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©2014 J.A. Woollam Co., Inc. www.jawoollam.com 1 Nina Hong 3B: Review U Penn, February 2014

Transcript of 3B: Reviewnanosop/documents/... · 10 15 20 25 Exp E 55° Exp E 57.5° Exp E 60° Exp E 62.5° Exp...

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Nina Hong

3B: Review

U Penn, February 2014

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Review

1A: Introduction to WVASE: Fun Quiz!

1B: Cauchy

2A: Pt-by-Pt and GenOsc

2B: Advanced GenOsc

3A: Non-Idealities

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If the left column shows the Psi and Delta for an

ideal glass substrate, can you identify the

complexity of the right column data?

Q1

Ideal Surface Roughness

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If the left column shows the Psi and Delta for an

ideal glass substrate, can you identify the

complexity of the right column data?

Q2

Ideal Backside Reflection

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If the left column shows the Psi and Delta for a

Si substrate, can you identify the complexity of

the right column data?

Q3

Ideal Backside Reflection

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What is the substrate type of the following

ellipsometric data?

①Transparent substrate (dielectric)② Semi-absorbing substrate (semiconductor)③ Absorbing substrate (Metal)

Q4

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What does ellipsometric measurement probe?

① Size of electric field② Shape of electric field

Q5

X

Y

ELess

Intense

X

Y EMore

IntenseDifferent Size

(Intensity).

Same Shape!

(Polarization)

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Q6Pseudo Optical Constants <n>, <k>Which one is corresponding to a single reflection on surface?

① ②

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Q7Unknown Film on GlassWhich spectral range does the film look transparent?

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Data Analysis Strategies

Substrates

S-1: Opaque Substrates

S-2: Semiconductor substrates

S-3: Transparent substrates

Films

F-1: Transparent films

F-2: Semi-Absorbing films

F-3: Absorbing films

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Psi stays near 45°

Delta away from 0°or 180°

Wavelength (nm)

200 400 600 800 1000 1200

Psi in

de

gre

es

36

38

40

42

44

46

65°75°85°

Wavelength (nm)

200 400 600 800 1000 1200

Delta

in d

egre

es

0

30

60

90

120

150

180

65°75°85°

S-1 Opaque Substrates

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S-1 Opaque Substrates

Two Categories

“Bulk” Samples No overlayers.

– Polished metal.

Optically thick films.

Fit Strategy“Invert” psi and delta for n and k.

Normal fit from reference values

2 Known: Ψ, Δ

2 Unknowns: n, k

Example 1 Optically Thick Cr Film

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Psi follows shape of absorption

Delta away from 0°or 180° when absorbing

Wavelength (nm)

200 400 600 800 1000 1200

Yin

de

gre

es

0

10

20

30

40

50

55°65°75°

Din

de

gre

es

1200

Wavelength (nm)

200 400 600 800 10000

50

100

150

200

55°65°75°

S-2 Semiconductor Substrates

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S-2 Semiconductor Substrates

Bulk semiconductor n&k are well known– Crystalline structure insures repeatable

optical/electrical properties.

Doping NOT important at VIS wavelengths– Doping Is important in the MID-IR, however (5

micron or longer).

Fit Strategy

– Use published index values.

– Fit for oxide thickness.

Example 2 Bare Si Wafer

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Psi flat and smooth- follows shape of index

Delta = 0°,180° - except for surface films

Wavelength (nm)

0 300 600 900 1200 1500 1800

Yin

de

gre

es

0

5

10

15

20

25

30

45°55°65°75°

Wavelength (nm)

0 300 600 900 1200 1500 1800

Din

de

gre

es

0

30

60

90

120

150

180

45°55°65°75°

0.5nm roughness

S-3 Transparent Substrates

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S-3 Transparent Substrates

Fit Strategy– Cauchy

Complexities– Surface roughness (Add srough)

– Backside reflection (Suppress or Model correction)

How to obtain small k-values

– Add Transmission data and fit k only.

Example 3 10mm bk7 (Two dat files: SE and T)Experimental Data

Wavelength (nm)

0 300 600 900 1200 1500 1800

Y in

de

gre

es

0

5

10

15

20

25

Exp E 55°Exp E 57.5°Exp E 60°Exp E 62.5°Exp E 65°Exp E 67.5°Exp E 70°

Experimental Data

Wavelength (nm)

0 300 600 900 1200 1500 1800

D in

de

gre

es

-50

0

50

100

150

200

Exp E 55°Exp E 57.5°Exp E 60°Exp E 62.5°Exp E 65°Exp E 67.5°Exp E 70°

Experimental Data

Wavelength (nm)

200 400 600 800 1000

Tra

nsm

issio

n

0.0

0.2

0.4

0.6

0.8

1.0

Exp pT 0°

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Each reflected wave will have a different

phase and amplitude.

0~n

1~n

2~n

Delay caused

by both index

and thickness

F-1 Transparent Films

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Interference shifts toward red as film grows.

