This document summarizes research on using multilayer mixing and lithography to create diverse patterns in block copolymer thin films. Specifically, it discusses how depositing a second layer of homopolymer shifts the morphology from lamellae to cylinders. It also explains how cross-linking part of a film before multilayer mixing allows placing different morphologies side by side. The goal is to expand the capabilities of lithography by combining it with self-assembly of block copolymers.

1. NNIN REU Convocation August 2015
Diverse Patterns and Geometries in Self-
Assembled Block Copolymer Thin Films
Through Multilayer Mixing
Christopher Phenicie, University of Minnesota—Twin Cities
PI: Mark Stoykovich, University of Colorado Boulder
Mentor: Garrett Chado, University of Colorado Boulder
REU Site: Colorado Nanofabrication Laboratory, University of Colorado Boulder
Block Copolymers
References
Acknowledgements
Lithography Plus Multilayer Mixing
Multilayer Mixing
● BCPs phase separate as a result of
the incompatibility of the domains (χ),
the volume fraction of each of the
domains (f), and the molecular weight
of the BCP (N) [1]
● Multilayer mixing aims to change the morphology
of the BCP by adding more of one polymer
through spin casting
● The BCP is then annealed in solvent vapor to
self-assemble
● This research was supported by the National Science Foundation under Grant No. ECCS-
0335765
● Thanks to my fellow REU students: Nathan Brooks, Molly Enenbach, Yusuke Hayashi,
Andrea Randolph, Michael Valerino, and Philip Zurek
● Thanks to CNL and NCF staff Tomoko Borsa, Alex Denton, Robert Mcgugan, Dakota Smith,
Bart Van Zeghbroeck, and Jan Van Zeghbroeck
● Extra thanks to my mentor Garrett Chado for his constant guidance and support
● By spin casting a second layer of PMMA
homopolymer, the volume fraction of PMMA in
the film increases. This causes a shift from
lamellae to cylinders. Best packing occurs when
fPMMA
=0.77
● Block copolymers (BCPs) are a class of
macromolecule consisting of two
chemically distinct domains covalently
bonded
fPMMA
=0.59fPMMA
=0.56
● We can combine what
we learned from
multilayer mixing with
optical lithography to
achieve diverse patterns
and geometries in close
proximity
● One block cross-links, so
exposed regions are
immune to multilayer
mixing
● This would allow us to
put diverse morphologies
next to each other with
high contrast
Lithography With Block Copolymers
Lamellae
(fPMMA
=0.56) block
copolymer
UV photopattern
part of the chip,
cross-linking the
exposed region
Deposit PMMA
homopolymer
via spin casting
Solvent anneal.
The un-linked
regions undergo
multilayer mixing
to become
cylinders
400 nm L0 = 48 nm L0 = 48 nm L0 = 48 nm
Solvent Anneal Cross-link Sonicate Regenerate
● On right (above): The cylindrical
domain with fPMMA
=0.77 was
created via multilayer mixing of
lamellar BCP with PMMA
homopolymer
● On right (below): Similarly, a
lamellar domain with larger
periodicity was created by mixing
both PMMA and PS homopolymer
[1] Marencic, A. P.; Register, R.A. Annual Review of Chemical and Biomolecular Engineering,
2010, 1, 277-297
[2] Kim, S. O., et al. Nature 2003, 424, 411-414
[3] Stoykovich, M. P., et al., ACS Nano 2007, 1, 168-1754
[4] He, C. et al., Small, 2015 DOI: 10.1002/smll.201403364
[5] He, C. et al., Advanced Functional Materials 2014, 24, 7078-7084
Deposit PMMA
homopolymer via
spin casting
Solvent anneal
fH
=0
fPMMA
=0.61 fPMMA
=0.68 fPMMA
=0.71 fPMMA
=0.73
fH
=0.17 fH
=0.22 fH
=0.33
fH
=0.34 fH
=0.41 fH
=0.47 fH
=0.52
● By adding equal volume
fractions of both PMMA and PS,
we can increase the periodicity
of the lamellae
● We determined experimentally the
phase behavior of the resulting BCP-
homopolymer blends
● With the techniques of cross-
linking and multilayer mixing, it is
possible to expand the limits of
optical lithography. Future work
could focus on the directed
assembly of the block copolymer,
bringing the technology one step
closer to implementation in
industrial use
● The phases of
interest for this
project are
cylinders and
lamellae, shown on
the right
Solvent
Annealing
Thermal
Annealing
Deposit PS
and PMMA
homopolymer
via spin casting
Solvent anneal.
The un-linked
regions undergo
multilayer mixing
to become larger
lamellae
Lamellar
(fPMMA
=0.56)
block copolymer
Deposit PS and
PMMA homopolymer
via spin casting
The new
morphology is
thicker lamellae
● Electron beam lithography
can be used to direct the
assembly of BCPs over
large areas to make device-
oriented geometries,
including lines [2], jogs (a-
c), and T-junctions (d) [3]
● Cross linked BCP is structurally resilient and insoluble in toluene [4]
● Cross-linkable BCP allows us
to use photolithography
techniques to spatially control
BCP self assembly
fPMMA
=0.77
fPMMA
=0.50 fPMMA
=0.60 fPMMA
=0.70 fPMMA
=0.75