POSITIVE RESIST COMPOSITION AND PATTERN FORMING PROCESS

Abstract

A positive resist composition is provided comprising a base polymer comprising repeat units having a carboxy group whose hydrogen is substituted by a nitrobenzene ring-containing tertiary hydrocarbyl group. The resist composition has a high sensitivity and resolution and forms a pattern of good profile with reduced edge roughness and size variation after exposure.

Claims

1. A positive resist composition comprising a base polymer comprising repeat units having a carboxy group whose hydrogen is substituted by a nitrobenzene ring-containing tertiary hydrocarbyl group.

2. The resist composition of claim 1 wherein the repeat units have the formula (a): ##STR00242## wherein R.sup.A is hydrogen or methyl, X.sup.1 is a single bond, phenylene, naphthylene, or a C.sub.1-C.sub.12 linking group containing at least one moiety selected from an ester bond, ether bond and lactone ring, and R is a group having the formula (a1): ##STR00243## wherein R.sup.1 and R.sup.2 are each independently a C.sub.1-C.sub.6 aliphatic hydrocarbyl group which may contain a heteroatom, R.sup.1 and R.sup.2 may bond together to form a ring with the carbon atom to which they are attached, R.sup.3 is hydrogen, halogen, a C.sub.1-C.sub.6 alkyl group, C.sub.1-C.sub.6 alkoxy group or C.sub.1-C.sub.6 acyloxy group, in is an integer of 1 to 4, n is 1 or 2, and the broken line designates a valence bond.

3. The resist composition of claim 1 wherein the base polymer further comprises repeat units of at least one type selected from repeat units having a carboxy group whose hydrogen is substituted by an acid labile group other than the nitrobenzene ring-containing tertiary hydrocarbyl group, and repeat units having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group.

4. The resist composition of claim 3 wherein the repeat units having a carboxy group whose hydrogen is substituted by an acid labile group other than the nitrobenzene ring-containing tertiary hydrocarbyl group have the formula (b1), and the repeat units having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group have the formula (b2): ##STR00244## wherein R.sup.A is each independently hydrogen or methyl, Y.sup.1 is a single bond, phenylene group, naphthylene group, or a C.sub.1-C.sub.12 linking group containing at least one moiety selected from an ester bond, ether bond and lactone ring, Y.sup.2 is a single bond, ester bond or amide bond, Y.sup.3 is a single bond, ether bond or ester bond, R.sup.11 is an acid labile group other than the nitrobenzene ring-containing tertiary hydrocarbyl group, R.sup.12 is an acid labile group, R.sup.13 is fluorine, trifluoromethyl, cyano or a C.sub.1-C.sub.6 saturated hydrocarbyl group, R.sup.14 is a single bond or a C.sub.1-C.sub.6 alkanediyl group in which some constituent —CH.sub.2— may be replaced by an ether bond or ester bond, a is 1 or 2, b is an integer of 0 to 4, and the sum of a+b is from 1 to 5.

5. The resist composition of claim 1 wherein the base polymer further comprises repeat units having an adhesive group which is selected from among hydroxy, carboxy, lactone ring, carbonate bond, thiocarbonate bond, carbonyl, cyclic acetal, ether bond, ester bond sulfonic ester bond, cyano, amide bond, —O—C(O)—S—, and —O—C(═O)—NH—.

6. The resist composition of claim 1 wherein the base polymer further comprises repeat units of at least one type selected from repeat units having the formulae (d1) to (d3): ##STR00245## wherein R.sup.A is each independently hydrogen or methyl, Z.sup.1 is a single bond, a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, naphthylene, or a C.sub.7-C.sub.18 group obtained by combining the foregoing, or —O—Z.sup.11—, —C(═O)—O—Z.sup.11— or —C(═O))—NH—Z.sup.11—, Z.sup.11 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, naphthylene, or a C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety, Z.sup.2 is a single bond or ester bond, Z.sup.3 is a single bond, —Z.sup.31—C(O)—O—, —Z.sup.31—O— or —Z.sup.31—O—C(═O)—, Z.sup.31 is a C.sub.1-C.sub.12 aliphatic hydrocarbylene group, phenylene group, or a C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond, iodine or bromine, Z.sup.4 is a methylene, 2,2,2-trifluoro-1,1-ethanediyl or carbonyl group, Z.sup.5 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, —O—Z.sup.51—, —C(═O)—O—Z.sup.51— or —C(O)—NH—Z.sup.51—, Z.sup.51 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, fluorinated phenylene, or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety, R.sup.21 to R.sup.28 are each independently halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, R.sup.23 and R.sup.24, or R.sup.26 and R.sup.27 may bond together to form a ring with the sulfur atom to which they are attached, and M.sup.− is a non-nucleophilic counter ion.

