Systems and methods for purifying solvents

Abstract

The present disclosure relates to methods and systems for purifying solvents, which can be used, for example, as pre-wet fluids, solution developers, and cleaning agents in multi-step semiconductor manufacturing processes.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the priority of U.S. Provisional Application No. 63 / 038,463, filed on June 12, 2020, the content of which is hereby incorporated by reference in its entirety into this specification.

[0002] 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 having high purity, low on - wafer particle count, and low on - wafer metal count.

Background Art

[0003] The semiconductor industry has achieved a rapid improvement in the integration density of electronic components resulting from the continuous reduction of component size. Ultimately, it becomes possible to integrate more of the smaller components in a given area. These improvements are mainly due to the development of new high - precision and high - resolution processing technologies.

[0004] In the manufacture of high - resolution integrated circuits (ICs), various processing liquids contact bare wafers or wafers with film coatings. For example, the manufacture of fine metal wiring generally includes a procedure of coating a substrate, subsequently coating a pre - wetting liquid, and then coating the substrate with a composite liquid to form a resist film. These processing liquids contain their own components and various additives and are known to be sources of contamination for IC wafers.

[0005] Even if trace amounts of contaminants are present in chemical liquids such as wafer pre-wetting solutions and developers, defects can occur in the resulting circuit patterns. For example, it is known that the presence of very small amounts of metallic impurities can interfere with the performance and stability of semiconductor devices. Depending on the type of metallic contaminant, oxide properties may deteriorate, inaccurate patterns may be formed, or the electrical performance of the semiconductor circuit may be impaired, potentially negatively impacting manufacturing yield.

[0006] Contamination by impurities such as metallic impurities, particulate matter, organic impurities, and moisture can be inadvertently introduced into chemical solutions at various stages of their manufacture. Examples include impurities contained in raw materials, by-products and unreacted reactants generated during chemical solution production, and foreign matter leaching or being extracted from the surfaces of manufacturing equipment, containers used for transportation, storage, and reaction, and reaction vessels. Therefore, reducing and removing insoluble and soluble contaminants from these chemical solutions used in the manufacture of high-precision and ultra-fine semiconductor electronic circuits is a fundamental requirement for producing defect-free ICs.

[0007] From this perspective, in order to produce high-purity chemical solutions essential for the manufacture of ultrafine and ultra-precise semiconductor electronic circuits, it is indispensable to significantly improve and strictly control the standards and quality of the chemical solution manufacturing process and system. [Overview of the project]

[0008] Therefore, ultra-high purity chemicals are required to form high-precision integrated circuits, and improving and controlling the quality of these chemicals is extremely important. Specific critical parameters that are subject to quality improvement and control include reducing the number of metals in the chemicals and on the wafer, reducing the number of particles in the chemicals and on the wafer, reducing defects on the wafer, and reducing organic contaminants.

[0009] In view of the above, this disclosure provides a purification system for producing a solvent for semiconductor manufacturing and a method for purifying a solvent (e.g., an organic solvent) using the same, which controls the amount of particles, metal impurities, organic impurities, and residual water in the solvent within a predetermined range, and provides a purification system and method for producing an ultra-high purity solvent without generating or introducing unknown or unwanted substances. As a result, the generation of residual defects and particle defects is suppressed, and the yield of semiconductor wafers is improved. Furthermore, the inventors have unexpectedly found that by purifying an organic solvent using a first distillation column having an inlet located at approximately 80% to 100% of the height of the first distillation column to remove low-boiling point organic impurities, and a second distillation column having an inlet located at approximately 0% to 30% of the height of the second distillation column to remove high-boiling point organic impurities, energy efficiency can be greatly increased, and the number of metal particles on the wafer and the number of particles on the wafer can be reduced when processing wafers with the purified organic solvent. Furthermore, the inventors have unexpectedly found that preheating the organic solvent to a temperature up to approximately 20°C lower than its boiling point before distillation can significantly improve the efficiency of the purification method described herein, reduce the energy required for solvent distillation, and lower purification costs.

[0010] In one embodiment, the present disclosure features a method for purifying an organic solvent (e.g., a continuous process) comprising: (1) distilling an organic solvent in a first distillation column to obtain an intermediate organic solvent; (2) transferring the intermediate organic solvent to a second distillation column; and (3) distilling the intermediate organic solvent in a second distillation column to obtain a distilled organic solvent. The first distillation column has an inlet located at about 80% to about 100% of the height of the first distillation column (e.g., to remove low-boiling organic impurities). The second distillation column has an inlet located at about 0% to about 30% of the height of the second distillation column (e.g., to remove high-boiling organic impurities).

[0011] In another embodiment, the present disclosure features a system comprising (1) a first distillation column having a first inlet and a first outlet, and (2) a second distillation column located downstream of the first distillation column and having a second inlet and a second outlet. The first inlet is located at approximately 80% to approximately 100% of the height of the first distillation column (for example, to remove low-boiling organic impurities). The second inlet is in fluid communication with the first outlet and is located at approximately 0% to approximately 30% of the height of the second distillation column (for example, to remove high-boiling organic impurities).

[0012] The embodiments may include one or more of the following features:

[0013] In some embodiments, impurities having a boiling point lower than the boiling point of the organic solvent are removed by distilling the organic solvent in a first distillation column. In some embodiments, impurities having a boiling point higher than the boiling point of the organic solvent are removed by distilling the intermediate organic solvent in a second distillation column.

[0014] In some embodiments, the method further includes preheating the organic solvent to a temperature at least about 20°C below the boiling point of the organic solvent before distilling the organic solvent in the first distillation column, and this preheating is performed by a preheater located upstream of the first distillation column and in fluid communication with the first distillation column.

[0015] In some embodiments, the method further comprises passing an organic solvent through a first filter unit upstream of a first distillation column, the first filter unit comprising a first housing and at least one first filter within the first housing, the at least one first filter comprising a filter medium. In some embodiments, the filter medium in the at least one first filter comprises a polyolefin (e.g., polypropylene), a polyamide (e.g., nylon), a fluoropolymer (e.g., polytetrafluoroethylene), or a copolymer thereof. In some embodiments, the filter medium in the at least one first filter has an average pore size of about 50 nm to about 250 nm. In some embodiments, the at least one first filter is a particle removal filter.

[0016] In some embodiments, the method further includes passing the distilled organic solvent through a second filter unit downstream of a second distillation column, the second filter unit comprising a second housing and at least one second filter within the second housing, the at least one second filter comprising a filter medium. In some embodiments, the filter medium in the at least one second filter comprises a polyolefin (e.g., polypropylene), a polyamide (e.g., nylon), a fluoropolymer (e.g., polytetrafluoroethylene), or a copolymer thereof. In some embodiments, the filter medium in the at least one second filter has an average pore size of about 2 nm to about 10 nm. In some embodiments, the at least one second filter is a particle removal filter.

