RESIST COMPOSITION AND PATTERN FORMING PROCESS

Abstract

A resist composition comprising a sulfonium salt having an acid labile group of aromatic ring-containing tertiary ester type in the cation as the acid generator exhibits a high sensitivity and reduced LWR or improved CDU.

Claims

1. A resist composition comprising an acid generator containing a sulfonium salt having the formula (1): ##STR00330## wherein m is an integer of 0 to 5, n is an integer of 0 to 3, p is 0 or 1, q is an integer of 0 to 4, r is 1 or 2, s is an integer of 1 to 3, R.sup.1 is a single bond, ether bond, thioether bond or ester bond, R.sup.2 is a single bond or a C.sub.1-C.sub.20 alkanediyl group which may contain fluorine or hydroxy, R.sup.3 and R.sup.4 are each independently a C.sub.1-C.sub.12 saturated hydrocarbyl group, C.sub.2-C.sub.8 alkenyl group, C.sub.2-C.sub.8 alkynyl group or C.sub.6-C.sub.10 aryl group, which may contain oxygen or sulfur, 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 is fluorine, iodine, optionally fluorinated C.sub.1-C.sub.4 alkyl group, optionally fluorinated C.sub.1-C.sub.4 alkoxy group, or optionally fluorinated C.sub.1-C.sub.4 alkylthio group, R.sup.6 is hydroxy, C.sub.2-C.sub.4 alkoxycarbonyl, nitro, cyano, chlorine, bromine or amino group, R.sup.7 is hydroxy, carboxy, nitro, cyano, fluorine, chlorine, bromine, iodine, or a C.sub.1-C.sub.20 saturated hydrocarbyl group, C.sub.1-C.sub.20 saturated hydrocarbyloxy group, C.sub.2-C.sub.20 saturated hydrocarbylcarbonyloxy group, C.sub.2-C.sub.20 saturated hydrocarbyloxycarbonyl group, or C.sub.1-C.sub.4 saturated hydrocarbylsulfonyloxy group, which may contain at least one moiety selected from fluorine, chlorine, bromine, iodine, hydroxy, amino and ether bond, R.sup.8 is a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, in case of s=1, two groups R.sup.1 may be the same or different and may bond together to form a ring with the sulfur atom to which they are attached, the circle Ar is a C.sub.6-C.sub.18 (m+n+1)-valent aromatic group or C.sub.5-C.sub.10 (m±n+1)-valent double bond-containing alicyclic hydrocarbon group, which may contain oxygen, sulfur or nitrogen, with the proviso that the circle Ar is not phenyl when both R.sup.1 and R.sup.4 are methyl and m=n=0, X.sup.− is a non-nucleophilic counter ion.

2. The resist composition of claim 1 wherein the non-nucleophilic counter ion is a sulfonate, imide or methide anion.

3. The resist composition of claim 1 wherein m is an integer of 1 to 5.

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

5. The resist composition of claim 1, further comprising a base polymer.

6. The resist composition of claim 5 wherein the base polymer comprises repeat units having the formula (a1) or repeat units having the formula (a2): ##STR00331## wherein R.sup.A is each independently hydrogen or methyl, X.sup.1 is a single bond phenylene, naphthylene, or a C.sub.1-C.sub.12 linking group containing at least one moiety selected from an ester bond, ether bond and lactone ring, X.sup.2 is a single bond or ester bond, X.sup.3 is a single bond, ether bond or ester bond, R.sup.11 and R.sup.12 are each independently an acid labile group, R.sup.13 is fluorine, trifluoromethyl, cyano, a C.sub.1-C.sub.6 saturated hydrocarbyl group, C.sub.1-C.sub.6 saturated hydrocarbyloxy group, C.sub.2-C.sub.7 saturated hydrocarbylcarbonyl group, C.sub.2-C.sub.7 saturated hydrocarbylcarbonyloxy group, or C.sub.2-C.sub.7 saturated hydrocarbyloxycarbonyl group, R.sup.14 is a single bond or a C.sub.1-C.sub.6 alkanediyl group in which some constituent —CH.sub.2— may be replaced by an ether bond or ester bond, a is 1 or 2, b is an integer of 0 to 4, and a+b is from 1 to 5.

7. The resist composition of claim 6 which is a chemically amplified positive resist composition.

8. The resist composition of claim 5 wherein the base polymer comprises repeat units of at least one type selected from repeat units having the formulae (f1) to (f3): ##STR00332## wherein R.sup.A is each independently hydrogen or methyl, Z.sup.1 is a single bond, a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, naphthylene or a C.sub.7-C.sub.18 group obtained by combining the foregoing, or —O—Z.sup.11—, —C(═O)—O—Z.sup.11— or —C(═O)—NH—Z.sup.11—, wherein Z.sup.11 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, naphthylene or a C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety, Z.sup.2 is a single bond or ester bond, Z.sup.3 is a single bond, —Z.sup.31—C(═O)—O—, —Z.sup.31—O— or —Z.sup.31—O—C(═O)—, wherein Z.sup.11 is a C.sub.1-C.sub.12 hydrocarbylene group, phenylene or a C-Cis group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond, iodine or bromine, Z.sup.4 is methylene, 2,2-trifluoro-1,1-ethanediyl or carbonyl, Z.sup.5 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, —O—Z.sup.51—, —C(═O)—O—Z.sup.51—, or —C(═O)—NH—Z.sup.51—, wherein Z.sup.51 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, fluorinated phenylene, or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond, hydroxy moiety or halogen, R.sup.21 to R.sup.28 are each independently halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, a pair of R.sup.23 and R.sup.24, or R.sup.26 and R.sup.27 may bond together to form a ring with the sulfur atom to which they are attached, and M.sup.− is a non-nucleophilic counter ion.

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

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

11. The pattern forming process of claim 10 wherein the high-energy radiation is KrF excimer laser, Arf excimer laser, EB, or EUV of wavelength 3 to 15 nm.

Description

DESCRIPTION OF EMBODIMENTS

[0042] As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. “Optional” or “optionally” means that the subsequently described event or circumstances may or may not occur, and that description includes instances where the event or circumstance occurs and instances where it does not. The notation (Cn-Cm) means a group containing from n to m carbon atoms per group. In chemical formulae, the broken line designates a valence bond; Me stands for methyl, and Ac for acetyl. As used herein the term “fluorinated” refers to a fluorine-substituted or fluorine-containing compound or group. The terms “group” and “moiety” are interchangeable.

[0043] The abbreviations and acronyms have the following meaning.

[0044] EB: electron beam

[0045] EUV: extreme ultraviolet

[0046] Mw: weight average molecular weight

[0047] Mn: number average molecular weight

[0048] Mw/Mn: molecular weight distribution or dispersity

[0049] CPC: gel permeation chromatography

[0050] PEB: post-exposure bake

[0051] PAG: photoacid generator

[0052] LWR: line width roughness

[0053] CDU: critical dimension uniformity

Resist Composition

[0054] The resist composition of the invention comprises an acid generator containing a sulfonium salt having an acid labile group of aromatic group-containing tertiary ester type in the cation.

Sulfonium Salt

[0055] The sulfonium salt having an acid labile group of aromatic group-containing tertiary ester type in the cation is represented by the formula (1).

##STR00004##

[0056] In formula (1), mu is an integer of 0 to 5, n is an integer of 0 to 3, p is 0 or 1, q is an integer of 0 to 4, r is 1 or 2, and s is an integer of 1 to 3. Preferably, m is an integer of 1 to 5.

[0057] In formula (1), R.sup.1 is aa single bond, ether bond, thioether bond or ester bond, preferably an ether bond or ester bond

[0058] In formula (1), R.sup.1 is a single bond- or a C.sub.1-C.sub.20 alkanediyl group which may contain fluorine or hydroxy. Examples of the alkanediyl group include methanediyl, ethane-1,1-diyl, ethane-1,2-diyl, propane-1,1-diyl, propane-1,2-diyl, propane-1,3-diyl, propane-2,2-diyl, butane-1,1-diyl, butane-1,2-diyl, butane-1,3-diyl, butane-2,3-diyl, butane-1,4-diyl, 1,1-dimethylethane-1,2-diyl, pentane-1,5-diyl, 2-methylbutane-1,2-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, and dodecane-1,12-diyl.

[0059] In formula (1) R.sup.3 and R.sup.4 are each independently a C.sub.1-C.sub.12 saturated hydrocarbyl group, C.sub.2-C.sub.8 alkenyl group, C.sub.2-C.sub.8 alkynyl group or C.sub.6-C.sub.10 aryl group, which may contain oxygen or sulfur. R.sup.3 and R.sup.4 may bond together to form a ring with the carbon atom to which they are attached.

[0060] Of the groups represented by R.sup.3 and R.sup.4, the C.sub.1-C.sub.12 saturated hydrocarbyl group may be straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.2 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, and n-hexyl; and C.sub.3-C.sub.12 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. Examples of the C.sub.2-C.sub.8 Alkenyl group include vinyl, 1-propenyl, 2-propenyl, butenyl and hexenyl. Examples of the C.sub.2-C.sub.8 alkynyl group include ethynyl and butynyl. Examples of the C.sub.6-C.sub.10 aryl group include phenyl and naphthyl.

