29  US 9,221,742 B2  30  The polymer comprising recurring units having formula 65  (2) functions such that it may be decomposed to generate  carboxylic acid under the action of an acid and turn alkali  soluble. The acid labile group represented by XA may be  selected from a variety of such groups. Examples of the acid  labile group include groups of the following general formulae  (Ll) to (L4), tertiary alkyl groups of 4 to 20 carbon atoms,  preferably 4 to 15 carbon atoms, trialkylsilyl groups in which  each alkyl moiety has 1 to 6 carbon atoms, and oxoalkyl  groups of 4 to 20 carbon atoms.  It is noted that the broken line denotes a valence bond.  In formula (Ll), RLoi and  RL $^{02 }$are hydrogen or straight,  branched or cyclic alkyl groups of 1 to 18 carbon atoms,  preferably 1 to 10 carbon atoms. Exemplary alkyl groups  include methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,  tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, n-octyl,  norbornyl, tricyclodecanyl, tetracyclododecanyl, and ada› mantyl.  RL $^{03 }$is a monovalent hydrocarbon group of 1 to 18  carbon atoms, preferably 1 to 10 carbon atoms, which may  contain a heteroatom such as oxygen, examples of which  include unsubstituted straight, branched or cyclic alkyl  groups and straight, branched or cyclic alkyl groups in which  some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo,  amino, alkylamino or the like, or in which an oxygen atom  intervenes between carbon atoms. Exemplary straight,  branched or cyclic alkyl groups include methyl, ethyl, propyl,  isopropyl, n-butyl, sec-butyl, tert-butyl, cyclopentyl, cyclo› hexyl, 2-ethylhexyl, n-octyl, norbornyl, tricyclodecanyl, tet› racyclododecanyl, and adamantyl. Illustrative examples of  the substituted alkyl groups are shown below.  (Ll)  RL0I  I  L03  ----C-OR  I  RL02  (L2)  0  II  -----(CH2)y-C-ORLo 4  (L3)  RL05  - - - -\}CH2)n•  CH=(CH2)m•  (L4)  RLl3  RLl4  ........_c,,.,,  I\  RL15  /  RL09  RLII  _..C ______ /  ........_C_.....- C  1,-----c...._  ~RL07  ’CI  I  C I  I  RLl2 RLl6  RLIO  RL06  RLOS  __ ,-~OH __ , -~O~  /~OH  , _,, ~OH  ,  ,--~yo  if  ’;==o  0  0  0  I  XA  (++)  if  ’;==o  0  ~o  0  0  I  XA  H  RI  0  H  R 1  H  RI  ’7i)’  o~o  0  0  I  I  XA  -continued 