[0017] In some embodiments, the method further includes recirculating the organic solvent exiting the second filter unit. In some embodiments, the recirculation includes moving the organic solvent exiting the second filter unit to a distilled solvent tank, and then passing the organic solvent through the second filter unit, the distilled solvent tank being located between the second distillation column and the second filter unit and being in fluid communication with the second distillation column and the second filter unit.

[0018] In some embodiments, the method further includes transferring the distilled organic solvent to a product container located downstream of the second distillation column and in fluid communication with the second distillation column.

[0019] In some embodiments, the organic solvent includes cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, 4-methyl-2-pentanol, or propylene carbonate.

[0020] In some embodiments, the system further includes a preheater located upstream of the first distillation column and in fluid communication with the first distillation column.

[0021] In some embodiments, the system further includes a first filter unit located upstream of the preheater and in fluid communication with the preheater, the first filter unit comprising a first housing and at least one first filter within the first housing, the at least one first filter comprising a filtration medium.

[0022] In some embodiments, the system further includes a second filter unit downstream of the second distillation column, the second filter unit including a second housing and at least one second filter within the second housing, the at least one second filter containing a filter medium.

[0023] In some embodiments, the system further includes a distilled solvent tank located between a second distillation column and a second filter unit, and in fluid communication with the second distillation column.

[0024] In some embodiments, the system further includes a recirculation loop, which includes a second filter unit and a distilled solvent tank.

[0025] In some embodiments, the system further includes a product container located downstream of the second distillation column and in fluid communication with the second distillation column.

Brief Description of the Drawings

[0026] [Figure 1] FIG. 1 is a schematic diagram showing an example of a purification system employed in a method for purifying an organic solvent according to some embodiments of the present disclosure.

Modes for Carrying Out the Invention

[0027] As defined herein, unless otherwise indicated, all percentages recited are to be understood as weight percentages based on the total weight of the composition. Unless otherwise indicated, the ambient temperature is defined as from about 16°C to about 27°C. As used herein, the term "solvent" means, unless otherwise indicated, a single solvent or a combination of two or more (e.g., three or four) solvents. In the present disclosure, based on the total weight of the composition, "ppm" means "parts per million", "ppb" means "parts per billion", and "ppt" means "parts per trillion".

[0028] Generally, the present disclosure features a system and method for purifying a solvent (e.g., an organic solvent). The solvent herein can be used as a solvent for a wafer processing liquid (e.g., a pre-wet liquid, a developer, a rinse liquid, a cleaning liquid, or a stripping liquid) or a solvent for semiconductor materials used in a semiconductor manufacturing process.

[0029] Prior to application of the purification method of this disclosure, the solvent may contain undesirable amounts of contaminants and impurities (such as organic impurities, metallic impurities, particles, and water). After the solvent has been treated by the purification method of this disclosure, a considerable amount of contaminants and impurities may be removed from the solvent. The pre-processed solvent is also referred to in this disclosure as the “unpurified solvent.” The pre-processed solvent may be synthesized in-house or commercially available through purchase from suppliers. The post-processed solvent is also referred to in this disclosure as the “purified solvent.” The “purified solvent” may contain impurities limited to a predetermined range.

[0030] Generally, the solvents described 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. Suitable organic solvents include methanol, ethanol, 1-propanol, isopropanol, n-propanol, 2-methyl-1-propanol, n-butanol, 2-butanol, tert-butanol, 1-pentanol, 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-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, and 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, methyl pyruvate, monomethyl ether, propylene glycol Examples include methyl 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.

[0031] In some embodiments, the solvent is a pre-wetting solution. Examples of pre-wetting solutions 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 some embodiments, the solvent may be a developer such as n-butyl acetate, or a rinsing liquid such as 4-methyl-2-pentanol (MIBC). In some embodiments, the solvent may be a rinse solvent used in wafer manufacturing processes, such as isopropyl alcohol.

[0032] In some embodiments, the pre-treated or unpurified organic solvent can have a purity of up to about 99.95% (e.g., up to about 99.5%, up to about 99%, up to about 98%, up to about 97%, up to about 96%, or up to about 95%). In some embodiments, the post-treated or purified organic solvent obtained from the methods described herein can have a purity of at least about 99.99% (e.g., at least about 99.995%, at least about 99.999%, at least about 99.9995%, at least about 99.9999%, or 100%). As used herein, “purity” means the weight percentage 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 spectrometer (GC-MS) (e.g., a thermal desorption (TD) GC-MS).

[0033] In some embodiments, the boiling points of the solvents described herein are at most about 200°C (e.g., at most about 175°C or at most about 150°C) or at least about 50°C (e.g., at least about 75°C or at least about 100°C) from the standpoint of improving the manufacturing yield of semiconductor chips. For example, if the solvent is cyclohexanone, its boiling point is about 155.6°C. In this disclosure, boiling point means boiling point measured at 1 atmosphere.

[0034] Generally, impurities in pre-treated organic solvents may include metallic impurities, particles, and other impurities (such as organic impurities and water).

[0035] As described herein, metallic impurities can be in solid form (e.g., elemental metals, particulate metal-containing compounds, etc.). In some embodiments, metallic impurities may include metals selected from the group consisting of alkali metals, alkaline earth metals, main group metals, transition metals, and lanthanide metals. Common examples of metallic impurities include heavy metals such as copper (Cu), iron (Fe), aluminum (Al), chromium (Cr), lead (Pb), nickel (Ni), zinc (Zn), and lead (Pb), as well as alkali metals and alkaline earth metals such as sodium (Na), potassium (K), and calcium (Ca). Depending on the type of metal, metallic impurities can degrade the integrity of the oxide, degrade the MOS gate stack, and shorten the device lifespan. In some embodiments, the content of each metallic component in the pre-treated solvent ranges from about 0.1 ppt to about 2000 ppt (e.g., about 200 ppt to about 1000 ppt, or about 500 ppt to about 1000 ppt).

[0036] In organic solvents purified by the methods described herein, the total trace metal content is within a predetermined range from a mass of 0 (e.g., at least about 1 ppt, at least about 5 ppt, or at least about 10 ppt) to a maximum of about 200 ppt (e.g., a maximum of about 180 ppt, a maximum of about 160 ppt, a maximum of about 150 ppt, a maximum of about 140 ppt, a maximum of about 120 ppt, a maximum of about 100 ppt, a maximum of about 50 ppt, or a maximum of about 20 ppt). Preferably, the content of each trace metal (e.g., Fe, Ni, Cr, Zn, Cu, K, Na, or Ca) is within a predetermined range by mass from 0 (e.g., at least about 1 ppt, at least about 2 ppt, or at least about 3 ppt) to a maximum of about 20 ppt (maximum about 15 ppt, maximum about 10 ppt, maximum about 8 ppt, maximum about 6 ppt, maximum about 5 ppt, maximum about 4 ppt, maximum about 3 ppt, or maximum about 2 ppt).

