PROCESS FOR PRODUCING PURIFIED SOLUTIONS OF BLOCKED POLYHYDROXYSTYRENE RESIN

Abstract: A process for making purified cross-linked polyhydroxystyrene resin, comprising the steps of: (1) forming an impure reaction solution comprising blocked polyhydroxystyrene resin and acidic catalyst in a reaction solvent; (2) adding amine, water, at least one hydrocarbon solvent, and at least one photoresist solvent, thereby forming and aqueous phase and an organic phase, said aqueous phase comprising water and at least one salt of the amine/acidic catalyst and the organic phase comprising the reaction solvent, the hydrocarbon solvent, the photoresist solvent and the blocked polyhydroxystyrene resin; (3) separating the aqueous phase from the organic phase; and (4) removing the hydrocarbon solvent and reaction solvent from the organic phase, thereby forming a purified solution of the blocked polyhydroxystyrene resin in the photoresist solvent.

Description: PROCESS FOR PRODUCING PURIFIED SOLUTIONS OF BLOCKED POLYHYDROXYSTYRENE RESIN BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to a process for producing blocked polyhydroxystyrene resins or blocked, crosslinked polyhydroxystyrene resins that are useful in chemical amplified photoresist formulations. 2. Brief Description of the Art Polyhydroxystyrene resins where some or all of the hydroxy groups in the resin are converted into acid-labile protecting groups ("blocked resins") are commonly used as polymeric materials in chemically amplified photoresists. These chemically amplified photoresists are employed in advanced photolithographic processes of semiconductor fabrication. Crosslinked polyhydroxystyrene resins having some or all of the hydroxy groups converted to acid-labile protecting groups and also possessing crosslinking moieties ("blocked, crosslinked polymers") are also well known. See, for example, European Published Patent Application Nos. 0718316 A2, published on June 26, 1996, and 0738744 A2, published on October 23, 1997. Both of these published European Patent Applications are incorporated herein by reference in their entireties. These blocked, crosslinked resins are employed instead of or in conjunction with blocked resins as the polymeric materials in chemical amplified photoresists. In making these blocked resins or these blocked, crosslinked polyhydroxystyrene resins, the precursors (e.g., the polyhydroxystyrene, the protecting group precursor and, optionally, the crosslinking agent) are reacted together in the presence of an acid catalyst and a suitable organic reaction solvent to form an impure solution of the blocked polymer or the blocked, crosslinked polymer in the reaction solvent. After the reaction was complete, the reaction mixture was then passed through a bed of strong base ion exchange resin to remove the acid catalyst. The treated reaction solution was then combined with deionized water or a mixture of deionized water and an alcohol (e.g., ethanol or isopropanol) to precipitate the blocked resin or blocked, crosslinked resin in solid form. The precipitated solid resin was then separated from the reaction mixture, preferably by filtration or centrifugation. The separated resin was then washed with more deionized water and then vacuum dried. The dried, solid blocked resin or blocked, crosslinked resin was later dissolved in a suitable organic photoresist solvent and then used to make a chemical amplified photoresist formulation. This prior art method of making these blocked resins and blocked, crosslinked resins has several disadvantages associated with it, including: (1) The resin bed employed to remove the acid catalyst must have a very low trace metals content. This need can be met by only either using a high purity and expensive ion exchange resin or using a special cleanup procedure for standard ion exchange resins after each run. Furthermore, the ion exchange resin bed must be very dry (i.e., contain no water therein) when the reaction mixture is passed through it. Otherwise, the water (in the presence of the catalyst or ion exchange resin) may hydrolyze the blocked polymer. Still further, in some cases, the ion exchange resin may act as a catalyst for unwanted reactions or may retain some of the blocked polymer or blocked, crosslinked polymer, thereby reducing the yield of the blocked polymers or blocked, crosslinked polymer. And, in any case, the employment of the ion exchange resin also requires cleanup and disposal. (2) The phase change precipitation step requires a large