ONIUM SALT, RESIST COMPOSITION, AND PATTERN FORMING PROCESS

Abstract

A chemically amplified resist composition is provided which is excellent in LWR and resolution and can prevent a resist pattern from collapsing in far ultraviolet lithography and EUV lithography, an onium salt for use therein, and a pattern forming process using the resist composition. The chemically amplified resist composition includes an onium salt having the following formula (1).

##STR00001##

Claims

1. An onium salt having the following formula (1): ##STR00357## wherein n1 is an integer of 0 to 6, n2 is an integer of 0 to 3, n3 is an integer of 1 to 4, W is a C.sub.2-C.sub.20 nitrogen atom-containing aliphatic heterocyclic ring which may contain a heteroatom, L.sup.A and L.sup.B are each independently a single bond, an ether bond, an ester bond, an amide bond, a sulfonic acid ester bond, a carbonate bond, or a carbamate bond, X.sup.L is a single bond or a C.sub.1-C.sub.40 hydrocarbylene group which may contain a heteroatom, R.sup.1 is a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, when n12, a plurality of R.sup.1's may bond together to form a ring with the carbon atom on W to which they are attached, Q.sup.1 to Q.sup.4 are each independently a hydrogen atom, a fluorine atom, a C.sub.1-C.sub.6 hydrocarbyl group, or a C.sub.1-C.sub.6 fluorinated hydrocarbyl group, provided that at least one of Q.sup.1 to Q.sup.4 is a fluorine atom or a C.sub.1-C.sub.6 fluorinated hydrocarbyl group, Q.sup.3 and Q.sup.4 may bond together to form a ring with the carbon atom to which they are attached, R.sup.AL is an acid labile group, and Z.sup.+ is an onium cation.

2. The onium salt according to claim 1, wherein R.sup.AL is a group having the following formula (AL-1) or (AL-2): ##STR00358## wherein LC is-Oor S, R.sup.2, R.sup.3, and R.sup.4 are each independently a C.sub.1-C.sub.10 hydrocarbyl group, any two of R.sup.2, R.sup.3, and R.sup.4 may bond together to form a ring with the carbon atom to which they are attached, R.sup.5 and R.sup.6 are each independently a hydrogen atom or a C.sub.1-C.sub.10 hydrocarbyl group, R.sup.7 is a C.sub.1-C.sub.20 hydrocarbyl group, some of CH.sub.2in the hydrocarbyl group may be replaced by O or S, R.sup.6 and R.sup.7 may bond together to form a C.sub.3-C.sub.20 heterocyclic group with the carbon atom and LC to which they are attached, some of CH.sub.2in the heterocyclic group may be replaced by Oor S, m1 and m2 are each independently 0 or 1, and * designates a point of attachment to the adjacent O.

3. The onium salt according to claim 1, wherein Z.sup.+ is a sulfonium cation having the following formula (cation-1), an iodonium cation having the following formula (cation-2), or an ammonium cation having the following formula (cation-3): ##STR00359## wherein R.sup.11 to R.sup.19 are each independently a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom, and R.sup.11 and R.sup.12 may bond together to form a ring with the sulfur atom to which they are attached.

4. The onium salt according to claim 1, which has the following formula (1A): ##STR00360## wherein n1 to n3, W, L.sup.A, X.sup.L, R.sup.1, Q to Q.sup.4, R.sup.AL, and Z.sup.+ are as defined above.

5. The onium salt according to claim 4, which has the following formula (1B): ##STR00361## wherein n1, W, L.sup.A, X.sup.L, R.sup.1, Q to Q.sup.3, R.sup.AL, and Z.sup.+ are as defined above.

6. A quencher comprising the onium salt according to claim 1.

7. A resist composition comprising the quencher according to claim 6.

8. The resist composition according to claim 7, further comprising an organic solvent.

9. The resist composition according to claim 7, further comprising a base polymer comprising repeat units having the following formula (a1): ##STR00362## wherein R.sup.A is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, X.sup.1 is a single bond, a phenylene group, a naphthylene group, or *C(O)OX.sup.11, the phenylene group or the naphthylene group may be substituted with a C.sub.1-C.sub.10 alkoxy group which may contain a fluorine atom, or a halogen atom, X.sup.11 is a C.sub.1-C.sub.10 saturated hydrocarbylene group, a phenylene group, or a naphthylene group, the saturated hydrocarbylene group may contain a hydroxy group, an ether bond, an ester bond, or a lactone ring, * designates a point of attachment to the carbon atom in the backbone, and AL.sup.1 is an acid labile group.

10. The resist composition according to claim 9, wherein the base polymer further comprises repeat units having the following formula (a2): ##STR00363## wherein R.sup.A is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, X.sup.2 is a single bond or *C(O)O, * designates a point of attachment to the carbon atom in the backbone, R.sup.21 is a halogen atom, a cyano group, a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, a C.sub.1-C.sub.20 hydrocarbyloxy group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyl group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyloxy group which may contain a heteroatom, or a C.sub.2-C.sub.20 hydrocarbyloxycarbonyl group which may contain a heteroatom, AL.sup.2 is an acid labile group, and a is an integer of 0 to 4.

11. The resist composition according to claim 9, wherein the base polymer further comprises repeat units having the following formula (b1) or (b2): ##STR00364## wherein R.sup.A is each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, Y.sup.1 is a single bond or *C(O)O, * designates a point of attachment to the carbon atom in the backbone, R.sup.22 is a hydrogen atom or a C.sub.1-C.sub.20 group containing at least one or more structures selected from a hydroxy group other than a phenolic hydroxy group, a cyano group, a carbonyl group, a carboxy group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, and a carboxylic anhydride (C(O)OC(O)), R.sup.23 is a halogen atom, a nitro group, a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, a C.sub.1-C.sub.20 hydrocarbyloxy group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyl group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyloxy group which may contain a heteroatom, or a C.sub.2-C.sub.20 hydrocarbyloxycarbonyl group which may contain a heteroatom, b is an integer of 1 to 4, and c is an integer of 0 to 4, provided that b+c is from 1 to 5.

12. The resist composition according to claim 9, wherein the base polymer further comprises repeat units having any one of the following formulae (c1) to (c4): ##STR00365## wherein R.sup.A is each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group, Z.sup.1 is a single bond or a phenylene group, Z.sup.2 is *C(O)OZ.sup.21, *C(O)NHZ.sup.21, or *OZ.sup.21, Z.sup.21 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, a phenylene group, or a divalent group obtained by combining the foregoing, which may contain a carbonyl group, an ester bond, an ether bond, or a hydroxy group, Z.sup.3 is each independently a single bond, a phenylene group, a naphthylene group, or *C(O)OZ.sup.31, Z.sup.31 is a C.sub.1-C.sub.10 aliphatic hydrocarbylene group, a phenylene group, or a naphthylene group, the aliphatic hydrocarbylene group may contain a hydroxy group, an ether bond, an ester bond, or a lactone ring, Z.sup.4 is each independently a single bond, *Z.sup.41C(O)O, *C(O)NHZ.sup.41, or *OZ.sup.41, Z.sup.41 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, Z.sup.5 is each independently a single bond, *Z.sup.31C(O)O, *C(O)NHZ.sup.51, or *OZ.sup.51, Z.sup.51 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, Z.sup.6 is a single bond, a methylene group, an ethylene group, a phenylene group, a fluorinated phenylene group, a trifluoromethyl group-substituted phenylene group, *C(O)OZ.sup.61, *C(O)N(H)Z.sup.61, or *OZ.sup.61, Z.sup.61 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, a phenylene group, a fluorinated phenylene group, or a trifluoromethyl group-substituted phenylene group, which may contain a carbonyl group, an ester bond, an ether bond, or a hydroxy group, * designates a point of attachment to the carbon atom in the backbone, R.sup.31 and R.sup.32 are each independently a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, R.sup.31 and R.sup.32 may bond together to form a ring with the sulfur atom to which they are attached, L.sup.1 is a single bond, an ether bond, an ester bond, a carbonyl group, a sulfonic acid ester bond, a carbonate bond, or a carbamate bond, Rf.sup.1 and Rf.sup.2 are each independently a fluorine atom or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, Rf.sup.3 and Rf.sup.4 are each independently a hydrogen atom, a fluorine atom, or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, Rf.sup.5 and Rf.sup.6 are each independently a hydrogen atom, a fluorine atom, or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, provided that all Rf.sup.5 and Rf.sup.6 are not a hydrogen atom at the same time, M.sup. is a non-nucleophilic counter ion, A.sup.+ is an onium cation, and d is an integer of 0 to 3.

13. The resist composition according to claim 7, further comprising a photoacid generator.

14. The resist composition according to claim 7, further comprising a quencher other than the quencher.

15. The resist composition according to claim 7, further comprising a surfactant.

16. A pattern forming process comprising the steps of: applying the resist composition according to claim 7 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.

17. The pattern forming process according to claim 16, wherein the high-energy radiation is KrF excimer laser, ArF excimer laser, EB, or EUV of wavelength 3 to 15 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] FIG. 1 is a .sup.1H-NMR spectrum of Onium Salt NSQ-1 obtained in Example 1-1.

DETAILED DESCRIPTION OF THE INVENTION

[Onium Salt]

[0089] An onium salt of the present invention has the following formula (1).

##STR00011##

[0090] In formula (1), n1 is an integer of 0 to 6. n2 is an integer of 0 to 3, preferably 0 or 1. n3 is an integer of 1 to 4, preferably 1 or 2, more preferably 1.

[0091] In formula (1), W is a C.sub.2-C.sub.20 nitrogen atom-containing aliphatic heterocyclic ring which may contain a heteroatom. Specific examples of the structure of W are shown below, but not limited thereto. In the following formula, * designates a point of attachment to L.sup.A, and ** designates a point of attachment to R.sup.ALOC(O).

##STR00012##

[0092] In formula (1), L.sup.A and L.sup.B are each independently a single bond, an ether bond, an ester bond, an amide bond, a sulfonic acid ester bond, a carbonate bond, or a carbamate bond. Of these, a single bond, an ether bond, an ester bond, or an amide bond is preferable, and a single bond, an ester bond, or an amide bond is more preferable.

[0093] In formula (1), X.sup.L is a single bond or a C.sub.1-C.sub.40 hydrocarbylene group which may contain a heteroatom. The hydrocarbylene group may be straight, branched, or cyclic, and specific examples thereof include an alkanediyl group and a cyclic saturated hydrocarbylene group. Specific examples of the heteroatom include an oxygen atom, a nitrogen atom, and a sulfur atom.

[0094] Specific examples of the C.sub.1-C.sub.40 hydrocarbylene group, which may contain a heteroatom, represented by X.sup.L are shown below, but not limited thereto. In the following formula, * designates a point of attachment to L.sup.A and L.sup.B.

##STR00013## ##STR00014## ##STR00015## ##STR00016##

[0095] Of these, X.sup.L-0 to X.sup.L-22 and X.sup.L-47 to X.sup.L-49 are preferable, and X.sup.L-0 to X.sup.L-17 are more preferable.

[0096] In formula (1), R.sup.1 is a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include C.sub.1-C.sub.20 alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a n-pentyl group, a tert-pentyl group, a n-hexyl group, a n-octyl group, a 2-ethylhexyl group, a n-nonyl group, and a n-decyl group; C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups such as a cyclopentyl group, a cyclohexyl group, a cyclopentylmethyl group, a cyclopentylethyl group, a cyclopentylbutyl group, a cyclohexylmethyl group, a cyclohexylethyl group, a cyclohexylbutyl group, a norbornyl group, a tricyclo[5.2.1.02.6]decyl group, an adamantyl group, and an adamantylmethyl group; C.sub.6-C.sub.20 aryl groups such as a phenyl group, a naphthyl group, and an anthryl group; and groups obtained by combining these. Some or all of the hydrogen atoms in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2 in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a carbamate bond, an amide bond, an imide bond, a lactone ring, a sultone ring, a thiolactone ring, a lactam ring, a sultam ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like.

[0097] When n12, a plurality of R.sup.1's may bond together to form a ring with the carbon atom on W to which they are attached. Specific examples of the ring formed at this time include a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring, a norbornane ring, and an adamantane ring. Some or all of the hydrogen atoms in the ring may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2 in the ring may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like. Two R.sup.1's bonded to the same atom forming W may bond together to form a ring, thereby forming a spiro ring.

[0098] In formula (1), Q.sup.1 to Q.sup.4 are each independently a hydrogen atom, a fluorine atom, a C.sub.1-C.sub.6 hydrocarbyl group, or a C.sub.1-C.sub.6 fluorinated hydrocarbyl group. Provided that at least one of Q.sup.1 to Q.sup.4 is a fluorine atom or a C.sub.1-C.sub.6 fluorinated hydrocarbyl group. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include those having 1 to 6 carbon atoms among those exemplified for the C.sub.1-C.sub.20 hydrocarbyl group represented by R.sup.1. A C.sub.1-C.sub.6 fluorinated hydrocarbyl group is preferably a trifluoromethyl group. Q.sup.3 and Q.sup.4 may bond together to form a ring with the carbon atom to which they are attached. Specific examples of the ring formed at this time include a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring, a norbornane ring, and an adamantane ring.

[0099] In formula (1), R.sup.AL is an acid labile group. Specifically, R.sup.AL is preferably a group having the following formula (AL-1) or (AL-2).

##STR00017## [0100] wherein * designates a point of attachment to the adjacent O.

[0101] In formula (AL-2), LC is-O or S.

