A sulfonium salt, an acid generator containing the sulfonium salt, and a photoresist containing the sulfonium salt.

Abstract

To provide a novel sulfonium salt that quickly decomposes to generate an acid when exposed to ultrashort-wavelength light.SOLUTION: A sulfonium salt is represented by the formula (1), where Ar1 and Ar2 are the same or different, and represent an aromatic ring structure, or a structure in which two or more aromatic rings are connected through a single bond or a linking group, and R1 represents a halogen atom or a C1-5 haloalkyl group. R2 represents a halogen atom, a C1-5 alkyl group, a C1-5 alkoxy group, a C1-5 haloalkyl group, or a C1-5 haloalkoxy group. n1 represents an integer of 1-5, and n2 represents an integer of 0-4. L represents a single bond or linking group, and X- represents a monovalent counter anion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel sulfonium salt, an acid generator containing the sulfonium salt, and a photoresist containing the acid generator. [Background technology]

[0002] As a chemically amplified photoresist, Patent Document 1 discloses a positive-type resist containing triphenylsulfonium trifluoromethanesulfonate and a photosensitive resin. It is also stated that when this resist is irradiated with KrF excimer laser light, fine patterns can be formed with high precision. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2003-177541 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In recent years, further miniaturization, increased capacity, and performance improvements have been required for electronic devices, and this can be achieved by shortening the wavelength of the light used in photolithography.

[0005] Furthermore, the use of ultrashort wavelength light, such as extreme ultraviolet (EUV; wavelength 13.5 nm), as the aforementioned light has been considered. However, a problem has been that triphenylsulfonium trifluoromethanesulfonate has low sensitivity to ultrashort wavelength light.

[0006] Therefore, the object of the present invention is to provide a novel sulfonium salt that rapidly decomposes and generates acid when irradiated with ultrashort wavelength light. Another object of the present invention is to provide an acid generator that is highly sensitive to ultrashort wavelength light. Another object of the present invention is to provide a photoresist capable of accurately transferring a fine pattern using an extreme ultraviolet light ray.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that the sulfonium salt represented by the following formula (1) has a structure in which a specific substituent is bonded to a triarylsulfonium skeleton, and thus is extremely sensitive to an extreme ultraviolet light ray, rapidly decomposes upon irradiation with an extreme ultraviolet light ray to generate an acid, has an effect of improving resist developability due to a carboxylic acid group, and is excellent in solvent solubility. The present invention has been completed based on this finding.

[0008] That is, a sulfonium salt represented by the following formula (1) is provided.

Chemical Formula

[0009] , Ar 2 is the same or different and is an aromatic ring structure or a structure in which two or more aromatic rings are bonded via a single bond or a linking group, and R 1 represents a halogen atom or a C 1-5 haloalkyl group. R 2 represents a halogen atom, a C 1-5 alkyl group, a C 1-5 alkoxy group, a C 1-5 haloalkyl group, or a C 1-5 haloalkoxy group. n1 represents an integer of 1 to 5, and n2 represents an integer of 0 to 4. L represents a single bond or a linking group, and X - represents a monovalent counter anion.)

[0009] The present invention also provides the sulfonium salt in which the formula (1) is the following formula (1-1a).

Chemical Formula

[0010] The present invention also provides the sulfonium salt wherein formula (1) is one of the following formulas (1-3). [ka] (In the formula, R 11 , R 12 Each is independently a halogen atom or C 1-5 R indicates a halo-alkyl group. 13 C is a halogen atom. 1-5 Alkyl alkyl group, C 1-5 Alkoxy group, C 1-5 Haloalkyl groups, or C 1-5 This represents a haloalkoxy group. n11 and n12 each independently represent integers from 1 to 5, and n13 represents an integer from 0 to 4. 1 X represents an oxygen atom or a sulfur atom, and n is an integer from 1 to 5. - (This indicates a monovalent pair anion.)

[0011] The present invention also relates to the R 11 , R 12 The present invention provides the sulfonium salt in which each of the atoms is independently a fluorine atom, an iodine atom, or a trifluoromethyl group.

[0012] The present invention also provides the sulfonium salt wherein the monovalent counteranion is a sulfonate anion or a sulfonylimide anion.

[0013] The present invention also provides an acid generator containing the sulfonium salt.

[0014] The present invention also provides an acid generator which is an acid generator for extreme ultraviolet light or an acid generator for electron beams.

[0015] The present invention also provides a photoresist comprising the acid generator and a photosensitive resin. [Effects of the Invention]

[0016] The sulfonium salt of the present invention contains a carboxyl group and therefore has good sensitivity to ultrashort wavelength light. When irradiated with ultrashort wavelength light, it rapidly decomposes into acid (H). + X - Furthermore, the sulfonium salt has excellent solvent solubility, so when added to a photoresist, it disperses uniformly. Moreover, the sulfonium salt has excellent developability and has the effect of reducing development residue. Therefore, by irradiating the photoresist containing the sulfonium salt with ultrashort wavelength light, a fine pattern can be transferred with high precision, and a resist film with a high-resolution fine pattern can be manufactured. By using the resist film with the fine pattern obtained in this way to etch a substrate (for example, dry etching using a reactive gas or plasma), semiconductor devices with high-resolution patterns (e.g., wiring patterns, circuit patterns, etc.) can be manufactured with a high yield. [Modes for carrying out the invention]

[0017] [Sulfonium salt] The sulfonium salt of the present invention is represented by the following formula (1). [ka] (In the formula, Ar 1 Ar 2 These are identical or different aromatic ring structures, or structures in which two or more aromatic rings are linked by a single bond or a linking group, R 1 is a halogen atom or C 1-5 R indicates a halo-alkyl group. 2 C is a halogen atom. 1-5Alkyl alkyl group, C 1-5 Alkoxy group, C 1-5 Haloalkyl groups, or C 1-5 This indicates a haloalkoxy group. n1 is an integer from 1 to 5, and n2 is an integer from 0 to 4. L indicates a single bond or a linking group, and X - (This indicates a monovalent pair anion.)

[0018] The expression shown in square brackets in equation (1) [(R 1 ) n1 -Ar 1 The two bases may be identical or different.

[0019] The aforementioned Ar 1 Ar 2 Examples of aromatic ring structures in this context include aromatic hydrocarbon rings with 6 to 15 carbon atoms, such as benzene rings, naphthalene rings, and anthracene rings.