[0061] In formula (1), R.sup.5 is fluorine, iodine, optionally fluorinated C.sub.1-C.sub.4 alkyl group, optionally fluorinated C.sub.1-C.sub.4 alkoxy group, or optionally fluorinated C.sub.1-C.sub.4 alkylthio group. R.sup.5 is preferably fluorine, fluorinated C.sub.1-C.sub.4 alkyl group, fluorinated C.sub.1-C.sub.4 alkoxy group, or fluorinated C.sub.1-C.sub.4 alkylthio group. The inclusion of a fluorinated acid labile group in the cation ensures a high dissolution contrast.

[0062] In formula (1), R.sup.6 is hydroxy, C.sub.2-C.sub.4 alkoxycarbonyl, nitro, cyano, chlorine, bromide or amino group.

[0063] In formula (1), R.sup.7 is hydroxy, carboxy, nitro, cyano, fluorine, chlorine, bromine, iodine, or a C.sub.1-C.sub.20 saturated hydrocarbyl group, C.sub.1-C.sub.20 saturated hydrocarbyloxy group, C.sub.2-C.sub.20 saturated hydrocarbylcarbonyloxy group, C.sub.2-C.sub.20 saturated hydrocarbyloxycarbonyl group, or C.sub.1-C.sub.4 saturated hydrocarbylsulfonyloxy group, which may contain at least one moiety selected from fluorine, chlorine, bromine, iodine, hydroxy, amino and ether bond.

[0064] The saturated hydrocarbyl group and saturated hydrocarbyl moiety of the saturated hydrocarbyloxy group, saturated hydrocarbylcarbonyloxy group, saturated hydrocarbyloxycarbonyl group, or saturated hydrocarbylsulfonyloxy group, represented by R.sup.7, may be straight, branched or cyclic. Examples thereof include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, see-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-decyl, n-dodecyl n-tridecyl, n-pentadecyl, and n-hexadecyl: and cyclic saturated hydrocarbyl groups such as cyclopentyl and cyclohexyl.

[0065] In formula (1), R.sup.8 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. Examples thereof include C.sub.1-C.sub.20 saturated hydrocarbyl groups, C.sub.2-C.sub.20 unsaturated aliphatic hydrocarbyl groups, C.sub.6-C.sub.20 aryl groups. C.sub.7-C.sub.20 aralkyl groups, and combinations thereof.

[0066] The saturated hydrocarbyl group may be straight, branched or cyclic. Examples thereof include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, see-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-pentadecyl, and n-hexadecyl; and cyclic saturated hydrocarbyl groups such as cyclopentyl and cyclohexyl.

[0067] The unsaturated aliphatic hydrocarbyl group may be straight, branched or cyclic, and examples thereof include alkenyl groups such as vinyl, 1-propenyl, 2-propenyl, butenyl and hexenyl; alkynyl groups such as ethynyl, propynyl and butynyl; and cyclic unsaturated hydrocarbyl groups such as cyclohexenyl.]

[0068] Examples of the aryl group include phenyl, methylphenyl, ethylphenyl, n-propylphenyl, isopropylphenyl, n-butylphenyl, isobutylphenyl, sec-butylphenyl, tert-butylphenyl, naphthyl, methylnaphthyl, ethylnaphthyl, n-propylnaphthyl, isopropylaaphlthyl, n-butylnaphthyl, isobutyinaphthyl, sec-butyhnaphlthyl, and tert-butylnaphthyl.

[0069] Exemplary of the aralkyl group are benzyl and phenethyl.

[0070] In the foregoing hydrocarbyl groups, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some constituent —CH.sub.2— may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy, carboxy, halogen, cyano, amino, nitro, sultone, sulfone, sulfonium salt-containing moiety, ether bond, ester bond, carbonyl, sulfide bond, sulfonyl, or amide bond.

[0071] In case of s=1, two groups R.sup.8 may be the same or different and may bond together to form a ring with the sulfur atom to which they are attached. Examples of the ring are shown below.

##STR00005##

Herein the broken hue designates a point of attachment to the aromatic ring in formula (1).

[0072] In formula (1), the circle Ar is a Cc-Cis (m+n+1)-valent aromatic group or C.sub.5-C.sub.10 (m+n+1)-valent double bond-containing alicyclic hydrocarbon group, which may contain oxygen, sulfur or nitrogen, with the proviso that the circle Ar is not a phenyl group when both R.sup.3 and R.sup.4 are methyl and m=n=0. Suitable aromatic groups include those groups obtained from such aromatic compounds as benzene, toluene, o-xylene, m-xylene, p-xylene and naphthalene by removing number (m+n+1) of hydrogen atoms on their aromatic ring. Examples of the double bond-containing alicyclic hydrocarbon group include those groups obtained from such alicyclic hydrocarbons as cyclopentene, cyclopentadiene, cyclohexene and norbornene by removing number (m+n+1) of hydrogen atoms on their ring.

[0073] The base polymer and the sulfonium salt turn soluble in alkaline developer as a result of their acid labile groups undergoing acid-catalyzed deprotection reaction, whereby a higher dissolution contrast is achieved. As a result, a higher sensitivity is achieved as well as a reduced LWR or improved CDL. Since the exposure dose achieving an improvement in the solubility of the base polymer via deprotection reaction is equal to the exposure dose for causing the sulfonium salt to be dissolved, a significant improvement in contrast is achievable.

[0074] Where the acid labile group in the base polymer and the acid labile group in the sulfonium salt are of the same structure, the sulfonium salt located in proximity to the generated acid is more prone to deprotection reaction. Even if deprotection reaction takes place simultaneously, the sulfonium salt having a lower molecular weight turns soluble in alkaline developer on the side of lower exposure dose. In the case of a conventional sulfonium salt substituted with an acid labile group, which is similar to the acid labile group on the base polymer, there exists a gap in deprotection reactivity between the base polymer and the sulfonium salt and so, the dissolution contrast-improving effect is low.

[0075] For eliminating the gap in deprotection reactivity between the base polymer and the sulfonium salt, it is preferred in the practice of the invention to use in the sulfonium salt an acid labile group of lower deprotection reactivity than the acid labile group in the base polymer. In the case of aromatic group-containing acid labile groups, for example, their deprotection reactivity can be adjusted low by introducing an electron withdrawing group such as halogen, cyano or nitro into the aromatic group.

[0076] Examples of the cation of the sulfonium salt having formula (1) are shown below, but not limited thereto.

##STR00006## ##STR00007## ##STR00008## ##STR00009## ##STR00010## ##STR00011## ##STR00012## ##STR00013## ##STR00014## ##STR00015## ##STR00016## ##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021## ##STR00022## ##STR00023## ##STR00024## ##STR00025## ##STR00026## ##STR00027## ##STR00028##

##STR00029## ##STR00030## ##STR00031## ##STR00032## ##STR00033## ##STR00034## ##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## ##STR00081## ##STR00082## ##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## ##STR00134## ##STR00135## ##STR00136## ##STR00137## ##STR00138## ##STR00139## ##STR00140## ##STR00141## ##STR00142## ##STR00143## ##STR00144## ##STR00145## ##STR00146## ##STR00147## ##STR00148## ##STR00149## ##STR00150## ##STR00151## ##STR00152## ##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## ##STR00187## ##STR00188## ##STR00189## ##STR00190## ##STR00191## ##STR00192## ##STR00193## ##STR00194## ##STR00195## ##STR00196## ##STR00197## ##STR00198## ##STR00199## ##STR00200## ##STR00201## ##STR00202## ##STR00203## ##STR00204##

[0077] In formula (1), M.sup.− is a non-nucleophilic counter ion. Examples of the non-nucleophilic counter ion include halide ions such as chloride and bromide ions; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such as mesylate and butanesulfonate: imide ions such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide: methide ions such as tris(trifluoromethylsulfonyl)methide and tris(perfluoroethylsulfonyl)methide.

[0078] Anions having the following formulae (1A) to (1D) are also useful as the non-nucleophilic counter ion.

##STR00205##

[0079] In formula (1A), R.sup.fa is fluorine 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. Examples thereof are as exemplified below for R.sup.fa1 in formula (1A).

[0080] Of the anions of formula (1A) an anion having the formula (1A′) is preferred.

##STR00206##

[0081] In formula (1A′), R.sup.HF is hydrogen or trifluoromethyl, preferably trifluoromethyl.

[0082] R.sup.fa1 is a C.sub.1-C.sub.38 hydrocarbyl group which may contain a heteroatom. As the heteroatom, oxygen, nitrogen, sulfur and halogen atoms are preferred, with oxygen being most preferred. Of the hydrocarbyl groups, those groups of 6 to 30 carbon atoms are preferred from the aspect of achieving a high resolution in forming patterns of small feature size. The hydrocarbyl groups may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include, but are not limited to, C.sub.1-C.sub.38 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, and eicosanyl; C.sub.3-C.sub.38 cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, 1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl, tricyclodecanyl, tetracyclododecanyl, tetracyclododecanylmethyl, and dicyclohexylmethyl; C.sub.2-C.sub.38 unsaturated aliphatic hydrocarbyl groups such as allyl and 3-cyclohexenyl; C.sub.6-C.sub.33 aryl groups such as phenyl, 1-naphthyl, 2-naphthyl and 9-fluorenyl; and C.sub.6-C.sub.38 aralkyl groups such as benzyl and diphenylmethyl, and combinations thereof.

