Patent Grant
9329486
The present disclosure relates generally to compositions having the ability to effectively remove photoresists from substrates and methods for their use. The compositions disclosed are stripper solutions for the removal of photo resists that have the ability to remain liquid at temperatures below normal room temperature and temperatures frequently encountered in transit and warehousing and additionally have advantageous loading capacities for the photoresist materials that are removed. Stripper solutions having reduced water content have proven particularly effective in cleanly removing photoresists, providing low copper etch rates, and increasing the solubility of photoresists in the stripper solution as evidenced by lower particle counts.
In broad terms, a first aspect of the present disclosure provides for a photoresist stripper solution for effectively removing or stripping a photoresist from a substrate, having particularly high loading capacities for the resist material, and the ability to remain a liquid when subjected to temperatures below normal room temperature that can be encountered in transit, warehousing and in use in some manufacturing facilities. The compositions according to this present disclosure can remain liquid to temperatures as low as about −20° C. to about +15° C. The compositions according to the present disclosure can contain dimethylsulfoxide (DMSO), a quaternary ammonium hydroxide, and an alkanolamine. One preferred embodiment contains from about 20% to about 90% dimethylsulfoxide, from about 1% to about 7% of a quaternary ammonium hydroxide, and from about 1% to about 75% of an alkanolamine having at least two carbon atoms, at least one amino substituent and at least one hydroxyl substituent, the amino and hydroxyl substituents can be attached to two different carbon atoms of the alkanolamine. The quaternary groups can include (C1-C8) alkyl, aryl alkyl and combinations thereof. An example of a quaternary ammonium hydroxide is tetramethylammonium hydroxide. The 1,2-alkanolamines can include compounds of the formula:
where R1 can be H, C1-C4 alkyl, or C1-C4 alkylamino. Alkanolamines of formula I, can have R1 that is H or —CH2CH2NH2. Solutions of this present disclosure can also include an additional or secondary solvent. For example, the secondary solvents can include glycols, glycol ethers and the like. In another example, the secondary solvent can include an alcohol. In particular, the secondary solvent can include a polyhydroxyl compound having two or more hydroxyl groups. Desirably, at least one of the hydroxyl groups is a primary hydroxyl group, or at least two hydroxyl groups are primary hydroxyl groups.
A second aspect of the present disclosure provides for methods of using the stripper solutions described herein to remove photoresist and related polymeric materials from a substrate. A photoresist can be removed from a selected substrate having a photoresist thereon by contacting the substrate with a stripping solution for a time sufficient to remove the desired amount of photoresist, by removing the substrate from the stripping solution, rinsing the stripping solution from the substrate with a solvent and drying the substrate.
A third aspect of the present disclosure includes electronic devices manufactured by the novel method disclosed.
A fourth aspect of the present disclosure includes preferred stripper solutions containing dimethylsulfoxide, a quaternary ammonium hydroxide, an alkanolamine, an optional secondary solvent with reduced amounts of water. The solutions can have a dryness coefficient of at least about 1. The solutions can also have a dryness coefficient of at least about 1.8, where the dryness coefficient (DC) is defined by the following equation:
A fifth aspect of the present disclosure includes a method for removing a photoresist from a substrate with the stripper solution described herein. The method involves selecting a substrate having a photoresist deposited on it, contacting the substrate including the photoresist with a stripper solution that contains dimethylsulfoxide, a quaternary ammonium hydroxide, an alkanolamine, an optional secondary solvent wherein the stripper solution has a dryness coefficient of at least about 1, removing the substrate from contact with the stripper solution and rinsing the stripper solution from the substrate.
A sixth aspect of the present disclosure includes an electronic device prepared in part by the method described above.
A seventh aspect of the present disclosure includes a method for providing a dry composition that includes dimethylsulfoxide, a quaternary ammonium hydroxide, an alkanolamine, an optional secondary solvent wherein the solution has a dryness coefficient of at least about 1.
An eighth aspect of the present disclosure includes a method for obtaining a quaternary ammonium hydroxide having reduced water content by forming a solution of the quaternary ammonium hydroxide, unwanted water and a sacrificial solvent and subjecting the solution to reduced pressure with slight warming. During the treatment a portion of sacrificial solvent and water are removed. During the process excessive heating should be avoided to prevent decomposition of the hydroxide. The addition and removal of the sacrificial solvent with water can be repeated as necessary until the water content is sufficiently reduced.