[0020] The aforementioned Ar 1 Ar 2 Examples of structures in which two or more aromatic rings are linked by single bonds or linking groups include structures in which two or more aromatic hydrocarbon rings are linked by single bonds, ether bonds (-O-), or thioether bonds (-S-).

[0021] The aforementioned Ar 1 Ar 2 From the viewpoint of increasing sensitivity to ultrashort wavelength light, it is preferable that the structure be a benzene ring structure or a structure in which two or more benzene rings are linked by a single bond or a linking group (preferably an ether bond or a thioether bond), and at least one structure selected from the benzene ring structure and the structures represented by the following formulas (ar-1) to (ar-3) is particularly preferred. [ka]

[0022] Said C 1-5Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, and pentyl groups. The alkyl group preferably has 1 to 3 carbon atoms, and most preferably 1 or 2 carbon atoms.

[0023] Said C 1-5 Haloalkyl groups are C 1-5 The group is one in which at least one of the hydrogen atoms of the alkyl group is substituted with a halogen atom, and among these, a group in which all of the hydrogen atoms of the alkyl group are substituted with halogen atoms (i.e., a perhalogenated hydrocarbon group) is preferred. Furthermore, the number of carbon atoms of the haloalkyl group is preferably 1 to 3, and particularly preferably 1 or 2.

[0024] Therefore, the C 1-5 The haloalkyl group is preferably C 1-3 Haloalkyl groups, particularly preferably C 1-2 It is a haloalkyl group.

[0025] Said C 1-5 The haloalkyl group is preferably C 1-3 Perhaloalkyl groups, particularly preferably C 1-2 It is a perhaloalkyl group.

[0026] Said C 1-5 Examples of alkoxy groups include methoxy groups, ethoxy groups, butoxy groups, and t-butoxy groups. The number of carbon atoms in the alkyl group is preferably 1 to 3, and particularly preferably 1 or 2. 1-5 The number of carbon atoms in the alkoxy group is preferably 1 to 3, and particularly preferably 1 or 2.

[0027] Said C 1-5 The haloalkoxy group is C 1-5 The alkoxy group is a group in which at least one of its hydrogen atoms is substituted with a halogen atom, and among these, a group in which all of its hydrogen atoms are substituted with halogen atoms is preferred. Furthermore, the number of carbon atoms in the haloalkoxy group is preferably 1 to 3, and particularly preferably 1 or 2.

[0028] Therefore, the C 1-5 The haloalkoxy group is preferably C 1-3 Haloalkoxy group, particularly preferably C 1-2 It is a haloalkoxy group.

[0029] Said C 1-5 The haloalkyl group is preferably C 1-3 A perhaloalkoxy group, particularly preferably C 1-2 It is a perhalalkoxy group.

[0030] The halogen atom, The C 1-5 Haloalkyl groups and the C 1-5 The halogen atom of the haloalkoxy group is preferably a fluorine atom or an iodine atom, and is particularly preferably a fluorine atom.

[0031] The L in the above-mentioned L represents a single bond or a linking group. The linking group is a divalent group having one or more atoms, and examples include a divalent hydrocarbon group, a carbonyl group (-CO-), an ether bond (-O-), a thioether bond (-S-), an ester bond (-COO-), an amide bond (-CONH-), a carbonate bond (-OCOO-), and a group formed by linking multiple such groups.

[0032] Examples of the divalent hydrocarbon groups include linear or branched alkylene groups having 1 to 5 carbon atoms, such as methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene; cycloalkylene groups having 3 to 18 carbon atoms, such as 1,2-cyclopentylene, 1,3-cyclopentylene, cyclopentylidene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, and cyclohexylidene; and arylene groups having 6 to 14 carbon atoms, such as o-phenylene, m-phenylene, p-phenylene, and naphthylene.

[0033] Among the Ls, a divalent group is preferred in which an ether bond (-O-) or a thioether bond (-S-) is bonded to a divalent hydrocarbon group, and in particular, a divalent group is preferred in which an ether bond (-O-) or a thioether bond (-S-) is bonded to a linear or branched alkylene group having 1 to 5 carbon atoms [C n H 2n A divalent base formed by combining [an integer n=1 to 5] is preferred.

[0034] Therefore, the above L is given by the formula [-L 1 -C n H 2n A divalent group represented by - is preferred. In the above formula, L 1 L represents an oxygen atom or a sulfur atom, and n represents an integer from 1 to 5. 1 The coupling extending to the left from is Ar in equation (1) above. 2 It bonds to the ring structure shown by . Additionally, the bonds emanating from the right side of the above formula (i.e., to the right of the alkylene group) bond to the carboxyl carbon in formula (1).

[0035] As for formula (1), formulas (1-1a), (1-1b), or (1-1c) below are preferred, and formula (1-1a) below is particularly preferred, due to their excellent sensitivity to ultrashort wavelength light. That is, the sulfonium salt of the present invention is preferably a sulfonium salt represented by formulas (1-1a), (1-1b), or (1-1c) below, and the sulfonium salt represented by formula (1-1a) below is particularly preferred. [ka]

[0036] In the above formula, R 11 , R 12 Each is independently a halogen atom or C 1-5 R indicates a halo-alkyl group. 13 C is a halogen atom. 1-5 Alkyl alkyl group, C 1-5 Alkoxy group, C 1-5 Haloalkyl groups, or C 1-5represents a haloalkoxy group. n11 and n12 each independently represent an integer from 1 to 5, and n13 represents an integer from 0 to 4. L represents a single bond or a linking group, and X - represents a monovalent counter anion.

[0037] In the above formula, n11 and n12 each independently represent an integer from 1 to 5, preferably an integer from 1 to 3, particularly preferably 1 or 2, and most preferably 2. n13 represents an integer from 0 to 4, preferably an integer from 1 to 4, particularly preferably 1 or 2, and most preferably 2.

[0038] In the above formula, R 11 , R 12 There is no particular limitation on the bonding position of the group represented by to the benzene ring.

[0039] In the above formula, R 13 There is no particular limitation on the bonding position of the group represented by to the benzene ring, but the meta position is preferred with respect to the position where the sulfur atom shown in the above formula is bonded.

[0040] In the above formula, as the bonding position of the group represented by [-L-COO - to the benzene ring, the para position is preferred with respect to the position where the sulfur atom shown in the above formula is bonded.

