96  95  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 roughness (LWR) is improved since the acid  generator is uniformly distributed. Where a base polymer  containing recurring units of at least one type selected from  recurring units (fl) to (f3) is used  the addition ofa 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)  (fl)  (f2) and (f3) as optional  components. A fraction of units (al)  (a2)  (b)  (c)  (d)  (e)   (fl)  (f2) and (f3) is: preferably 0sal <1.0  0sa2<1.0  0<al +  a2<1.0  0sbs0.9  0scs0.9  0sds0.8  0ses0.8  0sfls0.5   0sf2s0.5  and 0sf3s0.5; more preferably  0sals0.9   0sa2s0.9  0.lsal+a2s0.9  0sbs0.8  0scs0.8  0sds0.7   0ses0.7  0sfls0.4  0sf2s0.4  and 0sf3s0.4; and even more  preferably 0sals0.8  0sa2s0.8  0.lsal+a2s0.8  0sbs0.75   0scs0.75  0sds0.6  0ses0.6  0sfls0.3  0sf2s0.3  and  0sf3s0.3. Note al+a2+b+c+d+e+fl+f2+f3=1.0.  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 )  (fl)  (f2) and/or (f3).  A fraction of these units is: 0<bsl.0  0scs0.9  0sds0.8   0ses0.8  0sfls0.5  0sf2s0.5  and 0sf3s0.5; preferably  0.2sbsl.0  0scs0.8  0sds0.7  0ses0.7  0sfls0.4  0sf2s0.4   and 0sf3s0.4; and more preferably 0.3sbsl.0  0scs0.75   0sds0.6  0ses0.6  0sfls0.3  0sf2s0.3  and 0sf3s0.3. Note  b+c+d+e+fl +f2+f3=1.0.  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 polym› erization initiator used herein include 2 2’-azobisisobuty› ronitrile  (AIBN)   2 2’-azobis(2 4-dimethylvaleronitrile  )   dimethyl 2 2-azobis(2-methylpropionate )  benzoyl perox› ide  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 as mentioned above  for thereby con- verting  the  polymer  product  to  hydroxystyrene  or  hydroxyvinylnaphthalene. For alkaline hydrolysis  a base  such as aqueous ammonia or triethy !amine may be used. The  Q_  Q  - -continued  -continued 