JPH09278437A - Composition for forming zinc oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compsn. capable of easily forming a ZnO film even on an electrically nonconductive substrate without requiring large-scale facilities such as a vacuum evacuator by preparing an aq. soln. contg. Zn ions, nitrate ions and a specified complex. SOLUTION: This compsn. is an aq. soln. contg. Zn ions, nitrate ions and a borane-amine complex such as dimethylamine borane or trimethylamine borane. Zinc nitrate is preferably used as Zn ion and nitrate ion sources. The pref. concn. of the Zn ions and that of the nitrates ions are about 0.001-0.5mol/L [0.065-32.7g/L (expressed in terms of Zn)]. The pref. amt. of the borane-amine complex is about 0.001-0.5mol/L. A ZnO film can be formed by immersing a substrate in this compsn.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composition for forming a zinc oxide film.

[0002]

2. Description of the Related Art Zinc oxide is a compound semiconductor having a wurtzite structure and a band gap of about 3.3 eV, and has optical transparency, piezoelectricity, conductivity, luminescence, fluorescence, photocatalyst, etc. Excellent and abundant in resources, transparent conductive film, semiconductor laser, optical waveguide, gas or humidity detection sensor, surface acoustic wave element, light emitting element, various acoustic elements, electronic field such as thin film varistor, chemistry such as photocatalyst Widely applied in a wide range of fields such as the industrial field.

Conventionally, as a method for forming a zinc oxide film, C has been used.
Attempts have been made to form a film on a substrate by a dry method such as a VD method, a vapor deposition method, a sputtering method, an MBE method, a wet method such as a spray pyrolysis method, a sol-gel method or a liquid phase growth method. However, the sputtering method, C
In the dry method such as the VD method, the vapor deposition method and the MBE method, it is necessary to perform processing such as depressurization or gas mixing in the film forming chamber and heating of the substrate during film formation. A large-scale manufacturing device including a power source is required. Furthermore, these methods have drawbacks such as a low film formation rate, difficulty in controlling the composition and film thickness, and difficulty in forming a uniform film on a substrate having a complicated shape.

Further, in the spray pyrolysis method and the sol-gel method as well, in order to obtain a zinc oxide film, it is necessary to heat at 300 to 900 ° C. after the film is formed on the substrate, so that a heating furnace is required, There is also a problem that a low melting point material such as plastic cannot be used as a base material.

As another method for producing a zinc oxide film, a method for producing a zinc oxide film on a conductive substrate by a cathodic electrolysis method from an aqueous solution containing nitrate ions and zinc ions has been reported (55th application). Preparatory Lectures for Academic Lectures of the Physical Society of Japan, p. 396, published September 19, 1994) However, since this method is a cathodic electrolysis method, it is necessary that the base material on which the zinc oxide film is formed has good conductivity, and the zinc oxide film is formed on a non-conductive base material such as plastic or glass. Cannot be formed.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to:
An object of the present invention is to provide a method capable of easily forming a zinc oxide film on a non-conductive substrate without requiring large-scale equipment such as a vacuum exhaust device and a heating furnace.

[0007]

The present inventor has conducted extensive studies in view of the problems of the prior art as described above, and as a result, in the case of using an aqueous solution containing zinc ion, nitrate ion and borane-amine complex, The zinc oxide film can be formed at a relatively high film forming rate on both the conductive base material and the non-conductive base material simply by immersing the base material in this aqueous solution without energization. The inventors have found that a zinc oxide film having a uniform thickness and composition can be easily formed on a large-area substrate or a substrate having a complicated shape, and have completed the present invention.

