Note: Descriptions are shown in the official language in which they were submitted.
1~93~88
This invention relates to polyamides containing the
hexafluoroisopropylidene group (CF3-C-CF3); to protective
coatings and to positive photosensitive and radiation sensitive,
high temperature, photoresist compositions prepared therefrom and
to a method of preparing heat resistant protective coatings and
relief structures of such compositions.
Positive photoresist compositions and their use are well
known. Generally such photoresists compositions are prepared
from alkali-soluble, phenol-formaldehyde novolak resins and light
or radiation sensitive o-quinone diazides or naphthoquinone
diazides. Examples of such positive photoresists are described
in U.S. Patents 3,666,473; 4,115,128; and 4,173,470.
Conventional positive novolak resists have limited
temperature dimensional stability and are not well suited for
modern high temperature, processes, and applications. Heat
resistant, negative resists are known in the art and disclosed in
U.S. Patents 3,957,512; 4,045,223; 4,088,489; Re 30,186 and DE
3411659Al. Also heat resistant positive resists are known and
disclosed in U.S. Patents 4,093,461; 4,339,521; and 4,395,482.
The advantages of positive resists over negative resists are also
known in the art which include higher resolution and exposure
time stability in the presence of oxygen.
In the industrial application of positive resists, the
polymeric component and the photosensitizer are dissolved in an
organic solvent or mixture of solvents and appiied as a thin film
or coating to a substrate suitable for the desired application.
lZ~3~138
In most applications, the exposed and developed substrate
will be subjected to treatment by a substrate-etchant solution.
The photoresist coating protects the coated areas of the
su~strate from the etchant and thus the etchant is only able to
etch the uncoated areas of the substrate, which in the case of a
positive photoresist, corresponds to the areas that were exposed
to actinic radiation. Thus, an etched pattern can be created on
the substrate which corresponds to the pattern of the mask,
stencil, template, etc., that was used to create selective
exposure patterns on the coated substrate prior to development.
The relief pattern of photoresist on substrate produced by
the method described above is useful for various applications
including, for example, as an exposure mask or a pattern such as
is employed in the manufacture of miniaturized integrated
electronic components or the manufacture of a printing plate.
The properties of a photoresist composition which are
important in commercial practice include the solubility of the
resist in the application solvent, the photospeed of the resist,
development contrast, resist resolution, resist adhesion,
dimensional s.ability at elevated temperature and abrasion
resistance.
Photospeed is impcrtant fcr a photoresist, particularly in
applications where a number of exposures are needed, for example,
in generating multiple patterns by a repeated process, or where
light of reduced intensity is employed such as in projection
exposure techniques where-the light is passed through a series of
lenses and mono-chromatic filters. Thus, high, controlled
_ q _
31}88
photospeed is particularly important for a resist comFositi_n
employed in processes where a number of multiple exposures must
be made to produce a mask or series of circuit patterns on a
substrate. Control of the photospeed is extremely important in
order to produce high resolution relief patterns in micro-
circuitry - a photospeed too high can result in narrowing the
processing conditions.
Resist resolution refers to the capability of a resist
system to reproduce the smallest equally spaced line pairs and
intervening spaces of a mask which is utilized during exposure
with a high degree of image edge acuity in the developed exposed
spaces. In many industrial applications, particularly in the
manufacture of miniaturized electronic components, a photoresist
is required to provide a high degree of resolution for very small
line and space widths (on the order of a micron or so).
The ability of a resist to reproduce very small dimensions,
on the order of a micron or so, is extremely important in the
production of large scale integrated circuits on silicon chips
and similar components. Circuit density on such a chip can be
increased, ass~ming photolithography techniques are utilized, by
increasing the resolution capabilities of the resist.
Various attempts have been made in the prior art to produce
high temperature positive resists possessing the above desired
properties. For example, U.S. Patent 4,093,461 discloses a heat
resistant, positive resist composition comprising a quinone or
naphthoquinone diazide and the p~lycondensation product of an
aromatic dianhydride and an aromatic diamine. The properties of
the positive resist of the patent are discussed in U.S. Patent
4,395,482 (column 1, lines 46-64). There it is pointed out that
the positive resist composition of U.S. 4,093,461 has limited
storage life, insufficient stability to alkaline etching
solutions and relatively small differences in solubility between
the exposed and unexposed portion of the resist.
- ~Z93~88
U.S. Patent 4,395,~82 and U.S. Patent ~,339,521 disclose
positive resist compositions containing oligomer and/or polymeric
precursors of polyoxazoles in the form of - polycondensation
products of aromatic and/or heterocyclic dihydroxydiamino
compounds and dicarboxylic acid chlorides or esters. These
references specifically disclose a poly(benzidine isophthal-
amide). These positive resist compositions are said to have long
storage life, high heat resistance, good processability and
suitability of applications in microelectronics; i.e., the
preparation of finely structured patterns. They however have
several disadvantages which include low solubility in the
commonly used solvents and low photospeed relative to the resists
of this invention.
The present invention provides an improved high temperature
positive photoresist composition with impro~ed photospeed,
improved solubility in the typical organic solvents used in the
preparation of photoresist and improved adhesion properties while
at the same time -it-has-- good long term-storage stability, in
the dry and solution form, and high resolution. Additional
advantages of the photoresists of this invention are higher
transparency and low toxicity (the benzidine of Example l of U.S.
Patent No. 4,395,482 is listed as a carcinogen and it is
difficult to prepare). It has been noted that the poly(ben-
zidine isophthalamide) of the '482 patent is not gel free when
prepared and; it must be filtered prior to isolation from the
reaction solvent. Also a photoresist solution of this
poly(benzidine isophthalamide) forms gels upon standing whi-ch is
indicative of storage instability of the resist solution.
.
-- 5 --
~z9~
This invention is that of a novel polyamide typically
prepared by the condensation of hexafluoro-2,2-bis(3-amino-4-hy-
droxyphenyl) propane with a dibasic acid chloride and mixtures of
dibasic acid chlorides. A portion of the hexafluoro-2,2-bis(3-
amino-4-hydroxyphenyl) propane may be replaced with another
diamine comonomer optionally containing less hydroxy substituents
in order to reduce the solubility of the polymer in alkaline
aqueous photoresist developer and increase the polymer solubility
in solvent. Alternately, the developer solubility of the
polyamide can be reduced or its solvent solubility increased by
neutralizing the solubilizing effect of the hydroxy groups in the
preformed polymer by converting them to a less developer soluble
moiety; for example, by acylating a portion of the hydroxy groups
in the preformed polymer. The use of non-hydroxy comonomers or
post-polymerization neutralization of the hydroxy groups provides
another method of controlling the resist's photospeed.