[0037] In this disclosure, substances having a size of 0.03 μm or larger are referred to as "particles" or "fine particles." Examples of particles include dust, dirt, organic solids, and inorganic solids. Particles may also contain impurities in which metal atoms have formed colloids. The types of metal atoms that readily form colloids are 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 having a size of 0.03 μm or larger (e.g., 0.05 μm or larger) is preferably within a predetermined range of up to about 50 particles per 1 ml of solvent (up to about 40, up to about 20, up to about 10, up to about 5, up to about 1, or 0). The number of "particles" in a liquid medium can be measured by a light scattering type liquid particle counter and is called the liquid particle count (LPC).

[0038] In this specification, organic impurities, unlike organic solvents, refer to organic substances present in a concentration of 5000 ppm by mass or less relative to the total mass of a liquid containing both the organic solvent and the organic impurities. Organic impurities can be volatile organic compounds present in ambient air, even in a cleanroom. Some organic impurities originate from transportation and storage equipment, while others are present in the raw materials from the outset. Other examples of organic impurities include by-products and / or unreacted reactants generated during the synthesis of organic solvents. Examples of organic impurities include aliphatic hydrocarbons (e.g., C8-C24 alkanes or alkenes with 8 or more carbon atoms), aromatic hydrocarbons, ethers, esters, and aldehydes.

[0039] 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 may be at most about 500 ppm (e.g., at most about 400 ppm, at most about 300 ppm, at most about 200 ppm, at most about 100 ppm, at most about 50 ppm, at most about 20 ppm, at most about 10 ppm) and / or at least about 1 ppm (at least about 10 ppm, or at least about 100 ppm). In some embodiments, the purified organic solvent may contain trace amounts (e.g., at most about 1 ppm) of any measurable organic impurities. The content of organic impurities in the solvents described herein can be measured using a gas chromatography-mass spectrometry (GC-MS) instrument (e.g., a thermal desorption (TD) GC-MS instrument).

[0040] In some embodiments, the total amount of water or water content may be up to about 500 ppm (e.g., up to about 300 ppm, up to about 200 ppm, up to about 100 ppm, up to about 50 ppm) and / or at least about 10 ppm (e.g., at least about 50 ppm, at least about 100 ppm, or at least about 150 ppm). In some embodiments, the purified organic solvent is water-free. The water or water content in the solvents described herein can be measured using a volumetric or coulometric Karl Fischer titrator.

[0041] Figure 1 is a schematic diagram showing the configuration of a purification system according to some embodiments of the present disclosure. As shown in Figure 1, the purification system 100 includes a raw material supply container 1, a first filter unit 2, a raw material tank 3, a pump 4, a preheater 5, a first distillation column 6, a condenser 6a, a reboiler 6b, a pump 7, a second distillation column 8, a condenser 8a, a reboiler 8b, a distilled solvent tank 9, a pump 10, a heat exchanger 11, a second filter unit 12a, a third filter unit 12b, and a product container 13, all of which are in fluid communication with each other (for example, via one or more pipes or conduits). In the purification system 100, the distilled solvent tank 9, the pump 10, the heat exchanger 11, the second filter unit 12a, and the third filter unit 12b may be optional and can be in fluid communication with each other via an optional recirculation conduit 150 to form a recirculation loop. In general, the purification system 100 may include other components not shown in Figure 1 (such as pumps, temperature control units, supply ports, outlet ports, or valves).

[0042] Generally, the raw material supply container 1 is configured to hold or transport starting materials (e.g., pre-treated or unrefined organic solvents). By processing the starting materials with the purification system 100, it is possible to manufacture or produce purified organic solvents in which the number of undesirable contaminants (e.g., particulate matter, organic impurities, metallic impurities, and water) is limited to a predetermined range. The type of raw material supply container 1 is not particularly limited as long as it continuously or intermittently supplies the starting materials to the other components of the purification system 100. In some embodiments, the raw material supply container 1 may be a tank such as a stationary tank or a mobile tank. In some embodiments, the raw material supply container 1 may include a raw material containment tank, sensors such as a level gauge (not shown), a pump (not shown), and / or valves (not shown) for controlling the flow of the starting materials.

[0043] The purification system 100 may include at least one (e.g., two or three) pre-distillation filter units and at least one (e.g., two or three) post-distillation filter units. Generally, the pre-distillation filter unit performs initial filtration of the starting material (e.g., unpurified organic solvent) before distillation to remove large particles, and the post-distillation filter unit performs filtration after distillation to remove residual impurities (e.g., metallic or organic impurities) and fine particles to obtain ultra-high purity organic solvent. In some embodiments, each of the pre-distillation filter unit and the post-distillation filter unit may include a filter housing and one or more filters (e.g., 1 to 20 filters) within the filter housing. For example, the purification system 100 shown in Figure 1 includes one pre-distillation filter unit (i.e., the first filter unit 2) and two post-distillation filter units (i.e., the second filter unit 12a and the third filter unit 12b). The first distillation column 6 and the second distillation column 8 shown in Figure 1 are generally used to remove most organic and metallic impurities and particles.

[0044] In some embodiments, each filter unit of the purification system 100 may include a filter housing and one or more filters (e.g., two, three, four, five, six, or seven) within the filter housing. Each filter may be made from a suitable material and may include a filtration medium having a suitable average pore size. The filters may be arranged in parallel or in series within the filter housing. When two filters are arranged in parallel within the filter housing during use, the solvent to be purified passes through these two filters in parallel (i.e., substantially simultaneously). When two filters are arranged in series, the solvent to be purified passes through these two filters sequentially during use. In some embodiments, some filter units may include multiple filters in parallel within the filter housing, thereby increasing the overall flow rate and improving the capacity.

[0045] For example, the purification system 100 shown in Figure 1 includes three filter units (i.e., units 2, 6, and 8), each of which includes a filter housing and one or more filters within the filter housing. In other embodiments, the purification system 100 may also include other purification modules in addition to the three filter units shown in Figure 1.

[0046] Referring to Figure 1, filter units 2, 6, and 8 have different functions or characteristics and can provide different purification processes. In some embodiments, each filter unit can be independently selected from the group consisting of particle removal filters, ion exchange filters, and ion adsorption filters. In some embodiments, the filters housed in each of filter units 2, 6, and 8 may have the same or similar purification functions, physicochemical properties, pore size, and / or structural materials.

[0047] In some embodiments, the purification system 100 may include at least one (e.g., two or three) first filter unit 2 between the raw material supply container 1 and the first distillation column 6, providing fluid communication between the raw material supply container 1 and the first distillation column 6. The first filter unit 2 may include a filter housing and at least one (e.g., two, three, four, or five) filters within the filter housing. In some embodiments, if the first filter unit 2 includes two or more filters, these filters may be arranged in parallel to improve flow rate and capacity.

