HK1056919A1 - Photoresist composition - Google Patents

Description

Photoresist composition

Technical Field

The present invention relates to the field of photoresists. In particular, the present invention relates to photoresists having improved removal characteristics, particularly for use in the manufacture of printed wiring boards.

Background

Photoresists are photosensitive films used to transfer images to a substrate. A photoresist coating is formed on a substrate and then the photoresist layer is exposed to activating radiation through a mask. The mask has certain areas opaque to activating radiation and other areas transparent to activating radiation. Exposure to activating radiation provides a photo-induced chemical transformation in the photoresist coating that transfers the image of the reticle to the photoresist coated substrate. After exposure, the photoresist is developed to provide a relief image that allows the substrate to be selectively processed.

The photoresist may be positive acting or negative acting. In the case of negative-acting photoresists, the areas of the coating exposed to activating radiation undergo a polymerization or crosslinking reaction between the polymerizing agent of the photoresist composition and the photoactive compound. Thus, the exposed areas of the coating are less soluble in a developer solution than the unexposed areas. In the case of positive-working photoresists, the exposed areas are relatively soluble in the developer solution, and the unexposed areas remain relatively insoluble in the developer. Generally, photoresist compositions comprise at least a resinous binder component and a photoactive agent.

A variety of different polymeric or resin binders may be used for the photoresist. Such polymeric binders may comprise one or more acid functional monomers, such as acrylic acid or methacrylic acid, as a polymeric component. For example, U.S. patent No. 5,952,153 (Lundy et al) discloses a photo-imaging composition that contains sufficient functional acid as a polymeric binder to render the photo-imaging composition developable in an aqueous alkaline solution. U.S. Pat. No. 4,537,855 (Ide) discloses the use of polycarboxylic acids with ethylenically unsaturated compounds to form polymerizable ester derivatives. Such polymerizable ester derivatives are polymeric binders used to form photoimageable compositions.

The photoresist may be a liquid or a dry film. The photoresist liquid is first disposed on the substrate and then cured. The photoresist dry film may be typically laminated to a substrate. The photoresist dry film is particularly suitable for the manufacture of printed circuit boards. A problem with known photoresist dry film compositions is that they are difficult to remove from electrolytically plated circuit boards using known aqueous alkaline removal solutions (e.g., 3% sodium hydroxide solution). This problem is caused by the reduced size of the printed circuit board in order to increase its functionality, as a result of the manufacturer of the printed circuit board. Therefore, circuit lines and space of the circuit board are continuously reduced as more circuit circuits need to be accommodated in a smaller space. Meanwhile, the height of the plated metal must be higher than the thickness of the photoresist. The metal is suspended in the photoresist, and the narrow space containing the photoresist is substantially enclosed in the plated metal. The photoresist is confined to the plating cantilever making it difficult to access and remove by known methods. If the photoresist is not completely removed, it can cause undesirable rough copper circuit lines after etching, which can result in board shorts.

Some circuit board manufacturers attempt to increase the thickness of the photoresist while increasing the plating height to accommodate, however, this approach is expensive and limits the resolution of the circuit lines. Specifically, the use of organic-based (amine or organic solvent containing) alkaline scavenging solutions produces tiny scavenging particles that aid in scavenging. Thus, photoresist removal by such organic-based purges is preferred, but is more expensive relative to inorganic-based purges (e.g., sodium or potassium hydroxide) and has more associated waste disposal and environmental concerns. Photoresists that can clear solvent are also undesirable due to factory regulatory constraints or to reduce solvent emissions.

Accordingly, it would be desirable to provide a photoresist composition that is easily removable using an inorganic-based alkaline aqueous cleaning solution.

Disclosure of Invention

It has surprisingly been found that the addition of one or more non-polymeric organic acids provides a photoimageable composition having improved cleanability or removability. It has also been surprisingly found that such non-polymeric organic acids do not adversely affect other characteristics of the photoresist adhesive, such as chemical resistance. Thus, the compositions of the present invention exhibit improved scavenging without a substantial loss of chemical resistance as compared to otherwise identical compositions not containing the non-polymeric organic acid.

In one aspect, the invention provides a photoresist composition comprising a polymeric binder, a photoactive component, an organic acid, and optionally a crosslinker, wherein the organic acid and the polymeric binder, the optional crosslinker, or both are non-polymerizable.

In another aspect, the present invention provides a method of enhancing the removal of a photoresist composition from a substrate comprising the step of combining a photoresist composition comprising a polymeric binder, a photoactive component, and optionally a crosslinker, with an organic acid, wherein the organic acid and the polymeric binder, the optional crosslinker, or both are non-polymerizable.

In yet another aspect, the present invention provides a method of manufacturing a printed wiring board, comprising the steps of: a) disposing a photoresist composition on a substrate of a printed wiring board, the photoresist composition comprising a polymeric binder, a photoactive component, an organic acid, and optionally a crosslinker, wherein the organic acid and the polymeric binder and optionally the crosslinker are non-polymerizable; b) imaging the photoresist; and c) developing the photoresist.

Detailed Description

In this specification, unless otherwise indicated, the following abbreviations shall have the following meanings: DEG C is centigrade; g is gram; mg ═ mg; tg ═ glass transition temperature; f ═ Fahrenheit; wt% -% by weight; and mil 0.001 inch.

"resin" and "polymer" are used interchangeably in this specification. The term "alkyl" refers to straight, branched, and cyclic alkyl groups. "halogen" and "halo" include fluorine, chlorine, bromine and iodine. Thus, "halogenated" refers to fluorinated, chlorinated, brominated, and iodinated. "Polymer" refers to homopolymers and copolymers and includes dimers, trimers, oligomers, and the like. "(meth) acrylate" refers to both acrylate and methacrylate. Similarly, "(meth) acrylic" refers to both acrylic and methacrylic. "monomer" means any polymerizable ethylenically or acetylenically unsaturated compound. "crosslinker" and "crosslinker" are used interchangeably in this specification. "printed wiring board" and "printed circuit board" are used interchangeably in this specification.

