JP2002194556A - Plating solution, oxide thin film and method for manufacturing oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a functional oxide thin film such as PZT and PLZT with satisfactory efficiency and in a cheap cost, by employing a stable plating solution and a wet film-forming process. SOLUTION: The plating solution contains ions of Pb, Zr, Ti, La, and nitrate, and dimethylamine borane and trimethylamine borane. The oxide thin film is formed with the plating solution and boron content in the film of 0.01-2 volume %. A manufacturing method comprises forming an initial precipitate layer with a light-driving method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating solution, an oxide thin film and a method for producing an oxide thin film which can be widely used for various electronic parts, mechanical parts, optical parts and the like.

[0002]

2. Description of the Related Art Piezoelectric ceramic PZT [Pb
(Zr, Ti) O ₃ ] is a solid solution of PbZrO ₃ —PbTiO ₃ having an ABO3 type perovskite structure. Further, PLZT is made transparent by adding La to this PZT, and is widely applied because it has effects such as an electro-optic effect and a memory effect. As a method for forming such an oxide thin film, a single crystal method, a powder metallurgy method, a vacuum molecular beam epitaxy deposition method, and the like are known. However, each of these methods requires a large-scale and expensive apparatus, which is a factor of high cost.

On the other hand, as a method of forming a metal oxide thin film from an aqueous solution using an inexpensive apparatus, a method of forming a perovskite-based iron oxide thin film (ferrite) is disclosed in JP-B-63-15 / 1988.
No. 990. In this method, when a substrate having FeOH ⁺ having an OH group adsorbed on its surface is immersed in an aqueous solution (PH = 6.5-8.0) containing Fe2 ⁺ and another metal ion Mn ⁺ , Fe2 ⁺ and Mn ⁺ become OH Adsorbed to the substrate via the group. In this state, adding an oxidizing agent such as nitrous acid (NaNO ₂ ) or O ₂
Ferrite is formed with the oxidation reaction of e ²⁺ → Fe ³⁺ . Since OH groups are present on the surface of the ferrite layer, the reaction is repeated and the ferrite layer grows with time. The inventor of the present invention, Masaki Abe, calls this method a ferrite plating method. This method is an epoch-making method in that a film can be formed from a low-temperature aqueous solution, but its use has been limited only to iron oxides.

A novel method for forming a thin film of a metal oxide other than iron from an aqueous solution using an inexpensive apparatus is disclosed in
No. 1-71112 discloses a method for forming a film of zinc oxide or indium oxide from a solution containing nitrate and dimethylamine borane. After the catalyst is applied and the initial deposited layer is grown, the film can be grown by cathodic electrolysis. At first glance, this method is similar to the ferrite plating method described above, but is completely different. In other words, a nitrite-nitrite reduction reaction in which nitric acid is reduced to nitrite by utilizing a reducing agent called dimethylamine borane in the liquid is used. In addition, in IEICE Magnetics Research Group Material, MAG-00-18 (2000), 30
It is disclosed that by irradiating a substrate with light having a wavelength of 0 nm, a nitrite-nitrite reduction reaction starts and a ZnO film can be formed. However, the nitrite-nitrite reduction method uses ZnO, InO
Was only considered.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and uses a stable plating solution without the need for an expensive apparatus and efficiently uses PZT, PLZT by a wet film forming method. Etc. are provided at a low cost.

[0006]

The above-mentioned objects are attained by any one of the following (1) to (8) of the present invention. (1) A plating solution comprising a solution containing Pb ions, Zr ions, Ti ions, nitrate ions and a reducing agent. (2) The plating solution according to (1), wherein the reducing agent is at least one selected from dimethylamine borane and trimethylamine borane. (3) The plating solution according to (1) or (2), wherein the plating solution contains La ions as metal ions in addition to the above ions. (4) The plating solution according to (1) or (3), wherein the oxide thin film is formed by a nitric acid-nitrite reduction reaction. (5) An oxide thin film containing a Pb oxide, a Zr oxide, a Ti oxide, and boron. (6) A film is formed by a wet film forming method and has a boron content of 0.
The oxide thin film according to (5), wherein the content is 001 to 2% by volume. (7) The oxide thin film according to (5) or (6), comprising a La oxide. (8) An oxide layer is formed by irradiating light having a wavelength of 400 nm or less using a plating solution comprising a solution containing Pb ions, Zr ions, Ti ions, nitrate ions and a reducing agent. A method for producing an oxide thin film.

