LITHOGRAPHY WITH 157 NM LASERS

Projection photolithography at 157 nm was studied as a possible extens ion of current 248-nm and planned 193-nm technologies. At 157 nm, lase rs are available with similar to 8 W average power. Their line width i s narrow enough as to enable the use of catadioptric, and maybe all-re fractive optics similar to those used at 248 and 193 nm. The practical ity of such designs is further enhanced by measurements of calcium flu oride, which show that its absorption is sufficiently small (similar t o 0.004 cm(-1)) at 157 nm. Binary masks with chromium and chromeless p hase shifting masks were fabricated on calcium fluoride as the transpa rent substrate. Robust photoresists at 157 nm still need to be develop ed, and they probably will be of the top surface imaging or bilayer ty pe. Indeed, a silylation resist process was shown to have characterist ics at 157 nm similar to those at 193 nm. The calcium fluoride based m asks were integrated with the silylation process and a home-built, sma ll-field, 0.5-numerical aperture stepper to provide projection printin g with features as small as 80 nm. These initial results indicate that 157-nm lithography has the potential to become a manufacturing techno logy at dimensions well below 100 nm. (C) 1997 American Vacuum Society .