All amounts are weight% and all proportions are weight ratios unless otherwise indicated. All numerical ranges are inclusive and combinable.

The photoresist composition of the invention comprises a polymeric binder, a photoactive component, an organic acid, and optionally a crosslinker, wherein the organic acid is non-polymerizable with the polymeric binder, the optional crosslinker, or both.

A variety of polymeric binders may be suitable for use in the present invention. Suitable polymeric binders are those containing one or more ethylenically or propylenically unsaturated monomers as polymerized units. Suitable monomers include, but are not limited to: (meth) acrylic acid, (meth) acrylamide, alkyl (meth) acrylates, alkenyl (meth) acrylates, aromatic (meth) acrylates, vinyl aromatic monomers, nitrogen-containing compounds and their sulfur analogs, substituted vinyl monomers, cyclic olefins, substituted cyclic olefins, and the like. Preferred monomers comprise: (meth) acrylic acid, alkyl (meth) acrylates, and vinyl aromatic monomers. These polymeric binders may be homopolymers or copolymers, preferably copolymers. It is further understood that mixtures of binder polymers may also be used in the present invention. Thus, the light imaging compositions of the present invention may comprise one or more polymeric binders.

Specifically, the alkyl (meth) acrylate usable in the present invention is (C)₁-C₂₄) Alkyl (meth) acrylates. Suitable alkyl (meth) acrylates include, but are not limited to: "low cut" alkyl (meth) acrylates, "medium cut" alkyl (meth) acrylates, and "high cut" alkyl (meth) acrylates.

"Low cut" alkyl (meth) acrylates generally means that the alkyl group contains from 1 to 6 carbon atoms. Suitable low cut alkyl (meth) acrylates include, but are not limited to: methyl methacrylate ("MMA"), methyl acrylate, ethyl acrylate, propyl methacrylate, butyl methacrylate ("BMA"), butyl acrylate ("BA"), isobutyl methacrylate ("IBMA"), hexyl methacrylate, cyclohexyl acrylate, and mixtures thereof.

"cut-in" alkyl (meth) acrylates generally means that the alkyl group contains from 7 to 15 carbon atoms. Suitable middle distillate alkyl (meth) acrylates include, but are not limited to: 2-ethylhexyl acrylate ("EHA"), 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, isodecyl methacrylate ("IDMA", branched (C)₁₀) Mixtures predominantly of alkyl isomers), undecyl methacrylate, dodecyl methacrylate (i.e., lauryl methacrylate), tridecyl methacrylate, tetradecyl methacrylate (i.e., myristyl methacrylate), pentadecyl methacrylate, and mixtures thereof. Particularly useful mixtures comprise dodeca-pentadecyl methacrylate ("DPMA"); mixtures of linear and branched isomers of dodecyl, tridecyl, tetradecyl, and pentadecyl methacrylates; and lauryl-myristyl methacrylate ("LMA").

"high cut" alkyl (meth) acrylates generally means that the alkyl group contains from 16 to 24 carbon atoms. Suitable high cut alkyl (meth) acrylates include, but are not limited to: cetyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, cosyl methacrylate, eicosyl methacrylate, and mixtures thereof. Particularly useful high cut alkyl (meth) acrylate mixtures include, but are not limited to: cetyl-eicosyl methacrylate ("CEMA"), which is a mixture of cetyl, stearyl, cosyl and eicosyl methacrylates; and cetearyl methacrylate ("SMA"), which is a mixture of cetyl and stearyl methacrylates.

The above-mentioned medium-and high-cut alkyl (meth) acrylate monomers are generally prepared by standard esterification using technical-grade long chain aliphatic alcohols, whereas these commercially available alcohols are mixtures of alcohols containing between 10 and 15 carbon atoms or between 16 and 20 carbon atoms in the alkyl group. Examples of such alcohols are: various Ziegler-catalyzed ALFOL alcohols from Vista chemical company, ALFOL 1618 and ALFOL 1620; various Ziegler-catalyzed NEODOL alcohols from Shell chemical company, NEODOL 25L, and naturally occurring alcohols such as Proctor & Gamble TA-1618 and CO-1270. Thus, for the purposes of the present invention, alkyl (meth) acrylates are intended to comprise not only the individual alkyl (meth) acrylate products mentioned, but also mixtures of alkyl (meth) acrylates and the particularly predominant alkyl (meth) acrylates mentioned.

The alkyl (meth) acrylate monomers used in the present invention may be monomers or mixtures having different numbers of carbon atoms in the alkyl portion. In addition, the (meth) acrylamide and alkyl (meth) acrylate monomers used in the present invention may be optionally substituted. Suitable optionally substituted (meth) acrylamide and alkyl (meth) acrylate monomers include, but are not limited to: hydroxy (C)₂-C₆) Alkyl (meth) acrylate, dialkylamino (C)₂-C₆) Alkyl (meth) acrylate, dialkylamino (C)₂-C₆) Alkyl (meth) acrylamides.

Particularly useful substituted alkyl (meth) acrylate monomers are those having one or more hydroxyl groups in the alkyl group, particularly those having a hydroxyl group in the beta-position (2-position) of the alkyl group. (C) in which the substituted alkyl substituent is branched or unbranched in the hydroxyalkyl (meth) acrylate monomer₂-C₆) An alkyl group is preferred. Suitable hydroxyalkyl (meth) acrylate monomers include, but are not limited to: 2-hydroxyethyl methacrylate ("HEMA"), 2-hydroxyethyl acrylate ("HEA"), 2-hydroxypropyl methacrylate, 1-methyl-2-hydroxyethyl methacrylate, 2-hydroxy-propyl acrylate, 1-methyl-2-hydroxyethyl acrylate, 2-hydroxybutyl methacrylate, 2-hydroxybutyl acrylate andmixtures thereof. Preferred hydroxyalkyl (meth) acrylate monomers are HEMA, 1-methyl-2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and mixtures thereof. The mixture of the last two monomers is commonly referred to as "hydroxypropyl methacrylate" or HPMA.

