Resist effects at small pitches

Abstract

The ITRS roadmap and Moore’s law are driving us to print ever smaller features and ever tighter pitches. For these ultrasmall features and pitches, resist effects are expected to play a dominant role in limiting the overall lithographic process capability. To study the impact of resist parameters such as acid diffusion and quencher level on the lithographic performance, we have designed and formulated a matrix of 14 extreme ultraviolet (EUV) resists. In this article, we discuss results that we have obtained from EUV exposures of those resists on the 0.3 numerical aperture EUV Micro Exposure Tool at the Advanced Light Source at Lawrence Berkeley National Laboratories. In addition to exposure latitude and line edge roughness, acid diffusion lengths were characterized using a modification of the extended Nijboer–Zernike theory for each photoresist. A simple theory for the drop in resist contrast as function of the diffusion length is tested and leads to a verified correlation between exposure latitude and diffusion length. This theory gives guidelines to predict what acid diffusion lengths should be used for a certain lithography node. Line edge roughness analysis showed that shot noise statistics are present, and also points out that acid diffusion effects come into play. From the experimentally observed tendencies in this unique matrix of EUV photoresists, fundamental understanding was gained about prominent resist effects that will determine the lithographic performance of resist processes in future lithography nodes.