Note: Descriptions are shown in the official language in which they were submitted.
` 10~i2~2
BACKGROUND 0~ THE INVENTION
~ield of the Invention
This invention relates to the use of light sensitive
quinone diazide polymers in the graphic arts to produce photo-
mechanical images such as photoresists and lithographic plates.
More particularly, it relates to positive-working photoresists
containing light sensitive o-quinone diazide polymers having
incorporated therein a volatile carboxylic acid having in-
creased thermal stability, image quality and etch resistance. ;~
.
Description of the Prior Art
The use of light sensitive quinone diazides for themanufacture of photocopies, for photoresists and on lithographic
plates is well known and described for example in U.S. Patents
2,754,20g, issued July 10, 1956; 3,046,110, issued July 24,
1962; 3,046,112, issued July 24, 1962; 3,046,113, issued
July 24, 1962; 3,046,116, issued July 24, 1962; 3,046,118,
issued July 24, lg62; 3,647,443, issued March 7, 1972; 3,759~711,
issued September-18, 1973, and ~anadian Patent 602,987, issued
August 9, 1960. Exposure to light results in a solubility
differential between the exposed and unexposed areas such that
treatment with an appropriate solvent results in the desired
-`'..:
image areas being retained on a support while the other areas
are removed.
The quinone diazide materials which are commonly ;~
used in the art are monomeric materials. These may be
incorporated in an alkali soluble resinous binder or reacted
with an alkali soluble resinous material so that they can be
used satisfactorily as a resist material or can withstand the
wear on printing plates.
-2-
. ~:
~52~12
Although the literature relating to the decomposition
of quinone diazides in positive-worlcing photoresist compositions
is extensive, the exact structure oE the decomposition product
is not certain. Equation 1 is at least representative of the ;~
reasons for solubilization of said compositions upon exposure.
Equation 1 vr- ~r~
S2 S2 S2 SO2
H~O ~ ~
O C C=O '
O OH
Loss of nitrogen to form the ketocarbene is the expected initial
step; however, the fate of the ketocarbene is less predictable.
One documented reaction sequence is the rearrangement to ketene
followed by hydrolysis to free acid. Due to the immobility of a _;~
dry film, the formation of ketene via intramolecular rearrange~
ment is expected; however, alternate reactions before hydrolysis
have been reported. The following patents review the preparation
and application of light-sensitive phenol-formaldehyde polymers
containing quinone diazide substituents: U.S. Patent 3,046,120,
issued July 24, 1962; British Patents 1,026,144, issued April 14,
1966; 1.113,759, issued May 15, 1968; German Patents 1,803,712
and 1,911,497; and Canadian Patent 903,545, issued June 27, 1972.
The evolution of nitrogen during the storage of resists
containing o-quinone diazides (Equation 1) can adversely affect
the safe storage of such photoresists. Existing positive-
working photoresists can become a safety hazard if they are
stored at temperatures above 100F for extended periods of time.
'- `
~ - 3 -
` 1~85~12
The advantage of adding various ingredients to improve
adhesive characteristics, stability or receptlvity of photosen-
sitive compositions is described for example in Printy et al,
U.S. Patent 2,990,281, issued June 27, 1971. Printy et al disclose
the addition of very small amounts of stabilizing salts of organic -~
acids to photosensitive compositions comprising copolymers of
vinylidene compounds and dicarboxy compounds.
U.S. Patents 3,046,110, 3,046,112, 3,046,113; 3,046,116;
and 3,046,118 disclose the incorporation of small amounts of
10 solid, non-volatile fatty acids into light-sensitive compositions ~ ;~
to improve ink receptivity and stability. Although the additlon
- of non-volatile carboxylic acids (e.g. fatty acids) to photo- ~ -
resist compositions does reduce the rate of nitrogen formation
' from quinone diazide decompositions, ~pplicants have found that
Il the presence of the non-volatile acids causes unacceptable image
formation during processing of the dried resist layer. Therefore,
it has been desirable to find compounds for photoresist compo-
sitions comprising quinone diazide substituents that will increase
thermal stability and not reduce the image quality.
' 20 SUMMARY OF THE INVENTION
In one aspect of the present invention, a photosensitive
composition comprises a light sensitive polymeric compound formed
from the condensation reaction of a quinone diazide with a phenol-
formaldehyde resin having incorporated therein a volatile
carboxylic acid.
In another aspect of the present invention a photo-
sensitive element comprises a support bearing a photosensitive
composition comprising a light sensitive polymeric compound
formed from the condensation reaction of a auinone diazlde
,
~ ~4- ~
' '`
~.' , . ,
~' ' I
` ~8S2~2
with a phenol-formaldehyde resin, the improvement which comprises
the incorporation of a volatile carboxylic acid to increase
thermal stability while maintaining acceptable image quality.
