Secondary ion mass spectrometry · Sputter time (sec) Depth profile. 020 40 60 80 100 1 10 100 1000 10000. Counts/sec Mass (AMU) Mass spectrum. Ion image. 20 µm. MENA3100 - SIMS

MEN

A3100 -

SIM

S

1

Secondary ion mass spectrometrySecondary ion mass spectrometry (SIMS)(SIMS)

Lasse

Vines

MEN

A3100 -

SIM

S

2

Secondary ion mass spectrometrySecondary ion mass spectrometry

0 20 40 60 80 1001

10

100

1000

10000

Cou

nts/

sec

Mass (AMU)

Li

OO2

K

Zn

ZnO

ZnO2

Na Cr

1014

1015

1016

1017

1018

1019

1020

1021

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

PBAs

Atom

ic c

once

ntra

tion

(cm

-3)

Depth (um)

Si07

Ge0.3

MEN

A3100 -

SIM

S

3

ChemicalChemical identificationidentification

Impurity

identification Isotope ratio

64Zn 66Zn67Zn

68Zn

70Zn

MEN

A3100 -

SIM

S

4

Characterization of device structureCharacterization of device structure

1014

1015

1016

1017

1018

1019

1020

1021

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

PBAs

Atom

ic c

once

ntra

tion

(cm

-3)

Depth (um)

Si07

Ge0.3

MEN

A3100 -

SIM

S

5

Characterization of solar cellCharacterization of solar cell

Characterization•Optimization of processing•Trouble shooting

1,2

1,0

0,8

0,6

0,4

0,2

0,01E16 1E17 1E18 1E19 1E20

Dep

th (µ

m)

P Concentration (cm-3)

MEN

A3100 -

SIM

S

6

Ion Ion imagingimaging

Na distribution

MEN

A3100 -

SIM

S

7

OutlineOutline

•

Characteristic features–

Comparison with other techniques

•

Physical processes–

Sputtering

–

Ionization

•

SIMS instrumentation–

Types of mass spectrometers

–

Measurement modes: Mass spectra, Depth profiling, Ion imaging

•

Examples of applications–

Diffusion studies

–

Material development

MEN

A3100 -

SIM

S

8

Characteristic featuresCharacteristic features

•

Quantitative chemical analysis•

High detection sensitivity–

1016

– 1013

atoms/cm3 (ppm-ppb)–

Can measure H

•

Large dynamic range–

> 5 orders of magnitude

•

Very high depth resolution–

Resolution of 20 Å

can be obtained

•

Ion microscopy–

Lateral resolution < 0.5 µm

But,•

Limited to concentration <5%

•

Samples must be vacuum compatible •

Samples must be partially conductive

•

Destructive technique

MEN

A3100 -

SIM

S

9

Comparison to other techniquesComparison to other techniques

MEN

A3100 -

SIM

S

10

OutlineOutline

•



•


Sputtering

–

Ionization

•



–


•


Diffusion studies

–


MEN

A3100 -

SIM

S

11

Ion Ion –– solid interactionsolid interaction

Matrix atom

Impurityatom

Primary ion

Secondary ions are accelerated by an applied sample voltage

Primary beam

Energy is transferred from the energetic primary ions to atoms in the sample. Some of these receive enough energy to escape the sample.

MEN

A3100 -

SIM

S

12

SputteringSputtering

Sigmund P. Theory of Sputtering, Phys. Rev. 184(2), 383 (1969)

Sputtering Yield:number of sputtered atoms per incoming ion

it

in

0

iti E

ESUKES

8/3n 383/1ln5.0 S

Sputtering yield:

50.05for 3

keV5.321

it6/5

tiit

2/13/2t

3/2ititiit

ZZZZK

ZZZZMME

Mi , Zi : Ion mass and atomic numberMt , Zt : Target mass and atomic numberU0 : Surface escape barrier in eVEi : Ion energy

Nuclear stopping cross-section:Sputtering is a multiple collision process involving a cascade of moving target atoms, this cascade may extend over a considerable region inside the target.

