CA1285463C - Composition useful for stripping photoresist polymers - Google Patents

Abstract

ABSTRACT

Photohardened resist masks are stripped from substrate surfaces, particularly metal surfaces of printed circuit boards, using a solution of at least one lower alkyl monoether of propylene glycol, at least one alkanolamine and at least one quaternary ammonium hydroxide compound. The solution may be diluted with water in an amount of up to about eighty percent of composition weight. If the composition contains any C2-6 alkanol, it is present in less than 5 percent by weight.

34,908-F

Description

~2~i463 NOVEL COMPOSITION USEFUL FOR
STRIPPING PHOTORESIST POLYMERS

This invention concerns a novel composition useful for stripping photoresist polymers from substrates. This invention also concerns use of the novel composition to strip photoresist polymers.
Printed circuit boards are suitably manufactured by plating a thin layer of copper on an epoxy-glass cloth laminate board of uniform thickness.
A predetermined pattern o~ holes is drilled in the board to accommodate various electrical components. A
film of partially polymerized photoresist plastic is deposited on the laminate over the copper plating.
Photoresist films are commonly composed of acrylic resins, polyvinyl cinnamates, diazo compounds, phenol-formaldehydes, or other similar film-forming materials.
The plastic is further polymerized, or cross-linked, by the action of ultraviolet light, into a hard chemically resistant film-- By covering or masking portions of the photo-resist film prior to exposure to ultraviolet light, only the unmasked portions are hardened or cross-34,908-F _1_ linked. A variety of glass, plastic and other materials are used for masking. The resist film in the masked areas is left unchanged. The unchanged film is dissolved in a "developer" using a solvent such as 1,1,1-trichloroethane or a solution such as a mixture of butoxyethanol and sodium carbonate. The copper metal in the areas free of photoresist film may be removed by etching or built up with additional copper or other metals. In either event, the exposed hardened resist film must then be removed from the laminate.
Hardened resist films can be removed with strong organic solvents, e.g., methylene chloride or trichloroethylene. US Patent 3,789,007 describes treatment of a board with a mixture of methylene chloride and methanol. Other methylene chloride-containing photoresist stripper compositions are disclosed in US Patents 3,625,763 and 3,813,309. US
Patent 4,438,192 discloses an improved photoresist stripper composition containing methylene chloride, methanol and methyl formate.
US Patent 4,202,703 uses a solution of tetramethylammonium hydroxide and a surfactant in a lower alcohol to solubilize photoresist films without attacking other materials found in integrated circuit devices. A subsequent 1,1,1-trichloroethane rinse completely removes the photoresist film.
US Patent 3,796,6p2 teaches removal of hardened photoresist films from substrate surfaces,particularly metal surfaces of printed circuit boards, with a heated aqueous stripping liquid. The liquid contains 1 to 50 percent of a partially miscible organic solvent.
Organic solvents found particularly useful include 2-34,908-F -2-' ~Z~'54~3 butoxyethanol, et~1ylene glycol mono-isobutylether, ethylene glycol mono-n-hexylether, 2-propoxypropanol, 2-(2-butoxyethoxy)ethanol, diethylene glycol mono-n-hexylether, ethylene diacetate, diethyl malonate and furfural. The stripping liquid optionally contains up to about 0.5 percent by weight of surfactants and up to 10 percent of an alkaline agent.
Several known photoresist stripping com-positions contain toxic, corrosive, or hazardouscomponents. Many of these stripping compositions also do not expeditiously remove photoresist films.
A desirable stripping composition would contain reagents which are not toxic, corrosive or hazardous.
The desirable composition would also strip films faster than known stripping compositions.
A stripping composition having several characteristics of the desirable composition is disclosed US Patent 4,592,787. The composition comprises (a) a lower alkyl monoether of a propylene glycol, or a mixture of lower alkyl monoethers of propylene glycol; (b) a C2_6 alkanol; (c) an alkanolamine; and (d) a base. The composition is, however, volatile and loses its efficiency over time.
It also has an undesirable odor.
A more desirable stripping composition would 3 also have low volatility and minimal odor. Lower volatility means that active compone~ts have a longer effective life. Reduced odor makes working with the component more pleasant.
One aspect of the present invention is a concentrated composition suitable for stripping cross-34,908-F -3-~285463 linked photoresist polymer from a substrate comprising:
a) at least one lower alkyl monoether of propylene glycol; b) at least one alkanolamine; and c) at least one quaternary ammonium hydroxide compound, with the proviso that less then 5 percent by weight of the composition contains a C2_6 alkanol. The concentrated composition optionally includes water.
A second aspect of the present invention is a dilute composition, suitable for stripping cross-linked photoresist polymer from a substrate, comprising (a) at least one lower alkyl monoether of propylene glycol, (b) at least one alkanolamine, (c) at least one quaternary ammonium hydroxide compound and (d) water in an amount of less than about eighty percent by weight of composition. Stated differently, the dilute composition is simply the concentrated composition diluted with an amount of water sufficient to provide a total water content of no more than eighty percent by weight of composition.
A third aspect of the present invention is the use of either the concentrated or the dilute stripping composition to remove hardened photoresist films from substrates.
The stripping compositions of the present invention desirably comprise, based upon composition weight, (a) a total amount of lower alkyl monoethers of a propylene glycol of from ten to eighty weight percent; (b) from five to fifty weight percent of an alkanolamine; and (c) from one and one-half to twenty weight percent of a quaternary ammonium hydroxide 34,908-F -4-~Z854~;3 compound. The compositions optionally include from zero to 20 weight percent water.
The compositions of this invention may further comprise a nonionic surfactant. If used, the nonionic surfactant is present in an amount of from 0.1 to 0.5 percent by weight. The surfactant is beneficially a low foaming nonionic surfactant with an HLB of between about 12 to 16. Examples of suitable surfactants include TritonTM X-100, an octylphenoxypolyethoxyethanol commercially available from Rohm & Haas Company, ZonylTM
FS0, a fluoroalkyl-poly(oxyethylene)ethanol commercially available from E. I. Dupont deNemours Co. and TergitolTM MPX, a polyethylene glycol ether product commercially available from Union Carbide Corporation.
The stripping compositions of the present invention, either concentrated or diluted, provide satisfactory results in terms of stripping times. The concentrated compositions will provide faster stripping times than the diluted compositions but at a greater cost.

