CA1116059A

CA1116059A - Phenol-free and chlorinated hydrocarbon-free photoresist stripper

Info

Publication number: CA1116059A
Application number: CA326,518A
Authority: CA
Inventors: John E. Vander Mey
Original assignee: Allied Corp
Current assignee: Allied Corp
Priority date: 1978-05-22
Filing date: 1979-04-27
Publication date: 1982-01-12
Also published as: FR2426926B1; GB2021285A; DE2919666C2; JPS54153577A; FR2426926A1; DE2919666A1; JPH0253781B2; GB2021285B; IT7968069A0; IT1165205B

Abstract

ABSTRACT
PHENOL-FREE AND CHLORINATED HYDROCARBON-FREE
PHOTORESIST STRIPPER

Stripping solutions, free from phenol and chlor-inated hydrocarbon compounds, comprising a surfactant alkylarylsulfonic acid having 12-20 carbons, a hydrotropic aromatic sulfonic acid having 6-9 carbons and a halogen-free aromatic hydrocarbon solvent with a boiling point above 150°C. The stripping compositions effectively remove organic polymeric substances from inorganic substrates and are substantially clear water rinsable.

Description

DESCRIPTION
PHENOL-F'REE AND CHLORINATED
HYDROCARBON-FREE PHOI~RE3~SI S~.P~R
BACKGROUND OE THE_INVENI'ION
During manufacture of selliiconductors and selni-condllctor microcircuits, it is frequently necessary to coat the materials from which the semiconductors and microcircuits are manufactured with a polymeric organic substance, generally referred to as a photoresist, e.g., a substance which forms an etch resist upon exposure to light. These photoresists are used to protect selected areas of the surface of the substra~e, e.g. silicon, -SiO2 or aluminum, from the action of the etcning solu-tion, while such etchant selectively attacks the unpro-tecteA area of the substrate. Following completion of the etching operation and washing away of the residual etchant, it is necessary that the resist be removed from the protective surface to permit essential finishing operations.
A common method used in removing the photo-resist from the substrate is by contacting the substrate with an organic stripperO Heretofore these organic strippers have been composed of various components whose purpose it was to lift and remove the polymeric photo-;~ resist from the substrate. However, these stripping solutions have heretofore usually contained phenol or ;~ phenol compounds and chlorinated hydrocarbon colnpounds.
The use of phenol or phenol compounds or chlorinatedhydrocarbon compounds results in a distinct disadvan-tage due to the tOXlCity of phenol as well as the ~-:

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-2-pollution problems arising from the disposal of phenol or phenol compounds such as cresols, phenol sulfonic acid and the like or the disposal of chlorinated hydro-carbon compounds.
Phenol-free and chlorinated hydrocarbon-free strippers are described in U.S. Patent No. 4,070,203 (issued January 24, 1978 to Neisius et al.). These strippers, having only an alkylbenzenesulfonic acid corn-ponent of 12-20 carbons and a chlorine free, aromatic hydrocarbon component with a boiling point above 150C, suffer from the disadvantage that they cannot be easily rinsed off the inorganic substrate after stripping with aqueous rinsing ~,aterials such as deionized water.
Instead organic solvents are required to avoid either lS the polymer or the aromatic solvent precipitating or forming oil beads, respectively, or, if water is used, copious amounts are required. The formation of oil beads is called "oiling out" and may lead to an undesirably oily layer remaining on the inorganic substrate.
It is an object of this invention to provide an effective photoresist stripping solution which is essentially free of phenol, phenol compounds and chlor-inated hydrocarbon compounds.
It is an additional object of this invention to provide such a solution which is substantially clean water rinsable such that the hydrocarbon solvent does not oil out and the polymer does not reprecipitate dur-ing rinsing.
It is an additional object of this invention to provide a Method for removing photoresist polymeric coatings from inorganic substrates with such a strippin~
solution free from phenol, phenol compounds and chlorinated hydrocarbon compounds which can then be rinsed with an aqueous rinsing agellt such as deionized water.
These and other objects will become apparent from the description which follows.

