A new positive-type photoresist based on mono-substituted hydroquinone calix[8] arene and diazonaphthoquinone

Article abstract of DOI:10.1039/a807718e

Mono-substituted hydroquinone calix[8]arenes 1a and lb were synthesized by the debenzylation of O-substituted p-benzyloxyphenol calix[8]arenes which were prepared by the cyclization of p-benzyloxyphenol and paraformaldehyde in the presence of a base, followed by acylation with acetic anhydride or toluene-p-sulfonyl chloride. The calixarenes provide highly transparent films from their solutions in ethyl lactate (EL). A new positive-type photoresist based on the calix[8]arene lb having toluene-p-sulfonate groups as a base- developable matrix and diazonaphthoquinone-4-sulfonate [DNQ(4)] or -5- sulfonate [DNQ(5)] as a photoreactive dissolution inhibitor has been successfully developed. The difference of dissolution rates for this resist system toward 1.5 wt% aqueous tetramethylammonium hydroxide (TMAH) solution reached 1300-5000 times before and after UV radiation (200 mJ cm^-2). Thus, the photoresists containing 25 wt% of DNQs showed high sensitivities of 30- 37 mJ cm^-2 (D) and contrasts of 2.5-2.8 (γ) when they were exposed to 365 nm light and post-exposure baked (PEB) at 100 °C for 90 s, followed by developing with 1.5 wt% aqueous tetramethylammonium hydroxide (TMAH) solution at room temperature. A fine positive image featuring 1 μm of minimum line and space patterns was also printed on the film which was exposed to 40 mJ cm^-2 by the contact mode.

Full text of DOI:10.1039/a807718e

J O U R N A L O F
A new positive-type photoresist based on mono-substituted
hydroquinone calix[8]arene and diazonaphthoquinone
Tomonari Nakayama and Mitsuru Ueda*
Department of Human Sensing and Functional Sensor Engineering, Graduate School
of Engineering, Yamagata University, Yonezawa, Yamagata 992–8510, Japan.
E-mail: tc012@dipfr.dip.yz.yamagata-u.ac.jp
C H E M I S T R Y
Received 5th October 1998, Accepted 18th December 1998
Mono-substituted hydroquinone calix[8]arenes 1a and 1b were synthesized by the debenzylation of O-substituted
p-benzyloxyphenol calix[8]arenes which were prepared by the cyclization of p-benzyloxyphenol and
paraformaldehyde in the presence of a base, followed by acylation with acetic anhydride or toluene-p-sulfonyl
chloride. The calixarenes provide highly transparent films from their solutions in ethyl lactate (EL). A new positive-
type photoresist based on the calix[8]arene 1b having toluene-p-sulfonate groups as a base-developable matrix and
diazonaphthoquinone-4-sulfonate [DNQ(4)] or -5-sulfonate [DNQ(5)] as a photoreactive dissolution inhibitor has
been successfully developed. The difference of dissolution rates for this resist system toward 1.5 wt% aqueous
tetramethylammonium hydroxide (TMAH) solution reached 1300–5000 times before and after UV radiation
(200 mJ cm−2). Thus, the photoresists containing 25 wt% of DNQs showed high sensitivities of 30–37 mJ cm−2 (D)
and contrasts of 2.5–2.8 (c) when they were exposed to 365 nm light and post-exposure baked (PEB) at 100 °C for
90 s, followed by developing with 1.5 wt% aqueous tetramethylammonium hydroxide (TMAH) solution at room
temperature. A fine positive image featuring 1 mm of minimum line and space patterns was also printed on the film
which was exposed to 40 mJ cm−2 by the contact mode.