[0048] In some embodiments, the filter in the first filter unit 2 can be a particle removal filter for removing relatively large particles from the organic solvent. In some embodiments, the filter in the first filter unit 2 may include a filtration medium having an average pore size of up to about 0.25 μm, i.e., up to about 250 nm (e.g., up to about 240 nm, up to about 220 nm, up to about 200 nm, up to about 180 nm, up to about 160 nm, up to about 150 nm) and / or at least about 0.05 μm, i.e., at least about 50 nm (e.g., at least about 60 nm, at least about 70 nm, at least about 80 nm, at least about 90 nm, at least about 100 nm, at least about 110 nm, at least about 120 nm, at least about 130 nm, at least about 140 nm, or at least about 150 nm). Within the above range, foreign matter such as impurities and aggregates contained in the organic solvent can be reliably removed while suppressing clogging of the filter in the first filter unit 2.

[0049] Examples of suitable materials for the filtration medium in the filter within the first filter unit 2 include fluororesins (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymer (PFA), or modified polytetrafluoroethylene (MPTFE)), polyamides such as nylon (e.g., nylon 6 or nylon 66), polyolefins such as polyethylene (PE) and polypropylene (PP) (including high-density and ultra-high molecular weight resins), or copolymers thereof. For example, the filtration medium in a particle removal filter can be made from 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 polymer. Filters made from the above materials can effectively remove foreign matter (e.g., highly polar substances) that are likely to cause residual defects and particle defects, and can efficiently reduce the content of metal components in organic solvents.

[0050] In some embodiments, the first filter unit 2 may include two, three, or four filters arranged in series, having an average pore size of about 50 nm to 200 nm, and containing a filter medium made from polypropylene or polytetrafluoroethylene.

[0051] While not limited to theory, it is believed that using one or more filters containing a filter medium made from polytetrafluoroethylene with an average pore size of approximately 50 nm can significantly reduce the on-wafer metal count and on-wafer particle count of the purified solvent described herein. While not limited to theory, it is believed that filters containing a filter medium made from fluororesin (e.g., polytetrafluoroethylene) may produce fewer on-wafer particles than filters containing a filter medium made from polyolefin (e.g., polypropylene).

[0052] In some embodiments, the purification system 100 may optionally include a raw material tank 3 located between the first filter unit 2 and the first distillation column 6, and in fluid communication with both the first filter unit 2 and the first distillation column 6. The type of raw material tank 3 is not particularly limited, as long as it can hold the solvent filtered by the first filter unit 2. While not theoretical, it is conceivable that the raw material tank 3 can supply sufficient raw materials (e.g., solvent) for the remainder of the purification process, thereby maintaining the purification as a continuous process.

[0053] In some embodiments, the purification system 100 may include a pump 4 and a preheater 5 located between the raw material tank 3 and the first distillation column 6, and having fluid communication with the raw material tank 3 and the first distillation column 6. During use, the pump 4 can supply the solvent in the raw material tank 3 to the preheater 5 to heat it to a predetermined temperature, and then supply it to the first distillation column 6. As used herein, the pump 4 may be any suitable pump for transferring or supplying a liquid at its operating temperature, such as a metering pump or a diaphragm pump.

[0054] In general, the preheater 5 can be any suitable heating device. Examples of preheaters include heat exchangers, electric heaters, steam heaters, or mineral oil heaters. In general, the preheater 5 can heat an organic solvent to a desired temperature. In some embodiments, the preheater 5 can heat the organic solvent from a temperature at least about 20°C (e.g., at least about 19°C, at least about 18°C, at least about 17°C, at least about 16°C, or at least about 15°C) below the boiling point of the organic solvent to a temperature up to about 10°C (e.g., up to about 11°C, up to about 12°C, up to about 13°C, up to about 14°C, or up to about 15°C) below the boiling point of the organic solvent. For example, if the organic solvent to be purified is cyclohexanone (boiling point 155.6°C), the preheater 5 can heat the organic solvent to a temperature of at least about 135°C (e.g., at least about 136°C, at least about 137°C, at least about 138°C, at least about 139°C, or at least about 140°C) up to a maximum of about 145°C (e.g., a maximum of about 144°C, a maximum of about 143°C, a maximum of about 142°C, a maximum of about 141°C, or a maximum of about 140°C). While not strictly theoretical, it is believed that preheating the organic solvent to the above temperatures facilitates the removal of low-boiling point organic impurities from the first distillation column 6, enables the purification process to be carried out continuously, and improves the efficiency and productivity of the purification process. Furthermore, although not limited to theory, if the organic solvent is preheated to too high a temperature (e.g., within 10°C of its boiling point), it is thought that this could lead to temperature overshoot and damage to the equipment (e.g., damage to the heating elements in the heat exchanger), a decrease in product yield (e.g., a certain amount of organic solvent may be removed along with low-boiling point organic impurities by distillation from the top of the first distillation column 6), and an unstable continuous purification process. On the other hand, although not limited to theory, if the organic solvent is preheated to too low a temperature (e.g., more than 20°C below its boiling point), the organic solvent entering the first distillation column 6 may be too low in temperature, potentially interrupting the continuous distillation process, which is thought to reduce the overall efficiency of the purification process.

[0055] In some embodiments, the purification system 100 includes at least two (e.g., three or four) distillation columns. For example, as shown in Figure 1, the purification system 100 includes a first distillation column 6 and a second distillation column 8 located downstream of the preheater 5 and in fluid communication with the preheater 5. Generally, the first distillation column 6 and the second distillation column 8 can be used to purify the organic solvent by distillation and remove most organic and metallic impurities and particles. In some embodiments, the first distillation column 6 can be used to remove impurities having a boiling point lower than the boiling point of the organic solvent. In some embodiments, the second distillation column 8 can be used to remove impurities having a boiling point higher than the boiling point of the organic solvent, as well as metallic impurities and particles that cannot generally be removed by distillation. While not theoretical, it is thought that reversing the order of the first distillation column 6 and the second distillation column 8 would result in a decrease in performance, including an increase in the amount of trace metals, an increase in the number of metals on the wafer, and an increase in the number of particles on the wafer.

[0056] In some embodiments, the first distillation column 6 may include an inlet for receiving the organic solvent from the preheater 5 and a first outlet for supplying the organic solvent to the second distillation column 8. Generally, the inlet is located slightly above the packing material in the first distillation column 6 where the separation of low-boiling organic impurities from the organic solvent to be purified occurs. In some embodiments, the inlet may be located at a height of at least about 80% (e.g., at least about 82%, at least about 84%, at least about 86%, at least about 88%, or at least about 90%) to a maximum of about 100% (e.g., a maximum of about 98%, at a maximum of about 96%, at a maximum of about 94%, at a maximum of about 92%, or at a maximum of about 90%) of the height of the first distillation column. While not theoretical, it is thought that locating the inlet at the above positions can facilitate the removal of low-boiling organic impurities from the first distillation column 6, minimize the energy required to remove such impurities, and increase the efficiency of the purification process. Generally, the first outlet can be located at the bottom of the reboiler 6b of the first distillation column 6.