[0102] In formula (AL-1), R.sup.2, R.sup.3, and R.sup.4 are each independently a C.sub.1-C.sub.10 hydrocarbyl group. Any two of R.sup.2, R.sup.3, and R.sup.4 may bond together to form a ring with the carbon atom to which they are attached. m1 is 0 or 1.

[0103] In formula (AL-2), R.sup.5 and R.sup.6 are each independently a hydrogen atom or a C.sub.1-C.sub.10 hydrocarbyl group. R.sup.7 is a C.sub.1-C.sub.20 hydrocarbyl group, some of CH.sub.2 in the hydrocarbyl group may be replaced by O or S. R.sup.6 and R.sup.7 may bond together to form a C.sub.3-C.sub.20 heterocyclic group with the carbon atom and LC to which they are attached, some of CH.sub.2 in the heterocyclic group may be replaced by O or S. m2 is 0 or 1.

[0104] Specific examples of the acid labile group having formula (AL-1) are shown below, but not limited thereto. In the following formula, * designates a point of attachment to the adjacent O.

##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022## ##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028## ##STR00029##

[0105] Specific examples of the acid labile group having formula (AL-2) are shown below, but not limited thereto. In the following formula. * designates a point of attachment to the adjacent O.

##STR00030## ##STR00031## ##STR00032##

[0106] The onium salt having formula (1) preferably has the following formula (1A).

##STR00033## [0107] wherein n1 to n3, W, L.sup.A, X.sup.L, R.sup.1, Q.sup.1 to Q.sup.4, R.sup.AL, and Z.sup.+ are as defined above.

[0108] The onium salt having formula (1A) preferably has the following formula (1B).

##STR00034## [0109] wherein n1, W, L.sup.A, X.sup.L, R.sup.1, Q.sup.1 to Q.sup.3, R.sup.AL, and Z.sup.+ are as defined above.

[0110] Specific examples of the anion of the onium salt having formula (1) are shown below, but not limited thereto.

##STR00035## ##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040## ##STR00041## ##STR00042## ##STR00043## ##STR00044## ##STR00045##

##STR00046## ##STR00047## ##STR00048## ##STR00049## ##STR00050## ##STR00051## ##STR00052## ##STR00053## ##STR00054## ##STR00055## ##STR00056## ##STR00057## ##STR00058## ##STR00059## ##STR00060## ##STR00061## ##STR00062## ##STR00063## ##STR00064## ##STR00065## ##STR00066## ##STR00067## ##STR00068## ##STR00069## ##STR00070## ##STR00071## ##STR00072## ##STR00073## ##STR00074## ##STR00075## ##STR00076## ##STR00077## ##STR00078## ##STR00079## ##STR00080##

[0111] In formula (1). Z.sup.+ is an onium cation. The onium cation is preferably a sulfonium cation having the following formula (cation-1), an iodonium cation having the following formula (cation-2), or an ammonium cation having the following formula (cation-3):

##STR00081##

[0112] In formulae (cation-1) to (cation-3), R.sup.11 to R.sup.19 are each independently a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include C.sub.1-C.sub.30 alkyl groups such as a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, and a tert-butyl group; C.sub.3-C.sub.30 cyclic saturated hydrocarbyl groups such as a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a cyclopropylmethyl group, a 4-methylcyclohexyl group, a cyclohexylmethyl group, a norbornyl group, and an adamantyl group; C.sub.2-C.sub.30 alkenyl groups such as a vinyl group, an allyl group, a propenyl group, a butenyl group, and a hexenyl group; C.sub.3-C.sub.30 cyclic unsaturated hydrocarbyl groups such as a cyclohexenyl group; C.sub.6-C.sub.30 aryl groups such as a phenyl group, a naphthyl group, and a thienyl group; C.sub.7-C.sub.30 aralkyl groups such as a benzyl group, a 1-phenylethyl group, and a 2-phenylethyl group; and groups obtained by combining these, and an aryl group is preferable. Some or all of the hydrogen atoms in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2 in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like.

[0113] R.sup.11 and R.sup.12 may bond together to form a ring with the sulfur atom to which they are attached. Specific examples of the sulfonium cation having formula (cation-1) are those having the following formula.

##STR00082## [0114] wherein the broken line denotes a point of attachment to R.sup.13.

[0115] Specific examples of the cation of the sulfonium salt having formula (cation-1) are shown below, but not limited thereto.

##STR00083## ##STR00084## ##STR00085## ##STR00086## ##STR00087## ##STR00088## ##STR00089## ##STR00090## ##STR00091## ##STR00092## ##STR00093## ##STR00094## ##STR00095## ##STR00096## ##STR00097## ##STR00098## ##STR00099## ##STR00100## ##STR00101## ##STR00102## ##STR00103## ##STR00104## ##STR00105## ##STR00106## ##STR00107## ##STR00108## ##STR00109##

##STR00110## ##STR00111## ##STR00112## ##STR00113## ##STR00114## ##STR00115## ##STR00116## ##STR00117## ##STR00118## ##STR00119## ##STR00120## ##STR00121## ##STR00122## ##STR00123## ##STR00124## ##STR00125## ##STR00126## ##STR00127## ##STR00128## ##STR00129## ##STR00130## ##STR00131## ##STR00132## ##STR00133##

[0116] Specific examples of the iodonium cation having formula (cation-2) are shown below, but not limited thereto.

##STR00134## ##STR00135## ##STR00136##

[0117] Specific examples of the ammonium cation having formula (cation-3) are shown below, but not limited thereto.

##STR00137##

[0118] Specific examples of the onium salt of the present invention include arbitrary combinations of anions with cations, both as exemplified above.

[0119] The onium salt of the present invention can be synthesized by a known method. As an example, a method for producing an onium salt having the following formula (NSQ-1-ex) is described.

##STR00138## [0120] wherein n1 to n3, W, L.sup.A, X.sup.L, R.sup.1, Q.sup.1 to Q.sup.4, R.sup.AL, and Z.sup.+ are as defined above, RX is a group forming a primary or secondary ester with the adjacent CO.sub.2, M.sup.+ is a counter cation, and X.sup. is a counter anion.

[0121] The first step is to produce Intermediate In-1-ex by reaction between Raw Material SM-1 and Raw Material SM-2, which is commercially available or can be synthesized by a known synthesis method. Various condensing agents can be used when an ester bond is formed directly from the carboxy group in Raw Material SM-1 and the hydroxy group in Raw Material SM-2. Examples of the condensing agent to be used include N,N-dicyclohexylcarbodiimide, N,N-diisopropylcarbodiimide, 1-[3-(dimethylamino) propyl]-3-ethylcarbodiimide, and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride, and from the viewpoint of easy removal of a urea compound formed as the by-product after the reaction, it is preferred to use 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride. The reaction is performed by dissolving Raw Material SM-1 and Raw Material SM-2 in a halogen-based solvent such as methylene chloride and adding a condensing agent. The reaction rate can be improved by adding 4-dimethylaminopyridine as a catalyst. The reaction time is determined as appropriate by monitoring the reaction process by silica gel thin layer chromatography (TLC) because it is desirable from the yield aspect to drive the reaction to completion, but the reaction time is usually about 12 to 24 hours. After stopping the reaction, if necessary, the urea compound produced as a by-product is removed by filtration or water washing, and then the reaction solution is subjected to ordinary aqueous work-up, whereby Intermediate In-1-ex can be obtained. The resulting Intermediate In-1-ex can be purified by a conventional method such as distillation, chromatography, or recrystallization, if necessary.

[0122] The second step is to obtain Intermediate In-2-ex by subjecting Intermediate In-1-ex to alkaline hydrolysis. Specifically, this is a step of obtaining Intermediate In-2-ex, which is a carboxylate salt, by subjecting the carboxylic acid ester in Intermediate In-1-ex to alkaline hydrolysis using an alkali metal hydroxide salt or a hydroxide salt of an organic cation. Examples of the alkali metal hydroxide salt to be used include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the hydroxide salt of an organic cation include tetramethylammonium hydroxide and benzyltrimethylammonium hydroxide. The reaction is performed by dissolving Intermediate In-1-ex in an ether-based solvent such as tetrahydrofuran or 1,4-dioxane, and adding aqueous solutions of various hydroxide salts. The reaction time is determined as appropriate by monitoring the reaction process by silica gel thin layer chromatography (TLC) because it is desirable from the yield aspect to drive the reaction to completion, but the reaction time is usually about 12 to 24 hours. Intermediate In-2-ex can be obtained by subjecting the reaction mixture to ordinary aqueous work-up. The resulting Intermediate In-2-ex can be purified by a conventional method such as chromatography, or recrystallization, if necessary.

[0123] The third step is to obtain Onium Salt NSQ-1-ex by subjecting the resulting Intermediate In-2-ex to salt exchange with an onium salt represented by Z.sup.+X.sup.. As X.sup., a chloride ion, a bromide ion, an iodide ion, or a methylsulfate anion is preferable because the exchange reaction easily proceeds in a quantitative manner. It is preferred from the yield aspect to monitor the progress of reaction by silica gel thin layer chromatography (TLC). Onium Salt NSQ-1-ex can be obtained by subjecting the reaction mixture to ordinary aqueous work-up. The resulting Onium Salt NSQ-1-ex can be purified by a conventional method such as chromatography, or recrystallization, if necessary.

[0124] In the above scheme, the ion exchange in the third step may be readily performed by a known method, for example, with reference to JP-A 2007-145797.

[0125] The producing method is merely exemplary and the method for producing an onium salt of the present invention is not limited thereto.

[Quencher]

[0126] The onium salt of the present invention is useful as a quencher. In the present invention, the quencher is a material capable of trapping the acid generated by the photoacid generator in the resist composition to prevent the acid from diffusing to the unexposed area, for thereby forming a desired pattern.

[0127] When the onium salt of the present invention and an onium salt capable of generating strong acid such as -fluorinated sulfonic acid, imide acid, or methide acid are co-present, a corresponding carboxylic acid and strong acid generate upon light exposure. On the other hand, in the region receiving a reduced exposure dose, much onium salt remains undecomposed. The strong acid functions as a catalyst for inducing deprotection reaction to the acid labile group of the base polymer whereas the onium salt of the present invention induces little deprotection reaction. The strong acid undergoes ion exchange with the residual carboxylic acid sulfonium salt, is converted into a strong acid onium salt and instead, carboxylic acid is released. Differently stated, through ion exchange, the strong acid is neutralized with the carboxylic acid onium salt. That is, the onium salt of the present invention functions as a quencher. This onium salt type quencher tends to form a resist pattern with reduced LWR as compared with the conventional quenchers in the form of amine compounds.

[0128] Salt exchange between the strong acid and the carboxylic acid onium salt is infinitely repeated. The site where strong acid is generated at the end of exposure is different from the site where the onium salt of strong acid generation type is initially present. It is believed that since the cycle of photo-acid generation and salt exchange is repeated many times, the points of acid generation are averaged, which leads to a resist pattern with reduced LWR after development.

[0129] As the material that exerts a quencher effect by a similar mechanism, for example, Patent Documents 1 to 6 describe a carboxylic acid onium salt, an alkanesulfonic acid onium salt, an arenesulfonic acid onium salt, an ,-difluorocarboxylic acid onium salt, and the like. With respect to the type of the onium salt, sulfonium salts, iodonium salts, or ammonium salts are included. On use of an alkanesulfonic acid onium salt or arenesulfonic acid onium salt, the generated acid has a certain acid strength so that part thereof may induce deprotection reaction as the acid generator rather than as the quencher, leading to a lowering of resolution performance and an increase of acid diffusion, which invite losses of resist performance factors like exposure latitude (EL) and mask error factor (MEF). Also, the ,-difluorocarboxylic acid onium salt as described in Patent Document 6, despite a carboxylic acid onium salt, has possibility to provoke deprotection reaction depending on a choice of acid labile group on the base polymer, for the reason that the generated acid has a relatively high acidity like the sulfonic acid onium salt, due to the inclusion of a fluorine atom at -position of the carboxylate anion. Fluorocarboxylic acid onium salts obtained by simply extending the straight chain similarly allow for substantial acid diffusion and undergo salt exchange with strong acid in the unexposed area, probably leading to losses of resolution, EL, and MEF. The alkanecarboxylic acid onium salt is highly hydrophilic though it functions as a quencher. The fluoroalkanecarboxylic acid onium salt as described in Patent Document 3 has a somewhat controlled level of hydrophilicity as compared with the non-fluorinated type, but the control of hydrophilicity is insufficient when the carbon count is small. Although some onium salts of perfluoroalkanecarboxylic acid having a larger carbon count are known, they are deemed incompatible with resist compositions because the carboxylic acids have surfactant-like physical properties. Incompatibility with resist compositions can cause defect formation. Additionally, perfluoroalkanecarboxylic acids are unfavorable from the biotic and environmental aspects.

[0130] Patent Documents 7 to 9 describe a carboxylic acid onium salt having indole or indoline as a nitrogen-containing heterocyclic compound and a piperidinecarboxylic acid structure, Patent Document 10 describes a carboxylic acid onium salt having an aminobenzoic acid structure, and Patent Document 11 describes a carboxylic acid onium salt having an amide bond. Although these also act as a quencher, since aromatic amines and amide bonds are not highly basic, and thus acid diffusion controllability is not sufficient, and piperidinecarboxylic acid has extremely high water solubility, the permeation of the alkaline developer into the unexposed area is promoted, and there is a concern that the resist pattern may collapse or peeling of the resist pattern from the substrate may occur.

