JP2006219357A - Oxide sintered compact, sputtering target and transparent electroconductive membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amorphous transparent electroconductive membrane with a flat and smooth surface, which maintains the transmissivity of light and has a small specific resistance even if a substrate is not heated at the time of forming of the membrane. <P>SOLUTION: The oxide sintered compact comprises tungsten, zinc, magnesium and a remainder including indium, oxygen and unavoidable impurities, wherein tungsten is contained in an atomic number ratio of 0.004-0.033 relative to indium, zinc is contained in an atomic number ratio of 0.005-0.032 relative to indium, and magnesium is contained in an atomic number ratio of 0.007-0.056 relative to indium. The sputtering target is produced using the oxide sintered compact. The transparent conductive membrane is formed by carrying out sputtering with the resultant sputtering target. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oxide sintered body for producing a transparent conductive thin film, a sputtering target using the oxide sintered body, and a transparent conductive thin film. The obtained transparent conductive thin film can be used as an electrode in an organic device such as an organic electroluminescence (EL) element, a transistor, a solar cell, or a laser using an organic substance.

Since the transparent conductive thin film has high conductivity (for example, a specific resistance of 1 × 10 ⁻³ Ωcm or less) and high transmittance in the visible light region, it is a display element, a solar cell, and other various light receiving elements. In addition to electrodes for electronic devices such as light emitting elements, transistors, and lasers, it is also used as a transparent heating element for various types of antifogging, such as heat ray reflective films, antistatic films, and freezer showcases for automobiles and buildings. Has been.

  In recent years, flat panel displays such as liquid crystal displays (LCDs) and plasma displays (PDPs) have become widespread as display elements using transparent conductive thin films. However, as next-generation flat panel displays, electroluminescence ( EL) devices are attracting attention.

  An EL element using a transparent conductive thin film has high visibility because it emits light itself. Further, since it is a completely solid element, it can be applied to a device that can be flexibly deformed. For this reason, the EL element is expected to be applied to various fields.

  EL elements include an inorganic EL element using an inorganic compound as a light emitting material and an organic EL element using an organic compound as a light emitting material.

  Among them, the organic EL element is characterized in that it can be easily downsized because bright light emission can be obtained even when the driving voltage is significantly lowered (for example, at a DC voltage of 10 V or less).

  The structure of the organic EL element is based on a laminated structure of a transparent insulating substrate / anode (transparent electrode) / hole transport layer / light emitting layer / electron transport layer / cathode (metal electrode), and includes a hole transport layer, a light emitting layer, and The electron transport layer is an organic layer. Specifically, a bottom emission type in which a transparent conductive thin film is formed on a transparent insulating substrate such as a glass plate and the transparent conductive thin film is used as an anode is usually employed as the configuration of the organic EL element. Has been.

  On the other hand, when a TFT (thin-film transistor) substrate is used as the transparent insulating substrate, the transparent insulating substrate / anode (metal electrode) is used instead of the above-mentioned bottom emission type in order to increase the amount of extracted light. A top emission type having a laminated structure of / hole transport layer / light emitting layer / electron transport layer / cathode (transparent electrode) has also been proposed.

  In addition to organic EL elements, organic light-emitting elements that use organic substances, transistors, organic devices such as solar cells and lasers have recently attracted attention as elements that use transparent conductive thin films. The role of conductive thin films is expected to increase.

For transparent conductive thin films, tin oxide (SnO ₂ ) containing antimony or fluorine as a dopant, zinc oxide (ZnO) containing aluminum or gallium as a dopant, indium oxide (In ₂ O ₃ ) containing tin as a dopant, etc. However, it is widely used. Among these, an indium oxide film containing tin as a dopant (In ₂ O ₃ —Sn-based film) is referred to as an ITO (Indium Tin Oxide) film, and in particular, a low-resistance transparent conductive thin film can be easily obtained. Widely used.

  A sputtering method is often used as a method for producing these transparent conductive thin films. The sputtering method is an effective method when film formation of a material having a low vapor pressure and precise film thickness control is required, and the operation is very simple, so it is widely used industrially. Yes.

