JP2012106878A - Method for manufacturing zinc oxide-based transparent conductive film-forming material, target using the transparent conductive film-forming material, and method for forming zinc oxide-based transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium (low valence)-doped zinc oxide-based transparent conductive film-forming material enabling film formation of the transparent conductive film having excellent conductivity and being suppressed in abnormal discharge at film formation.SOLUTION: The method for manufacturing the zinc oxide-based transparent conductive film-forming material uses a raw material powder containing a mixed powder of a low-valence titanium oxide powder and a zinc oxide powder or a zinc hydroxide powder, or a zinc titanate compound powder, and having a proportion of the number of titanium atoms to the total number of metal atoms of >2% and ≤10%, and includes discharge plasma sintering in vacuum or in an inert atmosphere at ≥700°C and ≤1,200°C.

Description

  The present invention is an oxidation useful as a target used when a zinc oxide-based transparent conductive film is formed by sputtering, ion plating, pulse laser deposition (PLD), or electron beam evaporation (EB evaporation). The present invention relates to a method for producing a zinc oxide-based transparent conductive film forming material that is a sintered product, a target using the transparent conductive film forming material, and a transparent conductive substrate formed from the target.

  Transparent conductive films that combine electrical conductivity and light transmission have been used as electrodes in solar cells, liquid crystal display elements, and other various light receiving elements, as well as automotive window and heat ray reflective films for buildings, It is used for a wide range of applications such as anti-static films and transparent heating elements for anti-fogging in frozen showcases. In particular, it is known that a transparent conductive film having low resistance and excellent conductivity is suitable for a solar cell, a liquid crystal display element such as a liquid crystal, organic electroluminescence, and inorganic electroluminescence, a touch panel, and the like.

Conventionally, as the transparent conductive film, for example, a tin oxide (SnO ₂ ) -based thin film, a zinc oxide (ZnO) -based thin film, and an indium oxide (In ₂ O ₃ ) -based thin film are known.
Specifically, antimony-doped tin oxide (ATO) films using antimony as dopants and fluorine-doped tin oxide (FTO) films using fluorine as dopants are known as tin oxide-based transparent conductive films.
As a zinc oxide-based transparent conductive film, an aluminum-doped zinc oxide (AZO) film using aluminum as a dopant and a gallium-doped zinc oxide (GZO) film using gallium as a dopant are known.
As an indium oxide-based transparent conductive film, a tin-doped indium oxide (ITO) film using tin as a dopant is known. Among them, the most industrially used is an indium oxide-based transparent conductive film, and in particular, an ITO film is widely used because of its low resistance and excellent conductivity.

  Conventionally, when forming such a transparent conductive film, sputtering, ion plating, PLD, EB vapor deposition and the like are widely used industrially. The target used as a film raw material in these film forming methods is made of a solid containing a metal element constituting the film to be formed, and is a sintered body such as metal, metal oxide, metal nitride, metal carbide, In some cases, it is formed of a single crystal. As targets used industrially, oxide targets (that is, oxide sintered bodies) have been widely used.

  By the way, an indium oxide-based transparent conductive film such as an ITO film is expensive and may be depleted of resources because In (indium), which is an essential raw material, is a rare metal, and has toxicity and is harmful to the environment and the human body. It may have an adverse effect on it. Therefore, in recent years, an industrially versatile transparent conductive film that can be substituted for an ITO film has been demanded. Under such circumstances, a zinc oxide-based transparent conductive film that can be industrially manufactured by a sputtering method has attracted attention, and research is being conducted to improve its conductive performance.

Non-Patent Document 1 attempts to dope ZnO with various dopants in order to increase conductivity, and reports the optimum doping amount and the lowest resistivity for each of the various dopants. In this report, it is known that a zinc oxide-based transparent conductive film doped with Al ₂ O ₃ and Ga ₂ O ₃ exhibits a low resistance comparable to that of an ITO film. However, an Al ₂ O ₃ doped AZO film and a Ga ₂ O ₃ doped GZO film have low resistance, but are inferior in chemical durability and inferior in the near-infrared region.
Further, according to this report, for example, in the zinc oxide transparent conductive film doped with TiO ₂ having excellent chemical durability, the doping amount is optimally 2% by weight, and the minimum resistivity at that time is 5.6. Although it is shown that it is × 10 ⁻⁴ Ω · cm, the physical properties with low resistance cannot be obtained stably, and the resistance is inferior to that of the AZO film and the GZO film.
Moreover, the zinc oxide-based transparent conductive film using low-valent TiO (II) and Ti ₂ O ₃ (III) as raw materials is even lower than the zinc oxide-based transparent conductive film doped with TiO ₂ (IV). The inventor has already found that resistance can be achieved.

Monthly Display, September 1999, p10 “Trends in ZnO-based transparent conductive films”

However, when producing an oxide sintered body using Ti ₂ O ₃ (III) or TiO (II) as a dopant, the crystal structure of the oxide sintered body is titanium oxide together with zinc oxide in which titanium is partly dissolved. Zn ₂ TiO ₄ (composite oxide) is generated by a solid-phase reaction between zinc and zinc oxide. Since Zn ₂ TiO ₄ is an insulating layer, it becomes an insulating layer in the sintered body, and zinc oxide in which titanium is dissolved is a conductive layer.
In order to reduce the resistance of the transparent conductive film formed on the substrate by sputtering, the present inventor formed a composite oxide phase by dissolving titanium in zinc oxide as much as possible even in the oxide sintered body. It has been found that suppressing this is advantageous in reducing the resistance when sputtering film formation is performed.
In addition, if there is an insulating layer in the conductive layer of zinc oxide, which is the majority of sintered bodies, abnormal discharge frequently occurs during sputtering. If abnormal discharge occurs frequently, it does not discharge stably, which causes a decrease in productivity.
That is, the abnormal discharge occurs due to the fact that the target is non-uniform and there is a portion where the specific resistance is locally different, and the impedance of the discharge system including the target fluctuates during sputtering. The part where the specific resistance is locally different is a composite oxide phase (Zn ₂ TiO ₄ ). The complex oxide phase of such an insulating layer is distributed in some places in zinc oxide in which uniform titanium is partly dissolved. Therefore, it is effective for suppressing abnormal discharge to reduce the generation ratio of these composite oxide phases as much as possible.

