Rutherford Backscattering & Secondary Ion Mass Spectrometery

Advanced Materials Characterization WorkshopJune 3 and 4, 2013

University of Illinois at Urbana-Champaign | Materials Research Laboratory

© 2013 University of Illinois Board of Trustees. All rights reserved.

Rutherford Backscattering & Secondary Ion Mass Spectrometery

Timothy P. Spila, Ph.D.

Frederick Seitz Materials Research LaboratoryUniversity of Illinois at Urbana‐Champaign


Rutherford Backscattering Spectrometry

He+

He

RBS is an analytical technique where high energy ions (~2 MeV)are scattered from atomic nuclei in a sample. The energy of theback-scattered ions can be measured to give information onsample composition as a function of depth.


Geiger‐Marsden Experiment

Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.

Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.


Rutherford Backscattering Spectrometry

2 MeV Van de Graaff accelerator

beam size Φ1-3 mmflat samplecan be rotated


Primary Beam Energy

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]

ener

gy lo

ss p

er c

m lo

g(dE

/dx)

1 keV 1 MeV(log E)

1 keV 1 MeV


Elastic Two‐Body Collision

22 22 sin cost i i

i t

MMMKM M

E1 = KEo

M1<M2, 0 ≤θ≤180o

RBS: He backscatters from M2>4

0 ≤Φ≤90o

0 50 100 150 2000.0

0.2

0.4

0.6

0.8

1.0

= 150o

He4

Kin

emat

ic fa

ctor

: K

Target mass (amu)

M1vo2 = M1v1

2 + M2v22

M1vo = M1v1 + M2v2

Elastic Scattering


Rutherford Scattering Cross Section

2 241 2 21

2( , ) sin ( ) 2( )

4 2RZ Z ZME ME E

Coulomb interaction between the nuclei:exact expression -> quantitative method


Electron Stopping

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

1 keV

ener

gy lo

ss p

er c

m lo

g(dE

/dx)

1 MeV(log E)


RBS – Simulated Spectra

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

hypothetical alloy Au0.2In0.2Ti0.2Al0.2O0.2/C

Au

In

TiAlO

C10 ML 100 ML Au

In

TiAlOC

1200 8000

Au

In

TiAlOC

1000 ML16000

22( , )R

ZEE

0 50 100 150 2000.0

0.2

0.4

0.6

0.8

1.0

= 150o

He4

Kin

emat

ic fa

ctor

: K

Target mass (amu)

4000 ML 10000 ML20000 50000


SIMNRA Simulation Program for RBS and ERD


Thickness Effects

Series 0Series 1

Channel700650600550500450400350300250200150100500

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

2,000

1,500

1,000

500

0

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

Energy [keV]

N surface

300 nm

Ti surfaceTi interface

N, O, Mginterface

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]

Ti surface

400 nm

Ti interface

N, O, Mginterface

N surface

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]

600 nm

Ti surface

Ti interface

N, O, Mginterface

N surface

TiN/MgO

N

He

DScattered

15

15

Incident


Incident Angle Effects

TiN/MgO

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]

Ti surface400 nm

Ti interface

N, O, Mginterface

N surface

Series 0Simulated

Channel700650600550500450400350300250200150100500

Cou

nts

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

2,000

1,500

1,000

500

0

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

Energy [keV]

400 nm

N surface

Ti surface

Ti interface

N, O, Mginterface

22.5

52

N

N

He

Scattered

15

15

Incident

Surface peaks do not change position with incident angle;


Example: Average Composition

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

Annealed in atmosphere for 12 min at Ta = 600 °C

As-deposited

Experimental spectra and simulated spectra by RUMP


RBS Summary

N

He

DScattered

15

15

Incident

• 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 monolayers to 1 m


Secondary Ion Mass Spectrometry

SIMS is an analytical technique based on themeasurement of the mass of ions ejected from a solidsurface after the surface has been bombarded withhigh energy (1‐25 keV) primary ions.

Primary Ions Secondary Ions


Technique Comparison


Block Diagram of SIMS Technique


Comparison of Static and Dynamic SIMS

TECHNIQUE DYNAMIC STATICFLUX ~1017 ions/cm2

(minimum dose density)< 1013 ions/cm2

(per experiment)

INFORMATION Elemental Elemental + Molecular

SENSITIVITY < 1 ppm(ppb for some elements)

1 ppm

TYPE OF ANALYSIS Depth ProfileMass Spectrum3D Image Depth Profile

Surface Mass Spectrum2D Surface Ion Image

SAMPLING DEPTH 10 monolayers 2 monolayers

SPATIAL RESOLUTION

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

PHI TRIFT III0.1 m

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

Minimal


Magnetic Sector Mass Spectrometer

CAMECA ims 5f

PRIMARY ION COLUMN

SECONDARY ION COLUMN


Time of Flight Mass Spectrometer

Physical ElectronicsTRIFT III TOF-SIMS

Sample

Cs+ or O2+

Au+

Pre‐Spectrometer Blanker

SED

ContrastDiaphragm

EnergySlit

Post‐SpectrometerBlanker

ESA 1

ESA 2ESA 3

2

21 mveV


Ion Beam Sputtering

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


MD Simulation of ion impact

Enhancement of Sputtering Yields due to C60 vs. Ga Bombardment of Ag{111} as Explored by Molecular Dynamics Simulations, Z. Postawa, B. Czerwinski, M. Szewczyk, E. J. Smiley, N. Winograd and B. J. Garrison, Anal. Chem., 75, 4402-4407 (2003).

