Porous film, method for producing porous film, and method for producing purified chemical liquid for use in production of semiconductor element

Abstract

Provided are: a porous film which is capable of satisfactorily removing minute foreign matter in a chemical liquid by filtration; a method for producing the porous film; and a method for producing a purified chemical liquid for use in the production of a semiconductor element, the method including performing filtration using the porous film.　The present invention uses a porous film in which at least a portion of the surface of a porous base film is coated with a coating layer containing a polyamide resin, wherein the porous base film has a plurality of spherical holes therein, in which the plurality of spherical holes are connected to adjacent spherical holes to form communicated holes.

Description

Porous film, method for producing a porous film, and method for producing a purified chemical solution used in the production of semiconductor devices

[0001] The present invention relates to a porous film, a method for producing the porous film, a method for producing a purified chemical solution used in the production of semiconductor devices using the porous film, and a method for producing a purified chemical solution used in the production of semiconductor devices.

[0002] In recent years, in the production of semiconductor devices and liquid crystal display devices, pattern miniaturization has been rapidly progressing due to the advancement of lithography technology.

[0003] As pattern miniaturization progresses, the resist material is required to suppress the occurrence of defects (surface defects) while improving various lithography characteristics. Here, "defects" refer to all defects detected when observing the developed resist pattern from directly above, for example, by a surface defect observation device (trade name "KLA") manufactured by KLA Tencor Corporation. This defect includes, for example, defects caused by the adhesion of foreign substances and deposits such as scum (resist residue), bubbles, and dust on the surface of the resist pattern after development, defects related to the pattern shape such as bridges between line patterns and hole filling of holes in contact hole patterns, and unevenness in the color of the pattern.

[0004] Conventionally, in order to remove foreign substances from resist compositions used for manufacturing semiconductor devices and liquid crystal display devices, purification is generally performed by passing them through a filter. (For example, Patent Document 1).

[0005] In addition, in order to remove finer foreign substances from the resist composition, a porous membrane having spherical pores inside is also used as a filter. (For example, Patent Document 2).

[0006] Japanese Unexamined Patent Application Publication No. 2017 - 226836, Japanese Unexamined Patent Application Publication No. 2023 - 10711

[0007] The polyamide resin film described in Patent Document 1 is manufactured by a phase separation method. The phase separation method is a method that utilizes external stimuli such as cooling, contact with a non-solvent, evaporation of the solvent, and chemical reactions such as polymerization. Therefore, it is difficult to control the shape of the pores in the porous film, and there is a problem in that it is difficult to remove minute foreign matter.

[0008] Even with the porous film made of polyimide or the like described in Patent Document 2, it was sometimes difficult to remove minute foreign matter.

[0009] The present invention has been made in view of the above-mentioned problems, and aims to provide a porous film that can effectively remove minute foreign matter from a chemical solution by filtration, a method for manufacturing the porous film, and a method for producing a purified chemical solution used in the manufacture of semiconductor devices by performing filtration using the aforementioned porous film.

[0010] The inventors have discovered that the above problems can be solved by using a porous film in which at least a portion of the surface of a porous substrate film having a plurality of spherical pores inside, and in which the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores, is coated with a coating layer containing a polyamide resin, and have completed the present invention. More specifically, the present invention provides the following.

[0011] A first aspect of the present invention is a porous film having a plurality of spherical pores inside, wherein the porous film comprises a porous substrate film and a coating layer covering at least a portion of the surface of the porous substrate film, the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores, the coating layer contains a polyamide resin, and the mass ratio of the coating layer to the mass of the porous film is less than 5% by mass.

[0012] A second aspect of the present invention is a method for producing a porous film according to the first aspect, comprising: coating at least a portion of the surface of a porous substrate film with a solution in which a material constituting the coating layer is dissolved in an organic solvent; removing excess solution from the porous substrate film whose surface at least a portion is coated with the solution; after removing the excess solution, contacting the solution in the porous substrate film coated with the solution with a poor solvent for the material constituting the coating layer to form a coating layer on the surface of the porous substrate film; and drying the porous film after the coating layer has been formed.

[0013] A third aspect of the present invention is a method for purifying a crude chemical solution to produce a purified chemical solution used in the manufacture of a semiconductor device, comprising: filtering the crude chemical solution using a porous film according to the first aspect as a filter; and recovering the liquid that has passed through the filter as a purified chemical solution.

[0014] According to the present invention, it is possible to provide a porous film that can effectively remove minute foreign matter from a chemical solution by filtration, a method for manufacturing the porous film, and a method for producing a purified chemical solution used in the manufacture of semiconductor devices by performing filtration using the aforementioned porous film.

[0015] <Porous Film> A porous film has multiple spherical pores inside. These multiple spherical pores are connected to adjacent spherical pores to form communicating pores. The porous film consists of a porous substrate film and a coating layer that covers at least a portion of the surface of the porous substrate film. The coating layer contains a polyamide resin. The mass ratio of the coating layer is less than 5% by mass relative to the mass of the porous film.

[0016] As described above, the porous film has interconnecting pores. These interconnecting pores are formed by a series of adjacent spherical pores (hereinafter sometimes simply referred to as "spherical pores") that impart porousness to the porous film. Preferably, each spherical pore has a curved inner surface as described later, and more preferably it is a spherical pore or a substantially spherical pore as described later. In the porous film, the portion formed by adjacent individual spherical pores is the interconnecting pore. The interconnecting pore has a structure in which these individual spherical pores communicate with each other. Typically, multiple such pores are connected to form a flow path for the purified liquid. The "flow path" is usually formed by the continuous arrangement of individual "spherical pores" and / or "connecting pores". Individual pores can also be said to be pores formed when individual microparticles present in the polyimide resin-microparticle composite film are removed in a later process in the porous film manufacturing method described later.

[0017] Preferably, the porous film has communication holes such that the communication holes having openings on the outer surface of the porous film communicate with the interior of the porous film and also have openings on the outer surface on the opposite side (back side) of the porous film, thereby ensuring a fluid flow path through the porous film.

[0018] The average pore size of the porous film is preferably between 10 nm and 200 nm, and more preferably between 15 nm and 150 nm. The average pore size is the average pore size measured by a porometer.

[0019] The average pore size measured by a porometer is the average flow rate pore size due to liquid-liquid phase displacement. The average pore size can be measured, for example, using a liquid porometer LLP-1500A (ultra-low pressure, pore size distribution, and permeability performance measuring device) manufactured by PMI, according to the pore size distribution measurement test method [half-dry method (ASTM E1294-89)]. Perfluoropolyester (trade name Galwick) and isopropyl alcohol (interfacial tension value: 4.6 dyne / cm) are used as reagents for measuring the average pore size. After filling the pores of the porous membrane with isopropyl alcohol, one main surface of the porous membrane is filled with perfluoropolyester. Pressure is applied to the main surface side of the porous film filled with perfluoropolyester, gradually increasing the pressure using compressed air. The measurement temperature is 25°C, and the measurement pressure is in the range of 50 to 500 psi.