Accordingly, an object of the present invention is to provide a method for producing a titanium (low valence) -doped zinc oxide-based transparent conductive film that makes it possible to produce a transparent conductive film having excellent conductivity, and to use the transparent conductive film-forming material. The present invention provides a target, a method for forming a zinc oxide-based transparent conductive film, and a transparent conductive substrate using the same.
Another object of the present invention is to provide a method for producing a titanium (low valence) -doped zinc oxide-based transparent conductive film forming material capable of producing a transparent conductive film that suppresses abnormal discharge that occurs during film formation, and the transparent conductive film. The object is to provide a target using a forming material, a method for forming a zinc oxide-based transparent conductive film, and a transparent conductive substrate using the same.

In order to reduce the resistance of the transparent conductive film, it is important for the present inventor to reduce the generation ratio of the composite oxide phase. For this purpose, discharge plasma sintering (hereinafter sometimes referred to simply as SPS) is important. It was found that the formation of a composite oxide phase (Zn ₂ TiO ₄ ) can be suppressed by using.
The transparent conductive film manufactured by sputtering using the zinc oxide-based transparent conductive film forming material obtained by this method has low resistance, has sufficient weather resistance against temperature and humidity, and has an appropriate etching rate. The present inventors have found that it has excellent chemical durability and high transmittance in the near-infrared region, and has completed the present invention.
Moreover, since the production | generation of complex oxide phase decreases, the abnormal discharge at the time of sputtering film-forming can be suppressed, and productivity can be improved significantly.

That is, this invention consists of the following structures.
(1) Including a mixed powder of low-valent titanium oxide powder and zinc oxide powder or zinc hydroxide powder, or zinc titanate compound powder, the ratio of the number of titanium atoms to the total number of metal atoms is more than 2% and not more than 10% Zinc oxide, which is an oxide sintered body, characterized in that the raw material powder is placed in a mold and subjected to discharge plasma sintering at a sintering temperature of 700 ° C. or higher and 1200 ° C. or lower in a vacuum or in an inert atmosphere. Of manufacturing a transparent conductive film forming material.
(2) The method for producing a zinc oxide-based transparent conductive film forming material according to (1), wherein the mold includes a graphite die and a graphite punch.
(3) During the spark plasma sintering, the rate of temperature rise to the sintering temperature is 10 ° C./min to 200 ° C./min, and the sintering time at the sintering temperature is 10 seconds to 10 minutes. A method for producing a zinc oxide-based transparent conductive film forming material according to (1) or (2) above (4) An oxide sintered body obtained by the method according to any one of (1) to (3) A zinc oxide-based transparent conductive film forming material.
(5) The oxide sintered body substantially composed of zinc, titanium, and oxygen, wherein the titanium is contained in an atomic ratio such that Ti / (Zn + Ti) = 0.02 and 0.1 or less. The zinc oxide-based transparent conductive film forming material according to (4).
(6) The zinc oxide-based transparent conductive film forming material according to (4) or (5), wherein the oxide sintered body has a relative density of 93% or more.
(7) A target used for film formation by a sputtering method, wherein the target is obtained by processing the zinc oxide-based transparent conductive film forming material according to any one of (4) to (6).
(8) A method for forming a zinc oxide-based transparent conductive film, wherein a zinc oxide-based transparent conductive film is formed by a sputtering method using the target according to (7).
(9) A transparent conductive substrate comprising a zinc oxide-based transparent conductive film formed by the method for forming a zinc oxide-based transparent conductive film according to (8) above on a transparent substrate.

  According to the present invention, a target for forming a zinc oxide-based transparent conductive film having an appropriate etching rate during patterning can be obtained by doping with low-valent titanium oxide. In addition, the formed zinc oxide-based transparent conductive film has excellent conductivity and chemical durability [heat resistance, moisture resistance, chemical resistance (alkali resistance, acid resistance, etc.)] and high transmittance in the near infrared region. With. In addition, the zinc oxide-based transparent conductive film thus formed has the advantage that it does not require toxic indium which is a rare metal and is extremely useful industrially. Further, there is an effect that occurrence of abnormal discharge can be suppressed during sputtering.

(A) is an X-ray diffraction measurement result of the oxide sintered body obtained in Example 1, and (b) is an X-ray diffraction measurement of the oxide sintered body obtained in Comparative Example 1. It is a result. It is a FE-SEM (scanning electron microscope, the same applies hereinafter) photograph (magnification: 20,000 times) in which the surface of the oxide sintered body obtained in Example 1 is enlarged. 4 is an FE-SEM photograph (magnification: 20,000 times) in which the surface of the oxide sintered body obtained in Comparative Example 1 is enlarged.

  Hereinafter, the present invention will be described in detail.

(Method for manufacturing oxide sintered body)
The method for producing an oxide sintered body, which is a material for forming a zinc oxide-based transparent conductive film of the present invention, includes a mixed powder of low-valence titanium oxide powder and zinc oxide powder or zinc hydroxide powder, with titanium in a predetermined ratio. The raw material powder to be contained is put into a mold and subjected to discharge plasma sintering under a predetermined condition to obtain a zinc oxide-based transparent conductive film forming material that is an oxide sintered body.

