High refractive index immersion fluids for 193nm immersion lithography

For the next-generation immersion lithography technology, there is a growing interest in the immersion fluids having a refractive index larger than 1.5 and low absorbance at 193 nm wavelength. In this paper, we report our effort in identifying new immersion fluid candidates. The absolute refractive index values and thermo-optic coefficients, dn/dT, were measured with 1 x 10(-4) and 1 x 10(-5) accuracy respectively at 193 nm wavelength. The results showed promising candidates having refractive index ranging from 1.5 to 1.65 with low absorbance at 193 nm wavelength. Preliminary imaging results with a new immersion fluid gave good 65 nm Line/Space patterns. However, the minimum exposure time of 20sec is about ten times as needed for water, indicating the need to further reduce the absorbance of the immersion fluid.