Polymer and method for producing same

Abstract

The time when at least a monomer and a chain transfer agent are supplied in a reactor and the solution temperature in the reactor has reached a predetermined polymerization temperature is set as starting time (T.sub.0), and the time when a process to terminate the polymerization is started is set as ending time (T.sub.1). A polymerization initiator is supplied into the reactor between (T.sub.0) and just before [(T.sub.1)−(T.sub.0)/2] and between [(T.sub.1)−(T.sub.0)/2] and (T.sub.1). The total mass of the polymerization initiator supplied to the reactor between (T.sub.0) and (T.sub.1) is set as (I.sub.A), and the total mass of the polymerization initiator supplied between [(T.sub.0−T.sub.1)/2] and (T.sub.1) is set as (I.sub.B). The (I.sub.A) is set 50 to 100 mass % of the entire polymerization initiator. Using a production method in which 0.50<(I.sub.B)/(I.sub.A)<1.00 is satisfied, a polymer is produced at a high polymerization rate showing less variation of molecular weight and having less amount of chain transfer agent residue remaining at an end of the polymer chain.

Claims

1. A polymer, comprising: a structural unit having a group to be modified by acid, comprising a structural unit derived from at least one monomer selected from the group consisting of 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, 1-(1′-adamantyl)-1-methylethyl (meth)acrylate, 1-methyl cyclohexyl (meth)acrylate, 1-ethyl cyclohexyl (meth)acrylate, 1-methyl cyclopentyl (meth)acrylate, 1-ethyl cyclopentyl (meth)acrylate, isopropyl adamantyl (meth)acrylate, and 1-ethyl cyclooctyl (meth)acrylate, wherein the polymer has an end group having a thiocarbonylthio structure having the formula (10) ##STR00004## where Ar is an aromatic group or an aromatic group substituted with a halogen atom; a hydrogen group; an alkoxy group; an amino group; a nitro group; a cyano group; a group comprising carbonyl represented by —CORa in which Ra is an alkyl group or an allyl group having 1 to 8 carbon atoms or an alkoxy group or allyloxy group having 1 to 8 carbon atoms; a sulfonyl group; or a trifluoromethyl group, in an amount of from 0.001 to 30 mol % relative to all growing end groups of the polymer, and an amount of structural units that act as organic acid is less than 2 mol % relative to all structural units in the polymer.

2. The polymer according to claim 1, wherein the polymer is suitable for lithography applications.

3. The polymer according to claim 1, wherein the structural unit having a group to be modified by acid comprises a structural unit derived from at least one monomer selected from the group consisting of 1-ethyl cyclohexyl methacrylate, 2-ethyl-2-adamantyl methacrylate, 1-ethyl cyclopentyl methacrylate, and isopropyl adamantyl methacrylate.

4. The polymer according to claim 1, wherein an amount of the structural unit having a group to be modified by acid is from 20 to 60 mol % relative to all structural units in the polymer.

5. The polymer according to claim 1, wherein the thiocarbonylthio structure of the end group of the polymer is derived from a chain transfer agent having the thiocarbonylthio structure.

6. The polymer according to claim 1, further comprising: a structural unit having a group with a lactone skeleton; and a structural unit having a hydrophilic group.

7. The polymer according to claim 1, wherein, in the formula, Ar is an aromatic group.

8. The polymer according to claim 1, wherein a weight-average molecular weight of the polymer measured by gel permeation chromatography with a differential refractive index detector and determined in terms of polystyrene is from 2,500 to 1,000,000, and a peak area corresponding to a molecular weight of no greater than 1,000 in an elution curve is no greater than 1.0% of all peak areas of the polymer.

9. The polymer according to claim 8, wherein the structural unit having a group to be modified by acid comprises a structural unit derived from at least one monomer selected from the group consisting of 1-ethyl cyclohexyl methacrylate, 2-ethyl-2-adamantyl methacrylate, 1-ethyl cyclopentyl methacrylate, and isopropyl adamantyl methacrylate.

10. The polymer according to claim 8, further comprising: a structural unit having a group with a lactone skeleton.

11. The polymer according to claim 8, further comprising: a structural unit having a hydrophilic group.

12. The polymer according to claim 8, wherein an amount of the structural unit having a group to be modified by acid is from 20 to 60 mol % relative to all structural units in the polymer.