[0041] Further, as the formula (1), the following formula (1-2) is preferred from the viewpoint of excellent sensitivity to light of ultra-short wavelengths. That is, as the sulfonium salt of the present invention, the sulfonium salt represented by the following formula (1-2) is preferred. In the following formula, Ar 1 , Ar 2 , R 1 , R 2 , n1, n2, L 1 , n, X - are the same as described above. [Chemical formula]

[0042] Based on the above, as formula (1), formulas (1-3) below are particularly preferred in terms of their excellent sensitivity to ultrashort wavelength light. That is, as the sulfonium salt of the present invention, the sulfonium salt represented by formula (1-3) below is particularly preferred. In the following formulas, R 11 , R 12 , R 13 n11, n12, n13, L 1 , n, X - The same applies as above. [ka]

[0043] In the above formula, X - ∫ represents a monovalent counter anion, for example, halogen ions, halogen oxoate anions, boron anions, phosphate anions, sulfate anions, sulfonate anions, sulfonylimide anions, carboxylate anions, methide anions, antimony anions, OH - SCN - NO2 - NO3 - These are some examples.

[0044] Examples of the halogen ions include Cl - , Br - , I - These are some examples.

[0045] Examples of the halogen oxo acid anion include ClO4. - IO3 - , BrO3 - These are some examples.

[0046] Examples of the boron anion include Br3. - BF4 - Inorganic boron anions such as (C6F5)4B - ,((CF3)2C6H3)4B - Examples of organoboron anions include tetraphenylborate, tetrakis(monofluorophenyl)borate, tetrakis(difluorophenyl)borate, and tetrakis(trifluorophenyl)borate.

[0047] Examples of the phosphate anion include PF6 - , PF(C2F5)5 - , PF2(C2F5)4 - , PF3(C2F5)3 - , PF4(C2F5)2 - , PF5(C2F5) - , PO4 3- Examples include inorganic phosphate anions.

[0048] The aforementioned sulfonate anion can be represented, for example, by the following formula (s1). R s1 -SO3 - (s1) (In the formula, R s1 (This indicates an organic group.)

[0049] R s1 The organic group in this may be, for example, a C which may have substituents. 1-30 A hydrocarbon group, a heterocyclic group which may have substituents, and two or more of the said groups are connected by a single bond or by -O-, -CO2-, -S-, -SO3-, and -SO2N(R s2 )- A group linked by a linking group selected from the above R s2 is a hydrogen atom or an alkyl group (for example, C 1-30 The alkyl group is represented. Examples of the substituents include halogen atoms such as fluorine atoms.

[0050] Said C 1-30 The hydrocarbon group is C 1-30 Aliphatic hydrocarbon group, C 3-30 Alicyclic hydrocarbon group, C 6-30 This includes aromatic hydrocarbon groups and groups formed by the bonding of two of these groups.

[0051] Said C 1-30 As for hydrocarbon groups, C 1-30 Alkyl alkyl group, C 6-15 Aryl group, C 6-15 Cycloalkylene group, C 6-15Bridged cyclic hydrocarbon groups and groups formed by the bonding of two such groups are preferred.

[0052] The heterocyclic group is a group obtained by removing one hydrogen atom from the structural formula of a heterocycle. The heterocycle includes aromatic heterocycles and non-aromatic heterocycles. Examples of such heterocycles include 3- to 10-membered rings (preferably 4- to 6-membered rings) having carbon atoms and at least one heteroatom (e.g., oxygen atom, sulfur atom, nitrogen atom, etc.) as atoms constituting the ring, and fused rings thereof.

[0053] A specific example of the sulfonic acid anion is CH3SO3 - , C4H9SO3 - CF3SO3 - , C2F5C4H4SO3 - , C4F9SO3 - Examples include benzenesulfonate anions, p-toluenesulfonate anions, and camphorsulfonate anions.

[0054] The aforementioned sulfonylimide anion can be represented, for example, by the following formula (n1). (R n1 SO2)2N - (n1) (In the formula, two R n1 (These are the same or different, and represent organic groups.)

[0055] R n1 As for organic groups in this context, R s1 Similar examples can be given to organic groups in the context of [the subject].

[0056] A specific example of the sulfonylimide anion is (FSO2)2N - (CF3SO2)2N - (C4F9SO2)2N - (C2F5SO2)2N - These are some examples.

[0057] The carboxylic acid anion can be represented, for example, by the following formula (c1). R c1 -COO- (c1) (In the formula, R c1 (This indicates an organic group.)

[0058] R c1 As for organic groups in this context, R s1 Similar examples can be given to organic groups in the context of [the subject].

[0059] A specific example of the carboxylic acid anion is, for example, CF3CO2 - CH3CO2 - , C2H5CO2 - PhCO2 - These are some examples.

[0060] Examples of the methide anion include the sulfonylmethide anion represented by the following formula (m1). (R m1 SO2)3C - (m1) (In the formula, three R m1 (These are the same or different, and represent organic groups.)

[0061] R m1 As for organic groups in this context, R s1 Similar examples can be given to organic groups in the context of [the subject].

[0062] A specific example of the aforementioned methidoanion is (CF3SO2)3C - These are some examples.

[0063] Examples of the antimony anion include SbF6. - These are some examples.

[0064] In addition to those mentioned above, the monovalent counter anions include, for example, the anions described in Japanese Patent Publication Nos. 2013-47211, 2021-81708, 2013-80245, 2013-80240, and 2013-33161.

[0065] As the counter anion, sulfonic acid anions or sulfonylimide anions are preferred in terms of their excellent solvent solubility and fine pattern formation properties.

[0066] [Method for producing sulfonium salts] An example of a method for producing the sulfonium salt is shown below. Of the sulfonium salts mentioned above, for example, the sulfonium salt represented by the above formula (1-3) (= sulfonium salt (1-3)) can be produced by the following steps [I] [II] [III]. In the following formula, R 11 , R 12 , R 13 n11, n12, n13, L 1 , n, X - The same applies as above. [ka]

[0067] (Process I) Step I is a step in which a compound represented by formula (11) (=compound (11)) and a compound represented by formula (12) (=compound (12)) are reacted to obtain a compound represented by formula (13) (=compound (13)).

