Note: Descriptions are shown in the official language in which they were submitted.
1;~7~5g~i1
SOLVENTS FOR PHOTORESIST REMOVAL
BACKGROUND OF THE INVENTION
The present invention relates to novel solvent
systems, based on water-soluble amino derivatives and
propylene glycol compounds, that are useful for removing
photoresists.
Photoresists are used as masks in the production
of, via etching or implantation processes, integrated
component parts, circuit boards, and the like. Aster
having served their purposes, the masks are generally
removed, frequently by means of agents which, depending
on their mode of action, are known as "strippers" or
"removers".
Systems of this kind are described, for example,
by W.S. de Forest in "Photoresist: Materials and
Processes" pages 203 _ seq., McGraw-Hill Book Co., New
York, 1975. They contain, e.g., chlorinated hydrocar-
bons, such as methylenechloride; polar solvents, such as
dimethylformamide, N-methyl-2-pyrrolidone and monoetha-
nolamine; glycol ethers, such as ethylene glycol mono-
ethyl ether, ethylene glycol monobutyl ether and the ace-
tates thereof; strong bases, such as tetramethyl ammonium
hydroxide; and strong acids, such as sulfuric acid/H202
mixtures.
U.S. Patent No. 3,673,099 describes a mixture of
N-methyl-2-pyrrolidone and a strong base, such as tetra-
--1--
1;~ '7~
20731-1037
methyl ammonium hydroxide. It ls known that mixtures of this type
attack sensitive substratesr such as aluminum layers, when water
is added. It is, however, desirable for a product to be suitable
for removing photoresist coatings both from sensitive and less
sensitive substrate layers, since quite frequently these two types
of substrate layers are used simultaneously. Moreover,
tetramethyl ammonium hydroxide easily decomposes when heated, and
thus the stripping solution has a very short service life at
elevated temperatures.
U.S. Patent No. 3,796,602 describes a system comprising
an organic solvent which is partially misceable with water.
However, the compounds mentioned in this publication, such as
ethylene glycol monobutyl ether and monoaminoethanol, present
; toxicological problems. Furthermore, these compounds evaporate
easily due to their low boiling points and, hence, cannot be
employed at elevated temperatures.
European Patent Application No. 0 075 329 published
March 30, 1983 describes a mixture of a derivative of 2-
pyrrolidone and a diethylene glycol monoalkyl ether. Compounds ofthis kind are, however, hardly effective in their action. In the
examples of the document, for instance, a stripper bath
temperature of 75C is required for removal of a photoresist
sub~ected to a post-bake treatment at about 150C.
European Patent Application No. 0 145 973 published June
26, 1985 describes a system of a piperazine derivative and a N-
alkyl-2-pyrrolidone. The preferably employed N-aminoethyl
--2--
~;~79561
piperazine is classified as being toxic, whereas n-hydroxyethyl
piperazine is scarcely effective.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to
provide an agent for photoresist removal that can
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1~79561
be used at low temperatures and at elevated temperatures,
that does not cause toxic problems, that can be rinsed
off with water and is completely, or at least largely,
non-corrosive of sensitive substrates.
In accomplishing the foregoing object, there has
been provided, in accordance with one aspect of the pre-
sent invention, an agent for photoresist removal that is
comprised of:
(a) 10 to 100% by weight of at least one water-
soluble amine represented by the formula
l R3
H2N ~[(C)n - (C)m - O,~H]oH
R2 R4
in which
Rl, R2, R3, R4 denote ~ or alkyl groups
n,m denote 0 to 2, and
o denotes 1 to 3;
and
(b) 0 to 90% by weight of at least one water-
soluble propylene glycol derivative represented by the
formula
R3 - O - [CH2 - CH - O]p - R4
CH3
in which
R3, R4 denote H, alkyl or C-alkyl groups,
and o
P denotes 1 to 3.
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Other objects, features and advantages of the
present invention will become apparent from the following
detailed description. It should be understood, however,
that the detailed description and specific examples,
while indicating preferred embodiments of the invention,
are given by way of illustration only, since various
changes and modifications within the spirit and scope of
the invention will become apparent to those skilled in the
art from this detailed description.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The solvent systems of the present invention are
suitable for removing both positive-working resists and
photopolymerizable resists. Resists which can be deve-
loped with aqueous-alkaline solutions are preferably
removed.
It has been found that mixtures made according
to the instant invention, comprising water-soluble propy-
lene glycol ethers and amino compounds, can be used as
agents for photoresist removal, and do not exhibit the
disadvantages of the prior art cited above. Preference
is given to mixtures which, due to the high boiling tem-
peratures (at least 180C) of the individual components,
result in only slight weight losses when the agent is
used at elevated temperatures over a prolonged period of
time. A mixture of N-(2-amino-ethyl)ethanolamine and
tripropylene glycol methyl ether is particularly pre-
ferred.