Since novolac resin–diazonaphthoquinone (DNQ) photoresist
was first introduced for 16 Kbit DRAM production in 1972,
UV lithography has begun to be developed as a promising
technology for manufacturing DRAMs.1 The initial advan-
tages of the novolac–DNQ resist are the higher resist contrast
and the absence of swelling during development. The character-
istics which have led this resist system to the most successful
photoresist are their high dry-etch resistance and the environ-
mentally favorable aqueous base developer. Therefore
novolac–DNQ resist is still the ‘workhorse’.2
based on p-alkylphenol calix[6]arenes has been reported, but
O-acetylation and an organic developer were required.6
Calix[4]resorcinarenes (C4-RAs), which are readily pre-
pared by the acid-catalyzed condensation of resorcinol and
aldehydes, have a good solubility in high polar organic solvents
such as alcohols and aqueous alkaline bases.7 Because their
optical properties are similar to those of novolac resin, we
successfully introduced C4-RAs to the negative working pho-
toresist including a polyfunctional benzylic alcohol as a cross-
linker and a photo-acid generator.8
Recently Shirota et al. reported guidelines for molecular
design of low-molecular weight amorphous materials (called
‘amorphous molecular materials’),9 that is, increasing the
number of conformers by lowering the symmetry of non-
planar molecules. We are interested in the concept of amorph-
ous molecular materials that provide a new matrix in the resist
system in place of polymers. We also have found that O-
substitution of C4-RA with bulky groups gave more favorable
materials which belonged to the amorphous molecules.10
Nevertheless, C4-RAs still have some problems regarding their
characteristics for the DNQ resist.
We have focused on mono-substituted calix[8]arene (1) as
the amorphous molecular material, which consists of the
corresponding mono-substituted hydroquinone moieties and
m,m-methylene bridges.11 The calixarenes 1 were expected to
have suitable dissolution characteristics for the DNQ resist
because the phenolic hydroxy groups of 1 face out of the ring
in the planar model. In this paper, the syntheses and the
characterizations of mono-substituted hydroquinone calix[8]-
arenes 1a and 1b, and lithographic evaluations including
dissolution studies of DNQ resists based on 1 are described.
The growth of the recent resist is supported by the new
photo-imaging concept of ‘dissolution inhibition’ which is
fundamentally different from the classic rubber–bisazide
system.1 The ‘dissolution inhibition’ behavior is based on a
kinetic effect which is indicated as a difference in dissolution
speeds between exposed and unexposed regions, and not in
solubility, while the imaging process for the classic negative
resist depends on the insolubility of the fully exposed region.
The resist performance is influenced by various factors which
are induced by characteristics of novolac resin and DNQ,
therefore the influences have been continuously studied to
develop higher contrast photoresists.3 However, the synthesis
of novolac resin from o-cresol and formaldehyde cannot be
well controlled to give products with constant properties. Even
small changes in the experimental conditions affect the amount
of the different bond types, o,o-, o,o∞-, p,o-, and p,o∞-linkages,
which cause branched structures and changing of molecular
weight and molecular weight distribution.4 On the other hand,
macrocyclic novolac oligomers or ‘calixarenes’ which are pre-
pared by the base catalyzed condensation of p-alkylphenol
and formaldehyde have been found to have definite cyclic
structures consisting of the corresponding phenol moieties and
o,o-methylene bridges.5 Their highly regular structures, further-
more, allow them to be easily isolated by means of well-
controlled preparation conditions and further purification.
However, the formation of intramolecular hydrogen bonds
between hydroxy groups induces high melting points and low
solubility not only in most organic solvents, but also in
aqueous bases.5 The only example of an E-beam photoresist
Experimental
Materials
2,3,4-Tris[2-diazo-1-oxonaphthalen-4-ylsulfonyloxy]benzo-
phenone {diazonaphthoquinone-4-sulfonate [DNQ(4)]} and
2,3,4-tris [ 2-diazo-1-oxonaphthalen-5-ylsulfonyloxy] benzo-
J. Mater. Chem., 1999, 9, 697–702
697

Synthesis of 5,11,17,23,29,35,41,47-octakis(benzyloxy)-
49,50,51,52,53,54,55,56-octakis(p-tolylsulfonyloxy)
calix[8]arene (3b)
OH
OH
HO
A mixture of 2 (2.12 g, 1.25 mmol) and K CO (2.07 g,
2
3
O
R
15 mmol) in 60 ml of THF was refluxed for 1 h and then
toluene-p-sulfonyl chloride was added to the mixture. After
the mixture was refluxed for 12 h, it was filtered through a
filter paper and the filtrate was evaporated. The residue was
dissolved in ethyl acetate and the solution was washed with
10% aqueous Na CO solution and saturated aqueous NaCl
O
O
R
R
R
R
HO
O R
OH
R
O
R
O
O
O
2
3
solution. The organic phase was separated and dried over
MgSO and evaporated after the drying reagent was filtered
4
off. The residue was poured into hexane and a product was
OH
HO
collected as a precipitate. In order to remove remaining
toluene-p-sulfonyl chloride from the product, Soxhlet extrac-
tion was carried out with propan-2-ol. 2.18 g (60%) of 3b was
obtained as a yellow powder. IR (KBr) n 3000–3700 (O–H),
OH
1a: R = Ac
1b: R = p-Ts
1360 and 1170 cm−1 (SLO); 1H NMR (270 MHz, CDCl ) d
mono-substituted hydroquinone
calix[8]arene (1)
3
7.70 (s, ArH, 16H), 7.09 (s, ArH, 40H), 6.99 (s, ArH, 16H),
6.26 (s, ArH, 16H), 4.38 (s, CH , 16H), 3.78 (s, CH , 16H),
2
2
Planar models of mono-substituted hydroquinone calix[8]arene 1.