[0020] The porosity of the porous film is preferably 60% to 90%, and more preferably 60% to 80%. The porosity is the ratio of the volume of voids to the total volume of the porous film. The total volume of the porous film includes the volume of voids.

[0021] When a fluid is passed through a porous film having interconnected pores, the fluid can pass through the interior of the porous film. Preferably, the porous film has internal channels formed by interconnected individual pores, each having a curved surface on its inner surface. Therefore, not only can the fluid pass through the interior of the porous film, but as it passes through while in contact with the curved surfaces of the individual pores, the contact area with the inner surface of the pores increases, making it easier for minute substances such as metal particles present in the fluid to be adsorbed into the pores of the porous film.

[0022] As described above, the porous film is preferably a porous film containing pores having curved surfaces on its inner surface, and more preferably a large portion (preferably substantially all) of the pores in the porous film are formed with curved surfaces. In this specification, "having curved surfaces on its inner surface" means that at least the inner surface of the pores that give rise to the porousness has a curved surface in at least a portion of that inner surface.

[0023] In a porous film, it is preferable that substantially almost the entire inner surface of the spherical pores is curved. In this specification, "spherical pore" means a pore whose inner surface forms a spherical or substantially spherical space. In this specification, "spherical pore or substantially spherical" is a concept that includes a perfect sphere but is not necessarily limited to a perfect sphere, and includes a concept that includes substantially spherical objects. In this specification, "substantially spherical" means that the sphericity, defined by the value obtained by dividing the major axis of a particle by its minor axis, is within 1 ± 0.3. The sphericity of the spherical pores in a porous film is preferably 0.9 to 1.1, and more preferably 0.95 to 1.05.

[0024] Because the pores in a porous film have a curved inner surface, when a fluid passes through the porous film, the fluid can spread sufficiently into the pores and make sufficient contact with the inner surface of the pores. In some cases, it is possible that the fluid may convect along the curved inner surface. For these reasons, it is thought that minute substances such as metal particles present in the fluid are easily adsorbed into the pores or recesses that may exist on the inner surface of the pores in the porous film. Spherical pores may have further recesses on their inner surface. These recesses may be formed, for example, by pores with a smaller diameter than the spherical pores that have openings on the inner surface of the spherical pores.

[0025] From the viewpoint of achieving both excellent filtration speed and excellent film strength, the film thickness of the porous film is preferably 15 μm to 100 μm, and more preferably 20 μm to 40 μm.

[0026] <Porous Substrate Film> The porous substrate film is provided by covering at least a portion of its surface with a coating layer described later. As mentioned above, since the porous film has multiple spherical pores inside, the porous substrate film also has multiple spherical pores inside. Similar to the multiple spherical pores inside the porous film, the multiple spherical pores inside the porous substrate film are connected to adjacent spherical pores to form connecting pores.

[0027] The material of the porous substrate film is not particularly limited as long as it can form interconnected pores consisting of multiple spherical holes inside the porous substrate film and does not dissolve in the liquid through which it is to pass.

[0028] Examples of materials for porous substrate films include thermoplastic resins and thermosetting resins.

[0029] For example, when using a thermoplastic resin, a porous substrate film can be prepared by the following method. First, a thermoplastic resin composition is obtained by melt-kneading a thermoplastic resin with spherical inorganic fine particles. The obtained thermoplastic resin composition is then made into a film by a melt-film formation method such as the T-die method. Then, a porous substrate film made of thermoplastic resin is obtained by removing the inorganic fine particles from the film made of the thermoplastic resin composition. One method for removing inorganic fine particles from a film made of a thermoplastic resin composition is to bring the film made of the thermoplastic resin composition into contact with a liquid in which the inorganic fine particles are soluble.

[0030] When using a thermosetting resin, a porous substrate film can be prepared by the following method. First, a precursor of the thermosetting resin and spherical inorganic fine particles are dissolved in an organic solvent in which the thermosetting resin precursor is soluble to obtain a precursor slurry. The precursor slurry is applied to a substrate to form a coating film. Next, after drying the coating film, the thermosetting resin precursor in the coating film is thermoset. The film obtained by thermoseting, consisting of the thermosetting resin and inorganic fine particles, is brought into contact with a liquid in which the inorganic fine particles are soluble to dissolve the inorganic fine particles, thereby obtaining a porous substrate film made of thermosetting resin.

[0031] The above-described methods for producing a porous substrate film made of a thermoplastic resin and a porous substrate film made of a thermosetting resin are preferred examples. The methods for producing a porous substrate film made of a thermoplastic resin and a porous substrate film made of a thermosetting resin are not limited to the above methods.

[0032] Because of their excellent mechanical strength, solvent resistance, and heat resistance, the porous substrate film is preferably a porous polyimide film or a porous polyamide-imide film. Hereinafter, the term "porous polyimide film" may be used as a general term for both porous polyimide films and porous polyamide-imide films.

[0033] As mentioned above, the porous substrate film is a porous polyimide film or a porous polyamide-imide film. In this specification, the term "polyimide resin" may be used as a general term for polyimide resins and polyamide-imide resins.

[0034] <Method for Manufacturing Porous Polyimide Films> The method for manufacturing porous polyimide films is described below in detail, mainly using the preferred embodiment of a film (porous film) as an example. The film can be suitably manufactured using varnish.

[0035] [Varnish Manufacturing] Varnish can be manufactured by mixing an organic solvent in which fine particles are pre-dispersed with polyamic acid, polyimide, or polyamideimide in any ratio, or by polymerizing tetracarboxylic dianhydride and diamine in an organic solvent in which fine particles are pre-dispersed to form polyamic acid, or by further imidizing to form polyimide. The viscosity of the final varnish is preferably 300 cP to 2000 cP (0.3 Pa·s to 2 Pa·s), and more preferably 400 cP to 1800 cP (0.4 Pa·s to 1.8 Pa·s). If the viscosity of the varnish is within this range, it is easy to form a uniform film.

[0036] In varnish, fine particles can be mixed with a resin selected from polyamic acid, polyimide resin, and polyamide-imide resin such that the ratio of fine particles to polyimide resin when a polyimide resin-fine particle composite film is formed by firing (or drying if firing is optional) is, for example, 1 to 4 (by mass ratio). A fine particle-to-polyimide resin ratio of 1.1 to 3.5 (by mass ratio) is preferred. It is also preferable to mix fine particles with a resin selected from polyamic acid, polyimide resin, and polyamide-imide resin such that the volume ratio of fine particles to polyimide resin in the polyimide resin-fine particle composite film is, for example, 1.1 to 5. A volume ratio of fine particles to polyimide resin in the polyimide resin-fine particle composite film is more preferable to 1.1 to 4.5. If the mass ratio or volume ratio of fine particles to polyimide resin is within the above range, it is easy to form pores of appropriate density as a porous film, and stable film formation is easy without causing problems such as increased viscosity or cracking in the film. In this specification, volume percentages and volume ratios are values ​​at 25°C.