[0057] As shown in Figure 1, the first distillation column 6 includes a condenser 6a at the top and a reboiler 6b at the bottom. The condenser 6a can cool or condense low-boiling point organic impurities exiting the second outlet of the first distillation column 6 into a liquid, which can then be transferred to a waste container. Examples of condensers 6a include water-cooled condensers (such as tube-and-coil condensers, double-tube condensers, or tube-and-shell condensers) and air-cooled condensers. The reboiler 6b can supply heat to the organic solvent to be purified in the distillation column 6 to remove impurities with boiling points lower than the boiling point of the organic solvent from the top of the distillation column 6, and the partially purified organic solvent can be heated to an appropriate temperature (e.g., ±2°C above the boiling point of the organic solvent) before being transferred to the second distillation column 8, thereby improving the efficiency and productivity of the purification process. Examples of reboilers 6b include electric heaters, steam heaters, or mineral oil heaters.

[0058] During operation, low-boiling point organic impurities, upon entering the first distillation column 6 through the inlet, are distilled and removed from the top of the distillation column 6 through a second outlet for discharging low-boiling point organic impurities, cooled by a condenser 6a to a liquid, and transferred to a waste container (not shown in Figure 1). Since the organic solvent is preheated to a relatively high temperature, low-boiling point organic impurities can be separated from the organic solvent to be purified and distilled without the use of packing material, thereby reducing the energy required for distillation and the associated costs. The organic solvent to be purified is collected at the bottom of the first distillation column 6 as an intermediate organic solvent and can exit the first distillation column 6 through the aforementioned first outlet at the bottom of the reboiler 6b. The intermediate organic solvent that has exited the first distillation column 6 can be heated to a desired temperature by the reboiler 6b and then supplied to the second distillation column 8 via a pump 7. The pump 7 can be any high-purity pump that contains little to no metal components, for example, a diaphragm pump with PTFE contained in part or all of its inner surface.

[0059] In some embodiments, the second distillation column 8 may include an inlet for receiving the organic solvent from the first distillation column 6 and a first outlet for supplying the distilled organic solvent to the product container 13. Generally, the inlet is positioned slightly below the packing material in the second distillation column 8. In some embodiments, the inlet can be positioned from at least about 0% (e.g., at least about 5%, at least about 10%, at least about 15%, at least about 20%, or at least about 25%) to a maximum of about 30% (e.g., a maximum of about 25%, a maximum of about 20%, a maximum of about 15%, a maximum of about 10%, or a maximum of about 10%) of the height of the second distillation column. While not theoretical, it is thought that positioning the inlet in the above locations makes it easier to separate the organic solvent by distillation from high-boiling point organic impurities (e.g., those with a boiling point higher than the boiling point of the organic solvent to be purified), metallic impurities, and particles, and to remove these impurities from the second distillation column 8. Generally, the first outlet can be located at the top of the condenser 8a of the second distillation column 8 and above the packing material in the second distillation column 8.

[0060] As shown in Figure 1, the second distillation column 8 includes a condenser 8a at the top and a reboiler 8b at the bottom. The condenser 8a can cool or condense the organic solvent to be purified into a liquid, which can then be transferred to the distilled solvent tank 9. Examples of condensers 8a include water-cooled condensers (such as tube-and-coil condensers, double-tube condensers, or tube-and-shell condensers) and air-cooled condensers. The reboiler 8b can supply heat to the organic solvent to be purified and distill it from the top of the second distillation column 8 to remove impurities having a boiling point higher than the boiling point of the organic solvent from the bottom of the second distillation column 8. In some embodiments, the reboiler 8b maintains the temperature of the organic solvent within ±2°C of its boiling point. Examples of reboilers 8b include electric heaters, steam heaters, or mineral oil heaters.

[0061] During operation, as the organic solvent enters the second distillation column 8 through the inlet, it is separated by distillation from high-boiling organic impurities, metallic impurities, and particles, and can be recovered as distilled organic solvent from the top of the second distillation column 8 through the first outlet located above the condenser 8a. The high-boiling organic impurities, metallic impurities, and particles can be recovered from the bottom of the second distillation column 8 through the second outlet to feed these impurities into a waste container (not shown in Figure 1).

[0062] In some embodiments, the purification system 100 may optionally include at least one (e.g., two or three) distilled solvent tanks 9 located between a second distillation column 8 and an optional second filter unit 12a, and in fluid communication with the second distillation column 8 and unit 12a. Generally, the distilled solvent tanks 9 can be any suitable tank known in the art that can be used to store distilled organic solvents. In some embodiments, the distilled solvent tanks 9 may be filled with nitrogen to minimize moisture and oxidation of the solvent stored in the tanks. In some embodiments, during the purification process, if the purity level of the distilled organic solvent exiting the second distillation column 8 meets certain requirements (e.g., having a purity of at least about 99.99%, a maximum moisture content of about 100 ppm, and / or a total amount of metal impurities of up to about 200 ppt), the organic solvent may be transferred to a product container 13 without passing through tanks 9, filter unit 12a, or filter unit 12b. On the other hand, if the distilled organic solvent exiting the second distillation column 8 does not meet the required criteria, the organic solvent can first be transferred to the distilled solvent tank 9 and then passed through filter units 12a and / or 12b to remove additional impurities. Similarly, if the purity level of the organic solvent exiting filter units 12a and / or 12b meets the required criteria, the organic solvent can be transferred to the product container 13. On the other hand, if the purity level of the purified organic solvent exiting filter units 12a and / or 12b does not meet the required criteria, the organic solvent can be returned to the distilled solvent tank 9 through an optional recirculation conduit 150 and purified again by filter units 12a and / or 12b.

[0063] In general, the distilled solvent tank 9 can be any suitable container for storing the chemical solution. In some embodiments, the distilled solvent tank 9 can have a suitable volume. For example, the distilled solvent tank 9 can have a volume of at least about 1,000 liters (e.g., at least about 2,000 liters, at least about 3,000 liters, or at least about 5,000 liters) and / or up to about 30,000 liters (e.g., up to about 25,000 liters, up to about 20,000 liters, up to about 15,000 liters, or up to about 10,000 liters).

[0064] In some embodiments, if the distilled organic solvent requires further purification, it can be supplied from the distilled solvent tank 9 to a second filter unit 12a via pump 10 and heat exchanger 11. Pump 10 can be any pump capable of recirculating through the tank and filter, such as an electromagnetic pump or a centrifugal pump. Generally, the heat exchanger 11 can be used to control the temperature of the organic solvent during the subsequent filtration process. Not limited to theory, if the filtration temperature is too high, it is thought that side reactions will occur in the filtration process, thereby increasing the amount of impurities in the solvent. Furthermore, not limited to theory, if the filtration temperature is too low, the solvent may have increased viscosity, which may reduce the flow rate. In some embodiments, the heat exchanger 11 can control the filtration temperature to about 10°C to about 20°C to avoid underperformance or to avoid side reactions.

