CHEMICALLY AMPLIFIED NEGATIVE RESIST COMPOSITION AND RESIST PATTERN FORMING PROCESS

Abstract

A chemically amplified negative resist composition comprising (A) a quencher in the form of an onium salt containing an anion (Xq.sup.) which forms a conjugate acid (XqH) having a boiling point of lower than 165 C. and a molecular weight of up to 150, (B) a base polymer, and (C) a photoacid generator exhibits a high resolution and forms a pattern of satisfactory profile with low LER, fidelity and improved dose margin.

Claims

1. A chemically amplified negative resist composition comprising (A) a quencher, (B) a base polymer, and (C) a photoacid generator, said quencher (A) being an onium salt having the formula (A): ##STR00516## wherein Xq.sup. is an anion, which forms a conjugate acid (XqH) having a boiling point of lower than 165 C. and a molecular weight of up to 150, Z.sup.+ is a sulfonium cation having the formula (Z-1), a iodonium cation having the formula (Z-2), an ammonium cation having the formula (Z-3) or a sulfonium cation having the formula (Z-4): ##STR00517## wherein R.sup.1 to R.sup.9 are each independently halogen, or a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom, any two of R.sup.1 to R.sup.3 may bond together to form a ring with the sulfur atom to which they are attached, any two of R.sup.6 to R.sup.9 may bond together to form a ring with the nitrogen atom to which they are attached, ##STR00518## wherein m1 is 0 or 1, m2 is 0 or 1, m3 is 0 or 1, m4 is 0, 1, 2, 3 or 4, m5 is 0, 1, 2, 3 or 4, m6 is 0, 1, 2, 3, 4, 5 or 6, m7 is 0, 1, 2, 3, 4, 5 or 6, m8 is 0, 1 or 2, m9 is 0, 1 or 2, m10 is 0, 1 or 2, m11 is 0 or 1, m12 is 0, 1, 2, 3 or 4, m13 is 0, 1 or 2, m14 is 0, 1 or 2; meeting 0m6+m94 when m1=0, and 0m6+m96 when m1=1; 0m7+m104 when m2=0, and 0m7+m106 when m2=1; 1m4+m5+m8+m144 when m3=0, and 1m4+m5+m8+m146 when m3=1; 0m12+m134 when m11=0, and 0m12+m136 when m11=1, and m4+m121, R.sup.F1 to R.sup.F3 are each independently fluorine, a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, C.sub.1-C.sub.6 fluorinated saturated hydrocarbyloxy group, or C.sub.1-C.sub.6 fluorinated saturated hydrocarbylthio group, a plurality of RF may be identical or different when m5 is 2 or more, a plurality of R.sup.F2 may be identical or different when m6 is 2 or more, a plurality of R.sup.F3 may be identical or different when m7 is 2 or more, R.sup.10 to R.sup.13 are each independently halogen exclusive of iodine and fluorine, nitro, cyano, a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, C.sub.1-C.sub.20 hydrocarbyloxy group which may contain a heteroatom, or C.sub.1-C.sub.20 hydrocarbylthio group which may contain a heteroatom; when m8=2, two R.sup.10 may be identical or different and two R.sup.10 may bond together to form a ring with the carbon atoms to which they are attached; when m9=2, two R.sup.11 may be identical or different and two R.sup.11 may bond together to form a ring with the carbon atoms to which they are attached; when m10=2, two R.sup.12 may be identical or different and two R.sup.12 may bond together to form a ring with the carbon atoms to which they are attached; when m13=2, two R.sup.13 may be identical or different and two R.sup.13 may bond together to form a ring with the carbon atoms to which they are attached; the aromatic rings directly bonded to S.sup.+ in the sulfonium cation may bond together to form a ring with S.sup.+, L.sup.A and L.sup.B are each independently a single bond, ether bond, ester bond, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond, and X.sup.L is a single bond or a C.sub.1-C.sub.40 hydrocarbylene group which may contain a heteroatom; said base polymer containing a polymer comprising repeat units having the formula (B1): ##STR00519## wherein a1 is 0 or 1, a2 is 0, 1 or 2, a3 is an integer meeting 0a35+2(a2)a4, a4 is 1, 2 or 3, R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl, R.sup.21 is halogen, nitro group, carboxy group, an optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group, or optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, and A.sup.1 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some CH.sub.2 may be replaced by O.

2. The negative resist composition of claim 1 wherein the conjugate acid XqH of anion Xq.sup. is formic acid, acetic acid, propionic acid, butyric acid, trifluoroacetic acid, 3,3,3-trifluoropropionic acid, pivalic acid or nitric acid.

3. The negative resist composition of claim 1 wherein the polymer further comprises repeat units of at least one type selected from repeat units having the formula (B2) and repeat units having the formula (B3): ##STR00520## wherein b1 is 0 or 1, b2 is 0, 1 or 2, b3 is an integer meeting 0b35+2(b2)b4, b4 is 1, 2 or 3, b5 is 0, 1 or 2, b6 is 1 or 2, R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl, R.sup.31 is halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, R.sup.32 and R.sup.33 are each independently hydrogen, a C.sub.1-C.sub.15 saturated hydrocarbyl group which may be substituted with hydroxy or C.sub.1-C.sub.6 saturated hydrocarbyloxy moiety, or an optionally substituted C.sub.6-C.sub.15 aryl group, excluding that R.sup.32 and R.sup.33 are hydrogen at the same time, R.sup.32 and R.sup.33 may bond together to form a ring with the carbon atom to which they are attached, some CH.sub.2 in the ring may be replaced by O or S, R.sup.34 is halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, R.sup.35 and R.sup.36 are each independently hydrogen, a C.sub.1-C.sub.15 saturated hydrocarbyl group which may be substituted with hydroxy or C.sub.1-C.sub.6 saturated hydrocarbyloxy moiety, or an optionally substituted C.sub.6-C.sub.15 aryl group, excluding that R.sup.35 and R.sup.36 are hydrogen at the same time, R.sup.35 and R.sup.36 may bond together to form a ring with the carbon atom to which they are attached, some CH.sub.2 in the ring may be replaced by O or S, A.sup.2 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some CH.sub.2 may be replaced by O, W.sup.1 and W.sup.2 are each independently hydrogen, a C.sub.1-C.sub.10 aliphatic hydrocarbyl group, a C.sub.2-C.sub.10 aliphatic hydrocarbylcarbonyl group, or an optionally substituted C.sub.6-C.sub.15 aryl group.

4. The negative resist composition of claim 1 wherein the polymer further comprises repeat units of at least one type selected from repeat units having the formula (B4), repeat units having the formula (B5), and repeat units having the formula (B6): ##STR00521## wherein c and d are each independently 0, 1, 2, 3 or 4, e1 is 0 or 1, e2 is 0, 1 or 2, e3 is 0, 1, 2, 3, 4 or 5, R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl, R.sup.41 and R.sup.42 are each independently hydroxy, halogen, an optionally halogenated C.sub.1-C.sub.8 saturated hydrocarbyl group, optionally halogenated C.sub.1-C.sub.8 saturated hydrocarbyloxy group, or optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group, R.sup.43 is 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 hydrocarbyloxyhydrocarbyl group, C.sub.2-C.sub.20 saturated hydrocarbylthiohydrocarbyl group, halogen, nitro, cyano, C.sub.1-C.sub.20 saturated hydrocarbylsulfinyl group, or C.sub.1-C.sub.20 saturated hydrocarbylsulfonyl group, and A.sup.3 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some CH.sub.2 may be replaced by O.

5. The negative resist composition of claim 1 wherein the polymer further comprises repeat units of at least one type selected from repeat units having the formula (B7), repeat units having the formula (B8), repeat units having the formula (B9), repeat units having the formula (B10), and repeat units having the formula (B11): ##STR00522## wherein f1 and f2 are each independently 0, 1, 2 or 3, g1 is 0 or 1, g2 is 0, 1, 2, 3 or 4, g3 is 0, 1, 2, 3 or 4, meeting 0 g2+g34 when g1=0, and 0 g2+g36 when g1=1, R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl, Z.sup.1 is a single bond or an optionally substituted phenylene group, Z.sup.2 is a single bond, **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, phenylene group or a divalent group obtained by combining the foregoing, which may contain halogen, carbonyl moiety, ester bond, ether bond or hydroxy moiety, Z.sup.3 is a single bond, ether bond, ester bond, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond, Z.sup.4 is a single bond, or a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group or a divalent group obtained by combining the foregoing, which may contain halogen, carbonyl moiety, ester bond, ether bond or hydroxy moiety, Z.sup.5 is each independently a single bond, an optionally substituted phenylene, naphthylene, or *C(O)OZ.sup.5, Z.sup.51 is a C.sub.1-C.sub.10 aliphatic hydrocarbylene group which may contain halogen, hydroxy moiety, ether bond, ester bond or lactone ring, or phenylene or naphthylene group, Z.sup.6 is a single bond, ether bond, ester bond, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond, Z.sup.7 is each independently a single bond, ***Z.sup.71C(O)O, ***C(O)NHZ.sup.71, or ***OZ.sup.7, Z.sup.71 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, Z.sup.8 is each independently a single bond, ****Z.sup.81C(O)O, ****C(O)NHZ.sup.81, or ****OZ.sup.81, Z.sup.81 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, Z.sup.9 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, *C(O)OZ.sup.91, *C(O)N(H)Z.sup.91, or *OZ.sup.91, Z.sup.91 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety, * is a point of attachment to the carbon atom in the backbone, ** is a point of attachment to Z.sup.1, *** is a point of attachment to Z.sup.6, **** is a point of attachment to Z.sup.7, L.sup.1 is a single bond, ether bond, ester bond, carbonyl group, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond, Rf.sup.1 and Rf.sup.2 are each independently fluorine or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, Rf.sup.3 and Rf.sup.4 are each independently hydrogen, fluorine, or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, Rf.sup.5 and Rf.sup.6 are each independently hydrogen, fluorine, or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, excluding that all Rf.sup.V and Rf.sup.6 are hydrogen at the same time, Rf.sup.7 is fluorine, a C.sub.1-C.sub.6 fluorinated alkyl group, C.sub.1-C.sub.6 fluorinated alkoxy group, or C.sub.1-C.sub.6 fluorinated alkylthio group, R.sup.51 and R.sup.52 are each independently a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, R.sup.51 and R.sup.52 may bond together to form a ring with the sulfur atom to which they are attached, R.sup.53 is halogen exclusive of fluorine, or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom; when g3 is 2, 3 or 4, a plurality of R.sup.53 may be identical or different and a plurality of R.sup.53 may bond together to form a ring with the carbon atoms to which they are attached, M.sup. is a non-nucleophilic counter ion, and A.sup.+ is an onium cation.

6. The negative resist composition of claim 5 wherein the polymer comprises repeat units having formula (B1-1), repeat units having formula (B2-1), (B2-2) or (B3-1), and repeat units having formula (B8-1): ##STR00523## wherein a4, b4, b6, R.sup.A, R.sup.32, R.sup.33, R.sup.35, R.sup.36, and A.sup.+ are as defined above, R.sup.HF is hydrogen or trifluoromethyl, and Z.sup.10 is a single bond or *****Z.sup.101C(O)O, Z.sup.101 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, ***** designates a point of attachment to the oxygen atom in the formula.

7. The negative resist composition of claim 5 wherein the base polymer (B) contains a polymer comprising repeat units having formula (B1) and repeat units having formula (B2) or (B3), but not repeat units having formulae (B7) to (B11).

8. The negative resist composition of claim 1 wherein repeat units having an aromatic ring structure account for at least 60 mol % of the overall repeat units of the polymer in the base polymer.

9. The negative resist composition of claim 1, further comprising (D) a crosslinker.

10. The negative resist composition of claim 1 which is free of a crosslinker.

11. The negative resist composition of claim 1, further comprising (E) a fluorinated polymer comprising repeat units of at least one type selected from repeat units having the formula (E1), repeat units having the formula (E2), repeat units having the formula (E3) and repeat units having the formula (E4) and optionally repeat units of at least one type selected from repeat units having the formula (E5) and repeat units having the formula (E6): ##STR00524## wherein j1 is 1, 2 or 3, j2 is an integer meeting 0j25+2(j3)j1, j3 is 0 or 1, k is 1, 2 or 3, R.sup.B is each independently hydrogen, fluorine, methyl or trifluoromethyl, R.sup.C is each independently hydrogen or methyl, R.sup.101, R.sup.102, R.sup.104 and R.sup.105 are each independently hydrogen or a C.sub.1-C.sub.10 saturated hydrocarbyl group, R.sup.103, R.sup.106, R.sup.107 and R.sup.108 are each independently hydrogen, a C.sub.1-C.sub.15 hydrocarbyl group, C.sub.1-C.sub.15 fluorinated hydrocarbyl group, or acid labile group, and when R.sup.103, R.sup.106, R.sup.107 and R.sup.108 each are a hydrocarbyl or fluorinated hydrocarbyl group, an ether bond or carbonyl moiety may intervene in a carbon-carbon bond, R.sup.109 is hydrogen or a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond, R.sup.110 is a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond, R.sup.111 is a C.sub.1-C.sub.20 saturated hydrocarbyl group in which at least one hydrogen is substituted by fluorine, and in which some constituent CH.sub.2 may be replaced by an ester bond or ether bond, X.sup.1 is a C.sub.1-C.sub.20 (k+1)-valent hydrocarbon group or C.sub.1-C.sub.20 (k+1)-valent fluorinated hydrocarbon group, X.sup.2 is a single bond, *C(O)O or *C(O)NH, * designates a point of attachment to the carbon atom in the backbone, X.sup.3 is a single bond, O, *C(O)OX.sup.31-X.sup.32 or *C(O)NHX.sup.31-X.sup.32, X.sup.31 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group, X.sup.32 is a single bond, ester bond, ether bond, or sulfonamide bond, and * designates a point of attachment to the carbon atom in the backbone.

12. The negative resist composition of claim 1, further comprising (F) an organic solvent.

13. The negative resist composition of claim 1, further comprising (G) a quencher other than the quencher (A).

14. The negative resist composition of claim 13 wherein the acid generator (C) and the quencher (A) are present in a weight ratio of less than 6/1.

15. A resist pattern forming process comprising the steps of: applying the chemically amplified negative resist composition of claim 1 onto a substrate to form a resist film thereon, exposing the resist film patternwise to high-energy radiation, and developing the exposed resist film in an alkaline developer.

16. The process of claim 15 wherein the high-energy radiation is EUV of wavelength 3 to 15 nm or EB.

17. The process of claim 15 wherein the substrate has the outermost surface of a material containing at least one element selected from chromium, silicon, tantalum, molybdenum, cobalt, nickel, tungsten, and tin.