A ninth aspect of the present disclosure includes a method for maintaining a low water content for a stripper solution. The method involves selecting a dry stripper solution, establishing contact between the stripper solution and molecular sieves, and maintaining contact with the sieves until the stripper solution is utilized. This method is particularly useful in maintaining the stripper solutions in a dry form following manufacture, during storage and/or shipping and after the solution's container has been opened.
For the purposes of promoting an understanding of what is claimed, references will now be made to the embodiments illustrated and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of what is claimed is thereby intended, such alterations and further modifications and such further applications of the principles thereof as illustrated therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
The compositions according to this present disclosure include dimethylsulfoxide (DMSO), a quaternary ammonium hydroxide, and an alkanolamine. The alkanolamines can have at least two carbon atoms, at least one amino substituent and at least one hydroxyl substituent, where the amino and hydroxyl substituents are attached to two different carbon atoms of the alkanolamine. The quaternary substituents can include (C2-C8) alkyl, benzyl and combinations thereof. Compositions can have a freezing point of less than about −20° C. up to about +15° C. and a loading capacity of from about 15 cm3/liter up to about 90 cm3/liter. For the dry stripper solutions quaternary substituents can include C1-C4 alkyl, arylalkyl, or combinations thereof.
Formulations having increased levels of an alkanolamine are particularly noncorrosive to carbon steel and are less injurious to typical waste treatment systems and auxiliary equipment than other stripper solutions. Compositions can include 1,2-alkanolamines having the formula:
where R1 is hydrogen, (C1-C4) alkyl, or (C1-C4) alkylamino group. Formulations of the solution can additionally include a secondary solvent. Formulations of the solution can include from about 2% to about 75% of a secondary solvent. The secondary solvents can include glycols and their alkyl or aryl ethers described in more detail below. Additionally, in some cases, the secondary solvents can include an alcohol. In particular, the secondary solvents can include a polyhydroxyl compound having two or more hydroxyl groups. polyhydroxyl compound. The formulations can have freezing points sufficiently below 25° C. to minimize solidification during transportation and warehousing. The formulations can also have freezing points below about 15° C. Because the stripper solutions can remain liquid at low temperatures, the need to liquefy solidified drums of stripper solution received during cold weather or stored in unheated warehouses before the solution can be used is eliminated or minimized. The use of drum heaters to melt solidified stripper solution is time consuming, requires extra handling and can result in incomplete melting and modification of the melted solution's composition.
Additionally, compositions according to the present disclosure display high loading capacities enabling the composition to remove higher levels of photoresists without the precipitation of solids. The loading capacity is defined as the number of cm3 of photoresist or bilayer material that can be removed for each liter of stripper solution before material is re-deposited on the wafer or before residue remains on the wafer. For example, if 20 liters of a stripper solution can remove 300 cm3 of photoresist before either re-deposition occurs or residue remains on the wafer, the loading capacity is 300 cm3/20 liters=15 cm3/liter.
The compositions typically contain about 55% to about 95% solvent, all or most of which is DMSO. In an illustrative example, the solution can include an amount of DMSO included in a range of about 70% by weight to about 90% by weight for a total weight of the solution. Additionally, the compositions can include from about 2% to about 10% of the quaternary ammonium hydroxide. In some cases, the solutions can include an amount of quaternary ammonium hydroxide included in a range of about 1% by weight to about 7% by weight of a total weight of the solution. The quaternary substituents can include (C1-C8) alkyl, benzyl and combinations thereof.
When used, a secondary solvent typically comprises from about 2% to about 35% of the composition. In an illustrative example, the solution can include an amount of secondary solvent included in a range of about 5% by weight to about 20% by weight of a total weight of the solution. The stripping formulations can also contain an optional surfactant, typically at levels in the range of about 0.01% by weight to about 3% by weight of a total weight of the solution. Suitable amounts of the alkanolamine can range from about 2% to about 75% of the composition. For example, an amount of alkanolamine in the solution can be included in a range of about 3% by weight to about 15% by weight for a total weight of the solution. Because some of the stripper solution's components can be provided as aqueous solutions, the composition can optionally contain small amounts of water. All %'s provided herein are weight percents based on the weight of the composition.