2.24 (s, CH , 24H); 13C NMR (67.5 MHz, CDCl ) d 156.9,
3
3
145.7, 139.4, 136.4, 135.7, 133.2, 130.0, 128.3, 128.1, 127.8
127.5 and 115.3 (ArC), 69.5 (Ar-CH -O), 31.5 (Ar-CH -Ar),
2
2
21.4 (CH ); Anal. calc. for C
Found: C, 68.94; H, 4.93%.
H
O S : C, 68.83; H, 4.95%.
phenone {diazonaphthoquinone-5-sulfonate [DNQ(5)]} were
kindly donated by Toyo Gosei Kogyo and used without any
purification. Solvents were dried and purified in the usual
manner, and stored under an atmosphere of argon. Most
manipulations were carried out either under dry, oxygen-free
argon or nitrogen or under vacuum with Schlenk-type flasks.
3
168 144 32 8
Debenzylation of 3 with a palladium catalyst (synthesis of
debenzylated compound 1)
A mixture of 3 (1 mmol) and 0.25 g of 10% Pd/C in THF was
stirred at 50 °C under H atmosphere for 17 h. The Pd/C was
filtered off and the filtrate was evaporated. The residue was
dissolved in 50 ml of ethyl acetate and the solution was washed
2
Synthesis of 5,11,17,23,29,35,41,47-octakis(benzyloxy)-
49,50,51,52,53,54,55,56-octahydroxycalix[8]arene 2
with water. Then the organic phase was dried over MgSO
and filtered through a filter paper and the filtrate was concen-
To a hot solution of p-benzyloxyphenol (10.00 g, 0.05 mol) in
60 ml of xylene, which was placed in a 300 ml three-necked
flask equipped with a Dean–Stark trap, a nitrogen inlet, and
a glass cap and heated on an oil bath at 80 °C, was added
potassium tert-butoxide (0.25 g, 0.0011 mol). After the mix-
ture was stirred at 80 °C for 30 min, paraformaldehyde (2.62 g,
0.082 mol) was added to the mixture, and then the solution
turned clear immediately. The oil bath temperature was
increased to 150 °C over 1 h and kept at this temperature until
a precipitate appeared. Then the bath temperature was
increased to 170 °C and the reaction mixture was refluxed,
trapping the produced water, for 12 h. The mixture was cooled
with an ice bath and the precipitate was collected with a glass
filter. The brown powder obtained was added to 200 ml of
hot acetone and then the mixture was stirred for 2–3 h. The
pale yellow powder was collected, washed with acetone, and
dried under reduced pressure at 100 °C. Further purification
with hot acetone selectively gave the pure octamer [Yield:
4
trated. The concentrated solution was poured into hexane and
the precipitated product was collected with a glass filter. A
saturated solution of the product in 20 vol% aqueous methanol
solution was refluxed for 12 h to give a white powder.
Methanol included in the product was removed by co-evapor-
ation with acetone under reduced pressure. Reprecipitation in
hexane was finally carried out to give pure 1 as a white
fine powder.
49,50,51,52,53,54,55,56-Octakis(acetoxy)-5,11,17,23,29,
35,41,47-octahydroxycalix[8]arene 1a. Yield: 95%; IR (film on
NaCl) n 3000–3700 (O–H), 1759 cm−1 (CLO); 1H NMR
(270 MHz, DMSO-d ) d 9.25 (s, OH, 8H), 6.39 (s, ArH,
6
16H), 3.35 (s, CH , 16H), 1.96 (s, CH , 24H); 13C NMR
2
3
(67.5 MHz, DMSO-d ) d 169.4 (CLO), 155.1, 139.7, 133.3,
6
and 115.6 (ArC), 30.7 (Ar-CH -Ar), 20.0 (CH ); Anal. calc.
