US 9,665,002 B2  22  21  -continued  c  +-/-a)  (  H  ’j==o  H  ’j==o  0  0  H  6  ~o  o  I  XA  0  0  I  XA  Ria  ,ry  H  0  0  H  0  ~o  0  I  XA  Ria  0  ~o  o  I  XA  0  0  I  XA  0  H  0  H  Ria  0  I  XA  Ria  0  __ ,-~OH __ , -~O~  /~OH  -’,,  ~O~OH  ----yo\..--::,o  ----~OH  L;- (Ll)  (L2)  (L3)  (L4)  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, cyolohexyl, 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, cyclo› pentyl, cyclohexyl, 2-ethylhexyl, n-octyl, norbornyl, tricy› clodecanyl, tetracyclododecanyl, and adamantyl. Illustrative  examples of the substituted alkyl groups are shown below.  A pair ofRLoi and  RL 02 ,  RLoi and  RL 03 ,  or  RL $^{02 }$and  RL 03  may bond together to form a ring with the carbon and  oxygen atom to which they are attached. Each ofRL0 1 ,  RL 02  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 formu› lae (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. 