The quaternary ammonium hydroxide can include alkyl ammonium hydroxides. For example, the quaternary ammonium hydroxide can include tetramethylammonium hydroxide, diethyldimethylammonium hydroxide, dipropyldimethylammonium hydroxide, ethyltrimethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide. In an illustrative example, the solution can include one or more of tetramethylammonium hydroxide, dimethyldipropylammonium hydroxide, or methyltriethylammonium hydroxide.
The alkanolamines can have at least two carbon atoms and have the amino and hydroxyl substituents on different carbon atoms. Suitable alkanolamines include, but are not limited to, ethanolamine, N-methylethanolamine, N-ethylethanolamine, N-propylethanolamine, N-butylethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, isopropanolamine, diisopropanolamine, triisopropanolamine, N-methylisopropanolamine, N-ethylisopropanolamine, N-propylisopropanolamine, 2-aminopropane-1-ol, N-methyl-2-aminopropane-1-ol, N-ethyl-2-aminopropane-1-ol, 1-aminopropane-3-ol, N-methyl-1-aminopropane-3-ol, N-ethyl-1-aminopropane-3-ol, 1-aminobutane-2-ol, N-methyl-1-aminobutane-2-ol, N-ethyl-1-aminobutane-2-ol, 2-aminobutane-1-ol, N-methyl-2-aminobutane-1-ol, N-ethyl-2-aminobutane-1-ol, 3-aminobutane-1-ol, N-methyl-3-aminobutane-1-ol, N-ethyl-3-aminobutane-1-ol, 1-aminobutane-4-ol, N-methyl-1-aminobutane-4-ol, N-ethyl-1-aminobutane-4-ol, 1-amino-2-methylpropane-2-ol, 2-amino-2-methylpropane-1-ol, 1-aminopentane-4-ol, 2-amino-4-methylpentane-1-ol, 2-aminohexane-1-ol, 3-aminoheptane-4-ol, 1-aminooctane-2-ol, 5-aminooctane-ol, 1-aminopropane-2,3-polyhydroxyl compound, 2-aminopropane-1,3-polyhydroxyl compound, tris(oxymethyl)aminomethane, 1,2-diaminopropane-3-ol, 1,3-diaminopropane-2-ol, and 2(2-aminoethoxy)ethanol.
The secondary solvent can include glycol ether solvents, an alcohol, or a polyhydroxyl compound, or a combination of two or more of these.
Glycol ether solvents can include, but are not limited to, diethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutylether, diethylene glycol monoisobutyl ether, diethylene glycol monobenzyl ether, diethylene glycol diethylether, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, polyethylene glycol monomethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl acetate, dipropylene glycol, tripropylene glycol, propylene glycol monomethylether, propylene glycol dimethylether, propylene glycol monobutyl ether, dipropyelene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol dipropyl ether, dipropylene glycol diisopropyl ether, tripropylene glycol and tripropylene glycol monomethyl ether, 1-methoxy-2-butanol, 2-methoxy-1-butanol, 2-methoxy-2-methyl-2-butanol, 3-methoxy-3-methyl-1-butanol, dioxane, trioxane, 1,1-dimethoxyethane, tetrahydrofuran, crown ethers and the like.
The secondary solvent alcohols and polyhydroxyl compounds have two or more hydroxyl groups and do not contain ester, amine, or ether groups. The alcohol or polyhydroxyl compounds can be aliphatic, alicyclic, cyclic, or aromatic, but is desirably aliphatic or alicyclic. The alcohol or polyhydroxyl compound can be saturated or unsaturated, and desirably has one or less unsaturated bonds, or no unsaturated bonds. The alcohol and polyhydroxyl compounds desirably do not contain a heteroatom. The alcohol and polyhydroxyl compounds desirably contain only carbon and hydrogen atoms.
