Method for producing copper film

Abstract

A method for producing a copper film includes: a step for bringing metallic copper into contact with an ammonium aqueous solution of an acid which contains at least one acid selected from the group consisting of carboxylic acids, sulfuric acid, and nitric acid, ammonia, and a solvent to prepare an aqueous solution A for copper film formation; an oxygen supply step for supplying oxygen to the aqueous solution A for copper film formation to obtain an aqueous solution B for copper film formation; a step for mixing the obtained aqueous solution B for copper film formation with an organic reducing agent to prepare a composition for copper film formation; and a step for applying the obtained composition for copper film formation to a substrate.

Description

Method for manufacturing copper films

[0001] This disclosure relates to a method for manufacturing a copper film.

[0002] Copper films, which have excellent electrical and thermal conductivity, are used in a variety of applications. By reducing the thickness of the copper film, it can be made into a light-transmitting film. Copper films, which have high electrical conductivity and antibacterial properties, are useful for forming conductive layers, electromagnetic shields, and antibacterial components on substrate surfaces. Furthermore, copper films have good thermal conductivity, and can function as heat dissipation components when used in lighting equipment, for example.

[0003] However, obtaining high-purity copper from mined chalcopyrite requires first dissolving the chalcopyrite to obtain crude copper with few impurities, and then further refining such as electrolytic refining, which requires high energy. Therefore, there is a need for a simpler method to obtain high-purity copper from mined chalcopyrite.

[0004] Furthermore, because the amount of chalcopyrite mined is limited, the recycling of metallic copper is required from the perspective of ensuring a stable supply of resources. As a method of recycling metallic copper, for example, a heating and melting method is known in which solid copper wire is melted to remove impurities in order to recycle copper wire, which is a conductive material. However, for conductive copper thin films and copper thin films used as antibacterial materials formed on a substrate, it is difficult to peel off the copper thin film that is in close contact with the substrate, and the aforementioned heating and melting method was difficult to apply depending on the physical properties of the substrate, i.e., the heat resistance of the substrate.

[0005] A method has been proposed for forming a thin metal film, such as copper, on any substrate without applying conventionally known vapor phase methods. For example, as a method for producing a metal film that does not require heating treatment of 100°C or higher and can easily form a dense metal film on any substrate, a method has been proposed in which a metal film precursor liquid containing at least one selected from the group consisting of metal complexes and metal salts, and at least one selected from ammonia and amines, is used to form a metal film on any substrate by a liquid phase method (see Japanese Patent Publication No. 2021-70873: Patent Document 1). The method described in Patent Document 1 has the advantage of greater freedom in selecting the composition of the formed metal film, the material and shape of the substrate on which the metal film is formed, etc., compared to electrolytic plating, electroless plating, etc.

[0006] According to the technology described in Patent Document 1, a high-purity metal thin film with good adhesion can be formed on a substrate made of any material and having any shape. According to the method described in Patent Document 1, the formed metal thin film can be formed, for example, inside a tubular substrate. If such a high-purity metal thin film, especially a high-purity copper thin film, contained in the final product can be recycled as a resource, it would be useful in reducing fluctuations in resource prices and supply risks. However, for example, it is difficult to physically separate copper thin films from substrates that are not flat. Furthermore, when separating metallic copper thin films by dissolution, if a solvent capable of dissolving copper thin films is used, depending on the type of solvent, problems such as damage to the substrate, high environmental impact, and an increase in impurities in the resulting metal solution may occur, making the recycling of metallic copper difficult at present.

[0007] The object of one embodiment of this disclosure is to provide a method for manufacturing a copper film that can form a new high-purity copper film using used copper films and solid copper derived from crude copper containing impurities as raw materials.

[0008] The means for solving the above problems include the following embodiments: <1> A method for producing a copper film, comprising the steps of: preparing an aqueous solution A for copper film formation by contacting metallic copper with at least one acid selected from the group consisting of carboxylic acid, sulfuric acid, and nitric acid, ammonia, and an ammonium aqueous solution of an acid containing a solvent; supplying oxygen to the aqueous solution A for copper film formation to obtain an aqueous solution B for copper film formation; mixing the obtained aqueous solution B for copper film formation with an organic reducing agent to prepare a composition for copper film formation; and applying the obtained composition for copper film formation to a substrate. <2> The method for producing a copper film according to <1>, wherein the metallic copper is at least one solid copper selected from the group consisting of metallic copper contained in crude steel and recycled copper films.

[0009] <3> The method for producing a copper film according to <1> or <2>, wherein the oxygen supply step includes bubbling oxygen into the copper film forming aqueous solution A at a rate of 0.05 L / min to 10 L / min, supplying a total amount of 0.5 mol to 3.0 mol of oxygen per 1.0 mol of copper ions contained in the copper film forming aqueous solution A. <4> The method for producing a copper film according to at least one of <1> to <3>, wherein the carboxylic acid includes formic acid. <5> The method for producing a copper film according to at least one of <1> to <4>, wherein the organic reducing agent includes at least one selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid.

[0010] <6> The method for manufacturing a copper film according to at least one of <1> to <5>, wherein the oxygen supply step further includes a step of irradiating the copper film forming aqueous solution B with ultrasonic waves. <7> The method for manufacturing a copper film according to at least one of <1> to <6>, wherein the step of applying the copper film forming composition to a substrate includes at least one of the following: a step of coating the copper film forming composition onto the substrate, a step of immersing the substrate in the copper film forming composition, and a method of storing the copper film forming composition inside a container-shaped substrate.

[0011] According to one embodiment of the present invention, a method for producing a copper film can be provided that can form a new high-purity copper film using used copper films and solid copper derived from crude copper containing impurities as raw materials.

[0012] This graph shows the absorption spectra of aqueous solution B for copper film formation obtained in Examples 1 and 3 used in the copper film manufacturing method of this disclosure, and aqueous solution B for copper film formation prepared from the copper standard solution of Control Example 1. This is the XRD pattern of the copper film obtained by the manufacturing methods of Examples 1 and 3, and the copper film obtained by the manufacturing method of Control Example 1. This is an electron microscope image of the surface of the copper film obtained by the manufacturing method of Control Example 2. This is an electron microscope image of the surface of the copper film obtained by the manufacturing method of Example 7. This graph shows the absorption spectra of aqueous solution B for copper film formation obtained in Example 7 used in the copper film manufacturing method of this disclosure, and aqueous solution B for copper film formation prepared from the copper standard solution of Control Example 2. This is the XRD pattern of the copper film obtained by the manufacturing method of Example 7, and the copper film obtained by the manufacturing method of Control Example 2. This is an electron microscope image of the surface of the copper film obtained by the manufacturing method of Control Example 4. This is an electron microscope image of the surface of the copper film obtained by the manufacturing method of Example 8. This graph shows the absorption spectra of aqueous solution B for copper film formation obtained in Example 8 used in the copper film manufacturing method of this disclosure, and aqueous solution B for copper film formation prepared from the copper standard solution of Control Example 4. These are the XRD patterns of the copper film obtained by the manufacturing method in Example 8 and the copper film obtained by the manufacturing method in Control Example 4.

[0013] The method for manufacturing a copper film according to this disclosure will be described in detail below with reference to specific embodiments. The manufacturing method according to this disclosure is not limited to the following embodiments and can be implemented by various modifications as long as they do not contradict the spirit of the disclosure.

[0014] In this disclosure, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the lower and upper limits, respectively. In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this disclosure, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In numerical ranges described in steps in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described in steps. Also, in numerical ranges described in this disclosure, the upper or lower limit stated in one numerical range may be replaced with the value shown in the example. Also, in this disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In this disclosure, unless otherwise specified, room temperature and ambient temperature mean 25°C.

[0015] <Method for Manufacturing a Copper Film> The method for manufacturing a copper film according to the present disclosure (hereinafter sometimes simply referred to as "the method for manufacturing according to the present disclosure") includes the steps of: preparing an aqueous solution A for copper film formation by contacting metallic copper with at least one acid selected from the group consisting of carboxylic acid, sulfuric acid, and nitric acid, ammonia, and an aqueous ammonium solution of an acid containing a solvent (step a); supplying oxygen to the aqueous solution A for copper film formation to obtain an aqueous solution B for copper film formation (step b); mixing the obtained aqueous solution B for copper film formation with an organic reducing agent to prepare a composition for copper film formation (step c); and applying the obtained composition for copper film formation to a substrate (step d).