[0068] The molar ratio of compound (11) to compound (12) subjected to the above reaction (compound (11) / compound (12)) is, for example, 1 / 50 to 3 / 1, preferably 1 / 10 to 2 / 1.

[0069] The above reaction is preferably carried out in the presence of a dehydrating agent (HX'). Examples of dehydrating agents (HX') include concentrated sulfuric acid, phosphoric anhydride, methanesulfonic acid, trifluoromethanesulfonic acid, or their anhydrides. These can be used individually or in combination of two or more.

[0070] (Process II) Step II involves adding M to the compound (13) obtained through Step I. 1 X(X represents a monovalent pair anion, M 1This is a step in which an alkali metal is reacted with a compound represented by formula (14) to obtain a compound represented by formula (14) (= compound (14)).

[0071] Compound (13) and M to be subjected to the above reaction 1 Molar ratio of X (compound (13) / M) 1 X) is, for example, 1 / 3 to 3 / 1, preferably 1 / 2 to 2 / 1.

[0072] (Process III) Step III is a step in which the compound (14) obtained in Step II is reacted with the compound represented by formula (15) (=compound (15)) to obtain the sulfonium salt (1-3).

[0073] X in equation (15) 1 X represents a halogen atom. 2 represents a hydrogen atom or a protecting group (e.g., a t-butyl group). Compound (15) acts as an alkylating agent.

[0074] The molar ratio of compound (14) to compound (15) subjected to the above reaction (compound (14) / compound (15)) is, for example, 1 / 3 to 3 / 1, preferably 1 / 2 to 2 / 1.

[0075] The above reaction can be carried out in the presence of a solvent. Examples of the solvent include acetone, acetonitrile, and dimethyl sulfoxide. These can be used individually or in combination of two or more.

[0076] The reaction atmosphere for each step is not particularly limited as long as it does not inhibit the reaction, and may be any of the following: air, nitrogen, argon, etc. Furthermore, the reaction can be carried out in batch, semi-batch, or continuous manner.

[0077] Furthermore, after the reaction in each step is complete, the resulting reaction product may be subjected to general separation and purification processes (e.g., precipitation, washing, filtration, etc.).

[0078] [Acid Generator] The acid generator of the present invention comprises the sulfonium salt either alone or in combination of two or more types.

[0079] The acid generator may contain other components besides the sulfonium salt, but the proportion of the sulfonium salt in the total amount of compounds that decompose upon light irradiation to generate acid contained in the acid generator is, for example, 70% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more, particularly preferably 95% by weight or more, most preferably 99% by weight or more, and especially preferably 99.9% by weight or more. The upper limit is 100% by weight.

[0080] The acid generator (or the sulfonium salt) has excellent solubility in a solvent (e.g., PGMEA), and at room temperature and pressure, the amount of the acid generator (or the sulfonium salt) that dissolves in 100 parts by weight of PGMEA is, for example, more than 2 parts by weight, preferably 3 parts by weight or more, more preferably 4 parts by weight or more, particularly preferably 5 parts by weight or more, most preferably 8 parts by weight or more, and especially preferably 15 parts by weight or more. The upper limit is, for example, 30 parts by weight. Therefore, by adding the acid generator to the photoresist together with the solvent, the acid generator can be uniformly dispersed in the photoresist.

[0081] Furthermore, the acid generator (or the sulfonium salt) has excellent sensitivity to ultrashort wavelength light, and when irradiated with such light, it quickly generates acid (H + X - ;X - This generates a counter anion. The wavelength of the light is, for example, 100 nm or less (e.g., 1 to 100 nm), preferably 80 nm or less, particularly preferably 50 nm or less, most preferably 30 nm or less, and especially preferably 20 nm or less. The light includes, for example, X-rays, electron beams, EUV, etc.

[0082] The acid generator (or the sulfonium salt) has thermal stability and can suppress decomposition even when subjected to heat treatment (for example, heating at a temperature of 50°C or higher but less than 130°C for 1 to 5 minutes). Therefore, the coating film containing the acid generator can be heat-dried while maintaining its acid-generating ability, resulting in excellent workability.

[0083] The acid generator (or sulfonium salt) can, for example, be added to a cationic curable resin (for example, a resin having one or more cationic curable groups selected from epoxy groups, oxetanyl groups, vinyl ether groups, etc.) as a cationic polymerization initiator. However, as described above, it is preferable to use it in a photoresist that uses ultrashort wavelength light such as extreme ultraviolet light, electron beams, or X-rays (for example, a chemically amplified photoresist).

[0084] [Photoresist] The photoresist of the present invention comprises the acid generator (or the sulfonium salt) and a photosensitive resin. The acid generator and the photosensitive resin may each be contained individually or in combination of two or more types.

[0085] The content of the acid generator (or the sulfonium salt) is, for example, 0.001 to 20% by weight, preferably 0.01 to 15% by weight, and particularly preferably 0.05 to 7% by weight, based on the total amount of the photosensitive resin.

[0086] If the content of the acid generator (or the sulfonium salt) is 0.001% by weight or more, excellent photosensitivity to ultrashort wavelength light such as X-rays, electron beams, and EUV can be achieved. Furthermore, if the content is 20% by weight or less, the effect of improving the resolution of the photoresist can be obtained.

[0087] The aforementioned photosensitive resins include negative-type photosensitive resins (QN) whose solubility decreases upon light irradiation (or unexposed areas are removed), and positive-type photosensitive resins (QP) whose solubility increases upon light irradiation (or exposed areas are selectively removed). These can be selected and used according to the application.

[0088] A negative-type photosensitive resin (or negative-type chemically amplified resin; QN) is, for example, a composition containing one phenolic hydroxyl group-containing resin (QN1) and a crosslinking agent (QN2), either individually or in combination of two or more.

[0089] The phenolic hydroxyl group-containing resin (QN1) is not particularly limited as long as it is a resin containing phenolic hydroxyl groups. Examples include novolac resin, polyhydroxystyrene, copolymers of hydroxystyrene and styrene, copolymers of hydroxystyrene, styrene and (meth)acrylic acid derivatives, phenol-xylylene glycol condensation resin, cresol-xylylene glycol condensation resin, polyimide containing phenolic hydroxyl groups, polyamic acid containing phenolic hydroxyl groups, and phenol-dicyclopentadiene condensation resin.

[0090] The phenolic hydroxyl group-containing resin (QN1) may contain phenolic low-molecular-weight compounds as part of its components.

