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Supporting Information
Use of Supramolecular Assemblies as Lithographic Resists
Scott M. Lewis,* Antonio Fernandez, Guy A. DeRose, Matthew S. Hunt, George F. S. Whitehead,
Agnese Lagzda, Hayden R. Alty, Jesus Ferrando-Soria, Sarah Varey, Andreas K. Kostopoulos,
Fredrik Schedin, Christopher A. Muryn, Grigore A. Timco, Axel Scherer, Stephen G. Yeates, and
Richard E. P. Winpenny*
anie_201700224_sm_miscellaneous_information.pdf
1
SUPPORTING INFORMATION:
Experimental
Section
Compounds
1
-
5
were made as described in references 17, 19
21 of the main text. We
describe film fabrication for
1
; the films of
2
5
were spun in the same manner.
Film fabrication.
The fabrication proc
ess is as follows: for films with a thickness of 60 and 30 nm, compound
1
(15 mg) was dissolved in
2
.0
and 5.5 g
of
t
-
butylmethylether
, respectively.
T
he solution
s were
filtered using 0.2 μm PTFE syringe filter
s
. The resist
s
were
then spun onto 10 mm × 10 mm
silicon substrates using a spin cycle of 8000 rpm for 60 seconds, which was followed by a
soft
bake at 100 ̊C for 2 minutes, allowing the cast solvent to evaporate. T
he resist film
s
resulted with thickness
es
of 60 and 30 nm
,
respectively.
The chemical integrity of each film was checked by X
-
ray photoelectron spectroscopy. Data
were collected on a SPECS instrument equipped with a Phiobos 150 analyser and
monochromated
Al
-
K
source
(1486.6 eV). A flood gun was employed to compensate for
charging of the sample. Compositions have been calculated using CASA XPS
TM
sensitivity
correction factors and corrected for with the analyser transmission function.
Table 1 gives the cal
culated elemental and experimental compositions for the molecule with
ratios scaled to chlorine, the least abundant element present. The significant disagreement in
the carbon composition is attributable to “adventitious carbon”
that
is deposited on the s
urface
of the film. This contamination layer is always encountered for samples that have been
exposed to air, and is associated with hydrocarbons present in the atmosphere. This extra
layer of carbon on the surface has increased the percentage of carbon r
elative to the other
elements and consequently decreased the expected composition for all the other elements.
Smooth films were observed by atomic force microscopy (Figure S1).
Table
S
1.
Elemental composition of deposited film as measured by XPS.
Calcu
lated
Composition
for
1
%
Calculate
r
atio’s relative
to Cl
for
1
Experimental
Composition
of film of
1
%
Ratio’s relative
to Cl
of film of
1
Carbon
61.5
51
69.1
74
Oxygen
23.8
20
19.7
21
Fluorine
4.9
4
3.84
4
Chromium
4.3
3.6
3.33
3.5
Nickel
1.8
1.5
1.
41
1.5
Nitrogen
2.4
2
1.74
1.9
2
Chlorine
1.2
1
0.94
1
Fi
gure S1
: Atomic force microscopy of a film of
1
spun onto silicon from a
t
-
butylmethylether
solution and written to give 80 nm deep features. Panel bottom left shows a
track along the top of a fea
ture, path (a) in top left panel, with a surface roughness
less than
4
nm while panel bottom right shows features 80 nm
tall
, path (b)
in top left panel.
3
Experimental Lithography Conditions.
Two patterns were exposed; the first pattern consisted of a 1
-
dimensional matrix
that
had 200
single pixel lines separated by a pitch of 20 nm. The second pattern consisted of a 1
-
dimensional matrix
that had
200 single pixel lines separated by a pitch of 200 nm
;
this pattern
was used for the plasma etch experiments.
Each single pixel line was assigned with an
individual dose from 1 to 20.9 pC cm
-
1
in incremental steps of 0.1 pC cm
-
1
. All resists were
then exposed using a FEI Sirion Scanning Electron Microscope (SEM)
,
which had a
RaithElphy plus 6MHz pattern generator
attached to it. The exposed patterns were written
using an acceleration voltage of 30 keV
and
a probe current of 50 pA
;
the dwell time was 8
μS and the step size was 4 nm. From these exposure parameters, the base dose was calculated
to be 1000 pC cm
-
1
. Each pattern was exposed using a write field of 100 μm. Each material
was developed using a solution of hexane, for
10
s f
ollowed by an N
2
blow dry.
Etch Conditions.
Etching studies used
a Pseudo Bosch process
that used an
inductively coupled plasma (ICP)
of SF
6
and C
4
F
8
gases at 1200 W combined with a reactive ion etching (RIE) power of 20 W
for 90
and 210
seconds.
X
-
ray
Photoelectron Spectroscopy (XPS)
Compound
1
was spun coated on silicon where t
-
butylmethyl ether was the cast solvent and
was exposed to the electron beam at an acceleration voltage of 30KeV.
XPS
studies were
performed in order to understand the chemical a
nd physical processes that occurred when the
material was exposed to the electron beam. Table 1 gives the experimental compositions for
the molecule with ratios scaled to chlorine, the least abundant element present.
Table S2
: Elemental composition of u
nexposed and exposed material as measured by XPS.
C 1s %
O 1s %
F 1s %
Cr 2p %
Ni 2p %
N 1s %
Cl 2p%
Before e
-
beam exposure
69.1
19.7
3.84
3.33
1.41
1.74
0.94
After e
-
beam exposure at 30KeV
65.2
21.8
3.1
4.2
2.3
1.9
1.6
Figure S2a illustrates that th
e electron beam exposure has changed the structure of Carbon 1
s
,
the spectra shows a reduction in intensity at a binding energy of 288.5eV, this is due to the
damage caused by the electron beam. When the incident electrons collide with the pivolates
4
they e
xperience a scission, this results in a reduction in the carboxylate groups present. Thus
making the molecule insoluble to the developer which is Hexane.
The Cr 2p spectra shows significant changes with the peaks showing both broadening and a
shift to lo
wer binding energies. The broadening is indicative of multi oxidation states existing
in the Chromium with the shift to lower binding energies indicating reduction of the Cr
towards Cr 0, which is insoluble in Hexane. Typically, Chromium 2p
3/2
peak positi
ons are Cr
III oxide has a binding energy of ca. 576 eV, Cr IV oxide ca. 580 eV and Cr metal 574.4 eV.
The spectra of O 1
s
showed no change. The
o
xygen is bound to
c
hromium which form small
clusters of both Cr
x
O
y
and is insoluble in Hexane and provides the
mechanism to a very high
resistance to the etching process because the exposed molecule is not reactive in a SF
6
or C
4
F
8
plasma. Hence, the dry etch rate is extremely low.
Figure S2
: a) Photoelectron spectra of C 1s region from written and unwritt
en resist material,
b) Photoelectron spectra of Cr 2p region from written and unwritten resist material, c)
Photoelectron spectra of F 1s region from written and unwritten resist material, d)
Photoelectron spectra of O 1s
region from written and unwritten resist material.
5
Comparative Studies with Other Materials
Compounds
2
5
were deposited using very similar conditions. In Figure S
3
we show images
of these compounds and structures written into the resist using a 30 K
eV SEM as described
above.
Figure
S
3
:
a) 12
nm lines on a 200 nm pitch written in
2
. b)
2
4 nm lines on a 200 nm pitch
written in
3
.
c)
10
nm lines on a 200 nm pitch written in
4
.
d)
8
nm lines on a 200 nm pitch
written in
5
.
A
B
C
D
200nm