The resist blur due to photoacid diffusion is a significant issue for 45-nm half-pitch node and beyond.
Furthermore, it has been generally recognized that there is a trade-off between resist resolution and sensitivity. In
this paper, we study the influence of the resist blur on resolution and sensitivity in hyper-numerical aperture ArF
immersion lithography by utilizing a two-beam interferometric exposure tool. We evaluated the current photoresist
performance for some of the latest commercial resists, and estimated their acid diffusion lengths as 8 to 9 nm in
sigma assuming Gaussian blur kernel. In addition, we found that the acid diffusion length, that is, the resist
resolution was controllable by PAG anion size, polymer resin size, and PEB temperature. We also found that there
was the trade-off between resist resolution and sensitivity. Our results indicated that the resist blur is still a concern
in order to extend ArF lithography for 45-nm half-pitch node and beyond, however, it will not likely be a
showstopper. We consider that total optimization of resists and exposure tools is important in order to achieve
ultimate resolution in hyper-NA immersion lithography.