Note: Descriptions are shown in the official language in which they were submitted.
FN 915,166
POSITIVE-ACTING PHOTORESIST ~OMPOSITION
. . .
In the manufacture of dry photosensitive
elements such as lithographîc plates, photoresists, and
the like, photosensitive compositions are utilized which
are either negative-acting or positive-acting. Negative-
acting systems are those which become insolubilized in animagewise fashion upon exposure thereof to actinic
radiation. Since the exposed areas are rendered
relatively insoluble, selected developing solutions can
dissolve or otherwise remove the unexposed portions of the
composition while leaving the exposed areas intact.
Therefore1 the resulting image corresponds to the reverse
of the original in terms of contrast, i.e., a negative
image. Conversely, with positive-acting systems, exposed
portions thereof are rendered more soluble or developable
upon exposure to actinic radiation, and as such these
portions can be removed with selected developing
solutions, the unexposed portions remaining intactO Image
formation in this instance yields an image corresponding
to the original image in terms o~ contrast, i.e., yields a
positive image.
In the specific area of photoresist manufacture,
a photoresist is typically utilized to promote image
formation on substrates by imagewise protecting the
~ubstrate material from subsequent chemical or physical
manufacturing processes, such as chemical etching, vacuum
metalization, and electrolytic deposition In other
i~
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words, upon exposure and development of the photoresist
material~ the underlying substrate upon which the
photoresist is placed can be exposed to subsequent
physical processing in an imagewise fashion, the
processing affecting only in areas not protected by the
resist material. In the manufacture of copper-clad
circuit boards, a photoresist is typically applied to the
circuit board surface, and is followed by imaging and
developmentO Subsequent to such initial processing, ar,
etching solution typically is sprayed under high pressure
downward onto the substrate, the etchart removing the
copper metal which is unprotected by the photoresist,
thereby providing an imaged metal circuit configuration
after removal of the balance of the photoresist.
In order to accurately reproduce circuit
geometries, it is necessary that a photoresist have high
adhesion to the substrate to which it is applied and high
internal strength~ Adhesion is required to prevent
excessive undercutting of the resist by the etchant,
thereby decreasing image resolution, and internal strength
is necessary to rnaintain proper circuit geometries. Dry
film resists should have reasonable flexibility, ability
~or heat and pressure lamination, reasonably fast exposure
capability, excellent development characteristics with
moderate pressure sprays of developer solutions, excellent
coating quality (i.e., free from physical defects),
capability of rapid chemical stripping or removal of the
photoresist after use, and the production of a visible
image upon exposure thereof to actinic radiation.
Dry negative-acting film resists have of course
been known for quite some time. One important feature
necessary for any resist is resolution. Positive acting
resists have an inherently higher resolution capability
than do their negative-acting counterparts. This
difference is due, in part, to the generally necessary
presence of an oxygen-impermeable barrier film required
prior to and during negative resist exposure, since
conventional negative-acting materials are usually
oxygen-sensitive.
Some typical resolution requirements in the
electronics industry are as follows: In the production of
- 15 general purpose printed circuit boards, typically 10 mil
lines with 10 mil spaces are required; in precision
circuits, typically 1 mil lines with 1 mil spaces are
necessary; and in the microelectronics industry, better
than 0,1 mil lines and spaces are required.
ht the present time, the dry film resist market
consists of virtually only negative-acting resists. This
is essentially because positive-acting film photoresists
have not been developed which achieve the criteria noted
above, Positive film resists typically exhibit excessive
brittleness which allows flaking of'f of the resist with
even moderate flexing of the carrier sheet, coating
defects, a lack of internal cohe~ive ~trength which causes
-the resist to fracture during etching, and poor adhesion oE the photoresist to
the substrate surface.
