||||||IIIHHHHHIIIIUSOO539607A United States Patent (19) (11) Patent Number: 5,139,607 Ward et al. 45) Date of Patent: Aug. 18, 1992 54 ALKALINE STRIPPING COMPOSITIONS Attorney, Agent, or Firm-John Lezdey (75) Inventors: Irl E. Ward, Hatfield; Francis W. 57 ABSTRACT Michelotti, Easton, both of Pa. An alkaline positive and negative resist stripping com 73) Assignee: ACT, Inc., Allentown, Pa. position having low volatility and operable at tempera (21) Appl. No.: 690,110 tures less than about 90° C. which comprises, A. about 10 to 30% by weight of tetrahydrofurfuryl (22) Filed: Apr. 23, 1991 alcohol; 51) Int. Cl...... B44C 1/22; B29C 37/00 B. about 5 to 30% by weight of a polyhydric alcohol; 52 U.S. C...... 156/655; 156/668; C. about 10 to 30% by weight of the reaction product of 252/79.5; 430/329 one mole of furfuryl alcohol with about 1 to 20 moles (58) Field of Search...... 252/79.5, 156; 156/655, of an alkylene oxide, 156/659.1, 668; 430/329; 134/22.17, 29, 38, 40 D. about 1 to 30% by weight of a water soluble Bron (56 References Cited stead base type of hydroxide compound, and E. the remainder being water. U.S. PATENT DOCUMENTS The composition comprising a ratio of organic materials 4,078,102 3/1978 Bendz et al...... 252/79.5 X 4,686,002 8/1987 Tasset ...... 156/659.1 to inorganic materials to about 0.25:1 to 3:1. Primary Examiner-William A. Powell 11 Claims, No Drawings 5,139,607 1. 2 from substrates that heretofore have resisted ready re ALKALINE STRIPPING COMPOSITIONS moval with conventional available strippers. It is also desirable that effective stripping composi FIELD OF THE INVENTION tions be provided that are not considered undesirable by The present invention relates to novel stripping com regulatory agencies overseeing their production and positions for positive and negative photoresists having Se. non-corrosion sensitive substrates. More particularly, It is also most advantageous that stripping composi the invention is concerned with alkaline stripping con tions be provided with the above-identified desirable positions having low volatility, low odor and are biode characteristics which evidence synergistic stripping gradable which are particularly useful with photoresists O efficacy and stripping results not always obtainable with having a ceramic substrate. the additional components. U.S. Pat. No. 3,615,827 discloses an alkaline stripping BACKGROUND OF THE INVENTION composition containing a polyalkylene glycol, ethylene During manufacture of semiconductors and semicon glycol monophenyl ether and a phenol derivative. ductor microcircuits, it is frequently necessary to coat 5 U.S. Pat. No. 3,847,839 discloses an alkaline stripping the materials from which the semiconductors and mi composition which includes an alkoxylated furfuryl crocircuits are manufactured with a polymeric organic alcohol, namely, ethoxylated furfuryl alcohol and a substance, generally referred to as a photoresist, e.g., a glycol activating agent. substance which forms an etch resist upon exposure to light. These photoresists are used to protect selected 20 SUMMARY OF THE INVENTION areas of the surface of the substrate, e.g. silicon, SiO2 or The present invention provides a novel alkaline strip while such etchant selectively attacks the unprotected ping composition for both positive and negative photo area of the substrate. Following completion of the etch resists. More particularly, the stripping composition ing operation and washing away of the residual etchant, comprises: it is necessary that the resist be removed from the pro 25 1. about 5 to 30% by weight of tetrahydrofurfuryl tective surface to permit essential finishing operations. alcohol preferably about 15 to 20%; It is necessary in a photolithographic process that the 2. about 5 to 30% by weight of a polyhydric alcohol, photoresist material, following pattern delineation, be preferably about 10 to 20%; evenly and completely removed from all unexposed 3. about 10 to 30% by weight of the reaction product areas, in the case of positive resists, or exposed areas in 30 of one mole of furfuryl alcohol with about 1 to 5 moles the case of negative resists, so as to permit further litho of an alkylene oxide, preferably about 15 to 25% of the graphic operations. Even the partial remains of a resist furfuryl alcohol alkylene oxide by weight. in an area to be further patterned is undesirable. Also, 4. about 5 to 30% by weight of a water soluble Bron undesired resist residues between patterned lines can 35 stead base type hydroxide compound, preferably about have deleterious effects on subsequent processes, such 10 to 20% by weight, and as metallization, or cause undesirable surface states and 5. the remainder being water, charges. The composition comprises a ratio of organic materi A common method used in removing the photoresist als to inorganic materials of about 0.25:1 to 3:1. from the