Systems and methods for purifying solvents

Abstract

To provide a method and a system for purifying a solvent, which can provide a purified solvent that can be used for cleaning a semiconductor substrate in a multi-step semiconductor manufacturing process.SOLUTION: And passing the organic solvent through a first filter unit and a second filter unit to obtain a purified organic solvent, wherein the first filter unit comprises a first housing and at least one first filter in the first housing, wherein the first filter comprises a filtration medium comprising a positively charged ion exchange resin, and wherein the second filter unit comprises a second housing and at least one second filter in the second housing, wherein the second filter comprises a filtration medium comprising a negatively charged ion exchange resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application Serial No. 62 / 961,860, filed January 16, 2020, the contents of which are incorporated herein by reference in their entirety. FIELD OF THE DISCLOSURE The present disclosure relates to systems and methods for purifying solvents (e.g., organic solvents). In particular, the present disclosure relates to systems and methods that can be used to obtain organic solvents with very low amounts of metal impurities. [Background technology]

[0002] The semiconductor industry has achieved rapid improvements in the integration density of electronic components. This results from the continuous reduction in component size, ultimately allowing more and more smaller components to be integrated into a given area. These improvements are primarily due to the development of new precision and fine-grained processing techniques.

[0003] During the manufacturing of high-precision integrated circuits (ICs), various process fluids come into contact with bare or film-coated wafers. For example, the fabrication of fine metal interconnects typically involves coating the base material with a prewetting fluid before it is coated with a composite fluid to form a resist film. These process fluids, which contain unique components and various additives, are known sources of contamination for IC wafers.

[0004] Even trace amounts of contaminants in chemical solutions, such as wafer prewetting solutions and developers, can cause defects in the resulting circuit patterns. It has been shown that the presence of metal impurities at levels as low as 1.0 ppt can hinder the performance and stability of semiconductor devices. Furthermore, certain types of metal contaminants can degrade oxide properties, produce inaccurate patterns, and reduce the electrical performance of semiconductor circuits, ultimately negatively impacting manufacturing yields.

[0005] Contaminants, such as metallic impurities, particulates, organic impurities, and moisture, can be inadvertently introduced into chemical fluids during various stages of their manufacture. Examples include impurities present in raw materials, by-products, and residual unreacted reactants during chemical fluid manufacture, as well as foreign materials detached or extracted from manufacturing equipment surfaces or from vessels and reaction vessels used for transport, storage, or reaction. Therefore, reducing or eliminating insoluble and soluble contaminants from these chemical fluids used in the fabrication of high-precision, ultra-fine semiconductor electronic circuits essentially ensures the production of defect-free ICs.

[0006] In this regard, in order to produce the high-purity chemical liquids that are essential for the manufacture of ultra-fine and highly precise semiconductor electronic circuits, it is necessary to significantly improve and strictly control the standards and quality of chemical liquid manufacturing processes and systems. Summary of the Invention

[0007] Therefore, the need for ultra-high purity chemical fluids and the quality improvement and control of these fluids are very important for forming high precision integrated circuits. Specific key parameters targeted for quality improvement and control include reduced metals in the fluids and on the wafers, reduced particle counts in the fluids and on the wafers, reduced defects on the wafers, and reduced organic contaminants.

[0008] In view of the above, the present disclosure provides, inter alia, a purification system and a method using the same to purify a solvent (e.g., an organic solvent) to prepare a semiconductor manufacturing solvent, The present invention controls the amount of metal impurities in a solvent within a predetermined range, producing an ultra-high purity solvent without generating or introducing unknown unwanted substances. Therefore, the occurrence of residue and / or particle defects is suppressed, improving semiconductor wafer yield. Furthermore, the present inventors unexpectedly discovered that purifying a solvent using both an anionic ion exchange filter containing a positively charged ion exchange resin and a cationic ion exchange filter containing a negatively charged ion exchange resin can result in a purified solvent with relatively low amounts of metal impurities (e.g., metal impurities including Cu, Fe, Cr, K, Ni, and Zn).

[0009] In one aspect, the disclosure features a method for purifying an organic solvent, including passing the organic solvent through a first filter unit and a second filter unit to obtain a purified organic solvent. The first filter unit includes a first housing and at least one first filter within the first housing, the first filter including a filtration medium comprising a positively charged ion exchange resin. The second filter unit includes a second housing and at least one second filter within the second housing, the at least one second filter including a filtration medium comprising a negatively charged ion exchange resin.

[0010] In another aspect, the disclosure features a system including a first filter unit and a second filter unit in fluid communication with each other. The first filter unit includes a first housing and at least one first filter within the first housing, the first filter including a filtration medium comprising a positively charged ion exchange resin. The second filter unit includes a second housing and at least one second filter within the second housing, the at least one second filter including a filtration medium comprising a negatively charged ion exchange resin.

[0011] Implementations may include one or more of the following features.

[0012] In some embodiments, the filtration media in the first filter or the second filter comprises a polyamide (eg, nylon), a polyolefin (eg, high density polyethylene), a fluoropolymer (eg, polytetrafluoroethylene), or a copolymer thereof.

[0013] In some embodiments, the filtration medium in the first filter comprises a polyamide (e.g., nylon). In some embodiments, the filtration medium in the first filter comprises quaternary ammonium groups.

[0014] In some embodiments, the filtration medium in the second filter comprises high density polyethylene. In some embodiments, the filtration medium in the second filter comprises sulfonate groups.

[0015] In some embodiments, the first filter unit comprises 1-20 first filters and the second filter unit comprises 1-20 second filters.

[0016] In some embodiments, passing the organic solvent through the first filter unit or the second filter unit occurs at a temperature of about 80° F. or less. In some embodiments, the method further comprises passing the organic solvent through at least one heat exchanger to maintain the temperature of the organic solvent at about 80° F. or less. In some embodiments, the at least one heat exchanger is located upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit.

[0017] In some embodiments, the method further comprises passing the organic solvent through at least one particle removal filter unit, the at least one particle removal filter unit being located upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit. In some embodiments, the method further comprises moving the purified solvent to a packaging station.

[0018] In some embodiments, the organic solvent comprises cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 4-methyl-2-pentanol, or propylene carbonate.

[0019] In some embodiments, the organic solvent contains a metal impurity comprising a metal selected from the group consisting of alkali metals, alkaline earth metals, main group metals, transition metals, and lanthanide metals, hi some embodiments, the metal impurity comprises a metal selected from the group consisting of Cu, Fe, Cr, K, Ni, and Zn.

[0020] In some embodiments, the purified organic solvent comprises metal impurities in an amount of about 15 ppt or less of the purified organic solvent. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a purification system employed in a method for purifying an organic solvent according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0022] As defined herein, unless otherwise specified, all percentages expressed should be understood to be weight percent based on the total weight of the composition. Ambient temperature is defined as about 16 degrees Celsius to about 27 degrees Celsius (°C) unless otherwise specified. The term "solvent" referred to herein refers to a single solvent or a combination of two or more (e.g., three or four) solvents unless otherwise specified. In this disclosure, "ppm" means "parts per million," "ppb" means "parts per billion," and "ppt" means "parts per trillion."