18. The process of claim 15 wherein the substrate is a mask blank of transmission or reflection type.

19. A mask blank of transmission or reflection type which is coated with the chemically amplified negative resist composition of claim 1.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0103] 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, Me stands for methyl, and Ac for acetyl. Both the broken line (---) and the asterisk (*) designate a point of attachment or valence bond. As used herein, the term fluorinated refers to a fluorine-substituted or fluorine-containing compound or group. The terms group and moiety are interchangeable.

[0104] The abbreviations and acronyms have the following meaning. [0105] EB: electron beam [0106] EUV: extreme ultraviolet [0107] Mw: weight average molecular weight [0108] Mn: number average molecular weight [0109] Mw/Mn: molecular weight distribution or dispersity [0110] GPC: gel permeation chromatography [0111] PEB: post-exposure bake [0112] PAG: photoacid generator [0113] LER: line edge roughness [0114] CDU: critical dimension uniformity

[0115] It is understood that for some structures represented by chemical formulae, there can exist enantiomers and diastereomers because of the presence of asymmetric carbon atoms.

[0116] In such a case, a single formula collectively represents all such isomers. The isomers may be used alone or in admixture.

[Chemically Amplified Negative Resist Composition]

[0117] One embodiment of the invention is a chemically amplified negative resist composition comprising (A) a quencher in the form of an onium salt containing an anion (Xq.sup.) which forms a conjugate acid (XqH) having a boiling point of lower than 165 C. and a molecular weight of up to 150, (B) a base polymer containing a specific polymer, and (C) a photoacid generator.

(A) Quencher

[0118] The quencher as component (A) is an onium salt having the formula (A).

##STR00011##

[0119] In formula (A), Xq.sup. is an anion, which forms a conjugate acid (XqH) having a boiling point of lower than 165 C. and a molecular weight of up to 150. The conjugate acid XqH is, for example, formic acid, acetic acid, propionic acid, butyric acid, trifluoroacetic acid, 3,3,3-trifluoropropionic acid, pivalic acid or nitric acid. The preferred conjugate acid XqH has a boiling point of lower than 150 C. and a molecular weight of up to 120.

[0120] In formula (A), Z.sup.+ is an onium cation, which is preferably a sulfonium cation having the formula (Z-1), a iodonium cation having the formula (Z-2), or an ammonium cation having the formula (Z-3).

##STR00012##

[0121] In formulae (Z-1) to (Z-3), R.sup.1 to R.sup.9 are each independently halogen, or a C.sub.1-C.sub.30 hydrocarbyl group which may contain a heteroatom.

[0122] Suitable halogen atoms include fluorine, chlorine, bromine and iodine. The hydrocarbyl group R.sup.1 to R.sup.9 may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.30 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl; C.sub.3-C.sub.30 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, adamantyl; C.sub.2-C.sub.30 alkenyl groups such as vinyl, allyl, propenyl, butenyl, hexenyl; C.sub.3-C.sub.30 cyclic unsaturated hydrocarbyl groups such as cyclohexenyl; C.sub.6-C.sub.30 aryl groups such as phenyl, naphthyl, thienyl; C.sub.7-C.sub.30 aralkyl groups such as benzyl, 1-phenylethyl, 2-phenylethyl, and combinations thereof. Inter alia, the aryl groups are preferred. In the hydrocarbyl groups, some or all hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some 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, cyano, fluorine, chlorine, bromine, iodine, carbonyl, ether bond, ester bond, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(O)) or haloalkyl moiety.

[0123] Also, R.sup.1 and R.sup.2 may bond together to form a ring with the sulfur atom to which they are attached. Examples of the sulfonium cation having formula (Z-1) wherein R.sup.1 and R.sup.2 form a ring are shown below.

##STR00013##

[0124] Herein the broken line designates a point of attachment to R.sup.3.

[0125] Further, any two of R.sup.6 to R.sup.9 may bond together to form a ring with the nitrogen atom to which they are attached.

[0126] Examples of the sulfonium cation having formula (Z-1) include the cations described in JP-A 2024-003744, paragraphs [0102]-[0125] and JP-A 2023-169812, paragraphs [0070]-[0085], but are not limited thereto. Examples of the iodonium cation having formula (Z-2) include the cations described in JP-A 2024-000259, paragraph [0181], but are not limited thereto. Examples of the ammonium cation having formula (Z-3) include the cations described in JP-A 2024-000259, paragraph [0221], but are not limited thereto.

[0127] A sulfonium cation having the formula (Z-4) is also preferable as the onium cation Z.sup.+.

##STR00014##

[0128] In formula (Z-4), m1 is 0 or 1. The relevant structure is a benzene ring when m1=0, and a naphthalene ring when m1=1. The benzene ring corresponding to m1=0 is preferred from the aspect of solvent solubility. The subscript m2 is 0 or 1. The relevant structure is a benzene ring when m2=0, and a naphthalene ring when m2=1. The benzene ring corresponding to m2=0 is preferred from the aspect of solvent solubility. The subscript m3 is 0 or 1. The relevant structure is a benzene ring when m3=0, and a naphthalene ring when m3=1. The benzene ring corresponding to m3=0 is preferred from the aspect of solvent solubility.

[0129] In formula (Z-4), m4 is 0, 1, 2, 3 or 4. As the number of iodine atoms in the cation structure increases, the compound becomes more absorptive to EUV, but so poor in solvent solubility that it may precipitate in a resist composition. For this reason, m4 is preferably 0, 1, 2 or 3, more preferably 0, 1 or 2.

[0130] In formula (Z-4), m5 is 0, 1, 2, 3 or 4. From the aspect of reactant availability, m5 is preferably 0, 1, 2 or 3, more preferably 0, 1 or 2. The subscript m6 is 0, 1, 2, 3, 4, 5 or 6. From the aspect of reactant availability, m6 is preferably 0, 1, 2 or 3, more preferably 0, 1 or 2. The subscript m7 is 0, 1, 2, 3, 4, 5 or 6. From the aspect of reactant availability, m7 is preferably 0, 1, 2 or 3, more preferably 0, 1 or 2.

[0131] In formula (Z-4), m8 is 0, 1 or 2. From the aspect of reactant availability, m8 is preferably 0 or 1. The subscript m9 is 0, 1 or 2. From the aspect of reactant availability, m9 is preferably 0 or 1. The subscript m10 is 0, 1 or 2. From the aspect of reactant availability, m10 is preferably 0 or 1.

[0132] In formula (Z-4), m11 is 0 or 1. The relevant structure is a benzene ring when m11=0, and a naphthalene ring when m11=1. The benzene ring corresponding to m11=0 is preferred from the aspect of solvent solubility.

[0133] In formula (Z-4), m12 is 0, 1, 2, 3 or 4. As the number of iodine atoms in the cation structure increases, the compound becomes more absorptive to EUV, but so poor in solvent solubility that it may precipitate in a resist composition. For this reason, m12 is preferably 0, 1, 2 or 3, more preferably 0, 1 or 2.

[0134] In formula (Z-4), m13 is 0, 1 or 2. From the aspect of reactant availability, m13 is preferably 0 or 1. The subscript m14 is 0, 1 or 2. From the aspect of synthesis, m14 is preferably 0 or 1.

[0135] The subscripts m1 to m14 are in the range: 0m6+m94 when m1=0, 0m6+m96 when m1=1; 0m7+m104 when m2=0, 0m7+m106 when m2=1; 1m4+m5+m8+m144 when m3=0, 1m4+m5+m8+m146 when m3=1; 0m12+m134 when m11=0, 0m12+m136 when m11=1; and m4+m121.

[0136] In formula (Z-4), R.sup.F1 to R.sup.F3 are each independently fluorine, a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group, C.sub.1-C.sub.6 fluorinated saturated hydrocarbyloxy group, or C.sub.1-C.sub.6 fluorinated saturated hydrocarbylthio group. Of these, trifluoromethyl, trifluoromethoxy, and trifluorothiomethoxy are preferred. A plurality of R.sup.F1 may be identical or different when m5 is 2 or more, a plurality of R.sup.F2 may be identical or different when m6 is 2 or more, and a plurality of R.sup.F3 may be identical or different when m7 is 2 or more.

[0137] In formula (Z-4), R.sup.10 to R.sup.13 are each independently halogen exclusive of iodine and fluorine, nitro, cyano, a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom, C.sub.1-C.sub.20 hydrocarbyloxy group which may contain a heteroatom, or C.sub.1-C.sub.20 hydrocarbylthio group which may contain a heteroatom. The hydrocarbyl group and hydrocarbyl moiety in the hydrocarbyloxy and hydrocarbylthio groups may be saturated or unsaturated and straight, branched or cyclic. Examples thereof are as exemplified above for the hydrocarbyl group R.sup.1 to R.sup.9 in formula (Z-1). In the hydrocarbyl group and hydrocarbyl moiety in the hydrocarbyloxy and hydrocarbylthio 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 moiety, cyano moiety, fluorine, chlorine, bromine, iodine, carbonyl moiety, ether bond, ester bond, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(O)) or haloalkyl moiety.

[0138] When m8=2, two R.sup.10 may be identical or different and two R.sup.10 may bond together to form a ring with the carbon atoms to which they are attached. When m9=2, two R.sup.11 may be identical or different and two R.sup.11 may bond together to form a ring with the carbon atoms to which they are attached. When m10=2, two R.sup.12 may be identical or different and two R.sup.12 may bond together to form a ring with the carbon atoms to which they are attached. When m13=2, two R.sup.13 may be identical or different and two R.sup.13 may bond together to form a ring with the carbon atoms to which they are attached. Examples of the ring thus formed include cyclopropane, cyclobutane, cyclopentane, cyclohexane, norbornane, and adamantane rings. In the ring, 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 ring may contain a hydroxy moiety, fluorine, chlorine, bromine, iodine, cyano moiety, carbonyl moiety, ether bond, ester bond, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(O)) or haloalkyl moiety.

[0139] The aromatic rings directly bonded to S.sup.+ in the sulfonium cation having formula (Z-4) may bond together to form a ring with S.sup.+. Exemplary structures of the ring are shown below.

##STR00015##

[0140] In formula (Z-4), L.sup.A and L.sup.B are each independently a single bond, ether bond, ester bond, sulfonate ester bond, amide bond, sulfonamide bond, carbonate bond or carbamate bond. L.sup.A is preferably a single bond, ether bond, ester bond or sulfonate ester bond, more preferably an ester bond or sulfonate ester bond. L.sup.B is preferably a single bond, ether bond or ester bond, more preferably a single bond.

[0141] In formula (Z-4), 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. Examples thereof include alkanediyl and cyclic saturated hydrocarbylene groups. Suitable heteroatoms include oxygen, nitrogen and sulfur.

[0142] 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. Herein * designates a point of attachment to L.sup.A or L.sup.B.

##STR00016## ##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021##

[0143] Of these, X.sup.L-0 to X.sup.L-22 and X.sup.L-47 to X.sup.L-58 are preferred.

[0144] Of the sulfonium cations having formula (Z-4), those having the formula (Z-4-1) are preferred.

##STR00022##

[0145] Herein m4 to m10, m12 to m14, R.sup.F1 to R.sup.F3, R.sup.10 to R.sup.13, L.sup.A, L.sup.B, and X.sup.L are as defined above.

[0146] Of the sulfonium cations having formula (Z-4-1), those having the formula (Z-4-2) are preferred.

##STR00023##

[0147] Herein m4 to m10, R.sup.F1 to R.sup.F3, and R.sup.10 to R.sup.12 are as defined above.

[0148] Examples of the sulfonium cation having formula (Z-4) are shown below, but not limited thereto.

##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##

[0149] Examples of the onium salt include arbitrary combinations of anions with cations, both as exemplified above.

[0150] The onium salt having formula (A) can be synthesized, for example, by the method described in JP-A 2020-091312 (U.S. Pat. No. 11,586,111), but the synthesis method is not limited thereto.

[0151] The inventive onium salt is advantageously used as a quencher. As used herein, the term quencher refers to a compound capable of trapping the strong acid generated by a PAG in the resist composition to prevent the acid from diffusing to the unexposed region and to assist in forming the desired pattern. As used herein, the PAG refers to a compound capable of generating a strong acid upon exposure to high-energy radiation. The term strong acid refers to a compound having a sufficient acidity to induce deprotection reaction of an acid labile group. Since the acid formed by the inventive onium salt such as acetic acid, nitric acid or trifluoroacetic acid does not have an enough acidity to induce deprotection reaction of an acid labile group which is tertiary ester or tertiary ether, it is effective to separately add a PAG capable of generating a strong acid, i.e., -fluorinated sulfonic acid, imide acid or methide acid, for the purpose of inducing deprotection reaction of an acid labile group, as will be described later. It is noted that the PAG capable of generating an -fluorinated sulfonic acid, imide acid or methide acid may be of addition type or of polymer-bound type wherein the PAG is bound to a base polymer.

[0152] In a system where the inventive onium salt capable of generating an acid such as acetic acid, nitric acid or trifluoroacetic acid and a PAG capable of generating a strong sulfonic acid are co-present, the acid such as acetic acid, nitric acid or trifluoroacetic acid and the sulfonic acid generate upon light exposure. Since the PAG is not decomposed in its entirety, some PAG remains undecomposed nearby. If the onium salt capable of generating an acid such as acetic acid, nitric acid or trifluoroacetic acid and the sulfonic acid are co-present at this point of time, first an ion exchange occurs between the sulfonic acid and the onium salt capable of generating a carboxylic acid or nitric acid whereby an onium salt of sulfonic acid is generated and the acid such as acetic acid, nitric acid or trifluoroacetic acid is released. This is because the sulfonic acid salt having a high acid strength is more stable. On the other hand, where the sulfonic acid onium salt and the acid such as acetic acid, nitric acid or trifluoroacetic acid are co-present, no ion exchange occurs.

[0153] The inventive onium salt is structurally characterized by the anion (Xq.sup.) which forms a conjugate acid (XqH) having a boiling point of lower than 165 C. and a molecular weight of up to 150. Since the weak acid generated by the inventive onium salt has a low boiling point, it is presumed that some of the generated acid volatilizes off. In the case of negative resist using alkaline developer, the weak acid generated in the exposed region has so high affinity to the alkaline developer that the alkaline developer is taken into the exposed region, incurring pattern collapse or stripping from the substrate. In contrast, since the inventive onium salt generates a weak acid which will volatilize off, it mitigates the above-mentioned phenomenon. That is, the maximum resolution is improved. Since the anion has a low molecular weight and readily flows away with the developer, little of the unreacted onium salt (though in a trace amount) remaining in the unexposed region is left behind. As a result, LWR is improved. Since the quencher of onium salt type generates an acid which is a non-sulfonic weak acid, the advantage of low acid diffusion is obtained. When the PAG is of polymer-bound type wherein the PAG units are bound to a base polymer, acid diffusion is more controlled, with better results being expectable.

