US 10,698,314 B2  105  106  -continued  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.  The base polymer comprising recurring units  (f)  also  functions as the acid generator. Since this base polymer is  integrated with the acid generator, an acid generator of  addition type may or may not be added to the chemically  amplified resist composition.  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,  0scs0.9, 0sds0.8, 0ses0.8, and 0sfs0.5; more preferably  0sals0.9, 0sa2s0.9, 0.lsal+a2s0.9, 0sbs0.8, 0scs0.8,  0sds0.7, 0scs0.7, 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. In the embodiment wherein  the base polymer also functions as an acid generator, the  fraction of recurring units  (f)  is preferably 0<fs0.5, more  preferably  0.Olsfs0.4,  and  even  more  preferably  0.02sfs0.3. Notably, f=fl+f2+f3, meaning that unit  (f)  is at  least one of units (fl) to (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. In the  embodiment wherein the base polymer also functions as an  acid generator, the fraction of recurring units  (f)  is preferably  0<fs0.5, more preferably 0.0lsfs0.4, and even more pref› erably 0.02sfs0.3. Notably, f=fl+f2+f3, meaning that unit  (f)  is at least one of units (fl) to (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-