In still another aspect of the present invention, a
process for preparing a photomechanical image comprises exposing
to actinic radiation a photosensitive element comprising a support
bearing an alkali-insoluble photosensitive composition comprising
a light sensitive polymeric compound formed from the condensation
reaction of a quinone diazide with a phenol-formaldehyde resin
wherein the element comprises a volatile carboxylic acid to
increase thermal stability. On exposure to actinic radiation the
element undergoes substantially no crosslinking and the quinone ~-
diazide structure is decomposed rendering the exposed areas of
the photosensitive composition soluble in dilute aIkali. A
positive image is developed by removing the exposed areas of the
photosensitive composition with an aqueous alkaline developer.
Not only does the use of a volatile carboxylic acid
in photosensitive compositions and elements increase the safe
storage life of said compositi~ons and elements, but in comparison `;~
to like photosensitive compositions and elements containing base-
- soluble acids it offers an improvement to etch resistance, ex-
posure time~ and can eliminate the need to post-bake the elements
after development. Particularly, volatile carboxylic acids maintain ^
image quality unlike the nonvolatile carboxylic acids disclosed ~ ;
in the prior art. `
Accordingly, one obJect of the present invention is
to provide novel photosensitive compositions.
Another obJect is to provide an advance in the art of
photoresists for lithographic plates by providing improved
; 30 photosensitive elements.
' ~ '
-5- ~ _
` "` 1~8521~Z
Still another object is to provide novel photo-
sensitive compositions and elements which have greatly increased
safe storage life.
An additional object is to provide novel photosensitive
compositions and elements which have good image quality and
etch resistance.
I The above and additional ob~ects of the present
', invention will become apparent to those having ordinary skill
in the art from the further description of this invention
which follows.
,,, :
DESCRIPTION OF THE PREFERRED EMBODIMENTS ~`
The photosensitive composition of this invention ,
comprises~
A. a light sensitive polymeric compound formed from
the condensation reaction of a quinone diazide with a phenol-
formaldehyde resin; and `
B. a volatile carboxylic acid. `
`, In a preferred embodiment of the present invention,
~j the photosensitive composition as described above comprises a
' ~:
volatile carboxylic acid which has a formula
. `',`
..
1) R ( CH2 )m C-OH
'
wherein R is hydrogen or substituted or unsubstituted methyl and ~
.
m is an integer from 0 to 6 and wherein the hydrogen atoms
of the methylene can be substituted or unsubstituted.
A more preferred embodiment of the present invention
comprises a light sensitive polymeric compound formed from the ;;
condensation reaction of a quinone diazide with a phenol- ~
'` ' '` ;''
~,, 6
`;'`.', ' `
:1013S212
;:~
formaldehyde resin having therein a volatile carboxylic acid
having the formula
O "~" ' ''
R~ CH2 -)m C-OH
wherein R is hydrogen or substituted or unsubstituted methyl
and m is 0 or 1 and the hydrogen atoms of the methylene radical - ;;
can be substituted or ubsubstituted.
In another aspect of this invention, a photosensitive
element comprises a support bearing a photosensitive composition
comprising a light sensitive polymeric compound formed from the
condensation reaction of a quinone diazide with a phenol- j;
formaldehyde resin having incorporated therein a volatile
carboxylic acid to increase thermal stability.
The volatile carboxylic acids useful herein may be ;~;
:. ~
unsubstituted or substituted with one or more alkyls having
from 1 to about 3 carbon atoms, e.g., methyl, ethyl, propyl;
; alkoxy having from 1 to about 3 carbon atoms, e.g., methoxy,
., ;
ethoxy, propoxy; cyano; halide, such as bromide, chloride,
fluoride or iodide; nitro; or any other substituent that would
not substantially adversely affect the volatility of the
carboxylic acids. Likewise, the methyl groups of R can be
substituted with halogen, cyano or any of the groups described
above.
Thus, in accordance with the present teachings, a
photosensitive composition is provided which comprises~
a) a light sensitive polymeric compound which is
formed from the condensation reaction of a quinone diazide
with a phenol formaldehyde resin; and ;
b) a volatile aliphatic monocarboxylic acid which
has the formula
~ _7_
F :::
- ~0~2~2
,
,.
R ( CH2 ~ C-OH
wherein R is hydrogen or methyl and m i.s an integer from
0 to 6 and wherein the hydrogen atom of the methyl and
methylene are unsubstituted or substituted with one or more
alkyl groups having from 1 to 3 carbon atoms, alkoxy from
1 to 3 carbon atoms, cyano, halide or nitro and which has a
boiling point equal to or less than 200C at atmospheric '
pressure.