[0007]

Embodiments of the present invention will be described below in detail.

The wet oxide thin film of the present invention is formed by a nitrite-nitrite reduction reaction in which nitric acid is changed to nitrite. This reaction is represented by the following equations (1) to (5). That is, when dimethylamine borane is used as a reducing agent, dimethylamine borane emits electrons, which generate nitrous acid, and M ions (M = Pb, Zr, Ti, L) contained in the bath.
a) is formed on the surface as hydroxide M and then becomes oxide M. That is, the basic reaction is an immersion film forming method in which a film forming reaction proceeds without an external electric current by merely immersing the substrate in a plating solution. _{(CH 3) 2 NHBH 3 +} H 2 O → BO 2 - + (CH 3) 2 NH + 7H + + 6e - (1) NO 3 - + H 2 O + 2e - → NO 2 - 2OH - (2) ^{M X + + XOH - → M} (OH) X (3) M (OH) x → MOx + yH ₂ O (4) [Formation of Initial Deposition Layer] In the present invention, the film is continuous only on the initial deposition layer formed on the substrate by the method described below. It grows in a specific manner, and no production reaction occurs in other parts or liquids. The method of forming the initial deposited layer is roughly classified into two. A catalyst driving method using a noble metal catalyst layer of palladium, silver, or the like, and a light driving method by irradiating light, particularly, ultraviolet light having a short wavelength.

In the case of the catalyst drive system, palladium catalysis, which is widely used as a pretreatment for electroless plating, is preferably used. In this method, palladium metal is adsorbed on the surface by a method such as a sensitizing-activation method, a catalyst-accelerator method, or an alkaline catalyst method. Instead of palladium, a silver nitrate / nickel sulfate catalyst method using silver capable of forming a denser catalyst nucleus can also be preferably used. Moreover,
It is also effective to form a catalyst layer of platinum or the like by a vacuum film forming method such as sputtering. In this case, the catalyst layer is extremely thin and a thickness of 10 nm or less is sufficient, and need not be a continuous layer, and may be a cluster-like discontinuous layer.

Since the initial deposition is started only on the catalyst layer, the oxide thin film is patterned by forming the catalyst layer and then performing patterning by photolithography, a method of lowering the Sn activity by exposure to ultraviolet light, or the like. For example, it is also possible to form a minute circular dot of about several tens nm or a line.

[0011] The latter method of forming an initial deposited layer by an optical driving method is as follows.
It irradiates light of a short wavelength necessary to cause a nitrite-nitrite reduction reaction. For this reason, unlike light irradiation and long-wavelength laser irradiation for the purpose of applying heat, which is conventionally performed to increase the film forming rate by a known ferrite plating method, a wavelength of 400 nm or less, particularly preferably 3 nm or less.
Ultraviolet rays of 50 nm or less are irradiated by a high-pressure mercury lamp, an excimer laser, or the like. In addition, since it is used only to cause an initial reaction for forming an initial deposited layer, there is no need to continuously irradiate the film at all times during film formation. Completely different. Since such ultraviolet rays are very easily absorbed,
Although it is possible to form a thin solution layer on the surface of the substrate and irradiate from the surface, it is preferable to irradiate from the back surface of the substrate using a quartz substrate, a sapphire substrate or the like through which ultraviolet rays are transmitted. Also in the case of optical driving, patterning is possible by irradiating the irradiated light to only a part of the base with a mask or the like.

[Plating Solution and Film-Forming Conditions] In the present invention, it is essential to add a reducing agent to the plating solution. As the reducing agent, various known reducing agents can be used, but amine-borane complex, hypophosphorous acid and the like are preferable, and inexpensive dimethylamine borane and trimethylamine borane are particularly preferable. It is also possible to use two different reducing agents.

