Radiation induced decomposition mechanisms of high-sensitivity chlorinated resists

Oyama, Tomoko*; Enomoto, Kazuyuki*; Hosaka, Yuji*; Oshima, Akihiro*; Washio, Masakazu*; Tagawa, Seiichi*

ZEP520A (1:1 copolymer of -chloromethacrylate and -methylstyrene, ZEON) is a main-chain scission-type positive-tone resist widely used for electron beam (EB) lithography. ZEP520A has an excellent resolution as high as 10 nm, which is almost comparable to poly(methyl methacrylate) (PMMA), but its sensitivity is about 10 times higher than that of PMMA. In this study, ZEP520A was irradiated using a 100 kV EB, and the decomposition mechanisms were analyzed by gel permeation chromatography, X-ray photoelectron spectroscopy, NMR spectroscopy, and pulse radiolysis. Chlorines were confirmed to easily dissociate as Cl ions (dissociative electron attachment, DEA). Multiple channels could be considered for the main-chain scission, including DEA and the charge transfer complex between phenyl rings and chlorines.