Method for forming metal oxide coating

Abstract

It extends the lifespan of the plating solution used for forming metal oxide films, thereby enabling efficient use of the plating solution. A method for forming a metal oxide film comprises a process of forming a metal oxide film on the surface of a plating target using a plating solution containing a compound of a metal that forms a film and a compound of boron that is a reducing agent, and a process of regenerating the plating solution using an adsorption filter that adsorbs boric acid.

Description

Technology Field

[0001] The present disclosure relates to a method for forming a metal oxide film and a plating apparatus thereof. Background Technology

[0002] A method for forming a metal film on the surface of a non-conductive plating target, such as a glass substrate, is known, which involves forming a zinc oxide film on the surface of the plating target and then performing electroless plating of a metal film, such as copper or gold. While deposition, sputtering, and the sol-gel method are known as methods for forming a zinc oxide film on the surface of the plating target, the electroless plating method is attracting attention because it can easily form a zinc oxide film on the surface of the plating target.

[0003] The electroless plating method for a zinc oxide film is carried out using a plating solution containing zinc nitrate and a boron-based reducing agent such as dimethylaminoborane (DMAB). Since the method can be carried out simply by immersing the object to be plated in the plating solution, a zinc oxide film can be easily formed (for example, refer to Patent Document 1). Prior art literature

[0004] Patent Document 1: Japanese Patent Publication No. Hei 9-278437 The problem to be solved

[0005] However, plating solutions for zinc oxide films have a short lifespan. In the plating solution, boron-based reducing agents such as DMAB rapidly decompose to produce boric acid. Electroless plating of zinc oxide films proceeds with the involvement of hydroxide ions. Since boric acid in the plating solution inhibits the formation of hydroxide ions and zinc hydroxide, the deposition ability of the zinc oxide film rapidly decreases even though sufficient zinc ions or reducing agents remain in the plating solution. Therefore, it is necessary to frequently replace the plating solution.

[0006] This problem can occur not only in zinc oxide films but also in the formation of other metal oxide films using reducing agents containing boron.

[0007] The objective of the present disclosure is to extend the lifespan of a plating solution used for forming a metal oxide film, thereby enabling the plating solution to be used efficiently. means of solving the problem

[0008] One embodiment of the method for forming a metal oxide film of the present disclosure comprises a process of forming a metal oxide film on the surface of a plating target using a plating solution comprising a compound of a metal that forms a film and a compound of boron that is a reducing agent, and a process of regenerating the plating solution using an adsorption filter that adsorbs boric acid.

[0009] One embodiment of the method for forming a metal oxide film is that, because the plating solution is regenerated by a filter that adsorbs boric acid, the concentration of boric acid in the plating solution can be kept continuously low, allowing the plating solution to be used for a long period of time. As a result, productivity can be greatly improved. Effects of the invention

[0010] According to the method for forming a metal film of the present disclosure, the lifespan of the plating solution can be significantly extended, and the film can be formed efficiently. Brief explanation of the drawing

[0011] FIG. 1 is a schematic diagram showing an example of a plating apparatus used in the method for forming a metal oxide film of the present disclosure. Specific details for implementing the invention

[0012] The method for forming a metal oxide film according to the present embodiment can be carried out using a plating apparatus (100) as shown in FIG. 1. The plating apparatus (100) has a plating tank (101) containing a plating solution (104) and a circulation circuit (102) that circulates the plating solution (104) contained in the plating tank (101). The circulation circuit (102) has a circulation pump (121), a first filter (122), and a second filter (123). The first filter (122) is a conventional filtration filter that removes foreign substances, such as aggregates, from the plating solution (104). The second filter (123) is a column filled with beads of a chelating resin that selectively removes boric acid. The plating solution (104) is an electroless plating solution for a zinc oxide film containing zinc nitrate, which is a metal source, and DMAB, which is a reducing agent.

[0013] A zinc oxide film can be formed on the surface of a plating target (106), such as a glass substrate, by immersing the target (106) in a plating solution (104) in a plating bath (101). In the deposition of the zinc oxide film in the plating solution (104), boric acid and electrons (e) from DMAB, which is a reducing agent - ) occurs (Equation 1). Zinc nitrate dissociates into zinc ions and nitrate ions (Equation 2). Nitrate ions generate nitrite ions and hydroxide ions through water and electrons (Equation 3). Zinc ions combine with hydroxide ions to become zinc hydroxide, and as zinc hydroxide changes into zinc oxide, a zinc oxide film is deposited on the surface of the plating target (106) (Equations 4, 5).