[0016] (Metallic copper) The metallic copper includes at least one solid copper selected from the group consisting of metallic copper contained in crude steel and copper films for recycling. In the present disclosure, "solid copper" means a solid containing copper whose solid shape is maintained at room temperature. Therefore, "solid copper" does not include a liquid containing copper ions dissolved by a solvent and copper that is heated and melted and has fluidity. Examples of the recycled metallic copper to be recycled include used conductive copper thin films, metallic copper thin films used as antibacterial materials, and copper wires. As the copper as the recycled metallic copper, in one embodiment, it may be powder copper obtained by peeling a metallic copper thin film disposed on a substrate from the substrate and pulverizing it, or solid copper obtained by cutting or pulverizing a copper wire after peeling a coating layer from a copper wire having a coating layer. Examples of the metallic copper contained in crude steel include metallic copper contained in unrefined chalcopyrite and the like.

[0017] (Step a) Step a is a step of preparing an aqueous solution A for copper film formation by bringing metallic copper into contact with an ammonium aqueous solution of an acid containing at least one acid selected from the group consisting of carboxylic acid, sulfuric acid, and nitric acid, ammonia, and a solvent. In step a, an ammonium aqueous solution of an acid is brought into contact with metallic copper to be recycled or purified to dissolve the metallic copper, and an aqueous solution A for copper film formation containing copper ions in which ammonium is coordinated to copper is prepared. The ammonium aqueous solution of an acid is a mixed solution containing at least one acid selected from the group consisting of carboxylic acid, sulfuric acid, and nitric acid, ammonia, and a solvent, and the aqueous solution of an acid may be, for example, an ammonium carboxylate aqueous solution, an ammonium sulfate aqueous solution, or an ammonium nitrate aqueous solution. Examples of the carboxylic acid include monovalent carboxylic acids, and formic acid and alkyl carboxylic acids having an alkyl group with 1 to 5 carbon atoms. Among them, from the viewpoint of the solubility of metallic copper, the carboxylic acid preferably contains formic acid. From the viewpoint that it is easy to prepare an ammonium carboxylate aqueous solution, the carboxylic acid used for preparing the ammonium carboxylate aqueous solution is preferably used as an ammonium carboxylate salt. When an inorganic acid selected from sulfuric acid and nitric acid is used for preparing the ammonia aqueous solution of an acid, it is preferably used as an ammonium sulfate salt and an ammonium nitrate salt.

[0018] The aqueous ammonium carboxylate solution can be prepared by dissolving an ammonium carboxylate salt in an amount of 1.5 to 5 times the amount of copper contained in the solid copper used, and aqueous ammonia in an amount of 2 to 5 times the amount of copper contained in the solid copper, both based on mass, in water. The content of the ammonium carboxylate salt, preferably ammonium formate salt, is preferably 1.5 to 3 times the amount of copper, more preferably about 2 times the amount of copper, both based on mass.

[0019] The case of using an aqueous ammonium solution of an inorganic acid in step a will be described. Taking as an example the case of using at least one selected from an aqueous ammonium sulfate solution and an aqueous ammonium nitrate solution as the aqueous ammonium solution of an inorganic acid. In at least one selected from the aqueous ammonium sulfate solution and the aqueous ammonium nitrate solution, at least one salt selected from ammonium sulfate salt and ammonium nitrate salt in an amount of 1.5 to 5 times the amount of copper contained in the solid copper used, and aqueous ammonia in an amount of 2 to 5 times the amount of copper contained in the solid copper, both based on mass, can be dissolved in water for preparation. The content of at least one salt selected from ammonium sulfate salt and ammonium nitrate salt in the above aqueous solution is preferably 1.5 to 3 times the amount of copper, more preferably about 2 times the amount of copper, both based on mass. Here, about 2 times the amount means a range of 2 ± 0.1 times the amount.

[0020] The content of aqueous ammonia is preferably 3.5 to 4.5 times the amount of copper, more preferably about 4 times the amount of copper, both based on mass. Here, about 4 times the amount means a range of 4 ± 0.2 times the amount.

[0021] As the solvent in aqueous solution A for copper film formation, an aqueous solvent such as water or a mixture of water and alcohol can be used. The water is preferably low in impurities, particularly ions other than metal ions. From this viewpoint, purified water, ion-exchanged water, or pure water is preferred. Examples of alcohols include monohydric alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, isopropanol, n-propanol, isobutanol, and n-butanol, as well as polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, and glycerin.

[0022] From the viewpoint of solubility and handling of the ammonium salt of the acid in aqueous solution A for copper film formation, the aqueous solvent is preferably water or a mixture of water and a monohydric alcohol having 1 to 5 carbon atoms, more preferably water or a mixture of water and at least one alcohol selected from methanol, ethanol, and propanol, and even more preferably water. When a mixture of water and alcohol is used as the solvent, the mixing ratio is appropriately selected depending on the purpose. When a mixture of water and alcohol is used as the solvent, the alcohol content relative to the total amount of the water-alcohol mixture is preferably 1% to 60% by mass.

[0023] In step a, it is preferable to first mix the ammonium salt of the acid with a solvent such as water, and then add aqueous ammonia to prepare the aqueous solution. By adding aqueous ammonia to the solution of the ammonium salt of the acid, it is easy to control the mixing ratio of acid and ammonium in the aqueous solution of the ammonium acid.

[0024] The obtained ammonium aqueous solution of acid is brought into contact with metallic copper to dissolve the metallic copper. The metallic copper dissolves in the ammonium aqueous solution of acid and exists as copper ions, yielding aqueous solution A for copper film formation. From the viewpoint of copper film formation efficiency, the ratio of copper (Cu):carboxylic acid (e.g., HCOOH):ammonia (NH) is as follows, relative to the copper ion concentration. ３)(6.0 to 6.5) is preferably prepared in the range of 1:2:(6.0 to 6.5), and more preferably prepared in the range of 1:2:(6.2 to 6.5). The content ratio of copper ions to ammonia (hereinafter sometimes referred to as "Cu / NH ３ ") is considered to contribute to the copper film forming property in the copper film forming composition described later. The content ratio of copper ions to ammonia in the aqueous solution A for copper film formation can be easily controlled by the amount of aqueous ammonia used in the preparation of the aqueous solution A for copper film formation, as described above.

[0025] (Step b) Step b is an oxygen supply step of supplying oxygen to the aqueous solution A for copper film formation obtained in the above-described step a to obtain an aqueous solution B for copper film formation. By supplying oxygen to the aqueous solution A for copper film formation, the following reaction occurs, and it is considered that copper ions contained in the aqueous solution A for copper film formation form a complex with ammonia, and an aqueous solution B for copper film formation containing a copper ammonia complex is obtained. The following describes an example when formic acid is used as the acid. Cu + 2HCOONH ４ + 4NH ３ + 1 / 2O ２ → [[Cu(NH ３ ) ６ ２＋ + 2HCOO － + H ２ O

[0026] Since the aqueous solution B for copper film formation contains a copper complex ([Cu(NH ３ ) ６ ２＋ ), the formation of a copper film in the subsequent step becomes easy.

[0027] ​​To promote the reaction exemplified above, it is preferable to supply a sufficient amount of oxygen in step b. When supplying a sufficient amount of oxygen, it is preferable to gradually supply oxygen to the copper film-forming aqueous solution A as the reaction progresses, rather than supplying the amount of oxygen necessary for the reaction to sufficiently increase the dissolved oxygen concentration in the copper film-forming aqueous solution A obtained in step a from the beginning of step b. Considering the solubility of oxygen in the copper film-forming aqueous solution A, it is considered preferable to continuously supply oxygen as the reaction progresses, as this allows the reaction to proceed more efficiently. Therefore, it is preferable to supply oxygen by continuously supplying a constant amount of oxygen to the copper film-forming aqueous solution A by means of, for example, bubbling, and as a result, supply the amount of oxygen necessary for the reaction by the end of step b. From the above viewpoint, it is preferable that the oxygen supply step includes a step of bubbling oxygen into the copper film forming aqueous solution A at a rate of 0.05 L / min to 10 L / min, thereby supplying a total amount of 0.5 mol to 3.0 mol of oxygen per 1.0 mol of copper ions contained in the copper film forming aqueous solution A.