[0065] In some embodiments, the purification system 100 may optionally include at least one (e.g., two or three) second filter unit 12a located between the distilled solvent tank 9 and the third filter unit 12b, and in fluid communication with the distilled solvent tank 9 and the unit 12b. In some embodiments, the second filter unit 12a may include a filter housing and at least one (e.g., two, three, four, five, six, or seven) filters within the filter housing. The filters within the second filter unit 12a may be particle removal filters for removing relatively small particles from the organic solvent. In some embodiments, the filter in the second filter unit 12a may include a filter medium having an average pore size of up to about 10 nm (e.g., up to about 9 nm, up to about 8 nm, up to about 7 nm, up to about 6 nm, up to about 5 nm, or up to about 4 nm) and / or at least about 2 nm (e.g., at least about 3 nm, at least about 4 nm, at least about 5 nm, at least about 6 nm, at least about 7 nm, or at least about 8 nm). In some embodiments, the average pore size of the filter medium in the filter in the second filter unit 12a may be smaller than the average pore size of the filter medium in the filter in the first filter unit 2. In such embodiments, the second filter unit 12a can be used to remove particles smaller than those removed by the first filter unit 2.

[0066] Examples of suitable materials for the filtration medium in the filter within the second filter unit 12a include fluororesins (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymer (PFA), or modified polytetrafluoroethylene (MPTFE)), polyamides such as nylon (e.g., nylon 6 or nylon 66), polyolefins such as polyethylene (PE) and polypropylene (PP) (including high-density and ultra-high molecular weight resins), or copolymers thereof. For example, the filtration medium in a particle removal filter can be made from 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 polymer.

[0067] In some embodiments, the second filter unit 12a may include 3 to 7 filters arranged in series, having an average pore size of about 5 nm, and containing a filtration medium made of nylon.

[0068] In some embodiments, the purification system 100 may optionally include at least one (e.g., two or three) third filter unit 12b located between the second filter unit 12a and the product container 13 (i.e., downstream of unit 12b) and in fluid communication with the second filter unit 12a and the product container 13. In some embodiments, the third filter unit 12b may include a filter housing and at least one (e.g., two, three, four, or five) filters within the filter housing. The filters within the third filter unit 12b may be particle removal filters for removing relatively small particles from the organic solvent. In some embodiments, the filter in the third filter unit 12b may include a filter medium having an average pore size of up to about 10 nm (e.g., up to about 9 nm, up to about 8 nm, up to about 7 nm, up to about 6 nm, up to about 5 nm, or up to about 4 nm) and / or at least about 2 nm (e.g., at least about 3 nm, at least about 4 nm, at least about 5 nm, at least about 6 nm, at least about 7 nm, or at least about 8 nm). In some embodiments, the average pore size or filter medium in the filter in the third filter unit 12b may differ from the average pore size or filter medium in the filter in the second filter unit 12a. In such embodiments, the third filter unit 12b can be used to remove particles having a different size or properties than the particles removed by the second filter unit 12a. For example, if the second filter unit 12a includes a filter with a nylon filter medium, the third filter unit 12b may include a filter with a PTFE filter medium. While not strictly theoretical, nylon filters are thought to contain a non-sieving mechanism that can remove metal particles, while PTFE filters are thought to contain a sieving mechanism that can remove particles based on pore size.

[0069] Examples of suitable materials for the filtration medium in the filter within the third filter unit 12b include fluororesins (e.g., polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane polymer (PFA), or modified polytetrafluoroethylene (MPTFE)), polyamides such as nylon (e.g., nylon 6 or nylon 66), polyolefins such as polyethylene (PE) and polypropylene (PP) (including high-density and ultra-high molecular weight resins), or copolymers thereof. For example, the filtration medium in a particle removal filter can be made from 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 polymer. A filter made of the above materials can effectively remove foreign matter (e.g., highly polar substances) that are prone to causing residual defects and particle defects, and can efficiently reduce the content of metal components in organic solvents.

[0070] In some embodiments, the third filter unit 12b may include two to five filters arranged in series, having an average pore size of about 5 nm, and made from polytetrafluoroethylene.

[0071] In some embodiments, the purification system 100 may optionally include a recirculation conduit 150 to recirculate the partially-purified organic solvent back to the distilled solvent tank 9 and form a recirculation loop (which may include the distilled solvent tank 9, a pump 10, a heat exchanger 11, and filter units 12a and 12b) for further purification by filter units 12a and / or 12b. In some embodiments, the partially-purified organic solvent may be recirculated through the recirculation loop at least twice (e.g., at least three times, at least four times, or at least five times) before the organic solvent is transferred to the product container 13.

[0072] In some embodiments, the product container 13 may be a mobile storage tank (e.g., a tank on a tanker) or a fixed storage tank. In some embodiments, the product container 13 may be a fluororesin-lined facility (e.g., its inner surface may contain a fluororesin such as PTFE). In some embodiments, the product container 13 may have a volume of at least about 200 liters (e.g., at least about 300 liters, or at least about 500 liters) and / or up to about 1,500 liters (e.g., up to about 1,200 liters, up to about 1,000 liters, up to about 900 liters, up to about 800 liters, up to about 700 liters, or up to about 600 liters).

[0073] The disclosure also features a method for purifying a solvent (e.g., an organic solvent such as cyclohexanone). In some embodiments, the purification method may include (1) distilling the organic solvent in a first distillation column (e.g., a first distillation column 6) to obtain an intermediate organic solvent, the first distillation column having an inlet located at about 80% to about 100% of the height of the first distillation column; (2) transferring the intermediate organic solvent to a second distillation column (e.g., a second distillation column 8), the second distillation column having an inlet located at about 0% to about 30% of the height of the second distillation column; and (3) distilling the intermediate organic solvent in the second distillation column to obtain a distilled organic solvent.

[0074] For example, referring to Figure 1, an unpurified or pre-treated solvent (i.e., starting material) can be purified by the purification system 100 by passing the solvent from the material supply container 1 to the material tank 3 through the first filter unit 2 (where the solvent is pre-filtered). The solvent can then be transferred by pump 4 to a preheater 5, where it is preheated to a temperature of at least 20°C above its boiling point. After preheating, the solvent can be transferred to a first distillation column 6 to remove low-boiling organic impurities, and then to a second distillation column 8 to remove high-boiling organic impurities, metallic impurities, and particles. If further purification of the distilled solvent that has exited the second distillation column 8 is required, the distilled solvent can be supplied to a distilled solvent tank 9, and then supplied to filter units 12a and / or 12b through pump 10 and heat exchanger 11. If the solvent filtered by filter units 12a and / or 12b needs to be further purified, the solvent can be recirculated to the distilled solvent tank 9 through the recirculation conduit 150 and then filtered again by filter units 12a and / or 12b.

[0075] When the number of particles and the amount of impurities detected in the purified solvent at the end of the purification process are controlled to be within a predetermined range, an ultra-high purity solvent (for example, having a purity of at least about 99.99%, a maximum water content of about 100 ppm, and / or a total amount of metal impurities of up to about 200 ppt) is produced. The ultra-high purity solvent can then be transferred to a product container 13 for storage or to a manufacturing process for producing semiconductor products.