[0154] In the chemically amplified negative resist composition, the amount of quencher (A) is preferably 0.1 to 40 parts by weight, more preferably 0.5 to 30 parts by weight per 80 parts by weight of a base polymer to be described just below. As long as the amount of quencher (A) is in the range, good sensitivity and resolution are achievable and the risk of foreign particles being formed after development or during stripping of resist film is avoided. The quencher may be used alone or in admixture.

(B) Base Polymer

[0155] The resist composition further comprises (B) a base polymer containing a polymer comprising repeat units having the formula (B1). Notably, the polymer is referred to as polymer B and the repeat units are referred to as units B1, hereinafter. The repeat units B1 are effective for providing etch resistance, adhesion to substrates, and solubility in alkaline developer.

##STR00112##

[0156] In formula (B1), a1 is 0 or 1. The subscript a2 is 0, 1 or 2. The relevant structure is a benzene ring when a2=0, a naphthalene ring when a2=1, and an anthracene ring when a2=2. The subscript a3 is an integer meeting 0a3 5+2(a2)a4, and a4 is 1, 2 or 3. When a2 is 0, preferably a3 is 0, 1, 2 or 3 and a4 is 1, 2 or 3. When a2 is 1 or 2, preferably a3 is 0, 1, 2, 3 or 4 and a4 is 1, 2 or 3.

[0157] In formula (B1), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl.

[0158] In formula (B1), R.sup.21 is halogen, nitro, carboxy, an optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl group, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy group or optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group. The saturated hydrocarbyl group and saturated hydrocarbyl moiety in the saturated hydrocarbyloxy and saturated hydrocarbylcarbonyloxy groups may be straight, branched or cyclic. Examples thereof include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, and structural isomers thereof; cycloalkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl; and combinations thereof. A carbon count within the upper limit ensures a satisfactory solubility in alkaline developer. A plurality of R.sup.21 may be identical or different when a3 is 2 or more.

[0159] In formula (B1), A.sup.1 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O. The saturated hydrocarbylene group may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.10 alkanediyl groups such as methylene, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, and structural isomers thereof; C.sub.3-C.sub.10 cyclic saturated hydrocarbylene groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof. For the saturated hydrocarbylene group containing an ether bond, in case of a1=1 in formula (B1), the ether bond may be incorporated at any position excluding the position between the - and -carbons relative to the ester oxygen. In case of a1=0, the atom bonding to the backbone becomes an ether oxygen atom, and a second ether bond may be incorporated at any position excluding the position between the - and -carbons relative to the ether oxygen. Saturated hydrocarbylene groups having no more than 10 carbon atoms are desirable because of a sufficient solubility in alkaline developer.

[0160] Preferred examples of the repeat units B1 wherein a1=0 and A.sup.1 is a single bond (meaning that the aromatic ring is directly bonded to the backbone of the polymer), that is, repeat units free of a linker: C(O)O-A.sup.1- include units derived from 3-hydroxystyrene, 4-hydroxystyrene, 5-hydroxy-2-vinylnaphthalene, and 6-hydroxy-2-vinylnaphthalene. More preferred are repeat units having the formula (B1-1):

##STR00113##

wherein R.sup.A and a4 are as defined above.

[0161] Preferred examples of the repeat units B1 wherein a1=1, that is, having a linker: C(O)O-A.sup.1- are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00114##

[0162] The repeat units B1 may be of one type or a combination of plural types.

[0163] The polymer B may further comprise repeat units of at least one type selected from repeat units having the formula (B2) and repeat units having the formula (B3). Notably the repeat units having formulae (B2) and (B3) are simply referred to as repeat units B2 and B3. Of the polymers B, a polymer further comprising repeat units B2 and/or B3 is referred to as polymer B.

##STR00115##

[0164] Upon exposure to high-energy radiation, the repeat unit B2 or B3 functions such that OW.sup.1 or OW.sup.2 undergoes elimination reaction under the action of an acid which is generated by the acid generator. That is, the unit B2 or B3 induces insolubilization in alkaline developer and crosslinking reaction between polymer molecules. The repeat unit B2 or B3 provides for efficient progress of negative-working reaction, leading to an improvement in resolution performance.

[0165] In formula (B2), b1 is 0 or 1, b2 is 0, 1 or 2, b3 is an integer in the range: 0 b3 5+2(b2)b4, and b4 is 1, 2 or 3.

[0166] In formula (B3), b5 is 0, 1 or 2, preferably 0 or 1, and b6 is 1 or 2, preferably 1.

[0167] In formulae (B2) and (B3), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl. In formula (B3), R.sup.A is preferably hydrogen or methyl, more preferably hydrogen.

[0168] In formula (B2), R.sup.31 is halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. Suitable halogen atoms include fluorine, chlorine, bromine and iodine. The C.sub.1-C.sub.20 hydrocarbyl group may be saturated or unsaturated and straight, branched or cyclic, and examples thereof are as exemplified above for the hydrocarbyl group R.sup.1 in formula (A). When b3 is 2 or more, a plurality of R.sup.31 may be identical or different.

[0169] In formula (B2), R.sup.32 and R.sup.33 are each independently hydrogen, a C.sub.1-C.sub.15 saturated hydrocarbyl group or a C.sub.6-C.sub.15 aryl group. The hydrocarbyl group may be substituted with a hydroxy moiety or C.sub.1-C.sub.6 saturated hydrocarbyloxy moiety and the aryl group may be substituted. It is excluded that R.sup.32 and R.sup.33 are hydrogen at the same time. R.sup.32 and R.sup.33 may bond together to form a ring with the carbon atom to which they are attached, in which some CH.sub.2 may be replaced by O or S. R.sup.32 and R.sup.33 are preferably selected from alkyl groups such as methyl, ethyl, propyl, butyl and structural isomers thereof, and substituted forms of the foregoing alkyl groups in which some hydrogen is substituted by a hydroxy or saturated hydrocarbyloxy moiety.

[0170] In formula (B3), R.sup.34 is halogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. Suitable halogen atoms include fluorine, chlorine, bromine and iodine. The C.sub.1-C.sub.20 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 (A). When b5 is 2 or more, a plurality of R.sup.34 may be identical or different.

[0171] In formula (B3), R.sup.35 and R.sup.36 are each independently hydrogen, a C.sub.1-C.sub.15 saturated hydrocarbyl group or a C.sub.6-C.sub.15 aryl group. The hydrocarbyl group may be substituted with a hydroxy or C.sub.1-C.sub.6 saturated hydrocarbyloxy moiety and the aryl group may be substituted.

[0172] The C.sub.1-C.sub.15 saturated hydrocarbyl groups R.sup.35 and R.sup.36 may be straight, branched or cyclic, and examples thereof are as exemplified above for the hydrocarbyl groups R.sup.32 and R.sup.33.

[0173] Examples of the C.sub.6-C.sub.15 aryl groups R.sup.35 and R.sup.36 include phenyl, naphthyl and anthryl, with phenyl being preferred. The aryl group may have a substituent, examples of which include halogen, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl moieties, and optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy moieties.

[0174] It is excluded that R.sup.35 and R.sup.36 are hydrogen at the same time. When one of R.sup.35 and R.sup.36 is an optionally substituted aryl group, the preferred substituent on the other of R.sup.35 and R.sup.36 is hydrogen.

[0175] Preferably R.sup.35 and R.sup.36 are identical, more preferably both methyl.

[0176] R.sup.35 and R.sup.36 may bond together to form a ring with the carbon atom to which they are attached. In the ring, some CH.sub.2 may be replaced by O or S. Examples of the ring include cyclopropane, cyclobutene, cyclopentane, cyclohexane, norbornane, adamantane, tricyclo[5.2.1.0.sup.2,6]decane, tetracyclo[6.2.1.1.sup.3,6.0.sup.2,7]dodecane, oxanorbornane, and thianorbornane rings, but are not limited thereto.

[0177] In formula (B2), A.sup.2 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O. The saturated hydrocarbylene group may be straight, branched or cyclic and examples thereof include alkanediyl groups such as methylene, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, and structural isomers thereof; cyclic saturated hydrocarbylene groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof. For the saturated hydrocarbylene group containing an ether bond, in case of b1=1 in formula (B2), the ether bond may be incorporated at any position excluding the position between the - and -carbons relative to the ester oxygen. In case of b1=0, the atom bonding to the backbone becomes an ether oxygen atom, and a second ether bond may be incorporated at any position excluding the position between the - and -carbons relative to the ether oxygen.

[0178] In formulae (B2) and (B3), W.sup.1 and W.sup.2 are each independently hydrogen, a C.sub.1-C.sub.10 aliphatic hydrocarbyl group, C.sub.2-C.sub.10 aliphatic hydrocarbylcarbonyl group, or an optionally substituted C.sub.6-C.sub.15 aryl group.

[0179] The C.sub.1-C.sub.10 aliphatic hydrocarbyl groups W.sup.1 and W.sup.2 may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.10 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, and n-decyl; C.sub.3-C.sub.10 cyclic saturated hydrocarbyl groups such as cyclopentyl and cyclohexyl; C.sub.2-C.sub.10 alkenyl groups such as vinyl, 1-propenyl, 2-propenyl, butenyl and hexenyl; and C.sub.3-C.sub.10 cyclic unsaturated hydrocarbyl groups such as cyclohexenyl. The hydrocarbyl moiety in the C.sub.2-C.sub.10 aliphatic hydrocarbylcarbonyl groups W.sup.1 and W.sup.2 may be saturated or unsaturated and straight, branched or cyclic, and examples thereof include those illustrated above for the C.sub.1-C.sub.10 aliphatic hydrocarbyl groups W.sup.1 and W.sup.2, but of 1 to 9 carbon atoms. Examples of the aryl groups W.sup.1 and W.sup.2 include phenyl, naphthyl and anthryl, with phenyl being preferred. The aryl group may have a substituent, examples of which include halogen, optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyl moieties, and optionally halogenated C.sub.1-C.sub.6 saturated hydrocarbyloxy moieties.

[0180] Of the repeat units B2, repeat units having formula (B2-1) or (B2-2) are preferred.

##STR00116##

Herein b4, R.sup.A, R.sup.32, and R.sup.33 are as defined above.

[0181] Preferred examples of the repeat unit B2 are given below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00117## ##STR00118## ##STR00119## ##STR00120## ##STR00121## ##STR00122## ##STR00123## ##STR00124## ##STR00125## ##STR00126## ##STR00127## ##STR00128## ##STR00129##

##STR00130## ##STR00131## ##STR00132## ##STR00133## ##STR00134## ##STR00135##

[0182] The repeat unit B2 may be of one type or a combination of plural types.

[0183] Of the repeat units B3, repeat units having formula (B3-1) are preferred.

##STR00136##

[0184] Herein b6, R.sup.A, R.sup.35, and R.sup.36 are as defined above.

[0185] Preferred examples of the repeat unit B3 are given below, but not limited thereto. Herein R.sup.A is as defined above.

##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## ##STR00205## ##STR00206##

[0186] The repeat unit B3 may be of one type or a combination of plural types.

[0187] For the purpose of improving etch resistance, preferably the polymer B or B further comprises repeat units of at least one type selected from repeat units having the formula (B4), repeat units having the formula (B5) and repeat units having the formula (B6). Notably these units are simply referred to as repeat units B4, B5 and B6.

##STR00207##

[0188] In formulae (B4) and (B5), c and d are each independently 0, 1, 2, 3 or 4.

[0189] In formulae (B4) and (B5), R.sup.41 and R.sup.42 are each independently hydroxy, halogen, an optionally halogenated C.sub.1-C.sub.8 saturated hydrocarbyl group, optionally halogenated C.sub.1-C.sub.8 saturated hydrocarbyloxy group, or optionally halogenated C.sub.2-C.sub.8 saturated hydrocarbylcarbonyloxy group. The saturated hydrocarbyl group, saturated hydrocarbyloxy group, and saturated hydrocarbylcarbonyloxy group may be straight, branched or cyclic. When c is 2 or more, a plurality of R.sup.41 may be identical or different. When d is 2 or more, a plurality of R.sup.42 may be identical or different.

[0190] In formula (B6), e1 is 0 or 1. The subscript e2 is 0, 1 or 2; the corresponding structure represents a benzene skeleton when e2=0, a naphthalene skeleton when e2=1, and an anthracene skeleton when e2=2. The subscript e3 is 0, 1, 2, 3, 4 or 5. When e2=0, e3 is preferably 0, 1, 2 or 3. When e2=1 or 2, e3 is preferably 0, 1, 2, 3 or 4.

[0191] In formula (B6), R.sup.A is hydrogen, fluorine, methyl or trifluoromethyl.

[0192] In formula (B6), R.sup.43 is 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 hydrocarbyloxyhydrocarbyl group, C.sub.2-C.sub.20 saturated hydrocarbylthiohydrocarbyl group, halogen atom, nitro group, cyano group, C.sub.1-C.sub.20 saturated hydrocarbylsulfinyl group, or C.sub.1-C.sub.20 saturated hydrocarbylsulfonyl group. The saturated hydrocarbyl group, saturated hydrocarbyloxy group, saturated hydrocarbylcarbonyloxy group, saturated hydrocarbyloxyhydrocarbyl group, saturated hydrocarbylthiohydrocarbyl group, saturated hydrocarbylsulfinyl group, and saturated hydrocarbylsulfonyl group may be straight, branched or cyclic. When e3 is 2 or more, a plurality of R.sup.43 may be identical or different.

[0193] R.sup.43 is preferably selected from halogen atoms such as chlorine, bromine and iodine; saturated hydrocarbyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopentyl, cyclohexyl, and structural isomers thereof; and saturated hydrocarbyloxy groups such as methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy, cyclopentyloxy, cyclohexyloxy, and structural isomers of their hydrocarbon moiety. Inter alia, methoxy and ethoxy are most useful.

[0194] The saturated hydrocarbylcarbonyloxy group may be readily introduced into a polymer even after polymerization, by a chemical modification method and is advantageously utilized for fine adjustment of the solubility of the polymer in alkaline developer. Examples of the saturated hydrocarbylcarbonyloxy group include methylcarbonyloxy, ethylcarbonyloxy, propylcarbonyloxy, butylcarbonyloxy, pentylcarbonyloxy, hexylcarbonyloxy, cyclopentylcarbonyloxy, cyclohexylcarbonyloxy, benzoyloxy, and structural isomers of their hydrocarbon moiety. As long as the carbon count is equal to or less than 20, an appropriate effect of controlling or adjusting (typically reducing) the solubility of the polymer in alkaline developer is obtainable, and the generation of scum or development defects may be suppressed.

[0195] Of the foregoing preferred substituent groups, such substituent groups as chlorine, bromine, iodine, methyl, ethyl and methoxy are useful because the corresponding monomers may be readily prepared.

