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The negative resist composition of the present invention comprises (A) a sulfonium salt represented by formula (I), (D) a resin soluble in an alkali developer, and (E) an acid crosslinking agent capable of crosslinking with the resin soluble in an alkali developer under the action of an acid. 

[1] (A) Sulfonium Compound Represented by Formula (I) 

The resist composition of the present invention comprises a sulfonium compound represented by formula (I) (hereinaf› ter, sometimes simply referred to as a "sulfonium salt (A)) as a compound capable of generating an acid upon irradiation of actinic rays or radiation. 

wherein 

R$^{1 }$represents an alkyl group or an aryl group, 

R$^{2 }$to R$^{9 }$each independently represents a hydrogen atom or a substituent and may combine with each other to form a ring, 

Z represents an electron-withdrawing divalent linking group, 

xn- represents an n-valent anion, 

n represents an integer of 1 to 3, and 

m represents the number of anions necessary for neutral› izing the electric charge. 

The sulfonium compound (A) represented by formula (I) has an anion xn-. The anion is preferably an organic anion. The organic anion indicates an anion containing at least one carbon atom. The organic anion xn- is preferably a non› nucleophilic anion. 

The non-nucleophilic anion is an anion having a low ability of causing a nucleophilic reaction, and this anion can sup› press the decomposition in aging due to intramolecular nucleophilic reaction. Examples of the non-nucleophilic anion include a sulfonate anion, a carboxylate anion, a sulfo› nylimide anion, a bis(alkylsulfonyl)imide anion and a tris (alkylsulfonyl)methyl anion. 

Examples of the sulfonate anion include an alkylsulfonate anion, an arylsulfonate anion and a camphorsulfonate anion. 

Examples of the non-nucleophilic carboxylate anion include an alkylcarboxylate anion, an arylcarboxylate anion and an aralkylcarboxylate anion. 

The alkyl moiety in the alkylsulfonate anion may be an alkyl group or a cycloalkyl group and is preferably an alkyl group having a carbon number of 1 to 30 or a cycloalkyl group having a carbon number of 3 to 30, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec› butyl group, a pentyl group, aneopentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tet› radecyl group, a pentadecyl group, a hexadecyl group, a hep› tadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, anadamantyl group, a norbomyl group and a barony! group. 

<img src='content_image/912358.jpg'>

The aryl group in the arylsulfonate anion is preferably an aryl group having a carbon number of 6 to 14, and examples thereof include a phenyl group, a tolyl group and a naphthyl group. 

The alkyl group, cycloalkyl group and aryl group in the alkylsulfonate anion and arylsulfonate anion each may fur› ther have a substituent, and examples of the substituent which those groups may further have include a nitro group, a halo› gen atom ( e.g., fluorine, chlorine, bromine, iodine), a car- boxy! group, a hydroxyl group, an amino group, a cyano group, an alkoxy group (preferably having a carbon number of 1 to 5), a cycloalkyl group (preferably having a carbon number of3 to 15), an aryl group (preferably having a carbon number of 6 to 14), an alkoxycarbonyl group (preferably having a carbon number of 2 to 7), an acyl group (preferably having a carbon number of 2 to 12), and an alkoxycarbony› loxy group (preferably having a carbon number of 2 to 7). As for the aryl group or ring structure in each group, examples of the substituent further include an alkyl group (preferably having a carbon number of 1 to 15). 

Examples of the alkyl moiety in the alkylcarboxylate anion include the same alkyl group and cycloalkyl group as those described above for the alkylsulfonate anion. 

Examples of the aryl group in the arylcarboxylate anion include the same aryl group as those described above for the arylsulfonate anion. 

The aralkyl group in the aralkylcarboxylate anion is pref› erably an aralkyl group having a carbon number of 6 to 12, and examples thereof include a benzyl group, a phenethyl group, a naphthylethyl group and a naphthylmethyl group. 

The alkyl group, cycloalkyl group, aryl group and aralkyl group in the alkylcarboxylate anion, arylcarboxylate anion and aralkylcarboxylate anion each may further have a sub- stituent, and examples of the substituent which those groups may further have include the same halogen atom, alkyl group, cycloalkyl group, alkoxy group and alkylthio group as those described above for the arylsulfonate anion. 

Examples of the sulfonylimide anion include a saccharine amon. 

The alkyl group in the bis(alkylsulfonyl)imide anion and tris(alkylsulfonyl)methyl anion is preferably an alkyl group having a carbon number of 1 to 5, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec› butyl group, a pentyl group and a neopentyl group. This alkyl group may further have a substituent, and examples of the substituent which the alkyl group may further have include a halogen atom, an alkoxy group substituted by a halogen atom, an alkoxy group and an alkylthio group, with an alkyl group substituted by fluorine atom being preferred. 

Other examples of the non-nucleophilic anion include a phosphorus fluoride anion, a boron fluoride anion and an antimony fluoride anion. 

The non-nucleophilic anion is preferably a sulfonate anion. Specific preferred examples of the sulfonate anion include trifluoromethanesulfonate anion, pentafluoroethanesulfonate anion, heptafluoropropanesulfonate anion, perfluorobutane› sulfonate anion, perfluorohexanesulfonate anion, perfluo› rooctanesulfonate anion, pentafluorobenzenesulfonate anion, 3,5-bistrifluoromethylbenzenesulfonate anion, 2,4,6-triiso› propylbenzenesulfonate anion, perfluoroethoxyethane› sulfonate anion, 2,3,5,6-tetrafluoro-4-dodecyloxybenzene› sulfonate anion, methanesulfonate anion, p-toluenesulfonate anion, 3,5-bistrifluorobenzenesulfonate anion, pentafluo› robenzenesulfonate anion and 2,4,6-trimethylbenzene› sulfonate anion. 