  The raw material powder may be a mixed powder of low-valent titanium oxide powder and zinc oxide powder or zinc hydroxide powder, or a powder containing zinc titanate compound powder, and the titanium oxide powder and zinc oxide powder or A mixed powder of zinc hydroxide powder and zinc titanate compound powder may be used. Preferably, a powder containing a mixed powder of low-valent titanium oxide powder and zinc oxide powder or zinc hydroxide powder is preferable. On the other hand, for example, even if a combination of titanium metal and zinc oxide powder or zinc hydroxide powder or a combination of titanium oxide and zinc metal is used as a raw material powder, an oxide sintered body can be obtained. In that case, titanium and zinc metal particles are likely to be present in the oxide sintered body, and when this is used as a target, the metal particles on the target surface melt during the film formation and are not released from the target. The composition of the film obtained and the composition of the target tend to be greatly different.

The low valence titanium oxide is not only an oxide of a titanium element whose valence is a divalent or trivalent integer such as TiO (II) and Ti ₂ O ₃ (III), but also Ti ₃ O ₅ , Ti ₄ O ₇ , Ti ₆ O ₁₁ , Ti ₅ O ₉ , Ti ₈ O _{15 and} other general formula: TiO _{2 -X} (X = 0.1-1) Says titanium. As the low-valent titanium oxide powder, one kind of titanium oxide represented by the above general formula may be used alone, or a mixture of two or more kinds may be used. Among these, it is particularly preferable to use Ti ₂ O ₃ (III) powder. This is because Ti ₂ O _{3 has} an ionic radius of 0.67 、 and an ionic radius of zinc of 0.74 、, so that it is very close to the ionic radius of zinc and is easily dissolved by substitution during solid phase sintering. is there.
The structure of the low valence titanium oxide can be confirmed by instrumental analysis such as an X-ray diffraction apparatus (X-Ray Diffraction, XRD), an X-ray photoelectron spectrometer (X-ray Photoelectron Spectroscopy, XPS).

General formula including Ti ₃ O ₅ , Ti ₄ O ₇ , Ti ₆ O ₁₁ , Ti ₅ O ₉ , Ti ₈ O _15, etc .: TiO _2-X (X = 0.1-1) produces a single component Is difficult to obtain as a mixture. Usually, titanium oxide (TiO ₂ ) can be produced by heating in a reducing atmosphere such as a hydrogen atmosphere using carbon or the like as a reducing agent. By adjusting the hydrogen concentration, the amount of carbon as a reducing agent, and the heating temperature, the ratio of the low-valent titanium oxide mixture can be controlled.

As the zinc oxide powder, a powder of ZnO or the like having a wurtzite structure is usually used, and a powder obtained by firing this ZnO in advance in a reducing atmosphere and containing oxygen deficiency may be used.
The zinc hydroxide powder may be either amorphous or crystalline.
As the zinc titanate compound powder, powders of ZnTiO ₃ , Zn ₂ TiO _{4 and the} like can be used, and it is particularly preferable to use Zn ₂ TiO ₄ powder.
The average particle size of each compound (powder) used as the raw material powder is preferably 1 μm or less.

In the raw material powder in the present invention, it is important that it is contained in a proportion of more than 2% and not more than 10% with respect to the total number of metal atoms of titanium. Preferably, the number of titanium atoms is the total number of metal atoms. The content is 3% or more and 9% or less, more preferably 3% or more and 6% or less. When the ratio of the number of atoms of titanium is 2% or less, chemical durability such as chemical resistance of a film formed using the obtained oxide sintered body as a target becomes insufficient. On the other hand, when the ratio of the number of titanium atoms exceeds 10%, titanium oxide cannot be sufficiently substituted and dissolved in the zinc site, and the conductivity and transparency of the film formed using this oxide sintered body as a target are insufficient. It becomes.
Here, the total number of metal atoms is the total number of metal atoms contained in the raw material powder used for producing the oxide sintered body, and zinc occupies about 90 to 98% of the total number of metal atoms. Therefore, zinc oxide is the main component in the zinc oxide-based transparent conductive film forming material.

The raw material powder in the present invention also contains at least one element selected from the group consisting of gallium, aluminum, tin, silicon, germanium, zirconium, and hafnium (hereinafter, these may be referred to as “additive elements”). It is preferable. By containing such an additive element, the specific resistance of the oxide sintered body itself can be reduced in addition to the specific resistance of the film formed using the obtained oxide sintered body as a target. For example, the deposition rate during DC sputtering depends on the specific resistance of the oxide sintered body as a sputtering target, and the productivity during film formation is improved by lowering the specific resistance of the oxide sintered body itself. be able to. When an additive element is contained, the total content is preferably 0.05% or less with respect to the total amount of all metal elements constituting the oxide sintered body in terms of atomic ratio. When there is more content of an additional element than the said range, there exists a possibility that the specific resistance of the film | membrane formed using an oxide sintered compact as a target may increase.
The additive element may be present in the oxide sintered body in the form of an oxide, or may be present in a form substituted (solid solution) in a zinc site of a zinc oxide phase described later. The zinc titanate compound phase, which will be described later, may exist in a form substituted (solid solution) with titanium sites and / or zinc sites.

  Moreover, the raw material powder in the present invention may contain other elements such as indium, iridium, ruthenium, rhenium as impurities in addition to the essential elements zinc and titanium and the above-mentioned additive elements. The total content of elements contained as impurities is preferably 0.5% or less with respect to the total amount of all metal elements constituting the raw material powder in terms of atomic ratio, and the oxide obtained by atomic ratio. It is preferable to be 0.1% or less with respect to the total amount of all metal elements constituting the sintered body.

The raw material powder may be pulverized. By performing the pulverization treatment, the raw material powder is adjusted to have a narrow particle size distribution, and can be uniformly solid-phase sintered in the sintering described later to obtain a high-density oxide sintered body. it can.
The method for pulverization is not particularly limited. For example, when media is used, a method using a pulverizer equipped with a bead mill, a ball mill, a planetary mill, a sand grinder, a vibration mill, or an attritor, and no media are used. Examples thereof include a method using a wet ultrahigh pressure atomizer such as a jet mill, a nanomizer, and a starburst.

