High Index Resist for 193 nm Immersion Lithography

Leading edge semiconductor products are made by immersion lithography at 193 nm using water as a fluid medium. This imaging process enables production of 45 nm features. Extending immersion lithography to 32 nm or below requires increases in the refractive indices of the lens material, the immersion fluid, and the resist material. Future generations of resist materials require a refractive index approaching 1.9 at 193 nm. It is known that incorporation of sulfur atoms increases the refractive index of polymers. However, increasing the refractive index is normally linked to a corresponding increase in the absorbance. In attempt to design resist polymers with a high refractive index and low absorbance, we studied several new sulfur-containing monomers and polymers and found functionality that can increase the refractive index without increasing the absorbance at 193 nm. New thioester and sulfone structures are particularly useful in that regard. These new monomers have been used produce imageable polymers with a refractive index of 1.8 at 193 nm and an absorbance less than 1.4 μm -1 .