BACKGROUND OF THE INVENTION

The present invention relates to nonionic photoacid generator compounds useful in photolithographic compositions, and to methods for making said compounds.

It is known that photoacid generators in combination with acid sensitive polymers comprise photolithographic compositions wherein ultraviolet light exposure results in a difference in solubility between the photoexposed areas and the unexposed areas. Photoacid generator compounds are particularly useful in photoresists requiring sensitivity to deep ultraviolet exposure (220 to 300 nanometers). An object of the present invention is to provide novel photoacid generators having improved quantum efficiency.

The theoretical maximum quantum efficiency (the number of reactions divided by the number of photons impinging on the photoresist) of such a system is one, i.e. , each photon entering the photoresist would ideally result in formation of a solubilizing group. However, the quantum efficiency is usually much less than one. In order to overcome this limitation on quantum efficiency, systems have been developed which rely on photogenerated acid catalysts so that one photoreaction produces one catalyst which promotes many other reactions. U.S. Patent No. 5,230,984 uses photogenerated acid catalysts generated by exposures of 800 millijoules per square centimeter, which is a relatively high exposure dosage. Higher photosensitivity permitting lower exposure dosages would be desirable. Known agents for photo generating acid catalysts include sulfonate esters of nitrobenzyl alcohol, e.g.: G. G. Barclay et al., "The Photosensitized Dissociation of 4-Nitrobenzylsulfonate Esters by Phenolic Matrices," Chemistry of Materials 1995, 7(7), pages 1315-1324. Disclosures of mononitrobenzyl tosylates may be found in U.S. Patent Nos. 5,135,838 and 5,200,544. Dinitrobenzyl tosylates are disclosed in "Nitrobenzyl Ester Chemistry for Polymer Processes Involving Chemical Amplification" by F. M. Houlihan et al, Macromolecules, Vol. 21, No. 7, pages 2001-2006 (1988), European Patent Application 631 188, and Japanese Patent Specification 7-134410. U.S. Patent No. 4,996,136 discloses a molecular structure that theoretically includes substituted dinitrobenzyl tosylates, but provides no enablement for substituted dinitrobenzyl groups. Hayase et al. disclose nitrobenzylsilylethers in J. Electrochem. Soc: Solid-State Science and Technology, Vol. 134, No. 9, September 1987. Similar nitrobenzyl silane structures are disclosed in U.S. Patent No. 5,017,453. Photosensitive methyl methacrylic polymers containing nitrobenzyl groups are disclosed in U.S. Patent No. 4,666,820. A wide variety of nitrobenzyl alcohol structures are theoretically encompassed by generic structures in Japanese Patent Applications 63-146029, 03-131626, 03-141357, and 63- 247749. These applications disclose nitro-containing benzyl alcohol derivatives specifically for use in

applications employing short wavelength ultraviolet radiation in the region of 248 nanometers. They are non-enabling as to a synthesis for the particular dinitro structures of the present invention. The nitrobenzyl alcohol synthesis disclosed in the Japanese publications for other species is not suitable for producing the dinitrobenzyl alcohol intermediates of the present invention at practical yield levels. Commonly owned, copending U.S. Patent Application Serial No. 08/274,614 filed July 13, 1994, is directed to synthesis of dinitro-bis(chloromethyl)benzyl compounds that are used as intermediates in the production of the compounds of the present invention.

SUMMARY OF THE INVENTION

The photoacid generator compounds of the present invention are 2,6-dinitrobenzyl sulfonates substituted at the 4 position of the dinitrobenzyl group with an electron donating aryloxymethyl group. The photoacid generator compounds of the present invention may be represented by the following structure:

where R is an alkyl group, aryl group, or alkylaryl group, any of which may be substituted or unsubstituted.

The aryloxymethyl group substituted at the 4 position of the dinitrobenzyl group, by virtue of its being electron-rich, increases the quantum efficiency of the photoacid generator. This increase is attainable without significant loss of mermal stability. A wide variety of electron-rich aryloxymethyl groups may be employed in the compounds of the present invention. The R' substitution in the aryloxymethyl group in the structure shown above may include a wide range of groups, including hydrogen, alkyl, aryl, alkyloxy, dialkyloxy, aryloxy, diaryloxy, halo, or dialkylamino groups.