It has now been ascertained that a novel positive-acting photosensitive
composition can be utilizecl to prepare a dry film photoresist which meets many
of the foregoing criteria. In additi.on, the photosensitive composition, in its
cured sta-te, is oleophilic, i.e., ink-receptive, and can therefore be utilized
as a coating on aluminum or stainless steel surfaces to provide lithographic
printing plates, or in the manufacture of bimetallic printi.ng plates.
In accordance with the invention, there is provided a positive-acting
light sensitive compositlon having excellent utility as a photoresist, compris-
ing: ~a) a crosslinked urethane resin formed by a catalyzed crosslinking of
a non-heat reactive novalac phenolic resin and a polyisocyanate compound;
(b) an epoxy resin having an epoxida equivalent weight of less than about
~00 and a curing agent therefor; and ~c) a positive-acting photosensi.tizer.
Upon the preferred application of the composi.tion to a substrate
~which may be a temporary support layer and strippable film or a substrate
on which the composition is coated prior to processing) and dryi.ng, the epoxy
resin cures, and the resultant dry film has ideal utility as a dry film photo-
resist. In addition, the dry film is oleophi.lic, and therefore can be
utilized as a
. ~3 _~_
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printing plate surface.
In dry coated form, the positive actin~
composition of our invention basically comprises two
intermixed and intertwined polymeric resin networks. The
first of these networks comprises a crosslinked urethane
resin formed from crosslinking of a diisocyanate with a
novalac phenolic resin, and the second comprises a
heat-curable epoxy resin. The resin mixture contains a
blended-in amount of a positive-acting photosensitizer to
afford light sensitivity to the system~
The urethane resin is formed in solution by the
catalyzed crosslinking reaction of a novalac pheno:Lic
resin with a polyisocyanate, preferably a tri or
diisocyanate, and most preferably a long-chain
diisocyanate compound.
The components used in forming the urethane can
be simply dissolved in a suitable solvent together with an
appropriate catalyst, whereupon the crosslinking reaction
will ensue. When the solution viscosity stabilizes~
reaction is complete.
The novalac phenolic resin should typically
comprise from about 40 to about 80 and preferably between
50 and 70 percent by weight of the cornposition, and should
not be heat reactive, Non-heat-reactive according to the
2~ present invention means that the resin should not
substantially polymerize when heated alone. Substantial
polymerization would occur when the average molecular
--6--
weight in~reased by at least 10~. Preferably the average
molecular weight should increase by less than 4~ upon
heating, if at all. Increasing novalac concentration may
cause increased film brittleness and an undesirable
increase in the solubility of the unexposed film areas,
which can result in an insufficient solubility
differential between exposed and unexposed film areasD
Reduced concentrations may cause the film to fail to
develop properly after imagewise exposure to actinic
radiation. Preferred novalac resins include novalac
phenolic/formaldehyde resins of from about 500 to 1000
molecular weight. These resins include those of U.S~ Pat.
No. 4,1Ll8,655 where a number of different phenolic
components are used.
Polyisocyanates useful herein include
conventional aromatic and aliphatic polyisocyanates.
Preferably, the polyisocyanates are of long chain length,
i.e., where the isocyanate groups are connected by
linkages o~ from about 10 to about 40 or 50 carbon atoms.
Both smaller (e.g., 6 carbon atoms) and larger chain
aromatic and aliphatic diisocyanates would of course still
be useful in the practice of the present invention. For
example, lsophoronediisocyanate, toluene diisocyanate and
any other diisocyanates are particularly useful. The
2~ polyisocyanate should preferably be present in a
concentration of from about 6 to about 12 parts by weight
per 100 parts of novalac resin pr0sent, depending upon the
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molecular welght or isocyanate equivalent weight of the
polyisocyanate~ In general, the weight percent should not
exceed a range of from about 3 to 20 percent by weight of
the novolac resin. Increasing amounts tend to cause the
resultant f`ilm to be excessively brittle, to have
insuf`ficient internal strength, and, in the case of
photoresists, to exhibit reduced adhesion to the substrate
to which the film is laminated. Reduced amounts tend to
cause the film to fail to laminate properly and clean out
in exposed areas during development. Any catalyst known
to be useful in the catalysis of urethane formation may be
used. The most preferred catalysts include tertiary
amines, examples of which lnclude 1,4 dia~a-bicyclo-
(2,2,2)-octane, and 2,4,6-tris(dimethylaminomethyl)
phenol.
