Dissolution behavior of tetrafluoroethylene-based fluoropolymers for 157-nm resist materials

Article abstract of DOI:10.1016/j.jfluchem.2004.09.012

We have synthesized various main-chain fluorinated polymers and studied base-resin properties, such as transparency at 157 nm, solubility in a standard alkaline developer, and lithographic performance. Main-chain-fluorinated polymers were synthesized by copolymerization of tetrafluoroethylene (TFE) with cyclic monomers, especially newly synthesized norbornene derivatives. We studied the correlation between pK_a(OH) and the solubility of the copolymers of TFE and functional (fluoroalkyl alcohol group) norbornenes. Their solubility depends on the pK_a value of the fluoroalkyl alcohol groups. We studied the impact of the polymerization initiators on base-resin properties. High transparency was obtained by using the fluorocarbon initiator. It was also confirmed that the monocyclic component improves dry-etch resistance and that fluorination at the terminal groups improves alkaline solubility. In addition, we found that the development characteristics of TFE/norbornene copolymers were significantly improved by the stereoselective (endo versus exo) partial protection of the hydroxyl groups in the fluoroalkyl alcohol moiety attached to norbornene unit. The polymer protected only in the exo position of the norbornene unit in the copolymer had a higher R_max and a higher contrast. Positive-working resists based on these fluoropolymers were developed and 55 nm dense lines could be delineated by exposure at 157 nm wavelength with an alternating phase shift mask on a 0.9 NA 157 nm exposure tool. We have synthesized various main-chain fluorinated polymers and studied their transparency, dry-etch durability and solubility.

Full text of DOI:10.1016/j.jfluchem.2004.09.012

Journal of Fluorine Chemistry 125 (2004) 1791–1799
www.elsevier.com/locate/fluor
Dissolution behavior of tetrafluoroethylene-based fluoropolymers
for 157-nm resist materials
a,
a
a
a
*
Takuji Ishikawa , Tesuhiro Kodani , Tomohiro Yoshida , Tsukasa Moriya ,
Tsuneo Yamashitaa, Minoru Toriumia, Takayuki Arakia, Hirokazu Aoyamaa,
Takuya Hagiwarab, Takamitsu Furukawab, Toshiro Itanib, Kiyoshi Fujiib
aDakin Industries Ltd., 1-1 Nishi-Hitotsuya, Settsu, Osaka 566-8585, Japan
bSemiconductor Leading Edge Technologies, Inc. (Selete), 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan
Abstract
We have synthesized various main-chain fluorinated polymers and studied base-resin properties, such as transparency at 157 nm, solubility
in a standard alkaline developer, and lithographic performance. Main-chain-fluorinated polymers were synthesized by copolymerization of
tetrafluoroethylene (TFE) with cyclic monomers, especially newly synthesized norbornene derivatives. We studied the correlation between
pKa(OH) and the solubility of the copolymers of TFE and functional (fluoroalkyl alcohol group) norbornenes. Their solubility depends on the
pKa value of the fluoroalkyl alcohol groups.
We studied the impact of the polymerization initiators on base-resin properties. High transparency was obtained by using the fluorocarbon
initiator. It was also confirmed that the monocyclic component improves dry-etch resistance and that fluorination at the terminal groups
improves alkaline solubility.
In addition, we found that the development characteristics of TFE/norbornene copolymers were significantly improved by the
stereoselective (endo versus exo) partial protection of the hydroxyl groups in the fluoroalkyl alcohol moiety attached to norbornene unit.
The polymer protected only in the exo position of the norbornene unit in the copolymer had a higher Rmax and a higher contrast. Positive-
working resists based on these fluoropolymers were developed and 55 nm dense lines could be delineated by exposure at 157 nm wavelength
with an alternating phase shift mask on a 0.9 NA 157 nm exposure tool.
# 2004 Elsevier B.V. All rights reserved.
Keywords: 157-nm lithography; F2; Resist; Fluoropolymer; Tetrafluoroethylene; Norbornene; Hexafluoroisopropanol; Exo; Polymer reaction; Quartz crystal
microbalance
1. Introduction
difficult to use if the film thickness is greater than 100 nm
[1]. Fluorination of polymers has shown its potential for
achieving high transparency at 157 nm. Fluoropolymers
strongly shift the optical absorption edges to higher energies
or shorter wavelengths. This characteristic is one of the great
advantages of fluoropolymers for 157-nm lithography.