Any lower alkyl monoether of propylene glycol, or mixture of lower alkyl monoethers of propylene glycol, may be used in compositions the present invention. Desirable lower alkyl monoethers of propylene glycol correspond to the formula ,R2 R2 R1-OtCH-CH-O~nH

34,908-F -5-.285463 wherein R1 is C1_4 alkyl;
R2 is hydrogen or methyl; and n is an integer of 1 to 8, desirably 1 to 4, with the proviso that one R2 in each unit is methyl and the other is hydrogen. "Unit" refers herein to the moiety ,R2 ,R2 tCH-CH-o~

The lower alkyl monoethers of propylene glycol function as penetrating solvents. They dissolve the adhesive and lift the photoresist polymer from the sub-strate. The photoresist polymer is then readily broken up. The monoethers also serve as co-solvents for the photoresist polymer.
Illustrative lower alkyl monoethers of pro-pylene glycol include propylene glycol methylether, propylene glycol ethylether, propylene glycol isopro-pylether, propylene glycol butylether, propylene glycol isobutylether, propylene glycol n-propyl ether, 3 propyleneglycol phenyl ether, dipropylene glycol methylether, dipropylene glycol ethylether, dipropylene glycol propylether, dipropylene glycol isopropylether, dipropylene glycol butylether, dipropylene glycol isobutylether~ tripropylene glycol methylether, tripropylene glycol ethylether, tripropylene glycol 34,908-F -6-. . .