[0076] In some embodiments, solvents purified by the methods and systems described herein can form a film or coating on an entire wafer (e.g., a 12-inch wafer) having a maximum of about 500 particles (e.g., up to about 450, up to about 400, up to about 350, up to about 300, up to about 250, up to about 200, up to about 150, up to about 100, up to about 50, or up to about 25) or 0 particles (e.g., at least about 1, at least about 2, or at least about 5). 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) having a wafer metal count (e.g., total wafer metal count, or wafer metal count of a specific metal such as Fe or Ni) of up to about 100 (e.g., up to about 90, up to about 80, up to about 70, up to about 60, up to about 50, up to about 40, up to about 30, up to about 20, or up to about 10, up to about 5) or 0 (e.g., at least about 1, or at least about 2). In some embodiments, solvents purified by the methods and systems described herein can form a film or coating on an entire wafer (e.g., a 12-inch wafer) having a defect density of up to about 0.8 defects per square centimeter (e.g., up to about 0.7, up to about 0.6, up to about 0.5, up to about 0.4, up to about 0.3, up to about 0.2, up to about 0.1, up to about 0.07, up to about 0.05, up to about 0.03, up to about 0.02, up to about 0.01, up to about 0.007, up to about 0.005, up to about 0.004, up to about 0.003) or 0 defects (e.g., at least about 0.001, at least about 0.01, or at least about 0.1) (i.e., based on the total number of metals and particles on the wafer).

[0077] In some embodiments, the methods described herein may be either a continuous process or a batch process. When the methods described herein are a continuous process, the solvent may be purified at a relatively high flow rate. For example, the solvent may be purified through the purification system 10 at a flow rate of at least about 0.2 L / min (e.g., at least about 0.3 L / min, at least about 0.4 L / min, or at least about 0.5 L / min) and / or up to about 1 L / min (e.g., up to about 0.9 L / min, up to about 0.8 L / min, up to about 0.7 L / min, or up to about 0.6 L / min). Generally, the flow rate for purifying the solvent may vary depending on several factors, including the properties and viscosity of the solvent to be purified, the temperature, the number of filters (e.g., those arranged in parallel), and the type and number of other devices used in the purification process.

[0078] This disclosure is described in more detail with reference to the following embodiments, which are for illustrative purposes only and should not be construed as limiting the scope of this disclosure. [Examples]

[0079] General explanation of OWPC and OWMC measurements A solvent sample was collected and inserted into a wafer coating apparatus. After coating a bare wafer with the sample, the wafer was transferred to a laser inspection system for inspection. This laser inspection system used laser light to detect and count each particle on the wafer with a detection limit of 19 nm, and recorded the position and size of each particle. More specifically, particles larger than 19 nm were counted. Using this data, a wafer map was created and the total number of particles on the wafer (OWPC: On-Wafer Particle Counts) was calculated.

[0080] Next, the wafer was transferred and inspected using energy-dispersive X-ray (EDX). Each particle reported by the laser inspection system was also inspected using EDX to obtain elemental information. Any particle confirmed to generate any metallic signal exceeding a threshold calculated from a reference signal was counted as a metal-containing particle. The total number of particles with a metallic signature was tallied and reported as the On-Wafer Metal Particle (OWMP).

[0081] Example 1 The solvent purified in this example is cyclohexanone. Referring to Figure 1, cyclohexanone was purified using the following five purification systems (i.e., systems 1 to 5), each system comprising at least a pre-filter unit 2 and two distillation filtration systems 6 and 8. The differences between systems 1 to 5 are as follows.

[0082] In System 1, the first distillation column 6, pump 7, and second distillation column 8 were arranged in the order of second distillation column 8, pump 7, and first distillation column 6. System 1 also included one 200 nm polypropylene filter (i.e., a filter made of polypropylene with a filtration medium having an average pore size of 200 nm) in the first filter unit 2, but did not include a distilled solvent tank 9, pump 10, heat exchanger 11, second filter unit 12a, third filter unit 12b, and recirculation conduit 150.

[0083] In System 2, the first distillation column 6, pump 7, and second distillation column 8 were arranged in the order of first distillation column 6, pump 7, and second distillation column 8. Also, System 2 included one 200 nm polypropylene filter in the first filter unit 2, but did not include the distilled solvent tank 9, pump 10, heat exchanger 11, second filter unit 12a, third filter unit 12b, and recirculation conduit 150.

[0084] In System 3, the first distillation column 6, pump 7, and second distillation column 8 were arranged in the order of first distillation column 6, pump 7, and second distillation column 8. Also, System 3 included one 50 nm PTFE filter (i.e., a filter made of PTFE with a filtration medium having an average pore size of 50 nm) in the first filter unit 2, but did not include the distilled solvent tank 9, pump 10, heat exchanger 11, second filter unit 12a, third filter unit 12b, and recirculation conduit 150.

[0085] In System 4, the first distillation column 6, pump 7, and second distillation column 8 were arranged in the order of the first distillation column 6, pump 7, and second distillation column 8. System 4 also included one 50 nm PTFE filter in the first filter unit 2, a distilled solvent tank 9, a pump 10, a heat exchanger 11, seven 5 nm nylon filters arranged in series in the second filter unit 12a (i.e., filters made from nylon with a filtration medium of 5 nm), and a recirculation conduit 150, but did not include a third filter unit 12b. During purification, cyclohexanone was recirculated twice through the recirculation loop (i.e., filtered three times by filter unit 12a).

[0086] In System 5, the first distillation column 6, pump 7, and second distillation column 8 were arranged in the order of the first distillation column 6, pump 7, and second distillation column 8. System 5 also includes one 50 nm PTFE filter in the first filter unit 2, a distilled solvent tank 9, a pump 10, a heat exchanger 11, seven 5 nm nylon filters arranged in series in the second filter unit 12a, two 5 nm PTFE filters arranged in series in the third filter unit 12b (i.e., filters made from PTFE with a filtration medium having an average pore size of 5 nm), and a recirculation conduit 150. During purification, cyclohexanone was recirculated twice through the recirculation loop (i.e., filtered three times by filter units 12a and 12b).

[0087] The properties of cyclohexanone purified by the above-described systems 1 to 5 (including the number of particles on the wafer, the total number of metal particles on the wafer, the number of iron particles on the wafer, and the number of aluminum particles on the wafer) were evaluated and summarized in Table 1 below.

[0088] [Table 1]

[0089] As shown in Table 1, cyclohexanone purified by System 1 exhibited saturated, high wafer particle counts, total wafer metal counts, wafer iron counts, and wafer aluminum counts. Surprisingly, cyclohexanone purified by Systems 2-5 exhibited significantly lower wafer particle counts, total wafer metal counts, wafer iron counts, and wafer aluminum counts than cyclohexanone purified by System 1.

