Multilayer block copolymer meshes by orthogonal self-assembly

1. Multilayer block copolymer meshes
by orthogonal self-assembly

2. Understanding the Requirement
Driving Force for miniaturization
A constant commercial drive for smaller, faster and more energy efficient electronic
devices for which we need increased component density in integrated circuits, and
hence smaller component sizes.
Moore’s law
Moore’s Law states that the number of transistors per square centimeter roughly
doubles every 18–24 months without increase in cost.
The use of lithography in the semiconductor industry has been vital to the
successful development of integrated circuit technology, and the continual
fulfilment of Moore’s law.
Source: https://en.wikipedia.org/wiki/Moore%27s_law
Since the 1960s, computer chips have
been built using a process called
photolithography.
Source: Adam Nunns, Jessica Gwythe et. al. Inorganic block copolymer lithography. Polymer 54 (2013) 1269-1284
Source: Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature
Communications, 2016; 7:10518

3. Year Size
1971  10 µm
1974  6 µm
1977  3 µm
1982  1.5 µm
1985  1 µm
1989  800 nm
1994  600 nm
1995  350 nm
1997  250 nm
1999  180 nm
2001  130nm
2004  90 nm
2006  65 nm
2008  45 nm
2010  32 nm
2012  22 nm
2014  14 nm
In future
2016-17  10 nm
2017-18  7 nm
2020-21  5 nm
Source: https://en.wikipedia.org/wiki/Moore%27s_law
Size of Transistors

4. Source: https://en.wikipedia.org/wiki/Moore%27s_law
Source: Adam Nunns, Jessica Gwythe et. al. Inorganic block copolymer lithography. Polymer 54 (2013) 1269-1284
Source: Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature
Communications, 2016; 7:10518
Photolithography combined with techniques such as immersion lithography and
double patterning, is used currently to yield transisters.
Need for alternative due to
• Inherent limit of the wavelength of UV light sources
• High costs of photolithography.
Alternative processes to photolithography include-
• Top-down Processes  Other Lithography
techniques.
• Bottom-up processes  Under development as of
now.
Understanding the need for new technique

5. Sources:
• Adam Nunns, Jessica Gwythe et. al. Inorganic block copolymer lithography. Polymer 54 (2013) 1269-1284
• Caroline Ross, Kevin Gotrik, Hong Kyoon Choi et. al. Self-assembling polymer patterns could shrink lithographic limits, SPIE newsroom(2013)
• Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518
• Craig J. Hawker, Thomas P. Russell et. al. Block Copolymer Lithography: Merging “BottomUp” with “TopDown” Processes. MRS Bulletin (2006)
• Compatible with existing technological processes and manufacturing techniques
• Ease of Manufacturing
• Meets both short-term and long-term demands
• Higher-density i.e. smaller feature size
• Faster devices
• Low cost
New strategies to direct the self-assembly of block copolymers could provide an
alternative patterning approach to fabricate very small features below the
resolution limits of traditional optical lithography.
As thin films, immiscible BCPs self-assemble into a range of highly ordered
morphologies where the size scale of the features is only limited by the size of the
polymer chains and are, therefore nanoscopic.
Requirement from techniques
A robust solution to these challenges

6. Sources: self effort: Searches on Scopus, science direct and all
placing read paper across timelineDisclaimer: Data may be inaccurate.
1996-97 • Papers related to Block Copolymers Lithography published
• Were limited to macroscale order
Timeline for development of BCPs approach

7. Sources: self effort: Searches on Scopus, science direct and all
placing read paper across timelineDisclaimer: Data may be inaccurate.
1996-97 • Papers related to Block Copolymers Lithography published
• Were limited to macroscale order
Around 2000 • Papers related to guided self-assembly of block copolymer
• Were limited to monolayers
Timeline for development of BCPs approach

8. Sources: self effort: Searches on Scopus, science direct and all
placing read paper across timelineDisclaimer: Data may be inaccurate.
1996-97 • Papers related to Block Copolymers Lithography published
• Were limited to macroscale order
Around 2000 • Papers related to guided self-assembly of block copolymer
• Were limited to monolayers
Around 2005 • More no. of papers related to Stability and alignment of BCPs as well as
BCP lithography published
• Photolithography techniques limitation started highlighting
Timeline for development of BCPs approach

