Feb.28,2019  13  US 2019/0064665 Al  [0103]  Under the action of acid, a polymer comprising  recurring units of formula (a) is decomposed to generate  carboxylic acid, turning to be alkali soluble.  [0104]  The acid labile group  XA  may be selected from a  variety of such groups. Examples of the acid labile group  include groups of the following 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.  [0105]  In formula (Ll), RLoi and  RL $^{02 }$each are hydrogen  or a straight, branched or cyclic alky 1 group of 1 to 18 carbon  atoms, preferably 1 to 10 carbon atoms. Exemplary alkyl  groups include methyl, ethyl, propyl, isopropyl, n-butyl,  s-butyl, t-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, n-oc› tyl, norbomyl, tricyclodecanyl, tetracyclododecanyl, and  adamantyl.  [0106]  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 substituted forms of such alkyl groups in which  some hydrogen atoms are replaced by hydroxyl, alkoxy, oxo,  amino, alkylamino or the like, or in which at least one  carbon atom is replaced by a heteroatom such as oxygen.  -continued  H  RA  H  H  H  (Ll)  RLOI  I  L03  ----C-OR  I  RL02  (L2)  0  II  ----(CH2)x-C-OR 104  (L3)  (L4)  (++)  i  ’j=o  0  q_o  o  I  0  0  XA 