Apr. 18,  2019  4  US 2019/0113844 Al  as the quencher. Examples of the sulfonium or iodonium salt  to be added as the quencher include sulfonium or iodonium  salts of carboxylic acid, sulfonic acid, imide acid and  saccharin. The carboxylic acid used herein may or may not  be fluorinated at a-position.  [0047]  For the LWR improving purpose, it is effective to  prevent a polymer and/or acid generator from agglomera› tion. Effective means for preventing agglomeration of a  polymer is by reducing the difference between hydrophobic  and hydrophilic properties or by lowering the glass transi› tion temperature (Tg) thereof. Specifically, it is effective to  reduce the polarity difference between a hydrophobic acid  labile group and a hydrophilic adhesive group or to lower the  Tg by using a compact adhesive group like monocyclic  lactone. One effective means for preventing agglomeration  of an acid generator is by introducing a substituent into the  triphenylsulfonium cation. In particular, with respect to a  methacrylate polymer containing an alicyclic protective  group and a lactone adhesive group for ArF lithography, a  triphenylsulfonium composed solely of aromatic groups has  a heterogeneous structure and low compatibility. As the  substituent to be introduced into triphenylsulfonium, an  alicyclic group or lactone similar to those used in the base  polymer is regarded adequate. When lactone is introduced in  a sulfonium salt which is hydrophilic, the resulting sulfo› nium salt becomes too hydrophilic and thus less compatible  with a polymer, with a likelihood that the sulfonium salt will  agglomerate. When a hydrophobic alkyl group is introduced,  the sulfonium salt may be uniformly dispersed within the  resist film. WO 2011/048919 discloses the technique for  improving LWR by introducing an alkyl group into a sul› fonium salt capable of generating an a-fluorinated sulfone  imide acid.  [0048]  The dispersion of a quencher is a crucial factor for  LWR improvement. Even when the dispersion of an acid  generator in a resist film is improved, LWR is still low if a  quencher is unevenly distributed. For a quencher of sulfo› nium salt type, the introduction of an alkyl or similar  substituent into the triphenylsulfonium cation moiety is  effective for LWR improvement.  [0049]  The sulfonium salt of thiophenecarboxylic acid  exerts a LWR reducing effect, which may stand good either  in positive and negative tone pattern formation by alkaline  development or in negative tone pattern formation by  organic solvent development.  [0050]  Sulfonium Salt  [0051]  The sulfonium salt in the resist composition is a  thiophenecarboxylic acid sulfonium salt having the formula  (A).  [0052]  Herein R1, R 2  and R 3  are each independently  hydrogen, hydroxyl,  C$_{1 }$-C$_{6 }$ alkyl,  C$_{1 }$-C$_{6 }$ alkoxy,  C$_{2}$-C$_{6 }$ acyl,  C$_{2}$-C$_{6 }$ alkoxycarbonyl,  CcC$_{10 }$ aryl,  C$_{2}$-C$_{10 }$ heteroaryl, halo› gen, nitro, amino, or cyano group. In these groups, at least  [0056]  Examples of the anion in the sulfonium salt having  formula (A) are given below, but not limited thereto.  [0055]  R 4 , Rs and R $^{6 }$are each independently halogen or a  C$_{1 }$-C$_{20 }$monovalent hydrocarbon group which may contain a  heteroatom. Any two ofR 4 , Rs and R $^{6 }$may bond together to  form a ring with the sulfur atom to which they are attached.  The monovalent hydrocarbon group may be straight,  branched or cyclic and examples thereof include C$_{1 }$-C$_{12 }$ alkyl groups,  C$_{2}$-C$_{12 }$ alkenyl groups,  C$_{2}$-C$_{12 }$ alkynyl groups,  CcC$_{20 }$ aryl groups, and C$_{7}$-C$_{12 }$ aralkyl groups. Also  included are substituted forms of the foregoing in which at  least one ( one or more or even all) hydrogen is substituted  by hydroxyl, carboxyl, halogen, cyano, amide, nitro, mer› capto, sultone, sulfone moiety or sulfonium salt-containing  moiety, or in which at least one carbon is substituted by an  ether bond, ester bond, carbonyl moiety, carbonate moiety or  sulfonic acid ester bond.  [0054]  X is a single bond or a C$_{1 }$-C$_{10 }$ divalent aliphatic  hydrocarbon group in which at least one ( one or more or  even all) hydrogen may be substituted by halogen, or at least  one carbon may be substituted by an ether bond, ester bond  or carbonyl moiety. The divalent aliphatic hydrocarbon  groups are preferably straight or branched and examples  thereof include  C$_{1 }$-C$_{6 }$ alkylene groups and  C$_{2}$-C$_{6 }$ alkenylene  groups. Preferably X is selected from a single bond, C$_{1 }$-C$_{4 }$ alkylene groups, and C$_{2}$-C$_{4 }$ alkenylene groups.  [0053]  Suitable halogens include fluorine, chlorine, bro› mine and iodine. Examples of the alkyl group which may be  straight, branched or cyclic include methyl, ethyl, n-propyl,  isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert› butyl, cyclobutyl, n-pentyl, cyclopentyl, n-hexyl and cyclo› hexyl. Examples of the alkyl moiety in the alkoxy, acyl and  alkoxycarbonyl groups are as exemplified just above for the  alkyl group. Examples of the aryl group include phenyl,  naphthyl, anthryl, and phenanthryl. Examples of the het› eroaryl group include thienyl, imidazolyl, oxazolinyl, fury!,  pyrolyl, 2-pyridyl and quinolyl. Preferably, R 1 , R 2  and R 3  are selected from hydrogen, hydroxyl, halogen, C$_{1 }$-C$_{6 }$ alkyl,  phenyl and thienyl.  one (one or more or even all) hydrogen may be substituted  by C$_{1 }$-C$_{6 }$ alkyl, hydroxyl, halogen, nitro or amino moiety, or  at least one carbon may be substituted by an ether bond or  thioether bond. R 1  and R 2  may bond together to form an  alicyclic or aromatic ring with the carbon atom to which they  are attached, at least one ( one or more or even all) hydrogen  on the ring may be substituted by C$_{1 }$-C$_{6 }$ alkyl, hydroxyl,  halogen, nitro or amino moiety.  (A) 