POSITIVE PHOTORESIST STRIPPING COMPOSITION

Abstract: Piperazine containing positive photoresist stripping compositions are provided. Formulations include N-­ aminoalkylpiperazines with the formula bis-N-aminoalkylpiperazines of the formula N-hydroxyalkylpiperazine of the formula and bis-hydroxyalkylpiperazines with structure In the above formulae n = 1-6. Also included are piperazine derivatives such as those of the above formulae with a branch chain alkyl of 1-6 C atoms, and 5-6 C atom cycloalkyl substituted compounds wherein the cycloalkyl is substituted for -(CH₂) n -. Components which may be mixed with the above described piperazine in preparing the pos­ itive photoresist stripping compositions of the invention include alkyl or cycloalkyl-2-pyrrolidones of the formula Other amide type solvents with the boiling point in excess of 200°C as well as high boiling diethylene glycol ethers may also be incorporated.

Description: DESCKI PTItJN POSITIVE PHOTC#RESIST STRIPPING COMPOSITI()N This invention relates to novel strippiny compositions which are useful for removing positive photoresists primarily from substrates useful to integrated circuit manufacture. More particularly this invention relates to utilization of N-arnino-alkylpiper- azines and N-hydroxyalkylpiperazines either singly, together in admixture or diluted with certain polar solvent compositions for stripping positive photoresists. BACKGROUND O THE INVENTION In the manufacture of integrated circuits and related technology, organic composition are commonly used as stripping solutions for photoresists. botn positive and neyative resists are stripped usiny mixtures drawn from a group of substances includiny phenolics, sulfonic acids, chlorocarbons and hydrocarbons. Several commercially available strippiny solutions are constituted in this way. Chief amony disadvantages for some of these products is the toxic and skin penetrating nature of some components making handling personally hazardous and waste disposal by conventional dumping and landfill procedures undesirable. The inclusion of hygroscopic sulfonic acid components tends to cause water absorption that leads to corrosivity toward semiconductor substrate metals. Reaction between aluminum metal and chlorocarbon can yield low levels of chloride on substrate surtaces which in turn translates into device damage through corrosion. When photolithography device manutacture involves only positive photoresists, stripping may be done with a number of organic mixtures comprised of any of a number of polar solvents and mixtures of solvents. An indication of this is described by W.s. DeForest (Photoresist: Materials and Processes, McGraw-Hill, Inc. 1975). Some of these stripping compositions include dimethylformamide, N-methyl-2-pyrrolidone diethanolamine, triethanolamine, several glycol ethers (e.g., such as those available commercially under the brand names Cellosolv and Carbitol), and ketones (i.e. methylethylketone, acetone, methylisobutylketone, cyclohexanone). A number of stripping solutions currently on the market utilize mixtures of some ot these organic solvents and are designed for use exclusively in removing positive resists. The difficulty of photoresist stripping depends on process conditions used in device manufacture which may be determined by the type of device made. When most positive resists are cured by baking no higher than 150 C, removal using most solvent based stripping solutions is achieved at relatively low temperatures near normal room temperature. With bake temperatures between 1500 and 2000C photoresist stripping is more difficult and may require using higher temperatures for the stripping process. wnere photoresist films or patterns are exposed to plasma and ion implantation conditions during dry processing, very hard to strip material is formed. From experience with available stripping solutions, it has been found that mixtures comprised of "neutral" polar solvents such as amides (DMF, N-methyl-2pyrrolidone, etc.) glycol ethers (Cellosolv, Carbitols, etc.) sulfones (e.g., sulfolanes), ketones (e.y., acetone, methylethylketones and the like) are practical for stripping easy to remove (not baked or baked at 1350C maximum) positive photoresists. tor positive photoresists baked higher than 1500 or exposed to plasma or ion implantation processing, it is often advantageous to use stripping solutions consisting of amines or amines diluted with neutral polar solvents. It is desirable to operate photoresist stripping at low temperatures primarily for safety reasons minimizing both fire hazards from solvent fumes and contacting personnel with hot liquids and vapors. Lower temperature operation also minimizes problems