U.S. patent application number 09/422731 was filed with the patent office on 2001-08-09 for polysilane composition for forming a coating suitable for bearing a metal pattern, metal pattern forming method, wiring board preparing method.
Invention is credited to FUKUSHIMA, MOTOO, ITO, KUNIO, MORI, SHIGERU.
Application Number | 20010012869 09/422731 |
Document ID | / |
Family ID | 26562495 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012869 |
Kind Code |
A1 |
FUKUSHIMA, MOTOO ; et
al. |
August 9, 2001 |
POLYSILANE COMPOSITION FOR FORMING A COATING SUITABLE FOR BEARING A
METAL PATTERN, METAL PATTERN FORMING METHOD, WIRING BOARD PREPARING
METHOD
Abstract
A metal pattern is prepared by applying a polysilane composition
comprising a polysilane, a carbon functional silane, and a solvent
onto a substrate to form a patterned coating of the polysilane
composition, attaching catalytic metal nuclei to the patterned
coating, and immersing the substrate in an electroless plating bath
for thereby chemically depositing a metal film on the patterned
coating.
Inventors: |
FUKUSHIMA, MOTOO;
(GUNMA-KEN, JP) ; ITO, KUNIO; (GUNMA-KEN, JP)
; MORI, SHIGERU; (GUNMA-KEN, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH LLP
P O BOX 747
FALLS CHURCH
VA
220400747
|
Family ID: |
26562495 |
Appl. No.: |
09/422731 |
Filed: |
October 22, 1999 |
Current U.S.
Class: |
524/588 |
Current CPC
Class: |
H05K 2201/0355 20130101;
G03F 7/0757 20130101; C09D 183/16 20130101; G03F 7/11 20130101;
H05K 3/389 20130101; H05K 3/182 20130101; H05K 3/387 20130101; C08L
2666/44 20130101; H05K 3/184 20130101; C09D 183/16 20130101; H05K
2201/0162 20130101 |
Class at
Publication: |
524/588 |
International
Class: |
C08J 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 1998 |
JP |
10-300894 |
Oct 30, 1998 |
JP |
10-309793 |
Claims
1. A polysilane composition for forming a metal pattern-bearing
coating, comprising a polysilane, a carbon functional silane, and a
solvent.
2. The polysilane composition of claim 1 wherein the polysilane is
of the following formula (1):
(R.sup.1.sub.mR.sup.2.sub.nX.sub.pSi).sub.q (1) wherein R.sup.1 and
R.sup.2 each are hydrogen or a substituted or unsubstituted
monovalent hydrocarbon group, X is hydrogen or a substituted or
unsubstituted monovalent hydrocarbon group, alkoxy group or halogen
atom, m is a number of 0.1 to 2, n is a number of 0 to 1, p is a
number of 0 to 0.5, the sum of m+n+p is from 1 to 2.5, and q is an
integer of 4 to 100,000.
3. A metal pattern forming method comprising the steps of: applying
the polysilane composition of claim 1 onto a substrate by an
imprinting, ink jet printing or lithographic process, to form a
patterned coating of the polysilane composition, attaching
catalytic metal nuclei for electroless plating to the patterned
coating, and immersing the substrate in an electroless plating bath
and depositing an electroless plating film on the patterned
coating.
4. A method for preparing a wiring board comprising the steps of:
(1) forming a thin film of a carbon functional silane-containing
polysilane on a substrate and contacting a palladium salt with a
surface of the polysilane thin film to form a palladium colloid
layer thereon, (2) forming a photosensitive resin layer on the
polysilane thin film having the palladium colloid layer,
selectively irradiating light to the layer, and developing the
layer, to thereby form a predetermined pattern of channels in the
photosensitive resin layer so that the polysilane thin film having
the palladium colloid layer is exposed within the channels, and (3)
contacting an electroless plating solution with the polysilane thin
film having the palladium colloid layer exposed within the
channels, for thereby forming a conductive metal layer within the
channels.
5. The method of claim 4 wherein the polysilane is of the following
formula (1): (R.sup.1.sub.mR.sup.2.sub.nX.sub.pSi).sub.q (1)
wherein R.sup.1 and R.sup.2 each are hydrogen or a substituted or
unsubstituted monovalent aliphatic, alicyclic or aromatic
hydrocarbon group, X is hydrogen or a substituted or unsubstituted
monovalent aliphatic, alicyclic or aromatic hydrocarbon group,
alkoxy group or halogen atom, m is a number of 0.1 to 2, n is a
number of 0 to 1, p is a number of 0 to 0.5, the sum of m+n+p is
from 1 to 2.5, and q is an integer of 4 to 100,000.
6. The method of claim 4 wherein the carbon functional silane is an
amino group-containing alkoxysilane.
7. A method for preparing a wiring board comprising the steps of:
(I) forming a thin film of polysilane with SiH group on a substrate
and irradiating light to the thin film for crosslinking the
polysilane for thereby insolubilizing the polysilane, (II) forming
a photosensitive resin layer on the crosslinked polysilane thin
film, selectively irradiating light to the layer, and developing
the layer, to thereby form a predetermined pattern of channels in
the photosensitive resin layer so that the crosslinked polysilane
thin film is exposed within the channels, and (III) contacting a
palladium salt with the crosslinked polysilane thin film exposed
within the channels to form a palladium colloid layer and
contacting an electroless plating solution for thereby forming a
conductive metal layer within the channels.
8. The method of claim 7 wherein the polysilane is of the following
formula (2): (H.sub.mR.sup.2.sub.nX.sub.pSi).sub.q (2) wherein
R.sup.2 is hydrogen or a substituted or unsubstituted monovalent
aliphatic, alicyclic or aromatic hydrocarbon group, X is hydrogen
or a substituted or unsubstituted monovalent aliphatic, alicyclic
or aromatic hydrocarbon group, alkoxy group or halogen atom, m is a
number of 0.1 to 2, n is a number of 0 to 1, p is a number of 0 to
0.5, the sum of m+n+p is from 1 to 2.5, and q is an integer of 4 to
100,000.
9. The method of claim 7 wherein in step (I), the polysilane thin
film on the substrate is irradiated with light in an exposure of
0.001 to 100 J/cm.sup.2.
10. The method of claim 7 wherein the electroless plating solution
contains a copper or nickel ion.
Description
[0001] This invention relates to a polysilane composition for
forming a coating suitable for bearing a metal pattern, and a metal
pattern forming method using the same. It also relates to a method
for preparing a wiring board.
BACKGROUND OF THE INVENTION
[0002] Substrates having metal patterns formed thereon are used in
a variety of applications, for example, as printed circuit boards
and comb-shaped electrode substrates for sensors. Metallization on
such substrates is generally carried out by vapor phase methods
such as CVD and wet methods as typified by plating methods. The
metal is then patterned by a complex method which generally uses a
resist material and involves exposure and development steps.
[0003] To eliminate such complication, Whiteside et al. proposed a
novel metal patterning procedure. This procedure is to form a metal
pattern by immersing a rubber material having an irregular surface
in a dispersion of palladium colloid. The rubber material is then
pressed against a substrate whereby the palladium colloid on raised
portions is transferred to the substrate. The substrate is then
immersed in an electroless or chemical plating bath whereby a metal
deposits only on the palladium colloid-bearing areas. (See Langmuir
1996, 12, 1375-1380.)
[0004] Unfortunately, this procedure has the drawback that the
palladium colloid is very unstable. Typically, a surfactant such as
tetraammonium halide is added to the palladium colloid for
stabilizing the colloid. An attempt to apply the palladium colloid
by an imprinting, ink jet printing or lithographic process fails
because of coagulation and precipitation of the palladium colloid.
No uniform metal pattern is formed and the adhesion between the
substrate and the metal is insufficient.
