A novel photo-acid generator bound molecular glass resist with a single protecting group

Article abstract of DOI:10.1002/pola.26575

A novel photo-acid generator (PAG) bound molecular glass photoresist with a single protecting group has been developed as a promising resist material for use in microelectronics. This single component molecular resist was prepared in four steps starting from 9,9-bis(4-hydroxyphenyl)fluorene. The single component molecular resist exhibited good thermal properties, such as a 10% weight loss temperature of 200 °C and a glass transition temperature of 91 °C. This resist showed a good sensitivity of 60 μC/cm² with e-beam exposure (50 keV). On the other hand, the fine pattern with a half-pitch of 50 nm in the presence of 4 wt % quencher, trioctylamine, was obtained using electron-beam (100 keV) lithography. The LER value was 8.2 nm (3σ, 60 nm half-pitch patterns). 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 A novel photo-acid generator (PAG) bound molecular glass photoresist with a single protecting group has been developed as a promising resist material for use in microelectronics. Copyright

Full text of DOI:10.1002/pola.26575

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A Novel Photo-Acid Generator Bound Molecular Glass Resist with
a Single Protecting Group
Tatsuaki Kasai, Tomoya Higashihara, Mitsuru Ueda
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology,
Meguro-Ku, Tokyo 152-8552, Japan
Correspondence to: M. Ueda (E-mail: ueda.m.ad@m.titech.ac.jp)
Received 13 December 2012; accepted 12 January 2013; published online 7 February 2013
DOI: 10.1002/pola.26575
ABSTRACT: A novel photo-acid generator (PAG) bound molecu-
lar glass photoresist with a single protecting group has been
developed as a promising resist material for use in microelec-
tronics. This single component molecular resist was prepared
in four steps starting from 9,9-bis(4-hydroxyphenyl)fluorene.
The single component molecular resist exhibited good thermal
properties, such as a 10% weight loss temperature of 200 ꢀC
and a glass transition temperature of 91 ꢀC. This resist showed
a good sensitivity of 60 lC/cm2 with e-beam exposure (50 keV).
On the other hand, the fine pattern with a half-pitch of 50 nm
in the presence of wt quencher, trioctylamine, was
4
%
obtained using electron-beam (100 keV) lithography. The LER
C
V
value was 8.2 nm (3r, 60 nm half-pitch patterns). 2013 Wiley
Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51,
1956–1962
KEYWORDS: electron beam irradiation; molecular glass resist;
lithography; photoresist; photo-acid generator
INTRODUCTION Chemically amplified resists (CARs)1 have
contributed to the continuous evolution of electronic device
performance. The density of the patterning has been contin-
ued to rapidly increase according to Moore’s Law. In general,
it is necessary for modern CARs to improve their resolution,
sensitivity, and Line-Edge-Roughness (LER). Particularly, the
LER must be improved because a high LER leads to a
decrease in the electronic device performance. The target
LER value is less than 1.5 nm (3r) according to the ITRS
roadmap 2011 for the next generation of CARs.2 However,
there is a trade-off relationship among the resolution, sensi-
tivity and LER of CARs, which has been the barrier of meet-
ing the requirement of a low LER.3
the lithographic performance, and the molecular glass resists
with a single acid-labile protecting group showed a high
resolution of 25 nm and low LER of 3.6 nm (at 100 nm
half-pitch) by electron-beam (e-beam) exposure. These litho-
graphic performances were better than that of the conven-
tional poly(4-hydroxy styrene)-based photoresists.5,6
Another approach to improve the LER is reducing the num-
ber of photoresist components. For the CAR, it is necessary
to blend the resist resin, photo-acid generator (PAG) and
cross-linker in some cases; however, aggregation sometimes
occurred due to the immiscibility of each component. This
aggregation negatively affects the LER, therefore, the reduc-
tion of the number of resist components is an effective way
to improve the LER.7,8 In particular, the incorporation of PAG
moieties into the resists can not only avoid the negative
effects of aggregation, but also reduces the photo-generated
acid diffusion length due to large anionic species. A low
acid-diffusion length leads to an improved resolution and
LER due to the increased image contrast. Therefore, an ionic
photo-generated acid with large-sized anion moieties,9 PAG-
bound polymer photoresists,10 and PAG-bound molecular
glass resists11 were evaluated. Especially, Lawson et al.