The present invention further includes the synthesis of compounds of the above structure employing 2,6-dinitro-l ,4-bis(haloalkyl)benzene as an intermediate.

DETADLED DESCRIPTION

It is believed that dinitro substitution in the benzyl group increases photosensitivity compared to mononitro substitution in some prior art photoacid generating compounds. Even further enhancement of sensitivity is believed to be yielded by dinitro substitution in the 2,6 positions in particular. The photochemistry relies on the photooxidation of the benzyl group by the nitro groups. In the case where the dinitro compound includes an alkoxy sulfonate substitution at the 1 -position, each photoreaction causes die formation of a sulfonic acid group which provides acid catalyst for deprotection of acid sensitive polymers during a subsequent bake step. This is useful, for example, in positive-acting photoresist compositions. Characteristic of the present invention is an additional substitution at the 4 position on the dinitrobenzyl group of an electron donating aryloxyalkyl group, which increases the quantum efficiency of me photoacid generating sulfonate compound.

In the photoacid generator compounds of the present invention as represented by the following structure:

Structure 1

R is an alkyl group, aryl group, or alkylaryl group, any of which may be substituted or unsubstituted. Substitutions within R may include nitro groups and sulfonate groups. Particular examples of R include methyl, phenyl, p-toluyl, nitrophenyl, dinitrophenyl, p-methoxyphenyl, and benzenesulfonate groups. The R' substitution in the aryloxymethyl group may include a wide range of groups, including hydrogen, alkyl, aryl, alkyloxy, dialkyloxy, aryloxy, diaryloxy, halo, or dialkylamino groups. Specific preferred examples of R' include methyl, methoxy, phenyl, bromo, and dimethyl amino groups. In addition to the examples listed, other aryloxymethyl groups that are electron-rich may be used at the 4-position to attain the benefits of the present invention.

The first step in the production of the subject compounds is the synthesis of a bis(haloalkyl) dinitrobenzene compound. A specific method is described in greater detail in Example 1, and employs as the starting material commercially available α, α'-dichloro-p-xylene, which is nitrated to yield 2,6-dinitro-l ,4-bis(chloromethyl)benzene (Structure 2).

Structure 2

The 4-chloromethyl group can men be substituted with a phenol (R'ΦOH) to form a product having Structure 3 (where Φ represents a benzene ring) and R' is as defined above. The remaining chloro group in Structure 3 may then be converted to an alcohol such as by a hydrolysis technique. The alcohol group can then be reacted with a substituted or unsubstituted alkyl or aryl sulfonyl halide to form the sulfonate photoacid generator of the present invention represented by Structure 4 where Q is the sulfonate residue of the sulfonyl reactant.

Structure 3

Structure 4

The sulfonyl halide may, for example, be toluene sulfonyl chloride, nitrobenzene sulfonyl chloride, or benzene disulfonyl chloride. OύJer sulfonyl structures are known (see Barclay et al, supra) and may also be used.

Although not a limitation as to the scope of the invention, examples of compounds of Structures 3 and 4 have been synthesized where R'Φ- is: 4-methoxyphenyl, 2-biphenyl, 2,6- dimethoxyphenyl, 2-methylphenyl, 3-biphenyl, or 3-methylphenyl. Examples of compounds of the

present invention having Structure 4 have been synmesized with the following combinations of R'Φ- and Q:

R'Φ- Q

4-Methoxyphenyl H

4-Memoxyphenyl 4-methylbenzene sulfonate ("tosylate")