As examples of secondary solvent alcohols can be mentioned linear and branched chain and aromatic alcohols. To illustrate an alcohol of the solution can include methanol, ethanol, propanol, isopropyl alcohol, butanol, tert-butyl alcohol, tert-amyl alcohol, 3-methyl-3-pentanol, 1-octanol, 1-decanol, 1-undecanol, 1-dodecanol, 1-tridecanol, 1-tetradecanol, 1-pentadecanol, 1-hexadecanol, 9-hexadecen-1-ol, 1-heptadecanol, 1-octadecanol, 1-nonadecanol, 1-eicosanol, 1-heneicosanol, 1-docosanol, 13-docosen-1-ol, 1-tetracosanol, 1-hexacosanol, 1-heptacosanol, 1-octacosanol, 1-triacontanol, 1-dotriacontanol, 1-dotriacontanol, 1-tetratriacontanol, cetearyl alcohol, furfurylalcohol, tetrahydrofurfuryl alcohol. In an illustrative example, the solution can include one or more of furfurylalcohol, tetrahydrofurfuryl alcohol, tert-butyl alcohol, or 3-methyl-3-pentanol.
As mentioned above, the secondary solvent can be a polyhydroxyl compound having two or more hydroxyl groups. The polyhydroxyl compound desirably has a molecular weight of no more than 500, or no more than 400, or no more than 350, or no more than 300, or no more than 275, or no more than 250, or no more than 225, or no more than 200, or no more than 175, or no more than 150, or no more than 125, or no more than 100, or no more than 75.
The polyhydroxyl compound as a secondary solvent can include, ethylene glycol; 1,2-propanediol (propylene glycol); 1,3-propanediol, 1,2,3-propanetriol; 1,2-butanediol; 1,3-propanediol; 2,3-butanediol; 1,4-butanediol; 1,2,3-butanetriol; 1,2,4-butanetriol; 1,2-pentanediol; 1,3-pentanediol; 1,4-pentandiol; 2,3-pentanediol; 2,4-pentandiol; 3,4-pentanediol; 1,2,3-pentanetriol; 1,2,4-pentanetriol; 1,2,5-pentanetriol; 1,3,5-pentanetriol; etohexadiol; p-methane-3,8-polyhydroxyl compound; 2-methyl-2,4-pentanediol; 2,2-dimethyl-1,3-propanediol; glycerin; trirnethylolpropane; xylitol; arabitol; 1,2- or 1,3-cyclopentanediol; 1,2- or 1,3-cyclohexanediol; 2,3-norbornanediol; 1,8-octanediol; 1,2-cyclohexane-dimethanol; 1,3-cyclohexanedimethanol; 1,4-cyclohexanedimethanol; 2,2,4-trimethyl-1,3-pentanediol; hydroxypivalyl hydroxypivalate; 2-methyl-1,3-propanediol; 2-butyl-2-ethyl-1,3-propanediol; 2-ethyl-2-isobutyl-1,3-propanediol; 1,6-hexanediol; 2,2,4,4-tetramethyl-1,6-hexanediol; 1,10-decanediol; 1,4-benzenedimethanol; hydrogenated bisphenol A; 1,1,1-trimethylol propane; 1,1,1-trimethylolethane; pentaerythritol; erythritol; threitol; dipentaerythritol; sorbitol; and the like, and combinations of 2 or more of the aforementioned polyhydroxyl compounds. polyhydroxyl compound.
In an illustrative example, the solution can include one or more of the secondary polyhydroxyl solvents of ethylene glycol, 1,2-propanediol (propylene glycol), 1,3-propanediol, 1,4-pentanediol, 1,2-butanediol, or 1,3-butanediol.
The compositions can also optionally contain one or more corrosion inhibitors. Suitable corrosion inhibitors include, but are not limited to, aromatic hydroxyl compounds such as catechol; alkylcatechols such as methylcatechol, ethylcatechol and t-butylcateohol, phenols and pyrogallol; aromatic triazoles such as benzotriazole; alkylbenzotriazoles; carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, fumaric acid, benzoic acid, phthalic acid, 1,2,3-benzenetricarboxylic acid, glycolic acid, lactic acid, malic acid, citric acid, acetic anhydride, phthalic anhydride, maleic anhydride, succinic anhydride, salicylic acid, gallic acid, and gallic acid esters, such as methyl gallate and propyl gallate; organic salts of carboxyl containing organic containing compounds described above, basic substances such as ethanolamine, trimethylamine, diethylamine and pyridines, such as 2-aminopyridine, and the like, and chelate compounds such as phosphoric acid-based chelate compounds including 1,2-propanediaminetetramethylene phosphonic acid and hydroxyethane phosphonic acid, carboxylic acid-based chelate compounds such as ethylenediaminetetraacetic acid and its sodium and ammonium salts, dihydroxyethylglycine and nitrilotriacetic acid, amine-based chelate compounds such as bipyridine, tetraphenylporphyrin and phenanthroline, and oxime-based chelate compounds such as dimethylglyoxime and diphenylglyoxime. A single corrosion inhibitor may be used or a combination of corrosion inhibitors may be used. Corrosion inhibitors have proven useful at levels ranging from about 1 ppm to about 10%.