2
3
for C H O ·8H O: C, 60.85; H, 5.39%. Found: C, 61.01;
72 64 24
H, 5.40%.
5.98 g (56%)]. 1H-NMR (270 MHz, DMSO-d ) d 8.68 (s, OH,
2
6
8H), 7.23–7.30 (m, ArH, 40H), 6.61 (s, ArH, 16H), 4.83 (s,
CH , 16H), 3.78 (s, CH , 16H).
2
2
49,50,51,52,53,54,55,56-Octakis(p-tolylsulfonyloxy)-5,11,
17,23,29,35,41,47-octahydroxycalix[8]arene 1b. Yield: 82%; IR
(KBr) n 3000–3700 (O–H), 1360 and 1170 cm−1 (SLO); 1H
Synthesis of 49,50,51,52,53,54,55,56-octakis(acetoxy)-
5,11,17,23,29,35,41,47-octakis(benzyloxy)calix[8]arene (3a)
NMR (270 MHz, DMSO-d ) d 9.27 (s, OH, 8H), 7.68 (s,
6
To a mixture of 2 (2.00 g, 9.4 mmol) in 25 ml of acetic
anhydride were added a few drops of pyridine and then the
mixture was refluxed for 5 h. Excess acetic acid was quenched
with cold methanol, and the precipitate was collected with a
glass filter and washed with water and methanol. Cyclohexane
was slowly added to a saturated solution of the product in
toluene previously prepared. A precipitate was collected with
a glass filter and dried under reduced pressure at 100 °C. 1.57 g
(66%) of compound 3a was obtained. IR (KBr) n 1760 (CLO),
ArH, 16H), 7.31 (s, ArH, 16H), 6.10 (s, ArH, 16H), 3.59 (s,
CH , 16H), 2.23 (s, CH , 24H); 13C NMR (67.5 MHz,
2
3
DMSO-d ) d 155.8, 146.0, 137.8, 135.2, 132.6, 130.3, 127.7,
6
and 115.7 (ArC), 30.8 (Ar-CH -Ar), 20.9 (CH ); Anal. calc.
for C H O S : C, 60.86; H, 4.38%. Found: C, 60.51;
H, 4.43%.
2
3
112 96 32 8
Photosensitivity
1050 and 1210 cm−1 (C–O–C); 1H NMR (270 MHz, CDCl )
Compound 1 was dissolved at 20 wt% in ethyl lactate at room
temperature, and to this solution was added DNQ. Films spin-
cast at 2000 rpm for 20 s on silicon wafers were prebaked at
3
d 7.26 (s, ArH, 40H), 6.53 (s, ArH, 16H), 4.78 (s, CH , 16H),
2
3.55 (s, CH , 16H), 1.94 (s, CH , 24H).
2
3
698
J. Mater. Chem., 1999, 9, 697–702

100 °C for 60 s and exposed to a filtered super-high pressure
mercury lamp (Ushio USH-200DP). Imagewise exposure
through a mask was carried out in a contact-printing mode.
Dissolution rate
O
ButO-K+
O
Silicon wafers coated with 0.9 mm thick resist films, which
were prepared by the above procedure, were exposed at 365 nm
wavelength to the filtered super-high pressure mercury lamp
for the appropriate times. After the wafers were baked at
100 °C for 90 s, they were developed in a 1.5 wt% aqueous
tetramethylammonium hydroxide (TMAH) solution at room
temperature, and rinsed with water. The dissolution rates were
based on differences of the thickness of the exposed films
before and after development for 60 s. The changes in the film
thickness against exposure energy were measured by means of
a Dectak3 system (Vecco Instruments Inc.). Each plot on
the characteristic curves was obtained from a new exposure–
development (60 s) experiment on individual wafers.
+
(HCHO)n
Xylene, reflux
CH2
8
OH
OH
2 (56 %)
Ac2O, Py/
p-TsCl, K2CO3
OH
OR
Measurement
Pd/C, H2
THF, 50 °C, H2
CH2
8
O
Infrared spectra were recorded on a HORIBA FT-210 spectro-
photometer. 1H NMR spectra were recorded on a JEOL EX
270 spectrometer. UV spectra were obtained on a JASCO V-
560 spectrophotometer. Thermal analyses were performed on
a Seiko SSS 5200-TG/DTA 220 instrument at a heating rate
of 10 °C min−1 (TG) and a Seiko SSS 5200-DSC 220 at a
heating rate of 20 °C min−1 for differential scanning calor-
imetry (DSC) under nitrogen. Scanning electron micrographs
were obtained by a JEOL-5300 microscope.