amount of water (; ' .e., at least 20 times the weight of the reaction mixture). The use of smaller amounts of water will result in sticky solids that adhere to the sides of the precipitation vessel. The large amount of water results in a large quantity of wastewater that must be disposed of. Also, a large and costly precipitation vessel must be employed. (3) The separation step requires special and costly filtration and centrifugation equipment. Handling these solids during and after this separation step is a potential source of contamination because it is almost impossible to keep these solids isolated from the environment. (4) The drying of the solids is another potential source of contamination, both from the dryer equipment itself and the handling required to load and unload the dryer. Also, drying may cause unwanted side reactions in the product to occur. Accordingly, there is a need for an improved process for preparing pure blocked resins or pure blocked, crosslinked resins without the above disadvantages of the prior art. The present invention offers such a process. In particular, the process of the present invention reduces waste generation, reduces the probability of product contamination and eliminates solids handling. This process allows for the purified resin to be directly dissolved in the photoresist solvent rather than having this purified resin put in solid form and then redissolved in the photoresist solvent. BRIEF SUMMARY OF THE INVENTION One aspect of the present invention is directed to the process for preparing a purified solution of blocked polyhydroxystyrene resin in a photoresist solvent, comprising the steps of: (1) forming an impure reaction solution comprising blocked polyhydroxystyrene resin and acidic catalyst in reaction solvent; (2) adding amine, water, at least one hydrocarbon solvent, and at least one photoresist solvent, thereby forming an aqueous phase and an organic phase, said aqueous phase comprising water and salts of the amine/acidic catalyst and the organic phase comprising the reaction solvent, the photoresist solvent, the hydrocarbon solvent and the blocked polyhydroxystyrene resin; (3) separating the aqueous phase from the organic phase; and (4) removing the hydrocarbon solvent and reaction solvent from the organic phase, thereby forming a purified solution of the blocked polyhydroxystyrene resin in the photoresist solvent. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The term "reaction solvent" as used in the present specification and claims refers to any single solvent or mixture of solvents in which either the blocked polyhydroxy-styrene resin or blocked crosslinked polyhydroxystyrene resin is prepared. The preferred reaction solvent is tetrahydro-furan (THF). This solvent is preferred because it is a good solvent for reactants and products, is not reactive, is hydrophilic, has a low density (so that the resulting organic phase will have a density less than water), and has a relatively low boiling point (so it would be easy to separate from PGMEA or other selected photoresist solvents having higher boiling points). Another suitable reaction solvent is 1,4-dioxane. The term "photoresist solvent" as used in the present specification refers to the solvent or mixtures of solvents in which a radiation-sensitive composition such as a photoresist is prepared. Generally, such radiation- sensitive compositions of the present invention will contain the purified blocked polyhydroxystyrene resin or the purified blocked, crosslinked polyhydroxystyrene resin, as well as at least one photoacid generator and optionally other ingredients such as other resins and dissolution inhibitors and the like. The "photoresist solvent" as referred to herein is different from the "reaction solvent" referred to herein. The term "blocked hydroxystyrene resin" as used in the present specification refers to any and all polyhydroxystyrene resins that have some or all of the hydroxy groups in the resin converted to protecting groups (e.g., vinyl ether groups) and are useful in chemically amplified-type photoresists. The term "blocked polyhydroxystyrene resins" as used herein includes resins of the class "blocked, crosslinked polyhydroxy styrene resins". The term "blocked, crosslinked polyhydroxystyrene resins" as used in the present specification and claims refers to any and all polyhydroxystyrene resins that have some or all of the hydroxy groups in the resin converted to protecting groups (e.g., vinyl ether groups) and also contain