substrate is by contacting the substrate with an Advantageously, about 0.1 to 1.0% by weight of a organic stripper. Heretofore these organic strippers nonionic surfactant is added to the stripping composi have been composed of various components whose tion. purpose it was to lift and remove the polymeric photo Also, it is preferable that the furfuryl alcohol alkylene resist from the substrate. However, these stripping solu oxide is present in an excess of the tetrahydrofuryl alco tions have heretofore usually contained chlorinated 45 hol. hydrocarbon compounds and phenolic compounds The amount of the condensate of furfuryl alcohol can which resulted in a distinct disadvantage due to the be present in a ratio up to 3:1 of tetrahydrofurfuryl toxicity of these materials as well as the pollution prob alcohol. lems arising from their disposal. Because many of the toxic components of such strip DESCRIPTION OF THE PREFERRED ping compositions are highly volatile and subject to EMBODIMENTS unduly high evaporation rates, the stripping composi In accordance with the present invention, the alkaline tions require special human and environmental safety stripping composition comprises about 5 to 30% by precautions to be taken during storage and use of said weight of tetrahydrofurfuryl alcohol, preferably about compositions. 55 10 to 20% by weight. Recently, OSHA, EPA and other similar Federal, The stripping composition also contains about to State and Local Governmental Regulatory Agencies 30% by weight of a polyhydric alcohol, for example, have advocated a shift toward use of more human and polyalkylene glycols including propylene glycol, dipro environmentally compatible stripping compositions and pylene glycol, polypropylene glycol, polyethylene gly stripping methods that are not subject to the aforemen col, ethylene glycol, 1,3-butylene glycol, pinacol, and tioned drawbacks and problems. the like, as a transfer agent to maintain the base in solu It is also highly desirable that stripping compositions tion. be provided that exhibit very low vapor pressure at The composition contains about 10 to 30% by weight elevated temperatures thereby significantly reducing of a reaction product of one mole of furfuryl alcohol evaporation and thus contamination of the atmosphere. 65 which is reacted with about 1 to 5 moles of an alkylene Additionally, it is highly desirable that such stripping oxide, preferably ethylene oxide or propylene oxide, compositions be provided that are effective and effi preferably about 15 to 25% by weight of the furfuryl cient stripping compositions for removal of coatings alcohol alkylene oxide. 5,139,607 3 4. The composition also contains about 5 to 30% by Preferred nonionics, by example, are Igepal DM 710 weight of a water soluble Bronstead base type of hy and CO-610 (GAF Corp.); Pluradot HA430, Plurafac droxide compounds, preferably about 10 to 20% by RA-30 and 43, Pluronic L-62 and L-10 (BASF Wyan weight. The hydroxide compounds include alkali metal dotte Co.): Poly-Tergent LF-405 and SLF-18 and SLF hydroxides, ammonium hydroxide, tetramethylammo- 5 45 (olin Co.); Sandoxylate SX series (Sandoz Co.); nium hydroxide, and compounds which form Bronstead Emulphogene BC series (GAF Corp). base type hydroxides, for example, sodium silicate. Other suitable nonionic surfactants for use in the The remainder of the composition is water. Sufficient invention are disclosed in Kirk & Othmer, Encyclopedia water is added so as to dissolve the base compound. The of Chemical Technology, Vol. 19, pages 531 to 554, enti polyhydric alcohol is added in an amount to maintain 0 tled "Nonionic Surfactants', which is incorporated the base compound in the solution after the addition of herein by reference. the organic materials. The final product should contain The polymeric organic substances which are to be an amount of the organic materials relative to inorganic removed by the stripping solutions of the invention are materials preferably in a ratio from about 0.5:1 up to photoresists which generally comprise polymers se about 1:1. 15 lected from relatively low molecular weight polyiso A most preferred stripping composition of the inven prenes, polyvinyl cinnamates and phenol formaldehyde tion comprises: resins. In the case of negative resists, the photoresists A. about 15 to 20% by weight of tetrahydrofurfuryl are applied to a corrosion resistive substrate, (such as alcohol; ceramic). The masked substrate is then exposed to light, B. about 15 to 25% by weight of ethylene glycol; 20 e.g., a 120 volt 650 watt quartz lamp for 1-5 seconds at C. about 5 to 20% by weight of furfurylalcohol ethyl a distance of 6-12 inches to harden the exposed photo ene oxide addition product; resist. The portion of the photoresist which is not ex D. about 1 to 20% by weight of an alkali metal hy posed is removed by solvent development, thus leaving droxide, and