[0196] In formula (B6), A.sup.3 is a single bond or C.sub.1-C.sub.10 saturated hydrocarbylene group in which some constituent CH.sub.2 may be replaced by O. The saturated hydrocarbylene group may be straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.10 alkanediyl groups such as methylene, ethane-1,2-diyl, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, and structural isomers thereof; C.sub.3-C.sub.10 cyclic saturated hydrocarbylene groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof. For the saturated hydrocarbylene group containing an ether bond, in case of e1=1 in formula (B6), the ether bond may be incorporated at any position excluding the position between the - and -carbons relative to the ester oxygen. In case of e1=0, the atom bonding to the backbone becomes an ether oxygen atom, and a second ether bond may be incorporated at any position excluding the position between the - and -carbons relative to the ether oxygen. Saturated hydrocarbylene groups having no more than 10 carbon atoms are desirable because of a sufficient solubility in alkaline developer.

[0197] Preferred examples of the repeat units B6 wherein e1 is 0 and A.sup.3 is a single bond (meaning that the aromatic ring is directly bonded to the main chain of the polymer), that is, repeat units free of the linker: C(O)O-A.sup.3- include units derived from styrene, 4-chlorostyrene, 4-bromostyrene, 4-methylstyrene, 4-methoxystyrene, 4-acetoxystyrene, 2-hydroxypropylstyrene, 2-vinylnaphthalene, and 3-vinylnaphthalene.

[0198] Preferred examples of the repeat units B6 wherein e1 is 1, that is, having the linker: C(O)O-A.sup.3- are shown below, but not limited thereto. R.sup.A is as defined above.

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

[0199] When repeat units of at least one type selected from repeat units B4 to B6 are incorporated, better performance is obtained because not only the aromatic ring possesses etch resistance, but the cyclic structure incorporated into the main chain also exerts the effect of improving resistance to etching and EB irradiation during pattern inspection step.

[0200] The repeat units B4 to B6 may be of one type or a combination of plural types.

[0201] The polymer B may further comprise repeat units of at least one type selected from repeat units having the formula (B7), repeat units having the formula (B8), repeat units having the formula (B9), repeat units having the formula (B10), and repeat units having the formula (B11). Notably these repeat units are also referred to as repeat units B7 to B11.

##STR00211##

[0202] In formulae (B7) to (B11), R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl. Z.sup.1 is a single bond or an optionally substituted phenylene group. Z.sup.2 is a single bond, **C(O)OZ.sup.21, **C(O)NHZ.sup.21, or **OZ.sup.21, wherein Z.sup.21 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group or a divalent group obtained by combining the foregoing, which may contain halogen, carbonyl moiety, ester bond, ether bond or hydroxy moiety. Z.sup.3 is a single bond, ether bond, ester bond, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond. Z.sup.4 is a single bond, or a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group or a divalent group obtained by combining the foregoing, which may contain halogen, carbonyl moiety, ester bond, ether bond or hydroxy moiety. Z.sup.5 is each independently a single bond, an optionally substituted phenylene, naphthylene, or *C(O)OZ.sup.51, wherein Z.sup.51 is a C.sub.1-C.sub.10 aliphatic hydrocarbylene group which may contain halogen, hydroxy moiety, ether bond, ester bond or lactone ring, or phenylene or naphthylene group. Z.sup.6 is a single bond, ether bond, ester bond, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond. Z.sup.7 is each independently a single bond, ***Z.sup.71C(O)O, ***C(O)NHZ.sup.71, or ***OZ.sup.71, wherein Z.sup.71 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. Z.sup.8 is each independently a single bond, ****Z.sup.81C(O)O, ****C(O)NHZ.sup.81, or ****OZ.sup.81, wherein Z.sup.81 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. Z.sup.9 is a single bond, methylene, ethylene, phenylene, fluorinated phenylene, trifluoromethyl-substituted phenylene, *C(O)OZ.sup.91, *C(O)N(H)Z.sup.91, or *OZ.sup.91, wherein Z.sup.91 is a C.sub.1-C.sub.6 aliphatic hydrocarbylene group, phenylene group, fluorinated phenylene group or trifluoromethyl-substituted phenylene group, which may contain a carbonyl moiety, ester bond, ether bond or hydroxy moiety. The asterisk * designates a point of attachment to the carbon atom in the backbone, ** is a point of attachment to Z.sup.1, *** is a point of attachment to Z.sup.6, and **** is a point of attachment to Z.sup.7.

[0203] The aliphatic hydrocarbylene group represented by Z.sup.21, Z.sup.51 and Z.sup.91 may be straight, branched or cyclic. Examples thereof include alkanediyl groups such as 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, and hexane-1,6-diyl; cycloalkanediyl groups such as cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, and cyclohexanediyl; and combinations thereof.

[0204] The hydrocarbylene group which may contain a heteroatom, represented by Z.sup.71 and Z.sup.81, may be saturated or unsaturated and straight, branched or cyclic. Examples thereof are shown below, but not limited thereto.

##STR00212##

[0205] In formula (B7), R.sup.51 and R.sup.52 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. Examples thereof include C.sub.1-C.sub.20 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl; C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclopentyl, cyclohexyl, cyclopropylmethyl, 4-methylcyclohexyl, cyclohexylmethyl, norbornyl, and adamantyl; C.sub.2-C.sub.20 alkenyl groups such as vinyl, 1-propenyl, 2-propenyl, butenyl, and hexenyl; C.sub.3-C.sub.20 cyclic unsaturated hydrocarbyl groups such as cyclohexenyl; C.sub.6-C.sub.20 aryl groups such as phenyl, naphthyl and thienyl; C.sub.7-C.sub.20 aralkyl groups such as benzyl, 1-phenylethyl and 2-phenylethyl, and combinations thereof. Inter alia, aryl groups are preferred. 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, fluorine, chlorine, bromine, iodine, cyano, carbonyl, ether bond, ester bond, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(O)), or haloalkyl moiety.

[0206] R.sup.51 and R.sup.52 may bond together to form a ring with the sulfur atom to which they are attached. Examples of the ring are shown below.

##STR00213##

[0207] Herein the broken line designates a point of attachment to Z.sup.4.

[0208] Examples of the cation in repeat units B7 are shown below, but not limited thereto. Herein R.sup.A 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##

[0209] In formula (B7), M.sup. is a non-nucleophilic counter ion. Halide ions, sulfonate anions, imide anions, and methide anions are preferred. Examples of the non-nucleophilic counter ion include halide ions such as chloride and bromide ions; sulfonate anions, specifically 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.

[0210] Anions having the following formulae (B7-1) to (B7-4) are also useful as the non-nucleophilic counter ion.

##STR00238##

[0211] In formula (B7-1), 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 will be exemplified below for the hydrocarbyl group R.sup.fa1 in formula (B7-1-1).

[0212] Of the anions of formula (B7-1), an anion having the formula (B7-1-1) is preferred.

##STR00239##

[0213] In formula (B7-1-1), Q.sup.1 and Q.sup.2 are each independently hydrogen, fluorine or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. It is preferred for solvent solubility that at least one of Q.sup.1 and Q.sup.2 be trifluoromethyl. The subscript m is 0, 1, 2, 3 or 4, preferably 1.

[0214] R.sup.fa1 is a C.sub.1-C.sub.35 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 group may be saturated or unsaturated and straight, branched or cyclic. Examples thereof include C.sub.1-C.sub.35 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, and icosyl; C.sub.3-C.sub.35 cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, 1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylmethyl, tricyclodecyl, tetracyclododecyl, tetracyclododecylmethyl, and dicyclohexylmethyl; C.sub.2-C.sub.35 unsaturated aliphatic hydrocarbyl groups such as 2-propenyl and 3-cyclohexenyl; C.sub.6-C.sub.35 aryl groups such as phenyl, 1-naphthyl, 2-naphthyl and 9-fluorenyl; and C.sub.7-C.sub.35 aralkyl groups such as benzyl and diphenylmethyl, and combinations thereof.

[0215] 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, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(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.

[0216] In formula (B7-1-1), L.sup.a1 is a single bond, ether bond, ester bond, sulfonate ester bond, carbonate bond or carbamate bond. From the aspect of synthesis, an ether bond or ester bond is preferred, with the ester bond being more preferred.

[0217] Examples of the anion having formula (B7-1) are shown below, but not limited thereto. Herein Q.sup.1 is as defined above.

##STR00240## ##STR00241## ##STR00242## ##STR00243## ##STR00244## ##STR00245## ##STR00246## ##STR00247## ##STR00248## ##STR00249##

[0218] In formula (B7-2), 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 (B7-1-1). 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.2SO.sub.2NSO.sub.2CF.sub.2 to which they are attached. It is preferred that a combination of R.sup.11 and R.sup.12 be a fluorinated ethylene or fluorinated propylene group.

[0219] In formula (B7-3), 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 (B7-1-1). 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.2SO.sub.2CSO.sub.2CF.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.

[0220] In formula (B7-4), 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.sup.fa1 in formula (B7-1-1).

[0221] Examples of the anion having formula (B7-4) are shown below, but not limited thereto.

##STR00250## ##STR00251##

[0222] Anions having an iodized or brominated aromatic ring are also useful as the non-nucleophilic counter ion. These anions have the formula (B7-5).

##STR00252##

[0223] In formula (B7-5), x is 1, 2 or 3, y is 1, 2, 3, 4 or 5, z is 0, 1, 2 or 3, and y+z is from 1 to 5. Preferably, y is 1, 2 or 3, more preferably 2 or 3, and z is 0, 1 or 2.

[0224] In formula (B7-5), X.sup.B1 is iodine or bromine. A plurality of X.sup.B1 may be identical or different when x and/or y is 2 or more.

[0225] In formula (B7-5), L.sup.11 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.

[0226] In formula (B7-5), L.sup.12 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.

[0227] In formula (B7-5), R.sup.fe 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.20 hydrocarbylcarbonyl, C.sub.2-C.sub.20 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.feA)(R.sup.feB), N(R.sup.feC)C(O)R.sup.feD or N(R.sup.feC)C(O)OR.sup.feD. R.sup.feA and R.sup.feB are each independently hydrogen or a C.sub.1-C.sub.6 saturated hydrocarbyl group. R.sup.feC 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.feD 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. A plurality of R.sup.fe may be identical or different when x and/or z is 2 or more.

[0228] Of these, R.sup.fc is preferably hydroxy, N(R.sup.feC)C(O)R.sup.feDN(R.sup.feC)C(O)OR.sup.feD, fluorine, chlorine, bromine, methyl or methoxy.

[0229] In formula (B7-5), Rf.sup.11 to Rf.sup.14 are each independently hydrogen, fluorine or trifluoromethyl, at least one of Rf.sup.11 to Rf.sup.14 is fluorine or trifluoromethyl. Rf.sup.11 and Rf.sup.12, taken together, may form a carbonyl group. More preferably, both Rf.sup.13 and Rf.sup.14 are fluorine.

[0230] Examples of the anion having formula (B7-5) are shown below, but not limited thereto. X.sup.BI is as defined above.

##STR00253## ##STR00254## ##STR00255## ##STR00256## ##STR00257## ##STR00258## ##STR00259## ##STR00260## ##STR00261## ##STR00262## ##STR00263## ##STR00264## ##STR00265## ##STR00266## ##STR00267## ##STR00268## ##STR00269## ##STR00270## ##STR00271##

##STR00272## ##STR00273## ##STR00274## ##STR00275## ##STR00276## ##STR00277## ##STR00278## ##STR00279## ##STR00280## ##STR00281## ##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##

[0231] 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.

[0232] Further useful examples of the non-nucleophilic counter ion include fluorine-free bulky 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.

[0233] 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.

[0234] In formulae (B8) and (B9), f1 and f2 are each independently 0, 1, 2 or 3, preferably 1.

[0235] In formula (B10), g1 is 0 or 1, g2 is 0, 1, 2, 3 or 4, g3 is 0, 1, 2, 3 or 4, meeting 0g2+g34 when g1=0, and 0g2+g36 when g1=1.

[0236] In formulae (B8), (B9) and (B10), L.sup.1 is a single bond, ether bond, ester bond, carbonyl, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond. From the aspect of synthesis, an ether bond, ester bond or carbonyl is preferred, with the ester bond or carbonyl being more preferred.

[0237] In formula (B8), Rf.sup.1 and Rf.sup.2 are each independently fluorine or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. It is preferred that both Rf.sup.1 and Rf.sup.2 be fluorine because the generated acid has a higher acid strength. Rf.sup.3 and Rf.sup.4 are each independently hydrogen, fluorine or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. It is preferred for solvent solubility that at least one of Rf.sup.3 and Rf.sup.4 be trifluoromethyl.

[0238] In formula (B9), Rf.sup.5 and Rf.sup.6 are each independently hydrogen, fluorine or a C.sub.1-C.sub.6 fluorinated saturated hydrocarbyl group. It is excluded that all Rf.sup.5 and Rf.sup.6 are hydrogen at the same time. It is preferred for solvent solubility that at least one of Rf.sup.5 and Rf.sup.6 be trifluoromethyl.

[0239] In formula (B10), Rf.sup.7 is fluorine, a C.sub.1-C.sub.6 fluorinated alkyl group, C.sub.1-C.sub.6 fluorinated alkoxy group, or C.sub.1-C.sub.6 fluorinated alkylthio group. Rf.sup.7 is preferably fluorine, trifluoromethyl, difluoromethyl, trifluoromethoxy, difluoromethoxy, trifluoromethylthio or difluoromethylthio, more preferably fluorine, trifluoromethyl or trifluoromethoxy. When g2 is 2, 3 or 4, a plurality of Rf.sup.7 may be identical or different.

[0240] In formula (B10), R.sup.53 is halogen exclusive of fluorine 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 to R.sup.9 in formula (Z-1), but not limited thereto. When g3 is 2, 3 or 4, a plurality of R.sup.53 may be identical or different.

[0241] When g3 is 2, 3 or 4, a plurality of R.sup.53 may bond together to form a ring with the carbon atom to which they are attached. Examples of the ring thus formed include cyclopropane, cyclobutane, cyclopentane, cyclohexane, norbornane, and adamantane rings. In the ring, 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 ring may contain a hydroxy, fluorine, chlorine, bromine, iodine, cyano, carbonyl, ether bond, ester bond, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(O)) or haloalkyl moiety.