4-Methoxyphenyl 3-nitrobenzene sulfonate

4-Methoxyphenyl 4-nitrobenzene sulfonate

4-Methoxyphenyl 4-methoxybenzene sulfonate

2-Biphenyl H

2-Biphenyl tosylate

2-Biphenyl 3-nitrobenzene sulfonate

2-Biphenyl 4-nitrobenzene sulfonate

2-Biphenyl 4-methoxybenzene sulfonate

2 , 6-Dimethoxypheny 1 H

2,6-Dimethoxyphenyl tosylate

2,6-Dimethoxyphenyl 3-nitrobenzene sulfonate

2 ,6-Dimethoxyphenyl 4-nitrobenzene sulfonate

2-Methylphenyl H

2-Methylphenyl tosylate

2-Methylphenyl 3-nitrobenzene sulfonate

2-Methylphenyl 4-nitrobenzene sulfonate

2-Methylphenyl 4-methoxybenzene sulfonate

3-Biphenyl H

3-Biphenyl tosylate

3-Biphenyl 3-nitrobenzene sulfonate

3-Biphenyl 4-nitrobenzene sulfonate

3-Methylphenyl H

3-Methylphenyl tosylate

3-Methylphenyl 3-nitrobenzene sulfonate

3-Methylphenyl 4-nitrobenzene sulfonate

Alternatively, the bis(haloalkyl) dinitrobenzene compound may be dimerized by reaction with a di-functional material such as bisphenol A, yielding Structure 5. By the same technique described above, Structure 5 can then be converted to an alcohol and reacted with a sulfonyl halide compound to yield Structure 6 (where Q, as above, is the residue of the sulfonyl

compound. Examples of materials that may be used instead of bisphenol A include 4,4'- dihydroxybiphenyl, 4,4'-dihydroxybenzophenone, resorcinol, and 2,6-dihydroxynaphthalene.

Structure 5

Structure 6

Examples of compounds of the present invention having Structure 6 have been synthesized wherein Q is: H, tosylate, 3-nitrobenzene sulfonate, 4-nitrobenzene sulfonate, or 4-methoxybenzene sulfonate.

The following Examples 1 through 4 describe the synthesis steps for producing 2,6- dinitro-4-((4'-methoxy)phenoxy-methyl)benzyl tosylate, a preferred embodiment of photoacid generator of the present invention.

EXAMPLE 1 SYNTHESIS OF 2,6-DINITRO-l ,4-BIS(CHLOROMETHYL)BENZENE

Concentrated sulfuric acid (density 1.84, 95 milliliters), 13 milliliters of oleum (27- 33%, density 1.94) and 150 milliliters of concentrated nitric acid (at least 90%, density 1.50) were combined in an ice bath cooled 1 liter flask equipped with mechanical stirring, condenser, and thermometer. The acid mixture exothermed slightly upon mixing. After the mixture cooled to below 25°C, α, α'-dichloro-p-xylene (35.0 grams, 0.2 mole) was added in small portions over 30 minutes so that the reaction temperature did not exceed 35°C. After addition of the dichloride was complete, a premixed acid solution prepared from 5.0 milliliter each of sulfuric and nitric acids and

2.0 milliliter of oleum was added to the reaction flask over 30 minutes. Stirring at room temperature was continued for an additional two hours to ensure complete reaction. The reaction mixture was added carefully to 1 kilogram of ice and allowed to cool. The precipitate was collected by filtration and washed with distilled water. The solid product was taken up in methylene chloride, washed 3 times with saturated sodium bicarbonate solution, and dried with magnesium sulfate. The solvent was evaporated, and the product was recrystallized from ethanol to give 37.6 grams (71 %) of pure 2,6-dinitro-l,4-bis(chloromethyl)benzene (Structure 2) with a melting point of 106 °C. Also recovered from the reaction mixture were 10.5 grams of 2,5-dinitro-l,4-bis(chloromethyl)-benzene as a byproduct. The presence of both products was confirmed by NMR spectroscopy.

EXAMPLE 2 SYNTHESIS OF 2,6-DINITRO-4-((4'-METHOXY)PHENOXY-METHYL)BENZYL CHLORIDE

201.2 grams of 2,6-dinitro-l,4-bis(chloromethyl)benzene (Example 1) was added to 500 grams of anhydrous methanol at room temperature. Into this mixture was added over one hour a premixed solution consisting of: 120 grams p-methoxy phenol, 36.0 grams of lithium hydroxide monohydrate, and 500 grams methanol. The reaction mixture was stirred at room temperature for twelve hours. The product was filtered off, dissolved in methylene chloride and washed twice with 3% aqueous sodium bicarbonate. After drying over sodium sulfate, the solvent was evaporated giving 269 grams of pure product. The product is represented by Structure 7.

