 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing a semiconductor
having a thin film of a fluorine resin as a protective film.
2. Discussion of Background
Heretofore, it has been usually difficult to form a thin film of a fluorine
resin by coating, since the fluorine resin is usually insoluble in a
solvent. However, fluorine resins soluble in special solvents have been
developed as disclosed in Japanese Unexamined Patent Publications No.
238111/1988 and No. 260932/1988 and U.S. Pat. No. 4,754,009, and their
application to semiconductor protective films utilizing their electrical
properties and low water absorptivity, has been disclosed in European
Patent 0393682.
On the other hand, an organic thin film used as a protective film of a
semiconductor is required to be subjected to fine processing such as local
perforation processing to take electrical connection or wire bonding, and
photolithography using a photoresist is usually employed for this purpose.
However, the above fluorine resins have a high fluorine content and an
extremely low surface energy, and therefore they tend to repel a
photoresist solution, whereby it has been difficult to uniformly coat it
by e.g. spin coating, and it has been difficult to apply fine processing
by photolithography.
Further, in order to improve the uniformity in the application of a
photoresist, it has been common to employ a method wherein an
adhesion-improving agent such as HMDS (hexamethyl disilazane) is coated in
a liquid state, and a photoresist is coated thereon, followed by
photolithography. However, the above-mentioned fluorine resins tend to
repel even such a solution, and it has been difficult to improve the
adhesion by coating. Thus, there has been a problem that it is required to
heat the adhesion-improving agent to conduct treatment by its vapor, or it
is required to improve the wettability of the surface by such a method as
vapor deposition of e.g. a metal.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve such drawbacks of the
conventional process for producing a semiconductor using a fluorine resin
as a protective layer and to provide a new process for producing a
semiconductor excellent in the electrical properties and the moisture
resistance.
The present inventors have conducted extensive studies with recognition of
the above problems and as a result, have found it possible to conduct fine
processing of a fluorine resin having a low surface energy by
incorporating a surfactant to a solution of a photoresist or an
adhesion-improving agent and thereby to produce a semiconductor having a
protective layer of such a fluorine resin.
Thus, the present invention has been accomplished on the basis of the above
discovery, and it provides a process for producing a semiconductor having
a thin film of a fluorine resin as a protective film, which comprises
coating on the surface of a fluorine resin a photoresist solution
containing a surfactant, followed by exposure, development and etching for
fine processing of the fluorine resin.
The present invention also provides a process for producing a semiconductor
having a thin film of a fluorine resin as a protective film, which
comprises coating on the surface of a fluorine resin a liquid containing a
surfactant, then coating a solution of a photoresist, followed by
exposure, development and etching for fine processing of the fluorine
resin.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present invention, the fluorine resin may be a fluorine resin
obtained by homopolymerizing or copolymerizing a fluorine-containing
monomer such as tetrafluoroethylene, chlorotrifluoroethylene,
hexafluoropropylene or a perfluoroalkyl vinyl ether, a fluorine-containing
polyimide, a fluorine-containing acrylic polymer or a polymer having a
fluorine-containing alicyclic structure. Among them, a polymer having a
fluorine-containing alicyclic structure is preferred from such viewpoints
that a thin film can be formed by coating, the dielectric constant is low
whereby an improvement in the response speed of a semiconductor element
can be expected, and the water absorptivity is low whereby an improvement
in the moisture resistant stability of the element can be expected.
In the present invention, as the polymer having a fluorine-containing
alicyclic structure, a wide range of polymers including known or well
known polymers may be mentioned. Thus, in the present invention, a
fluorine-containing polymer having such a specific cyclic structure in the
backbone chain is preferably employed.
For example, those having cyclic structures of the following formulas 1, 2,
3 and 4 may be mentioned. In the formulas 1, 2, 3 and 4, h is from 0 to 5,
i is from 0 to 4, k is from 0 to 1, h+i+k is from 1 to 6, R is F or
CF.sub.3, each of j, p and q is from 0 to 5, provided j+p+q is from 1 to
6, and each of R.sub.1 and R.sub.2 is F or CF.sub.3.
