6  US 7,541,131 B2  5  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 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.  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.  [1]  (A) Sulfonium Compound Represented by Formula (I)  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.  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.  Examples of the non-nucleophilic carboxylate anion  include an alkylcarboxylate anion, an arylcarboxylate anion  and an aralkylcarboxylate anion.  Examples of the sulfonate anion include an alkylsulfonate  anion, an arylsulfonate anion and a camphorsulfonate 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.  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.  m represents the number of anions necessary for neutral› izing the electric charge.  wherein  R$^{2 }$to R$^{9 }$each independently represents a hydrogen atom or  a substituent and may combine with each other to form a ring,  R$^{1 }$represents an alkyl group or an aryl group,  Z represents an electron-withdrawing divalent linking  group,  xn- represents an n-valent anion,  n represents an integer of  1  to 3, and  (I)