The amounts of dimethylamine borane and trimethylamine borane in the solution are not particularly limited, but may be 0.00
It is preferably from 0.01 to 1.0 mol / l, particularly preferably from 0.0005 to 0.5 mol / l. Below the above range, the film forming rate is low, and above the above range, the solution becomes unstable and self-decomposes easily, which is not practical.

As the nitrate ion source, various known nitrate ion-containing chemicals, for example, nitric acid, Pb nitrate, ammonium nitrate, sodium nitrate, lithium nitrate, urea nitrate and the like can be used. In the present invention, nitrite ions and nitrite ions are fundamentally different from the mechanism in which the reaction proceeds as in the above-described ferrite plating method. But it must be nitrate. The same applies to the initial deposited layer. Even if the nitrous acid is irradiated with ultraviolet light, it does not return to nitric acid nor is it reduced to ammonia, so that no film is formed. The reaction is the same when a catalyst is used.

As the metal ion source, sulfate, hydrochloride,
It is possible to use various salts such as carbonates, but nitrates are particularly preferred. This is because the presence of an anion other than the nitrate ion facilitates the formation of a hydroxide.

The metal ion concentration and the nitrate ion concentration can be adjusted in a wide range, but if any of the concentrations is low, the film forming rate becomes extremely slow, and if any of the concentrations is too high, metal hydroxide is formed. And the crystallinity of the film is lowered, so that good characteristics cannot be obtained. Therefore, the metal ion concentration and the nitrate ion concentration are each preferably 0.001 to 5 mol / l, particularly preferably 0.01 to 0.5 mol / l, and the ratio of the metal ion concentration to the nitrate ion concentration is It is preferably in the range of 0.1 to 10.

The temperature of the plating solution is not particularly limited.
To 95 ° C, particularly preferably 10 to 30 ° C for an optical drive system, and 20 to 70 ° C for a catalyst drive system.
It is. If it is too low, the film forming rate will be low. If it is too high, the decomposition reaction of the reducing agent tends to proceed.

The pH of the plating solution is not particularly limited, but is preferably about 2 to 9, particularly preferably 2 to 8. Below the above range, the film forming rate becomes slow, and above the above range, the liquid becomes unstable and tends to self-decompose. The composition of the deposited film is greatly affected by the pH. For this reason, it is also possible to add a known buffer to the bath in order to stably maintain the predetermined pH. For example, potassium dihydrogen phosphate,
Potassium phthalate, borax and the like.

In order to improve the film quality, various known organic compounds can be added to the solution. For example,
Dextrin, sucrose and the like.

The plating solution of the present invention is stable and can be used for a long period of time. Since metal ions and reducing agent decrease as the film is formed, it can be used for a longer period of time by appropriately replenishing it.

[Deposition Apparatus and Substrate] FIG. 1 is a schematic view of an optically driven plating apparatus that can be used in the present invention. The plating bath 13 is filled with a plating solution 14, and a substrate 11 is mounted on an opening portion opened on one side thereof to form a thin film 12. The plating tank 13 is provided with a lid 21 and is immersed in a heating tank 16 filled with water 15 controlled at a predetermined temperature. Temperature control means 18 for controlling the heater 17 is connected to the heating tank 16.
The water 15 in the heating tank can be heated and maintained at a predetermined temperature. Further, an ultraviolet irradiation device 19 is arranged behind the substrate mounted on the plating tank so that ultraviolet light 20 can be irradiated from the back side of the substrate.

Further, in order to improve the uniformity of the film, it is possible to use various known stirring methods. For example, bubble stirring using air, nitrogen, oxygen, or the like, a cathode lock method for moving the substrate, paddle stirring for moving a rod-shaped stirring mechanism near the substrate, or superimposed ultrasonic waves (especially 28 kHz) in which ultrasonic waves having different frequencies are superimposed. , 45k
It is also possible to use a method of changing the frequency with time or to use a high-frequency ultrasonic wave whose frequency has been increased to about 1 GHz.

The plating solution of the present invention is placed in a plating tank having these predetermined heating devices and filter devices, and the substrate is immersed in the plating solution to form a film.