7. The resist composition of claim 1, further comprising an acid generator.

8. The resist composition of claim 1, further comprising an organic solvent.

9. The resist composition of claim 1, further comprising a quencher.

10. The resist composition of claim 1, further comprising a surfactant.

11. A pattern forming process comprising the steps of applying the positive resist composition of claim 1 onto a substrate to form a resist film thereon, exposing the resist film to high-energy radiation, and developing the exposed resist film in a developer.

12. The pattern forming process of claim 11 wherein the high-energy radiation is i-line, ArF excimer laser, KrF excimer laser, EB, or EUV of wavelength 3 to 15 nm.

Description

EXAMPLES

[0181] Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviation “pbw” is parts by weight.

[1] Synthesis of monomers

Synthesis Example 1-1

[0182] Synthesis of Monomer M-1

[0183] In a reactor, 9.06 g of 2-(4-nitrophenyl)-2-propanol, 8.60 g of triethylamine, and 0.61 g of 4-dimethylaminopyridine were dissolved in 25 mL of acetonitrile. While the reactor was kept at an internal temperature of 40-60° C., 7.32 g of methacrylic chloride was added dropwise thereto. Stirring was continued for 19 hours at the internal temperature of 60° C. The reaction solution was cooled to which 20 mL of saturated sodium bicarbonate aqueous solution was added to quench the reaction. The end compound was extracted with a mixture of 25 mL toluene, 15 mL hexane and 15 mL ethyl acetate. This was followed by standard aqueous workup, solvent distillation, and vacuum distillation, obtaining 9.02 g of Monomer M-1 as colorless transparent oil.

##STR00212##

Synthesis Example 1-2

[0184] Synthesis of Monomer M-2

[0185] Monomer M-2, shown below, was synthesized by the same procedure as in Synthesis Example 1-1 except that 2-(3-nitrophenyl)-2-propanol was used instead of 2-(4-nitrophenyl)-2-propanol.

##STR00213##

Synthesis Example 1-3

[0186] Synthesis of Monomer M-3

[0187] Monomer M-3, shown below, was synthesized by the same procedure as in Synthesis Example 1-1 except that 2-(3-fluoro-4 nitrophenyl)-2-propanol was used instead of 2-(4-nitrophenyl)-2-propanol.

##STR00214##

Synthesis Example 1-4

[0188] Synthesis of Monomer M-4

[0189] Monomer M-4, shown below, was synthesized by the same procedure as in Synthesis Example 1-1 except that Compound C-1, shown below, was used instead of 2-(4-nitrophenyl)-2-propanol.

##STR00215##

Synthesis Example 1-5

[0190] Synthesis of Monomer M-5

[0191] Monomer M-5, shown below, was synthesized by the same procedure as in Synthesis Example 1-1 except that Compound C-2, shown below, was used instead of 2-(4 nitrophenyl)-2-propanol.

##STR00216##

[2] Synthesis of polymers

[0192] Monomers PM-1 to PM-4, AM-1 to AM-5, FM-1 and FM-2 used in the synthesis of polymers have the structure shown below. The polymer is analyzed for composition by .sup.13C— and .sup.1H-NMR spectroscopy and for Mw and Mw/Mn by GPC versus polystyrene standards using tetrahydrofuran (THF) solvent.