Other substituted (meth) acrylate and (meth) acrylamide monomers useful in the present invention refer to monomers having a dialkylamino group or dialkylaminoalkyl group in the alkyl group. Examples of such substituted (meth) acrylates and (meth) acrylamides include, but are not limited to: dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, N-dimethylaminoethyl methacrylamide, N-dimethyl-aminopropyl methacrylamide, N-dimethylaminobutyl methacrylamide, N-diethylaminoethyl methacrylamide, N-diethylaminopropyl methacrylamide, N-diethylaminobutyl methacrylamide, N- (1, 1-dimethyl-3-oxobutyl) acrylamide, N- (1, 3-diphenyl-1-ethyl-3-oxobutyl) acrylamide, N- (1-methyl-1-phenyl-3-oxobutyl) methacrylamide and 2-hydroxyethyl acrylamide, N-methacrylamide of aminoethyl ethylene urea, N-methacryloyloxyethyl morpholine, N-cis-butadienimide of dimethylaminopropylamine and mixtures thereof.

Other substituted (meth) acrylate monomers useful in the present invention are silicon-containing monomers, such as gamma-propyltri (C)₁-C₆) Alkoxysilyl (meth) acrylate, gamma-propyltri (C)₁-C₆) Alkylsilyl (meth) acrylate, gamma-propyldi (C)₁-C₆) Alkoxy (C)₁-C₆) Alkylsilyl (meth) acrylate, gamma-propyldi (C)₁-C₆) Alkyl radical (C)₁-C₆) Alkoxysilyl (meth) acrylate, vinyl tris (C)₁-C₆) Alkoxysilyl (meth) acrylate, vinyl di (C)₁-C₆) Alkoxy (C)₁-C₆) Alkylsilyl (meth) acrylate, vinyl (C)₁-C₆) Alkoxy di (C)₁-C₆) Alkylsilyl (silyl)Base) acrylate, vinyl tri (C)₁-C₆) Alkylsilyl (meth) acrylates, 2-propylsiloxane half (meth) acrylates and mixtures thereof.

The vinyl aromatic monomers that can be used as the unsaturated monomer in the present invention include, but are not limited to: styrene ("STY"), hydroxystyrene, alpha-methylstyrene, vinyltoluene, p-methylstyrene, ethylvinylbenzene, vinylnaphthalene, vinylxylene, and mixtures thereof. Vinyl aromatic monomers also include their corresponding substituted counterparts, e.g., halogenated derivatives, i.e., containing one or more halogen groups, such as fluorine, chlorine or bromine; and nitro, cyano, (C)₁-C₁₀) Alkoxy, halo (C)₁-C₁₀) Alkyl, carbonyl (C)₁-C₁₀) Alkoxy, carboxyl, amine, (C)₁-C₁₀) Alkylamine derivatives, and the like.

Nitrogen-containing compounds and sulfur-analogs thereof useful as unsaturated monomers in the present invention include, but are not limited to: vinylpyridines, such as 2-vinylpyridine or 4-vinylpyridine; lower alkyl (C)₁-C₈) Substituted N-vinylpyridines, such as 2-methyl-5-vinylpyridine, 2-ethyl-5-vinylpyridine, 3-methyl-5-vinylpyridine, 2, 3-dimethyl-5-vinylpyridine and 2-methyl-3-ethyl-5-vinylpyridine; methyl-substituted quinolines and isoquinolines; n-vinyl caprolactam; n-vinyl butyrolactam; n-vinyl pyrrolidone; vinylimidazole; n-vinylcarbazole; n-vinyl-succinimide; (meth) acrylonitrile; ortho-, meta-, or para-aminostyrene; maleimide; n-vinyl-oxazolidinone; n, N-dimethylaminoethyl-vinyl-ether; ethyl-2-cyanoacrylate; vinyl acetonitrile; n-vinyl phthalimide; n-vinyl-pyrrolidones, e.g. N-vinyl-thio-pyrrolidone, 3-methyl-1-vinyl-pyrrolidone, 4-methyl-1-vinyl-pyrrolidone, 5-methyl-1-vinyl-pyrrolidone, 3-ethyl-1-vinyl-pyrrolidone, 3-butyl-1-vinyl-pyrrolidone, 3-dimethyl-1-vinyl-pyrrolidone, 4, 5-dimethyl-1-vinyl-pyrrolidone, 5-dimethyl-1-vinyl-pyrrolidoneKetones, 3, 5-trimethyl-1-vinyl-pyrrolidone, 4-ethyl-1-vinyl-pyrrolidone, 5-methyl-5-ethyl-1-vinyl-pyrrolidone and 3, 4, 5-trimethyl-1-vinyl-pyrrolidone; vinyl pyrrole; vinylaniline and vinyl hexahydropiperidine.

Substituted ethylene monomers useful as unsaturated monomers in the present invention include, but are not limited to: vinyl acetate, vinyl formamide, vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, vinylidene fluoride, vinylidene bromide, tetrafluoroethylene, trifluoroethylene, trifluoromethyl vinyl acetate, vinyl ether and decomposed aconitic anhydride.