[0023] In general, the present disclosure features systems and methods for purifying solvents (e.g., organic solvents). The solvents described herein can be used as wafer processing fluids (such as prewetting fluids, developers, rinses, cleaning fluids, stripping fluids, etc.) or as solvents for semiconductor materials used in semiconductor manufacturing processes.

[0024] Before being subjected to the purification method of the present disclosure, the solvent may contain an undesirable amount of contaminants and impurities. After the solvent is treated by the purification method of the present disclosure, a significant amount of contaminants and impurities may be removed from the solvent. The solvent before treatment is also referred to as "unpurified solvent" in this disclosure. The solvent before treatment can be synthesized in a factory or purchased commercially from a supplier. The solvent after treatment is also referred to as "purified solvent" in this disclosure. The "purified solvent" may contain impurities limited within a predetermined range.

[0025] Generally, the solvents referred to herein may include at least one (e.g., two, three, or four) organic solvents (such as alcohols, ethers, hydrocarbons, halogenated hydrocarbons, esters, ketones, or carbonates). Examples of suitable organic solvents include methanol, ethanol, 1-propanol, isopropanol, n-propanol, 2-methyl-1-propanol, n-butanol, 2-butanol, tert-butanol, 1-pentanol, 2-isopropyl alcohol ... alcohol, 2-pentanol, 3-pentanol, n-hexanol, cyclohexanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-1-pentanol, 2-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-1-pentanol, 3-methyl-2-pentanol, 3-methyl-3-pentanol, 4-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, 2,2- Dimethyl-3-pentanol, 2,3-dimethyl-3-pentanol, 2,4-dimethyl-3-pentanol, 4,4-dimethyl-2-pentanol, 3-ethyl-3-heptanol, 1-heptanol, 2-heptanol, 3-heptanol, 2-methyl-2-hexanol, 2-methyl-3-hexanol, 5-methyl-1-hexanol, 5-methyl-2-hexanol, 2-ethyl-1-hexanol, methylcyclohexanol, trimethylcyclohexanol, 4-methyl-3-heptanol, 6-methyl-2- Heptanol, 1-octanol, 2-octanol, 3-octanol, 2-propyl-1-pentanol, 2,6-dimethyl-4-heptanol, 2-nonanol, 3,7-dimethyl-3-octanol, ethylene glycol, propylene glycol, diethyl ether, dipropyl ether, diisopropyl ether, butyl methyl ether, butyl ethyl ether, butyl propyl ether, dibutyl ether, diisobutyl ether, tert-butyl methyl ether, tert-butyl ethyl ether, tert-butyl propyl ether, di-tert-butyl ether, dipentyl ether, diisoamyl ether, cyclopentyl methyl ether, cyclohexyl methyl ether, bromomethyl methyl ether, α,α-dichloromethyl methyl ether, chloromethyl ethyl ether, 2-chloroethyl methyl ether, 2-bromoethyl methyl ether, 2,2-dichloroethyl methyl ether, 2-chloroethyl ethyl ether, 2-bromoethyl ethyl ether, (±)-1,2-dichloroethyl ethyl ether, 2,2,2-Trifluoroethyl ether, ethyl vinyl ether, butyl vinyl ether, allyl ethyl ether, allyl propyl ether, allyl butyl ether, diallyl ether, 2-methoxypropene, ethyl-1-propenyl ether, cis-1-bromo-2-ethoxyethylene, 2-chloroethyl vinyl ether, allyl-1,1,2,2-tetrafluoroethyl ether, octane, isooctane, nonane, decane, methylcyclohexane, decalin, xylene, ethylbenzene, diethylbenzene, cumene, sec-butylbenzene, cymene, dipentene, pyrubicin Examples of suitable solvents include methyl acrylate, monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monomethyl ether acetate, ethyl lactate, methyl methoxypropionate, cyclopentanone, cyclohexanone, n-butyl acetate, γ-butyrolactone, diisoamyl ether, isoamyl acetate, chloroform, dichloromethane, 1,4-dioxane, hexyl alcohol, 2-heptanone, isoamyl acetate, propylene carbonate, and tetrahydrofuran.

[0026] In some embodiments, the solvent is a prewetting liquid. Examples of prewetting liquids include at least one of cyclopentanone (CyPe), cyclohexanone (CyH), monomethyl ether, propylene glycol monomethyl ether (PGME), propylene glycol monoethyl ether (PGEE), propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monopropyl ether (PGPE), and ethyl lactate (EL). In other embodiments, the solvent can be a developer such as n-butyl acetate or a rinse liquid such as 4-methyl-2-pentanol (MIBC). In some embodiments, the solvent can be a rinse solvent used in a wafer fabrication process, such as isopropyl alcohol.

[0027] In some embodiments, the raw or unpurified organic solvent has a purity of about 95% or greater (e.g., about 96% or greater, about 97% or greater, about 98% or greater, or about 99% or greater). In some embodiments, the treated or purified organic solvent obtained from the methods described herein can have a purity of about 99.5% or more (e.g., about 99.9% or more, about 99.95% or more, about 99.99% or more, about 99.995% or more, or about 99.999% or more). As used herein, "purity" refers to the weight percent of the solvent in the total weight of the liquid. The content of the organic solvent in the liquid can be measured using a gas chromatography-mass spectrometry (GC-MS) device (e.g., a thermal desorption (TD) GC-MS device).

[0028] In some embodiments, the boiling point of the solvents described herein is about 200° C. or less (e.g., about 150° C. or less) or about 50° C. or more (e.g., about 100° C. or more) from the viewpoint of improving the manufacturing yield of semiconductor chips. In this disclosure, boiling point means the boiling point measured at 1 atmosphere.

[0029] Generally, impurities contained in the organic solvent before treatment may include metal impurities, particles, and others such as organic impurities and moisture.

[0030] As described herein, metal impurities can be in solid form (e.g., metal alone, particulate metal-containing compounds, etc.). In some embodiments, metal impurities can include metals selected from the group consisting of alkali metals, alkaline earth metals, main group metals, transition metals, and lanthanide metals. Examples of common metal impurities include heavy metals such as copper (Cu), iron (Fe), aluminum (Al), chromium (Cr), lead (Pb), nickel (Ni), and zinc (Zn), as well as ionic metals such as sodium (Na), potassium (K), and calcium (Ca). Depending on the type of metal, metal impurities can reduce oxide integrity, degrade MOS gate stacks, and shorten device lifetime. In organic solvents purified by the methods described herein, the total trace metal content is preferably within a predetermined range of 0 to about 300 ppt by weight (e.g., 0 to about 150 ppt by weight), with the amount of each metal preferably within a predetermined range of 0 to about 15 ppt by weight (e.g., 0 to about 10 ppt by weight).

[0031] In the organic solvent purified by the method described herein, the total trace metal content is preferably within a predetermined range of 0 (e.g., about 1 mass ppt or more, about 5 mass ppt or more, or about 10 mass ppt or more) to about 200 mass ppt or less (e.g., about 180 mass ppt or less, about 160 mass ppt or less, about 150 mass ppt or less, about 140 mass ppt or less, about 120 mass ppt or less, about 100 mass ppt or less, about 50 mass ppt or less, or about 20 mass ppt or less), and the content of each trace metal (e.g., The amount of Fe, Ni, Cr, Zn, Cu, K, Na, or Ca) is preferably within a predetermined range of 0 (e.g., about 1 ppt by mass or more, about 2 ppt by mass or more, or about 3 ppt by mass or more) to about 50 ppt by mass or less (e.g., about 40 ppt by mass or less, about 30 ppt by mass or less, about 20 ppt by mass or less, about 15 ppt by mass or less, about 10 ppt by mass or less, about 8 ppt by mass or less, about 6 ppt by mass or less, about 5 ppt by mass or less, about 4 ppt by mass or less, about 3 ppt by mass or less, or about 2 ppt by mass or less).