The invention also is that of a positive high temperature
photoresist composition comprising the above described polyamide
and o-quinone and/or o-naphthoquinone diazide photosensitizer\or
radiation sensitizer.
It has also been found that the solvent solubility and
photospeed of the resists of this invention may be controlled by
employing a mixture of dibasic acid chlorides in the preparation
of the polyamide component of the resist and/or a mixture of
hexafluoro-2,2-bis(3-amino-4-hydroxyphenyl)-propane and another
diamine. Particularly preferred dibasic acid chlorides useful
for this purpose are isophthaloyl chloride and hexafluoro-2,2-
bis(4-chlorocarbonylphenyl)-propane. Isophthaloyl chloride when
polymerized with hexafluoro-2,2-bis(3-amino-4-hydroxyphenyl-
propane produces a polyamide which when employed in a positive
photoresist composition gives a resist having an extremely high
photospeed Preferably, the isophthaloyl chloride is used in
lZ93('i88
admixture with another dibasic acid chl~ride and polymerized with
hexafluoro-2,2-bis-(3-amino-~-hydroxyphenyl)-propane. Preferred
dibasic acid chloride admixtures are 30 to 70 mole percent of
isophthaloyl dichloride with 70 to 30 percent terephthaloyl
chloride or hexafluoro-2,2-bis-(4-chlorocarbonyl-phenyl)-propane;
preferably 50 mole percent isophthaloyl chloride; said molar
percentages being based upon the dibasic acid chloride content of
the mixture.
This invention, therefore, provides a method for making a
positive photoresist composition of predetermined solvent
solubility and photospeed. The photosensitivity of the resists
of the invention can be controlled, for example, from about 10
mJ/cm2 to about 300. This result is achieved by controlling the
polyamide component's composition. Surprisingly, the
hexafluoroisopropylidene group when used as a linking group in
the diamine component of the polyamide provides increased
photospeed and solvent solubility while in the dibasic acid
chloride it reduces the photospeed and increases solvent
solubility.
This positive resist after coating and exposure in the
conventional manner can be developed in alkaline aqueous
photoresist developer to provide fine structured relief
structures suitable for use in microelectronic and printing
applications and the photospeed of the resist can be cor.trolled
to suit the particular application at hand. The photoresist has
high thermal stability (250 - 350C), improved photospeed,
improved solubility in the commonly used coating solvents and
superior adhesion.
The invention also relates to a method of improving the heat
resistance of such fine structured relief patterns by thermally
curing the developed photoresist to convert the polyamide into a
polybenzoxazole which is thermally stable at temperatures up to
550C
_ ~ _
1~93~8~1
The polyamides of the invention also are useful in producing
high-heat, protective coatings per se because of their increased
solubility in commonly used solvents, superior adhesion and
superior heat resistance.
3(~8t~
This invention is that of a high temperature polyamide
containing the hexafluoroisopropylidene group. These polyamides
have the following general formula (1):
~H-X-NH) a ( C-Y-C ) b ~N~-Z-NH~C-Y-C~ ( 1 )
where: X is the divalent group:
RO ~ --~OR
a = 0.10 to 0.50 mole fraction, preferably from about 0.25 to
about 0.5~,
b = 0.25 to 0.50 mole fraction
c = 0.00 to 0.40 mole fraction
d = 0.00 to 0.25 mole fraction
where: a ~ b + c + d = 1, said mole fractions being based upon
the total moles of X ~ Y + Z in the polymer.
where: n is an integer from about 2 - 500; preferably 20 - 300
and for photoresist application most preferably about
5 - 200.
wherein ~ is independently selected from hydrogen and a
substituted or unsubstituted aliphatic or aromatic monovalent
gro~p having up to nine carbons; preferably, R is selected from
hydrogen, methyl, ethyl and phenyl.
The groups Y and Z are unsubstituted or a substituted aliphatic,
aromatic or alicyclic divalent group having up to 60 carbons and
mixtures thereof.
- 10 --
~;~93(~8~3
The divalent group Y is independently selected from methylene and
difluoromethylene and both the divalent groups Y and Z are
independently selected from polydifluoromethylene of 2 to 12
carbons; a substitued or unsubstituted polymethylene of 2 to 12
carbons; cyclohexylene; cyclohexenylene; piperazinylene; arylene;
biarylene; napthalenylene; and polyarylene wherein the lin~ing
group (hereinafter W) between the arylene rings is independently
selected from a single carbon to carbon bond; methylene; poly-
methylene of 2 to lZ carbons; difluoromethylene, polydi1uoro-
methylene from 2 to 12 carbons; hexafluoroisopropylidene;
isopropylidene; oxy; thio; sulfinyl; sulfonyl; sulfonyldioxy;
sulfonamido; carbonyl;
( o-SiA2-o )n~ ; - SiA2-
--SiA2--O--SiA2 ; --O
O O O H
Il 11 11 1
- C-C- ; . -C-N-
O A A
Il l I
--C--N~ N--
A A
r_ f
A ; H
O O A
Il 11 1
- O-S-O- ; -S-N-
. O
-- 11 --
~Z93~B
1 3 ~I F2~ n~F
_~_ C--
A ; A
O O
Il 11
_p --o--P--o--
A ; A
N - N
~/ \~
\0/
D--~CH2tn" D -;
----~CH2 ~ D (CH2)n'' ; - ~
N N
' \C/
., 11 -
cyclohexylene; cyclohexenylene; naphthalenylene and mixtures
thereof.
The substituent A is independently selected from substituted or
unsubstituted: alkyl of 1 to 8 carbons, phenyl and naphthyl.
1~93~88
The group D is independently selected from: oxy, thio, carbonyl,
oxycarbonyl, sulfonamido, sulfinyl, sulforlyl, sulfonyloioxy,
benzenedicarbonyl, benzenedioxycarbonyl
O H O A
îl l 11 1
- C-N - ; - C-N - and
o A A A
~1 1. 1.
