JPH09324264A - Sputtering target - Google Patents

Abstract

(57) Abstract: A transparent adhesive thin film (21), a transparent or reflective silver-based thin film (22), and a transparent protective film (23) on the surface of a glass substrate (10).
In order to improve the moisture resistance of various conductive films such as a multi-layer thin film and a multi-layer thin film including the conductive thin film 24 having a three-layer structure, and to improve a sputtering target so as to prevent an adverse effect of a gas atmosphere such as oxygen during sputtering. is there. SOLUTION: 0.1-2.5 at% gold, and 0.3-
A sputtering target composed of a silver alloy or a silver-based composite metal containing 3 at% of copper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering method applied when a silver-based thin film of a three-layer conductive film having a structure in which a silver-based thin film is sandwiched between metal oxide-based thin films is formed by a sputtering method. More specifically, the present invention relates to an improvement of a sputtering target for forming a conductive film having excellent moisture resistance and optical characteristics.

[0002]

2. Description of the Related Art A multi-layered thin film formed by providing a transparent conductive protective film of a metal oxide such as an ITO thin film on the surface of a silver thin film has extremely high conductivity, and therefore utilizes this high conductivity. Attempts have been made to apply the multilayer thin film to various fields.

For example, in Japanese Examined Patent Publication No. 1-126363 or Japanese Unexamined Patent Publication No. 61-25125, the transparency is ensured by thinning a silver coating, and an ITO thin film is laminated on the surface to form a transparent multilayer structure. We have proposed various conductive multi-layer thin films. Since this transparent multi-layered thin film has an extremely high conductivity as compared with a thin film of ITO alone, for example, an ITO thin film has a sheet resistance value of 8Ω when its film thickness is 250 nm.
(Or Ω / □, □; referred to as square), whereas the transparent multilayer thin film has a total film thickness of at most 9
Even with a very thin film of 0 nm, a low sheet resistance value (high conductivity) of about 5Ω can be realized.

Further, paying attention to high conductivity and transparency of such a transparent multilayer thin film, in JP-A-63-173395, a multilayer thin film having a similar layer structure is used as a transparent electromagnetic wave shielding film. We are proposing the technology to use.

Further, in a conductive film having a three-layer structure in which a silver-based thin film is sandwiched between metal oxide-based thin films, the thickness of the silver-based thin film is 5
Since it has a good transmittance for visible light in the range of up to 20 nm, its application to a transparent electrode such as a liquid crystal display is under study. The conductive film having a three-layer structure having the above-described structure has a silver-based thin film having a thickness of 50 nm or less, for example, 5 to
When it is set in the range of 25 nm, preferably in the range of 8 to 22 nm, it becomes a conductive film having good light transmissivity, and when it is set thicker than 50 nm, it becomes a conductive film having good light reflectivity.

[0006] Furthermore, the 7th held in Japan in 1982.
In the ICVM, the multi-layer thin film having the same layer structure is applied to the heat ray reflecting film (heat ray blocking film), paying attention to the fact that the multi-layer thin film having the same layer structure is excellent in the ability to block light on the long wavelength side. Technology is proposed.

On the other hand, regarding a silver thin film having a relatively large film thickness, attention is paid to the fact that the light reflectance thereof is high over almost the entire visible region.
A technique of applying a light-reflecting multilayer thin film having a multilayer structure by stacking an ITO thin film and the like on a silver thin film of about 0 nm as a light reflecting plate of a reflective liquid crystal display or a reflective metal electrode (reflective electrode) is also proposed. ing.

[0008]

By the way, in the production of these multilayer thin films, the silver thin film is usually formed by a sputtering method using a silver sputtering target, and a metal sandwiching the silver thin film is used. The oxide is also usually formed by sputtering or vapor deposition. The conductive film having a three-layer structure manufactured by such a film forming method may have spots on the conductive film even if it is left alone after the film formation due to the influence of humidity, or microscopically (microscopically). However, there is a problem that the three-layer structure of the conductive film is destroyed, or silver agglomerates to deteriorate the conductivity and optical characteristics of the conductive film, and therefore improvement in moisture resistance is desired.