Fluoropolymers for 157-nm resist base resins have been
intensively studied over the past 5 years [2–6]. Two main
types of fluoropolymers for 157-nm photoresist have been
reported: side-chain-fluorinated polymers and main-chain-
fluorinated polymers.
Photolithography using F2 laser sources operating at
157 nm is expected to yield the next generation of devices at
the sub-65-nm node. One of the key elements required for a
successful and timely introduction of 157-nm lithography is
the development of a highly transparent resist system that
can delineate the fine patterns needed with high aspect
ratios. The polymers used in conventional resists show
significantly high absorbance at 157 nm, making them
The main-chain-fluorinated polymers have a high fluorine
content in the main chain. Fluoro-chemical companies have
* Corresponding author. Tel.: +81 6 6349 5331; fax: +81 6 6349 4751.
E-mail address: takuji.ishikawa@daikin.co.jp (T. Ishikawa).
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.09.012

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T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
been quite active in developing fluoropolymers for use in 157-
nm lithography [6–10]. Two types of polymers are widely
known: copolymers of tetrafluoroethylene (TFE)/norbornene
derivatives and cyclic polymers. These resists are highly
transparent; their absorption coefficient is less than 1 mmÀ1
and can approach ca. 0.4 mmÀ1. Fluorination of the polymer
backbone effectively reduces the transparency at 157 nm and
strengthens dry-etching durability. Main-chain-fluorinated
polymers also have the advantage of high transparency at the
wavelength of 157 nm, so they are a practical choice for the
single-layer resist process [5].
Fig. 1. Norbornenes isomers.
2. Results and discussion
2.1. Synthesis of monomer and polymer
The other equally important point is solubility of the
hydrophobic fluoropolymers in aqueous bases due to the
importance of high dissolution rates. One answer is the use
of fluoroalchol moiety, especially hexafluoroisopropanol
(HFA) group, which has an acidity similar to that of phenolic
hydroxyl group. Various new fluoropolymers using HFA
as an acidic unit have been reported for 157-nm lithography
[2–6]. Unfortunately, the dissolution rate of these polymers
is still not high enough.
Our approach to the design of 157 nm fluoropolymers is
to alternate the copolymers of tetrafluoroethylene and HFA-
substituted norbornenes (Fig. 2). Our functional norbor-
nenes differ from those reported by others; the main-chain-
fluorinated polymer composed of our functional norbor-
nenes has stronger hydrophilicity. Alkaline solubility of the
polymer depends on their acidities, which can be changed by
introducing fluorine into the neighborhood of the HFA
group. The hydroxyl group in the side chain offers several
benefits such as better substrate adhesion during the spin-
coating process, wettability, solubility during the develop-
ment process and so on.
We have intensively studied the modification of polymers
of TFE/norbornene as the main-chain-fluorinated polymers
to enhance their dissolution rates [9,10]. In this paper, we
report the synthesis of main-chain-fluorinated base-resins
using the copolymer of TFE and the HFA group containing
norbornene, and the relationship between the dissolution
behavior and the pKa of the HFA group of the norbornene
monomer. The dissolution rate depends on the pKa value of
the HFA group, which enhances by increasing the number of
fluorine substituents in the molecule. Our investigations
show that the dissolution property, transparency and
development characteristics can be effectively enhanced
by changing the end group of the polymer to a fluoroalkyl
group.
The HFA group containing norbornenes were synthesized
by the Diels–Alder reaction of cyclopentadiene and
fluorinated vinyl compounds (Fig. 3). In particular,
norbornene 4 was obtained in 90% yield with an exo-rich
adduct through two-step reaction as shown in Fig. 4. The
ratio of endo/exo isomer was 30/70 after distillation. While
in general, the Diels–Alder reaction of cyclopentadiene with
acrylate derivatives selectively yields an endo-rich adduct, it
was reported that a-fluoro-acrylate derivatives selectively
yields an exo-rich adduct [12].
Furthermore, we found that the development character-
istics of TFE/norbornene copolymers was significantly
improved by the stereoselective (endo versus exo) partial
protection of the hydroxyl groups in the HFA moiety
attached to norbornene unit. For the exo- or endo-selective
synthesis of partially protected polymers, we used two
methods on the basis of the difference of chemical reactivity
of functional group in exo and endo substituent attached to
norbornene unit (Fig. 1) [11]. One is copolymerization of
TFE and the hydroxyl-protected norbornene and the other is
selective introduction of the protective group to exo HFA
moiety in the parent polymer. We describe an endo/exo
effect on their fundamental properties, such as structure,
reactivity and transparency at 157 nm, as well as solubility
in a standard alkaline developer.