[0083] In the foregoing hydrocarbyl groups, some or all hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or some constituent —CH.sub.2— may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy, fluorine, chlorine, bromine, iodine, cyano, nitro, carbonyl, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (—C(═O)—O—C(═O)—) or haloalkyl moiety. Examples of the heteroatom-containing hydrocarbyl group include tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl, acetamidomethyl, trifluoroethyl, (2-methoxyethoxy)methyl, acetoxymethyl, 2-carboxy-1-cyclohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and 3-oxocyclohexyl.

[0084] Examples of the anion having formula (1A) are shown below, but not limited thereto.

##STR00207## ##STR00208## ##STR00209## ##STR00210##

[0085] In formula (1B) R.sup.fb1 and R.sup.fb2 are each independently fluorine 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. Examples thereof are as exemplified above for R.sup.fa1 in formula (1A′). Preferably R.sup.fb1 and R.sup.fb2 are fluorine or C.sub.1-C.sub.4 straight fluorinated alkyl groups. Also, R.sup.fb1 and R.sup.fb2 may bond together to form a ring with the linkage: —CF.sub.2—SO.sub.2—N.sup.−—SO.sub.2—CF.sub.2— to which they are attached. It is preferred that a combination of R.sup.fb1 and R.sup.fb2 be a fluorinated ethylene or fluorinated propylene group.

[0086] In formula (1C), R.sup.fc1, R.sup.fc2 and R.sup.fc3 are each independently fluorine 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. Examples thereof are as exemplified for R.sup.fa1 in formula (1A′). Preferably R.sup.fc1, R.sup.fc2 and R.sup.fc3 are fluorine or C.sub.1-C.sub.4 straight fluorinated alkyl groups. Also, R.sup.fc1 and R.sup.fc2 may bond together to form a ring with the linkage: —CF.sub.2—SO.sub.2—C.sup.−—SO.sub.2—CF.sub.2— to which they are attached. It is preferred that a combination of R.sup.fc1 and R.sup.fc2 be a fluorinated ethylene or fluorinated propylene group.

[0087] In formula (1D), 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. Examples thereof are as exemplified above for R.

[0088] Examples of the anion having formula (1D) are shown below, but not limited thereto.

##STR00211## ##STR00212##

[0089] Anion having an iodized or brominated aromatic ring are also useful as the non-nucleophilic counter ion. These anions have the formula (1E).

##STR00213##

[0090] An formula (1E), x is an integer of 1 to 3, y is an integer of 1 to 5, z is an integer of 0 to 3, and 1≤y+z≤5; preferably, y is an integer of 1 to 3, more preferably 2 or 3, and z is an integer of 0 to 2.

[0091] X.sup.B1 is iodine or bromine, and may be identical or different when x and/or y is 2 or more.

[0092] L.sup.1 is a single bond, ether bond, ester bond, or a C.sub.1-C.sub.6 saturated hydrocarbylene group which may contain an ether bond or ester bond. The saturated hydrocarbylene group may be straight, branched or cyclic.

[0093] L.sup.2 is a single bond or a C.sub.1-C.sub.20 divalent linking group when x=1, or a C.sub.1-C.sub.20 (x+1)-valent linking group when x=2 or 3. The linking group may contain an oxygen, sulfur or nitrogen atom.

[0094] R.sup.9 is hydroxy, carboxy, fluorine, chlorine, bromine, amino group, or a C.sub.1-C.sub.20 hydrocarbyl, C.sub.1-C.sub.20 hydrocarbyloxy, C.sub.2-C.sub.2n hydrocarbylcarbonyl, C.sub.2-C.sub.1 hydrocarbyloxycarbonyl, C.sub.2-C.sub.20 hydrocarbylcarbonyloxy, or C.sub.1-C.sub.20 hydrocarbylsulfonyloxy group, which may contain fluorine, chlorine, bromine, hydroxy, amino or ether bond, or —N(R.sup.9A)(R.sup.9B), —N(R.sup.9C)—C(═O)—R.sup.9D or —N(R.sup.9C(═O)—O—R.sup.9D. R.sup.9A and R.sup.9B are each independently hydrogen or a C.sub.1-C.sub.6 saturated hydrocarbyl group. R is hydrogen, or a C.sub.1-C.sub.6 saturated hydrocarbyl group which may contain halogen, hydroxy, C.sub.1-C.sub.6 saturated hydrocarbyloxy, C.sub.2-C.sub.6 saturated hydrocarbylcarbonyl or C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy moiety. R.sup.9D is a C.sub.1-C.sub.16 aliphatic hydrocarbyl group, C.sub.6-C.sub.12 aryl group or C.sub.7-C.sub.15 aralkyl group, which may contain halogen, hydroxy, C.sub.1-C.sub.6 saturated hydrocarbyloxy, C.sub.2-C.sub.6 saturated hydrocarbylcarbonyl or C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy moiety. The aliphatic hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. The hydrocarbyl, hydrocarbyloxy, hydrocarbylcarbonyl, hydrocarbyloxycarbonyl, hydrocarbylcarbonyloxy, and hydrocarbylsulfonyloxy groups may be straight, branched or cyclic. Groups R.sup.9 may be identical or different when x and/or z is 2 or more.

[0095] Of these, R.sup.9 is preferably hydroxy, —N(R.sup.9C)—C(═O)—R.sup.9D, —N(R.sup.9C)—C(═O)—O—R.sup.9D, fluorine, chlorine, bromine, methyl or methoxy.

[0096] Rf.sup.1 to Rf.sup.4 are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf.sup.1 to Rf.sup.4 is fluorine or trifluoromethyl, or Rf.sup.1 and Rf.sup.2, taken together, may form a carbonyl group. More preferably, both Rf.sup.3 and Rf.sup.4 are fluorine.

[0097] Examples of the anion having formula (1E) are shown below, but not limited thereto. X.sup.B1 is as defined above.

##STR00214## ##STR00215## ##STR00216## ##STR00217## ##STR00218## ##STR00219## ##STR00220## ##STR00221## ##STR00222## ##STR00223## ##STR00224## ##STR00225## ##STR00226## ##STR00227## ##STR00228## ##STR00229## ##STR00230## ##STR00231##

##STR00232## ##STR00233## ##STR00234## ##STR00235## ##STR00236## ##STR00237##

##STR00238## ##STR00239## ##STR00240## ##STR00241## ##STR00242## ##STR00243## ##STR00244## ##STR00245## ##STR00246## ##STR00247## ##STR00248## ##STR00249## ##STR00250## ##STR00251## ##STR00252##

##STR00253## ##STR00254## ##STR00255## ##STR00256## ##STR00257## ##STR00258## ##STR00259## ##STR00260## ##STR00261## ##STR00262## ##STR00263##

[0098] 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 2021-035935, and anions as described in JP-A 2018-092159.

[0099] 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 2016-065016, and JP-A 2019-202974; fluorine-free benzenesulfonic acid or alkylsulfonic acid anions having an iodized aromatic group bonded thereto as described in JP 6645464.

[0100] Also useful are 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.

[0101] The sulfonium salt having formula (1) may be synthesized, for example, by an ion exchange between a weak acid salt of the sulfonium cation and an ammonium salt having the non-nucleophilic counter ion.

[0102] In the resist composition, the sulfonium salt having formula (1) is preferably present in an amount of 0.01 to 1,000 pats by weight, more preferably 0.05 to 500 parts by weight per 100 parts by weight of the base polymer to be described below, in view of sensitivity and acid diffusion-suppressing effect.

Base Polymer

[0103] In one preferred embodiment, the resist composition comprises a base polymer. When the resist composition is of positive tone, a base polymer comprising repeat units having an acid labile group is used. The repeat units having an acid labile group are preferably repeat units having the formula (a1) or repeat units having the formula (a2. These repeat units are also referred to as repeat units (a1) or (a2).

##STR00264##

[0104] In formulae (a1) and (a2) R.sup.A is each independently hydrogen or methyl. X.sup.1 is a single bond, phenylene, naphthylene, or a C.sub.1-C.sub.12 linking group containing at least one moiety selected from an ester bond, ether bond and lactone ring. X.sup.2 is a single bond or ester bond. X.sup.3 is a single bond, ether bond or ester bond. R.sup.11 and R.sup.12 are each independently an acid labile group. R.sup.13 is fluorine, trifluoromethyl, cyano, a C.sub.1-C.sub.6 saturated hydrocarbyl group, C.sub.1-C.sub.6 saturated hydrocarbyloxy group, C.sub.2-C.sub.7 saturated hydrocarbylcarbonyl group, C.sub.2-C.sub.7 saturated hydrocarbylcarbonyloxy group, Or C.sub.2-C.sub.7 saturated hydrocarbyloxycarbonyl group. R.sup.14 is a single bond or a C.sub.1-C.sub.6 alkanediyl group in which some constituent —CH.sub.2— may be replaced by an ether bond or ester bond. The subscript “a” is 1 or 2, “b” is an integer of 0 to 4, and a+b is from 1 to 5.

