An effective filter start-up method has been required by semiconductor device manufacturers, mainly in order to reduce waste volume of lithography process chemicals, which become more expensive as lithography technology advances. To quantify filter start-up status, remaining air in the filter was monitored during static-pressure-driven filter start-up using a sub-1 nm rated Pall high density polyethylene (HDPE) membrane filter varying the solvent type. As a result, correlation for the solvent throughput required for filter start-up to the solvent-membrane material affinity defined by Hansen solubility parameter (HSP) was seen. This is similar to Nylon 6,6 membrane filter results in our previous study. There are exceptions such as nBA requires less throughput than dodecane and so does PGME/PGMEA 7/3 mixture than cyclohexanone, while dodecane and cyclohexanone have better affinity to HDPE (=lower HSP distance). These exceptions can be explained by lower viscosity of nBA and PGME/PGMEA 7/3 mixture probably increasing solvent penetration speed into the filter membrane pores. These results show that quicker start-up of HDPE filtration products can be achieved for solvents with higher affinity and lower viscosity.
Lifetime extension of metal removal application utilizing Nylon 6,6 membrane was investigated with point of use (POU) filters. In this study, new samples which applied Nylon 6,6 membrane with different membrane properties including thickness, area and volume as well as ref. sample with standard membrane were prepared to investigate parameters which are expected to affect the metal removal capacity with breakthrough testing to analyze of metal removal effectiveness. As a result, it was found that the sample with thicker membrane leading to a larger membrane volume tended to show increased metal removal performance. Best correlation was seen with membrane volume (thickness × area) for metal removal performance. Data of flow dP(differential pressure), liquid particle count and initial cleanliness using metal extractions were also collected as fundamental filter performance. Lastly, we confirmed that these new samples showed lower flow dP and comparable cleanliness performance to ref. sample. Based on this study, we successfully developed a new Nylon filter which extends the metal removal lifetime while keeping comparable cleanliness and greater flow dP (differential pressure) performance using the same capsule format. These findings will be very useful in the development of next-generation filtration products, ultimately contributing toward reduced defectivity and increased yield within next-generation lithography processes.
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.
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.
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.
A new 2 nm rated Nylon filter was developed to have features required for lithography filtration process such as finer pore size, extended contact time for adsorption enhancement and updated cleanliness for faster start-up. The contact time is extended by 1.6 times of the 10 nm rated product in the same sized capsule filter. Finer pore size is achieved and demonstrated by the removal performance of gold nanoparticles. For start-up performance, particles and metal cleanliness were improved.
To validate the features applied for the new 2 nm Nylon filter, on-wafer tests are conducted in comparison to conventional product such as 5 nm Nylon filter. Filter start up performance is tested with KLA Tencor Surfscan SP5XP inspection on solvent spin coated Si wafer. For bridge defects, 40 nm half pitch after development pattern defectivity with ArF immersion lithography is tested. The new 2 nm rated Nylon 6,6 filter performed best for all the tests. Cleanliness probably played a role in start-up performance. Sieving, which is related to filter pore size was effective in resist coating defectivity. And both the finer pore size and hydrophilic adsorption are effective in after development inspection at 40 nm half pitch L/S pattern, which is nearly the theoretical limit of the ArF immersion lithography.
Negative tone development is being employed widely because of its superior resolution. Pall is developing filtration products specially targeted for these high resolution applications. High particle retention and low extractables are key aspects of filtration products known to improve on-wafer defectivity. In the current study, we have found that filtration efficiency of the various filter types towards palladium-heptylamine nanoparticles correlates strongly to actual particle removal determined by on-wafer inspection metrology. Furthermore, using the afore mentioned nanoparticle testing metrology, high retention membranes with low extractables were selected. Particle challenge testing is much simpler than on-wafer defectivity inspection and enables faster and effective filtration membrane selection. Based on these results, the selected filtration membrane is expected to perform effective real particle removal in negative tone developer.
OK73 thinner and cyclohexanone, both of which were spiked with metals were passed through Nylon 6,6 filter, varying flow rate, which include the conditions of both point-of-use and bulk filtrations. The influent and effluent metal concentrations were measured using ICP-MS for metal removal efficiency of the filtration. As a result, removal efficiency for some metals descended depending on the flow rate, while others maintained. Slower flow rate is recommended to maintain low metal concentration in bulk filtration based on the result. Metals in cyclohexanone were reduced at higher efficiency than in OK73 thinner, agrees with a metal removal model of hydrophilic adsorbent in organic solvent, evidenced in our previous paper. Further, metal reduction on 300 mm φ Si wafer after coating organic solvents with Nylon 6,6 filtration was evidenced with TREX analysis.