13. The polymer according to claim 8, further comprising: a structural unit having a group with a lactone skeleton; and a structural unit having a hydrophilic group.

14. The polymer according to claim 8, wherein, in the formula, Ar is an aromatic group.

15. The polymer according to claim 1, further comprising: a structural unit having a group with a lactone skeleton.

16. The polymer according to claim 15, wherein an amount of the structural unit having a group with a lactone skeleton is from 20 to 60 mol % relative to all structural units in the polymer.

17. The polymer according to claim 15, wherein the structural unit having a group with a lactone skeleton comprises a structural unit derived from at least one monomer selected from the group consisting of β-(meth)acryloyloxy-β-methyl-δ-valerolactone, 4,4-dimethyl-2-methylene-γ-butyrolactone β-(meth)acryloyloxy-γ-butyrolactone, β-(meth)acryloyloxy-β-methyl-γ-butyrolactone, α-(meth)acryloyloxy-γ-butyrolactone, 2-(1-(meth)acryloyloxy)ethyl-4-butanolide (meth)acrylic acid pantoyl lactone, 5-(meth)acryloyloxy-2,6-norbornane carbolactone, 8-methacryloxy-4-oxatricyclo[5.2.1.0.sup.2,6]decane-3-one, and 9-methacryloxy-4-oxatricyclo[5.2.1.0.sup.2,6]decane-3-one.

18. The polymer according to claim 1, further comprising: a structural unit having a hydrophilic group.

19. The polymer according to claim 18, wherein an amount of the structural unit having a hydrophilic group is from 5 to 50 mol % relative to all structural units in the polymer.

20. The polymer according to claim 18, wherein the structural unit having a hydrophilic group comprises a structural unit derived from at least one monomer selected from the group consisting of (meth)acrylic acid, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxy-n-propyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 3-hydroxyadmantyl (meth)acrylate, 2- or 3-cyano-5-norbornene (meth)acrylate, and 2-cyanomethyl-2-adamantyl (meth)acrylate.

Description

EXAMPLES

(1) In the following, the present invention is described according to examples. However, the present invention is not limited to those examples. Also, “parts” in examples and comparative examples are “parts by mass” unless otherwise indicated. Measurement methods and evaluation methods are as follows.

(2) <Measuring Molecular Weight>

(3) The weight-average molecular weight (Mw), number-average molecular weight (Mn) and molecular-weight distribution (Mw/Mn) of a monomer were obtained using gel permeation chromatography under the following conditions (GPC conditions) in terms of polystyrene.

(4) [GPC Conditions]

(5) Instrument: HLC-8220GPC (brand name), Tosoh high-performance GPC system, made by Tosoh Biochemical LLC

(6) Separation column: three Shodex GPC K-805L (brand name) connected in series, made by Showa Denko K.K.

(7) Measurement temperature: 40° C.

(8) Eluent: tetrahydrofuran (THF)

(9) Sample (for a polymer): solution prepared by dissolving approximately 20 grams of a polymer in 5 mL of THF and by filtering the mixture using a 0.5 μm-membrane filter

(10) Sample (for a polymerization solution): solution prepared by dissolving approximately 30 mg of the sample polymerization solution in 5 mL of THF and by filtering the mixture using a 0.5 μm-membrane filter

(11) Flow rate: 1 mL/min

(12) Injection amount: 0.1 mL

(13) Detector: differential refractometer (refractive index detector).

(14) Calibration curve (I): a solution was prepared by dissolving approximately 20 mg of standard polystyrene in 5 mL of THF, which was then filtered using a 0.5 μm-membrane filter. The prepared solution was injected into the separation column under the above conditions and the relationship between the elution time and the molecular weight was obtained. Standard types of polystyrene made by Tosoh Biochemical LLC (each is a brand name) were used.

(15) F-80 (Mw=706,000)

(16) F-20 (Mw=190,000)

(17) F-4 (Mw=37,900)

(18) F-1 (Mw=10,200)

(19) A-2500 (Mw=2,630)

(20) A-500 (a mixture of Mw=682, 578, 474, 370, 260)

(21) <Measuring GPC Area Proportion of Molecular Weight of 1000 or Less>

(22) The same as above, the molecular weight was measured to calculate the rate of positive peak areas corresponding to molecular weight of 1000 or less to all the peak areas of the polymer shown on the elution curve detected by a differential refractometer (rate (%) of GPC areas of molecular weight of 1000 or less).