[0091] The polystyrene-equivalent weight-average molecular weight (Mw) of phenolic hydroxyl group-containing resin (QN1), as measured by GPC, is, for example, 2000 to 20000.

[0092] The crosslinking agent (QN2) can be any compound capable of crosslinking the phenolic hydroxyl group-containing resin (QN1) with the acid generated from the acid generator. Examples include bisphenol A epoxy compounds, bisphenol F epoxy compounds, bisphenol S epoxy compounds, novolac resin epoxy compounds, resol resin epoxy compounds, poly(hydroxystyrene) epoxy compounds, oxetane compounds, methylol group-containing melamine compounds, methylol group-containing benzoguanamine compounds, methylol group-containing urea compounds, methylol group-containing phenol compounds, alkoxyalkyl group-containing melamine compounds, alkoxyalkyl group-containing benzoguanamine compounds, alkoxyalkyl group-containing urea compounds, alkoxyalkyl group-containing phenol compounds, carboxymethyl group-containing melamine resins, carboxymethyl group-containing benzoguanamine resins, carboxymethyl group-containing urea resins, carboxymethyl group-containing phenol resins, carboxymethyl group-containing melamine compounds, carboxymethyl group-containing benzoguanamine compounds, carboxymethyl group-containing urea compounds, and carboxymethyl group-containing phenol compounds. These can be used individually or in combination of two or more.

[0093] From the viewpoint of forming patterns with high precision, the content of the crosslinking agent (QN2) is, for example, 10 to 40 mol% relative to the total acidic functional groups in the phenolic hydroxyl group-containing resin (QN1).

[0094] Positive-type photosensitive resins (or positive-type chemically amplified resins; QP) include alkali-soluble resins (protective group-introduced resins; QP1) into which acid-dissociable groups are introduced as protecting groups.

[0095] Protecting group-introduced resins (QP1) are resins in which some or all of the hydrogen atoms of acidic functional groups (e.g., phenolic hydroxyl groups, carboxyl groups, sulfonyl groups, etc.) in an alkali-soluble resin are replaced with acid-dissociable groups.

[0096] The protective group-introducing resin (QP1) itself is an alkali-insoluble or alkali-slightly alkali-soluble resin, and the acid (H) generated from the acid generator + X- When the acid-dissociable groups dissociate due to ), an alkali-soluble resin that readily dissolves in alkaline developer is formed.

[0097] The alkali-soluble resin is, for example, a resin with an HLB value of 4 to 19 (preferably 5 to 18, particularly preferably 6 to 17).

[0098] Alkali-soluble resins include resins containing phenolic hydroxyl groups, resins containing carboxyl groups, and resins containing sulfonic acid groups.

[0099] Examples of phenolic hydroxyl group-containing resins include resins similar to the phenolic hydroxyl group-containing resin (QN1) described above.

[0100] The carboxyl group-containing resin is not particularly limited as long as it is a polymer having carboxyl groups. Examples include homopolymers of carboxyl group-containing vinyl monomers (Ba) and homopolymers of carboxyl group-containing vinyl monomers (Ba) and hydrophobic group-containing vinyl monomers (Bb).

[0101] An example of a carboxyl group-containing vinyl monomer (Ba) is (meth)acrylic acid.

[0102] Examples of hydrophobic group-containing vinyl monomers (Bb) include C 1-20 Examples include (meth)acrylic acid esters (Bb1) such as alkyl (meth)acrylates and alicyclic group-containing (meth)acrylates, and aromatic hydrocarbon monomers (Bb2) such as hydrocarbon monomers having a styrene skeleton and vinylnaphthalene.

[0103] The sulfonic acid group-containing resin is not particularly limited as long as it is a polymer having sulfonic acid groups. For example, it can be obtained by vinyl polymerization of a sulfonic acid group-containing vinyl monomer (Bc), such as vinyl sulfonic acid or styrene sulfonic acid, and, if necessary, a hydrophobic group-containing vinyl monomer (Bb).

[0104] Examples of acid-dissociable groups in the protecting group-introducing resin (QP1) include 1-substituted methyl groups such as methoxymethyl, benzyl, and tert-butoxycarbonylmethyl groups; 1-substituted ethyl groups such as 1-methoxyethyl and 1-ethoxyethyl groups; 1-branched alkyl groups such as tert-butyl groups; silyl groups such as trimethylsilyl groups; gelmyl groups such as trimethylgermyl groups; alkoxycarbonyl groups such as tert-butoxycarbonyl groups; acyl groups; and cyclic acid-dissociable groups such as tetrahydropyranyl, tetrahydrofuranyl, tetrahydrothiopyranyl, and tetrahydrothiofuranyl groups. These may be present individually or in combination of two or more.

[0105] The rate of introduction of acid-dissociable groups in the protecting group-introduced resin (QP1) {the ratio of the number of acid-dissociable groups to the total number of unprotected acidic functional groups and acid-dissociable groups in the protecting group-introduced resin (QP1)} cannot be defined in general terms depending on the type of acid-dissociable group and the alkali-soluble resin into which the group is introduced, but it is preferably 10 to 100%, and more preferably 15 to 100%.

[0106] The polystyrene-equivalent weight-average molecular weight (Mw) of the protective group-introduced resin (QP1), as measured by GPC, is, for example, 1,000 to 150,000, preferably 3,000 to 100,000.

[0107] The photoresist of the present invention can be prepared, for example, by dissolving the acid generator (or the sulfonium salt) in a solvent and mixing it with a photosensitive resin.

[0108] The photoresist of the present invention may contain one or more other components as needed, in addition to the acid generator (or the sulfonium salt) and the photosensitive resin. Examples of other components include solvents, pigments, dyes, photosensitizers, dispersants, surfactants, fillers, leveling agents, defoamers, antistatic agents, ultraviolet absorbers, pH adjusters, surface modifiers, plasticizers, drying accelerators, and the like.

[0109] The solvent can be any solvent that can dissolve the photosensitive resin and impart good coatability to the photoresist, but it is preferable to use one with a boiling point of 200°C or lower, as this allows for easy drying after application of the photoresist. Preferred solvents include aromatic hydrocarbons such as toluene; alcohols such as ethanol and methanol; ketones such as cyclohexanone, methyl ethyl ketone, and acetone; esters such as ethyl acetate, butyl acetate, and ethyl lactate; and glycol monoether monoesters such as propylene glycol monomethyl ether acetate (PGMEA). These can be used individually or in combination of two or more.

