JPH10245682A - Formation of wiring and wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain transparent and conductive wirings without using resist by immersing a substrate into an aq. soln. contg. zinc nitrate and a reducing agent and selectively irradiating this substrate with light of energy above the optical band gap of zinc oxide, thereby forming wirings contg. the zinc oxide on the substrate. SOLUTION: The zinc oxide itself has no self-catalyst capacity to chemical deposition (electroless plating) and cannot, therefore, make self-growth and self-deposition. The zinc oxide, however, has a photocatalyst capacity and, therefore, photo-excited electrons are generated from the zinc oxide by selectively irradiating the surface of the substrate 1 with the light B having energy above the optical band gap possessed by the zinc oxide. This photo-excited electrons selectively deposits the zinc oxide only on the photoirradiated parts. The photo-excited electrons selectively generated in such a manner further deposit the zinc oxide only on the photoirradiated parts and the wirings 5 are eventually formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a wiring and a wiring. More specifically, the present invention relates to a method for forming a wiring by a plating method using a photocatalytic reaction.
The wiring obtained by the formation method of the present invention can be suitably used for an electrode of a liquid crystal display, a plasma display and the like.

[0002]

2. Description of the Related Art Conventionally, in a flat panel display such as a liquid crystal display (LCD) and a plasma display (PDP), a counter electrode of a matrix electrode is formed on a glass panel side. This opposite pole,
NESA film (mixed crystal film of antimony oxide and tin oxide), I
A transparent conductive oxide film such as a TO film (a mixed crystal film of indium oxide and tin oxide) is generally used.

Here, the counter electrode is formed by forming a transparent conductive oxide film on the entire surface of the substrate by a vacuum film forming method such as sputtering, and then patterning by a subtractive technique using an etching resist and an etchant. Have been. However, the conventional material used for the transparent conductive oxide film has a problem that processing by etching is difficult and the material itself is expensive.

Under such circumstances, a transparent conductive oxide film whose electrical resistivity is adjusted by doping aluminum or the like with zinc oxide as a base material has been actively studied in recent years. As a method for forming a transparent conductive oxide film containing zinc oxide over the entire surface of a substrate, see, for example, JP-A-2-3048.
No. 11, JP-A-4-94174 reports a vacuum film forming method such as sputtering. As another method, electrolytic deposition of zinc oxide (so-called electroplating)
A low-cost wet film formation method such as a method and a chemical deposition (so-called electroless plating) method is reported by Osaka City Industrial Research Institute.

[0005]

However, in the above-described film forming method, since the transparent conductive oxide film is formed on the entire surface of the substrate, it is necessary to use the above-described subtractive technique in order to form a wiring having a desired pattern. There is. In order to form a wiring having a desired pattern by using a subtractive technique, it is necessary to remove a transparent conductive oxide film other than a desired portion by etching using a resist, that is, to perform patterning. That is, in the conventional forming method, an increase in the number of steps related to the patterning using the resist is inevitable. Further, since the resist is finally stripped and removed as an unnecessary substance, there has been a problem that the resist itself becomes an industrial waste.

[0006]

Means for Solving the Problems The present inventors have found that if the photocatalytic ability of zinc oxide is effectively utilized, it is possible to form a wiring having a desired pattern without using a resist. The present invention has been found. Thus, according to the present invention, the substrate is immersed in an aqueous solution containing zinc nitrate and a reducing agent, and the substrate is selectively irradiated with light having an energy equal to or greater than the optical band gap of zinc oxide. And a method for forming a wiring, characterized by forming a wiring including:

Further, according to the present invention, there is provided a substrate on which wiring is formed by the above-described wiring forming method.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The substrate which can be used in the present invention is not particularly limited, and includes a glass substrate, a quartz substrate, a silicon substrate and the like. Of these, a transparent substrate such as a glass substrate or a quartz substrate is preferable in consideration of the property that the formed wiring is transparent. Next, a wiring containing zinc oxide is formed on the substrate. That is, the substrate is immersed in an aqueous solution containing zinc nitrate and a reducing agent, and the substrate is selectively irradiated with light having energy equal to or greater than the optical band gap of zinc oxide, thereby forming a wiring containing zinc oxide on the substrate. can do.