propylether, tripropylene glycol isopropylether, tri-propylene glycol butylether, and tripropylene glycol isobutylether. Beneficial results are obtained with lower alkyl monoethers of propylene glycol selected from the group consisting of propylene glycol methylether, propylene glycol ethylether, propylene glycol isopropylether, propylene glycol propylether, dipropylene glycol methylether, dipropylene glycol propylether, dipropylene glycol isopropylether and tri-propylene glycol methylether. The lower alkylmonoether of propylene glycol is desirably propylene glycol n-propylether, propylene glycol isopropylether or propylene glycol methylether.
The stripping compositions of the present invention can include a minor amount, e.g., less than five percent by weight of composition, of an alcohol having from two to six carbon atoms. The alcohols are, however, volatile and readily eliminated from the compositions at use temperatures. As such the stripping compositions preferably contain no alcohol other than that which is present in commercially available forms of some of the quaternary ammonium hydroxide com- pounds described herein. The volatility of lower alcohols, particularly at elevated temperatures, causes a rapid decline in their contribution to stripping effectiveness. It also leads to an imbalance of remaining components over a short 3 period of time unless steps are taken to addalcohol as needed, an inexact and time-consuming procedure. In other words, the incorporation of amounts of alcohol in excess of that admixed with the quaternary ammonium compounds, while permitted, is neither necessary nor, in many cases, desirable.
.

34,908-F -7-Alkanolamines useful in this invention include sec-butanolamine, di-sec-butanolamine, monoisopropanolamine, monoethanolamine, mono-sec-butanolmonoethanolamine, methyldiethanolamine, methylamino-2-methyl-1-propanol, dimethylethanolamine, aminoethylethanolamine, monopropanolamine, isopropanol-sec-butanolamine and the like. The alkanolamine is desirably monoethanolamine, monopro- panolamine or monoisopropanolamine and preferably mono-isopropanolamine.
The alkanolamines function as a buffer to helpmaintain the composition at a desired pH. The alkanol-amines also protect the substrate by coating it to prevent redeposition of the photoresist polymer thereon.
Quaternary ammonium hydroxide compounds suitable for purposes of the present invention correspond to the formula [R3)3 - N - R4]+ OH- where R3 is an alkyl group having from one to four carbon atoms inclusive, and R4 is independently an alkyl group having from one to four carbon atoms inclusive, a phenyl group or a substituted phenyl group. If R4 is an alkyl group, it need not be identical to R3 although quaternary compounds wherein R4 equals R3 are preferred.
Illustrative quaternary ammonium hydroxides : 35 include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium 34,908-F -8-8~463 g hydroxide, tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, beta-hydroxyethyl trimethyl ammonium hydroxide and benzyltri-methylammonium hydroxide.

The quaternary ammonium compounds are not stable as free bases. As such, they are either prepared as hydrates or prepared and maintained in solution form in a dissociating medium. Water and lower alcohols, such as methanol, are typical dissociating media. When the quaternary ammonium compound is in-corporated into stripping compositions of the present invention as such a solution, the dissociating medium, or solvent, may remain as an innocuous component of the compositions. The solvent will usually be present in amounts of less than ten times, more frequently less than four times, the weight of the quaternary ammonium compound.
Satisfactory results are obtained with a strip-ping composition comprising dipropylene glycol methyl ether, monopropylene glycol n-propyl ether, mono-ethanolamine and tetramethylammonium hydroxide. Other satisfactory compositions are obtained by substituting tetraethylammonium hydroxide or tetrabutylammonium hydroxide for tetraethylammonium hydroxide. Varying the composition by substituting other components specified herein also produces satisfactory results.
3o Crosslinked photoresist polymer films are readily stripped or removed from a substrate when the film-substrate combination is contacted by one of the stripping compositions of the present invention.
- 35 Thecompositions are applied for a time, and under 34,908-F -9-128$463 - 1 o -conditions, sufficient to strip the crosslinked photoresist polymer from the substrate.
The stripping composition has a pH which is suitably 9 or greater, beneficially between lO and 14 and desirably between 11 and 13.5. At a pH of less than 9, unwanted byproducts are formed.
Stripping is usually accomplished at a tempera-ture below that at which the composition begins toundergo phase separation. The temperature is suitably between about 20C and 55C and beneficially between about 25C and 53C. Satisfactory stripping times are attainable, however, with some of the compositions 15 which have undergone phase separation.
The contact time needed to effect removal of the crosslinked photoresist polymer from a circuit board or test panel is suitably less than three 20 minutes. The time is beneficially less than two minutes, desirably from 30 to 90 seconds, preferably from 30 to 80 seconds and most preferably from 35 to 65 seconds. Contact times of more than three minutes, while possible, are generally viewed as uneconomical.
The stripping compositions of the present invention will remove photoresist polymer films prepared from compositions such as those described by Plambeck (US Patent 2,760,863), Alles (US Patents 3 3,458,311 and 3,475,171), Celeste (US Patent 3,469,982) and Hurley (US Patent 3,622,334). Additional photoresist polymers removable by the stripping compositions of the present invention include those 35 described by Celeste (US Patent 3,526,504), Minsk et al. (US Patent 2,670,286), Giangualano et al. (US