[0014] (CH3)2NHBH3+3H2O→H3BO3+(CH3)2H2N + +5H + +6e - (Equation 1)

[0015] Zn(NO3)2→Zn 2+ +2NO3 - (Equation 2)

[0016] NO3 - +H2O+2e - →NO2 -+2OH - (Equation 3)

[0017] Zn 2+ +2OH - →Zn(OH)2(Equation 4)

[0018] Zn(OH)2→ZnO+H2O (Equation 5)

[0019] Boric acid generated in DMAB has a buffering function, so it inhibits the reaction of Equation (4). Therefore, as the plating reaction progresses, the concentration of boric acid in the plating bath (104) increases, and the film-forming ability decreases rapidly, so it is usually necessary to replace the plating bath (104) every time. However, in this embodiment, boric acid in the plating bath (104) is continuously removed by the second filter (123). Therefore, since the increase in the concentration of boric acid in the plating bath (104) is suppressed, the lifespan of the plating bath (104) is extended, and it can be used efficiently.

[0020] The generation of boric acid by the decomposition of DMAB proceeds even when the plating target (106) is not immersed in the plating bath (104). Therefore, it is desirable to remove boric acid by operating the circulation pump (121) continuously. However, the circulation pump (121) may be operated intermittently. Additionally, the boric acid concentration in the plating solution (104) may be monitored, and the circulation pump (121) may be operated when the boric acid concentration exceeds a predetermined value. A plating cycle in which the plating target (106) is immersed in the plating solution (104) and a regeneration cycle in which the plating solution (104) is regenerated by operating the circulation pump (121) to remove boric acid from the plating solution (104) may be performed alternately.

[0021] The configuration of a plating device (100) that removes boric acid by circulating the plating solution (104) in the plating tank (101) by a circulation pump (121) is shown. However, it may also be a batch-type plating device that removes the plating solution (104) from the plating tank (101) to regenerate it, and then returns the plating solution (104) after regeneration back to the plating tank (101).

[0022] The second filter (123) for removing boric acid is a column filled with chelating resin beads that selectively remove boric acid. By making it a column, it becomes easier to handle and can be efficiently brought into contact with the plating solution, thereby increasing the boric acid removal efficiency. In addition to beads, it can be a column filled with powder or fibers. A column filled with large-sized beads is preferable because it makes it less likely for clogging to occur. Porous resin beads or resin fibers may also be used. This increases the contact surface area, thereby improving the boric acid removal efficiency.

[0023] The chelate resin may have a chelate-forming portion that selectively forms a chelate with boric acid. The chelate-forming portion may have a structure such as a polyhydric alcohol having multiple hydroxyl groups or catechol. Among these, it is preferable to have a glucamine group (N-methylglucamine group) as the chelate-forming portion. The carrier supporting the chelate-forming portion is not limited to resin, and inorganic particles such as silica may also be used. Additionally, a column filled with cerium hydroxide or hydrotalcite may be used as the second filter (123).

[0024] The first filter (122) is not specifically limited and may use a non-woven fabric filter, etc. Additionally, the first filter (122) may be placed as needed, or it may not be placed. The first filter (122) may also be placed downstream of the second filter (123).

[0025] Although an example has been shown in which the metal source of the plating solution (104) is zinc nitrate, it is not limited to zinc nitrate, and other zinc-containing compounds such as zinc chloride, zinc carbonate, and zinc sulfate may be used. When forming a metal oxide film other than zinc oxide, compounds such as cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), aluminum (Al), titanium (Ti), zirconium (Zr), tin (Sn), and silicon (Si) may be used. The concentration of the metal compound serving as the metal source can be appropriately selected according to the type and use of the film, but is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, preferably 0.2 mol / L or less, more preferably 0.09 mol / L or less.