[0242] Examples of the anion in repeat unit B8 are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00321## ##STR00322## ##STR00323## ##STR00324## ##STR00325## ##STR00326## ##STR00327## ##STR00328## ##STR00329## ##STR00330## ##STR00331## ##STR00332## ##STR00333## ##STR00334## ##STR00335## ##STR00336## ##STR00337## ##STR00338## ##STR00339## ##STR00340## ##STR00341## ##STR00342## ##STR00343## ##STR00344## ##STR00345## ##STR00346## ##STR00347##

##STR00348## ##STR00349## ##STR00350## ##STR00351## ##STR00352## ##STR00353## ##STR00354## ##STR00355## ##STR00356## ##STR00357## ##STR00358## ##STR00359##

[0243] Examples of the anion in repeat unit B9 are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00360## ##STR00361## ##STR00362## ##STR00363## ##STR00364## ##STR00365## ##STR00366## ##STR00367## ##STR00368## ##STR00369## ##STR00370## ##STR00371## ##STR00372## ##STR00373## ##STR00374## ##STR00375## ##STR00376## ##STR00377## ##STR00378## ##STR00379## ##STR00380## ##STR00381## ##STR00382## ##STR00383## ##STR00384## ##STR00385## ##STR00386## ##STR00387## ##STR00388##

##STR00389## ##STR00390## ##STR00391## ##STR00392## ##STR00393## ##STR00394## ##STR00395## ##STR00396##

[0244] Examples of the anion in repeat unit B10 are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00397## ##STR00398## ##STR00399## ##STR00400## ##STR00401## ##STR00402## ##STR00403## ##STR00404## ##STR00405## ##STR00406## ##STR00407## ##STR00408##

##STR00409## ##STR00410## ##STR00411## ##STR00412## ##STR00413## ##STR00414## ##STR00415## ##STR00416## ##STR00417## ##STR00418## ##STR00419## ##STR00420## ##STR00421## ##STR00422##

[0245] Examples of the anion in repeat unit B11 are shown below, but not limited thereto. Herein R.sup.A is as defined above.

##STR00423##

[0246] In formulae (B8) to (B11), A.sup.+ is an onium cation. Suitable onium cations include sulfonium, iodonium and ammonium cations, with the sulfonium and iodonium cations being preferred. Examples of the sulfonium cation include those exemplified above for the sulfonium cation having formula (Z-1) and those exemplified above for the sulfonium cation having formula (Z-4), but are not limited thereto. Examples of the iodonium cation include those exemplified above for the iodonium cation having formula (Z-2), but are not limited thereto. Examples of the ammonium cation are as will be exemplified later as the ammonium cation having formula (Z-3), but not limited thereto.

[0247] Illustrative structures of repeat units B7 to B11 include arbitrary combinations of anions with cations, both as mentioned above.

[0248] The repeat units B7 to B11 are capable of generating an acid upon exposure to high-energy radiation. It is believed that binding of the relevant units to a polymer enables to appropriately control acid diffusion and to form a pattern with reduced LER. Since the acid-generating unit is bound to a polymer, the phenomenon that acid volatilizes from the exposed region and re-deposits on the unexposed region during bake in vacuum is suppressed. This is effective for reducing LER and for suppressing unwanted negative-working reaction in the unexposed region for reducing defectiveness.

[0249] Each of repeat units B7 to B11 may be of one type or a mixture of two or more types.

[0250] The polymer B or B may further comprise (meth)acrylate units having an adhesive group such as lactone structure or hydroxy group other than phenolic hydroxy. These repeat units are effective for fine adjustment of properties of a resist film.

[0251] Examples of the (meth)acrylate unit having an adhesive group include repeat units having the following formulae (B12) to (B14), which are also referred to as repeat units B12 to B14. While these units do not exhibit acidity, they may be used as auxiliary units for providing adhesion to substrates or adjusting solubility.

##STR00424##

[0252] In formulae (B12) to (B14), R.sup.A is each independently hydrogen, fluorine, methyl or trifluoromethyl. R.sup.61 is O or methylene. R.sup.62 is hydrogen or hydroxy. R.sup.63 is a C.sub.1-C.sub.4 saturated hydrocarbyl group, and h is 0, 1, 2 or 3.

[0253] In polymer B, the content of repeat units B1 is preferably 30 to 95 mol %, more preferably 50 to 85 mol % of the overall units of the polymer for establishing a high contrast between regions exposed to high-energy radiation (or negative-turning regions) and unexposed regions (or non-negative-turning regions) to gain a high resolution. When the polymer further comprises repeat units B2 and/or B3, the content of repeat units B2 and B3 is preferably 5 to 70 mol %, more preferably 10 to 60 mol % for promoting negative-turning reaction. The content of repeat units B4 to B6 is preferably 0 to 30 mol %, more preferably 3 to 20 mol % for improving etch resistance. The polymer may further contain 0 to 30 mol %, preferably 0 to 20 mol % of other repeat units.

[0254] When polymer B does not contain repeat units B7 to B11, the content of repeat units B1 is preferably 25 to 95 mol %, more preferably 40 to 85 mol % of the overall units of the polymer. The content of repeat units B4 to B6 is preferably 0 to 30 mol %, more preferably 3 to 20 mol %. The content of repeat units B2 and B3 is preferably 5 to 70 mol %, more preferably 10 to 60 mol %. The polymer may further contain 0 to 30 mol %, preferably 0 to 20 mol % of other repeat units.

[0255] When polymer B contains repeat units B7 to B11, the content of repeat units B1 is preferably 25 to 94.5 mol %, more preferably 36 to 85 mol % of the overall units of the polymer. The content of repeat units B4 to B6 is preferably 0 to 30 mol %, more preferably 3 to 20 mol %. The content of repeat units B2 and B3 is preferably 5 to 70 mol %, more preferably 10 to 60 mol %. The total content of repeat units B1 to B6 is preferably 60 to 99.5 mol %. The content of repeat units B7 to B11 is preferably 0.5 to 20 mol %, more preferably 1 to 10 mol %. The polymer may further contain 0 to 30 mol %, preferably 0 to 20 mol % of other repeat units.

[0256] The content of repeat units B1 to B6 is preferably at least 60 mol %, more preferably at least 70 mol %, even more preferably at least 80 mol % based on the overall repeat units of the polymer. The range ensures that the chemically amplified negative resist composition has the necessary properties.

[0257] The preferred polymer B comprises repeat units having the formula (B1-1), repeat units having the formula (B2-1), (B2-2) or (B3-1), and repeat units having the formula (B8-1), all shown below.

##STR00425##

[0258] Herein, a4, b4, b6, R.sup.A, R.sup.22, R.sup.23, R.sup.32, R.sup.33, and A.sup.+ are as defined above. R.sup.HF is hydrogen or trifluoromethyl. Z.sup.10 is a single bond or *****Z.sup.101C(O)O wherein Z.sup.101 is a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom, and ***** designates a point of attachment to the oxygen in the formula.

[0259] When polymer B is used as the base polymer (B), it may be a mixture of a polymer containing repeat units B7 to B14 and a polymer free of repeat units B7 to B14. In the chemically amplified negative resist composition, the polymer free of repeat units B7 to B14 is preferably present in an amount of 2 to 5,000 parts by weight, more preferably 10 to 1,000 parts by weight per 100 parts by weight of the polymer containing repeat units B7 to B14.

[0260] Reference is now made to the use of the chemically amplified negative resist composition in the fabrication of photomasks. The lithography of the advanced generation employs a coating film having a thickness of up to 150 nm, preferably up to 100 nm. Since an intense development process is often employed to minimize defects resulting from resist residues, the base polymer should preferably have a dissolution rate in alkaline developer (typically 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solution) of up to 80 nm/sec, more preferably up to 50 nm/sec in order to form a small size pattern. When the chemically amplified negative resist composition is used in the EUV lithography process for fabricating an LSI chip from a wafer, for example, the coating film often has a thickness of up to 100 nm, in view of the necessity of patterning narrow lines of 50 nm or less. In consideration of the risk that the pattern of such thin film can be degraded by development, the polymer preferably has a dissolution rate of up to 80 nm/sec, more preferably up to 50 nm/sec.

[0261] The polymer may be synthesized by combining suitable monomers optionally protected with a protective group, copolymerizing them in the standard way, and effecting deprotection reaction if necessary. The copolymerization reaction is preferably radical or anionic polymerization though not limited thereto. For the polymerization reaction, reference may be made to WO 2006/121096, JP-A 2004-115630, JP-A 2008-102383, and JP-A 2008-304590.

[0262] The polymer should preferably have a Mw of 1,000 to 50,000, and more preferably 2,000 to 20,000. A Mw of at least 1,000 eliminates the risk that pattern features are rounded at their top, inviting degradations of resolution and LER. A Mw of up to 50,000 eliminates the risk that LER is increased when a pattern with a line width of up to 100 nm is formed. As used herein, Mw is measured by GPC versus polystyrene standards using tetrahydrofuran (THF) or dimethylformamide (DMF).

[0263] The polymer preferably has a narrow molecular weight distribution or dispersity (Mw/Mn) of 1.0 to 2.0, more preferably 1.0 to 1.8. A polymer with such a narrow dispersity eliminates the risk that foreign particles are left on the pattern after development and the pattern profile is aggravated.

(C) Photoacid Generator

[0264] The chemically amplified negative resist composition further comprises a photoacid generator (PAG) as component (C). The PAG used herein may be any compound capable of generating an acid upon exposure to high-energy radiation. Suitable PAGs include sulfonium salts, iodonium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acid generators.

[0265] Suitable PAGs include nonafluorobutane sulfonate, partially fluorinated sulfonates described in JP-A 2012-189977, paragraphs [0247]-[0251], partially fluorinated sulfonates described in JP-A 2013-101271, paragraphs [0261]-[0265], and those described in JP-A 2008-111103, paragraphs [0122]-[0142] and JP-A 2010-215608, paragraphs [0080]-[0081]. Among others, arylsulfonate and alkanesulfonate type PAGs are preferred because they generate acids having an appropriate strength to deprotect the acid labile group in repeat unit B2.

[0266] To obtain the effect of improving LER and CDU by combining the PAG (C) with the quencher (A), it is preferred that the acid generated by the PAG have a pKa value of 3.0 or larger, more preferably 3.0 to 2.0, even more preferably 2.0 to 1.5.

[0267] The preferred PAGs are salt compounds having an anion of the structure shown below.

##STR00426##

[0268] Preferred examples of the anion in the PAG include those described in JP 7032549, paragraphs [0220]-[0225](U.S. Pat. No. 12,164,230), JP 6248882, paragraphs [0027]-[0029], JP 7067271, paragraphs [0028]-[0029], JP-A 2023-177038, paragraphs [0039]-[0066], and JP-A 2024-077330, paragraphs [0229]-[0231].

[0269] The preferred PAGs are salt compounds having an anion of the structure shown below.

##STR00427## ##STR00428## ##STR00429## ##STR00430## ##STR00431## ##STR00432## ##STR00433## ##STR00434## ##STR00435## ##STR00436## ##STR00437## ##STR00438## ##STR00439##

##STR00440## ##STR00441## ##STR00442## ##STR00443## ##STR00444## ##STR00445## ##STR00446## ##STR00447## ##STR00448## ##STR00449## ##STR00450## ##STR00451## ##STR00452## ##STR00453## ##STR00454## ##STR00455## ##STR00456## ##STR00457## ##STR00458## ##STR00459## ##STR00460## ##STR00461## ##STR00462## ##STR00463## ##STR00464## ##STR00465## ##STR00466## ##STR00467## ##STR00468## ##STR00469## ##STR00470## ##STR00471## ##STR00472##

[0270] Preferred examples of the cation that pairs with the anion include those exemplified above for the sulfonium cations having formulae (Z-1) and (Z-4), and those exemplified above for the iodonium cation having formula (Z-2).

[0271] When the resist composition contains the PAG (C), the amount of the PAG (C) used is preferably 1 to 30 parts, more preferably 2 to 20 parts by weight per 80 parts by weight of the base polymer (B). The PAG (C) may be omitted when the base polymer contains repeat units B6 to B13, i.e., polymer-bound acid generator. The PAG may be used alone or in admixture.

[0272] When the chemically amplified negative resist composition contains both the PAG (C) and the quencher (A), the weight ratio of the PAG to the quencher, (C)/(A) is preferably less than 6/1, more preferably less than 5/1, even more preferably less than 4/1. As long as the weight ratio of the PAG to the quencher is in the range, the resist composition is able to fully suppress acid diffusion, leading to improved resolution and dimensional uniformity.

(D) Crosslinker

[0273] When the base polymer (B) does not contain polymer B, the negative resist composition preferably comprises a crosslinker as component (D). When the base polymer (B) contains polymer B, a crosslinker need not be added.

[0274] 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.

[0275] Of the foregoing crosslinkers, examples of suitable epoxy compounds include tris(2,3-epoxypropyl) isocyanurate, trimethylolmethane triglycidyl ether, trimethylolpropane triglycidyl ether, and triethylolethane triglycidyl ether.

[0276] Examples of the melamine compound include hexamethylol melamine, hexamethoxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups methoxymethylated and mixtures thereof, hexamethoxyethyl melamine, hexaacyloxymethyl melamine, hexamethylol melamine compounds having 1 to 6 methylol groups acyloxymethylated and mixtures thereof.

[0277] Examples of the guanamine compound include tetramethylol guanamine, tetramethoxymethyl guanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, tetramethoxyethyl guanamine, tetraacyloxyguanamine, tetramethylol guanamine compounds having 1 to 4 methylol groups acyloxymethylated and mixtures thereof.

[0278] 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.

[0279] Examples of the urea compound include tetramethylol urea, tetramethoxymethyl urea, tetramethylol urea compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, and tetramethoxyethyl urea.

[0280] Suitable isocyanate compounds include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and cyclohexane diisocyanate.

[0281] Suitable azide compounds include 1,1-biphenyl-4,4-bisazide, 4,4-methylidenebisazide, and 4,4-oxybisazide.

[0282] Examples of the alkenyloxy-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, 1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitol pentavinyl ether, and trimethylol propane trivinyl ether.

[0283] An appropriate amount of the crosslinker (C) used is 0.1 to 50 parts, and more preferably 1 to 30 parts by weight per 80 parts by weight of the base polymer (B). As long as the amount of the crosslinker is in the range, the risk of resolution being reduced by forming bridges between pattern features is mitigated. The crosslinkers may be used alone or in admixture.

(E) Fluorinated Polymer

[0284] The negative resist composition may further comprise a fluorinated polymer for the purposes of enhancing contrast, preventing chemical flare of acid upon exposure to high-energy radiation, preventing mixing of acid from an anti-charging film in the step of coating an anti-charging film-forming material on a resist film, and suppressing unexpected unnecessary pattern degradation. The fluorinated polymer contains repeat units of at least one type selected from repeat units having the formula (E1), repeat units having the formula (E2), repeat units having the formula (E3), and repeat units having the formula (E4), and may contain repeat units of at least one type selected from repeat units having the formula (E5) and repeat units having the formula (E6). It is noted that repeat units having formulae (E1), (E2), (E3), (E4), (E5), and (E6) are also referred to as repeat units E1, E2, E3, E4, E5, and E6, respectively, hereinafter. Since the fluorinated polymer also has a surface active function, it can prevent insoluble residues from re-depositing onto the substrate during the development step and is thus effective for preventing development defects.