34, 908-F -lO-~2~54~i3 Patent 3,462,267) and by Joaromir Kosar in chapter 4 of "Light Sensitive Systems", John Wiley ~ Sons, Inc., Ne~
York. The stripping compositions will also remove polymer or colloid masks prepared by other processes such as heat hardening, thermographic, photosolubilization, photodeactivation and the like.
The stripping compositions can be applied to a variety of substrates having an outer layer of photoresist polymer. The compositions are particularly suitable for use in stripping photoresist polymers from circuit boards.
Stripping compositions can be applied to sub-strates by a variety of techniques. Substrates can beimmersed in the stripping compositions. Stripping compositions can also be sprayed against substrates using either a horizontal or a vertical spraying apparatus. Beneficial results are obtained when a combination of a dip tank and full jet nozzles is used to recirculate and apply stripping compositions, with pressure, against substrates.
The compositions of this invention are also useful as an ink solvent, a wax stripper, and the like.
The following examples are included for illus-trative purposes only, and do not limit the scope of the claims or the invention. Unless otherwise stated, 3 all parts and percentages are by weight.
Example 1 - Spray Bath Test Usin~ Choline Base as the Quaternary Ammonium Compound Two gallons of stripping composition were ----placed into a covered spray bath apparatus, heated to a 34,908-F -11-~2854fi3 temperature of 125 Fahrenheit (51.67 Centigrade) and sprayed, at a pressure of 18 pounds per square inch gauge (psig) [124.1 kilopascals (kPa)] onto test panels coated with a one to two mil (.0254 to .0508 millimeters) thickness of crosslinked photoresist polymer. The photoresist polymer was commercially available from E. I. duPont de Nemours & Co. under the trade designation RISTONTM. The concentrated composition comprised, based upon composition weight, 26 percent monopropylene glycol n-propyl ether, 35 percent dipropylene glycol methyl ether, 19 percent monoethanolamine, 10 percent choline base (a 45 percent solution of beta-hydroxyethyl trimethyl-ammonium hydroxide in methanol) and 10 percent water. When diluted for the stripping trial, the stripping composition comprised 8.8 percent dipropylene glycol methyl ether, 6.6 percent monopropylene glycol n-propyl ether, 4.7 percent monoethanol amine, 0.2 percent vanillin, 2.3 percent choline base (effective quaternary ammonium hydroxide concentration of 1.05 percent) and 77.4 percent water. Vanillin was an optional component added as an odor mask. The time for complete removal of the photoresist polymer from a test panel was measured hourly. Results of the stripping trials are shown in Table I.

--34,908-F -12-.. . . ....