As a measure for improving the moisture resistance of a conductive film having a three-layer structure, the present inventors have found that a silver-based thin film made of a silver alloy in which gold is added to silver is effective in significantly improving the moisture resistance. We have found this and proposed this structure, and the amount of gold added to the above silver is 4 at% (hereinafter referred to as atomic weight).
%, Atomic weight% is referred to as at%) or less, for example, 0.1 to
It has been found that there is a sufficient effect of improving the moisture resistance in the range of 3 at%.

Further, the conductive film having a three-layer structure using a silver-based thin film of silver-gold alloy has a drawback that it is easily affected by a gas atmosphere at the time of film formation by sputtering as described below. For example, in the case of a conductive film having a three-layer structure assuming a transparent electrode such as an electrode substrate for a transmissive liquid crystal display, the light transmittance (reflection The light reflectance of the electrode is likely to decrease.

FIG. 6 shows a three-layer structure in which a silver thin film made of silver or a silver thin film made of a silver-gold alloy (containing 0 to 0.4 at% of gold) having a thickness of 15 nm is sandwiched between metal oxide thin films. It is a graph which shows the spectral characteristic (spectral transmittance) of the transparent conductive film of a structure.

The graph in FIG. 6 is for a silver thin film of 0 at% gold, and the graph (broken line) is 0.10 at% gold.
This is the case with a silver-based thin film of 0.20a
This is the case with a t% silver-based thin film, and the graph shows gold 0.4
The spectral transmittance of each transparent conductive film having a three-layer structure when a silver-based thin film of 0 at% is used. The total film thickness of the conductive films is about 90 nm and the sheet resistance value is about 3Ω.

As shown in FIG. 6, the transparent conductive film having a three-layer structure is composed of a silver thin film shown in the graph, a silver-based thin film containing 0.20 at% gold in the graph, and a silver-based thin film containing 0.40 at% gold in the graph. In the film, the light wavelength 470
It is shown that the transmittance decreases in the vicinity of nm. In the transparent conductive film having a three-layer structure of the silver-based thin film added with 0.10 at% gold in the graph (broken line), the above-mentioned decrease in transmittance is observed. I can't.

Similarly, in FIG. 7, 0.8 to 2.5 atm of gold is used.
% Is a spectral characteristic curve of a transparent conductive film having a three-layer structure containing
The graph in FIG. 7 shows a silver-based thin film of 0.8 at% gold, the graph (dashed line) shows a silver-based thin film of 1.52 at% gold, and the graph shows a three-layer structure of a silver-based thin film of 2.5 at% gold. It is the spectral transmittance of the transparent conductive film, the total film thickness of the conductive film is about 90 nm, and the sheet resistance value is about 3Ω.

According to FIG. 7, the graph, the graph (broken line), and the transparent conductive films each having a three-layer structure shown in the graph show a decrease in the transmittance near the light wavelength of 470 nm.

This decrease in transmittance can be reduced in a batch type film forming apparatus by sufficiently exhausting gas during film formation of a silver-based thin film to reduce the influence of oxygen. In the type of film forming apparatus, oxygen is easily introduced because oxygen is introduced when forming the metal oxide thin films on both sides (front and back) of the three-layer conductive film.

FIG. 4 is graphs A and B showing the spectral characteristics (spectral reflectance) of a reflective conductive film having a three-layer structure made of a silver-based thin film having a film thickness of 150 nm. It is the spectral reflectance of a reflective conductive film made of a silver-gold alloy to which 1 at% of gold is added. The reduction of the light reflectance on the short wavelength side and the depression of the curve in the graph near the light wavelength of 460 nm are seen.

The phenomenon of such a curve depression becomes more remarkable by increasing the introduction of oxygen gas during film formation, as in the case of the light transmittance of the above-mentioned light-transmissive transparent electrode.
By adding a predetermined amount of gold to a silver-based thin film to form a film,
It has been found that it is possible to prevent the above-described curve depression phenomenon due to oxygen during film formation.

An object of the present invention is to improve a sputtering target for solving the above-mentioned problems, and various kinds of multi-layer thin films, multi-layer thin films and the like including the above-mentioned conductive thin film having a three-layer structure. It is to improve the moisture resistance of the conductive film and to improve the sputtering target so that the adverse effect of a gas atmosphere such as oxygen at the time of sputtering can be prevented.