reported that the ionic single molecular resist based on a tri-
arylsulfonium PAG showed 55 nm lines and 105 nm spaces
that were nominally patterned at 80 nm 1:1 lines/spaces
using electron beam (e-beam) lithography. The LER was
found to be 3.9 nm.12 This resist suffered from a significant
Molecular glass resists are known as one of the ways to
reduce the LER.4 They have several advantages compared
with conventional polymer photoresists, such as their mono-
dispersity and small molecular size. A high resolution and
low LER are expected by using the molecular glass resist
because these advantages reduce defects at the boundary
area between the exposed and unexposed areas. Further-
more, the chemical structures of the molecular glass resists
can be precisely designed; therefore, their chemical proper-
ties can be faithfully modified. For example, Shiono et al.
controlled the number of protecting groups in the molecular
glass resists in order to control the distribution of solubility
of the molecular glass resists to an alkaline developer. They
revealed that a precise solubility control significantly affects
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form (CDCl3) or dimethylsulfoxide (DMSO-d6) on a JEOL
JNM-AL400 spectrometer. Fourier-transferred (FT-IR) spectra
were recorded on Horiba FT-720. Thermal analysis was
performed on a Seiko EXSTAR 6000 TG/DTA 6300 thermal
analyzer at a heating rate of 10 ꢀC/min for thermogravime-
try (TG) and a Seiko EXSTAR 6000 DSCꢀ6200 connectꢀed to a
cooling system at a heating rate of 10 C/min or 20 C/min
for differential scanning calorimetry (DSC). The film thick-
ness was measured by Veeco Instrument Dektak3 surface
profiler.
Synthesis of 9-(4-Hydroxyphenyl)-9-(4-(2-methyl-2-
adamantyloxycarbonylmethyloxy)phenyl)fluorene (1)
To a solution of 9,9-bis(4-hydroxyphenyl)fluorene (13.0 g,
37.2 mmol) and 2-methyl-2-adamantyl bromoacetate (5.34 g,
18.6 mmol) in anhydrous acetonitrile (160 mL), potassium
carbonate (20.5 g, 149 mmol) and 18-crown-6 (0.39 g, 1.49
mmol) were added and the solution was stirred overnight at
60 ꢀC. Then, the reaction solution was added to water and
neutralized by citric acid. The solution was extracted with
ethyl acetate, and then the organic layer was separated,
washed with water three times, and dried over MgSO4. The
solvent was removed under reduced pressure to afford a
white solid. The solid was then purified by silica gel column
chromatography (eluent: ethyl acetate: hexane ¼ 1:3, Rf ¼
FIGURE 1 Chemical structure of the single component molecu-
lar resist 4.
dark loss due to the intrinsic solubility of the ionic com-
pounds in water, which limits the positive tone imaging.
Although it has several problems regarding its solubility,
glass transition temperature, and sensitivity, this single-com-
ponent molecular resist provided all the basic requirements
to serve as functional chemically amplified resists, which
prompted us to develop another single-component molecular
resist.
ꢀ
0.40) and dried at 60 C in vacuo to give 1 as a white solid
(5.08 g, yield:49%).
1H NMR (300 MHz, DMSO-d6, ppm, TMS); 9.21 (s, 1H, –OH),
7.9–6.6 (16H, ArH), 4.65 (s, 2H, –OCH2C(¼O)O–), 2.2–1.2
(17H, adamantyl group). 13C NMR (75 MHz, DMSO-d6, ppm,
TMS); 167.70, 156.38, 156.11, 151.36, 139.39, 138.51,
135.74, 128.70, 128.64, 127.77, 127.44, 125.92, 120.45,
115.01, 114.14, 87.81, 64.74, 63.63, 37.52, 35.71, 33.84,
32.19, 26.00, 22.06. IR (KBr, cmꢁ1); 1727 (–C(¼O)O–). Anal.
Calcd. for C38H36O4: C, 81.99; H, 6.52; found: C, 81.39; H,
6.56.
In this study, we designed a novel PAG bound molecular
glass resist (single component molecular resist 4, Fig. 1).
