Photoresist strippers containing reducing agents to reduce metal corrosion

FIELD OF THE INVENTION
 This invention relates to alkaline photoresist stripping compositions
 containing reducing agents and the use of such stripping compositions to
 reduce or inhibit metal corrosion and/or metal loss when stripping
 photoresists from substrates containing metals such as tungsten and/or
 copper and its alloys with aluminum.
 BACKGROUND OF THE INVENTION
 An integral part of microelectronic fabrication is the use of photoresists
 to transfer an image from a mask or reticle to the desired substrate
 circuit layer. After the desired image transfer has been achieved, the
 photoresist is removed, that is, stripped from the substrate before
 proceeding to some subsequent process step. Starting around 1980, amides
 and mixtures of amides with various co-solvents have routinely been used
 for this stripping step, see for example Ward et al., U.S. Pat. Nos.
 4,395,479; 4,428,871 and 4,401,748.
 Depending on the type of processing that is performed while the photoresist
 is in place on the substrate, the photoresist polymer may be cross-linked
 or hardened to the extent that amide-based solvents will no longer
 effectively strip the photoresist. Starting around 1985, the use of amide
 mixtures containing additional alkaline components, such as organic
 amines, (see Johnson U.S. Pat. No. 4,592,787; Merrem U.S. Pat. No.
 4,765,844; Sizensky U.S. Pat. No. 4,617,251; Turner WO 87/05314 and Thomas
 et al. U.S. Pat. No. 4,791,043) or quaternary ammonium hydroxides (see
 Steppan et al. U.S. Pat. No. 4,776,892; Haq U.S. Pat. No. 4,744,834;
 Martin WO 88/05813) was introduced to facilitate the removal of such
 hardened photoresists.
 The use of these alkaline components in strippers on microcircuits
 containing metals, particularly tungsten or copper and its alloys with
 aluminum, can lead to metal loss. Various types of metal corrosion, such
 as for example corrosion whiskers, pitting and notching of metal lines,
 have been observed during the use of these alkaline strippers. In the case
 of tungsten and copper corrosion can occur in the heated dry organic
 stripping composition mixtures with dissolved oxygen providing the
 cathodic reaction.
 It would therefore be most desirable to be able to provide
 alkaline-containing photoresist stripping compositions suitable for
 stripping cross-linked or hardened photoresist polymer from substrates
 containing metal in which metal corrosion and/or metal loss is reduced or
 inhibited. A further object of this invention is to provide a method of
 stripping cross-linked or hardened photoresist from a metal-containing
 substrate using an alkaline-containing photoresist stripping composition
 containing an agent to reduce or inhibit such metal corrosion or metal
 loss.
 BRIEF SUMMARY OF THE INVENTION
 It has now been discovered that the inclusion of certain reducing agents in
 alkaline-containing photoresist stripping compositions produces
 photoresist stripping compositions that reduce or inhibit metal corrosion
 and/or metal loss when such photoresist stripping compositions are
 employed to remove cross-linked or hardened photoresist from substrates
 containing metal. Reducing agents suitable for use in alkaline-containing
 photoresist stripping compositions of this invention are the following:
 ascorbic acid, butyne diols, unsaturated ketones, uric acid, tetramisole,
 hydrazines and its derivatives including carbazates, oximes, hydroquinone,
 pyrogallol, gallic acid, 2,4,5-trihydroxybutyrophenone, tocopherol,
 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid,
 butylatedhydroxytoluene (BHT), butylatedhydroxyanisole (BHA),
 2,6-di-tert-butyl-4-hydroxymethylphenol, thiols, salicylaldehyde,
 4-hydroxybenzaldehyde and glycol aldehyde dialkyl acetals and mixtures
 thereof. The amount of reducing agent employed in the photoresist
 stripping compositions of this invention is any amount effective to reduce
 or inhibit metal corrosion or metal loss and will generally be an amount
 within the range of from about 0.1 to about 10% by weight based upon the
 total weight of the photoresist stripping composition.
 DETAILED DESCRIPTION OF THE INVENTION
 The improved metal corrosion resistant photoresist stripping compositions
 of this invention comprise an organic solvent system, alkaline components
 and at least one of the suitable reducing agents. The organic solvent
 system employed in the photoresist stripping compositions of this
 invention is generally one having a solubility parameter of from about 8
 to about 15 obtained by taking the square root of the sum of the squares
 of the three Hansen solubility parameters (dispersive, polar and hydrogen
 bonding). The solvent system may comprise any of a number of individual
 solvents or a mixture of several different solvents. As examples of such
 solvents there may be mentioned, various pyrrolidinone compounds such as
 2-pyrroli-dinone, 1-methyl-2-pyrrolidinone, 1-ethyl-2-pyrrolidinone,
 1-propyl-2-pyrrolidinone, 1-hydroxyethyl-2-pyrrolidinone,
 1-hydroxypropyl-2-pyrrolidinone, N-cyclohexylpyrrolidinone, and the like,
 tri- or diethylene glycol monoalkyl ethers such as those of the formula
 ##STR1##
 where R is an alkyl radical of from 1 to 4 carbon atoms and x is 2 or 3,
 compounds containing sulfur oxides such as dialkyl sulfones of the formula
 ##STR2##
 where R.sup.1 and R.sup.2 are alkyl of 1 to 4 carbon atoms, dimethyl
 sulfoxide (DMSO), tetrahydrothiophene-1,1-dioxide compounds of the formula
 ##STR3##
 wherein R.sup.3 is hydrogen, methyl or ethyl, such as sulfolane, methyl
 sulfolane and ethyl sulfolane, as well as polyethylene glycols,
 dimethylacetamide or dimethylformamide. The solvent system portion of the
 stripper compositions of this invention will generally comprise from about
 50% to about 98% by weight of the composition, preferably about 70% to
 about 90% by weight.