[0037] <Fine particles> Spherical fine particles are incorporated into the varnish. The material of the fine particles incorporated into the varnish is not particularly limited, as long as it is insoluble in the organic solvent used in the varnish and can be selectively removed after film formation. For example, as inorganic materials, silica (silicon dioxide), titanium dioxide, and alumina (Al ２ O ３ Examples of materials include metal oxides such as calcium carbonate. Examples of organic materials include high molecular weight polyolefins (polypropylene and polyethylene, etc.), polystyrene, acrylic resins (polymethyl methacrylate (PMMA) and polyisobutyl methacrylate, etc.), epoxy resins, cellulose, polyvinyl alcohol, polyvinyl butyral, polyester, and polyether resin fine particles.

[0038] As for the fine particles, inorganic fine particles such as silica, including colloidal silica, and organic polymer fine particles such as PMMA fine particles are preferred because they easily form minute pores with curved surfaces on their inner surfaces.

[0039] The particle size of the fine particles is appropriately selected according to the average pore size of the porous membrane that is ultimately formed. A particle size of 0.05 μm to 1.0 μm is preferred.

[0040] A dispersant may be added to the varnish along with the fine particles for the purpose of uniformly dispersing the fine particles in the varnish. By adding a dispersant, the resin selected from polyamic acid, polyimide resin, and polyamide-imide resin can be mixed more uniformly with the fine particles. Furthermore, the fine particles in the molded or deposited precursor film can be uniformly distributed. As a result, it becomes possible to create dense openings on the surface of the final porous film and to form connecting pores that efficiently connect the front and back surfaces of the porous film, thereby improving the air permeability of the porous film.

[0041] The dispersant is not particularly limited. Examples of dispersants include anionic surfactants such as coconut fatty acid salt, castor sulfate, lauryl sulfate, polyoxyalkylene allylphenyl ether sulfate, alkylbenzene sulfonic acid, alkylbenzene sulfonate, alkyldiphenyl ether disulfonate, alkylnaphthalene sulfonate, dialkyl sulfosuccinate, isopropyl phosphate, polyoxyethylene alkyl ether phosphate, and polyoxyethylene allylphenyl ether phosphate; cationic surfactants such as oleylamine acetate, laurylpyridinium chloride, cetylpyridinium chloride, lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, behenyltrimethylammonium chloride, and didecyldimethylammonium chloride; amphoteric surfactants such as coconut alkyldimethylamine oxide, fatty acid amidopropyl dimethylamine oxide, alkylpolyaminoethylglycine hydrochloride, amide betaine type surfactant, alanine type surfactant, and lauryliminodipropionic acid; and poly Examples of nonionic surfactants include, but are not limited to, polyoxyalkylene primary alkyl ethers or polyoxyalkylene secondary alkyl ethers such as oxyethylene octyl ether, polyoxyethylene decyl ether, polyoxyethylene lauryl ether, polyoxyethylene laurylamine, polyoxyethylene oleylamine, polyoxyethylene polystyrylphenyl ether, and polyoxyalkylene polystyrylphenyl ether; other polyoxyalkylene-based nonionic surfactants such as polyoxyethylene dilaurate, polyoxyethylene laurate, polyoxyethylene-derived castor oil, polyoxyethylene-derived hydrogenated castor oil, sorbitan laurate, polyoxyethylene sorbitan laurate, and fatty acid diethanolamide; fatty acid alkyl esters such as octyl stearate and trimethylolpropane tridecanoate; and polyether polyols such as polyoxyalkylene butyl ether, polyoxyalkylene oleyl ether, and trimethylolpropane tris(polyoxyalkylene) ether.In addition, two or more kinds of the above dispersants can be mixed and used.

[0042] <Polyamic acid> As the polyamic acid, a resin obtained by polymerizing any tetracarboxylic dianhydride and any diamine can be used without particular limitation. The amounts of the tetracarboxylic dianhydride and the diamine used are not particularly limited. It is preferable to use 0.50 mol or more and 1.50 mol or less of the diamine with respect to 1 mol of the tetracarboxylic dianhydride, more preferably 0.60 or more and 1.30 mol or less, and particularly preferably 0.70 or more and 1.20 mol or less.

[0043] The tetracarboxylic dianhydride can be appropriately selected from the tetracarboxylic dianhydrides conventionally used as raw materials for synthesizing polyamic acid. The tetracarboxylic dianhydride may be an aromatic tetracarboxylic dianhydride or an aliphatic tetracarboxylic dianhydride. From the viewpoint of the heat resistance of the obtained polyimide resin, it is preferable to use an aromatic tetracarboxylic dianhydride. Two or more kinds of the tetracarboxylic dianhydrides may be used in combination.

[0044] Suitable specific examples of aromatic tetracarboxylic dianhydrides include pyromellitic dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, and 2,2,6,6-biphenyltetra Carboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 3,3',4,4'-benzophenone tetra Carboxylic acid dianhydrides, bis(3,4-dicarboxyphenyl) ether dianhydrides, bis(2,3-dicarboxyphenyl) ether dianhydrides, 2,2',3,3'-benzophenonetetracarboxylic acid dianhydrides, 4,4-(p-phenylenedioxy)diphthalic acid dianhydrides, 4,4-(m-phenylenedioxy)diphthalic acid dianhydrides, 1,2,5,6-naphthalenetetracarbone dianhydrides, 1,4,5,8-naphthalenetetracarboxylic acid Examples of dianhydrides include 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid dianhydride, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrenetetracarboxylic acid dianhydride, 9,9-bisphthalic anhydride fluorene, and 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride. Examples of aliphatic tetracarboxylic acid dianhydrides include ethylenetetracarboxylic acid dianhydride, butanetetracarboxylic acid dianhydride, cyclopentanetetracarboxylic acid dianhydride, cyclohexanetetracarboxylic acid dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, and 1,2,3,4-cyclohexanetetracarboxylic acid dianhydride.Among these, 3,3',4,4'-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride are preferable in terms of price, availability, etc. These tetracarboxylic dianhydrides can be used alone or in combination of two or more.

[0045] The diamine can be appropriately selected from diamines that have been conventionally used as raw materials for synthesizing polyamic acid. This diamine may be an aromatic diamine or an aliphatic diamine, but an aromatic diamine is preferable from the viewpoint of the heat resistance of the obtained polyimide resin. These diamines may be used in combination of two or more.

[0046] The aromatic diamine may be a diamine containing one benzene ring, or may be a polycyclic aromatic diamino compound in which two or more and ten or less benzene rings are condensed with each other, bonded via a single bond, or an arbitrary linking group. Specific examples of the aromatic diamine include phenylenediamine and its derivatives, diaminobiphenyl compounds and their derivatives, diaminodiphenyl compounds and their derivatives, diaminotriphenyl compounds and their derivatives, diaminonaphthalene and its derivatives, aminophenylaminoindane and its derivatives, diaminotetraphenyl compounds and their derivatives, diaminohexaphenyl compounds and their derivatives, and cardo-type fluorenediamine derivatives.

