Index of refraction of high-index lithographic immersion fluids and its variability

Abstract

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 193 nm to replace the water used in first-generation immersion systems. To understand the behavior and performance of different fluid classes, we use spectral index mea- surements, based on the prism minimum deviation method, to charac- terize 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 dn/dT by measuring the index change versus temperature at two different laser wavelengths, 632.8 and 193.4 nm. Also, we determined the batch-to-batch within a 6-month period, before and after irradiation at 193.4 nm, before and after air exposure, and before and after resist exposure image printing test variations of index and n/. The optical properties of these second-generation immersion fluids mostly compare favorably to water; the ratio of index of refraction at 193.4 nm is 1.644/1.437, the dispersion from d-line n193-d is 0.160 versus 0.103 and dn/dT at 193.4 is 55010 6 /K vs. 9310 6 /K, respectively. © 2009 Society of Photo-Optical