Dec. 3, 2020  98  US 2020/0379345 Al  [0217]  a:(b+b’):( c+c’)=l:4-7:0.01-1 (molar ratio)  [0218]  Mw=l,500  [0219]  In a 50-mL vial, 80 parts by weight of each onium  compound (PAG-1, PAG-2, PAG-A, PAG-B) was dissolved  in 960 parts by weight of DAA, after which 2,240 parts by  weight of PGMEA was added. Using a magnetic stirrer, the  mixture was stirred at 23°  C. for 24 hours, obtaining a resist  composition (R-01, R-02, R-20, R-21). The liquid in the vial  was visually observed to evaluate solubility. It was rated  "good" when the compound was fully dissolved in the  solvents and "poor" when the liquid looked white turbid.  The results are shown in Table 4.  [0220]  As seen from Table 4, the onium compounds used  in resist compositions of Examples are fully soluble in  solvents, demonstrating that molecular resist compositions  are constructed using the onium compounds.  [0221]  A silicon substrate having a diameter of 8 inches  was primed with hexamethyldisilazane (HMDS). Using a  coater/developer system Clean Track ACT™ 8 (Tokyo Elec› tron Ltd.), each of the resist compositions (R-03, R-04,  R-05, R-22, R-25) was spin coated onto the substrate at  1,500 rpm, pre-baked on a hotplate at 100° C. for 60  seconds, and cooled at 23°  C. for 30 seconds. A resist film  on the substrate was visually observed. The film formation  was rated "good" when a resist film was confirmed and  "poor" when striae or pinholes were observed. Thereafter,  using an ellipsometer Atlas XP+(Nanometrics Inc.), the  thickness of the resist film on the silicon substrate was  measured at 29 points which were equally spaced apart in X  axis direction, to evaluate a variation of film thickness. The  results are shown in Table 5.  [0213]  poly(2,2,3,3,4,4,4-heptafluoro-l-isobutyl-1-bu› tyl methacrylate/9-(2,2,2-trifluoro-l-trifluoroethyloxy› carbonyl)-4-oxatricyclo[ 4.2. l .0 3 • $^{7}$]nonan-5-on-2-yl  methacry late)  [0214]  Mw=7,700  [0215]  Mw/Mn=l.82  [4] Resist Composition Evaluation #2: Film  Forming Test  Examples 3-1 to 3-3 and Comparative Examples  3-1 to 3-2  [3] Resist Composition Evaluation #1: Casting  Solution Dissolution Test  Examples 2-1 to 2-2 and Comparative Examples  2-1 to 2-2  Q-2  0  -continued  F3CI  ~of  ~ot- -+HJ  TABLE 4  Resist  Onium  composition  compound  Solubility  Example  2-1  R-01  PAG-1  good  2-2  R-02  PAG-2  good  Comparative Example  2-1  R-20  PAG-A  poor  2-2  R-21  PAG-B  poor  SF-1  [0216]  3-methyl-3-(2,2,2-trifluoroethoxymethyl)oxet- ane/tetrahydrofuran/2,2-dimethyl-1,3-propane  dial  copolymer (Onmova Solutions, Inc.)  Alkali-Soluble Surfactant SF-1:  Surfactant A:  -continued 