[0131] The onium salt of the present invention can solve the above problems. An onium salt having a nitrogen atom-containing aliphatic heterocyclic ring and a fluorocarboxylic acid structure in an anion acts as a quencher, effectively traps the strong acid generated from an acid generator in the exposed area at a fluorocarboxylic acid anion site, and causes an acid labile group protecting the nitrogen atom-containing aliphatic heterocyclic site to undergo a deprotection reaction by the strong acid, thereby producing a nitrogen atom-containing aliphatic heterocyclic compound having high basicity. Since the deprotection reaction with an acid proceeds to form a nitrogen atom-containing aliphatic heterocyclic structure having high basicity, a fluorocarboxylic acid is formed in the exposed area, but the deprotection reaction of the base polymer is not caused. The nitrogen atom-containing aliphatic heterocyclic site having high basicity suppresses excessive diffusion of the acid into the unexposed area, and the carboxylic acid anion site continuously repeats proton exchange with the strong acid. It is considered that favorable lithographic performance can be achieved even in fine pattern formation by improving the dissolution contrast between the exposed area and the unexposed area and appropriately controlling the acid diffusion of the strong acid by these synergistic effects. Since the organic solvent solubility is improved by having an appropriate number of carbon atoms due to the fluorocarboxylic acid structure and the acid labile group protecting the nitrogen atom-containing aliphatic heterocyclic site, it is possible to effectively suppress the permeation of the alkaline developer into the unexposed area and the collapse and peeling of the resist pattern accompanying the permeation.

[Resist Composition]

[0132] The resist composition of the present invention comprises [0133] (A) a quencher comprising the onium salt having formula (1) as an essential component.

[0134] The content of the quencher (A) in the resist composition of the present invention is preferably 0.1 to 40 parts by weight and more preferably 1 to 20 parts by weight per 80 parts by weight of a base polymer (C) described below. When the content of the quencher (A) is in the above range, the quencher sufficiently functions as a quencher, and there is no possibility of performance deterioration such as deterioration in sensitivity or generation of foreign matter due to insufficient solubility.

[Organic Solvent (B)]

[0135] The resist composition of the present invention may comprise an organic solvent as a component (B). The organic solvent (B) is not particularly limited as long as the component (A) and each component described below can be dissolved. Specific examples of such an organic solvent include ketones such as cyclopentanone, cyclohexanone, and methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ketoalcohols such as diacetone alcohol (DAA); ethers such as propylene glycol monomethyl ether (PGME), ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; lactones such as -butyrolactone (GBL), and mixed solvents thereof.

[0136] Of the foregoing organic solvents, it is recommended to use PGME, PGMEA, cyclohexanone, GBL, DAA, ethyl lactate, and mixed solvents thereof because the base polymer of the component (C) is most soluble therein.

[0137] The content of the organic solvent (B) in the resist composition of the present invention is preferably 200 to 5000 parts by weight and more preferably 400 to 3500 parts by weight per 80 parts by weight of a base polymer (C) described below. The organic solvent (B) may be used alone or in admixture of two or more kinds thereof.

[Base Polymer (C)]

[0138] The resist composition of the present invention may comprise a base polymer as a component (C). The base polymer (C) comprises repeat units having the following formula (a1) (also referred to as repeat units a1, hereinafter).

##STR00139##

[0139] In formula (a1), R.sup.A is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. X.sup.1 is a single bond, a phenylene group, a naphthylene group, or *C(O)OX.sup.11, the phenylene group or the naphthylene group may be substituted with a C.sub.1-C.sub.10 alkoxy group which may contain a fluorine atom, or a halogen atom. X.sup.11 is a C.sub.1-C.sub.10 saturated hydrocarbylene group, a phenylene group, or a naphthylene group, the saturated hydrocarbylene group may contain a hydroxy group, an ether bond, an ester bond, or a lactone ring. * designates a point of attachment to the carbon atom in the backbone.

[0140] In formula (a1), AL.sup.1 is an acid labile group. Examples of the acid labile group include those groups described in JP-A 2013-80033 and JP-A 2013-83821.

[0141] Typical examples of the acid labile group include groups having the following formulae (AL-3) to (AL-5).

##STR00140## [0142] wherein the broken line denotes a point of attachment.

[0143] In formulae (AL-3) and (AL-4), R.sup.L1 and R.sup.L2 are each independently a C.sub.1-C.sub.40 saturated hydrocarbyl group, which may contain a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a fluorine atom. The saturated hydrocarbyl group may be straight, branched, or cyclic. The saturated hydrocarbyl group is preferably a C.sub.1-C.sub.20 saturated hydrocarbyl group.

[0144] In formula (AL-3), k is an integer of 0 to 10 and preferably an integer of 1 to 5.

[0145] In formula (AL-4), R.sup.L3 and R.sup.L4 are each independently a hydrogen atom or a C.sub.1-C.sub.20 saturated hydrocarbyl group, which may contain a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a fluorine atom. The hydrocarbylene group may be straight, branched, or cyclic. Any two of R.sup.L2, R.sup.L3, and R.sup.L4 may bond together to form a C.sub.3-C.sub.20 ring with the carbon atom or carbon and oxygen atoms to which they are attached. The ring is preferably a C.sub.4-C.sub.16 ring and particularly preferably an alicyclic ring.

[0146] In formula (AL-5), R.sup.L5, R.sup.L6, and R.sup.L7 are each independently a C.sub.1-C.sub.20 saturated hydrocarbyl group, which may contain a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a fluorine atom. The hydrocarbylene group may be straight, branched, or cyclic. Any two of R.sup.L5, R.sup.L6, and R.sup.L7 may bond together to form a C.sub.3-C.sub.20 ring with the carbon atom to which they are attached. The ring is preferably a C.sub.4-C.sub.16 ring and particularly preferably an alicyclic ring.

[0147] Specific examples of the repeat units a1 are shown below, but not limited thereto. In the following formula, R.sup.A and AL.sup.1 are as defined above.

##STR00141## ##STR00142## ##STR00143## ##STR00144## ##STR00145## ##STR00146##

[0148] The base polymer may further comprise repeat units having the following formula (a2) (also referred to as repeat units a2, hereinafter).

##STR00147##

[0149] In formula (a2), R.sup.A is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. X.sup.2 is a single bond or *C(O)O. * designates a point of attachment to the carbon atom in the backbone. R.sup.21 is a halogen atom, a cyano group, a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, a C.sub.1-C.sub.20 hydrocarbyloxy group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyl group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyloxy group which may contain a heteroatom, or a C.sub.2-C.sub.20 hydrocarbyloxycarbonyl group which may contain a heteroatom. AL.sup.2 is an acid labile group. Examples of the acid labile group are as exemplified above for the acid labile group represented by AL.sup.1. a is an integer of 0 to 4, preferably 0 or 1.

[0150] Specific examples of the repeat units a2 are shown below, but not limited thereto. In the following formula, R.sup.A and AL.sup.2 are as defined above.

##STR00148## ##STR00149## ##STR00150## ##STR00151##

[0151] The base polymer preferably further comprises repeat units having the following formula (b1) (also referred to as repeat units b1, hereinafter) or repeat units having the following formula (b2) (also referred to as repeat units b2, hereinafter).

##STR00152##

[0152] In formulae (b1) and (b2), R.sup.A is each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Y.sup.1 is a single bond or *C(O)O. * designates a point of attachment to the carbon atom in the backbone. R.sup.22 is a hydrogen atom or a C.sub.1-C.sub.20 group containing at least one or more structures selected from a hydroxy group other than a phenolic hydroxy group, a cyano group, a carbonyl group, a carboxy group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, and a carboxylic anhydride (C(O)OC(O)). R.sup.23 is a halogen atom, a nitro group, a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, a C.sub.1-C.sub.20 hydrocarbyloxy group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyl group which may contain a heteroatom, a C.sub.2-C.sub.20 hydrocarbylcarbonyloxy group which may contain a heteroatom, or a C.sub.2-C.sub.20 hydrocarbyloxycarbonyl group which may contain a heteroatom. b is an integer of 1 to 4. c is an integer of 0 to 4. Provided that b+c is from 1 to 5.

[0153] Specific examples of the repeat units b1 are shown below, but not limited thereto. In the following formula, R.sup.A is as defined above.

##STR00153## ##STR00154## ##STR00155## ##STR00156## ##STR00157## ##STR00158## ##STR00159## ##STR00160## ##STR00161## ##STR00162## ##STR00163## ##STR00164## ##STR00165## ##STR00166## ##STR00167## ##STR00168## ##STR00169##

##STR00170## ##STR00171## ##STR00172## ##STR00173## ##STR00174## ##STR00175## ##STR00176## ##STR00177## ##STR00178## ##STR00179## ##STR00180## ##STR00181## ##STR00182## ##STR00183## ##STR00184## ##STR00185## ##STR00186##

[0154] Specific examples of the repeat units b2 are shown below, but not limited thereto. In the following formula. R.sup.A is as defined above.

##STR00187## ##STR00188## ##STR00189## ##STR00190## ##STR00191## ##STR00192## ##STR00193## ##STR00194## ##STR00195##

[0155] As the repeat units b1 or b2, those units having a lactone ring as a polar group are particularly preferred in the case of ArF lithography, and those units having a phenol site as a polar group are preferred in the case of KrF lithography, EB lithography, and EUV lithography.

[0156] The base polymer may further comprise repeat units having any one of the following formulae (c1) to (c4) (also referred to as repeat units c1 to c4, hereinafter).

##STR00196##

[0157] In formulae (c1) to (c4), R.sup.A is each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Z.sup.1 is a single bond or a phenylene group. Z.sup.2 is *C(O)OZ.sup.21, *C(O)NHZ.sup.21, or *OZ.sup.21. Z.sup.21 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, a phenylene group, or a divalent group obtained by combining the foregoing, which may contain a carbonyl group, an ester bond, an ether bond, or a hydroxy group. Z.sup.3 is each independently a single bond, a phenylene group, a naphthylene group, or *C(O)OZ.sup.31. Z.sup.31 is a C.sub.1-C.sub.10 aliphatic hydrocarbylene group, a phenylene group, or a naphthylene group, the aliphatic hydrocarbylene group may contain a hydroxy group, an ether bond, an ester bond, or a lactone ring. Z.sup.4 is each independently a single bond, *Z.sup.41C(O)O, *C(O)NHZ.sup.41, or *OZ.sup.41. Z.sup.41 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. Z.sup.5 is each independently a single bond, *Z.sup.51C(O)O, *C(O)NHZ.sup.51, or *OZ.sup.51. 751 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. Z.sup.6 is a single bond, a methylene group, an ethylene group, a phenylene group, a fluorinated phenylene group, a trifluoromethyl group-substituted phenylene group, *C(O)OZ.sup.61, * C(O)N(H)Z.sup.61, or *OZ.sup.61. Z.sup.61 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, a phenylene group, a fluorinated phenylene group, or a trifluoromethyl group-substituted phenylene group, which may contain a carbonyl group, an ester bond, an ether bond, or a hydroxy group. * designates a point of attachment to the carbon atom in the backbone.

[0158] The aliphatic hydrocarbylene group represented by Z.sup.21, Z.sup.31, and Z.sup.61 may be straight, branched, or cyclic, and specific examples thereof include alkanediyl groups such as a methanediyl group, an ethane-1,1-diyl group, an ethane-1,2-diyl group, a propane-1,1-diyl group, a propane-1,2-diyl group, a propane-1,3-diyl group, a propane-2,2-diyl group, a butane-1,1-diyl group, a butane-1,2-diyl group, a butane-1,3-diyl group, a butane-2,3-diyl group, a butane-1,4-diyl group, a 1,1-dimethylethane-1,2-diyl group, a pentane-1,5-diyl group, a 2-methylbutane-1,2-diyl group, and a hexane-1,6-diyl group; cycloalkanediyl groups such as a cyclopropanediyl group, a cyclobutanediyl group, a cyclopentanediyl group, and a cyclohexanediyl group; and groups obtained by combining these.

[0159] The hydrocarbylene group represented by Z.sup.41 and Z.sup.51 may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are shown below, but not limited thereto.

##STR00197## [0160] wherein the broken line denotes a point of attachment.

[0161] In formula (c1), R.sup.31 and R.sup.32 are each independently a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include C.sub.1-C.sub.20 alkyl groups such as a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, and a tert-butyl group; C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups such as a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a cyclopropylmethyl group, a 4-methylcyclohexyl group, a cyclohexylmethyl group, a norbornyl group, and an adamantyl group; C.sub.2-C.sub.20 alkenyl groups such as a vinyl group, an allyl group, a propenyl group, a butenyl group, and a hexenyl group; C.sub.3-C.sub.20 cyclic unsaturated hydrocarbyl groups such as a cyclohexenyl group; C.sub.6-C.sub.20 aryl groups such as a phenyl group, a naphthyl group, and a thienyl group; aralkyl groups such as a benzyl group, a 1-phenylethyl group, and a 2-phenylethyl group; and groups obtained by combining these, and an aryl group is preferable. Some or all of the hydrogen atoms in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2 in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like.

[0162] R.sup.31 and R.sup.32 may bond together to form a ring with the sulfur atom to which they are attached. In this case, examples of the ring are as exemplified above for the ring that R.sup.11 and R.sup.12 in the description of formula (cation-1) may bond together to form with the sulfur atom to which they are attached.

[0163] Specific examples of the cation of the repeat units c1 are shown below, but not limited thereto. In the following formula, R.sup.A is as defined above.