The TFE/functional norbornene polymers are easily
synthesized in a solution of TFE and functional norbornene
with radical initiators. The resulting copolymers were found
to have Tg of 125–135 8C and Mw of 2000–10,000.
2.2. Dissolution rate and pKa(OH) of functional
norbornenes
We studied the relationship between the dissolution
behavior of copolymers and pKa of the HFA group of the
norbornene monomer. The dissolution behavior was
measured by a quartz crystal microbalance (QCM) method
[13]. The developer used was 0.26N tetramethylammonium
hydroxide (TMAH) aqueous solution. We also measured the
contact angles of water drops on the copolymers. Table 1
Fig. 2. TFE/functional norbornene copolymer for 157-nm lithography resist.

T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
1793
Table 2
Initiators and experimental results
Initiator Terminal
a
Absorption
Dry-etching
rate relative
to KrF resist
Dissolution
rate (nm/s)
3
size (A ) coefficient (mmÀ1
)
˚
A
B
C
D
E
F
52
135
74
0.42
0.72
0.80
0.93
0.46
0.39
1.7
1.7
1.9
1.7
1.6
2.0
320
9
Fig. 3. Synthesis of functional norbornenes.
480
170
130
860
182
153
52
Table 1
Norbornenes and experimental results
a
Norbornene
pKa
Dissolution
rates (nm/s)
Contact
Polymer
Terminal size was determined by iso-electron density volumes quan-
angle (8)
F cont. (%)
tum-chemically calculated on the typical terminal structure.
1
2
3
4
5
11.5
10.5
10.2
9.0
0
0
75
72
72
77
92
54
53
53
55
60
7
polymers prepared using these initiators. The former group
shows a carbonyl vibration peak in the IR chart, while
the latter does not. The difference in the polymerization
mechanisms can explain this effect as shown in Fig. 7.
Fig. 7(b) shows the conventional reaction mechanism of the
latter initiator group, initiators A, B, E and F. The reaction
produces alkyl radicals after the thermal decomposition and
decarboxylation. Those radicals can initiate the polymer-
ization or terminate the reaction by radical recombination.
The fluoropolymers may have the alkyloxy end-capping
terminal in the case of termination. This mechanism does not
include the formation of a carbonyl group at the terminals. In
the case of the former initiator group, C and D, this
intermediate or the carboxyl radical may contribute to the
mechanism before decarboxylation (see Fig. 7(a)). For
instance, this is true when the initiation fluoropolymer has a
carbonyl end-capping, even though this mechanism is a
competitive reaction with the conventional reaction channel.
This mechanism can well explain the IR experimental
results, which shows the existence of a carbonyl group.
Molecular sizes of end-capping groups are also listed in
Table 2. It shows that the smaller terminals reduce the
absorption coefficients. This is a dilution effect, which
shows up more notably with smaller terminals.
170
40
8.3
shows fluorine content and pKa(OH) of the monomers,
dissolution rates and copolymer water contact angles.
This shows that the dissolution rates of copolymers
increased with the acidity of the –OH groups. The pKa(OH)
of the monomers increased with fluorine concentration
around the –OH groups, so in addition to acidity, water
repellency was also increased. When polymer water
repellency was too high, the polymer had poor dissolution
rate even if it incorporated –OH with high acidity. Thus,
control of the fluorine content is important for obtaining a
highly soluble copolymer.
2.3. Terminal effects of the TFE/functional norbornene
polymers
The synthesized fluoropolymers had almost the same
molecular weight, 5000. The terminal effects of the
polymers can be clearly recognized at low molecular
weight. The effect decreases as the molecular weight of the
polymer increases.
2.3.1. Optical characteristics
2.3.2. Dry-etching durability
Fig. 5 shows the polymerization initiators evaluated:
A–F. Fig. 6 shows the VUV spectra of the fluoropolymers
polymerized by two typical initiators D and F. The
absorption coefficients are summarized in Table 2. The
initiators can be classified into two groups: initiators C and
D, and the other initiators. The former initiator group
produces polymers with larger absorption coefficients at
157 nm, and the latter group polymers with lower absorption
coefficients. We measured the infrared (IR) spectrum of the
The carbonyl group also affects the dry-etch durability.