[0105] Examples of the monomer from which repeat units (a1) are derived are shown below, but not limited thereto. Herein R.sup.A and R.sup.11 are as defined above.

##STR00265## ##STR00266##

[0106] Examples of the monomer from which repeat units (a2) are derived are shown below, but not limited thereto. Herein R.sup.A and R.sup.12 are as defied above.

##STR00267##

[0107] The acid labile groups represented by R.sup.11 and R.sup.12 in formulae (a1) and (a2) include those described in USP 8,5741,817 (JP-A 2013-080033) and USP 8,846, 303 (JP-A 2013-083821).

[0108] Typically, the acid labile groups are selected from groups having the following formulae (L-1) to (L-3).

##STR00268##

[0109] In formulae (L-1) and (L-2), R.sup.L1 and R.sup.L2 are each independently a C.sub.1-C.sub.40, hydrocarbyl group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Preferred are C.sub.1-C.sub.40, especially C.sub.1-C.sub.20 saturated hydrocarbyl groups.

[0110] In formula (L-1), c is an integer of 0 to 10, preferably 1 to 5.

[0111] In formula (L-2), R.sup.L3 and R.sup.L4 are each independently hydrogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Preferred are C.sub.1-C.sub.20 saturated hydrocarbyl groups. Any two of R.sup.L2, R.sup.L3 and R.sup.L4 may bond together to form a ring, typically alicyclic, with the carbon atom or carbon and oxygen atoms to which they are attached, the ring containing 3 to 20 Carbon atoms, preferably 4 to 16 carbon atoms.

[0112] In formula (L-3), R.sup.L5, R.sup.L6 and R.sup.L7 are each independently a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom such as oxygen, sulfur, nitrogen or fluorine. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Preferred are C.sub.1-C.sub.20 saturated hydrocarbyl groups. Any two of R.sup.L5, R.sup.L6 and R.sup.L7 may bond together to form a ring, typically alicyclic, with the carbon atom to which they are attached, the ring containing 3 to 20 carbon atoms, preferably 4 to 16 carbon atoms.

[0113] The base polymer may further comprise repeat units (b) having a phenolic hydroxy group as an adhesive group. Examples of suitable monomers from which repeat units (b) are derived are given below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00269##

[0114] Further, repeat units (c) having another adhesive group selected from hydroxy (other than the foregoing phenolic hydroxy), lactone ring, sultone ring, ether bond, ester bond, sulfonic ester bond, carbonyl, sulfonyl, cyano and carboxy groups may also be incorporated in the base polymer. Examples of suitable monomers from which repeat units (c) are derived are given below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00270## ##STR00271## ##STR00272## ##STR00273## ##STR00274## ##STR00275## ##STR00276## ##STR00277## ##STR00278## ##STR00279##

##STR00280## ##STR00281## ##STR00282##

##STR00283## ##STR00284## ##STR00285## ##STR00286## ##STR00287## ##STR00288## ##STR00289##

[0115] In another preferred embodiment, the base polymer may further comprise repeat units (d) derived from indene, benzofuran, benzothiophene, acenaphthylene, chromone, coumarin, and norbornadiene, or derivatives thereof. Examples of suitable monomers from which repeat units (d) are derived are given below, but not limited thereto.

##STR00290##

[0116] The base polymer may further include repeat units (e) which are derived from styrene, vinylnaphthalene, vinylanthracene, vinylpyrene, methyleneindene, vinylpyridine, vinylcarbazole, or derivatives thereof.

[0117] In a further embodiment, the base polymer may further comprise repeat units (f) derived from an onium salt having a polymerizable unsaturated bond. The preferred repeat units (f) include repeat units having formula (f1), repeat units having formula (f2), and repeat units having formula (f3). These nits are simply referred to as repeat units (f1), (f2) and (f3), which may be used alone or in combination of two or more types.

##STR00291##

[0118] In formulae (f1) to (f3) R.sup.A is each independently hydrogen or methyl. Z.sup.1 is a single bond, a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, naphthylene or a C.sub.7-C.sub.18 group obtained by combining the foregoing, or —O—Z.sup.11—, —C(═O)—O—Z.sup.11— or —C(═O)—NH—Z.sup.11—, wherein Z.sup.11 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, naphthylene or a C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety. Z.sup.2 is a single bond or ester bond. Z.sup.3 is a single bond, —Z.sup.31—C(═O)—O—, —Z.sup.31—O— or —Z.sup.31—O—C(═O)—, wherein Z.sup.31 is a C.sub.1-C.sub.12 hydrocarbylene group, phenylene or a C.sub.7-C.sub.18 group obtained by combining the foregoing, which may contain a carbonyl moiety, ester bond, ether bond, iodine or bromine. Z.sup.4 is methylene, 2,2,2-trifluoro-1,1-ethanediyl or carbonyl. Z.sup.5 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, —O—Z.sup.51—, —C(═O)—O—Z.sup.51—, or —C(═O)—NH—Z.sup.51—, wherein Z.sup.51 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene, fluorinated phenylene, or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond, halogen or hydroxy moiety.

[0119] In formulae (f1) to (3), R.sup.21 to R.sup.28 are each independently halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. The hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof are as exemplified above for the hydrocarbyl group R.sup.1 in formula (1). In the hydrocarbyl group, some or all hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen and some constituent —CH.sub.2— may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain hydroxy, fluorine, chlorine, bromine, iodine, cyano, nitro, carbonyl, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (—C(═O)—O—C(═O)—), or haloalkyl moiety. A pair of R.sup.23 and R.sup.24, or R.sup.26 and R.sup.27 may bond together to form a ring with the sulfur atom to which they are attached. Examples of the ring are as exemplified for the ring that two groups R.sup.8 in formula (1), taken together, form with the sulfur atom to which they are attached.

[0120] In formula (f1), M.sup.− is a non-nucleophilic counter ion. Examples thereof include halide ions such as chloride and bromide ions; fluoroalkylsulfonate ions such as triflate, 1,1,1-trifluoroethanesulfonate, and nonafluorobutanesulfonate; arylsulfonate ions such as tosylate, benzenesulfonate. 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluorobenzenesulfonate; alkylsulfonate ions such as mesylate and butanesulfonate; imide ions such as bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide and bis(perfluorobutylsulfonyl)imide; and methide ions such as tris(trifluoromethylsulfonyl)methide and tris(perfluoroethylsulfonyl)methide.

[0121] As the non-nucleophilic counter ion M.sup.−, an anion having any one of formulae (1A) to (1E) is also applicable.

[0122] Examples of the cation in the monomer from which repeat unit (f1) is derived are shown below, but not limited thereto. R.sup.A is as defined above.

##STR00292## ##STR00293## ##STR00294## ##STR00295##

[0123] Examples of the cation in the monomer from which repeat unit (2) or (3) is derived include the sulfenium cations described in JP-A 2017-219836.

[0124] Examples of the anion in the monomer from which repeat unit (f2) is derived are shown below, but not limited thereto. R.sup.A is as defined above.

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

##STR00306## ##STR00307## ##STR00308## ##STR00309## ##STR00310## ##STR00311## ##STR00312## ##STR00313##

[0125] Examples of the anion in the monomer from which repeat unit (f3) is derived are shown below, but not limited thereto. R.sup.A is as defined above.

##STR00314##

[0126] The attachment of an acid generator to the polymer main chain is effective in restraining acid diffusion, thereby preventing a reduction of resolution due to blur by acid diffusion. Also LWR or CDU is improved since the acid generator is uniformly distributed.

[0127] The base polymer for formulating the positive resist composition comprises repeat units (a1) or (a2) having an acid labile group as essential component and additional repeat units (b), (c), (d), (e), and (f) as optional components. A fraction of units (a1), (a2) (b), (c), (d), (e), and (f) is: preferably 0≤a1<1.0, 0≤a2<1.0, 0<a1+a2<1.0, 0≤b≤0.9, 0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, and 0≤f≤0.5; more preferably 0≤a1≤0.9, 0≤a2≤0.9, 0.1≤a1+a2≤0.9, 0≤b≤0.8, 0≤c≤0.8, 0≤d≤0.7, 0≤e≤0.7, and 0≤f≤0.4; and even more preferably 0≤a1≤0.8, 0≤a2≤0.8, 0.1≤a1+a2≤0.8, 0≤b≤0.75, 0≤c≤0.75, 0≤d≤0.6, 0≤e≤0.6, and 0≤f≤0.3. Notably, f=f1+f2+f3, meaning that unit (f) is at least one of units (f1) to (f3), and a1+a2+b+c+d+e+f=1.0.

[0128] For the base polymer for formulating the negative resist composition, an acid labile group is not necessarily essential. The base polymer comprises repeat units (b), and optionally repeat units (c), (d) (e), and/or (f). A fraction of these units is: preferably 0<b≤1.0, 0≤c≤0.9, 0≤d≤0.8, 0≤e≤0.8, and 0≤f≤0.05; more preferably 0.2≤b≤1.0, 0≤c≤0.8, 0≤d≤0.7, 0≤e≤0.7, and 0≤f≤0.4; and even more preferably 0.3≤b≤1.0, 0≤c≤0.75, 0≤d≤0.6, 0≤e≤0.6, and 0≤f≤0.3. Notably, f=f1+f2+f3, meaning that unit (f) is at least one of units (f1) to (3), and b+c+d+e+f=1.0.