  When performing spark plasma sintering (SPS) using the raw material powder, for example, a method in which a predetermined amount of the obtained raw material powder is put in a die and sandwiched by a punch, the raw material powder and an aqueous solvent are mixed and obtained. The obtained slurry is sufficiently mixed by wet mixing, followed by solid-liquid separation, drying and granulation, and the resulting granulated product is formed.

The aqueous solvent contains water as a main component and may be water alone, or may be a mixture of water and alcohol such as methanol or ethanol.
The wet mixing may be performed by, for example, a wet ball mill using a hard ZrO ₂ ball or a vibration mill, and the mixing time when a wet ball mill or a vibration mill is used is preferably about 12 to 78 hours. In addition, although raw material powder may be dry-mixed as it is, wet mixing is more preferable.

  For solid-liquid separation / drying / granulation, known methods may be employed.

A predetermined amount of the obtained raw material powder is put into a carbon die, sandwiched between carbon punches and set in a discharge plasma sintering (SPS) apparatus, and discharge plasma sintering is performed in an inert gas atmosphere such as vacuum or Ar. Thus, discharge plasma sintering (SPS) is characterized by simultaneous forming and sintering.
The SPS device consists of a sintering machine body with a vertical uniaxial pressurizing mechanism, a special energizing mechanism with a built-in water cooling unit, a water cooling vacuum chamber, an atmosphere control mechanism, a vacuum exhaust device, a special DC pulse power supply, a centralized operation control panel It is configured. When the die / punch mold filled with the powder to be processed is set on the sintering stage in the chamber, sandwiched between the electrodes, and pulsed while energized, it takes several minutes to several tens of minutes depending on the size of the carbon die and carbon punch. Within a short time from room temperature to 1000 to 2500 ° C., sintering can achieve a high-density sintered body in a short time of several minutes to several tens of minutes.
The amount of pressurization is preferably 10 MPa to 100 MPa.
In the case of this material, since the total heat history time required for the processed powder (raw material powder) is small in this way, a composite oxide phase is formed, and there is no time to grow the crystal phase. Phase growth is suppressed. On the other hand, the growth of the zinc oxide phase in which titanium is partly dissolved does not occur.
In addition, since the sintering time can be shortened, it is possible to suppress the growth of crystal grains and to suppress the coarsening of vacancies and hence the increase of the maximum vacancy diameter, thereby further suppressing the growth of crystal grains. Since sintered powder is also conductive, current flows, surface diffusion between the concentrating grains and grain boundary diffusion occur rapidly, and sintering proceeds, so a high sintering density can be obtained. it can.
In summary, the discharge plasma sintering method can suppress the formation of complex oxides even at the same sintering density as compared with the normal atmospheric pressure sintering method, the hot press method, and the like.

The discharge plasma sintering is performed at a sintering temperature of 700 ° C. or more and 1200 ° C. or less in a vacuum atmosphere or an inert atmosphere.
By performing the discharge plasma sintering in a vacuum atmosphere or an inert atmosphere, oxygen is not present, so that the oxidation of titanium oxide can be suppressed and the generated oxide sintered body can be made to have a high density. This is presumably because sintering proceeds more in the absence of oxygen.
A vacuum atmosphere refers to an atmosphere having an oxygen concentration of 1 ppm or less. The inert atmosphere is an atmosphere made of an inert gas such as nitrogen, argon, helium, carbon dioxide, or hydrogen.

The sintering temperature is 700 to 1200 ° C, preferably 750 to 900 ° C. If the sintering temperature is less than 700 ° C., the sintering density may be lowered, and if the sintering temperature exceeds 1200 ° C., zinc may be largely volatilized.
The heating rate up to the sintering temperature is 10 ° C./min to 200 ° C./min, preferably 50 ° C./min to 200 ° C./min. If the rate of temperature rise is lower than 10 ° C / min, the growth of the composite oxide may not be suppressed. If the rate of temperature rise is higher than 200 ° C / min, the entire sintered body cannot be heated uniformly, resulting in uneven temperature distribution. May occur.
The sintering time at the sintering temperature is 10 seconds to 10 minutes, preferably 30 seconds to 8 minutes, more preferably 1 minute to 5 minutes. If the sintering time is less than 10 seconds, the sintering does not proceed sufficiently and the mechanical strength may be lowered. If the sintering time is longer than 10 minutes, zinc is volatilized and the sintering density is reduced. May decrease.
The material of the mold (die, punch) may be any material as long as it is conductive, but a carbon material such as graphite is preferable.

When a mixed powder of titanium oxide powder and zinc oxide powder or zinc hydroxide powder is used as the raw material powder, or a mixed powder of titanium oxide powder and zinc oxide powder or zinc hydroxide powder and zinc titanate compound powder is used The mixing ratio of each powder is appropriately determined so that the value of Ti / (Zn + Ti) is in the above-described range in terms of the atomic ratio in the finally obtained oxide sintered body according to the type of compound (powder) used. You only have to set it. At that time, considering that zinc has a higher vapor pressure than titanium and is likely to be volatilized when sintered, the desired composition of the desired oxide sintered body (atomic ratio of Zn and Ti), It is preferable to set the mixing ratio in advance so that the amount of zinc increases. What is specified in the present invention is SPS sintered in a vacuum or an inert atmosphere.
Specifically, the ease of volatilization of zinc varies depending on the atmosphere during sintering. For example, when zinc oxide powder is used, sintering in an inert atmosphere or a reducing atmosphere reduces the zinc oxide. Since it becomes metallic zinc which is more easily volatilized than zinc oxide, the disappearance amount of zinc increases. Therefore, the amount of zinc to be increased with respect to the target composition is 1.1 to 1.3 times the amount of the desired atomic ratio when sintering in an inert atmosphere or a reducing atmosphere. It should be about. In addition, each compound (powder) used as the raw material powder may be only one kind or two or more kinds.

