Fluids and resists for hyper na immersion lithography

Immersion lithography at 193 nm has rapidly changed status from a novel technology to the top contender for the 45 nm device node. The likelihood of implementation has raised interest in extending its capabilities. One way to extend immersion lithography would be to develop immersion fluids and resists with higher refractive indices than those currently available (n 193 nm = 1.44 for water and n 193 nm = 1.7 for typical resists). This work explores methods by which the index of refraction of immersion fluid could be increased to that of calcium fluoride (n 193 nm = 1.56) or higher. A survey of the optical properties of various aqueous solutions was performed using spectroscopic ellipsometry. The refractive index of the solutions is measured to identify additives that might increase index while maintaining suitable pH, viscosity and contact angle. Also, ways to increase the index of model resist systems were explored. Higher index resists would help improve contrast in hyper-NA exposure tools.