Catalyst concentration is not critical, as long
as a sufficient amount is present to incure crpsslinking.
Typically1 greater than about 0.05 parts by weight per tOO
parts of novalac resin is more than sufficient to insure
complete crosslinking, although as little as 0.01 parts
can be sufficient.
Once the urethane formation is complete, a
polymerizable epoxy resin having an epoxide equivalent
weight of less than about 400 is added to the solution,
along with a curing agent therefor. A typical and
preferred epoxy resin i3 diglycidyl ether of bisphenol A.
Epoxy resin concentrations should be from about 20 to
l~LY~ 4~7
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about 40 parts by weight per 100 parts of novalac resin.
Incre~sed concentratiorls tend to increase the flexibility
of the resultant dry photosensitive film, but the
capability of imagewise exposure and development is
reduced. Decreasing concentrations tend to reduce the
adhesion and handling characteristics of the resultant dry
film.
Exemplary epoxy curing agents include aliphatic
or aromatic amines, aliphatic or aromatic anhydrides~
disulfones, nitriles, and other known epoxy curing agents.
Any of these and other curing agents may be used in
practice of the present invention. Preferred curing
agents include phthalic anhydride, diamino diphenyl-
sulphone or a combination thereof~ Typically, from about
5 to about 50 parts of curing agent per lO0 parts of epoxy
resin are sufficient to insure curing of the epoxy.
Without inclusion of the epoxy curing agent or
successful curing of the epoxy resin, the resultant film
tends to be brittle and lacks the internal cohesive
strength necessary for photoresist performance.
Conversely, when the epoxy is satisfactorily cured, the
resultant film has significantly greater flexibility and
cohesive strength so as to be extremely useful as a
photoresist.
The positive acking photo3ensitizer i3
conveniently added by thorough mixing to the solutlon
containing the urethane, polymerizable epoxy resin, and
epoxy curing a~ent. Exernplary photosensitizers include
diazo oxides, as known in the art, e.~., naphthoquinone~
1,2-diaYide-~2~ 5-sulphonic-p-methylphenyl ester, as in
U.S. Patent Nos. 3,046,120; 3,046,121; and 3,211,553, and
diazo sulfones as known in the art, e.g.~ in U.S. Patent
Nos. 2,465,760; 3,113,865; and 3,661,573; and U.K. Patent
No. 1,277,428. Tha photosensitizers should be soluble in
the solvent utilized for the coatirg solution applica-
tions. A particularly use~ul photosensitizer which is
commercially available un~er the trade~ iazo LL," is
a naphthoquinone~tl,2)-dlazide-sulfonic-(5)-naphtha-
diester, available from the Molecular Rearrangement
Company. The positive acting photosensitizers of U.S.
Patent No. 4,148,654 are also useful in the present
invention. A positive acting photosensitizer according to
the present invention is a material which when struck by
radiation1 preferably actinic radiation, decomposes into a
material which is more acidic than the photosensitizer.
Preferably the original photosensitizer is neutral or
basic to provide the greatest change in pH. The photo-
sensitizer component need not provide any structural
integrity by itself as it is blended into the mixture of
urethane, polymerizable epoxy resin, and curing agent.
Concentratiorl of the photosensitizer can be from
about lO parts by weight per 100 parts of novalac resin up
to solution saturation.
Solvents utilized in the formation of the photo-
- lo~
sensitive ~ol~tion are a matter of choice and convenience,
and include, for example~ methyl isobutyl ketone, methyl
ethyl ketone, etc.