[0047] The phenylenediamine is m-phenylenediamine, p-phenylenediamine, etc. Examples of the phenylenediamine derivative include phenylenediamine to which an alkyl group such as a methyl group and an ethyl group is bonded. Specific examples of the phenylenediamine derivative include 2,4-diaminotoluene, 2,4-triphenylenediamine, etc.

[0048] The diaminobiphenyl compound is one in which two aminophenyl groups are bonded by phenyl groups. For example, 4,4'-diaminobiphenyl, 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, etc.

[0049] Diaminodiphenyl compounds are compounds in which two aminophenyl groups are bonded to each other via other groups. These other groups can be ether bonds, sulfonyl bonds, thioether bonds, alkylene or its derivative groups, imino bonds, azo bonds, phosphine oxide bonds, amide bonds, and ureylene bonds. The alkylene bond (alkylene group) preferably has 1 to 6 carbon atoms. Its derivative group is a group in which one or more hydrogen atoms of the alkylene group are replaced by halogen atoms or the like.

[0050] Examples of diaminodiphenyl compounds include 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl ketone, 3,4'-diaminodiphenyl ketone, 2,2-bis(p-aminophenyl)propane, 2,2'-bis(p-aminophenyl)hexafluoropropane, 4-methyl-2,4-bis(p-aminophenyl)-1-pentene, and 4-methyl-2,4-bis(p-aminophenyl Examples include )-2-pentene, iminodianiline, 4-methyl-2,4-bis(p-aminophenyl)pentane, bis(p-aminophenyl)phosphine oxide, 4,4'-diaminoazobenzene, 4,4'-diaminodiphenylurea, 4,4'-diaminodiphenylamide, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane.

[0051] Among these, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, and 4,4'-diaminodiphenyl ether are preferred due to their price, availability, etc.

[0052] Diaminotriphenyl compounds consist of two aminophenyl groups and one phenylene group, each bonded via other groups. These other groups are typically the same as those found in diaminodiphenyl compounds. Examples of diaminotriphenyl compounds include 1,3-bis(m-aminophenoxy)benzene, 1,3-bis(p-aminophenoxy)benzene, and 1,4-bis(p-aminophenoxy)benzene.

[0053] Examples of diaminonaphthalenes include 1,5-diaminonaphthalene and 2,6-diaminonaphthalene.

[0054] An example of aminophenylaminoindanes is 5 or 6-amino-1-(p-aminophenyl)-1,3,3-trimethylindanes.

[0055] Examples of diaminotetraphenyl compounds include 4,4'-bis(p-aminophenoxy)biphenyl, 2,2'-bis[p-(p'-aminophenoxy)phenyl]propane, 2,2'-bis[p-(p'-aminophenoxy)biphenyl]propane, and 2,2'-bis[p-(m-aminophenoxy)phenyl]benzophenone.

[0056] Examples of cardo-type fluororangeamine derivatives include 9,9-bisanilinefluorene.

[0057] The number of carbon atoms in the aliphatic diamine is preferably between 2 and 15. Suitable specific examples of aliphatic diamines include pentamethylenediamine, hexamethylenediamine, and heptamethylenediamine.

[0058] Furthermore, these diamines may be compounds in which the hydrogen atoms are substituted with at least one substituent selected from the group consisting of halogen atoms, methyl groups, methoxy groups, cyano groups, and phenyl groups.

[0059] There are no particular restrictions on the means used to produce polyamic acid; for example, known methods such as reacting a tetracarboxylic dianhydride and a diamine in an organic solvent can be used.

[0060] The reaction between tetracarboxylic dianhydride and diamine is usually carried out in an organic solvent. The organic solvent used in the reaction between tetracarboxylic dianhydride and diamine is not particularly limited as long as it can dissolve the tetracarboxylic dianhydride and diamine and does not react with them. The organic solvent can be used alone or in a mixture of two or more.

[0061] Examples of organic solvents used in the reaction between tetracarboxylic dianhydrides and diamines include nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea; lactone-based polar solvents such as β-propiolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, and ε-caprolactone; dimethyl sulfoxide; acetonitrile; fatty acid esters such as ethyl lactate and butyl lactate; ethers such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, dioxane, tetrahydrofuran, methyl cellulose acetate, and ethyl cellulose acetate; and phenolic solvents such as cresols. These organic solvents can be used individually or in combination of two or more. In particular, a combination of a nitrogen-containing polar solvent and a lactone-based polar solvent is preferred.

[0062] There are no particular restrictions on the amount of organic solvent used. However, it is desirable that the amount of organic solvent used be such that the polyamic acid content in the reaction solution after the reaction is between 5% and 50% by mass.

[0063] Among these organic solvents, nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, N,N-diethylformamide, N-methylcaprolactam, and N,N,N',N'-tetramethylurea are preferred due to their solubility of the resulting polyamic acid. Furthermore, from the viewpoint of film-forming properties, mixed solvents with added lactone-based polar solvents such as γ-butyrolactone are also preferred. In the mixed solvent, it is preferable that the lactone-based polar solvent is added in an amount of 1% to 20% by mass relative to the total amount of the mixed solvent, and more preferably 5% to 15% by mass.

[0064] The polymerization temperature is generally preferably between -10°C and 120°C, and more preferably between 5°C and 30°C. The polymerization time varies depending on the composition of the raw materials used, but is usually preferably between 3 hours and 24 hours. The intrinsic viscosity of the polyamic acid solution obtained under these conditions is preferably between 1000 cP and 100,000 cP, and more preferably between 5,000 cP and 70,000 cP.

[0065] <Polyimide Resin> The polyimide resin is not limited in structure or molecular weight, as long as it is a soluble polyimide that can dissolve in the organic solvent contained in the varnish. The polyimide resin may have condensable functional groups such as carboxyl groups or functional groups that promote crosslinking reactions during firing in its side chains.

[0066] To produce polyimide resins soluble in organic solvents, it is effective to use monomers that introduce a flexible, bendable structure into the main chain. Examples of such monomers include aliphatic diamines such as ethylenediamine, hexamethylenediamine, 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, and 4,4'-diaminodicyclohexylmethane; aromatic diamines such as 2-methyl-1,4-phenylenediamine, o-tolidine, m-tolidine, 3,3'-dimethoxybenzidine, and 4,4'-diaminobenzanilide; polyoxyalkylenediamines such as polyoxyethylenediamine, polyoxypropylenediamine, and polyoxybutylenediamine; polysiloxanediamines; 2,3,3',4'-oxydiphthalic anhydride, 3,4,3',4'-oxydiphthalic anhydride, and 2,2-bis(4-hydroxyphenyl)propanedibenzoate-3,3',4,4'-tetracarboxylic dianhydride. The use of monomers having functional groups that improve solubility in organic solvents is also effective. Examples of such monomers include fluorinated diamines such as 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl and 2-trifluoromethyl-1,4-phenylenediamine. Furthermore, in addition to monomers for improving the solubility of the polyimide resin, the same monomers listed in the polyamic acid section above can also be used in combination, as long as they do not inhibit solubility.