-N - ; - Sl-O-Sl-
A A
The integer n' is 1 to 25.
The integer n" is 1 to 12.
The terms aromatic and alicyclic as used herein include hetero-
aromatics and hetero-alicyclics wherein one or more of the carbon
atoms have been replaced with O - I - S - , or - N - atoms.
The term polyarylene is used herein to describe the divalent
group having the formula: ~
~ ~wl~
wherein W is the linking groups identified above and it is
independently selected. The integer n"' is 0, 1, 2 or 3 with the
proviso that when n"' is zero then W is not a carbon to carbon
bond.
The hydrogen atoms of the divalent group Y may be
substituted with compatible substituents. Exemplary substituents
include chloro, bromo, fluoro, alkyl from 1 to 6 carbons,
perfluoroalkyl from 1 to 6 carbons, substituted or unsubs.ituted
- 13 -
~93(~8
aryl of 6 to 12 carbons, alky or aryl carboxylic esters of 2 to
9 ca:bons, alkoxy of 1 to 6 carbons, aryloxy of 6 to 10 carbons,
acy]amino of 1 to 6 carbons, substituted or unsubstituted
a]Kylaryl of ~ to 12 carbons and substituted or unsubstituted
arylalkyl of 7 to 12 carbons.
The hydrogen atoms of the divalent group ~ may also be
substituted with compatible substituents. Exemplary substituents
include hydroxy, chloro, bromo, fluoro, alkyl from 1 to 6
carbons, perfluoroalkyl from 1 to 6 carbons , substituted or
ùnsùbstituted aryl of 6 to 12 carbons, alkyl or aryl carboxylic
esters of-2 to 9 carbons, alkoxy of 1 to 6 carbons, aryloxy of 6
to 10 carbons, acylamino of l to 6 carbons, substituted or
unsubstituted alkylaryl of 7 to 12 carbons and substituted or
unsubstituted arylalkyl of 7 to 12.
Preferably, Y is at least 70 mole percent of an aromatic
divalent group. More preferably, Y is selected from phenylene
and hexaflùoro-2,2-bis(phenyl)-propane and mixtures thereof.
Most preferably Yisa mixture of meta-phenylene, para-phenylene
and hexafluoro-2,2-bis(para-phenyl)-propane comprising about
20 - 100 mole percent of the meta-phenylene group, more
preferably about 30 - 7~ mole percent, most preferably about 40 -
~ mole percent of the meta-phenylene group. Particularly
preferred mixtures of the divalent group Y are:
1. an equal molar mixture of meta-phenylene and para-
phenylene;
2. an equal molar mixture of meta-phenylene and
hexafluoro-2,2-bis(para-phenyl)-propane;
3. a mixture of 50 mole percent meta-phenylene, 25 mole
percent para-phenylene and 25 mole percent of
hexafluoro-2,2-bis(para-phenyl)-propane
4. a equal molar mixture of meta-phenylene and
para-phenylene and hexafluoro-2,2-bis(para-phenyl)-
propane.
The above molar percentages being based up the total moles
of the group Y in the polymer.
- 14 -
1293C~88
20731-976
Preferably z is at least 70 mole percent of an
aromatic divalent group and more preferably Z is:
~R " '--~1
wherein R' and R" are independently selected from hydrogen,
hydroxy, lower alkyl of 1 to 6 carbons, lower alkoxy of 1 to 6
carbons, aryloxy of 6 to 10 carbons, chloro, fluoro, nitro, and
carboxylic aliphatic or aromatic ester having up to 10 carbons;
with the proviso that when R" ' iS the hexafluoroisopropylidene
group, R ' and R" are not both hydroxy.
wherein R" ' iS independently selected from a carbon to carbon
bond, methylene, a polymethylene having from 2 to 16 carbons
isopropylidene, difluoromethylene, a polydifluoromethylene having
2 to 12 carbons, sulfonyl, sulfinyl, sulfur, oxygen, carbonyl,
oxycarbonyl, hexafluoroisopropylidene benzenedicarbonyl and
benzenedioxycarbonyl.
Preferably Z comprises a~out 40 to about 60 mole percent of
meta-phenylene and about 60 - 40 mole percent of para-phenylene.
More preferably Z comprises about 40 to 60 mole percent of
meta-phenylene and 60 to 40 mole percent of a divalent group Y
having the formula: CF3
CF3
Most preferably Z is:
lZ93~
20731-976
R' R"
Since the preparation of the polyamides of this
invention can be conducted by a random polymerization procedure,
it is apparent that the general formula (1) is intended to
represent the average molecular configuration of the polyamides
of this invention and that the divalent group Z cannot be
methylene or difluoromethylene.
- 15a -
lZ93(~B
The polyamides of the i~vention can be prepared by the
condensation of approximately equal molar quantitites of
hexafluoro-2,2-bis~3-amino-4-hydroxyphenyl)-propane and a dibasic
acid chloride, preferably a mixture of such acid chlorides.
