Apr. 18,  2019  43  US 2019/0113844 Al  [0086]  The attachment of an acid generator to the polymer  main chain is effective in restraining acid diffusion, thereby  preventing a reduction of resolution due to blur by acid  diffusion. Also edge roughness is improved since the acid  generator is uniformly distributed. Where a base polymer  containing recurring units  (f)  is used, the addition of a  separate PAG (to be described later) may be omitted.  [0087]  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  components. A fraction of units (al), (a2), (b), (c), (d), (e),  and  (f)  is: preferably 0sal <1.0, 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, 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, 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.  [0088]  For the base polymer for formulating the negative  resist composition, an acid labile group is not necessarily  essential. 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  -continued 