[0005] Printed circuit boards now encounter a strong need for
higher density because of the widespread use of ultra-thin
equipment. In prior art printed circuit boards, after a copper foil
is bonded to a resin substrate with an adhesive, patterning is
carried out using a resist (subtractive process). However, a proper
adhesive must be used depending on a particular resin selected from
among phenolic resins, polyester resins, epoxy resins, polyimide
resins, and bismaleimide triazine resins. A complex bonding process
is necessary. The bond strength is not fully high.
[0006] In recent years, a need to form a finer metal pattern
promotes research efforts on the additive process of metallizing a
resin substrate, rather than the subtractive process suffering from
the thinning of a metal film by over-etching, so that the additive
process may be employed on a commercially acceptable level. For the
additive process, however, an improvement in the adhesion between
the resin substrate and the metallization is of significance.
[0007] For logic devices and system LSI's, there is a strong need
to increase the degree of integration and operational speed of
circuits in order to realize high-speed electronic equipment. In
this regard, an attention is paid to copper as a low resistance
wiring material. In the prior art semiconductor device manufacture,
aluminum is used as the material for forming fine metal circuits on
semiconductor and a CVD process is used for its application. Copper
is more difficult to work than aluminum. Then there is an urgent
desire to establish a micro-wiring technique for copper. One
solution to the above-described problem is electrolytic plating. It
has been studied to apply electrolytic plating to the copper wiring
process on a commercially acceptable level (see monthly
Semiconductor World, February 1998, pp. 82-85).
[0008] However, the electrolytic plating has the drawback that the
thickness of metal coating locally varies and is not reproducible,
which becomes a neck to mass manufacture. When the electrolytic
plating is combined with a resist material and resist process
necessary to form a fine metal pattern in a mass scale, optimum
conditions of the electrolytic plating have not been fully
established.
[0009] Polysilane is an interesting polymer because of its UV
absorption properties due to the metallic property and unique
electron delocalization of silicon as compared with carbon, as well
as its high heat resistance, flexibility, and good thin film
forming properties. Active research efforts have been made on
polysilane for the purpose of developing a photoresist capable of
forming a micropattern at a high precision (see, for example, JP-A
6-291273 and 7-114188).
[0010] Finding that a palladium colloid forms when a polysilane is
contacted with a solution of a palladium salt, and that UV
irradiation causes the conversion of polysilane into polysiloxane,
the inventors proposed a pattern forming method. The inventors also
found that a metal pattern can be formed by combining such
characteristics of a polysilane thin film with electroless plating
catalyzed by palladium colloid (JP-A 10-325957). However, this
method still requires the steps of light irradiation and
exposure.
[0011] JP-A 5-72694 discloses the use of a polysilane in a method
for preparing a semiconductor integrated circuit. This method is
characterized in that a film of polysilane optionally doped with
iodine is used as a conductive layer and a siloxane layer converted
from polysilane by light irradiation is used as an insulating
layer. It has thus been contemplated to apply the polysilane or
polymer having a Si-to-Si bond as conductive material.
[0012] However, the semiconductor integrated circuit obtained by
the above method has the problems that the conductive areas
consisting solely of polysilane are not fully conductive and the
use of potentially corrosive iodine becomes a serious obstacle to
the application of polysilane to electronic material. Additionally,
since the polysilane which is likely to convert into siloxane upon
exposure to moisture, oxygen or light in the ambient atmosphere is
used as conductive material, its application to electronic material
requiring reliability encounters great difficulty.
[0013] JP-A 57-11339 discloses a method for forming a metal image
by exposing a compound having a Si-to-Si bond to light and
contacting it with a metal salt solution. When the compound having
a Si-to-Si bond is contacted with the metal salt solution, the
metal salt is reduced to the metal. Utilizing this phenomenon, a
metal layer is formed in the unexposed area. To define a definite
image by this method, the exposed area must be completely deprived
of reducing property, which requires to irradiate a large quantity
of light. Upon light exposure, the polysilane is converted into
siloxane. Once a finely defined circuit is formed by UV
irradiation, it becomes very difficult to further convert the
siloxane into a polycarbosilane or polysilazane which is an
insulating ceramic precursor having heat resistance and
toughness.
[0014] There is a desire to have a technique of manufacturing a
wiring board of high quality in an industrially advantageous
manner.
SUMMARY OF THE INVENTION
[0015] One object of the invention is to provide a method of
forming a metal pattern on a substrate by a simple step such as a
conventionally employed imprinting, ink jet printing or
lithographic process without a need for light irradiation and
exposure. Another object is to provide a polysilane composition
used in the method for forming a coating suitable for bearing a
metal pattern.
[0016] A further object is to provide a method for preparing a
wiring board having a pattern of highly conductive areas and
insulating areas through simple and inexpensive steps so that the
wiring board may have high heat resistance and pattern definition
and be used in a variety of applications in the electric,
electronic and communication fields.
[0017] In a first embodiment of the invention, there is provided a
polysilane composition for forming a coating suitable for bearing a
metal pattern thereon, comprising a polysilane, a carbon functional
silane, and a solvent.
[0018] In a second embodiment of the invention, there is provided a
metal pattern forming method comprising the steps of:
[0019] applying the above-defined polysilane composition onto a
substrate by an imprinting, ink jet printing or lithographic
process, to form a patterned coating of the polysilane
composition,
[0020] attaching catalytic metal nuclei for electroless plating to
the patterned coating, and
[0021] immersing the substrate in an electroless plating bath and
depositing an electroless plating film on the patterned
coating.
[0022] The inventors have found that a composition comprising a
polysilane and a carbon functional silane (sometimes abbreviated as
CF silane) forms a coating which readily captures a palladium salt
and thus ensures that an electroless plating film forms thereon
with a firm bond. The coating itself has a high strength. Using the
polysilane composition, a patterned film of polysilane can be
easily formed on a substrate by an imprinting, ink jet printing or
lithographic process. After catalytic metal nuclei such as
palladium nuclei are distributed on the patterned coating, the
substrate is immersed in an electroless plating bath. In this way,
a metal pattern can be formed by a simple inexpensive process
without a need for exposure and development steps.
[0023] In a third embodiment of the invention, there is provided a
method for preparing a wiring board comprising the steps of:
[0024] (1) forming a carbon functional silane-containing polysilane
thin film on a substrate and contacting a palladium salt with a
surface of the polysilane thin film to form a palladium colloid
layer thereon,
[0025] (2) forming a photosensitive resin layer on the polysilane
thin film having the palladium colloid layer, selectively
irradiating light to the layer, and developing the layer, to
thereby form a predetermined pattern of channels in the
photosensitive resin layer so that the polysilane thin film having
the palladium colloid layer is exposed within the channels, and
[0026] (3) contacting an electroless plating solution with the
polysilane thin film having the palladium colloid layer exposed
within the channels, for thereby forming a conductive metal layer
within the channels.
[0027] In a fourth embodiment of the invention, there is provided a
method for preparing a wiring board comprising the steps of:
[0028] (I) forming a SiH group-containing polysilane thin film on a
substrate and irradiating light to the thin film for crosslinking
the polysilane for thereby insolubilizing the polysilane,
[0029] (II) forming a photosensitive resin layer on the crosslinked
polysilane thin film, selectively irradiating light to the layer,
and developing the layer, to thereby form a predetermined pattern
of channels in the photosensitive resin layer so that the
crosslinked polysilane thin film is exposed within the channels,
and
[0030] (III) contacting a palladium salt with the crosslinked
polysilane thin film exposed within the channels to form a
palladium colloid layer and contacting an electroless plating
solution for thereby forming a conductive metal layer within the
channels.
[0031] The inventors found that when a polysilane is previously
irradiated with UV radiation, the polysilane is converted into a
polysiloxane so that the surface is changed to be polar. When this
polysiloxane is contacted with a palladium salt solution, a
palladium colloid can be formed, which enables pattern formation.