Suitable cycloolefin monomers in the present invention are (C)₅-C₁₀) Cyclic olefins such as cyclopentene, cyclopentadiene, dicyclopentene, cyclohexene, cyclohexadiene, cycloheptene, cycloheptadiene, cyclooctene, cyclooctadiene, norbornene, maleic anhydride, and the like. Such cyclic olefins also include spirocyclic olefin monomers such as spironorbornyl monomers, spirocyclic cyclohexene monomers, spirocyclic cycloheptene monomers, and mixtures thereof. Suitable substituted cyclic olefin monomers include, but are not limited to: a cyclic olefin having one or more substituents selected from the group consisting of: hydroxy, aryloxy, halo, (C)₁-C₁₂) Alkyl, (C)₁-C₁₂) Haloalkyl, (C)₁-C₁₂) Hydroxyalkyl radical, (C)₁-C₁₂) Halo-hydroxyalkyl radicals, e.g. (CH)₂)_n’C(CF₃)₂OH, n' is 0 to 4, (C)₁-C₁₂) Alkoxy, thio, amino, (C)₁-C₆) Alkylamine, (C)₁-C₆) Dialkylamine, (C)₁-C₁₂) Alkyl sulfur, carbonyl (C)₁-C₂₀) Alkoxy, carbonyl (C)₁-C₂₀) Haloalkoxy, (C)₁-C₁₂) Acyl, (C)₁-C₆) Alkylcarbonyl (C)₁-C₆) Alkyl groups, and the like. Particularly suitable substituted cycloalkenes comprise: maleic anhydride and compound containing one or more hydroxy, aryloxy, (C)₁-C₁₂) Alkyl, (C)₁-C₁₂) Haloalkyl, (C)₁-C₁₂) Hydroxyalkyl radical, (C)₁-C₁₂) Halohydroxyalkyl, carbonyl (C)₁-C₂₀) Alkoxy and carbonyl (C)₁-C₂₀) Haloalkoxy cycloalkenes. It is well known to those skilled in the art that alkyl and alkoxy substituents may optionally be substituted, for example with halogen, hydroxy, cyano, (C)₁-C₆) Alkoxy, mercapto, (C)₁-C₆) Alkylthio, amino, acid labile leaving groups, and the like. Suitable carbons (C)₁-C₂₀) Alkoxy substituents include, but are not limited to: those of the formula C (O) O-LG, wherein LG is a leaving group, include, but are not limited to: alkyl radicals having 4 or more carbon atoms and at least one quaternary carbon atom directly bonded to the oxo radical, e.g. tert-butyl, 2, 3-dimethylbutyl, 2-methylpentyl, 2, 3, 4-trimethylpentyl, cycloaliphatic, acetal or ketal formed from vinyl ethers, or alkenols, e.g. -O- (CH)₃)OC₂H₅) or-O- (CH)₂OC₂H₅) Tetrahydropyran ("THP"). Alicyclic esters suitable as leaving groups include adamantyl, methyladamantyl, ethyladamantyl, methylnorbornyl, ethylnorbornyl, ethyltrimethylnorbornyl, ethylfenchyl alcohol and the like.

Also preferred are polymeric binders that contain sufficient functional acid to render the binding polymer soluble and removable after development. "functional acid" refers to any functionality that can form a salt upon contact with an alkaline developer; alkaline developers, for example dilute aqueous sodium or potassium hydroxide solutions, such as 1 to 3% by weight solutions. Suitable functional acids include, but are not limited to: carboxylic acids, sulfonic acids, phosphonic acids, and phenols. Generally, the binding polymer has an acid number of up to about 250, preferably up to about 200. Typical acid numbers range from 15 to 250, preferably 50 to 250. The acid number is based on the amount (mg) of KOH (potassium hydroxide) required to neutralize 1 gram (dry weight) of the binding polymer.

Suitable polymeric binders are commercially available from a variety of different sources, such as Rohm and Haas corporation (philiadelphia, Pennsylvania) or are prepared by various methods known in the literature. Specifically, the polymeric binder is present in the optical imaging composition in an amount of up to 90% by weight, preferably 20 to 90% by weight, more preferably 25 to 85% by weight, and even more preferably 30 to 80% by weight, based on the total weight of the composition.

A variety of different organic acids can be used in the present invention that are non-polymeric with the polymeric binder, the optional crosslinker, or both, without incorporating an adhesive polymer or crosslinker. The organic acids used in the present invention are substantially non-incorporated, preferably without the incorporation of an adhesive polymerization agent or crosslinking agent.

Suitable organic acids include, but are not limited to: carboxylic acids, such as alkanecarboxylic acids and arenecarboxylic acids, sulfonic acids, such as alkanesulfonic acids and arenesulfonic acids, phosphonic acids, such as alkylphosphonic acids and arylphosphonic acids, and the like. Examples of carboxylic acids include, but are not limited to: (C)₁-C₁₂) Alkyl carboxylic acids; (C)₁-C₁₂) Alkyl dicarboxylic acids; (C)₁-C₁₂) Alkyl tricarboxylic acids; substituted (C)₁-C₁₂) Alkyl carboxylic acids; substituted (C)₁-C₁₂) Alkyl dicarboxylic acids; substituted (C)₁-C₁₂) Alkyl tricarboxylic acids; amine carboxylic acids such as ethylenediaminetetraacetic acid; aromatic carboxylic acids such as aromatic monocarboxylic acids, aromatic dicarboxylic acids and aromatic tricarboxylic acids; and substituted aryl carboxylic acids. Preferred organic acids include: formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, glycolic acid, lactic acid, tartaric acid, citric acid or malic acid, ethylenediaminetetraacetic acid, acids, benzenetricarboxylic acid, salicylic acid, cyclohexanecarboxylic acid, 1, 4-cyclohexanedicarboxylic acid and sebacic acid.

It is well known to those skilled in the art that more than one organic acid may be suitably employed in the compositions of the present invention. Accordingly, the light imaging composition of the present invention may comprise one or more organic acids. It will also be appreciated by those skilled in the art that increasing the amount of such non-polymeric organic acids in the compositions of the present invention allows for the use of polymeric binders having less functional acids without substantially diminishing the cleaning efficacy. Thus, polymeric binders having other improved properties (e.g., increased chemical resistance), but lacking desirable scavenging properties, can be used in combination with the organic acids of the present invention to provide readily removable photoimaging compositions.