(23) <Determination of Polymerization Rate>

(24) The residual amount of each monomer remaining in the polymerization mixture was obtained by the following method.

(25) From the reactor, 0.5 grams of the polymerization mixture was taken and diluted by acetonitrile to set the entire amount to be 50 mL using a measuring flask. The dilution was filtered using a 0.2 μm-membrane filter. Then, the unreacted amount of each monomer (residual monomer amount) in the dilution was measured using a high-performance liquid chromatograph HPLC-8020 (brand name), made by Tosoh Biochemical LLC.

(26) The amount of each polymerized monomer was calculated by subtracting the residual monomer amount from the entire amount of the monomer supplied to the reactor. Then, the polymerization rate (mass %) was obtained as the rate of the amount of the polymerized monomer to the entire amount of the monomer supplied to the reactor.

(27) The following were used for the measurement above.

(28) One separation column: Inertsil ODS-2 (brand name) made by GL Science, Inc.

(29) Mobile phase: water/acetonitrile gradient

(30) Flow rate: 0.8 mL/min.

(31) Detector: UV-8020 (brand name) UV-visible spectrophotometer, made by Tosoh Biochemical LLC

(32) Detection wavelength: 220 nm

(33) Measurement temperature: 40° C.

(34) Injection amount: 4 μL

(35) As a separation column, Inertsil ODS-2 (brand name), silica gel with a particle diameter of 5 μm and a 4.6-mm inner diameter×450-mm long column, was used. Also, the gradient conditions of the mobile phase were as follows, using solution A of water and solution B of acetonitrile. To determine the unreacted amount of a monomer, monomer solutions with different concentration rates were used as standard samples.

(36) Measurement time 0 through 3 minutes: solution A/solution B=90 volume %/10 volume %

(37) Measurement time 3 through 24 minutes: solution A/solution B=90 volume %/10 volume % to 50 volume %/50 volume %

(38) Measurement time 24 through 36.5 minutes: solution A/solution B=50 volume %/50 volume % to 0 volume %/100 volume %

(39) Measurement time 36.5 through 44 minutes: solution A/solution B=0 volume %/100 volume %

(40) <Determination of End Group Having Thiocarbonylthio Structure>

(41) A sample solution was prepared by dissolving 5 parts of the polymer in approximately 95 parts of dimethylsulfoxide. The sample solution was placed into an NMR tube and analyzed using .sup.1H-NMR (made by JEOL Ltd., resonance frequency of 270 MHz). From the integrated intensity of the signal derived from the thiocarbonylthio structure present in an end of the polymer chain, the ratio of the end group having a thiocarbonylthio structure to all the end groups of the polymer chain was calculated. The ratio corresponds to the ratio of the end group having a thiocarbonylthio structure (RAFT residue) to all the end groups of the polymer chain.

(42) In the following examples, the ends (growing ends) of the polymer chain are either a polymerization initiator residue (not containing a sulfur atom) or RAFT residue (containing a sulfur atom). Thus, the number of moles of the end group having a sulfur atom is the number of moles of the end group having a thiocarbonylthio structure.

(43) The sum of the end groups not containing a sulfur atom and the end groups containing a sulfur atom is the totality of the end groups. A lower ratio of end groups containing a sulfur atom means less RAFT residue remaining at the ends of the polymer chain.

(44) <Determination of Organic Acid (Structural Unit Acting as Organic Acid)>

(45) In a polymer in the following examples, a group capable of generating organic acid is limited to an acid leaving group and RAFT agent residue remaining at an end of the polymer chain. When the acid leaving group or RAFT agent residue is decomposed by heat or acid, carboxylic acid or dithiocarboxylic acid is generated as a result. Therefore, the sum of the number of moles of structural units having a carboxylic-acid structure or a dithiocarboxylic-acid structure is the number of moles of structural units acting as organic acids in the polymer.

(46) The ratio (amount of organic acid contained in the polymer) of the number of structural units acting as organic acid to the number of all the structural units in the polymer was obtained by the following method.

