Jul.  30,  2020  97  US 2020/0241417 Al  Synthesis Example  Synthesis of Base Polymers (Polymers 1 to 4)  [0163]  Base polymers were prepared by combining suit› able monomers, effecting copolymerization reaction thereof  in tetrahydrofuran (THF) solvent, pouring the reaction solu› tion into methanol for crystallization, repeatedly washing  with hexane, isolation, and drying. The resulting polymers,  designated Polymers 1 to 4, were analyzed for composition  by $^{1}$H-NMR spectroscopy, and for Mw and Mw/Mn by GPC  versus polystyrene standards using THF solvent.  [0164]  Resist compositions were prepared by dissolving  various components in a solvent in accordance with the  recipe shown in Tables 1 to 3, and filtering through a filter  having a pore size of0.2 µm.  The solvent contained 100 ppm  of surfactant Polyfox PF-636 (Onmova Solutions Inc.). The  resist compositions of Examples 1 to 24, 26 to 30, and  Comparative Examples 1 to 6 were of positive tone, while  Examples 1 to 30 and Comparative Examples 1 to  7  r,  a  a  I  OH  r,  0  0  F2  0  C  Y’s03- 0  CF3  Polymer  1  Mw~ 8,600  Mw/Mn~ 1.73  Polymer 3  Mw~7,600  Mw/Mn~ 1.73  Polymer 4  Mw~ 6,900  Mw/Mn~ 1.62  Polymer 2  Mw~ 8,900  Mw/Mn~ 1.89 