In addition to ordinary immersion plating, a spraying method in which a solution is sprayed on a substrate, and a spin coating method in which the solution is supplied while rotating the substrate, are also possible. In particular, in the case of these techniques, the solution can be easily recovered and reused. In this case, it is preferable to use after filtering with a filter of about 0.2 μm mesh or the like.

When it is desired to increase the film forming rate, it is possible to form a film at a temperature of 100 ° C. or more by applying a high pressure in a pressure vessel. The use of a pre-heated substrate also increases the actual reaction temperature.

When using a light-driven plating apparatus for irradiating light from the back surface of the substrate shown in FIG. 1, a glass substrate such as a quartz substrate through which light is transmitted is used as the substrate. Otherwise,
There is no particular limitation on the material used as the substrate. For example, copper,
Examples include metal materials such as aluminum, glass materials such as soda glass and non-alkali glass, ceramic materials, and plastic materials. Further, a substrate in which a polyimide resin is applied to the surface of an alumina ceramic plate or a titanium oxide fine particle composite Teflon (registered trademark) film is provided can also be used.

Each substrate needs to be subjected to optimal pretreatment, cleaning, surface adjustment, etching, etc. depending on its properties and surface condition. There is no particular limitation on the shape used as the substrate. It is possible to form a film not only on a flat surface but also on a special complicated three-dimensional surface such as only a powdery, fibrous or tubular inner wall.

[Structure and Characteristics of Oxide Film] The feature of the oxide thin film formed by the wet film forming method of the present invention is that boron is contained by a side reaction of dimethylamine borane and trimethylamine borane. is there. Its content is 0.01 to 2% by volume. This boron content is very important. Below the above range, the action as a reducing agent is insufficient and the film forming rate is slow and not practical. Above the above range, the side reaction has progressed and good properties (surface property, crystallinity , Magnetic properties, etc.). These oxide thin films formed by methods other than the present invention do not contain boron.

The oxide thin film of the present invention can be used in the case where the plating solution contains only Pb, Zr and Ti as metal ions.
It becomes T. When La is included, PLZT is obtained.

The oxide thin film of the present invention contains various elements inevitably contained during the production in addition to the above-mentioned main components. Although it is technically possible to remove them, a certain amount can be mixed in from the viewpoint of cost. As the purity of the reagent used in the present invention, JIS reagent standard grade 1 or higher, preferably special grade is used. The amount of impurities mixed into the film and the plating solution is determined from the purity of these reagents. That is, there is no problem even if it is mixed in the amount of various impurity elements contained in the primary reagent. Further, a light element such as M or hydrogen in a metallic state or Na or K may be mixed. As with the above-mentioned impurities, a small amount of these may be mixed.

The metal oxide thin film of the present invention can be subjected to a heat treatment as needed after the formation. Generally, by performing the heat treatment, the strain is reduced, and a film having higher crystallinity can be obtained. However, depending on the conditions,
Since the crystal structure may change to a different one, the heat treatment temperature, atmosphere, and time are selected according to the purpose. For example, 20
By performing the heat treatment at 0 to 1000 ° C. for 10 minutes to 10 hours, the light transmittance of PLZT is improved.

The oxide thin film of the present invention is used after patterning or cutting and separating the entire substrate according to the purpose. If necessary, it can be laminated with another functional layer, for example, a coil layer. In the case of a high-resistance oxide thin film, the oxide thin film can be laminated with a conductor coil without using an insulating layer.

The oxide thin film of the present invention has a thickness of 0.01 μm.
It can be selected according to the purpose within the range of m to 1 mm, preferably 0.1 to 100 μm. If it is less than the electrical range, it is difficult to form a uniform film, and if it is more than the above range, it takes a long time to form a film and it is difficult to put it into practical use.

The method for producing an oxide thin film according to the present invention comprises:
By changing the composition of the plating solution, an oxide thin film such as Sn oxide, In oxide, and ITO (SnO2-In2O3) can be manufactured. That is, the above-described oxide thin film can be formed from a plating solution containing Sn ions and In ions in the same manner. These oxide thin films also contain 0.001-2% by volume of boron in the films manufactured according to the present invention.