~ ~854~

TABLE_I - STRIPPING SPEED VARIATION OVER TIME
ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
5 ( HOURS) (C) (SECONDS) O Ambient -- Started heater and pump 1 51.67 37.28 2 51.67 36.98 3 51.67 35.67 Turned heater & pump off overnight O Ambient --- Started heater and pump 1 51.67 38.11 2 51.67 38.66 3 51.67 37.26 4 51.67 37.60 51.67 36.73 6 51.67 37.78 7 51.67 37.80 8 51.67 38.89 Turned heater and pump 9 51.67 39.31 off overnight O Amblent - -- Started heater and pump 1 51.67 39.85 2 51.67 42.40 3 51.67 41.32 4 51.67 40.81 51.67 41.75 6 51.67 43.27 Turned heater and pump 7 51.67 42.82 off overnight O Ambient -- Started heater and pump 1 51.67 46.55 2 51.67 54.19 3 3 51.67 47.03 Turned heater and pump 4 51.67 70.46 off overnight 34,908-F _ 13_ 1~854~i3 TABLE I (CONTINUED) ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
(HOU~S) (C) (SECONDS) 51.67 75.38 Sample taken to analyze composition for mono-propylene glycol n-propyl ether content -determined to be 0.47 percent 5.15 --- --- Added sufficient mono-propylene glycol n-propyl ether to raise concentra-tion to 4.7 percent 5.67 --- --- Added sufficient mono-propylene glycol n-propyl ether to raise concentra-tion to 5.8 percent 6 51.67 48.68 7 51.67 53.25 --- not measured The data presented in Table I illustrate several points. First, the compositions of the present invention provide rapid stripping. All stripping times were less than one minute save for two readings when the monopropylene glycol n-propyl ether content was low. Second, the stripping compositions have an extensive useful life. Stripping times of less than 80 seconds were observed at one hour intervals over a time span of 26 hours. Third, the compositions may be 34,908-F -14-~2~5~63 rejuvenated by replenishing the lower alkyl monoether of propylene glycol.
Examples 2, 3 and 4 - Spra~ Bath Test Usin~ Tetramethyl Ammonium H~droxide as the Quaternary Ammonium Compound The procedure of Example 1 was duplicated over a shorter time interval with different stripping compo-sitions. Concentrated composition A comprised, based upon composition weight, 26.0 percent monopropylene glycol n-propyl ether, 35.0 percent dipropylene glycol methyl ether, 19.0 percent monoethanol amine, 13.8 percent of a 25 percent solution of tetramethyl ammonium hydroxide in methanol and 6. 2 percent water.
15 When diluted for the stripping trial, composition A
comprised 6.5 percent monopropylene glycol n-propyl ether, 8.7 percent dipropylene glycol methyl ether, 4. 7 percent monoethanol amine, 3.4 percent tetramethyl ammonium hydroxide solution (effective quaternary ammonium hydroxide content of 0. 86 percent) and 76.7 percent water. Dilute composition A had a pH of 12. 95 before the trials and a pH of 12.35 after the trials.
Concentrated composition B comprised, based upon 25 composition weight, 25.99 percent monopropylene glycol n-propyl ether, 35.0 percent dipropylene glycol methyl ether, 19.0 percent monoethanol amine, 13. 82 percent of a 25 percent aqueous solution of tetramethyl ammonium hydroxide and 6.19 percent water. When diluted for the 30 stripping trial, composition B comprised 6.5 percent monopropylene glycol n-propyl ether, 8.75 percent dipropylene glycol methyl ether, 4. 75 percent monoethanol amine, 3.46 percent tetramethyl ammonium hydroxide solution (effective quaternary ammonium 35 hydroxide content of 0. 86 percent) and 76. 54 percent water. The effective amount of water, including that 34,908-F -15-1~t'35463 in the quaternary ammoniu~ hydroxide solution, was 79.14 percent. Concentrated composition C comprised, based upon composition weight, 26.92 percent monopropylene glycol n-propyl ether, 37.88 percent di-propylene glycol methyl ether, 20.97 percentmonoethanol amine and 14.23 percent of a 25 percent aqueous solution of tetramethyl ammonium hydroxide.
When diluted for the stripping trial, composition C
comprised 6.73 percent monopropylene glycol n-propyl ether, 9.47 percent dipropylene glycol methyl ether, 5.24 percent monoethanol amine, 3.56 percent tetramethyl ammonium hydroxide solution (effective quaternary ammonium hydroxide content of 0.86 percent) and 75.0 percent water. The effective amount of water, including that in the quaternary ammonium hydroxide solution, was 77.7 percent. The pH values for compositions B and C were not measured. Results of the stripping trials are shown in Table II.