[0028] In the oxygen supply process, oxygen may be supplied using either oxygen gas or air. Oxygen can be supplied, for example, by bubbling, in which a glass bubbler is attached to the end of a rubber tube connected to an oxygen cylinder, the tip of the bubbler is inserted into the copper film-forming aqueous solution A, and oxygen is supplied to the copper film-forming aqueous solution A in the form of bubbles. In one embodiment, the tip of the bubbler is inserted into a container filled with the copper film-forming aqueous solution A to which the regenerated copper film to be dissolved is attached, and oxygen can be supplied by blowing, for example, 0.1 L / min of oxygen through for 30 minutes. By supplying oxygen to the copper film-forming aqueous solution A by bubbling, a copper ammonia complex is rapidly formed by the reaction described above, and a copper film-forming aqueous solution B containing copper ammonium complex ions can be obtained. Alternatively, since air contains oxygen, air may be used instead of oxygen gas, and oxygen may be supplied to the copper film-forming aqueous solution A by bubbling air into the copper film-forming aqueous solution A using a glass bubbler. By adjusting the amount of air supplied and the supply time, i.e., the duration of bubbling, the same effect as when oxygen gas is bubbling can be achieved. In one embodiment, supplying a total amount of 0.5 mol to 3.0 mol of oxygen into the copper film forming aqueous solution A is preferable because it produces the same effect as when oxygen gas is bubbling.

[0029] (Step c) Step c is a step of preparing a copper film-forming composition by mixing the copper film-forming aqueous solution B obtained in step b with an organic reducing agent. The organic reducing agent includes at least one selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid. From the viewpoint of better copper film formation, it is preferable that the organic reducing agent is at least one selected from ascorbic acid, citric acid, and 3,4,5-trihydroxybenzoic acid, and more preferably at least one selected from ascorbic acid and citric acid. By including ascorbic acid as the organic reducing agent in the copper film-forming composition, copper film formation on the substrate and the like is performed more efficiently.

[0030] The organic reducing agent may be mixed with the copper film-forming aqueous solution B in a solid, i.e., powder state, or it may be mixed as an aqueous solution of the organic reducing agent that has been dissolved in water beforehand. The copper film-forming composition is NH capable of forming copper complexes as described above. ３ Ligand, or RNH ２ It is believed to be a composition containing a reaction product between a ligand (R represents an alkylene group) and copper ions. The copper film-forming composition containing aqueous solution B for copper film formation and an organic reducing agent such as ascorbic acid functions as a copper precursor solution for copper film formation.

[0031] In step c, the amount of organic reducing agent relative to the copper content in the copper ions or copper-ammonium complex ions contained in the copper film-forming composition can be 2 to 5 times by mass, and in particular, from the viewpoint of obtaining better copper film-forming properties of the obtained copper film-forming composition, it is preferable that the amount of organic reducing agent relative to the copper content in the copper ions or copper-ammonium complex ions is 3 to 4 times by mass. The obtained copper film-forming composition is useful for forming copper films.

[0032] In step c, after the oxygen supply step when preparing the copper film-forming aqueous solution B, it is preferable to further include a step of irradiating the copper film-forming aqueous solution B with ultrasound. Irradiating the copper film-forming aqueous solution B with ultrasound increases the amount of dissolved oxygen due to the oxygen supplied to the copper film-forming aqueous solution A, and the above-mentioned reaction in the resulting copper film-forming composition is promoted. As a result, the content of copper ammonium complex ions in the resulting copper film-forming composition increases, and it is thought that the amount and quality of the copper film formed in step d described later will be further improved. Furthermore, it can be expected that residual gas in the aqueous solution will be removed by irradiating with ultrasound. The pH of the copper film-forming composition in this disclosure at room temperature (liquid temperature of the composition: 25°C) is preferably 6 to 8, and more preferably in the neutral range around pH 7.5. The pH of the copper film-forming composition can be measured with a known pH meter.

[0033] (Step d) Step d is a step of applying the copper film-forming composition obtained in step c to the substrate. There are no particular restrictions on the step of applying the copper film-forming composition to the substrate, and various known methods such as coating methods and immersion methods can be applied depending on the material, shape, etc. of the substrate. In particular, it is preferable that step d includes at least one of the following: a step of coating the copper film-forming composition to the substrate, a step of immersing the substrate in the copper film-forming composition, and a method of storing the copper film-forming composition inside a container-shaped substrate.

[0034] Methods for applying the copper film-forming composition to a substrate include, for example, spray coating, spin coating, blade coating, bar coating, roll coating, die coating, and flow coating. Alternatively, the copper film-forming composition may be applied to the substrate by casting. Printing methods such as screen printing and inkjet printing can be applied locally to the substrate. Using printing methods allows for the formation of a copper film locally only in desired areas of the substrate. Generally, the amount of copper film-forming composition applied is preferably in the range of 1 μm to 10 μm, and more preferably in the range of 3 μm to 5 μm, in terms of wet film thickness.

[0035] When applying a copper film-forming composition, such as by immersion, an immersion method is used, which involves immersing the substrate in the copper film-forming composition. This method allows for easy formation of a copper film on a molded substrate of any shape, or formation of a copper film on both sides of a flat substrate.

[0036] According to the manufacturing method of this disclosure, a copper film can be formed on the surface of a substrate simply by bringing the copper film-forming composition into contact with the substrate surface. Therefore, by employing a method of storing the copper film-forming composition inside a container-shaped substrate, a copper film can be formed only on the inner surface of the container-shaped substrate. For example, when forming a copper film only on the inner surface of a glass container having one end open and the other sealed, the copper film-forming composition can be injected into the glass container from the open end and stored inside the glass container, thereby forming a copper film only on the inside of the glass container. Examples of glass container shapes include cylindrical and prismatic shapes. Furthermore, when forming a copper film on a plate-shaped substrate, the plate-shaped substrate can be placed in a water-impermeable box-shaped or petri dish-shaped container, and the copper film-forming composition can be injected into the container and stored therein, thereby forming a copper film on the plate-shaped substrate. When forming a copper film on only one side of the substrate, masking can be applied to the side where the copper film is not to be formed. By applying this method, a copper film can be easily formed only on the contact surface between the copper film-forming composition and a substrate of any shape by bringing the copper film-forming composition into contact with the substrate and leaving it for a predetermined time. Furthermore, a copper film can be formed on the inner surface of any hollow tube by injecting the copper film-forming composition into a hollow tube such as a cylindrical or prismatic tube and sealing both ends.

[0037] After applying the copper film-forming composition to the substrate to form a coating film (copper film-forming composition layer), it is preferable to allow it to stand for a certain period of time, from the viewpoint of forming a denser film. The standing time is preferably 6 hours or more, and more preferably 12 hours or more, at room temperature (25°C). By allowing the copper film-forming composition layer formed on the substrate to stand, copper ions, copper ammonium complex ions, etc., contained in the copper film-forming composition are adsorbed onto the substrate to form a copper film. There is no particular upper limit to the standing time, but considering productivity, it can be 120 hours or less, and preferably 90 hours or less. When allowing the standing time after applying the copper film-forming composition to the substrate to form a copper film-forming composition layer, the ambient temperature of the standing area and the liquid temperature of the formed copper film-forming composition layer to be above room temperature, for example, 30°C or higher, preferably 40°C or higher, increases the reaction rate, and a denser copper film can be formed in a shorter standing time. The ambient temperature of the area where the material is left to stand is preferably 80°C or lower, from the viewpoint of minimizing the impact on the copper film-forming composition. After the copper film is formed, any remaining copper film-forming composition may be removed.