Volatile carboxylic acids, as defined for the purposes ~:i
of the present invention, are carboxylic acids which have
boiling points typically below 200C at atmospheric pressure~
Some of the acids useful in the present invention are listed in
Table I
,'.
.'
', ~.
' .
`, '
' ~:
:: .
,`
.
. 30
-7a- ;
~ ' , .
' LF : "
10~52~
belo~ with~their respect~ve boiling and melting points
Table I :: :
Volatile Carboxvlic Acids*
m . p . & b p C :
( 760 ~ g) ( 760 mmHg) :.
Formic Acid 8 100 . 5 ~
Acetic Acid 16.6 118 ~:
Propi on ic Ac id- 2 2 la~
Butyric Acid -6 164 :~.;- .
~10 Valeric Acid =34 187 _ .
*Morrison and Boyd, Organic Chemistry, 2nd Ed., 1966, p. 579
Acids having slightly higher boiling points have been
. ;,.
found to be unacceptable such as caproic acid at 205C, caprylic
! acid at 23~C, benzoic acid at 250C and cyclohexane carboxylic
acid at 233C. .~
Fatty acids both saturated and unsaturated, such as ~ ~-
those used in prior art photosensitive compositions, are
solids and are nonvolatile carbox~lic acids. As has been
20 pointed out above, they provide added stability in photo- ^-
sensitive compositions and elements but deleteriously affect
image quality.
Although the amount of volatile carboxylic acid used
can vary widely, the concentration of the volatile carboxylic
acid in the photosensitive compositions and elements disclosed
herein is preferably within the range of about 1 to about 50
percent by weight based on the total solids of said composition,
and more preferably within the range of about 1 to about 20 percent
by weight.
The photosensitive compositions and elements disclosed -
herein comprise a light sensitive polymeric compound formed -~
from the condensation reaction of a quinone diazide with a phenol- ;~
formaldehyde resin. Preferably, the quinone diazide useful in
the practice of this invention has a linkage independently
selected from the group consisting of sulfonyl
-i -8-
! .. ': - ' '
~135212
o o o o
,. .. .. ..
(-S-~, carbonyl (-C-), carbonyloxy (~C-O-), and sulfinyloxy (-S-O-).
O ~i;
Most preferred is 1,2-naphthoquinone-2~diazide-5-sulfonyl chloride, ;
having the formula
S02Cl ''''
~ ~ R4
wherein R4 and R5 are interchangeably N2 or O, and R4 and R5
are not the same.
Other quinone diazides useful in the practice of this
invention are the acid esters and acid halides of o-benzoquinone
diazide, 1,2-napthoquinone-1-diazide, 7-methoxy-1,2-naphthoquinone-
2-diazide, 6-chloro-1,2-naphthoquinone-2-diazide, 7-chloro-1,2-
naphthoquinone-2-diazide, 6-nitro-1,2-naphthoquinone-2~diazide, `~
5-tcarboxymethyl)-1,2-naphthoquinone-1-diazide, 3,3',4,4'-diphenyl-
bis-quinone-4,4'-diazide, 2,3-phenanthrenequinone-2-diazide,
9,lO-phenanthrenequinoné-lO-diazide, 3,4-chrysenequinone-3- - -
diazide, and the like, including quinone diazides substituted ;
with such groups as alkyl generally having one to eight carbon
atoms, e.g., methyl, ethyl, propyl, butyl, amyl, hexyl, heptyl,
octyl, etc.; alkoxy generally having 1 to 8 carbon atoms, e.g.,
methoxy, ethoxy, propoxy, butoxy, amyloxy, hexyloxy, heptyloxy,
octyloxy, etc.; and like substituents which do not interfere
with the photosensitive pXoperties of the quinone diazide.
The phenol-formaldehyde resins used in the practice of
i this invention, such as novolac or resole resins, are
described in Chapter XV of "Synthetic Resins in Coatings",
H. P. Preuss, Noyes Development Corporation (1965), Pearl River,
` ~ew York.
_9- :
~01~5212
~ he novolac resins are prepared by the condensation of
phenols and aldehydes under acidic conditions whereas the resole
resins are prepared under basic conclitions. Less than 6 moles
of formaldehyde are used per 7 moles of phenol to provide products
which are permanently fusible and soluble. In a typical synthesis,
novolacs are prepared by heating 1 mole of phenol with 0.5 mole
of formaldehyde under acidic conditions. The temperatures at
which the reaction is conducted are generally from about 25C.
to about 175 & .
