High index nanocomposite photoresist for 193 nm lithography

In immersion lithography, high index fluids are used to increase the numerical aperture (NA) of the imaging system and decrease the minimum printable feature size. Water has been used in first generation immersion lithography at 193 nm to reach the 45 nm node, but to reach the 38 and 32 nm nodes, fluids and resists with a higher index than water are needed. A critical issue hindering the implementation of 193i at the 32 nm node is the availability of high refractive index (n > 1.8) and low optical absorption fluids and resists. It is critical to note that high index resists are necessary only when a high refractive index fluid is in use. High index resist improves the depth of focus (DOF) even without high index fluids. In this study, high refractive index nanoparticles have been synthesized and introduced into a resist matrix to increase the overall refractive index. The strategy followed is to synthesize PGMEA-soluble nanoparticles and then disperse them into a 193 nm resist. High index nanoparticles 1-2 nm in diameter were synthesized by a combination of hydrolysis and sol-gel methods. A ligand exchange method was used, allowing the surface of the nanoparticles to be modified with photoresist-friendly moieties to help them disperse uniformly in the resist matrix. The refractive index and ultraviolet absorbance were measured to evaluate the quality of next generation immersion lithography resist materials.