[0090] More specifically, System 1 differs from System 2 in the order of its two distillation columns. In other words, the cyclohexanone purified by System 1 was first distilled in a column with an inlet at the bottom, and then in a column with an inlet at the top. On the other hand, the cyclohexanone purified by System 2 was first distilled in a column with an inlet at the top, and then in a column with an inlet at the bottom. Surprisingly, it was found that System 2 could significantly reduce the number of particles on the wafer, the total number of metals on the wafer, the number of iron particles on the wafer, and the number of aluminum particles on the wafer compared to System 1.

[0091] Furthermore, System 3 differs from System 2 in that it replaces the 200nm propylene prefilter with a 50nm PTFE prefilter. Surprisingly, it was found that System 3 can significantly reduce the number of particles on the wafer, the total number of metal particles on the wafer, the number of iron particles on the wafer, and the number of aluminum particles on the wafer compared to System 2.

[0092] Furthermore, System 4 differs from System 3 in that it includes a 5nm nylon filter after the second distillation column. Surprisingly, it was found that System 4 can significantly reduce the number of particles on the wafer, the total number of metal particles on the wafer, the number of iron particles on the wafer, and the number of aluminum particles on the wafer compared to System 3.

[0093] Finally, System 5 differs from System 4 in that it includes a 5nm PTFE filter after the 5nm nylon filter. Surprisingly, the results showed that System 5 could further reduce the number of particles on the wafer, the total number of metal particles on the wafer, the number of iron particles on the wafer, and the number of aluminum particles on the wafer compared to System 4.

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

Claims

1. A method for purifying an organic solvent having a boiling point in the range of 100°C to 200°C, The method involves distilling the aforementioned organic solvent in a first distillation column to obtain an intermediate organic solvent, wherein the first distillation column has an inlet positioned at 80% to 100% of the height of the first distillation column, and by distilling the organic solvent in the first distillation column, impurities having a boiling point lower than the boiling point of the organic solvent are removed to obtain an intermediate organic solvent. The intermediate organic solvent is transferred to a second distillation column, wherein the second distillation column has an inlet located at a position between 0% and 30% of the height of the second distillation column. The intermediate organic solvent is distilled in the second distillation column to obtain the distilled organic solvent. A method that includes this.

2. The method according to claim 1, wherein the intermediate organic solvent is distilled in the second distillation column to remove impurities having a boiling point higher than the boiling point of the organic solvent.

3. The method according to claim 1, further comprising preheating the organic solvent to a temperature at least 20°C below the boiling point of the organic solvent before distilling the organic solvent in the first distillation column, wherein the preheating is performed by a preheater located upstream of the first distillation column and in fluid communication with the first distillation column.

4. The method according to claim 1, further comprising passing the organic solvent through a first filter unit upstream of the first distillation column, wherein the first filter unit comprises a first housing and at least one first filter within the first housing, and the at least one first filter comprises a filtration medium.

5. The method according to claim 4, wherein the filtration medium in the at least one first filter comprises a polyolefin, a polyamide, a fluororesin, or a copolymer thereof.

6. The method according to claim 5, wherein the filtration medium in the at least one first filter comprises polypropylene or polytetrafluoroethylene.

7. The method according to claim 4, wherein the filtration medium in the at least one first filter has an average pore size of 50 nm to 250 nm.

8. The method according to claim 4, wherein the at least one first filter is a particle removal filter.

9. The method according to claim 1, further comprising passing the distilled organic solvent through a second filter unit downstream of the second distillation column, wherein the second filter unit comprises a second housing and at least one second filter within the second housing, and the at least one second filter comprises a filtration medium.

10. The method according to claim 9, wherein the filtration medium in the at least one second filter comprises a polyolefin, a polyamide, a fluororesin, or a copolymer thereof.

11. The method according to claim 10, wherein the filtration medium in the at least one second filter comprises nylon or polytetrafluoroethylene.

12. The method according to claim 9, wherein the filtration medium in at least one second filter has an average pore size of 2 nm to 10 nm.

13. The method according to claim 9, wherein the at least one second filter is a particle removal filter.

14. The method according to claim 9, further comprising recirculating the organic solvent that has exited the second filter unit.

15. The method according to claim 14, wherein the recirculation includes transferring the organic solvent that has exited the second filter unit to a distilled solvent tank, and then passing the organic solvent through the second filter unit, the distilled solvent tank being located between the second distillation column and the second filter unit, and being in fluid communication with the second distillation column and the second filter unit.

16. The method according to claim 1, further comprising moving the distilled organic solvent to a product container located downstream of the second distillation column and in fluid communication with the second distillation column.

17. The method according to claim 1, wherein the organic solvent comprises cyclohexanone, ethyl lactate, n-butyl acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, or 4-methyl-2-pentanol.

18. A system for purifying an organic solvent having a boiling point in the range of 100°C to 200°C, A first distillation column having a first inlet and a first outlet, wherein the first inlet is located at a position between 80% and 100% of the height of the first distillation column, A second distillation column located downstream of the first distillation column, having a second inlet and a second outlet, wherein the second inlet is in fluid communication with the first outlet, and the second inlet is positioned at a height of 0% to 30% of the second distillation column, A system equipped with these features.

19. The system according to claim 18, further comprising a preheater, the preheater being located upstream of the first distillation column and in fluid communication with the first distillation column.

20. The system according to claim 19, further comprising a first filter unit located upstream of the preheater and in fluid communication with the preheater, wherein the first filter unit comprises a first housing and at least one first filter within the first housing, and the at least one first filter comprises a filtration medium.

21. The system according to claim 20, wherein the filtration medium in the at least one first filter comprises a polyolefin, a polyamide, a fluororesin, or a copolymer thereof.

22. The system according to claim 21, wherein the filtration medium in the at least one first filter comprises polypropylene or polytetrafluoroethylene.

23. The system according to claim 20, wherein the filtration medium in the at least one first filter has an average pore size of 50 nm to 250 nm.

24. The system according to claim 20, wherein the at least one first filter is a particle removal filter.

25. The system according to claim 18, further comprising a second filter unit located downstream of the second distillation column, wherein the second filter unit comprises a second housing and at least one second filter within the second housing, and the at least one second filter comprises a filtration medium.

26. The system according to claim 25, wherein the filtration medium in at least one second filter comprises a polyolefin, a polyamide, a fluororesin, or a copolymer thereof.

27. The system according to claim 26, wherein the filtration medium in at least one second filter comprises nylon or polytetrafluoroethylene.

28. The system according to claim 25, wherein the filtration medium in at least one second filter has an average pore size of 2 nm to 10 nm.

29. The system according to claim 25, wherein the at least one second filter is a particle removal filter.

30. The system according to claim 25, further comprising a distilled solvent tank located between the second distillation column and the second filter unit, and in fluid communication with the second distillation column and the second filter unit.

31. The system according to claim 30, further comprising a recirculation loop, wherein the recirculation loop comprises the second filter unit and the distilled solvent tank.

32. The system according to claim 18, further comprising a product container located downstream of the second distillation column and in fluid communication with the second distillation column.

33. The method according to claim 1, wherein the organic solvent is cyclohexanone.

34. The system according to claim 18, wherein the organic solvent is cyclohexanone.

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