optionally, up to about 8~ mole percent preferably up to about 50
mole percent and more preferably about 30 mole percent of the
above hexfluoro-2,2-bis(3-amino-4-hydroxyphenyl)-propane monomer
may be replaced with another diamino comonomer; optionally
containing less hydroxy substituents in order to control the
photospeed of positive resist compositions containing the
polyamide. xamples of such comonomers which may be used are
m-phenylene diamine; p-phenylene diamine; 4,4'diaminodiphenyl
ether; 3,3'-diaminodiphenyl ether; 3,4'-diaminodiphenyl ether;
1,3-bis-(aminophenoxy)benzene (m-APB); 1,4-bis(aminophenoxy)-
benzene (p-APB); benzidine; 3,3'-dimethoxy benzidine;
3,3'-dimethyl benzidine; 3,3'-dihydroxy benzidine; 3,3'-diamino-
diphenyl methane; 4,4'-diaminodiphenyl methane; 4,4'-diamino-
diphenyl propane; 3,3'-diaminodiphenyl sulfone; 4,4'-diamino-
diphenyl sulfone; 4,4'-diaminodiphenyl sulfide; 3,3'-dihydroxy-
4,4'-diaminodiphenyl sulfone; bis-(3-hydroxy-4-aminophenyl)-
methane; 3,3'-dihydroxy-4,4'-diaminobenzophenone; ~,~ -bis(amino-
phenyl)p-diisopropylbenzene; 1,3-bis[4(4-aminophenoxy)- ~
bistrifluoromethyl]benzene; 2,2-bis[4-(4-aminophenoxy)-phenyl]-
hexafluoropropane; hexafluoro-2,2-bis-(3-amino-4-methylhexa-
fluoro-2,2-bis-(4-aminophenyl)propane; hexafluoro-2,2-bis-
(3-aminophenyl)propane; 1-2-bis(3-aminopropoxy)ethane;
m-xylylenediamine; p-xylylenediamine; bis-(4-aminocyclohexyl)-
methane; hexamethylenediamine; octamethylene diamine;
decamethylene diamine; dodecamethylene diamine; 1,4-cyclohexane
diamine; bis(3-aminopropyl)sulfide; N-methyl-bis(3-aminopropyl)-
amine;4,4'-bis(p-aminophenoxy)diphenyl sulfide; 4,4'-bis
(3n-aminophenoxy)diphenyl sulfide; 4,4'(3"-aminophenoxy-(4'-
aminophenoxy)-diphenyl sulfide; 4,4'-bis(p-aminophenoxy)diphenyl
- 16 -
1~,93~88
sulfone; ~,4'-bis-(3n-aminophenyl sulfone; 2,2-bis-~4'-p-amino-
pheroxy)phenyl] propane; 2,2-bis-[3'p-aminophenoxy)phenyl]-
propane; l,l-bis-~4'(p-aminophenoxy)phenyl]ethylbenzene and
mixtures thereof.
Alternately, the polyamide can be modified after polymeri-
zation for example, by acylating a portion of the hydroxyl gro~ps
in the preformed polymer with a carboxylic aliphatic or aromatic
acylating agent having up to 10 carbons such as acetic anhydride,
propanoic anhydride, benzoyl chloride, and diketene.
The diamino and dibasic acid chloride monomers use~ul in the
preparation of the polyamides of this invention can be prepared
by known methods; see, for example, Synthesis of Polymer Inter-
mediates Containing the Hexafluoroisopropylidene Group,
Lau, K.S.; Landis, A.L.; Kelleghan, W.J. and Beard, C.D.;
J. Polym. Sci; ~'ol~ 20, page 2381-2391 (1982).
The polyamides of the invention are prepared by known
polymerization methods; typically by the condensation of a
diamine and acid chloride; see, for example, Preparationof Fully
Aromatic Polybenzoxazoles, Kubota, T.; Nakanishiu, R.; Polymer
Letters, Vol. 2, 655-659 (1964).
The polyamides of this invention are prepared from hexa-
fluoro-2,2-bis(3-amino-4-hydroxyphenyl)propane or its reactive
equivalent for e.g. hexafluoro-2,2-bis(3-amino-4-methoxyphenyl)-
propane wherein the hydroxy group may be repla-ed by an alkoxy or
aryloxy containing up to ten carbon atoms for example, ethoxy,
propoxy, butoxy, phenoxy etc. This diamine is used in an amount
of from about 20 to 100 mole percent, preferably about 50 mole
percent and most preferably about 70 to 100 mole percent of the
diamine components present in the polymer.
Typical acid chlorides useful in the prepara-ion of the
polyamides of the invention are the acid chlorides of isophthalic
- 17 -
1293~88
acid; terephthalic acid; 4,4'-hexafluoro isopropylidene dibenzoic
acid; 1,4-cyclohexane dicarboxylic acid; pentanedioic acid;
hexanedioic acid; phthalic acid; 2,4-furandicarboxylic acid;
1,4-phenylene- diethanoic acid; 4,4'-biphenyl dicarboxylic acid;
1,1-bis(4-carboxyphenyl)-1-phenyl-2,2,2-trifluoroethane;
4,4'-dicarboxy diphenyl ether; bis-(4-carboxyphenyl)-methyl
phosphane oxide; 4,4'-dicarboxyltetraphenylsilane;
bis(4-carboxyphenol)-sulfone; 5-tertiary butyl isophthalic acid;
5-bromoisophthalic acid; 5-fluoro-isophthalic acid;
5-chloroisophthalic acid; 2,2-bis-(p-carboxyphenyl)propane,
4,4'(p-phenylenedioxy) dibenzoic acid, 2,6-naphthalene
dicarboxylic acid and mixtures thereof.
The polyamides of the present invention are useful in the
preparation of positive photoresist compositions. These resist
compositions co~prise a polyamide as heretofore described and a
;radiation or light sensitizer. The polyamide and sensitizer are
disssolved in a suitable solvent and applied to the desired
substrate. The procedures for the preparation of resist are well
known.
Similarly, the use of o-quinone diazides is well known to
the skilled artisan as demonstrated by Light Sensitive Svstems,
Xosar, J.: John Wiley & Sons, New York, 1965 in Chapter 7.4.
These sensitizers
which comprise a component of the resist compositions of the
present invention are selected from the group of substituted
naphthoquinone diazide sensitizers which are conventionally used
in the art in positive photoresist formulations. Such
sensitizing compounds are disclosed, for example, in U.S. Patent
Nos. 2,797,213; 3,1a6,465; 3,1~8,983; 3,130,047;
3,201,329;3,785,825; and 3,802,885. Useful photosensitizers
include 1,2-naphthoquinonediazide-5-sulfonyl chloride, and
1,2-naphthoquinonedia%ide-4-sulfonyl chloride condensed with
phenolic compounds such as hydroxy benzophenones.
- 18 -
1293~1~38
Additives such as colorants, dyes, anti-striation agents,
plasticizers, adhesion promoters, speed enhancers, solvents and
such surfactants as non-ionic surfactants may be added to the
solution of polyamide, sensitizer and solvent before the solution
i5 coated onto a substrate.
Examples of dye additives that may be used together with the
photoresist compositions of the present invention include Methyl
Violet 2B (C.I. No. 42535), Crystal Violet (C.I. 42555),
Malachite Green (C.I. No. 42000), Victoria Blue B (C.I. 4~045)
and Neutral Red (C.I. No. 50040) at one to ten percent weight
based on the combined weight of polyamide and sensitizer. The
dye additives help provide increased resolution by inhibiting
back scattering of light off the substrate.