##STR00217## ##STR00218##

Synthesis Example 2-1

[0193] Synthesis of Polymer P-1

[0194] A 2-L flask was charged with 14.9 g of Monomer M-1, 4.8 g of 4-hydroxystyrene, and 40 g of THE solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of azobisisobutyronitrile (AIBN) as polymerization initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of isopropyl alcohol (IPA) for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-1. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00219##

Synthesis Example 2-2

[0195] Synthesis of Polymer P-2

[0196] A 2-L flask was charged with 6.3 g of Monomer M-1, 5.1 g of Monomer AM-2, 6.0 g of 3-hydroxystyrene, and 40 g of THE solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-2. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00220##

Synthesis Example 2-3

[0197] Synthesis of Polymer P-3

[0198] A 2-L flask was charged with 7.5 g of Monomer M-1, 4.6 g of Monomer AM-3, 6.0 g of 3-hydroxystyrene, and 40 g of THE solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-3. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00221##

Synthesis Example 2-4

[0199] Synthesis of Polymer P-4

[0200] A 2-L flask was charged with 12.5 g of Monomer M-1, 4.2 g of 3-hydroxystyrene, 11.9 g of Monomer PM-1, and 40 g of THE solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P4. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00222##

Synthesis Example 2-5

[0201] Synthesis of Polymer P-5

[0202] A 2-L flask was charged with 2.5 g of Monomer M-2, 5.2 g of 1-(cyclopropyl-1 yl)-1-methylethyl methacrylate, 3.5 g of 3-fluoro-4-(methylcyclohexyloxy)styrene, 4.8 g of 3-hydroxystyrene, 11.2 g of Monomer PM-3, and 40 g of THE solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-5. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00223##

Synthesis Example 2-6

[0203] Synthesis of Polymer P-6

[0204] A 2-L flask was charged with 3.2 g of Monomer M-3, 6.4 g of 1-methyl-1-cyclopentyl methacrylate, 4.2 g of 4-hydroxystyrene, 11.0 g of Monomer PM-2, and 40 g of THE solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-6. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00224##

Synthesis Example 2-7

[0205] Synthesis of Polymer P-7

[0206] A 2-L flask was charged with 3.7 g of Monomer M-1, 7.8 g of Monomer AM-1, 4.2 g of 3-hydroxystyrene, 11.0 g of Monomer PM-2, and 40 g of THE solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-7. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00225##

Synthesis Example 2-8

[0207] Synthesis of Polymer P-8

[0208] A 2-L flask was charged with 3.0 g of Monomer M-1, 6.4 g of 1-methyl-1-cyclopentyl methacrylate, 4.2 g of 4-hydroxystyrene, 9.6 g of Monomer PM-3, and 40 g of THF solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-8. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00226##

Synthesis Example 2-9

[0209] Synthesis of Polymer P-9

[0210] A 2-L flask was charged with 3.0 g of Monomer M-1, 5.9 g of tert-amyl methacrylate, 4.2 g of 4-hydroxystyrene, 11.9 g of Monomer PM-4, and 40 g of THE solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-9. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00227##

Synthesis Example 2-10

[0211] Synthesis of Polymer P-10

[0212] A 2-L flask was charged with 14.9 g of Monomer M-1, 4.2 g of 4-hydroxystyrene, 4.0 g of Monomer PM-2, and 40 g of THE solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-10. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00228##

Synthesis Example 2-11

[0213] Synthesis of Polymer P-11

[0214] A 2-L flask was charged with 14.9 g of Monomer M-1, 3.2 g of 4-hydroxystyrene, 3.6 g of Monomer FM-1, and 40 g of THF solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-11. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00229##

Synthesis Example 2-12

[0215] Synthesis of Polymer P-12

[0216] A 2-L flask was charged with 14.9 g of Monomer M-1, 3.6 g of 4-hydroxystyrene, 3.3 g of Monomer FM-2, and 40 g of THF solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-12. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00230##

Synthesis Example 2-13

[0217] Synthesis of Polymer P-13

[0218] A 2-L flask was charged with 7.5 g of Monomer M-1, 3.6 g of Monomer AM-4, 6.0 g of 3-hydroxystyrene, and 40 g of THF solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-13. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00231##

