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Surface Analysis II:

2008 Advanced Materials Characterization Workshop

ySecondary Ion Mass Spectrometry

Rutherford BackscatteringTim Spila, Judy Baker, and Ivan Petrov

Sponsors:

The Frederick Seitz Materials Research LaboratoryUniversity of Illinois at Urbana-Champaign

Supported by the U.S. Department of Energy under grant DEFG02-91-ER45439© 2007 University of Illinois Board of Trustees. All rights reserved.

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Sponsors:

Supported by the U.S. Department of Energy under grants DEFG02-07-ER46453 and DEFG02-07-ER46471© 2008 University of Illinois Board of Trustees. All rights reserved.

Secondary Ion Mass Spectrometry

• SIMS is an analytical technique based th t f th fon the measurement of the mass of

ions ejected from a solid surface after the surface has been bombarded with high energy primary ions.

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Ion Beam Sputtering

Graphics courtesy of Charles Evans & Associatesweb site: http://www.cea.com

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Sputtered species include:• Monoatomic and polyatomic particles of sample material (positive, negative or neutral)• Resputtered primary species (positive, negative or neutral)• Electrons• Photons

Block Diagram of SIMS Technique

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Comparison of Static and Dynamic SIMS

TECHNIQUE DYNAMIC STATICFLUX ~1017 ions/cm2

(minimum dose density)< 1013 ions/cm2

(per experiment)

INFORMATION Elemental Elemental + MolecularINFORMATION Elemental Elemental Molecular

SENSITIVITY < 1 ppm(ppb for some elements)

1 ppm

TYPE OF ANALYSIS Depth ProfileMass Spectrum2D Ion Image3D Image Depth Profile

Surface Mass Spectrum2D Surface Ion ImageElemental Depth Profiling3D Image Depth Profiling

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SAMPLING DEPTH 10 monolayers 2 monolayers

SPATIAL RESOLUTION

Cameca ims 5fProbe mode: 200 nmMicroscope mode: 1 μm

PHI TRIFT III0.1 μm

SAMPLE DAMAGE Destructive in analyzed area – up to 500 μm per area

Minimal

Technique Comparison

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Magnetic Sector Mass SpectrometerCAMECA ims 5f

SECONDARY ION COLUMN

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PRIMARY ION COLUMN

Time of Flight Mass Spectrometer

ESA 2ESA 3Physical ElectronicsTRIFT III TOF-SIMS

Cs+ or O2+

SED

EnergySlitPost-

SpectrometerBlanker

e

8

Ga+ or Au+

Pre-SpectrometerBlanker

Detector

ContrastDiaphragm

ESA 1

Sam

ple

2

21 mveV =

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Quantitative Surface Analysis: SIMS

In SIMS, the yield of secondary ions is strongly influenced by the electronicstrongly influenced by the electronic state of the material being analyzed.

ηθα mmpms yII +=

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Ism = secondary ion current of species m

Ip = primary particle fluxym = sputter yieldα+ = ionization probability to positive ionsθm = factional concentration of m in the surface layerη = transmission of the analysis system

ηmmps y

Total Ion Sputtering Yield

Courtesy of Prof. Rockett

Sputter yield: ratio of number of atoms sputtered to number of impinging ions, typically 5-15p g g , yp y

Ion sputter yield: ratio of ionized atoms sputtered to number of impinging ions, 10-6 to 10-2

Ion sputter yield may be influenced by:•Matrix effects•Surface coverage of reactive elements•Background pressure in the sample environment•Orientation of crystallographic axes with respect to the sample surface

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+

First principles prediction of ion sputter yields is not possible with this technique.

•Angle of emission of detected secondary ions

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Effect of Primary Beam on Secondary Ion Yields

Oxygen bombardment

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

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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 affinity and the metal is left with the positive charge. Elements inyellow analyzed with oxygen bombardment, positive secondary ions for best sensitivity.

Cesium bombardmentWhen sputtering with a cesium beam, cesium is implanted into the sample surface which reduces the work function allowing more secondary electrons to be excited over the surface potential barrier. With the increased availability of electrons, there is more negative ion formation. Elements in green analyzed with cesium, negative secondary ions for best sensitivity.

Relative Secondary Ion Yield ComparisonCs+, Negative Secondary Ions O-, Positve Secondary Ions

From Storms, et al., Anal. Chem. 49, 2023 (1977).

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Relative Secondary Ion Yield ComparisonFrom Storms, et al., Anal. Chem. 49, 2023 (1977).