We measured the dry-etch rate relative to KrF resist under
the contact hole etching condition; the results are
summarized in Table 2. The monocyclic functional group
improves the dry-etch resistance (compare initiator C to
initiator D). The fluoroalkyl terminals of initiator F show
weaker durability. Fluorination might increase the dry-
etching rate because volatile fluorides are generated during
the etch process.
Fig. 4. Synthesis of functional norbornene 4.

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T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
Fig. 6. VUV spectra of the tetrafluoroethylene/functionalized norbornene
polymers obtained using initiators D and F.
depressed by the molecular structure of moderately
hydrophilic norbornene derivatives. The smaller terminals
offer larger dissolution rates. The larger terminals may
decrease the dissolution rate due to their larger hydro-
phobicity.
Note that the fluoroalkyl terminal shows the largest
dissolution rate in Table 2. This is considered to be the result
of the increase in acidity induced by the initiator. Fluorine
attracts the electrons in the neighborhood. This reduces the
electron density at the acidic functional group and facilitates
the dissociation of the proton yielding an acidic functional
group with higher acidity. This fluorination effect was
evaluated theoretically by quantum chemistry. We calcu-
lated the pKa of the model compounds shown in Fig. 9. The
semi-empirical quantum-chemical calculation, PM1, shows
that the pKa of fluoropolymer decreases from 6.0 (a) to 5.0
(b) when the hydrocarbon terminal is replaced by the
fluorocarbon terminal. The increase in acidity by the
fluorination of the polymer terminals is another advantage,
in addition to the higher transparency at 157 nm.
Fig. 5. Molecular structures of the evaluated initiators.
2.3.3. Dissolution characteristics
Unprotected fluoropolymers should show larger dissolu-
tion rates without swelling in the standard developer (a
2.38 wt.% tetramethylammonium hydroxide aqueous solu-
tion). The dissolution rates are summarized in Table 2 and
Fig. 8. All evaluated fluoropolymers dissolved well without
swelling in the standard developer. The swelling was
Fig. 7. Polymerization kinetics of (a) initiators C and D and (b) initiators A, B, E and F.

T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
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Fig. 11. VUV spectra for the protected TFE/functional norbornene poly-
mer: (a) polymer A (partial protection by copolymerization (Method A))
and (b) polymer B (partial protection by polymer reaction (Method B)).
Fig. 8. Dissolution behavior of fluoropolymers polymerized by initiators
A–F.
merizing TFE with a mixture of protected and unprotected
monomer (Method A). The monomer was protected by the
ethoxymethyl group. The partial protection by polymer
reaction was carried out by reacting the unprotected polymer
with ethoxymethyl chloride in the presence of amine
(Method B). Both polymers showed excellent 157-nm
transparency (absorption coefficient of 0.33 and 0.34,
respectively) as shown in Fig. 11.
Fig. 12 shows the 19F NMR spectra of partially protected
polymers. Peaks I (57 ppm) and II (62 ppm) were assigned
to the CF3 of the protected HFA group derived from endo
and exo position, respectively. Peak III (66 ppm) was
identified with CF3 of the unprotected HFA group. There is a
difference in the 19F NMR spectra between methods A and
B. The polymer A (partial protection by copolymerization
(Method A)) exhibited peaks I, II and III because it was
polymerized using the mixture of protected endo and exo
isomers. The polymer B (partial protection by polymer
reaction (Method B)) showed peaks II and III, but peak I
was not observed. Therefore, only the HFA group in the exo
position in the polymer was protected in the polymer
reaction.
Fig. 9. Model compounds to evaluate the pKa change by terminal effects.
2.4. Exo/endo selectivity and reactivity of the protective
group in the polymer
2.4.1. Partial protection: exo/endo selectivity
The HFA group is easily protected by conventional
methods. Protection alters the sensitivity and imaging ability
of the resist materials. Partial protection of the hydroxyl
groups derived from TFE/functional norbornene polymers
was carried out by two methods (Fig. 10): copolymerization
(Method A) or polymer reaction (Method B). The partial
protection by copolymerization was conducted by copoly-
2.4.2. Reactivity of the protective group in the polymer
Next, the partially protected polymers shown in Fig. 12
were deprotected in mild condition (aq. HCl in MeOH for
3 h) to investigate the reactivity of the protective group in the
Fig. 10. Partial protection of hydroxyl groups derived from TFE/functional norbornene polymers.