##STR1##
Among these, polymers having the following cyclic structures are
representative. However, it should be understood that the present
invention is by no means restricted to such specific examples.
##STR2##
The following two methods are available for the production of such
polymers. However, the present invention is by no means restricted to such
methods.
1. Cyclic polymerization
##STR3##
2. By means of a cyclic monomer (U.S. Pat. No. 3,978,030)
##STR4##
In the foregoing, polymers having perfluoroalicyclic structures have been
described. However, in the present invention, those corresponding to the
above described polymers wherein some of fluorine atoms are substituted by
hydrogen atoms or organic groups, or those having cyclic structures having
the following formulas 11 and 12, may also be employed:
##STR5##
Thus, the polymer having a specific cyclic structure in the present
invention can be smoothly and advantageously obtained by the cyclic
polymerization as described above. Particularly when a monomer having two
polymerizable groups having different polymerizability in one molecule,
wherein the number of atoms in the straight chain portion of the
connecting chain connecting the two polymerizable groups is from 2 to 7,
is used, the cyclic polymerization can be proceeded smoothly and
advantageously while suppressing gelation, without employing super high
pressure conditions or substantial diluting conditions.
Firstly, the monomer suitable for such cyclic polymerization preferably has
two carbon-carbon multiple bonds having different polymerizability.
Usually, carbon-carbon double bonds are employed. For example, a
fluorine-containing monomer having two multiple bonds having asymmetrical
structures, a combination of a vinyl group and an allyl group, a
combination of a vinyl ether group and a vinyl group, a combination of a
fluorine-containing multiple bond and a hydrocarbon multiple bond, or a
combination of a perfluoromultiple bond and a partially fluorinated
multiple bond, may be mentioned.
Secondly, the number of atoms in the straight chain portion of the
connecting chain which connects these two carbon-carbon multiple bonds, is
from 2 to 7. If the number of atoms in the straight chain portion of the
connecting chain is 0 or 1, the cyclic polymerization hardly takes place,
and the same is true also in the case where the number of atoms is 8 or
more. Usually, such a number of atoms is preferably from 2 to 5. The
connecting chain is not restricted to a straight chain, and may have a
side chain structure or a cyclic structure. Further, the constituting
atoms are not restricted to carbon atoms, but may include hetero atoms
such as O, S and N.
Thirdly, the one having a fluorine content of at least 10% by weight, is
preferred. If the fluorine content is too small, the specificity depending
on the fluorine atoms tends to be hardly obtainable. Needless to say, a
perfluoromonomer may suitably be employed.
Specific examples of such specific fluorine-containing monomer include the
following:
##STR6##
In the present invention, the one having one vinyl ether group of CF.sub.2
.dbd.CFO--is preferably employed from the viewpoint of the polymerization
reactivity, the cyclic polymerizability, the gelation suppression, etc.
Particularly preferred are perfluoroallyl vinyl ether (CF.sub.2
.dbd.CFOCF.sub.2 CF.dbd.CF.sub.2) and perfluorobutenyl vinyl ether
(CF.sub.2 .dbd.CFOCF.sub.2 CF.sub.2 CF.dbd.CF.sub.2).
The above-mentioned monomer components may be used alone or in combination
as a mixture of two or more of them. Further, to such an extent that the
essential characteristics of these components are not impaired, other
copolymerizable components may be incorporated and copolymerized. If
necessary, the polymer may be crosslinked by a certain method, as the case
requires.
Such other copolymerizable monomers are not particularly limited so long as
they are monomers having radical polymerizability, and a wide range of
fluorine-containing monomers, hydrocarbon monomers and other monomers, may
be mentioned. It is of course possible that these other monomers may be
used alone or in combination as a mixture of two or more of them for the
radical copolymerization with the above-mentioned monomer capable of
introducing the specific cyclic structure.
In the present invention, as such other monomers, fluorine-containing
monomers such as fluoroolefins and fluorovinyl ethers, are preferably
selected. For example, tetrafluoroethylene, perfluoromethyl vinyl ether,
perfluoropropyl vinyl ether or perfluorovinyl ether containing a
functional group such as a carboxylic acid group or a sulfonic acid group,
is preferred. Further, vinylidene fluoride, vinyl fluoride or
chlorotrifluoroethylene may also be mentioned.