[0035]

Examples and Comparative Examples Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 A chromic acid-etched quartz substrate (350 μm in thickness) was subjected to a Pd / Sn catalysis treatment. Plating nitrate, Zr nitrate,
A solution of Ti nitrate, 0.01 mol / l each, dimethylamine borane, 0.03 mol / l was prepared,
Warmed to ° C. The catalyzed substrate was immersed in a plating solution, and a film was formed for 150 minutes while stirring with a stirrer.

On the surface of the substrate, a black specular film was formed to a thickness of 5 μm. As a result of X-ray fluorescence analysis, this film was [2]
Pb-Zr-Ti] composition and oxide
T was determined. As a result of plasma emission analysis, this film contained 0.15% by volume of boron.

Further, a PZT film was formed on 20 similar substrates for 3 days using the plating solution used in this example, but a stable film formation was possible to the end.

Next, the same film formation was performed by changing the amount of dimethylamine borane in the plating solution to 0.00001 to 1.5 mol / liter, and the same evaluation was performed.
As a result, the boron content in the film was 0.001-2% by volume.
It was found that the films having the above-mentioned range showed good appearance, excellent bath stability, and the film formation rate was within a practically acceptable range.

Example 2 An oxide thin film was formed on a quartz substrate through which light having a wavelength of 300 nm was transmitted using the light-driven plating apparatus shown in FIG. As a plating solution, a solution of Pb nitrate, Zr nitrate, Ti nitrate, 0.01 mol / l of each, trimethylamine borane, 0.01 mol / l was prepared and heated to 20 ° C. The substrate was irradiated with ultraviolet light having a wavelength of 300 nm through a mask for 5 minutes, and after confirming that film formation was started, film formation was performed for 180 minutes without irradiation.

On the surface of the substrate, a black specular film was formed to a thickness of 5 μm. As a result of X-ray fluorescence analysis, this film was [2
Pb-Zr-Ti] composition and oxide
T was determined. As a result of plasma emission analysis, this film contained 0.11% by volume of boron.

Example 3 As in Example 1, nitric acid P
b, 0.02 mol / L, Zr nitrate, 0.013 mol / L, Ti nitrate, 0.004 mol / L,
Film formation was performed for 500 minutes under the same conditions using a bath of La nitrate and 0.004 mol / liter. This film is translucent and has almost the desired PLZT composition [91Pb-9La-65].
Zr-35Ti]. In addition, this film has 0.3
It contained boron by volume.

From the above results, the effect of the present invention is clear.

[0044]

According to the present invention, a functional oxide thin film such as PZT or PLZT can be efficiently and inexpensively provided by a wet film forming method using a stable plating solution without requiring an expensive apparatus. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic view of a light-driven plating apparatus that can be used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Thin film 13 Plating tank 14 Plating solution 15 Water 16 Heating tank 17 Heater 18 Temperature control means 19 Ultraviolet irradiation device 20 Ultraviolet 21 Lid

Claims (8)

[Claims] 1. Pb ion, Zr ion, Ti ion,
A plating solution comprising a solution containing nitrate ions and a reducing agent. 2. The plating solution according to claim 1, wherein the reducing agent is at least one selected from dimethylamine borane and trimethylamine borane. 3. A metal ion in addition to the above ion,
The plating solution according to claim 1, wherein the plating solution contains La ions. 4. The plating solution according to claim 1, wherein an oxide thin film is formed by a nitric acid-nitrite reduction reaction. 5. An oxide thin film containing a Pb oxide, a Zr oxide, a Ti oxide and boron. 6. The oxide thin film according to claim 5, wherein the oxide thin film is formed by a wet film forming method and has a boron content of 0.001 to 2% by volume. 7. The oxide thin film according to claim 5, comprising a La oxide. 8. Pb ions, Zr ions, Ti ions,
A method for producing an oxide thin film, comprising forming an oxide layer by irradiating light having a wavelength of 400 nm or less with a plating solution comprising a solution containing nitrate ions and a reducing agent.