As long as the palladium colloid is attached to the surface of a
resin coating, the electroless plating method permits a metal film
of uniform thickness to form on a variety of resins. A metal
pattern of copper can be formed by combining the above-described
characteristics of a polysilane thin film with electroless plating
catalyzed by palladium colloid. A circuit board having improved
heat resistance and pattern definition can be manufactured by a
simple inexpensive process. This process is proposed in Japanese
Patent Application No. 10-94111.
[0032] Continuing the research, the inventors found that in a
method for preparing a circuit board utilizing a metal pattern, the
metal pattern sometimes has an unsatisfactory adhesion to the
substrate. When the metal pattern is formed utilizing the optically
defined resist pattern, the metal area partially spreads with the
progress of metal deposition. Then, the pattern resulting from the
resist becomes far from satisfactory.
[0033] Then the inventors made further research to produce a wiring
board which has improved adhesion between a metal pattern and a
substrate and an improved pattern profile. In the wiring board
preparing method according to the third embodiment of the
invention, a composition comprising a polysilane and a CF silane as
main components is applied onto a substrate to form a CF-silane
containing polysilane thin film having an improved film strength.
When the polysilane thin film is contacted with a palladium salt,
the palladium salt is readily captured by the polysilane thin film
to form a palladium colloid layer thereon. Then a photosensitive
resin layer is formed on the palladium colloid layer for forming a
pattern of channels. The CF-silane containing polysilane thin film
is exposed within the channels. Then electroless plating is carried
out. The adhesion between the conductive metal layer of copper or
the like formed by the electroless plating and the substrate is
strong. Since the conductive metal layer is formed within the
channels, there is no risk that the conductive metal area spreads
out.
[0034] In the wiring board preparing method according to the fourth
embodiment of the invention, a polysilane undergoes crosslinking
reaction under irradiation of light such as ultraviolet radiation
and becomes insoluble in solvents. Even after being crosslinked by
light irradiation, this polymer is effective for readily reducing a
palladium salt in contact therewith, to form a palladium colloid. A
photosensitive resin layer is then formed on the crosslinked
polysilane thin film to define a predetermined pattern of channels
so that the crosslinked polysilane thin film is exposed within the
channels. After a palladium colloid layer is formed thereat,
electroless plating is carried out to form a conductive metal layer
as in the third embodiment. In this way, there can be formed a
metal pattern which has improved adhesion to the substrate, and is
stable and free of the risk that the conductive metal area spreads
out. A conductive wiring pattern having satisfactory definition can
be manufactured by a simple inexpensive process.
[0035] The wiring board preparing method of the invention can
fabricate, through simple and inexpensive steps, a wiring board
which has high heat resistance and a high degree of pattern
definition and can be used in a variety of applications in the
electric, electronic and communication fields.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 schematically illustrates a wiring board preparing
method according to the third embodiment of the invention.
[0037] FIG. 2 schematically illustrates a wiring board preparing
method according to the fourth embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The polysilane composition according to the invention is
defined as comprising a polysilane, a carbon functional silane (CF
silane), and a solvent in which these components are dissolved. The
composition is effective for forming a coating suitable for bearing
a metal pattern thereon.
[0039] The polysilane used herein may be of any type as long as it
can form a coating. Preferably, the polysilane is of the following
formula (1):
(R.sup.1.sub.mR.sup.2.sub.nX.sub.pSi).sub.q (1)
[0040] wherein R.sup.1 and R.sup.2 each are hydrogen or a
substituted or unsubstituted monovalent hydrocarbon group, X is
hydrogen or a substituted or unsubstituted monovalent hydrocarbon
group, alkoxy group or halogen atom, m is a number of 0.1 to 2, n
is a number of 0 to 1, p is a number of 0 to 0.5, the sum of m+n+p
is from 1 to 2.5, and q is an integer of 4 to 100,000.
[0041] The monovalent hydrocarbon groups represented by R.sup.1 and
R.sup.2 include substituted or unsubstituted aliphatic, alicyclic
and aromatic hydrocarbon groups. Preferred aliphatic and alicyclic
hydrocarbon groups are those of 1 to 12 carbon atoms, especially 1
to 8 carbon atoms, for example, but not limited to, alkyl and
cycloalkyl groups such as methyl, ethyl, propyl, butyl, pentyl,
hexyl, cyclopentyl and cyclohexyl. Preferred aromatic hydrocarbon
groups are those of 6 to 14 carbon atoms, especially 6 to 10 carbon
atoms, for example, but not limited to, aryl groups such as phenyl,
tolyl, xylyl and naphthyl and aralkyl groups such as phenylethyl.
The substituted hydrocarbon groups are the above-described
unsubstituted aliphatic, alicyclic and aromatic hydrocarbon groups
in which some or all of the hydrogen atoms are replaced by halogen
atoms, alkoxy groups, amino groups, aminoalkyl groups and other
substituents, for example, but not limited to, monofluoromethyl,
trifluoromethyl, p-dimethylaminophenyl, and
m-dimethylaminophenyl.
[0042] X represents groups as defined for R.sup.1 or alkoxy groups
or halogen atoms. Exemplary alkoxy groups are those of 1 to 4
carbon atoms, such as methoxy and ethoxy. Preferred halogen atoms
are fluorine, chlorine and bromine. Of these, chlorine atoms,
methoxy and ethoxy groups are preferable. It is noted that the
group represented by X is effective for preventing the polysilane
coating from separating from the substrate and thus improving the
adhesion of the coating to the substrate.
[0043] The letters m, n and p are numbers satisfying
0.1.ltoreq.m.ltoreq.2, preferably 0.5.ltoreq.m.ltoreq.2, 0
.ltoreq.n.ltoreq.1, preferably 0.5.ltoreq.n.ltoreq.1,
0.ltoreq.p.ltoreq.0.5, preferably 0.ltoreq.p.ltoreq.0.2, and
1.ltoreq.m+n+p.ltoreq.2.5, preferably 1.5.ltoreq.m+n+p.ltoreq.2.5.
The letter q is an integer of 4.ltoreq.q.ltoreq.100,000, preferably
10.ltoreq.q.ltoreq.10,000.
[0044] The polysilane of formula (1) can be readily synthesized,
for example, by adding an alkali metal catalyst (e.g., metallic
sodium) to an organic solvent (e.g., toluene) in a nitrogen stream,
and agitating the mixture at a high speed while heating, thereby
effecting dispersion. To the dispersion, a silicon compound (e.g.,
dichloroorganosilane) is slowly added dropwise in an amount of
about 1 mol of the silicon compound relative to 2 or 3 mol of
metallic sodium. The reaction solution is agitated for 1 to 8 hours
until the silicon compound disappears. After the completion of
reaction, the reaction solution is allowed to cool down, filtered
to remove the salt, and concentrated.
[0045] The CF silane is preferably of the following general formula
(3):
Y--(CH.sub.2).sub.b--SiR.sub.a(OR).sub.3-a (3)
[0046] wherein Y is a functional group such as a vinyl, epoxy,
amino, mercapto, methacryloxy or acryloxy functional group, R is a
substituted or unsubstituted monovalent hydrocarbon group, b is an
integer of 0 to 3, and a is equal to 0 or 1.
[0047] R represents monovalent hydrocarbon group as defined above
for R.sup.1 and R.sup.2, preferably alkyl groups of 1 to 5 carbon
atoms. An exemplary vinyl functional group is CH.sub.2.dbd.CH--,
exemplary epoxy functional groups are .gamma.-glycidoxy and
3,4-epoxycyclohexyl, exemplary amino functional groups are
NH.sub.2-- and NH.sub.2CH.sub.2CH.sub.2NH--, an exemplary mercapto
functional group is mercapto, exemplary methacryloxy and acryloxy
functional groups are methacryloxy and acryloxy.