(47) A sample solution was prepared by dissolving approximately 5 parts of the polymer in approximately 95 parts of dimethylsulfoxide. The sample solution was placed into an NMR tube and analyzed using .sup.1H-NMR (made by JEOL Ltd., resonance frequency of 270 MHz). From the integrated intensity of the signal derived from the carboxylic-acid structure and dithiocarboxylic-acid structure, the proportion (mol %) of structural units acting as organic acid to the number of all the structural units was calculated. Signals derived from the carboxylic-acid or dithiocarboxylic-acid structure are observed near each other in the .sup.1H-NMR analysis.

(48) <Evaluation of Polymer Solubility>

(49) Ten parts of a polymer and 90 parts of PGMEA were mixed and stirred under constant conditions while a temperature of 25° C. was maintained. Whether or not the polymer was completely dissolved was visually determined, and the time until complete dissolution was recorded. The shorter the time taken until complete dissolution, the better was the solubility of the polymer.

(50) <Evaluation of Transparency of Resist Composition>

(51) The resist composition was spin-coated on a 4-inch quartz wafer and prebaked (PAB) on a hotplate at 120° C. for 60 seconds to form 1000 nm-thick resist film. Using a UV-visible spectrophotometer (brand name: UV-3100, made by Shimadzu Corporation), the transmittance of 193 nm light was measured. “193 nm” is the wavelength of ArF excimer laser light.

(52) <Evaluation of Sensitivity of Resist Composition>

(53) The resist composition was spin-coated on a 6-inch silicon wafer and prebaked (PAB) on a hotplate at 120° C. for 60 seconds to form 300 nm-thick resist film.

(54) Using an ArF excimer laser exposure instrument (brand name: VUVES-4500, made by Litho Tech Japan Corp.), 18-shot irradiation was conducted on a 10 mm×10 mm area while the exposure amount was changed.

(55) Next, the resist film was post-baked (PEB) at 110° C. for 60 seconds and developed for 65 seconds in a 2.38% tetramethylammonium hydroxide solution at 23.5° C. using a resist development analyzer (brand name: RDA-806, made by Litho Tech Japan Corp.) For each resist film exposed to different amounts of light, chronological change in the resist film thickness during development was measured.

(56) Based on the data on chronological change in the resist film thickness, by plotting the relationship between the logarithm of exposure amount (mJ/cm.sup.2) and the rate (%) of remaining film thickness after development of 30 seconds relative to the initial film thickness (hereinafter referred to as a residual film rate), a curve showing the relationship of an exposure amount to the residual film rate was prepared. Based on the curve, the necessary exposure amount (Eth) to achieve the residual film rate of 0% was obtained. Namely, the exposure amount (mJ/cm.sup.2) obtained at the point where the curve showing the relationship of an exposure amount to the residual film rate crosses the straight line at a residual film rate of 0% was set as (Eth). The value of (Eth) indicates sensitivity; the lower the value (Eth), the higher the sensitivity.

(57) In the examples, monomers (m-1), (m-2), (m-3), (m-4), RAFT agent (R-1), polymerization initiators (I-1), (I-2) are as follows.

(58) monomer (m-1): compound represented by formula (m-1) shown below.

(59) monomer (m-2): compound represented by formula (m-2) shown below.

(60) monomer (m-3): compound represented by formula (m-3) shown below.

(61) monomer (m-4): compound represented by formula (m-4) shown below.

(62) RAFT agent (R-1): compound represented by formula (R-1) shown below.

(63) polymerization initiator (I-1): dimethyl-2,2′-azobisisobutylate, V601 (brand name), made by Wako Pure Chemical Industries.

(64) polymerization initiator (I-2): 2,2′-azobis(2,4-dimethylvaleronitrile, V65 (brand name), made by Wako Pure Chemical Industries.

(65) ##STR00003##

Example 1

(66) In a 25 mL Schlenk flask, 8.4 parts of PGMEA, 2.72 parts of monomer (m-1), 3.07 parts of monomer (m-2), 1.89 parts of monomer (m-3), 0.18 parts (0.8 mmol) of RAFT agent (R-1) were supplied, and nitrogen was blown at 200 mL/min for 1 minute into the mixture in the flask. Then, the flask was placed over an 80° C. heating bath to raise the temperature inside the flask to 80° C. (predetermined polymerization temperature).

(67) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA, 0.050 parts (0.2 mmol) of polymerization initiator (I-1) and 0.002 parts (0.02 mmol) of triethylamine was supplied into the flask all at once, and the mixture in the flask was stirred for 5 hours while its temperature was maintained.