##STR00198## ##STR00199## ##STR00200## ##STR00201## ##STR00202## ##STR00203## ##STR00204## ##STR00205## ##STR00206## ##STR00207## ##STR00208## ##STR00209## ##STR00210## ##STR00211##

[0164] In formula (c1), M.sup. is a non-nucleophilic counter ion. Specific examples of the non-nucleophilic counter ion include halide ions such as chloride ions and bromide ions; fluoroalkylsulfonate ions such as triflate ions, 1,1,1-trifluoroethanesulfonate ions, and nonafluorobutanesulfonate ions; arylsulfonate ions such as tosylate ions, benzenesulfonate ions, 4-fluorobenzenesulfonate ions, and 1,2,3,4,5-pentafluorobenzenesulfonate ions; alkylsulfonate ions such as mesylate ions and butanesulfonate ions; imide ions such as bis(trifluoromethylsulfonyl) imide ions, bis(perfluoroethylsulfonyl) imide ions, and bis(perfluorobutylsulfonyl) imide ions; and methide ions such as tris(trifluoromethylsulfonyl) methide ions and tris(perfluoroethylsulfonyl) methide ions.

[0165] Other specific examples of the non-nucleophilic counter ion include sulfonate anions having fluorine substituted at -position as represented by the following formula (c1-1) and sulfonate anions having fluorine substituted at -position and trifluoromethyl at -position as represented by the following formula (c1-2).

##STR00212##

[0166] In formula (c1-1), R.sup.33 is a hydrogen atom, a C.sub.1-C.sub.30 hydrocarbyl group, a C.sub.2-C.sub.30 hydrocarbylcarbonyloxy group, or a C.sub.2-C.sub.30 hydrocarbyloxycarbonyl group, and the hydrocarbyl group may contain, a halogen atom, an ether bond, an ester bond, a carbonyl group, or a lactone ring. The hydrocarbyl moiety of the hydrocarbyl group, the hydrocarbylcarbonyloxy group, and the hydrocarbyloxycarbonyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A) described below.

[0167] In formula (c1-2), R.sup.34 is a hydrogen atom, a C.sub.1-C.sub.30 hydrocarbyl group, or a C.sub.2-C.sub.30 hydrocarbylcarbonyl group, and the hydrocarbyl group and hydrocarbylcarbonyl group may contain a halogen atom, an ether bond, an ester bond, a carbonyl group, or a lactone ring. R.sup.35 is a hydrogen atom, a fluorine atom, or a C.sub.1-C.sub.6 fluorinated alkyl group. The hydrocarbyl moiety of the hydrocarbyl group and the hydrocarbylcarbonyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A) described below. R.sup.35 is preferably a trifluoromethyl group.

[0168] Specific examples of the sulfonate anion having formula (c1-1) or (c1-2) are shown below, but not limited thereto. In the following formula, R.sup.35 is as defined above, and Ac is an acetyl group.

##STR00213## ##STR00214## ##STR00215## ##STR00216## ##STR00217## ##STR00218## ##STR00219## ##STR00220## ##STR00221## ##STR00222##

[0169] In formulae (C.sub.2) and (C.sub.3). L is a single bond, an ether bond, an ester bond, a carbonyl group, a sulfonic acid ester bond, a carbonate bond, or a carbamate bond. Of these, from the viewpoint of synthesis, an ether bond, an ester bond, and a carbonyl group are preferable, and an ester bond and a carbonyl group are more preferable.

[0170] In formula (C.sub.2), Rf.sup.1 and Rf.sup.2 are each independently a fluorine atom or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. Of these, Rf.sup.1 and Rf.sup.2 are each preferably a fluorine atom in order to increase the acid strength of the generated acid. Rf.sup.3 and Rf.sup.4 are each independently a hydrogen atom, a fluorine atom, or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. Of these, at least one of Rf.sup.3 and Rf.sup.4 is preferably a trifluoromethyl group for improving solvent solubility.

[0171] In formula (C.sub.3), Rf.sup.5 and Rf.sup.6 are each independently a hydrogen atom, a fluorine atom, or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. Provided that all Rf.sup.5 and Rf.sup.6 are not a hydrogen atom at the same time. Of these, at least one of Rf.sup.5 and Rf.sup.6 is preferably a trifluoromethyl group for improving solvent solubility.

[0172] In formulae (C.sub.2) and (C.sub.3), d is an integer of 0 to 3, preferably 1.

[0173] Specific examples of the anion of the repeat units c2 are shown below, but not limited thereto. In the following formula, R.sup.A is as defined above.

##STR00223## ##STR00224## ##STR00225## ##STR00226## ##STR00227## ##STR00228## ##STR00229## ##STR00230## ##STR00231## ##STR00232## ##STR00233## ##STR00234## ##STR00235## ##STR00236## ##STR00237## ##STR00238## ##STR00239## ##STR00240## ##STR00241## ##STR00242##

[0174] Specific examples of the anion of the repeat units c3 are shown below, but not limited thereto. In the following formula. R.sup.A is as defined above.

##STR00243## ##STR00244## ##STR00245## ##STR00246## ##STR00247## ##STR00248## ##STR00249## ##STR00250## ##STR00251## ##STR00252## ##STR00253## ##STR00254## ##STR00255## ##STR00256## ##STR00257## ##STR00258## ##STR00259## ##STR00260## ##STR00261## ##STR00262## ##STR00263## ##STR00264## ##STR00265## ##STR00266## ##STR00267## ##STR00268## ##STR00269## ##STR00270##

[0175] Specific examples of the anion of the repeat units c4 are shown below, but not limited thereto. In the following formula. R.sup.A is as defined above.

##STR00271## ##STR00272##

[0176] In formulae (C.sub.2) to (C.sub.4), A.sup.+ is an onium cation. Examples of the onium cation include a sulfonium cation, an iodonium cation, and an ammonium cation, and a sulfonium cation and an iodonium cation are preferable. Specific structures thereof are as exemplified for the cations having formulae (cation-1) to (cation-3).

[0177] The repeat units c1 to c4 function as a photoacid generator. In the case of using the base polymer comprising the repeat units c1 to c4 (that is, polymer-bound acid generator), the resist composition of the present invention may or may not comprise a photoacid generator (D) described below.

[0178] The base polymer may further comprise repeat units having a structure having a hydroxy group protected with an acid labile group (also referred to as repeat units d, hereinafter). The repeat unit d is not particularly limited as long as the unit includes one or two or more structures having a hydroxy group protected with a protective group such that the protective group is decomposed to generate the hydroxy group under the action of acid, but repeat units having the following formula (d1) are preferable.

##STR00273##

[0179] In formula (d1), R.sup.A is as defined above. R.sup.41 is a C.sub.1-C.sub.30 (e+1)-valent hydrocarbon group which may contain a heteroatom. R.sup.42 is an acid labile group. e is an integer of 1 to 4.

[0180] In formula (d1), the acid labile group represented by R.sup.42 may be any group that is deprotected under the action of acid so that a hydroxy group is generated. The structure of R.sup.42 is not particularly limited, an acetal structure, a ketal structure, an alkoxycarbonyl group, an alkoxymethyl group having the following formula (d2), and the like are preferable, and an alkoxymethyl group having the following formula (d2) is particularly preferable.

##STR00274## [0181] wherein * designates a point of attachment, and R.sup.43 is a C.sub.1-C.sub.15 hydrocarbyl group.

[0182] Specific examples of the acid labile group represented by R.sup.42, the alkoxymethyl group having formula (d2), and the repeat units d are as exemplified for the repeat units d described in JP-A 2020-111564.

[0183] The base polymer may further include repeat units e derived from indene, benzofuran, benzothiophene, acenaphthylene, chromone, coumarin, norbornadiene, or derivatives thereof. Specific examples of the monomer from which repeat units e are derived are shown below, but not limited thereto.

##STR00275##

[0184] The base polymer may further comprise repeat units f derived from indane, vinylpyridine, or vinylcarbazole.

[0185] In the polymer of the present invention, the repeat units a1, a2, b1, b2, c1 to c4, d, e, and f are incorporated in a ratio of preferably 0<a10.8, 0a20.8, 0<a1+a20.8, 0b10.6, 0b20.6, 0b1+b20.6, 0c10.4, 0c20.4, 0c30.4, 0c40.4, 0c1+c2+c3+c40.4, 0d0.5, 0e0.3, and 0f0.3, more preferably 0<a10.7, 0a20.7, 0<a1+a20.7, 0b10.5, 0b20.5, 0b1+b20.5, 0c10.3, 0c20.3, 0c30.3, 0c40.3, 0c1+c2+c3+c40.3, 0d0.3, 0c0.3, and 0f0.3. Provided that a1+a2+b1+b2+c1+c2+c3+c4+d+c+f=1.0.

[0186] The weight average molecular weight (Mw) of the polymer is preferably 1000 to 500000 and more preferably 3000 to 100000. When Mw is in this range, sufficient etching resistance is obtained, and there is no possibility of degradation of resolution due to a failure to acquire a difference in dissolution rate before and after exposure. In the present invention, Mw is a value measured by gel permeation chromatography (GPC) with tetrahydrofuran (THF) or N,N-dimethylformamide (DMF) as a solvent, and calculated as polystyrene.

[0187] Since the influence of the molecular weight distribution (Mw/Mn) becomes stronger as the pattern rule becomes finer, the Mw/Mn of the polymer preferably has narrow dispersity of 1.0 to 2.0 in order to obtain a resist composition suitable for micropatterning to a small feature size. Within the above range, there is little polymer having a low molecular weight or a high molecular weight, and there is no possibility that foreign matter is observed on the pattern or the shape of the pattern is deteriorated after exposure.

[0188] In order to synthesize the polymer, for example, a monomer from which the foregoing repeat units are derived may be heated in an organic solvent with a radical polymerization initiator added thereto to perform polymerization.

[0189] Examples of the organic solvent used during polymerization include toluene, benzene, THF, diethyl ether, dioxane, cyclohexane, cyclopentane, methyl ethyl ketone (MEK), PGMEA, and GBL. Examples of the polymerization initiator include 2,2-azobisisobutyronitrile (AIBN), 2,2-azobis(2,4-dimethylvaleronitrile), dimethyl-2,2-azobis(2-methylpropionate), 1,1-azobis(1-acetoxy-1-phenylethane), benzoyl peroxide, and lauroyl peroxide. The initiator is preferably added in an amount of 0.01 to 25 mol % based on the total of monomers to be polymerized. The reaction temperature is preferably 50 to 150 C., more preferably 60 to 100 C. The reaction time is preferably 2 to 24 hours, more preferably 2 to 12 hours in viewpoint of production efficiency.

[0190] The polymerization initiator may be fed to the reactor either by adding the initiator to the monomer solution and feeding the solution to the reactor, or by dissolving the initiator in a solvent to form an initiator solution and feeding the initiator solution and the monomer solution independently to the reactor. Because of a possibility that in the standby duration, the initiator generates a radical which triggers polymerization reaction to form an ultra high-molecular-weight polymer, it is preferred from the viewpoint of quality control to prepare the monomer solution and the initiator solution separately and add them dropwise. The acid labile group that has been incorporated in the monomer may be kept as such, or polymerization may be followed by protection or partial protection. Any known chain transfer agent such as dodecyl mercaptan or 2-mercaptoethanol may be used in combination for molecular weight control purpose. In this case, these chain transfer agents are preferably added in an amount of 0.01 to 20 mol % based on the total of monomers to be polymerized.

[0191] In the case of a monomer containing a hydroxy group, the hydroxy group may be substituted with an acetal group susceptible to deprotection with an acid such as an ethoxyethoxy group during polymerization, and then deprotected by a weak acid and water, or may be substituted with an acetyl group, a formyl group, a pivaloyl group, or the like, and then alkaline hydrolysis may be performed after polymerization.

[0192] When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, hydroxystyrene or hydroxyvinylnaphthalene and another monomer may be heated and polymerized by adding a radical polymerization initiator in an organic solvent, but acetoxystyrene or acetoxyvinylnaphthalene may be used, and the acetoxy group may be deprotected by alkaline hydrolysis after polymerization to obtain polyhydroxystyrene or hydroxypolyvinylnaphthalenc.

[0193] As a base during the alkaline hydrolysis, aqueous ammonia, triethylamine, or the like can be used. The reaction temperature is preferably-20 to 100 C. and more preferably 0 to 60 C. The reaction time is preferably 0.2 to 100 hours and more preferably 0.5 to 20 hours.

[0194] The amount of each monomer in the monomer solution may be appropriately set, for example, so as to have a preferred content ratio of the repeat units.

[0195] Regarding the polymer obtained by the production method, a reaction solution resulting from polymerization reaction may be used as a final product, or a powder obtained through a purifying step such as re-precipitation method in which a polymerization liquid is added to a poor solvent to obtain a powder may be used as a final product, but from the viewpoints of operation efficiency and consistent quality, it is preferable to use a polymer solution obtained by dissolving the powder resulting from the purifying step in a solvent as a final product.

[0196] Specific examples of the solvent used at that time include ketones such as cyclohexanone and methyl-2-n-pentyl ketone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as PGME, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethyl ether, and diethylene glycol dimethyl ether; esters such as PGMEA, propylene glycol monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate, tert-butyl propionate, and propylene glycol mono-tert-butyl ether acetate; lactones such as GBL; alcohols such as DAA; high-boiling-point alcohol-based solvents such as diethylene glycol, propylene glycol, glycerin, 1,4-butanediol, and 1,3-butanediol; and a mixed solvent thereof, which are described in JP-A 2008-111103, paragraphs [0144] to [0145].