MEN

A3100 -

SIM

S

13


•

Dependence of ion

MEN

A3100 -

SIM

S

14


•

Example of dependence of target on sputtering yield: (Si1-x

Gex

)

0 20 40 60 80 100

1

2

3

Nor

mal

ized

ion

yiel

d

Ge content (%)

MEN

A3100 -

SIM

S

15


•

Example of sputtering of polycrystalline Fe surface

The erosion rate is different for the different grains: Sputtering yield vary with the crystal orientation

MEN

A3100 -

SIM

S

16


•

Example of sputtering yield:

200 µm

0 100 200 300 400 500

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

Dep

th (µ

m)

Width (µm)

Material removed: 1200200 µ3

= 410-8

cm3

≈

21015

atoms

Current: 200 nASputtering time: 700 sec

Incoming ions: 20010-9A

6.241018

ions/C

700 sec = 9x1014

ions

Sputtering Yield = 2.2 atoms/ion

MEN

A3100 -

SIM

S

17

Sputtering Sputtering –– Secondary ionsSecondary ions

•

Energy distribution of secondary ions

0 20 40 60 80 10010

100

1000

10000

100000

28Si4

28Si3

28Si2

Sec

onda

ry in

tens

ity (a

rb. u

nit)

Energy (eV)

28Si

MEN

A3100 -

SIM

S

18

IonizationIonization

•

Ion yield/ionization efficiency : The fraction of sputtered ions that becomes ionized.

•

Ion yield can generally not be predicted theoretically.•

Ion yield can vary by several orders of magnitude depending on element and chemistry of the sputtered surface.

•

Oxygen on the surface will increase positive ion yield•

Cesium on the surface will increase negative ion yield

MEN

A3100 -

SIM

S

19

IonizationIonizationNegative secondary

Positive secondary

vAC

vEC i

/exp YieldIon Negative

/exp YieldIon Positive

EiA

C±: Constantsv: velocity perpendicular to surface: work function

(Cs)

(O)

MEN

A3100 -

SIM

S

20


64 66 68 70100

101

102

103

104

105

106

107

Sec

onda

ry In

tens

ity(c

ps)

M/q (AMU)

Negative modePositive mode

Mass

spectrum

of ZnO, Zn peaks.64Zn

(48.6%)66Zn

(27.9%)

67Zn

(4.1%)

68Zn

(18.8%)

70Zn

(0.6%)

MEN

A3100 -

SIM

S

21


0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0 20 40 60 80 100

Nor

mal

ized

P- - y

ield

Ge concentration (%)

Phosphorus in Si1-x Gex

•

Limits the quantification procedure:–

SIMS is mainly a tool for measuring small concentrations in a given matrix

MEN

A3100 -

SIM

S

22

General YieldGeneral Yield

•

Measured intensity It for a specific target atom

TCYII ttPt

IP : Primary ion current Y : Sputtering yield

(number of sputtered particles per impinging primary ion)

[Ct ]: Concentration of species t t : Secondary ion formation and

survival probability (ionization efficiency)

T: Instrument transmission function

t

is highly dependent on species and matrix

MEN

A3100 -

SIM

S

23

OutlineOutline

•



•


Sputtering

–

Ionization

•



–


•


Diffusion studies

–


MEN

A3100 -

SIM

S

24

The SIMS instrumentThe SIMS instrument

Focused

ion beamMass

Spectrometer

MEN

A3100 -

SIM

S

25

The SIMS instrumentThe SIMS instrument

•

Instruments are usually classified by the type of mass spectrometer:–

Time of Flight•

Simultaneous detection of many elements

•

High transmission•

Measures large molecules

–

Quadrupole•

Low impact energy

–

Magnetic Sector•

High mass resolution

•

High transmission•

Low detection limit

MEN

A3100 -

SIM

S

26

Time of Time of FlightFlight SIMSSIMS

MEN

A3100 -

SIM

S

27

QuadrupoleQuadrupole SIMSSIMS

MEN

A3100 -

SIM

S

28

Magnetic sector Magnetic sector -- mass mass spectrometer spectrometer

sample

detector

ion source

electrostatic sector analyser

magnetic sector analyser

Primary beam

Seco

ndar

y be

amre rm

E0B

Lorenz’ force: BvEF qq

Centripetal force:rr

mv rF2

2

e0 r

mvqE

Electrostaticsector analyser

2

mrmvqvB

Magneticsector analyser

2

0e

m

ErBr

qm

MEN

A3100 -

SIM

S

29

Secondary ion mass spectrometrySecondary ion mass spectrometry

2m

0 e

Brmq E r

sample

detector

ion source

electrostatic sector analyser


Primary beam

Seco

ndar

y be

am

re rm

E0B

0 100 200 300 400 500 6001

10

100

1000

10000

Inte

nsity

(cou

nts/

sec)

Sputter time (sec)

Depth profile

0 20 40 60 80 1001

10

100

1000

10000

Cou

nts/

sec

Mass (AMU)

Mass spectrum

Ion image

20 µm

MEN

A3100 -

SIM

S

30

InstrumentationInstrumentationion sources

sample chamber

electrostatic

sector

analysermagnetic

sector

analyser

detectors

MEN

A3100 -

SIM

S

31

MassMass spectrumspectrum

0 20 40 60 80 1001

10

100

1000

10000

Cou

nts/

sec

Mass (AMU)

Li

OO2

K

Zn

ZnO

ZnO2

Na Cr

Mass

spectrum

of a ZnO-sample

with

traces of Li, Na, K, and Cr.