crosslinking moieties linking separate polymeric chains and are useful in chemically amplified-type photoresists. The phrase "impure solution of blocked polyhydroxystyrene resin in reaction solvent" as used in the present specification and claims refers to any and all solutions containing blocked polyhydroxystyrene resins in a single reaction solvent or a mixture of reaction solvents and further contain unacceptable amounts of impurities and/or reaction by-products and/or unreacted reaction precursors. The phrase "purified solution of blocked polyhydroxy-styrene resin in the photoresist solvent" as used in the present specification and claims refers to any and all solutions containing blocked polyhydroxystyrene resins in photoresist solvent or mixture of solvents and further contains acceptably low amounts of impurities so that the purified solution may be used in chemically amplified-type photoresists. The first step of the present invention is directed to forming an impure reaction solution containing the blocked, polyhydroxystyrene resin and acidic catalyst in a reaction solvent or solvents. This impure reaction solution is preferably prepared by adding the desired amounts of at least one polyhydroxystyrene resin, at least one protecting group precursor, the acid catalyst and, optionally, at least one crosslinking agent to a reactor containing the reaction solvent and then heating this reaction mixture to a desired reaction temperature for a sufficient amount of time to produce the blocked polyhydroxy-styrene resin or the crosslinked, blocked polyhydroxystyrene resin in the reaction mixture. The polyhydroxystyrene resins useful for this process would include any polymeric resin that contains hydroxystyrene repeating units, including poly(4-hydroxystyrene) homopolymers, poly(4-hydroxy-a-methylstyrene) 5 homopolymers and poly(3-hydroxystyrene) homopolymers or co-polymers formed from hydroxystyrene-containing monomers (e.g., 4 — hydroxystyrene) with other monomers such as acrylic acid, methacrylic acid, alkyl methacrylates, alkyl acrylates, styrene, fumaronitrile, vinylcyclohexanol, maleic anhydride, maleimide and derivatives thereof or mixtures of such homopolymers or copolymers. Preferred polyhydroxystyrene resin precursors include those disclosed in European Patent Application Nos. 718316 and 738744. The protecting group precursors added to this reaction mixture are any such compounds capable of forming an acid-labile protecting or blocking group on the hydroxy groups in the side chain of the polyhydroxystyrene resin. These preferably include vinyl ethers (e.g., tert.- butylvinyl ether or ethylvinyl ether), carbonates (e.g., tert.-butyl carbonate) or other precursors to suitable acid-labile protecting groups including silyl ether, cumyl ester, tetrahydropyranyl ester, tetrahydropyranyl ester, enol ether, enol ester, tert-.alkyl ether, tert.-alkyl ester, tert. alkyl carbonate, acetal and ketal groups. Mixtures of protecting group precursors may also be added to the reaction mixture. The optional crosslinking agent or agents may include any suitable chemical agent that crosslinks polyhydroxystyrene in a desirable way to achieve a suitable resin for a photoresist application. One preferred crosslinking agent is 4,4'-isopropylidene dicyclohexanol. This reaction is carried out in the presence of an acidic catalyst. Examples of suitable acidic catalysts include acidic ionic exchanger resins or acids such as sulfonic acids (preferably, toluene sulfonic acid) or salts thereof, for example, pyridinium tosylate. The reaction is also carried out in the presence of a suitable reaction solvent. This reaction is generally carried out at reaction temperatures from about 10°C to about 80°C for a sufficient amount of time so that sufficient conversion of the hydroxyl groups to protecting groups and optional resin crosslinking occurs. The reaction is generally carried out in any standard 6 reactor apparatus, preferably a glass or Teflon-lined reactor to prevent an increase in cationic and anionic impurities in the reaction mixture. The relative percentages of the resin precursors added to the reactor will depend upon the final desired characteristics of the resin. Generally, the resultant blocked polyhydroxy-styrene or blocked, crosslinked polyhydroxystyrene resins will preferably have a weight- average molecular weight of from 1 ,000 to 1 ,000,000; more preferably from about 3,000 to about 500,000 and most preferably from about 6,000 to about 100,000. The percentage