Animations downloaded from http://galilei.chem.psu.edu/sputtering-animations.html.


Quantitative Surface Analysis: SIMS

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

Ism = secondary ion current of species m

Ip = primary particle fluxym = sputter yield+ = ionization probability to positive ionsm = factional concentration of m in the layer = transmission of the analysis system

mmpms yII


Total Ion Sputtering Yield

+

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

Courtesy of Prof. Rockett

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

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•Angle of emission of detected secondary ions


Effect 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 affinity and the metal is left with the positive charge. Elements in yellow 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 moresecondary 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.

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


Relative Secondary Ion Yield Comparison

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


Relative Secondary Ion Yield Comparison

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


Determination of RSF Using Ion Implants

ii

m

IIRSF

CdIIdCtIRSF

bi

m

LevelProfile:

GaussianProfile:

RSF = Relative Sensitivity FactorIm, Ii = ion intensity (counts/sec) = atom density (atoms/cm3) = implant fluence (atoms/cm2)

mmpms yII

C = # measurement cyclest = analysis time (s/cycle)d = crater depth (cm)Ib = background ion counts

Where:


Positive and Negative Secondary Ions

0 100 200 300 400 500 600 70010-1

1

10

102

103

104

105

106

Ion implanted P standard

O+2 beam

Si P

Cs+ beam Si P

Cou

nts

/ sec

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

1017

1018

1019

1020

1021

1022

1023 Ion implanted P standard

O+2 beam

Si P

Cs+ beam Si P

Con

cent

ratio

n (a

tom

s/cm

3 )

Depth (nm)


Definition of Mass Resolution

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

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


Depth Profile Application with Hydrogen

Detects hydrogen Large dynamic range


Isotopic Analysis

(b)

(c)

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

0

20

40

60

80

100

Ni Al3NiO, NiAl O , Al O 42 32NiOO

xyge

n Io

n Yi

eld

(% L

inea

r Cou

nts)

16M O

M O18

(a)

AE

S A

tom

ic C

onc

en

tra

tion

(%

)

0

10

20

30

40

50

70

60

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

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

(a) (b)

(c)

M16OM18O

16O+

18O+O

Al

Ni


B Depth Profile in Si(001)

SIMS depth profiles through a B modulation-doped Si(001):B film grown by GS-MBE from Si2H6and B2H6 at Ts=600 °C. The incident Si2H6 flux was JSi2H6 = 2.2x1016 cm-2 s-1 while the B flux JB2H6 was varied from 8.4x1013 to 1.2x1016 cm-2 s-1. The deposition time for each layer was constant at 1 h.

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


Depth Resolution and Ion Beam Mixing

SIMS depth profiles through a B -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 B2H6flux, 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, 3067 (1995).


Static and Dynamic SIMS

Dynamic SIMS Static SIMS

•Material removal•Elemental analysis•Depth profiling

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

Courtesy Gregory L. Fisher, Physical Electronics


Extreme Mass Range

0 2000 4000 6000 8000010

110

210

310

410

510

610

710

Tota

l Cou

nts

(9.4

3 am

u bi

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

256015762166

118217731379

788

985394

591

197

Mass (amu)

Tota

l Cou

nts


Trace AnalysisGaAs Wafer

85.85 85.90 85.95 86.00Mass [m/z]

0

5000

10000

15000

20000

Coun

ts

GaOH

GaNH3m/m = 11,600

Si Wafer

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

010

110

210

310

410

510

610

Coun

ts

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.


InAs/GaAs Quantum Dots

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


GaAs/AlGaAs Depth Profile

Al

Ga

Analysis beam: 15kV Ga+

Sputter Beam: 300V O2+

with oxygen flood


200 400 600 800 1000Time (Seconds)

010

110

210

310

410

510

Cou

nts

Total_Ion

U

UO

Nd

NdO

200 400 600 800 1000Time (Seconds)

010

110

210

310

410

510

Cou

nts

Total_Ion

UUO

Nd

NdO

Depth Profile Beam Alignment


TOF‐SIMS Imaging of Patterned Sample

O OO

Br

OS

O OSi

O

OH

O h(nm)

H2O

OS

O OSi

O

OH

OH

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

400 mS

400 mBr

50 mBr


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


TOF‐SIMS Ion Images of Songbird Brain

Selected ion images from the songbird brain. Each ion imageconsists of ~11.5 million pixels within the tissue section and isthe combination of 194 individual 600m×600m ion imagesprepared on the same relative intensity scale. Ion images are(A) phosphate PO3− (m/z 79.0); (B) cholesterol (m/z 385.4);(C) arachidonic acid C20:4 (m/z 303.2); (D) palmitic acidC16:0 (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/z281.2); (H) linoleic acid C18:2 (m/z 279.23); and (I) -linolenicacid C18:3 (m/z 277.2). Scale bars = 2 mm.

Courtesy Kensey R. Amaya, Eric B. Monroe, Jonathan V. Sweedler, David F. Clayton. International Journal of Mass Spectrometry 260, 121 (2007).


Diamond‐Like‐Carbon Friction Testing

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

DLC coated ball

DLC coated disk

Oxygen Carbon C + O Overlay

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


3‐D TOF‐SIMS imaging of DLCWear 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

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


SIMS Summary

Probe/Detected Species InformationSurface Mass Spectrum2D Surface Ion ImageElemental Depth Profiling3D Image Depth Profiling

Elements DetectableH and above

Sensitivityppb - atomic %

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


Acknowledgments

Documents

Rutherford Backscattering & Secondary Ion Mass Spectrometery