Anti-striation agents may be used up to five percent weight
level, based on the combined weight of polyamide and sensitizer.
Adhesion promoters which may be used include, for example,
beta-(3,4-epoxy-cyclohexyl)-ethyltrimethoxysilane; p-methyl-
disilane-methyl methacrylate; vinyltrichlorosilane; and
~-amino-propyl triethoxysilane up to a 4 percent weight level,
based on the combined weight of polyamide and sensitizer.
Speed enhancers that may be used include, for example,
picric acid, nicotinic acid or nitrocinnamic acid at a weight
level of up to 20 percent, based on the combined weight of
polyamide and sensitizer. These enhancers tend to increase the
solubility of the photoresist coating in both the exposed and
unexposed areas, and thus they are used in applications when
speed of development is the overriding consideration even though
some degree of contrast may be sacrificed; i.e., while the
exposed areas of the photoresist coating will be dissolved more
quickly by the developer, the speed enhancers will also cause a
larger loss of photoresist coating from the unexposed areas.
Typical commercial solvents employed in the art may be used
preparing the resist compositions of this invention. .he amount
- 19 -
i~3~
of solvent used in the preparation of the resist solution may
range up to about 95% by weight of the sol~tion. The p~lyar~)ides
of the prior art have limited solubility in N-methylpyrrolidone
and dimethylacetamide whereas the polyamides of the present
invention have enhanced solubility in those solvents and
additional solvent acceptable for commercial use. Typical useful
solvents are N-methylpyrrolidone, dimethylacetamide, propylene
glycol methyl ether, methylethyl ketone, cyclohexanone,
butyrolactone and mixtures thereof; preferred solvents are
N-methylpyrrolidone and propylene glycol methyl ether.
The prepared resist solution can be applied to a substrate
by any conventional method used in the photoresist art, including
dipping, spraying, whirling and spin coating. When spin coating,
for example, the resist solution can be adjusted as to the
percentage of solids content in order to provide coating of the
desired thickness given the type of spinning equipment utilized
and the amount of time allowed for the spinning process.
Suitable substrates include silicon, aluminum or polymeric
resins, silicon dioxide, doped silicon dioxide, silicon nitride,
tantalum, copper, polysilicon, ceramics and aluminum/copper
mixtures.
The photoresist coatings produced by the above described
procedure are particularly suitable for application to thermally -
grown silicon/silicon dioxide coated wafers such as are utilized
in the production of microprocessors and other miniaturized
integrated circuit components. An aluminum/aluminum oxide
substrate can be used as well. The substrate may also comprise
various polymeric resins especially transparent polymers such as
polyesters.
Suitable developing solutions for the radiation sensitive
composition of the present invention are aqueous solutions of
inorganic alkaline compounds such as those of sodium silicate,
potassium silicate, sodium hydroxide, potassium hydroxide,
- 20 -
1~93~38
lithium hydroxide, sodium phosphate, sodium monohydrogen
phosphate, ammonium phosphate, ammoni~m monohydrogen phosphate,
sodium metasilicate, sodium bicarbonate, ammonia, etc., with a
suitable concentration of these compounds being between about 0.1
about 10, more preferably between 0.5 and 5%, by weight.
Specific examples of developer solutions are disclosed in ~.S.
Patent Nos. 3,110,596; 3,173,7~8; 3,586,504; etc.
Such an alkaline solution can also contain certain organic
solvents such as alcohols (e.g., methanol, ethanol, benzyl
alcohol, etc.) as well as a surface active agent (e.g., sodium
alkylnaphthalene sulfonate, sodium lauryl sulfate, etc.)
depending on the requirements.
After the resist composition solution is coated onto the
substrate, the substrate is baked at approximately 80 to 105C,
preferably at about 90C until substantially all the solvent has
evaporated and only a thin coating of photoresist composition on
the order of a micron in thickness remains on the substrate. The
coated substrate can then be exposed to actinic radiation in any
desired exposure pattern, produced by use of suitable masks,
negatives, stencils, templates, etc.
The exposed resist-coated substrates are next substantially
immersed in alkaline developing solution. The solution is
preferably agitated, for example, by nitrogen burst agitation.
The substrates are allowed to remain in the developer until
all, or substantially all, of the resist coating has dissolved
from the exposed areas.
After removal of the coated wafers from the developing
solution, a post-development heat trea'ment or bake may be
employed to increase the coating's adhesion and chemical
resistance to etching solutions and other substances. In fact,
-the resist formulations of the present invention ~ave excellent
adhesion to substrates such as silicon wafers, aluminum plates,
glass, polyester films etc. No adhesion promotor was necessary
- 21 -
l~g3~8
20731-976
for the photoresist processing. The post-development heat
treatment can comprise the oven baking of the coating and sub-
strate below the coating's softening point; at a temperature
from about 80 - 375C, preferably at 225 - 350C. The heat
treatment time ranging from 0.5 to about 2.0 hours. Typically,
the glass transition temperature (Tg) of the polyamide prior to
heat treatment is in the order of about 250C - 300C and after
heat treatment and conversion to a polyoxazole structure about
300 - 350C, typically about 305C - 325C.
After curing the developed substrate may be treated
with a buffered hydrofluoric acid or alkaline etching solution.
The resist composition of the invention are resistant to both
acid and base etching solutions and provide effective protec-
tion for the unexposed - resist-coated areas of the substrate.
The developed, cured photoresist provides relief structures of
excellent resolution and high thermal stability.
Although the above description is in terms of a wet-
etching process, the relief patterns of the invention may be
used in both wet and dry etching processes. The resulting
structures are particularly useful insulating layers in micro-
circuitry applications, as masks in vapor depositions process-
es, ion implantation processes etc. Similarly, the photore-
sists of this invention may be used in the preparation of
printing plates, lithographic proofing applications, litho-
graphic transfer foils and other similar applications. The
preparation of printing plates using positive photoresists is
well known in the art; see e.g. U.S. Patent No. 3,493,371.
They may be used as general protective coatings in numerous
other applications readily apparent to one skilled in the art;
1293~;8~ 20731-976
e.g. the high solubility of the polyamides of the present in-
vention make them particularly suited for high temperature
protective coatings per se as well as in photoresist applica-
tions. In a typical coating application, a
- 22a -
lZ93(~88
coating composition comprising about 5 - 30 weight percent of the
polyamide of the invention in solution is applied to a substrate.