Here, the aqueous solution used for forming the wiring preferably uses zinc nitrate and a reducing agent in amounts of 0.5 mol / l or less, particularly in the range of 0.01 to 0.1 mol / l. Is preferably used. If zinc nitrate is used in an amount of more than 0.5 mol / liter, zinc hydroxide is generated, and zinc oxide cannot be efficiently formed, which is not preferable. If the reducing agent is used in an amount of more than 0.5 mol / l, the aqueous solution for chemical deposition itself will not react normally and cannot be used as an aqueous solution for chemical deposition. Note that examples of the reducing agent include dimethylamine borane and hypophosphite.

The aqueous solution contains a pH of inorganic acids such as ammonia and nitric acid, and organic acids such as malic acid, tartaric acid and citric acid.
Even if a water-soluble dye or a water-soluble metal salt for adjusting (photosensitizing) the optical band gap of a transparent conductive oxide thin film such as a regulator, a cyanine dye, a xanthene dye, or ruthenium chloride is added. Good. In addition, the formation condition is that the pH is 5
-7, the temperature is preferably 40-70 ° C. pH
Is higher than 7 or lower than 5, zinc oxide is an amphoteric compound, so that the wiring itself dissolves, which is not preferable. On the other hand, when the formation temperature is lower than 40 ° C., it is necessary to increase the activity of the reducing agent in the aqueous solution by another means.
If the temperature is higher than 0 ° C., the reducing agent is decomposed, which is not preferable. Next, the irradiated light is ultraviolet light or visible light (when the optical band gap of the transparent conductive oxide thin film is adjusted).
It is preferable that the light energy is not less than 3.3 eV = 5.3 × 10 ⁻¹⁹ J of the optical band gap of zinc oxide.

As a method for selectively irradiating the substrate with light, (1) a mask (for example, a glass mask) having a pattern formed so as to allow light to pass only in a portion where wiring is desired to be formed, is used. By irradiating the entire substrate with light through a mask, a method of irradiating light only to a portion where wiring is desired to be formed, and (2) a method of scanning a laser beam only to a portion where wiring is desired to be formed, etc. No.

Prior to the formation of wiring, pretreatment such as cleaning of the substrate surface, matting of the substrate surface, formation of catalyst nuclei, formation of a transparent conductive oxide thin film by chemical deposition (electroless plating), etc. May be performed. The purpose of cleaning the substrate surface is mainly for degreasing. For example, isopropyl alcohol (IP
A), by immersing the substrate in an organic solvent such as acetone. Note that the cleaning effect can be further improved by applying ultrasonic waves to the substrate during immersion in the organic solvent. Furthermore, before cleaning with an organic solvent, the surface of the substrate may be subjected to a cleaning treatment with a known detergent in advance.

The surface of the substrate can be made into a satin finish by treating it with a strongly acidic solution such as sulfuric acid or hydrofluoric acid or a strongly alkaline solution such as sodium hydroxide or potassium hydroxide. It is preferable that the degree of the pear ground is Ra = about 10 to 50 nm. By making the surface of the substrate a satin finish, it is possible to improve the subsequent adsorption rate of the catalyst nucleus and the adhesion between the transparent conductive oxide thin film and the wiring and the substrate.

Next, a catalyst nucleus may be formed on the substrate.
By the formation of the catalyst nucleus, a wiring made of a later transparent conductive oxide thin film or zinc oxide can be efficiently formed. Examples of the catalyst nucleus include noble metals such as Pd, Pt, and Au, and colloids such as Pd-Sn. The catalyst nucleus can be easily formed by, for example, immersing the catalyst nucleus in an aqueous solution of a metal constituting the catalyst nucleus. More specifically, when forming a catalyst core composed of a Pd-Sn colloid, 10 to 30 g per liter of water is used.
By dipping the substrate in an aqueous solution containing tin chloride and 0.1-1 g of palladium chloride, Pd-Sn
The catalyst nucleus composed of colloid can be adsorbed and carried. Note that an inorganic acid such as hydrochloric acid may be added to the aqueous solution.