  In the sputtering method, a sputtering target is used as a raw material for supplying film components. In general, under a gas pressure of about 10 Pa or less, a substrate is used as an anode, a sputtering target is used as a cathode, glow discharge is generated between them, argon plasma is generated, and argon cations in the plasma are converted into cathodes. The target component particles which are caused to collide with the sputtering target and are blown off by this are deposited on the substrate to form a film.

  Sputtering methods are classified according to the method of generating argon plasma, which includes a high-frequency sputtering method using high-frequency plasma and a direct-current sputtering method using direct-current plasma. There is also a magnetron sputtering method in which a magnet is disposed on the back side of the sputtering target to increase the generation efficiency of argon ions even at a low gas pressure, and the plasma is concentrated directly on the sputtering target. In general, the direct current sputtering method requires the use of a conductive target, but it is widely used industrially for reasons such as higher film formation speed, lower power supply facilities, and easier film formation operation than the high frequency sputtering method. Has been.

  However, although the ITO film has low resistance, the crystallization temperature is as low as around 150 ° C. For this reason, even when the substrate is not heated in sputtering, a crystal phase is likely to be generated, and irregularities are likely to be generated on the surface of the transparent conductive thin film. In the bottom emission type organic EL element, when an ITO film having irregularities on the anode on the hole transport layer side is used, an overcurrent flows through the organic layer of the ultrathin film due to the irregularities on the surface, and black spots ( Dark spots) will occur.

  Therefore, when using an ITO film as an anode on the hole transport layer side, after forming an ITO film serving as an anode on a transparent insulating substrate, removing surface irregularities by polishing, etc., and smoothing the surface, It becomes necessary to laminate a hole transport layer.

  In addition, in a top emission type organic EL device, when an ITO film having a crystal phase is used for the cathode on the electron transport layer side, moisture, oxygen, etc. diffuse through the grain boundary to the organic layer on the base side and cause damage. Therefore, the device life is shortened. However, if the cathode is an amorphous film, there is no crystal grain boundary, so that moisture, oxygen, and the like are difficult to diffuse.

  Therefore, when the transparent conductive thin film is used as an anode of an organic EL element and an organic device, it is desired that the surface is smooth and that it is amorphous and has little diffusion of moisture and oxygen.

Furthermore, it is desired that the conductive thin film has a lower resistance when used as an electrode. However, in the case of an ITO film, it is difficult to realize a low resistance thin film by film formation at a low temperature. In order to obtain this film, it is necessary to promote crystallization and increase mobility at a temperature higher than the crystallization temperature. However, since the organic layer has poor heat resistance, it is impossible to form the film by heating the substrate when forming the transparent conductive thin film on the organic layer. When the film is formed at room temperature, the specific resistance of the ITO film is about 6 × 10 ⁻⁴ Ωcm.

  Therefore, it is desired to form a film without heating the substrate so that a low resistance transparent conductive thin film can be obtained.

  On the other hand, in the process of forming the transparent conductive thin film, black matter (nodules) is generated in the sputtering target regardless of whether it is a bottom emission type organic EL element or a top emission type organic EL element. Coarse particles are present in the thin film. In the case of the bottom emission type, the organic layer cannot be deposited on the coarse particles, resulting in dark spots. In the case of the top emission type, coarse particles enter the organic layer, and the coarse particle portion does not function as the organic layer and becomes a defect such as a dark spot. Therefore, in any case, the function as an element is deteriorated.

  For this reason, when manufacturing a transparent conductive thin film by sputtering method, it is desired to use a sputtering target with little generation of nodules. In the production of ITO films, measures to suppress the generation of nodules include increasing the sintered density of the sintered body used for the sputtering target, controlling the pores in the sintered body, and increasing the strength of the sintered body. In other words, it is known to form a uniform sintered body. If these measures are taken, the generation of nodules in the sputtering target is certainly reduced. However, the generation of nodules has not been completely suppressed. For this reason, nodules are still generated in the production of ITO films, and defects are generated in the formed conductive thin film, resulting in poor product yield.