[0032] In this disclosure, substances with a size of 0.03 μm or greater are referred to as "particles" or "particulate matter." Examples of particles include dust, dirt, organic solids, and inorganic solids. Particles may also include colloidal metal atom impurities. The type of metal atom that is easily colloidalized is not particularly limited, and may include at least one metal atom selected from the group consisting of Na, K, Ca, Fe, Cu, Mg, Mn, Li, Al, Cr, Ni, Zn, and Pb. In organic solvents purified by the methods described herein, the total number of particles with a size of 0.03 μm or greater is preferably within a predetermined range of 100 or less (e.g., 80 or less, 60 or less, 50 or less, 40 or less, or 20 or less) per ml of solvent. The number of "particles" in a liquid medium can be counted using a light-scattering liquid particle counter (LPC). number).

[0033] As used herein, organic impurities refer to organic substances, distinct from organic solvents, present in a concentration of 5,000 ppm by mass or less based on the total mass of the liquid containing the organic solvent and the organic impurities. Organic impurities can be volatile organic compounds present in the atmosphere, even in clean rooms. Some organic impurities originate from transportation and storage facilities, while others are originally present in the raw materials. Other examples of organic impurities include by-products and / or unreacted reactants produced when the organic solvent is synthesized.

[0034] The total content of organic impurities in the purified organic solvent is not particularly limited. From the viewpoint of improving the manufacturing yield of semiconductor devices, the total content of organic impurities in the purified organic solvent may be 0.1 to 5000 ppm by mass (e.g., 1 to 2000 ppm by mass, 1 to 1000 ppm by mass, 1 to 500 ppm by mass, or 1 to 100 ppm by mass). The content of organic impurities in the solvents described herein may be measured using a gas chromatography-mass spectrometry (GC-MS) device.

[0035] Figure 1 is a schematic diagram illustrating a purification system configuration according to some embodiments of the present disclosure. As shown in Figure 1, purification system 10 includes a supply unit 20, a first filtration system 110, a storage tank 130, a second filtration system 120, and a packaging station 140, all of which are fluidly connected to each other (e.g., via one or more conduits).

[0036] Generally, the supply unit 20 (e.g., a tank) is configured to hold or transport a starting material (e.g., an untreated or unpurified organic solvent). The starting material may be processed by the purification system 10 to generate or produce a purified organic solvent having a number of unwanted contaminants (e.g., particulate matter, organic impurities, metal impurities) limited within a predetermined range. The type of supply unit 20 is not particularly limited, as long as it continuously or intermittently supplies the starting material to other components of the purification system 10. In some embodiments, the supply unit 20 may include a material receiving tank, a sensor such as a level gauge (not shown), a pump (not shown), and / or a valve (not shown) for controlling the flow of the starting material. In FIG. 1 , the purification system 10 includes one supply unit 20. However, in some embodiments, multiple supply units 20 may be provided (e.g., in parallel or series) for various starting materials processed by the purification system 10.

[0037] Purification system 10 may include at least one first filtration system 110 and at least one second filtration system 120. Generally, first filtration system 110 performs initial filtration of the starting material (e.g., crude organic solvent) to remove a majority of impurities and / or particles, and second filtration system 120 performs subsequent filtration to remove remaining impurities and particulates to obtain ultra-pure organic solvent. In some embodiments, first filtration system 110 and second filtration system 120 may each include one or more filter units, each of which may include a filter housing and one or more filters (e.g., 1 to 20 filters).

[0038] In some embodiments, purification system 10 may optionally include at least one temperature control unit 100 for setting or maintaining the temperature of the organic solvent within a specific temperature range so that the organic solvent is maintained at a substantially constant temperature during the purification process. As described herein, the temperature control unit may include, for example, but is not limited to, a commercially available recirculating heating / cooling unit, a condenser, or a heat exchanger that may be installed in the conduits of purification system 10. Temperature control unit 100 may be configured, for example, between supply unit 20 and first filtration system 110. In some embodiments, temperature control unit 100 may be configured to: The temperature of the organic solvent may be set at about 80° F. or less (e.g., about 75° F. or less, about 70° F. or less, about 65° F. or less, or about 60° F. or less) and / or about 30° F. or more (e.g., about 40° F. or more, about 50° F. or more, or about 60° F. or more). In some embodiments, because the pumps used in purification system 10 may generate heat and increase the solvent temperature, purification system 10 may include additional temperature control units (e.g., units 170 and 180, described below) in appropriate locations to maintain the solvent temperature at a predetermined value.

[0039] Referring to FIG. 1, the first filtration system 110 may include an optional temperature control unit 100, a supply port 110a, one or more (e.g., 2, 3, 4, 5, or 10) filter units (e.g., units 112, 114, 116, and 118), an outlet port 110b, an optional recirculation conduit 160h, and one or more optional temperature control units 170, all of which are fluidly connected to each other (e.g., via one or more conduits).

[0040] In some embodiments, each filter unit in the first filtration system 110 may include a filter housing and one or more (e.g., 2, 3, 4, 5, or 6) filters within the filter housing. Each filter may include a filtration medium having an appropriate average pore size. The filters may be arranged in parallel or in series within the filter housing. During use, if two filters are arranged in parallel, the solvent to be purified passes through the two filters in parallel (i.e., substantially simultaneously). On the other hand, when two filters are arranged in series, the solvent to be purified passes through the two filters sequentially during use. In some embodiments, some filter units may include multiple filters in parallel within the filter housing to increase flow rate and improve productivity.

[0041] For example, the first filtration system 110 shown in Figure 1 includes four filter units (i.e., units 112, 114, 116, and 118), each including a filter housing and one or more filters (e.g., filters 112a, 114a, 116a, and 118a) within the filter housing. In other embodiments, the first filtration system 110 may also include other purification modules (not shown) in addition to the four filter units shown in Figure 1.

[0042] 1, filters 112a, 114a, 116a, and 118a may have different functions or characteristics and may provide different purification processes. In some embodiments, the particular filters (e.g., 112a, 114a, 116a, or 118a) housed within corresponding filter units (e.g., 112, 114, 116, and 118) may have the same or similar purification functions, physicochemical properties, pore sizes, and / or materials of construction. In some embodiments, each filter within a filter unit may be independently selected from the group consisting of particle removal filters, ion exchange filters, and ion absorption filters.

[0043] In some embodiments, the filter unit 112 may include a filter housing and at least one (e.g., two or three) filters 112a within the filter housing. In some embodiments, when the filter unit 112 includes two or more filters 112a, the filters 112a may be arranged in parallel.