a pattern, e.g., a portion of an electrical circuit pattern, 25 on the exposed substrate. The remaining photoresist is E, the remainder water, then baked for further hardening and the portion of the Optionally, there is included about 0.1 to 1.0% by substrate which is not covered by the photoresist is weight of a nonionic surfactant. etched or otherwise treated. The etchant may be a buff Advantageously the amount of organic materials ered oxide, acid or plasma etchant which may further present is near to or greater than the inorganic materi- 30 processed or used. In employing the stripping solutions als. of the invention for either positive or negative resists, The stripping compositions of this invention may also temperatures from about 20' C. to about 90' C., prefera contain, if desired, any suitable water miscible nonionic bly between 25' and 70' C. are employed. The period detergent which does not adversely affect the stripping required for stripping the photoresist varies to quite an action of the compositions of this invention, generally in 35 extent, depending on the specific polymer used in the an amount of about 0.1 to about 2% by weight of the photoresist and photoresist processing conditions. Gen total composition. erally, the time involved will be between 1 and 20 min The nonionic detergents which may be utilized can utes, although some resists, depending upon the bake be of the three basic types-the alkylene oxide conden temperature, may require 25 minutes, 40 minutes or sates, the amides and the semi-polar nonionics. Prefera- 40 longer before the polymeric photoresist is loosened bly, the nonionic detergent is an ethoxylated alkyl from the substrate. It should be appreciated that many phenol or alkylphenoxypoly (ethyleneoxy) ethanol, an photoresists are completely dissolved while others may ethoxylated aliphatic alcohol; polyoxyethylene, a car be loosened from the substrate, floated off, and then boxylic ester like a glycerol ester (mono- or di-), and dissolved in the stripping composition. other equivalent nonionic surfactants. Typical suitable 45 After the photoresist has been stripped from the sub ethoxylated alkylphenols are alkylphenols of Cs to C12 strate, the substrate is rinsed in any aqueous rinsing alkylphenols. It is most preferred that they be water liquid. A solvent rinse may follow the stripping step, soluble, those having at least 60 weight percent of poly with solvents such as isopropanol, butylcellosolve or oxyethylene groups being particularly well suited. Such methylcellosolve being used. Since, however, the pres ethoxylated alkylphenols are well known under various so ent compositions are substantially and cleanly water trademarks such as Igepal of GAF Corporation, Leve rinsable, it is acceptable to rinse with deionized water of lene, Neutronyx, Solar NP, the Surfonic series, and the the purity commonly found in semiconductor process Triton N and X series marketed by Rohm and Haas Co., ing directly after stripping. just to name a few. The stripping compositions of this invention are espe Among the polyoxyethylenes suitable for use in ac-55 cially useful and advantageous for numerous reasons cordance with the invention are the mono- and dialkyl among which may be mentioned the following. The ethers of ethylene glycols and their derivatives. Typical stripping compositions are water soluble, high strip of other nonionics are the monobutyl ether, ethylene efficacy, non-flammable and of low toxicity to humans glycol monobutyl ether acetate, ethylene glycol mono and the environment. Because of the low ambient vapor ethyl ether acetate, ethylene glycol dibutyl ether, ethyl- 60 pressure of the compositions they evidence substantially ene glycol monohexyl ether, ethylene glycol mono less evaporation than prior compositions and are non methyl ether, ethylene glycol monomethyl ether ace reactive and environmentally compatible. The stripping tate, ethylene glycol monophenyl ether and other compositions may be partially recycled or easily dis equivalent ethers of ethylene glycol. Another group of posed of in an environmentally safe manner without the nonionics are the polyethylene glycols and the alkoxy 65 necessity for burdensome safety precautions. After neu derivatives, particularly lower alkoxy, such as methoxy tralization, the stripping compositions are fully biode polyethylene glycol; also diethylene glycols, propylene gradable. The stripping compositions of this invention glycol and other similar glycols. evidence higher stripping efficiency at lower tempera 5,139,607 5 6 tures for a wide variety of coatings and substrates. What is claimed is: Moreover, the stripping compositions are easily pre 1. An alkaline positive and negative resist stripping pared by simply mixing the components at room tem composition having low volatility and operable at tem perature and thus require no special