[0020]

The present invention provides 0.1-2.
A sputtering target comprising a silver alloy or a silver-based composite metal containing 5 at% of gold and 0.3 to 3 at% of copper.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The sputtering target of the present invention will be described below in detail according to the embodiments.

The inventors of the present invention, as a means for reducing the influence of the gas atmosphere when forming a silver-based thin film by sputtering, use an alloy of silver (Ag) and gold (Au) with a small amount of copper (C).
It has been found that good results can be obtained by forming a silver-based thin film using a silver-gold-copper alloy containing u).

In this case, the addition amount of both gold and copper is 3
A small amount of at% or less (at%; atomic weight%) is sufficient, and by adding a small amount of the above-mentioned copper, in the short wavelength side of various conductive films such as multi-layer thin films using silver-containing thin films containing gold and multi-layer thin films. It is possible to eliminate the decrease in the light transmittance T (or the light reflectance R) of.

The amount of gold added to the silver-based thin film is 0.1 at% for improving the moisture resistance of the conductive film.
The effect occurs from the addition of a small amount of, and the moisture resistance improves as the amount of addition increases. However, when the amount of gold added increases, the resistance value of the conductive film increases, and the amount of gold added is 2.5a.
If it is t% or more, a residue tends to remain during etching of the conductive film.

FIG. 5 shows a transparent conductive thin film (thickness: about 85 nm) having a three-layer structure formed on a transparent substrate, in which copper (Cu) is added to the silver-based thin film in the conductive thin film. 6 is a graph showing the relationship between the rate (0 to 3.0 at%) and the spectral transmittance T (%) at that time. The amount of copper added to the silver-based thin film is 0.3 at, as shown in FIG. %, There is an effect of gradually increasing the drop in transmittance on the short wavelength side.

Since copper takes a eutectic form (not a perfect solid solution) with silver, when the amount of copper added increases, the transmittance (or reflectance) is adversely affected. Further, when the amount of copper added increases, the resistance value of the conductive film tends to increase. For example, when the thickness of the silver-based thin film is 10 nm and the amount of copper added is 3 at% or more, the area is The resistance value exceeds 5Ω (or 5Ω / □).

The sputtering target according to the present invention includes gold, copper, and other simple metallic elements within a range that does not substantially affect the light transmittance or the light reflectance of the multilayer thin film and the multilayer thin film. It may contain a transition metal element, a metalloid element, or the like.

The above sputtering target is composed of a silver alloy containing a small amount of gold and copper with respect to the main silver, and these silver, gold and copper are heated and melted and poured into a mold. By molding and cooling and solidifying, a plate-shaped sputtering target can be manufactured. The heating and melting atmosphere may be an inert gas or the atmosphere.

Plate-shaped sputtering target (plate material)
As a method of obtaining, there is a method of casting with a plate-shaped mold, a method of rolling an ingot into a plate shape, a method of directly obtaining a plate material by a continuous casting method without using a mold, etc. Even when the method is used, a plate material satisfying the effects of the present invention can be obtained.

The polishing method for polishing the obtained plate material to obtain a target is not particularly limited, and surface polishing which is usually performed may be used.

Further, as the silver alloy target in the sputtering target of the present invention, in addition to the silver alloy target described above, gold and copper may be added to a part of the silver target so as to have a predetermined ratio, if necessary. Composite metal with small amount embedded (0.1-2.5 at% gold and 0.3-3a)
It may be a silver alloy target with t% copper).

A conductive film having a multi-layer structure such as a three-layer structure in which a silver-based thin film is sandwiched between metal oxide-based thin films as described in the prior art is a DC (direct current) method or an RF (alternating current) method.
It is general to form a film by a sputtering method such as a sputtering method or an RF-DC method. For example, a sputtering target (sputtering source) for forming a silver alloy target of the above composite metal in which a small amount of gold and copper are embedded in a silver base. )
When used as, the composition ratio and the film thickness of the silver-gold alloy of the silver-based thin film formed on the substrate are likely to be uneven between the buried alloy element vicinity region and other regions. Therefore, it is necessary to give sufficient consideration so that nonuniform differences do not occur in the formed silver-based thin film.

