New measuring technique of complex index of immersion liquids

摘要

A new sensitive in line refractometer has been designed to measure, at 193 nm, the refractive index of liquids used in immersion lithography. The thermalized cell contains a grating used to determine the refractive index value with extreme precision, the variation of refractive index and absorption coefficient on a flowing or static HIF and this system is designed to be integrated on the fluidic of scanners in order to monitor the RI in real time without any moving part nor contamination. The first experiment with D.I. Water shows for the complex refractive index n-ik, a sensitivity better than 2xE-5 for N and 0,01cm~(-1) for absorption. The refractive index can range from 1 (vacuum) to 2, continuously and a calibration procedure has been established with the same accuracy as for water. The new cell has been designed to keep the DI water temperature stable.