38  US 9,703,193 B2  37  -continued  (L2)  (L3)  (L4)  In formula (Ll), RLoi and  RL 02  each are hydrogen or a  straight, branched or cyclic alkyl 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.  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 a  heteroatom such as oxygen intervenes between carbon  atoms. Suitable alkyl groups are as exemplified above for  RL01 and  RL02_  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 atoms to which they are attached. Ring-forming  participants of RLoi,  RL $^{02 }$and  RL $^{03 }$represent a straight or  branched alkylene group of  1  to 18 carbon atoms, preferably  1  to  10  carbon atoms.  In formula (L2),  RL $^{04 }$is a tertiary alkyl group of  4  to  carbon atoms, preferably  4  to 15 carbon atoms, a trialkylsilyl  group in which each alkyl moiety has  1  to 6 carbon atoms,  an oxoalkyl group of  4  to 20 carbon atoms, or a group of  formula (Ll). Exemplary tertiary alkyl groups are t-butyl,  t-pentyl, 1,1-diethylpropyl, 2-cyclopentylpropan-2-yl, 2-cy› clohexylpropan-2-yl, 2-(bicyclo[2.2.1 ]heptan-2-yl)propan- 2-yl,  2-(adamantan-l-yl)propan-2-yl,  1-ethylcyolopentyl,  1-butylcyclopentyl, 1-ethylcyclohexyl, 1-butylcyclohexyl,  1-ethy 1-2-cyclopenteny  1,  1-ethy 1-2-cyclohexenyl, 2-methyl- 2-adamanty  l,  and 2-ethyl-2-adamantyl. Exemplary trialkyl- 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 formulae (Ll) to (L4), 55  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.  Under the action of acid, a polymer comprising recurring 50  units of formula (2) is decomposed to generate carboxylic  acid, turning to be an alkali soluble polymer.  (Ll)  0  0  H  -continued 