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The data presented in Table II show that tetra-methyl ammonium hydroxide is an effective substitute for beta-hydroxyethyltrimethyl ammonium hydroxide. The data also show that alcohol is not an essential component of the composition. The data further show that stripping speeds increase as dilution of the compositions with water increases.
Example 5 - SPray Bath Test Usin~ Tetraethyl Ammonium Hydroxide as the Quaternary Ammonium Compound The procedure of Example 1 was duplicated over a shorter time interval with a different stripping composition. The concentrated composition comprised 35.0 percent dipropylene glycol methyl ether, 26.0 percent monopropylene glycol n-propyl ether, 16.8 percent monoethanol amine, and 22.2 per cent of a 25.0 percent solution of tetraethyl ammonium hydroxide in methanol. The dilute composition used for the stripping trial comprised 8.75 percent dipropylene glycol methyl ether, 6.5 percent monopropylene glycol n-propyl ether, 4.19 percent monoethanol amine, 75.0 percent water and 5.56 percent of the tetraethyl ammonium hydroxide solution (effective quaternary ammonium hydroxide concentration of 1.39 percent). The stripping composition had a pH before the trial of 13.6 and a pH after the trial of 13.1. ~esults of the stripping trial are shown in Table III.
3o 34,908-F -19-~. ~85463 TABLE III - STRIPPING SPEED WITH TETRAETHYL AMMONIUM
HYDROXIDE AS THE QUATERNARY AMMONIUM COMPOUND

ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
(HOURS) (C) (SECONDS) O Ambient -- Started heater and pump 1 51.67 44 49 2 51.67 43.60 3 51.67 49.06 Stopped heater & pump overnight O Ambient --- Started heater and pump 1 51.67 45.48 2 51.67 54.88 3 51.67 54.97 51.67 63.65 6 51.67 78.36 7 51.67 62.51 Stopped heater and pump The data presented in Table III show that tetraethyl ammonium hydroxide is an effective substitute for beta-hydroxyethyl trimethylammonium hydroxide. The stripping time of 78.36 seconds is believed to be an aberration due to photoresist coating thickness variations.
ExamPle 6 - SPray Bath Test Usin~ Benzyl Trimethyl Ammonium Hydroxide as the Quaternary Ammonium Compound 3o The procedure of Example l was duplicated over a shorter time interval with a different stripping composition. The concentrated composition comprised 25.85 percent monopropylene glycol n-propyl ether, 35.4 :-~ 35 percent dipropylene glycol methyl ether, 23.02 percent monoethanol amine and 15.73 percent of a 40 percent 34,908-F -20-~ 285463 aqueous solution of benzyl trimethyl ammonium hy-droxide. The dilute composition used for the strippin~
trial comprised 6.46 percent monopropylene glycol n-propyl ether, 8.85 percent dipropylene glycol methyl ether, 5.76 percent monoethanol amine, 3.93 percent of the 40 percent aqueous solution o~benzyl trimethyl ammonium hydroxide (e~fective quaternary ammonium hydroxide concentration of 1.57 percent), and 75.0 percent water. The composition pH was not measured.
Results of the stripping trial are shown in Table IV.