MEN

A3100 -

SIM

S

32

MassMass InterferenceInterference

11,5 12,0 12,5 13,0 13,5

100

101

102

103

104

105

106

Sec

onda

ry in

tens

ity (c

ps)

Mass (AMU)

Mass

spectrum of graphite

91.6%

8.4%

MEN

A3100 -

SIM

S

33

Mass interferenceMass interference

•

Several ions/ionic molecules have similar mass to charge ratios:

10B -

30Si3+ Monitor 11B

75As - 29Si30Si16O

MEN

A3100 -

SIM

S

34

Energy selectionEnergy selectionelectrostatic sector analyser

Seco

ndar

y be

am

re

E0

2

e0 r

mvqE

Increasing kinetic energy

Energy selection slit

Ejection energy (eV)lo

g (

ion

in

ten

sity

)

75As

29Si30Si16O

0 50 100

MEN

A3100 -

SIM

S

35

MassMass interferenceinterference

•

Several

ions/ionic

molecules

have similar mass

to charge

ratios:

10B -

30Si3+ Monitor 11B

75As - 29Si30Si16O Energy selection

31P - 30Si1H

MEN

A3100 -

SIM

S

36

HighHigh massmass resolutionresolution

30,85 30,90 30,95 31,00 31,05 31,10

100

1000

10000

Inte

nsity

(cou

nts/

sec)

Mass (AMU)


rm

B

2

mrmvqvB

Exit slit

Discriminating

between

31P and 30Si1H:

M(31P) = 30.973761M(30Si1H) =30.98160

30,85 30,90 30,95 31,00 31,05 31,10

100

1000

10000

Inte

nsity

(cou

nts/

sec)

Mass (AMU)

31P

30Si1H

MEN

A3100 -

SIM

S

37

Mass interferenceMass interference

•

Several ions/ionic molecules have similar mass to charge ratios:

10B -

30Si3+ Monitor 11B

75As - 29Si30Si16O Energy selection

31P - 30Si1H High mass resolution

MEN

A3100 -

SIM

S

38

SIMS SIMS –– depth profilingdepth profiling

0 100 200 300 400 500 6001

10

100

1000

10000

Inte

nsity

(cou

nts/

sec)

Sputter time (sec)

Primary beam

MEN

A3100 -

SIM

S

39

0 100 200 300 400 500 600 700

1

10

100

Inte

nsity

(cou

nts/

sec)

Sputter time (sec)

CalibrationCalibration of of depthdepth profilesprofiles

”Raw”

phosphorus

profile

0 100 200 300 400 500

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

Dep

th (µ

m)

Width (µm)

Depth calibration

Sputter time: 700 sec Depth: 9310 Å

Erosion rate:13,3 Å/sec

MEN

A3100 -

SIM

S

40

0 100 200 300 400 500 600 700

1

10

100

Inte

nsity

(cou

nts/

sec)

Sputter time (sec)

CalibrationCalibration of of depthdepth profilesprofiles

TCYII ttPt

”Raw”

phosphorus

profile

t1 CS

S: Sensitivity

factor

0 100 200 300 400 500 6000,1

1

10

100

1000

10000

Inte

nsity

(cou

nts/

sec)

Sputter time (sec)

Concentration calibration

Ion implanted sample:P dose 1e15 P/cm2

sensitivity factor:Relate the intensity to atomic concentration

xxIS

d Dose

Sensitivity factor:1 count/sec = 3,41015

P/cm3

MEN

A3100 -

SIM

S

41

Calibration of depth profilesCalibration of depth profiles

0,0 0,2 0,4 0,6 0,81E14

1E15

1E16

1E17

1E18

P co

ncen

tratio

n (c

m-3)

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

1

10

100

Inte

nsity

(cou

nts/

sec)

Sputter time (sec)

”Raw”

phosphorus profile

Calibratedphosphorus profile

Erosion rate:13,3 Å/sec

Sensitivity factor:1 count/sec = 3,41015

P/cm3

MEN

A3100 -

SIM

S

42

Ion imagingIon imaging

Distribution of given atoms at the surface

Primary

beam

Secondary beam to detector

Intensity recorded as a function of primary beam position

Sample Surface

MEN

A3100 -

SIM

S

43

Ion Ion imagingimaging

Documents

Secondary ion mass spectrometry · Sputter time (sec) Depth profile. 020 40 60 80 100 1 10 100 1000 10000. Counts/sec Mass (AMU) Mass spectrum. Ion image. 20 µm. MENA3100 - SIMS