New negative-type photosensitive polyimide based on hyperbranched poly(ether imide), a cross-linker, and a photoacid generator

Article abstract of DOI:10.1246/cl.2001.762

A new negative working photosensitive polyimide, based on hyperbranched poly(ether imide) (1), 4,4′-methylenebis[2,6-bis(hydroxymethyl)]phenol (2) as a cross-linker, and a photoacid generator diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (3) has been developed. 1 was prepared by polycon-densation of N-[3,5-di-(tert-butyldimethylsilyloxy)phenyl]-4-fluorophthalimide (4), followed by deprotection of tert-butyldimethylsilyl group with KF-HBr. The photosensitive polyimide containing 1 (70 wt%), 2 (20 wt%) and 3 (10 wt%) gave a clear negative pattern when it was exposed to 365 nm light and postbaked at 120 °C, followed by developing with a 2.38 wt% aqueous tetramethylammonium hydroxide (TMAH) solution at room temperature.

Full text of DOI:10.1246/cl.2001.762

762
Chemistry Letters 2001
New Negative-Type Photosensitive Polyimide Based on Hyperbranched
Poly(ether imide), a Cross-Linker, and a Photoacid Generator
Masaki Okazaki, Yuji Shibasaki, and Mitsuru Ueda*
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552
(Received April 26, 2001; CL-010382)
A new negative working photosensitive polyimide, based
on hyperbranched poly(ether imide) (1), 4,4'-methylenebis[2,6-
bis(hydroxymethyl)]phenol (2) as a cross-linker, and a pho-
toacid generator diphenyliodonium 9,10-dimethoxyanthracene-
2-sulfonate (3) has been developed. 1 was prepared by polycon-
densation of N-[3,5-di-(tert-butyldimethylsilyloxy)phenyl]-4-
fluorophthalimide (4), followed by deprotection of tert-butyl-
dimethylsilyl group with KF-HBr. The photosensitive poly-
imide containing 1 (70 wt%), 2 (20 wt%) and 3 (10 wt%) gave
a clear negative pattern when it was exposed to 365 nm light
and postbaked at 120 °C, followed by developing with a 2.38
wt% aqueous tetramethylammonium hydroxide (TMAH) solu-
tion at room temperature.
To remedy these problems, an acid-catalyzed cross-linking
system into hyperbranched polymers is suitable. And, hyper-
branched poly(ether imide)s having imide backbones and many
phenolic hydroxy groups on terminal units would be a good
candidate as a matrix polymer for developing the alkaline
developable photosensitive materials
This paper describes the synthesis of a negative-type alka-
line developable PSPI system based on hyperbranched
poly(ether imide) (1), 4,4'-methylenebis[2,6-bis(hydroxy-
methyl)] phenol (2) as a cross-linker and a photoacid generator
diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (3).
Recently, Moore et al. reported the synthesis of hyper-
branched polymer 1 from N-[3,5-di(tert-butyldimethylsilyl-
oxy)phenyl]-4-fluorophthalimide (4) as an AB2 monomer.11
Thus, polymer 1 was selected as the matrix polymer for the for-
mation of a new photosensitive system. Monomer 4 was pre-
pared as shown in Scheme 1, which is different from the report-
ed method.11 Polymerization of monomer 4 was carried out in
diphenyl sulfone (DPS) in the presence of cesium fluoride at 240
°C for 30 min, giving TBDMS-protected polymer 5 (TBDMS =
tert-butyldimethylsilyl) and deprotection of TBDMS groups was
achieved with KF–HBr (Scheme 2). The polymer was identi-
Polyimides have excellent electrical property and high
thermal stability for application in microelectronics industry.
Photosensitive polyimides (PSPIs) are widely applied as
protection and insulation layers in manufacturing semiconduc-
tor because the number of processing steps is simplified by
avoiding the use of usual photoresists. Although various nega-
tive and positive type PSPIs have been reported up to now,1,2
most of these resist systems require thermal treatment in high
temperature for the imidization after development, which is not
suitable for semiconductor manufacturing. For example most
of the negative-type PSPIs are prepared from poly(amic acid)s
containing photo-polymerization sites such as acryloyl groups
on the polymer backbone.3 The positive-type PSPIs consist of
poly(amic acid)s and dissolution inhibitors such as o-diazo-
naphthoquinone, 1,4-dihydropyridine derivatives,4,5 and o-
nitrobenzyl esters of poly(amic acid).6 Furthermore, both nega-
tive and positive type alkaline developable PSPIs based on
poly(hydroxyimide)s as a matrix have been reported.7,8 Most
of the standard resist materials used in semiconductor manufac-
turing are an alkaline developable positive type resist based on
novolac resin with diazonaphthoquinone. Thus, aqueous alka-
line developable PSPIs are preferable to PSPIs developed with
organic solvents.
1
fied as the corresponding 1 by IR, H and 13C NMR spectro-
1
scopies.11 The degree of branching determined by H NMR
spectroscopy was 50%. The molecular weight of the polymer
In general, these polyimide matrixes have a poor solubility
for organic solvents and a problem to introduce alkaline devel-
opable functional groups.
Recently, hyperbranched polymers have been receiving a
great attention for their unique properties such as intrinsic glob-
ular structure, low viscosity, high solubility and large number
of terminal functional groups. There have been many reports
on the synthesis and characterization of hyperbranched poly-
mer, and various applications such as blend components,
nanoforms, nonlinear optics and catalysts.9,10 However, little
work has been done for testing potential application to photo-
sensitive materials because of poor mechanical properties of
those films.
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
763
was determined by GPC. The chromatogram was a unimodal
distribution, and indicated the Mn and Mw values were 27000
and 60000, respectively, using polystyrene standard, and the
ratio of Mw/Mn was 2.2.
The thermal stability of 1 was examined by thermo-
gravimetry (TG) and differential scanning calorimetry (DSC).
The polymer showed a 10% weight loss at 500 °C in nitrogen
and the glass transition temperature was observed at 250 °C
(Figure 1). The transmission of UV–vis spectrum of 1 in DMF
solution was measured. It was found that an i-line (365 nm)
developed with a 2.38 wt% aqueous tetramethylammonium
hydroxide solution. The resist is capable of resolving 4.5 µm
features when 1.4 µm thick film is used. A photogenerated acid
catalyzes the formation of benzylic carbocation speices, which
undergo electrophilic aromatic substitution to produce a C- and
O-alkylated polymers. This reaction converts the soluble poly-
mer 1 to insoluble cross-linked polymer (Scheme 3).8 To
achieve an excellent resolution, a detailed optimization study
involving the loading 2 and 3, and postbaked temperatures is in
progress.
References and Notes
1
2
3
4
5
6
7
8
9
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irradiation was possible for this polymer because the transmit-
tance of 1 at 365 nm was more than 90%.
We formulated a photosensitive polyimide system consist-
ing of 1 (70 wt%), 2 (20 wt%), and 3 (10 wt%) in 2-
methoxyethanol. In Figure 2 is presented a scanning electron
micrograph of the contact-printed negative image that was post-
baked at 120 ˚C for 5 min after exposure to 200 mJ·cm–2, and
10 B. Voit, J. Polym. Sci., Part A: Polym. Chem. 38, 2505
(2000).
11 D. S. Thompson, J. L. Markoski, and J. S. Moore,
Macromolecule, 32, 4764 (1999).