9. Sources: self effort: Searches on Scopus, science direct and all
placing read paper across timelineDisclaimer: Data may be inaccurate.
1996-97 • Papers related to Block Copolymers Lithography published
• Were limited to macroscale order
Around 2000 • Papers related to guided self-assembly of block copolymer
• Were limited to monolayers
Around 2005 • More no. of papers related to Stability and alignment of BCPs as well as
BCP lithography published
• Photolithography techniques limitation started highlighting
Around 2010 • Papers related to ways of improvement related to stability, alignment,
increasing long range order of BCPs with patterned substrate published
• Approach required both top-down as well as bottoms-up
Timeline for development of BCPs approach

10. Sources: self effort: Searches on Scopus, science direct and all
placing read paper across timelineDisclaimer: Data may be inaccurate.
1996-97 • Papers related to Block Copolymers Lithography published
• Were limited to macroscale order
Around 2000 • Papers related to guided self-assembly of block copolymer
• Were limited to monolayers
Around 2005 • More no. of papers related to Stability and alignment of BCPs as well as
BCP lithography published
• Photolithography techniques limitation started highlighting
Around 2010 • Papers related to ways of improvement related to stability, alignment,
increasing long range order of BCPs with patterned substrate published
• Approach required both top-down as well as bottoms-up
Around 2015 • Papers related to well ordered structure of BCPs, enhancement of
kinetics for self assembly were published
• Still technique required additional approaches to yield final product
Timeline for development of BCPs approach

11. Sources: self effort: Searches on Scopus, science direct and all
placing read paper across timelineDisclaimer: Data may be inaccurate.
1996-97 • Papers related to Block Copolymers Lithography published
• Were limited to macroscale order
Around 2000 • Papers related to guided self-assembly of block copolymer
• Were limited to monolayers
Around 2005 • More no. of papers related to Stability and alignment of BCPs as well as
BCP lithography published
• Photolithography techniques limitation started highlighting
Around 2010 • Papers related to ways of improvement related to stability, alignment,
increasing long range order of BCPs with patterned substrate published
• Approach required both top-down as well as bottoms-up
Around 2015 • Papers related to well ordered structure of BCPs, enhancement of
kinetics for self assembly were published
• Still technique required additional approaches to yield final product
Beginning of
2016
• Paper related to stacking layers of BCPs wires perpendicular to below
layer
• Also doesn’t require any top-down approach
Timeline for development of BCPs approach

12. Block Copolymer (BCP)
These are polymers made of two or more different monomer or block units
covalently bonded together in a variety of different architectures.
Self assembly and Nano/Micro domains
Due to BCPs segmented structures they have a tendency to phase-separate and
order themselves (self assemble) into a range of complex morphologies on the
nanoscale known as Nanodomains.
Sources:
• Image: Courtesy of T.P. Lodge, University of Minnesota.
• Adam Nunns, Jessica Gwythe et. al. Inorganic block copolymer lithography. Polymer 54 (2013) 1269-1284
• Craig J. Hawker, Thomas P. Russell et. al. Block Copolymer Lithography: Merging “BottomUp” with “TopDown” Processes. MRS Bulletin (2006)
• Matsen, M. W. Thin films of block copolymer. J. Chem. Phys. 106, 7781–7791 (1997)
• As the volume fraction of components in the diblock copolymer is varied, it assembles
into morphologies ranging from SL.
• The molecular weight of the block copolymer dictates the size of the domains
spherical (S) cylindrical (C) gyroid (G) lamellar (L) reversed polymer components of the G, C, and S
Diagram of the nanodomain morphologies of diblock copolymers.
Understanding the basics for this approach

13. In BCPs, the constituent polymers are chosen so that they're chemically incompatible
with each other so that they can self-organize.
One of the constituent polymers is carbon-based, the other silicon-based.
Sources:
• Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518
• Massachusetts Institute of Technology. "Self-stacking nanogrids: Polymer nanowires that assemble in perpendicular layers could offer route to
tinier chip components." ScienceDaily. ScienceDaily, 22 January 2016.
Selection of polymers
Idea behind process
To escape the carbon-based polymer, the silicon-based polymers folds forming
cylinders with loops of silicon-based polymer on the inside and the other polymer
bristling on the outside. When the cylinders are exposed to an oxygen plasma, the
carbon-based polymer burns away and the silicon oxidizes, leaving glass-like
cylinders attached to a base.
For second layer of cylinders, the researchers simply repeat the process, but using
copolymers with slightly different chain lengths. The cylinders in the new layer
naturally orient themselves perpendicularly to those in the first.