[0197] The polymer solution preferably has a polymer concentration of 0.01 to 30 wt %, more preferably 0.1 to 20 wt %.

[0198] The reaction solution or polymer solution is preferably filtered through a filter. Filtration is effective in terms of consistent quality because foreign matter and gel which may cause defects can be removed.

[0199] Examples of the material for the filter used for the filter filtration include fluorocarbon-based, cellulose-based, nylon-based, polyester-based, and hydrocarbon-based materials, and in the filtration step of the resist composition, a filter formed of a fluorocarbon-based material called Teflon, a hydrocarbon-based material such as polyethylene and polypropylene, or nylon is preferable. While the pore size of the filter may be selected appropriate to comply with the desired cleanness, the filter preferably has a pore size of 100 nm or less, more preferably 20 nm or less. A single filter may be used or a plurality of filters may be used in combination. Although the filtering method may be single pass of the solution, preferably the filtering step is repeated by flowing the solution in a circulating manner. In the polymer production step, the filtration step may be carried out any times, in any order and in any stage, but the reaction solution after the polymerization reaction or the polymer solution may be filtered, preferably both are filtered.

[0200] The base polymer (C) may be used alone or in combination of two or more polymers which are different in compositional ratio, Mw and/or Mw/Mn. The base polymer (C) may contain a hydrogenated ring-opened metathesis polymer in addition to the polymer, and as the hydrogenated ring-opened metathesis polymer, a polymer described in JP-A 2003-66612 can be used.

[Photoacid Generator (D)]

[0201] The resist composition of the present invention may comprise a photoacid generator as a component (D). The photoacid generator of the component (D) is not particularly limited as long as it is a compound capable of generating strong acid by irradiation with high-energy radiation. Specific examples of suitable photoacid generators include those having the following formula (2-1) or (2-2):

##STR00276##

[0202] In formulae (2-1) and (2-2), R.sup.101 to R.sup.105 are each independently a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom. Any two of R.sup.101, R.sup.102, and R.sup.103 may bond together to form a ring with the sulfur atom to which they are attached.

[0203] Specific examples of the sulfonium cation having formula (2-1) are exemplified above for the sulfonium cation having formula (cation-1), but not limited thereto. Specific examples of the iodonium cation having formula (2-2) are exemplified above for the iodonium cation having formula (cation-2), but not limited thereto.

[0204] In formulae (2-1) and (2-2), Xa.sup. is an anion selected from the following formulae (2A) to (2D).

##STR00277##

[0205] In formula (2A), R.sup.fa1 is a fluorine atom, or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A) described below.

[0206] The anion having formula (2A) preferably has the following formula (2A).

##STR00278##

[0207] In formula (2A), R.sup.HF represents a hydrogen atom or a trifluoromethyl group, is a hydrogen atom or a trifluoromethyl group, and preferably a trifluoromethyl group.

[0208] R.sup.fa1 is a C.sub.1-C.sub.38 hydrocarbyl group which may contain a heteroatom. The heteroatom is preferably an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom, or the like, and more preferably an oxygen atom. The hydrocarbyl group is particularly preferably a C.sub.6-C.sub.30 hydrocarbyl group from the viewpoint of obtaining a high resolution in fine pattern formation.

[0209] The C.sub.1-C.sub.38 hydrocarbyl group represented by R.sup.fa1 may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include C.sub.1-C.sub.38 alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a pentadecyl group, a heptadecyl group, and an icosyl group; C.sub.3-C.sub.38 cyclic saturated hydrocarbyl groups such as a cyclopentyl group, a cyclohexyl group, a 1-adamantyl group, a 2-adamantyl group, a 1-adamantylmethyl group, a norbornyl group, a norbornylmethyl group, a tricyclodecyl group, a tetracyclododecyl group, a tetracyclododecylmethyl group, and a dicyclohexylmethyl group; C.sub.2-C.sub.38 unsaturated aliphatic hydrocarbyl groups such as an allyl group and a 3-cyclohexenyl group; C.sub.6-C.sub.38 aryl groups such as a phenyl group, a 1-naphthyl group, and a 2-naphthyl group; C.sub.7-C.sub.38 aralkyl groups such as a benzyl group and a diphenylmethyl group; and groups obtained by combining these.

[0210] Some or all of the hydrogen atoms in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2 in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like. Specific examples of the heteroatom-containing hydrocarbyl group include a tetrahydrofuryl group, a methoxymethyl group, an ethoxymethyl group, a methylthiomethyl group, an acetamidomethyl group, a trifluoroethyl group, a (2-methoxyethoxy)methyl group, an acetoxymethyl group, a 2-carboxy-1-cyclohexyl group, a 2-oxopropyl group, a 4-oxo-1-adamantyl group, a 5-hydroxy-1-adamantyl group, a 5-tert-butylcarbonyloxy-1-adamantyl group, a 4-oxatricyclo[4.2.1.03.7]nonane-5-one-2-yl group, and a 3-oxocyclohexyl group.

[0211] With respect to the synthesis of the sulfonium salt having an anion of formula (2A), reference is made to JP-A 2007-145797, JP-A 2008-106045, JP-A 2009-7327, JP-A 2009-258695, and the like. Also useful are the sulfonium salts described in JP-A 2010-215608, JP-A 2012-41320, JP-A 2012-106986, JP-A 2012-153644, and the like.

[0212] Specific examples of the anion having formula (2A) are as exemplified for the anions having formulae (c1-1) and (c1-2).

[0213] In formula (2B), R.sup.fb1 and R.sup.fb2 are each independently a fluorine atom, or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A). Preferably, R.sup.fb1 and R.sup.fb2 each are a fluorine atom or a straight C.sub.1-C.sub.4 fluorinated alkyl group. R.sup.fb1 and R.sup.fb2 may bond together to form a ring with the group (CF.sub.2SO.sub.2N.sup.SO.sub.2CF.sub.2) to which they are attached, and in this case, the group obtained by bonding R.sup.fb1 and R.sup.fb2 to each other is preferably a fluorinated ethylene group or a fluorinated propylene group.

[0214] In formula (2C), R.sup.fc1, R.sup.fc2, and R.sup.fc3 are each independently a fluorine atom, or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A). Preferably, R.sup.fc1, R.sup.fc2, and R.sup.fc3 each are a fluorine atom or a straight C.sub.1-C.sub.4 fluorinated alkyl group. R.sup.fc1 and R.sup.fc2 may bond together to form a ring with the group (CF.sub.2SO.sub.2C.sup.SO.sub.2CF.sub.2) to which they are attached, and in this case, the group obtained by bonding R.sup.fc1 and R.sup.fc2 to each other is preferably a fluorinated ethylene group or a fluorinated propylene group.

[0215] In formula (2D), R.sup.fd is a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A).

[0216] With respect to the synthesis of the sulfonium salt having an anion of formula (2D), reference is made to JP-A 2010-215608 and JP-A 2014-133723.

[0217] Specific examples of the anion having formula (2D) are shown below, but not limited thereto.

##STR00279## ##STR00280##

[0218] Examples of the non-nucleophilic counter ion further include an anion having an aromatic ring substituted with an iodine atom or a bromine atom. Specific examples of such an anion include those having the following formula (2E).

##STR00281##

[0219] In formula (2E), x is an integer satisfying 1x3. y and z are integers satisfying 1y5, 0z3, and 1y+z5. y is preferably an integer satisfying 1y3 and more preferably 2 or 3. z is preferably an integer satisfying 0z2.

[0220] In formula (2E), X.sup.BI is an iodine atom or a bromine atom, and may be the same or different when x and/or y is 2 or more.

[0221] In formula (2E), L.sup.11 is a single bond, an ether bond, an ester bond, or a C.sub.1-C.sub.6 saturated hydrocarbylene group which may contain an ether bond or an ester bond. The saturated hydrocarbylene group may be straight, branched, or cyclic.

[0222] In formula (2E), L.sup.12 is a single bond or a C.sub.1-C.sub.20 divalent linking group when x is 1, and a C.sub.1-C.sub.20 (x+1)-valent linking group which may contain an oxygen atom, a sulfur atom, or a nitrogen atom when x is 2 or 3.

[0223] In formula (2E), R.sup.fc is a hydroxy group, a carboxy group, a fluorine atom, a chlorine atom, a bromine atom, an amino group, a C.sub.1-C.sub.20 hydrocarbyl group, C.sub.1-C.sub.20 hydrocarbyloxy group, C.sub.2-C.sub.20 hydrocarbylcarbonyl group, C.sub.2-C.sub.10 hydrocarbyloxycarbonyl group, C.sub.2-C.sub.20 hydrocarbylcarbonyloxy group, or C.sub.1-C.sub.20 hydrocarbylsulfonyloxy group, which may contain a fluorine atom, a chlorine atom, a bromine atom, a hydroxy group, an amino group, or an ether bond, or N(R.sup.fcA) (R.sup.fcB), N(R.sup.fcC)C(O)R.sup.fcD, or N(R.sup.fcC)C(O)OR.sup.fcD. R.sup.fcA and R.sup.fcB are each independently a hydrogen atom or a C.sub.1-C.sub.6 saturated hydrocarbyl group. R.sup.fcC is a hydrogen atom or a C.sub.1-C.sub.6 saturated hydrocarbyl group, which may contain a halogen atom, a hydroxy group, a C.sub.1-C.sub.6 saturated hydrocarbyloxy group, a C.sub.2-C.sub.6 saturated hydrocarbylcarbonyl group, or a C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy group. R.sup.fcD is a C.sub.1-C.sub.16 aliphatic hydrocarbyl group, a C.sub.6-C.sub.12 aryl group, or a C.sub.7-C.sub.15 aralkyl group, which may contain a halogen atom, a hydroxy group, a C.sub.1-C.sub.6 saturated hydrocarbyloxy group, a C.sub.2-C.sub.6 saturated hydrocarbylcarbonyl group, or a C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy group. The aliphatic hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. The hydrocarbyl group, the hydrocarbyloxy group, the hydrocarbylcarbonyl group, the hydrocarbyloxycarbonyl group, the hydrocarbylcarbonyloxy group, and the hydrocarbylsulfonyloxy group may be straight, branched, or cyclic. When x and/or z is 2 or more, respective R.sup.8 may be the same as or different from each other.

[0224] Of these, R.sup.fc is preferably a hydroxy group, N(R.sup.fcC)C(O)R.sup.fcD, N(R.sup.fcC)C(O)OR.sup.fcD, a fluorine atom, a chlorine atom, a bromine atom, a methyl group, a methoxy group, or the like.

[0225] In formula (2E), Rf.sup.11 to Rf.sup.14 are each independently a hydrogen atom, a fluorine atom, or a trifluoromethyl group, and of these, at least one of Rf.sup.11 to Rf.sup.14 is a fluorine atom or a trifluoromethyl group. Rf.sup.11 and Rf.sup.12, taken together, may form a carbonyl group. Particularly, both Rf.sup.13 and Rf.sup.14 are a fluorine atom.

[0226] Specific examples of the anion of the onium salt having formula (2E) are shown below, but not limited thereto. In the following formula, X.sup.BI is as defined above.

##STR00282## ##STR00283## ##STR00284## ##STR00285## ##STR00286## ##STR00287## ##STR00288## ##STR00289## ##STR00290## ##STR00291## ##STR00292## ##STR00293## ##STR00294## ##STR00295##

##STR00296## ##STR00297## ##STR00298## ##STR00299## ##STR00300## ##STR00301## ##STR00302## ##STR00303## ##STR00304## ##STR00305## ##STR00306## ##STR00307##

##STR00308## ##STR00309## ##STR00310## ##STR00311## ##STR00312## ##STR00313## ##STR00314## ##STR00315## ##STR00316## ##STR00317## ##STR00318## ##STR00319## ##STR00320## ##STR00321## ##STR00322##

##STR00323## ##STR00324## ##STR00325## ##STR00326## ##STR00327## ##STR00328## ##STR00329## ##STR00330## ##STR00331## ##STR00332## ##STR00333## ##STR00334##

[0227] Other useful examples of the non-nucleophilic counter ion include fluorobenzenesulfonic acid anions having an iodized aromatic ring bonded thereto as described in JP 6648726, anions having an acid-catalyzed decomposition mechanism as described in WO 2021/200056 and JP-A 2021-070692, anions having a cyclic ether group as described in JP-A 2018-180525 and JP-A 2021-35935, and anions as described in JP-A 2018-092159.

[0228] Further useful examples of the non-nucleophilic counter ion include bulky fluorine-free benzenesulfonic acid anions as described in JP-A 2006-276759, JP-A 2015-117200, JP-A 2016-65016, and JP-A 2019-202974, and fluorine-free benzenesulfonic acid or alkylsulfonic acid anions having an iodized aromatic group bonded thereto as described in JP 6645464.

[0229] Also useful examples of the non-nucleophilic counter ion include bissulfonic acid anions as described in JP-A 2015-206932, sulfonamide or sulfonimide anions having sulfonic acid side and different side as described in WO 2020/158366, and anions having a sulfonic acid side and a carboxylic acid side as described in JP-A 2015-024989.

[0230] The photoacid generator of the component (D) preferably has the following formula (3).

##STR00335##

[0231] In formula (3), R.sup.201 and R.sup.202 are each independently a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom. R.sup.203 is a C.sub.1-C.sub.30 hydrocarbylene group which may contain a heteroatom. Any two of R.sup.201, R.sup.202, and R.sup.203 may bond together to form a ring with the sulfur atom to which they are attached.