[0038] (Substrate) The substrate for forming the copper film can be appropriately selected according to the purpose. According to the manufacturing method of this disclosure, a copper film can be formed on the substrate simply by applying the copper film forming composition to the substrate. Therefore, according to the manufacturing method of this disclosure, if we focus on the material, a copper film can be formed on substrates such as non-conductive substrates and substrates with low heat resistance. Furthermore, if we focus on the shape of the substrate, a copper film can be formed on substrates of any shape, such as curved substrates, porous substrates, and the inside of cylindrical substrates. Accordingly, depending on the intended use of the copper film, a substrate having various physical properties such as heat resistance, dimensional stability, solvent resistance, electrical insulation, processability, gas barrier properties, low moisture absorption, and waterproofing can be arbitrarily selected and used. For example, materials commonly used as circuit boards can be used as substrates. As a substrate, inorganic substrates such as glass, ceramics, and metals are preferred from the viewpoint of good dimensional stability. More specifically, inorganic substrates include glass substrates such as alkali-free glass substrates, soda glass substrates, Pyrex® glass substrates, and quartz glass substrates; semiconductor substrates such as silicon substrates; metal substrates such as stainless steel substrates, aluminum substrates, and zirconium substrates; and metal oxide substrates such as alumina substrates.

[0039] The manufacturing method of this disclosure does not require heat treatment at 100°C or higher, and since it is possible to form a copper film on a substrate, organic substrates can also be suitably used. As organic substrates, copper films can be easily formed not only on resin substrates such as thermosetting resins with relatively high heat resistance, such as engineering plastics, but also on organic substrates containing resins with relatively low heat resistance, such as certain thermoplastic resins and thermosetting resins. Therefore, the manufacturing method of this disclosure also has the advantage that, for example, a copper film can be easily formed on any surface of a molded body, even on a pre-molded thermosetting resin molded body, a thermoplastic resin molded body, etc. Examples of resins that can be used as organic substrates include fluororesins such as tetrafluoroethylene, and resins with relatively good heat resistance such as polyethylene terephthalate (PET), high-density polyethylene, and polyimide.

[0040] The copper film-forming composition obtained through step c described above contains copper-ammonium complex ions derived from solid copper uniformly and at a high concentration in the aqueous solvent, and the stability of the copper-ammonium complex ions is good due to the function of the coexisting organic reducing agent. Since the copper-ammonium complex ions contained in the copper film-forming composition have good adsorption properties to the surface of hard substrates, a copper film with a dense structure can be formed on any substrate surface. That is, according to the manufacturing method of this disclosure, copper ions contained in the aqueous solution for copper film formation containing copper ions derived from solid copper become copper-ammonium complex ions, and by applying the copper film-forming composition containing copper-ammonium complex ions to any substrate, the copper-ammonium complex ions are adsorbed onto the substrate surface, and a dense copper film is formed.

[0041] Therefore, by using an ammonium formate aqueous solution, for example, to elute copper ions from copper thin films and crude copper containing impurities that are submitted for recycling, and converting the copper ions into copper-ammonium complex ions, a high-purity copper film can be formed on any substrate. According to the copper film-forming composition in the manufacturing method of this disclosure, copper nanoparticles derived from copper-ammonium complex ions adhere to the substrate to form a copper film, and the formed copper film has excellent electrical and thermal conductivity. Furthermore, since the copper-ammonium complex contained in the copper film-forming composition has a ligand derived from ammonium, it exhibits good adhesion to inorganic substrates, especially glass substrates. Therefore, a copper film formed using copper-ammonium complex ions can be expected to have excellent adhesion to inorganic substrates.

[0042] The copper thin film formed on the substrate may be subjected to a drying process. Performing a drying process allows for the more rapid formation of a copper film that adheres closely to the substrate. Drying may be carried out at room temperature or by heating under conditions that do not affect the substrate.

[0043] In the manufacturing method of the present disclosure, when forming a thicker copper film, the steps of applying the copper film-forming composition to the substrate (step d) and drying the copper film-forming composition applied to the substrate can be performed multiple times.

[0044] The thickness of the copper film obtained by the manufacturing method of this disclosure is selected according to the purpose. Since the copper film-forming composition in this disclosure contains a uniform amount of copper ammonium complex in a dissolved state, it is possible to form an extremely thin copper film, for example, 10 nm to 200 nm thick. Furthermore, by applying a method that involves repeatedly applying the copper film-forming composition and drying the copper film-forming composition multiple times, it is possible to easily form a thicker copper film, specifically a copper film with a thickness of several microns. When using the copper film-forming composition described above, the thickness of the copper film formed in a single application is preferably 50 nm to 150 nm. The thickness of the obtained copper film can be measured by observing a cross-section of the copper film formed on the substrate with a scanning electron microscope or the like, using a known measurement method.

[0045] According to the manufacturing method of this disclosure, by obtaining a copper film-forming composition derived from solid copper, it is possible to form a high-purity copper film on conductive and non-conductive substrates of various shapes, including not only flat substrates but also curved substrates and porous substrates, thus having a wide range of applications.

[0046] The manufacturing method of this disclosure will be described in detail below with reference to examples, but this disclosure is not limited to the following examples and can be implemented in various modified forms as long as it does not exceed the spirit of the disclosure.

[0047] [Example 1] (1. Preparation of Aqueous Solution A for Copper Film Formation and Dissolution of Metallic Copper) A solution containing 208 g of purified water, 17.0 g of ammonium formate aqueous solution (ammonium formate concentration: 1.0 mmol / g: manufactured by Kanto Chemical Co., Ltd.), and 37.3 g of 25% to 28% by mass aqueous ammonia solution (manufactured by Taisei Chemical Co., Ltd.) was prepared and stirred at 500 rpm (revolutions / min: the same applies hereafter) for 10 minutes to obtain ammonium formate aqueous solution. The obtained ammonium formate aqueous solution was poured into a cylindrical glass container (diameter: 16 mm, length: 1.5 m) on which a copper film with a thickness of approximately 5 μm was formed on the inside, and the copper film was dissolved to obtain aqueous solution A for copper film formation. The obtained aqueous solution A for copper film formation was observed to be pale blue in color by visual inspection. (Step a)

[0048] (2. Preparation of Copper Film Forming Aqueous Solution B) To the copper film forming aqueous solution A obtained above, oxygen gas was passed through the cylindrical glass container at a rate of 1.0 L / min for 15 minutes using a bubbler, and then the container was shaken and stirred for 1 hour to obtain copper film forming aqueous solution B. Copper film forming aqueous solution B contained dissolved oxygen and copper ions dissolved from the metallic copper on the inside of the glass container at a concentration of approximately 0.2 mmol / g. Visual observation revealed that the obtained copper film forming aqueous solution B was dark blue in color. (Step b) The copper ion content in copper film forming aqueous solution B was measured by atomic absorption spectroscopy (AAS). AAS is a method that utilizes the property of atoms to absorb light of a specific wavelength, atomizing the sample at high temperature and measuring the amount of light absorbed at that time to perform quantitative analysis of elements. In this disclosure, copper was used as the target of measurement, and the values ​​obtained using an atomic absorption spectrophotometer (AA-7000, manufactured by Shimadzu Corporation) were adopted as the instrument.

[0049] (3. Preparation of the copper film-forming composition) 311 g of ascorbic acid powder (manufactured by Kanto Chemical Co., Ltd.) was added to the obtained copper film-forming aqueous solution B, and the mixture was stirred at a liquid temperature of 26°C for 20 minutes to thoroughly dissolve the ascorbic acid powder and obtain the copper film-forming composition. Cu:NH in the copper film-forming composition ３ (Step c) The content ratio of each component in the copper film-forming composition was adjusted by adding aqueous ammonia so that the content ratio of ascorbic acid was 1:6.2:3.4. (Step c) The pH of the copper film-forming composition obtained in Example 1 was measured using a pH meter (PICCOLO+, HANNA Instruments), and the pH of the copper film-forming composition at 25°C was 7.5.