As the copolymer composition, the composition of the cyclic structure
preferably constitutes at least 20%, more preferably at least 40%, in
order to obtain the properties of the specific fluorine containing
alicyclic structure intended by the present invention.
In the present invention, a method commonly used for crosslinking may
suitably be employed as a method for crosslinking the fluorine-containing
polymer. For example, crosslinking may be conducted by copolymerizing a
monomer having a crosslinkable site, or by incorporating a crosslinking
agent. Otherwise, crosslinking can be conducted by means of radiation.
The photoresist to be used in the present invention may suitably be
selected among positive and negative photoresists commonly employed, and
the best photoresist may be selected depending upon the size of the
desired pattern, the required degree of precision, the properties of
exposure apparatus, etc. Further, the viscosity of the photoresist
solution is preferably at a high level from the viewpoint such that it can
readily be coated on the surface of a fluorine resin by spin-coating.
In the present invention, a surfactant may be incorporated to a photoresist
solution, and such a solution is directly coated on the surface of a
fluorine resin. However, when an adequate adhesion can not be obtained by
this method, the adhesion can be improved by coating a liquid containing a
surfactant, followed by coating a photoresist solution. According to the
latter method, it is unnecessary to incorporate a surfactant to the
photoresist solution. Further, the liquid containing a surfactant to be
used in the latter method may be a liquid prepared by adding a surfactant
to a solution so-called an adhesion-improving agent, which improves the
adhesion between the fluorine resin and the photoresist.
The adhesion-improving agent to be used in the present invention is not
particularly limited so long as it is capable of improving the uniformity
in coating a photoresist solution to a fluorine resin surface and capable
of improving the adhesion. However, hexamethyl disilazane (HMDS) is
preferably employed.
The surfactant to be used in the present invention is not particularly
limited, so long as it has an effect of lowering the surface tension of
the liquid. All types of surfactants including anionic, cationic,
nonionic, water-soluble and oil soluble surfactants, may be employed.
Further, it is not limited to so-called surfactant, so long as it has the
above effects. For example, a surface-modifying agent or a leveling agent,
which is used for other purposes, may also be used for this purpose.
Among them, a surfactant compatible with the photoresist or the
adhesion-improving agent is preferred to form a uniform coated layer of a
resist.
The surfactant to be used in the present invention may not necessarily have
a surface tension smaller than the surface tension of the fluorine resin.
However, the lower the surface tension, the better. As a surfactant having
a particularly low surface tension, a fluorine-containing surfactant is
preferably employed.
As to the type of the surfactant, any of anionic, cationic, nonionic or
amphoteric type may be used. However, from the viewpoint of the solubility
in a photoresist solution, a nonionic surfactant is preferred. Further, it
may be of a polymeric type (oligomer type) such as acrylate oligomers
having polyfluoroalkyl groups.
The amount of the surfactant in the present invention should better be
smaller within a range sufficient to impart an adequate coating property
to the surface of the fluorine resin. If the amount is too much, foaming
of the liquid is likely to take place, whereby it tends to be difficult to
coat the liquid uniformly. When a surfactant is added to a photoresist
solution, if the amount is too much, it tends to adversely affect e.g. the
resolution of the photoresist.
According to the process of the present invention, a photoresist is coated
and if necessary, dried. Then, exposure is conducted by g-line, i-line, a
laser beam, an electron beam, etc. by means of a photomask having a
desired pattern in accordance with a method commonly employed, followed by
development by means of a developing solution suitable for the resist
solution to transfer the pattern on the resist. Then, etching is conducted
by wet etching with a fluorine type solvent capable of dissolving the
fluorine resin used as a protective film or by dry etching employing a
plasma of e.g. argon, CF.sub.4, CHF.sub.3 or oxygen, followed by removal
of the resist with e.g. alkali to form a protective film of a fluorine
resin having a desired pattern.
Now, the present invention will be described in further detail with
reference to Examples. However, it should be understood that the present
invention is by no means restricted by such specific Examples.