Antioxidants, U.V. stabilizers, adhesion promoters, colorants,
flame retardants, fillers and other auxillary agents up to about
20 weight percent may be optionally employed in the coating
composition. The solvent is removed at a suitable temperature
generally about 90 - 150C and a reduced pressure may be
employed to facilitate the solvent removal. After removal of the
solvent, the polyamide coated substrate is heated to about
200 - 350C for about 0.5 - 6.0 hours and the polyamide is
converted into a polyoxazole of high heat resistance.
The following specific examples will provide detailed
illustrations of the methods of producing and utilizing composi-
tions of the preser,t invention. These examples are not intended,
however, to limit or restrict the scope of the invention in any
way and should be construed as providing conditions, parameters
of values which must be utilized exclusively in order to practice
the present invention. In the following examples the term Dark
Film Erosion Rate is abbreviated to Erosion Rate.
EXAMPLE 1
.
The polyamide of the following formula was synthesized by
the solution polycondensation method:
r~
- 23 -
~93~88
where Y = 50/50 equal molar mixture of isophthaloyl/terephthaloyl
radicals and n was approximately 2~0.
To a solution of hexafluoro-2,2-bis(3-amino-4-hydroxy-
phenyl)propane (0.01 mole = 3.66 mg~ in dimethyl acetamide (16.5
ml) and pyridine (3 ml) was added a 50/50 mixture of isophthaloyl
chloride and terephthaloyl chloride (0.0055 moles isophthaloyl
chloride = 1.1165 mg) and (0.0055 moles terephthaloyl = 1.1165
mg) in cyclohexanone (G.5 ml) dropwise with rapid stirring at
-10 to -15C for 30 min. After stirring over night (24 hrs) at
room temperature, the resulting so~ution was poured into an
ice water mixture to precipitate the polymer. The polyamide was
filtered, washed with water, and dried under vacuum at 90
overnight.
The yield was almost quantitative and inherent viscosity of the
polymer was 0.40 dlg 1 in dimethyl acetamide (0.5% conc. 25C).
EXAMPLE 2
A photoresist solution was prepared by dissolving 10 parts
of polybenzoxazole precursor of Example 1 and 5 parts by weight
of photosensitizer (mixed tris ester of trihydroxybenzophenone)
and 0.08 parts by weight of red dye in 12 parts by weight of
methylethyl ketone and 8.0 parts by weight of propylene glycol
methyl ether . The solution was filtered and then roller coated
on an anodized aluminum plate. After drying for 3 minutes at
90C, a resist film having thickness of 2 - 3 ym was obtained.
This film was covered with a photomask having a stripped pattern
so that the film and the photomask were in tight contact. Then
UV light was irradiated thereon for 60 seconds by the use of
mercury vapor lamp of 200 W. The intensity of the UV light at
the film surface was 5 mW/cm2 at a wavelength of 365 nm. After
the irradiation, the coating was developed using 1:5 alkaline
developer (AZ Developer):water mixture. The developed plate was
washed with water to obtain a fine, uniform relief pattern havins
- 24 -
~93~8
a minimum line width of 3~m. The developed plate was then given
a post-development heat treatment at 250C. for 1 hour.
The pattern obtained showed no blurring or loss of resolu-
tion after heating for up to 6 hours at a temperature of 250C.
Further, microcracks were not observed in the pattern after
development or thermal treatment although some film thickness
reduction was noticed after the heat treatment.
EXAMPLE 3
A photoresist solution was prepared by dissolving 10 parts
of polybenzoxazole precursor, the polycondensation product of
hexafluoro-2,2-bis(3-amino-4-hydroxyphenyl)propane and
terephthaloyl dichloride which was prepared in accordance with
the general procedure of Example 1, and 5 parts by weight of
photosensitizer (mixed tris ester of trihydroxybenzophenone) and
0.08 parts by weight of a red dye (disperse red 179) in 12 parts
by weight of methyl ethyl ketone and 8.0 parts by weight of
propylene glycol methyl ether. The formulation was then filtered
and roller coated on an anodized aluminum plate. The coated
plate was dried at 90C for 3 minutes to obtain a resist film
having thickness of 2 - 3~m. The film was then covered with a
photomask having a stripped pattern so that the film and the
photomask were in tight contact. Then UV light was irradiated
thereon for 60 seconds using a mercury vapor lamp of 20~w. The
intensity of the UV light at the film surface was 5 mW/cm2 at a
wavelength of 365. After the irradiation, the photoresist was
developed using a 1:5 AZ alkaline developer:water solution and
rinsed with water to obtain a relief pattern having a minimum
line width of 2Jum. The deve_oped plate was then given a post
heat treatment at 250C for 1 hour.
The pattern obtained showed no blurring or loss of resolu-
tion after heating for up to 6 hours at a temperature of 250C.
Futher, microcracks were not observed in the pattern after
- 25 -
i;~93(~8
development or thermal treatment.
EXAMPLE 4
-
The following example illustrates the acetylation of the
hydroxyl groups in a preformed polyamide of the invention (the
condensation products of hexafluoro-2,2-bis(3-amino-9-hydroxy-
phenyl)propane and a 50/50 mixture of isophthaloyl and
terephthaloyl chloride) The polyamide copolymer, 4.96mg (0.01
mole) was dissolved in 25 ml of dimethyl acetamide in a 100 ml,
three-neck flask equipped with a stirrer, condenser, and
thermometer, and heated to 100C under agitation. Then 0.2 mg of
acetic anhydride was added and the reaction mixture was heated at
l00C for 7 hours. The reaction mixture was drowned into ice
water. The polymer obtained was a white fibrous solid. It was
washed with water and dried in a vacuum oven at 100C overnight.
Approximately 20% of the polymer's hydroxyl groups were
esterified.
The following table illustrates the improved solubility of
the polyamide precursors of this invention. The data is
quantitative~ Polymer A is a condensation product of hexafluoro-
2,2-bis-(3-amino-4-hydroxyphenyl)-propane with 50/50 molar
mixture of isophthaloyl chloride and terephthaloyl chloride.