[0026] The reducing agent is not limited to DMAB, and a boron-based reducing agent may be used. For example, sodium borohydride, trimethylaminoborane (TMAB), etc. may be used. The concentration of the reducing agent can be appropriately selected depending on the type and application of the film, but preferably 0.0001 mol / L or more, more preferably 0.0005 mol / L or more, and even more preferably 0.001 mol / L or more; preferably 0.5 mol / L or less, more preferably 0.3 mol / L or less, and even more preferably 0.2 mol / L or less.

[0027] In addition to the metal source and reducing agent, the plating solution (104) may include a pH adjusting agent such as nitric acid, hydrochloric acid, and sulfuric acid as needed. The pH of the plating solution (104) is not particularly limited, but it is preferable to have it at around 4 to 6. The plating solution (104) can be used at a temperature of preferably 10°C or higher, more preferably 50°C or higher, preferably 90°C or lower, and more preferably 80°C or lower. The immersion time of the plating target (106) in the plating solution (104) can be selected according to the type, thickness, and application of the required film, but is preferably 10 minutes or more, more preferably 15 minutes or more, preferably 200 minutes or less, more preferably 100 minutes or less, and even more preferably 30 minutes or less.

[0028] In the method for forming a metal oxide film according to the present embodiment, the concentration of boric acid in the plating solution (104) used is preferably maintained at 1.0 g / L or less, more preferably at 0.5 g / L or less, and even more preferably at 0.3 g / L or less. By maintaining the concentration at such a level and performing the formation of the metal oxide film, a metal oxide film with excellent peel strength can be formed.

[0029] When the plating solution (104) is used continuously, the amount of metal source and reducing agent consumed can be replenished so that the concentrations of the metal source and reducing agent do not fluctuate significantly over time. In terms of forming a uniform film, it is desirable to maintain the concentrations of the metal source and reducing agent at 90% to 110% of the initial value, and more preferably at 95% to 105%. Additionally, the pH can be adjusted by adding an acid or an alkali as appropriate.

[0030] The plating target in this embodiment may be a material having hydroxyl groups (-OH) on its surface, such as glass. It is not limited to glass and may be a non-conductive material, such as ceramic or resin, having hydroxyl groups on its surface. Additionally, a material that normally does not have hydroxyl groups may be surface-treated to introduce hydroxyl groups. The shape of the plating target is not limited to a flat plate, such as a substrate, but may have a three-dimensional shape.

[0031] The metal oxide formed in the method for forming a metal oxide film of the present embodiment can be used as an adhesion enhancing layer for difficult-to-plat materials (such as glass) for which adhesion cannot be obtained at all by conventional methods.

[0032] Although the method for forming a zinc oxide film has been described in this embodiment, it can be similarly carried out for the formation of other metal oxide films using a boron-based reducing agent. For example, it can be carried out in the same way for oxide films of cobalt (Co), iron (Fe), manganese (Mn), molybdenum (Mo), aluminum (Al), titanium (Ti), tin (Sn), and silicon (Si).

[0033] Examples

[0034] The present invention will be explained in more detail below using examples. The following examples are illustrative and are not intended to limit the invention.

[0035] <Measurement of Zinc Concentration>

[0036] The zinc concentration in the plating solution was measured by chelation titration.

[0037] <Measurement of Reducing Agent Concentration>

[0038] The concentration of the reducing agent in the plating solution was measured by redox titration.

[0039] <Boric Acid Concentration Measurement>

[0040] The concentration of boric acid in the plating solution was measured by neutralization titration.

[0041] <Measurement of Film Thickness>

[0042] The thickness of the film was calculated by measuring the difference between the mass before and after plating, and the area of ​​the substrate and the density of zinc oxide.

[0043] <Peel Strength Measurement>

[0044] The peel strength of the film was measured using an Autograph (SHIMADZU Autograph AGS-X).

[0045] Assessment of the Effects of Boric Acid

[0046] Different amounts of boric acid were added to the plating solution, and the peel strength of the film obtained by immersing a glass substrate (5 cm x 5 cm) at 80°C for 20 minutes was measured.

[0047] The plating solution was prepared with a zinc nitrate (hexahydrate) concentration of 14.9 g / L (0.05 mol / L) and a DMAB concentration of 1.2 g / L (0.02 mol / L). Boric acid was added in amounts of 1.1 g, 3.1 g, 5.1 g, and 10.1 g per 1 L of plating solution.

