Impact of acid diffusion length on resist LER and LWR measured by CD-AFM and CD-SEM

Abstract

The improvement of devices performances is due to many factors such as new architectures, new materials and better lithography resolution. Resist chemical components play a key role in the final performance of a specific resist. In addition to resist characteristics such as: resolution, etching selectivity, the final resist line edge roughness (LER) and line width roughness (LWR) becomes a critical issue because it can degrade resolution and linewidth accuracy and causes fluctuations of transistors performances^1,2. LER and LWR are currently calculated with top-down view SEM images. With chemically amplified resists, we can play on photoacid generator size to partially control acid diffusion length during the post exposure bake. In this paper we propose to compare two techniques, the CD-AFM and CD SEM in order to study the impact of various acid diffusion lengths on LER and LWR. The results show that globally the two techniques agree on most of the results and show the same trends. However, when the profiles vary the linearity between the two techniques can vary drastically. In addition, as a complementary technique to the CD-SEM technique, the CD-AFM gives additional information such as height (top loss), top rounding and sidewall angle which allow us to understand more deeply the impact of PAG size. Therefore, these additional information have a non negligible impact on near term new resist development and lithography processes development. As an illustration of this work, we will present the latest resist development coming from this understanding and leading to very low LER and LWR. Finally, we will propose strengths and weakness of each technique.