^O Structure 7

EXAMPLE 3 SYNTHESIS OF 2,6-DINITRO-4-((4'-METHOXY)PHENOXY-METHYL)BENZYL ALCOHOL

167.0 grams of 2,6-dinitro-4-((4'-methoxy)phenoxy-methyl)benzyl chloride from Example 2 was added to 243.3 grams of dimethyl formamide and 43.5 gram of 90% formic acid and heated under nitrogen to 110°C. To this solution was added over 45 minutes a predissolved mixture of 94.6 grams of distilled water and 27.25 grams of potassium hydroxide. The temperature was held

at reflux for six hours until the starting material had been consumed as shown by thin layer chromatography. The reaction mixture was allowed to cool to 60°C and 465 grams of a 7.5 percent solution of sodium bicarbonate in water was added over 15 minutes. After cooling to room temperature, 700 grams of water and 500 milliliters of methylene chloride were added. After transfer to a separatory funnel, the layers were separated. The aqueous layer was washed twice with methylene chloride. The organic washes were combined and washed once with dilute bicarbonate solution and filtered through silica gel. After removal of the solvent and recrystallization from a mixture of l-methoxy-2-propanol and water, 141.7 grams of product were obtained. The product is represented by Structure 8.

Structure 8

EXAMPLE 4

SYNTHESIS OF 2,6-DINITRO-4-((4'-METHOXY)PHENOXY-METHYL)BENZYL TOSYLATE

5.0 grams of 2,6-dinitro-4-((4'-methoxy)phenoxy-methyl)benzyl alcohol (Example 3), 4.28 grams of toluene sulfonyl chloride and 75 grams of acetone were cooled to 5°C. To this was added 6.8 grams of dicyclohexyl amine in 20 grams of acetone over twenty minutes. After stirring for one hour, the reaction mixture was allowed to warm to room temperature and stirred for 3 hours. 500 milliliters of water, 1.0 grams of concentrated HC1 and 200 grams of meϋϊylene chloride were added and stirred for 2 minutes. The layers were separated and die organic extract was washed with water. After drying and removal of solvent, the crude material was recry stall ized

from a mixture of acetone and methanol to yield 7.3 grams (62.3 %) of pure material. The product is represented by Structure 9.

Structure 9

The following Example 5 is a description of a synthesis of a resin that may be combined with the photoacid generator compounds of the present invention to enable measurement of acid generation upon exposure to light. In Example 6, this resin was combined with the photoacid generating compound of Example 4 and tested for photoactivity.

EXAMPLE 5 ACRYLIC CARRIER RESIN

The following initial charge and feeds were used in the preparation of an acrylic polymer via solution polymerization technique.

Ingredients Parts by Weight

Initial Charge n-Butyl acetate 100.00

Feed l n-Butyl acrylate 123.64

Methyl methacrylate 174.16

Acrylic acid 23.78 α-Methyl styrene dimer (chain transfer agent) 17.00

Feed 2 t-Butyl perbenzoate 3.50 n-Butyl acetate 50.00 Feed 3 t-Butyl perbenzoate 1.00 n-Butyl acetate 5.00

The initial charge was heated in a reactor with agitation to reflux temperature (110°C). Then Feed 1 was added in a continuous manner over a period of 3 hours. At the completion of Feed 1, the reaction mixture was held at reflux for 30 minutes. Then one half of Feed 3 was added and held for one hour, followed by the addition of the remainder of Feed 3 and a 30 minute hold. The product was then cooled and poured from the vessel. The resultant acrylic polymer had a total solids content of 67.98 percent determined at 110°C. for one hour and a theoretical T _g of 28.97 °C.