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BRIÆ D13SCRIPTION Oli' T~l~ INVE~L~'rIOli~
Briefly/ in accordance with this invention, there is provided a stripping solution for relnoving polymeric organic substances froln an inorganic substrate, said solution being essentially free of phenol compounds and chlorinated hydrocarbon compounds and beiny substan tially clear water rinsable and comprising a~ from about 5 to about 60 weight percent of a surfactant alkylarylsulfonic acid having 12-20 carbons;
b) from about 15 to about 95 weight percent of a hydrotropic aromatic sulfonic acid having 6-9 carbons;
and c) from about 5 to about 40 weight percent of a halogen free aromatic hydrocarbon solvent with a boil~
ing point above 150C.
Also in accordance with this invention, there is provided a method for removing a photoresist organic polymeric coating material from the surface of an inorganic substrate which comprises contacting said coated substance for a time sufficient to loosen said coating with the above stripping composition and rinsing the composition and photoresist from the substrate with an aqueous rinsing agent.
DETAILED DESCRIPTION OF THE INVE~TION
_ _ _ The present invention provides a composition which is effective in removin~ photoresist, and a method for removing photoresist from inorganic substrates, without the use of phenol or phenol compounds or chlorinated hydrocarbon compounds and their correspond-ing disadvantages. Surprisinyly, it has been found that the surfactant sulfonic acid itself acts effectively as a photoresist stripper. This is unexpected in the sense that the prior art relating to such stripping solutions employed such compounds in their compositions as surface active agents and yet felt that phenol or phenol COM-pounds were necessary to effectively remove the photo-resist from the substrate.
Certain surfactant sulfonic acids have been '.