[0050] (4. Application of copper film-forming composition to substrate) A borosilicate glass substrate (length: 100 mm, width: 100 mm, thickness: 1.1 mm) was thoroughly washed with pure water, and masking tape was applied to the side opposite to the side on which the copper film would be formed (hereinafter also referred to as the back side) to mask it, and it was used as a substrate. The prepared glass substrate was placed in a plastic tray (inner dimensions: 280 mm x 190 mm, depth 24.0 mm) with the masked side in contact with the bottom of the container. The copper film-forming composition obtained in step c was poured into the container in an amount that completely immersed the glass substrate, a plastic corrugated cardboard lid was placed over the container, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film-forming composition was discharged from the container, and a copper film was formed on one side of the glass substrate. The glass substrate on which the copper film was formed was washed with pure water and then dried at 70°C for 1 hour to obtain a glass substrate on which a copper film was formed on one side. (Step d)

[0051] [Example 2] Except for changing the standing temperature conditions after injecting the copper film-forming composition obtained in step c in step d of Example 1 from 24°C to 25±1°C, a copper film was formed on one side of a borosilicate glass substrate in the same manner as in Example 1.

[0052] [Example 3] During the preparation of the copper film-forming composition in step c of Example 1, the Cu:NH in the copper film-forming composition ３ A copper film was formed on one side of a borosilicate glass substrate in the same manner as in Example 1, except that the amount of ammonia water added was controlled so that the ascorbic acid content ratio was 1:6.5:3.4 to obtain a composition for forming a copper film.

[0053] [Example 4] In Example 1, a copper film was formed on one side of a borosilicate glass substrate in the same manner as in Example 1, except that after supplying oxygen, ultrasonic waves were irradiated for 10 minutes using an ultrasonic oscillator (product name: 3510J-MT, manufactured by Yamato Scientific Co., Ltd.) when preparing the aqueous solution B for copper film formation in step b of Example 1.

[0054] [Example 5] During the preparation of the copper film-forming composition in step c of Example 1, the Cu:NH in the copper film-forming composition ３A copper film was formed on one side of a borosilicate glass substrate in the same manner as in Example 1, except that the amount of ammonia water added was controlled so that the ascorbic acid content ratio was 1:6.0:3.4 to obtain a composition for forming a copper film.

[0055] [Example 6] During the preparation of the copper film-forming composition in step c of Example 1, the Cu:NH in the copper film-forming composition ３ A copper film was formed on one side of a borosilicate glass substrate in the same manner as in Example 1, except that the amount of ammonia water added was controlled so that the ascorbic acid content ratio was 1:6.4:3.4 to obtain a composition for forming a copper film.

[0056] [Control Example 1] (1. Preparation of Copper Film Forming Composition) Instead of the regenerated copper film, a copper film forming composition A was prepared using a reagent containing copper ions. 35 g of pure water was mixed with 5.78 g of copper formate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a metal salt, and 10.48 g of 25% by mass aqueous ammonia. The mixture was stirred at room temperature at 500 rpm for 1 hour to obtain a mixture (copper film forming aqueous solution B). Further pure water was added to adjust the copper ion concentration in the mixture to 0.2 mmol / g. Then, 8 g of ascorbic acid was mixed in and stirred at room temperature (25°C) at 500 rpm for 30 minutes. After that, further pure water was added to obtain the standard copper film forming composition. A copper film was formed on one surface of a borosilicate glass substrate in the same manner as in Example 1, except that the copper film-forming composition obtained by the manufacturing method of Control Example 1 was obtained during the preparation of the copper film-forming composition in step c of Example 1.

[0057] [Evaluation of copper film-forming composition and obtained copper film] (1. pH of copper film-forming composition) NH ３ The pH of the copper film-forming compositions obtained in Examples 1, 3, 5, and 6, each with a different Cu ratio, was measured at a liquid temperature of 25°C using a pH meter (PICCOLO+, HANNA Instruments). The results are shown in Table 1 below.

[0058] (2. Amount of copper deposited) The amount of copper deposited in the copper film formed using the copper film-forming compositions obtained by the manufacturing methods of Examples 1 to 6 and Control Example 1 was measured by the following method. In step d, the mass of the borosilicate glass substrate (with masking layer) before injection of the copper film-forming composition was measured. Then, the copper film-forming composition obtained in step c was injected into a container in which the borosilicate glass substrate was placed, and a copper film was formed on one side of the borosilicate glass substrate in the same manner as in Example 1. After 24 hours, the copper film-forming composition was discharged from the container in which the borosilicate glass substrate was placed, the borosilicate glass substrate was washed with pure water, and then dried at 70°C for 1 hour to obtain a glass substrate with a copper film formed on one side, and its mass was measured. The difference in mass of the glass substrate before and after copper film formation was calculated and taken as the amount of copper deposited. The measurement was performed five times using different glass substrates, and the average value was taken as the amount of copper deposited (g). The results are shown in Table 1 below.

[0059]

[0060] As shown in Table 1, NH ３ As the Cu / H ratio increased from 6.0 to 6.5, the pH of the copper film-forming composition tended to rise. ３ In Example 3, where the Cu / Cu ratio was 6.5, the pH of the composition was higher than that of Control Example 1, which used a standard solution. Although the amount of copper film deposited in Example 3 was relatively small, the formed copper film had good uniformity in appearance. Furthermore, the copper films obtained by the manufacturing methods of Examples 1 to 6 showed almost the same amount of copper deposition as the copper film formed by the manufacturing method of Control Example 1, using a reagent containing copper ions as a raw material.

[0061] (3. Absorption spectrum of copper film forming composition) Of the above examples, NH ３The absorption spectra of the copper film-forming aqueous solution B obtained in Examples 1 and 3 with different Cu ratios, and the copper film-forming aqueous solution B prepared from the copper standard solution of Control Example 1 described later, were measured under the following conditions. The results are shown in Figure 1. As is clear from the graph showing the absorption spectra in Figure 1, the absorption spectra of the copper film-forming aqueous solution B derived from existing copper films and the copper film-forming aqueous solution B prepared from the copper standard solution in the control example are in good agreement. This indicates that the copper film-forming aqueous solution B obtained in Examples 1 and 3 derived from existing copper films is useful for forming high-purity copper films, similar to the copper film-forming aqueous solution B prepared with reagents.

[0062] (4. Composition of Copper Film) X-ray diffraction (XRD) was measured on the copper films formed from the copper film-forming compositions obtained in Example 1, Example 3, and Control Example 1 using a SMART Lab apparatus (RIGAKU Corporation) with a parallel beam optical system at an incident angle of 0.3°, measuring the intensity in 0.05° steps from 2θ of 10° to 80°, with a fixed time of 5° / min. The obtained XRD patterns are shown in Figure 2. As is clear from Figure 2, the films obtained in Example 1 and Example 3 were confirmed to be single-phase copper, similar to the film obtained in Control Example 1.

[0063] (5. Resistance of the Copper Film) For Examples 1 to 4, in which the amount of copper film deposition was relatively good, the resistance of the copper film was measured using the following method. To measure the resistance (surface resistance) of the copper film formed on the surface of the prepared glass substrate, a pair of measuring terminals located at the ends of a pair of conductors connected to a resistance meter were applied to two points near the opposing ends of the glass substrate on which the copper film was formed, and the measurement was performed using the two-terminal method with a resistance meter (Sanwa Electric Instrument Co., Ltd.). The results are shown in Table 2 below.

[0064]

[0065] From the results in Table 2, Cu:NH in copper film forming composition ３ Example 1, in which the ascorbic acid content ratio was 1:6.2:3.4, showed a large amount of copper deposition, a low resistance value of the formed copper film, and good electrical conductivity. Furthermore, the Cu:NH in the copper film forming composition ３In Example 3, where the ascorbic acid content ratio was 1:6.5:3.4, the amount of copper deposited was small, but the appearance of the film was uniform, the resistance of the formed copper film was low, and the electrical conductivity was good. Furthermore, in Example 2, where the standing temperature was increased and the standing conditions were changed in Example 1, and in Example 4, where ultrasound was irradiated after oxygen supply, the amount of copper deposited was greater and the resistance of the formed copper film was lower compared to Example 1.