 Alkaline stripper components that may be used in this invention also cover
 a wide range of structural types. Their dissociation constants, expressed
 as pKa values, range from about 9 to 11 for the beta-oxygen or -nitrogen
 substituted amines to 8.3 for the secondary amine, morpholine and
 hydroxylamines and hydroxylamine derivatives of somewhat lower pKa values.
 Among the alkaline components that may be used there may be mentioned,
 nucleophilic amines, preferably for example, 1-amino-2-propanol,
 1-amino-3-propanol, 2-(2-aminoethoxy)ethanol, 2-aminoethanol,
 2-(2-aminoethylamino)ethanol, 2-(2-aminoethylamino)ethylamine,
 1-(2-aminoethylpiperazine), and the like. More important than the actual
 pKa value of an amine is its nucleophilicity which should be high. The
 amount of amine component employed in the stripping compositions of this
 invention is from about 1% to about 50%, preferably about 10% to about 30%
 by weight of the composition.
 Reducing agents effective as oxygen scavengers useful as the reducing
 agents in the improved photoresist compositions of this invention are the
 following:
 compounds containing reactive double bonds, that is, ascorbic acid, uric
 acid, butyne diols, unsaturated ketones such as cyclohexenylacetone and
 3-nonene-2-one, and tetramisole;
 hydrazine and its derivatives, that is, compounds of the formula R.sup.4
 --NH--NH.sup.2 where R.sup.4 is hydrogen or an organic radical, preferably
 a hydrogen, a formyl radical, an alkyl radical, an oxycarbonyl radical, a
 hydroxyalkyl radical, an alkylcarboxy radical or an aryl radical, for
 example, a phenyl radical;
 oximes;
 readily oxidized aromatic compounds and oxidation inhibitors, that is,
 hydroquinone, pyrogallol, gallic acid and alkyl esters thereof,
 tocopherol, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid,
 butylatedhydroxytoluene, butylatedhydroxyanisole, and
 2,6-di-tert-butyl-4-hydroxymethylphenol;
 thiols of the formula R.sup.5 SH where R.sup.5 is an organic radical such
 as a heterocylic radical, carboxyaryl radical, a dicarboxyalkyl radical,
 an amino substituted carboxyalkyl radical or a radical of the formula
 ##STR4##
 where R.sup.6 and R.sup.7 are alkyl radicals; and
 aldehydes and derivatives thereof, that is salicylaldehyde,
 4-hydroxybenzaldehyde and glycol aldehyde dialkyl acetals, particularly
 glycol aldehyde diethyl acetal. Alkyl in the aforementioned reducing
 agents will generally be alkyl of 1 to about 12 carbon atoms, preferably
 alkyl of 1 to 6 carbon atoms and more preferably alkyl of 1 to 4 carbon
 atoms.
 Especially preferred as reducing agents for use in the stripping
 compositions of this invention are ascorbic acid, uric acid,
 2-butyne-1,4-diol, 1-cyclohexenyl acetone, 3-nonene-2-one,
 2,3,5,6-tetrahydro-6-phenylimidazo[2,1-b] thiazole and the hydrochloride
 thereof, hydrazine, p-toluenesulfonylhydrazide, formic hydrazide, maleic
 hydrazide, hydrazine hydrate, hydroxyethyl hydrazine, phenyl hydrazine,
 t-butyl carbazate, ethyl carbazate, salicylaldoxime, acetone oxime,
 pyrogallol, gallic acid, 2,4,5-trihydroxybutyrophenone,
 3,5-di-tert-butyl-4-hydroxytoluene, 3-tert-butyl-4-hydroxyanisole,
 2,6-di-tert-butyl-4-hydroxymethylphenol, tocopherol (Vitamin E),
 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, 2-mercapto-4 [3H]
 quinazoline, dodecylmercaptopropionate, thiosalicylic acid,
 mercaptosuccinic acid, cysteine, 2-mercaptobenzoxazole, salicylaldehyde,
 4-hydroxybenzaldehyde and glycol aldehyde diethyl acetal.