trom changing composition due to selective vaporization of more volatile components. One of the major drawbacks in stripping solutions which are effective for very hard to strip material is that they usually contain environmentally hazardous or toxic ingredients such as phenolics or chlorinated hydrocarbons. Accordingly, a need exists for an improved environmentally safe, relatively non-toxic positive photoresist stripping composition which is effective in removing hard to strip positive photoresists. SUMMARY Ot THE INVENTION The invention involves the use ot substituted piperazines alone or diluted with certain polar solvents as stripping solutions for use on positive photoresist compositions. Using mixtures of these components allows overcoming of many problems associated witn resist stripping. Components are relatively non-toxic allowing minimized hazards in use areas. For application with resists cured by thermal bake stripping at relatively low temperature (room temperature to 700C) is practical. Components are sufficiently high boiling to allow high temperature operation when necessary to strip more difficult photoresist residues (i.e., plasma exposed and ion implant exposed photoresist). To that end adjustment in the composition is possible to allow for synergistic action between piperazine derived components. The stripping compositions of the present invention include N-aminoalkylpiperazines or the formula EMI3.1 bis-N-aminoalkylpiperazines or the formula EMI3.2 N-hydroxyalkylpiperazine of the formula EMI3.3 and bis hydroxyalkypiperazines with structure EMI4.1 In the above formulae n = 1-6. Also included are piperazine derivatives such as those of the above formulae with a branch chain alkyl of 1-6 C atoms, and 5-6 C atom cycloalkyl substituted compounds wherein the cycloalkyl is substituted for -(CH2)n¯. Components which may be mixed with the above described piperazines in preparing the positive photoresist stripping compositions of the invention include alkyl-or cycloalkyl-2-pyrrolidones of the formula EMI4.2 where R is an alkyl group of 1-6 carbon atoms or 5 or 6 member cycloalkyl, and also aminoalkyl and including hydroxyalkyl of 1-6 carbon atoms. Other amide type solvents with a boiling point in excess of 2000C e.g., N-formylmorpholine, may also be incorporated in amounts of up to about 70 percent by weight. The stripping mixtures may also include glycol ethers having boiling points exceeding 200 C, e.y., nonoethyl, monobutyl, or monohexyl ethers of diethylene glycol. The respective components in the stripping compositions of the invention comprise Naminoalkylpiperazine in a range between 0% and 90 by weight; N-hydroxyalkylpiperazine between 0% and 90% by weight provided that at least one of said piperazines is present in amounts of at least 10% by weight; N-methyl2-pyrrolidone between 0% and 90% by weight and diethylene glycol monobutyl ether between 0% and 25 by weight. Preferred compositions for general applicatiOn comprise between 28 and 15% by weight N hydroxyalkylpiperazine, 10-30% by weight N-aminoalkylpiperazine, 0-20% by weight diethylene glycol monobutyl ether and 70-80% by weignt N-methyl-2-pyrrolidone; DESCRIPTION OF THE PREFERRED EMBODIMENT The novel stripping compositions comprising the subject matter of the present invention which are usetul for removing positive photoresists primarily from substrates useful to integrated circuit manufacture utilize N-aminoalkylpiperazines and Nhydroxyalkylpiperazines either singly or together in admixture or diluted with certain polar solvent compositions. Phenolics and chlorinated hydrocarbon compounds are excluded giving low toxicity and minimized waste disposal problems. The substituted piperazines may be used alone or diluted with certain polar solvents as stripping solutions for positive photoresists. Using mixtures or these components allows overcoming of problems associated with resist stripping. And because the components used are relatively non-toxic, they present minimized hazards in the work areas. For application with resists cured by thermal bake stripping at relatively low temperature (room temperature to 700C) is practical. Components are sufficiently high boiling to allow high temperature operation when necessary to strip more difficult photoresist residues (i.e., plasma exposed and ion implant exposed photoresist) with considerable adjustment possible in the composition to allow for optimum stripping action between piperazine derived components. Included in the stripping compositions or this invention are the N-aminoalkylpiperazines of tne formula: EMI5.1 bis N-aminoalkylpiperazines of the formula EMI5.2 N-hydroxyalkylpiperazine of the formula EMI6.1 