Jan. 10, 2019  51  US 2019/0010119 Al  added to 120 g of diisopropyl ether dropwise, followed by  stirring at 0°  C. for 30 minutes to precipitate solids. The  precipitated solids were filtered off, followed by drying in  vacuum to give 2.9 g of the intended photo-acid generator  (PAG-7) as solids (yield: 55%).  [0233]  The results of the nuclear magnetic resonance  spectrum (1H-NMR/DMSO-d$_{6}$ )  is shown in FIG.  9.  (PAG-1)  (PAG-7)  <PAG-7>  [0232]  A mixed solution of 3.1 g of the sulfonium salt  (PAG-1), 3.2 g of the sulfonate salt (1-5), 20 g of methyl  isobutyl ketone, and 15 g of pure water was stirred for 30  minutes, and the organic layer was separated. The obtained  organic layer was washed with 30 g of pure water for once,  30 g of 5 mass % aqueous sulfonate salt (1-5) solution for  twice, and 30 g of pure water for four times, and was  subjected to concentration in vacuum to remove the solvent.  This was dissolved in 8 g of added methylene chloride, and  (1-5)  [Synthesis Example 1-7] Synthesis of PAG-7  [0231] 