CH2
8
OR
1a; R = Ac (95 %)
1b; R = Ts (82 %)
3a; R = Ac (66 %)
3b; R = Ts (60 %)
Scheme 1 Synthesis of mono-substituted hydroquinone calix[8]-
arene 1.
Results and discussion
Synthesis of mono-substituted hydroquinone calix[8]arenes
phase HPLC. In the 1H NMR spectra of 1a and 1b, methylene
and phenyl protons due to the benzyl groups disappeared in
the reactions (Fig. 1). Both 1H NMR spectra of 1a and 1b
showed a sharp peak around d 9.2 ppm due to their hydroxy
groups. The 1H NMR spectrum of compound 2 exhibited a
broad peak at d 8.7 ppm due to the hydroxy groups on its
lower rim. In the case of calix[4]resorcinarene, a sharp peak
Synthesis of mono-substituted hydroquinone calix[8]arenes
was carried out as shown in Scheme 1. p-(Benzyloxy)-
calix[8]arene (2) was first prepared by the condensation of p-
benzyloxyphenol and paraformaldehyde in the presence of a
small amount of base. Casnati et al. reported that a mixture
of six-, seven-, and eight-membered rings was produced by the
base-catalyzed condensation and the ratio among the three
isomers depended on the bases used in the condensation.11 We
found potassium tert-butoxide gave octamer 2 more effectively
than sodium hydroxide and potassium hydroxide. Octamer 2
was easily isolated by simple filtration from refluxing acetone
and characterized by its 1H NMR spectrum in DMSO-d . The
6
acetylation of 2 was performed in refluxing acetic anhydride
with a few drops of pyridine and acetylated product 3a was
purified by reprecipitation. The reaction of 2 and toluene-p-
sulfonyl chloride was carried out in the presence of potassium
carbonate in refluxing THF and then excess toluene-p-sulfonyl
chloride was removed from the mixture of products in a
Soxhlet-extraction apparatus with propan-2-ol. Product 3b
after the extraction was pure enough for the next reaction.
The structures of 3a and 3b were characterized by 1H NMR
and IR spectroscopies.
The debenzylation of O-substituted-p-benzyloxyphenol
calix[8]arenes with Pd/C under H atmosphere has been
2
reported to be very difficult.11 However, we successfully
obtained debenzylated products, such as mono-acetyl and p-
tolylsulfonyl hydroquinone calix[8]arenes, 1a and 1b by cata-
lytic reaction with Pd/C under H . The acetone solution of 1a
2
was reprecipitated with hexane. Compound 1a was soluble in
highly polar solvents such as acetone and alcohols. On the
other hand, 1b was purified by refluxing in a mixture of
methanol and water. The obtained solids were insoluble in
methanol, but the solubility of 1b was recovered by removing
the methanol that was included in the calixarene core. The
purity of compounds 1a and 1b was confirmed by reversed-
Fig. 1 1H NMR (270 MHz) spectra of 1a and 1b in DMSO-d .
6
J. Mater. Chem., 1999, 9, 697–702
699

Fig. 3 DSC traces for 1b at the rate of 20 °C min−1 under nitrogen.
Fig. 2 IR spectra of calixarenes: (a) 2 in a KBr pellet, (b) 1a and
(c) 1b films cast on a NaCl plate from THF.
was observed at d 8.6 ppm. In addition, a comparison of the
IR spectra of 2, 1a, and 1b is shown in Fig. 2. Compound 2
shows a strong absorption band at 3220 cm−1 due to the
hydroxy stretching absorption as p-tert-butyl calix[8]arene
and p-tert-butyl novolac oligomer resin do, indicating that
their hydroxy groups readily form intramolecular hydrogen
bonds.12 On the other hand, 1a exhibits an absorption band
at 3360 cm−1 due to the intermolecular hydrogen bonds
between the hydroxy groups. Two different absorption bands
induced by the intramolecular and the intermolecular hydrogen
bonds were observed in the IR spectrum of 1b. These results
indicate that simple modification of 2 gives high solubility to
the resulting O-substituted hydroxyphenol calix[8]arenes 1a
and 1b. Thus, these compounds are soluble in polar solvents
such as alcohols, ethyl acetate, acetone, tetrahydrofuran, 1-
acetoxy-2-methoxyethane (PMA) and ethyl lactate (EL), and
highly transparent films were easily cast from the solution in
PMA or EL.