Next, the sputtering target according to the present invention is fixed on a backing plate and used as a target for a DC sputtering method, a DC sputtering method such as an RF-DC sputtering method, or a radio frequency (RF) sputtering method. It is used to form a silver-based thin film having the same composition as that of this sputtering target. The material of the backing plate is preferably one having a high cooling effect during water cooling, for example, a copper alloy, oxygen-free copper or the like can be used, and as a method of fixing the sputtering target to the backing plate, For example, a fixing method such as metal bonding or resin fixing can be applied.

The silver-based thin film thus formed has conductivity, and when the film thickness is less than 50 nm,
For example, in the case of 2 nm or less, it has good light transmittance,
Transparent electrodes for transmissive liquid crystal displays and solar cells,
Alternatively, it can be used as a transparent electromagnetic wave shield film or the like.

When the silver-based thin film is used as a light-reflective thin film, it is desirable to form the film to a thickness of 50 nm or more. The silver-based thin film thus formed has conductivity and light reflectivity. Thus, it can be used as, for example, a reflection type liquid crystal display or a reflection electrode of a solar cell, an electromagnetic wave shield film, or the like.

As a film forming method for forming a conductive film such as a silver-based thin film using the above sputtering target, a direct current (DC) sputtering method is preferable from the viewpoint of the film forming speed. In addition, when forming a film, it is desirable to form a film on a high vacuum side at a high film forming speed, while removing water in the film forming apparatus as much as possible, and a silver-based thin film to be formed It is desirable to form a film at a low substrate temperature in order to obtain a fine crystalline state.

A protective film is formed on the surface side of the silver-based thin film to be formed, for example, in the case of a three-layer conductive film, the silver-based thin film is provided on the upper and lower sides (front and back sides) on a substrate such as glass. The protective film is formed as a conductive thin film on the front surface side of the conductive thin films that are sandwiched and formed.

Examples of the protective film include zinc oxide,
A transparent mixed oxide thin film made of gallium oxide, tin oxide, indium oxide, or a mixture of indium oxide with another inorganic oxide can be used.

Further, in particular, as the above-mentioned protective film, a mixed metal oxide type thin film formed by adding an oxide of a metal element, which does not have a solid solution area with silver or has a small solid solution area, to indium oxide or the like. When the film is formed, the thin film has a moisture-proof property and blocks moisture in the air, so that it is possible to prevent deterioration or deterioration of the silver-based thin film with time due to this moisture.

Here, as the metal element which does not have a solid solution area with silver or has a small solid solution area as described above, an element whose solid solution amount with respect to silver is less than 10 at% near room temperature, for example, Ti, Zr, Examples include semi-metal elements such as Ge and Si.

Further, when the content of these elements is less than 5 at% as compared with the indium element, although the improvement of the moisture-proof property is observed, the effect is insufficient, so that it is desirable to contain 5 at% or more, As a result, the mixed metal oxide-based thin film containing the above elements exhibits extremely high moisture resistance, and the temporal change or deterioration of the silver-based thin film formed by using the sputtering target of the present invention, which is the underlying layer, Can be further prevented.

When the metal element having no or small solid solution region with silver used in the protective film is one or more elements selected from titanium and cerium, the refractive index of the protective film is about 2.1. Therefore, if the silver-based thin film is thin and transparent, the protective film is a silver-based thin film antireflection film (a film that prevents reflection of light on the long wavelength side in the visible region). It is possible to increase the light transmittance on the long wavelength side, and as a result,
Since it has a high light transmittance over the entire visible region, bright and bright white light can be transmitted.

When the protective film has indium oxide as a base material, both the protective film containing indium oxide as a main component and the above-mentioned silver-based thin film are subjected to an etching treatment using a nitric acid-based etchant as an etching solution. Can be used for patterning. That is, after forming two layers of a silver-based thin film and a protective film on a substrate such as glass or synthetic resin, and forming a resist film on the exposed protective film in a pattern by a photolithography method or the like. By etching the portion exposed from the resist film with a nitric acid-based etching solution, it is possible to pattern-etch the two-layered thin films together in a pattern.