(Zinc oxide-based transparent conductive film forming material)
The zinc oxide-based transparent conductive film forming material obtained by the production method of the present invention is an oxide sintered body containing zinc oxide as a main component and containing titanium oxide, and is substantially composed of zinc, titanium, and oxygen. Become.
Here, “substantially” means that 99% or more of all atoms constituting the oxide sintered body are composed of zinc, titanium, or oxygen.

The oxide sintered body in the present invention is preferably formed only from a zinc oxide phase as much as possible. The production amount of a composite oxide phase (Zn ₂ TiO ₄ ) produced by solid phase reaction between titanium oxide (II, III) and zinc oxide is suppressed as much as possible. By suppressing the generation amount of the zinc titanate compound phase as much as possible, the occurrence of abnormal discharge during sputtering can be suppressed as much as possible, so that the film can be stably formed and the productivity can be improved.
The zinc titanate compound phase specifically includes ZnTiO ₃ , Zn ₂ TiO ₄ , those in which a titanium element is dissolved in these zinc sites, oxygen deficiency introduced, Non-stoichiometric compositions with a Zn / Ti ratio slightly deviating from these compounds are also included.
In addition, the zinc oxide phase specifically includes ZnO, a solution in which a titanium element is dissolved, an oxygen deficiency introduced, or a non-stoichiometric composition due to zinc deficiency. Including things. The zinc oxide phase usually has a wurtzite structure.

The oxide sintered body in the present invention preferably has a Ti / (Zn + Ti) value of more than 0.02 and less than 0.1 in terms of atomic ratio, that is, substantially does not contain a crystal phase of titanium oxide. That is, in an oxide sintered body in which the value of Ti / (Zn + Ti) is less than 0.02 in terms of atomic ratio, titanium reacts completely with zinc oxide. Although no phase is produced, the resulting film does not exhibit a sufficiently low resistance due to the low doping amount of titanium. When the value of Ti / (Zn + Ti) exceeds 0.1 or more, generally, titanium cannot fully react with zinc oxide, so that titanium oxide is likely to be generated in the oxide sintered body. However, if the oxide sintered body contains a crystal phase of titanium oxide, the resulting film may have uneven physical properties such as specific resistance and may lack uniformity. In the oxide sintered body, it is preferable that the value of Ti / (Zn + Ti) is in the above range and substantially no titanium oxide crystal phase is contained.
In addition, the crystal phase of titanium oxide specifically includes TiO ₂ , Ti ₂ O ₃ , and TiO as well as substances in which other elements such as Zn are dissolved in these crystals.

  The specific resistance of the oxide sintered body in the present invention is preferably 5 kΩ · cm or less. For example, the deposition rate during direct current sputtering depends on the specific resistance of the oxide sintered body as a sputtering target. Therefore, if the specific resistance of the oxide sintered body exceeds 5 kΩ · cm, the direct current sputtering is stable. There is a risk that film formation cannot be performed. Considering the productivity at the time of film formation, the specific resistance of the oxide sintered body in the present invention is preferably as low as possible, and specifically 100 Ω · cm or less.

  The oxide sintered body in the present invention as described above is preferably obtained by the method for producing a zinc oxide-based transparent conductive film forming material of the present invention described above, but is not limited to the one obtained by the production method. Absent. For example, a combination of titanium metal and zinc oxide powder or zinc hydroxide powder, or a combination of titanium oxide and zinc metal may be obtained as a raw material powder. Normally, when the oxide sintered body is sintered in a reducing atmosphere, the specific resistance of the oxide sintered body is reduced by introducing oxygen deficiency, and when the oxide sintered body is sintered in an oxidizing atmosphere, the specific resistance is high. Become.

  The oxide sintered body in the present invention has a relative density of 93% or more, preferably 95 to 100%. Here, the relative density is defined as the density of the oxide sintered body divided by the theoretical density and multiplied by 100. If the relative density is less than 93%, the characteristics of the sintered body, such as the high film formation speed and the possibility of stable film formation, may be impaired.

(target)
The target of the present invention is a target used for film formation by sputtering. In addition, although the solid material used in the film formation may be referred to as “tablet”, in the present invention, these are referred to as “target”.

The target of the present invention is obtained by processing the above-described zinc oxide-based transparent conductive film forming material of the present invention.
A processing method in particular is not restrict | limited, What is necessary is just to employ | adopt a well-known method suitably. For example, the target of the present invention can be obtained by subjecting the zinc oxide-based transparent conductive film forming material to surface grinding or the like and then cutting it to a predetermined size and then attaching it to a support base. Moreover, it is good also as a large area target (composite target) by arranging several oxide sintered compacts in a division | segmentation shape as needed.

  The method for forming a zinc oxide-based transparent conductive film of the present invention is to form a film by a sputtering method, but there are no particular restrictions on the specific method and conditions in that case, other than using the above-described target. Any known sputtering method and conditions may be employed as appropriate.

  The zinc oxide-based transparent conductive film formed using the zinc oxide-based transparent conductive film forming material or target of the present invention has excellent conductivity and chemical durability (heat resistance, moisture resistance, chemical resistance (alkali resistance, Etc.) and high transmittance in the near infrared region. Therefore, for example, transparent electrodes such as liquid crystal displays, plasma displays, inorganic EL (electroluminescence) displays, organic EL displays, and electronic papers, window electrodes of photoelectric conversion elements of solar cells, electrodes of input devices such as transparent touch panels, electromagnetic It is suitably used for applications such as shield electromagnetic shielding films. Furthermore, the zinc oxide-based transparent conductive film formed using the zinc oxide-based transparent conductive film forming material or the target of the present invention can be used as a transparent radio wave absorber, an ultraviolet absorber, and a transparent semiconductor device as another metal film or It can also be used in combination with a metal oxide film.