The organic acid is generally commercially available from a variety of different sources, such as aldrich chemical Co, (Milwaukee, Wisconsin), and is used without further purification. Generally, the compositions of the present invention comprise one or more organic acids in an amount of up to about 10 weight percent, preferably up to about 8 weight percent, and more preferably up to about 5 weight percent, based on the total dry weight of the adhesive polymer. Specifically, the one or more organic acids are present in an amount of 0.125 wt% or more. The organic acid is present in an amount of 0.5 to 5 parts per 40 parts of the polymeric binder on a dry weight/weight basis.

Suitable crosslinking agents for use in the present invention comprise di-, tri-, tetra-or more functional ethylenically unsaturated monomers. Examples of crosslinking agents useful in the present invention include, but are not limited to: trivinylbenzene, divinyltoluene, divinylpyridine, divinylnaphthalene and divinylxylene, and also, for example, ethylene glycol diacrylate, trimethylolpropane triacrylate ("TMPTA"), diethylene glycol divinyl ether, trivinylcyclohexane, allyl methacrylate ("ALMA"), ethylene glycol dimethacrylate ("EGDMA"), diethylene glycol dimethacrylate ("DEGDMA"), propylene glycol dimethacrylate, propylene glycol diacrylate, trimethylolpropane trimethacrylate ("TMPTMA"), divinylbenzene ("DVB"), glycidyl methacrylate, 2-dimethylpropane 1, 3-diacrylate, 1, 3-butanediol dimethacrylate, 1, 4-butanediol diacrylate, diethylene glycol diacrylate, diethylene glycol dimethacrylate, 1, 6-hexanediol diacrylate, 1, 6-hexanediol dimethacrylate, tripropylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, polyethylene glycol 200 diacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, ethoxylated bisphenol A diacrylate, oxidized bisphenol A dimethacrylate, polyethylene glycol 600 dimethacrylate, poly (butylene glycol) diacrylate, pentaerythritol triacrylate, trimethylolpropane triethoxy triacrylate, glyceryl propoxy triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, diisopentaerythritol monohydroxypentaacrylate, ethoxylated diacrylate, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, propylene glycol, Ethoxylated triacrylates (e.g., ethoxylated TMPTA and ethoxylated TMPTMA), ethoxylated tetraacrylates, divinylsilane, trivinylsilane, dimethyldivinylsilane, divinylmethylsilane, methyltrivinylsilane, diphenyldivinylsilane, divinylphenylsilane, trivinylphenylsilane, divinylmethylphenylsilane, tetravinylsilane, dimethylvinyldisiloxane, poly (methylvinylsiloxane), poly (vinylhydrosiloxane), poly (phenylvinylsiloxane), saccharide radicals (including di-, tri-and tetra-saccharide ureas), epoxies, and mixtures thereof. These crosslinking agents are generally commercially available.

It is well known to those skilled in the art that the desired properties of a photoimageable composition can be imparted by combining two or more crosslinking agents. Therefore, a mixture of crosslinking agents is preferably used in the present invention. The photoresist composition of the present invention preferably comprises one or more crosslinking agents. Specifically, in the optical imaging composition of the present invention, the content of such a crosslinking agent is from 5 to 75% by weight, preferably from 15 to 70% by weight, more preferably from 20 to 65% by weight.

In another embodiment, one or more monomers are desirably combined with one or more crosslinkers to provide a curing agent system. In the curing agent system, one or more monomers are selected to provide certain desired properties in the cured photoresist. For example, the (meth) acrylate functional crosslinker may be combined with one or more monomers, preferably one or more (meth) acrylate monomers. "(meth) acrylate functional crosslinker" means a crosslinker having one or more (meth) acrylate groups, preferably two or more (meth) acrylate groupsThe ester group is the formula H₂C＝C(H or CH₃) C (O) -O-. Specifically, the amount of crosslinker and monomer in the curative system is selected to provide the desired net (meth) acrylate functionality. "neat (meth) acrylate functionality" refers to the average (meth) acrylate functionality in the curative component. The net (meth) acrylate functionality is determined by averaging the amounts of the multi- (meth) acrylate functional compound (i.e., crosslinker) and the mono- (meth) acrylate functional compound (i.e., (meth) acrylate monomer) on a weight basis. For example, a triacrylate crosslinker (e.g., TMPTA) used in a 1: 1 weight mixture with acrylate monomers (i.e., compounds having one acrylate substituent) will have a net (meth) acrylate functionality of about 2. In the optical imaging composition of the present invention, it is preferable to use a curing agent system as the crosslinking agent.

By selecting the neat (meth) acrylate functionality, the resistance of the photoresist to the chemistry of the photo-set is balanced for ease of cleaning or removal of the photoresist. Generally, increasing the branching of the cured photoresist (i.e., increasing the amount of crosslinking) increases the chemical resistance. Reducing the branching of the cured photoresist (i.e., reducing the amount of crosslinking) increases the cleaning efficacy of the cured photoresist, while reducing the chemical resistance of the cured photoresist. It has surprisingly been found that when the neat (meth) acrylic acid finger functionality is about 2, excellent chemical resistance is provided while providing enhanced cleaning efficacy of the cured photoresist. When the neat (meth) acrylate functionality is higher than 2, the chemical resistance of the cured photoresist increases, but is not conducive to the removal of such cured photoresist. When the net (meth) acrylate functionality is less than 2, the removal efficiency of the cured photoresist is increased, but the chemical resistance of the cured photoresist is not favored.