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T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
Fig. 14. Dissolution behavior of the deprotected TFE/functional norbor-
nene polymer in 0.26N TMAH: (a) deprotection of polymer A and (b)
deprotection of polymer B.
Fig. 12. 19F NMR spectra of the protected TFE/functional norbornene
polymer in aceton-d6: (a) polymer A (partial protection by copolymeriza-
tion) and (b) polymer B (partial protection by polymer reaction).
polymer. Fig. 13 shows the 19F NMR spectra of the resulting
polymers. In deprotection of the polymer A, protective
groups in the exo position changed to hydroxyl groups but in
the endo position remained. On the other hand, all protective
groups changed to hydroxyl groups in the deprotection of
the polymer B. It is considered that the reactivity of
deprotection at the endo position is much lower than that at
the exo position, because the endo position exhibits larger
steric hindrance at the reaction site.
Fig. 15. Dissolution contrast of the TFE/functional norbornene polymer
with TPSTf: (a) polymer A and (b) polymer B.
The dissolution behavior of spin-coated films in 0.26N
TMAH was investigated using QCM to compare the
behavior of two deprotected polymers as shown in Fig. 14.
The polymer B had a higher dissolution rate (291 nm/s versus
233 nm/s), although the deprotection condition and the
molecular weight of the polymers evaluated in Fig. 14 were
almost the same.
to F2 laser. Then, the dissolution behavior of the exposed
films in alkaline developer was investigated using QCM.
The exposure was changed from 0.5 to 100 mJ/cm2. The
dissolution rate of the exposed polymer was measured using
QCM. The polymer B had a higher dissolution rate (Rmax
and a higher contrast.
)
2.4.3. Development characteristic
The development characteristic of a resist based on the
polymers A and B was also investigated (see Fig. 15). A
resist formulation was made by dissolving TFE/functional
norbornene polymer (the polymer A or B) and TPSTf in
2-heptanone. Initially, the spin-coated films were exposed
2.4.4. Lithograph performance
A preliminary formulation was made by dissolving a
platform polymer B and TPSTf in 2-heptanone. The contrast
curve for a resist based on polymer B is shown in Fig. 16.
The onset of de-protection is observed at about 3.7 mJ/cm2.
It did not exhibit any negative-tone behavior up to 100 mJ/
cm2. Fig. 17 shows typical imaging result using an Exitech
Fig. 13. 19F NMR spectra of the deprotected TFE/functional norbornene
polymer in acetone-d6: (a) deprotection of polymer A and (b) deprotection
of polymer B.
Fig. 16. Sensitivity curve of a resist based on polymer B.

T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
1797
in the exo position. Preliminary trials showed that resists
based on our polymer can provide excellent lithographic
performance for dense 55-nm 1:1 line and space patterns in a
150-nm thick film.
4. Experimental
4.1. Materials
All materials were obtained from commercial suppliers
and used without further purification, unless otherwise
noted. Functional norbornene 4 was prepared by the
cycloaddition of cyclopentadiene and a-fluoro-acryl fluoride
as described in the literature [12].
Fig. 17. 157-nm exposure of a resist based on polymer B. Conditions:
150 nm thickness, Exitech Microstepper, NA = 0.90, s = 0.3, alternating
phase-shift mask, PB 110 8C, 90 s, PEB 110 8C, 90 s, DEV 60 s.
mini-stepper (0.90 NA) by using an alternating phase-shift
mask. We achieved 55 nm 1:1 line and space patterns in a
150-nm thick film using the resist formulation based on
polymer B.
4.1.1. Synthesis of 1,1,1,3,3,3-hexafluoro-2-(2-fluoro-
bicyclo[2.2.1]hept-5-en-2-yl)-propan-2-ol (4)
2-Fluoro-bicyclo[2.2.1]hept-5-ene-2-carbonyl fluoride
(126 g, 0.80 mol) was added to a suspension of dry KF
(51 g, 0.88 mol) and dry CsF (12 g, 0.08 mol) in anhydrous
THF (1.0 l) under nitrogen. Trifluoromethyltrimethylsilane
(250 g, 1.76 mol) was slowly added dropwise into the
mixture under nitrogen at 10 8C. The reaction mixture was
stirred at room temperature overnight. After the reaction was
completed, 500 ml of 1.0N HCl was added to the mixture
and extracted with 500 ml of diethyl ether. The combined
ether extracts were washed with 1.0N HCl, water and brine.
