Water immersion optical lithography at 193 nm

Historically, the application of immersion optics to microlithography has not been seriously pursued because of the alternative technologies available. As the challenges of shorter wavelength become increasingly difficult, immersion imaging becomes more feasible. We present results from research into 193-nm excimer laser immersion lithography at extreme propagation angles. This is being carried out in a fluid that is most compatible in a manufacturable process, namely water. By designing a system around the optical properties of water, we are able to image with wavelengths down to 193 nm. Measured absorption is below 0.50 cm(-1) at 185 nm and below 0.05 cm(-1) at 193 nm. Furthermore, through the development of oblique angle imaging numerical apertures approaching 1.0 in air and 1.44 in water are feasible. The refractive index of water at 193 nm allows for exploration of the following: k(1) values near 0.25 leading to half-pitch resolution approaching 35 nm at a 193-nm wavelength; polarization effects at oblique angles (extreme NA); immersion and photoresist interactions with polarization; immersion fluid composition, temperature, flow, and micro-bubble influence on optical properties (index, absorption, aberration, birefringence); mechanical requirements for imaging, scanning, and wafer transport in a water media; and synthesizing conventional projection imaging via interferometric imaging. (C) 2004 Society of Photo-Optical Instrumentation Engineers.