PREPARATION EXAMPLE 1
20 g of 1,1,2,4,4,5,5-heptafluoro-3-oxa-1,6-heptadiene and 40 g of
trichlorotrifluoroethane (hereinafter referred to simply as R113) were
charged into a three-necked flask flushed with a nitrogen, and 20 g of
(C.sub.3 F.sub.7 COO).sub.2 was added thereto as a polymerization
initiator. The interior of the reaction system was further flushed with
nitrogen, and polymerization was conducted at 18.degree. C. for 10 hours.
As a result, 10 g of polymer A was obtained. This polymer was a polymer
soluble in R-113, and the intrinsic viscosity [.eta.] was 0.96 dl/g as
measured at 30.degree. C. in m-xylene hexafluoride. By .sup.19 F and
.sup.1 H NMR, the product was confirmed to be a polymer having a cyclic
structure in its backbone chain. Further, this polymer was colorless
transparent and had a surface energy of 20 dyn/cm.sup.2.
PREPARATION EXAMPLE 2
35 g of perfluorobutenyl vinyl ether, 5 g of R113, 150 g of deionized water
and 90 mg of ((CH.sub.3).sub.2 CHOCOO).sub.2 as a polymerization initiator
were charged into a pressure resistant glass autoclave having an internal
capacity of 200 ml. The interior of the system was flushed three times
with nitrogen, and then suspension polymerization was conducted at
40.degree. C. for 22 hours. As a result, 28 g of polymer B was obtained.
The intrinsic viscosity [.eta.] of this polymer was 0.24 dl/g as measured
at 30.degree. C. in perfluoro(2-butyltetrahydrofuran). The glass
transition temperature of the polymer was 108.degree. C., and it was a
tough transparent glass-like polymer at room temperature. Further, a 10%
thermal decomposition temperature was 465.degree. C., and the light
transmittance was as high as at least 95%. The surface energy of this
polymer was 19 dyn/cm.sup.2.
PREPARATION EXAMPLE 3
Perfluoro(2,2-dimethyl-1,3-dioxole) and tetrafluoroethylene were
radical-polymerized to obtain copolymer C having a glass transition
temperature of 160.degree. C. This polymer was colorless transparent. The
refractive index was 1.3, and the light transmittance is high. The surface
energy of this polymer was 19 dyn/cm.sup.2.
EXAMPLE 1
The fluorine-containing polymer obtained in Preparation Example 1 was
dissolved in perfluorotributylamine to obtain a 9% solution. This solution
was coated by a spin coater on a 6 inch wafer having a semiconductor
element (CMOS-DRAM) formed thereon, followed by drying at 50.degree. C.
for one hour and at 180.degree. C. for one hour to form a protective film
having a thickness of 3 .mu.m.
On this wafer having the fluorine resin protective film formed thereon, a
solution prepared by adding 0.05% of Surflon S-381 (acrylate oligomer
having polyfluoroalkyl groups, manufactured by Asahi Glass Company Ltd.)
as a surfactant to a 27.3% solution of a positive photoresist OFPR-800
(manufactured by Tokyo Ohka Kogyo Co., Ltd.), was coated by spin coating,
followed by drying on a hot plate, then by baking, exposure and
development, and then etching by an oxygen plasma was conducted to carry
out perforation processing to form 100 .mu.m angular holes for wire
bonding on the fluorine resin protective film. The semiconductor element
having a protective film thus formed had excellent properties even after a
moisture resistance test.
EXAMPLE 2
A semiconductor having a protective film was prepared in the same manner as
in Example 1 except that a fluorine-containing polymer obtained in
Preparation Example 2 was used, and Surflon S-382 (acrylate oligomer
having polyfluoroalkyl groups, manufactured by Asahi Glass Company Ltd.)
was used as a surfactant. The semiconductor element thus obtained showed
excellent properties at the initial stage and after the moisture
resistance test.
EXAMPLE 3
A semiconductor having a protective film was prepared in the same manner as
in Example 1 except that the fluorine-containing polymer obtained in
Preparation Example 3 was used, and Surflon S-207 (acrylate oligomer
having polyfluoroalkyl groups, manufactured by Asahi Glass Company Ltd.)
was used as a surfactant. The semiconductor element thus obtained showed
excellent properties at the initial stage and after the moisture
resistance test.