[0129] The base polymer may be synthesized by any desired methods, for example, by dissolving one or more monomers selected from the monomers corresponding to the foregoing repeat units in an organic solvent, adding a radical polymerization initiator thereto, and heating for polymerization. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahydrofuran, diethyl ether, and dioxane. Examples of the polymerization initiator used herein include 2,2′-azobisisobutyronitrile (AIBN), 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2-azobis(2-methylpropionate), benzoyl peroxide, and lauroyl peroxide. Preferably the polymerization temperature is 50 to 80° C., and the reaction time is 2 to 100 hours, more preferably 5 to 20 hours.

[0130] When a monomer having a hydroxy group is copolymerized, the hydroxy group may be replaced by an acetal group susceptible to deprotection with acid, typically ethoxyethoxy, prior to polymerization, and the polymerization be followed by deprotection with weak acid and water. Alternatively, the hydroxy group may be replaced by an acetyl, formyl, pivaloyl or similar group prior to polymerization, and the polymerization be followed by alkaline hydrolysis.

[0131] When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, an alternative method is possible. Specifically, acetoxystyrene or acetoxyvinylnaphthalene is used instead of hydroxystyrene or hydroxyvinylnaphthalene, and after polymerization, the acetoxy group is deprotected by alkaline hydrolysis, for thereby converting the polymer product to hydroxystyrene or hydroxyvinylnaphthalene. For alkaline hydrolysis, a base such as aqeuous ammonia or triethylamine may be used. Preferably the reaction temperature is −20° C. to 100° C., more preferably 0° C. to 60° C., and the reaction time is 0.2 to 100 hours, more preferably 0.5 to 20 hours.

[0132] The base polymer should preferably have a weight average molecular weight (Mw) in the range of 1,000 to 500,000, and more preferably 2,000 to 30,000, as measured by GPC versus polystyrene standards using tetrahydrofuran (TI-IF) solvent. A Mw in the range ensures that the resist film has heat resistance and high solubility in alkaline developer.

[0133] If a base polymer has a wide molecular weight distribution or dispersity (Mw/Mn), which indicates the presence of lower and higher molecular weight polymer fractions, there is a possibility that foreign matter is left on the pattern or the pattern profile is degraded. The influences of Mw and Mw/n become stronger as the pattern rule becomes finer. Therefore, the base polymer should preferably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size.

[0134] It is understood that a blend of two or more polymers which differ in compositional ratio, Mw or Mw/Mn is acceptable.

Organic Solvent

[0135] An organic solvent may be added to the resist composition. The organic solvent used herein is not particularly limited as long as the foregoing and other components are soluble therein. Examples of the organic solvent are described in JP-A 2008-111103, paragraphs [0144]-[0145] (U.S. Pat. No. 7,537,880). Exemplary solvents include ketones such as cyclohexanone, cyclopentanone, methyl-2-n-pentyl ketone and 2-heptanone; alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol and diacetone alcohol (DAA); ether such as propylene glycol monomethyl ether (PGME), ethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol dimethylether, 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, propylene glycol mono-tert-butyl ether acetate, methyl 2-hydroxyisobutyrate, ethyl 2-hydroxyisobutyrate, propyl 2-hydroxyisobutyrate, and butyl 2-hydroxyisobutyrate; and lactones such as γ-butyrolactone, which may be used alone or in admixture.

[0136] The organic solvent is preferably added in an amount of 100 to 10.000 parts, and more preferably 200 to 8,000 parts by weight per 100 parts by weight of the base polymer.

Quencher

[0137] The resist composition may further comprise a quencher. As used herein, the “quencher” refers to a compound capable of trapping the acid generated from the acid generator for thereby preventing the acid from diffusing to the unexposed region.

[0138] The quencher is typically selected from conventional basic compounds. Conventional basic compounds include primary, secondary, and tertiary aliphatic amines, mixed ammines, aromatic amines, heterocyclic amines, nitrogen-containing compounds with carboxy group, nitrogen-containing compounds with sulfonyl group, nitrogen-containing compounds with hydroxy group, nitrogen-containing compounds with hydroxyphenyl group, alcoholic nitrogen-containing compounds, amide derivatives, imide derivatives, and carbamate derivatives. Also included are primary, secondary, and tertiary amine compounds, specifically amine compounds having a hydroxy, ether bond, ester bond, lactone ring, cyano, or sulfonic ester bond as described in JP-A 2008-111103, paragraphs [0146]-[0164], and compounds having a carbamate group as described in JP 3790649. Addition of a basic compound may be effective for further suppressing the diffusion rate of acid in the resist film or correcting the pattern profile.

[0139] Suitable quenchers also include onium salts such as sulfonium salts, iodonium salts and ammonium salts of sulfonic acids which are not fluorinated at α-position, carboxylic acids or fluorinated alkoxides, as described in JP-A 2008-158339. While an α-fluorinated sulfonic acid, imide acid, and methide acid are necessary to deprotect the acid labile group of carboxylic acid ester, an α-non-fluorinated sulfonic acid, carboxylic acid or fluorinated alcohol is released by salt exchange with an α-non-fluorinated onium salt. The α-non-fluorinated sulfonic acid, carboxylic acid and fluorinated alcohol function as a quencher because they do not induce deprotection reaction.

[0140] Exemplary such quenchers include a compound (onium salt of α-non-fluorinated sulfonic acid) having the formula (2), a compound (onium salt of carboxylic acid) having the formula (3), and a compound (onium salt of alkoxide) having the formula (4).

R.sup.101—SO.sub.3.sup.− Mq.sup.+  (2)

R.sup.102—Co.sub.2.sup.− Mq.sup.+  (3)

R.sup.103—O.sup.− Mq.sup.+  (4)

[0141] In formula (2), R.sup.101 is hydrogen or a C.sub.1-C.sub.4n hydrocarbyl group which may contain a heteroatom, exclusive of the hydrocarbyl group in which the hydrogen bonded to the carbon atom at α-position of the sulfo group is substituted by fluorine or fluoroalkyl moiety.

[0142] The C.sub.1-C.sub.40 hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.40 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl tert-pentyl, pentyl, n-hexyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl; C.sub.3-C.sub.40 Cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, cycloheptylmethyl, cyclopentylethyl, cycloheptylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, tricyclo[5.2.1.0.sup.2,6]decanyl, adamantyl, and adamantylmethyl; C.sub.2-C.sub.40 alkenyl groups such as vinyl, allyl, propenyl, butenyl and hexenyl; C.sub.3-C.sub.40 cyclic unsaturated aliphatic hydrocarbyl groups such as cyclohexenyl; C.sub.6-C.sub.40 aryl groups such as phenyl, naphthyl, alkylphenyl groups (e.g., 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-tert-butylphenyl, 4-n-butylphenyl), dialkylphenyl groups (e.g., 2,4-dimethylphenyl and 2,4,6-triisopropylphenyl), alkylnaphthyl groups (e.g., methylnaphthyl and ethylnaphthyl), dialkylnaphthyl groups (e.g., dimethylnaphthyl and diethylnaphthyl); and C.sub.7-C.sub.40 aralkyl groups such as benzyl, 1-phenylethyl and 2-phenylethyl.

[0143] In the hydrocarbyl group, some or all of the hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some constituent —CH.sub.2— may be replaced by a moiety containing a heteroatom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxy moiety, cyano moiety, carbonyl moiety, ether bond, ester bond, sulfonic ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (—C(═O)—O—C(═O)—), or haloalkyl moiety. Suitable heteroatom-containing hydrocarbyl groups include heteroaryl groups such as thienyl, 4-hydroxyphenyl, alkoxyphenyl groups such as 4-methoxyphenyl, 3-methoxyphenyl, 2-methoxyphenyl, 4-ethoxyphenyl, 4-tert-butoxyphenyl, 3-tert-butoxyphenyl; alkoxynaphthyl groups such as methoxynaphthyl, ethoxynaphthyl, n-propoxynaphthyl and n-butoxynaphthyl; dialkoxynaphthyl groups such as dimethoxynaphthyl and diethoxynaphthyl; and aryloxyalkyl groups, typically 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl, 2-(1-naphthyl)-2-oxoethyl and 2-(2-naphthyl)-2-oxoethyl.

[0144] In formula (3), R.sup.102 is as C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom. Examples of the hydrocarbyl group R.sup.102 are as exemplified above for the hydrocarbyl group R.sup.101. Also included are fluorinated alkyl groups such as trifluoromethyl, trifluoroethyl, 2,22-trifluoro-1-methyl-1-hydroxyethyl, 2,2,2-trifluoro-1-(trifluoromethyl)-1-hydroxyethyl, and fluorinated aryl groups such as pentafluorophenyl and 4-trifluoromethylphenyl.

[0145] In formula (4). R.sup.103 is a C.sub.1-C.sub.8 saturated hydrocarbyl group containing at least 3 fluorine atoms or a C.sub.6-C.sub.10 aryl group containing at least 3 fluorine atoms, the hydrocarbyl and aryl groups optionally containing a nitro moiety.