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found to be effective, per se, for relnovin~ organic photoresist, that i5, those having 12-20 carbons.
Exemplary of such aryl sulfonic acids suitable for use in accordance with the present invention are hexylbenzene sulfonic acid, heptylbenzenesulfonic acid, octylbenzenesulfonic acid, decylbenzenesulfonic acid, dodecylbenzenesulfonic acid, tridecyl~enzenesulfonic acid, quadecylbenzenesulfonic acid, and the like.
Blends of these surfactant sulfonic acids ~nay also be employed so long as the number average carbon nulober is between 12 and 20. Solutions containing a major proportion of hi~her sulfonic acid of over 15 carbons, which is particularly dodecylbenæenesulfonic acid are among the preferred blends.
The preferred surfactant sulfonic acid ~or use in accordance with this invention is dodecylbenzene-sulfonic acid, although decylbenzenesulfonic acid has also been found to be particularly effective.
Because the viscosity of the sulfonic acids is fairly high, it is desirable to lower the viscosity to reduce the quantity of material that is taken out of the strippin~ solution upon removal of the substrate after treatment with the stripping solution. The vis-cosity of the surfactant sulEonic acid can be reduced by the addition of a hydrocarbon solvent. The solvent or solvent systems which are to be used must be materials which do not deter frorn the stripping effec-tiveness of the surfactant sulfonic acid. The solvent or solvent system itself is not critical to the stripping, ie., the function of the sulfonic acid, since the function of the solvent is merely to reduce the viscosity and to render the sulfonic acid Inore readily water rinsable. Of course, the solvent should be miscible with the sulfonic acid and not react there-with and the most desirable solvents are those whichdo not induce corrosion on materials such as aluminum~
For the present invention, the solvent must not contain chlorinated hydrocarbons, phenol or phenol compounds.
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Within these guidelines, it has been found that solvents employed in conjunction with the surfactant sulfonic acids in accordance with this invention may be halogen~
free aromatic hydrocarbons having a boiling point above 5 150C. Other solvents which can be used in ad~ition to the aromatic hydrocarbon include isoparaffinic hydrocar-bons with relatively high bo:iling points, but relatively low melting points, as are commonly produced by modern synthesis from selected petroleum derived raw materials.
10 The isoparaffinic should be liquid or room temperature or slightly above and not bo:il under about 150C. They may be straight or branched chained as long as they fall within the selected parameters. Typical isoparaffinic hydrocarbons are available under the trade name Isopar 15 and can be generally characterized as containing about 60 percent of C-ll compounds, 20 percent of C-10 compounds and 20 percent of C-12 com~ounds. Preferably the isoparaf~inics are present at about 2-30 weight per-cent paraffinic solvent by weight of aromatic hydro-20 carbon solvent.
Among the preferred colnponents of the aromatic hydrocarbon solvent are alkylaryl compounds having 1-14 alkyl carbons.
Such compounds contain a benzene ring with one ` 25 or more alkyl chains. Each alkyl chain may be straight or branched, but the straight-chain alkyl groups are preferred for biodegradability. Preferred examples of such compounds include toluene, xylene, ethylbenzene, trimethylbenzene, cumene, phenyl octane and dodecylben-30 zene. Other preferred examples include phenyl nonane, tridecylbenzene, tridecyltoluene and triethylbenzene.
Mixtures of such coMpounds may also be used. The pre-ferred aromatic hydrocarbon solvents are mixtures of ;~ compounds with 9-13 alkyl carbons or 15-19 total 35 carbons. Most preferred is dodecylbenzene or mixtures having an average of about 18 total carbons.
The composition preferably contains about 5-30 `
weight percent aroMatic hydrocarbon compound or com-æ ~
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pounds. For example, about 5-30 weight percen~ of tlle preferred aromatic hydrocarbons having 15-l~ car~ons or the most preferred dodecylbenzene may be used.
The composition is free of halogenated hydro-carbons such as perchloroethylene and dichlorobenzene.
Such solutions are generally bio~egradable as compàred to solutions containing halogenated hydrocarbons.
Of course other so:Lvents may also be used within the requirements of beiny free of phenol, phenol compounds and chlorinated hydrocarbon free. However, such other cornponents are preferred only in smaller quantities than the aromatic hydrocarbon.
The present invention also includes a hydro-tropic aromatic sulfonic acid of 6-9 carbons wllich may be benzenesulfonic acid, toluenesulfonic acid, xylene-sulfonic acid, ethylbenzenesulfonic acid, methylethyl-benzenesuIfonic acid, trimethylbenzenesulfonic acid, propylbenzenesulfonic acid, cumenesulfonic acid or mix-tures thereof. The total group of named hydrotropic sulfonic acids will sometimes be referred to herein as "hydrotropes" and the group excluding benzenesulfonic acid will be referred to as "alkylaryl hydrotropes." It should be appreciated that the alkylaryl hydrotropes have 7-5 carbons. Preferred are toluenesulfonic acid and benzenesulfonic acid, with benzenesulfonic acid being more preferred. Tl~e several alkylbenzene sulfonic acids may be one isorner such as parasulfonic acid or a mixture of isomers such as para- and orthotoluene-' sulfonic acid.
;~ 30 It has also been surprisingly found that the hydrotropic arornatic sulfonic acids are themselves effective stripping agents such that, particularly if benzenesulfonic acid is the pre~ominant hydrotrope~ a minimum of the larger surfactant alkylarylsulfonic aciàs are requiredO Thus the hydrotropic aromatic sulfonic acid may comprise from about 15 to about 95 weight percent of the total composition, preferably about 25 to about 85 weight percent of tne total composition. It ,' . ~