(68) Next, a solution containing 0.5 parts of PGMEA and 0.992 parts (4 mmol) of polymerization initiator (I-2) was added into the flask all at once, and after the mixture was stirred for an hour while its temperature was maintained, a solution containing 0.5 parts of PGMEA and 0.992 parts (4 mmol) of polymerization initiator (I-2) was further supplied into the flask all at once, and the mixture was stirred for an hour while its temperature was maintained. Then, the reaction mixture was cooled to room temperature to terminate the reaction. Residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(69) In the present example, the time when the temperature in the flask reached 80° C. is set as (T.sub.0), and the time when cooling the reaction mixture in the flask started is set as (T.sub.1). Amount (I.sub.A) of the polymerization initiators supplied between (T.sub.0) and (T.sub.1) was (0.05+0.992+0992) parts. Amount (I.sub.B) of the polymerization initiators supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was (0.992+0992) parts. Thus, (I.sub.B)/(I.sub.A)=0.975.

(70) <Purification of Polymer>

(71) The polymerization mixture in the flask was added drop by dropp into a heptane solution of approximately 10 times the amount of the polymerization mixture while the mixture was being stirred, and a sedimentation of a white precipitate (polymer A-1) was obtained. The sedimentation was filtered and put into the same amount of methanol as above and washed while the mixture was being stirred. Then, the sedimentation after washing was filtered again to obtain a wet polymer powder. The wet polymer powder was dried at 40° C. for approximately 40 hours under reduced pressure. For obtained polymer (A-1), Mw, Mw/Mn, the rate of GPC areas of molecular weight of 1000 or less, the content of sulfur atoms at an end of the polymer chain (the proportion of end groups containing a sulfur atom to all the end groups of the polymer) and organic acid content were measured to evaluate the solubility of the polymer. The results are shown in Table 1.

(72) <Preparing Resist Composition>

(73) A solution containing 100 parts of polymer (A-1), 2 parts of triphenylsulfonium triflate as a photoacid generator and PGMEA as a solvent was mixed homogeneously to have a polymer concentration of 10.0 mass % and filtered using a 0.1 μm-diameter membrane filter to obtain a resist composition. The transparency and sensitivity of the resist composition was evaluated using the above method. The results are shown in Table 1.

Example 2

(74) The same steps for supplying PGMEA, monomers (m-1), (m-2) and (m-3) and RAFT agent (R-1) in a Schlenk flask, blowing nitrogen and raising the temperature in the flask to 80° C. were conducted as in example 1.

(75) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA, 0.050 parts (0.2 mmol) of polymerization initiator (I-1) and 0.002 parts (0.02 mmol) of triethylamine was supplied into the flask all at once, and the mixture was stirred for 5 hours while its temperature was maintained.

(76) Next, a solution containing 1.0 parts of PGMEA and 1.84 parts (8 mmol) of polymerization initiator (I-1) was added into the flask all at once, and the mixture was stirred for 2 hours while its temperature was maintained. Then, the reaction mixture was cooled to room temperature to terminate the reaction. The residual monomer amount in the reaction mixture at that time was determined and the polymerization rate was obtained. The results are shown in Table 1.

(77) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was (0.05+1.84) parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was 1.84 parts. Thus, (I.sub.B)/(I.sub.A)=0.974.

(78) The polymerization mixture was purified the same as in example 1 to obtain polymer (A-2). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Example 3

(79) The same steps for supplying PGMEA, monomers (m-1), (m-2) and (m-3) and RAFT agent (R-1) in a Sehlenk flask, blowing nitrogen and raising the temperature in the flask to 80° C. were conducted as in example 1.

(80) Ten minutes after the temperature of the solution reached 80° C., a solution containing 1.0 parts of PGMEA, 0.050 parts (0.2 mmol) of polymerization initiator (I-2) and 0.002 parts (0.02 mmol) of triethylamine was added into the flask all at once, and the mixture was stirred for 4 hours while its temperature was maintained.

(81) Next, a solution containing 1.0 parts of PGMEA and 0.055 parts (0.22 mmol) of polymerization initiator (I-2) was supplied into the flask all at once, and the mixture was stirred for 3 hours while its temperature was maintained. Then, the reaction mixture was cooled to room temperature to terminate the reaction. The residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(82) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was (0.05+0.055) parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was 0.055 parts. Thus, (I.sub.B)/(I.sub.A)=0.524.