  The film thickness of the zinc oxide-based transparent conductive film of the present invention may be appropriately set depending on the application and is not particularly limited, but is preferably 50 to 600 nm, more preferably 100 to 500 nm. If the thickness is less than 50 nm, sufficient specific resistance may not be ensured. On the other hand, if the thickness exceeds 600 nm, the film may be colored.

(Transparent conductive substrate)
The transparent conductive substrate of the present invention comprises a zinc oxide-based transparent conductive film formed on a transparent substrate by the above-described method for forming a zinc oxide-based transparent conductive film.
The transparent substrate is not particularly limited as long as it can maintain the shape under the film forming conditions by the sputtering method. For example, inorganic materials such as various glasses, thermoplastic resins and thermosetting resins (for example, epoxy resin, polymethyl methacrylate, polycarbonate, polystyrene, polyethylene sulfide, polyethersulfone, polyolefin, polyethylene terephthalate, polyethylene naphthalate, triacetyl cellulose) Plate-like material, sheet-like material, film-like material, etc. formed of a resin such as a plastic such as polyimide), and in particular, any of a glass plate, a resin film or a resin sheet Is preferred. The visible light transmittance of the transparent substrate is usually 90% or more, preferably 95% or more.

  In addition, when using a resin film or a resin sheet as the transparent substrate, in order to disperse and uniformize the damage received by the film formation by the sputtering method, it is unrolled by a roll-to-roll film formation method that is performed industrially. It is preferable to form a film in a state where a tensile stress is applied while controlling the speed and the winding speed. Furthermore, the resin film or the resin sheet may be formed in a heated state in advance, or the resin film or the resin sheet may be cooled during the film formation. It is also effective to increase the speed of transporting the resin film or resin sheet (for example, 1.0 m / min or more) in order to reduce the time for damage caused by film formation by sputtering. For example, film formation is possible even if the distance between the target resin film or resin sheet and the target is short, which is advantageous as an industrial process.

  The transparent substrate may be formed with any of a single layer or multiple layers of an insulating layer, a semiconductor layer, a gas barrier layer, or a protective layer as necessary. Examples of the insulating layer include a silicon oxide film and a silicon nitride oxide film. Examples of the semiconductor layer include a thin film transistor (TFT), and the semiconductor layer is mainly formed on a glass substrate. Examples of the gas barrier layer include a silicon oxide film, a silicon nitride oxide film, and a magnesium aluminate film, and the gas barrier layer is formed on a resin plate or a resin film as a water vapor barrier film. A protective layer is for protecting the surface of a base material from a damage | wound and an impact, and various coating layers, such as Si type | system | group, Ti type | system | group, and an acrylic resin type | system | group, are mentioned.

The specific resistance of the zinc oxide based transparent conductive substrate of the present invention is usually 2 × 10 ⁻³ Ω · cm or less, preferably 8 × 10 ⁻⁴ Ω · cm or less. The surface resistance (sheet resistance) varies depending on the application, but is usually 5 to 10,000 Ω / □, preferably 10 to 300 Ω / □. In addition, specific resistance and surface resistance can be measured by the method mentioned later in an Example, for example.
The transmittance of the zinc oxide-based transparent conductive substrate of the present invention is usually 85% or more, preferably 90% or more in the visible light region. The total light transmittance is preferably 80% or more, more preferably 85% or more, and the haze value is preferably 10% or less, more preferably 5% or less. The transmittance can be measured by, for example, a method described later in the examples.

The thickness of the zinc oxide-based transparent conductive film in the transparent conductive substrate of the present invention is preferably 50 to 600 nm. In this film thickness range, although it varies depending on the application, it is possible to obtain a continuous film in which flexibility is maintained. Furthermore, the film thickness of the transparent conductive film of the present invention is desirably 100 to 500 nm depending on the application.
In the transparent conductive substrate of the present invention, if necessary, as an outermost layer, any resin that functions as a protective film, an antireflection film, a filter, etc., functions of adjusting the viewing angle of liquid crystal, preventing fogging, etc. Alternatively, one layer or two or more layers of inorganic compounds can be stacked.

  The transparent conductive substrate of the present invention has good transparency as described above, and excellent conductivity and chemical durability (heat resistance, moisture resistance, chemical resistance (alkali resistance) as described above. , Acid resistance, etc.). Therefore, for example, transparent electrodes such as liquid crystal displays, plasma displays, inorganic EL (electroluminescence) displays, organic EL displays, and electronic papers, window electrodes of photoelectric conversion elements of solar cells, electrodes of input devices such as transparent touch panels, electromagnetic It can be used in combination with other metal film / metal oxide film as an electromagnetic shielding film of a shield, a transparent radio wave absorber, an ultraviolet absorber, and a transparent semiconductor device.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.
In addition, evaluation of the obtained transparent conductive substrate was performed by the following method.

<Resistivity>
The specific resistance was measured by a four-terminal four-probe method using a resistivity meter (“LORESTA-GP, MCP-T610” manufactured by Mitsubishi Chemical Corporation). Specifically, four needle-shaped electrodes are placed on a straight line on the sample, a constant current is passed between the outer two probes, a constant current is passed between the inner two probes, and the inner two probes are The resulting potential difference was measured to determine the resistance.

<Surface resistance>
The surface resistance (Ω / □) was calculated by dividing the specific resistance (Ω · cm) by the film thickness (cm).
<Transmittance> The transmittance was measured using an ultraviolet-visible near-infrared spectrophotometer ("V-670" manufactured by JASCO Corporation).