As the etching liquid, nitric acid-based mixed liquid obtained by adding other kinds of acids such as hydrochloric acid, sulfuric acid, or acetic acid to nitric acid in addition to nitric acid, or nitric acid with a small amount of surfactant added is used. it can.

Next, as the substrate on which the silver-based thin film is formed by using the sputtering target according to the present invention, for example, glass, plastic board, plastic film or the like can be used. A substrate provided with a light-scattering layer (light-diffusing layer for expanding the viewing angle) can also be used.

When a plastic board or plastic film is used as a substrate, moisture on the surface of the plastic board or plastic film is prevented from being damaged by moisture in the air from damaging the silver-based thin film. It is desirable to form a silver-based thin film after providing a conductive coating layer.

Further, in order to increase the adhesion between the silver-based thin film and the substrate, it is possible to provide a transparent adhesive thin film between the silver-based thin film and the substrate. As the thin film, a thin film made of the same material as the protective film can be used.

Since the adhesive thin film having the same material as the protective film can be etched with nitric acid or a nitric acid-based mixed liquid, three layers of the adhesive thin film, the silver-based thin film and the protective film are formed on the substrate. Can be formed in this order, and a resist film can be formed in a pattern on the protective film on the surface by a photolithography method or the like, and then the three layers can be collectively patterned into the above pattern by etching. Is.

[0049]

EXAMPLES Specific examples of the present invention will be described below.

<Example 1> A sputtering target according to Example 1 is 1.0 at% gold and 1.5 at%.
% Copper and 97.5 at% silver, both of which are used to melt a predetermined amount of 99.99% pure metal in a melting furnace in the atmosphere, stir and mix, and then cast into a plate shape. A plate material of a sputtering target was manufactured by casting with a mold having the shape of. The casting method using the mold is not particularly limited, but in Example 1, the molten silver alloy was poured into the water-cooled mold (mold), cast, and cooled for about 3 hours. did.

Subsequently, the surface of the plate material of the sputtering target obtained by casting is smoothly ground (polished) by a surface grinder (surface grinder), and the end surface of the plate material is processed (molded).
By doing so, a sputtering target was manufactured.

Next, this sputtering target was fixed on a backing plate made of copper, and an adhesive thin film 11 having a thickness of 39 nm and a thickness of 10 nm was formed on a transparent glass substrate 10 by a sputtering method as shown in FIG. Silver thin film 1
2 (light-transmissive thin film), a multilayer thin film 14 (three-layer transparent conductive thin film) composed of a protective film 13 having a thickness of 39 nm
Was formed. The sputtering apparatus is a DC magnetron sputtering apparatus, and the glass substrate 10 is kept at room temperature to continuously form the multilayer thin film 14 without taking the glass substrate 10 out of the apparatus.
The multi-layer thin film 14 thus formed is 270 ° C.
An annealing treatment for 1 hour was performed as needed.

The silver-based thin film 12 has the same composition as the sputter-link target, while the adhesive thin film 11 and the protective film 13 are both mixed metal oxides of indium oxide, titanium oxide and cerium oxide. It is composed of objects.

The content of each metal element of the mixed metal oxide of the adhesive thin film 11 and the protective film 13 is 100 at% of the total atomic weight of the metal elements (total atomic weight of indium element, titanium element, and cerium element). At that time, for example, the content was set to 80 at% of indium element, 19 at% of titanium element, and 1 at% of cerium element.

The above multi-layered thin film 1 thus formed
The sheet resistance value of the whole 4 was 4.6Ω. Further, the spectral transmittance T of the multilayer thin film 14 formed on the transparent substrate 10 is
Looks like Figure 2.

As can be seen from FIG. 2, the wavelength is 430 nm.
It was confirmed that the spectral transmittance was close to 97% in a wide range of up to 620 nm, and that it had a uniform and high transmittance over almost the entire visible region.

<Example 2> The sputtering target according to Example 2 was manufactured in the same manner as in Example 1 above.

