As the semiconductor industry continues to advance and on-wafer defect reduction by liquid filtration has become “universal” as a process enabler for advanced technology nodes, the need for innovative filtration solutions that reduces target contaminants has become critical.
Filtration technologies for metal cleanliness in photochemicals, including lithography materials and solvents, continue to grow and contribute to die yield improvement at wafer level. Both point-of-use (POU) and bulk filtration play important roles in achieving high-purity chemicals and processes by eliminating metal contaminants in critical fluids. However, the increasing complexity of photochemicals, such as multicomponent resist formulations (organic or inorganic), necessitates advanced filtration membrane technology that is compatible with their various components, including the metal oxide nanoparticles.
In this regard, the ideal filtration technology should rely on functionalization with tailored chemistries to selectively remove target metals, without interactions with the key components in photoresist formulations. Also, due to the variation in forms and species of metals in different fluids, the next generation filtration technology should be able to act as a versatile platform with customization capability to optimize removal efficiency in each fluid.
The objective of this study is to demonstrate the metal removal performance of different functionalization chemistries on PTFE and HDPE membrane and investigate the impact of various surface modification designs on removal selectivity and efficiency.
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.
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