It was not foreseeable that the photoresist
remover of the present invention, comprising high-boiling
propylene glycol ether derivatives such as tripropylene
glycol methyl ether, would exhibit satisfactory proper-
ties even at room temperature. Thus, it is possible to
use the remover of the present invention to particular
advantage for the purposes of the invention, since it can
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be employed effectively at room temperature and, due to
its favorable evaporation characteristics, at elevated
bath temperatures as well.
It has also been found that the particularly
preferred mixture of tripropylene glycol methyl ether and
N-(2-aminoethyl)-ethanolamine has a synergetic effect.
Since, in practice, photoresist layers which
were not exposed to high temperatures have to be removed
quite frequently, mixtures whose individual components
have boiling points of 160C or higher are also pre-
ferable. Of these, mixtures of dipropylene glycol methyl
ether and isopropanolamine are particularly preferred.
These systems, too, exhibit the advantages described
above, i.e., they can be used at room temperature and at
elevated temperatures. Due to their higher evaporation
rates, however, these removers are preferably employed at
relatively low bath temperatures, and they have a
synergetic effect.
It is true that the propylene glycol ethers,
such as dipropylene glycol methyl ether or tripropylene
glycol methyl ether which are preferably employed within
this invention, are distinctly more hydrophobic than com-
parable ethylene glycol ether products, and hence they
possess good solubilizing properties with respect to
organic polymers. Nevertheless, the compounds used in
the present invention can be easily rinsed off with water
without leaving any residues.
Despite their high efficiency, the mixtures
according to the present invention do not corrode sen-
sitive substrates, such as aluminum layers.
Mixtures containing lO to 90% by weight, and in
particular 20 to 70% by weight, bf the amine and lO to 90%
by weight, and in particular 30 to 80% by weight, of the
propylene glycol derivative, are preferred. It is par-
ticularly preferred that these ratios be employed with
isopropanolamine and/or N-(2-amino-ethyl)ethanolamine and
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di- or tripropylene glycol methyl ether.
Apart from their low toxicity, the mentioned
systems exhibit the advantage of having only a very faint
odor, so that it is, for example, also possible to use
them in uncovered baths.
It is self-evident that mixtures of one or
several amines with one or several propylene glycol deri-
vatives also come within the scope of the present inven-
tion.
Although it is customary to remove photoresists
in an immersion process, whereby the substrates carrying
photoresist coatings are usually moved in a bath or,
alternatively, the bath is moved, for example, by means
of a circulation pump, the remover solutions of the pre-
sent invention are also suitable for use in other pro-
cesses, such as spray or puddle processes.
The present invention will now be explained in
greater detail by references to the following, non-
limiting examples.
Examples 1 to 5
To test the effectiveness of the remover, pho-
toresist coatings conventionally employed in the produc-
tion of integrated circuits were used. A commercially
available photoresist on a diazoquinone/novolak basis
(AZ 1350 J) was spin-coated onto silicon wafers at
4,000 rpm and dried at 90C for 30 minutes. A coating
thickness of 1.8 ~m was measured. Subsequently, the
substrates were baked at 200~C for 30 minutes.
The removal tests were performed in a moving
bath having a temperature of 80C. After a dwell time of
minutes in the bath, the wafers were rinsed with
deionized water and the remaining thickness of the resist
coating was measured. The results, which are compiled in
Table 1, clearly show the superior effectiveness of N-(2-
aminoethyl)-ethanolamine (AEEA) and isopropanolamine
--6--
9~
(IPA), which were employed in accordance with the inven-
tion. Triethylene-tetraamine also had a good removing
action, but because of its toxicity this compound is not
preferred.
The amines used for comparative tests were added
in equimolar amounts.
Examples 6 to 12
The following examples also served to test the
effectiveness of various amino compounds. Here, too, the
compositions were mixed such that equimolar amounts were
present in each case.
The test conditions were the same as in Examples
1 to 5, except that the substrates had been baked at
160C for 30 minutes. The bath temperature was 22C, and
the dwell time in the remover bath was 10 minutes.
Again, the thickness of the resist coating was measured.
The results shown in Table 2 indicate that even
at 22C the removing action of N-(2-amino-ethyl)-ethanol-
amine and triethylenetetraamine is superior. Whereas in
this case the combination of isopropanolamine and tripro-
pylene glycol methyl ether (TPM) is considered less pre-
ferable, the mixture of isopropanolamine and dipropylene
glycol methyl ether exhibited good properties at room
temperature.
Examples 13 to 18
As described in Examples 1 to 5, various mix-
tures of N-(2-aminoethyl)-ethanolamine and tripropylene
glycol methyl ether were tested. The substrates had been
baked at 200C for 30 minutes, and the baths had a tem-
perature of 80C.