(83) The polymerization mixture was purified the same as in example 1 to obtain polymer (A-3). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Example 4

(84) In a flask with the attached nitrogen inlet, condenser, stirrer, dropping funnel and thermometer, 42.0 parts of PGMEA, 13.60 parts of monomer (m-1), 15.68 parts of monomer (m-2), 9.44 parts of monomer (m-3) and 1.77 parts (8 mmol) of RAFT agent (R-1) were supplied under nitrogen atmosphere. The flask was put over a heating bath and the temperature of the hot bath was raised to 80° C. while the mixture in the flask was being stirred.

(85) Ten minutes after the temperature in the flask reached 80° C., a solution containing 4.4 parts of PGMEA, 0.23 parts (1 mmol) of polymerization initiator (I-1) and 0.081 parts (0.8 mmol) of triethylamine was added into the flask all at once, while 13.60 parts of monomer (m-1), 15.68 parts of monomer (m-2), 9.44 parts of monomer (m-3), 47.3 parts of PGMEA and 0.23 parts (1 mmol) of polymerization initiator (I-1) in the dropping funnel were added drop by drop out in 4 hours at a constant rate. Then, the mixture was stirred for an hour while the temperature was maintained. Next, after 27.6 parts of PGMEA and 18.4 parts (80 mmol) of polymerization initiator (I-2) in the dropping funnel were added drop by drop into the flask at a constant rate for 10 minutes, the mixture was stirred for one hour and 50 minutes while its temperature was maintained. Then, the reaction mixture was cooled to room temperature to terminate the reaction. Residual monomer amounts at that time were determined to obtain the polymerization rate. The results are shown in Table 1.

(86) In the present example, amount (I.sub.A) of the polymerization initiators supplied between (T.sub.0) and (T.sub.1) was (0.23+0.23+18.4) parts. Amount (I.sub.B) of the polymerization initiators supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was (0.029+18.40) parts. Thus, (I.sub.B)/(I.sub.A)=0.977.

(87) The polymerization mixture was purified the same as in example 1 to obtain polymer (A-4). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Example 5

(88) In a Schlenk flask, 4.2 parts of PGMEA, 1.36 parts of monomer (m-1), 1.98 parts of monomer (m-4), 0.94 parts of monomer (m-2), 0.09 parts (0.4 mmol) of RAFT agent (R-1) were supplied, and nitrogen was blown at 200 mL/min for 1 minute into the solution in the flask. Then, the flask was placed over an 80° C. heating bath to raise the temperature inside the flask to 80° C. (predetermined polymerization temperature).

(89) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA, 0.023 parts (0.1 mmol) of polymerization initiator (I-1), and 0.008 parts (0.08 mmol) of triethylamine was supplied into the flask all at once, and the mixture in the flask was stirred for 5 hours while the temperature was maintained.

(90) Next, a solution containing 1.0 part of PGMEA and 1.84 parts (8 mmol) of polymerization initiator (I-1) was added into the flask all at once, and after the mixture was stirred for 2 hours while its temperature was maintained, the reaction mixture was cooled to room temperature to terminate the reaction. Residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(91) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was (0.023+1.84) parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was 1.84 parts. Thus, (I.sub.B)/(I.sub.A)=0.988.

(92) The polymerization mixture in the flask was added drop by drop into a mixed solution of heptane/isopropanol (volume ratio of 70/30) at approximately 10 times the amount of the polymerization mixture while the mixture was being stirred, and a white sedimentation (polymer A-5) was obtained. The sedimentation was filtered and put again into the same amount of methanol as above and washed while being stirred. Then, the sedimentation after washing was filtered to obtain a wet polymer powder. The wet polymer powder was dried at 40° C. for approximately 40 hours under reduced pressure. For obtained polymer (A-5), the same measurements and evaluation were conducted as in example 1. The results are shown in Table 1.

Example 6

(93) In a Schlenk flask, 4.2 parts of PGMEA, 1.36 parts of monomer (m-1), 1.98 parts of monomer (m-4), 0.94 parts of monomer (m-2) and 0.09 parts (0.4 mmol) of RAFT agent (R-1) were supplied, and nitrogen was blown at 200 mL/min for 1 minute into the solution in the flask. Then, the flask was placed over an 80° C. heating bath to raise the temperature inside the flask to 80° C.