The features of the single component resist 4 are as follows:
(i) single component resist 4 has just one acid-labile methyl-
adamanthyl ester group as a protecting group, therefore, the
distribution of the dissolution rate in the alkaline developer
will be suppressed. (ii) As an anionic moiety of the PAG is
incorporated into the resist core, it is expected to make the
diffusion length shorter. (iii) The problem of the low glass
transition temperature (Tg) of the molecular resists will be
resolved by increasing the molecular weight of the molecular
resists. These well-controlled solubilities and acid diffusion
lengths would lead to an improve the lithographic
performance.
Synthesis of 9-(4-Hydroxycarbonylmethoxyphenyl)-9-
(4-(2-methyl-2-adamantyloxycarbonylmethyloxy)phenyl)
fluorene (2)
The solution of 1 (3.18 g, 5.71 mmol) in THF (25 mL) was
slowly added to a solution of sodium hydride (1.10 g, 8.65
ꢀ
mmol) in THF (25 mL) at 0 C, and the solution was stirred
for 1 h at room temperature. To this solution, the solution of
bromoacetic acid (ꢀ1.19 g, 8.56 mmol) in THF (25 mL) was
slowly added at 0 C, and then the solution was refluxed for
24 h. After the reaction, water was added to the solution to
quench the residual sodium hydrate, and the reaction mix-
ture was neutralized with citric acid. The solution was
extracted with ethyl acetate, and then the organic layer was
separated, washed with water three times, and dried over
MgSO4. The solvent was removed under reduced pressure to
afford a white solid. The solid was purified by silica gel
column chromatography (eluent: ethyl acetate: hexane ¼ 1:3,
then acetone) and dried at 60 ꢀC in vacuo to give 2 as a
white solid (2.89 g, yield: 82%).
EXPERIMENTAL
Materials
Sodium hydride was used after washing with hexane to
remove oil. Anhydrous tetrahydrofuran (THF), N,N-dimethyl-
formamide (DMF), acetone, and acetonitrile were used in
all cases. Sodium 2,3,5,6-tetrafluoro-4-hydroxybenzenesulfo-
nate13 and 2-methyl-2-adamantyl bromoacetate14 were
synthesized according to the literatures. Other reagents and
solvents were used as received.
Measurements
1H NMR spectra and 13C NMR were recorded in chloroform
(CDCl3) or dimethylsulfoxide (DMSO-d6) on a BRUKER DPX-
300 spectrometer. 19F NMR spectra were recorded in chloro-
1H NMR (300 MHz, DMSO-d6, ppm, TMS); 7.9–6.6 (16H, ArH),
4.65 (s, 2H, –OCH2C(¼O)O–), 4.52 (s, 2H, –OCH2C(¼O)OH),
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2.2–1.2 (17H, adamantyl group). 13C NMR (75 MHz, DMSO-d6,
ppm, TMS); 170.14, 167.40, 156.81, 156.34, 151.06, 139.23,
138.11, 137.46, 128.51, 128.39, 127.59, 127.34, 125.71,
120.26, 114.12, 87.70, 65.46, 64.89, 63.53, 37.35, 35.65,
33.70, 32.12, 26.53, 25.87, 21.94. IR (KBr, cmꢁ1); 1751
(–C(¼O)O–), 1718 (–C(¼O)OH). Anal. Calcd. for C40H38O6: C,
78.15; H. 6.23, found: C, 78.04; H, 6.33.
separated, and washed with 0.1 M citric acid aqueous solu-
tion twice, water three times, and dried over MgSO4. The sol-
vent was removed under reduced pressure to afford a white
solid. The solid was purified by silica gel column chromatog-
raphy (eluent: acetone: chloroform ¼ 6:4, Rf ¼ 0.25) and
ꢀ
dried in vacuo at 60 C to give single component resist 4 as
a white solid (0.334 g, yield: 83%).
Synthesis of Sodium 4-(9-(4-(2-methyl-2-
1H NMR (300 MHz, DMSO-d6, ppm, TMS); 7.9–6.6 (31H, ArH),
5.25 (s, 2H, –OCH2C(¼O)OAr–), 4.65 (s, 2H, –OCH2C(¼O)O–),
2.2–1.2 (17H, adamantyl group). 13C NMR (75 MHz, CDCl3,
ppm, TMS); 167.90, 165.29, 156.86, 156.29, 151.50, 143.92
(J ¼ 253 Hz), 140.57 (J ¼ 252 Hz), 140.01, 140.00, 138.69,
134.66, 134.62, 131.63, 131.37, 129.53, 129.30, 127.86,
127.55, 126.15, 124.68, 120.26, 114.46, 114.34, 89.36, 65.65,
64.75, 64.22, 38.12, 36.27, 34.60, 32.99, 27.29, 26.62, 22.45.