[0067] There are no particular restrictions on the means for producing polyimide resins soluble in organic solvents. For example, known methods such as chemically imidizing or thermally imidizing a polyamic acid and dissolving it in an organic solvent can be used. Examples of polyimide resins soluble in organic solvents include aliphatic polyimide resins (all-aliphatic polyimide resins) and aromatic polyimide resins, with aromatic polyimide resins being preferred. Examples of aromatic polyimide resins include polyamide resins obtained by thermal or chemical ring-closing reactions of polyamic acid having repeating units shown in formula (1), or polyimide resins having repeating units shown in formula (2). In the formula, Ar represents an aryl group.

[0068] <Polyamide-imide resin> Any known polyamide-imide resin that is soluble in the organic solvent contained in the varnish can be used, without being limited by its structure or molecular weight. The polyamide-imide may have condensable functional groups such as carboxyl groups or functional groups that promote crosslinking reactions during firing in its side chains.

[0069] The polyamide-imide resin can be any resin obtained by reacting any trimellitic anhydride with a diisocyanate, or a precursor polymer obtained by imidizing a reaction between any reactive derivative of trimellitic anhydride and a diamine, without any particular limitations.

[0070] Examples of any trimetic anhydride or its reactive derivatives include trimellitic anhydride, trimellitic anhydride halides such as trimellitic anhydride chloride, and trimellitic anhydride esters.

[0071] Examples of any diisocyanate include metaphenylenediisocyanate, p-phenylenediisocyanate, o-tolidine diisocyanate, p-phenylenediisocyanate, m-phenylenediisocyanate, 4,4'-oxybis(phenylisocyanate), 4,4'-diisocyanatediphenylmethane, bis[4-(4-isocyanatephenoxy)phenyl]sulfone, 2,2'-bis[4-(4-isocyanatephenoxy)phenyl]propane, 2,4- Examples include leylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, 3,3'-diethyldiphenyl-4,4'-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, m-xylene diisocyanate, p-xylene diisocyanate, and naphthalene diisocyanate.

[0072] Examples of the above-mentioned optional diamines include those similar to those exemplified in the description of polyamic acids.

[0073] <Organic Solvents> The varnish contains organic solvents. The organic solvent is not particularly limited as long as it can dissolve polyamic acid and / or polyimide resins and does not dissolve fine particles. Examples of such organic solvents include those used as solvents in the reaction between tetracarboxylic dianhydride and diamine. The solvent may be used alone or in combination of two or more types.

[0074] The amount of organic solvent in the varnish is preferably 50% to 95% by mass, more preferably 60% to 85% by mass. The solid content concentration in the varnish is preferably 5% to 50% by mass, more preferably 15% to 40% by mass.

[0075] In addition to the components mentioned above, known components such as antistatic agents, flame retardants, chemical imidizing agents, condensing agents, mold release agents, and surface modifiers may be included in the varnish as needed for purposes such as antistatic properties, flame retardancy, low-temperature firing, mold release properties, and coatability.

[0076] [Manufacturing of Unfired Composite Films] In the case of film formation, an unfired composite film containing polyamic acid or polyimide resin and fine particles is formed by applying the above varnish to a substrate and drying it under normal pressure or vacuum at a temperature preferably between 0°C and 120°C, more preferably between 0°C and 100°C. More preferably, the unfired composite film is formed by drying at a temperature between 60°C and 95°C under normal pressure, and particularly preferably between 65°C and 90°C under normal pressure.

[0077] The coating thickness is not particularly limited. The coating thickness is appropriately selected according to the desired thickness of the porous film. A release layer may be provided on the substrate as needed. Furthermore, in the production of the unfired composite film, an immersion step in a solvent containing water, a pressing step, and a drying step after the immersion step may be provided as optional steps before the production of the polyimide resin-fine particle composite film (firing step) described later.

[0078] The release layer can be manufactured by applying a release agent to a substrate and drying or baking it. Known release agents such as alkylammonium phosphate-based release agents, fluorine-based release agents, and silicone-based release agents can be used without particular limitation. When peeling an unfired composite film containing dried polyamic acid or polyimide resin and fine particles from a substrate, a small amount of release agent remains on the peeled surface of the unfired composite film. Since this remaining release agent can affect the wettability of the porous film surface and the inclusion of impurities, it is preferable to remove it.

[0079] Therefore, it is preferable to clean the unfired composite film peeled off from the substrate using an organic solvent or the like. The cleaning method can be selected from known methods such as immersing the unfired composite film in a cleaning solution and then removing it, or using a shower cleaning method. Furthermore, the unfired composite film after cleaning is dried by known methods such as air-drying at room temperature or heating it to an appropriate set temperature in a constant temperature bath. For example, the edges of the unfired composite film can be fixed to a stainless steel mold or the like to prevent deformation.

[0080] On the other hand, when forming an unfired composite film, if the substrate is used as is without a release layer, the steps of forming the release layer and cleaning the unfired composite film can be omitted.

[0081] [Manufacturing of Polyimide Resin-Microparticle Composite Film (Firing Process)] The unfired composite film after drying is subjected to post-treatment by heating (firing) to form a composite film (polyimide resin-microparticle composite film) consisting of polyimide resin and microparticles. If the varnish contains polyamic acid, it is preferable to complete the imidation process in the firing process. Note that the firing process is an optional step. In particular, if polyimide or polyamideimide is used in the varnish, the firing process may not be performed.

[0082] The firing temperature varies depending on the structure of the polyamic acid or polyimide resin contained in the unfired composite film and the presence or absence of a condensing agent, but is preferably 120°C to 400°C, and more preferably 150°C to 375°C.

[0083] The firing process and the drying process do not necessarily need to be clearly separated. For example, when firing at 375°C, one can use a method where the temperature is raised from room temperature to 375°C over 3 hours and then held at 375°C for 20 minutes, or a stepwise drying-thermal imidization method can be used where the temperature is raised from room temperature in 50°C increments to 375°C (held for 20 minutes at each step) and finally held at 375°C for 20 minutes. In this case, the edges of the unfired composite film may be fixed to a stainless steel mold or the like to prevent deformation.

[0084] [Fine particle removal process (porosity creation of polyimide resin-fine particle composite film)] By selecting an appropriate method to remove fine particles from a polyimide resin-fine particle composite film, a porous film with micropores can be manufactured with high reproducibility. For example, if silica is used as the fine particles, the polyimide resin-fine particle composite film can be made porous by dissolving and removing the silica with a low concentration of hydrogen fluoride (HF) or the like. If the fine particles are resin fine particles, they can be removed by heating the film to a temperature above the thermal decomposition temperature of the resin fine particles but below the thermal decomposition temperature of the polyimide resin to decompose the resin fine particles.