These resins are prepared by the condensation of phenol
10 with formaldehyde, more generally by the reaction of a phenolic ;~
compound having two or three reactive aromatic ring hydrogen
positions with an aldehyde or aldehyde-liberating compound
capable of undergoing phenol-aldehyde condensation. Illustrative
of particularly useful phenolic compounds are cresol, ~ylenol,
ethylphenol, butylphenol, isopropylmethoxy-phenol, chlorophenol,
resorcinol, hydroquinone, naphthol, 2,2-bis(p-hydroxyphenyl)pro-
pane and the like. Illustrative of expecially efficacious alde-
hydes are formaldehyde, acetaldehyde, acrolein, crotonaldehyde,
furfural, and the like. Illustrative of aldehyde-liberating com-
pounds are 1,3,5-trioxane, etc. Ketones such as acetone are also ;
capable of condeasing with the phenolic compounds.
The most suitable phenolic resins are those which are
insoluble in water and trichloroethylene but readily soluble in
conventional organic solvents such as methyl ethyl ketone, acetone,
methanol, ethanol, etc. Phenolic resins having a particularly
desirable combination of properties are those which have an
; average molecular weight in the range between about 350 and ~0,000,
and preferably in the range between about 350 and 2000.
--10--
.. , "" . . , : . ~:: .. :: : .. :. . : :: : :
:~0~5212
Preferred phenol-formaldehyde resins are cresol-
formaldehyde and phenol-formaldehyde.
In a preferred embodiment of this invention, a
photosensitive composition comprises a light sensitive polymer
compound having the formula
~2
100-X
~5 R
wherein R3 is hydrogen or methyl; R4 and R5 are interchangeably ~ ~-
N2 or 0, but not the same; and X is from about 1 to 100 mole
percent. Applicants have found, however that acceptable
., ... _ ~ . .
imaging properties in short development times are obtained
when X is from about 1 to about 50 mole percent, and best
results when X is from 4 to about 20 mole percent.
The light sensitive polymeric compounds useful in
the present invention are prepared from condensation reactions
of a suitable quinone diazide (e.g. one of those listed above)
with a suitable phenol-formaldehyde resin. These reactions are
usually carried out in an organic medium, such as dioxane,
tetrahydrofuron, ace~one, etc., where ~le con~erltrat1on ~f ~e
reactive compounds is in the range of 1 to 50 percent of the
solution weight; at a temperature in the range of 0C to 78C
and at various pressures, preferably atmospheric pressure. The
molar ratio of quinone diazide to phenol-formaldehyde resin is ;~
in the range of about 99:1 to about 1:99 and preferably from 1:25
.: . -: :: :::; .: .:: :.; ::, . ~,. . ~ , ,,, ",: . .
SZlZ
to 1:5. The resulting quinone diazide phenol-formaldehyde poly-
mer can be collected by precipitation of the reaction product
into a dilute acid, such as hydrochloric acid and filtering.
In another preferred embodiment of the present
invention, the photosensitive compositions disclosed herein
may further comprise a non-light sensitive film forming polymer
wherein the weight ratio of light sensitive polymer to non-light
sensitive polymer is in the range of about 1:1 to about 99:1. As
the amount of quinone diazide used in a photosensitive composition
10 is increased the described amount of non-light sensitive polymer ~ -
increases.
The non-light sensitive polymers are addition homo-
polymers or interpolymers formed by the addition polymerization
;"" ! ~
of one or more unsaturated compounds containing the unit C=C =
and generally having a molecular weight in the range of about
2000 to about 50,000, although they can have higher or lower
molecular weights for particular applications. ~
Unsaturated compounds which can be homopolymerized ~ ;
or interpolym~ri~ed and used-~s~non-light sensitive polymeric
materials include vinyl amines, vinyl imines, substituted and
unsubstituted styrenes, acrylates and methacrylates such as
alkyl acrylates and alkylmethacrylates, vinyl halides, vinyl
esters, vinyl ethers, vinyl ketones, divinyl ethers, acrylonitrile,
mixed esteramides and maleic anhydride, 1,3-butadiene, isoprene,
chloroprene, divinylbenzene, acrylic and methacrylic acid
derivatives such as nitriles and amides, and others known to ~ -
those having ordinary skill in the art.
Interpolymers and homopolymers can be prepared by
any suitable method including addition polymerization, for example,
bulk, solution, bead and emulsion polymerization methods in the
presence of a polymerization initiator. For example, polymeri-
-12-
. . . .. .. . .. . . . . .... ~
~085;~$2
zation of aminostyrene is conveniently carried out by contacting
a mixture of aminostyrene and another polymerizable ethylenically
unsaturated compound with from 0.1% to 10%, preferably 0.2 to 2%,
of a free radical liberating polymerization initiator.