Synthesis Example 2-14

[0219] Synthesis of Polymer P-14

[0220] A 2-L flask was charged with 7.5 g of Monomer M-1, 3.6 g of Monomer AM-5, 6.0 g of 4-hydroxystyrene, and 40 g of THF solvent. The reactor was cooled at −70° C. in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C. and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-14. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00232##

Synthesis Example 2-15

[0221] Synthesis of Polymer P-15

[0222] A 2-L flask was charged with 5.0 g of Monomer M-1, 4.5 g of Monomer AM-1, 10.7 g of 2-hydroxyphenyl methacrylate, and 40 g of THF solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-15. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00233##

Synthesis Example 2-16

[0223] Synthesis of Polymer P-16

[0224] A 2-L flask was charged with 5.0 g of Monomer M-1, 6.7 g of Monomer AM-1, 8.9 g of 3-hydroxyphenyl methacrylate, and 40 g of THF solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-16 The polymer war analyzed by NMR spectroscopy and GPC.

##STR00234##

Synthesis Example 2-17

[0225] Synthesis of Polymer P-17

[0226] A 2-L flask was charged with 7.5 g of Monomer M-1, 7.5 g of Monomer AM-1, 7.1 g of 4-hydroxyphenyl methacrylate, and 40 g of THF solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-17. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00235##

Synthesis Example 2-18

[0227] Synthesis of Polymer P-18

[0228] A 2-L flask was charged with 16.5 g of Monomer M-4, 4.8 g of 4-hydroxystyrene, and 40 g of THF solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-18. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00236##

Synthesis Example 2-19

[0229] Synthesis of Polymer P-19

[0230] A 2-L flask was charged with 17.5 g of Monomer M-5, 4.8 g of 4-hydroxystyrene, and 40 g of THE solvent. The reactor was cooled at −70° C., in a nitrogen atmosphere, after which vacuum pumping and nitrogen blow were repeated three times. The reactor was warmed up to room temperature, whereupon 1.2 g of AIBN initiator was added. The reactor was heated at 60° C., and held at the temperature for 15 hours for reaction. The reaction solution was poured into 1 L of IPA for precipitation. The resulting white solid was collected by filtration and dried in vacuum at 60° C., obtaining Polymer P-19. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00237##

Comparative Synthesis Example 1

[0231] Synthesis of Comparative Polymer cP-1

[0232] Comparative Polymer cP-1 was synthesized by the same procedure as in Synthesis Example 2-1 except that 1-methyl-1-cyclopentyl methacrylate was used instead of Monomer M-1. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00238##

Comparative Synthesis Example 2

[0233] Synthesis of Comparative Polymer cP-2

[0234] Comparative Polymer cP-2 was synthesized by the same procedure as in Synthesis Example 2-6 aside from omitting Monomer M-3. The polymer was analyzed by NMR spectroscopy and GPC.

##STR00239##

[3] Preparation and Evaluation of Positive Resist Compositions

Examples 1 to 19 and Comparative Examples 1, 2

(1) Preparation of Positive Resist Compositions

[0235] Positive resist compositions were prepared by dissolving the selected components in a solvent in accordance with the recipe shown in Table 1, and filtering through a filter having a pore size of 0.2 μm. The solvent contained 50 ppm of surfactant PolyFox PF-636 (Omnova Solutions Inc.).

[0236] The components in Table 1 are as identified below.

Organic Solvents:

[0237] PGMEA (propylene glycol monomethyl ether acetate)

[0238] DAA (diacetone alcohol)

[0239] EL (ethyl lactate)

Acid Generators: PAG-1, PAG-2

[0240] ##STR00240##

Quenchers: Q-1 to Q-3

[0241] ##STR00241##

(2) EUV lithography test

[0242] Each of the positive resist compositions in Table 1 was spin coated on a silicon substrate having a 20 nm coating of silicon-containing spin-on hard mask SHB-A940 (Shin-Etsu Chemical Co., Ltd., silicon content 43 wt %) and prebaked on a hotplate at 105° C. for 60 seconds to form a resist film of 60 nm thick Using an EUV scanner NXE3300 (ASML, NA 0.33, v 0.9/0.6, quadrupole illumination), the resist film was exposed to EUV through a mask bearing a hole pattern having a pitch (on-wafer size) of 46 nm+20% bias. The resist film was baked (PEB) on a hotplate at the temperature shown in Table 1 for 60 seconds and developed in a 2.38 wt % TMAH aqueous solution for 30 seconds to form a hole pattern having a size of 23 nm.