[0232] The C.sub.1-C.sub.30 hydrocarbyl group represented by R.sup.201 to R.sup.202 may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include C.sub.1-C.sub.30 alkyl groups such as a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, a sec-butyl group, a tert-butyl group, a tert-pentyl group, a n-pentyl group, a n-hexyl group, a n-octyl group, a 2-ethylhexyl group, a n-nonyl group, and a n-decyl group; C.sub.3-C.sub.30 cyclic saturated hydrocarbyl groups such as a cyclopentyl group, a cyclohexyl group, a cyclopentylmethyl group, a cyclopentylethyl group, a cyclopentylbutyl group, a cyclohexylmethyl group, a cyclohexylethyl group, a cyclohexylbutyl group, a norbornyl group, an oxanorbornyl group, a tricyclo[5.2.1.0.sup.2.6]decyl group, and an adamantyl group; C.sub.6-C.sub.30 aryl groups such as a phenyl group, a methylphenyl group, an ethylphenyl group, a n-propylphenyl group, an isopropylphenyl group, a n-butylphenyl group, an isobutylphenyl group, a sec-butylphenyl group, a tert-butylphenyl group, a naphthyl group, a methylnaphthyl group, an ethylnaphthyl group, a n-propylnaphthyl group, an isopropylnaphthyl group, a n-butylnaphthyl group, an isobutylnaphthyl group, a sec-butylnaphthyl group, a tert-butylnaphthyl group, and an anthracenyl group; and groups obtained by combining these. Some or all of the hydrogen atoms in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2in the hydrocarbyl group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a cyano group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like.

[0233] The C.sub.1-C.sub.30 hydrocarbylene group represented by R.sup.203 may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include C.sub.1-C.sub.30 alkanediyl groups such as a methanediyl group, an ethane-1,1-diyl group, an ethane-1,2-diyl group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl group, a nonane-1,9-diyl group, a decane-1,10-diyl group, an undecane-1,11-diyl group, a dodecane-1,12-diyl group, a tridecane-1,13-diyl group, a tetradecane-1,14-diyl group, a pentadecane-1,15-diyl group, a hexadecane-1,16-diyl group, and a heptadecane-1,17-diyl group; C.sub.3-C.sub.30 cyclic saturated hydrocarbylene groups such as a cyclopentanediyl group, a cyclohexanediyl group, a norbornanediyl group, and an adamantanediyl group; and C.sub.6-C.sub.30 arylene groups such as a phenylene group, a methylphenylene group, an ethylphenylene group, a n-propylphenylene group, an isopropylphenylene group, a n-butylphenylene group, an isobutylphenylene group, a sec-butylphenylene group, a tert-butylphenylene group, a naphthylene group, a methylnaphthylene group, an ethylnaphthylene group, a n-propylnaphthylene group, an isopropylnaphthylene group, a n-butylnaphthylene group, an isobutylnaphthylene group, a sec-butylnaphthylene group, and a tert-butylnaphthylene group. Some or all of the hydrogen atoms in the hydrocarbylene group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, a nitrogen atom, or a halogen atom, some of CH.sub.2in the hydrocarbylene group may be substituted with a group containing a heteroatom such as an oxygen atom, a sulfur atom, or a nitrogen atom, so that the group may contain a hydroxy group, a cyano group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a carbonyl group, an ether bond, an ester bond, a sulfonic acid ester bond, a carbonate bond, a lactone ring, a sultone ring, a carboxylic anhydride (C(O)OC(O)), a haloalkyl group, or the like. The heteroatom is preferably an oxygen atom.

[0234] In formula (3), L.sup.A is a single bond, an ether bond, or a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. The hydrocarbylene group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbylene group represented by R.sup.203.

[0235] In formula (3), X.sup.a, X.sup.b, X.sup.c, and X.sup.d are each independently a hydrogen atom, a fluorine atom, or a trifluoromethyl group. Provided that at least one of X.sup.a, X.sup.b, X.sup.c, and X.sup.d is a fluorine atom or a trifluoromethyl group.

[0236] The photoacid generator having formula (3) preferably has the following formula (3).

##STR00336##

[0237] In formula (3), L.sup.A is as defined above. X.sup.c is a hydrogen atom or a trifluoromethyl group and preferably a trifluoromethyl group. R.sup.301, R.sup.302, and R.sup.303 are each independently a hydrogen atom, or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof are as exemplified above for the hydrocarbyl group represented by R.sup.fa1 in formula (2A). p1 and p2 are each independently an integer of 0 to 5, and p3 is an integer of 0 to 4.

[0238] Examples of the photoacid generator having formula (3) are as exemplified for the photoacid generator having formula (2) in JP-A 2017-026980.

[0239] Of the foregoing other photoacid generators, those having an anion of formula (2A) or (2D) are particularly preferred because of reduced acid diffusion and high solubility in the solvent. Those having formula (3) are particularly preferred because of extremely reduced acid diffusion.

[0240] When the resist composition of the present invention comprises the photoacid generator (D), the content thereof is preferably 0.1 to 40 parts by weight and more preferably 0.5 to 20 parts by weight per 80 parts by weight of the base polymer (C). When the added amount of the photoacid generator of the component (D) is in the above range, the resolution is favorable, and there is no possibility that a problem of foreign matter occurs after development or peeling of the resist film, which is preferable. The photoacid generator of the component (D) may be used alone or in combination of two or more kinds thereof. The resist composition of the present invention can function as a chemically amplified resist composition when the base polymer comprises any of the repeat units c1 to c4 and/or the photoacid generator (D) is contained.

[Nitrogen-Containing Compound (E)]

[0241] In the resist composition of the present invention, the quencher of the component (A) is an essential component, but in addition to this, a nitrogen-containing compound may be contained as another quencher. Examples of such a nitrogen-containing compound include primary, secondary, and tertiary amine compounds, specifically amine compounds having a hydroxy group, an ether bond, an ester bond, a lactone ring, a cyano group, or a sulfonic acid ester bond as described in JP-A 2008-111103, paragraphs to [0164]. as in the compound described in JP 3790649, a compound in which a primary or secondary amine is protected with a carbamate group can also be mentioned.

[0242] A sulfonium sulfonate having a nitrogen-containing substituent may be used as the nitrogen-containing compound. Such a compound functions as a quencher in the unexposed area, and the exposed area functions as a so-called photodegradable base that loses quencher capability by neutralization with its own generated acid. By using the photodegradable base, the contrast between the exposed area and the unexposed area can be further enhanced. As the photodegradable base, for example, JP-A 2009-109595, JP-A 2012-46501, and the like can be referred to.

[0243] When the resist composition of the present invention comprises the nitrogen-containing compound (E), the content thereof is preferably 0.001 to 12 parts by weight and more preferably 0.01 to 8 parts by weight per 80 parts by weight of the base polymer (C). The nitrogen-containing compound (E) may be used alone or in combination of two or more kinds thereof.

[Surfactant (F)]

[0244] The resist composition of the present invention may further comprise a surfactant (F). The surfactant of the component (F) is preferably a surfactant insoluble or sparingly soluble in water and soluble in an alkaline developer, or a surfactant insoluble or sparingly soluble in water and an alkaline developer. As such a surfactant, those described in JP-A 2010-215608 and JP-A 2011-16746 can be referred to.

[0245] As the surfactant insoluble or sparingly soluble in water and an alkaline developer, among the surfactants described in the above publication, FC-4430 (manufactured by 3M), SURFLON S-381 (manufactured by AGC Seimi Chemical Co., Ltd.), OLFINE E1004 (manufactured by Nissin Chemical Industry Co., Ltd.), KH-20, KH-30 (manufactured by AGC Seimi Chemical Co., Ltd.), an oxetane ring-opening polymer having the following formula (surf-1), and the like are preferable.

##STR00337##

[0246] R, Rf, A, B, C, m, and n apply only to formula (surf-1), regardless of the foregoing description. R is a di- to tetra-valent C.sub.2-C.sub.5 aliphatic group. Examples of the divalent aliphatic group include an ethylene group, a 1,4-butylene group, a 1,2-propylene group, a 2,2-dimethyl-1,3-propylene group, and a 1,5-pentylene group, and examples of the tri- and tetra-valent aliphatic group are shown below.

##STR00338## [0247] wherein the broken line denotes a point of attachment, and these formulae are partial structures derived from glycerol, trimethylolethane, trimethylolpropane, and pentaerythritol.

[0248] Of these, a 1,4-butylene group, a 2,2-dimethyl-1,3-propylene group, and the like are preferable.

[0249] Rf is a trifluoromethyl group or a pentafluoroethyl group, preferably a trifluoromethyl group. m is an integer of 0 to 3, n is an integer of 1 to 4, and the sum of n and m, which represents the valence of R, is an integer of 2 to 4. A is 1. B is an integer of 2 to 25, preferably an integer of 4 to 20. C is an integer of 0 to 10, preferably 0 or 1. Each constituent unit in formula (surf-1) does not prescribe the arrangement thereof, and may be arranged either blockwise or randomly. For the preparation of surfactants in the form of partially fluorinated oxetane ring-opened polymers, reference should be made to U.S. Pat. No. 5,650,483 and the like.

[0250] When a resist protective film is not used in ArF immersion lithography, the surfactant insoluble or sparingly soluble in water and soluble in an alkaline developer has a function of minimizing water penetration or leaching by being oriented on the surface of the resist film. Therefore, the surfactant is useful for preventing water-soluble components from being leached out of the resist film for minimizing any damage to the exposure tool, and is also useful because it becomes solubilized during alkaline aqueous solution development after exposure or after PEB, and thus forms few or no foreign matter which become defects. Such a surfactant has a property of being insoluble or sparingly soluble in water and being soluble in an alkaline developer, is also called a polymeric surfactant, and is particularly preferably a surfactant having high water repellency and improving lubricity.

[0251] Specific examples of such a polymeric surfactant include those containing at least one selected from repeat units having the following formulae (4A) to (4E).

##STR00339##

[0252] In formulae (4A) to (4E), RB is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. W.sup.1 is-CH.sub.2, CH.sub.2CH.sub.2, O, or two separate H. R.sup.s1 is each independently a hydrogen atom or a C.sub.1-C.sub.10 hydrocarbyl group. R.sup.s2 is a single bond or a C.sub.1-C.sub.5 straight or branched hydrocarbylene group. R.sup.s3 is each independently a hydrogen atom, a C.sub.1-Cis hydrocarbyl group or fluorinated hydrocarbyl group, or an acid labile group. When R.sup.s3 is a hydrocarbyl group or fluorinated hydrocarbyl group, an ether bond or a carbonyl group may intervene in a carbon-carbon bond. R.sup.s4 is a C.sub.1-C.sub.20 (u+1)-valent hydrocarbon group or fluorinated hydrocarbon group. u is an integer of 1 to 3. R.sup.s5 is each independently a hydrogen atom or a group having formula-C(O)OR.sup.sa, and R.sup.sa is a C.sub.1-C.sub.20 fluorinated hydrocarbyl group. R.sup.s6 is a C.sub.1-C.sub.15 hydrocarbyl group or fluorinated hydrocarbyl group, and an ether bond or a carbonyl group may intervene in a carbon-carbon bond thereof.

[0253] The hydrocarbyl group represented by R.sup.s1 is preferably a saturated hydrocarbyl group and may be straight, branched, or cyclic. Specific examples thereof include alkyl groups such as a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, a n-hexyl group, a n-heptyl group, a n-octyl group, a n-nonyl group, and a n-decyl group; and cyclic saturated hydrocarbyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, an adamantyl group, and a norbornyl group. Of these, C.sub.1-C.sub.6 groups are preferable.

[0254] The hydrocarbylene group represented by R.sup.s2 is preferably a saturated hydrocarbylene group and may be straight, branched, or cyclic. Specific examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, and a pentylene group.

[0255] The hydrocarbyl group represented by R.sup.s3 or R.sup.s6 may be saturated or unsaturated and straight, branched, or cyclic. Specific examples thereof include aliphatic unsaturated hydrocarbyl groups such as a saturated hydrocarbyl group, an alkenyl group, and an alkynyl group, and a saturated hydrocarbyl group is preferable. Examples of the saturated hydrocarbyl group include a n-undecyl group, a n-dodecyl group, a tridecyl group, a tetradecyl group, and a pentadecyl group in addition to those exemplified as the hydrocarbyl group represented by R.sup.s1. Examples of the fluorinated hydrocarbyl group represented by R $3 or R.sup.s6 include groups in which some or all hydrogen atoms bonded to carbon atoms of the foregoing hydrocarbyl group are substituted by fluorine atoms. As described above, an ether bond or a carbonyl group may be interposed between these carbon-carbon bonds.

[0256] Specific examples of the acid labile group represented by R.sup.s3 include the groups having formulae (AL-3) to (AL-5), trialkylsilyl groups in which each alkyl group is a C.sub.1-C.sub.6 alkyl group, and C.sub.4-C.sub.20 oxo group-containing alkyl groups.

[0257] The (u+1)-valent hydrocarbon or fluorinated hydrocarbon group represented by R $4 may be straight, branched, or cyclic, and specific examples thereof include the foregoing hydrocarbyl or fluorinated hydrocarbyl groups from which u number of hydrogen atoms are eliminated.