The ether solution was dried over MgSO4, evaporated and
distilled at 60 8C at 5 mmHg to yield 198 g (90%) of
functional norbornene (2) as a colorless oil.
3. Conclusion
We synthesized various main-chain fluorinated polymers
by co- or terpolymerization of tetrafluoroethylene (TFE)
with cyclic monomers, with particular emphasis on newly
synthesized norbornene derivatives. We studied the correla-
tion between pKa(OH) and the solubility of the copolymers
of TFE and functional (fluoroalkyl alcohol group) norbor-
nenes. The pKa(OH) of fluoroalkyl alcohol groups was lower
with higher fluorine contents, and the solubility of the
copolymers tended to be higher with lower pKa(OH) of the
fluoroalkyl alcohol groups. We found norbornene derivative
4 which has compatible acidity and water repellence. We
also obtained a TFE/functional norbornene that has high
dissolution rate in the standard developer.
4.1.2. Radical polymerization
The typical polymerization procedure is as follows. A
100-ml stainless steel pressure vessel was charged with a
solution of monomers, solvents, and initiator. The vessel
was closed, purged with nitrogen, cooled, evacuated, and
charged with TFE monomer. Radical copolymerization was
carried out at 40 8C and maintained for 18–24 h. The reac-
tion mixture was poured into hexane, and the precipitates
washed by hexane. The resulting polymer powder was dried
in vacuum.
We investigated the impact of polymerization initiator on
the polymerization of TFE and functionalized norbornene.
The carbonyl group incorporated into the polymer chain
deteriorates the optical transparency at 157 nm and the dry-
etch resistance. Some initiators yield a high transparency of
0.39–0.46 mmÀ1, a reasonable dry-etch resistance of only
1.6–1.7 times larger than that of KrF resists, and larger
dissolution rates. Fluorocarbon initiators in particular
resulted in dissolution rates of up to 800 nm/s in the
standard developer.
4.2. Characterization
The polymer structures and compositions were deter-
1
mined from the NMR spectra. Namely, H and 19F NMR
We demonstrated that the development characteristics of
a TFE/HFA group containing norbornenes could be
improved by increasing the reactivity of the protective
group in the copolymer. We showed that the protective group
was introduced only in the exo position of the norbornene
unit in the copolymer when partial protection was carried out
by the polymer reaction (Method B). The polymer protected
by the polymer reaction (polymer B) had a higher Rmax and a
higher contrast due to the higher reactivity of the HFA group
spectra were obtained at room temperature in acetone-d6 or
CDCl3 using a Brucker AC-300P FT-NMR spectrometer.
The polymer structures were also confirmed by the FT-IR
spectra recorded by a Perkin Elmer 1760X FT-IR spectro-
meter.
UV measurements at 157 nm were performed using a
VUV-VASE spectroscopic ellipsometer (J.A. Woollam Co.,
Inc.). The sample films were cast on a CaF2 plate from
solutions and baked at 110 8C for 60 s prior to measure-

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[2] H. Ito, W.D. Hinsberg, L.F. Rhodes, C. Chang, Proc. SPIE 5039 (2003)
70–79;
ments. Film thickness was measured by using an inter-
ferometer. All absorbance data reported are in the base of 10.
The dissolution behavior (i.e. the dissolution kinetics of
the polymer film) during the development of the film was
studied by a quartz crystal microbalance (QCM, Maxtek
Model TM-400) in a fashion similar to a reported procedure
[14]. The QCM instrumentation in combination with a
compensated phase-locked oscillator circuit can measure the
changes of film mass and motional resistance simulta-
neously during development. The developer used was a
0.262N tetramethylammonium hydroxide (TMAH) aqueous
solution (PD-523) supplied from Japan Synthetic Rubber
Co., Ltd.
H. Ito, H.D. Truong, M. Okazaki, D.C. Miller, N. Fender, G. Breyta,
P.J. Brock, G.M. Wallraff, C.E. Larson, R.D. Allen, Proc. SPIE 4690
(2002) 18–28;
H. Ito, G.M. Wallraff, P. Brock, N. Fender, W.D. Hinsberg, H. Truong,
G. Breyta, D.C. Miller, M.H. Sherwood, R.D. Allen, Proc. SPIE 4345
(2001) 273–284.