More Interference oscillations as film grows.

Wavelength (nm)

0 300 600 900 1200 1500 1800

Yin

degre

es

0

20

40

60

80

100

25nm50nm

100nm

200nm

300nm

400nm500nm

0nm

75nm

F-1 Thickness Effects

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Index difference affects Interference

oscillations (Mostly Psi amplitude).

Wavelength (nm)

0 300 600 900 1200 1500 1800

Yin

degre

es

0

20

40

60

80

100n=1.5

n=1.75n=2.0

n=2.25

n=2.5

n=2.75

n=3.5

n=3.0

n=3.75

n=3.25

n=4.0

F-1 Effect of Film Index

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Adjust Index to match Psi peak height.

Adjust Thickness to match oscillation period.

Experimental Data

Wavelength (nm)

600 700 800 900 1000 1100

Yin

de

gre

es

0

15

30

45

60

75

90

Exp E 75°

n=1.5

n=2

n=2.5

n=3

Generated and Experimental

Wavelength (nm)

600 700 800 900 1000 1100

Y in d

egre

es

0

5

10

15

20

25

30

Model Fit Exp E 75°

F-1 Using This Information

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1. Adjust An parameter to approximate index.

– Psi amplitude can help estimate.

2. Adjust thickness to match # of oscillations.

3. Fit Thickness, An and Bn.

4. Add Cn. Does it improve the MSE?

5. Normal dispersion???

Normal Fit IF Model is Close to Answer!

RESET if fit fails!!!

F-1 Cauchy Procedure

Example 4 Al2O3 on Si

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If light is absorbed before returning to surface, only top

reflection is ‘seen’ (Film appears as Substrate)

Wavelength (nm)

120 150 180 210 240 270 300

Din

degre

es

-50

0

50

100

150

200

250

300

F-2 Semi-Absorbing Films

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Fit Cauchy to Transparent region

– determine thickness.

Fix thickness and fit “n,k” at all wavelengths

using point-by-point fit.

When in doubt, convert to Genosc to insure

Kramers-Kronig consistency.

Surface roughness, grading, and anisotropy can

be added if they improve MSE.

F-2 Choosing a Model

Example 5 Semi Absorbing Film on Si

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Roughness sensitivity when material is

absorbing or has high index.

Grading and roughness often correlated when

both lower index toward surface.

When grading increases index toward surface,

may also be sensitive to roughness.

F-2 Surface Roughness / Index Grading

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Most metal films are opaque above 50-

100nm thickness.

Absorption at all wavelengths prevents

periodic oscillations from thickness.

Data will appear similar to absorbing

substrates:

– Psi large and never close to zero.

– Delta between 0 and 180.

– Pseudos from different angles the same.

F-3 Absorbing Films

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No new information!

Wavelength (nm)

200 400 600 800 1000 1200

Y in d

egre

es

15

20

25

30

35

40

Exp E 45°Exp E 55°Exp E 65°Exp E 75°

Wavelength (nm)

200 400 600 800 1000 1200

D in d

egre

es

40

60

80

100

120

140

160

180

Exp E 45°Exp E 55°Exp E 65°Exp E 75°

Wavelength (nm)

200 400 600 800 1000 1200<

1>

<

2 >

-5.0

-2.5

0.0

2.5

5.0

0

5

10

15

20

25

30

Exp <1>-E 65°Exp <1>-E 75°Exp <2>-E 65°Exp <2>-E 75°

F-3 Multiple angles

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Challenge:

More unknown

sample properties

than measured

values.

Solution:

Measure additional

information or

reduce number of

unknown properties.

Known Substrate

n(l), k(l) d

Y(l), D(l)

F-3 Modeling?

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Opaque Layer

Transparent Region

Optical Constant Parameterization

Multiple Angles

Interference Enhancement

SE + Intensity

Multiple-Sample

In-Situ

Multiple-Ambient

J. Hilfiker, “Survey of methods to characterize thin absorbing

films with Spectroscopic Ellipsometry” Thin Solid Films 516 (2008) 7979-7989.

F-3 Methods for Absorbing Films

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Preferred Method #1

– Measure n,k from single-layers: use dispersion models.

– Fit thickness only.

– If poor fit, add dispersion parms. for least stable film.

Substrate

Film A

Substrate

Film B

Substrate

Film C

Substrate

Film A

Film B

Film C

Multi-Layer Strategies

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Preferred Method #2

– Measure n,k for each “new” layer with previous layers

fixed: use dispersion models.

– If poor fit, add thickness and then dispersion

parameters for previous layers.

Substrate

Film A

Film B

Film C

Substrate

Film A

Substrate

Film A

Film B

Multi-Layer Strategies

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6 Example 6-poly Si on 100nm TOx on Si

Two Film layers

– Unknown thickness poly Si

– ~100nm Thermal Oxide

Build your own method to fit the

data.

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Thank You & Good Luck!