In this paper, we presented the filtration effects on block copolymers (BCP) that are commonly used in directed self-assembly lithographic (DSAL) imaging schemes. Specifically we focused on filtration effects on micro-contaminants such as metal ions and metal induced gels.
Gel removal efficiency studies carried out with HDPE, Nylon and PTFE filters pointed out that Nylon 6,6 membrane is the most effective in removing gels in block copolymer (BCP) solutions.
Metal removal efficiency studies were conducted using multistep filtrations such as repetitive filtration of single membrane material and combination of different type of membranes. Results showed that a combination of Nylon-6,6 and ion-exchange filters is highly effective in reducing metals such as Li, Mg and Al to > 99.99% efficiency. The mechanism of metal removal efficiency is discussed in detail.
We explored the metal removal efficiency of Nylon 6,6 and HDPE (High Density Polyethylene) membrane based filters, in solvents of varying degree of polarity such as Cyclohexanone and 70:30 mixture of PGME (Propylene Glycol Monomethyl Ether) and PGMEA (Propylene Glycol Monomethyl Ether), In all the solvents tested, Nylon 6,6 membrane filtration was found to be significantly more effective in removing metals than HDPE membranes, regardless of their respective membrane pore sizes. Hydrophilic interaction chromatography (HILIC) mechanism was invoked to rationalize metal removal efficiency dependence on solvent hydrophobicity.
It is well known that point-of-use (POU) filtration is an effective means of reducing microbridging defects in lithographic processes involving photoresists. To date, most of the optimization studies have been targeted toward understanding the microbridging defects in positive tone imaging (PTI) process. Considering that negative tone imaging (NTI) process has recently been introduced in advanced technology nodes, we focused our POU filtration studies on understanding the factors that modulate microbridging in NTI and PTI processes. Our studies pointed out that Nylon 6,6 membrane is distinctly more effective in reducing microbridging defects in NTI resists, whereas HDPE membranes show significant improvement in PTI resists. These results were rationalized based on the polarity differences of microbridges in PTI and NTI processes.
Wet particle reduction during filter installation and start-up aligns closely with initiatives to reduce both chemical
consumption and preventative maintenance time. The present study focuses on the effects of filter materials cleanliness
on wet particle defectivity through evaluation of filters that have been treated with a new enhanced cleaning process
focused on organic compounds reduction. Little difference in filter performance is observed between the two filter types
at a size detection threshold of 60 nm, while clear differences are observed at that of 26 nm. It can be suggested that
organic compounds can be identified as a potential source of wet particles. Pall recommends filters that have been
treated with the special cleaning process for applications with a critical defect size of less than 60 nm. Standard filter
products are capable to satisfy wet particle defect performance criteria in less critical lithography applications.
It is known that DUV resist filtration using Nylon 6,6 membrane significantly reduces microbridge defects. Previous
work has described a method to determine an adsorption performance index using modified metal nanoparticles, which
simulate interactions with microbridge defect precursors. In this paper, the effects of filter grade, filter material, and
solvent type on adsorptive retention are explored. The adsorption rate in Nylon 6,6 40 nm filter was observed to be
greater in both lower-LogPow and lower-viscosity solvents, possibly providing a direction for improved filtration
performance based on the solvent properties. The complementary adsorption kinetics parameters give a more accurate
suggestion for the filter performance in lithography applications combined with the conventional sieving filter ratings.
The typical performance index of microelectronics-grade filter products is based upon mechanical sieving. However, adsorption also plays a critical role for reducing certain defects. To provide a more accurate metric, a complementary adsorption performance index is introduced for lithography process filters. In this study, heptylamine-substituted palladium nanoparticles were used to simulate the adsorptive characteristics of microbridge defect precursors. Adsorption kinetic parameters were calculated for Nylon 6,6 and HDPE filters that were challenged with the simulation particles. Nylon 6,6 media quantitatively demonstrated superior adsorptive retention characteristics. The new index is expected to guide both filter product development and filter recommendation for next generation lithography processes.
An effective filter start-up method has been required by device manufacturers, mainly in order to reduce waste volume of
lithography process chemicals, which become more expensive as lithography technology advances. Remaining air was
monitored during static-pressure-driven filter start-up. As a result, 3500 ml of the resist was needed to eliminate
remaining air. For improvement, cyclohexanone pre-wetting was applied prior to the resist introduction. As a result, the
resist volume needed for the solvent displacement was 1900 ml, approximately half the volume required for staticpressure-
driven start-up. Other solvents were evaluated for the pre-wetting start-up method. Results, in descending
order of performance were PGME (best) < PGMEA = IPA < cyclohexanone (worst). Moreover, air displacement
performance strongly correlated with Hansen solubility parameter distance between each solvent and nylon 6,6 material.