of hydroxy groups in the polyhydroxystyrene resin precursor converted to acid-labile protecting groups will generally be from about 5% to about 95%, more preferably, from about 10% to 50%. The degree of crosslinking [v = o/m+n+o] will preferably be from 0.001 to 0.5, more preferably, from 0.002 to 0.2, wherein m is the average number of acid-cleavable protecting groups per resultant resin molecule; n is the sum of COOH groups and phenolic hydroxyls per resultant resin and o is the number of bridging groups per resultant resin. After the reaction is complete, at least one photoresist solvent and at least one hydrocarbon solvent are added to the reaction mixture, along with water and an amine compound. Their addition results in the formation of organic phase and aqueous phase in the resulting mixture. The photoresist solvent is preferably propylene glycol monomethyl ether acetate (PGMEA). Other conventional photoresist solvents may also be employed. The hydrocarbon solvent is preferably hexane and is employed because of its hydrophobic nature and its ability to dissolve impurities in the organic phase. Generally, the amounts of photoresist solvent and hydrocarbon solvent are about 1 :20 to 20:1 by weight. The use of hexane as the hydrocarbon solvent is particularly preferred because this solvent has minimal water solubility; is capable of aiding the solubility of the blocked resin; has a low density (so that the resultant organic phase has a density less than water) and has a lower 7 boiling point than conventional photoresist solvents such as propylene glycol monomethyl ether acetate (PGMEA). In all, this solvent has been found to provide a good organic phase and aqueous phase separation when PGMEA is the photoresist solvent. The relative amount of water is preferably about 1 : 10 to about 10:1 of the total amount of organic solvents. The amount of amine is preferably sufficient to neutralize the amount of acidic catalyst present. Any conventional amine useful for this purpose may be used. Triethylamine is particularly preferred. Next, the resulting organic phase is separated from the aqueous phase. This is generally accomplished by simple phase separation. The bottom aqueous phase is normally drawn out of the reactor, leaving the organic phase in the reactor. Preferably, after this phase separation, additional water washes are optionally carried out. This encompasses adding an amount of water to the reactor, allowing the reaction mixture to settle and then removing the added water. Generally, it is preferred to conduct at least one water wash operation. After the phase separation step and any optional water washes, the hydrocarbon solvent is removed from the reaction mixture. Preferably, this is accomplished by simple distillation to distill off the hydrocarbon solvent and leave a final purified solution comprised of the photoresist solvent and the blocked polyhydroxystyrene resin or the blocked, crosslinked polyhydroxystyrene resin. A photoresist composition can be prepared by simply adding other photoresist components such as at least one photoacid generator, at least one optional dissolution inhibitor, and, if desired, more photoresist solvent and/or other photoresist solvents to this purified solution. The following Examples and Comparison Example are provided to better illustrate the present invention. All parts and percentages are by weight and all temperatures are in degrees Celsius unless explicitly stated otherwise. 8 EXAMPLE 1 A. Synthesis of Blocked Crosslinked Polyhydroxystyrene 380 grams of dry polyhydroxystyrene (PHS) (weight average molecular weight (Mw) = 8700), 7.8 grams of 4,4' -isopropylidene dicyclohexanol (IPDCH) and 1592.7 grams of tetrahydrofuran (THF) were added to a 2 liter plastic bottle. The bottle was rolled for 2 days to dissolve the solids. The solution was transferred to a 5 liter kettle. 100.2 grams of t-butyl vinyl ether (TBVE) (0.315 moles per mole PHS) and 26.75 grams of a 0.1 wt. % solution of p-toluene sulfonic acid catalyst (PTSA) in THF were added to the kettle. The material in the kettle was mixed at 25°C overnight. The next morning, the contents of the kettle were divided into two portions and further processed as described below. B. Processing of Blocked Crosslinked Polyhydroxystyrene by Extraction 1.47 grams of a 1.0 wt. % solution of triethylamine (TEA) in THF were added to the first portion of the material in the kettle (1662.98 grams) synthesized in (A) above. 