[0048] Illustrative examples of the CF silane of formula (3)
include vinyltrimethoxysilane (KBM-1003), vinyltriethoxy-silane
(KBE-1003), .beta.-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane
(KBM-303), .gamma.-glycidoxypropyl-trimethoxysilane (KBM-403),
N-.beta.-(aminoethyl)-.gamma.-amino-propylmethyldimethoxysilane
(KBM-602),
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane
(KBM-603), .gamma.-aminopropyl-trimethoxysilane (KBM-903), and
.gamma.-aminopropyltriethoxysilane (KBE-903), all commercially
available under the indicated trade name from Shin-Etsu Chemical
Co., Ltd. Of these, amino group-containing CF silanes: KBM-602,
KBM-603, KBM-902, KBM-903, KBE-602, KBE-603, KBE-902 and KBE-903
are preferable.
[0049] An appropriate amount of the CF silane added is 0.01 to 200
parts, especially 0.1 to 10 parts by weight per 100 parts by weight
of the polysilane. Outside the range, a less amount of the CF
silane would fail to achieve sufficient adhesion whereas an
excessive amount of the CF silane would sometimes adversely affect
film formation and rather lower the adhesion.
[0050] The addition of the CF silane improves the strength of a
polysilane coating and permits the polysilane coating to readily
capture a palladium salt when the palladium salt is brought into
contact therewith, which in turn, enables that a metal film (e.g.,
of copper) having improved adhesion to the substrate is formed by
electroless plating.
[0051] The polysilane and the CF silane are dissolved in a suitable
organic solvent. Examples of the solvent used herein include
aromatic hydrocarbon solvents such as benzene, toluene and xylene,
ether solvents such as tetrahydrofuran and dibutyl ether, alcohol
solvents such as methanol and ethanol, alkoxyethanol solvents such
as ethyl cellosolve and methyl cellosolve, ketone solvents such as
acetone and methyl ethyl ketone, ester solvents such as ethyl
acetate, butyl acetate, methyl lactate, and ethyl lactate, and
ether ester solvents such as PGMEA. An appropriate amount of the
solvent used is about 10 to about 10,000 parts by weight per 100
parts by weight of the silicon components (polysilane and CF
silane) combined.
[0052] To the composition, inorganic powders such as fumed silica
and alkoxysilanes such as tetraethoxysilane may be added if
necessary.
[0053] The metal pattern forming method according to the second
embodiment of the invention uses the above-defined polysilane
composition and involves the steps of:
[0054] (1) forming a polysilane pattern on a substrate by an
imprinting, ink jet printing or lithographic process, and
[0055] (2) immersing the substrate in a solution of a catalytic
metal salt such as a palladium salt and then in an electroless
plating bath for depositing a metal on the pattern.
[0056] If desired, the substrate resulting from step (1) and/or (2)
is subjected to UV irradiation or heating for improving the
adhesion between the metal and the substrate. There is obtained a
substrate having a metal pattern formed thereon and firmly adhered
thereto.
[0057] The substrate used herein may be made of insulating
materials such as glass, ceramics and plastics, semiconductors such
as silicon, and conductors such as copper. Among these, resins or
plastics such as phenolic resins, polyester resins, epoxy resins,
polyimide resins, and bismaleimide triazine resins are
preferable.
[0058] The imprinting, ink jet printing and lithographic processes
are included in conventional printing processes. They have the
following features when used in forming a patterned coating of
polysilane on a substrate surface.
[0059] The imprinting process involves immersing a rubber plate
having a pattern of raised portions in a polysilane composition,
and pressing the rubber plate against a substrate for thereby
transferring the silicon components (polysilane and CF silane) on
the raised portions to the substrate. Although the number of
printable members is small, the imprinting process is advantageous
in that a metal pattern can be formed even on a curved surface.
[0060] The ink jet printing process is by ejecting toward a
substrate droplets of the polysilane composition having a size of a
picoliter order through nozzle orifices in accordance with record
signals to form a pattern. This process is advantageous in forming
a micropattern.
[0061] The lithographic process uses a lithographic plate having
image areas and non-image areas arranged on a support in a planar
fashion. When the polysilane composition is supplied to the surface
of the plate, the silicon components (polysilane and CF silane)
adhere to only the lipophilic image areas. This process is
advantageous in operation, economy and the number of printable
members.
[0062] After a pattern of silicon components (polysilane and CF
silane) is formed on a substrate by any of the above-described
processes, the pattern is preferably dried by allowing the
substrate to stand for some time in a dry atmosphere or keeping the
substrate in vacuum at a temperature of about 40 to 150.degree. C.
The polysilane composition used preferably has a concentration of
0.1 to 50% by weight whereby a pattern of silicon components
(polysilane and CF silane) is formed to a thickness of 0.01 to 100
.mu.m.
[0063] Next, the substrate having a pattern of silicon components
formed thereon is immersed in a solution of a catalytic metal salt
such as a palladium or silver salt and then in an electroless
plating solution.
[0064] The palladium salt used herein contains Pd.sup.2+ and is
generally represented by Pd-Z.sub.2 wherein Z is a halogen such as
Cl, Br or I, acetate, trifluoroacetate, acetylacetonate, carbonate,
perchlorate, nitrate, sulfate or oxide. Preferred exemplary
palladium salts are PdCl.sub.2, PdBr.sub.2, PdI.sub.2,
Pd(OCOCH.sub.3).sub.2, Pd(OCOCF.sub.3).sub.2, PdSO.sub.4,
Pd(NO.sub.3).sub.2, and PdO. A halide such as hydrochloric acid or
sodium chloride may be added to the palladium salt solution in
order to enhance the stability thereof.
[0065] For the solution, there is used a solvent in which the
palladium salt is highly soluble and which does not dissolve or
attack the pattern of silicon components. Exemplary solvents
include water, ketones such as acetone and methyl ethyl ketone,
esters such as ethyl acetate, alcohols such as methanol and
ethanol, and aprotic polar solvents such as dimethylformamide,
dimethyl sulfoxide and hexamethylphosphoric triamide, as well as
nitromethane and acetonitrile. Among others, water is most
preferable.
[0066] The substrate is immersed in the palladium salt solution for
about 1 second to about 10 minutes, washed with water and dried.
There is obtained the substrate on which the palladium salt has
been reduced into palladium particles on the polysilane pattern
surface. If desired, the substrate is heat treated at 40 to
200.degree. C. for promoting the reduction into palladium on the
polysilane surface. Drying is generally effected at 10 to
200.degree. C. under atmospheric pressure or vacuum.
[0067] Next, the structure is immersed in an electroless plating
solution, from which a metal film deposits while palladium serves
as the catalyst.
[0068] The electroless or chemical plating solution used herein is
preferably a solution containing a metal ion such as copper,
nickel, palladium, gold, platinum or rhodium. The electroless
plating solution is generally prepared by formulating in water a
water-soluble metal salt, a reducing agent (e.g., sodium
hypophosphite, hydrazine, sodium boron hydride or
dimethylaminoboran), and a complexing agent (e.g., sodium acetate,
phenylenediamine or sodium potassium tartrate). Suitable
electroless plating solutions are commercially available at
reasonable costs.
[0069] Appropriate contact conditions with the electroless plating
solution include a temperature of 15 to 120.degree. C., especially
25 to 85.degree. C. and a time of 1 minute to 16 hours, especially
10 to 60 minutes. It is practical to deposit a metal film to a
thickness of 0.01 to 100 .mu.m, especially 0.1 to 20 .mu.m although
the thickness varies with a particular purpose.
[0070] After the electroless plating, the structure is heated for
improving the adhesion between the metal and the substrate, if
desired. For example, the substrate is heated in an inert
atmosphere such as argon or in vacuum, at a temperature of 60 to
300.degree. C. for about 1 minutes to about 24 hours. Then the
metal film resulting from electroless plating has a higher
conductivity and hardness and better adhesion to the substrate.