human or environ peratures less than about 90° C. for use with resists mental safety precautions. Furthermore, the compo having non-corrosive sensitive substrates which com nents of the stripping compositions of this invention prises, provide synergistic stripping action and permit readily A. about 5 to 30% by weight of tetrahydrofurfuryl and substantially complete removal of coatings from alcohol; substrates. B. about 5 to 30% by weight of a polyhydric alcohol; The compositions of the invention are particularly 10 C. about 10 to 30% by weight of the reaction product useful to remove dielectric components, i.e. silanes and of one mole of furfuryl alcohol with about 1 to 20 siloxanes which may be found in some resists. moles of an alkylene oxide, said furfuryl alcohol The effectiveness and unexpected nature of the strip reaction product being present in an amount ping compositions of this invention is illustrated, but not greater than tetrahydrofurfuryl alcohol, limited by the data presented in the following example. D. about 1 to 30% by weight of a water soluble Bron 15 stead base type of hydroxide compound, and EXAMPLE 1. E. the remainder being water, said composition com A photoresist stripping composition was prepared by prising a ratio of organic materials to inorganic mixing the following components. materials of about 0.25:1 to 3:1. 2. The composition of claim 1 including about 0.1 to 1.0% by weight of a nonionic surfactant. Component % Wt 3. The composition of claim 1 wherein said polyhyd Tetrahydrofurfuryl alcohol 18.6 ric alcohol is selected from the group consisting of Ethylene glycol S.0 ethylene glycol and propylene glycol. Furfuryl alcohol ethylene oxide 22.0 4. The composition of claim 1 wherein said alkylene addition product 25 Potassium hydroxide 2.2 oxide of part C is selected from the group consisting of Water 32.2 ethylene oxide and propylene oxide. 100.0% 5. An alkaline positive and negative photoresist strip ping composition for use with resists having non-corro sive sensitive substrates which comprises: If desired about 0.1 to 1.0% by weight of a nonionic 30 A. about 15 to 20% by weight of tetrahydrofurfuryl surfactant may be added. Also, in place of all or part of alcohol, the furfuryl alcohol ethylene oxide product, there may B. about 10 to 20% by weight of ethylene glycol, be used the furfuryl oxide propylene oxide reaction C. about 15 to 25% by weight of the reaction product product. or furfuryl alcohol and ethylene oxide, The composition is especially useful for removing the 35 D. about to 20% by weight of an alkali metal hydrox organic materials from photoresists having a ceramic ide, and substrate. E. the remainder being water. 6. The composition of claim 6 wherein said alkali EXAMPLES 2-6 metal hydroxide is potassium hydroxide. The following compositions were prepared and com-40 7. The composition of claim 6 including about 0.1 to pared with respect to selectivity of attack on the sub 1% by weight of a nonionic surfactant. strate versus efficacy in removal of resist. 8. A process for removing a coating from a coated non-corrosive sensitive substrate comprising applying Examples to said coated substrate an effective amount of a strip 2 3 4. 5 6 45 ping composition of claim 1, permitting said stripping Ingredients WT a composition to reside on said coated substrate for an Tetrahydrofurfuryl 8 30 30 8 8 effective period of time. Alcohol 9. A process for removing a coating from a coated Ethylene glycol 0. 25 20 10 16 non-corrosive sensitive substrate comprising applying Furfuryl alcohol 12 12 10 to said coated substrate a stripping effective amount of Ethylene oxide addition Product a stripping composition of claim 2, permitting said strip Potassium hydroxide s 3 ping composition to reside on said coated substrate for Potassium thiocyanate 16 a stripping effective period of time and removing the Lithiun Hydroxide 25 coating from the substrate. Triethanolamine 6 10. A process for removing a coating from a coated Tetramethylammonium 55 Hydroxide non-corrosive sensitive substrate comprising applying Water 35 to said coated substrate an effective amount of a strip Cab-O-Sil 1. ping composition of claim 6, permitting said stripping Results: composition to reside on said coated substrate for a Selectivity' 0 7 stripping effective period of time and removing the (Substrate) inertness coating from the substrate. Resist Renova 10 7 8 Performance 11. A process for removing a coating from a coated Cornments: non-corrosive sensitive substrate comprising applying (1) "O = Poor Lio No to said coated substrate an effective amount of a strip 10 s. Best didn't Removal ping composition of claim 7, permitting said stripping (2) Substrate: SiO2 dissolve of Resist 65 composition to reside on said coated substrate for a Si epi-Si stripping effective period of time and removing the A-me coating from the substrate.