[0146] In formulae (2), (3) and (4). Mq.sup.+ is an onium cation. The onium cation is preferably a sulfonium iodonium or ammonium cation, with the sulfonium cation being more preferred. Suitable sulfonium cations are as exemplified in U.S. Pat. No. 10,295,904 (JP-A 2017-219836).

[0147] A sulfonium salt of iodized benzene ring-containing carboxylic acid having the formula (5) is also useful as the quencher.

##STR00315##

[0148] In formula (5), R.sup.201 is hydroxy, fluorine, chlorine, bromine, amino, nitro, cyano, or a C.sub.1-C.sub.6 saturated hydrocarbyl, C.sub.1-C.sub.6 saturated hydrocarbyloxy, C.sub.2-C.sub.6 saturated hydrocarbylcarbonyloxy, or C.sub.1-C.sub.4 saturated hydrocarbylsulfonyloxy group, in which some or all hydrogen may be substituted by halogen, or —N(R.sup.201A)—C(═O)—R.sup.201B or —N(R.sup.201A)—C(═O)—O—R.sup.201B, wherein R.sup.201A is hydrogen or a C.sub.1-C.sub.6 saturated hydrocarbyl group and R.sup.201B is a C.sub.1-C.sub.6 saturated hydrocarbyl or C.sub.2-C.sub.8 unsaturated aliphatic hydrocarbyl group.

[0149] In formula (5), x′ is an integer of 1 to 5, y′ is an integer of 0 to 3, and z′ is an integer of 1 to 3. L.sup.11 is a single bond, or a C.sub.1-C.sub.20 (z′+1)-valent linking group which may contain an ether bond, carbonyl, ester bond, amide bond, sultone ring, lactam ring, carbonate bond, halogen, hydroxy or carboxy moiety or a mixture thereof. The saturated hydrocarbyl, saturated hydrocarbyloxy, saturated hydrocarbylcarbonyloxy and saturated hydrocarbylsulfonyloxy groups may be straight, branched or cyclic. Groups R.sup.201 may be identical or different when y′ and/or z′ is 2 or 3.

[0150] In formula (5), R.sup.202, R.sup.203 and R.sup.204 are each independently halogen 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. Examples thereof are as exemplified for the hydrocarbyl group R.sup.8 in formula (1). In these hydrocarbyl groups, some or all hydrogen may be substituted by hydroxy, carboxy, halogen, oxo, cyano, nitro, sultone, sulfone, or sulfonium salt-containing moiety, or some constituent —CH.sub.2— may be replaced by an ether bond, ester bond, carbonyl, amide bond, carbonate bond or sulfonic ester bond. A pair of R.sup.202 and R.sup.203 may bond together to form a ring with the sulfur atom to which they are attached.

[0151] Examples of the compound having formula (5) include those described in U.S. Pat. No. 10,295,904 (JP-A 2017-219836) and US 20210188770 (JP-A 2021-091666).

[0152] Also useful are quenchers of polymer type as described in U.S. Pat. No. 7,598,016 (JP-A 2008-239918). The polymeric quencher segregates at the resist film surface and thus enhances the rectangularity of resist pattern. When a protective film is applied as is often the case in the immersion lithography, the polymeric quencher is also effective for preventing a film thickness loss of resist pattern or rounding of pattern top.

[0153] Other useful quenchers include sulfonium salts of betaine structure as described in JP 6848776 and JP-A 2020-037544, fluorine-free methide acids as described in JP-A 2020-055797, sulfonium salts of sulfonamide as described in JP 5807552, and sulfonium salts of iodized sulfonamide as described in JP-A 2019-211751.

[0154] The quencher is preferably added in an amount of 0 to 5 parts, more preferably 0 to 4 parts by weight per 100 parts by weight of the base polymer. The quencher may be used alone or in admixture.

Other Components

[0155] In addition to the foregoing components, the resist composition may contain other components such as an acid generator other than the sulfonium salt having formula (1), surfactant, dissolution inhibitor, crosslinker, water repellency improver and acetylene alcohol. Each of the other components may be used alone or in admixture.

[0156] The other acid generator is typically a compound (PAG) capable of generating an acid upon exposure to actinic ray or radiation. Although the PAG used herein may be any compound capable of generating an acid upon exposure to high-energy radiation, those compounds capable of generating sulfonic acid, imide acid (imidic acid) or methide acid are preferred. Suitable PAGs include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. Exemplary PAGs are described in JP-A 2008-111103, paragraphs [0122]-[0142] (U.S. Pat. No. 7,537,880), JP-A 2018-005224, and JP-A 2018-025789. The other acid generator is preferably used in an amount of 0 to 200 parts, more preferably 0.1 to 100 parts by weight per 100 parts by weight of the base polymer.

[0157] Exemplary surfactants are described in JP-A 2008-111103, paragraphs [0165]-[0166]. Inclusion of a surfactant may improve or control the coating characteristics of the resist composition. The surfactant is preferably added in an amount of 0.0001 to 10 parts by weight per 100 parts by weight of the base polymer.

[0158] In the embodiment wherein the resist composition is of positive tone, the inclusion of a dissolution inhibitor may lead to an increased difference in dissolution rate between exposed and unexposed areas and a further improvement in resolution. The dissolution inhibitor is typically a compound having at least two phenolic hydroxy groups on the molecule, in which an average of from 0 to 100 mol % of all the hydrogen atoms on the phenolic hydroxy groups are replaced by acid labile groups or a compound having at least one carboxy group on the molecule, in which an average of 50 to 100 mol % of all the hydrogen atoms on the carboxy groups are replaced by acid labile groups, both the compounds having a molecular weight of 100 to 1,000, and preferably 150 to 800. Typical are bisphenol A, trisphenol, phenolphthalein, cresol novolac, naphthalenecarboxylic acid, adamantanecarboxylic acid, and cholic acid derivatives in which the hydrogen atom on the hydroxy or carboxy group is replaced by an acid labile group, as described in USP 7.771,914 (JP-A 2008-122932, paragraphs [0155]-[0178]).

[0159] The dissolution inhibitor is preferably added in an amount of 0 to 50 parts, more preferably 5 to 40 parts by weight per 100 parts by weight of the base polymer.

[0160] In the case of negative resist compositions, a negative pattern may be formed by adding a crosslinker to reduce the dissolution rate of exposed area. Suitable crosslinkers which can be used herein include epoxy compounds, melamine compounds, guanamine compounds, glycoluril compounds and urea compounds having substituted thereon at least one group selected from among methylol, alkoxymethyl and acyloxymethyl groups, isocyanate compounds, azide compounds, and compounds having a double bond such as an alkenyloxy group. These compounds may be used as an additive or introduced into a polymer side chain as a pendant. Hydroxy-containing compounds may also be used as the crosslinker.

[0161] Suitable epoxy compounds include tris(2,3-epoxypropyl) isocyanurate, trimethylolethane triglycidyl ether, trimethylolpropane triglycidyl ether, and triethylolethane triglycidyl ether. Examples of the melamine compound include hexamethylol melamine, hexamethoxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups methoxymethylated and mixtures thereof, hexanmethoxyethyl melamine, hexaacyloxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups acyloxymethylated and mixtures thereof. Examples of the guanamine compound include tetramethylol guanamine, tetramethoxymethyl guanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, tetramethoxymethyl guanamine, tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof. Examples of the glycoluril compound include tetramethylol glycoluril, tetramethoxyglycoluril, tetramethoxymethyl glycoluril, tetramethylol glycoluril compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, tetramethylol glycoluril compounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof. Examples of the urea compound include tetramethylol urea, tetramethoxymethyl urea, tetramethylol urea compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, and tetramethoxymethyl urea.

[0162] Suitable isocyanate compounds include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexane diisocyanate. Suitable azide compounds include 1,1′-biphenyl-44′-bisazide, 4,4′-methylidenebisazide, and 4,4′-oxybisazide. Examples of the alkenyl ether group-containing compound include ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,2-propanediol divinyl ether, 1,4-butanediol divinyl ether, tetramethylene glycol divinyl ether, neopentyl glycol divinyl ether, trimethylol propane trivinyl ether, hexanediol divinyl ether, 14-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitol pentavinyl ether, and trimethylol propane trivinyl ether.

[0163] In the negative resist composition, the crosslinker is preferably added in an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weight per 100 parts by weight of the base polymer.

[0164] To the resist composition, a water repellency improver may also be added for improving the water repellency on surface of a resist film. The water repellency improver may be used in the topcoatless immersion lithography. Suitable water repellency improvers include polymers having a fluoroalkyl group and polymers having a specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue and are described in JP-A 2007-297590 and JP-A 2008-111103, for example. The water repellency improver to be added to the resist composition should be soluble in alkaline developers and organic solvent developers. The water repellency improver of specific structure with a 1,1,1,3,3,3-hexafluoro-2-propanol residue is well soluble in the developer. A polymer having an amino group or amine salt copolymerized as repeat units may serve as the water repellent additive and is effective for preventing evaporation of acid during PEB, thus preventing any hole pattern opening failure after development. An appropriate amount of the water repellency improver is 0 to 20 parts, preferably 0.5 to 10 parts by weight per 100 parts by weight of the base polymer.