[0110] The photoresist of the present invention contains a sulfonium salt that has high photosensitivity to ultrashort wavelength light such as X-rays, electron beams, and EUV. Therefore, by using the photoresist of the present invention, a resist film with a high resolution and fine pattern can be manufactured by photolithography using ultrashort wavelength light.

[0111] A preferred method for forming a pattern using the aforementioned photoresist via photolithography includes, for example, a method comprising the following steps 1 to 3.

[0112] Step 1: A step of forming a photoresist coating on a substrate. Step 2: A step of transferring a pattern by irradiating the coating film with light. Step 3: Alkaline development process

[0113] (Process 1) This process involves forming a photoresist coating on a substrate to be etched. The photoresist coating can be formed by applying the photoresist to the substrate using known methods such as spin coating, curtain coating, roll coating, spray coating, or screen printing, and then drying it.

[0114] As for the drying method of the photoresist, natural drying is possible, but since the sulfonium salt has thermal stability, it can also be dried by heating (for example, heating at a temperature of 50°C or higher but less than 130°C for 1 to 5 minutes), which offers excellent workability.

[0115] The thickness of the coating film is, for example, 1 to 1000 nm.

[0116] (Process 2) This step involves transferring a pattern to the coating film obtained in step 1 by irradiating it with light, for example, by irradiating it with light through a photomask having a pattern.

[0117] The light used for light irradiation is an acid (H) that decomposes the sulfonium salt contained in the coating film. + X - ;X - There are no particular restrictions as long as a counter anion can be generated, but from the viewpoint of further refining the pattern, it is preferable to use ultrashort wavelength light rays, and the wavelength of the light rays is preferably 100 nm or less (e.g., 1 to 100 nm), more preferably 80 nm or less, particularly preferably 50 nm or less, most preferably 30 nm or less, and especially preferably 20 nm or less. The light rays include, for example, X-rays, electron beams, EUV, etc.

[0118] After light irradiation, heating at a temperature of 60 to 200°C for about 0.1 to 120 minutes is preferable because it can increase the difference in solubility in the alkaline developer between the exposed and unexposed areas.

[0119] (Step 3) This step involves subjecting the photoresist coating, which has undergone step 2, to an alkaline development treatment.

[0120] Examples of alkaline developers used in alkaline development include aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, sodium bicarbonate, and aqueous tetramethylammonium salt solution.

[0121] Methanol, ethanol, isopropyl alcohol, tetrahydrofuran, N-methylpyrrolidone, etc. may be added to the alkaline developer.

[0122] The alkaline developing process is carried out by applying the alkaline developing solution to the coating film using methods such as a dipping method, a shower method, or a spray method.

[0123] The temperature of the alkaline developer is, for example, 25-40°C. The alkaline development time is determined appropriately depending on the thickness of the resist, but is typically around 1-5 minutes.

[0124] During alkaline development, a large difference in solubility between the exposed and unexposed areas of the photoresist coating is preferable from the viewpoint of forming a fine pattern with good accuracy. This is because if there is a large amount of development residue, problems such as abnormal wiring shapes are likely to occur. Furthermore, as described above, the photoresist of the present invention contains a sulfonium salt having a carboxyl group, which improves the developability of the resist during alkaline development and reduces development residue. Therefore, products without defects can be manufactured with a high yield.

[0125] After step 3, a resist film with a highly accurate fine pattern can be formed on the substrate. By etching the substrate using the resist film obtained in this way, a high-precision electronic device can be manufactured.

[0126] The aforementioned electronic devices include, for example, display devices such as organic EL displays and liquid crystal displays; input devices such as touch panels; light-emitting devices; sensor devices; and MEMS (Micro Electro Mechanical Systems) devices such as optical scanners, optical switches, accelerometers, pressure sensors, gyroscopes, microfluidics, and inkjet heads.

[0127] The configurations and combinations thereof described above are merely examples, and additions, omissions, substitutions, and modifications to the configurations are permitted as appropriate, without departing from the spirit of the present invention. Furthermore, the present invention is not limited by the embodiments, but is limited solely by the claims. [Examples]

[0128] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0129] Example 1 A THF solution of 3,5-difluorophenylmagnesium bromide was prepared by dispersing 13.4 g (0.55 mol) of magnesium in 400 g of tetrahydrofuran (THF) to a dispersion, and then adding 96.5 g (0.50 mol) of 1-bromo-3,5-difluorobenzene dropwise while stirring, maintaining the system temperature in the range of 40-50°C. To a THF solution of the prepared 3,5-difluorophenylmagnesium bromide, a solution of 28.6 g (0.24 mol) of thionyl chloride diluted with 50 g of THF was added dropwise at a rate that did not exceed -5°C in system temperature. After the addition was complete, the reaction was allowed to continue at room temperature for 1 hour to complete the reaction.

[0130] The reaction solution was added to 500 g of deionized water at a rate that did not exceed 15°C, and the mixture was stirred for 1 hour. Then, 300 g of ethyl acetate was added and the mixture was stirred for 1 hour. After removing the aqueous layer, the mixture was washed three times with 300 g of deionized water. The organic layer was decolorized by passing it through a silica gel column. Subsequently, the decolorized organic layer was desolvented and recrystallized with cyclohexane to obtain 26.0 g of bis(3,5-difluorophenyl) sulfoxide.

[0131] 6.86 g (0.025 mol) of the obtained bis(3,5-difluorophenyl) sulfoxide was dissolved in 15.3 g (0.125 mol) of 2,6-dimethylphenol and 24.0 g (0.25 mol) of methanesulfonic acid, and 7.1 g (0.05 mol) of anhydrous phosphoric acid was added dropwise at a rate that did not exceed 25°C in the system. After the addition was complete, the reaction was allowed to continue at room temperature for 24 hours to complete the reaction. Next, the reaction mixture was slowly added to 150 g of deionized water, stirred for a while, and then 50 g of methanol was added. 50 g of toluene was added to this solution, stirred for 30 minutes, and then allowed to stand to remove the upper toluene layer. This toluene washing was repeated two more times.

