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.
Extreme Ultra-Violet (EUV) lithography is pushing material suppliers to provide the cleanest possible products for tight quality standards. The emphasis on minimizing residual particles, metals, and organics coming from materials and equipment continues to increase. Filter design and its key sub-components such as membrane continue to play a significant role to enhance performance in EUV lithography by reducing defectivity. This necessitates an improvement in retention and cleanliness for both bulk and point-of-use (POU) filters. While POU filtration targets high retention, typically achieved by membrane’s reduced pore size, the main requirement of bulk filtration is maximizing the amount of material recirculated through the filter per unit of time and is achieved with improved tortuosity and well-defined pore structure. In this study, we present a novel HDPE filter specifically designed to provide a high flow (lower differential pressure) without sacrificing retention characteristics. The new membrane was assembled in a POU filter format and compared head-to-head with a state-of-the-art HDPE membrane filter for POU application. The flow performance was assessed by differential pressure (dP) measurement, which showed an enhanced performance benefit of dP reduction by 50% compared to the reference filter, while all other test parameters are improved or at least comparable. The filter cleanliness was quantified by liquid particle counter (LPC), GC-MS, and ICP/MS measurements. Finally, comparative defect data was obtained from the blanket and pattern wafers, prepared on imec EUV cluster comprised of TEL Clean Track LITHIUS Pro-Z and ASML NXE:3400B with a 16nm L/S test vehicle.
The availability of EUV lithography is the mainstream for resolving critical dimension of the advanced technology nodes, currently in the range of 18nm and below [1]. The first insertion of EUVL into manufacturing utilizes chemically amplified resist (CAR) [2]. The filtration of CAR, both at bulk and point-of-use (POU), has already demonstrated in ArF and ArF immersion lithography to play a significant role for microbridges reduction essentially by removing hard particle and gels [3-6]. With respect to ArFi, EUV is bringing new challenges not only for the achievement of the required line roughness, sensitivity and resolution, but also for the need of a substantial reduction of defects such as line collapse, microbridges and broken lines. In this study, it demonstrated the ability of utilizing novel POU filtration to modulate microbridges and achieving superior start-up behavior, both crucial for enabling EUVL at high volume manufacturing. Different POU filters were tested at the imec EUV cluster comprised of TEL CleanTrack LITHIUS Pro-Z and ASML NXE:3400B. The start-up performance, assessed by measuring defects down to 19nm size as a function of the flushing solvent volume, has shown the fast achievement of attaining a stable baseline. Lithography experiments targeting reduction of on-wafer defectivity, carried out with commercially available photoresists, have consistently shown a substantial reduction of after resist development (ADI) and after resist etch (AEI) microbridges on a 16nm L/S test vehicles. The effect of membrane physical intrinsic designs and novel cleaning of POU devices are discussed.
Currently, there are many developments in the field of advanced lithography that are helping to move it towards increased HVM feasibility1,2,3,4. Targeted improvements in hardware design for advanced lithography are of interest to our group specifically for HVM metrics such as LWR improvement, dose reduction processes, and defect density reduction. In this work we are building on our experience to improve LWR in an advanced lithographic process by employing novel hardware solutions on our SCREEN DUO coat develop track system5 . Our approach is to implement post-litho annealing to improve resist line roughness. Although it is preferable to achieve such improvements post-etch process we feel, as many do, that post-patterning improvements are a precursor to improvements after etching6 . We hereby present our work utilizing the SCREEN DUO coat develop track system to improve aggressive dense L/S patterns.
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