The Physics and Applications of

Block Copolymer Films

StatMech Day IV, WIS --- 23/6/11

The Physics and Applications of

Block Copolymer Films

coworkers: Xingkun Man (TAU) & H. Orland (Saclay)

Experiments: J. Daillant & P. Guenoun (Saclay)

• Introduction: the physics of block copolymers

• Surfaces & Electric Fields: nanostructures, chemical surface patterns & nano-imprint templates, surface-induced orientation, electrically-induced orientation

Polymer Self-assembly on Surfaces: Future Nano-Lithography

Yang et al ‘10

100 nm

cylinders on dot-patterned

surfaces

directed patterns to replace photomasks?

What are Block Co-Polymers?

• Repulsive Interaction: polystyrene-polyisoprene

– Phase separation: PS/PI

• Competition: chemical link & entropy

– Self-Assembly

Micro-phase separation (nano-scale)

PSPI

Applications:

Nano-Structures; Bottom-up Functional Composites

Why periodic structures ?

00 2 / qinterfacial

tension

10 - 100 nm

ABBA

BA

A

B

100 nm

1/3 2/3

0 ~ ( )AB N

AB

TEM: lamellae

Tri-Blocks: other phases

many complex morphologies

bi-continuous

Thomas Zheng & Wang ‘95

Knitting pattern

A – B – C

Stadler

Phase Diagram of di-Blocks

f = NA /N

Khandpur ‘95

N

~ 1

/T

f 1-f

disorder

f fraction of A

Flory parameter

A B

Bulk Free Energy : Ginzburg-Landau expansion

(r) = A - f order parameter

Flory parameter

=2N(c- ) reduced temperature

q0 1.9/Rg dominant mode close to ODT

f10

L CH

ODT

N

C H

Block Co-Polymers:

Coarse-grained Models

2

2 2 2 3 4 3

bulk 02 2 4!3!

h uF q d r

10.49cN

ODT= Order Disorder Temperature

0q q

Leibler ’80

0t

t

End-integrated polymer propagator: , ,q t r du Q t r u

22,

, ,6

q t r aq t r r q t r

t

( )r

( )r r

Self-Consistent Field Theory: The Edwards’ Method

,Q t r u

u

r

Schrödinger-like eq.

t N

Concentration r

Mean-Field

Auxiliary field

X

Z

surface energy of B monomers

surface energy of A monomers

strength of surface interaction

2

surf uF d r

Effect of Surface:

Arbitrary Chemical Patterns

bulk surfF F F

Patterned surfaces:

Total Free Energy

BCP concentration:

AuBu

BAu uu

( , )u x z

( , , )x y z

Minimize the total free energy respecting the boundaries

Y

0 1 2 30

5

10

15

20

25

u

L/l0

LL

||

Orientation Transition of Lamellae

Theory: Masten; Tsori & DA

L

||L

L||L

Para

Perp

AFM: Guenoun & Daillant

u

u

u

surface treatment u vs. thickness L

Parallel to Perpendicular Transition

Perp

• Problem: the Perp phase is not aligned in the plane

• How to align ? Directed Self-Assembly…

Top view

defects 0 2 4 6 8 10

0

2

4

6

8

10

x/l0

y/l 0

Chemical nano-patterned surface

BCP replicatesthe patterns

Char et al; Nealey et al

uniformsurface

0dKim et al ’03

d

Topographic Guiding Patterns

Park et al ‘07

Problem: The wafer has to be modified for each repeated sample

perp 1 para perp 2uu

Nano Imprint Lithography - NIL

Releaseu > 0

Li & Huck; Char et al; Daillant & Guenoun

mold

Directed Perp Phase

0 5 10 15 20 25 30 35 400.0

0.2

0.4

0.6

0.8

1.0

1.2

x/l0

z/l 0

020d

Perfect Perp phaseside view

Man, Orland & DA ’ 10

0d

Top view: SEM

Daillant & Guenoun ’ 10

Produce Perp Phase

0 5 10 15 20 25 30 35 400.0

0.2

0.4

0.6

0.8

1.0

1.2

x/l0

z/l 0

020d

Perfect Perp phaseside view

Man, Orland & DA ’ 10

0d

Zoom in

Daillant & Guenoun ’ 10

SCF calculations

Flat Surfaces NIL

In-plane alignment

In-plane defects

x

z d

hl lLhL

3 The top surface preference 0.02u

20 0 in experiment30 s20l h l hd

1 Gradual temperature quench0 5 10 15 20 25 30 35 40

0.0

0.2

0.4

0.6

0.8

1.0

1.2

x/l0

z/l 0

Three important findings for NIL

perppara

E

Orientation with Electric Field

• Surface interactions prefer para orientation

• Dielectric boundaries prefer to align parallel to E (perp)

Anything in between?

L ~ 10 mm

V ~ 100 V

E ~ 10 V/mm

V

moderate voltages

high fields

B

A

A

A AB BB

L

Confined lamellae

U = -½ C V2

1

4

SC

L

0u

0u

Phase Diagrams

perp mixed para

T

u

L

E

E

Tsori & DA ‘02

a

E – L plane

E – plane

mixed

Mixed MorphologyElectron Microscopy

• PS-PMMA block copolymer

• Annealing in E-field

• Competition: Surface & E-field

40 V/ mm

6 hours 16 hours

Russell + Gido ‘03

0.6 mm

Para

Para

Perp

Conclusions

• Surface patterns, templates & electric fields for Block Copolymers

– self-assembly, nano-patterns and structures: applications to nano-

lithography

• Challenge: defect-free orientation & alignment with minimal

surface treatment

• Challenge: Metastability, traps, film rheology

Electric Field

Orientation of lamellae

Thurn-Albrecht, Russell et al.Nature ‘00

BCP Films :

Templates for Nano-wires

Russell et al, Science ’96

No Applied Field Annealed Under Applied Field

TEM Micrographs of PS-PMMA

electrode

E

electrode

perppara

E

Orientation with Electric Field

• Surface interactions prefer para orientation

• Dielectric boundaries prefer to align parallel to E (perp)

Anything in between?

L ~ 10 mm

V ~ 100 V

E ~ 10 V/mm

V

moderate voltages

high fields

B

A

A

A AB BB

L

Confined lamellae

U = -½ C V2

1

4

SC

L

0u

0u

perp domain

• Sharp interfaces (strong segregation)

• Effect of surfaces has finite range

• Mixed State:

Two parallel layers of width a

Perpendicular domain in the middle: L - 2a

para domain

MIXED MORPHOLOGY

EL

a

L - 2a

Phase Diagrams

E – plane

E – L plane

perp mixed para

T

u

L

E

E

L

E1 30V/µ2/1

1 ~ LE

Tsori & DA ‘02

Conclusions

• Surface patterns & templates for Block Copolymers

– self-assembly, nano-patterns and structures

– Challenge: defect-free orientation & alignment with minimal surface

treatment

– Challenge: Metastability, traps, film rheology

• Nanolithography: - ‘bottom up’ approach

– Device Design & Fabrication? Pattern Quality? Multi-mask?

– There is potential but we are not yet there…

• E-field: Versatile tool in Block Copolymer

– Orientation control of block copolymer films;

– Phase transitions; roles of ionic impurities