That is, the present invention relates to a zinc oxide film-forming composition comprising an aqueous solution containing zinc ions, nitrate ions and borane-amine complex.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The composition for forming a zinc oxide film of the present invention is an aqueous solution containing zinc ions, nitrate ions and borane-amine complex. It is possible to form a zinc oxide film by using such an aqueous solution containing both zinc ions and nitrate ions at the same time. However, from an aqueous solution containing only zinc ions and not containing nitrate ions, the oxidation A zinc film cannot be formed. As the compound serving as the zinc ion ion source, a water-soluble zinc salt may be used, and specific examples thereof include zinc nitrate,
Examples thereof include zinc sulfate, zinc chloride, zinc acetate, zinc phosphate, zinc pyrophosphate, zinc carbonate and the like. As the nitrate ion source, nitric acid, water-soluble nitrate or the like can be used, and specific examples of the nitrate include zinc nitrate, ammonium nitrate, sodium nitrate, potassium nitrate, lithium nitrate, urea nitrate and the like. The compound serving as a zinc ion source and the compound serving as a nitrate ion source may be used alone or in combination of two or more, and zinc nitrate may be used alone as an ion source for both zinc ion and nitrate ion. You may use. In particular, when zinc nitrate is used alone, there are not many unnecessary components in the bath, formation of zinc hydroxide is suppressed, and a zinc oxide film with high purity is formed in a wide concentration range. It becomes possible.

In the composition of the present invention, the concentration of zinc ions and nitrate ions can be adjusted in a wide range, but if the ion concentration of either one is too low, the zinc oxide film cannot be formed, and any one of them can be formed. On the other hand, if the ion concentration is too high, the zinc hydroxide film is likely to be formed, and the purity of the zinc oxide film is likely to decrease. Therefore, the concentration of each of zinc ion and nitrate ion is 0.001 mol / l to 0.5 mo.
It is preferably in the range of about 1 / l (0.065-32.7 g / l in terms of zinc content), and 0.01 mol / l
~ 0.2 mol / l (0.65 to 13 g / zin equivalent)
It is more preferable that it is within the range of about 1).

Further, it is necessary to incorporate a borane-amine complex into the composition of the present invention. By using the aqueous solution containing the borane-amine complex, it is possible to form the zinc oxide film without energizing the substrate simply by immersing the substrate in the aqueous solution. As the borane-amine complex, any water-soluble compound can be used, and specific examples thereof include dimethylamine borane and trimethylamine borane. In particular, when trimethylamine borane is used, the stability of the bath becomes good, and a good zinc oxide film can be continuously formed for a long time.

The blending amount of the amine-borane complex is not particularly limited. However, when the blending amount is too small, the stability of the aqueous solution is improved but the zinc oxide precipitation rate becomes slow, while the blending amount is too small. If the amount is too large, there is a problem that the dissolution becomes difficult and, in addition, the stability of the bath is lowered and the precipitate is easily generated when heated. Therefore, the compounding amount of the amine-borane complex is
It is preferably about 0.001 mol / l to 0.5 mol / l, and 0.005 mol / l to 0.1 mol / l.
More preferably, it is about 1.

According to the composition of the present invention having the above-mentioned composition, the desired zinc oxide film can be formed simply by immersing various kinds of substrates in the composition.

The liquid temperature of the composition of the present invention is preferably about 40 to 90 ° C, more preferably about 60 to 70 ° C. The pH of the composition is not particularly limited, but when the pH is low, the stability of the bath is improved, but the film formation rate decreases, while when the pH is high, the film formation Although the speed is improved, the stability of the bath is reduced and precipitates are easily generated, making it difficult to obtain a zinc oxide film.
From these points, the pH of the composition is preferably about 4.0 to 7.0.

When dipping the substrate in the composition of the present invention,
The composition may be unstirred or in a stirring state, and a known stirring method can be appropriately adopted as the stirring method. Since the thickness of the formed zinc oxide film increases with the immersion time, the zinc oxide film having a desired thickness can be formed by appropriately setting the immersion time.

After the zinc oxide film is formed, usual post-treatment operations such as washing with water and drying can be performed.

