Acid diffusion length dependency for 32-nm node attenuated and chromeless phase shift mask

We applied the immersion lithography to get 32 nm node pattern with 1.55 NA, without using double exposure / double patterning. A chromeless phase shift mask is compared with an attenuated phase shift mask to make 32 nm dense 1:1 line and space pattern. We compared the aerial image, normalized image log slope, exposure latitude, and depth of focus for each mask type in order to see the effect of the post exposure bake and acid diffusion length. The process window shrinks fast if the diffusion length is larger than 10 nm for both mask types. However, up to 20 nm diffusion length, 32 nm can be processible if the exposure latitude of 5% is used in production.