##STR00473##

[0285] In formulae (E1) to (E6), j1 is 1, 2 or 3, j2 is an integer satisfying: 0j25+2(j3)j1, j3 is 0 or 1, and k is 1, 2 or 3. R.sup.B is each independently hydrogen, fluorine, methyl or trifluoromethyl. R.sup.C is each independently hydrogen or methyl. R.sup.101, R.sup.102, R.sup.104 and R.sup.105 are each independently hydrogen or a C.sub.1-C.sub.10 saturated hydrocarbyl group. R.sup.103, R.sup.106, R.sup.107 and R.sup.108 are each independently hydrogen, a C.sub.1-C.sub.15 hydrocarbyl group or fluorinated hydrocarbyl group, or an acid labile group, with the proviso that an ether bond or carbonyl moiety may intervene in a carbon-carbon bond in the hydrocarbyl groups or fluorinated hydrocarbyl groups represented by R.sup.103, R.sup.106, R.sup.107 and R.sup.108. R.sup.109 is hydrogen or a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond. R.sup.110 is a C.sub.1-C.sub.5 straight or branched hydrocarbyl group in which a heteroatom-containing moiety may intervene in a carbon-carbon bond. R.sup.111 is a C.sub.1-C.sub.20 saturated hydrocarbyl group in which at least one hydrogen is substituted by fluorine and some constituent CH.sub.2 may be replaced by an ester bond or ether bond. X.sup.1 is a C.sub.1-C.sub.20 (k+1)-valent hydrocarbon group or C.sub.1-C.sub.20 (k+1)-valent fluorinated hydrocarbon group. X.sup.2 is a single bond, *C(O)O or *C(O)NH wherein * designates a point of attachment to the carbon atom in the backbone. X.sup.3 is a single bond, O, *C(O)OX.sup.31X.sup.32 or *C(O)NHX.sup.31X.sup.32, wherein X.sup.31 is a single bond or a C.sub.1-C.sub.10 saturated hydrocarbylene group, X.sup.32 is a single bond, ester bond, ether bond or sulfonamide bond, and * designates a point of attachment to the carbon atom in the backbone.

[0286] In formulae (E1) and (E2), examples of the C.sub.1-C.sub.10 saturated hydrocarbyl group represented by R.sup.101, R.sup.102, R.sup.104 and R.sup.105 include C.sub.1-C.sub.10 alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl, and C.sub.3-C.sub.10 cyclic saturated hydrocarbyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, adamantyl, and norbornyl. Inter alia, C.sub.1-C.sub.6 saturated hydrocarbyl groups are preferred.

[0287] In formulae (E1) to (E4), the C.sub.1-C.sub.15 hydrocarbyl group represented by R.sup.103, R.sup.106, R.sup.107 and R.sup.108 may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.15 alkyl, C.sub.2-C.sub.15 alkenyl and C.sub.2-C.sub.15 alkynyl groups, with the alkyl groups being preferred. Suitable alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl and n-pentadecyl. The fluorinated hydrocarbyl groups correspond to the foregoing hydrocarbyl groups in which some or all carbon-bonded hydrogen atoms are substituted by fluorine atoms.

[0288] In formula (E4), examples of the C.sub.1-C.sub.20 (k+1)-valent hydrocarbon group X.sup.1 include the foregoing C.sub.1-C.sub.20 alkyl groups and C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups, with k number of hydrogen atoms being eliminated. Examples of the C.sub.1-C.sub.20 (k+1)-valent fluorinated hydrocarbon group X.sup.1 include the foregoing (k+1)-valent hydrocarbon groups in which at least one hydrogen atom is substituted by fluorine.

[0289] Examples of the repeat units E1 to E4 are given below, but not limited thereto. Herein R.sup.B is as defined above.

##STR00474## ##STR00475## ##STR00476## ##STR00477##

[0290] In formula (E5), examples of the C.sub.1-C.sub.5 hydrocarbyl groups R.sup.109 and R.sup.110 include alkyl, alkenyl and alkynyl groups, with the alkyl groups being preferred. Suitable alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and n-pentyl. In these groups, a moiety containing a heteroatom such as oxygen, sulfur or nitrogen may intervene in a carbon-carbon bond.

[0291] In formula (E5), OR.sup.109 is preferably a hydrophilic group. In this case, R.sup.109 is preferably hydrogen or a C.sub.1-C.sub.5 alkyl group in which oxygen intervenes in a carbon-carbon bond.

[0292] In formula (E5), X.sup.2 is preferably *C(O)O or *C(O)NH. Also preferably R.sup.C is methyl. The inclusion of carbonyl in X.sup.2 enhances the ability to trap the acid originating from the anti-charging film. A polymer wherein RD is methyl is a robust polymer having a high glass transition temperature (Tg) which is effective for suppressing acid diffusion. As a result, the resist film is improved in stability with time, and neither resolution nor pattern profile is degraded.

[0293] Examples of the repeat unit E5 are given below, but not limited thereto. Herein R.sup.C is as defined above.

##STR00478## ##STR00479## ##STR00480##

[0294] In formula (E6), the C.sub.1-C.sub.10 saturated hydrocarbylene group X.sup.3 may be straight, branched or cyclic and examples thereof 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, and 1,1-dimethylethane-1,2-diyl.

[0295] The C.sub.1-C.sub.20 saturated hydrocarbyl group having at least one hydrogen substituted by fluorine, represented by R.sup.111, may be straight, branched or cyclic and examples thereof include C.sub.1-C.sub.20 alkyl groups and C.sub.3-C.sub.20 cyclic saturated hydrocarbyl groups in which at least one hydrogen is substituted by fluorine.

[0296] Examples of the repeat unit E6 are given below, but not limited thereto. Herein R.sup.C is as defined above.

##STR00481## ##STR00482## ##STR00483## ##STR00484## ##STR00485## ##STR00486## ##STR00487##

[0297] The repeat units E1 to E4 are preferably incorporated in an amount of 15 to 95 mol %, more preferably 20 to 85 mol % based on the overall repeat units of the fluorinated polymer. The repeat unit E5 and/or E6 is preferably incorporated in an amount of 5 to 85 mol %, more preferably 15 to 80 mol % based on the overall repeat units of the fluorinated polymer. Each of repeat units E1 to E6 may be used alone or in admixture.

[0298] The fluorinated polymer may comprise additional repeat units as well as the repeat units E1 to E6. Suitable additional repeat units include those described in U.S. Pat. No. 9,091,918 (JP-A 2014-177407, paragraphs [0046]-[0078]). When the fluorinated polymer comprises additional repeat units, their content is preferably up to 50 mol % based on the overall repeat units.

[0299] The fluorinated polymer may be synthesized by combining suitable monomers optionally protected with a protective group, copolymerizing them in the standard way, and effecting deprotection reaction if necessary. The copolymerization reaction is preferably radical or anionic polymerization though not limited thereto. For the polymerization reaction, reference may be made to JP-A 2004-115630.

[0300] The fluorinated polymer should preferably have a Mw of 2,000 to 50,000, and more preferably 3,000 to 20,000. A fluorinated polymer with a Mw of less than 2,000 helps acid diffusion, degrading resolution and detracting from age stability. A polymer with too high Mw has a reduced solubility in solvent, with a risk of leaving coating defects. The fluorinated polymer preferably has a dispersity (Mw/Mn) of 1.0 to 2.2, more preferably 1.0 to 1.7.

[0301] In the negative resist composition, the fluorinated polymer (E) is preferably used in an amount of 0.01 to 30 parts, more preferably 0.1 to 20 parts, even more preferably 0.5 to 10 parts by weight per 80 parts by weight of the base polymer (B). The fluorinated polymer may be used alone or in admixture.

(F) Organic Solvent

[0302] The chemically amplified negative resist composition may further comprise an organic solvent as component (F). The organic solvent used herein is not particularly limited as long as the components are soluble therein. Examples of the organic solvent are described in JP-A 2008-111103, paragraphs [0144] to [0145](U.S. Pat. No. 7,537,880). Specifically, 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; 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 (EL), ethyl pyruvate, butyl acetate, methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, t-butyl acetate, t-butyl propionate, and propylene glycol mono-t-butyl ether acetate; and lactones such as -butyrolactone (GBL), and mixtures thereof.

[0303] Of the above organic solvents, it is recommended to use 1-ethoxy-2-propanol, PGMEA, PGME, cyclohexanone, EL, GBL, and mixtures thereof.

[0304] In the negative resist composition, the organic solvent (F) is preferably used in an amount of 200 to 10,000 parts, more preferably 400 to 6,000 parts by weight per 80 parts by weight of the base polymer (B). The organic solvent may be used alone or in admixture.

(G) Other Quencher

[0305] The chemically amplified negative resist composition optionally comprises a quencher other than the quencher (A) as component (G). The quencher is effective for holding down the rate of diffusion of the acid (generated by the acid generator) in the resist film. Even when a substrate whose outermost surface is made of a chromium-containing material is used, the quencher is effective for suppressing the influence of the acid (generated in the resist film) on the chromium-containing material.

[0306] The other quencher is typically selected from conventional basic compounds. Conventional basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, 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 sulfonate ester group as described in JP-A 2008-111103, paragraphs [0146]-[0164], and compounds having a carbamate group as described in JP 3790649. Inter alia, tris[2-(methoxymethoxy)ethyl]amine, tris[2-(methoxymethoxy)ethyl]amine-N-oxide, dibutylaminobenzoic acid, morpholine derivatives, and imidazole derivatives are preferred. 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.

[0307] Onium salts such as sulfonium, iodonium and ammonium salts of carboxylic acids which are not fluorinated at -position as described in U.S. Pat. No. 8,795,942 (JP-A 2008-158339) may also be used as the other quencher. While an -fluorinated sulfonic acid, imide acid, and methide acid are necessary to deprotect the acid labile group, an -non-fluorinated carboxylic acid is released by salt exchange with an -non-fluorinated onium salt. The -non-fluorinated carboxylic acid functions as a quencher because it does not induce substantial deprotection reaction.

[0308] Examples of the onium salt of -non-fluorinated carboxylic acid include compounds having the formula (G1).

##STR00488##

[0309] In formula (G1), R.sup.201 is hydrogen or a C.sub.1-C.sub.40 hydrocarbyl group which may contain a heteroatom, exclusive of the hydrocarbyl group in which the hydrogen bonded to the carbon atom at -position of the carboxy group is substituted by fluorine or fluoroalkyl.

[0310] The hydrocarbyl group R.sup.201 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-butyl, n-pentyl, tert-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, cyclopentylmethyl, cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, norbornyl, tricyclo[5.2.1.0.sup.2,6]decyl, 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), di- or trialkylphenyl 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.

[0311] In the hydrocarbyl groups, some or all hydrogen may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, and some 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, thioether bond, ester bond, sulfonate ester bond, carbonate bond, lactone ring, sultone ring, carboxylic anhydride (C(O)OC(O)), or haloalkyl moiety. Suitable heteroatom-containing hydrocarbyl groups include heteroaryl groups such as thienyl; alkoxyphenyl groups such as 4-hydroxyphenyl, 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 aryloxoalkyl groups, typically 2-aryl-2-oxoethyl groups such as 2-phenyl-2-oxoethyl, 2-(1-naphthyl)-2-oxoethyl and 2-(2-naphthyl)-2-oxoethyl.

[0312] In formula (G1), Mq.sub.A.sup.+ is an onium cation. The onium cation is preferably selected from sulfonium, iodonium and ammonium cations, more preferably sulfonium and iodonium cations. Exemplary sulfonium cations include those exemplified above for the sulfonium cation having formula (Z-1) and the sulfonium cation having formula (Z-4). Exemplary iodonium cations include those exemplified above for the iodonium cation having formula (Z-2). Exemplary ammonium cations include those exemplified above for the ammonium cation having formula (Z-3).

[0313] Examples of the anion in the onium salt having formula (G1) are shown below, but not limited thereto.

##STR00489## ##STR00490## ##STR00491## ##STR00492## ##STR00493##

[0314] A sulfonium salt of iodized benzene ring-containing carboxylic acid having the formula (G2) is also useful as the quencher.

##STR00494##

[0315] In formula (G2), s is 1, 2, 3, 4 or 5, t is 0, 1, 2 or 3, s+t is from 1 to 5, and u is 1, 2 or 3.

[0316] In formula (G2), R.sup.211 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.211A)C(O)R.sup.211, or N(R.sup.211A)C(O)OR.sup.211. R.sup.211A is hydrogen or a C.sub.1-C.sub.6 saturated hydrocarbyl group. R.sup.211B is a C.sub.1-C.sub.6 saturated hydrocarbyl or C.sub.2-C.sub.8 unsaturated aliphatic hydrocarbyl group. A plurality of R.sup.211 may be identical or different when t and/or u is 2 or 3.

[0317] In formula (G2), L.sup.21 is a single bond or a C.sub.1-C.sub.20 (u+1)-valent linking group which may contain at least one moiety selected from ether bond, carbonyl moiety, ester bond, amide bond, sultone ring, lactam ring, carbonate bond, halogen, hydroxy moiety, and carboxy moiety. The saturated hydrocarbyl, saturated hydrocarbyloxy, saturated hydrocarbylcarbonyloxy, and saturated hydrocarbylsulfonyloxy groups may be straight, branched or cyclic.

[0318] In formula (G2), R.sup.212, R.sup.213 and R.sup.214 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 include C.sub.1-C.sub.20 alkyl, C.sub.2-C.sub.20 alkenyl, C.sub.6-C.sub.20 aryl, and C.sub.7-C.sub.20 aralkyl groups. In these groups, some or all hydrogen may be substituted by hydroxy, carboxy, halogen, oxo, cyano, nitro, sultone ring, sulfo, or sulfonium salt-containing moiety, or some CH.sub.2 may be replaced by an ether bond, ester bond, carbonyl moiety, amide bond, carbonate bond or sulfonate ester bond. Also, R.sup.112 and R.sup.113 may bond together to form a ring with the sulfur atom to which they are attached.

[0319] Examples of the compound having formula (G2) include those described in U.S. Pat. No. 10,295,904 (JP-A 2017-219836). These compounds exert a sensitizing effect due to remarkable absorption and an acid diffusion-controlling effect.

[0320] A nitrogen-containing carboxylic acid salt compound having the formula (G3) is also useful as the quencher.

##STR00495##

[0321] In formula (G3), R.sup.221 to R.sup.224 are each independently hydrogen, -L.sup.22-CO.sub.2.sup., or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom. R.sup.221 and R.sup.222, R.sup.222 and R.sup.223 or R.sup.223 and R.sup.224 may bond together to form a ring with the carbon atom to which they are attached. L.sup.22 is a single bond or a C.sub.1-C.sub.20 hydrocarbylene group which may contain a heteroatom. R.sup.221 is hydrogen or a C.sub.1-C.sub.20 hydrocarbyl group which may contain a heteroatom.

[0322] In formula (G3), the ring R.sup.r is a C.sub.2-C.sub.6 ring containing the carbon and nitrogen atoms in the formula, in which some or all of the carbon-bonded hydrogen atoms may be substituted by a C.sub.1-C.sub.20 hydrocarbyl group or -L.sup.22-CO.sub.2 and in which some carbon may be replaced by sulfur, oxygen or nitrogen. The ring may be alicyclic or aromatic and is preferably a 5- or 6-membered ring. Suitable rings include pyridine, pyrrole, pyrrolidine, piperidine, pyrazole, imidazoline, pyridazine, pyrimidine, pyrazine, imidazoline, oxazole, thiazole, morpholine, thiazine, and triazole rings.