Further, chemical deposition (electroless plating) on the substrate
Alternatively, a transparent conductive oxide thin film may be formed by a vacuum film formation method such as sputtering. This transparent conductive oxide thin film functions as a so-called catalyst for efficiently forming a wiring containing zinc oxide later. The transparent conductive oxide thin film may be formed after forming the catalyst nucleus, or may be formed on a substrate on which no catalyst nucleus is formed. Here, zinc oxide, titanium oxide, or the like can be used for the transparent conductive oxide thin film, but it is preferable to use zinc oxide in consideration of later formation of wiring. Note that the thickness of the transparent conductive oxide thin film is preferably from 10 to 100 nm.

The aqueous solution for chemical deposition used for forming the transparent conductive oxide thin film may be the same as the aqueous solution for forming the wiring. Further, the formation of the transparent conductive oxide thin film and the formation of the wiring may be performed using an aqueous solution having the same composition, or an aqueous solution having a different composition may be used. When an aqueous solution having the same composition is used, the formation of the transparent conductive oxide thin film and the formation of the wiring may be performed continuously without removing the substrate from the aqueous solution. May be immersed in the substrate.

Preferably, the conditions for forming the transparent conductive oxide thin film are a pH of 5 to 7 and a temperature of 40 to 70 ° C. If the pH is higher than 7 or lower than 5, the transparent conductive oxide thin film made of zinc oxide is an amphoteric compound, and thus the thin film itself is undesirably dissolved. On the other hand, if the formation temperature is lower than 40 ° C., it is necessary to increase the activity of the reducing agent in the aqueous solution, while if it is higher than 70 ° C.,
Since the reducing agent decomposes, it is not preferable.Since the transparent conductive oxide thin film made of zinc oxide does not itself have an autocatalytic ability, the film thickness obtained only by immersing the substrate in an aqueous solution is a few. It is as thin as nm. When a thicker transparent conductive oxide thin film is desired, the transparent conductive oxide thin film may be formed while irradiating light having energy equal to or more than the optical band gap of zinc oxide. Here, the same light as the light irradiated at the time of forming the wiring can be used.

Thereafter, when the transparent conductive oxide thin film on the substrate is selectively irradiated with light to form a wiring, the substrate is subjected to a soft etching process to form a wiring on the upper portion. Independent wirings can be formed by removing the transparent conductive oxide thin film that is exposed in advance and exposing the substrate. An etchant that can be used for soft etching includes an aqueous solution of an inorganic acid such as hydrochloric acid, and a commercially available hydrochloric acid having a concentration of about several tens of ml / liter can be used. Note that the soft etching is preferably performed at room temperature.

Before or after removing the transparent conductive oxide thin film, the temperature is 100 ° C. or more (more preferably, 100 to 2 ° C.).
(00 ° C.). This heat treatment can further improve the adhesion between the wiring and the substrate. Here, the method for forming a wiring according to the present invention will be described with reference to FIGS. Zinc oxide by itself does not have the ability to self-catalyze chemical deposition (electroless plating) and therefore cannot grow and deposit itself. However, since zinc oxide has a photocatalytic ability, photoexcited electrons are generated from zinc oxide by irradiating light having energy equal to or more than the optical band gap as shown in FIG. By utilizing this photoexcited electron, it becomes possible to impart pseudo autocatalytic capability to zinc oxide. In the figure, e ⁻ indicates photoexcited electrons, and h ⁺ indicates photoexcited holes. FIG. 2 shows that photoexcited electrons reduce nitrate ions and water molecules to be converted to nitrite ions and hydroxide ions, and photoexcited holes oxidize a reducing agent to be converted to oxidized forms. ing.

When zinc oxide having photocatalytic ability is used, for example, as shown in FIG. 1, the substrate 1 is selectively irradiated with light having energy equal to or more than the optical band gap of zinc oxide. In addition, by precipitating zinc oxide, photoexcited electrons can be selectively generated in the light-irradiated region (in the figure, A indicates an unirradiated portion, and B indicates light). The selectively generated photo-excited electrons cause the zinc oxide to be selectively deposited only on the light-irradiated portion to form the wiring 5. Therefore, wiring can be formed without using a conventional subtractive technique.