[0044] In some embodiments, filter 112a can be a particle removal filter for removing relatively large particles from the organic solvent. ... The filter 112a may include a filtration medium having an average pore size of about 50 nm or more (e.g., about 60 nm or more, about 70 nm or more, about 80 nm or more, about 90 nm or more, or about 100 nm or more). Within the above range, foreign matter such as impurities and aggregates contained in the organic solvent can be reliably removed while preventing clogging of the filter 112a.

[0045] Examples of suitable materials for the filter 112a include fluoropolymers (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymers (PFA), or modified polytetrafluoroethylene (MPTFE)), polyamide resins such as nylon (e.g., nylon 6 or nylon 66), and polyolefin resins (including high-density and ultra-high molecular weight resins) such as polyethylene (PE) and polypropylene (PP). For example, the filtration medium in the particle removal filter may be made of at least one polymer selected from the group consisting of polypropylene (e.g., high-density polypropylene), polyethylene (e.g., high-density polyethylene (HDPE) or ultra-high molecular weight polyethylene (UPE)), nylon, polytetrafluoroethylene, or perfluoroalkoxyalkane polymers. Filters made of the above materials may effectively remove foreign matter (e.g., highly polar) that tends to cause residue and / or particle defects and efficiently reduce the content of metal components in the chemical solution. In some embodiments, the filter unit 112 may include one filter 112a made of polypropylene having an average pore size of approximately 200 nm.

[0046] In some embodiments, filter unit 118 may include a filter housing and at least one (e.g., two or three) filter 118a within the filter housing. Filter 118a may be a particle removal filter for removing relatively small particles from organic solvents. In some embodiments, filter 118a may include a filtration medium having an average pore size of about 50 nm or less (e.g., about 45 nm or less, about 40 nm or less, about 35 nm or less, about 30 nm or less, about 25 nm or less, or about 20 nm or less) and / or about 10 nm or more (e.g., about 15 nm or more, about 20 nm or more, about 25 nm or more, or about 30 nm or more). In some embodiments, the average pore size of the filtration medium within filter 118a may be smaller than the average pore size of the filtration medium within filter 112a. In such embodiments, filter 118a may be used to remove particles smaller than those removed by filter 112a.

[0047] In some embodiments, the filter 118a in the filter unit 118 may include an ion-absorbing membrane for removing relatively small particles and / or metal ions from an organic solvent. The ion-absorbing membrane may have a porous membrane material and may have ion exchange functionality. Examples of suitable materials that can be used to fabricate the ion-absorbing membrane include, but are not limited to, microfiltration membrane film materials such as cellulose, diatomaceous earth, polyamide resins such as nylon (e.g., nylon 6 or nylon 66), polyethylene (e.g., high-density polyethylene or ultra-high-molecular-weight polyethylene), polypropylene, polystyrene, resins having imide groups, resins having amide and imide groups, fluororesins (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymers (PFA), or modified polytetrafluoroethylene (MPTFE)), membrane materials with ion-exchange functional groups, and the like. For example, the filter 118a may include at least one polymer selected from the group consisting of polypropylene (e.g., high-density polypropylene), polyethylene (e.g., high-density polyethylene or ultra-high-molecular-weight polyethylene), nylon, polytetrafluoroethylene, or perfluoroalkoxyalkane polymers.

[0048] In some embodiments, at least some (e.g., all) of the filters 118a may be arranged in parallel within the filter unit 118, and the remaining filters 118a (if any) within the filter unit 118 may be arranged in series. When two filters are arranged in parallel, the organic solvent to be purified may pass through the two filters in parallel (e.g., simultaneously). In some embodiments, the number of filters 118a (e.g., arranged in parallel) in filter unit 118 may be greater than the number of filters 112a in filter unit 112. For example, if filter unit 112 includes one filter 112a, filter unit 118 may include two or three filters 118a arranged in parallel. Without wishing to be bound by theory, it is believed that an advantage of having more filters arranged in parallel in filter unit 118 than in filter unit 112 is that system 10 may provide increased flow rates and have improved productivity, or the flow rate of system 10 may be maintained without increasing system backpressure. Without wishing to be bound by theory, it is believed that if the average pore size of the filtration medium in filter 118a is smaller than the average pore size of the filtration medium in filter 112a, the flow rate of the organic solvent through filter 118a may be reduced compared to the flow rate of the organic solvent through filter 112a. Therefore, it is believed that the flow rate and productivity of the system 10 may be increased by placing multiple filters 118a in parallel.

[0049] In some embodiments, the filter unit 118 may include three filters 118a arranged in parallel and having an average pore size of about 50 nm and made of ultra-high molecular weight polyethylene.

[0050] In some embodiments, purification system 10 may include two ion exchange filter units: filter unit 114 and filter unit 116. In some embodiments, one of filter unit 114 and filter unit 116 is a cationic ion exchange filter unit (i.e., includes one or more filters comprising negatively charged ion exchange resins), and the other of filter unit 114 and filter unit 116 is an anionic ion exchange filter unit (i.e., includes one or more filters comprising positively charged ion exchange resins). For example, in some embodiments, unit 114 may be a cationic ion exchange filter unit and unit 116 may be an anionic ion exchange filter unit. In other embodiments, unit 116 may be a cationic ion exchange filter unit and unit 114 may be an anionic ion exchange filter unit. While not wishing to be bound by theory, the inventors have surprisingly discovered that including both a cation ion exchange filter unit and an anion ion exchange filter unit in purification system 10 can significantly reduce the amount of metal impurities (e.g., metal impurities including Cu, Fe, Cr, K, Ni, and Zn) in the purified organic solvent compared to a system using only one type of ion exchange filter unit. Furthermore, without wishing to be bound by theory, it is believed that this surprising result can be attributed to the fact that metal impurities exist in the organic solvent in the form of both positively and negatively charged species, which is contrary to conventional wisdom that metals exist only as positive ions in organic solvents.

[0051] In some embodiments, the filter unit 114 may include a filter housing and at least one (e.g., two or three) filters 114a within the filter housing. In some embodiments, at least some (e.g., all) of the filters 114a may be arranged in parallel within the filter unit 114, and the remaining filters 114a (if any) may be arranged in series.

[0052] In some embodiments, the filter 114a in the filter unit 114 may be a cationic ion exchange filter that includes a filtration medium that includes a negatively charged ion exchange resin. For example, the filter 114a may include one or more ion exchange resin membranes for removing positively charged particles and / or cationic metal ions from the organic solvent. The cationic ion-exchange resin membrane used in the present disclosure is not particularly limited, and filters containing ion-exchange resins with suitable ion-exchange groups fixed to the resin membrane can be used. Examples of such ion-exchange resin membranes include strongly acidic cation-exchange resins with chemically modified cation-exchange groups (such as sulfonic acid or sulfonate groups) on the resin membrane. Examples of suitable resin membranes include those containing cellulose, diatomaceous earth, nylon (a resin with amide groups), polyethylene (e.g., high-density polyethylene or ultra-high-molecular-weight polyethylene), polyolefins such as polypropylene, polystyrene, resins with imide groups, resins with both amide and imide groups, fluoropolymers (e.g., polytetrafluoroethylene or perfluoroalkoxyalkane polymers), or combinations thereof. In some embodiments, the ion-exchange resin membrane can be a membrane having an integrated structure of a particle-removal membrane and an ion-exchange resin membrane. Polyalkylene (e.g., PE or PP) membranes chemically modified with cation-exchange groups (e.g., sulfonate groups) on the membrane are preferred. The filter with a cation-exchange resin membrane used in the present disclosure can be a commercially available filter with metal ion removal function. A commercially available example of such a cation exchange filter is IonKleen, available from Pall Corporation, Port Washington, NY. These filters can be selected based on ion exchange efficiency and have estimated pore sizes ranging from about 100 nm to about 500 nm.