[3] V.R. Vohra, X. Liu, K. Douki, C.K. Ober, Proc. SPIE 5039 (2003) 539–
547;
V.R. Vohra, K. Douki, Y. Kwark, X. Liu, C.K. Ober, Y.C. Bae, Proc.
SPIE 4690 (2002) 84–93;
Y.C. Bae, K. Douki, T. Yu, J. Dai, D. Schmaljohann, S.H. Kang,
K.H. Kim, H. Koerner, W. Conley, D. Miller, R. Balasubramania,
S. Holl, C.K. Ober, J. Photopolym. Sci. Technol. 14 (2001) 613–
620;
Water repellency of the polymer was estimated from the
contact angle of a water drop on the sample film. The sample
was dissolved in acetone and cast onto a glass substrate,
and dried at room temperature for over 12 h. A 0.3-ml water
drop was placed on the film and its contact angle was
measured.
D. Schmaljohann, Y.C. Bae, G.L. Weibel, A.H. Hamad, C.K. Ober,
Proc. SPIE 3999 (2000) 330–334.
[4] Y. Uetani, K. Hashimoto, Y. Miya, I. Yoshida, M. Takigawa, R.
Hanawa, Proc. SPIE 4345 (2001) 379.
[5] T. Chiba, R.J. Hung, S. Yamada, B. Trinque, M. Yamachika, C.
Brodsky, K. Patterson, A. Heyden, A. Anthony, S.-H. Jamison, M.
Lin, J. Somervell, W. Byers, C.G. Conley, J. Willson, Photopolym. Sci.
Technol. 13 (2000) 657–664;
R.J. Hung, H.V. Tran, B.C. Trinque, T. Chiba, S. Yamada, D.P.
Sanders, E.F. Connor, R.H. Grubbs, J. Klopp, J.M.J. Frechet, B.H.
Thomas, G.J. Shafer, D.D. DesMarteau, W. Conley, C.G. Willson,
Proc. SPIE 4345 (2001) 385–395;
4.3. Lithography
Polymers were dissolved in casting solvent, to which was
added a photoacid generator (PAG). Triphenylsulfonium
triflate (TPSTf), obtained from Midori Kagaku Co. Ltd.,
which was used in this study as a standard onium PAG. The
resist solution was filtered through a 0.2-mm membrane
filter. Resist-formulation solvents used in this study included
2-heptanone. The resist solution was spin-coated onto
silicon wafers treated with organic antireflective coatings.
Pre-application baking and post-exposure baking were
carried out in the temperature range of 110 8C for 60–
90 s, and the resist was developed. Contrast measurements
were conducted by open-frame exposures. From these
measurements, the clearing dose for the resist was
determined. Cross-sectional scanning electron micrographs
were recorded with a Hitachi S-5000 scanning electron
microscope.
B.C. Trinque, B.P. Osborn, C.R. Chambers, Y. Hsieh, S. Corry, T.
Chiba, R.J. Hung, H.V. Tran, P. Zimmerman, D. Miller, W. Conley,
C.G. Willson, Proc. SPIE 4690 (2002) 58–68;
R.R. Dammel, R. Sakamuri, S. Lee, M.D. Rahman, T. Kudo, A.
Romano, L. Rhodes, J. Lipian, C. Hacker, D.A. Barnes, Proc. SPIE
4690 (2002) 101–111;
L. Sharif, D. DesMarteau, L. Ford, G.J. Shafer, B. Thomas, W. Conley,
P. Zimmerman, D. Miller, G.S. Lee, C.R. Chambers, B.C. Trinque,
T. Chiba, B.P. Osborn, C.G. Willson, Proc. SPIE 5039 (2003)
33–42.
[6] M.K. Crawford, A.E. Feiring, J. Feldman, R.H. French, M. Periya-
samy, F.L. Schadt III., R.J. Smalley, F.C. Zumsteg, R.R. Kunz, V. Rao,
L. Liao, S.M. Holl, Proc. SPIE 3999 (2000) 357–364;
M.K. Crawford, A.E. Feiring, J. Feldman, R.H. French, V.A. Petrov,
F.L. Schadt III., R.J. Smalley, F.C. Zumsteg, Proc. SPIE 4345 (2001)
428–438;
M.K. Crawford, W.B. Farnham, A.E. Feiring, J. Feldman, K.W.
Leffew, V.A. Petrov, W. Qiu, F.L. Schadt III., H.V. Tran, R.C. Whe-
land, F.C. Zumsteg, Proc. SPIE 5039 (2003) 80–92.
