Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Removal of imaged layers
Reexamination Certificate
2001-10-02
2004-06-15
Barreca, Nicole (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Removal of imaged layers
C430S322000, C430S325000, C430S464000, C510S176000, C134S001300
Reexamination Certificate
active
06749998
ABSTRACT:
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. No. 4,395,479; U.S. Pat. No. 4,428,871 and U.S. Pat. No. 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-pyrrolidinone, 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 HO(CH
2
CH
2
—O&Parenclosest;
x
R 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
where R
1
and R
2
are alkyl of 1 to 4 carbon atoms, dimethyl sulfoxide (DMSO), tetrahydrothiophene-1,1-dioxide compounds of the formula
wherein R
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 pRa 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
4
—NH—NH
2
where R
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
5
SH where R
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
where R
6
and R
7
are alkyl radicals; and
aldehydes and derivatives thereof, that is salicylaldehyde, 4-hydroxybenzaldehyde and glycol aldehyde dialkyl acetals, particularly glycol aldehyde diethyl acetal.
Schwartzkopf George
Surendran Geetha
Barreca Nicole
Mallinckrodt Baker Inc.
Rauchfuss, Esq. George W.
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