(94) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA, 0.023 parts (0.1 mmol) of polymerization initiator (I-1), and 0.008 parts (0.08 mmol) of triethylamine was added into the flask all at once, and the mixture in the flask was stirred for 7 hours while its temperature was maintained. Then, the reaction mixture was cooled to room temperature to terminate the reaction. Residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(95) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was 0.023 parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was zero. Thus, (I.sub.B)/(I.sub.A)=0.

(96) The polymerization mixture was purified the same as in example 5 to obtain polymer (A-6). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Comparative Example 1

(97) The same steps for supplying PGMEA, monomers (m-1), (m-2) and (m-3) and RAFT agent (R-1) in a Schlenk flask, blowing nitrogen and raising the temperature in the flask to 80° C. were conducted as in example 1.

(98) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA and 0.050 parts (0.2 mmol) of polymerization initiator (I-1) was added into the flask all at once, and the mixture in the flask was stirred for 7 hours while its temperature was maintained. Then, the reaction mixture was cooled to room temperature to terminate the reaction. Residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(99) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was 0.05 parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was zero. Thus, (I.sub.B)/(I.sub.A)=0.

(100) The polymerization mixture was purified the same as in example 1 to obtain polymer (B-1). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Comparative Example 2

(101) The same steps for supplying PGMEA, monomers (m-1), (m-2) and (m-3) and RAFT agent (R-1) in a Schlenk flask, blowing nitrogen and raising the temperature in the flask to 80° C. were conducted as in example 1.

(102) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA and 0.050 parts (0.2 mmol) of polymerization initiator (I-2) was added into the flask all at once, and the mixture in the flask was stirred for 7 hours while its temperature was maintained. Then, the reaction was terminated by cooling the reaction mixture to room temperature. Residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(103) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was 0.05 parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was zero. Thus, (I.sub.B)/(I.sub.A)=0.

(104) The polymerization mixture was purified the same as in example 1 to obtain polymer (B-2). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Comparative Example 3

(105) In a Schlenk flask, 8.4 parts of PGMEA, 2.72 parts of monomer (m-1), 3.07 parts of monomer (m-2), 1.89 parts of monomer (m-3), 0.18 parts (0.8 mmol) of RAFT agent (R-1) and 0.050 parts (0.2 mmol) of polymerization initiator (I-2) were supplied, and nitrogen was blown at 200 mL/min for 1 minute into the solution in the flask. Then, the flask was placed over an 80° C. heating bath to raise the temperature inside the flask to 80° C. It took one hour for the temperature in the flask to reach 80° C.

(106) After the temperature reached 80° C., the mixture was stirred for 5 hours while its temperature was maintained.

(107) Next, a solution containing 0.5 parts of PGMEA and 0.050 parts (0.2 mmol) of polymerization initiator (I-2) was added into the flask all at once, and the mixture in the flask was stirred for 2 hours while its temperature was maintained. Then the reaction mixture was cooled to room temperature to terminate the reaction. Residual monomer amounts in the reaction mixture at that time were determined and the polymerization rate was obtained. The results are shown in Table 1.

(108) In the present example, the time when the temperature in the flask reached 80° C. is set as (T.sub.0), and the time when cooling the reaction mixture started is set as (T.sub.1). Mass amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was 0.050 parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was 0.050 parts. Thus, (I.sub.B)/(I.sub.A)=1.

(109) The polymerization mixture was purified the same as in example 1 to obtain polymer (B-3). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

Comparative Example 4

(110) The same steps for supplying PGMEA, monomers (m-1), (m-4) and (m-3) and RAFT agent (R-1) in a Schlenk flask, blowing nitrogen and raising the temperature in the flask to 80° C. were conducted as in example 5.

(111) Ten minutes after the temperature reached 80° C., a solution containing 1.0 part of PGMEA and 0.023 parts (0.1 mmol) of polymerization initiator (I-1) was added into the flask all at once, and the mixture in the flask was stirred for 7 hours while its temperature was maintained. Then the reaction mixture was cooled to room temperature to terminate the reaction. A while solid precipitated in the reaction mixture 2.5 hours after the polymerization initiator was added, but the reaction was continued in a heterogeneous reaction system. Residual monomer amounts in the reaction mixture after the reaction was terminated were determined and the polymerization rate was obtained. The results are shown in Table 1.