[7] T. Yamazaki, T. Furukawa, T. Itani, T. Ishikawa, M. Koh, T. Araki, M.
Toriumi, T. Kodani, H. Aoyama, T. Yamashita, Proc. SPIE 5039
(2003) 103–112;
Acknowledgments
S. Ishikawa, S. Irie, T. Itani, Y. Kawaguchi, O. Yokokoji, S. Komada,
Proc. SPIE 5039 (2003) 580–588;
The authors thank Dr. Yuzo Komatsu and Takuji Kume of
the chemical division for synthesizing the monomers.
M. Toriumi, N. Shida, H. Watanabe, T. Yamazaki, S. Ishikawa, T. Itani,
Proc. SPIE 4690 (2002) 191–199;
N. Shida, H. Watanabe, T. Yamazaki, S. Ishikawa, M. Toriumi, T. Itani,
Proc. SPIE 4690 (2002) 497–503;
M. Toriumi, S. Ishikawa, S. Miyoshi, T. Naito, T. Yamazaki, M.
Watanabe, T. Itani, Proc. SPIE 4345 (2001) 371–378.
[8] Y. Kawaguchi, J. Irisawa, S. Kodama, S. Okada, Y. Takebe, I. Kaneko,
O. Yokokoji, S. Ishikawa, S. Irie, T. Hagiwara, T. Itani, Proc. SPIE
5039 (2003) 43–52;
References
[1] R.R. Kunz, T.M. Bloomstein, D.E. Hardy, R.B. Goodman, D.K.
Downs, J.E. Curtin, Proc. SPIE 3678 (1999) 13–23;
S. Kodama, I. Kaneko, Y. Takebe, S. Okada, Y. Kawaguchi, N.
Shida, S. Ishikawa, M. Toriumi, T. Itani, Proc. SPIE 4690 (2002)
76–83.
T.H. Fedynyshyn, R.R. Kunz, S.O. Doran, R.B. Goodman, M.L. Lind,
J.E. Curtin, Proc. SPIE 3999 (2000) 335–346;
T.H. Fedynyshyn, R.R. Kunz, R.F. Sinta, M. Sworin, W.A. Mowers,
R.B. Goodman, S.P. Doran, Proc. SPIE 4345 (2001) 296–307;
T.H. Fedynyshyn, W.A. Mowers, R.R. Kunz, R.F. Sinta, M. Sworin,
R.B. Goodman, Proc. SPIE 4690 (2002) 29–40.
[9] M. Koh, T. Ishikawa, T. Araki, H. Aoyama, T. Yamashita, T.
Yamazaki, H. Watanabe, M. Toriumi, T. Itani, Proc. SPIE 5039
(2003) 589–599.

T. Ishikawa et al. / Journal of Fluorine Chemistry 125 (2004) 1791–1799
1799
[10] M. Toriumi, M. Koh, T. Ishikawa, T. Kodani, T. Araki, H. Aoyama,
T. Yamashita, T. Yamazaki, T. Furukawa, T. Itani, Proc. SPIE 5039
(2003) 53–60.
[13] H. Ito, N. Seehof, R. Sato, T. Nakayama, M. Ueda, ACS Symp. Ser.
706 (1998) 208–223.
[14] M. Toriumi, T. Ohfuji, M. Endo, H. Morimoto, J. Photopolym. Sci.
Technol. 12 (1999) 545–552;
[11] A.E. Feiring, M.K. Crawford, W.B. Farnham, J. Feldman, R.H.
French, K.W. Leffew, V.A. Petrov, F.L. Schadt III., R.C. Wheland,
F.C. Zumsteg, J. Fluorine Chem. 122 (2003) 11–16, Polymerization of
TFE and norbornenes:.
M. Toriumi, S. Ishikawa, T. Itani, Forefront of Lithographic Materials
Research, Society of Plastic Engineers, Society of Plastic Engineers,
Mid Hudson Section., 2001, pp. 271–281;
[12] M. Essers, C. M-Lichtenfeld, G. Haufe, J. Org. Chem. 67 (2002)
4715–4721;
M. Toriumi, T. Itani, J. Yamashita, T. Sekine, K. Nakatani, Proc. SPIE
4690 (2002) 904–910, and references therein.
H. Ito, A. Saito, A. Kakuuchi, T. Taguchi, Tetrahedron 55 (1999)
12741–12750.