[0258] The fluorinated hydrocarbyl group represented by R.sup.sa is preferably saturated and may be straight, branched, or cyclic. Specific examples thereof include the foregoing hydrocarbyl groups in which some or all hydrogen atoms are substituted by fluorine atoms, and examples thereof include a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a 3,3,3-trifluoro-1-propyl group, a 3,3,3-trifluoro-2-propyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, a 2,2,3,3,4,4,4-heptafluorobutyl group, a 2,2,3,3,4,4,5,5-octafluoropentyl group, a 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl group, a 2-(perfluorobutyl)ethyl group, a 2-(perfluorohexyl)ethyl group, a 2-(perfluorooctyl)ethyl group, and a 2-(perfluorodecyl)ethyl group.

[0259] Specific examples of the repeat units having formulae (4A) to (4E) are shown below, but not limited thereto. In the following formula, RB is as defined above.

##STR00340## ##STR00341## ##STR00342## ##STR00343## ##STR00344## ##STR00345## ##STR00346## ##STR00347##

[0260] The polymeric surfactant may further contain repeat units other than the repeat units having formulae (4A) to (4E). Examples of the other repeat units include repeat units derived from methacrylic acid, an -trifluoromethylacrylic acid derivative, or the like. In the polymeric surfactant, the content of the repeat units having formulae (4A) to (4E) is preferably 20 mol % or more, more preferably 60 mol % or more, and still more preferably 100 mol % of the overall repeat units.

[0261] The Mw of the polymeric surfactant is preferably 1000 to 500000, more preferably 3000 to 100000. Mw/Mn is preferably 1.0 to 2.0, more preferably 1.0 to 1.6.

[0262] Examples of the method for synthesizing the polymeric surfactant include a method of dissolving an unsaturated bond-containing monomer providing repeat units having formulae (4A) to (4E) and optionally other repeat units in an organic solvent, adding a radical initiator, and heating for polymerization. Examples of the organic solvent used in the polymerization include toluene, benzene, THF, diethyl ether, and dioxane. Examples of the polymerization initiator include AIBN, 2,2-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. The reaction temperature is preferably 50 to 100 C. The reaction time is preferably 4 to 24 hours. The acid labile group that has been incorporated in the monomer may be kept as such, or polymerization may be followed by protection or partial protection.

[0263] In the case of synthesizing the polymeric surfactant, any known chain transfer agent such as dodecyl mercaptan or 2-mercaptoethanol may be used for molecular weight control purpose. In this case, these chain transfer agents are preferably added in an amount of 0.01 to 10 mol % based on the total number of moles of monomers to be polymerized.

[0264] When the resist composition of the present invention comprises the surfactant (F), the content thereof is preferably 0.1 to 50 parts by weight and more preferably 0.5 to 10 parts by weight per 80 parts by weight of the base polymer (C). When the content of the surfactant (F) is 0.1 parts by weight or more, the receding contact angle with water of the resist film at its surface is sufficiently improved, and when the content thereof is 50 parts by weight or less, the dissolution rate of the resist film at its surface in the developer is low, and the height of the formed fine pattern is sufficiently maintained. The surfactant (F) may be used alone or in combination of two or more kinds thereof.

Other Components (G)

[0265] The resist composition of the present invention may comprise a compound which is decomposed with an acid to generate another acid (acid amplifier compound), an organic acid derivative, a fluorinated alcohol, a compound having a Mw of 3000 or less which changes its solubility in a developer under the action of acid (dissolution inhibitor), and the like as other components (G). As the acid amplifier compound, a compound described in JP-A 2009-269953 or JP-A 2010-215608 can be referred to. When the resist composition comprises the acid amplifier compound, the content thereof is preferably 0 to 5 parts by weight and more preferably 0 to 3 parts by weight per 80 parts by weight of the base polymer (C). When the content thereof is too large, it is difficult to control acid diffusion, and resolution and pattern profile may be deteriorated. As the organic acid derivative, the fluorinated alcohol, and the dissolution inhibitor, compounds described in JP-A 2009-269953 or JP-A 2010-215608 can be referred to.

[Pattern Forming Process]

[0266] A pattern forming process of the present invention comprises the steps of: applying the resist composition defined above 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.

[0267] As the substrate, for example, substrates for integrated circuit fabrication (such as Si, SiO.sub.2, SiN, SION, TIN, WSi, BPSG, SOG, and organic antireflective coating), or substrates for mask circuit fabrication (such as Cr, CrO, CrON, MoSi.sub.2, and SiO.sub.2) can be used.

[0268] The resist film can be formed by, for example, applying the resist composition by a method such as spin coating so that the film thickness is preferably 0.05 to 2 m, and prebaking the resist composition on a hotplate at preferably 60 to 150 C. for 1 to 10 minutes, more preferably 80 to 140 C. for 1 to 5 minutes.

[0269] Examples of the high-energy radiation used for exposure of the resist film include i-ray, KrF excimer laser, ArF excimer laser, EB, and EUV. In the case of using KrF excimer laser, ArF excimer laser, or EUV, exposure can be performed by using a mask for forming a target pattern and performing irradiation so that the exposure dose is preferably 1 to 200 mJ/cm.sup.2, more preferably 10 to 100 mJ/cm.sup.2. In the case of using EB, irradiation is performed using a mask for forming a target pattern or directly so that the exposure dose is preferably 1 to 300 C/cm.sup.2, more preferably 10 to 200 C/cm.sup.2.

[0270] In addition to a normal exposure method, it is also possible to use an immersion method in which exposure is performed by interposing a liquid having a refractive index of 1.0 or more between a resist film and a projection lens. In this case, it is also possible to use a protective film insoluble in water.

[0271] The water-insoluble protective film is used to prevent an eluate from the resist film and to increase the lubricity of the film surface, and is generally divided into two types. The first type is an organic solvent-strippable protective film in which peeling is required before alkaline aqueous solution development by an organic solvent that does not dissolve a resist film, and the second type is an alkaline aqueous solution-soluble protective film which is soluble in an alkaline developer so that the protective film is removed simultaneously with the removal of solubilized regions of the resist film. The protective film of the second type is particularly preferably of a material comprising a polymer having a 1,1,1,3,3,3-hexafluoro-2-propanol residue, which is insoluble in water and soluble in an alkaline developer, as a base and dissolved in an alcohol-based solvent of 4 or more carbon atoms, an ether-based solvent of 8 to 12 carbon atoms, and a mixed solvent thereof. A material obtained by dissolving the surfactant, which is insoluble in water and soluble in an alkaline developer, in an alcohol-based solvent of 4 or more carbon atoms, an ether-based solvent of 8 to 12 carbon atoms, or a mixed solvent thereof can also be used.

[0272] After the exposure, PEB may be performed. PEB can be performed, for example, by heating on a hotplate at preferably 60 to 150 C. for 1 to 5 minutes, more preferably 80 to 140 C. for 1 to 3 minutes.

[0273] For example, the resist film is developed with a developer in the form of an alkaline aqueous solution such as tetramethylammonium hydroxide (TMAH) in an amount of preferably 0.1 to 5 wt %, more preferably 2 to 3 wt % for preferably 0.1 to 3 minutes, more preferably 0.5 to 2 minutes by conventional techniques such as dip, puddle, and spray techniques. In this way, the exposed area is dissolved and a target pattern is formed on the substrate.

[0274] After the resist film is formed, the acid generator or the like may be extracted from the film surface by performing rinsing with pure water, or particles may be washed off, or rinsing for removing water remaining on the film after exposure may be performed.

[0275] Pattern formation may be performed by a double patterning process. Examples of the double patterning process include a trench process of processing an underlay to 1:3 trench pattern by a first step of exposure and etching, shifting the position, and forming a 1:3 trench pattern by a second step of exposure, for forming a 1:1 pattern, and a line process of processing a first underlay to a 1:3 isolated left pattern by a first step of exposure and etching, shifting the position, processing a second underlay formed below the first underlay by a second step of exposure through the 1:3 isolated left pattern, for forming a half-pitch 1:1 pattern.

[0276] In the pattern forming process of the present invention, a method of negative tone development in which an organic solvent is used instead of the alkaline aqueous solution as the developer for dissolving away the unexposed area may be used. For the organic solvent development, as the developer, 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-heptanone, 2-hexanone, 3-hexanone, diisobutyl ketone, methylcyclohexanone, acetophenone, methylacetophenone, propyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate, butyl formate, isobutyl formate, pentyl formate, isopentyl formate, methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate, pentyl lactate, isopentyl lactate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, ethyl phenylacetate, benzyl formate, phenylethyl formate, methyl 3-phenylpropionate, benzyl propionate, 2-phenylethyl acetate, and the like can be used. These organic solvents may be used alone or in admixture of two or more kinds thereof.

EXAMPLES

[0277] Hereinafter, the present invention is specifically described with reference to Synthesis Examples, Examples, and Comparative Examples, but the present invention is not limited to the following Examples. The devices used are as follows. [0278] IR: NICOLET 6700 manufactured by Thermo Fisher Scientific Inc. [0279] .sup.1H-NMR: ECA-500 manufactured by JEOL Ltd. [0280] MALDI TOF-MS: S3000 manufactured by JEOL Ltd.

[1] Synthesis of Onium Salt

[Example 1-1] Synthesis of Onium Salt NSQ-1

[0281] ##STR00348##

(1) Synthesis of Intermediate In-1

[0282] In a nitrogen atmosphere, a reaction vessel was charged with Compound SM-1 (10.2 g), Compound SM-2 (7.9 g), 4-dimethylaminopyridine (DMAP) (0.5 g), and methylene chloride (50 g), and cooled in an ice bath. 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (9.2 g) was added as a powder while the temperature in the reaction vessel was kept at 20 C. or lower. After addition, the reaction mixture was warmed up to room temperature, and aged for 12 hours. After aging, water was added to stop the reaction, followed by ordinary aqueous work-up and solvent distillation to obtain Intermediate In-1 as oily matter (yield: 16.4 g, yield percentage: 95%).

(2) Synthesis of Intermediate In-2

[0283] In a nitrogen atmosphere, Intermediate In-1 (16.2 g) was dissolved in THF (40 g). Thereafter, a 25 wt % benzyltrimethylammonium hydroxide aqueous solution (23.9 g) was added dropwise thereto. After the dropwise addition, the reaction solution was heated to 40 C. and aged for 4 hours. After aging, the reaction system was cooled to room temperature, and the solvent was distilled off, then diisopropyl ether was added thereto, and washing was performed to obtain Intermediate In-2 as oily matter (yield: 19.9 g, yield percentage: 90%).

(3) Synthesis of Onium Salt NSQ-1

[0284] In a nitrogen atmosphere, Intermediate In-2 (19.9 g) and Compound SM-3 (13.4 g) were mixed with methylene chloride (100 g) and water (80 g), and the mixture was stirred at room temperature for 2 hours. After stirring, ordinary aqueous work-up was performed, the solvent was distilled off, then diisopropyl ether was added thereto, and washing was performed to obtain Onium Salt NSQ-1 as oily matter (yield: 20.6 g, yield percentage: 86%).

[0285] The IR spectrum data and results of TOF-MS of Onium Salt NSQ-1 are shown below. The results of the nuclear magnetic resonance spectrum (.sup.1H-NMR/DMSO-d.sub.6) is shown in FIG. 1. In the results of the nuclear magnetic resonance spectrum (.sup.1H-NMR/DMSO-d.sub.6), methylene chloride used as a solvent and diisopropyl ether used for washing were detected. [0286] IR (D-ATR): v=3409, 3086, 3059, 2985, 2873, 1736, 1687, 1652, 1469, 1448, 1427, 1374, 1313, 1292, 1274, 1175, 1126, 1090, 1037, 1000, 933, 866, 800, 764, 735, 707, 681, 613, 526, 490, 424 cm-1. [0287] MALDI TOF-MS: [0288] POSITIVE M.sup.+261 (corresponding to C.sub.18H.sub.13S.sup.+) [0289] NEGATIVE M.sup.404 (corresponding to C.sub.19H.sub.28F.sub.2NO.sub.6.sup.)

[Examples 1-2 to 1-6] Synthesis of Onium Salts NSQ-2 to NSQ-7

[0290] Onium Salts NSQ-2 to NSQ-7 having the following formulae were synthesized using corresponding raw materials and known organic chemical reactions.

##STR00349## ##STR00350## ##STR00351##

[Synthesis Examples] Synthesis of Base Polymers (Polymers P-1 to P-5)

[0291] Base polymers (Polymers P-1 to P-5) of the composition shown below were synthesized by combining respective monomers, effecting copolymerization reaction in MEK as a solvent, pouring the reaction solution into hexane, washing the solid precipitate with hexane, isolation, and drying. The obtained base polymers were analyzed for composition by .sup.1H-NMR spectroscopy and for Mw and Mw/Mn by GPC (solvent: DMF, standard: polystyrene).

##STR00352## ##STR00353## ##STR00354##

[3] Preparation of Resist Composition

Examples 2-1 to 2-20 and Comparative Examples 1-1 to 1-12

[0292] Resist compositions were prepared by dissolving the onium salt (NSQ-1 to NSQ-6) of the present invention, a comparative quencher (SQ-A to SQ-D, AQ-A), a base polymer (P-1 to P-5), and a photoacid generator (PAG-1, PAG-2) in a solvent in which 100 ppm of FC-4430 manufactured by 3M as a surfactant was dissolved, in accordance with the formulation shown in Tables 1 and 2 below to prepare a solution, and filtering the solution through a 0.2 m Teflon filter.

[0293] The components in Tables 1 and 2 are identified below.