[0132] After removing the toluene layer, 4.7 g (0.025 mol) of potassium trifluoromethanesulfonate and 80 g of dichloromethane were added to the aqueous layer. The mixture was stirred for 1 hour, then allowed to stand, and the upper aqueous layer was removed. This washing procedure was repeated two more times. The dichloromethane layer after removing the aqueous layer was concentrated to obtain 3.1 g (0.006 mol) of a sulfonium intermediate.

[0133] Next, 10 g of acetonitrile, 1.7 g (0.009 mol) of t-butyl bromoacetate, and 2.5 g (0.018 mol) of potassium carbonate were added to this intermediate, and the reaction was carried out at 60°C for 36 hours. After that, the reaction mixture was filtered and the filtrate was collected. The collected filtrate was concentrated and then washed with t-butyl methyl ether to collect 3.5 g of the insoluble portion.

[0134] The insoluble portion was dissolved in 100 g of isopropanol, then 1 g of sulfuric acid was added and the mixture was reacted at 70°C for 5 hours. The solvent was then removed by concentration. Next, 50 g of dichloromethane and 50 g of deionized water were added, and after stirring for 1 hour, the mixture was allowed to stand and the upper aqueous layer was removed. This washing procedure was repeated two more times. After concentrating the dichloromethane layer after the removal of the aqueous phase, it was recrystallized with butyl acetate. This yielded 2.3 g of the target product, [bis(3,5-difluorophenyl)](4-carboxymethoxy-3,5-dimethylphenyl)sulfonium trifluoromethanesulfonate.

[0135] Example 2 20.0 g of bis(2-trifluoromethylphenyl) sulfoxide was obtained in the same manner as in Example 1, except that 112.5 g (0.50 mol) of 2-bromobenzotrifluoride was used instead of 96.5 g of 1-bromo-3,5-difluorobenzene.

[0136] [Bis(2-trifluoromethylphenyl)](4-(1-carboxypropoxy)-3,5-dimethylphenyl)sulfonium nonafluorobutanesulfonate was obtained by the same method as in Example 1, except that bis(2-trifluoromethylphenyl)sulfoxide was used instead of bis(3,5-difluorophenyl)sulfoxide, 2-t-butyl bromobutyrate was used instead of t-butyl bromoacetate, and potassium nonafluorobutanesulfonate was used instead of potassium trifluoromethanesulfonate.

[0137] Example 3 29.1 g of bis(4-trifluoromethylphenyl) sulfoxide was obtained in the same manner as in Example 1, except that 112.5 g (0.50 mol) of 4-bromobenzotrifluoride was used instead of 96.5 g of 1-bromo-3,5-difluorobenzene.

[0138] [Bis(4-trifluoromethylphenyl)](4-carboxymethylthiophenyl)sulfonium bis(trifluoromethanesulfonyl)imide was obtained in the same manner as in Example 1, except that bis(4-trifluoromethylphenyl)](4-carboxymethylthiophenyl)sulfonium bis(trifluoromethanesulfonyl)imide was used instead of bis(3,5-difluorophenyl)sulfoxide, thiophenol was used instead of 2,6-dimethylphenol, and potassium bis(trifluoromethanesulfonyl)imide was used instead of potassium trifluoromethanesulfonate.

[0139] Example 4 28.6 g (0.24 mol) of thionyl chloride and 100 g (0.48 mol) of iodobenzene were diluted with 500 g of THF to which 50 g (0.48 mol) of perchloric acid was added dropwise. After the addition was complete, the reaction was allowed to continue at room temperature for 5 hours to complete. Next, the reaction solution was slowly added to 1500 g of deionized water, followed by the addition of 300 g of dichloromethane. The mixture was stirred for 1 hour, and then allowed to stand to remove the upper aqueous layer. The dichloromethane layer after the removal of the aqueous phase was concentrated and recrystallized with butyl acetate to obtain 54 g of bis(4-iodophenyl) sulfoxide.

[0140] [Bis(4-iodophenyl)](4-carboxyphenyl)sulfonium nonafluorobutanesulfonate was obtained in the same manner as in Example 1, except that bis(4-iodophenyl)sulfoxide was used instead of bis(3,5-difluorophenyl)sulfoxide, t-butyl benzoate was used instead of 2,6-dimethylphenol, potassium nonafluorobutanesulfonate was used instead of potassium trifluoromethanesulfonate, and t-butyl bromoacetate was not used.

[0141] Example 5 27.4 g (0.10 mol) of bis(3,5-difluorophenyl) sulfoxide was dissolved in 200 g of sulfuric acid, and 45.0 g (0.20 mol) of N-iodosuccinimide was added in portions. The reaction was then allowed to proceed at room temperature for 3 hours. Next, the reaction mixture was slowly added to 1500 g of deionized water, 200 g of dichloromethane was added, and after stirring for 1 hour, the mixture was allowed to stand and the upper aqueous layer was removed. The dichloromethane layer after the removal of the aqueous phase was concentrated and recrystallized with butyl acetate to obtain 23.3 g of bis(3,5-difluoro-2-iodophenyl) sulfoxide.

[0142] [Bis(3,5-difluoro-2-iodophenyl)](4-carboxymethoxy-3,5-dimethylphenyl)sulfonium bis(trifluoromethanesulfonyl)imide was obtained by the same method as in Example 1, except that bis(3,5-difluoro-2-iodophenyl)sulfoxide was replaced with bis(3,5-difluoro-2-iodophenyl)sulfoxide and potassium bis(trifluoromethanesulfonyl)imide was replaced with potassium bis(trifluoromethanesulfonyl)imide.

[0143] Comparative Example 1 Diphenyl-4-carboxymethoxy-3,5-dimethylphenyl)sulfonium trifluoromethanesulfonate was obtained in the same manner as in Example 1, except that diphenyl sulfoxide was used instead of bis(3,5-difluorophenyl) sulfoxide.

[0144] Comparative Example 2 28.1 g of bis(3-trifluoromethylphenyl) sulfoxide was obtained in the same manner as in Example 1, except that 112.5 g (0.50 mol) of 3-bromobenzotrifluoride was used instead of 96.5 g of 1-bromo-3,5-difluorobenzene.