[0323] The carboxylic onium salt having formula (G3) has at least one -L.sup.22-CO.sub.2.sup.. That is, at least one of R.sup.221 to R.sup.224 is -L.sup.22-CO.sub.2.sup., and/or at least one of hydrogen atoms bonded to carbon atoms in the ring R.sup.r is substituted by -L.sup.22-CO.sub.2.sup..

[0324] In formula (G3), Mq.sub.B.sup.+ is a sulfonium, iodonium or ammonium cation, with the sulfonium cation being preferred. Examples of the sulfonium cation include those exemplified above for the sulfonium cation having formula (Z-1) and the sulfonium cation having formula (Z-4).

[0325] Examples of the anion in the compound having formula (G3) are shown below, but not limited thereto.

##STR00496## ##STR00497## ##STR00498## ##STR00499## ##STR00500## ##STR00501## ##STR00502##

[0326] Weak acid betaine compounds are also useful as the quencher. Non-limiting examples thereof are shown below.

##STR00503## ##STR00504##

[0327] 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 surface after coating 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.

[0328] When used, the other quencher (G) is preferably added in an amount of 0 to 50 parts, more preferably 0.1 to 40 parts by weight per 80 parts by weight of the base polymer (B). The quencher may be used alone or in admixture.

(H) Surfactant

[0329] The resist composition may contain any conventional surfactants for facilitating to coat the composition to the substrate. A number of surfactants are known in the art as described in JP-A 2004-115630, and any suitable one may be chosen therefrom. Typical of the surfactant are PF-636 (Omnova Solutions, Inc.) and FC-4430 (3M). When the resist composition contains the surfactant (H), the amount of the surfactant (H) added is preferably 0 to 5 parts by weight per 80 parts by weight of the base polymer (B). The surfactant may be used alone or in admixture.

[Process]

[0330] Another embodiment of the invention is a resist pattern forming process comprising the steps of applying the negative resist composition defined above onto a substrate to form a resist film thereon, exposing the resist film patternwise to high-energy radiation, and developing the resist film in an alkaline developer to form a resist pattern.

[0331] Pattern formation using the negative resist composition of the invention may be performed by well-known lithography processes. In general, the resist composition is first applied onto a substrate for IC fabrication (e.g., Si, SiO, SiO.sub.2, SiN, SiON, TiN, WSi, BPSG, SOG, organic antireflective coating, etc.) or a substrate for mask circuit fabrication (e.g., Cr, CrO, CrON, MoSi.sub.2, Si, SiO, SiO.sub.2, SiON, SiONC, CoTa, NiTa, TaBN, SnO.sub.2, etc.) by a suitable coating technique such as spin coating. The coating is prebaked on a hotplate preferably at a temperature of 60 to 150 C. for 1 to 20 minutes, more preferably at 80 to 140 C. for 1 to 10 minutes to form a resist film of 0.03 to 2 m thick.

[0332] Then the resist film is exposed patternwise to high-energy radiation such as UV, deep-UV, excimer laser (KrF, ArF), EUV of wavelength 3 to 15 nm, x-ray, -ray or synchrotron radiation or EB. The resist composition of the invention is especially effective in the EUV or EB lithography.

[0333] On use of UV, deep-UV, EUV, excimer laser, x-ray, -ray or synchrotron radiation as the high-energy radiation, the resist film is exposed through a mask having a desired pattern, preferably in a dose of 1 to 500 mJ/cm.sup.2, more preferably 10 to 400 mJ/cm.sup.2. On use of EB, a pattern may be written directly in a dose of preferably 1 to 500 C/cm.sup.2, more preferably 10 to 400 C/cm.sup.2.

[0334] The exposure may be performed by conventional lithography whereas the immersion lithography of holding a liquid, typically water between the mask and the resist film may be employed if desired. In the case of immersion lithography, a protective film which is insoluble in water may be used.

[0335] The resist film is then baked (PEB) on a hotplate preferably at 60 to 150 C. for 1 to 20 minutes, more preferably at 80 to 140 C. for 1 to 10 minutes.

[0336] Thereafter, the resist film is developed with a developer in the form of an aqueous base solution, for example, 0.1 to 5 wt %, preferably 2 to 3 wt % aqueous solution of tetramethylammonium hydroxide (TMAH) preferably for 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, a desired resist pattern is formed on the substrate.

[0337] From the negative resist composition, a pattern with a high resolution and minimal LER can be formed. The resist composition is effectively applicable to a substrate, specifically a substrate having a surface layer of material to which a resist film is less adherent and which is likely to invite pattern stripping or pattern collapse, and particularly a substrate having sputter deposited on its outermost surface metallic chromium or a chromium compound containing at least one light element selected from oxygen, nitrogen and carbon or a substrate having an outermost surface layer of SiO, SiO.sub.x, or a tantalum, molybdenum, cobalt, nickel, tungsten or tin compound. The substrate to which the negative resist composition is applied is most typically a photomask blank which may be either of transmission or reflection type.

[0338] The mask blank of transmission type is typically a photomask blank having a light-shielding film of chromium-based material. It may be either a photomask blank for binary masks or a photomask blank for phase shift masks. In the case of the binary mask-forming photomask blank, the light-shielding film may include an antireflection layer of chromium-based material and a light-shielding layer. In one example, the antireflection layer on the surface layer side is entirely composed of a chromium-based material. In an alternative example, only a surface side portion of the antireflection layer on the surface layer side is composed of a chromium-based material and the remaining portion is composed of a silicon compound-based material which may contain a transition metal. In the case of the phase shift mask-forming photomask blank, it may include a phase shift film and a chromium-based light-shielding film thereon.

[0339] Photomask blanks having an outermost layer of chromium base material are well known as described in JP-A 2008-026500 and JP-A 2007-302873 and the references cited therein. Although the detail description is omitted herein, the following layer construction may be employed when a light-shielding film including an antireflective layer and a light-shielding layer is composed of chromium base materials.

[0340] In the example where a light-shielding film including an antireflective layer and a light-shielding layer is composed of chromium base materials, layers may be stacked in the order of an antireflective layer and a light-shielding layer from the outer surface side, or layers may be stacked in the order of an antireflective layer, a light-shielding layer, and an antireflective layer from the outer surface side. Each of the antireflective layer and the light-shielding layer may be composed of multiple sub-layers. When the sub-layers have different compositions, the composition may be graded discontinuously or continuously from sub-layer to sub-layer. The chromium base material used herein may be metallic chromium or a material consisting of metallic chromium and a light element such as oxygen, nitrogen or carbon. Examples used herein include metallic chromium, chromium oxide, chromium nitride, chromium carbide, chromium oxynitride, chromium oxycarbide, chromium nitride carbide, and chromium oxide nitride carbide.

[0341] The mask blank of reflection type includes a substrate, a multilayer reflective film formed on one major surface (front surface) of the substrate, for example, a multilayer reflective film of reflecting exposure radiation such as EUV radiation, and an absorber film formed on the multilayer reflective film, for example, an absorber film of absorbing exposure radiation such as EUV radiation to reduce reflectivity. From the reflection type mask blank (reflection type mask blank for EUV lithography), a reflection type mask (reflection type mask for EUV lithography) having an absorber pattern (patterned absorber film) formed by patterning the absorber film is produced. The EUV radiation used in the EUV lithography has a wavelength of 13 to 14 nm, typically about 13.5 nm.

[0342] The multilayer reflective film is preferably formed contiguous to one major surface of a substrate. An underlay film may be disposed between the substrate and the multilayer reflective film as long as the benefits of the invention are not lost. The absorber film may be formed contiguous to the multilayer reflective film while a protective film (protective film for the multilayer reflective film) may be disposed between the multilayer reflective film and the absorber film, preferably contiguous to the multilayer reflective film, more preferably contiguous to the multilayer reflective film and the absorber film. The protective film is used for protecting the multilayer reflective film in a cleaning, tailoring or otherwise processing step. Also preferably, the protective film has an additional function of protecting the multilayer reflective film or preventing the multilayer reflective film from oxidation during the step of patterning the absorber film by etching. Besides, an electroconductive film, which is used for electrostatic chucking of the reflection type mask to an exposure tool, may be disposed below the other major surface (back side surface) which is opposed to the one major surface of the substrate, preferably contiguous to the other major surface. It is provided herein that a substrate has one major surface which is a front or upper side surface and another major surface which is a back or lower side surface. The terms front and back sides or upper and lower sides are used for the sake of convenience. One or another major surface may be either of the two major surfaces (film-bearing surfaces) of a substrate, and in this sense, front and back or upper and lower are exchangeable. Specifically, the multilayer reflective film may be formed by any of the methods of JP-A 2021-139970 and the references cited therein.

[0343] The resist pattern forming process is successful in forming patterns having a very high resolution, fidelity, reduced LER, and improved dose margin, even on a substrate (typically mask blank of transmission or reflection type) whose outermost surface is made of a material tending to affect resist pattern profile such as a chromium or silicon-containing material.

EXAMPLES

[0344] Examples of the invention are given below by way of illustration and not by way of limitation. The abbreviation pbw is parts by weight. Analysis is made by time-of-flight mass spectrometry (TOF-MS) using an analyzer, MALDI TOF-MS: S3000 by JEOL Ltd.

[1] Synthesis of Onium Salts

Synthesis Example 1

Synthesis of Onium Salt SQ-1

##STR00505##

[0345] Under nitrogen atmosphere, a reactor was charged with 8.2 g of reactant SM-1, 1.7 g of sodium nitrate, 40 g of methylene chloride, and 10 g of water, which were stirred for 15 minutes. The organic layer was then taken out, washed with water, and concentrated under reduced pressure. 50 g of methyl isobutyl ketone was added to the concentrate, followed by azeotropic dewatering. Diisopropyl ether was added to the residue for washing. There was obtained 5.7 g of the target compound, onium salt SQ-1 as oily matter (yield 72%).

MALDI TOF-MS:

[0346] positive M.sup.+ 335 (corresponding to C.sub.18H.sub.11F.sub.4S.sup.+) [0347] negative M.sup. 62 (corresponding to NO.sub.3.sup.)

Synthesis Examples 2 to 8

Synthesis of SQ-2 to SQ-8

[0348] Onium salts SQ-2 to SQ-8 shown below were synthesized by well-known organic synthesis reaction using corresponding reactants.

##STR00506##

[2] Preparation of Chemically Amplified Negative Resist Compositions

Examples 1-1 to 1-50 and Comparative Examples 1-1 to 1-25

[0349] Chemically amplified negative resist compositions (R-1 to R-50, CR-1 to CR-25) were prepared by dissolving selected components in an organic solvent in accordance with the formulation shown in Tables 1 to 3, and filtering the solution through a UPE filter and/or nylon filter with a pore size of 10 nm, 5 nm, 3 nm or 1 nm. The organic solvent was a mixture of 790 pbw of PGMEA, 1,580 pbw of EL, and 1,580 pbw of PGME. To some compositions, fluorinated polymer (Polymers FP-1 to FP-5) as additive, tetramethoxymethylglycoluril (TMGU) as crosslinker, and PF-636 (Omnova Solutions Inc.) as surfactant were added.

TABLE-US-00001 TABLE 1 Resist Polymer Polymer Photoacid Cross- Fluorinated Sur- compo- Quencher 1 2 generator linker polymer factant sition (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) Example 1-1 R-1 SQ-1 P-1 PAG-A (8) TMGU PF-636 (6.0) (80) PAG-B (2) (8.154) (0.075) 1-2 R-2 SQ-1 P-1 PAG-A (8) TMGU FP-1 PF-636 (6.0) (80) PAG-B (2) (8.154) (3) (0.075) 1-3 R-3 SQ-1 P-2 PAG-A (8) TMGU PF-636 (6.0) (80) PAG-B (2) (8.154) (0.075) 1-4 R-4 SQ-1 P-3 PAG-B (6.0) (80) (5) 1-5 R-5 SQ-1 P-3 PAG-B FP-1 (6.0) (80) (5) (3) 1-6 R-6 SQ-1 P-3 PAG-B FP-2 (6.0) (80) (5) (3) 1-7 R-7 SQ-1 P-3 PAG-B FP-3 (6.0) (80) (5) (3) 1-8 R-8 SQ-1 P-3 PAG-B FP-4 (6.0) (80) (5) (3) 1-9 R-9 SQ-1 P-3 PAG-B FP-5 (6.0) (80) (5) (1.5) 1-10 R-10 SQ-1 P-4 PAG-B FP-1 (6.0) (80) (5) (3) 1-11 R-11 SQ-1 P-5 PAG-B FP-1 (6.0) (80) (5) (3) 1-12 R-12 SQ-1 P-6 PAG-B FP-1 (6.0) (80) (5) (3) 1-13 R-13 SQ-1 P-7 PAG-B FP-1 (6.0) (80) (5) (3) 1-14 R-14 SQ-1 P-8 PAG-B FP-1 (6.0) (80) (5) (3) 1-15 R-15 SQ-1 P-9 FP-1 (12.0) (80) (3) 1-16 R-16 SQ-1 P-9 PAG-B FP-1 (8.0) (80) (5) (3) 1-17 R-17 SQ-1 P-18 PAG-B FP-1 (8.0) (80) (5) (3) 1-18 R-18 SQ-1 P-19 PAG-B FP-1 (8.0) (80) (5) (3) 1-19 R-19 SQ-1 P-21 PAG-B FP-1 (8.0) (80) (5) (3) 1-20 R-20 SQ-1 P-22 PAG-B FP-1 (8.0) (80) (5) (3) 1-21 R-21 SQ-1 P-23 PAG-B FP-1 (8.0) (80) (5) (3) 1-22 R-22 SQ-1 P-24 PAG-B FP-1 (6.0) (80) (5) (3) 1-23 R-23 SQ-1 P-27 PAG-B FP-1 (6.0) (80) (5) (3) 1-24 R-24 SQ-1 P-9 P-3 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-25 R-25 SQ-1 P-9 P-3 PAG-C (1.5) TMGU FP-1 (6.0) (40 (40) PAG-E (3) (2.0) (3)