1256.13 grams of propylene glycol monomethyl ether acetate (PGMEA) and 451.12 grams of hexane were also added. After mixing the solution in the kettle, 585.74 grams of deionized (Dl) water were added to the kettle (first wash). The material in the kettle was mixed for 5 minutes, the agitator was stopped and the material was allowed to settle into two phases, a first aqueous phase and a first organic phase. The aqueous phase contained water with minor amounts of triethylamine/p-toluene sulfonic acid salt, as well as residual vinyl ether, water-soluble by-products, THF, a small amount of PGMEA and trace metals. The organic phase contained most of the PGMEA, THF, hexane, as well as some water besides the blocked, crosslinked polystyrene. After a 90-minute hold, 582.18 grams of the first aqueous layer were removed from the bottom of the kettle and 586.31 grams of more Dl water were added to the kettle (second wash). The material in the kettle was mixed for 9 5 minutes, the agitator was stopped and the material was allowed to settle. After an 80-minute hold, 755.8 grams of the second aqueous layer were removed from the bottom of the kettle and 586.54 grams more of Dl water were added to the kettle (third wash). The material in the kettle was mixed for 5 minutes, the agitator was stopped and the material was allowed to settle. After a 75 minute hold, 751.08 grams of the third aqueous layer were removed from the bottom of the kettle. The organic layer remaining in the kettle was transferred to a rotary evaporation system where the THF, hexane, residual water, and some PGMEA were removed under vacuum at a bath temperature of 55°C. The mixture was stripped until the resulting solution contained 0.07 wt. % water and 45.1 wt. % total solids. 401.3 grams of PGMEA were added to 830.19 grams of the stripped solution to give a solution containing about 30 wt. % solids. The solids yield was about 99%, based on the solids in the solution and assuming all of the PHS plus 85% of the IPDCH and 85% of the vinyl ether should end up in the solids. COMPARISON EXAMPLE 1 The second portion of the blocked crosslinked polyhydroxystyrene material synthesized in (A) above (443.24 grams) was placed in an additional funnel. 0.42 grams of 1.0 wt. % solution of pyridine in THF was added to the funnel, and shaken to mix in the pyridine solution. This mixture was passed through a column of AMBERSEP 900 (OH) strong base ion exchange resin equilibrated with THF and into 8750 grams of Dl water in a 10 liter resin kettle. Addition time was about 60 minutes. After the addition was complete, the additional funnel and resin bed were rinsed with 20 ml of THF which was also added to the Dl water. Precipitated solids were recovered from the Dl water by vacuum filtration in a Buchner filter. Recovered solids were washed twice with 500 ml of Dl water and dried in a vacuum drier at 50°C for about 20 hours. 90.6 grams of solid polymer were recovered with a water content of 1.08 wt. %. Solids yield was about 91%. 10 The solid polymers and the polymer solutions from Example 1 and Comparison Example 1 were analyzed by GPC for molecular weight distribution and by 13 C NMR for blocking level within the accuracy of the tests, the two polymers were identical. COMPARISON EXAMPLE 2 Another experiment was done just like Example 1 except a slightly larger amount of TBVE (0.36 moles per mole of PHS) was used to give a higher blocking level. However, the two polymers were completely different. The polymer in solution had the expected blocking level and molecular weight distribution. The solid polymer had very low blocking level and a low molecular weight. Apparently, the solid polymer was contaminated during solids recovery or drying and had deblocked. EXAMPLE 2 About 650 grams of PHS were dried in a vacuum oven overnight to give a water content of 0.65 wt. %. 299.6 grams of the dried PHS, 12.24 grams of IPDCH, and 1320.05 grams of THF were added to a 4 liter resin kettle. The mixture was agitated for 80 minutes until the solids were dissolved. 68.41 grams of ethyl vinyl ether and 90.0 grams of a 0.1 wt. % solution of PTSA in THF were added to the resin kettle. This mixture was agitated overnight at room temperature. After the overnight mixing, 5.83 grams of a 1.0 wt. % solution of triethylamine in THF were added to the reaction mix to neutralize the PTSA catalyst. 