Cs+, Positive Secondary Ions of M+ Cs+, Positive Secondary Ions of CsM+

Depth Profile Application with Hydrogen

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

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Definition of Mass Resolution

Mass resolution defined by m/ΔmMass resolution of ~1600 required to resolve 32S from 16O2

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

Isotopic Analysis

(b) 100(a) ) 70

Ni Al 600 C: 4 h 18O , 16 h 16O3 2 2R.T. Haasch, A.M. Venezia, and C.M. Loxton. J. Mater.Res., 7, 1341 (1992).

(a) (b)

0 50 100 150 200 250 300 350Sputter Time (min.)

0

20

40

60

80

Oxy

gen

Ion

Yiel

d(%

Lin

ear C

ount

s)

( )

AE

S A

tom

ic C

onc

en

tra

tion

(%

0

10

20

30

40

50

60(a) (b)

(c)

16O+

18O+O

Al

Ni

16

(c)

Ni Al3NiO, NiAl O , Al O 42 32NiO

16M O

M O18

(a) AES composition depth profile(b) SIMS isotopic oxygen diffusion profile expressed as a

percentage of the total oxygen(c) Schematic of layered oxide structure

(c)

M16OM18O

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B Depth Profile in Si(001)

G. Glass, H. Kim, P. Desjardins, N. Taylor, T. Spila, Q. Lu, and J. E. Greene. Phys. Rev. B, 61,7628 (2000).

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SIMS depth profiles through a B modulation-doped Si(001):B film grown by GS-MBE from Si2H6 and B2H6 atTs=600 °C. The incident Si2H6 flux was JSi2H6 = 2.2x1016 cm-2 s-1 while the B flux JB2H6 was varied from 8.4x1013 to1.2x1016 cm-2 s-1. The deposition time for each layer was constant at 1 h.

B Delta doping in Si(001)

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SIMS depth profiles through a B δ-doped layers in a Si(001) film grown by GS-MBE from Si2H6 at TS=700 °C. The Si2H6, flux, JSi2H6, was 5X1016 cm-2 s-1 while the B2H6 flux, JB2H6 varied from 0.16-7.8X1014 cm-2 s-1. The inset shows the two-dimensional B concentration NB

2D as a function of JB2H6.

Q. Lu, T. R. Bramblett, N.-E. Lee, M.-A. Hasan, T. Karasawa, and J. E. Greene. J. Appl. Phys. 77, 1037 (1995).

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Depth Resolution and Ion Beam Mixing

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Ion Imaging with Dynamic SIMS

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

Two Dimensional Imaging with Dynamic SIMS

Determination of RSF Using Ion Implants

I

ηθα mmpms yII +=

22

ii

m

IIRSF ρ=

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

CdIIdCtIRSF

bi

m

−=

∑φ

Level Profile:

Gaussian Profile:

RSF = Relative Sensitivity FactorIm, Ii = ion intensity (counts/sec)ρ = atom density (atoms/cm3)φ = implant fluence (atoms/cm2)C = # measurement cyclest = analysis time (s/cycle)d = crater depth (cm)Ib = background ion counts

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Positive and Negative Secondary Ions

105

106

Ion implanted P standard1023 Ion implanted P standard

Raw Data Processed Data

10

102

103

104

O+2 beam

Si P

Cs+ beam Si P

Cou

nts

/ sec

1019

1020

1021

1022

O+2 beam

Si P

Cs+ beam Si P

ncen

tratio

n (a

tom

s/cm

3 )

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0 100 200 300 400 500 600 70010-1

1

Depth (nm)0 100 200 300 400 500 600 700

1017

1018Con

Depth (nm)

Static and Dynamic SIMS

Dynamic SIMS Static SIMS

•Material removal•Elemental analysis

•Ultra surface analysis•Elemental or molecular analysis

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•Elemental analysis•Depth profiling

•Elemental or molecular analysis•Analysis complete before significant fraction of molecules destroyed

Courtesy Gregory L. Fisher, Physical Electronics

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Extreme Mass Range

710

Integral: 1922 TG_SCAN03_NEGSEC_AU2_22KV_BUNCHED_2NA_400UM_90MIN_CDOUT_CHGCOMP_0-10000AMU.TDC - Ions 400µm 17452848 cts

107

310

410

510

610

Tota

l Cou

nts

(9.4

3 am

u bi

n)

256015762166

118217731379

788

985394

591

197

Tota

l Cou

nts

103

104

105

106

25

0 2000 4000 6000 8000010

110

210

0 2000 4000 6000 8000 10000Mass (amu)