 The reducing agents of this invention will be employed in the
 alkaline-containing stripping compositions in an amount effective to
 reduce or inhibit metal corrosion or metal loss and will generally be
 within the range of from about 0.1 to about 10% by weight, preferably
 within from about 0.1 to about 5% by weight, more preferably within from
 about 0.1 to about 3% by weight and even more preferably within from about
 1 to 3% by weight, based upon the total weight of the composition.
 The stripping compositions of this invention are effective in stripping a
 wide and varied range of photoresists especially positive photoresists.
 Most photoresists consist of an ortho naphthoquinone diazide sulfonic acid
 ester or amide sensitizer or photoactive component, with novolak, resole,
 polyacrylamide or acrylic copolymer type binders or resins. Such
 photoresists are well known in the art. Such resists and sensitizers are
 described for example, in U.S. Pat. Nos. 3,046,118; 3,046,121; 3,106,465;
 3,201,239; 3,538,137; 3,666,473; 3,934,057; 3,984,582 and 4,007,047. As
 examples of photoresist compositions for which the stripping composition
 of this invention may be used there may be mentioned: OCG Microelectronics
 Materials Series CAMP-6, HiPR 6500, HPR500, OCG 825, OCG 895, OCG 897 and
 OiR 32 photoresists; Hoechst Celanese Series AZ 1500, 6100, 6200B, 7500,
 7500T, DX, P4000, and PF 500 photoresists; Shipley Company's Megaposit
 S1400, S1800, S3800, SPR2, SPR500-A, and SPRT500-A photoresists; Morton
 Electronic Materials' EL-,NOVA, and OFPR- series photoresists; Toray
 Industries' EBR-9; and UCB-JSR Electronics' PFR- series photoresists.
 The improved properties of stripping compositions of this invention are
 illustrated in the following example. In the example, the
 alkaline-containing solvent system stripping compositions to which a
 reducing agent of this invention has been added are the following
 compositions A through O:

Composition Components (Part by Weight)
 A dimethylformamide (90) + 2-aminoethanol (10)
 B dimethylacetamide (90) + 2-aminoethanol (10)
 C dimethylacetamide (90) + 1-amino-3-propanol (10)
 D dimethylacetamide (90) + 1-amino-2-propanol (10)
 E dimethylacetamide (60) + 1-amino-2-propanol (10) +
 sulfolane (30)
 F N-methylpyrrolidinone (60) + 1-amino-2-propanol
 (10) + N-cyclohexylpyrrolidinone (30)
 G N-methylpyrrolidinone (70) + 1-amino-2-propanol
 (30)
 H N-methylpyrrolidinone (90) +
 2-(2-aminoethylamino)ethanol (10)
 I dimethyl sulfoxide (90) +
 1-(2-aminoethylpiperazine)
 J N-methylpyrrolidinone (80) +
 2-(2-aminoethylamino)ethanol (10) +
 N-(2-hydroxyethyl)pyrrolidinone (10)
 K N-methylpyrrolidinone (70) +
 2-(2-aminoethylamino)ethanol (10) +
 triethylene glycol monomethyl ether (20)
 L N-methylpyrrolidinone (60) +
 2-(2-aminoethylamino)ethanol (10) +
 diethylene glycol monoethyl ether (30)
 M dimethyl sulfoxide (70) + 1-amino-2-propanol (30)
 N N-methylpyrrolidinone (50) +
 2-(2-aminoethoxy)ethanol (40) + sulfolane (10)
 O N-methylpyrrolidinone (60) + 1-amino-2-propanol
 (10) + sulfolane (30).
 The corrosion rates of the above alkaline-containing stripping composition
 were measured with and without added reducing agents of this invention and
 then the percent corrosion inhibition for the stripping compositions of
 this invention were calculated. The corrosion rates were measured using
 the three following methods:
 METHOD 1: Coupons of 99.9+% tungsten (0.05.times.12.times.50 mm) were
 cleaned in acetone, dried, and weighed. Coupons were heated in one of the
 above alkaline test compositions (plus 1% water to accentuate corrosion)
 with and without added reducing agents. After immersion in the test
 compositions for 4 hours at 85.degree. C., the coupons were removed,
 rinsed with acetone, dried and reweighed. Weight losses were converted to
 corrosion rates and finally to percent inhibition for the reducing agent
 used.
 METHOD 2: Identical to Method 1 except that the coupons were of 99.98%
 copper (0.025.times.12.times.50 mm).
 METHOD 3: Copper coupons (0.05.times.10.times.30 mm) were cleaned in
 isopropyl alcohol, dried then heated in 10 mL of stripping composition for
 one hour at 80.degree. C. Copper uptake of the test solution was then
 measured using atomic absorption spectroscopy and converted to percent
 inhibition for the reducing agent used.
 Corrosion rates for stripping compositions A through O (without a reducing
 agent of this invention) using methods 1, 2 and 3 are listed below in
 Angstroms per hour. Results were as follows:

EXAMPLE
 Inclusion of reducing agents of this invention in the aforedescribed
 alkaline-containing stripping compositions A through O produced the
 following inhibition results.