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Angle Dependent XPS

1

M

SCA LaB6 Scanning Electron Source

Al Anode

5-Axis Sample Stage

• Electrons

• Photoelectrons

• X-rays

Multi

Chan

nel

Detec

tor

Scanning Input Lens

A

EllipsoidalMonochromator

The analysis depth is varied by changing the sample tilt angle

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Angle Dependent XPS

2

q = 90° q = 10°q

q

d = l sin qd = analysis depth l = electron mean free path q = photoelectron take off angle

dd

X-ray BeamX-ray Beam

AnalyzerInput Lens

AnalyzerInput Lens

e - e -

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ADXPS Profile of theNative Oxide on a Si Wafer Surface

3

280285

2902950

2

4

60

500

1000

1500

Binding Energy (eV)c/

s

C 1s

525530

5355400

2

4

60

5

10

15

Binding Energy (eV)

c/s

O 1sx103

95100

1051100

2

4

60

5

10

Binding Energy (eV)

c/s

Si 2pmetal

oxide

x103

Corrected for Take-Off-Angle intensity variation

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 15

10

15

20

25

30

35

40

45

50

55

Sine of the Photoelectron Take-off Angle

Ato

mic

Con

cent

ratio

n (%

)

O 1s

C 1s

Si 2p - metal

Si 2p - oxide

Chemical Composition Atomic Concentration Profile

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ADXPS Profile of theNative Oxide on a Si Wafer Surface

4

929496981001021041061081101120

500

1000

1500

2000

2500

3000

3500

4000

Binding Energy (eV)

c/s

Pos. Chem. State 99.51 Si 2p3 metal100.11 Si 2p1 metal103.36 Si 2p oxide

Si 2p

Curve Fitting Used to Isolate Si Metal and OxideChemical Composition Atomic Concentration Profile

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 15

10

15

20

25

30

35

40

45

50

55

sine [toa]

Ato

mic

Con

cent

ratio

n (%

)

O 1s

C 1s

Si 2p - metal

Si 2p - oxide

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Interpretation of ADXPS ProfilesUsing a Stratification Algorithm

The stratification algorithm requires peak intensity data

from two or more take off angles. The minimum data set

should include a high and low take off angle.

Estimation of layer order– The peak intensity ratios of all peaks are compared between all

the measured take off angles. The number of layers and layer

order is based on the correlation of peak intensity ratios.

Estimation of film thickness and composition– The peak intensities measured at the high take off angle and

the layer order information are used to calculate layer thickness

and composition.

– The algorithm is useful for qualitative sample to sample

comparisons

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Assumptions and Limitations of theStratification Algorithm

Stratification model assumptions– Individual layers are continuous and uniform in thickness

– Individual layers are uniform in composition

– Interfaces are abrupt

Stratification model limitations– Generic electron mean free paths are applied for thickness

calculations• Since the model is not calibrated for the sample being

measured, the absolute layer thicknesses may contain

systematic error

– If the actual sample composition violates any of the

assumptions, this will impact the layer detection process,

composition, and thickness results

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Stratification Algorithm Interpretation of theADXPS Profile of the Native Oxide on a Si Wafer

7

Structure Analysis with automatic layer assignment

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 15

10

15

20

25

30

35

40

45

50

55

sine [toa]

Ato

mic

Con

cent

ratio

n (%

)

O 1s

C 1s

Si 2p - metal

Si 2p - oxide

Chemical Composition Atomic Concentration Profile

Structure Description

-2.5

-2

-1.5

-1

-0.5

0

D

epth

(nm

)

C 1s (100.0 %)

O 1s (67.0 %) Si 2p – oxide (33.0 %)

Si2p – metal (100.0 %) Layer1

Layer2(2.03 nm)

Residue (1.77e-008)

Top Layer(0.19 nm)

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ADXPS Profile of a Self AssembledThiol Monolayer on Au

8

808590950

50

0.5

1

1.5

2

x 105

Binding Energy (eV)

c/s

Au4f

5255305355400

50

2000

4000

6000

Binding Energy (eV)

c/s

O1s

2802852902950

50

5000

10000

Binding Energy (eV)

c/s

C1s

1551601651700

50

500

1000

1500

Binding Energy (eV)

c/s

S2p

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

10

20

30

40

50

60

sine [toa]

Ato

mic

Con

cent

ratio

n (%

)

S 2p

O1s

Au 4f

C 1s (C-C/C-H)

C 1s (C-O)

Chemical Composition Atomic Concentration Profile

Sample in courtesy of Dr. Sophie NoelLaboratoire de Génie Electrique de ParisURA CNRS Universités Paris

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ADXPS Profile of a Self AssembledThiol Monolayer on Au

9

2782802822842862882902922942962981

1.1

1.2

1.3

1.4

1.5

1.6

1.7x 104

Binding Energy (eV)

c/s

Pos. Sep. %Area284.82 0.00 84.38 C-C/C-H286.88 2.06 15.62 C-O

C 1s

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

10

20

30

40

50

60

sine [toa]

Ato

mic

Con

cent

ratio

n (%

)

S 2p

O1s

Au 4f

C 1s (C-C/C-H)

C 1s (C-O)

Chemical Composition Atomic Concentration Profile Peak Fit Routine Separating C 1s Chemical States

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ADXPS Profile of a Self AssembledThiol Monolayer on Au

10

Structure Description

-2.5

-2

-1.5

-1

-0.5

0

Dep

th (

nm)

O 1s (41.3 %)

C 1s C-O (58.7 %)

C 1s C-C/C-H (100.0 %)

S 2p (100.0 %)

Au 4f (100.0 %) Layer1

Layer2(0.11 nm)

Layer3(1.58 nm)

Top Layer(0.31 nm)

Residue (1.18e-010)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

10

20

30

40

50

60

sine [toa]

Ato

mic

Con

cent

ratio

n (%

)

S 2p

O1s

Au 4f

C 1s (C-C/C-H)

C 1s (C-O)

Chemical Composition Atomic Concentration ProfileStructure Analysis with automatic layer assignment

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HfO2 on Si

0.4 0.5 0.6 0.7 0.8 0.9 10

20

40

60

80

100ADXPS Profile

sine [toa]

Ato

mic

Con

cent

ratio

n (%

)

O 1s

C 1s

Hf 4f

Si 2p (oxide)Si 2p (metal)

141822263020°

30°

45°

75°

0

0.5

1

1.5

2

2.5x 104

Binding Energy (eV)

c/s

Hf 4f

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HfO2 on Si

1 2-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0Structure Analysis

Dep

th (

nm)

1.11 nm O 1s 71.2% Hf 4f 28.8%

2.96 nm O 1s 65.2% Si 2p 13.8% Hf 4f 21.0%

Si 2p 100%

This model was created by a stratification analysis tool in MultiPak. Generic attenuation lengths were used.