Study of acid diffusion of anionic or cationic polymer bound PAG

Abstract

The main issue for developing EUV resist is to satisfy the ITRS target of sensitivity, line edge roughness(LER), and resolution simultaneously. However, Resist researchers have difficulty in EUV resist development because they are tradeoff relationships each other. Among them, LER is closely related to acid diffusion length of photo acid generator. Researchers have tried to accomplish uniform distribution and diffusion minimization of PAG in photoresist film in order to improve LER. They are mainly using two kinds of method for PAG introduction for uniform distribution and diffusion minimization. One is use of sulfonium salts having ultra bulky anion or cation for the acid diffusion suppression, the other is direct incorporation of the PAG into the polymer backbone. In that regard, we have pursued development of a variety of 193nm and EUV CARs that contain photoacid generator(PAG) units covalently bonded directly to the resin polymer backbone. When we consider polymer bound PAG, there can be anionic polymer bound PAG resist, cationic polymer bound PAG resist and nonionic polymer bound resist. In this work, we will discuss diffusion length and line edge roughness(LER) of these polymers. Acid diffusion length(Ld) and diffusion coefficient(D) were calculated by according to the modified Fick,s equation. As a result of this measurements we knew that diffusion length of general PAG use as ArF photoresist composition was ranged from thousands of nm to ten of nm and PAG diffusion length having bulky anion and cation is was within a ten nm. In case of anionic polymer bound PAG, acid diffusion length showed under 10nm.