The results achieved with a bath dwell time of 4
minutes are compiled in Table 3. Under these conditions,-
the photoresist coatings were not yet removed completely,
but the synergetic effect between N-(2-aminoethyl)-eth-
--7--
. ~
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anolamine and tripropylene glycol methyl ether wasimpressively demonstrated by the measurement of the
resist thicknesses of incompletely removed photoresist
portions. A mixture comprised of 51% by weight of
N-(2-aminoethyl)ethanolamine and 49% by weight of tripro-
pylene glycol methyl ether was found to be the optimum
composition.
Examples 19 to 21
As described in Examples 13 to 18, the synerge-
tic effect between isopropanolamine and dipropylene gly-
col methyl ether (DPM) was determined. In these
examples, too, the dwell time in the remover bath had
been chosen such that measurable resist coatings remained
on the substrate.
The results compiled in Table 4 show that an
optimum effectiveness is achieved when the mixture is
comprised of 22.5% by weight of isopropanolamine and
77.5~ by weight of dipropylene glycol methyl e.her.
Examples 22 and 23
In these examples, the behavior of the removers
towards aluminum layers was tested by heating the com-
positions corresponding to Examples 13 and 19 to a tem-
perature of 80C and allowing them to act on
aluminum-coated wafers for 30 minutes. No attack of the
aluminum layer was observed.
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. Table 1:
.
Example Composition* Thickness of
: No. . resist coatinc
l 64.4% Di-(n-propylene)-triamine 0.380 ~m
35.6% Tripropylene-glycol-methyl
ether (TPM)
.
2 50.7% Diethylene-triamine 0.249 ~m
49.3% TPM -
3 71.8% Triethylene-tetraamine 0 ~m
28.2~ TPM
4 36.9% Isopropanolamine (IPA) 0 ~m
63.1% TPM
51.0% N-(2-aminoethyl)-ethanol
amine (AEEA) 0 ~m
49.0% TPM
* Percentages expressed by weight
. _g_
1;~795~;1
Table 2:
Example Composition* jThickness of
No. . resist coatinc
6 63.9~ Hydroxyethyl piperazine 1.517 ~m
36.1~ TPM
7 51.6~ Aminoethoxyethanol 0.396 ~m
48.4~ TPM
8 50.7% Diethylene triamine 0.369 ~m
49.3% TPM
9 36.9% IPA 0.293 ~m
63.1~ TPM
71.8% Triethylene tetramine O ~m
28.2% TPM
11 51.0~ AEEA O ~m
49.0% TPM
12 36.9% IPA
63.1% Dipropylene glycol methyl O ~m
. ether (DPM)
* Percentages expressed by weight
. --10--
~Z79S~l
Table 3:
Example Composition* Thickness of
No resist coatin
_
13 75~ N-~2-aminoethyl)-ethanol
amine (AEEA) 0.652 ~m
25% Tripropylene-glycol-methyl
ether (TPM) _
14 51% AEEA 0.387 ~m
49% TPM
35~ AEEA 0.758 ~m
65~ TPM
16 25% AEEA 0.860 ~m
75% TPM
17 15% AEEA 0.896 ~m
85% TPM
18 10% AEEA 1.174 ~m
90~ TPM
* Percentages expressed by weight
--11--
. . .
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Table 4.
Example Composition Thickness of
No resist coatinc
_
19 10.0% IPA 1.22 ~m
90.0% DPM
20. 22.5% IPA 0.S0 ~m
77.5% DPM _
21 36.9% IPA 0.83 ~m
63.1% DPM _
* Percentages expressed by weight
Examples 24 to 27
To test the effectiveness of removers of the
present invention, photopolymerizable photoresists were
used that are developable by means of aqueous-alkaline
developers and are customarily employed in the production
of circuit boards. A commercially available dry resist
(Ozatec~ T 138, made by Hoechst AG) was bonded to a
copper-clad laminate board at 115 C, exposed for 8
seconds to a 5 kw metal halide lamp arranged at a
distance of 60 cm, and developed in a 1% strength aqueous
Na2C3 solution having a temperature of 30C for 70
seconds.
The removal tests were performed in a movin~
bath having a temperature of 50 C. After 10 minutes,
the results compiled in Table 5 were achieved. The re-
sists were removed both by undiluted removal agents and
by agents that had been diluted with water.
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Table 5:
Example No. ComPOsition Resist removed
24 51% AEEA yes
49% TPM
12.75% AEEA yes
12.25% TPM
75~ water
26 22.5% IPA yes
; 77.5% DPM
27 5.63% IPA yes
19.37% DPM
: 7s% water
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