EXAMPLE 6 PERFORMANCE TESTING

The carrier resin of Example 5 was mixed with me photoacid generator of Example

4 to formulate a positive acting photoresist in the following proportions:

Ingredient Parts by Weight

Acrylic resin (Example 5) 8.361 Tosylate of Example 4 0.75

Tetrahydrofuran 9.0

The photoresist composition had 15 percent by weight solids. The composition was drawn down onto six separate copper laminates that had been precleaned. Coating mickness was about 8 microns. All the coated laminates were baked for 5 minutes at 110°C, after which each was weighed. Each laminate was exposed to 365 nanometer U. V. light in a range of exposure dosages from 0 to 836 millijoules per square centimeter as indicated in Table I. After exposure, each laminate was washed in m-pyrol and rinsed with acetone. The laminates were dried for 5 minutes at 110°C, cooled, and the weight loss measured for each. Acid values of the dissolved portions of the coatings were determined by titration of the solvent, from which the amount of acid generated by the photoexposure was calculated. These results are shown in Table I, where the gross acid value includes the acid content of the acrylic resin plus that attributable to the photoacid generator. The percent of

theoretical figures represent the percentage of photoacid generators present that cleaved to form acid groups. Acid value is measured in terms of milligrams KOH to neutralize one gram of resin.

TABLE I RESULTS OF EXAMPLE 6

The following Examples 7, 8, and 9 describe syntiieses of some alternative embodiments of photoacid generator compounds of the present invention.

EXAMPLE 7 SYNTHESIS OF 2,6-DINITRO-4-((4'-METHOXY)PHENOXY-METHYL)BENZYL-3-

NITROBENZENESULFONATE

5.0 grams of 2,6-dinitro-4-((4'-methoxy)phenoxy-methyl)benzyl alcohol from Example 3 were added to 6.63 grams of 3-nitrobenzenesulfonyl chloride in 75 grams of dry acetone at 0°C. To this solution was added 5.42 grams of dicyclohexyl amine in 20 grams of acetone over twenty minutes. The reaction mixture was stirred for 3 hours at which point thin layer chromatography indicated that the reaction was complete. 500 grams of water, 1.0 grams of concentrated HCl and 200 grams of methylene chloride were added and stirred for two minutes. The layers were separated and the organic extract was washed with deionized water. After drying and

removal of the solvent, die crude product was recrystallized from a mixture of acetone and methanol to give 6.66 grams of pure material. The product is represented by Structure 10.

^ό

U

v

Structure 10

EXAMPLE 8 SYNTHESIS OF 2,6-DINITRO-4-((4'-METHOXY)PHENOXY-METHYL)BENZYL-4-

NITROBENZENESULFONATE

5.0 grams of 2,6-dinitro-4-((4'-methoxy)phenoxy-methyl)benzyl alcohol from Example 3 were added to 5.02 grams of 4-nitrobenzenesulfonyl chloride in 75 grams of dry acetone at 0°C. To this solution was added 6.78 grams of dicyclohexyl amine in 20 grams of acetone over twenty minutes. The reaction mixture was stirred for 3 hours at which point ϋϋn layer chromatography indicated diat the reaction was complete. 500 grams of water, 1.0 grams of concentrated HCl and 200 grams of methylene chloride were added and stirred for two minutes. The layers were separated and the organic extract was washed with deionized water. After drying and removal of the solvent, the crude product was recrystallized from acetone/methanol to give 4.32 grams of pure material. The product is represented by Structure 11.

Structure 11

EXAMPLE 9 SYNTHESIS OF 2,6-DINITRO-4-((4'-METHOXY)PHENOXY-METHYL)BENZYL-

METHYLSULFONATE

3.524 grams of 2,6-dinitro-4-((4'-methoxy)phenoxy-methyI)benzyl alcohol from Example 3 were added to 1.374 grams of meuiane sulfonyl chloride in 50 grams of tetrahydrofuran at 0°C. To this solution was added 1.112 grams of triethyl amine over five minutes. The reaction mixture was stirred for four hours at 40°C at which point thin layer chromatography indicated that the reaction was complete. The reaction mixture was added to 250 grams of deionized water and 2.0 grams of concentrated HCl. The product was extracted three times with methylene chloride. The layers were separated and the organic extract was washed with dilute HCl. After drying and removal of the solvent, the crude product was filtered and dried under vacuum. The product is represented by Structure 12.

Structure 12

Although specific embodiments of the invention have been described in detail for the purpose of illustrating the best mode of the invention, it is to be understood that such detail is solely for that purpose and mat variations and modification as would be apparent to those skilled in the art are wiϋiin the spirit and scope of the invention as defined by die claims.