[0053] In some embodiments, filter unit 114 may include at least three (eg, four, five, six, or seven) filters 114a arranged in parallel and comprising high-density polyethylene modified with sulfonate groups as the filtration medium.

[0054] In some embodiments, the filter unit 116 may include a filter housing and at least one (e.g., two or three) filters 116a within the filter housing. In some embodiments, at least some (e.g., all) of the filters 116a may be arranged in parallel within the filter unit 116, and the remaining filters 116a (if any) may be arranged in series.

[0055] In some embodiments, filter 116a in filter unit 116 may be an anionic ion exchange filter containing a filtration medium containing a positively charged ion exchange resin. For example, filter 116a may include one or more ion exchange resin membranes for removing negatively charged particles and / or anionic metal-containing species from organic solvents. The anionic ion exchange resin membrane used in this disclosure is not particularly limited, and filters containing ion exchange resins with suitable ion exchange groups immobilized on the resin membrane may be used. Examples of such ion exchange resin membranes include resins with chemically modified anion exchange groups (e.g., quaternary ammonium groups) on the resin membrane. Examples of suitable resin membranes include those containing cellulose, diatomaceous earth, nylon (a resin with amide groups), polyethylene (e.g., high-density polyethylene or ultra-high molecular weight polyethylene), polyolefins such as polypropylene, polystyrene, resins with imide groups, resins with both amide and imide groups, fluoropolymers (e.g., polytetrafluoroethylene or perfluoroalkoxyalkane polymers), or combinations thereof. In some embodiments, the ion exchange resin membrane may be a membrane having an integral structure of a particle removal membrane and an ion exchange resin membrane. Polyamide (e.g., nylon) membranes chemically modified with anion-exchange groups (e.g., quaternary ammonium groups) on the membrane are preferred. The filter with anion-exchange resin membrane used in this disclosure can be a commercially available filter with metal ion removal capabilities. A commercially available example of such an anion-exchange filter is Nylon EMZ, available from 3M Purification Inc. (Meriden, Connecticut). These filters are classified based on ion exchange efficiency. The pore size can be selected from a range of about 40 nm to about 450 nm.

[0056] In some embodiments, the filter units 116 are arranged in parallel and include a filtration medium The filter 116 may include at least three (eg, four, five, six, or seven) filters 116a, each comprising nylon modified with quaternary ammonium groups as a filter.

[0057] In some embodiments, the number of filters 114a or 116a (e.g., arranged in parallel) in filter unit 114 or 116 may be greater than the number of filters 112a in filter unit 112. For example, if filter unit 112 includes one filter 112a, filter unit 114 or 116 may include two or three filters 114a or 116a (e.g., arranged in parallel). Without wishing to be bound by theory, it is believed that an advantage of having more filters arranged in parallel in filter unit 114 or 116 than in filter unit 112 is that system 10 may provide increased flow rates and have improved productivity, or the flow rate of system 10 may be maintained without increasing backpressure in the system.

[0058] Examples of the shape of the membrane material in filter 114a or 116a include pleated, flat membrane, hollow fiber, and the porous body described in JP 2003-112060 A. Since the ion adsorption membrane is porous, it is also possible to remove some of the fine particles.

[0059] In some embodiments, first filtration system 110 may optionally include a recirculation conduit 160h to form a recirculation loop for recirculating the partially purified organic solvent back to first filtration system 110 for processing again by a filter in first filtration system 110. In some embodiments, the partially purified organic solvent is recycled at least two times (e.g., at least three times, at least four times, or at least five times) before being transferred to storage tank 130.

[0060] Generally, the storage tank may be any suitable container for storing chemical liquid. In some embodiments, the storage tank 130 may have a suitable capacity. For example, the storage tank 130 may have a capacity of about 1000 liters or more (e.g., about 2000 liters or more, about 3000 liters or more, or about 5000 liters or more) and / or about 30,000 liters or less (e.g., about 25,000 liters or less, about 20,000 liters or less, about 15,000 liters or less, or about 10,000 liters or less).

[0061] In some embodiments, an optional temperature control unit 170 (e.g., a heat exchanger) may be configured along recirculation conduit 160h. In such embodiments, temperature control unit 170 may be configured for a temperature of about 80°F or less (e.g., about 75°F or less, about 70°F or less, or about 65°F or less) and / or about 30°F or more (e.g., about 40°F or more, about 50°F or more, or about 60°F or more), thereby maintaining the temperature of the partially purified organic solvent at about 80°F or less and recirculating it to first filtration system 110. In the example shown in FIG. 1 , recirculation conduit 160h is configured upstream of outlet port 110b of first filtration system 110. In some embodiments, recirculation conduit 160h may be configured downstream of outlet port 110b. It is understood that pumps and valves may be installed in the various conduits, outlet and supply ports of first filtration system 110, supply unit 20, and temperature control unit 100, as needed.

[0062] As an example shown in FIG. 1 , purification system 110 may optionally include a temperature control unit 170 (e.g., a heat exchanger) configured between filter unit 112 and filter unit 114 to control the temperature of the organic solvent to about 80°F or less (e.g., about 75°F or less, about 70°F or less, or about 65°F or less) and / or about 30°F or more (e.g., about 40°F or more, about 50°F or more, or about 60°F or more) before the organic solvent enters filter unit 114 for processing.

[0063] It should also be noted that the location of temperature control unit 170 is not limited to the above examples. In some embodiments, temperature control unit 170 may be configured upstream of filter unit 112, between filter units 114 and 116, between filter units 116 and 118, or downstream of filter unit 118. In such embodiments, another temperature control unit may or may not be installed downstream of filter unit 112 and before entry into a subsequent filter unit (e.g., filter units 114, 116, and / or 118). Configuring another temperature control unit downstream of filter unit 112 is optional, as long as other means or devices (e.g., pumps) capable of reintroducing thermal energy to the organic solvent are not installed or disposed between filter unit 112 and a subsequent filter (e.g., filter 114, 116, or 118).

[0064] In some embodiments, filter units 112, 114, 116, and 118 in first filtration system 110 may not include filter housings, and filters 112a, 114a, 116a, and 118a may be configured without compartmentalization within first filtration system 110. For example, first filtration system 110 may be a multi-stage system including interchangeable filters (e.g., 112a, 114a, 116a, and 118a) linked together within first filtration system 110, and the organic solvent may be passed through these filters in series. In such embodiments, temperature control unit 170 may be configured anywhere upstream of the first ion exchange filter or ion adsorption filter through which the organic solvent passes or passes in series. For example, if the first filtration system 110 contains, in sequence and downstream of the supply port 110a, a particle removal filter A, a particle removal filter B, an ion exchange membrane A, an ion exchange membrane B, and an ion adsorption membrane A, a temperature control unit 170 may be configured between the particle removal filter B and the ion exchange membrane A to adjust and control the temperature of the organic solvent to about 80° F. or less before the organic solvent is processed through the ion exchange membrane A and the subsequent ion exchange membrane B and ion adsorption membrane A. It should be noted that the above example is for illustrative purposes and is not intended to be limiting.