TABLE IV - STRIPPING SPEED WITH BENZYL TRIMETHYL
AMMONIUM HYDROXIDE AS THE QUATERNARY AMMONIUM
COMPOUND
ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
(HOURS) (C) (SECONDS) O Ambient -- Started heater and pump 20 1 51.67 56.9 2 51.67 53.8 3 51.67 58.4 4 51.67 57. 3 Stopped heater & pump The stripping solution, following the trial, contained very fine particles of semiaqueous photoresist polymer. The data shown in Table IV
demonstrate that benzyl trimethyl ammonium hydroxide is an effective substitute for beta-hydroxyethyl trimethylammonium hydroxide.
ExamPle 7 - Spra~ Bath Test With Propylene Glycol Ethers Other Than Those Used in Example 1 34,908-F -21-`
`:

- ~85463 The procedure of Example l was duplicated with different propylene glycol ethers o~ler a shorter time interval. The composition, before dilution, comprised 57.97 percent propylene glycol isopropylether, 3.05 percent dipropylene glycol isopropyl ether, l9.0 percent monoethanol amine, 7.6 percent choline base (6 percent solution of beta-hydroxyetr.~l trimethyl ammonium hydroxide in methanol), an.: 12.38 percent water. The dilute composition used for the stripping trial comprised 14.49 percent propylene glycol isopropyl ether, 0.76 percent dipropylene glycol isopropyl ether, 4.75 percent monoethanol amine, l.90 percent choline base (effective ~uaternary ammonium hydroxide concentration of 1.14 percent) and 78.1 percent water. The composition pH was not measured.
Reqults of the stripping trial are shown in Table V.

TABLE V - STRIPPING SPEED WITH CHOLINE BASE
AS THE QUATERNARY AMMONIUM HYDROXIDE AND
DIFFERENT PROPYLENE GLYCOL ETHERS
ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
25 (HOURS) (C) (SECONDS) O Ambient -- Started heater and pump 1 51.67 72.0 2 51.67 84.3 3 51.67 87.9 4 51.67 105.9 Stopped heater and pump The data presented in Table V show that a 35 mixture of propylene glycol isopropyl ether and dipropylene glycol isopropyl ether will produce .

34,908-E -22-3546;3 reasonable results albeit not as effective as the combination of monopropylene glycol n-propyl ether and dipropylene glycol methyl ether used in Example 1.
Example 8 - Spray Bath Test With Prop~lene Glycol Methyl Ether as the Propylene Gl~col Ether The procedure of Example 1 was duplicated over a shorter time interval with a different stripping composition. The dilute composition comprised 15.26 .percent propylene glycol methyl ether, 4.75 percent monoethanol amine, 1.90 percent choline base [(60 percent solution of beta-hydroxyethyl trimethyl ammonium hydroxide in methanol) (effective quaternary ammonium hydroxide concentration of 1.14 percent)] and 78.09 percent water. Results of the stripping trial are shown in Table VI.
TABLE VI - STRIPPING SPEED TRIAL WITH PROPYLENE
~ GLYCOL METHYL ETHER AS THE PROPYLENE GLYCOL ETHER

ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
(HOURS) (C) (SECONDS) O Ambient --- Started heater and pump 1 51.67 44.8 2 51.67 65.3 Stopped heater and pump An examination of the stripping bath following the trial showed that the photoresist polymer had broken into "rod-like" pieces rather than small particles. Notwithstanding this difference, the data presented in Table VI show that propylene glycol methyl 34,908-F -23-12~54~3 ether is an effective substitute for the blend of pro-pylene giycol ethers used in Example 1.
Example 9 - Spra~ Bath Test Usin~ Pro~lene Glycol Phen~l Ether as the Propylene Gl~col Ether The procedure of Example 1 was duplicated over a shorter time interval with a different stripping composition. The concentrated composition comprised ~o 60.75 percent propylene glycol phenyl ether, 19.31 percent monoethanol amine, 7.56 percent choline base (60 percent solution of beta-hydroxyethyl trimethylammonium hydroxide in methanol) and 12.38 per-cent water. The dilute composition used ~or the 15 stripping trial comprised 15.19 percent propylene glycol phenyl ether, 4.83 percent monoethanol amine, 1.89 percent choline base (effective quaternary ammonium hydroxide concentration of 1.13 percent) and 78.09 percent water. The dilute composition was a two-phase mixture rather than a homogeneous solution. The composition pH was not measured. Results of the strip-ping trial are shown in Table YII.
TABLE VII - STRIPPING TRIAL WITH PROPYLENE GLYCOL
PHENYL ETHER AS THE PROPYLENE GLYCOL ETHER
ELAPSED TEMPERA- STRIPPING
TIME TURE SPEED REMARKS
(HOURS) (C) (SECONDS) o Ambient -- Started heater and pump 1 51.67 85.7 2 51.67 83.7 3 51.67 83.o 4 51.67 83.5 Stopped heater & pump 34, 908-E -24-~2854f~3 The data presented in Table VII demonstrate that the composition is reasonably effective for stripping photoresist polymers notwithstanding its lack of homogeneity. As such propylene glycol phenyl ether is a suitable substitute for the blend of glycol ethers used in Example l provided slower stripping speeds and a two phase mixture are acceptable.