1

10

102

Trace Analysis

GaAs Wafer

20000GaOH

Si Wafer

510

610

C3H3

10000

15000

Cou

nts

GaNH3m/Δm = 11,600

210

310

410

Cou

nts

KC2HN

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85.85 85.90 85.95 86.00Mass [m/z]

0

5000

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

010

110

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

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InAs/GaAs Quantum Dots

In+ Linescans of Quantum Dots

15

20

µm0 0.5 1.0 1.5

0

5

10

20

25

Cts: 550893; Max: 36; Scale: 1µm

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µm0 0.5 1.0 1.5 2.0

0

5

10

15

µm0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

0

5

10

15

GaAs/AlGaAs Depth ProfileAnalysis beam: 15kV Ga+

Sputter Beam: 300V O2+ with oxygen flood

Al

28

Ga

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TOF-SIMS Imaging of Patterned Sample

O OO

Br

OS

O OSi

O

OH

O hν (∼375 nm)

H2O

OS

O OSi

O

OH

OH

O OO

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Courtesy Josh Ritchey, Audrey Bowen, Ralph Nuzzo and Jeffrey Moore, University of Illinois

400 μmS

400 μmBr

50 μmBr

TOF-SIMS Ion Images of an Isolated NeuronFirst Images of Vitamin E Distribution in a Cell

Courtesy E.B. Monroe,J.C. Jurchen, S.S. Rubakhin,J.V. Sweedler. University ofIllinois at Urbana-Champaign

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Cellular lipids:fragment (m/z 69)

Vitamin E(m/z 430)

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TOF-SIMS Ion Images of songbird brain

Courtesy Kensey R. Amaya, Eric B. Monroe, Jonathan V. Sweedler, David F. Clayton. International Journal of Mass

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Selected ion images from the songbird brain. Each ion image consists of ~11.5 million pixels within the tissue section and is thecombination of 194 individual 600m×600m ion images prepared on the same relative intensity scale. Ion images are (A) phosphatePO3− (m/z 79.0); (B) cholesterol (m/z 385.4); (C) arachidonic acid C20:4 (m/z 303.2); (D) palmitic acid C16:0 (m/z 255.2); (E)palmitoleic acid C16:1 (m/z 253.2); (F) stearic acid C18:0 (m/z 283.3); (G) oleic acid C18:1 (m/z 281.2); (H) linoleic acid C18:2 (m/z279.23); and (I) -linolenic acid C18:3 (m/z 277.2). Scale bars = 2 mm.

Spectrometry 260, 121 (2007).

Diamond-Like-Carbon Friction Testing

DLC coated disk

DLC coated ball

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wear tracks and scars formed on DLC-coated disk and ball sides during test in dry oxygen

Oxygen Carbon C + O Overlay

Courtesy O.L. Eryilmaz and A. ErdemirEnergy Systems Division, Argonne National Laboratory Argonne, IL 60439 USA

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3-D TOF-SIMS Imaging of DLC

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Wear track from hydrogenated DLC tested in dry nitrogenCourtesy O.L. Eryilmaz and A. ErdemirEnergy Systems Division, Argonne National Laboratory Argonne, IL 60439 USA

3-D TOF-SIMS Movies of DLC

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H CH C2H C2H2O

NFC6 H2 Environment TOF-SIMS ImagesCourtesy O.L. Eryilmaz and A. ErdemirEnergy Systems Division, Argonne National Laboratory Argonne, IL 60439 USA

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SIMS Summary

Probe/Detected Species

InformationSurface Mass Spectrum2D Surface Ion ImageElemental Depth Profiling3D Image Depth Profiling

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Elements DetectableH and above

Sensitivityppb - atomic %

Analysis Diameter/Sampling Depth~1 μm - several mm/0.5 - 1nm

2 MeV Van de Graaff accelerator 4.6 MeV Tandetron accelerator

Rutherford backscattering spectrometry

magnet RBS chamber

Beam lines

beam size Φ1-3 mmflat samplecan be rotated

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Rutherford scattering cross section

Coulomb interaction between the nuclei:exact expression > quantitative method

2 241 2 21

2( , ) sin ( ) 2( )