[0165] Also, an acetylene alcohol may be blended in the resist composition. Suitable acetylene alcohols are described in JP-A 2008-122932, paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcohol blended is 0 to 5 parts by weight per 100 parts by weight of the base polymer.

[0166] The resist composition of the invention may be prepared by intimately mixing the selected components to form a solution, adjusting so as to meet a predetermined range of sensitivity and film thickness, and filtering the solution. The filtering step is important for reducing the number of defects in a resist pattern after development. The membrane for filtration or filter has a pore size of preferably up to 1 μm, more preferably up to 10 μm, even more preferably up to 5 nm. As the filter pore size is smaller, the number of defects in a small size pattern is reduced. The membrane is typically made of such materials as tetrafluoroethylene, polyethylene, polypropylene, nylon, polyurethane, polycarbonate, polyimide, polyamide-imide, and polysulfone. Membranes of tetrafluoroethylene, polyethylene and polypropylene which have been surface-modified so as to increase an adsorption ability are also useful, Unlike the membranes of nylon, polyurethane, polycarbonate and polyimide possessing an ability to adsorb gel and metal ions due to their polarity, men branes of tetrafluoroethylene, polyethylene and polypropylene which are non-polar do not possess the gel/metal ion adsorption ability in themselves, but can be endowed with the adsorption ability by surface modification with a functional group having polarity. In particular, filters obtained from surface modification of membranes of polyethylene and polypropylene in which pores of a smaller size can be perforated are effective for removing not only submicron particles, but also polar particles and metal ions. A laminate of membranes of different materials or a laminate of membranes having different pore sizes is also useful.

[0167] A membrane having an ion exchange ability may also be used as the filter. For example, an ion-exchange membrane capable of adsorbing cations acts to adsorb metal ions for thereby reducing metal impurities.

[0168] In the practice of filtration, a plurality of filters may be connected through serial or parallel pipes. The type and pore size of membranes in the plural filters may be the same or different. The filter may be disposed in a conduit between vessels. Alternatively, the filter is disposed in a conduit between inlet and outlet ports of a single vessel so that the solution is filtered while it is circulated.

Process

[0169] The resist composition is used in the fabrication of various integrated circuits. Pattern formation using the resist composition may be performed by well-known lithography processes. The process generally involves the steps of applying the resist composition 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. If necessary, any additional steps may be added.

[0170] Specifically, the resist composition is first applied onto a substrate on which an integrated circuit is to be formed (e.g, Si, SiO.sub.2, SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating) or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO, CrON, MoSi.sub.2, SiO.sub.2, MoSi.sub.2 μmultilayer film, Ta, TaN, TaCN, Ru, Nb, Mo, Mn, Co, Ni or alloys thereof) by a suitable coating technique such as spin coating, roll coating, flow coating, dipping, spraying or doctor coating. The coating is prebaked on a hotplate preferably at a temperature of 60 to 150° C. for 10 seconds to 30 minutes, more preferably at 80 to 120° C. for 30 seconds to 20 minutes. The resulting resist film is generally 0.01 to 2 pin thick.

[0171] The resist film is then exposed to a desired pattern of high-energy radiation such as UV, deep-UV, EB, EUV of wavelength 3 to 15 nm, x-ray, soft x-ray, excimer laser light, γ-ray or synchrotron radiation. When UV, deep-UV, EUV, x-ray, soft x-ray, excimer laser light, γ-ray or synchrotron radiation is used as the high-energy radiation, the resist film is exposed thereto directly or through a mask having a desired pattern in a dose of preferably about 1 to 200 mJ/cm.sup.2, more preferably about 10 to 100 mJ/cm.sup.2. When EB is used as the high-energy radiation, the resist film is exposed thereto directly or through a mask having a desired pattern in a dose of preferably about 0.1 to 300 ρC/cm.sup.2, more preferably about 0.5 to 200 μC/cm.sup.2. It is appreciated that the inventive resist composition is suited in micropatterning using KrF excimer laser, ArF excimer laser, EB. EUV, x-ray, soft x-ray, γ-ray or synchrotron radiation, especially in micropatterning using EB or EUV.

[0172] After the exposure, the resist film may be baked (PEB) on a hotplate or in an oven preferably at 30 to 150° C. for 10 seconds to 30 minutes, more preferably at 50 to 120° C. for 30 seconds to 20 minutes.

[0173] After the exposure or PEB, the resist film is developed in a developer in the form of an aqueous base solution for 3 seconds to 3 minutes, preferably 5 seconds to 2 minutes by conventional techniques such as dip, puddle and spray techniques. A typical developer is a 0.1 to 10 wt % preferably 2 to 5 wt % aqueous solution of tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), or tetrabutylammonium hydroxide (TBAH). In the case of positive tone, the resist film in the exposed area is dissolved in the developer whereas the resist film in the unexposed area is not dissolved. In this way, the desired positive pattern is formed on the substrate. In the case of negative tone, inversely the resist film in the exposed area is insolubilized whereas the resist film in the unexposed area is dissolved away.

[0174] In an alternative embodiment, a negative pattern can be obtained from the positive resist composition comprising a base polymer containing acid labile groups by effecting organic solvent development. The developer used herein is preferably selected from among 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, benzyl formate, phenylethyl formate, methyl 3-phenylpropionate, benzyl propionate, ethyl phenylacetate, and 2-phenylethyl acetate, and mixtures thereof.

[0175] At the end of development, the resist film is rinsed. As the rinsing liquid, a solvent which is miscible with the developer and does not dissolve the resist film is preferred. Suitable solvents include alcohols of 3 to 10 carbon atoms, ether compounds of 8 to 12 carbon atoms, alkanes, alkenes, and alkynes of 6 to 12 carbon atoms, and aromatic solvents. Specifically, suitable alcohols of 3 to 10 carbon atoms include n-propyl alcohol, isopropyl alcohol, 1-butyl alcohol, 2-butyl alcohol, isobutyl alcohol, t-butyl alcohol, 1-pentanol, 2-pentanol, 3-pentanol, t-pentyl alcohol, neopentyl alcohol, 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-3-pentanol, cyclopentanol, 1-hexanol, 2-hexanol, 3-hexanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 3,3-dimethyl-2-butanol, 2-ethyl-1-butanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol. 4-methyl-3-pentanol, cyclohexanol, and 1-octanol. Suitable ether compounds of 8 to 12 carbon atoms include di-n-butyl ether, diisobutyl ether, di-s-butyl ether, di-n-pentyl ether, diisopentyl ether, di-s-pentyl ether, di-t-pentyl ether, and di-n-hexyl ether. Suitable alkanes of*6 to 12 carbon atoms include hexane, heptane, octane, nonane, decane, undecane, dodecane, methylcyclopentane, dimethylcyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, cycloheptane, cyclooctane, and cyclononane. Suitable alkenes of 6 to 12 carbon atoms include hexene, heptene, octene, cyclohexene, methylcyclohexene, dimethylcyclohexene, cycloheptene, and cyclooctene. Suitable alkynes of 6 to 12 carbon atoms include hexyne, heptyne, and octyne. Suitable aromatic solvents include toluene, xylene, ethylbenzene, isopropylbenzene, t-butylbenzene and mesitylene.

[0176] Rinsing is effective for minimizing the risks of resist pattern collapse and defect formation. However, rinsing is not essential. If rinsing is omitted, the amount of solvent used may be reduced.

[0177] A hole or trench pattern after development may be shrunk by the thermal flow, RELACS® or DSA process. A hole pattern is shrunk by coating a shrink agent thereto, and baking such that the shrink agent may undergo crosslinking at the resist surface as a result of the acid catalyst diffusing from the resist layer during bake, and the shrink agent may attach to the sidewall of the hole pattern. The bake is preferably at a temperature of 70 to 180′C, more preferably 80 to 170° C., for a time of 10 to 300 seconds. The extra shrink agent is stripped and the hole pattern is shrunk.

EXAMPLES

[0178] Examples of the invention are given below by way of illustration and not by way of limitation. All parts are by weight (pbw). THE stands for tetrahydrofuran.

[0179] Acid generators PAG-1 to PAG-38 in the form of sulfonium salts used in resist compositions have the structure shown below. PAG-1 to PAG-38 were synthesized by ion exchange between an ammonium salt of fluorinated sulfonic acid providing the anion shown below and a sulfonium chloride providing the cation shown below.

##STR00316## ##STR00317## ##STR00318## ##STR00319## ##STR00320## ##STR00321## ##STR00322## ##STR00323## ##STR00324## ##STR00325##

Synthesis Example

[0180] Synthesis of Base Polymers (Polymers P-1 to P-5)

[0181] Base polymers (Polymers P-1 to P-5) of the structure shown below were synthesized by combining selected monomers, effecting copolymerization reaction in THF solvent, pouring the reaction solution into methanol, washing the solid precipitate with hexane, isolating, and drying. The base polymers were analyzed for composition by .sup.1H-NMR spectroscopy and for Mw and Mw/Mn by GPC versus polystyrene standards using THF solvent.

##STR00326##

Examples 1 to 43 and Comparative Examples 1 to 4

Preparation and Evaluation of Resist Compositions

(1) Preparation of Resist Compositions

[0182] Resist compositions were prepared by dissolving components in a solvent in accordance with the recipe shown in Tables 1 to 4, and filtering the solution through a filter having a pore size of 0.2 μm. The solvent contained 100 ppm of surfactant Polyfox PF-636 (Oumova Solutions, Inc.).