.

--~

34,908-F -25-

Claims (18)

1. A composition, suitable for stripping a cross-linked photoresist polymer from a substrate, comprising:
a. at least one lower alkyl monoether of propylene glycol;
b. at least one alkanolamine; and c. at least one quaternary ammonium hydroxide compound;
with the proviso that less than 5 percent by weight of the composition contains a C2-6 alkanol.

2. The composition of Claim 1 further comprising water.

3. The composition of Claim 2 wherein the pH
is 9 or greater.

34,908-F -26-

4. The composition of Claim 1 wherein lower alkyl monoethers of propylene glycol correspond to the formula wherein R1 is C1-4 alkyl;
R2 is hydrogen or methyl; and n is an integer of 1 to 8, with the proviso that one R2 in each unit is methyl and the other is hydrogen.

5. The composition of Claim 4 wherein n is an integer of from one to eight inclusive.

6. The composition of Claim 1 wherein the quaternary ammonium hydroxide compound corresponds to the formula [(R3)3 - N - R4]+OH-where R3 is an alkyl group having from one to four carbon atoms inclusive and R4 is independently an alkyl group having from one to four atoms inclusive, a phenyl group or a substituted phenyl group.

34,908-F -27-

7. The composition of Claim 1 or 2 wherein a nonionic surfactant is also present.

8. The composition of Claim 1 comprising, based upon weight of composition, a. a total amount of lower alkyl monoether of propylene glycol of from ten to eighty weight percent;
b. from five to fifty weight percent alkanolamine; and c. from one and one-half to twenty weight percent quaternary ammonium hydroxide compound.

9. The composition of Claim 8 further comprising from zero to twenty weight percent water.

10. The composition of Claim 8 or 9 wherein from 0.1 to 0.5 weight percent of nonionic surfactant is also present.

11. The composition of Claim 1 wherein the alkanolamine is monoethanolamine, monopropanolamine or monoisopropanolamine.

12. The composition of Claim 1 further comprising a mixture of at least two lower alkyl monoethers of propylene glycol.

13. The composition of Claim 3 wherein the pH
is from 10 to 14.

14. The composition of Claim 2 comprising 34,908-F -28-a. dipropylene glycol isopropylether;
b. propylene glycol isopropylether;
c. monoethanolamine;
d. a quaternary ammonium hydroxide compound selected from the group consisting of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetra-propylammonium hydroxide, tetraisopropylammonium hydroxide, beta-hydroxyethyl trimethyl ammonium hydroxide and benzyltrimethylammonium hydroxide;
and;
e. water.

15. A method of stripping a cross-linked photoresist polymer from a substrate which comprises contacting a substrate upon which a cross-linked photoresist polymer is adhered with a stripper composition at a temperature at which the stripper composition is a single phase, for a time sufficient to strip the cross-linked photoresist polymer from the substrate, the stripper composition having a pH of 9 or greater and comprising a composition of Claim 1, 2, 8 or 9.

16. The method of Claim 15 wherein the substrate is a printed circuit board.

17. The method of Claim 15 wherein the substrate is immersed in a bath of the stripping composition.

18. The method of Claim 15 wherein the stripping composition is sprayed on the substrate.

34,908-F -30-