Defectivity reduction in EUV resists through novel high-performance Point-Of-Use (POU) filters

Filters for Extreme Ultra-Violet (EUV) lithography chemicals, like chemically amplified photoresist (CAR), are attractive because of their capabilities to remove aggregated species and reduce microbridges in high volume manufacturing. Unlike bulk filters used in high-flow circulation mode, point-of-use (POU) filter is used in single-pass mode, so the retention performance and cleanliness become the most critical factors. Earlier presentations have demonstrated the benefit of reducing on-wafer defectivities through filtration of EUV photoresists with the state-of-the-art HDPE membranes filters, Pall® sub-1nm HDPE (XPR3L). In this study, we present a novel HDPE filter specifically designed to provide high retention performance, which is mainly enabled by an improvement in retention characteristics of membrane and cleanliness in finished POU filters. The membrane was designed to have a finer pore size and better pore geometry to improve defect retention. To expedite the filter start-up process, optimized device cleaning process was applied to further improve initial cleanliness, which was indicated by GC-MS, LC-MS/MS and ICP-MS measurements, etc. Finally, the POU filters were evaluated at imec EUV cluster consisting of TEL CleanTrack™ LITHIUS Pro™-Z and ASML NXE:3400B, and comparative defect data was obtained from patterned wafers with 16nm L/S.