Examples of suitable initiators are peroxy compounds,
for example, benzoyl peroxide or di(tertiary amyl)peroxide and
azo initiators, for example, l,l'-azodicyclohexanecarbonitrile or
azodiisobutyronitrile. The polymerization can be carried out in
the presence or absence of an inert solvent such as a hydrocarbon,
for e~ample, benzene, white mineral oil, or lubricating oil,
acetic acid, dioxane, etc., and preferably in an inert atmosphere,
for example, under a blanket of nitrogen. The mixture is main-
tained at a temperature at which the polymerization initiator
generates free radicals rapidly. The exact temperature selected
depends on the particular initiator being used. Temperatures
ranging from room temperature or lower up to 150C. or higher
are suitable. It is usually desirable to carry the polymerization
substantially to completeness so that no unpolymerized monomer ;-
remains and the proportions of each component in the final product
are essentially those of the original monomer mixture.
Other non-light sensitive polymers suitable for use
in the present invention are film forming condensation resins,
such as phenol formaldehyde resins and othersknown to those
having ordinary s}cill in the art.
Photosensitive compositions can be prepared by ~orming
a solution of the light sensitive polymeric compound alone or
mixed with a film ~orming non-light sensitive material. These ;
compositions can then be used to form resists or lithographic
plates.
- 13 -
.: . : : ., . : , :: . : ,. :.:; . :
` 101~2~2
The solvents which can be employed as coating solvents
in preparing coating compositions with the light sensitive
materials of our invention are preferably organic solvents ;
which may be selected from those which are capable of dissolving
at least 0.2% by weight of the light sensitive materials employed
but are unreactive toward the light sensitive materials and which
are substantially incapable of attacking the substrates employed. ;
Exemplary solvents include dimethylformamide, cyclohexane, cyclo~
hexanone, acetonitrile, 2-ethoxyethanol, acetone, 4-butyrolactone
ethylene glycol monomethyl ether acetate, 2-methoxyethyl acetate,
butyl acetate, and mixtures of these solvents with each other or `
with one or more of the lower alcohols and ketones.
The concentrations of light sensitive polymer in the
coating solutions are dependent upon the nature of the light
.:
sensitive materials, the supports and the coating methods employed.
Particularly useful coatings are ob~tained when the coating solutions
contain from about 0.05 to about 25 percent by weight of light
sensitive material~
It will be recognized that additional components can be
i - :.
l 20 included in the coating compositions of the present invention~ ~
i
For example, dyes and/or pigments can be included to obtain
colored images; resins, stabilizers and surface active agents
may serve to improve film formation, coating properties, adhesion
of the coatings to the supports employed, mechanical strength,
chemical resistance, etc.
Photosensitive elements bearing layers of the polymeric
materials disclosed herein can be prepared by coating the photo~
sensitive compositions from solvents onto supports in accordance
,' '`: ~' :
-14- ~ ;
',
,.......... ;,, ;, ! ,, . ~ !
. '. . ' ~ ' . ' ' .: . : , .. . ., ... :,.. . ... ..... ...... ... .
3S2~L~
with usual practices. Suitable support materials include fiber
base materials such as paper, polyethylene-coated paper, poly-
propylene-coated paper, parchment, cloth, etc.; sheets and foils
of such metals as aluminum, copper, magnesium, zinc, etc.; glass
and glass coated with such metals as chromium, chromium alloys,
steel, silver, gold, platinum, etc.; synthetic polymeric materials
such as poly(alkyl methacrylates), e.g., poly(methyl methacrylate),
polyester film base, e.g., poly(ethylene terephthalate), poly-
(vinyl-acetals), polyamides, e.g., nylon, cellulose ester film
base, e.g., cellulose nitrate, cellulose acetate, cellulose acetate
propionate, cellulose acetate butyrate, and the like. The supports,
and especially polymeric supports such as poly(ethylene
.
~; terephthalate), can be subcoated with materials which aid adhesion
to the support. A preferred class of subcoatings are polymers,
copolymers and terpolymers of vinylidene chloride alone or with
acrylic monomers such as acrylonitrile, methyl acrylate, etc.,
- and unsaturated-dicarboxyli~ acids such as itaconic acid, etc.
The support can also carry a filter or antihalation layer composed
of a dyed polymer layer which absorbs the exposing radiation after
it passes through the light-sensitive layer and eliminates un-
wanted reflection from the support. A yellow dye in a polymeric
binder, such as one of the polymers referred to above as suitable
subcoatings, is an especially effective antihalation layer when
ultraviolet radiation is employed as the exposing radiation. The
optimum coating thickness of the light-sensitive layer will depend
upon such factors as the use to which the coating will be put,
the particular light-sensitive polymer employed, and the nature
of other components which may be present in the coating. Typical
coating thicknesses for use in preparing resists can be from
3 about 0.1 to 0.5 mils.