1320.02 grams of PGMEA, 311.98 grams of hexane, and 311.98 grams of Dl water were added to the kettle (first wash). The resulting mixture was agitated for 8 minutes and then the agitation was stopped and the mixture was allowed to settle for about an hour. 183.86 grams of the first aqueous layer were removed from the bottom of the kettle and 312.94 grams of Dl water were added to the kettle (second wash). The material in the kettle was mixed for 15 minutes, the agitator was stopped and the 11 material was allowed to settle for about an hour. 420.89 grams of the second aqueous layer were removed from the bottom of the kettle and 311.98 grams of Dl water were added to the kettle (third wash). The material in the kettle was mixed for about 15 minutes, the agitator was stopped and the material was allowed to settle for about an hour. 438.32 grams of the third aqueous layer were removed from the bottom of the kettle. The organic layer remaining in the kettle on the third wash was transferred to a rotary evaporation system where THF, hexane, residual water, and some PGMEA were removed under vacuum at a bath temperature of 55°C. The mixture was stripped until the resulting solution contained 0.06 wt. % water and 39.9 wt. % total solids. PGMEA was added to the stripped solution to give a solution containing about 30 wt. % solids. Solids yield was approximately 99%. This resin in this product was analyzed by GPC to have a M w of 32,995 and an X re ι of 2.22. [The relative crosslinking (X re ι) equals (total molecular weight of the resin divided by molecular weight of the uncrosslinked portion of the resin) minus one]. While the invention has been described above with reference to specific embodiments thereof, it is apparent that many changes, modifications, and variations can be made without departing from the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modifications, and variations that fall within the spirit and broad scope of the appended claims. All patent applications, patents, and other publications cited herein are incorporated by reference in their entirety. 12

Claims: WHAT IS CLAIMED IS: 1. A process for making purified blocked crosslinked polyhydroxystyrene resin, comprising the steps of: (1) forming an impure reaction solution comprising blocked polyhydroxystyrene resin and acidic catalyst in a reaction solvent; (2) adding amine, water, at least one hydrocarbon solvent, at least one photoresist solvent, thereby forming an aqueous phase and an organic phase, said aqueous phase comprising water and at least one salt of the amine/acidic catalyst and the organic phase comprising the reaction solvent, the hydrocarbon solvent, the photoresist solvent, and the blocked, polyhydroxystyrene resin; (3) separating the aqueous phase from the organic phase; and (4) removing the hydrocarbon solvent and reaction solvent from the organic phase, thereby forming a purified solution of the blocked polyhydroxystyrene resin in the photoresist solvent. 2. The process of claim 1 wherein the blocking group of said blocked polyhydroxystyrene resin is t-butyl vinyl ether. 3. The process of claim 1 wherein said removing step comprises simple distillation. 4. The process of claim 1 wherein said reaction solvent is tetrahydrofuran. 5. The process of claim 1 wherein said acidic catalyst is toluene sulfonic acid. 6. The process of claim 1 wherein said amine is triethylamine. 13 7. The process of claim 1 wherein said hydrocarbon solvent is hexane. 8. The process of claim 1 wherein said photoresist solvent is propylene glycol monomethyl ether acetate (PGMEA). 9. The process of claim 1 wherein said separated organic phase is subjected to at least one water wash operation after step (3) and before step (4). 10. The process of claim 1 wherein said blocked polyhydroxystyrene resin is a blocked, crosslinked polyhydroxystyrene resin. 11. The process of claim 10 wherein said blocked crosslinked resin is formed with ethyl vinyl ether as a protecting group precursor and isopropylidene dicyclohexanol is the crosslinking agent. 12. The process for producing a chemically amplified photoresist formulation comprising adding at least one photo-acid generator to the purified solution of blocked poly-hydroxystyrene resin produced by the process of claim 1. 13. The process for producing a chemically amplified photoresist formulation comprising adding at least one photoacid generator to the purified solution of blocked, crosslinked polyhydroxystyrene resin produced by claim 10. 14

Inventors: DAVIDSON JAMES M, DAVIDSON, JAMES, M.
Applicants: ARCH SPEC CHEM INC, ARCH SPECIALTY CHEMICALS, INC.
Application year: 1999
Main classification: C08F6
IPC codes: C08F6, C08F8, C08F12, C08J3, G03F7