Chemistry Letters Vol.36, No.11 (2007)
1309
1.0
0.8
0.6
0.4
0.2
0.0
Figure 3. Lithographic image of a 10-mm line and space film of
1 sensitized with 10 wt % PBG.
was reduced to 10 mJ/cm2 when the film was heated to 140 ꢁC
for a period of 9 min. These results show that the base prolifer-
ation reaction of 1 proceeded effectively to proliferate amino
groups, leading to the enhancement of the base-catalyzed hydro-
lytic condensation reaction of the residual ethoxysilyl groups of
1, resulting in the formation of an insoluble resin. Resin 1 sensi-
tized with PBG exhibited a higher photosensitivity compared
with conventional photoresists that rely on base-catalyzed reac-
tions.6
Microphotopatterning was carried out in a preliminary eval-
uation.5 A 1.0-mm thick film of 1 containing 10 wt % PBG was
exposed to light at 365 nm with a dose of 300 mJ/cm2, heated
to 130 ꢁC for a period of 10 min, and developed with chloroform
for a period of 30 s. A clear negative-tone image with a 10-mm
line and space resolution was obtained, as shown in Figure 3,
although further optimization is needed.
In summary, we have developed a thermally stable base-
amplifying silicone resin 1 having phenylsulfonylethyl units.
Films of resin 1 underwent base proliferation reactions that were
triggered by a small amount of photogenerated amine molecules.
Combining this resin with PBG provided a negative-working
photoimaging material. In addition, the photosensitivity increas-
ed with increasing heating period, and the exposure dose was
reduced to 10 mJ/cm2 for a film of 1 heated to 140 ꢁC for a pe-
riod of 9 min. This system showed a higher photosensitivity
compared with conventional photoimaging materials utilizing
base-catalyzed reactions.
1
10
100
1000
-2
·
Irradiation energy / mJ cm
Figure 2. Photosensitivity curves of films of 1 composed of
10 wt % PBG exposed to light at 365 nm and heated to 140 ꢁC
for a period of: 6 min ( ), 7 min ( ), 8 min ( ), and 9 min ( ).
ing PBG was evaluated using UV absorption measurements.5
The progress of the base proliferation reaction of 1 results in
the elimination of its aromatic rings, which are immediately va-
porized. This enables us to examine the decomposition of films
of 1 by monitoring the changes in the UV absorption spectra due
to the loss of the aromatic rings of 1. The data shown in Figure 1
were obtained by plotting the peak intensity of the absorption
band at 230 nm from a film of 1 containing PBG as a function
of heating time. The peak intensity decreased immediately, dis-
playing an S-shaped conversion curve. An S-shaped conversion
curve means that there was a progression of the base prolifera-
tion reaction of 1, even in the film state. The data in Figure 1 also
show that the induction period depended on the UV-irradiation
energy. This means that the base proliferation reaction of 1
was triggered by photogenerated bases.
The base proliferation reaction of 1 gives rise to the autoca-
talytic formation of amino groups in its side chains. These amino
groups accelerate the base-catalyzed hydrolytic condensation re-
actions of the residual ethoxysilyl units in its main chain to form
a cross-linked network. Consequently, resin 1 may be insoluble
in organic solvents. Films of 1 sensitized with PBG after irradi-
ation with light at 365 nm and a heat treatment were developed
using chloroform. The residual film thickness was measured to
obtain the photosensitivity curves.5 Films for sensitivity determi-
nation were about three times as thick as films used in Figure 1
and were thermally stable during the conditions to determine
sensitivity. As shown in Figure 2, negative-type photosensitivity
curves were obtained. It is clear that the photosensitivity, which
was defined as the irradiation energy required for the reduction
of a normalized film thickness by a value of 0.4, was influenced
by the heating period. As shown in Table 1, the exposure dose
This study was supported by the Tokyo Ohka Foundation for
the Promotion of Science and Technology. We wish to express
our appreciation to Associate Professor Takahiro Gunji of Tokyo
University of Science for his helpful discussions.
References and Notes
1
a) Y. Morikawa, K. Arimitsu, T. Gunji, Y. Abe, K. Ichimura, J. Photo-
2
Table 1. Sensitivity of films of 1 containing 10 wt % PBGa
Run
Heating periodsb/min
Sensitivityc/mJꢂcmꢃ2
200
3
4
5
K. Arimitsu, Y. Morikawa, T. Gunji, Y. Abe, K. Ichimura, Proc. Rad-
Tech Asia ’03, RadTech, Japan, 2003, p. 312.
M. Miyamoto, K. Arimitsu, K. Ichimura, J. Photopolym. Sci. Technol.
1999, 12, 317.
The synthesis and evaluation procedure is given in the Supporting
Information, which is available electronically at the CSJ Journal
1
2
3
4
6
7
8
9
100
30
10
aFilms of 1 developed with chloroform. Films of 1 heated
b
to 140 ꢁC. Sensitivity is defined as the irradiation energy
´
J. M. J. Frechet, M. Leung, E. J. Urankar, C. G. Willson, J. F. Cameron,
c
6
required for the reduction of the normalized film thickness
by a value of 0.4.
´
Inoue, Satoru