[0085] <Coating Layer> The coating layer, which covers at least a portion of the surface of the porous substrate film, contains a polyamide resin. The ratio of the mass of the coating layer to the mass of the porous film is less than 5% by mass, preferably 1% by mass or more and less than 5% by mass, and more preferably 2% by mass or more and 4.5% by mass or less. If the thermal decomposition temperature of the porous substrate film material is sufficiently higher than the thermal decomposition temperature of the coating layer material, the ratio of the mass of the coating layer to the mass of the porous film can be determined by measuring the weight loss rate due to thermal decomposition of the coating layer in the porous film using a TG-DTA (differential thermogravimetric analyzer).

[0086] The ratio of the mass of the polyamide resin to the mass of the coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass. The coating layer may contain other resins and various additives along with the polyamide resin.

[0087] Any known polyamide resin can be used without particular limitation as the polyamide resin. The polyamide resin may be a ring-opening polymer of lactam or a condensed polymer of hydroxycarboxylic acid. The ring-opening polymer of lactam and the condensed polymer of hydroxycarboxylic acid may be a homopolymer or a copolymer. The polyamide resin may also be a condensed polymer obtained by condensing a diamine component and a dicarboxylic acid component. The condensed polymer obtained by condensing a diamine component and a dicarboxylic acid component may contain two or more constituent units derived from the diamine component and two or more constituent units derived from the dicarboxylic acid component. The polyamide resin may be a polymer obtained by polymerizing lactam and / or hydroxycarboxylic acid, and a diamine component and a dicarboxylic acid component. Two or more lactams, hydroxycarboxylic acids, diamine components, and dicarboxylic acid components may each be used in combination.

[0088] Specific examples of polyamide resins include aliphatic polyamides such as nylon 6, nylon 7, nylon 9, nylon 11, nylon 12, nylon 26, nylon 46, nylon 66, nylon 610, nylon 612, nylon 86, nylon 108, nylon 6 / 12, nylon 6 / 9, nylon 6 / 66, nylon 12 / 66, nylon 26 / 66, nylon 66 / 610, and nylon 6 / 66 / 610). The names of these nylons are based on JIS K 6920-1. Furthermore, the raw materials for the above nylons are not particularly limited. For example, nylon 6 is generally produced by ring-opening polymerization of caprolactam. However, nylon 6 is not limited to ring-opening polymers of caprolactam, but may also be a condensation polymer of 6-aminohexanoic acid.

[0089] Other specific examples of polyamide resins include aromatic polyamides such as polyhexamethylene isophthalamide, polyhexamethylene terephthalamide, polymetaxylylene adipamide, hexamethylene isophthalamide / terephthalamide copolymer, poly-p-phenylene terephthalamide, and poly-p-phenylene-3,4'-oxydiphenylene terephthalamide, as well as various amorphous polyamides.

[0090] The polyamide resin described above may undergo various known modifications.

[0091] ≪Method for Manufacturing a Porous Film≫ The above-mentioned porous film can be manufactured by a method comprising: coating at least a portion of the surface of a porous substrate film with a solution in which the material constituting the coating layer is dissolved in an organic solvent; removing excess solution from the porous substrate film whose surface at least a portion is coated with the above solution; after removing the excess solution, contacting the solution in the porous substrate film coated with the above solution with a poor solvent for the material constituting the coating layer to form a coating layer on the surface of the porous substrate film; and drying the porous film after the coating layer has been formed.

[0092] Hereinafter, the process of coating at least a portion of the surface of the porous substrate film with a solution in which the material constituting the coating layer is dissolved in an organic solvent will also be referred to as the "coating process." The process of removing excess solution from the porous substrate film, from which at least a portion of the surface has been coated with the above solution will also be referred to as the "solution removal process." After the removal of excess solution, the process of bringing the solution on the porous substrate film coated with the above solution into contact with a poor solvent for the material constituting the coating layer to form a coating layer on the surface of the porous substrate film will also be referred to as the "coating layer formation process." After the coating layer has been formed, the process of drying the porous film will also be referred to as the "drying process."

[0093] <Coating Process> In the coating process, at least a portion of the surface of the porous substrate film is coated with a solution in which the materials constituting the coating layer are dissolved in an organic solvent.

[0094] As described above, the coating layer is formed on the surface of the porous substrate film using a solution in which the materials constituting the coating layer are dissolved in an organic solvent.

[0095] The organic solvent used in the coating solution is not particularly limited as long as it dissolves the materials constituting the coating layer, but it is preferable that it contains formic acid. In addition, the organic solvent may also contain alcohols such as methanol, ethanol, propanol, isopropyl alcohol, n-butyl alcohol, tert-butyl alcohol, and n-pentyl alcohol; diols such as ethylene glycol, propylene glycol, and 1,4-butanediol; and so on.

[0096] The concentration of the polyamide resin in the above solution is not particularly limited, but is preferably 1% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less, relative to the mass of the solution.

[0097] The method of coating at least a portion of the surface of a porous substrate film with a solution in which the material constituting the coating layer is dissolved in an organic solvent is not particularly limited. Examples of methods for coating at least a portion of the surface of a porous substrate film with a solution in which the material constituting the coating layer is dissolved in an organic solvent include applying the above solution to the surface of the porous substrate film or immersing the porous substrate film in the above solution. When applying the above solution to the surface of a porous substrate film, a certain amount of the solution penetrates into the pores within the porous film by capillary action. Among the above methods, the method of immersing the porous substrate film in the above solution is preferred.

[0098] <Solution Removal Process> In the solution removal process, excess solution is removed from the porous substrate film, on which at least a portion of the surface is coated with the above-mentioned solution.

[0099] The method for removing excess solution is not particularly limited. For example, the excess solution can be removed by placing a porous substrate film coated with the above solution between two layers of plastic film and rolling a rubber roll, such as a hand roller, over it to push it out. Alternatively, the excess coating solution can be removed using an air knife, which directs an airflow directly onto the outer surface of the coated porous substrate film.

[0100] <Coating Layer Formation Process> In the coating layer formation process, after removing excess solution, the solution in the porous substrate film coated with the above solution is brought into contact with a poor solvent for the material constituting the coating layer to form a coating layer on the surface of the porous substrate film. When the solution containing the material constituting the coating layer comes into contact with the above poor solvent, a coating layer is formed on the surface of the porous substrate film by phase separation, and a porous film having a coating layer on its surface is obtained.

[0101] The poor solvent is not particularly limited as long as it is a poor solvent for the polyamide resin in the coating layer. Examples of poor solvents include water; alcohols such as methanol and ethanol; ethers such as diethyl ether; and aliphatic hydrocarbons such as hexane.

[0102] The porous film obtained by contact with a poor solvent is preferably washed with the poor solvent or water.

[0103] <Drying Process> In the drying process, the porous film is dried after the coating layer has been formed. The drying method is not particularly limited, but drying by heating is preferred.

[0104] ≪Method for producing purified chemical solution≫ The method for producing purified chemical solution is used to produce purified chemical solution for use in the manufacture of semiconductor devices.