[0065] 1, purification system 10 also includes a second filtration system 120 in fluid communication between storage tank 130 and packaging station 140. Second filtration system 120 may include a supply port 120a, one or more (e.g., two, three, four, five, or ten) filter units 122, an outlet port 120b, an optional recirculation conduit 160f, and one or more optional temperature control units 180, all in fluid communication with each other (via one or more conduits). It is understood that pumps and valves may be installed in the various conduits, outlet and supply ports, and temperature control units in second filtration system 120, as needed.

[0066] In some embodiments, filter unit 122 may include a filter housing and at least one filter 122a within the filter housing. For example, filter unit 122 may include 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14 filters 122a within the filter housing. The second filtration system 120 shown in FIG. 1 includes one filter unit 122. In some embodiments, second filtration system 120 may include two or more (e.g., three or four) filter units 122. In such embodiments, filter unit 122 may not have a separate housing, and filter 122a may be configured without compartmentalization within second filtration system 110. In other embodiments, second filtration system 120 may also include other purification modules (not shown) in addition to filter unit 122.

[0067] In some embodiments, filters 122a may have different functionality or characteristics and provide different purification processes. In some embodiments, filters 122a housed within filter unit 122 may have the same or similar purification function, physicochemical properties, pore size, and / or materials of construction. In some embodiments, each filter 122a may be independently selected from the group consisting of a particle removal filter, an ion exchange filter, and an ion absorption filter.

[0068] In some embodiments, filter 122a may include an ion-absorbing membrane (such as that described above with respect to filter 118a) for removing fine charged particles and / or metal ions in the organic solvent being purified. In some embodiments, filter 122a may include a filtration medium having an average pore size (also referred to herein as a fourth average pore size) of about 10 nm or less (e.g., about 7 nm or less, about 5 nm or less, about 3 nm or less, or about 1 nm or less) and / or about 1 nm or more (e.g., about 3 nm or more, or about 5 nm or more). In some embodiments, filter 122a may perform both a sieving function (e.g., to remove particulates) and an ion exchange function (e.g., to remove charged particles and / or metal ions). In some embodiments, the average pore size of the filtration medium in filter 122a may be smaller than the average pore size of the filtration medium in filter 118a. In such embodiments, filter 122a may be used to remove particles smaller than those removed by filter 118a.

[0069] Examples of suitable materials that can be used as the filtration media in filter 122a include polypropylene (e.g., high density polypropylene), polyethylene (e.g., high density polyethylene or ultra-high molecular weight polyethylene), nylon (e.g., nylon 6 or nylon 66), polytetrafluoroethylene, or perfluoroalkoxyalkane polymers. In some embodiments, filter 122a, as well as filters 112a, 114a, 116a, and 118a described above, can be made from non-fluoropolymers.

[0070] In some embodiments, the filters 122a (e.g., ion absorption filters) may have the same characteristics (e.g., the same pore size) except that they are made from different materials. For example, in some embodiments, if the filtration medium in one filter 122a is made from ultra-high molecular weight polyethylene, the filtration medium in another filter 122a may be made from a fluoropolymer (e.g., PTFE). Without wishing to be bound by theory, it is believed that using a combination of filters 122a having filtration media made from different materials can maximize the reduction of impurities, particles, and metal ions to obtain ultra-high purity organic solvents.

[0071] In some embodiments, at least some (e.g., all) of the filters 122a may be arranged in parallel within the filter unit 122, and the remaining filters 122a (if any) within the filter unit 122 may be arranged in series. In some embodiments, the number of filters 122a (e.g., arranged in parallel) within the filter unit 122 may be greater than the number of filters 118a within the filter unit 118. For example, if the filter unit 118 includes three filters 118a, the filter unit 122 may have four or more (e.g., six) filters 122a arranged in parallel. Without wishing to be bound by theory, it is believed that an advantage of having more filters arranged in parallel within the filter unit 122 than within the filter unit 118 is that the system 10 may provide increased flow rates and have improved productivity. Without wishing to be bound by theory, it is believed that if the average pore size of the filtration medium in filter 122a is smaller than the average pore size of the filtration medium in filter 118a, the flow rate of the organic solvent through filter 112a may be reduced compared to the flow rate of the organic solvent through filter 118a. It is believed that placing the pumps 122a in parallel can increase the flow rate and productivity of the system 10.

[0072] In some embodiments, the filter unit 122 may include six filters 122a arranged in parallel and having an average pore size of about 3 nm and made from ultra-high molecular weight polyethylene.

[0073] 1 , the second filtration system 120 includes an optional recirculation conduit 160 f for recirculating the partially purified organic solvent to the storage tank 130 to form a recirculation loop for reprocessing by the filter unit 122 in the second filtration system 120. In some embodiments, the partially purified organic solvent is recirculated at least two times (e.g., at least three times, at least four times, or at least five times) before the purification process is completed and the organic solvent is transferred to the packaging station 140. In some embodiments, without wishing to be bound by theory, it is believed that recirculating the partially purified solvent more than two times within the second filtration system 120 may not achieve further improvement in impurity removal. In the example shown in FIG. 1 , the recirculation conduit 160 f is configured downstream of the outlet port 120 b of the second filtration system 120. In other examples, the recirculation conduit 160 f may be configured upstream of the outlet port 120 b.

[0074] In some embodiments, second filtration system 120 may include one or more optional temperature control units 180 (e.g., heat exchangers) in any suitable location. For example, temperature control unit 180 may be configured along recirculation conduit 160f. In some embodiments, temperature control unit 180 may be configured between inlet port 120a and filter unit 122, and between filter unit 122 and outlet port 120b. In some embodiments, temperature control unit 180 may be configured for a temperature of about 80°F or less (e.g., about 75°F or less, about 70°F or less, or about 65°F or less) and / or about 30°F or more (e.g., about 40°F or more, about 50°F or more, or about 60°F or more), thereby maintaining the temperature of the organic solvent in second filtration system 120 at about 80°F or less.

[0075] In some embodiments, packaging station 140 may be a mobile storage tank (e.g., a tank on a tanker) or a fixed storage tank. In some embodiments, packaging station 140 may be a fluoropolymer-lined device (e.g., the interior surface may include a fluoropolymer such as PTFE).

[0076] The present disclosure also features a method for purifying a solvent (e.g., an organic solvent). Generally, the purification method can include passing the solvent through at least two ion exchange filter units (e.g., filter unit 114 and filter unit 116 shown in FIG. 1 ), where one filter unit is a cationic ion exchange filter unit (i.e., includes one or more filters containing negatively charged ion exchange resins) and the other filter unit is an anionic ion exchange filter unit (i.e., includes one or more filters containing positively charged ion exchange resins).