19F NMR (CDCl3, ppm, CCl3F): ꢁ144.8, ꢁ160.3. IR (KBr,
cmꢁ1); 1808 (–C(¼O)OAr–), 1743 (–C(¼O)O–), 1180, 1041 (–
SO3ꢁ). Anal. Calcd. for C64H52F4O9S2ꢂ1.76H2O: C, 67.61; H,
4.92, found: C, 67.49; H, 4.79.
adamantyloxycarbonylmethyloxy)phenyl) fluorene-9-
yl)phenoxyacetyl-2,3,5,6-tetrafluorobenzenesulfonate (3)
A solution of 2 (1.03 g, 1.68 mmol), sodium 4-hydroxy-
2,3,5,6-tetrafluorobenzenesulfonate (0.456 g, 1.68 mmol) and
N,N0-dicyclohexylcarbodiimide (1.05 g, 5.10 mmol) in the
mixture of acetone (34 mL) and DMF (1.7 mL) was stirred
for overnight at 50 ꢀC. The precipitate was then filtrated by
suction through Celite on a sintered glass funnel, and the fil-
trate was removed under reduced pressure to afford a white
solid. The solid was purified by silica gel column chromatog-
raphy (eluent: acetone: chloroform ¼ 6:4, Rf ¼ 0.25) and
dried in vacuo at 60 ꢀC to give 3 as a white solid (0.76 g,
yield: 52%).
Fabrication of the Fine Patterns using High-Pressure-
Mercury-Lamp Exposure
1H NMR (300 MHz, DMSO-d6, ppm, TMS); 7.9–6.6 (16H,
ArH), 5.25 (s, 2H, –OCH2C(¼O)OAr–), 4.65 (s, 2H,
–OCH2C(¼O)O–), 2.2–1.2 (17H, adamantyl group). 13C NMR
(75 MHz, DMSO-d6, ppm, TMS); 169.88, 167.42, 156.42,
156.37, 151.01, 143.08 (J ¼ 251 Hz), 139.26, 138.02, 137.97,
137.72 (J ¼ 251 Hz), 136.05, 128.51, 127.61, 127.38, 125.73,
120.29, 114.14, 87.69, 64.84, 64.49, 63.52, 37.40, 35.64,
33.71, 32.13, 26.55, 25.86, 21.90. 19F NMR (DMSO-d6, ppm,
CCl3F): ꢁ145.9, ꢁ160.1. IR (KBr, cmꢁ1); 1812 (–C(¼O)OAr–),
1751 (–C(¼O)O–), 1180, 1049(–SO3ꢁ). Anal. Calcd. for
The photoresist films with 0.7 lm thickness on a silicon
wafer were prepared from a cyclopentanone solutioꢀn of
single component resist 4. After the pre-bake (PB) (70 C, 3
min), the prepared resist films were exposed using super-
high-pressure mercury lamp (250 W) without any optical
filter for 45 min. The resist film was then post-exposure-
baked (PEB) (70 ꢀC for 2 min) and developed with 2.38 wt
%
tetramethyl ammonium hydroxide (TMAH) aqueous
solution, and obtained fine patterns were observed by field
emission scanning electron microscopy (SEM).
C46H37F4NaO9Sꢂ1.02H2O: C, 62.56; H, 4.46, found: C, 62.60;
Fabrication of the Fine Pattern with
Electron-Beam Exposure
H, 4.50.
Synthesis of Triphenylsulfonium Chloride
Aqueous Solution
The photoresist films with 70 nm thickness on a silicon
wafer were prepared from a cyclopentanone solution of
single component resist 4 and trioctylamine in some cases.
The PB temperature, PB time, PEB temperature, and PEB
time were 80 ꢀC for 90 s, 80 ꢀC for 90 s, respectively. The
obtained resist films were exposed to electron-beam
(100 keV), and developed with 2.38 wt % TMAH aqueous
solution. Obtained fine patterns were observed by SEM.