;; 15
1~3S2~2
The photographic elements employed in the present
invention can be imagewise exposed by conventional methods to a
source of actinic radiation which is preferably a source which
is rich ln ultraviolet light. Suitable sources include carbon
arc lamps, mercury vapor lamps, fluorescent lamps, tungsten
.
filament lamps, lasers, and the like. The exposed elements
can then be developed by flushing, soaking, swabbing, or
otherwise treating the light-sensitive layers with a solvent
or solvent system which exhibits a differential solvating
action on the exposed and unexposed materials. The exposed
areas of the coating will be removed by the solvent while ~ -
the unexposed areas will be unaffected. These developing
solvents may be organic or aqueous in nature and will vary
with the composition of the photographic layer to be developed.
Exemplary solvents include water, aqueous alkali, the lower
alcohols and ketones, and aqueous solutions of the lower alcohols ~-
and ketones. The resulting images may then be treated in any
known manner consistent with their intended use such as treatment
with desensitizing etches, plate lacquers, etc.
.. .. . ............ ~ . :
A preferred process for forming and treating the element
~ comprises applying the photorèsist solution to a clean surface to
be etched by spraying, dipping, whirling etc., and air dried.
If desired, a prebake of 10 to 15 minutes at~ooc is given to
remove residual solvent and the coating is exposed through a
pattern to a light source. The resist coating, is then placed ;
in a developer solvent such as an aqueous alkaline developer, to
remove the exposed areas. The developer can also contain dyes
and/or pigments and hardening agents. The developed image is
' rinsed with distilled water, dried and optionally postbaked for
' 30 15 to 30 minutes at 80C to 120C. The substrate can then be
etched by acid etching solutions such as ferric chloride.
,:,
-16- ~;
, ~,. .. _ , .. , ,.. _ _ .. ~.. ,.. , .. ,, ., ... _ . . . . _ . ._._ _ . ..... _ ., ,_ .. _ .. .. ~__ ~
S2~2
The following preparations are lncluded to lllustrate
the production of materials useful in the practice Or o~r invention:
; Preparation 1: Esterification of Alnovol~ 429K Resin*
with 1,2-naPhthaquinone-2-diazide-5-_
sulfonyl chloride (NDS-cl)
Six grams ~50 millimoles) of Alnovol 429K Resin* were
dissolved in 50 ml of dioxane and were added to 10% excess 1,2-
naphthaquinone-2-diazide-5-sulfonyl chloride (~DS-Cl) (15 9,
55 millimoles) dlssolved in 100 ml of dioxane. As the solution
10 was stirred, a 33% solution of triethylamine (7.5 g, 75 millLmoles)
in dioxane was added dropwise. After stirring for three
hours, distilled water was added (15 ml) to dissolve a gummy
precipitate which had formed during the reaction. This fraction
is believed to be aminehydrochloride and a high molecular weight
polymer.
The gummy precipitate was kept in solutio~ during the `-
reaction by replacing addition of amine with addition of small ~;
amounts of distilled water ~ntil the solution clears up and then
continuing the amine addition. This procedure was repeated until
all the amine had been added.
The solution was then precipitated into 4 liters of
0.1% hydrochloric acid, filtered, washed with distilled water,
and air dried at 40& . for 16 hours to yield fully esterified
polymer. The polym~r yielded an infrared spectrum with the -~
expected absorption at 2,183 and 2,119 cm 1 (-C-C-) and a
reduced absorption at 3,333 cm 1 (-OH). (See Table II).
.
*Alnovol~ 429K is a cresol formaldeh~de resin produced b~
Chemische '.Jerlce Albert, 7;Tiesbaden-Biebrich and sold by
American Hoechst Corp., North Somerville, New Jersey.
.~ , .
,.
~ -17-
S2~2
Preparation 2: Esterlfication Or Durite~ * ~-3
resln with ~DS~
Several samples of Durite~ * S-3937 resin were
esterified with 1,2-naphthaquinone-2-diazide-5~sulfonyl chloride
to 100%, 70%, 60%, 50% and 30% of available reactive phenol
groups, respectively. The procedures used were similar to
that described in Preparation 1 (See Table II).
*~urlte~S-3~37 is a Dhenol-formaldehy~e resin prepared by
Borden Chemical Division.
Preparation 3: Low NDS Esterification of Cresol
Novolak Resins
Twelve grams (100 millimoles) of a cresol
novolak resin were dissolved in 100 ml of dioxane and added to a
solution of NDS-Cl (2.7 g, 10 millimoles) dissolved in lO0 ml of
dioxane. The mixture was placed in a 500 ml, three-neck, round-
bottom flask fitted with an electric stirrer and a separatory
tunnel. The reaction flask was chilled in a water bath to lo&.
As the solution was stirred, triethylamine (2.G 9, 20 millimoles)
dissolved in 30 ml of dioxane was added dropwise.
