Updated UPE filter design for point-of-use EUV CAR photoresist filtration for defect improvement

Extreme Ultraviolet (EUV) patterning technology was deployed for the mass production of 7nm logic devices in 2018 and recently achieved 5nm. The demand for device scaling has produced more complex processes and expensive multiple-patterning requirements. Broad consensus on the direction of EUV technology has triggered the semiconductor industry to aggressively push new resist material development, particularly designed to overcome stochastic issues, which coincides with the establishment of the single-print capability infrastructure for the high numerical aperture (NA) EUV scanner. Although standard chemically amplified resists (CAR) have been struggling to overcome stochastic issues, they have improved significantly to demonstrate 24nm resolution with single exposure patterning using ASML's NXE3400B. At the point of use filtration, ultrahigh molecular weight polyethylene (UPE) filters have been widely used to eliminate traditional sources of defectivity, such as particles and aggregates in photoresist materials thanks to their high retention efficiency and excellent photochemical compatibility. However, newly designed UPE filters with innovative membrane morphology are needed to further lower defectivity rates. This paper describes our efforts to optimize filtration and improve photoresist defectivity. A comparative study of the patterning performance of various POU filters is presented. Several filters utilizing a variety of retention ratings and membrane designs were installed on a TEL Clean Track^TM Lithius Pro^TM Z series. An EUV CAR resist was filtered and coated on wafers that were subsequently exposed, etched in hardmask stack, and analyzed for patterning defect performance. This study examines the efficacy of optimized filter design to reduce defects and provides a recommendation to achieve lower defect density.