Characterization of the Photoacid Diffusion Length

摘要

The photoacid diffusion length is a critical issue for extreme ultraviolet (EUV) lithography because it governs the criticaldimension (CD), line-edge-roughness (LER), and line-width-roughness (LWR) of photoresist materials. Laboratory-based experimental methods that complement full lithographic testing would enable a rapid screening of materials andprocess conditions. This paper provides an approach to characterize the photoacid diffusion length by applying a bilayerstack technique. The method involves quantitative measurements of the deprotection kinetics as well as film thickness ateach process step: radiation exposure, post-exposure bake, and development. Analogous to a contrast curve, bycomparing the film thickness of the bilayer before and after development, the photoacid diffusion length was deduced ina commercial EUV photoresist and compared to EUV lithography. Further, by combining the experiments with kineticsmodeling, the measured photoacid diffusion length was predicted. Lastly, based upon the measured kinetics parameters,a criterion was developed that next-generation resists must meet to achieve a 16 nm photoacid diffusion length. Theseguidelines are discussed in terms of correlations and contributions from the photoacid and resist properties. In particular,the trapping kinetics of the photoacid provides a route to reduce LER and the CD at low dose.