2~ The reaction was allowed to proceed for 2 hours during
which time a gummy precipitate separated. The reaction solution
was filtered and the supernatant precipitated in 4 liters of 0.1%
hydrochloric acid. The resulting product was suction filtered,
washed with distilled water, and air dried at 40C. for 16 h~urs.
The light yellow product yielded an infrared spectrum similar to
the polymer prepared in Preparation 1. ApproxL~ately l~/o of the
cresol-novolak was esteri~ied (Tahle II).
.,,j.
~ ,
-18-
,:
`' ~E~
:~ .
_, _ .... . _ . . _ .
5Z~2
Preparation 4: A Micropositive Photoreslst Element
Containing Pol~mers with Hlgh NDS-Cl
Content
Photoreslst Composition
1 g Light-sensitive polymer FF (Table II)
3 g Alnovol 429K
17 g Cyclohexanone
The above resist was coated on 81 llcon wafers at
4500 rpm to give a resist film of 6000 to 8000A. The coated
wafers were prebaked for 20 minutes at BOC, exposed for 10
seconds to a colight "Exposer I" tmercury vapor) light source,
and developed for 2.5 minutes in a developer comprising:
10 ml 2-ethoxyethanol
7 ml a nonyl phenoxypolyglycidol (Olin~ Surfactant lOG)
27 ml distilled water or 45 seconds in a metal 10n
free aqueous solution developer (Shipley's MF 312) dlluted 1:1 wlth
distilled water. Lines or spaces of less than 2 microns were
resolved using either developer. After etching away 8000 A
of silicon dioxide in a buffered hydrofluoric acid solution,
all original lines 4f 3 microns or wider were retained.
The other high percent NDS-Cl esteri~ied light-sensitive
polymers AA through JJ from Table II were subsequently examined
via the procedure of Preparation 4, and all produced images.
;Variations in image quality were observed and difrerent exposure
and development times were required.
As the NDS-Cl content of the Novolak polymer was lncreased
from 50% to 100% of the available reactive sides,on the phenol-
~ormaldehyde resin, poorer quality lmages, longer development
times and some attack of the image edges were observed. Optimum
results were obtained wlth polymers having ~rom about 5% to 10%
NDS-Cl content.
- ' .
,, - 19 -
,
52~;:
Table II
NDS Sulfonated Polymers Pre~ared as in
Preparations 1 throu~h 3
Light Sensitive Theoretical
Polymer % NDS Novolak Polymer
AA 100 Alnovol 429K
BB 50 Alnoval 429K
CC 100 Durite S-3937
DD 70 Durite S-3937
EE 60 Durite S-3937
FF 50 Durite S-3937
GG 40 Durite S-3937
HH 30 Durite S-3937
II 50 Cresol Nouolak
(low mol. wt.)
J~ 40 Cresol Novolak
(low mol. wt.) -
KK 10 Cresol Novolak
tlow mol. wt.)
LL 7.5 Cresol Novolak
(low mol. wt.) ~
MM 5 Cresol Novolak :
(low mol. wt.)
NN 10 Cresol Novolak
(high mol. wt.)
00 6 Cresol Novolak
(high mol. wt.) `
,:
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- 20 -
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-- 11)85;2~2
Non-Light Sensitive Polymer for
Photoresist Formulations
The following reagents were placed in a three liter,
three-neck flash equipped with a nitrogen inlet tube, and a
water-jacketed condenser fitted wlth a constricted outlet to
reduce air backflow into the flask.
- - 1440 g 2-ethoxyethyl acetate
144 g ethyl acrylate
16 g methacrylic acid
1.6 g 2,2'-azobis(2-methylpropionitrile)
recrystallized from methanol
The reaction mixture was flushed with nitrogen for one hour and
subsequently immersed in a 90C water bath for 16 hours. The
flow of nitrogen was continued during the polymerization.
No isolation of the resulting polymer was required.
The polymer/solvent mixture can be used directly in the preparation
of a micropositive resist.
Analysis of the resulting polymer gave the following
data:
Number Ave. Mol. Wt. 7,600
Weight Ave. Mol. Wt. 1~,100
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- 21 -
The following examples compare positive photoresist ;~
formulations containing nonvolatile carboxylic acids, such as
decanoic acid, with positive photoresist formulations of the
present invention comprising volatile carboxylic acids in three
properties: thermal stability, image quality and etch resistance.
The examples illustrate the novel and unexpected results obtained
in these properties by including a volatile carboxylic acid in '
a positive photoresist formulation.