~ 7--is also preferred that benzenesulfonic be the pre~om-inant hydrotrope, with 0 to abo~Jt 10 wei~nt percent of the total composition being at least one o~ the above alkylaryl hydrotropes, and the balance of the h~drotro~e being benzenesulfonic acid. Es~eciall~ preferred is 0 to about 10 weight percent of the com~osition being toluenesulfonic acid and the balance of the hydrotrope being benzenesulfonic acid.
The hydrotropic sulfonic acid should be present in sufficient amounts to prevent the aromatic hydrocarbon (if present) from oiling out on rinsing with water. Proportions within the range of about 15-55 weight percent hydrotropic sulEonic acid may not be sufficient for the several alkylbenzenesulfonic acids, even toluenesulfonic acid. Benzenesulfonic acid is norrnally sufficient at anywhere from about 15 to a~out 45 weight percent to ~revent the aromatic hydrocarbon solvent from oiling out, although the lower end of this range, below about 25~, is less preferred if the solvent is over about 30~ of the composition. Within these ranges, satisfactory amounts of a selected hydrotropic sulfonic acid for the selected surfactant sulfonic acid and aromatic hydrocarbon solvent can be readily deter-mined by adding water to a sample and looking for oil droplets.
It should be appreciated that a degree of cloudiness in the water rinse in tolerable and, there-fore the present invention is not limited to completely ; clear water rinsable strippers. Oil droplets large enough to be visually observed are intolerable, however, since they indicated a likelihood of oiling out on the substrate. Thus the present compositions should be "substantially clear water rinsable" such that a water rinse will remain clear or only turn cloudly and not form visible droplets. Preferably, however, the present colnpositions are "clear water rinsable" in that a water rinse remains "water white" after being used to rinse the present compositions in reasonable proportions such as 'IE3 :'`

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ten to one hundred parts by volume of water per part of stripper that enters the rinse bath or spray.
The overall range of proportions, by weiyht, is about 5-60~ surfactant sulfonic acid, about 15-95 weight percent hydrotropic sul~onic acid and ~ to about 40 weight percent aromatic hydrocarbon solvent.
Preferably the hydrotropic sulfonic acid is benzenesul~onic acid. Preferably the surfactant is dodecylbenzenesulfonic acicl. A preferred range is about 1015-55~ surfactant alkylarylsulfonic acid, about 25-80 hydrotropic aromatic sulfonic acid and about 5-30 aromatic hydrocarbon solvent.
Two especially preferred ranges are the following by weight percent:
15Surfactant ~ Solvent A about 45-55% about 20-50% about 5-25 B about 5-~5~ about 50-85~ 0 to about 10 Composition A represents a highly preferred group of strippers, having (1) the larger surfactant in quanti-ties sufficient to perform rapid and complete stripping of most photoresists and (2) hydrotrope in quantities sufficient to keep the solvent frorn oiling out upon rinsin~. The hydrotrope in cor~lposition A probably ~er-forms only a secondary stripping role. Composition s represents a highly preferred group of strippers wherein the hydrotrope is present in quantities sufficient to perform rapid and complete stripping of most photo-resists, as well as keepiny the relatively low propor-tions of solvent from oiling out. The choice between these two types of preferred strippers may depend upon the type of photoresist and its history on the substrate (especially bake time and temperature), the permissible stripping conditions, desired physical properties oE the stripper during manufacture, storage and use and other secondary factors.
The present cor,lpositions are preferably sta-bilized against metal corrosion by a fluoride inhibitor as described in U.S. Patent No. 4,165,295 issued to -B~j ` ' ' , . : :.:, , : :.