<Moisture resistance>
The transparent conductive substrate was subjected to a moisture resistance test in which the transparent conductive substrate was held in an atmosphere at a temperature of 60 ° C. and a relative humidity of 90% for 1000 hours, and then the surface resistance was measured. It can be said that the surface resistance after the moisture resistance test is excellent in moisture resistance when the surface resistance before the moisture resistance test is twice or less.

<Heat resistance>
The transparent conductive substrate was subjected to a heat resistance test in which the transparent conductive substrate was held in the atmosphere at a temperature of 200 ° C. for 5 hours, and then the surface resistance was measured. When the surface resistance after the heat test is 1.5 times or less than the surface resistance before the heat test, it can be said that the heat resistance is excellent.

<Alkali resistance>
The transparent conductive substrate was immersed in a 3% NaOH aqueous solution (40 ° C.) for 10 minutes, and the presence or absence of a change in film quality on the substrate before and after immersion was confirmed visually.

<Acid resistance>
The transparent conductive substrate was immersed in a 3% aqueous HCl solution (40 ° C.) for 10 minutes, and the presence or absence of a change in film quality on the substrate before and after immersion was confirmed visually.

[Example 1]
Zinc oxide (ZnO, manufactured by Kishida Chemical Co., Ltd.), titanium oxide (TiO, manufactured by Kojundo Chemical Laboratory Co., Ltd.), zinc element and titanium element in atomic ratio Zn: Ti = 97.0: 3. It was weighed so as to be 0, placed in a polypropylene container, and further 2 mmφ zirconia balls and ethanol as a mixed solvent were added. This was mixed by a ball mill to obtain a raw material powder.

After the mixing operation, the 2 mmφ zirconia balls and the raw material powder obtained by removing ethanol were placed in a mold (die) made of graphite, and pressurized with a punch made of graphite under a pressure of 40 MPa in an Ar atmosphere. Thereafter, the temperature was raised from room temperature to the sintering temperature (850 ° C.) in about 5 minutes, and an SPS (discharge plasma sintering) treatment was performed at 850 ° C. for 3 minutes to obtain a disk-shaped sintered body.
The sintered body was subjected to X-ray diffraction (XRD) measurement, and the result is shown in FIG. 1 that the Zn ₂ TiO ₄ peak in the sintered body of Example 1 is reduced compared to the Zn ₂ TiO ₄ peak in the sintered body of Comparative Example 1 described later. The surface FE-SEM image is shown in FIG. Observation of the SEM image shows that the growth of crystal grains is suppressed as compared with the sintered body of Comparative Example 1 described later. The relative density of the sintered body was calculated from the size and weight of the sintered body and found to be 96.2%. Further, the crystal grains on the surface of the sintered body were observed. The relative density is obtained by multiplying the unit density of zinc oxide and titanium oxide by the weight ratio of the mixture and taking the sum as the theoretical density of 100% (see the following formula, and the same in the following examples). Asked). The obtained sintered body was ground and polished to obtain a sintered body having a diameter of 50.8 mmφ and a thickness of 3 mm.
Relative density = 100 × [(density of sintered body) / (theoretical density)]
Theoretical density = (Zinc oxide simple substance density x mixing weight ratio + Titanium oxide simple substance density x mixing weight ratio)

The obtained sintered body was bonded using indium solder using a copper plate as a backing plate to obtain a sputtering target.
Using the obtained sputtering target, a film was formed by sputtering.
Abnormal discharge hardly occurred. The sputtering conditions were as follows, and a thin film having a thickness of about 500 nm was obtained.
Target size: 50.8 mmφ × 3 mm thickness Sputtering device: “E-200S” manufactured by Canon Anelva Co., Ltd.
Sputtering method: DC magnetron sputtering Ultimate vacuum: 2.0 × 10 ⁻⁴ Pa
Ar pressure: 0.5 Pa
Substrate temperature: 250 ° C
Sputtering power: 30W
Substrate used: Quartz glass (50.8 mm x 50.8 mm x 0.7 mm)

The obtained thin film was dissolved in 2-fold diluted hydrochloric acid, and the thin film composition was measured by ICP-AES (Thermo Scientific "Thermo-6500"). As a result, a thin film having a composition almost equal to the target composition was obtained. It was.
The transparent conductive film is subjected to X-ray diffraction using an attachment for thin film measurement using an X-ray diffractometer ("RINT2000" manufactured by Rigaku Corporation) and an energy dispersive X-ray microanalyzer (TEM-). EDX) was used to investigate the doping state of titanium into zinc, and further the crystal structure was examined using a field emission electron microscope (FE-SEM). Was found to be substituted and dissolved in zinc.

The sheet resistance of the obtained thin film was measured by a four-probe method (“Loresta” manufactured by Mitsubishi Chemical Corporation), and the film thickness was measured using “Alpha-Step IQ” manufactured by KLA-Tencor Corporation. The calculated value was 4.0 × 10 ⁻⁴ Ω · cm. The surface resistance was 8.0Ω / □. The specific resistance distribution on the transparent substrate was uniform in the plane.
The transmittance of the obtained transparent conductive substrate was 89% on the average in the visible region (380 nm to 780 nm) and 89% on the average in the infrared region (780 nm to 1500 nm). The transmittance in the visible region (380 nm to 780 nm) of the quartz glass substrate before film formation was 94% on average, and the transmittance in the infrared region (780 nm to 1500 nm) was 94% on average.
When the moisture resistance of the obtained transparent conductive substrate was evaluated, it was found that the surface resistance after the moisture resistance test was 1.2 times the surface resistance before the moisture resistance test, and the moisture resistance was excellent. Moreover, when the heat resistance of the obtained transparent conductive substrate was evaluated, the surface resistance after the heat test was 1.2 times the surface resistance before the heat test, and it was found that the heat resistance was excellent.
When the alkali resistance of the obtained transparent conductive substrate was evaluated, it was found that there was no change in film quality before and after immersion, and the alkali resistance was excellent. Moreover, when the acid resistance of the obtained transparent conductive substrate was evaluated, it was found that after immersion, the film thickness was thin and dissolved, but the film quality did not change before and after immersion, and the acid resistance was excellent. It was.