[0071] Accordingly, the invention is successful in forming an
adherent metal pattern by way of an imprinting, ink jet printing or
lithographic process which is a simple inexpensive process
eliminating a need for exposure and development steps. The metal
pattern forming method of the invention can form on any type of
substrate a metal pattern having improved adhesion between the
metal and the substrate by a simple inexpensive process. Since the
metal patterns can find use as printed circuit boards, flexible
switches, battery electrodes, solar batteries, sensors, antistatic
protective films, electromagnetic shield casings, integrated
circuits, motor casings, and flat display panels, the inventive
method is useful in the electric, electronic and communication
fields.
[0072] Next, the method for preparing a wiring board according to
the third and fourth embodiments of the invention is described.
[0073] The method according to the third embodiment is to prepare a
wiring board through the following successive steps (1) to (3).
There is obtained a printed wiring board having a fine metal
pattern featuring improved adhesion between the substrate resin and
the metal.
[0074] The method according to the third embodiment includes the
steps of:
[0075] (1) forming a CF-silane containing polysilane thin film on a
substrate and contacting a palladium salt with a surface of the
polysilane thin film to form a palladium colloid layer thereon,
[0076] (2) forming a photosensitive resin layer on the polysilane
thin film having the palladium colloid layer, selectively
irradiating light to the layer, and developing the layer, to
thereby form a predetermined pattern of channels in the
photosensitive resin layer so that the polysilane thin film having
the palladium colloid layer is exposed within the channels, and
[0077] (3) contacting an electroless plating solution with the
polysilane thin film having the palladium colloid layer exposed
within the channels, for thereby forming a conductive metal layer
within the channels.
[0078] Referring to FIG. 1, step (1) includes forming a CF-silane
containing polysilane thin film 2 on a substrate 1 and contacting a
palladium salt with a surface of the polysilane thin film 2 to form
a palladium colloid layer 3 thereon.
[0079] The polysilane and CF silane used in forming the CF-silane
containing polysilane thin film on the substrate are preferably
those of formulae (1) and (3) defined above, respectively.
[0080] The substrate on which the CF-silane containing polysilane
thin film is to be formed may be made of insulating materials such
as quartz glass, ceramics, plastics, and resins, semiconductors
such as silicon, and conductors such as copper. Among these, resins
or plastics such as phenolic resins, polyester resins, epoxy
resins, polyimide resins, and bismaleimide triazine resins are
preferable.
[0081] In forming the CF-silane containing polysilane thin film,
any desired technique may be used, for example, conventional
polysilane thin film forming techniques such as spin coating,
dipping, casting, vacuum evaporation and Langmuir-Blodgett (LB)
techniques. Preferred is the spin coating technique including
mixing a polysilane with a CF silane, dissolving them in a suitable
solvent, and applying the solution to the substrate while rotating
the substrate at a high speed.
[0082] In connection with the spin coating technique used in
forming the CF-silane containing polysilane thin film, the solvent
in which the polysilane and CF silane are dissolved may be selected
from aromatic hydrocarbon solvents such as benzene, toluene and
xylene, and ether solvents such as tetrahydrofuran and dibutyl
ether. The solvent is preferably used in such amounts that the
solution may have a polysilane plus CF silane concentration of 1 to
20% by weight. After the CF-silane containing polysilane thin film
is formed, it is preferably dried by allowing it to stand for some
time in a dry atmosphere or keeping it at about 40 to 60.degree. C.
in vacuum. In step (1), the CF-silane containing polysilane thin
film formed on the substrate preferably has a thickness of 0.01 to
100 .mu.m, especially 0.1 to 10 .mu.m.
[0083] Since the thin film formed on the substrate contains the
polysilane and CF silane as main components, the film not only has
a high strength, but also readily captures a palladium salt when
the palladium salt is brought into contact therewith. Thus a
palladium colloid layer is readily formed on the polysilane thin
film. This, in turn, enables that a conductive metal layer (e.g.,
of copper) having improved adhesion to the substrate is formed by
electroless plating.
[0084] Next, the CF-silane containing polysilane thin film formed
on the substrate is contacted with a palladium salt. Contact is
preferably effected by treating the substrate with a solution
containing a palladium salt. The palladium salt used herein
contains Pd.sup.2+ and is generally represented by Pd-Z.sub.2
wherein Z is a halogen such as Cl, Br or I, acetate,
trifluoroacetate, acetylacetonate, carbonate, perchlorate, nitrate,
sulfate or oxide. Preferred exemplary palladium salts are
PdCl.sub.2, PdBr.sub.2, PdI.sub.2, Pd(OCOCH.sub.3).sub.2,
Pd(OCOCF.sub.3).sub.2, PdSO.sub.4, Pd(NO.sub.3).sub.2, and PdO.
[0085] For contacting the thin film with the palladium salt, a
solution technique is preferably employed. The solution technique
includes dissolving or dispersing the palladium salt in a suitable
solvent and immersing in the solution or dispersion the substrate
having the CF-silane containing polysilane thin film formed
thereon.
[0086] In the solution technique, there is used a solvent in which
the palladium salt is highly soluble and which does not dissolve
the CF-silane containing polysilane thin film. Exemplary solvents
include water, ketones such as acetone and methyl ethyl ketone,
esters such as ethyl acetate, alcohols such as methanol and
ethanol, and aprotic polar solvents such as dimethylformamide,
dimethyl sulfoxide and hexamethylphosphoric triamide, as well as
nitromethane and acetonitrile. Among others, water and alcohols
such as ethanol are most preferable. A halide such as hydrochloric
acid or sodium chloride may be added to the palladium salt solution
in order to enhance the stability thereof.
[0087] The CF-silane containing polysilane thin film is preferably
immersed in the palladium salt solution or dispersion for about 1
second to about 10 minutes. The immersion is preferably followed by
drying. Then, the palladium salt is reduced into palladium
particles on the surface of the CF-silane containing polysilane
thin film. There is obtained the substrate having a palladium
colloid layer formed thereon. After the contact with the palladium
salt, if desired, the substrate is heat treated at 40 to
200.degree. C. for promoting the reduction of the palladium salt
into palladium on the CF-silane containing polysilane thin film
surface. Drying is generally effected at 10 to 200.degree. C. under
atmospheric pressure or vacuum.
[0088] In the subsequent step (2), a photosensitive resin layer 4
is formed on the palladium colloid layer 3. The photosensitive
resin layer 4 is selectively irradiated with light and developed to
form a predetermined pattern of channels 5 (only one channel is
shown) in the photosensitive resin layer 4. The polysilane thin
film 2 having the palladium colloid layer 3 is exposed within the
channel 5, forming a pattern latent image.
[0089] For the photosensitive resin layer, either a positive resist
or a negative resist may be used. In general, using a variety of
existing photosensitive resins such as novolac-photoacid generator
systems, chemically amplified silicon polymer systems, and
polysilane systems which are known as positive working resist
material, a layer may be formed in a conventional manner. The
invention favors the use of polysilane resist materials, but not
limited thereto.
[0090] In step (2), a photomask 6 of a predetermined pattern is
positioned over the photosensitive resin layer 4 on the substrate
1. UV or visible light is irradiated from a suitable light source
to the photosensitive resin layer 4 through the mask 6. Then, in
the case of positive resist, only the exposed area of the
photosensitive resin layer is converted to be soluble in a suitable
solvent whereupon development is effected with the solvent to form
the predetermined pattern of channels 5. The CF-silane containing
polysilane thin film 2, specifically the palladium colloid layer 3,
becomes exposed in the channels 5. The thickness of the
photosensitive resin layer is desirably approximate to that of a
metal thin film to be formed, typically 0.1 to 10 .mu.m. Since the
CF-silane containing polysilane film absorbs light or UV radiation
and provides anti-reflection effect in the exposure step, the
pattern shape is well retained.