Further, the solution can optionally include one or more surfactants, such as fluorosurfactants. One example of a fluorosurfactant that can be included in the solution is DuPont FSO (fluorinated telomere B mono ether with polyethylene glycol (50%), ethylene glycol (25%), 1,4-dioxane (<0.1%), water (25%)).
Temperatures of at least 50° C. can be used for contacting the substrate whereas for a majority of applications, temperatures of from about 50° C. to about 75° C. can be utilized. For particular applications where the substrate is either sensitive or longer removal times are required, lower contacting temperatures are appropriate. For example, when reworking substrates, it may be appropriate to maintain the stripper solution at a temperature of at least 20° C. for a longer time to remove the photoresist and avoid damaging to the substrate. If longer contact times are required for complete resist removal, placing a blanket of dry nitrogen over the stripper solution can reduce water uptake from the atmosphere and maintain the dry stripper solution's improved performance.
When immersing a substrate, agitation of the composition additionally facilitates photoresist removal. Agitation can be effected by mechanical stirring, circulating, or by bubbling an inert gas through the composition. Upon removal of the desired amount of photoresist, the substrate is removed from contact with the stripper solution and rinsed with water or an alcohol. For example, deionized (DI) water can be used to rinse the substrate. In another example, isopropanol can be used to rinse the substrate. For substrates having components subject to oxidation, rinsing can be performed under an inert atmosphere. Stripper solutions according to the present disclosure can have improved loading capacities for photoresist materials compared to current commercial products and are able to process a larger number of substrates with a given volume of stripper solution.
The stripper solutions provided in this disclosure can be used to remove polymeric resist materials present in a single layer or certain types of bilayer resists. For example, bilayer resists typically have either a first inorganic layer covered by a second polymeric layer or can have two polymeric layers. Utilizing the methods described herein, a single layer of polymeric resist can be effectively removed from a standard wafer having a single polymer layer. The same methods can also be used to remove a single polymer layer from a wafer having a bilayer composed of a first inorganic layer and a second or outer polymer layer. Finally, two polymer layers can be effectively removed from a wafer having a bilayer composed of two polymeric layers. The dry stripper solutions can be used to remove one, two or more resist layers.
Dry stripper solutions can include dimethylsulfoxide, a quaternary ammonium hydroxide, an alkanolamine, an optional secondary solvent and less than about 3 wt. % of water. Secondary solvents can include glycol ethers, alcohols, and/or polyhydroxyl compounds. Dry stripper solutions can also include dimethylsulfoxide, a quaternary ammonium hydroxide, an alkanolamine, a glycol ether solvent, a polyhydroxyl secondary solvent, and a dryness coefficient of at least about 1.8. Dry stripper solutions can also include dimethylsulfoxide, a quaternary ammonium hydroxide, an alkanolamine, a secondary solvent such as an alcohol or a polyhydroxyl secondary solvent, and a dryness coefficient of at least about 1.8.
Use of the dry photoresist stripper solution is similar to that described above for stripper solutions having a low freezing point. However, it is helpful to maintain the stripper solution in a dry form prior to use and to minimize water uptake during its use by maintaining a generally dry environment in the area involved with resist removal. Stripper solutions can be maintained in a dry state by maintaining contact between the stripper solution and active molecular sieves during storage, transit and after opening a container prior to its use.
The dry stripper solutions described herein should be prepared from dry components to the extent possible. Because quaternary ammonium hydroxides are hygroscopic and are generally available as aqueous solutions or their hydrates, water contained in the solution or associated with the hydrate must generally be removed to provide a dry stripper solution having a dryness coefficient of at least about 1. Efforts to dry quaternary ammonium hydroxides at elevated temperatures and to a dry state generally results in decomposition of the hydroxide. It has surprisingly been found that quaternary ammonium hydroxides in a volatile solvent can be pre-dried to give a solvent wet, paste having reduced water content without decomposition. A dry stripper solution containing a quaternary ammonium hydroxide can be prepared by pre-drying the quaternary ammonium hydroxide and combining it with other substantially dry components to maintain a low water content or by subsequently drying an initially fanned wet stripper solution formed from water-containing components.