In practice, the solution can be simply coated
by any known means onto a suport material, followed by
drying at a temperature sufficient to cure the epoxy
resin~ Xn the case of a photoresist applied from a
transfer film, th~ fllm backing should contain a releas~
agent thereon, such as methyl cellulose, polyvinyl
pyrrolidone, and copolymers of methyl vinyl ether and
maleic anhydride to allow easy removal of the film
backing, e.g., polyester from the photoresist layer.
Following drying, the photoresist composition can be
simply laminated by means of heat and pressure to a
variety of substrates such as metals including copper,
stainless stee ~ and gold, ceramics, glass, silicon
dioxide, and organic polymers such as polyimide, epoxy,
resin 7 and polysiloxanes and polyester.
Furthermore, the liquid photosensitive solution
2~ can be coated onto stainless steel for the purpose of
manufacturing bimetallic printing plates by means of
electrode deposition subsequent to imaging and development
of the light sensitive material, or can be applied onto
aluminum and sllicated aluminum to manufacture printing
plates, since the dry composition is oleophilic in nature.
Prior to coating onto a support, materials suCh
as epoxy or amine functionalized alkoxy silane coupling
agents c~n be added to the solution to promoke the
adhesion to substrates such as glass9 silicon dioxide or
other surfaces. Examples of such materials include
Y~aminopropyltrlethoxy silane and ~-glycidoxypropyl
trimethoxy silane~
Exposure can be undertaken by conventional
techniques, e.g. 9 carbon arc, etc., depending upon the
radiation to which the photosensiti~er i~ sensitive.
Development of the image is undertaken using developers
such as weak alkaline solutions, etc., which are
conventional with the sensitizers utilized.
Our invention will now be more speci~ically
described by the aid of the ~ollowing non-limiting
examples, wherein all parts are by weight unless otherwise
speci~ied.
Example 1
A positive-acting composition was prepared by
mixing the following components at room temperature-
Methyl ethyl ketone 27.6
Resinox, trade~ for a phenol/
formaldehyde resin commercially
available from Monsanto Company 11.0
2,4,6-tris(dimethylaminomethyl)phenol 0.23
DDX-14l0, trade~ for an aliphatic
(approximately 36 carbon atom
bridging group) diisocyanate
commercially available from
General Mills Ch0micals, Inc. 1.00
-12-
The solution containing the above components was
mixed until the solution viscosity (measured with a
conventional Brookfield viscometer with a No. 2 spindle)
stabilized at about 17 centipoise, after which the
following were addeci:
Methyl ethyl ketone 11.0
DER 331, trade~e`~or diglycidyl ether
of bi~phenol A having an epoxy
equivalent weight of 186 to 192,
commercially available ~rom the
Dow Chemical Company 3.31
Phthalic anhydride 0~26
Diaminodiphenylsulfone 0.13
1,2-naphthoquinone diazide-5-p tert~
butylphenylsulfonate 3.6
After thorough mixing, the solution was knife coated onto
2 mil thick polyester sheeting which had been precoated
with 50 milligrams per square foot of methyl cellulose,
the photosensitive coating then being dried at 180F for 4
minute~. During drying, the epoxy resin was cured.
The resulting film was sufficiently flexible to
withstand moderate flexing of the support without breaking
away, The film was laminated to sheet copper using a
heated roll lamlnator at 100C. The polye~ter backing was
stripped from the photoresist following lamination and the
resi~t exposed through an original to a carbon arc for 50
seconds. The exposed resist was then developed by
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- 1 3
spraying the resis~ with a 1~ aqueous sodiu.m hydroxide
solution for 2 minutesO The exposed copper could then be
etched or electropl.ated in accordance with normal
industrial techniques.
Example 2
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A positive-acting composition was prepared by
mixing khe following:
Methyl ethyl ketone 27.7
Resinox ll,0
1,4-diazabicyclo(2,2,2)octane 0.01
DDI-1410 1.23
until. the viscosity of the solution stabilized at about 50
centipoise.
