Exemplary structures for the onium salt include arbitrary  combinations of anions with cations, both as exemplified  above, but are not limited thereto.  The monomer of formula (1) is characterized by a high  freedom of structural design because the L 3  and A $^{1 }$moieties  of the anion and the cation M+ may be freely designed. An  optimum structural design may be made so as to be com› pliant with variable factors in a particular application includ- 5  65 (la)  Base  - o txt  Cl-ri-N--LI  ?  L $^{2}$-A1  M/  0  Xb  m  (lb)  o txt  Z-L $^{3}$-0-ri-N--L1  ?  L $^{2}$-A1  0  Xb  m  (le)  Base  o txt  Z-L $^{3}$-0-ri-N--L1  ?  L $^{2}$-A1  M+  0  Xb  m  (1)  A solvent may be used for the reaction. Suitable solvents  include hydrocarbons such as toluene, xylene, hexane and  heptane; chlorinated solvents such as methylene chloride,  chloroform, and dichloroethane; ethers such as diethyl ether,  tetrahydrofuran and dibutyl ether; ketones such as acetone  and 2-butanone; esters such as ethyl acetate and butyl  An  appropriate amount of the base used is 0.5 to 10 moles,  more preferably 1.0 to 4.0 moles per mole of amide com› pound (la).  An  appropriate amount of sulfuryl chloride used  is 0.5 to 3.0 moles, more preferably 0.8 to 1.5 moles per  mole of amide compound (la). Outside the range, a less  amount of the base or sulfuryl chloride may be insufficient  to promote reaction whereas an excessive amount may  induce side reactions and increase the reactant cost.  Examples of the base which can be used herein include  amines such as ammonia, triethylamine, pyridine, 4-dimeth› ylaminopyridine, lutidine, collidine, and N,N-dimethylani› line; hydroxides such as sodium hydroxide, potassium  hydroxide, and tetramethylammonium hydroxide; carbon› ates such as potassium carbonate and sodium hydrogencar› bonate; metals such as sodium; metal hydrides such as  sodium hydride; metal alkoxides such as sodium methoxide  and potassium t-butoxide; organometallic compounds such  as butyl lithium and ethylmagnesium bromide; and metal  amides such as lithium diisopropylamide, which may be  used alone or in admixture. Inter alia, pyridine is preferred  from the standpoint of base stability of the intermediate.  First, amide compound (la) is reacted with sulfuryl chlo› ride under basic conditions to synthesize a sulfuryl chloride  derivative (1 b) having imide acid structure. At this point, the  sulfuryl chloride derivative (1 b) may be isolated or passed as  such in one-pot to subsequent reaction without isolation.  Herein Z, L1, L 2 ,  L 3 ,  A1,  xa,  X 6 ,  m, and M+ are as defined  above, Ma+ and Mb+ each are a cation, and x- is an anion,  The inventive monomer may be synthesized according to  the following scheme, for example, although the synthesis  route is not limited thereto.  ing exposure wavelength, other copolymerized units in the  base resin, and a casting solvent in a resist composition.  32  31  US 10,054,853 B2  -continued  0  +O  MeO 