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The attachment of an acid generator to the polymer main chain is effective in restraining acid diffusion, thereby pre› venting a reduction of resolution due to blur by acid diffu› sion. Also edge roughness is improved since the acid gen› erator is uniformly distributed. Where a base polymer containing recurring units (f) is used, the addition of a separate PAG may be omitted. 

The base polymer for formulating the positive resist composition comprises recurring units (al) or ( a2) having an acid labile group as essential component and additional recurring units (b), (c), (d), (e), and (f) as optional compo- nents. A fraction of units (al), (a2), (b), (c), (d), (e), and (f) is: preferably 0sal<l.0, 0sa2<1.0, 0<al+a2<1.0, 0sbs0.9, to 0scs0.9, 0sds0.8, 0ses0.8, and0sfs0.5; more preferably 0sal s0.9, 0sa2s0.9, 0.1 <al +a2s0.9, 0sbs0.8, 0scs0.8, 0sds0.7, 0ses0.7, and 0sfs0.4; and even more preferably 0sals0.8, 0sa2s0.8, 0.lsal+a2s0.8, 0sbs0.75, 0scs0.75, 0sds0.6, 0ses0.6, and 0sfs0.3. Notably, unit (f) is at least one of units (fl), (f2) and (f3), i.e., f=fl+f2+f3, and al+a2+ b+c+d+e+f=l .0. 

For the base polymer for formulating the negative resist composition, an acid labile group is not necessarily essen› tial. The base polymer comprises recurring units (b ), and optionally recurring units (c), (d), (e), and/or (f). A fraction of these units is: preferably 0<bsl.0, 0scs0.9, 0sds0.8, 0ses0.8, and 0sfs0.5; more preferably 0.2sbsl .0, 0scs0.8, 0sds0.7, 0ses0.7, and 0sfs0.4; and even more preferably 0.3sbsl.0, 0scs0.75, 0sds0.6, 0ses0.6, and 0sfs0.3. Nota› bly, unit (f) is at least one of units (fl), (f2) and (f3), i.e., f=fl+f2+f3, and b+c+d+e+f=l.0. 

The base polymer may be synthesized by any desired methods, for example, by dissolving one or more monomers selected from the monomers corresponding to the foregoing recurring units in an organic solvent, adding a radical polymerization initiator thereto, and effecting heat polym- erization. Examples of the organic solvent which can be used for polymerization include toluene, benzene, tetrahy› drofuran, diethyl ether, and dioxane. Examples of the polymerization initiator used herein include 2,2’-azobi› sisobutyronitrile (AIBN), 2,2’-azobis(2,4-dimethylvaleroni- trile ), dimethyl 2,2-azobis(2-methylpropionate ), benzoyl peroxide, and lauroyl peroxide. Preferably the system 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. 

When hydroxystyrene or hydroxyvinylnaphthalene is copolymerized, an alternative method is possible. Specifi› cally, 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 polymer product to hydroxystyrene or hydroxyvinylnaphthalene. For alkaline hydrolysis, a base such as aqueous ammonia or triethylamine may be used. Preferably the reaction tempera- 