':
Example 1 (contro~ _ The Rate of_Thermal
Deqradation of a Micropositive Photoresist
1.2 g 6-nitroveratraldehyde
3.6 g light-sensitive polymer* `
6.4 g 2-methoxyethyl acetate
6.4 g butyl acetate -
*m-cresol novolak resin having the formula
~ ~C~ ( c~
CH2 ~ - --~ CH
\ H /loo k \ /X
S O2
~; ,,
\\N
O - .~ :'
wherein X is about 10 mole percent. The molecular weight is
about 1500 to about 2500.
,~
~` A stainless steel container fitted with a 30 lb/in
20 (1550 mmHg) pressure gauge was filled to 92% of capacity with
- 22 -
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i2~1L2
this positive photoresist formulation and stored at 44C. The
increase in pressure from release of' n~tr~en ~as ~rom the re~lst
contalnlng aci~ is com~ared to a control reslst which did not
contain volatlle acid. The results are recorded .
.... . , . . . . , _ _
in Table III below. .
Example 2 (Control): The Ra~e of Thermal Deqradation
Qf a MicroPositive Photoreslst Containinq Two o-2uinone-
diazide Polymers
2.4 9 Acryloi ~ AT-75 (non-light sensitive polymer made b~
Rohm and Haas)
1.8 g light-sensitive polymer Or Example 1
1.8 g light-sensitive polymer~
6.9 g 2-methoxyethyl acetate
6.9 g butyl acetate
* This light-sensitive polymer has the same formula as in Example
1 wherein X is about 5 mole percent.
Acryloid AT-75 is a commercial non-light sensitive polymer
of poly(acrylic acid-co-ethyl acrylate) used as a binder.
This photoresist formulation was placed in a stainless
container and~~tDred at 44 & as in Example 1. The r~te of
pressure build-up from released nitrogen gas is recorded in
Table III.
Examples 3-6:.. The Rate of Thermal Deqradation of
Micropositive Photoresist Formulations Containin~
Stabilizers
The photoresist formulation of Example 2 was altered
by the addition of various possibl~ stabilizer~ (welght percent
based on weight o~ total solids)~ ~ach photoresist was placed
in a stainless steel container and stored at 44 C as in Example
: 1. The rates of pressure build-up from released nitrogen
gas are recorded in Table III.
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In determining thermal stability, a pressure build-up
of less than 7 lb/in2 (365 mmHg) over a period of three weeks -
at 44C is considered to be an ind:ication of excellent stability
for long term storage of positive resists.
The formulations were coated on silicon dioxide wafers,
exposed, and developed by immersing in a dilute alkaline developer
comprising sodium phosphate and sodium silicate to determine
the image quality. The image quality was measured by
determining the dimensions of the smallest lines of the photo-
10 resist that can be measured. To test for etch resistance, the .
¢oated resists were etched for 10 minutes in buffered hydro-
fluoric acid. A photoresist is determined to have excellent
etch resistance when the etch factor does not exceed 1.
In Table III, Control A contains no carboxylic acid
in the photoresist formulation. Thermal stability is unacceptable.
Examples 3-6 are photoresist formulations of the present
invention comprising a volatile carboxylic acid. Thermal stability --
~and image quality are excellent in each example. Etch resistance
is sub-standard~for resists containing benzoic acid and hexanoic
acid. The most preferred embodiments of this invention are
shown in Examples 3-5 wherein formic acid, acetic acid and
propionic acid are used to give excellent results in all
properties.
These unexpected results are compared with the photo-
resist formulations comprising a non-volatile carboxylic acid such
as a fatty acid like stearic acid, in Controls B, C, D, E, F and
G. The thermal stability is improved, but image quality and etch
resistance are unacceptable in every formulation. It is believed
; that image quality may be deleteriously affected because the solid
1 30 non-volatile acids cannot be removed from the formulations prior
: - .
~85Z12
to the formation of the image. The present Examples show the
`, novel and unexpected results obtained over conventional positive
photoresists of the prior art.
Example 7 -
A lithographic plate was prepared by coating on to a
6 mil anodized aluminum support a photosensitive composition
comprising 180 gm of the NDS-Cl novolak condensation product
MM described on page 21; 500 grams of the acrylic binder of
preparation 5, 6 grams of glacial acetic acid and 0.9 grams
of Sudan IV dye at a coverage of 200 mg/ft2. The coating was
dried under a coating drum at a temperature of 80F in a forced
air cabinet at 134F.
,
The element was exposed for 2 minutes to a carbon
arc source and developed by swabbing for 1 minute with a sodium ~-
phosphate (tribasic) with sodium silicate developer. The litho-
graphic plate was capable of making greater than 10,000 impressions.
- The invention has been~described in detail with
particular reference to preferred embodiments thereof, but
it will be understood that variations and modifications can
, 20 be effected within the spirit and scope of the invention.
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- 26 -
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