16  US 9,152,050 B2  15  group. Where the hydroxyl group is replaced by an acetyl  group, the polymerization may be followed by alkaline  hydrolysis to deprotect the acetyl group into a hydroxyl  group. Where the hydroxyl group is replaced by an acid labile  group such as acetal, deprotection via hydrolysis with an acid  catalyst may be carried out to restore a hydroxyl group.  In addition to the recurring units  (p ), (  q 1) and ( q2) in  formula (2), the polymer to be added to the resist composition  may have further copolymerized therein recurring units (r)  having a carboxyl group for the purposes of improving alkali  solubility and rendering the resist film after development  more hydrophilic.  Examples of the recurring units (r) having a carboxyl group  are given below.  In the case of a monomer having a hydroxyl group, the  hydroxyl group may be replaced by an acetyl, acetal or simi- lar group at the monomer stage, and the polymerization be  followed by deprotection reaction to restore the hydroxyl  -continued  OH  HO  HO  /0  ’---o  0  /0  co  I  0  ~  I  ~  ~  #  I  0  0  I  /0  ’---o  HOt:’  OT  OH  HrH:tHX’  ~  ~  O’yOH  O\OH  0  0  r  ~OH  qo  ~o  HO  0  OH  OH  r  r  ~H 