[0091] The light source used herein may be a UV light source or
visible light source. Illustrative examples are continuous spectrum
light sources such as hydrogen discharge lamps, rare gas discharge
lamps, tungsten lamps, and halogen lamps, lasers such as KrF and
ArF lasers, and discontinuous spectrum light sources such as
mercury lamps. A choice of the light source depends on the type of
photosensitive resin. Mercury lamps having a radiation source of
248 to 254 nm in wavelength are preferable because of low costs and
ease of handling. The light source preferably has a light quantity
of 0.01 to 10 mJ/cm.sup.2, especially 0.1 to 1 mJ/cm.sup.2, per
photosensitive resin layer thickness of 0.1 .mu.m. If the light
quantity is below the range, the underlying CF-silane containing
polysilane thin film would be insufficiently exposed. A light
quantity above the range would cause the CF-silane containing
polysilane to be converted into a siloxane having no palladium
reducing capability. These situations are detrimental to the
subsequent formation of a satisfactory metal pattern.
[0092] After the light exposure, development is carried out. That
is, the exposed area (in the case of positive resist) or unexposed
area (in the case of negative resist) is removed using a developer.
The developer used herein is a solution which can dissolve away
only the exposed area (in the case of positive resist) or unexposed
area (in the case of negative resist). It may be either an organic
solvent or an aqueous base solution. By this development, the
predetermined pattern of channels 5 is formed in the photosensitive
resin layer 4. The CF-silane containing polysilane thin film 2
having the palladium colloid layer 3 is exposed within the channel
5.
[0093] In step (3), an electroless plating solution is contacted
with the CF-silane containing polysilane thin film 2 having the
palladium colloid layer 3 within the channel 5 to deposit a
conductive metal layer 7 within the channel 5.
[0094] The electroless plating solution used herein is as
previously described. Appropriate contact conditions with the
electroless plating solution include a temperature of 15 to
120.degree. C., especially 25 to 85.degree. C. and a time of 1
minute to 16 hours, especially 10 to 60 minutes. It is practical to
deposit a metal film to a thickness of 0.01 to 100 .mu.m,
especially 0.1 to 20 .mu.m although the thickness varies with a
particular purpose.
[0095] After step (3), the following step is carried out if
desired. The structure resulting from step (3) is treated with a
solvent for removing the photosensitive resin layer, or heated for
further improving the adhesion between the metal and the substrate.
If the photosensitive resin layer is formed of a polysilane base
material, heat treatment is carried out at high temperatures to
convert all polymer layers into ceramic or insulating layers and
further stabilize the conductive metal layer formed by electroless
plating. As a result, a wiring board having a more adherent metal
pattern is obtained. For example, by the heat treatment at high
temperatures of the structure resulting from step (3), all the
polymer layers are converted into insulating layers consisting of
ceramic material and the conductive metal layer resulting from
electroless plating is stabilized. The heat treatment is generally
effected at a temperature of about 200 to 1,200.degree. C. for
about 1 minute to about 24 hours and desirably, at about 300 to
900.degree. C. for about 1/2 to 4 hours. Through the
high-temperature treatment, the metal layer resulting from
electroless plating acquires a higher conductivity and hardness and
the ceramic converted from the polysilane possesses a higher heat
resistance, insulating property and adhesion.
[0096] It is noted that by the high-temperature treatment of
polysilane, Si-to-Si bonds are severed allowing various elements to
be incorporated therein so that the material is stabilized. That
is, the high-temperature treatment leads to the formation of a
silicon oxide base ceramic material if the treatment is effected in
an oxidizing atmosphere, typically air, a silicon nitride base
ceramic material if effected in a reducing atmosphere, typically
ammonia gas, or a silicon carbide base ceramic material if effected
in an inert atmosphere, typically argon or in vacuum.
[0097] The method according to the fourth embodiment includes the
steps of:
[0098] (I) forming a thin film of a polysilane with SiH group on a
substrate and irradiating light to the thin film for crosslinking
the polysilane for thereby insolubilizing the polysilane,
[0099] (II) forming a photosensitive resin layer on the crosslinked
polysilane thin film, selectively irradiating light to the layer,
and developing the layer, to thereby form a predetermined pattern
of channels in the photosensitive resin layer so that the
crosslinked polysilane thin film is exposed within the channels,
and
[0100] (III) contacting a palladium salt with the crosslinked
polysilane thin film exposed within the channels to form a
palladium colloid layer and contacting an electroless plating
solution for thereby forming a conductive metal layer within the
channels.
[0101] There is obtained a printed wiring board having a metal
pattern featuring a high degree of definition.
[0102] Referring to FIG. 2, step (I) includes forming a SiH
group-containing polysilane thin film 8 on a substrate 1. The
polysilane thin film formed on the substrate is preferably formed
of a material primarily comprising a polysilane of the following
general formula (2).
(H.sub.mR.sup.2.sub.nX.sub.pSi).sub.q (2)
[0103] wherein R.sup.2 is hydrogen or a substituted or
unsubstituted monovalent aliphatic, alicyclic or aromatic
hydrocarbon group, X is as defined for R.sup.2 or an alkoxy group
or halogen atom, m is a number of 0.1 to 2, n is a number of 0 to
1, p is a number of 0 to 0.5, the sum of m+n+p is from 1 to 2.5,
and q is an integer of 4 to 100,000. Illustrative examples of the
groups represented by R.sup.2 and X and the preferred ranges of m,
n, p and q are as described above for formula (1).
[0104] It is known from Fukushima et al., Chem. Lett., 1998, 347
that upon exposure to light, typically UV radiation, a polysilane
having SiH bonds in a molecule represented by formula (2) undergoes
crosslinking reaction and turns to be insoluble in solvents. In the
method of the fourth embodiment of the invention, a polysilane
having SiH bonds in a molecule undergoes crosslinking reaction and
becomes insolubilized upon exposure to UV, and this polymer even
after crosslinking by light exposure is effective for readily
reduce a palladium salt to form a palladium colloid, which enables
formation of a metal film (e.g., of copper) by electroless
plating.
[0105] The substrate, the method of forming a polysilane film, the
solvent in which polysilane is soluble, and the forming conditions
are the same as in the third embodiment. The polysilane thin film
formed on the substrate preferably has a thickness of 0.01 to 100
.mu.m, especially 0.1 to 10 .mu.m.
[0106] Then, the polysilane thin film 8 on the substrate 1 is
irradiated with light (shown by arrows) whereby the polysilane is
crosslinked for insolubilization, resulting in a crosslinked
polysilane thin film 8'.
[0107] The light source used herein preferably emits light having a
wavelength of at least 300 nm and may be a UV light source or
visible light source. Illustrative examples are continuous spectrum
light sources such as hydrogen discharge lamps, rare gas discharge
lamps, tungsten lamps, and halogen lamps, lasers, and discontinuous
spectrum light sources such as mercury lamps. Mercury lamps are
preferable because of low costs and ease of handling. The light
source preferably has a light quantity of 0.001 to 100 J/cm.sup.2,
especially 0.1 to 1 J/cm.sup.2, per polysilane film thickness of 1
.mu.m. A light quantity below the range would result in short
crosslinking whereas a light quantity above the range would be
detrimental to the subsequent formation of a palladium colloid in
step (III).
[0108] Step (II) includes forming a photosensitive resin layer 4 on
the crosslinked polysilane thin film 8' on the substrate,
selectively irradiating light to the layer, and developing the
layer, to thereby form a predetermined pattern of channels in the
photosensitive resin layer 4 so that the crosslinked polysilane
thin film 8' is exposed within the channel 5. The photosensitive
resin layer may be formed as in the third embodiment and patterned
using a patterned photomask 6 as in the third embodiment.
Similarly, development is effected as in the third embodiment.
[0109] The thickness of the photosensitive resin layer is 30
desirably approximate to that of a metal thin film to be formed,
typically 0.1 to 10 .mu.m. Since the polysilane film absorbs UV
radiation and provides anti-reflection effect in the exposure step,
the pattern shape is well retained.
