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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. 

[0069] Other Components 

[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. 

[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]). 

[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. 

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[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. 

[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). 

