Line-Edge Roughness: Characterization and Material Origin

Abstract

Line-edge roughness (LER) is a serious problem that we encounter in nanolithography as pattern sizes shrink. Two critical issues concerning the LER of resist patterns are its characterization and its origin. In this study, characterization involved estimating the LER of 300-nm line-&-space patterns in ZEP520 resist of various thicknesses by three standard metrological methods: top-down scanning electron microscope (SEM) method, top-down atomic force microscope (AFM) method, and sidewall AFM method. In this paper, we review these methods and compare their results. Regarding the origin, sidewall AFM measurements revealed polymer aggregates naturally contained in resist films to be the origin of LER in chain-scission-type resists. How the aggregates contribute to LER during the development process was also clarified.