[0110] The light source used herein is preferably a laser 35 such
as KrF or ArF laser or a mercury lamp having a radiation source of
248 to 254 nm in wavelength. A stepper or scanner type exposure
equipment having such a light source incorporated therein is
preferably used. For the photomask, masks of the Levenson or
halftone type based on the phase-shift mask technology may be
used.
[0111] Step (III) includes contacting a palladium salt with the
grooved photosensitive resin layer-bearing substrate to form a
palladium colloid layer 9 on the crosslinked polysilane thin film
8' exposed within the channel 5, removing the unnecessary palladium
salt, and contacting an electroless plating solution with the
palladium colloid layer-bearing crosslinked polysilane film 8' for
thereby forming a conductive metal layer 7 on the crosslinked
polysilane film 8' within the channel 5.
[0112] More specifically, step (III) includes:
[0113] step (III-1) of contacting a palladium salt with the
structure resulting from step (II) to form a palladium colloid
layer 9 at least on the crosslinked polysilane thin film 8' exposed
within the channel 5 in the photosensitive resin layer 4,
[0114] step (III-2) of washing the structure resulting from step
(III-1) to remove an unnecessary palladium salt layer 10, and
[0115] step (III-3) of contacting an electroless plating solution
with the structure resulting from step (III-2) to form a conductive
metal layer 7 on the crosslinked polysilane film 8' and the
palladium colloid layer 9 within the channel 5.
[0116] First described is step (III-1). For contacting the thin
film with the palladium salt, a technique as used in the third
embodiment may be used while the palladium salt and its solution
used may also be the same as in the third embodiment. Similarly,
the palladium salt is contacted with the polysilane film using a
solvent which does not dissolve the polysilane film, but in which
the palladium salt is dissolved or dispersed, thereby forming a
palladium colloid layer. In such a solution technique, a solvent
which fully dissolves the palladium salt, but does not attack the
pattern of polysilane is advantageously used. The solvent may be
selected from the solvents exemplified in the solution technique of
the third embodiment as the solvent for dissolving the palladium
salt although a choice of the solvent depends on the solubility
therein of a particular photosensitive resin used. Of these
solvents, alcohols such as ethanol are favorable when
phenylmethylpolysilane is used as the photosensitive resin.
[0117] The palladium salt is dissolved or dispersed in such a
solvent. The structure having the pattern of channels formed
subsequent to exposure is immersed in the solution or dispersion
for about 1 second to 10 minutes, followed by drying. On the
exposed area of the polysilane thin film within the patterned
channel, which is hydrophilic, the palladium salt is reduced into
palladium particles. On the unexposed area of the photosensitive
resin layer, no palladium particles are formed. That is, an
(unnecessary) palladium salt layer 10 is left on the photosensitive
resin layer 4. In this way, the desirably patterned polysilane
film-bearing substrate is obtained. Furthermore, if desired, the
resulting structure is heat treated at a temperature of about 40 to
200.degree. C. for promoting the reduction of the palladium salt
into palladium on the polysilane thin film. Drying is desirably
effected at a temperature of 10 to 200.degree. C. under atmospheric
pressure or in vacuum.
[0118] In step (III-2), the structure resulting from step (III-1)
is washed to remove the unnecessary palladium salt layer 10. To
this end, the structure is immersed in the solvent which can
dissolve the palladium salt. Alternatively, the surface of the
structure is scraped off by mechanical grinding. The unnecessary
palladium salt layer 10 left on the photosensitive resin layer 4 is
readily removed in this way. Whether the removal step is by
dissolution or mechanical grinding, the palladium colloid layer
within the channel is left intact after the removal step because
palladium has been changed from ion to colloid.
[0119] In step (III-3), the structure resulting from step (III-2)
is contacted with an electroless plating solution whereby a
conductive metal layer 7 deposits on the crosslinked polysilane
film 8' and specifically the palladium colloid layer 9 within the
channel 5. The type of electroless plating solution and the plating
conditions are the same as in the third embodiment.
[0120] After step (III), the structure may be treated as in the
third embodiment. There is obtained a wiring board having a metal
pattern featuring a high degree of definition.
[0121] The wiring board preparing method of the invention can form
a metal wiring pattern having improved heat resistance and a high
degree of definition by a simple inexpensive process. Specifically,
the wiring board preparing method according to the third embodiment
of the invention can form on any type of resin substrate a metal
wiring pattern having improved adhesion between the metal and the
substrate and a high degree of definition. The wiring board
preparing method according to the fourth embodiment of the
invention can form a conductive metal layer having improved
adhesion between the metal and the substrate in a pattern having a
high degree of definition. There is obtained a board having a high
definition metal circuit formed thereon which is applicable to
logic circuits and memory devices. Since the conductive wiring
patterns can find use as printed circuit boards, various devices,
flexible switches, battery electrodes, solar batteries, sensors,
antistatic protective films, electromagnetic shield casings,
integrated circuits, and motor casings, the wiring board preparing
method is useful in the electric, electronic and communication
fields.
EXAMPLE
[0122] Examples of the invention are given below by way of
illustration and not by way of limitation. All parts are by
weight.
Synthetic Example 1
[0123] Synthesis of phenylhydrogenpolysilane (PPHS)
[0124] To a flask purged with argon, a diethyl ether solution of
bis(cyclopentadienyl)dichlorozirconium was added, whereby
bis(cyclopentadienyl)dimethylzirconium serving as a catalyst was
prepared in the system. Per mol of this
bis(cyclopentadienyl)dimethylzirconium, 50 mol of phenylsilane was
added. The mixture was heated and stirred at 100.degree. C. for 24
hours. A molecular sieve was added to the reaction solution, which
was filtered to remove the catalyst. Phenylhydrogenpolysilane
having a weight average molecular weight of 2,600 was obtained as
solids in a substantially quantitative manner.
Synthetic Example 2
[0125] Synthesis of phenylmethylpolysilane (PMPS)
[0126] In a nitrogen stream, 5.06 g (220 mmol) of metallic sodium
was added to 60 ml of toluene. While heating at 110.degree. C., the
mixture was agitated at a high speed for dispersion. To the
dispersion, 19.1 g (100 mmol) of phenylmethyldichlorosilane was
slowly added dropwise with stirring. Agitation was continued for 4
hours until the reactant disappeared, completing the reaction.
After the reaction solution was allowed to cool down, the salt was
filtered off, and the residue was concentrated, obtaining 10.0 g
(crude yield 83%) of a polysilane crude product. This polymer was
dissolved in 30 ml of toluene again and 120 ml of hexane was added
whereupon the polymer precipitated and separated. There was
obtained 6.6 g (yield 55%) of phenylmethylpolysilane having a
weight average molecular weight of 45,000.
Example 1 and Comparative Example 1
[0127] In 9.2 g of toluene were dissolved 0.8 g of the polysilane
(phenylhydrogenpolysilane, abbreviated as PPHS) synthesized in
Synthetic Example 1 and 8 mg of
N-.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxys- ilane as a
CF-silane (corresponding to 1 part of the CF-silane per 100 parts
by weight of the polysilane). This polysilane composition was
applied onto a glass fiber-filled epoxy resin substrate by an
imprinting, ink jet printing or lithographic process to form a
pattern of silane components, which was dried at 50.degree. C. and
2 mmHg. This is Step 1.
[0128] Next, the above substrate was immersed for one minute in a
3% aqueous solution of palladium chloride and washed with water.
The treated substrate was then immersed in an electroless plating
solution, which contained 20 g of nickel sulfate, 20 g of sodium
hypophosphite and 30 g of sodium acetate in 1,000 g of water, at
80.degree. C. for 10 minutes whereby a nickel metal pattern was
formed. The substrate was washed with pure water, dried at
60.degree. C. for 5 minutes, and heat treated in nitrogen at
150.degree. C. for 1/2 hour. There was obtained a glass
fiber-filled epoxy resin substrate having a nickel pattern formed
thereon. This is Step 2.