[0105] A method for producing a purified drug solution includes filtering a crude drug solution using the aforementioned porous film as a filter, and recovering the liquid that has passed through the filter as a purified drug solution.

[0106] Hereafter, the filtration of the crude chemical solution using the aforementioned porous film as a filter will also be referred to as the "filtration process." The recovery of the liquid that has passed through the filter as the purified chemical solution will also be referred to as the "recovery process."

[0107] <Filtration Process> In the filtration process, the crude chemical solution is filtered using the aforementioned porous film as a filter.

[0108] [Chemical Solution] A crude chemical solution is purified to produce a purified chemical solution used in the manufacture of semiconductor devices. The chemical solution used in the manufacture of semiconductor devices is not particularly limited. Examples of chemical solutions include chemical solutions for forming protective films to modify substrates, chemical solutions for cleaning silicon wafers, chemical solutions containing photosensitive materials such as resist compositions, anti-reflective film forming materials such as SiARC and BARC, and raw material chemical solutions for photosensitive materials such as resin solutions.

[0109] Examples of photosensitive materials include photosensitive resin compositions that become sparingly soluble in a developer upon exposure, or readily soluble in a developer upon exposure. A photosensitive resin composition that becomes sparingly soluble in a developer upon exposure is a so-called negative-type photosensitive resin composition. A photosensitive resin composition that becomes readily soluble in a developer upon exposure is a so-called positive-type photosensitive composition.

[0110] A preferred positive-type photosensitive resin composition is one which comprises an acid generator (A) that generates acid upon irradiation with active light or radiation, a resin (B) whose solubility in alkali increases due to the action of the acid, and an organic solvent (C).

[0111] By filtering these chemical solutions using the aforementioned porous polyamide film, metallic impurities, such as iron and zinc, and other minute foreign substances can be removed with a very high removal rate.

[0112] The filter made of the porous film described above is used to purify crude chemical solutions containing the aforementioned impurities. This filter is particularly suitable for filtering crude chemical solutions containing fine particles. Fine particles are defined as particles with a diameter of 0.135 μm or more in 1 mL of sample, as measured using a light scattering particle size counter.

[0113] <Recovery Process> In the recovery process, the liquid that has passed through the filter is recovered as a purified chemical solution. It is preferable that the amount of metal impurities in the recovered purified chemical solution is less than the amount of metal impurities in the crude chemical solution. It is also preferable that the number of fine particles in the recovered purified chemical solution is less than the number of fine particles in the crude chemical solution. The number of fine particles is the number of particles with a diameter of 0.135 μm or more in 1 mL of sample, measured using a light scattering type liquid particle size counter.

[0114] As described above, the present inventors provide the following [1] to

[11] . [1] A porous film having a plurality of spherical pores inside, wherein the porous film comprises a porous substrate film and a coating layer covering at least a part of the surface of the porous substrate film, the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores, the coating layer contains a polyamide resin, and the ratio of the mass of the coating layer to the mass of the porous film is less than 5% by mass. [2] The porous film according to [1], wherein the porous substrate film is a porous polyimide film having a plurality of spherical pores inside, and in the porous polyimide film, the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores. [3] The porous film according to [1] or [2], wherein the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less. [4] The porous film according to any one of [1] to [3], wherein the ratio of the mass of the polyamide resin to the mass of the coating layer is 80% by mass or more. [5] A method for producing a porous film according to any one of [1] to [4], comprising: coating at least a portion of the surface of a porous substrate film with a solution in which the material constituting the coating layer is dissolved in an organic solvent; removing excess solution from the porous substrate film whose surface at least a portion is coated with the solution; after removing the excess solution, contacting the solution in the porous substrate film coated with the solution with a poor solvent for the material constituting the coating layer to form a coating layer on the surface of the porous substrate film; and drying the porous film after forming the coating layer. [6] The method for producing a porous film according to [5], wherein the porous substrate film is a porous polyimide film having a plurality of spherical pores inside, and in the porous polyimide film, the plurality of spherical pores are connected to adjacent spherical pores to form a communication pore. [7] The method for producing a porous film according to [5] or [6], wherein the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less. [8] A method for producing a porous film according to any one of [5] to [7], wherein the ratio of the mass of the polyamide resin to the mass of the coating layer is 80% by mass or more.[9] A method for producing a purified chemical solution for use in the manufacture of semiconductor devices by purifying a crude chemical solution, comprising: filtering the crude chemical solution using a porous film described in any one of [1] to [4] as a filter; and recovering the liquid that has passed through the filter as a purified chemical solution.

[10] The method according to [9], wherein the amount of metal impurities contained in the purified chemical solution is less than the amount of metal impurities contained in the crude chemical solution.

[11] The method according to [9] or

[10] , wherein the number of minute particles contained in the purified chemical solution is less than the number of minute particles contained in the crude chemical solution, and the number of minute particles is the number of particles with a diameter of 0.135 μm or more in 1 mL of sample, as measured using a light scattering type liquid particle size counter.

[0115] The present invention will be described in detail below with reference to examples. The scope of the present invention is not limited to these examples.

[0116] [Example 1] A porous polyimide film with a thickness of 40 μm, an average pore size of 30 nm, and a porosity of 70% was used as the porous substrate film. A 3% by weight solution of nylon 6 was prepared by dissolving 3 g of nylon 6 in 77 g of 98% by weight formic acid and 20 g of isopropanol. 100 cm ２ The porous polyimide film described above was immersed in the nylon 6 solution described above for 1 minute. The porous polyimide film was removed from the nylon 6 solution and placed between two polyethylene sheets. Excess nylon 6 solution was removed from the porous polyimide film by rolling a rubber roller over the side of the porous polyimide film that was not in contact with the table, while the film was sandwiched between polyethylene sheets placed flat on a table. After removing the porous polyimide film from between the polyethylene sheets, it was immersed in pure water for 2 minutes to induce phase separation of nylon 6 on the surface of the porous polyimide film, thereby forming a coating layer. The porous polyimide film with the coating layer formed was immersed in methanol solution for 1 minute, then washed with pure water and dried to produce a porous film with a thickness of 40 μm.

[0117] [Comparative Example 1] In this comparative example, the porous polyimide film used as the porous substrate film in Example 1 was used as the porous film.

[0118] [Comparative Example 2] A formic acid solution of nylon 6 containing nylon 6 at a concentration of 10% by mass was applied to a PET (polyethylene terephthalate) substrate using an applicator to form a coating film. The PET substrate with the coating film was immersed in pure water at 25°C for 5 minutes to induce phase separation in the nylon 6. After immersion for a predetermined time, the PET substrate with the porous polyamide film formed by the phase separation was removed from the pure water. The porous polyamide film on the PET substrate removed from the pure water was washed with pure water, dried, and then peeled off from the PET substrate to obtain the porous polyamide film of Comparative Example 2. The thickness of the porous polyamide film was 100 μm. When the cross-section of the obtained porous polyamide film was observed with a scanning electron microscope (SEM), a structure in which irregularly shaped pores were interconnected was observed inside the porous polyamide film.