A pre-dried form of a quaternary ammonium hydroxide can be obtained by subjecting a hydrated or otherwise wet form of a quaternary ammonium hydroxide to a reduced pressure with very slight warming. Water removal may be facilitated by dissolving the quaternary ammonium hydroxide in a solvent such as an alcohol prior to subjecting the hydroxide to reduced pressure. Based on work carried out thus far with methanol, during treatment, a substantial portion of the water and alcohol are removed to provide an alcohol wet paste of the quaternary ammonium hydroxide. Depending on the level of dryness desired, additional dry alcohol can be added to the initially treated hydroxide and the treatment at reduced pressure repeated one or more times. Treatments can be carried out at pressures of from about 0.001 to about 30 mmhg and at temperatures of up to at least about 35° C. without substantial decomposition of the quaternary ammonium hydroxide. Treatments can also be carried out at pressures of from about 0.01 to about 10 mmhg.
For wet formulations with or without a secondary solvent, drying can be carried out on the stripper solution after the addition of all components by contacting the stripper solution with a solid drying agent, such as for example, molecular sieves, calcium hydride, calcium sulfate or a combination of drying agents. An example drying agent can include an activated 3 A or 4 A molecular sieve. For dry stripper solutions containing a secondary solvent, the quaternary ammonium hydroxide can be combined with any other wet components, contact the resulting solution with an active drying agent such as molecular sieves, separate the dry solution from the spent drying agent and add any remaining dry components to the dry solution. Contact with the molecular sieves or other solid drying agent can be by any known method, such as slurrying the solution with drying agent and filtering the dry slurry. Similarly, any of the wet solutions described above can be dried by passing the wet solution through pelletized activated molecular sieves or other drying agent in a column. Suitable molecular sieves include type 3 A, 4 A and 5 A sieves.
Molecular sieves can also be used as a drying agent or desiccant to maintain the stripper solution in a dry state. For example, the pellet form can be used because it allows removal of the dry stripper solution by simple decantation. However, for applications in which decantation does not provide an adequate separation, molecular sieves, whether powder or pellets can be incorporated into a “tea bag” arrangement that will allow equilibrium with the solution, but not allow any sieve particles to contaminate the solution. Dry stripper solutions containing molecular sieves can be maintained in a dry state for extended periods of time after a container has been opened, depending on the amount of molecular sieves included with the stripper solution, the surrounding humidity and the amount of time the container is open.
The reactants listed in Table I were separately combined with stirring to give each of the 13 homogeneous stripper solutions. The freezing points were determined and are also provided in Table I. The compositions of Examples 1-13 can optionally be formulated without a surfactant and formulated to include a corrosion inhibitor.
A silicon wafer having a photoresist thereon is immersed in the stripping solution from Example 1, maintained at a temperature of about 70° C. with stirring for from about 30 to about 60 minutes. The wafer is removed, rinsed with DI water and dried. Examination of the wafer will demonstrate removal of substantially all of the photoresist. For some applications, superior results may be obtained by immersing the wafer in the stripping solution without stirring and/or immersing the wafer for up to 150 minutes. The preferred manner of removing the photoresist from a wafer can readily be determined without undue experimentation. This method can be used to remove a single layer of polymeric photoresist or two polymeric layers present in bilayer resists having two polymer layers.
A silicon wafer having a photoresist thereon is mounted in a standard spray device and sprayed with the stripper solution from Example 2, maintained at about 50° C. The spraying can optionally be carried out under an inert atmosphere or optionally in the presence of an active gas such as, for example, oxygen, fluorine or silane. The wafer can be removed periodically and inspected to determine when sufficient photoresist has been removed. When sufficient photoresist has been removed, the wafer can be rinsed with isopropanol and dried. This method can be used to remove a single layer of polymeric photoresist or two polymeric layers present in bilayer resists having two polymer layers.
The method described in Example f4 was used to remove photoresist from the wafers described below in Table II. Twenty liter volumes of three stripper solutions were used until either a residue of photoresist polymer remained on the wafer or until re-deposition of the polymer or its degradation products onto the wafer occurred, at which point the solutions loading capacity was reached. With this method the loading capacity was determined for the two stripper solutions described in Examples 1 and 2 above and for a comparative example that is generally typical of current commercial stripper solutions.