Then, this sputtering target was fixed to a backing plate made of copper, and an adhesive thin film 21 having a thickness of 10 nm and a thickness of 10 nm was formed on a transparent or opaque glass substrate 20 as shown in FIG. 3 by a sputtering method. 15
0 nm silver-based thin film 22 (light-reflecting thin film), thickness 75 nm
A multilayer thin film 24 (a conductive thin film having a three-layer structure) composed of the protective film 23 was formed. A DC magnetron sputtering apparatus was used as the sputtering apparatus, and the glass substrate 20 was kept at room temperature.
Of the above-mentioned multilayer thin film 2 continuously without taking out the
4 is formed, and the multilayer thin film 24 thus formed is formed.
Then, an annealing treatment at 230 ° C. for 1 hour was performed as necessary.

The silver-based thin film 22 has the same composition as the sputter-link target, while the adhesive thin film 21 and the protective film 23 are both made of a mixed metal oxide of indium oxide and cerium oxide. It is configured.

The content of each metal element in the mixed metal oxide of the adhesive thin film 21 and the protective film 23 is such that the total atomic weight of the metal elements (total atomic weight of indium element and cerium element) is 100 at%. For example, the content was set to 68 at% of indium element and 32 at% of cerium element.

The sheet resistance of the whole multilayer thin film 24 formed by annealing in this way was 2.9Ω. In addition, the multilayer thin film 2 formed on the substrate 20
The spectral reflectance R of No. 4 is as shown in graph A of FIG.

As can be seen from FIG. 4, the wavelength is 400 nm.
In a wide range of up to 620 nm, the spectral reflectance was improved by up to about 15% as compared with the conventional graph B, and it was confirmed that the spectral reflectance was uniform and high over almost the entire visible region.

[0063]

The sputtering target of the present invention is
A target made of a silver alloy in which a small amount of gold and copper are heated and dissolved in silver and mixed, or a target made of a composite metal in which a small amount of gold and copper are embedded in a silver base, and high humidity resistance by using this, In addition, it is possible to manufacture a conductive multi-layered thin film having a high transmittance when the transparent electrode is premised and a high reflectance when the reflective electrode is premised.

By carrying out the sputtering film formation using the sputtering target of the present invention, the influence of oxygen in the atmosphere during the film formation is suppressed, and the allowable value under the film formation conditions etc. is relaxed, and it is comparatively better than the conventional one. There is an effect that it can be manufactured in a work area with a wide membrane work margin.

In particular, in the in-line type sputtering apparatus, the adhesive thin film made of a metal oxide or the surface protective film and the silver thin film can be formed in the same sputtering chamber, which makes it less susceptible to oxygen. It has a remarkable effect such as being able to.

[Brief description of drawings]

FIG. 1 is a side sectional view for explaining a transparent conductive thin film formed by sputtering on a transparent glass substrate using the sputtering target of the present invention.

FIG. 2 is a graph showing the spectral transmittance of a transparent conductive thin film formed by sputtering on a transparent glass substrate using the sputtering target of the present invention.

FIG. 3 is a side sectional view for explaining a reflective conductive thin film formed by sputtering on a glass substrate using the sputtering target of the present invention.

FIG. 4 is a spectral reflectance of a reflective conductive thin film (graph A) sputter-deposited on a glass substrate using the sputtering target of the present invention, and a spectral reflectance of a conventional reflective conductive thin film (graph B). ) And a graph showing.

FIG. 5 is a graph showing the relationship between the content of copper contained in a transparent silver-based thin film and the spectral transmittance.

FIG. 6 is a graph showing the relationship between the content of gold contained in a transparent silver-based thin film and the spectral transmittance.

FIG. 7 is a graph showing the relationship between the content ratio of gold contained in a reflective silver-based thin film and the spectral reflectance.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Transparent glass substrate 11 ... Adhesive thin film 12 ... Silver thin film 13 ... Protective film 14 ... Transparent conductive thin film 20 ... Transparent or opaque glass substrate 21 ... Adhesive thin film
22 ... Silver-based thin film 23 ... Protective film 24 ... Reflective conductive thin film

Front page continuation (72) Inventor Tadashi Kato 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Metal Mining Co., Ltd. (72) Inventor Tatsuo 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Metal Mining Co., Ltd.

Claims (1)

[Claims] 1. Gold of 0.1-2.5 at%, and 0.3-
A sputtering target comprising a silver alloy or a silver-based composite metal containing 3 at% of copper.