and bis-hydroxyalkypiperazines with structure EMI6.2 In the above formulae n = 1-6. Also included are piperazine derivatives such as those of the above formulae with a branch chain alkyl of 1-6 C atoms, and 5-6 C atom cycloalkyl substituted compounds wherein the cycloalkyl is substituted for -(CH2)n-. Components which may he mixed with the above described piperazine in preparing the positive photoresist stripping compositions of the invention include alkyl or cycloalkyl-2-pyrrolidones of the formula EMI6.3 where R is an alkyl group of 1-6 carbon atoms or a 5 or 6 member cycloalkyl and including aminoalkyl ana hydroxyalkyl of 1-6 carbon atoms. Other amide type solvents with a boiling point in excess of 000C may also be incorporated into the stripping compositions, for example, N-formylmorpholine and other polar organic compounds that are compatible with the above piperazines e.g., glycol ethers having boiling points exceeding 2000C (such as monoethyl, monobutyl, or monohexyl ethers of diethylene glycol) in amounts of up to about 70% by weight. The proportions of components in the piperazlne containing stripper may vary within fairly broad limits, providing that at least one ot the piverazines is present in an amount or at least 10% by weight, ana include N-aminoethylpiperazine (NAEP) in a range between 0% and 90% by weight; N-hydroxyethyl piperazine (NOSE) between 0% and 9()% by weight. Other components, e.W., N-methyl-2-pyrrolidone (NMP) may be incorporated in amounts of between 5% and 90% by weight; and butylcarbitol (BC) in amounts between 0% and 25% by weight. Preferred compositions for general application comprise combinations of hydroxyalkylpiperazines, especially hydroxyethylpiperazine and aminoalkyl piperazines, especially aminoethylpiperazine in tne range by weight of 10%-308 by weight N-aminoethylpiperazine, 28-15% by weight N-hydroxyethylpiperazine, and 70%-80% by weight N-methyl-2-pyrrolidone. The invention will be further described by the following specific examples. It should be understood, however, that although these examples may describe in detail certain preferred operating conditions of the invention, they are given primarily for purposes ot illustration, and the invention in its broader aspects is not limited thereto. Parts expressed are parts by weight unless otherwise stated. GENERAL Pa UE In preparing the stripping compositions ot the invention, no particular order of addition need be employed. The various components are measured in tne desired proportion and introduced into a suitable mixing vessel and thoroughly mixed by stirring. Any alternate suitable means to effectively intermix the components such as by concurrent introduction of streams ot the respective components, or any other suitable known means that fully intersperse the components may be used. once mixed, the stripping composition is stable, with no detectable separation of components and has excellent shelf life. The photoresist compositions employed are any ot the commercially available organic photosensitizer alkaline soluble resin formulations which comprise (a) a suitable sensitizer such as diazo ketone compounds, e.g., naphthaquinone-l, 2-diazo sultonic acid esters, (b) a novalak resin and (c) a suitable solvent sucn as xylene. Photoresists are generally described, ror example, on page 67 in the work by D.J. Elliot in Integrated Circuit Fabrication Technology, McGraw-Hill Book Company, 1982. EXAMPLES 1-6 Table 1 summarizes examples 1-6 showing comparative results in stripping 1 thick, non-patterned films of commercially available resist (Shipley 147U) prebaked at 900C followed by final hard bake at 1350C and ZU0 C each for 30 minutes. The stripping method involved soaking coated wafers in a temperature controlled tank of stripping solution. The stripped waters are rinsed in copious amounts of deionized water. After air drying completeness of strip was judged by visual inspection with and without moisture film deposition. From these examples, using compositions claimed by the present invention, the following attributes are noted: a) Fast stripping of high temperature (2000C) baked resist can be accomplished at relatively low operating temperature. b) Suitable fast stripping rates of resists baked up to 1350C can be effected by room temperature stripping. TABLE I - STRIPPING THERMALLY CURED POSITIVE RESIST Example Stripper 70 C Strip Room Temp. (25 C) Composition 2000C bake 1350C bake (1) 70% NMP 4.5 min. 3.5 min. 30% NAEP (2) 10% NMP 36 min. 7.3 min. 90% (6/1-NAEP/NHEP) (3) 70% BC 36 min. 3U min. 30% NAEP (4) 70% NMP 4 min. 3 min. 302 (6/1-NAEP/NHEP) (5) 70% NMP 3.7 min. 3 min. 30t (2/1-NAEP/NHEP 70 70% NMP 1.5 min. 2.25 min. 30% NHEP EXAMPLES 