Resolution enhancement of 157 nm lithography by liquid immersion

Abstract

We present the results of a preliminary feasibility study of liquid immersion lithography at 157 nm. A key enabler has been the identification of a class of commercially available liquids, perfluoropolyethers, with low 157 nm absorbance α157 ∼ 10 cm−1 base 10. With 157 nm index of refraction around 1.36, these liquids could enable lithography at numerical aperture ∼1.25 and thus resolution of 50 nm for k1 = 0.4. We have also performed preliminary studies on the optical, chemical, and physical suitability of these liquids for use in high throughput lithography. We also note that at longer wavelengths, there is a wider selection of transparent immersion liquids. At 193 nm, the most transparent liquid measured, de-ionized water, has α193 = 0.036 cm−1 base 10. Water immersion lithography at 193 nm would enable resolution of 60 nm with k1 = 0.4.