TABLE-US-00002 TABLE 2 Resist Polymer Polymer Photoacid Cross- Fluorinated Sur- compo- Quencher 1 2 generator linker polymer factant sition (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) Example 1-26 R-26 SQ-1 P-9 P-3 PAG-B (5) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-27 R-27 SQ-1 P-9 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-28 R-28 SQ-1 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-29 R-29 SQ-1 P-10 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-30 R-30 SQ-1 P-11 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-31 R-31 SQ-1 P-12 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-32 R-32 SQ-1 P-13 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-33 R-33 SQ-1 P-14 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-34 R-34 SQ-1 P-15 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-35 R-35 SQ-1 P-16 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-36 R-36 SQ-1 P-17 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-37 R-37 SQ-1 P-20 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-38 R-38 SQ-1 P-28 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-39 R-39 SQ-1 P-29 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-40 R-40 SQ-1 P-30 P-7 PAG-C (1.5) FP-1 (6.0) (40) (40) PAG-E (3) (3) 1-41 R-41 SQ-2 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-42 R-42 SQ-3 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-43 R-43 SQ-4 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-44 R-44 SQ-5 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-45 R-45 SQ-6 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-46 R-46 SQ-7 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-47 R-47 SQ-8 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-48 R-48 SQ-1 P-9 P-7 PAG-E (9) FP-1 (6.0) (40) (40) PAG-F (2) (3) 1-49 R-49 SQ-1 P-9 P-7 PAG-D (9) FP-1 (3.0) (40) (40) PAG-F (2) (3) 1-50 R-50 SQ-2 P-9 P-7 PAG-D (9) FP-1 (2.0) (40) (40) PAG-F (2) (3)

TABLE-US-00003 TABLE 3 Resist Polymer Polymer Photoacid Cross- Fluorinated Sur- compo- Quencher 1 2 generator linker polymer factant sition (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) (pbw) Comparative 1-1 CR-1 cQ-1 P-1 PAG-A (8) TMGU PF-636 Example (6.0) (80) PAG-B (2) (8.154) (0.075) 1-2 CR-2 cQ-2 P-3 PAG-B FP-1 (6.0) (80) (5) (3) 1-3 CR-3 cQ-3 P-3 PAG-B FP-2 (6.0) (80) (5) (3) 1-4 CR-4 cQ-3 P-3 PAG-B FP-3 (6.0) (80) (5) (3) 1-5 CR-5 cQ-3 P-3 PAG-B FP-4 (6.0) (80) (5) (3) 1-6 CR-6 cQ-3 P-3 PAG-B FP-5 (6.0) (80) (5) (1.5) 1-7 CR-7 cQ-2 P-5 PAG-B FP-1 (6.0) (80) (5) (3) 1-8 CR-8 cQ-3 P-6 PAG-B FP-1 (6.0) (80) (5) (3) 1-9 CR-9 cQ-2 P-22 PAG-B FP-1 (6.0) (80) (5) (3) 1-10 CR-10 cQ-3 P-23 PAG-B FP-1 (6.0) (80) (5) (3) 1-11 CR-11 cQ-2 P-24 PAG-B FP-1 (6.0) (80) (5) (3) 1-12 CR-12 cQ-3 P-27 PAG-B FP-1 (6.0) (80) (5) (3) 1-13 CR-13 cQ-1 P-9 P-3 PAG-C (1.5) FP-1 (8.0) (40) (40) PAG-E (3) (3) 1-14 CR-14 cQ-2 P-9 P-3 PAG-C (1.5) FP-1 (14.0) (40) (40) PAG-E (3) (3) 1-15 CR-15 cQ-3 P-9 P-3 PAG-C (1.5) FP-1 (12.0) (40) (40) PAG-E (3) (3) 1-16 CR-16 cQ-1 P-20 P-7 PAG-C (1.5) FP-1 (8.0) (40) (40) PAG-E (3) (3) 1-17 CR-17 cQ-2 P-28 P-7 PAG-C (1.5) FP-1 (14.0) (40) (40) PAG-E (3) (3) 1-18 CR-18 cQ-3 P-29 P-7 PAG-C (1.5) FP-1 (12.0) (40) (40) PAG-E (3) (3) 1-19 CR-19 cQ-3 P-30 P-7 PAG-C (1.5) FP-1 (12.0) (40) (40) PAG-E (3) (3) 1-20 CR-20 cQ-1 P-9 P-7 PAG-E (9) FP-1 (8.0) (40) (40) PAG-F (2) (3) 1-21 CR-21 cQ-2 P-9 P-7 PAG-E (9) FP-1 (14.0) (40) (40) PAG-F (2) (3) 1-22 CR-22 cQ-3 P-9 P-7 PAG-E (9) FP-1 (12.0) (40) (40) PAG-F (2) (3) 1-23 CR-23 cQ-3 P-9 P-3 PAG-C (1.5) TMGU FP-1 (12.0) (40) (40) PAG-E (3) (2.0) (3) 1-24 CR-24 cQ-2 P-9 P-7 PAG-D (9) FP-1 (14.0) (40) (40) PAG-F (2) (3) 1-25 CR-25 cQ-3 P-9 P-7 PAG-D (9) FP-1 (12.0) (40) (40) PAG-F (2) (3)

[0350] Polymers P-1 to P-30 used in resist compositions have the structure shown in Table 4. The polymer was analyzed for Mw and Mw/Mn by GPC versus polystyrene standards using THF or DMF solvent.

TABLE-US-00004 TABLE 4 Incor- Incor- Incor- Incor- Incor- poration poration poration poration poration Poly- Unit ratio Unit ratio Unit ratio Unit ratio Unit ratio mer 1 (mol %) 2 (mol %) 3 (mol %) 4 (mol %) 5 (mol %) Mw Mw/Mn P-1 A-1 80 B-1 10 B-5 10 4,500 1.65 P-2 A-1 80 B-2 8 B-4 12 4,400 1.64 P-3 A-1 60 B-2 10 C-1 30 3,700 1.62 P-4 A-1 70 B-2 7 C-2 23 3,600 1.63 P-5 A-1 70 B-2 5 C-3 25 3,900 1.65 P-6 A-1 70 B-2 7 C-4 23 3,800 1.63 P-7 A-1 45 B-2 10 C-5 45 4,100 1.63 P-8 A-1 55 B-4 10 C-1 35 4,000 1.63 P-9 A-1 66 B-2 9 C-1 21.5 E-1 3.5 13,000 1.62 P-10 A-1 60 B-2 4 C-1 24 E-1 12 14,900 1.64 P-11 A-1 67 B-2 10 C-1 18.5 E-2 4.5 14,000 1.64 P-12 A-1 67 B-2 9 C-1 20 E-3 4 13,600 1.62 P-13 A-1 67 B-2 10 C-1 18 E-4 5 13,300 1.63 P-14 A-1 64 B-2 10 C-1 22 E-5 4 12,900 1.64 P-15 A-1 64 B-2 10 C-1 24 E-6 4 13,500 1.63 P-16 A-1 62 B-3 10 C-1 24 E-1 4 12,400 1.64 P-17 A-2 61 B-4 10 C-1 24 E-2 5 12,200 1.65 P-18 A-1 70 C-1 30 4,200 1.68 P-19 A-1 80 B-2 5 C-1 15 4,400 1.67 P-20 A-3 80 B-2 2.5 C-1 15 E-1 2.5 12,000 1.67 P-21 A-2 50 C-1 30 D-1 20 4,500 1.66 P-22 A-2 50 C-1 30 D-2 20 5,300 1.69 P-23 A-2 50 C-1 30 D-3 20 6,000 1.68 P-24 A-2 50 C-1 30 D-4 20 6,700 1.67 P-25 A-1 65 C-1 25 E-7 10 13,100 1.71 P-26 A-1 65 C-1 25 E-8 10 12,700 1.69 P-27 A-3 76 B-2 6 C-1 18 4,400 1.67 P-28 A-1 50 B-2 2.5 C-1 30 D-1 15 E-1 2.5 12,700 1.64 P-29 A-1 50 B-2 2.5 C-1 30 D-1 15 E-3 2.5 12,600 1.62 P-30 A-1 50 B-2 2.5 C-1 30 D-1 15 E-6 2.5 13,000 1.63

[0351] The structure of each unit in Table 4 is shown below.

##STR00507## ##STR00508## ##STR00509## ##STR00510## ##STR00511## ##STR00512##

[0352] In Tables 1 to 3, comparative quenchers cQ-1 to cQ-3, photoacid generators PAG-A to PAG-F, and fluorinated polymers FP-1 to FP-5 have the following structure.

##STR00513## ##STR00514## ##STR00515##

[3] EB Lithography Test

Examples 2-1 to 2-50 and Comparative Examples 2-1 to 2-25

[0353] Using a coater/developer system ACT-M (Tokyo Electron Ltd.), each of the negative resist compositions (R-1 to R-50 and CR-1 to CR-25) was spin coated onto a mask blank of 152 mm squares having the outermost surface of a silicon oxide film, which had been vapor primed with hexamethyldisilazane (HMDS), and prebaked on a hotplate at 110 C. for 600 seconds to form a resist film of 80 nm thick. The thickness of the resist film was measured by an optical film thickness measurement system Nanospec (Nanometrics Inc.). Measurement was made at 81 points in the plane of the blank substrate excluding a peripheral band extending 10 mm inward from the blank periphery, and an average film thickness and a film thickness range were computed therefrom.

[0354] The resist film was exposed to EB using an EB writer system EBM-5000Plus (NuFlare Technology Inc., accelerating voltage 50 kV), then baked (PEB) at 120 C. for 600 seconds, and developed in a 2.38 wt % TMAH aqueous solution, thereby yielding a negative pattern.

[0355] The resist pattern was evaluated as follows. The patterned mask blank was observed under a top-down scanning electron microscope (TDSEM). The optimum dose (Eop) was defined as the exposure dose (C/cm.sup.2) which provided a 1:1 resolution at the top and bottom of a 200-nm 1:1 line-and-space (LS) pattern. The resolution (or maximum resolution) was defined as the minimum line width of a LS pattern that could be resolved at the optimum dose. The 200-nm LS pattern printed by exposure at the optimum dose (Eop) was observed under SEM. For each of the edges of 32 lines of the LS pattern, edge detection was carried out at 80 points, from which a 3-fold value (3) of the standard deviation () or variation was determined and reported as LER (nm). A change of CD per C relative to the exposure dose providing 1:1 resolution was determined from the dose curve. The results are shown in Tables 5 to 7.

TABLE-US-00005 TABLE 5 Resist Eop Maximum compo- (C/ resolution LER CD sition cm.sup.2) (nm) (nm) (nm) Ex- 2-1 R-1 110 40 4.5 0.5 ample 2-2 R-2 110 38 4.4 0.5 2-3 R-3 120 38 4.4 0.5 2-4 R-4 110 36 4.1 0.5 2-5 R-5 120 38 4.2 0.5 2-6 R-6 110 36 4.2 0.5 2-7 R-7 110 36 4.2 0.5 2-8 R-8 100 36 4.2 0.5 2-9 R-9 110 38 4.2 0.5 2-10 R-10 110 36 4.2 0.5 2-11 R-11 120 36 4.1 0.5 2-12 R-12 110 38 4.1 0.5 2-13 R-13 120 36 4.2 0.6 2-14 R-14 110 36 4.2 0.5 2-15 R-15 100 36 4.1 0.5 2-16 R-16 110 38 4.2 0.5 2-17 R-17 110 38 4.2 0.5 2-18 R-18 120 36 4.2 0.5 2-19 R-19 110 38 4.2 0.5 2-20 R-20 100 36 4.1 0.5 2-21 R-21 110 36 4.2 0.5 2-22 R-22 120 36 4.2 0.5 2-23 R-23 110 36 4.1 0.5 2-24 R-24 110 36 4.2 0.5 2-25 R-25 100 36 4.2 0.6

TABLE-US-00006 TABLE 6 Resist Eop Maximum compo- (C/ resolution LER CD sition cm.sup.2) (nm) (nm) (nm) Ex- 2-26 R-26 110 38 4.1 0.5 ample 2-27 R-27 130 36 4.2 0.5 2-28 R-28 120 36 4.2 0.5 2-29 R-29 110 36 4.2 0.5 2-30 R-30 110 36 4.1 0.5 2-31 R-31 100 38 4.2 0.6 2-32 R-32 110 36 4.1 0.5 2-33 R-33 120 36 4.2 0.5 2-34 R-34 110 36 4.2 0.5 2-35 R-35 130 36 4.2 0.5 2-36 R-36 120 38 4.1 0.5 2-37 R-37 110 36 4.2 0.6 2-38 R-38 100 36 4.2 0.5 2-39 R-39 110 36 4.2 0.5 2-40 R-40 110 38 4.1 0.5 2-41 R-41 110 36 4.2 0.5 2-42 R-42 110 38 4.1 0.5 2-43 R-43 120 36 4.2 0.5 2-44 R-44 100 36 4.2 0.6 2-45 R-45 110 36 4.2 0.5 2-46 R-46 120 36 4.1 0.5 2-47 R-47 100 38 4.2 0.5 2-48 R-48 110 36 4.2 0.5 2-49 R-49 60 44 4.9 0.5 2-50 R-50 40 44 5 0.7

TABLE-US-00007 TABLE 7 Resist Eop Maximum compo- (C/ resolution LER CD sition cm.sup.2) (nm) (nm) (nm) Com- 2-1 CR-1 110 60 4.8 1.2 para- 2-2 CR-2 110 52 4.7 1.2 tive 2-3 CR-3 110 48 4.8 1.2 Ex- 2-4 CR-4 120 52 4.9 1.1 ample 2-5 CR-5 100 50 4.8 1.2 2-6 CR-6 110 48 4.8 1.2 2-7 CR-7 100 46 4.8 1.2 2-8 CR-8 120 48 4.7 1.2 2-9 CR-9 110 50 4.7 1.1 2-10 CR-10 110 46 4.8 1.2 2-11 CR-11 110 50 4.8 1.2 2-12 CR-12 110 48 4.9 1.2 2-13 CR-13 120 46 4.8 1.2 2-14 CR-14 110 46 4.7 1.2 2-15 CR-15 130 50 4.9 1.2 2-16 CR-16 100 48 4.8 1.1 2-17 CR-17 110 50 4.8 1.2 2-18 CR-18 120 46 4.7 1.2 2-19 CR-19 110 48 4.8 1.2 2-20 CR-20 100 48 4.9 1.2 2-21 CR-21 120 48 4.7 1.2 2-22 CR-22 130 50 4.8 1.2 2-23 CR-23 110 48 4.7 1.2 2-24 CR-24 60 54 5.6 1.2 2-25 CR-25 40 50 5.5 1.3

[0356] Owing to the onium salt of formula (A) which is effective for controlling acid diffusion, the chemically amplified negative resist compositions (R-1 to R-50) within the scope of the invention show satisfactory resolution, reduced LER, and improved dose margin, as compared with the comparative resist compositions (CR-1 to CR-25). A comparison of R-49 and R-50 reveals that the benefits of the invention become outstanding when the optimum dose is 50 C or greater.

[0357] It is demonstrated that a pattern having a very high resolution, reduced LER, and improved dose margin can be formed from the chemically amplified negative resist composition. The resist pattern forming process using the negative resist composition is useful in photolithography for the fabrication of semiconductor devices and the processing of photomask blanks of transmission or reflection type.

[0358] Japanese Patent Application No. 2024-148110 is incorporated herein by reference.

[0359] 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.