(112) In the present example, amount (I.sub.A) of the polymerization initiator supplied between (T.sub.0) and (T.sub.1) was 0.023 parts. Amount (I.sub.B) of the polymerization initiator supplied between (T.sub.1−T.sub.0)/2 and (T.sub.1) was zero. Thus, (I.sub.B)/(I.sub.A)=0.

(113) The polymerization mixture was purified the same as in example 1 to obtain polymer (B-4). Measurements and evaluation were conducted the same as in example 1. The results are shown in Table 1.

(114) TABLE-US-00001 TABLE 1 proportion proporiton of proportion of polymer- of end structural unit GPC areas of solubility transmittance ization group with acting as molecular weight of rate of rate sulfur atom organic acid 1000 or less polymer resist film sensitivity polymer I.sub.B/I.sub.A [mass %] Mw Mw/Mn [mol %] [mol %] [%] [min] [%] [mJ/cm.sup.2] example 1 A-1 0.975 94 9700 1.2 4 0 0.7 24 43.5 1.15 example 2 A-2 0.974 96 9800 1.2 6 0 0.6 22 47.2 1.12 example 3 A-3 0.524 92 8500 1.3 28 0 0.8 35 40.1 1.26 example 4 A-4 0.977 99 10400 1.2 3 0 0.3 15 48.3 1.03 example 5 A-5 0.974 95 9000 1.3 4 0 0.9 19 46.8 0.61 example 6 A-6 0 82 9200 1.2 78 0 1.3 26 35.1 1.36 comparative B-1 0 88 9200 1.2 81 3 1.4 45 34.7 1.61 example 1 comparative B-2 0 72 7600 1.3 79 3 1.5 57 33.2 1.55 example 2 comparative B-3 1 85 6900 1.5 65 4 1.4 42 36.1 1.48 example 3 comparative B-4 0 86 4300 2.0 43 32 1.3 not impossible impossible example 4 dissolved to measure to measure

(115) As shown in Table 1, in each of polymers (A-1) to (A-5) obtained in examples 1 to 5, which satisfies 0.50<(I.sub.B)/(I.sub.A)<1.00, the molecular-weight distribution is narrowed, variation of molecular weight is small, the ratio of end groups containing a sulfur atom is low, and there is less RAFT agent residue remaining at an end of the polymer chain.

(116) In examples 1 to 5, where each polymer mixture was purified by being brought into contact with both a polar protic poor solvent and a nonpolar aprotic poor solvent, the rate of GPC areas of molecular weight at 1000 or less is small, each polymer has excellent solubility, and resist film has high transmittance of ArF excimer laser light with a wavelength (193 nm), and exhibits excellent transparency and sensitivity.

(117) In each of examples 1 to 6, a basic compound was also present in the reaction system, and organic acid (structural unit acting as an organic acid) was not detected in obtained polymers (A-1) to (A-6). It is found that an acid leaving group during the polymerization was suppressed from decomposing.

(118) By contrast, in comparative examples 1, 2 and 4, a basic compound was not present in the reaction system, and a polymerization initiator was not supplied additionally in the latter half of the polymerization (namely, (I.sub.B)/(I.sub.A)=0). In each of those comparative examples, an organic acid derived from the decomposed acid leaving group (structural unit acting as organic acid) was detected, the polymerization rate was low, and the ratio of end groups containing a sulfur atom was high. Especially, since a large amount of organic acid (structural unit acting as an organic acid) was produced during polymerization in comparative example 4, reaction in a homogeneous system could not be continued and the polymer did not dissolve in a resist solvent. Thus, evaluation results on transparency and sensitivity were not obtained.

(119) Also, in example 3, a basic compound did not coexist in the reaction system, a polymerization initiator was supplied before the solution temperature in the reactor reached the polymerization temperature for the polymerization to progress, and the polymerization initiator was supplied additionally in the latter half of the polymerization (namely, (I.sub.B)/(I.sub.A)=1). In example 3, an organic acid (structural unit acting as an organic acid) derived from the decomposed acid leaving group was detected, the dispersion in molecular weights was wide, the polymerization rate was low, and the ratio of end groups containing a sulfur atom was high.