14. Sources:
• Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518
• Massachusetts Institute of Technology. "Self-stacking nanogrids: Polymer nanowires that assemble in perpendicular layers could offer route to
tinier chip components." ScienceDaily. ScienceDaily, 22 January 2016.
Advantages
• It’s a first technique for stacking layers of BCP wires through which orthogonal
mesh is obtained.
→ Orthogonal meshes A route to tinier chip components by enable
simplified addressability and circuit interconnection in IC manufacturing
and nanotechnology.
• Doesn’t require separate generation of template for primary deposition.
• Thin film of BCP can be used like photoresist, by etching one block away and
using the resulting self-assembled structure as a hard mask for patterning the
underlying substrate.
• The ease of producing "mesh structures" makes this technique a practical
approach for miniaturized device manufacturing.
Understanding the basics for this approach

15. • The geometry of the cylinders in the bottom layer limited the possible
orientations of the cylinders in the upper layer.
→ If the walls of the lower cylinders are too steep to permit the upper cylinders
from fitting in comfortably, the upper cylinders will try to find a different
orientation.
• Chemically treating the surface helps in the formation of parallel rows of cylinder.
→ But if the cylinders in the bottom layer are allowed to form randomly, the
cylinders in the second layer will maintain their relative orientation, creating
their own elaborate, but perpendicular, patterns.
• Chemical Interaction b/w upper and lower layer will determine the type of
stacking.
→ If strong interaction the upper cylinders will try to stack themselves on top of
the lower ones like logs on a pile.
Sources:
• Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518
• Massachusetts Institute of Technology. "Self-stacking nanogrids: Polymer nanowires that assemble in perpendicular layers could offer route to
tinier chip components." ScienceDaily. ScienceDaily, 22 January 2016.
Factors affecting growth

16. • Bottom layer formed orderly
• Both layer have weak
chemical interaction
• Bottom layer formed randomly
• Both layer have weak chemical
interaction
Factors affecting growth

17. Glass-like wires are not directly useful for electronic applications, but it might be
possible to seed them with other types of molecules, which would make them
electronically active, or to use them as a template for depositing other materials
which is electrically active.
Supplement info
Properties -- cylinder geometry and chemical interaction -- can be predicted from
the physics of polymer molecules.
Sources:
• Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518
• Massachusetts Institute of Technology. "Self-stacking nanogrids: Polymer nanowires that assemble in perpendicular layers could offer route to
tinier chip components." ScienceDaily. ScienceDaily, 22 January 2016.
What will we gain by forming Glass like structure?
Future Aspects
• The researchers hope that they can reproduce their results with more functional
polymers.
• The ability to easily produce such "mesh structures" could make self-assembly a
much more practical way to manufacture memory, optical chips, and even future
generations of computer processors.

18. UNDERSTANDING THE APPROACH
Block Copolymer (BCPs)
• Made of two or more monomers or block units covalently bonded together in different
architecture.
• Constituent units are chemically incompatible with each other
• Tendency to phase-separate and order themselves (self assemble) into a range of
complex morphologies on the nanoscale known as Nanodomains
• Volume fraction , morphologies ranges SL.
• Size of domain ∝ Molecular weight
spherical (S) cylindrical (C) gyroid (G) lamellar (L) reversed polymer components of the G, C, and S
Diagram of the nanodomain morphologies of diblock copolymers.

19. UNDERSTANDING THE APPROACH
Factors affecting order-disorder transition
• Volume fraction of components (f)
• Flory-Huggins interaction parameters between two chains (X)
• Polymerization index (N)
XN represents segregation
Sources: 1. Book : Roel Gronheid , Paul Nealey, “Directed self assembly of Block Copolymers for Nano-manufacturing”, 2015
2. G. M. Miyake et al “Synthesis of Isocyanate-Based Brush Block Copolymers and Their Rapid Self-Assembly to Infrared-Reflecting Photonic
Crystals”, J. Am. Chem. Soc. (2012)
The transition takes place without degradation in case of low molecular weight
copolymers. But high molecular weight BCPs, capable of forming large domains
posses extreme polymer chain entanglement. To overcome this , domain size is
enlarged swelling with additives, namely solvent molecules or homopolymers
although these approaches generally require complicated annealing procedures.