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A:Llied Chemical Corp. on ~ugus-t 21, 197~. Thus about 5-500 ppm fluoride is preferably present in the COlllpOSi-tion, with about 10-200 ppm fluoride being more pre~
ferred. This fluoride may be complexed as described in U.S. Patent No. 4,215,005 issued to ~llied Chemical Corp. on July 29, 1980 with a nitrogen-containin~ CO~
plexing agent such as morpholine, dimeth~l forn,amide, aniline or the like, prefera~ly at a molar ratio of com-plexing agent to fluoride between about 10:1 and about 1:10, and more preferably at such a molar ratio between about 2:1 and about 1:2. Tne fluoride may be inhibited from vaporizing duriny storage and use in other ways as well.
The present composition are pre~erably su~stan-tially anhydrous to prevent metal corrosion during strip-ping by the combination of sulfonic acid and water; con-taining, for example, less than 1% water, preferably less than 0.5% water and more preferably less than 0.2% water.
The polymeric organic substances which are to be removed by the stripping solutions of this invention are photoresists which generally comprise polymers selected from relatively low rnolecular weight polyiso-prenes, polyvinyl cinnamates and phenol formaldehyde resins. These photoresists are applied to a substrate, e.g., SiO2, silicon or aluminum and portions are masked.
The masked substrate is then exposed to light, e.g., a 120 volt 650 watt quartz lamp for 1-15 seconds at a dis-tance of 6-12 inches to harden the exposed photoresist.
For negative photoresists,- the portion of the photo-resist which is not exposed, i.e., masked from thelight9 is then removed by a mild solvent which does not dissolve the exposed photoresist, thus leaving a pattern, e.g., a portion of an electrical circuit pattern, on the exposed substrate. For positive photo-resists it is the exposed photoresist portions that areremoved. The remaining photoresist is then baked for further hardening and the portion of the substrate which is not covered by the photoresist is etched or otherwise ~B :

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3~.3 treated. The etchant may be a buf~ered oxide, acid or plasrna etchant which may further har~en the photoresist.
The hardened photoresist must then be removed before the substrate can be further processed or used. In employing the stripping solutions of this invention, the substrate covered with the baked photoresist is con-tacted with the stripping so:Lution at a temperature of from about 50 to about 180~C, preferably between 90 and 120C. Times required for stripping the photoresist vary to quite an e~tent, depending on the specific polymer used in the photoresist and photoresist process-ing conditions. Generally, the time involved will be between l and lO minutes although some resists, depend-ing upon the bake temperature, may require 15 minutes, 30 minutes or even an hour of contact with the stripping solution before the poly~neric photoresist is loosened from the substrate. It should be appreciated that many photoresists are complete and dissolved off of the sub-strate while others may be loosened, then floated off and then dissolved in the strippin~ composition.
Examples of photoresists which may be stripped by the present composition are the following positive and negative resists:
Type ~rademark~s~ Source Negative Polyisoprene Microneg 752 or 747 Eastman Kodak Company Waycoat IC or SC Phillip A. Hunt, Inc.
Waycoat HR-lO0 or Phillip A. Hunt, Inc.