Chlorotrimethylsilane (30.0 mmol, 2.65 mL) was slowly
added to a solution of diphenyl sulfoxide (2.02 g, 10.0
15
ꢀ
mmol) in dichloromethane at 0 C. After stirring for 1 h at
room temperature, 2 M phenylmagnesium chloride in THF
solution (15 mL) was slowly added to this solution at 0 ꢀC
and the solution was stirred for 1 h at room temperature.
Then, small amount of water was added to this solution to
quench excess amount of phenylmagnesium chloride, and 30
mL of 0.2 N HCl aqueous solution was added to acidify the
solution. After removing organic phase, the remaining aque-
ous solution was washed with ether twice. The triphenylsul-
fonium (TPS) chloride aqueous solution was used without
further purification.
RESULTS AND DISCUSSION
Design of Single Component Resist 4
A new single component resist 4 was designed according to
the basic three concepts described in the introduction.
Furthermore, a rigid and bulky fluorene structure was intro-
duced into the core of the molecular glass resist in order to
increase its glass transition temperature, because molecular
glass resists generally show a low glass temperature and
high crystallinity which lead to a negative effect on the
lithographic performance, such as a high LER and poor film-
forming property. Also, when the resist 4 is used as a single
component resist, the PAG loading in a resist becomes rela-
tively high due to the existence of one PAG group per mole-
cule. As a high PAG loading is effective for a high sensitivity
1H NMR (300 MHz, DMSO-d6, TMS); 7.9–7.7 (ArH).
Synthesis of Triphenylsulfonium 4-(9-(4-(2-methyl-2-
adamantyloxycarbonylmethyloxy)phenyl) fluorene-9-
yl)phenoxyacetyl-2,3,5,6-tetrafluorobenzenesulfonate (4)
A solution of 3 (0.317 g, 0.366 mmol) in dichloromethane
was added to an aqueous solution of TPS chloride, and
stirred for 1 h at room temperature. The organic layer was
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SCHEME 1 Synthesis of the single component resist 4.
and low LER,16 it is expected that single component resist 4
shows a better lithographic performance. Furthermore, single
component resist 4 can avoid such a negative effect of aggre-
gation of each resist component due to the incorporation of
the PAG group into the photoresist. For the conventional
resists, positive-type resists are generally a mixture of resist
polymers, PAG etc., however, it have been reported that the
aggregation of each resist component leads to a poor litho-
graphic performance.7
For the synthesis of 1, the feed ratio of 9,9-bis(4-hydroxy-
phenyl)fluorene to 2-methyl-2-adamantyl bromoacetate was
fixed at 2:1 in order to suppress the formation of the deriva-
tives with two protecting groups, and compound 1 was
obtained in the good yield of 49%. Next, the nucleophilic
substitution reaction between 1 and a-bromoacetic acid was
conducted, producing compound 2 in an excellent yield. The
1H-NMR spectrum of 2 showed characteristic signals at 4.65
ppm and 4.52 ppm, which correspond to the a-methylene of
methyladamantyl ester and acetic acid, respectively, and sig-
nals of the methyladamantyl group were observed at 1.2 to
2.0 ppm. The FT-IR spectrum of 2 exhibited characteristic
absorptions of the C¼O of carboxylic acid at 1718 cmꢁ1 and
the C¼O of the methyladamantyl ester at 1751 cmꢁ1. Com-
pound 3 was then prepared from 2 and sodium 2,3,5,6-
Synthesis of Single Component Resist 4
The single component resist 4 was prepared in four steps
according to Scheme 1. The chemical structure of each com-
1
pound was determined by H, 13C, 19F-NMR, IR, and elemen-
tal analyses.
FIGURE 2 1H-NMR spectrum of the single component resist 4 in DMSO.