Fig. 4 UV–vis spectra of the 1a and 1b films cast on a quartz plate
from EL.
substituted calix[8]arenes 1 because DNQs have been standard
photo-reactive compounds for novolac base positive-type pho-
toresists since the 1970s. Calixarenes 1 would be very interes-
ting materials as photoresists if DNQ inhibits their dissolution
because DNQ has rarely found a better partner than novolac.
We examined whether DNQ acted as a dissolution inhibitor
in an aqueous base solution against 1a. Dissolution inhibition
by DNQ was not observed under any conditions because of
the low hydrophobicity of the acetate groups. On the other
hand, the film of 1b containing 30 wt% of DNQ showed a
dissolution inhibition effect toward a standard alkaline devel-
oper, 2.38 wt% aqueous TMAH solution. These results suggest
that the hydrophobicity of substituents affects the dissolution
of 1, and the higher hydrophobicity of p-tosylate groups is
expected to provide 1b with suitable dissolution properties for
the DNQ resist system. After the preliminary experiments, we
selected 1b and 1.5 wt% aqueous TMAH solution as a matrix
and a developer, respectively.
Thermal properties
The thermal behavior of 1a and 1b was investigated by
thermogravimetry (TG) and differential scanning calorimetry
(DSC). Compound 1a shows an initial weight loss below 5%
around 200 °C probably due to the vaporization of included
solvents and high thermal stability up to 300 °C. On the other
hand, 1b displays a large weight loss around 250 °C. Both
DSC curves of 1a and 1b showed no endothermic peak due
to the melting point being below 200 °C and only 1b exhibits
a glass transition temperature (T ) at 170 °C on the 2nd heating
g
(Fig. 3). No T of 1a, however, is observed below 200 °C.
g
These results suggest that compound 1b, having bulky
substituents such as toluene-p-sulfonate groups, is clearly more
amorphous than 1a.
Lithographic evaluation
2,3,4-Tris[2-diazo-1-oxonaphthalen-4-ylsulfonyloxy]benzo-
phenone [DNQ(4)] and 2,3,4-tris[2-diazo-1-oxonaphthalen-5-
ylsulfonyloxy]benzophenone [DNQ(5)] were employed as the
photo-reactive compound (Scheme 2). In Fig. 5, the
UV–visible spectra of the resist films containing DNQ(4) and
DNQ(5) are shown. The typical absorption bands for DNQ(5)
are observed at 350 and 400 nm while the absorption bands
for DNQ(4) are shifted to 310 and 390 nm. DNQ(5) and
DNQ(4) are photochemically transformed to indenecarboxylic
acid and 3-sulfoindenecarboxylic acid, respectively.13 The latter
is a stronger acid than the former. Therefore, higher dissolution
The UV spectra of films of compounds 1a and 1b (1 mm thick)
are shown in Fig. 4. Both films are transparent above 300 nm,
indicating that it is possible to use them for i-line (365 nm)
lithography. Furthermore, the optical density of the 1a film is
only 0.3 mm−1 at 248 nm and it can be used for a wide range
of lithography from g-line through KrF eximer laser. On the
other hand, 1b has a strong absorption below 300 nm due to
toluene-p-sulfonate groups.
Diazonaphthoquinones (DNQs) were chosen as photo-
reactive compounds for the new photoresist based on mono-
700
J. Mater. Chem., 1999, 9, 697–702

Diazonaphthoquinone-4-sulfonate [DNQ(4)]
O
O
C
N2
hυ
– N2
SO2
Ar
SO2
Ar
+H2O
O
C
O
OH
C
OH
+H2O
Fig. 6 Photochemical effects on the dissolution rates in 1.5 wt%
aqueous TMAH solution of the resist films containing 1b with
(a) 25 wt% of DNQ(4) and (b) 25 wt% of DNQ(5).