[0119] For the porous films of Example 1, Comparative Example 1, and Comparative Example 2, the average pore size was measured using a liquid porometer (manufactured by Porometer Inc.) according to the method described above. Furthermore, for the porous film obtained in Example 1, the weight loss rate when heated to 400°C was measured using a TG-DTA (differential thermal-thermogravimetric analyzer, manufactured by Hitachi High-Tech Science Corporation, TG / DTA6200R), and the weight loss rate was 4% by mass. This weight loss rate is the weight loss rate due to the decomposition of the polyamide constituting the coating layer in the porous film. In other words, the ratio of the mass of the coating layer to the mass of the porous film in Example 1 is 4% by mass.

[0120] Furthermore, the porous films of Example 1, Comparative Example 1, and Comparative Example 2 were used to filter the chemical solution, and the following evaluations were performed.

[0121] In the evaluation of the drug history by filtration, the following resist composition was used as the crude drug solution. The resist composition used as the crude drug solution had the following formula as its resin component: 100 parts by mass of a copolymer represented by the following formula, and the following formula as an acid generator: 19 parts by mass of a compound represented by the following formula, and an acid diffusion control agent with the following formula: The solution consists of 6 parts by mass of the compound represented by [formula] and 2,500 parts by mass of a mixed solvent of propylene glycol monomethyl ether acetate / propylene glycol monomethyl ether = 60 / 40 (mass ratio).

[0122] The above resin contained in the crude chemical solution has a weight-average molecular weight (Mw) of 5100, a molecular weight dispersion (Mw / Mn) of 1.65, and a copolymerization composition ratio l / m of 40 / 60. Mn is the number-average molecular weight.

[0123] The porous films of Example 1, Comparative Example 1, and Comparative Example 2 were each cut into circles with a diameter of 47 mm and used as filters. After setting the filters in a perfluoroalkoxyalkane (PFA) filtration holder, 1000 mL of OK73 thinner was passed through the filters to wash them. The crude chemical solution described above was passed through the washed filters while pressurizing with nitrogen to a pressure of 0.08 MPa (G), and the purified chemical solution obtained by filtration was obtained as the filtrate.

[0124] [Measurement of Metal Atom Content] The metal compounds contained in the chemical solution samples filtered through the porous film of Example 1, Comparative Example 1, and Comparative Example 2 were heated at 600°C. After heating, the content of the metal compounds was determined from the mass of the remaining metal oxides. From the content of the metal compounds in the chemical solution samples, the content of metal atoms (mass ppb) relative to the total mass of the chemical solution purified by filtration was calculated. The metal atom content is shown in Table 1.

[0125] [Evaluation of Particle Quantity] For the purified chemical solutions filtered through the porous film of Example 1, Comparative Example 1, and Comparative Example 2, the number of particles larger than 0.135 μm was counted using a light scattering type liquid particle counter [manufactured by Rion Co., Ltd., model number: KS-41, light source: semiconductor laser-pumped solid-state laser (wavelength 830 nm, rated output 0.2 W), flow rate: 10 mL / min] based on the dynamic light scattering method. The counting was performed three times, and the average value was taken as the measured value. The above light scattering type liquid particle counter was calibrated with PSL (PolystyreneLatex) standard particle solution before use. The results are shown in Table 1 as "Particle Quantity".

[0126] [Evaluation of Defect Count] On a 12-inch silicon substrate treated with hexamethyldisilazane (HMDS), the chemical solutions filtered through the porous films of Example 1, Comparative Example 1, and Comparative Example 2 were applied using a spinner. The silicon substrate with the formed coating film was pre-baked (PAB) on a hot plate at 80°C for 60 seconds to form a resin film with a thickness of 40 nm. The number of defects larger than 40 nm was measured on the obtained resin film using a surface defect observation device (KLA-Tencor, SurfScanSP5 instrument). The number of defects in the resin film formed using the chemical solutions filtered through the porous films of Example 1, Comparative Example 1, and Comparative Example 2 was determined as a relative value, with the number of defects in the resin film formed using the chemical solution filtered through the porous polyamide film obtained in Example 1 set to 1. The number of defects is shown in Table 1.

[0127]

[0128] Table 1 shows that when the porous film of Example 1, which has multiple spherical pores inside, with multiple spherical pores forming interconnected pores, and is provided with a polyamide-containing coating layer on its surface, and the mass ratio of the coating layer to the mass of the porous film is less than 5% by mass, is used as a filter to filter a crude chemical solution, metal impurities and fine particles can be effectively removed.

Claims

1. A porous film having a plurality of spherical pores inside, wherein the porous film comprises a porous substrate film and a coating layer covering at least a portion of the surface of the porous substrate film, the plurality of spherical pores are connected to adjacent spherical pores to form communicating pores, the coating layer contains a polyamide resin, and the ratio of the mass of the coating layer to the mass of the porous film is less than 5% by mass.

2. The porous film according to claim 1, wherein the porous substrate film is a porous polyimide film having a plurality of spherical pores inside, and in the porous polyimide film, the plurality of spherical pores are connected to adjacent spherical pores to form a communication pore.

3. The porous film according to claim 1, wherein the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less.

4. The porous film according to claim 1, wherein the ratio of the mass of the polyamide resin to the mass of the coating layer is 80% by mass or more.

5. A method for producing the porous film described in claim 1, comprising: coating at least a portion of the surface of the porous substrate film with a solution in which the material constituting the coating layer is dissolved in an organic solvent; removing excess of the solution from the porous substrate film whose surface at least a portion is coated with the solution; after removing excess of the solution, contacting the solution on the porous substrate film coated with the solution with a poor solvent for the material constituting the coating layer to form the coating layer on the surface of the porous substrate film; and drying the porous film after forming the coating layer.

6. The method for manufacturing a porous film according to claim 5, wherein the porous substrate film is a porous polyimide film having a plurality of spherical pores inside, and in the porous polyimide film, the plurality of spherical pores are connected to adjacent spherical pores to form a communication pore.

7. The method for producing a porous film according to claim 5, wherein the average pore diameter of the spherical pores is 10 nm or more and 200 nm or less.

8. The method for producing a porous film according to claim 5, wherein the ratio of the mass of the polyamide resin to the mass of the coating layer is 80% by mass or more.

9. A method for producing a purified chemical solution for use in the manufacture of semiconductor devices by purifying a crude chemical solution, comprising: filtering the crude chemical solution using a porous film described in any one of claims 1 to 4 as a filter; and recovering the liquid that has passed through the filter as the purified chemical solution.

10. The method according to claim 9, wherein the amount of metal impurities contained in the purified chemical solution is less than the amount of metal impurities contained in the crude chemical solution.

11. The method according to claim 9, wherein the number of fine particles contained in the purified drug solution is less than the number of fine particles contained in the crude drug solution, and the number of fine particles is the number of particles with a diameter of 0.135 μm or more in 1 mL of sample, as measured using a light scattering type liquid particle size counter.

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