[0048] The peel strength when no boric acid was added was 900 gf / cm. When 1.1 g of boric acid was added, the peel strength was 401 gf / cm. When 3.1 g of boric acid was added, film precipitation was confirmed, but blistering occurred and peeling occurred immediately, so the peel strength could not be measured. When 5.1 g and 10.1 g of boric acid were added, film precipitation was not confirmed.

[0049] (Example 1)

[0050] 2.8 L of a zinc nitrate (hexahydrate) solution (14.9 g / L, 0.05 mol / L) was added to the plating tank of the apparatus configured as shown in Fig. 1, the temperature was set to 80°C, and the solution was circulated at a flow rate of 450 mL / min. The first filter was a nonwoven filter (FSG-1 cartridge filter manufactured by Nihon Filter Co., Ltd.). The second filter was a column packed with 300 g of a chelating resin (DIAION CRB-05 manufactured by Mitsubishi Chemical Co., Ltd.) having N-methylglucarmine as a chelating part.

[0051] DMAB was added to the plating bath to a concentration of 1.2 g / L (0.02 mol / L), and a glass substrate was immersed. After 20 minutes, the substrate was removed, and the zinc concentration and DMAB concentration were measured to replenish the consumed zinc nitrate and DMAB. Five minutes after removing the first glass substrate, the glass substrate was immersed again to perform the second film formation. The film formation process was repeated in the same manner up to the 15th time.

[0052] From the 1st to the 15th, the film thickness after 20 minutes of immersion was nearly constant at approximately 0.2 μm. The peel strength of the film ranged from approximately 600 gf / cm to 900 gf / cm. Good films could be formed from the 1st to the 15th. The boric acid concentration after film formation was 5.4 ppm for the 5th and 10th tests, and 20.8 ppm for the 15th test. The results are summarized in Table 1.

[0053]

[0054] (Comparative Example 1)

[0055] A film was formed on a glass substrate in the same manner as in Example 1 without circulating through a filter. The first film had a film thickness of 0.2 μm and a peel strength of 902 gf / cm. However, a blister occurred in the second film, so the peel strength could not be measured. Industrial applicability

[0056] The method for forming a metal oxide film of the present disclosure can efficiently form a film by stabilizing the plating solution, and is useful in the field of film formation. Explanation of the symbols

[0057] 100 : Plating device 101 : Plating tank 102: Circular circuit 104 : Plating solution 106 : Plating target 121: Circulation pump 122 : First filter 123 : Second filter

Claims

Claim 1 A method for forming a metal oxide film, comprising: a process of forming a metal oxide film on the surface of a plating target using a plating solution containing a metal compound that forms a film and a boron compound that is a reducing agent; and a process of regenerating the plating solution by adsorbing boric acid generated by the decomposition of the reducing agent using an adsorption filter that adsorbs boric acid. Claim 2 A method for forming a metal oxide film according to claim 1, wherein the adsorption filter comprises a chelate resin that selectively adsorbs boric acid. Claim 3 A method for forming a metal oxide film according to paragraph 2, wherein the chelate resin is a resin having a methylglucarmine group as a chelate-forming part. Claim 4 A method for forming a metal oxide film according to claim 1, wherein the process of forming the film is carried out by immersing the plating target in a plating tank containing the plating solution, and the regeneration process is carried out by circulating the plating solution in the plating tank by passing it through the adsorption filter. Claim 5 A method for forming a metal oxide film according to claim 4, wherein the process of forming the film and the process of regenerating are carried out simultaneously in parallel. Claim 6 A method for forming a metal oxide film according to claim 1, wherein the reducing agent comprises dimethylaminoborane (DMAB). Claim 7 A method for forming a metal oxide film according to claim 1, wherein the metal is zinc. Claim 8 A plating apparatus comprising: a plating tank containing a plating solution comprising a compound of a metal forming a film and a compound of boron as a reducing agent, wherein a plating target is immersed to form a film of a metal oxide on the surface of the plating target; and a plating solution regeneration unit that adsorbs boric acid generated by the decomposition of the reducing agent to regenerate the plating solution in the plating tank, wherein the plating solution regeneration unit comprises an adsorption filter that adsorbs boric acid and a pump that returns the plating solution in the plating tank to the plating tank through the adsorption filter.

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