Dimethylsulfoxide (85.5 g), diethyleneglycol monomethyl ether (6.0 g), aminoethylethanolamine (2.7 g) and tetramethylammonium hydroxide pentahydrate (5.5 g) were combined to provide a stripper solution containing about 3 wt. % water and a dryness coefficient of about 0.9. Dissolution of the hydroxide pentahydrate was facilitated by slightly agitating the mixture. The about 3 wt. % water in the solution came substantially from the pentahydrate.
Active 3 A molecular sieves were added to three different samples of the stripper solution prepared according to the method of Example 17 and maintained in contact with the stripper solutions for 72 hours at ambient temperature. The sieves were removed by filtration and the moisture content of the initial and dried solutions determined by the Karl Fischer method. The dried stripper solutions were stored in closed container. The spent sieves could be dried for reuse or disposed of. The specific details for this experiment are tabulated below in Table III.
Three silicon wafers having a negative acrylate polymer-based dry film photoresist (120/μm) placed thereon over a Copper region were separately immersed in the three dried stripper solutions prepared in Example 18 and maintained at 70° C. for 60 minutes. The samples were removed and rinsed with deionized water for one minute. The resulting stripper solutions were analyzed for the number of particles of photoresist suspended therein utilizing a LiQuilaz SO5 particle analyzer and the copper etch rate determined for each wafer. The results are tabulated in Table IV provided below. LiQuilaz is a registered trademark of Particle Measuring Systems, Inc., 5475 Airport Blvd., Boulder, Colo., 80301.
Photoresist removal as described above can be carried out at temperatures ranging from about 70° C. to about 80° C. without taking any measures to exclude moisture. However, when photoresist removal is carried out at lower temperatures, of less than about 70° C., it may be helpful to take measures to minimize the uptake of moisture from the atmosphere. Providing a blanket of dry nitrogen over the stripper solution maintained at less than about 70° C. has proven effective to minimize water uptake by the stripper solution with longer exposures to a moist atmosphere. The ability of the dry stripper solutions described above to dissolve larger amounts of photoresists and minimize the number of particles dispersed in the stripper solutions extends the stripper solutions effective lifetime and reduces overall costs.
A 25 wt. % solution of tetramethylammonium hydroxide pentahydrate in methanol was prepared and 40.8 grams of the solution was warmed to about 30° C. in a water bath and maintained at a pressure of about 0.01 mmhg for about 75 minutes. Condensate was collected in a Dewar flask cooled with liquid nitrogen. After about 75 minutes, the temperature of the water bath was raised to about 35° C. and maintained at that temperature for an additional 105 minutes. A white paste resulted. The vacuum was broken and 85.8 g of dry DMSO was added to dissolve the white solid after which were added 6.0 g of diethyleneglycol monomethyl ether and 2.7 g of aminoethylethanolamine to provide a substantially dry version of the stripper solution described in Example 1, Table 1. The dry stripper solution's water content was found to be 0.71% by the Karl Fischer method and the solution contained less than 1% methanol. Lower levels of water can be obtained by adding additional methanol to the white paste and maintaining the resulting solution at reduced pressure for an additional 2 to 5 hours.
Appropriate quantities of dry stripper solutions of the type described in Example 18 are packaged with active molecular sieves to maintain the stripper solutions in a dry condition for longer periods of time. About 5 to about 10 gram of active sieves are added for each 100 g of stripper solution maintained in a closed and sealed container. Molecular sieves in the form of pellets are preferred. However, powdered sieves can be used if removed by filtration prior to use or if small amounts of particulate matter do not interfere with use of the dry stripper solution.
While applicant's disclosure has been provided with reference to specific embodiments above, it will be understood that modifications and alterations in the embodiments disclosed may be made by those practiced in the art without departing from the spirit and scope of the disclosure. All such modifications and alterations are intended to be covered.
This application is a continuation-in part of U.S. application Ser. No. 13/759,237 filed on Feb. 5, 2013, which is a continuation of Ser. No. 12/091,808 filed on Oct. 24, 2006, which is a Continuation-In-Part of U.S. application Ser. No. 11/260,912 filed on Oct. 28, 2005, which are each incorporated fully herein by reference.
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