4 2RZ Z ZME ME E

θσ θ −⎛ ⎞ ⎡ ⎤ ⎛ ⎞∝ − ∝⎜ ⎟ ⎜ ⎟⎢ ⎥⎝ ⎠ ⎣ ⎦ ⎝ ⎠

exact expression -> quantitative method

Elastic two-body collision

M1vo2 = M1v1

2 + M2v22

22 22 sin cost i i

i t

MMMKM M

θ θ⎛ ⎞+−= ⎜ ⎟⎜ ⎟+⎝ ⎠

E1 = KEo M1<M2, 0 ≤θ≤180o

RBS: He backscatters from M2>40 ≤Φ≤90o

1.0

M1vo = M1v1 + M2v2

M1>M2, 0 ≤θ≤90o

0 ≤Φ≤90o

ERD: He recoils H forward0 50 100 150 2000.0

0.2

0.4

0.6

0.8

θ = 150o

He4

Kin

emat

ic fa

ctor

: K

Target mass (amu)

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Rutherford backscattering spectrometry

cm lo

g(dE

/dx)

1 keV

ener

gy lo

ss p

er

1 MeV(log E)

thin film projected on to a plane: atoms/cm2

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

(Nt)[at/cm2] = N[at/cm3] * t[cm]

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

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

10 ML 100 ML Au1200 8000

22( , )R

ZEE

σ θ ⎛ ⎞∝ ⎜ ⎟⎝ ⎠

Ti

Au

In

TiAlO

C10 ML 100 ML Au

In

TiAlOC

16000 20000 50000

⎝ ⎠

0 50 100 150 2000.0

0.2

0.4

0.6

0.8

1.0

θ = 150o

He4

Kine

mat

ic fa

ctor

: K

Target mass (amu)

Au

In

Ti

AlO

C Au

InTi

Al

O

4000 ML 10000 ML

Au

In

TiAlOC

1000 ML16000 20000

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Series 0Series 1

Cou

nts

11,500

11,000

10,500

10,000

9,500

9,000

8,500

8,000

7,500

7,000

6,500

6,000

5,500

5,000

4,500

4,000

3,500

3,000

2,500

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

Thickness effects

TiN/MgON surface

300 nm

Ti surfaceTiN, O, Mg

N

DScattered

15

15

IncidentChannel

700650600550500450400350300250200150100500

2,000

1,500

1,000

500

0

Series 0Simulated

Cou

nts

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

Ti surface

400 nm

Ti interface

Ti interface

N, O, Mginterface

N, O, Mginterface

N surface

HeIncident

Series 0Simulated

Channel700650600550500450400350300250200150100500

Cou

nts

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

Channel700650600550500450400350300250200150100500

0

600 nm

Ti surface

Ti interface

N, O, Mginterface

N surface

N

D

15

15

Incident angle effects

TiN/MgO

52N

Scattered

15

15

Series 0Simulated

Coun

ts

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

Ti surface400 nm

N surface

Series 0Simulated

Cou

nts

8,500

8,000

7,500

7,000

6,500

6,000

5,500

5,000

4,500

4,000

3,500

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

400 nm

N surface

Ti surface

22.5

NHe

15

Incident

Channel700650600550500450400350300250200150100500

6,000

5,000

4,000

3,000

2,000

1,000

0

Ti interface

N, O, Mginterface

Channel700650600550500450400350300250200150100500

3,000

2,500

2,000

1,500

1,000

500

0

Ti interface

N, O, Mginterface

Surface peaks do not change position with incident angle;

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

I. Petrov, P. Losbichler, J. E. Greene, W.-D. Münz, T. Hurkmans, and T. Trinh, Thin Solid Films, 302 179 (1997)

RBS: Oxidation behavior

TiN/SiO2

A d i d

TiN

Experimental and simulated spectra by RUMP

RBS: Oxidation behavior

As-deposited

TiO

y

Ta = 600 °C for 12 min in atmosphere.

Annealed

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SIMNRA simulation program for RBS and ERD

http://www.rzg.mpg.de/~mam/

Elastic Recoil Detection of Hydrogen

1500

2000

1500

2000

s

1500

2000 Polyethylene CH2 Nano-diamond film (ANL)

C0.33H0.67C0.92H0.08

200 400 600 800 10000

500

1000

0

500

1000 coun

ts

channel #200 400 600 800 1000

0

500

1000

channel #

coun

ts

He scattered from C

Recoil H

Dr. Yan Wu

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Summary

Rutherford backscattering spectrometry

• Quantitative technique for elemental composition• Requires flat samples; beam size Φ1-3 mm• Non-destructive• Detection limit varies from 0.1 to 10-6, depending on Z

•optimum for heavy elements in/on light matrix, e.g. Ta/Si, Au/C…• Depth information from ML to 1 μm