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FIGURE 3 TGA and DSC curves of the single component resist 4.
tetrafluoro-4-hydroxybenzenesulfonate using N,N0-dicyclohex-
ylcarbodiimide as a condensation agent. In the H-NMR spec-
line developer was investigated. The solution of the single
component resist 4 (15 wt %) in cyclopentanone was spin-
coated on a Si wafer. PB was then conducted at 70 ꢀC for 3
min. Next, the resist films were exposed to a high pressure
mercury lamp without any optical filters for 45 min due to
the very weak absorption of the compound 4 underꢀthis ex-
posure. Subsequently, the PEB was performed at 70 C for 2
min, and the films were dipped in a 2.38 wt % TMAH alka-
line developer for 1 min. The fine patterns of the single com-
ponent resist 4 were observed as shown in Figure 4. These
results indicated that the catalytic deprotection reaction pro-
ceeded using the photo-generated acids, and the single com-
ponent resist 4 became soluble in the alkaline developer by
exposure to a high pressure mercury lamp and subsequent
PEB treatment. Therefore, the single component resist 4
resist has the ability to fabricate fine patterns by exposure
to certain wavelength light.
1
trum of 3, the signal of the a-methylene of acetic acid was
shifted from 4.52 ppm to 5.25, and the FT-IR spectrum of 3
also showed the characteristic ester absorption at 1812
cmꢁ1. The spectral evidence clearly supported the formation
of the expected ester bond. Finally, the single component
resist 4 was prepared by the salt exchange reaction of 3
with TPS-chloride at room temperature. The 1H-NMR spec-
trum of the single component resist 4 is shown in Figure 2.
The characteristic signals of the TPS group are observed
around 7.7 to 7.9 ppm, and the conversion of the salt
exchange reaction calculated from the integration ratio of the
TPS groups to the a-methylene of the ester groups was
quantitative. The single component resist 4 was soluble in
the common organic solvents, such as dichloromethane, chlo-
roform, acetone, cyclopentanone, and dimethyl sulfoxide,
probably due to the introduction of the bulky fluorene unit
which contributes to weakening the molecular interaction.
Furthermore, the elemental analyses also supported the
formation of each compound.
Characteristic Photosensitive Curve of the Single
Component Resist 4 for e-Beam Exposure
Based on the UV lithography, the sensitivity of the single
component resist 4 for e-beam exposureꢀ(50 keV) was meas-
ured using a 70-nm thick film, PB at 80 C for 2 min, PEB at
Evaluation of Chemical Properties and Lithographic
Performance
ꢀ
80 C for 90 s, and developed in a 2.38 wt % TMAH aqueous
solution for 30 s at 25 ꢀC. The photosensitive curve of the
single component resist 4 is shown in Figure 5. This single
component resist 4 has a good sensitivity of 60 lC/cm2 and
contrast of 1.7 with e-beam exposure.
Thermal Properties of Single Component Resist 4
The thermal properties of the single component resist 4
were measured by TGA and DSC at the heating ratio of
10 ꢀC/min and 20 ꢀC/min, respectively (Fig. 3). The single
component resist 4 possessed a relatively high thermal sta-
ꢀ
ꢀ
bility over 192 C (Td5%) and the weight loss around 200 C
corresponded to the weight ratio of the adamantyl group to
the single component resist 4, which indicated that the
decomposition of the adamantyl ester group occurs around
200 ꢀC. The single component resist 4 showed the glass
transition at 91 ꢀC, which is higher than that of previously
reported PAG-bound molecular glass resists.12 Therefore, the
following evaluation of the lithographic performance for the
single component resistꢀ4 was decided to be done at a tem-
perature lower than 91 C.
Pattern Formation with High Pressure Mercury
Lamp Exposure
At first, whether or not the single component resist 4 after
UV exposure and PEB treatment became soluble in an alka-
FIGURE 4 SEM image of positive patterns by high pressure
mercury lamp exposure.
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Pattern Formation with Electron-Beam Exposure
The pattern formation by e-beam lithography was carried
out by 100 keV electron-beam exposure. The lithographic
condition was as follows: a 2 wt % solution of the single
component resist 4 in cyclopentanone was spin-coated on
ꢀ
the silicon wafer, prebaked at 80 C for 90 s on the hot plate,
exposed to the e-beam, PEB at 80 ꢀC for ꢀ90 s, then devel-
oped with 2.38 wt % TMAH for 60 s at 25 C. The film thick-
ness before and after the development were 70 nm and 50
nm, respectively. The lithographic performance of the single
component resist 4 without a base quencher is shown in
Figure 6. The resolution limit of this resist is around 80 nm,
and smaller patterns suffer from no pattern formation (less
than 40 nm line) due to the high acid diffusion length and
FIGURE 5 Characteristic photosensitive curve of the single
component resist 4 by 50 keV e-beam exposure.