Following the completion of the urethane
formation, the following components were added to the
solution:
DER 331 3-
Phthalic anhydride 0.3
1,2-naphthoquinone diazide-5~p-tert-
butylphenylsulfonate 3.0
After coating, exposing and developing as per Example l,
the film disp:Layed excellent flexibility and photoresist
properties.
l4-
Example 3
A positive-acting cornposition was prepared by
mixing:
Methyl ethyl ketone 27.7
Resi.nox 11.0
1,4-diazabicyclo(2,2,2)octane 0.06
DDI-1410 1.18
until the vlscosity of the solution ~tabilized.
The following component were then added to th~
solution:
DER 331 2.15
Diaminodiphenylsul~one 0.40
1,2-naphthoquinone diazide s-p-tert-
butylphenylsulfonate 3.0
After coating, drying, exposing and developing as per
Example 1, the film di.splayed good flexibility and
photoresist properties.
~1~
A photosensitive composition was prepared by
mixing the following:
-15
The reaction product of '1Resinox1'
and DDI-14l0 given in Example 1 100
DER 331 9
Diaminodiphenylsulfone 1.7
5 "Diazo L.L", tradename for a naphtho-
quinone¢1,2)-diazide (1)-sulfonic
(5)-naphtho-diester sold by
Molecular Rearrangement, Inc. 11. 6
~-aminopropyltriethoxysilane 0.26
The solution was coated onto silicated aluminum and dried
at 180F. The resulting composition was used as a
printing plate, i.e., it was exposed to actinic radiation
in an image-wlse manner, developed, and inked. It was
found that the film took ink and was functional as a
printing plate.
Example 5
The present example shows the desirability of
curing the epoxy resin in the presence of the polyurethane
to form an interlocking dual polymer network.
A positive-acting composition was prepared by
mixing the following components at room temperature:
Acetone 27.6
Res:inox, tradename for a phenol/
forma.ldehyde res.in commercially
avallable from Monsanto Company 11~0
2,ll,6-tris(dimethylamino~ethyl) phenol 0.23
DDl-1410, tradename for an aliphatic
diisocyanate commercially available
from General Mills Chemicals, Inc. 1.00
The solution containing the above components was mixed
until the solution viscosity, measured with a conventional
Brookfield viscometer stabili~ed at about 15 centipoise.
This solution was combined with another one which had been
prepared in the following way:
Acetone 11.0
Epon 328, trade~e for a di~lycidyl
ether o:f bisphenol A having an epoxy
equivalent weight of 186 to 192
commercially available from the Shell
Chemical Company 3.31
Phthalic anhydride 0~26
Diaminodiphenylsulfone 0.13
These components of the second solution were boiled under
reflux for 20 hours. To the combined solut:ions was added:
1,2-naphthoquinone diazide-5-p-tert
butylphenylsulfonate 3.6
After thorough mixing9 the combined solution was knife
coated onto 2 mil polye~ter ~heeting whi.ch had been
'7
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precoated with a 50 milligram per sguare foot methyl
cellulose coating or precoated with a 50 milligram per
square foot hydroly~ed copolymer formed from
methylvinylether and malaic anhydride. The photosensitive
coating was dried at 180F for 4 minutes.
The film was laminated to a sheet of copper
using a heated roll laminator at 100C. The polyester
backing was stripped from the photoresist following
lamination and the resist exposed through a photomask to
UV light. The exposed portion of the resist was developed
by spraying it with a 1% aqueous solution of sodium
hydroxide.
The resists made in this manner were inferior to
those made in the manner of Examples 1~4. Stripping of
the polyester backing was difficult. Image quality was
poorer and some bleeding of material from the unexposed
resist image was noted. The resist also was more brittle
than coatings described in the Examples 1-4. These
coatings were still as good as many others used
commerciallyO