KTFR, KME~ Eastman ~odak Company Polyvinyl Cinnamate KP~ Eastman Kodak Company Positive Phenol Shipley AZ 1350 Shipley Co., Inc.
Formaldehyde or AZ lll Waycoat HP-104 Phillip A. Hunt, Inc.
or HP-204 Micropos 809 Eastman Kodak Company After the photoresist has been stripped from the substrate, the substrate is rinsed in any aqueous rinsing liquid. A solvent rinse rnay follow the , .
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-~11-stripping step, with solvents such as butylcellusolve or methylcellusolve being used. Since, however, the present compositions are substantially clear water rins able in that little or no oiling out of aromatic hydro-carbon or reprecipitation of polymer occurs when wateralone is used, it is preferred to rinse with deionized water of the purity commonly found in serlliconductor processing directly after stripping.
The compositions of the present invention, and modifications thereof can also be used to strip a variety of polymeric resins, including paints, varnishes, fluxes and the like, as well as photoresists, from a variety of inert substrates. ~hus the present invention includes also a method of stripping a polymeric resin from an inert substrate which comprises contacting the substrate coated with the resin for a period of time sufficient to loosen the resin by a com~
position which comprises:
a) from 0 to about 60 weight % of a surfac-tant alkylarylsulfonic acid having 12-20 carbons, b) from about 20 to 100~i by weight of a hydrotropic aromatic sulfonic acid having 6-9 carbons~
c) from 0 to about 20 weight ~i of a halo~en-free aromatic hydrocarbon solvent with a boiling point above 150C, and said composition being free of phenol compounds and chlorinated hydrocarbon cornpounds and being substantially clear ~ater rinsable; and then rinsing the composition and photoresist froM the sub- j strate with an aqueous rinsing agent. ~i Preferred forms of such ~nethod are those wherein the polymeric resin is a polyisoprene, poly-vinyl cinnaMate or phenol formaldehyde photoresist.
More preferred are such methods wherein the composition is of the proportions indicated by compositions "A" and "B" above.
DESCRIPTION OF T~E PREFE~RED EMBO~IMEIJT~
Examples 1 32 A silicon dioxide substrate was coated with : . . :, . . .
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12_ two organic photoresists, a neyative resist of the polyisoprene type (Waycoat MR-100 from Phillip A. Hunt, Inc.) and a positive resist of the phenol formaldehyde type (Shipley AZ 13S0 from Shipley Co., IncO).
The positive resist was ba~ed on each substrate at 180C for 30 ~ninutes. The ne~ati~e resist was baked on each substrate at 150C for 60 minutes.
The substrates were then placed in the various strip~ing compositions shown in Table 1 for 1 minute and then removed and placed in a bea~er of water ~ith mild agitation~ If photoresist remained on the substrate, the exa~,ple was repeated at 2 n;inutes stripLvincJ time.
If photoresist still remained on the substrate, the example was repeated at 3 minutes stripping time and so on up to 10 minutes, until no photoresist was detected on the substrate. Once stripping time was determined, the beaker oE rinse water used for that run was examined and noted as "clear" if water white, "cloudy" if opague and "oily" if oil droplets or an oil layer were observed.
As Table I indicatest very effective results are achieved in employiny the present compositions which are free of phenol, phenol compounds, and chlorinated hydrocarbon compounds to remove polymeric photoresist from inorganic substrates with a water rinse. In Tables 1 and 2 the following abbreviations are used: BSA - benzenesulfonic acid obtained from Jin, Walter Associates, contains about 1.0% free sulfuric acid. DDBSA -dodecylbenzenesulfonic acid obtained from Stepan Chemical Co., contains a carbon distribution of about 18% C-16, 38% C-17, 33% C-18 and 10% C-l9 and contains about 2.0% free hydrocarbon and 0.5% free sulfuric acid. TSA - toluenesulfonic acid obtained fro Jim Walters Associates, contains about 1.0% free sulfuric acid. DDB - dodecylbenzene obtained from Stepan Chemical Co., contains a carbon distri~ution of about 18% C-16, 38~ C-17, 33% C-18 and 10% C-19.
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CSA ~ cumenesulfonic acid.
XSA - xylenesulfonic acid.
EBSA - ethylbenzenesulfonlc acid.
HESA - hexylbenzenesulfonic acid or s~lfonic acid with average carbon number about 22.
DBSA - decylbenzenesulfonic acid or sulfonic acid with average carbon number about 16.
TDBSA - tridecylbenzenesulfon.ic acid or sulfollic acid with average carbon number about 19.
HDB - hexadecylbenzene or arornatic hydrocarbon with average carbon umber about 12,.
D~ - decylbenzene or aromatic hydrocarbon with average carbon number abo~t 16.
TDB - tridecylbenzene or aromatic hydrocarbon with average carbon number about 19.
The photoresists used/ identified above by their trade-marks or trade names, are believed to be as follows:
Abbre- Tradename Source Type ~ , _ viation ~0 747 MicroNeg 747 Kodak Polyisoprene 809 MicroPos 809 Kodak Phenol Formaldehyde KTFR KTFR Kodak Polyisoprene ..
KPR KPR Kodak Polyvinyl Cinnamate HR-100 Waycoat HR-100 Hunt Polyisoprene HP-204 Waycoat HP-204 Hunt Phenol Formaldehyde AZ-1350J Shipley AZ 1350J Shipley Phenol Forrnaldehyde Examples 33 - 39 The stripping procedure of Examples 1-32 is repeated using the compositions shown in Table 2. ~apid stripping of the photoresists shown in Table 2 by each example is found with little or no oiling out or repre-cipitation of photoresist polymer.
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STRIPPING TIME IN MIN A'I' 100C
WEIGHT ~ POSITIVE NFJ'GATIVE Il~ ~A~'ER
BSAD~BSA DDB TSAA~1350J HR~100

