr Cr

Cr

VV VVV

TiTi

TiTiTi

Sc M

1M4M

4

Sc M

2,3M

4M4

Cou

nts

(arb

. uni

ts)

N K

L 2,3L

2,3

Sc L

3M2,

3M2,

3Sc

L3M

2,3M

4,5

Sc L

3M4,

5M4,

53 keV spectra - as deposited

Kinetic energy (eV)

N(E

)

dN(E

)/dE

E,E,

Auger Electron Spectroscopy First-Row Transition Metal Nitrides: ScN, TiN, VN, and CrN

raw spectra differentiated spectra

AES analysis:

Electron Beam:Voltage: 3, 5, 10 or 20 keVCurrent: 210 nARaster: 0.2 mm x 0.2 mm

Analyzer:Resolution: 0.25 %Step size:0.2 eV/step

Ion Beam: 3 keV Ar+, 0.30 mA/cm2

XPS and UPS analysis:

X-ray source:Al mono 500 W, 15 kVMg Kα 400W, 15 kV

UV source:He I 0.520 kV, 55 mAHe II 0.580 kV, 56 mA

Spot size:1 mm selected area aperture

Analyzer resolution:XPS Survey: 178.95 eV pass energy (2.8 eV resolution), 1 eV/stepElemental regions: 17.95 eV pass energy (0.28 eV resolution), 0.05 eV/stepUPS valence band: 8.95 eV pass energy (0.13 eV resolution), 0.05 eV/step

Emission angle:XPS: 45°UPS: 90°

Ion Beam: 3 keV Ar+, 4.3 µA/cm2

X-ray Photoelectron SpectroscopySmall Area Detection

XX--ray Beamray Beam

XX--ray penetration ray penetration depth ~1depth ~1µµm.m.Electrons can be Electrons can be excited in this excited in this entire volume.entire volume.

XX--ray excitation area ~1x1 cmray excitation area ~1x1 cm22. Electrons . Electrons are emitted from this entire areaare emitted from this entire area

Electrons are extracted Electrons are extracted only from a narrow solid only from a narrow solid angle.angle.

1 mm1 mm22

10 nm10 nm

Photoelectron and Auger Electron Emission

Conduction BandConduction Band

Valence BandValence Band

Fermi LevelFermi Level

Incident XIncident X--rayray

1s1s

2s2s

2p2p

Ejected PhotoelectronEjected Photoelectron

Conduction BandConduction Band

Valence BandValence Band

L2,L3L2,L3

L1L1

KK

Free Electron LevelFree Electron Level

Emitted Auger ElectronEmitted Auger Electron

X-ray Photoelectron Spectrometer

5 4 . 7

XX--rayraySourceSource

ElectronElectronOpticsOptics

Hemispherical Energy AnalyzerHemispherical Energy Analyzer

Position Position Sensitive Sensitive Detector Detector (PSD)(PSD)

Magnetic ShieldShieldOuter SphereOuter Sphere

Inner SphereInner Sphere

SampleSample

Computer Computer SystemSystem

Elemental Shifts

Binding Energy (eV)

Element 2p3/2 3p ∆

Fe 707 53 654

Co 778 60 718

Ni 853 67 786

Cu 933 75 858

Zn 1022 89 933

Electron-nucleus attraction helps us identify theelements

Chemical Shifts

FunctionalGroup

Binding Energy(eV)

hydrocarbon C-H, C -C 285.0

amine C-N 286.0

alcohol, ether C-O-H, C -O-C 286.5

Cl bound to C C-Cl 286.5

F bound to C C-F 287.8

carbonyl C=O 288.0

1200 1000 800 600 400 200 0

CrN

VN

TiN

ScN

Cou

nts

(arb

. uni

ts)

Binding energy (eV)

Metal and N Auger Lines

N1s

N1s

N1s

N1s

Sc2p

Sc2s

Ti2p

V2p

Cr2p

Ti2s

V2s

Cr2s

Sc3pSc3s

Ti3s

V3s

Cr3s

Ti3p

V3p

Cr3p

X-ray Photoelectron SpectroscopyFirst-Row Transition Metal Nitrides: ScN, TiN, VN, and CrN

Analysis of Materials for Solar Energy Collection by XPS Depth Profiling-

The amorphous-SiC/SnO2 InterfaceThe profile indicates a reduction of the SnOThe profile indicates a reduction of the SnO22occurred at the interface during deposition. occurred at the interface during deposition. Such a reduction would effect the collectorSuch a reduction would effect the collector’’s s efficiency.efficiency.

PhotoPhoto--voltaic Collectorvoltaic Collector

Conductive OxideConductive Oxide-- SnOSnO22

pp--type atype a--SiCSiC

aa--SiSi

Solar EnergySolar Energy

SnOSnO22

SnSn

Depth500 496 492 488 484 480

Binding Energy, eV

Data courtesy A. Nurrudin and J. Abelson, University of Illinois

2 MeV Van de Graaff accelerator

4 MeV Tandetron accelerator

Rutherford backscattering spectrometry

0 50 100 150 2000.0

0.2

0.4

0.6

0.8

1.0

θ = 150o

He4

Kin

emat

ic fa

ctor

: K

Target mass (amu)

22 22 sin cost i i

i t

MMMKM M

θ θ +−= +

24( , ) sin ( ) 2( )

4 2 t

i t iR

Z Z ME MEθσ θ − ∝ −

Rutherford backscattering spectrometry, cont.

Elastic scattering

E1 = KEo

Rutherford scattering cross section

Coulomb interaction between the nuclei:exact expression

Rutherford backscattering spectrometry, cont.

atoms/cm2

Figure after W.-K. Chu, J. W. Mayer, and M.-A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

Au

In

TiAlO

C10 ML 100 ML

RBS – simulated spectrahypothetical alloy Au0.2In0.2Ti0.2Al0.2O0.2/C

Au

In

TiAlOC

Au

In

TiAlOC

Au

In

TiAlOC

Au

In

Ti

AlO

C Au

InTi

Al

O

1000 ML

2000 ML 4000 ML 10000 ML

Element (Z,M): O(8,16), Al(13,27), Ti(22,48), In(49,115), Au(79,197)

RBS: Oxidation behavior

TiN/SiO2TaN/SiO2

Ta = 600 °C for 12 min in atmosphere

As-deposited

Annealed

I. Petrov, P. Losbichler, J. E. Greene, W.-D. Münz, T. Hurkmans, and T. Trinh, Ion-Assisted Growth of Ti1-xAlxN/Ti1-

yNbyN Multilayers by Combined Cathodic-Arc/Magnetron-Sputter Deposition, Thin Solid Films, 302 179 (1997)

Example: average composition Ti0.27Al0.20Nb0.02N0.51

Comparison of Detection Limits by TechniqueComparison of Detection Limits by Technique