In the present invention, the type of substrate for forming the zinc oxide film is not particularly limited, and any material can be used as long as it does not deteriorate when immersed in the composition of the present invention. It may be either a conductive material or a non-conductive material. Specific examples thereof include metal materials such as copper, iron and aluminum, conductive glass such as NESA glass and ITO glass, non-conductive glass materials such as soda lime glass and alkali-free glass (Corning 7059 glass),
Examples thereof include ceramic materials and plastics materials.

When glass, ceramics, plastics or the like is used as the substrate, palladium, iron, cobalt, nickel used for forming the electroless plating film before the substrate is dipped in the composition of the present invention. , A process of applying a catalytic metal such as platinum is performed. As a specific method of the catalyst application treatment, any known method similar to the catalyst application method for forming an electroless plating film can be applied, and a method of applying palladium is generally performed widely, for example, The catalyst may be added by a sensitizing-activation method, a catalyst-accelerator method, an alkaline catalyst method or the like.

[0019]

According to the composition for forming a zinc oxide film of the present invention, a zinc oxide film can be formed by a very simple operation of immersing a substrate in the composition. It is possible to use a simple apparatus such as an electroless plating apparatus that is industrially used without requiring a large-scale apparatus such as a heating furnace or a heating furnace. Further, according to the composition of the present invention, a zinc oxide film can be easily formed on any material of a conductive base material and a non-conductive base material, and a large area base material or a base material having a complicated shape can be formed. Can form a zinc oxide film having a uniform film thickness and composition, and its control is easy. The formed zinc oxide film has a forbidden band width of about 3.3 eV.
Is a wurtzite structure zinc oxide semiconductor film, and is extremely useful as a transparent conductive film, optical waveguide, gas and humidity detection sensor, surface acoustic wave element, light emitting element, various acoustic elements, thin film varistor, liquid crystal filter, photocatalyst, etc. It is very useful.

[0020]

EXAMPLES The features of the present invention will be further clarified by showing Examples and Comparative Examples below.

Example 1 A zinc oxide film-forming composition having the composition shown in Table 1 below was prepared. The amount of zinc salt and nitrate in the composition is mo
It is shown by 1 / l.

[0022]

[Table 1]

Alkali-free glass (Corning 7059 glass), which is a standard substrate for solar cells, was used as a substrate, and was immersed in 50 g / l aqueous solution of immersion degreasing (Aesculin A-220 (trademark: degreasing agent manufactured by Okuno Chemical Industries Co.) at 50 ° C. 5 minutes immersion)
After that, sensitizing (immersion in 100 ml / l aqueous solution of sensitizer manufactured by Okuno Seiyaku Kogyo for 1 minute at room temperature) and activation (Activator 100 manufactured by Okuno Seiyaku Kogyo)
The palladium catalyst was applied to the surface of the base material by immersion in a ml / l aqueous solution for 1 minute at room temperature. Then, the substrate was immersed in each composition for 30 minutes under the film forming conditions shown in Table 1 to obtain a zinc oxide film.

Table 2 below shows the presence or absence of film formation, the type of film formed, and the forbidden band width. The presence or absence of film formation was confirmed by SEM observation, and the type of film was determined by X-ray diffraction. The forbidden band was obtained from the absorption edge wavelength of the absorption curve measured in the range of 180 to 900 nm.

[0025]

[Table 2]

Comparative Example 1 A zinc oxide film-forming composition having the composition shown in Table 3 below was prepared. The compounding amount of zinc salt and nitrate in the composition is mol / l
Indicated by

[0027]

[Table 3]

A substrate was immersed in each composition in the same manner as in Example 1 except that the above-mentioned compositions were used and the film forming conditions shown in Table 3 were used.

The results of confirming the presence or absence of film formation in the same manner as in Example 1 are shown in Table 4 below.

[0030]

[Table 4]

Claims (2)

[Claims] 1. A zinc oxide film forming composition comprising an aqueous solution containing zinc ions, nitrate ions and borane-amine complex. 2. The composition for forming a zinc oxide film according to claim 1, wherein zinc nitrate is blended as a zinc ion source and a nitrate ion source.