FIGURE 6 SEM images of the positive patterns by e-beam exposure.
FIGURE 7 SEM images of positive patterns by e-beam exposure with a 4 wt % quencher.
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ACKNOWLEDGMENTS
severe pattern collapse (50 nm line) because the high hydro-
philicity of the single component resist 4 results in strong
capillary forces during development and drying.
The authors thank Dr. Kenichi Okuyama (Dai Nippon Printings
Co. Ltd.) and people in Nano-Processing Facility supported by
IBEC Innovation Platform (AIST.) for evaluation of resists with
electron-beam exposure and SEM observation.
Figure 7 shows SEM images of the positive patterns by
e-beam exposure for the dose of 500 lC/cm2 with a 4 wt %
quencher, trioctylamine. In this evaluation, the addition of a
base results in the reduced diffusion of the photo-generated
acid and better patterns are obtained. The fine pattern with
a half-pitch of 50 nm is formed and the blurred patterns are
observed in the patterns with a half-pitch of less than 40
nm. Serious bridging randomly appeared between the
resolved resist lines that limited the resist resolution to an
approximate 50 nm half-pitch. The bridging problem may be
due to some combination of a lack of compatibility between
the single component resist 4 and the base, trioctylamine,
insufficient image contrast, and pattern collapse by capillary
force during the rinse process because of the hydrophilic sin-
gle component resist 4. The LER value calculated from the
60-nm line-and-space pattern is 8.2 nm, which is still higher
than the target value.
REFERENCES AND NOTES
1 H. Ito, C. G. Wilson, J. M. J. Frechet, In Digest Technical
Papers of 1982 Symposium on VLSI Technology, Institute of
Electrical and Electronics Engineers Inc., USA: 1982.
2 ITRS Roadmap, 2011. Available at: http://www.itrs.net/home.
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3 G. M. Gallatin, Proc. SPIE 2005, 5754, 38–52
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5 D. Shiono, H. Hada, K. Sato, Y. Fukushima, T. Watanabe, H.
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6 D. Shiono, H. Hada, T. Hirayama, J. Onodera, T. Watanabe,
H. Kinoshita, Proc. SPIE 2009, 7273, 727330.
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CONCLUSIONS
A new single component molecular glass resist 4, which has
a single acid-labile protecting group and a PAG functional
group within its molecule structure, has been developed. The
single component resist 4 has a relatively good thermal
stability and the high glass transition temperature of 91 ꢀC.
This resist showed the good sensitivity of 60 lC/cm2 with e-
beam exposure (50 keV). On the other hand, and the fine
patterns with a half-pitch of 50 nm in the presence of 4 wt
% quencher, trioctylamine, were obtained using e-beam (100
keV) lithography and the LER value was 8.2 nm (3r, 60 nm
half-pitch patterns). Further optimization is required to
obtain a sub-30 nm half-pitch and lower LER. Future work
will focus on the design of a single-component resist mate-
rial with a more reduced hydrophilicity by using a non-ionic
PAG unit and higher Tg to control the acid diffusion length.
8 T. Kasai, T. Higashihara, M. Ueda, J. Photopolym. Sci. Tech-
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9 S. Tarutani, H. Tamaoki, H. Tsubaki, T. Takahashi, J. Photo-
polym. Sci. Technol. 2011 24, 185–191.
10 J. W. Thackeray, Proc. SPIE 2011, 7972, 797204.
11 H. Oizumi, K. Matsunaga, K. Kaneyama, J. J. Santillan, G.
Shiraishi, T. Itani, Proc. SPIE 2011, 7972, 797209.
12 R. Lawson, L. Tolbert, C. Henderson, Proc. SPIE 2009, 7273,
72733C.
13 K. R. Gee, E. A. Archer, H. C. Kang, Tetrahedron Lett. 1999,
40, 1471–1474.
14 M. Echigo, D. Oguro, Proc. SPIE 2009, 7273, 72732Q.
15 Japan Kokai Patent P,200,874,10A, January 17, 2008.
16 C. Higgins, A. Antohe, G. Denbeaux, S. Kruger, J. Georger,
R. Brainard, Proc. SPIE 2009, 7271, 727147.
1962
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