4 19 44 37 - - 1 OILY

5 26 49 25 - 1 1 CLEAR

6 30 46 24 - 1 1 CLEA2~

7 33 44 23 - 1 1 CLOUDY

8 40 40 20 - 1 1 CLOUDY

9 25 62 13 - 2 1 CLEA2~

10 35 65 -- - 2 1 CL¢AR

11 40 60 -- - 1 1 CLEAR

29100 - - ~ 2 2* CLOUDY
30 95 5 - - 1 2* CLOUDY
31 97 3 - - 2 2* CLOUDY
35 32 -- 70 30 - 10 1 CLO~DY
*Slight residue observed on substrate . .. -' ~, ' ' I ' ' ': ' ~. . 1 , HYUROTROPE SURFACTANT SOLVENT PHOTOf~ SIS'l' % ~i 33 BSA 70 CSA 5 DDBSA 25 5 AZ-135l 34 BSA 55 TSA 5 DDBSA 35 I)DB 5 MR--li)0 39 BSA 35 - - DDBSA 55 EIDB 10 KTFIi~

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Claims

I claim:

1. A composition for stripping photoresist from an inorganic substrate comprising in combination:
a) from about 5 to about 60 weight percent of a surfactant alkylarylsulfonic acid having 12-20 carbons;
b) from about 15 to about 95 weight percent of a hydrotropic aromatic sulfonic acid having 6-9 carbons; and c) from 0 to about 40 weight percent of a halo-gen-free aromatic hydrocarbon solvent with a boiling point above 150°C;
said composition being free of phenol compounds and chlorinated hydrocarbon compounds and being substan-tially clear water rinsable.

2. The composition of claim 1 wherein said hydrotropic aromatic sulfonic acid is benzenesulfonic acid.

3. The composition of claim 2 wherein said surfactant sulfonic acid is dodecylbenzenesulfonic acid.

4. The composition of claim 1 comprising from about 15 to about 55 weight percent surfactant alkylaryl-sulfonic acid, from about 25 to about 80 weight percent hydrotropic aromatic sulfonic acid and from about 5 to about 30 weight percent halogen-free aromatic hydrocarbon solvent.

5. The composition of claim 1 comprising from about 45 to about 55 weight percent surfactant alkylaryl-sulfonic acid, from about 20 to about 50 weight percent hydrotropic aromatic sulfonic acid and from about 5 to about 25 weight percent halogen-free aromatic hydrocarbon solvent.

6. The composition of claim 1 comprising from about 5 to about 45 weight percent surfactant alkylaryl-sulfonic acid, from about 50 to about 85 weight percent hydrotropic aromatic sulfonic acid and 0 to about 10 weight percent halogen-free aromatic hydrocarbon solvent.

7. The composition of claim 1 wherein said hydrotropic aromatic sulfonic acid consists of benzene-sulfonic acid and 0 to about 10 weight percent, by weight of composition, of at least one alkylarylsulfonic acid of 7-9 carbons.

8. A method of stripping a photoresist from an inert substrate which comprises contacting the substrate coated with photoresist by the composition of claim 1 for a period of time sufficient to loosen the photoresist and rinsing the composition and photoresist from the substrate with an aqueous rinsing agent.

9. The method of claim 8 wherein said aqueous rinsing agent is deionized water.

10. The method of claim 8 wherein said photoresist is a polymeric resin selected from the group consisting of polyisoprene, polyvinyl cinnamate and phenol formaldehyde photoresists.