[0066] Next, a copper film was formed using a copper film-forming composition containing a different copper ion reagent, and its physical properties were measured as the copper film formed in Control Examples 2 to 4. Then, the copper film obtained in the control examples was used as recycled metallic copper, and a recycled copper film was formed by applying the recycled metallic copper using the manufacturing method of the present disclosure, and the physical properties of the two films were compared.

[0067] [Control Example 2] (1. Preparation of Copper Film Forming Composition) Instead of the regenerated copper film, a copper film forming composition was prepared using a reagent containing copper ions, specifically copper formate tetrahydrate, a metal salt. 78 g of pure water was mixed with 7.298 g of 28.8% by mass aqueous ammonia and stirred at room temperature (25°C) for 1 minute. The pH of the liquid was then adjusted to 11.8 with 2.5% by mass aqueous ammonia, and 4.06 g of copper formate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a metal salt, was added. The mixture was stirred at room temperature at 500 rpm for 1 hour to obtain the mixture. Pure water was further added to adjust the copper ion concentration in the mixture to 0.2 mmol / g to obtain an aqueous copper complex solution. To the aqueous solution of the copper complex, 10.78 g (61 mmol) of ascorbic acid was added and mixed, and the mixture was stirred at 500 rpm for 20 minutes at room temperature (25°C). Then, pure water was added to obtain the standard copper film-forming composition, Control Example 1. The content ratio of copper, ammonia, and ascorbic acid in the obtained copper film-forming composition of Control Example 1 was calculated (Cu ２＋ : NH ３ : H ２ The ratio of AA was 1.0:6.9:3.4.

[0068] (2. Formation and evaluation of copper film on borosilicate glass substrate) A glass substrate of the size (length: 20 mm, width: 20 mm, thickness: 1.1 mm) was used as the borosilicate glass substrate, and a masked glass substrate was prepared in the same manner as in Control Example 1. A Petri dish (inner diameter φ35.0 mm, depth 9.4 mm) was prepared, and the prepared glass substrate was placed in it so that the masked surface was in contact with the container. The copper film forming composition obtained above from Control Example 2 was poured into the Petri dish in an amount that completely immersed the glass substrate, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film forming composition was discharged from the container, and a copper film was formed on one side of the glass substrate. The glass substrate with the copper film formed on it was immersed in 1 L of pure water and shaken for 1 minute, and this was repeated three times to wash it with pure water, and then dried at 70°C for 1 hour to obtain a glass substrate with a copper film formed on one side. The yield of the obtained copper film was 0.016 g, the film thickness was 7.4 μm, and the density of the copper film was 5.6 g / cm³. ３ Therefore, the resistivity (volume resistivity) of the copper film measured by the method described above is 8.1 × 10⁻⁶. －４ The resistance was Ωcm, confirming that the formed copper film was conductive. In control example 2, the resistivity of the copper film was measured using the four-probe method. The measurements were performed using a digital multimeter: VOAC7512, manufactured by Iwasaki Communications Co., Ltd., and a KEITHLEY Model 2010 Multimeter (both trade names). Using the four-probe method, five points were measured on the sample, and the average value was calculated from the three points excluding the maximum and minimum measured values ​​to obtain the electrical resistance value of the copper film. The four-probe method allows for the measurement of the volume resistivity of the copper film.

[0069] [Control Example 3] (1. Preparation of Copper Film Forming Composition) An aqueous solution of the copper complex was obtained in the same manner as in Control Example 1. To the obtained aqueous solution of the copper complex, 53.89 g (306 mmol) of ascorbic acid was added and mixed, and the mixture was stirred at 500 rpm for 20 minutes at room temperature (25°C). Then, pure water was added to obtain the copper film forming composition of Control Example 3. The content ratio of copper, ammonia, and ascorbic acid in the obtained copper film forming composition of Control Example 3 (Cu ２＋ : NH ３ : H ２The ratio of AA was 1.0:6.9:3.4. The pH of the solution, measured in the same manner as in Example 1, was 10.7.

[0070] (2. Formation and Evaluation of Copper Film on Borosilicate Glass Substrate) A masked glass substrate was prepared in the same manner as in Control Example 1, except that a borosilicate glass substrate (length: 100 mm, width: 100 mm, thickness: 1.1 mm) was used. The glass substrate was placed in a plastic tray (internal dimensions: 280 mm x 190 mm, depth: 24.0 mm) similar to that in Example 1. The copper film-forming composition obtained in Control Example 2 was poured into the container in an amount sufficient to completely immerse the glass substrate. A corrugated plastic lid was placed over the container, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film-forming composition was discharged from the container, and a copper film was formed on one side of the glass substrate. The glass substrate with the copper film formed on it was immersed in 1 L of pure water and shaken for 1 minute. This was repeated three times to wash it with pure water, and then dried at 70°C for 1 hour to obtain a glass substrate with a copper film formed on one side. The yield of the obtained copper film was 1.16 g, the film thickness was 15.4 μm, and the density of the copper film was 5.7 g / cm³. ３ Therefore, the resistivity of the copper film measured using the four-probe method, similar to control example 2, was 1.6 × 10⁻⁶. －３ The coefficient of conductivity was Ωcm, and it was confirmed that the copper film formed by the manufacturing method of control example 3 was electrically conductive.

[0071] Next, a glass substrate with dimensions of (length: 20 mm, width: 20 mm, thickness: 1.1 mm) was used as the borosilicate glass substrate, and a masked glass substrate was prepared in the same manner as in Control Example 1. A Petri dish (inner diameter φ35.0 mm, depth 9.4 mm) was prepared, and the prepared glass substrate was placed in it so that the masked surface was in contact with the container. The copper film-forming composition obtained above from Control Example 3 was poured into the Petri dish in an amount sufficient to completely immerse the glass substrate, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film-forming composition was drained from the container, and a copper film was formed on one side of the glass substrate. The glass substrate with the copper film formed on it was immersed in 1 L of pure water and shaken for 1 minute, and this was repeated three times to wash it with pure water. After that, it was dried at 70°C for 1 hour to obtain a glass substrate with a copper film formed on one side. The yield of the obtained copper film was 17 mg, the film thickness was 7.1 μm, and the density of the copper film was 5.9 g / cm³. ３ Therefore, the resistivity of the copper film measured using the four-probe method, similar to control example 2, was 3.3 × 10⁻⁶. －４ The coefficient of conductivity was Ωcm, and it was confirmed that the copper film formed by the manufacturing method of control example 3 was electrically conductive.

[0072] [Example 7] The copper film prepared in Control Example 2 was used as recycled metallic copper. The copper powder obtained by peeling the copper film obtained in Control Example 2 from the glass substrate with a spatula was used as recycled metallic copper powder.

[0073] (1. Preparation of Copper Film Forming Composition) 2.27 g (36 mmol) of ammonium formate was added to 80 g of pure water, and then 4.97 g (77 mmol) of 28.8% aqueous ammonia was added. The mixture was stirred at room temperature (25°C) for 10 minutes to obtain an aqueous solution of ammonium formate. The pH of the aqueous solution of ammonium formate was 10.0. 1.14 g (18 mmol) of the recycled metallic copper powder obtained above was added to this solution. The mixture was stirred at room temperature at 500 rpm for 1 hour while bubbling air (0.1 L / min), and then ultrasonically irradiated for 10 minutes to obtain a mixture. The copper ion concentration in the mixture (aqueous solution of recycled copper complex) was measured to be 0.2 mmol / g. The copper ion concentration was measured by atomic absorption spectroscopy in the same manner as the method used to measure the copper ion content in aqueous solution B for copper film formation in Example 1. The pH of the recycled copper complex aqueous solution, measured in the same manner as in Example 1, was 10.6, which was approximately the same as the pH of the copper film-forming composition used in Control Example 2.

[0074] To the aqueous solution of the regenerated copper complex, 10.78 g (61 mmol) of ascorbic acid was added and mixed, and the mixture was stirred at 500 rpm for 20 minutes at room temperature (25°C). Then, pure water was added to obtain the copper film-forming composition of Example 7. The content ratio of copper, ammonia, and ascorbic acid in the obtained copper film-forming composition of Example 7 (Cu ２＋ : NH ３ : H ２ The ratio of AA was 1.0:7.1:3.4.