Polymer B is the condensation product of 3,3'-dihydroxy-
benzidine and isophthaloyl chloride. Polymer A was prepared in
accordance with the procedure of Example l. Polymer B was
prepared in accordance with the polymerization procedure of
Example l of U.S. Patent 4,395,482.
- 26 -
1~3(~i~8
Table 1
Solubility - weight percent
Solvent Polymer A Polymer B
N-methylpyrrolidone 30 < 20*
Dimethylacetamide 30 < 20*
Propylene glycol ~ethyl ether 30 insoluble
Methylethyl ketone 20 "
Cyclohexanone 20 "
Butyrolactone 20 "
* not completely dissolved, gels present
The following comparative examples were prepared in order to
illustrate the improved positive photoresist compositions
obtained using the polyamide of this invention over those of
prior art.
Photoresist compositions were prepared using the polyamides
(polyoxazole precursors) of the present invention prepared
substantially in accordance with Example 1 of the instant
application and a poly(benzidine isophthalamide) which was
prepared substantially in accordance with Example 1 of U.S.
Patent No. 4,339,521.
The photosensitivity (speed) of each resist composition was
evaluated using the following general procedure. Bake time,
spinspeed and other experimental conditions and results for each
experiment are reported below.
The photoresist is spin-coated on several silicon wafers at
a constant, predetermined spin speed ranging from 500 to 1500
rpm. The wafers are then baked at 90oc for 30 - 45 minutes to
remove the solvent. The initial film thicknesses of coated
resist are measured by a Rudolf film Thickness Monitor. Photo-
sensitivity is measured by generating a contrast curve as
- 27 -
1~930;8~3
described (C.G. Willson in "Introduction to Microlithography,"
Chapter 3, p. 105, American Chemical Society, Washinyton, D.C.
1983). One plots film thickness loss after one minute
development versus the logarithm (ln) of the UV exposure dose.
Film thickness is monitored by laser interferometry using the
technique described. The resist was then developed using
alkaline aqueous developer tAZ Developer, available from Hoechst
Celanese Corpora~on,- ~omerville, New Jersey) diluted with
deionized water, at 25.0+0.5C. By extrapolation of the plot to
total film thickness loss, one obtains the photosensitivity value
( mJ/cm2 ) .
The following photosensitizers were used in these
experiments and are identified using the following abbreviations:
(a) 1,2-naphthoquinone-diazido-5-sulfonic acid mixed
ester of trihydroxybenzophenone;
(b) 1,2-naphthoquinone-diazido-5-sulfonic acid tris-
ester of trihydroxy-octanophenone,
(c) bis-naphthoquinone-(1,2)-(2)-5-sulfonic acid ester
of 2,2-bis-(4-hydroxyphenyl)-propane (sensitizer of
Example 1 of U.S. Patent No. 4,339 521).
EXAMPLE 5
A photoresist solution was prepared by dissolving 15 parts
of the polyamide of Example l of this application and l5 parts of
sensitizer (b) in 70 parts of a mixed solvent consisting of
equal parts by weight of propylene glycol methyl ether and
N-methylpyrrolidone. The wafer was spincoated with the resulting
solution, dried and exposed to a mercury lamp of 200 W having
wavelength of 365 nm as explained above. The developer
concentration was l part AZ Developer to 2 parts water. The
resist was evaluated using the procedure set forth above and the
results were:
Photosensitivity 76.4 mJ/cm2
Erosion Rate 0.007 ~m/min
- 28 -
~93U1~
The characteristic curve was normal and resist adhesion to
the wafer was excellent.
EXAMPLE 6
A photoresist solution was prepared using 16 parts of the
polyamide of Example 1 of this application, 8 parts of sensitl-
zer (b), and 76 parts of a 50/50 mixture of N-methylpyrroli-
done and propylene glycol methyl ether. The procedure of Example
5 was repeated and the resist developed in a 1:8, AZ
Developer:water solution.
The results were:
Photosensitivity 74.8 mJ/cm2
Erosion Rate 0.019 ~um/min
The characteristic curve was normal and resist adhesion to
the wafer was excellent.
EXAMPLE 7
A polyamide was prepared substantially in accordance with
the procedure of Example 1 of the present invention except that 30
mole percent of the hexafluoro-2,2-bis(3-amino-4-hydroxyphenyl)-
propane monomer was replaced with an equal molar quantity of
hexafluoro-2,2-bis(3-amino-4-methylphenyl)-propane. The
resulting polyamide was~used in the resist formulation of Example
5. The resist was evaluated as in Example 5 except 1:6 AZ
Developer:water solution was used.
The results of the evaluation were:
Photosensitivity 65 mJ/cm2
Erosion Rate 0.016 ym/min
The characteristic curve was normal and resist adhesion to
the wafer was excellent.
- - EXAMPLE 8
The polyamide of Example 7 was evaluated as a photoresist
using the same procedure as previously outlined. The resist
- 29 -
1~33~
compositi`on was prepared by dissolving 20 parts of the polyamide
of Example 7 and 10 parts of sensitizer (b) in 70 parts of a
50/5~ mixture of propylene glycol methyl ether and
N-methylpyrrolidone. The developer solution was 1 part AZ
Developer to 2 parts water. The result was as follows:
Photosensitivity 81 mJJcm2
Erosion Rate 0.0~7 ~m/mim
EXAMPLE 9
The polyamide of Example 4 evaluated as a photoresist using
the procedure of Example 5. The photoresist composition was 13
parts of the acylated polyamide of Example 4 and 13 parts of sensi-
tizer (b) dissolved in 74 parts of mixed solvent consisting of
equal amounts of N-methylpyrrolidone and propylene glycol methyl
ether. The developer concentration was 1 part of AZ Developer to
2 parts water. The results were as follows:
Photosensitivity 77.6 mJ/cm2
Erosion Rate 0.011 jum/min -
The characteristic curve was normal and adhesion of theresist to the wafer was excellent.
EXAMPLE 10
A polyamide was prepared substantially in accordance with
the procedure of Example 1 except that 3~% (molar) of the diamino
monomer of Example 1 was replaced with dianisidine as a comonomer
and 100% terephthaloyl chloride as the acid chloride.