The wiring obtained by the forming method of the present invention is
It can be used for wiring in any field. However,
Taking advantage of the property of being transparent, it is preferable to use it as an electrode on the transparent substrate side of LCDs, PDPs and the like.

[0022]

Next, the present invention will be specifically described based on examples.

Embodiment 1 FIG. 3 is a schematic cross-sectional process diagram of a method for forming a wiring according to Embodiment 1. In the figure, 1 is a substrate (insulating glass substrate), 2 is Sn
-Pd catalyst nucleus, 3 is a transparent conductive oxide thin film, 4
Is a photomask (glass mask), 5 is wiring, 6 is an aqueous solution for forming wiring containing zinc nitrate and a reducing agent, and B is light. Hereinafter, a method for forming the wiring will be described.

Step 1 For the purpose of cleaning (mainly degreasing) the surface of the substrate 1,
The substrate 1 was washed in an organic solvent such as isopropyl alcohol (IPA) and acetone.

Step 2 (see FIG. 3 (a)) Next, the surface of the substrate 1 is made into a satin finish using a strongly acidic solution such as sulfuric acid or hydrofluoric acid or a strongly alkaline solution such as sodium hydroxide or potassium hydroxide. Ra = about 10 to 50 nm)
did. Since the specific surface area of the substrate 1 is increased by the formation of the pears, the amount of catalyst nuclei adsorbed can be increased, and the adhesion between the substrate and the transparent conductive oxide thin film is improved by a so-called anchor effect. be able to.

Then, at about 40 ° C., an aqueous solution of tin chloride (several tens of ml of commercially available hydrochloric acid and tens of g of tin chloride per liter of pure water) and an aqueous solution of palladium chloride (one liter of pure water, commercially available hydrochloric acid The catalyst nucleus 2 made of Sn-Pd was formed on the substrate 1 by successively immersing the substrate 1 in the substrate 1 and a few hundred mg of tin chloride.

Step 3 (see FIG. 3B) Next, a transparent conductive oxide thin film 3 was formed by chemical deposition (electroless plating) based on the catalyst core 2 by the following method. That is, as an electroless plating solution, zinc nitrate (0.5 mol / l or less) and a reducing agent (dimethylamine borane 1 mol / l) are added to pure water having an electric conductivity of 10 μS / cm or less.
(Liters or less) was used.
The aqueous solution 6 is heated to 40 to 70 ° C. and the substrate 1 is immersed in the transparent conductive oxide thin film 3 having a thickness of several tens nm.
Was formed.

Step 4 (see FIG. 3C) A photomask 4 having an opening in a portion where a wiring is desired to be formed was placed on the substrate 1. Next, the substrate 1 and the photomask 4
Is immersed in the same aqueous solution 6 as in the above step 3, and the energy (3.3 eV =
Light (ultraviolet light) B having 5.3 × 10 ⁻¹⁹ J) was applied. Due to this irradiation, the wiring 5 grew thickly only on the substrate 1 irradiated with the light B (thickness: about 5 μm).

It is considered that the mechanism of the growth of the wiring 5 is based on the following equations (i) to (iv). First,
As shown in the following formula (i), zinc ions and nitrate ions are generated by dissolution of zinc nitrate. Next, photo-excited electrons and photo-excited holes are generated in the transparent conductive oxide thin film by irradiation with ultraviolet light. Photoexcited holes are aqueous solution 6
It is consumed by the reducing agent inside. On the other hand, photoexcited electrons are involved in the chemical reaction of the following formula (ii) to generate nitrite ions and hydroxide ions. The hydroxide ion generated here is
It combines with zinc ions to form zinc hydroxide (see formula (iii) below). Thereafter, the zinc hydroxide is dehydrated, and it is considered that zinc oxide precipitates. Therefore, in this reaction,
It is believed that the photoexcited electrons act as pseudo autocatalysts for depositing zinc oxide. (I) Zn (NO ₃ ) ₂ → Zn ²⁺ + 2NO ₃ ⁻ (ii) NO ₃ ⁻ + H ₂ O + 2e → NO ₂ ⁻ + 2OH ⁻ (iii) Zn ²⁺ + 2OH ⁻ → Zn (OH) ₂ (iv) Zn ( OH) ₂ → ZnO + H ₂ O

Step 5 (see FIG. 3D) The substrate 1 obtained in Step 4 is immersed in dilute hydrochloric acid for several tens of seconds to remove the portion of the transparent conductive oxide thin film 3 where no wiring is formed. Thus, the wiring 5 made of zinc oxide could be formed without using an etching resist or a plating resist.