Accordingly, the present invention provides a method of enhancing the removal of a photoresist composition from a substrate comprising the step of combining a curing agent having a net (meth) acrylate functionality of about 2 or greater with a photoresist composition comprising a polymeric binder and a photoactive component. When the curing agent comprises acrylate functionality, the net acrylate functionality is preferably about 2 or more, with about 2 being preferred. When the curing agent comprises methacrylate functionality, the neat methacrylate functionality is preferably 2 or less. The curing agent preferably comprises one or more acrylate crosslinkers, and one or more non-crosslinking acrylate monomers. The curing agent preferably comprises a triacrylate cross-linking agent and a non-cross-linkable acrylate monomer. Preferred curing agents are those containing ethoxylated TMPTA as the crosslinking agent and the reaction product of epsilon caprolactone with HEA as the monomer. Still more preferably, the weight ratio of triacrylate crosslinker to non-crosslinkable acrylate monomer is about 1: 1. The curing agent is preferably free of methacrylate functionality.

The present invention further provides a photoimageable composition comprising one or more polymeric binders, one or more photoactive components, and a curing agent system comprising one or more crosslinkers and one or more monomers, wherein the curing agent system has a net (meth) acrylate functionality of about 2.

The inventive photoimageable compositions contain one or more photoactive components. The photoactive component used in the present invention may be a photoacid generator, a photobase generator, or a radical generator. The light imaging composition of the present invention can be either positive phase or negative phase, preferably negative phase. It will be well known to those skilled in the art that mixtures of photoactive components can render the composition photoactive as appropriate for a particular application.

Suitable photoacid generators include halogenated triazines, onium salts, sulfonated esters, halogenated sulfonyloxy dicarboxylic acid imides, diazo disulfones, alpha-cyanoamine sulfonates, imide sulfonates, ketone diazo sulfones, sulfonyl diazo esters, 1, 2- (arylsulfonyl) s, and the like. Particularly useful halogenated triazines include halomethyl-S-triazines.

Suitable free radical generators include, but are not limited to: n-phenylglycine, aromatic ketones such as diphenyl ketone, N ' -tetramethyl-4, 4 ' -diaminediphenyl ketone "Michler's ketone", N ' -tetraethyl-4, 4 ' -diaminediphenyl ketone, 4-methoxy-4 ' -dimethylamine diphenyl ketone, 3 ' -dimethyl-4-methoxydiphenyl ketone, p ' -bis (dimethylamine) diphenyl ketone, p ' -bis (diethylamine) diphenyl ketone, anthraquinone, 2-ethylanthraquinone, naphthoquinone and phenanthrenequinone; benzophenones, such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin phenyl ether, methyl benzoin, and ethyl benzoin; benzyl derivatives such as benzhydryl, benzhydryldithio and benzhydryldimethyl ketal; acridine derivatives, such as 9-phenylacridine and 1, 7-bis (9-acridinyl) heptane; 9-oxodibenzothiopyran compounds, such as 2-chloro-9-oxodibenzothiopyran, 2-methyl-9-oxodibenzothiopyran, 2, 4-diethyl-9-oxodibenzothiopyran, 2, 4-dimethyl-9-oxodibenzothiopyran and 2-isopropyl-9-oxodibenzothiopyran; acetophenones, such as 1, 1-dichloroacetophenone, p-tert-butyldichloro-acetophenone, 2-diethoxyacetophenone, 2-dimethoxy-2-phenylacetophenone and 2, 2-dichloro-4-phenoxyacetophenone; 2, 4, 5-triarylimidazole dimers such as 2- (o-chlorophenyl) -4, 5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4, 5-bis (m-methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4, 5-diphenylimidazole dimer, 2- (o-methoxyphenyl) -4, 5-diphenylimidazole dimer, 2- (p-methoxyphenyl) -4, 5-diphenylimidazole dimer, 2, 4-bis (p-methoxyphenyl) -5-phenylimidazole dimer, 2- (2, 4-dimethoxyphenyl) -4, 5-diphenylimidazole dimer and 2- (p-methylthiophenyl) -4, 5-diphenylimidazole dimer, and the like. However, the free radical generator (triphenylphosphine) is not included in the photoactive chemical system as a catalyst. Such free radical generators are suitable for use in negative working photoimaging compositions, and are preferred for use in dry films of the negative working photoimaging compositions of the present invention.

In particular, the amount of the photoactive composition is from 0.05 to 10% by weight, preferably from 0.1 to 5% by weight, more preferably from 0.1 to 2% by weight, based on the total weight of the composition.

The optical imaging composition of the present invention may optionally contain a solvent. Suitable solvents include, but are not limited to: ketone solvents such as ethanone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, and 2-heptanone; polyhydric alcohols and derivatives thereof, such as ethylene glycol, ethylene glycol monoethyl ester, diethylene glycol monoethyl ester, propylene glycol monoethyl ester, dipropylene glycol and dipropylene glycol monoethyl ester, and monomethyl, monoethyl, monopropyl, monobutyl and monophenyl ethers thereof; cyclic ether solvents such as dioxane; ester solvents such as methyl lactate, ethyl lactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxy propionate, and ethyl ethoxy propionate; amide solvents such as N, N-dimethylformamide, N-dimethylacetamide, N-methyl-2-pyrrolidone; 3-ethoxyethyl propionate; 2-heptanone; gamma-butyrolactone and mixtures thereof.

Additives that may be optionally used in the photo-imaging composition of the present invention include, but are not limited to: anti-striation agent, plasticizer, speed enhancer, filler, dye, plastic agent, photoresist removal enhancer containing hydrophobic trihalomethyl, etc. Suitable plasticizers include esters, such as benzoate. The photoimageable compositions of the present invention preferably incorporate one or more photoresist removal enhancers which contain a hydrophobic trihalomethyl group. Suitable photoresist stripping enhancements containing hydrophobic trihalomethyl groups include a variety of different compounds containing trihalomethyl groups that hydrolyze to carboxylate anions during photoresist stripping. The hydrophobic trihalomethyl-containing photoresist removal enhancer is preferably α -tribromomethylbenzyl acetate. These optional additives may be present in the photoresist composition in various concentrations. For example, fillers and dyes may be used in relatively large concentrations, for example in amounts of from about 5 to 30% by weight, based on the total weight of the dry ingredients of the composition.