[0075] (2. Formation and Evaluation of Copper Film on Borosilicate Glass Substrate) A glass substrate with dimensions of (length: 20 mm, width: 20 mm, thickness: 1.1 mm) was used as the borosilicate glass substrate, and a masked glass substrate was prepared in the same manner as in the manufacturing method of Control Example 1. A Petri dish (inner diameter φ35.0 mm, depth: 9.4 mm) was prepared, and the prepared glass substrate was placed in it so that the masked surface was in contact with the container. The copper film forming composition of Control Example 2 obtained above was poured into the Petri dish in an amount sufficient to completely immerse the glass substrate, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film forming composition was discharged from the container, and a copper film was formed on one side of the glass substrate. The glass substrate with the copper film formed on it was immersed in 1 L of pure water and shaken for 1 minute, and this was repeated three times to wash it with pure water, and then dried at 70°C for 1 hour to obtain a glass substrate with a copper film made of recycled metallic copper formed on one side. The yield of the obtained copper film was 0.015 g, the film thickness was 7.5 μm, and the density of the copper film was 4.9 g / cm³. ３ Therefore, the resistivity of the copper film measured using the four-probe method, similar to control example 2, was 2.0 × 10⁻⁶. －３ The coefficient of conductivity was Ωcm, and it was confirmed that the formed copper film was electrically conductive.

[0076] (Appearance of the copper film) Figures 3A and 3B show images of the surfaces of the copper film obtained by the manufacturing method of Example 7 and the copper film obtained by the manufacturing method of Control Example 2, taken with an electron microscope (device name: JSM-6701F, JEOL Ltd., magnification: 1000). As is clear from Figures 3A and 3B, the surface condition of the copper film obtained by the manufacturing method of Control Example 2 using a copper standard solution and the copper film obtained by the manufacturing method of Example 7, which was regenerated from that copper film, are almost identical.

[0077] (Absorption Spectra of Copper Film Forming Composition) The absorption spectra of the copper film forming aqueous solution B obtained by the manufacturing method of Example 7 and the copper film forming aqueous solution B prepared from the copper standard solution of Control Example 2 were measured under the following conditions. The results are shown in Figure 4. As is clear from the graph showing the absorption spectra in Figure 4, the absorption spectrum of the copper film forming aqueous solution B obtained by the manufacturing method of Control Example 2 is in good agreement with the copper film forming aqueous solution B derived from the regenerated copper film obtained in Example 7, which was obtained by regenerating the copper film obtained by the manufacturing method of Control Example 2. This indicates that the copper film forming aqueous solution B obtained in Example 8 derived from the regenerated copper film is useful for copper film formation, similar to the copper film forming aqueous solution B prepared with reagents in the manufacturing method of Control Example 2.

[0078] (Composition of copper film) X-ray diffraction (XRD) was performed on the copper films formed from the copper film-forming compositions obtained by the manufacturing methods of Example 7 and Control Example 2 using a SMART Lab apparatus (RIGAKU Corporation). The intensity was measured using a parallel beam optical system with an incident angle of 0.3°, in 0.05° steps from 2θ of 10° to 80°, with a fixed time of 5° / min. The obtained XRD patterns are shown in Figure 5. As is clear from Figure 5, the copper films obtained by the manufacturing method of Example 7, which are derived from recycled metallic copper, were confirmed to be single-phase copper films, similar to the copper films obtained in Control Example 2.

[0079] [Control Example 4] (1. Preparation of Copper Film Forming Composition) Instead of the regenerated copper film, a copper film forming composition was prepared using a reagent containing copper ions, specifically using copper sulfate tetrahydrate, a metal salt. 7.29 g of 28.8% by mass aqueous ammonia was added to 78 g of pure water and stirred at room temperature (25°C) for 1 minute. Then, the pH of the liquid was adjusted to 11.8 with 2.5% by mass aqueous ammonia, and 4.49 g (18 mmol) of copper sulfate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a metal salt, was added and stirred at room temperature at 500 rpm for 1 hour to obtain a mixture. Pure water was further added to adjust the copper ion concentration in the mixture to 0.2 mmol / g to obtain an aqueous copper complex solution. To the aqueous solution of the copper complex, 10.78 g (61 mmol) of ascorbic acid was added and mixed, and the mixture was stirred at 500 rpm for 20 minutes at room temperature (25°C). Then, pure water was added to obtain the copper film-forming composition of Control Example 4. The content ratio of copper, ammonia, and ascorbic acid in the obtained copper film-forming composition of Control Example 4 was calculated (Cu ２＋ : NH ３ : H ２ The ratio of AA was 1.0:6.9:3.4. The pH of the solution, measured in the same manner as in Example 1, was 10.8.

[0080] (2. Formation and evaluation of copper film on borosilicate glass substrate) A glass substrate was prepared using a borosilicate glass substrate (length: 100 mm, width: 100 mm, thickness: 1.1 mm) and masked in the same manner as in Control Example 1. The glass substrate was placed in a plastic tray (internal dimensions: 280 mm x 190 mm, depth: 24.0 mm) similar to that in Example 1. The copper film-forming composition obtained above from Control Example 2 was poured into the container in an amount sufficient to completely immerse the glass substrate. A piece of corrugated plastic was placed over the container as a lid, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film-forming composition was drained from the container, and a copper film was formed on one side of the glass substrate. The glass substrate with the copper film formed on it was immersed in 1 L of pure water and shaken for 1 minute. This was repeated three times to wash it with pure water, and then dried at 70°C for 1 hour to obtain a glass substrate with a copper film formed on one side. The yield of the copper film obtained by the manufacturing method of Control Example 4 was 1.16 g, the film thickness was 15.4 μm, and the density of the copper film was 6.5 g / cm³. ３ The resistivity of the copper film measured by the method described above was 3.3 × 10⁻⁶. －４ The coefficient of conductivity was Ωcm, and it was confirmed that the formed copper film was electrically conductive.

[0081] [Control Examples 5-6] Except that the amount of ascorbic acid added to the aqueous solution of the copper complex in Control Example 4 was changed to 53.89 g (306 mmol), a copper film-forming composition was obtained using the same method as in Control Example 4, but in the same manner as in Control Example 4.

[0082] First, a glass substrate was prepared using a borosilicate glass substrate (length: 100 mm, width: 100 mm, thickness: 1.1 mm) and masked in the same manner as in Control Example 1. The glass substrate was placed in a plastic tray (internal dimensions: 280 mm x 190 mm, depth: 24.0 mm) similar to that in Example 1. The copper film-forming composition of Control Example 5 obtained above was poured into the container in an amount sufficient to completely immerse the glass substrate. A corrugated plastic lid was placed over the container, and a copper film was obtained using the manufacturing method of Control Example 5 in the same manner as in Control Example 4. [Control Example 5] The yield of the obtained copper film was 1.12 g, the film thickness was 15.6 μm, and the density of the copper film was 6.5 g / cm³. ３ The resistivity of the copper film measured by the method described above was 3.3 × 10⁻⁶.－４ The coefficient of conductivity was Ωcm, and it was confirmed that the formed copper film was electrically conductive.

[0083] Next, a glass substrate with dimensions of (length: 20 mm, width: 20 mm, thickness: 1.1 mm) was used as a borosilicate glass substrate, and a masked glass substrate was prepared in the same manner as in Control Example 1. A Petri dish (inner diameter φ35.0 mm, depth 9.4 mm) was prepared, and the prepared glass substrate was placed in it so that the masked surface was in contact with the container. The copper film-forming composition of Control Example 5 obtained above was poured into the Petri dish in an amount sufficient to completely immerse the glass substrate, and a glass substrate with a copper film made of recycled metallic copper formed on one surface was obtained using the same manufacturing method as in Control Example 3. [Control Example 6] The yield of the copper film obtained by the manufacturing method of Control Example 6 was 16 mg, the film thickness was 6.8 μm, and the density of the copper film was 6.0 g / cm³. ３ Therefore, the resistivity of the copper film measured by the method described above was 1.9 × 10⁻⁶. －４ The coefficient of conductivity was Ωcm, and it was confirmed that the formed copper film was electrically conductive.