The photoresist properties were determined using the same
procedure as Example 5. The photoresist composition was 15 parts
of the polyamide compolymer, 15 parts of photosensitizer (b),- and
70 parts of equal amounts of N-methylpyrrolidone and propylene
glycol methyl ether. The developer concentration was 1 part AZ
Developer to 2 parts water.
Photosensitivity 199.5 mJ/cm2
Erosion Rate 0.013 ~m/min
- 3~ -
lZ93~
EXAMPLE 11
A polyamide was prepared substantially in accordance with
the procedure of Example 1 except that 20% (molar) of the diamino
monomer of Example 1 was replaced with an equal molar quantity of
hexafluoro-2,2-bis (3-amino-~-methylphenyl)-propane and lD0%
terephthaloyl chloride was used as the dibasic acid chloride.
The resulting polyamide was used to make a photoresist
composition by dissolving 15 parts of the polyamide and 15 parts
of sensitizer (a)--- in 70 parts of N-methylpyrrolidone. The test
wafers were processed according ~o the same procedure as used in
the previous Examples. The developer solution was 1 part AZ
Developer to 2 parts water. The results were:
Photosensitivity 237.9
Erosion Rate 0.008 ~um/min
COMPARATIVE EXAMPLE 12
The procedure of Example 5 was repeated using 8.5 parts of
poly (dihydroxybenzidine isophthalamide) prepared in accordance
with Example 1 of U.S. 4,339,521, 8.5 parts of sensitizer (b)-
and 83 parts of N-methylpyrrolidone and a coating speed of 500
RPM. The developer solution was AZ Developer at a 1:5 dilution
ratio. The results of this experiment were:
Photosensitivity 589 mJ/cm2
Erosion Rate 0.015 ~m/min
COMPARATIVE EXAMPLE 13
Example 12 was repeated except 6.8 parts of poly (dihydroxy-
benzidine isophthalamide), 6.8 parts of sensitizer (c),_-- and
84.4 parts of N-methylpyrrolidone were used. The developer
solution was concentrated AZ Developer. The results of this
experiment were:
Photosensitivity 364 mJ~cm2
Erosion Rate e.007 ~m/min
- 31 -
12~3a!8B
The following Table 2 summarizes the results of these
experiments:
TABLE 2
PHOTOSPEED_EVALUATIO~
EXAMPLE PHOTOSENSITIVITY
mJ/cm
1 76.4
6 1 74.8
7 1 65.0
8 THIS 81.0
9 INVENTION 77.6
1 199.5
11 1 237.9
12 PRIOR ART 589
13 1 364
A series of additional experiments were conducted to show
the improved properties of the polyamides of this invention using
a lithographic technique. The polyamide to sensitizer ratio was
varied in these experiments.
The following general procedure was used in this evaluation.
The polyamide and photosensitizer were dissolved in solvent and
roller coated on an anodized aluminum plate. The solvent was
removed by drying at approximately 90C to produce a resist film
of 2 - 3 ~m thick. The film was covered with a GATF Sensitivity
Guide photomask consisting of a continuous-tone gray scale with
21 numbered step densities. The Sensitivity Guide was produced
in accordance with the specifications in GATF Research Bulletin
215. The increase in density per step is 0.15.
The coated plate was exposed to UV radiation through the
Sensitivity Guide! developed in alkaline aqueous developer and
scale readings from the Sensitivity Guide developed image were
read. Exposed time, developer concentration, development time,
and and polyamide to sensitizer ratio are noted below.
The following polyamides were prepared using the procedure
of Example 1.
- 32 -
lZ93SJ88
EX A l`~lP L E 1 4
The condensation product of hexafluoro-2,2-bis(3-amino-4-
hydroxyphenyl)-propane and terephthaloyl chloride.
EXAMPLE 15
The condensation product of hexafluoro-2,2-bis(3-amino-4-
hydroxyphenyl)-propane and isophthaloyl chloride.
EXAMPLE 1 6
The condensation product of hexafluoro-2,2-bis(3-amino-4-
hydroxyphenyl)-propane with hexafluoro-2,2-bis(4-chlorocarbonyl-
phenyl)-propane.
EXAMPLE 17
The condensation product of hexafluoro-2,2-bis(3-amino-4-
hydroxyphenyl)-propane and a 50/50 (molar) mixture of the
hexafluoro-2,2-bis(4-chlorocarbonylphenyl)-propane and
isophthaloyl chloride.
~ The polyamides of Example 1, 14, 15, 16 and 17 were prepared
into photoresist coating compositions. The solvent was a 60/30
weight percent mixture of methylethyl ketone and propylene glycol
methyl ether. The photosensitizer was (a) and the developer
(AZ Developer) was diluted with one part water. The development
time was held constant at 90 seconds as was the W expose time -
90 seconds at 365 nm. The total solids content (polyamide plus
sensitizer) was 10 weight percent in each case. The following
Table 3 summarizes the results of these tests.
~93~813
Table 3
_______________________________________________________________
Polyamide Polyamide/Sensitizer Sensitivity Photospeed
_ Ratio Guide Reading Remarks
________________________________________________________________
Example 1 1:1 7 good
6:1 21 fast
Example 14 1:1 4 slow
6:1 - 21 fast
Example 15 1:1 21 fast
6:1 21 fast
Example lh 1:1 2 slow
6:1 6 good
Example 17 1:1 7 good
6:1 21 fast
The above listed data shows that the polyamide/sensitizer
ratio can be varied to control the resist's photospeed. The
photospeed of the resist composition based on the polyamide of
Example 16 was extremely high. In addition, the resist
composition based upon the polyamide of Example 18 gave the best
resolution and adhesion of the test group.
EXAMPLE 18
The polyamide of Example 16 was used to prepare a photo-
resist coating composition by dissolving the polyamide in a i0/90
weight percent mixture of methylethyl ketone and propylene glycol
methyl ether. The same procedure as reported above (Sensitivity
Guide/coated aluminum plate) was used except the exposure time
was 120 second and the alkaline aqueous developer was used
without dilution with water. The results were as follows:
Polyamide: Sensitizer Sensitivity
Ratio
1:1 3
2:1 5
3:1 6
4:1 6
5:1 7
6:1 7
- 34 -
1~33~88
The adhesion of the resist coating to the aluminum plate was
very high indicating that the polyamide would make an excellent
protective coating in other than the photoresist area.
- 3~ -