[0129] The nickel section of the structure had a conductivity of
1.times.10.sup.4 S/cm and the substrate section had a conductivity
of 1.times.10.sup.-9 S/cm. The nickel pattern had a fineness of 100
.mu.m when the imprinting process was used, 10 .mu.m when the ink
jet printing process was used, and 20 .mu.m when the lithography
was used. The adhesion between the nickel film and the substrate
was examined using an adhesive tape, finding no peeling.
[0130] In Comparative Example 1, the same procedure as above was
repeated except that the CF silane was omitted. In the adhesive
tape test, partial peeling of the nickel film from the substrate
was found. Also, the same procedure as above was repeated except
that the polysilane was omitted. Little nickel deposited on the
substrate.
Examples 2-6
[0131] The polysilane (PPHS) synthesized in Synthetic Example 1,
0.8 g, and a CF-silane, the type and amount of which are shown in
Table 1, were dissolved in 9.2 g of toluene to give a 8% solution.
This CF-silane containing polysilane composition was applied onto a
glass fiber-filled epoxy resin substrate by spin coating at 3,000
rpm for 10 seconds and dried at 50.degree. C. and 2 mmHg, forming a
thin film of 0.3 .mu.m thick. The epoxy resin substrate having the
polysilane thin film formed thereon was immersed for one minute in
a 3% ethanol solution of palladium chloride and then dried for 30
minutes at 35.degree. C. This is Step 1.
[0132] The polysilane (phenylmethylpolysilane, abbreviated as PMPS)
synthesized in Synthetic Example 2 was used as a photosensitive
resin. The PMPS was dissolved in toluene to form a 5% solution.
This polysilane solution was applied onto the quartz glass plate
having the CF-silane containing PPHS film formed thereon in Step 1,
by spin coating at 2,000 rpm for 5 seconds. Drying at 50.degree. C.
and 2 mmHg gave a photosensitive resin layer. The resulting
structure was a substrate on which a pattern was to be formed. The
thickness of the CF-silane containing PPHS film and the
photosensitive resin layer combined was 0.6 .mu.m. A photomask was
positioned over the substrate, which was exposed, using a 20-W
low-pressure mercury lamp, to UV radiation of 254 nm in a light
quantity of 10 J/cm.sup.2. By development with ethanol, the exposed
area was removed. This is Step 2.
[0133] The structure resulting from Step 2 was then immersed in an
electroless plating solution, which contained 20 g of nickel
sulfate, 10 g of sodium hypophosphite and 30 g of sodium acetate in
1,000 g of water, at 50.degree. C. for 30 minutes whereby a nickel
metal circuit was formed. This is Step 3.
[0134] The structure was washed with pure water, dried at
60.degree. C. for 5 minutes, and heat treated in nitrogen at
150.degree. C. for 1/2 hour. There was obtained a glass
fiber-filled epoxy resin substrate having a nickel pattern formed
thereon.
[0135] The nickel section of the structure had a conductivity of
1.times.10.sup.4 S/cm and the unexposed section had a conductivity
of 1.times.10.sup.-12 S/cm.
[0136] The adhesion between the nickel film and the substrate was
examined by the adhesive tape test, with the results being shown in
Table 1.
Comparative Example 2
[0137] The same procedure as above was repeated except that in Step
1, the polysilane film was formed using a CF silane-free
polysilane. There was obtained a glass fiber-filled epoxy resin
substrate having a nickel pattern formed thereon.
[0138] The adhesion between the nickel film and the substrate was
examined by the adhesive tape test, with the results being shown in
Table 1.
1 TABLE 1 CF silane, Adhesive tape test blend amount mg, (pph*) (%
adhesion) Example 2 KBM-603 Excellent 8 mg (1) (100) Example 3
KBM-603 Excellent (10) (95) Example 4 KBM-603 Good (50) (60)
Example 5 KBM-903 Excellent (1) (100) Example 6 KBM-403 Good (1)
(70) Comparative -- Poor Example 2 (5) *parts by weight of CF
silane per 100 parts by weight of polysilane
Example 7
[0139] The polysilane (PPHS) synthesized in Synthetic Example 1 was
dissolved in toluene to give a 8% solution. The polysilane solution
was applied onto a quartz glass plate by spin coating at 3,000 rpm
for 10 seconds and dried at 50.degree. C. and 2 mmHg, forming a
thin film of 0.3 .mu.m thick. The entire surface of the substrate
was exposed to UV radiation in a light quantity of 100 mJ/cm.sup.2
using a low-pressure mercury lamp of 20 W and an alkali glass
filter of 0.1 mm thick for cutting UV radiation having a wavelength
of shorter than 300 nm. By irradiation, the polysilane was
crosslinked and insolubilized. This is Step I.
[0140] The polysilane (PMPS) synthesized in Synthetic Example 2 as
a photosensitive resin was dissolved in toluene to form a 5%
solution. This polysilane solution was applied onto the quartz
glass plate having the crosslinked PPHS film formed thereon in Step
1, by spin coating at 3,000 rpm for 10 seconds. Drying at
50.degree. C. and 2 mmHg gave a photosensitive resin layer. The
resulting structure was a substrate on which a pattern was to be
formed. The thickness of the crosslinked PPHS film and the
photosensitive resin layer combined was 0.6 .mu.m. A photomask was
positioned over the structure, which was exposed, using a
low-pressure mercury lamp of 20 W, to UV radiation of 254 nm in a
light quantity of 5 J/Cm.sup.2. By development with ethanol, the
exposed area of PMPS was removed. This is Step II.
[0141] The structure resulting from Step II was contacted with a 3%
ethanol solution of palladium chloride (Step III-1). It was washed
with ethanol. The surface of the PMPS layer was ground to remove
the palladium on the surface (Step III-2). This structure was then
immersed in an electroless copper plating solution at 25.degree. C.
for 15 minutes. The electroless plating solution was a 1:1 (by
volume) mixture of a plating solution A containing 2.5 g of copper
sulfate pentahydrate, 11.3 g of potassium sodium tartrate
pentahydrate, and 2.8 g of potassium hydroxide in 83.4 g of water
and a plating solution B containing 7 g of a 37% formalin aqueous
solution in 93 g of water. This electroless plating formed a copper
circuit having a high degree of pattern definition. This is Step
III-3.
[0142] The structure was washed with pure water, dried at
60.degree. C. for 5 minutes, and heat treated at 100.degree. C. for
one hour. There was obtained a quartz glass substrate having a
conductive layer of copper formed within channels (wiring board).
The copper circuit section on the quartz glass substrate was
measured for conductivity and minimum line width. The conductivity
was measured by a four-probe method on the copper film. The line
width of the copper circuit was measured under a microscope. The
results are given below.
[0143] Conductivity: 1.times.10.sup.4 S/cm
[0144] Minimum line width: 1 .mu.m
[0145] It was confirmed that a metal pattern having a high degree
of definition was obtained.
Comparative Example 3
[0146] A quartz glass substrate was processed as in Example 7
except that the step of light irradiation for crosslinking was
omitted from Step I. On the resulting substrate, copper was present
only at the boundary between the exposed and unexposed areas and no
copper formed on the exposed and unexposed areas.
Comparative Example 4
[0147] A quartz glass substrate was processed as in Example 7
except that the step of light irradiation for crosslinking was
omitted from Step I and the step of PMPS surface grinding was
omitted from Step III-2. The copper circuit section on the quartz
glass substrate was measured for conductivity and minimum line
width by the same procedures as above. The results are given
below.
[0148] Conductivity: 1.times.10.sup.4 S/cm
[0149] Minimum line width: 20 .mu.m
[0150] Japanese Patent Application Nos. 10-300894 and 10-309793 are
incorporated herein by reference.
[0151] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
* * * * *