  From the above, the film on the obtained transparent conductive substrate is a transparent conductive film that is transparent and has low resistance, and also has chemical durability (heat resistance, moisture resistance, alkali resistance, acid resistance). It is clear that there is. Moreover, since it is excellent in alkali resistance and acid resistance, it is estimated that it has an appropriate etching rate at the time of patterning.

[Comparative Example 1]
Zinc oxide (ZnO, manufactured by Kishida Chemical Co., Ltd.), titanium oxide (TiO, manufactured by Kojundo Chemical Laboratory Co., Ltd.), zinc element and titanium element in atomic ratio Zn: Ti = 97.0: 3. The raw material powder obtained by weighing in the same manner as in Example 1 was put into a mold (die) made of graphite, and was vacuum-pressed at a pressure of 40 MPa with a punch made of graphite at 1000 ° C. A heat treatment was performed for 4 hours to obtain a disk-shaped sintered body. The XRD measurement of this sintered body was performed, and the result is shown in FIG. Generation of the composite oxide by the hot press sintering (Zn 2 _{TiO 4)} It can be seen that more than generation of the composite oxides by SPS sintering. The surface FE-SEM image is shown in FIG. This FE-SEM observation also shows that the crystal grain size is large and coarse grains are present, so that the relative density is low. When the relative density of the sintered body was calculated from the size of the sintered body, it was 95.6%.

The obtained sintered body was formed into a film by sputtering in the same manner as in Example 1. Abnormal discharge partially occurred during film formation.
When the thin film composition was measured, a thin film having a composition almost equal to the target composition was obtained.
Further, with respect to this transparent conductive film, the doped state of titanium into zinc was investigated in the same manner as in Example 1, and further the crystal structure was examined. As a result, it was a wurtzite single phase with C-axis orientation, and titanium was converted into zinc. It was found that the solution was substituted.
When the sheet resistance of the obtained thin film was measured in the same manner as in Example 1 and the resistivity was calculated, it was 4.2 × 10 ⁻⁴ Ω · cm. The surface resistance was 8.4Ω / □. The specific resistance distribution on the transparent substrate was uniform in the plane.
The transmittance of the obtained transparent conductive substrate was 89% on the average in the visible region (380 nm to 780 nm) and 89% on the average in the infrared region (780 nm to 1500 nm). The transmittance in the visible region (380 nm to 780 nm) of the quartz glass substrate before film formation was 94% on average, and the transmittance in the infrared region (780 nm to 1500 nm) was 94% on average.
When the moisture resistance of the obtained transparent conductive substrate was evaluated, it was found that the surface resistance after the moisture resistance test was 1.2 times the surface resistance before the moisture resistance test, and the moisture resistance was excellent. Moreover, when the heat resistance of the obtained transparent conductive substrate was evaluated, the surface resistance after the heat test was 1.2 times the surface resistance before the heat test, and it was found that the heat resistance was excellent.
When the alkali resistance of the obtained transparent conductive substrate was evaluated, it was found that there was no change in film quality before and after immersion, and the alkali resistance was excellent. Moreover, when the acid resistance of the obtained transparent conductive substrate was evaluated, it was found that after immersion, the film thickness was thin and dissolved, but the film quality did not change before and after immersion, and the acid resistance was excellent. It was.

  From the above, the film on the obtained transparent conductive substrate is a transparent conductive film that is transparent and has low resistance, and also has chemical durability (heat resistance, moisture resistance, alkali resistance, acid resistance). It is clear that there is. Moreover, since it is excellent in alkali resistance and acid resistance, it is estimated that it has an appropriate etching rate at the time of patterning.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above embodiment, A various improvement and change are possible.

Claims (9)

  A raw material containing a mixed powder of low-valent titanium oxide powder and zinc oxide powder or zinc hydroxide powder, or zinc titanate compound powder, wherein the ratio of the number of titanium atoms to the total number of metal atoms is more than 2% and not more than 10% A zinc oxide-based transparent conductive material, which is an oxide sintered body, is characterized by performing powder plasma sintering at a sintering temperature of 700 ° C. or higher and 1200 ° C. or lower in vacuum or in an inert atmosphere. Manufacturing method of film forming material.   The method for producing a zinc oxide-based transparent conductive film forming material according to claim 1, wherein the mold is made of a graphite die and a graphite punch.   The rate of temperature rise to the sintering temperature during the spark plasma sintering is 10 ° C / min to 200 ° C / min, and the sintering time at the sintering temperature is 10 seconds to 10 minutes. The manufacturing method of the zinc oxide type transparent conductive film formation material of 1 or 2   A zinc oxide-based transparent conductive film forming material, which is an oxide sintered body obtained by the method according to claim 1.   The oxide sintered body substantially consisting of zinc, titanium, and oxygen, wherein the titanium is contained so that the atomic ratio is Ti / (Zn + Ti) = 0.02 and 0.1 or less. Item 5. The zinc oxide-based transparent conductive film forming material according to Item 4.   The zinc oxide-based transparent conductive film forming material according to claim 4 or 5, wherein a relative density of the oxide sintered body is 93% or more.   It is a target used for film-forming by sputtering method, Comprising: The target formed by processing the zinc oxide type transparent conductive film formation material in any one of Claims 4-6.   A method for forming a zinc oxide-based transparent conductive film, wherein a zinc oxide-based transparent conductive film is formed by a sputtering method using the target according to claim 7.   A transparent conductive substrate comprising a zinc oxide-based transparent conductive film formed on the transparent base material by the method for forming a zinc oxide-based transparent conductive film according to claim 8.