Session 8 Non-idealities8/Sessions+8.pdfMicrosoft PowerPoint - Session 8.pptx Author jsun Created Date 10/19/2010 8:02:18 AM

Session 8Non-idealities

U. Utah WVASE at JAW, Oct 2010

Jianing Sun

© 2010 J.A. Woollam Co., All Rights Reserved

Ideal System

Film: uniform and isotropic

INPUT POLARIZATIO

N

ANALYZER

DETECTOR

Interface and surface: sharp and parallel

Specu

lar

reflec

tion

Collimated

monochromatic beam

Substrate: Optically semi-infinite, smooth


What can be non-ideal?

INPUT POLARIZATIO

N

ANALYZER

DETECTOR

Film: non-uniform, anisotropic

Substrate: Backside reflection

Interface and surface: rough

Reduce

d

intensit

y

Angular and

bandwith spread


Typical Non-idealities

Sample related– Backside reflection– Thickness non-uniformity– Grading– Anisotropy– Roughness– Patterned layers

System related– Bandwidth– Angular spread

© 2010 J.A. Woollam Co., All Rights Reserved5

Index Grading

Optical properties can vary through film thickness.Model this behavior by dividing film into ‘slices’where optical constants vary between each.

Wavelength (nm)400 600 800 1000 1200

Ψin

deg

rees

Δin degrees

8

10

12

14

-90

0

90

180

270Model Fit Exp Ψ -E 65°Exp Δ-E 65°

(B)

Ψin

deg

rees Δ

in degrees

8

10

12

14

-90

0

90

180


(A)

Ψin

deg

rees Δ

in degrees

-90

0

90

180


(A)

BK7

TiO2

Ψin

deg

rees Δ

in degrees

-90

0

90

180


(A)

Ψin

deg

rees Δ

in degrees

-90

0

90

180


(A)

BK7

TiO2

BK7

TiO2

BK7

2

BK7

Graded TiO2


Grading in WVASE32™

Position mouse over layer and right-click mouse – this will access new features.

– “Convert to Simple Grade”.

Two Types:– Simple Grading– Function-Based Grading.

(Not covered here).


Simple Grading

Describes index variation between top and bottom of film.

Fit: %variation, total thickness.

Graph shows grading profile.– Choose ‘Wavelength’ for graph.

– Click on graph to update.

Average index comes from reference material.


Simple GradingCoupled material is average index.

Optical Constants

Wavelength (nm)600 800 1000 1200 1400 1600 1800

Inde

x of

refra

ctio

n '

n'

2.15

2.20

2.25

2.30

2.35

2.40

2.45

cauchySimpleGraded topSimpleGraded bottom

Optical Constants

Wavelength (nm)600 800 1000 1200 1400 1600 1800

Inde

x of

refra

ctio

n '

n'

2.20

2.25

2.30

2.35

2.40

2.45

cauchySimpleGraded topSimpleGraded bottom


DEMONSTRATION

Example_5_SiC on Si.datFit with CauchyDoes Roughness and/or Grading improve

model?

9


Function-based GradeUse when model parameter is varying from bottom to top of filmAny “fit” parameter can be graded.– Examples: Oscillator amplitude, Drude resistivity

term

Tauc-Lorentz model for TiO2 Grade oscillator amplitude


Function-based Grade

“Nodes” to describe grading profile

11

Depth Profile of Optical Constants at 500nm

Distance from Substrate in Å-200 0 200 400 600 800

Inde

x of

refra

ctio

n '

n'

Extinction C

oefficient 'k'

1.4

1.6

1.8

2.0

2.2

2.4

2.6

0.00

0.02

0.04

0.06

0.08

0.10

nk

Node 1Interface (0%)

Node 2(61.5%)

Node 3 surface(100%)


Transparent Conductive OxideLow absorption in visibleAbsorption in NIR due to free carriersAbsorption in UV due to electronic transitions

Photon Energy (eV)0.0 1.0 2.0 3.0 4.0 5.0

Imag

(Die

lect

ricC

onst

ant),

ε 2

0.0

0.5

1.0

1.5

2.0

2.5

ITO pbpDrudeGaussianTauc-Lorentz

Drude

Gaussian

Tauc-Lorentz

12

ITO (Indium Tin Oxide)


3-node Function-Based Grading

13

ITO: Function-based Grading on Drude

resistivity vs. depth (Ω-cm) n & k vs. depth

Node 1 Node 2 Node 3


Demo_4_ITO-2_7059.dat– Use Oscillator Model for ITO.– Add Function-based Grading.– Add extra nodes.

(only if MSE improves)

DEMO: Function-Based Grading

14


Extra slides

15


Model Options Dialog Box


Non-uniform ThicknessMeasurement spot can be large enough to see variation in film thickness within the measured area– Discrete thickness actually a “spread” of

thicknesses.

t


Thickness Non-uniformity

How are data affected by measurements over “spread” of thicknesses.

t

Off peak: Data from thicker and thinner film go in opposite directions – average together.

Experimental Data

Wavelength (nm)0 300 600 900 1200 1500 1800

Ψ in

deg

rees

0

20

40

60

80Ideal FilmSame Film, 3% Thickness Non-Uniformity

Ideal DataWith 3% non-uniformityVaried Thickness Data


Thickness Non-uniformity

Near a sharp feature, the data are affected by the thickness variation.

Peak-to-valley shrinks: Data from thicker and thinner film go in same directions – pulls average down.

Experimental Data

Wavelength (nm)0 300 600 900 1200 1500 1800

Ψ in

deg

rees

0

20

40

60

80Ideal FilmSame Film, 3% Thickness Non-Uniformity

Ideal DataWith 3% non-uniformityVaried Thickness Data


Thickness UniformityThe uniformity of a film is more important as the film thickness increases.

Experimental Data

Wavelength (nm)0 300 600 900 1200 1500 1800

%D

epol

ariza

tion

0

20

40

60

80

200nm thick, 3% non-uniform3 microns thick, 3% non-uniform


Example, Thickness Non-Uniformity

“Example_6_organic on silicon.dat”

Adjust Thickness, Cauchy amplitude (An) and Thickness Nonuniformity to match “Psi” and “Depolarization”.

– Use Cauchy and try to fit the data.– Tricks:

• Range-select 1 angle• Global Fit (thickness and An parameter)

Documents

Session 8 Non-idealities8/Sessions+8.pdfMicrosoft PowerPoint - Session 8.pptx Author jsun Created Date 10/19/2010 8:02:18 AM