A new method for rating retention in lithography process filters has been developed. The method employs a gold
nanoparticle contaminant challenge, inductively coupled plasma mass spectrometry as a concentration detector, and
dynamic light scattering as a particle size detector, all of which enable accurate, reliable filter retention rating below 30
nm. There is good agreement between results obtained with the new method and results obtained with a conventional
polystyrene latex bead challenge. A filter that was rated at 10 nm using extrapolative methods was confirmed to be 10
nm using the new challenge test. Microbridge removal efficiency of polyethylene filters rated by the new method was
studied in a 193 nm (dry) lithography process and the new method was verified. When applied to commercially available filters that are rated below 30 nm, the new method revealed significant differences in removal efficiency among similarly labeled filters.
Filtration products utilizing Nylon 6,6 membrane technology have demonstrated effectiveness in reducing microbridge
defects in DUV photoresist patterning. The effects of fluid flow characteristics on defect reduction using a point-of-use
Nylon 6,6 filtration product are explored. Lower filtration pressure and longer contact time were found to enhance the
removal of gel-like microbridge defect precursors during point-of-use filtration of photoresist polymer solution. A
kinetic study of high-pressure filtration, where a strong dependency of gel removal on contact time is observed, revealed
the gel-like precursors are adsorbed to a greater extent at sites of polar Nylon 6,6 throughout the membrane depth. A
study of gel capturing position by ICP-MS for low-pressure filtration, where gel removal is independent of contact time,
revealed the gels are captured at the inlet portion of the filter, due to smaller transportation force, as compared to deeper
into the filter media depth.
These findings will be very useful both in optimizing filter operating procedures and in the development of next-generation
filtration products, ultimately contributing toward reduced defectivity and increased yield within next-generation
lithography processes.
The impact of pore size and membrane material polarity on the effectiveness of point-of-use filtration is evaluated here.
Decreased pore size and increased polarity in membrane materials were confirmed to positively influence the
effectiveness of microbridge defect removal by a point-of-use filter in the LITHIUS ProTM coater/developer system.
Comparative analysis of different solvent systems validates a model of competitive adsorption whereby morehydrophilic
solvents and gel-like agglomerates preferentially interact with the Nylon 6,6 membrane surface. This
suggests that adsorption is the dominant mechanism for microbridge defect removal via filtration. Therefore, utilizing
filtration products built around polar membrane materials (like hydrophilic Nylon 6,6) will result in greater microbridge
defect reduction than solely reducing filter pore size.
In previous studies, we identified filter properties that have a strong effect on microbubble formation on the downstream side of the filter membrane. A new Highly Asymmetric Polyarylsulfone (HAPAS) filter was developed based on the findings.
In the current study, we evaluated newly-developed HAPAS filter in environmentally preferred non-PFOS TARC in a laboratory setting. Test results confirmed that microbubble counts downstream of the filter were lower than those of a conventional HDPE filter. Further testing in a manufacturing environment confirmed that HAPAS filtration of TARC at point of use was able to reduce defectivity caused by microbubbles on both unpatterned and patterned wafers, compared with a HDPE filter.
Microbubble in filtering Tetra Methyl Ammonium Hydroxide (TMAH) were counted to find the filter which generates the lowest microbubble in resist development process. Hydrophilic Highly Asymmetric Poly Aryl Sulfone (HAPAS) filter was developed and tested. The result showed that generation of microbubbles was as low as that of the Nylon 6,6 filter which had the best performance to date.
Microbubbles in TARC are counted using the same method as the developer testing described above except for mainstream flow rate and the counter model. The results show that counts in the small channel could be reduced by smaller pore size filter such as conventional 0.02um rated filter. However, counts in the larger channel could be reduced by larger pore size filter such as 0.1um rated filter. Based on the above results, 0.02um rated asymmetric nylon 6,6 filter was developed. As a result, 0.02um rated asymmetric Nylon 6,6 filter achieved relatively lower count at any channel as compared to the standard 0.04um rated Nylon 6,6 filter.
Nylon 6,6 filters were installed in resist as an improvement for preventive maintenance (PM) at Wafertech, L.L.C. instead of the currently used filter which has more hydrophobic membrane material. Using the Nylon 6,6 membrane, the number of defects immediately after filter change greatly decreased from 493 pcs of the more hydrophobic filter to 6 pcs/wafer, then after purging with about 250ml, the number of defects reduced within the process specification while the more hydrophobic filter had required 2L purging and 12-36 hours of PM time.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.