CNT EUV pellicle tunability and performance in a scanner-like environment

Abstract

The advent of extreme ultraviolet (EUV) lithography to enable smaller circuit dimensions introduced a new application for carbon nanotubes (CNTs): the EUV-transparent pellicle used during lithography to protect the photomask from fall-on particles. Diversity of CNT structures and tunability of their configuration within the CNT film (density, bundle size, composition etc.) allow to tailor the CNT EUV pellicle properties for optimal performance. Thin, free-standing CNT films are characterized by very high EUV transmission, mechanical and thermal stability, and can be scaled up to a full pellicle size. A remaining challenge is extending the CNT EUV pellicle lifetime in the scanner environment of EUV-induced plasma. In this work, optical properties of different uncoated CNT pellicles and their performance under high EUV power exposure in the hydrogen-based environment are reported. Transmission, spectroscopic and chemical mapping of the exposed CNT membranes are performed to explore the material modifications under various exposure conditions. These investigations add to the understanding of lifetime limiters of CNT EUV pellicles under the influence of EUV radiation and plasma. Uncoated CNT pellicles withstand 600 W source power equivalent in the EUV scanner-like gas environment but exhibit structural changes with prolonged exposure. Therefore, we anticipate the need for coating the CNT pellicle to protect the CNT material against plasma damage for the current scanner conditions.