EXAMPLE 4
The fluorine-containing polymer obtained in Preparation Example 1 was
dissolved in perfluorotributylamine to obtain a 9% solution. This solution
was coated by a spin coater on a 6 inch wafer having a semiconductor
element (CMOS-DRAM) formed thereon, followed by drying at 50.degree. C.
for one hour and at 180.degree. C. for one hour to form a protective film
having a thickness of 3 .mu.m.
On this wafer having the fluorine resin protective film formed thereon, an
adhesion-improving agent (OAP, tradename, manufactured by Tokyo Ohka Kogyo
Co., Ltd.) having 0.05% of Surflon SC-101 (acrylate oligomer having
polyfluoroalkyl groups, manufactured by Asahi Glass Company Ltd.) added as
a surfactant, was coated by spin coating, followed by drying on a hot
plate. Then, a positive photoresist HPR-207 (manufactured by Fuji-Hunt
Electronics Technology Co., Ltd.) was spin-coated thereon, followed by
baking, exposure and development, and then etching by an oxygen plasma was
conducted to carry out perforation processing to form 100 .mu.m angular
holes for wire bonding on the fluorine resin protective film. The
semiconductor element having a protective film thus formed, had excellent
properties even after the moisture resistance test.
EXAMPLE 5
A semiconductor having a protective film was prepared in the same manner as
in Example 4 except that the fluorine-containing polymer obtained in
Preparation Example 2 was used, and Surflon S-105 (acrylate oligomer
having polyfluoroalkyl groups, manufactured by Asahi Glass Company Ltd.)
was used as a surfactant. The semiconductor element thus obtained showed
excellent properties at the initial stage and after the moisture
resistance test.
EXAMPLE 6
A semiconductor having a protective film was prepared in the same manner as
in Example 4 except that the fluorine-containing polymer obtained in
Preparation Example 3 was used, and Surflon S-111 (acrylate oligomer
having polyfluoroalkyl groups, manufactured by Asahi Glass Company Ltd.)
was used as a surfactant. The semiconductor element thus obtained showed
excellent properties at the initial stage and after the moisture
resistance test.
COMPARATIVE EXAMPLE 1
The fluorine-containing polymer obtained in Preparation Example 2 was
dissolved in perfluorotributylamine to obtain a 9% solution. This solution
was coated by a spin coater on a 6 inch wafer having a semiconductor
element (CMOS-DRAM) formed thereon, followed by drying at 50.degree. C.
for one hour and at 80.degree. C. for one hour to form a protective film
having a thickness of 3 .mu.m. On this wafer having the fluorine resin
protective film formed thereon, a 27.3% solution of a positive photoresist
OFPR-800 (manufactured by Tokyo Ohka Kogyo Co., Ltd.) was coated by spin
coating at 500 rpm, whereby the photoresist solution was entirely
scattered during the rotation, and it was impossible to form a photoresist
layer.
COMPARATIVE EXAMPLE 2
A protective film having a thickness of 3 .mu.m was formed in the same
manner as in Comparative Example 1 using the fluorine-containing polymer
obtained in Preparation Example 2. Then, a positive photoresist HPR-207
(Manufactured by Fuji-Hunt Electronic Technology Co., Ltd.) was spin
coated. The photoresist layer was partially repelled and non-uniform.
Then, baking, exposure and development were conducted by usual methods,
and etching by an oxygen plasma was conducted to carry out perforation
processing to form 100 .mu.m angular holes for wire bonding on the
fluorine resin protective film. With the semiconductor element having a
protective film thus formed, the defective ratio by the moisture
resistance test was high.
According to the present invention, a photoresist or adhesion-improving
agent having a surfactant incorporated thereto, is used, whereby fine
processing of the fluorine resin thin film having a high fluorine content
and a low surface energy can be made possible, and it is possible to
obtain a semiconductor element having a protective film having excellent
properties such as a low dielectric constant and a low water absorptivity.
* * * * *
|
|
 |
|
 |
Description |
|
