We have developed a number of second-generation high-index candidate immersion fluids that exceed the 1.6 refractive index requirement for immersion lithography at to replace the water used in first-generation immersion systems. To understand the behavior and performance of different fluid classes, we use spectral index measurements, based on the prism minimum deviation method, to characterize the index dispersion. In addition to fluid absorbance and index requirements, the temperature coefficient of the refractive index is a key parameter. We have used a laser-based Hilger–Chance refractometer system to determine the thermo-optic coefficient by measuring the index change versus temperature at two different laser wavelengths, 632.8 and . Also, we determined the batch-to-batch (within a period), before and after irradiation (at ), before and after air exposure, and before and after resist exposure (image printing test) variations of index and . The optical properties of these second-generation immersion fluids mostly compare favorably to water; the ratio of index of refraction at is , the dispersion from d-line is 0.160 versus 0.103 and at 193.4 is vs. , respectively.