[0145] A sulfonium intermediate was obtained in the same manner as in Example 1, except that bis(3-trifluoromethylphenyl) sulfoxide was used instead of bis(3,5-difluorophenyl) sulfoxide, benzene was used instead of 15.3 g (0.125 mol) of 2,6-dimethylphenol, and potassium nonafluorobutanesulfonate was used instead of potassium trifluoromethanesulfonate. This intermediate was recrystallized in a mixed solvent of ethyl acetate and butyl acetate to obtain [bis(4-trifluoromethylphenyl)]phenylsulfonium nonafluorobutanesulfonate.

[0146] The sulfonium salts obtained in Examples 1-5 and Comparative Examples 1-2, as well as triphenylsulfonium trifluoromethanesulfonate as Comparative Example 3, were evaluated for solvent solubility and photosensitivity using the following method.

[0147] (Solvent solubility evaluation) 0.2 g of each sulfonium salt from the examples and comparative examples was placed in a test tube, and 0.2 to 0.5 g of PGMEA was added at a time under temperature control at 25°C until the sulfonium salt was completely dissolved. The concentration of the completely dissolved sulfonium salt was defined as the solvent solubility. If the sulfonium salt did not completely dissolve even after adding 30 g of PGMEA, it was evaluated as not soluble. The results are shown in the table below.

[0148] (Photosensitivity evaluation) Each sulfonium salt from the examples and comparative examples was mixed with a positive-type photosensitive resin (a copolymer of polyhydroxystyrene and t-butoxyacrylate) in a weight ratio of 20 times, and dissolved in PGMEA to a molar concentration of 2.0 mM of the sulfonium salt to prepare a photoresist. Next, the obtained photoresist was spread onto a substrate treated with hexamethyldisilazane (HMDS) using a spin coater, and the solvent was removed by heating at 130°C for 60 seconds to create a coating film with a thickness of approximately 50 nm. The resulting coating was placed in BL-3 of the NewSUBARU Synchrotron Radiation Facility at the University of Hyogo and irradiated with 13.5 nm synchrotron radiation. Next, the light-irradiated samples were heated at 110°C for 90 seconds, developed with a 2.38% aqueous solution of tetramethylammonium hydroxide for 60 seconds, and rinsed with running water for 30 seconds. The samples were observed under a microscope after development and rinsing to determine the minimum exposure dose (Eth) required for complete removal of the resist film. The ratio of the minimum exposure dose (Eth) to the minimum exposure dose (Eth') when using the photoresist containing the sulfonium salt in Comparative Example 3 was calculated using the following formula and used as an indicator of photosensitivity. A smaller minimum exposure dose ratio indicates better photosensitivity. Minimum exposure ratio = Eth / Eth'

[0149] [Table 1]

[0150] [Table 2]

[0151] Table 1 above shows that the sulfonium salt of the present invention has higher sensitivity to 13.5 nm synchrotron radiation compared to triphenylsulfonium trifluoromethanesulfonate (Comparative Example 3). It also shows good solubility in solvents. Because the sulfonium salt of the present invention possesses the above properties, it is suitable for photoresist applications (especially photoresist applications using ultrashort wavelength light).

[0152] In summary, the configuration of the present invention and its variations are described below. [1] Formula (1) (where Ar 1 Ar 2 These are identical or different aromatic ring structures, or structures in which two or more aromatic rings are linked by a single bond or a linking group, R 1 is a halogen atom or C 1-5 R indicates a halo-alkyl group. 2 C is a halogen atom. 1-5 Alkyl alkyl group, C 1-5 Alkoxy group, C 1-5 Haloalkyl groups, or C 1-5 This indicates a haloalkoxy group. n1 is an integer from 1 to 5, and n2 is an integer from 0 to 4. L indicates a single bond or a linking group, and X - The ∫ represents a monovalent counter anion. ) A sulfonium salt represented by ∫. [2] The above equation (1) is equation (1-1a) (wherein R 11 , R 12 Each is independently a halogen atom or C 1-5 R indicates a halo-alkyl group. 13 C is a halogen atom. 1-5 Alkyl alkyl group, C 1-5 Alkoxy group, C 1-5 Haloalkyl groups, or C 1-5 This represents a haloalkoxy group. n11 and n12 each independently represent integers from 1 to 5, and n13 represents an integer from 0 to 4. L represents a single bond or a linking group, and X -The sulfonium salt described in [1] (where represents a monovalent counter anion). [3] The above equation (1) is equation (1-3) (wherein R 11 , R 12 Each is independently a halogen atom or C 1-5 R indicates a halo-alkyl group. 13 C is a halogen atom. 1-5 Alkyl alkyl group, C 1-5 Alkoxy group, C 1-5 Haloalkyl groups, or C 1-5 This represents a haloalkoxy group. n11 and n12 each independently represent integers from 1 to 5, and n13 represents an integer from 0 to 4. 1 X represents an oxygen atom or a sulfur atom, and n is an integer from 1 to 5. - The sulfonium salt described in [1] (where represents a monovalent counter anion). [4] The aforementioned R 11 , R 12 The sulfonium salt according to [2] or [3], wherein each is independently a fluorine atom, an iodine atom, or a trifluoromethyl group. [5] A sulfonium salt according to any one of [1] to [4], wherein the monovalent counter anion is a sulfonate anion or a sulfonylimide anion. [6] An acid generator containing a sulfonium salt as described in any one of [1] to [5]. [7] The acid generator described in [6], which is an acid generator for extreme ultraviolet light or an acid generator for electron beams. A photoresist comprising the acid generator described in [8] [6] and a photosensitive resin.

Claims

1. A sulfonium salt represented by the following formulas (1-3). 【Chemistry 1】 (In the formula, R 11 and R 12 each independently represent a fluorine atom, an iodine atom, or a trifluoromethyl group. R 13 represents a halogen atom, a C1-5 alkyl group, a C1-5 alkoxy group, a C1-5 haloalkyl group, or a C1-5 haloalkoxy group. n 11 and n 12 each independently represent an integer from 1 to 5, and n 13 represents an integer from 0 to 4. L 1 represents an oxygen atom or a sulfur atom, and n represents an integer from 1 to 5. X- represents a monovalent counteranion.)

2. The sulfonium salt according to claim 1, wherein the monovalent counter anion is a sulfonate anion or a sulfonylimide anion.

3. An acid generator comprising the sulfonium salt described in claim 1.

4. The acid generator according to claim 3, which is an acid generator for extreme ultraviolet light or an acid generator for electron beams.

5. A photoresist comprising the acid generator described in claim 3 and a photosensitive resin.

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