US 2018/0335696 Al  44  Nov. 22, 2018  0sbls0.8, 0sb2s0.8, 0.lsbl+b2<0.8, 0scs0.7, 0sds0.7,  0ses0.6, 0sfs0.6, and 0sgs0.2. Notably, al+a2+bl+b2+c+  d+e+f+g=l .0.  [0063]  For the base polymer for formulating the negative  resist composition, an acid labile group is not necessarily  essential. The base polymer comprises recurring units (al)  and/or (a2) as essential component, and additional recurring  units (c), (d), (e),  (f)  and (g) as optional components. A  fraction of these units is: preferably 0sal <1.0, 0sa2<1.0,  0<al+a2<1.0, 0sc<l.0, 00sds0.9, 0ses0.8, 0sfs0.8, and  0sgs0.4; more preferably 0sals0.7, 0sa2s0.7, 0.02sal+  a2s0.7, 0.2sc<l.0, 0sds0.8, 0ses0.7, 0sfs0.7, and 0<gs0.  3; and even more preferably 0sals0.5, 0sa2s0.5, 0.03sal+  a2s0.5, 0.3sc<l .0, 0sds0.75, 0ses0.6, 0sfs0.6, and 0sgs0.  2. Notably, al+a2+c+d+e+f+g=l.0.  [0064]  The polymer-bound acid generator may be synthe› sized by any desired methods, for example, by dissolving  suitable monomers selected from the monomers correspond› ing to the foregoing recurring units in an organic solvent,  adding a radical polymerization initiator thereto, and heating  to conduct polymerization. Examples of the organic solvent  which can be used for polymerization include toluene,  benzene, tetrahydrofuran (THF), diethyl ether, and dioxane.  Examples of the polymerization initiator used herein include  2,2’-azobisisobutyronitrile (AIBN), 2,2’-azobis(2,4-dimeth› ylvaleronitrile ), dimethyl 2,2-azobis(2-methylpropionate ),  benzoyl peroxide, and lauroyl peroxide. Preferably the sys› tem is heated at 50 to 80°  C. for polymerization to take  place. The reaction time is 2 to 100 hours, preferably 5 to 20  hours.  [0065]  When hydroxystyrene or hydroxyvinylnaphthalene  is copolymerized, an alternative method is possible. Spe› cifically, acetoxystyrene or acetoxyvinylnaphthalene is used  instead of hydroxystyrene or hydroxyvinylnaphthalene, and  after polymerization, the acetoxy group is deprotected by  alkaline hydrolysis, for thereby converting the relevant units  to hydroxystyrene or hydroxyvinylnaphthalene units. For  alkaline hydrolysis, a base such as aqueous ammonia or  triethylamine may be used. Preferably the reaction tempera› ture is -20°  C. to 100°  C., more preferably 0°  C. to 60°  C.,  and the reaction time is 0.2 to 100 hours, more preferably 0.5  to 20 hours.  [0066]  The polymer-bound acid generator should prefer› ably have a weight average molecular weight (Mw) in the  range of 1,000 to 500,000, and more preferably 2,000 to  30,000, as measured by GPC versus polystyrene standards  using THF solvent. A Mw in the range ensures that the resist  composition is heat resistant.  [0067]  If a base polymer has a wide molecular weight  distribution or dispersity (Mw/Mn), which indicates the  presence of lower and higher molecular weight polymer  fractions, there is a possibility that foreign matter is left on  the pattern or the pattern profile is degraded. The influences  of molecular weight and dispersity become stronger as the  pattern rule becomes finer. Therefore, the polymer-bound  acid generator should preferably have a narrow dispersity  (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to  provide a resist composition suitable for micropatterning to  a small feature size.  [0068]  It is understood that a blend of two or more  polymer-bound acid generators which differ in composi› tional ratio. Mw or Mw/Mn is acceptable.  [0074]  The cation moiety in the sulfonium salt having  formula (1-1) is as exemplified above for the cation moiety  in recurring unit (al). The cation moiety in the iodonium salt  having formula (1-2) is as exemplified above for the cation  moiety in recurring unit (a2).  [0073]  In formulae (1-1) and (1-2), R 101 , R 102 , R 103 , R 104  and R $^{105 }$are each independently a C$_{5}$ -C$_{20 }$straight, branched  or cyclic monovalent hydrocarbon group which may contain  a heteroatom, any two of R 101 , R 102  and R 103  may bond  together to form a ring with the sulfur atom to which they are  attached.  [0072]  Also, a sulfonium salt having the formula (1-1) and  a iodonium salt having the formula (1-2) are advantageously  used as the other acid generator.  [0071]  The resist composition may contain an acid gen› erator other than the polymer-bound acid generator as long  as the benefits of the invention are not compromised. The  other acid generator is typically a compound (PAG) capable  of generating an acid upon exposure to actinic ray or  radiation. Although the PAG used herein may be any com› pound capable of generating an acid upon exposure to  high-energy radiation, those compounds capable of gener› ating sulfonic acid, imide acid (imidic acid) or methide acid  are preferred. Suitable PAGs include sulfonium salts, iodo› nium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and  oxime-O-sulfonate acid generators. Exemplary acid genera› tors are described in U.S. Pat. No. 7,537,880 (JP-A 2008- 111103, paragraphs [0122]-[0142]).  [0070]  With the polymer-bound acid generator defined  above, other components such as another acid generator, an  organic solvent, surfactant, dissolution inhibitor, crosslinker,  and quencher may be blended in any desired combination to  formulate a chemically amplified positive or negative resist  composition. This positive or negative resist composition  has a very high sensitivity in that the dissolution rate in  developer of the base polymer in exposed areas is acceler› ated by catalytic reaction. In addition, the resist film has a  high dissolution contrast, resolution, exposure latitude, and  process adaptability, and provides a good pattern profile  after exposure, and minimal proximity bias because of  restrained acid diffusion. By virtue of these advantages, the  composition is fully useful in commercial application and  suited as a pattern-forming material for the fabrication of  VLSis. Particularly when a chemically amplified positive  resist composition capable of utilizing acid catalyzed reac› tion is formulated, the composition has a higher sensitivity  and is further improved in the properties described above.  [0069]  Other Components  (1-1)  (1-2)  R104  I  1+  x- i  RIOS 