20. UNDERSTANDING THE APPROACH
• BCPs self assembly is used in thin films, naopores and nanomesh.
• Nanomesh : Formed by bilayer/multilayer stacks of orthogonal line pattern
• Applications: Photonic materials, Graphene nanomesh devices, optical chips,
computer processors and next-generation integrated-circuit architecture
Cross-sectional SEM image of the bilayer mesh
Source: Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518

21. FABRICATION OF MULTILAYER NANOMESH
Source: Amir Tavakkoli K. G., Samue et.al. Multilayer block copolymer meshes by orthogonal self-assembly. Nature Communications, 2016; 7:10518
Three different in-plane cylindrical-morphology poly(styrene-b-dimethylsiloxane)
(PS-b-PDMS) BCPs were used in the experiments:
• 45.5 kg mol-1 (SD45; fraction of PDMS fPDMS = 32%, period L0 = 43 nm)
• 16 kg mol -1 (SD16; fPDMS = 31%, L0 = 19 nm)
• 10.7 kg mol-1 (SD10; fPDMS = 25%, L0 = 15 nm).
Silicon substrate
(1.5 cm2)

22. IMPORTANT STEPS INVOLVED
• Selection of substrate
BCP film thickness depends on the chemical functionality and topographic pattern
of substrate
• BCP spin coating
• Solvent Annealing
(a) Toluene vapor  SD45
(b) Acetone vapor  SD16, SD10
Annealing time ↑ order ↑
• CF4 Reactive ion Etching
(a) 5sec for SD45
(b) 3 sec for SD16
(c) 2 sec for SD10
• O2 Reactive ion etching
(a) 22 sec for SD45
(b) 14 sec for SD16
(c) 12 sec for SD10
SEM image of a three layer nanomesh pattern in which the
first and third layers of cylinders (SD45 and SD10) are parallel
to each other and orthogonal to the middle layer of cylinders
(SD16). Scale bars, 100 nm

23. PARAMETERS
• Formation of Nanomesh regardless of whether the Si substrate was initially
attractive to PDMS
• Bottom pattern periodicity
• Height of bottom layer pattern
• Chemical interaction between upper and lower layers

24. • Bottom layer formed
orderly
• Both layer have weak
chemical interaction
• Bottom layer formed
randomly
• Both layer have weak
chemical interaction
In order to avoid piling of the cylinders (mesh), it is important that the upper
and lower layers should have weak chemical interaction.
Scale bars, 100nm.

25. SCFT simulation
2D simulation of an A-B BCP between two parallel walls.

26. Simulation - Annealing conditions
According to simulation annealing leads to well arranged
structures (experimentally confirmed).

27. Simulation - Parameters
The volume fraction of block A (fA) was 0.5 and the calculations used a
wN value of 17, where w is the Flory–Huggins interaction parameter
and N is the degree of polymerization.
Regarding the Flory-Huggins interaction parameter:
Here x12 is the Flory-Huggins parameter
SCFT seeks minima in the energy landscape that are physically
realizable.

28. Strong attraction at the walls enforced order parallel to the walls and
created a propagating front that aligns the microdomains, resulting in an
in-plane parallel structure.
On the contrary, for weak interaction, an interconnected network of
microdomains was formed in which microdomains protruded orthogonal
to the surface into the bulk.
Simulation and Modeling

29. Mathematical models for simulation
n A-B BCP of volume V,
with each diblock molecule composed of N
segments.
The A and B blocks consists of fN and (1-f)N
chain segments, respectively.
Flory–Huggins parameter, w, the free energy
of the system F
phi(r) is the volume fraction of species at
position r.
Q[w A ,w B ] is the partition function
q(r, s) is a restricted chain partition function

30. Summary
In summary, it demonstrates as to how nanoscale 3D crosspoint
structures can be synthesized by orthogonal self-assembly of multilayers
of BCPs with different molecular weights.