Second Embodiment FIG. 4 is a schematic cross-sectional process diagram of a method for forming a wiring according to a second embodiment. In the figure, 1 is a substrate (insulating glass substrate), 2 is Sn
-Pd catalyst nucleus, 7 is a transparent conductive oxide thin film, 8
Is a wiring, 9 is an aqueous solution for forming wiring containing zinc nitrate and a reducing agent, and B is light. Hereinafter, a method for forming the wiring will be described.

Steps 1 and 2 were performed in the same manner as in Example 1 (see FIG. 4A). Step 3 (see FIG. 4B) As an aqueous solution for forming the transparent conductive oxide thin film 7, zinc nitrate (0.5%) was added to pure water having an electric conductivity of 10 μS / cm or less.
Mol / l or less), a reducing agent (dimethylamine borane 1 mol / l or less), a water-soluble dye (cyanine dye or xanthene dye) for adjusting (photosensitizing) the optical band gap of zinc oxide, and A transparent conductive oxide thin film 7 was formed in the same manner as in Example 1, except that an aqueous solution 9 having a pH of 6 containing a water-soluble metal salt (ruthenium chloride) was used.

Step 4 (see FIG. 4C) Next, the substrate 1 is immersed in an aqueous solution 9 and an argon laser beam having energy equal to or more than the adjusted (photosensitized) optical band gap of zinc oxide is applied. Spot light (beam light) B converged to several tens μm or less in diameter by an optical lens system was irradiated and scanned in a desired pattern. As a result of this irradiation scanning, the wiring 8 grew thickly (about 5 μm thick) only on the portion of the substrate 1 irradiated and scanned with the light B.

Step 5 (see FIG. 4D) By immersing in dilute hydrochloric acid in the same manner as in Example 1, the wiring 8 made of zinc oxide could be formed.

[0035]

According to the method for forming a wiring of the present invention, a substrate is immersed in an aqueous solution containing zinc nitrate and a reducing agent, and the substrate is selectively irradiated with light having an energy greater than the optical band gap of zinc oxide. Accordingly, a wiring containing zinc oxide is formed on a substrate. In other words, by effectively utilizing the photocatalytic reaction of zinc oxide, a transparent and conductive wiring can be formed by a simple plating method without using a conventional subtractive technique (that is, without using a resist). can do. Therefore, it is possible to reduce the cost of forming the wiring.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the principle of the present invention.

FIG. 2 is a schematic diagram illustrating the principle of the present invention.

FIG. 3 is a schematic process sectional view of a method for forming a wiring according to the first embodiment;

FIG. 4 is a schematic process sectional view of a method for forming a wiring according to a second embodiment;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Catalyst core 3, 7 Transparent conductive oxide thin film 5, 8 Wiring 4 Photomask 6, 9 Aqueous solution A Non-irradiated part B Light

Claims (4)

[Claims] 1. A method comprising: immersing a substrate in an aqueous solution containing zinc nitrate and a reducing agent; and selectively irradiating the substrate with light having an energy equal to or more than the optical band gap of zinc oxide, whereby the substrate contains zinc oxide. A method for forming a wiring, comprising forming a wiring. 2. The method according to claim 1, further comprising: forming a transparent conductive oxide thin film on the substrate before forming the wiring, and removing the transparent conductive oxide thin film exposed after forming the wiring. Method. 3. The method according to claim 1, wherein a catalyst nucleus is formed on the substrate before forming the wiring or before forming the transparent conductive oxide thin film. 4. A wiring board on which wiring is formed by the wiring forming method according to claim 1.