[0077] For example, referring to FIG. 1 , unpurified or unprocessed solvent (i.e., starting material) is purified by purification system 10 by passing the solvent from supply unit 20 through filter units 112, 114, 116, and 118 in first filtration system 110 (as described above, filter units 114 and 116 are ion exchange filter units containing differently charged ion exchange resins) to be collected in storage tank 130, and passing the solvent from storage tank 130 through filter unit 122 in second filtration system 120 (e.g., having a capacity of about 100-1000 liters) to packaging station 140. In some embodiments, the purification methods described herein may include recirculating the solvent at least once (e.g., two or three times) through a recirculation loop in second filtration system 120 (e.g., via storage tank 130, filter unit 122, and recirculation conduit 116h) before transferring the purified solvent to packaging station 140. In some embodiments, the purification methods described herein may include recirculating the solvent at least once (e.g., two or three times) through a recirculation loop in first filtration system 110 (e.g., via filter units 112, 114, 116, and 118 and recirculation conduit 160h) before transferring the partially purified solvent to storage tank 130.

[0078] In some embodiments, the crude or pre-processed solvent may comprise an organic solvent containing a metal element selected from the group consisting of sodium (Na), potassium (K), aluminum (Al), calcium (Ca), copper (Cu), iron (Fe), chromium (Cr), nickel (Ni), zinc (Zn), and lead (Pb). In some embodiments, the content of each metal component in the pre-processed solvent is in the range of about 0.1 to 1000 ppt by weight (e.g., 200 to 1000 ppt by weight or 500 to 1000 ppt by weight).

[0079] 1, when the raw solvent reaches a temperature control unit (e.g., unit 100, or a subsequent temperature control unit such as units 170 and 180), the temperature of the solvent can be adjusted to a predetermined optimal temperature range (e.g., 30°F to 80°F, 30°F to 70°F, 41°F to 67°F, or 50°F to 65°F). For example, the solvent temperature can be adjusted to 70°F, 68.5°F, or 67.5°F. Generally, the temperature control unit can maintain or adjust the temperature of the solvent at a specific location within purification system 10 (e.g., before entering a filter) or throughout purification system 10.

[0080] At the end of processing by the first and second filtration systems 110 and 120, if the number of particles and the amount of impurities detected in the purified solvent are controlled within a predetermined range, an ultra-high purity solvent (e.g., containing 0.1 to 100 parts per trillion by mass of metal components, such as those selected from the group of metal elements consisting of Cu, Fe, Cr, K, Ni, and Zn) is produced. The ultra-high purity solvent can then be transferred to either a packaging station 140 or a manufacturing process for producing semiconductor products.

[0081] In some embodiments, solvents purified by the methods and systems described herein may have a purity of about 99.5% or greater (e.g., about 99.9% or greater, about 99.95% or greater, about 99.99% or greater, about 99.995% or greater, or about 99.999% or greater). In some embodiments, solvents purified by the methods and systems described herein may contain various metal impurities (e.g., including one of Cu, Fe, Cr, K, Ni, and Zn) or elemental metals (e.g., Cu, Fe, Cr, K, Ni, or Zn) in amounts of about 5 ppb or less (e.g., about 1 ppb or less, about 500 ppt or less, about 100 ppt or less, about 80 ppt or less, about 60 ppt or less, about 50 ppt or less, about 30 ppt or less, about 20 ppt or less, about 15 ppt or less, about 12 ppt or less, about 10 ppt or less, about 8 ppt or less, about 6 ppt or less, about 5 ppt or less, about 4 ppt or less, about 2 ppt or less, or about 1 ppt or less) and / or 0 ppt of solvent.

[0082] In some embodiments, solvents purified by the methods and systems described herein can form films or coatings on an entire wafer (e.g., a 12-inch wafer) with particle counts of about 500 or less (e.g., about 450 or less, about 400 or less, about 350 or less, about 300 or less, about 250 or less, about 200 or less, about 150 or less, about 100 or less, about 50 or less, or about 25 or less) or 0. ... (c) On the basis of the above, a film or coating can be formed having an on-wafer metal count of about 100 or less (e.g., about 90 or less, about 80 or less, about 70 or less, about 60 or less, about 50 or less, about 40 or less, about 30 or less, about 20 or less, or about 10 or less) or 0 (e.g., either the total on-wafer metal count or the on-wafer metal count of a specific metal, such as Fe or Ni). In some embodiments, solvents purified by the methods and systems described herein may form films or coatings having a defect density (i.e., based on the total number of metals and particles on the wafer) of about 1.5 or less (e.g., about 1.4 or less, about 1.2 or less, about 1 or less, about 0.8 or less, about 0.6 or less, about 0.5 or less, about 0.4 or less, about 0.2 or less, about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.03 or less, about 0.02 or less, about 0.01 or less, about 0.007 or less, about 0.005 or less, about 0.004 or less, about 0.003 or less) or zero per square centimeter on an entire wafer (e.g., a 12-inch wafer).

[0083] In some embodiments, solvents can be purified by the methods and systems described herein at relatively high flow rates (e.g., through the first filtration system 110 or the second filtration system 120) of about 25 L / min or more (e.g., about 30 L / min or more, about 40 L / min or more, about 50 L / min or more, about 60 L / min or more, about 80 L / min or more, about 100 L / min or more, or about 120 L / min or more) and / or about 170 L / min or less (e.g., about 160 L / min or less, about 150 L / min or less, about 140 L / min or less, about 130 L / min or less, about 120 L / min or less, about 110 L / min or less, or about 100 L / min or less). In general, the flow rate of the purifying solvent can vary depending on many factors, including the nature and viscosity of the solvent being purified, the temperature, the number of filters (e.g., arranged in parallel), and the type and number of other equipment used in the purification process. Without wishing to be bound by theory, it is believed that the flow rate of the solvent being purified should not be too high to minimize defects on the wafer and to minimize static charge buildup on the interior surfaces of conduits or vessels (which can erode the conduits or vessels).

[0084] The present disclosure is illustrated in more detail with reference to the following examples, which are for illustrative purposes and should not be construed as limiting the scope of the disclosure. [Example]

[0085] Total and Trace Metals Measurement Overview

[0086] The total trace metal concentration of each solvent sample was tested using inductively coupled plasma mass spectrometry (ICP-MS). Using a method developed by Fujifilm, each sample was tested for the presence of 26 metal species. Detection limits were metal-specific, but typical detection limits ranged from 0.00010 to 0.030 ppb. The concentrations of each metal species were then summed to calculate a value expressed as total trace metals (ppb).

[0087] Example 1

[0088] 4-Methyl-2-pentanol (MIBC) was purified in three purification systems (i.e., purification systems 1, 2, and 3).

[0089] Purification system 1 included a cationic ion exchange filter unit 114 and an anionic ion exchange filter unit 116. Filter unit 114 included one cationic ion exchange filter 114a arranged in parallel and made from negatively charged high density polyethylene (i.e., IonKleen). Filter unit 116 included one anionic ion exchange filter 114b arranged in parallel and made from positively charged nylon (Nylon EMZ). It contained a nonionic ion exchange filter 116a.

[0090] Purification system 2 was similar to purification system 1 except that it did not include filter unit 116. Purification system 3 was similar to purification system 1 except that it did not include filter unit 114.

[0091] The test results are summarized in Table 1 below.

[0092] [Table 1]

[0093] As shown in Table 1, the amount of trace metals purified by Purification System 1 (which includes both cationic and anionic ion exchange filter units) was significantly reduced compared to the amount of trace metals purified by Purification System 2 (which does not include anionic ion exchange resin) or Purification System 3 (which does not include cationic ion exchange resin).