The photoresist compositions of the present invention are typically prepared in any order in combination with a polymeric binder, a photoactive component, an organic acid, an optional crosslinker, an optional solvent, and optional additives.

The process of the photoimaging or photoresist composition of the present invention may be any conventional method. In a typical process, a photoresist layer applied to a substrate may be formed from a liquid composition or converted from a dry film to a photoresist layer. When a liquid photoresist composition is used, it may be applied to the substrate by any known method, such as spin coating, dip coating, roll coating, and the like.

The photoresist compositions of the present invention can be used for a variety of substrates used in the manufacture of electronic components such as printed wiring boards and integrated circuits. Suitable substrates include: copper surfaces of copper-plated boards, inner and outer layers of printed wiring boards, wafers used in the manufacture of integrated circuits, and the like.

After the photoresist is applied to the substrate, it is exposed to an activating radiation source in an image or through an appropriate pattern. In the case of negative-acting photoresists, the activating radiation source polymerizes the crosslinking agent in the exposed areas, creating a crosslinked structure that is resistant to the developer. Subsequently, the composition was developed using a diluted aqueous alkaline solution. Suitable developers comprise 1 to 3% by weight aqueous sodium hydroxide or potassium hydroxide. An organic-based developer (e.g., a tetraalkylammonium hydroxide alkaline developer) can be used, but this is not preferred. During development, the acidic groups of the binding polymer form salts, which render the binding polymer soluble or removable.

In the case of a negative-acting photoresist applied to the copper surface of a copper plating plate, the areas of the copper that have had its photoresist removed themselves can be removed using an etchant after development to form a printed circuit. The remaining photoresist is then removed with a scavenger.

Accordingly, the present invention provides a method of manufacturing a printed wiring board, comprising the steps of: a) disposing a photoresist composition on a substrate of a printed wiring board, the composition comprising a polymeric binder, a photoactive component, an organic acid, and optionally a crosslinker, wherein the organic acid and the polymeric binder and optionally the crosslinker are non-polymerizable; b) imaging the photoresist; and c) developing the photoresist.

The photoresist composition of the present invention exhibits improved removal compared to photoresists that typically do not contain non-polymeric organic acids. Accordingly, the present invention also provides a method of enhancing the removal of a photoresist composition from a substrate comprising the step of combining a photoresist composition comprising a polymeric binder, a photoactive component, and optionally a crosslinker, with an organic acid, wherein the organic acid and the polymeric binder, the optional crosslinker, or both are non-polymerizable.

It has also been surprisingly found that such non-polymeric organic acids do not adversely affect other characteristics of the photoresist adhesive, such as chemical resistance. Thus, the photoresist compositions of the invention exhibit improved removal without a substantial loss of chemical resistance as compared to the same compositions without the non-polymeric organic acid.

The following examples are intended to illustrate various aspects of the present invention in further detail, and are not intended to limit the scope of the present invention in any way.

Examples

Example 1

Three negative-acting photoresist composition dry film samples a-C were prepared combining the amounts of ingredients listed in table 1. The polymeric binder is a functional acid. A mixture of ethoxylated TMPTA was used as the curative and the reaction product of epsilon-caprolactone and HEA was used as the hydroxy-functional mono-acrylate monomer and mixed in a 1: 1 weight ratio to give a net acrylate functionality of about 2. A mixture of three free-radical generators was used as a light-starting system. A mixture of two adhesion promoters was used in each sample. Trichloromethyl benzyl phenyl acetate ("TCMBA"), a photoresist strip enhancement containing a hydrophobic trihalomethyl group was added to sample C. The dye package used is a photochromic tautomer dye mixture. Samples A through C were prepared as dry films of photoresist, respectively, according to conventional process techniques.

TABLE 1

Sample (I)	A	B	C
				(meth) acrylate adhesive Polymer 1(g)	0	0	40
(meth) acrylate adhesive Polymer 3(g)	30	30	0
				(meth) acrylate adhesive Polymer 4(g)	10	10	0
Curing agent (g)	30	30	28
				Light initiator system (g)	4	4	6
Sebacic acid (g)	0	3	0
				1, 4-Cyclohexanedicarboxylic acid (g)	3	0	2
TCMBA(g)	0	0	0
				Adhesion promoter (g)	0.1	0.1	0.1
Dye bag (g)	0.6	0.6	0.6
				Other Compounds (g)	0.3	0.3	0.3

Example 2

Samples a to C of example 1 were applied to a separation panel. Comparative samples C-1 and C-2 were applied to separate panels. Each panel was treated in the same manner, i.e., using the same pre-plating procedure, cleaning procedure, etc. Comparative sample C1 is a commercially available dry film negative-acting electroplated photoresist (available from Shipley, MA), comprising an acid-functional (meth) acrylate binder, a curing agent comprising a crosslinker and a mono (meth) acrylate, a free-radical generating photoinitiator system, and a dye package. Comparative sample C1 did not contain a non-polymeric organic acid nor any hydrophobic trihalomethyl-containing photoresist removal enhancements. Comparative sample C2 is a commercially available dry film electroplated photoresist (RISTON)^TM9020) (available from Dupont printedcuicts (Wilmingto, DE)) and is free of non-polymeric organic acids and any hydrophobic trihalomethyl-containing photoresist removal enhancements contained in C1.