SO2
SO3H
Diazonaphthoquinone-5-sulfonate [DNQ(5)]
O
acceleration in the resist containing DNQ(4) after UV-
irradiation would be expected. We, however, considered both
DNQ sulfonates for the new positive-type photoresist with
i-line.
O
C
N2
hυ
The resist was formulated by mixing 1b and DNQ in ethyl
lactate (EL) [451516 w/w]. The films spin-cast on silicon wafer
were prebaked at 100 °C for 90 s. We plotted the correlation
between the exposure dose to i-line and the dissolution rate of
the exposed part toward 1.5 wt% aqueous TMAH solution
(Fig. 6). The dissolution rate of the resist film before UV
– N2
SO2
Ar
SO2
Ar
+H2O
˚
irradiation (R ) is reduced to about 10−1 A s−1 by the addition
0
˚
of DNQs while that of 1b film without DNQ is 240 A s−1.
The actual dissolution rates of the resist film containing
O
C
O
˚
DNQ(4) and DNQ(5) are 0.28 and 0.60 A s−1, respectively.
OH
C
OH
These large inhibition effects may be attributed to the inter-
actions between the resist matrix 1b and DNQs. On the other
hand, the dissolution rate of the exposed films
SO2
Ar
SO3H
(200 mJ cm−2)(R
cate that the addition of DNQ(4) is very effective in increasing
) containing DNQ(4) and DNQ(5)
reached 1470 and 820 A s−1, respectively. These findings indi-
200
˚
the dissolution contrast between R
and R by about 5200
200
0
O
O
times, probably due to strong acid formation. DNQ(5) also
demonstrated the high dissolution contrast of over 1000 times.
Thermal treatment after UV exposure, called ‘Post Exposure
Bake (PEB)’ generally improves the resist profile. The effects
of the PEB temperature on the dissolution rates of both
exposed and unexposed films were investigated, but no large
changes were observed up to 120 °C. A higher temperature
than 120 °C induces the decomposition of DNQs.
O
O
Ar =
Scheme 2 Comparison of the photolysis between DNQ(4) and
DNQ(5).
The effect of the DNQ loading on the sensitivity and the
contrast was investigated. The film spin-cast on silicon wafer
was prebaked at 80 °C for 10 min, exposed to i-line radiation,
postbaked at 100 °C for 3 min, and developed in a positive
mode with 1.5% aqueous TMAH solution at room tempera-
ture. The results are summarized in Table 1. The best sensitivity
(D) and contrast (c) were obtained at a 25% loading of
Table 1 Performance of the resist consisting of 1b and DNQs
DNQ(4)
DNQ(5)
Loadinga (wt%)
D (mJ cm−2)b
cc
D (mJ cm−2)b
cc
20
25
30
33
30
40
2.1
2.8
2.0
—
37
40
—
2.5
2.1
aWeight ratio of DNQ against 1b. bSensitivity estimated with the
characteristic curves. cContrast estimated with the characteristic
curves.
Fig. 5 UV–vis spectra of the resist films containing 1b with (a) 25 wt%
of DNQ(4) and (b) 25 wt% of DNQ(5).
J. Mater. Chem., 1999, 9, 697–702
701

TMAH solution for 40 s at room temperature. A high reso-
lution positive image featuring 1 mm line and space patterns,
which is the limitation of our exposure system, was obtained
on the 0.9 mm thick film.
Conclusions
We have successfully designed a new monodisperse compound
as a matrix for photoresist, that is, the new positive working
photoresist was formulated by mixing p-tolylsulfonyl hydro-
quinone calix[8]arene 1b and DNQ(4) or (5) as the dissolution
inhibitor, and it was found to be an alkaline-developable
positive type resist. The new resist consisting of 1b and 25 wt%
loading of DNQ(4) showed a sensitivity of 30 mJ cm−2 and
contrast of 2.8. Fine images were also available on the resist
film by exposure to i-line through a mask. Some calixarenes
are potentially transparent around 250 nm wavelength, there-
fore they are expected to be useful for KrF eximer-laser
lithography.
Fig. 7 Characteristic curves of the resist containing 1b, exposed to
i-line: with (a) 20 wt%, (b) 25 wt%, and (c) 30 wt% of DNQ(4).
Acknowledgement
The authors are indebted to Sadao Kato for his technical
assistance and Takeyoshi Takahashi for performing the
elemental analyses.
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J. Mater. Chem., 1999, 9, 697–702