[0084] [Example 8] The copper film prepared in Control Example 4 was used as recycled metallic copper. The copper powder obtained by peeling the copper film obtained in Control Example 4 from the glass substrate with a spatula was used as recycled metallic copper powder.

[0085] (1. Preparation of Copper Film Forming Composition) 2.38 g (18 mmol) of ammonium sulfate was added to 81 g of pure water, and then 4.97 g (77 mmol) of 28.8% aqueous ammonia was added. The mixture was stirred at room temperature (25°C) for 10 minutes to obtain an aqueous solution of ammonium sulfate. The pH of the aqueous solution of ammonium sulfate was measured in the same manner as in Example 1 and was 10.1. 1.14 g (18 mmol) of the recycled metallic copper powder obtained above was added to this solution. The mixture was stirred at room temperature at 500 rpm for 1 hour while bubbling air (0.1 L / min), and then ultrasonically irradiated for 10 minutes to obtain a mixture. The concentration of copper ions in the mixture (aqueous solution of recycled copper complex) was confirmed to be 0.2 mmol / g by atomic absorption spectroscopy as described above. To the aqueous solution of the regenerated copper complex, 10.78 g (61 mmol) of ascorbic acid was added and mixed, and the mixture was stirred at 500 rpm for 20 minutes at room temperature (25°C). Then, pure water was added to obtain the copper film-forming composition of Example 8. The content ratio of copper, ammonia, and ascorbic acid in the obtained copper film-forming composition of Example 8 (Cu ２＋ : NH ３ : H ２ The ratio of AA was 1.0:7.1:3.4.

[0086] (2. Formation and Evaluation of Copper Film on Borosilicate Glass Substrate) A glass substrate with dimensions of (length: 20 mm, width: 20 mm, thickness: 1.1 mm) was used as the borosilicate glass substrate, and a masked glass substrate was prepared in the same manner as in Control Example 1. A Petri dish (inner diameter φ35.0 mm, depth 9.4 mm) was prepared, and the prepared glass substrate was placed in it so that the masked surface was in contact with the container. The copper film forming composition obtained above from Control Example 1 was poured into the Petri dish in an amount sufficient to completely immerse the glass substrate, and it was left to stand in a 24°C incubator for 24 hours. After 24 hours, the copper film forming composition was discharged from the container, and a copper film was formed on one side of the glass substrate. The glass substrate with the copper film formed on it was immersed in 1 L of pure water and shaken for 1 minute, and this was repeated three times to wash it with pure water. After that, it was dried at 70°C for 1 hour to obtain a glass substrate with a copper film made of recycled metallic copper formed on one side. The yield of the obtained copper film was 0.012 g, the film thickness was 5.1 μm, and the density of the copper film was 6.1 g / cm³. ３ The resistivity of the copper film measured by the method described above was 5.8 × 10⁻⁶. －４ The coefficient of conductivity was Ωcm, confirming that the copper film formed by the manufacturing method of Example 8 is electrically conductive.

[0087] (Appearance of the copper film) Figures 6A and 6B show images of the surfaces of the copper film obtained by the manufacturing method of Example 8 and the copper film obtained by the manufacturing method of Control Example 4, taken with an electron microscope (device name: JSM-6701F, JEOL Ltd., magnification: 1000). As is clear from Figures 6A and 6B, the surface condition of the copper film obtained by the manufacturing method of Control Example 4 using a copper standard solution and the copper film obtained by the manufacturing method of Example 8, which was regenerated from that copper film, are almost identical.

[0088] (Absorption Spectra of Copper Film Forming Composition) The absorption spectra of the copper film forming aqueous solution B obtained by the manufacturing method of Example 8 and the copper film forming aqueous solution B prepared from the copper standard solution of Control Example 4 were measured under the following conditions. The results are shown in Figure 7. As is clear from the graph showing the absorption spectra in Figure 7, the absorption spectrum of the copper film forming aqueous solution B obtained by the manufacturing method of Control Example 4 originates from recycled metallic copper obtained by regenerating the copper film obtained by the manufacturing method of Control Example 4, and is in good agreement with the copper film forming aqueous solution B obtained by the manufacturing method of Example 8. This indicates that the copper film forming aqueous solution B obtained by the manufacturing method of Example 8, derived from recycled copper film, is useful for copper film formation, similar to the copper film forming aqueous solution B prepared with reagents in the manufacturing method of Control Example 4.

[0089] (Composition of copper film) X-ray diffraction (XRD) was measured on the copper films formed from the copper film-forming compositions obtained by the respective manufacturing methods of Example 8 and Control Example 4 using a SMART Lab apparatus (RIGAKU Corporation). The intensity was measured in 0.05° steps from 2θ of 10° to 80° using a parallel beam optical system with an incident angle of 0.3°, with a fixed time of 5° / min. The obtained XRD patterns are shown in Figure 8. As is clear from Figure 8, the copper films obtained by the manufacturing method of Example 8, derived from recycled metallic copper, were confirmed to be single-phase copper, similar to the copper films obtained by the manufacturing method of Control Example 4.

[0090] From the evaluation results of the copper films obtained by the manufacturing methods of Examples 7 and 8, it was found that a conductive copper film can be formed from recycled metallic copper whether formic acid, an organic acid, or sulfuric acid, an inorganic acid, is used as the acid to contact the metallic copper. Furthermore, it was found that the obtained copper film had almost the same properties as standard metallic copper, and that a copper film with few impurities could be obtained.

[0091] According to one embodiment of the present disclosure, a method for manufacturing a copper film is provided that allows for the formation of a high-purity copper film from used solid copper and copper-containing crude steel in a simple manner. The manufacturing method of the present disclosure facilitates the recycling of copper films formed on any surface of a substrate of any shape, not just flat plates. Furthermore, since an aqueous ammonium carboxylate solution, an aqueous solvent, is used to obtain the copper film-forming composition from solid copper, a low environmental impact is also an advantage. Therefore, the manufacturing method of the present disclosure can be applied to various fields because it allows for the regeneration or formation of high-purity copper films from used solid copper and crude copper containing impurities.

[0092] The disclosure of Japanese Patent Application No. 2024-198462, filed on 13 November 2024, is incorporated by reference into this Disclosure. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard had been specifically and individually noted as being incorporated by reference.

Claims

1. A method for producing a copper film, comprising the steps of: preparing an aqueous solution A for copper film formation by contacting metallic copper with at least one acid selected from the group consisting of carboxylic acid, sulfuric acid, and nitric acid, ammonia, and an aqueous ammonium solution of an acid containing a solvent; supplying oxygen to the aqueous solution A for copper film formation to obtain an aqueous solution B for copper film formation; mixing the obtained aqueous solution B for copper film formation with an organic reducing agent to prepare a composition for copper film formation; and applying the obtained composition for copper film formation to a substrate.

2. The method for producing a copper film according to claim 1, wherein the metallic copper is at least one solid copper selected from the group consisting of metallic copper contained in crude steel and copper films for recycling.

3. The method for producing a copper film according to claim 1 or claim 2, wherein the oxygen supply step includes a step of bubbling oxygen into an aqueous solution A for copper film formation at a rate of 0.05 L / min to 10 L / min, thereby supplying a total amount of 0.5 mol to 3.0 mol of oxygen per 1.0 mol of copper ions contained in the aqueous solution A for copper film formation.

4. The method for producing a copper film according to claim 1 or claim 2, wherein the acid includes formic acid, sulfuric acid, or nitric acid.

5. The method for producing a copper film according to claim 1 or claim 2, wherein the organic reducing agent comprises at least one selected from the group consisting of ascorbic acid, citric acid, oxalic acid, formic acid, and 3,4,5-trihydroxybenzoic acid.

6. The method for manufacturing a copper film according to claim 1 or claim 2, wherein the oxygen supply step further includes a step of irradiating the copper film forming aqueous solution B with ultrasonic waves.

7. The method for producing a copper film according to claim 1 or claim 2, wherein the step of applying the copper film-forming composition to a substrate comprises at least one of the following steps: applying the copper film-forming composition to the substrate; immersing the substrate in the copper film-forming composition; and storing the copper film-forming composition inside a container-shaped substrate.

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