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Advances in patterning materials for 193 nm immersion lithography.

Advancements in optical lithography tools, processes, and patterning materials have been critical to the continued performance increases of semiconductor devices as well as to the overall economics of the semiconductor industry.1 Reducing the wavelength of the source radiation has been a traditional pathway to increase resolution in optical lithography.1-3 In recent years, the technological challenges and the soaring costs associated with developing new exposure tools and new imaging materials have slowed the progress of wavelength scaling, evidenced by the decision not to commercialize 157 nm (F2 excimer) lithography in 2004.4 Rather than reducing the vacuum wavelength of the illumination, the semiconductor industry instead turned to scaling the effective wavelength via immersion lithography to extend the resolution capabilities of 193 nm lithography. Immersion lithography, which utilizes a coupling medium with a refractive index greater than that of air between the last lens element (LLE) and the photoresist, provides an increased depth-of-focus (DOF) and enables imaging systems with numerical apertures greater than one.5-13 This approach is economically attractive since it continues to use large amounts of the existing lithographic tooling infrastructure and patterning materials. In particular, the rapid development and commercialization of 193 nm water immersion lithography helped seal the fate of 157 nm lithography.