Organic Solvents:

[0294] PGMEA (propylene glycol monomethyl ether acetate) [0295] DAA (diacetone alcohol) [0296] Photoacid generators: PAG-1 and PAG-2

##STR00355##

Comparative Quenchers: SQ-A to SQ-D and AQ-A

[0297] ##STR00356##

TABLE-US-00001 TABLE 1 Resist Base polymer Photoacid generator Quencher Organic solvent 1 Organic solvent 2 composition (pbw) (pbw) (pbw) (pbw) (pbw) Example 2-1 R-1 P-1 (80) PAG-1 (30.4) NSQ-1 (4.5) PGMEA (3000) DAA (900) 2-2 R-2 P-1 (80) PAG-2 (25.8) NSQ-2 (4.3) PGMEA (3000) DAA (900) 2-3 R-3 P-1 (80) PAG-1 (28.4) NSQ-3 (4.5) PGMEA (3000) DAA (900) 2-4 R-4 P-1 (80) PAG-2 (24.8) NSQ-4 (4.5) PGMEA (3000) DAA (900) 2-5 R-5 P-2 (80) PAG-1 (30.4) NSQ-1 (4.5) PGMEA (3000) DAA (900) 2-6 R-6 P-2 (80) PAG-1 (29.4) NSQ-2 (4.3) PGMEA (3000) DAA (900) 2-7 R-7 P-2 (80) PAG-2 (25.8) NSQ-5 (4.2) PGMEA (3000) DAA (900) 2-8 R-8 P-2 (80) PAG-2 (24.8) NSQ-6 (4.1) PGMEA (3000) DAA (900) 2-9 R-9 P-3 (80) NSQ-1 (4.5) PGMEA (3000) DAA (900) 2-10 R-10 P-3 (80) NSQ-4 (4.2) PGMEA (3000) DAA (900) 2-11 R-11 P-3 (80) NSQ-5 (4.2) PGMEA (3000) DAA (900) 2-12 R-12 P-3 (80) PAG-1 (10.4) NSQ-1 (4.4) PGMEA (3000) DAA (900) 2-13 R-13 P-4 (80) NSQ-1 (4.5) PGMEA (3000) DAA (900) 2-14 R-14 P-4 (80) NSQ-2 (4.7) PGMEA (3000) DAA (900) 2-15 R-15 P-4 (80) NSQ-4 (4.1) PGMEA (3000) DAA (900) 2-16 R-16 P-4 (80) PAG-2 (8.4) NSQ-1 (4.3) PGMEA (3000) DAA (900) 2-17 R-17 P-5 (80) NSQ-1 (4.5) PGMEA (3000) DAA (900) 2-18 R-18 P-5 (80) NSQ-2 (4.3) PGMEA (3000) DAA (900) 2-19 R-19 P-5 (80) NSQ-7 (4.7) PGMEA (3000) DAA (900) 2-20 R-20 P-5 (80) PAG-1 (6.4) NSQ-1 (4.6) PGMEA (3000) DAA (900)

TABLE-US-00002 TABLE 2 Resist Base polymer Photoacid generator Quencher Organic solvent 1 Organic solvent 2 composition (pbw) (pbw) (pbw) (pbw) (pbw) Comparative 1-1 CR-1 P-1 (80) PAG-1 (30.4) SQ-A (4.4) PGMEA (3000) DAA (900) Example 1-2 CR-2 P-1 (80) PAG-2 (25.8) SQ-B (4.3) PGMEA (3000) DAA (900) 1-3 CR-3 P-1 (80) PAG-1 (28.4) SQ-C (4.6) PGMEA (3000) DAA (900) 1-4 CR-4 P-1 (80) PAG-2 (24.8) AQ-A (4.8) PGMEA (3000) DAA (900) 1-5 CR-5 P-2 (80) PAG-1 (29.4) SQ-B (4.3) PGMEA (3000) DAA (900) 1-6 CR-6 P-2 (80) PAG-2 (25.8) SQ-D (3.3) PGMEA (3000) DAA (900) 1-7 CR-7 P-3 (80) SQ-B (4.3) PGMEA (3000) DAA (900) 1-8 CR-8 P-3 (80) PAG-1 (10.4) SQ-A (4.6) PGMEA (3000) DAA (900) 1-9 CR-9 P-4 (80) SQ-A (4.8) PGMEA (3000) DAA (900) 1-10 CR-10 P-4 (80) PAG-2 (8.4) AQ-A (4.5) PGMEA (3000) DAA (900) 1-11 CR-11 P-5 (80) SQ-A (4.8) PGMEA (3000) DAA (900) 1-12 CR-12 P-5 (80) PAG-1 (6.4) SQ-B (4.3) PGMEA (3000) DAA (900)

[4] EUV Lithography Test (1)

Examples 3-1 to 3-20 and Comparative Examples 2-1 to 2-12

[0298] Each chemically amplified resist composition (R-1 to R-20 and CR-1 to CR-12) was spin coated on a Si substrate having a 20-nm coating of silicon-containing spin-on hard mask SHB-A940 manufactured by Shin-Etsu Chemical Co., Ltd. (content of silicon: 43 wt %) and prebaked on a hotplate at 100 C. for 60 seconds to form a resist film of 50 nm thick. Using an EUV scanner NXE3300 (NA 0.33, 0.9/0.6, dipole illumination) manufactured by ASML, the resist film was exposed to EUV through a LS pattern having a size of 18 nm and a pitch of 36 nm (on-wafer size) while varying the exposure dose and focus (exposure dose pitch: 1 mJ/cm.sup.2, focus pitch: 0.020 m), and after the exposure, the resist film was subjected to PEB at the temperature shown in Tables 3 and 4 for 60 seconds. Thereafter, the resist film was puddle developed in a 2.38 wt % TMAH aqueous solution for 30 seconds, rinsed with a surfactant-containing rinse material, and spin-dried to obtain a positive pattern.

[0299] The LS pattern after development was observed with a critical dimension SEM (CG6300) manufactured by Hitachi High-Technologies Corp. and evaluated for sensitivity, EL, LWR, DOF, and collapse limit by the following methods. The results are shown in Tables 5 and 6.

[Sensitivity Evaluation]

[0300] An optimum exposure dose E.sub.op (mJ/cm.sup.2) which provided a LS pattern with a line width of 18 nm and a pitch of 36 nm was determined and taken as sensitivity.

[EL Evaluation]

[0301] EL (unit: %) was determined from the exposure dose which provided a LS pattern with a space width of 18 nm10% (16.2 to 19.8 nm) according to the following equation. A greater value indicates better performance.

[00001]$\mathrm{EL}\left(\%\right)=\left(.Math.E_1-E_2.Math./E_{op}\right)100$ [0302] E.sub.1: optimum exposure dose which provides a LS pattern with a line width of 16.2 nm and a pitch of 36 nm [0303] E.sub.2: optimum exposure dose which provides a LS pattern with a line width of 19.8 nm and a pitch of 36 nm [0304] E.sub.op: optimum exposure dose which provides a LS pattern with a line width of 18 nm and a pitch of 36 nm

[Lwr Evaluation]

[0305] For the LS pattern formed by exposure at the optimum dose E.sub.op, the line width was measured at 10 longitudinally spaced apart points, from which a 3-fold value (3) of the standard deviation () was determined as LWR. As this value is smaller, a pattern having small roughness and uniform line width can be obtained.

[DOF Evaluation]

[0306] As evaluation of the depth of focus, a range of focus which provided a LS pattern with a size of 18 nm10% (16.2 to 19.8 nm) was determined. A greater value indicates a wider depth of focus.

[Evaluation of Collapse Limit of Line Pattern]

[0307] For the LS pattern formed by exposure at the exposure dose corresponding to the optimum focus, the line width was measured at 10 longitudinally spaced apart points. The minimum line size above which lines could be resolved without collapse was determined and reported as collapse limit. A smaller value indicates better collapse limit.

TABLE-US-00003 TABLE 3 Resist PEB temperature Optimum exposure dose EL LWR DOF Collapse limit composition ( C.) (mJ/cm.sup.2) (%) (nm) (nm) (nm) Example 3-1 R-1 105 32 18 2.7 120 10.4 3-2 R-2 100 31 17 2.8 110 10.7 3-3 R-3 100 32 18 2.8 110 10.5 3-4 R-4 105 32 17 2.8 110 10.6 3-5 R-5 100 32 18 2.9 110 10.7 3-6 R-6 95 31 18 3 120 11.3 3-7 R-7 100 31 19 2.7 100 11.2 3-8 R-8 100 30 18 2.8 120 11.0 3-9 R-9 95 26 18 2.9 110 11.3 3-10 R-10 105 27 18 2.8 110 10.7 3-11 R-11 95 27 19 2.8 120 10.7 3-12 R-12 100 28 17 2.7 100 11.3 3-13 R-13 100 27 18 2.9 110 11.2 3-14 R-14 105 27 19 2.7 120 10.8 3-15 R-15 100 26 18 2.7 120 11.1 3-16 R-16 100 27 18 2.9 110 10.9 3-17 R-17 105 26 17 2.6 120 11.5 3-18 R-18 100 27 18 2.8 110 10.8 3-19 R-19 105 27 18 2.6 110 11.2 3-20 R-20 95 26 17 2.8 110 11.1

TABLE-US-00004 TABLE 4 Resist PEB temperature Optimum exposure dose EL LWR DOF Collapse limit composition ( C.) (mJ/cm.sup.2) (%) (nm) (nm) (nm) Comparative 2-1 CR-1 105 35 13 3.7 90 13.8 Example 2-2 CR-2 105 37 15 3.9 80 14.6 2-3 CR-3 100 37 14 3.8 70 14.6 2-4 CR-4 105 37 13 3.8 70 14.1 2-5 CR-5 105 36 14 4 80 14.2 2-6 CR-6 100 36 13 3.8 90 14 2-7 CR-7 105 29 14 3.9 70 14.5 2-8 CR-8 95 28 14 4.1 80 13.7 2-9 CR-9 105 27 15 3.8 90 13.9 2-10 CR-10 100 29 14 3.9 70 13.6 2-11 CR-11 100 28 14 3.9 90 13.5 2-12 CR-12 110 29 15 3.8 80 14

[0308] From the results shown in Tables 3 and 4, it has been confirmed that the resist composition of the present invention has favorable sensitivity, is excellent in various lithographic performances, and exhibits performance resistant to pattern collapse.

[5] EUV Lithography Test (2)

Examples 4-1 to 4-20 and Comparative Examples 3-1 to 3-12

[0309] Each chemically amplified resist composition (R-1 to R-20 and CR-1 to CR-12) was spin coated on a Si substrate having a 20-nm coating of silicon-containing spin-on hard mask SHB-A940 manufactured by Shin-Etsu Chemical Co., Ltd. (content of silicon: 43 wt %) and prebaked on a hotplate at 100 C. for 60 seconds to form a resist film of 60 nm thick. Using an EUV scanner NXE3400 (NA 0.33, 0.9/0.6, quadrupole illumination, mask bearing a hole pattern at a pitch 44 nm (on-wafer size) and +20% bias) manufactured by ASML, the resist film was exposed to EUV, the resist film was baked (PEB) on a hotplate at the temperature shown in Tables 5 and 6 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 22 nm in Examples 4-1 to 4-18 and Comparative Examples 3-1 to 3-10 or a hole pattern having a size of 22 nm in Examples 4-19 and 4-20 and Comparative Examples 3-11 and 3-12.

[0310] The exposure dose that provides a hole or dot pattern having a size of 22 nm was measured using length measurement SEM (CG6300) manufactured by Hitachi High-Tech Corporation and taken as sensitivity, the size of 50 holes or dots at that dose was measured, from which a 3-fold value (3) of the standard deviation () was computed and taken as CDU. The results are shown in Tables 5 and 6.

TABLE-US-00005 TABLE 5 PEB Optimum Resist temperature exposure dose CDU composition ( C.) (mJ/cm.sup.2) (nm) Example 4-1 R-1 90 30 3.0 4-2 R-2 90 31 3.2 4-3 R-3 85 31 3.1 4-4 R-4 90 30 2.8 4-5 R-5 90 28 3.0 4-6 R-6 85 30 2.9 4-7 R-7 95 32 2.8 4-8 R-8 95 29 2.8 4-9 R-9 90 27 3.0 4-10 R-10 85 26 3.2 4-11 R-11 90 27 2.8 4-12 R-12 90 28 2.8 4-13 R-13 95 27 2.9 4-14 R-14 95 26 2.8 4-15 R-15 90 26 2.7 4-16 R-16 85 27 3.0 4-17 R-17 90 26 2.8 4-18 R-18 90 27 2.9 4-19 R-19 95 26 2.8 4-20 R-20 90 27 2.7

TABLE-US-00006 TABLE 6 PEB Optimum Resist temperature exposure dose CDU composition ( C.) (mJ/cm.sup.2) (nm) Comparative 3-1 CR-1 90 34 3.6 Example 3-2 CR-2 95 33 4.0 3-3 CR-3 85 35 3.8 3-4 CR-4 90 34 3.9 3-5 CR-5 85 35 4.2 3-6 CR-6 90 31 3.9 3-7 CR-7 90 32 4.1 3-8 CR-8 90 30 4.2 3-9 CR-9 95 29 4.3 3-10 CR-10 90 30 4.1 3-11 CR-11 85 31 4.0 3-12 CR-12 90 30 3.9

[0311] From the results shown in Tables 5 and 6, it was confirmed that the chemically amplified resist composition comprising a quencher composed of an onium salt of the present invention has favorable sensitivity and is excellent in CDU.

[0312] Japanese Patent Application No. 2023-064766 is incorporated herein by reference. 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.