7-10 Examples 7-10 employed the same stripping method described with reference to Examples 1-6 except resist patterns were stripped at 1500C and evaluated visually at 100 magnification; the results are summarized in Table II. These examples in a relative way demonstrate the following: a) Stripping plasma and ion implant exposed photoresist requires relatively high stripping temperatures. b) Synergistic effects are indicated amony the three components. Examples 9, 11 and 12 show a region in plasma stripping of constant NAE;p/NHEp ratio with a maximum stripping rate in the vicinity of 12% NMP. Examples 7, 9 and 10 suggest a maximum stripping rate in ion implant stripping over a range of NAEP/NHEP ratios. c) Effectiveness for stripping boron ion implanted wafers occurs with different mixtures than those effective with plasma exposed resist. TABLE II - HIGH ENERGY EXPOSED Example Stripper Cm4/02 Plasma Boron Ion Implant Composition (7) NAEP 76% hO stripped 100% stripped NHEP 12% 60 min. 60 min. NMP 12 (8) NAEP 81 30E stripped 40% stripped NHEP 14 60 min. 60 min. NMP 5 (9) NAEP 70 902 stripped 40% stripped NHEP 18 60 min. 60 min. NMP 12 (10) NAEP 58% 80% stripped #j% stripped NHEP 30 60 min. 60 min. NMP 12 (11) NAEP 76 15 stripped 30 stripped NHEP 19 60 min. 60 min. NMP 5 (12) NAEP 64 30% stripped 35% stripped NHEP 16 60 min. 60 min. NMP 20 The positive photoresist stripping composition of the invention allows operation at relatively low temperatures which is advantageous for satety reasons and especially because lower temperatures minimize the fire hazard from solvent fumes which would pose a greater danger to personnel when hot liquids and vapors are present. Additionally, the lower temperature substantially facilitates renewal of the stripping solutions during operations. Also, operation at lower temperature reduces vaporization which can lead to an objectionable change in the stripping solution composition. It will be understood that considerable variation in the conditions and materials may be made within the dislosure provided herein and, therefore, it is not intended that the invention be limited except as set forth in the claims.

Claims: WHAT IS CLAIMED IS: A stripping composition for removing an organic positive photoresist composition from the surface of a substrate containing such photoresist comprising (a) from 10% to 100% of at least one piperazine selected from the group consisting of piperazines of the formula EMI11.1 bis-N-aminoalkylpiperazines of the tormula EMI11.2 N-hydroxyalkylpiperazine of the formula EMI11.3 and bis-hydroxyalkypiperazines with structure EMI11.4 In the above formulae n = 1-6. Also included are piperazine derivatives such as those of the above formulae with a branch chain alkyl of 1-6 C atoms, and 5-E C atom cycloalkyl substituted compounds wherein the cycloalkyl is substituted for -(CH2), and (b) an alkyl or cycloalkyl-2-pyrvolidone of the formula EMI11.5 where R is an alkyl group of 1-6 carbon atoms or a 5 or 6 member cycloalkyl, and including aminoalkyl and hydroxyalkyl of 1-6 carbon atoms or a polar organic component which is compatible with and substantial miscible in (a) in amounts of from about 90 percent by weight to about 0 percent by weight. 2. The stripping composition of claim 1 wherein (a) comprises a blend of N-aminoethylpiperazine and N-hydroxyethylpiperazine. 3. The stripping composition of claim-l wherein (b) is selected from the group consisting of an alkyl or cycloalkyl-2-pyyrolidone of the formula EMI12.1 where R is an alkyl group of 1 - 6 carbon atoms; aminoalkyl-N-pyrrolidones and hydroxyalkyl-2pyrrolidones where the alkyl group comprises 1-6 carbon atoms; monoethyl ether of diethylene glycol, monobutyl ether of diethylene glycol, monohexyl ether of diethylene glycol formylmorpholine and mixtures thereot. 4. The stripping composition of claim 2 wherein the (b) component comprises N-methyl-2-pyrrolidone. 5. The stripping composition of claim 2 wherein (a) comprises a blend of N-aminoethylpiperazine and N-hydroxyethylpiperazine in a ratio respectively of 1:1 to about 10:1 in an amount of about 30 percent by weight and (b) comprises N-methyl-2-pyrrolidone in an amount ot about 7n percent by weight. 6. A method of stripping positive photoresist trom a substrate surface having a layer of said photoresist applied thereon comprising contacting the photoresist layer with the composition of claim 1 at a temperature between about 150C and about 1600C until said photoresist is substantially removed.

Inventors: COOK, KANE DAVID, SMALLEY, EDMUND WALTER, THOMAS, EVAN GOWER
Applicants: HMC PATENTS HOLDING CO., INC.
Application year: 1984
Main classification: G03F7
IPC codes: G03C11, G03F7, H01L21