High-refractive-index fluids (HIFs) are being considered to replace water as the immersion fluid in
next generation 193nm immersion scanner. We have demonstrated the attractive optical properties for our HIF
candidates, HIL-001, HIL-203 and HIL-204. Especially, HIL-203 and HIL-204 have higher transmittance
compared to water. In this paper, we describe our latest results on the comparative evaluations including
photo-degradation behavior and lens contamination phenomenon in a flow system. For laser induced fluid
degradation behavior, it was shown the higher initial transmittance resulted in the higher laser durability.
However, the complicated phenomenon was observed for the lens contamination test. That is, HIL-204 with
higher initial transmittance showed higher lens contamination rate than HIL-203. From several analyses, the
complicated behaviors among HILs were speculated to be caused by the different nature of photo-degraded
impurities. In order to control the fluid transmittance change and suppress the lens contamination during
exposure, the refining process was definitely necessary for HIL reuse system. Based on the refining mechanism
and the refining material design, we have developed an appropriate refinement unit named Refine B. This
approach provided us with the result that Refine B could control the change of fluid transmittance and suppress
the lens contamination rate.