The panels containing the photoresists of samples a through C and comparative samples C-1 and C-2 were evaluated for development limit, exposure rate (photospeed), post-exposure contrast, post-developed photoresist sidewall appearance, copper/tin plating performance, and photoresist clean-up time. The evaluation results are shown in Table 2. The exposure rate was determined using a Stouffer 21 stepped optical wedge (copper 9) at 50% (i.e., through the developing chamber while the unexposed resist was being washed away). The post-exposure contrast was obtained by visually inspecting the color difference between the exposed area and the unexposed area of the panel, and the grade "1" indicated the best.

The developed photoresist sidewall appearance was determined by scanning electron microscopy. The exposed scanning electron micrographs of the panels were evaluated to determine the side erosion and/or pedestal grade of the photoresist sidewalls. A sidewall rating of "1" indicates substantially no side etch or pedestal, and a rating of "2" or "3" indicates a partial side etch or pedestal of the photoresist sidewall.

Copper/tin ("Cu/Sn") plating efficacy is a measure of the platability of a photoresist. According to this performance test, the vertical electroplated copper traces are inspected to determine if the photoresist has been washed away. The photoresist wash-out can be determined with bottom electroplated copper. Each panel was punched to one square centimeter and the amount of bottom plating was visually inspected by an optical microscope. A rating of "1" indicates substantially no bottom plating, and a rating of "2" or "3" indicates varying degrees of bottom plating.

The photoresist clean time is the number of seconds required to completely clean or remove the photoresist at 130 ° F using 3% caustic soda.

TABLE 2

Sample (I)	A	B	C	C-1*	C-2*
						Development Limit (seconds)	35.9	31.5	25.9	24.8	25.1
Exposure Rate (Cu 9, 50%) (mj/cm)2)	120	84	60	84	84
						Contrast after exposure	1	1	1	3	2
Post-development photoresist sidewall appearance	1	1	1	3	1
						Copper/tin plating performance	1	1	1	1	2
Photoresist clean time (seconds)	31.7	35.8	35.7	50.3	52.2

The above data clearly show that the photoresist composition of the present invention has improved performance over known dry film photoresists and can be removed significantly more rapidly than known photoresists.

Claims (9)

1. A photoresist composition comprising a polymeric binder, a photoactive component, an organic acid, and optionally a crosslinking agent, wherein the organic acid and the polymeric binder, the optional crosslinking agent, or both are non-polymeric and the organic acid is selected from a carboxylic acid or a sulfonic acid, wherein the amount is from 0.5 to 5 parts per 40 parts of the polymeric binder based on the dry weight of the polymeric binder.

2. The composition of claim 1 wherein the organic acid is selected from the group consisting of an alkane carboxylic acid, an aromatic carboxylic acid, an alkane sulfonic acid, and an aromatic sulfonic acid.

3. Composition according to claim 2, characterized in that the organic acid is chosen from (C)₁-C₁₂) Alkyl carboxylic acid, (C)₁-C₁₂) Alkyl dicarboxylic acid, (C)₁-C₁₂) Alkyltricarboxylic acids, substituted (C)₁-C₁₂) Alkyl carboxylic acid, substituted (C)₁-C₁₂) Alkyl dicarboxylic acids, substituted (C)₁-C₁₂) Alkyl tricarboxylic acids, amine carboxylic acids, aromatic dicarboxylic acids, or substituted aromatic carboxylic acids.

4. A method of enhancing the removal of a photoresist composition from a substrate comprising the step of combining a photoresist composition with an organic acid, the photoresist composition comprising a polymeric binder, a photoactive component, and an optional crosslinker, characterized in that the organic acid and the polymeric binder, the optional crosslinker, or both are non-polymeric and the organic acid is selected from the group consisting of carboxylic acids or sulfonic acids, wherein 0.5 to 5 parts per 40 parts of the polymeric binder, based on the dry weight of the polymeric binder.

5. A process according to claim 4, characterised in that the organic acid is selected from the group consisting of alkane carboxylic acids, aromatic carboxylic acids, alkane sulphonic acids or aromatic sulphonic acids.

6. The process as claimed in claim 5, characterized in that the organic acid is selected from (C)₁-C₁₂) Alkyl carboxylic acid, (C)₁-C₁₂) Alkyl dicarboxylic acid, (C)₁-C₁₂) Alkyltricarboxylic acids, substituted (C)₁-C₁₂) Alkyl carboxylic acid, substituted (C)₁-C₁₂) Alkyl dicarboxylic acids, substituted (C)₁-C₁₂) Alkyl tricarboxylic acids, amine carboxylic acids, aromatic dicarboxylic acids, or substituted aromatic carboxylic acids.

7. A method of manufacturing a printed wiring board, comprising the steps of: a) disposing a photoresist composition on a substrate of a printed wiring board, the photoresist composition comprising a polymeric binder, a photoactive component, an organic acid, and optionally a crosslinking agent, wherein the organic acid is non-polymerizable with the polymeric binder and optionally the crosslinking agent, and the organic acid is selected from a carboxylic acid or a sulfonic acid, wherein the amount of the organic acid is from 0.5 to 5 parts per 40 parts of the polymeric binder based on the dry weight of the polymeric binder; b) imaging the photoresist; and c) developing the photoresist.

8. A process according to claim 7, characterised in that the organic acid is selected from the group consisting of alkane carboxylic acids, aromatic carboxylic acids, alkane sulphonic acids or aromatic sulphonic acids.

9. The process as claimed in claim 8, characterized in that the organic acid is selected from (C)₁-C₁₂) Alkyl carboxylic acid, (C)₁-C₁₂) Alkyl dicarboxylic acid, (C)₁-C₁₂) Alkyltricarboxylic acids, substituted (C)₁-C₁₂) Alkyl carboxylic acid, substituted (C)₁-C₁₂) Alkyl dicarboxylic acids, substituted (C)₁-C₁₂) Alkyl tricarboxylic acids, amine carboxylic acids, aromatic dicarboxylic acids, or substituted aromatic carboxylic acids.