[0243] The resist pattern was observed under CD-SEM (CG-5000, Hitachi High-Technologies Corp.). The exposure dose that provides a hole pattern of 23 nm size is reported as sensitivity. The size of 50 holes was measured, from which a 3-fold value (3σ) of standard deviation (σ) was computed and reported as CDU.

[0244] The resist composition is shown in Table 1 together with the sensitivity and CDU of EUV lithography.

TABLE-US-00001 TABLE 1 Base polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm.sup.2) (nm) Example 1 P-1 PAG-1 Q-1 PGMEA (2,000) 90 31 2.9 (100) (25.0) (6.51) DAA (500) 2 P-2 PAG-1 Q-1 PGMEA (2,000) 85 34 2.7 (100) (25.0) (6.51) DAA (500) 3 P-3 PAG-1 Q-1 PGMEA (2,000) 85 36 2.8 (100) (25.0) (6.51) DAA (500) 4 P-4 — Q-2 PGMEA (2,000) 95 31 2.3 (100) (4.72) DAA (500) 5 P-5 — Q-2 EL (2,000) 95 33 2.4 (100) (4.72) DAA (500) 6 P-6 — Q-2 EL (2,000) 95 31 2.2 (100) (4.72) DAA (500) 7 P-7 — Q-2 EL (2,000) 95 29 2.2 (100) (4.72) DAA (500) 8 P-8 — Q-2 PGMEA (500) 95 33 2.2 (100) (4.72) EL (1,500) DAA (500) 9 P-9 — Q-3 PGMEA (2,000) 95 32 2.2 (100) (4.54) DAA (500) 10 P-10 PAG-2 Q-2 PGMEA (2,000) 95 28 2.6 (100) (25.0) (4.72) DAA (500) 11 P-11 PAG-1 Q-1 PGMEA (2,000) 85 32 2.7 (100) (25.0) (6.51) DAA (500) 12 P-12 PAG-1 Q-1 PGMEA (2,000) 85 33 2.8 (100) (25.0) (6.51) DAA (500) 13 P-13 PAG-2 Q-2 PGMEA (2,000) 85 32 2.6 (100) (25.0) (4.72) DAA (500) 14 P-14 PAG-1 Q-1 PGMEA (2,000) 85 33 2.7 (100) (25.0) (6.51) DAA (500) 15 P-15 PAG-1 Q-1 PGMEA (2,000) 85 30 2.8 (100) (25.0) (6.51) DAA (500) 16 P-16 PAG-1 Q-1 PGMEA (2,000) 85 29 2.8 (100) (25.0) (6.51) DAA (500) 17 P-17 PAG-1 Q-1 PGMEA (2,000) 85 28 2.9 (100) (25.0) (6.51) DAA (500) 18 P-18 PAG-1 Q-1 PGMEA (2,000) 85 28 2.8 (100) (25.0) (6.51) DAA (500) 19 P-19 PAG-1 Q-1 PGMEA (2,000) 85 27 2.9 (100) (25.0) (6.51) DAA (500) Comparative 1 cP-1 PAG-1 Q-2 PGMEA (2,000) 90 33 4.6 Example (100) (25.0) (4.72) DAA (500) 2 cP-2 — Q-2 PGMEA (2,000) 95 35 3.3 (100) (4.72) DAA (500)

[0245] It is demonstrated in Table 1 that positive resist compositions comprising a base polymer comprising repeat units (a) having a carboxy group whose hydrogen is substituted by a nitrobenzene ring-containing tertiary hydrocarbyl group have a high sensitivity and form patterns with improved CDU.

[0246] Japanese Patent Application No. 2021-090241 is incorporated herein by reference.

[0247] Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.