Effects of Photoresist Polymer Molecular Weight and Acid-Diffusion on Line-Edge Roughness

Important factors contributing to line-edge roughness (LER) of chemically amplified resists are, among others, acid diffusion, and photoresist polymer molecular weight ( M W ). Their effects on the final LER are combined and simulations indicated that acid diffusion can be the major LER modifying factor. Acid-diffusion increases LER overall in a chemically amplified resist in comparison with a conventional one under the same deprotection fraction. In addition, extremely high values of acid-diffusion range can result in smaller LER for higher M W polymers. Under normal acid diffusion conditions, the effect M W on LER is seen to be of secondary importance. Explanations are given based on the critical ionization model for the resist film dissolution, and experimental verification is done with top-down scanning electron microscope (SEM) images for extreme-ultraviolet lithography (EUVL) photoresist.