[0183] The components in Tables 1 to 4 are identified below.

Organic Solvents:

[0184] PGMEA (propylene glycol monomethyl ether acetate)

[0185] EL (ethyl lactate)

[0186] DAA (diacetone alcohol)

Blending acid generators: bPAG-1 and bPAG-2.

##STR00327##

Comparative Acid Generators: cPAG-1 to cPAG-4

##STR00328##

Quenchers: Q-1 and Q-2

[0187] ##STR00329##

(2) EL Lithography Test

[0188] Each of the resist compositions in Tables 1 to 4 was spin coated on a silicon substrate having a 20-nm coating of silicon-containing spin-on hard mask SHB-A940 (Shin-Etsu Chemical Co., Ltd., Si content 43 wt) and prebaked on a hotplate at 105° C. for 60 seconds to form a resist film of 50 nm thick. Using an EV scanner NXE3400 (ASML, NA 0.33, σ 0.90.6, quadrupole illumination), the resist film was exposed to EL through a mask bearing a hole pattern at a pitch 40 nm (on-wafer size) and +20% bias. The resist film was baked (PEB) on a hotplate at the temperature shown in Tables 1 to 4 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 20 nm.

[0189] The resist pattern was observed under CD-SEM (CG6300, Hitachi High-Technologies Corp.). The exposure dose that provides a hole pattern having a size of 20 inn is reported as sensitivity. The size of 50 holes printed at that dose was measured, from which a 3-fold value (3σ) of the standard deviation (σ) was computed and reported as CDU.

[0190] The resist compositions are shown in Tables 1 to 4 together with the sensitivity and CDU of EUV lithography.

TABLE-US-00001 TABLE 1 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU Example (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm.sup.2) (nm) 1 P-1 PAG-1 Q-1 PGMEA (500) 80 36 3.0 (100) (20.8) (5.28) EL (2,000) 2 p-1 PAG-2 Q-1 PGMEA (500) 80 28 3.1 (100) (30.3) (5.28) EL (2,000) 3 p-1 PAG-3 Q-1 PGMEA (500) 80 33 2.9 (100) (29.3) (5.28) EL (2,000) 4 p-1 PAG-4 Q-1 PGMEA (2,000) 80 35 3.2 (100) (27.9) (5.28) DAA (500) 5 p-1 PAG-5 Q-1 PGMEA (2,000) 80 35 2.9 (100) (27.8) (5.28) DAA (500) 6 P-1 PAG-6 Q-1 PGMEA (2.000) 80 34 2.9 (100) (31.6) (5.28) DAA (500) 7 P-1 PAG-7 Q-1 PGMEA (2,000) 80 35 2.9 (100) (30.2) (5.28) DAA (500) 8 P-1 PAG-8 Q-1 PGMEA (2,000) 80 34 3.0 (100) (27.5) (5.28) DAA (500) 9 P-1 PAG-9 Q-1 PGMEA (2.000) 80 35 3.2 (100) (30.2) (5.28) DAA (500) 10 P-1 PAG-10 Q-1 PGMEA (2,000) 80 31 3.0 (100) (31.4) (5.28) DAA (500) 11 P-1 PAG-11 Q-1 PGMEA (2,000) 80 33 3.1 (100) (30.9) (5.28) DAA (500) 12 P-1 PAG-12 Q-1 PGMEA (2,000) 80 30 2.8 (100) (31.6) (5.28) DAA (500) 13 P-2 PAG-12 Q-1 PGMEA (2.000) 80 29 2.9 (100) (31.6) (5.28) DAA (500) 14 P-3 PAG-12 Q-1 PGMEA (2,000) 80 28 2.7 (100) (31.6) (5.28) DAA (500) 15 P-4 PAG-12 Q-1 PGMEA (2,000) 80 32 3.2 (100) (31.6) (5.28) DAA (500) 16 P-5 PAG-12 Q-2 PGMEA (2.000) 80 28 3.4 (100) (12.7) (6.52) DAA (500) 17 P-4 PAG-13 Q-1 PGMEA (2,000) 80 33 3.2 (100) (23.9) (5.28) DAA (500) 18 P-4 PAG-14 Q-1 PGMEA (2,000) 80 34 3.3 (100) (24.1) (5.28) DAA (500) 19 P-4 PAG-15 Q-1 PGMEA (2,000) 80 28 3.2 (100) (34.8) (5.28) DAA (500) 20 P-4 PAG-16 Q-1 PGMEA (2,000) 80 30 3.1 (100) (34.8) (5.28) DAA (500)

TABLE-US-00002 TABLE 2 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU Example (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm.sup.2) (am) 21 P-2 PAG-17 Q-1 PGMEA (2,000) 80 32 3.3 (100) (33.3) (5.28) DAA (500) 30 P-2 PAG-18 Q-1 PGMEA (2,000) 80 28 3.2 (100) (34.3) (5.28) DAA (500) 23 P-2 PAG-19 Q-1 PGMEA (2,000) 80 27 3.1 (100) (35.7) (5.28) DAA (500) 24 P-4 PAG-19 Q-1 PGMEA (500) 90 34 3.3 (100) (28.6) (4.50) EL (2,000) PAG-20 (5.8) 25 P-4 PAG-19 Q-1 PGMEA (500) 90 31 3.1 (100) (28.6) (4.50) EL (2,000) PAG-21 (6.1) 26 P-4 PAG-22 Q-1 PGMEA (2,000) 80 29 3.3 (100) (30.7) (5.28) DAA (500) 27 P-2 PAG-23 Q-1 PGMEA (2,000) 80 26 3.0 (100) (29.0) (5.28) DAA (500) 28 P-2 PAG-21 Q-1 PGMEA (2.000) 90 29 3.1 (100) (28.1) (5.28) DAA (500) 29 P-1 PAG-25 Q-1 PGMEA (2,000) 80 29 3.1 (100) (29.3) (5.28) DAA (500) 30 p-1 PAG-26 Q-1 PGMEA (2,000) 80 29 3.0 (100) (29.3) (5.28) DAA (500) 31 p-1 PAG-27 Q-1 PGMEA (2,000) 80 26 3.5 (100) (28.5) (5.28) DAA (500) 32 p-1 PAG-28 Q-1 PGMEA (2,000) 80 177 3.4 (100) (28.4) (5.28) DAA (500)

TABLE-US-00003 TABLE 3 Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU Example (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm.sup.2) (nm) 33 P-1 PAG-29 Q-1 PGMEA (2,000) 80 26 3.1 (100) (11.8) (5.28) DAA (500) bPAG-1 (14.6) 34 P-1 PAG-30 Q-1 PGMEA (2,000) 80 26 3.0 (100) (12.01 (5.28) DAA (500) bPAG-1 (14.6) 35 P-2 PAG-15 Q-1 PGMEA (2,000) 90 28 3.1 (100) (117.4) (5.28) DAA (500) bPAG-2 (11.0) 36 p-1 PAG-31 Q-1 PGMEA (2.000) 80 27 3.1 (100) (29.8) (5.28) DAA (500) P-1 PAG-32 Q-1 PGMEA (2,000) 80 23 3.0 (100) (31.1) (5.28) DAA (500) 38 P-1 PAG-33 Q-1 PGMEA (2,000) 80 26 3.2 (100) (29.9) (5.28) DAA (500) 39 P-1 PAG-34 Q-1 PGMEA (2.000) 80 27 3.1 (100) (28.8) (5.28) DAA (500) 40 P-1 PAG-35 Q-1 PGMEA (2,000) 80 24 3.3 (100) (27.5) (5.28) DAA (500) 41 P-1 PAG-36 Q-1 PGMEA (2,000) 80 73 3.4 (100) (27.6) (5.28) DAA (500) 42 P-1 PAG-37 Q-1 PGMEA (2,000) 80 28 3.1 (100) (28.1) (5.28) DAA (500) 43 P-1 PAG-38 Q-1 PGMEA (2,000) 80 26 3.0 (100) (28-1) (5.28) DAA (500)

TABLE-US-00004 TABLE 4 Comparative Polymer Acid generator Quencher Organic solvent PEB temp. Sensitivity CDU Example (pbw) (pbw) (pbw) (pbw) (° C.) (mJ/cm.sup.2) (nm) 1 P-1 cPAG-1 Q-1 PGMEA (2,000) 80 35 4.1 (100) (14.9) (5.28) DAA (500) 2 P-1 cPAG-2 Q-1 PGMEA (2,000) 80 38 4.3 (100) (16.3) (5.28) DAA (500) 3 P-1 cPAG-3 Q-1 PGMEA (2,000) 80 40 4.2 (100) (21.15) (5.28) DAA (500) 4 p-1 cPAG-4 Q-1 PGMEA (2,000) 80 38 3.8 (100) (20.4) (5.28) DAA (500)

[0191] It is demonstrated in Tables 1 to 4 that resist compositions comprising a sulfonium salt having formula (1) as the acid generator offer a high sensitivity and excellent CDU.

[0192] Japanese Patent Application No. 2022-010596 is incorporated herein by reference.

[0193] 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 to without departing from the scope of the appended claims.