[0094] Although the invention has been described in detail with reference to specific embodiments thereof, it will be understood that modifications and variations are encompassed within the spirit and scope of what is described and claimed.

[0095] The present invention also includes the following aspects. <1> 1. A method for removing metal impurities from an organic solvent, comprising: passing the organic solvent through a first filter unit and a second filter unit to obtain a purified organic solvent; the first filter unit includes a first housing and at least one first filter within the first housing, the first filter including a filtration medium including a positively charged ion exchange resin; the second filter unit includes a second housing and at least one second filter within the second housing, the second filter including a filtration medium including a negatively charged ion exchange resin; method. <2> the filtration media in the first filter or the second filter comprises polyamide, polyolefin, fluoropolymer, or copolymers thereof; <1> The method described below. <3> the filtration media in the first filter comprises polyamide; <1> The method described below. <4> the filtration media in the first filter comprises nylon; <3> The method described below. <5> the filtration media in the first filter includes quaternary ammonium groups; <1> The method described below. <6> the filtration media in the second filter comprises high density polyethylene; <1> The method described below. <7> the filtration media in the second filter comprises sulfonate groups; <1> The method described below. <8> the filtration media in the first filter or the second filter comprises polytetrafluoroethylene; <1> The method described below. <9> The first filter unit includes 1 to 20 first filters, and the second filter unit includes 1 to 20 second filters. <1> The method described below. <10> passing the organic solvent through the first filter unit or the second filter unit is performed at a temperature of about 80° F. or less; <1> The method described below. <11> further comprising passing the organic solvent through at least one heat exchanger to maintain the temperature of the organic solvent at or below about 80°F. <1> The method described below. <12> further comprising passing the organic solvent through at least one particle removal filter unit; the at least one particle removal filter unit is disposed upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit; <1> The method described below. <13> further comprising transferring the purified solvent to a packaging station. <1> The method described below. <14> The organic solvent comprises cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 4-methyl-2-pentanol, or propylene carbonate; <1> The method described below. <15> the organic solvent contains metallic impurities comprising metals selected from the group consisting of alkali metals, alkaline earth metals, main group metals, transition metals, and lanthanide metals; <1> The method described below. <16> The metal impurities include metals selected from the group consisting of Cu, Fe, Cr, K, Ni, and Zn; <15> The method described below. <17> the purified organic solvent contains metal impurities in an amount of about 15 ppt or less of the purified organic solvent; <15> The method described below. <18> 1. A system comprising a first filter unit and a second filter unit in fluid communication with each other, the first filter unit includes a first housing and at least one first filter within the first housing, the first filter including a filtration medium including a positively charged ion exchange resin; the second filter unit includes a second housing and at least one second filter within the second housing, the second filter including a filtration medium including a negatively charged ion exchange resin; system. <19> the filtration media in the first filter or the second filter comprises polyamide, polyolefin, fluoropolymer, or copolymers thereof; <18> The system described in <20> the filtration media in the first filter comprises polyamide; <19> The system described in <21> the filtration media in the first filter comprises nylon; <20> The system described in <22> the filtration media in the first filter includes quaternary ammonium groups; <18> The system described in <23> the filtration media in the second filter comprises high density polyethylene; <18> The system described in <24> the filtration media in the second filter comprises sulfonate groups; <18> The system described in <25> the filtration media in the first filter or the second filter comprises polytetrafluoroethylene; <18> The system described in <26> The first filter unit includes 1 to 20 first filters, and the second filter unit includes 1 to 20 second filters. <18> The system described in <27> further comprising at least one heat exchanger upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit; <18> The system described in <28> further comprising at least one particle removal filter unit upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit; <18> The system described in

Claims

1. 1. A method for removing metal impurities from an organic solvent, comprising: passing the organic solvent through a first filter unit and a second filter unit to obtain a purified organic solvent; the first filter unit includes a first housing and at least one first filter within the first housing, the first filter including a filtration medium including a positively charged ion exchange resin including nylon; the second filter unit includes a second housing and at least one second filter within the second housing, the second filter including a filtration medium including a negatively charged ion exchange resin including high density polyethylene; the purified organic solvent contains metal impurities in an amount of 15 ppt or less in the purified organic solvent; method.

2. The method of claim 1 , wherein the filtration media in the first filter or the second filter comprises a polyamide, a polyolefin, a fluoropolymer, or a copolymer thereof.

3. The method of claim 1 , wherein the filtration media in the first filter comprises a polyamide.

4. The method of claim 1 , wherein the filtration media in the first filter comprises quaternary ammonium groups.

5. The method of claim 1 , wherein the filtration media in the second filter comprises sulfonate groups.

6. The method of claim 1 , wherein the filtration media in the first filter or the second filter comprises polytetrafluoroethylene.

7. 10. The method of claim 1, wherein the first filter unit comprises 1 to 20 first filters and the second filter unit comprises 1 to 20 second filters.

8. 10. The method of claim 1, wherein passing the organic solvent through the first filter unit or the second filter unit is performed at a temperature of 26.7°C (corresponding to 80°F) or less.

9. 10. The method of claim 1, further comprising passing the organic solvent through at least one heat exchanger to maintain the temperature of the organic solvent at or below 80°F.

10. further comprising passing the organic solvent through at least one particle removal filter unit; 2. The method of claim 1, wherein the at least one particle removal filter unit is disposed upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit.

11. The method of claim 1 further comprising transferring the purified solvent to a storage tank.

12. 10. The method of claim 1, wherein the organic solvent comprises cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 4-methyl-2-pentanol, or propylene carbonate.

13. 10. The method of claim 1, wherein the organic solvent contains metallic impurities comprising metals selected from the group consisting of alkali metals, alkaline earth metals, main group metals, transition metals, and lanthanide metals.

14. 14. The method of claim 13, wherein the metallic impurities comprise metals selected from the group consisting of Cu, Fe, Cr, K, Ni, and Zn.

15. 1. A system comprising a first filter unit and a second filter unit in fluid communication with each other, the first filter unit includes a first housing and at least one first filter within the first housing, the first filter including a filtration medium including a positively charged ion exchange resin including nylon; the second filter unit includes a second housing and at least one second filter within the second housing, the second filter including a filtration medium including a negatively charged ion exchange resin including high density polyethylene; system.

16. 16. The system of claim 15, wherein the filtration media in the first filter or the second filter comprises a polyamide, a polyolefin, a fluoropolymer, or a copolymer thereof.

17. 17. The system of claim 16, wherein the filtration media in the first filter comprises polyamide.

18. 16. The system of claim 15, wherein the filtration media in the first filter comprises quaternary ammonium groups.

19. 16. The system of claim 15, wherein the filtration media in the second filter comprises sulfonate groups.

20. 16. The system of claim 15, wherein the filtration media in the first filter or the second filter comprises polytetrafluoroethylene.

21. 16. The system of claim 15, wherein the first filter unit comprises 1 to 20 first filters and the second filter unit comprises 1 to 20 second filters.

22. 16. The system of claim 15, further comprising at least one heat exchanger upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit.

23. 16. The system of claim 15, further comprising at least one particle removal filter unit upstream of the first filter unit and the second filter unit, between the first filter unit and the second filter unit, or downstream of the first filter unit and the second filter unit.

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