We previously succeeded in fabricating 60-nm line-and-space (L/S) patterns with fluorine-containing silsesquioxane-type (F-SSQ) resist, BARRIERTA® J25V immersion fluid, and NovecTM HFE-7200 rinse liquid using our two-beam interferometer. In the study reported here, we tried to fabricate a finer resist pattern with this immersion fluid, but 40-nm L/S could not be resolved because of the T-top shapes produced under the same conditions. The cause of the T-top shape was photo-acid generator (PAG) leaching into HFE-7200, which in effect caused the resist layer to swell. When FluorinertTM FC-84 with the CF3 functional group, which has the lowest reactivity, was used as a rinse liquid, the resolution of 40- and 32-nm L/S without T-top shape was achieved. Next, to fabricate finer patterns, we considered improving the molecular structure to raise the refractive index. As a result of an examination based on perfluoroalkane, which has high transparency, we found that it is effective to reduce the fluorine atom concentration, transform the molecular structure to a steric structure without reducing molar refractivity, and attach a functional group such as a cyclohexyl or chloro group. Finally, with the high-refractive index immersion fluid, we attempted to fabricate 28-nm L/S. Although we tried pattern fabrication with two immersion fluid candidates, transfer of the interference patterns to the resist has not been confirmed at this time. However, since we checked that the light did reach the resist, we speculate that it will be possible to fabricate 28-nm L/S by making a minor change.