Performance evaluation of transparent materials for EUV lithography

In the semiconductor industry, transferring ultra-fine circuits on wafers has been important, and extreme ultraviolet (EUV) lithography, which can print sub-10 nm patterns, has become a key technology for high-volume manufacturing (HVM) [1]. For successful patterning with nanoscale resolution, EUV materials such as pellicles, photoresists, and multilayer mirrors are needed, and that performance is quantitatively estimated to secure enough process windows. Especially, pattern typical defects, including necking, bridge, and edge placement errors, are caused by inappropriate materials or optical components. Among them, the EUV pellicle is a transparent component to protect the pattern mask from contaminants, and it requires high transmittance uniformity—the defects on the pellicle print pattern imperfection on the wafers, and lead to yield reduction. Therefore, the optical properties of transparent optical components need to be evaluated accurately. In this work, we focused on developing an evaluation system for optical transmittance of EUV pellicles. It consists of an EUV source based on discharge-produced plasma, a pair of reflective mirrors, and a detector. The transmittance is determined by comparing EUV power with and without the pellicle. As a result, the optical properties of transparent materials are quantitively evaluated.