  In addition, even if the sintering density of the sputtering target is increased, if sintering cracks occur during sputtering, the generation probability of nodules at that portion is increased. It is necessary to increase the strength. As a method for increasing the strength of the sintered body, there is a method for reducing the crystal grain size.

  As described above, the transparent conductive thin film of the organic EL element has a smooth surface, is amorphous, and has a specific resistance regardless of whether it is a bottom emission type or a top emission type. Small things are desired. Further, for the sputtering target, it is desired to suppress the generation of nodules. These required characteristics are the same for organic devices used in light emitting elements, transistors, solar cells, lasers and the like in addition to organic EL elements.

  As for the indium oxide-based transparent conductive thin film, an indium oxide-based transparent conductive thin film containing additives other than tin has been studied, and several materials having characteristics not found in the ITO film have been found.

Patent Document 1 (Japanese Patent Laid-Open No. 61-136954) discloses indium oxide containing silicon oxide (SiO ₂ ) and / or germanium oxide (GeO ₂ ) as a raw material for producing an indium oxide-based transparent conductive thin film. Patent Document 2 (Japanese Patent Laid-Open No. 62-202415) uses an indium oxide-based sintered body containing such silicon oxide and / or germanium oxide. A method is described in which a Si-added indium oxide film or the like is formed by high-frequency sputtering or electron beam evaporation.

According to this method, an Si-added indium oxide film in which film defects are eliminated can be obtained, but the sputtering target to be used is an indium oxide system containing silicon oxide (SiO ₂ ) and / or germanium oxide (GeO ₂ ). This is a sintered body that contains silicon oxide and / or germanium oxide, which is a high-resistance material. When direct current sputtering is performed, arcing and the like are likely to occur and stable formation is achieved. There is a problem that the film cannot be formed.

  In addition, if a large amount of DC power is input, charging of the high-resistance substance is likely to occur, and the frequency of arcing during film formation increases. Therefore, it is difficult to input high power to increase the film formation speed.

  Furthermore, since the crystal structure of the obtained transparent conductive thin film is not specified, it is unclear whether the film quality is amorphous or not, and even if this method is used to form a film by high-frequency sputtering in pure argon gas. It is unclear whether a film having a smooth surface can be obtained.

On the other hand, Patent Document 3 (Japanese Patent No. 3224396) describes a Zn-added In ₂ O ₃ film as a transparent conductive thin film used for an organic EL element. The Zn-added In ₂ O ₃ film tends to have an amorphous structure, and does not crystallize when heated to 200 ° C., for example, not only when the substrate temperature during film formation is room temperature. Therefore, it also has an advantage that a transparent conductive thin film excellent in surface smoothness can be stably produced.

However, the Zn-doped In ₂ O ₃ film described in Patent Document 3 (Japanese Patent No. 3224396) has a problem that the transmittance in a short wavelength region, specifically, the transmittance of light having a wavelength of 400 nm is lower than that of ITO. There is.

Japanese Patent Laid-Open No. 61-136954

JP-A-62-202415

Japanese Patent No. 3224396

  The present invention has been made in view of such a problem, and maintains the light transmittance, has a smooth surface, is amorphous, and does not require heating the substrate during film formation. An object of the present invention is to provide a transparent conductive thin film having a low resistance, and to provide an oxide sintered body and a sputtering target capable of stably forming such a transparent conductive thin film.

  The oxide sintered body according to the present invention is an oxide sintered body containing tungsten, zinc, and magnesium, with the balance being indium, oxygen, and inevitable impurities, and the tungsten has an atomic ratio of 0.1 to indium. 004 to 0.033, zinc is contained in a ratio of 0.005 to 0.032 in terms of the number of atoms with respect to indium, and magnesium is contained in a ratio of 0.007 to 0.056 in terms of the number of atoms with respect to indium.

In the oxide sintered body, it is preferable that an indium oxide crystal phase having a bixbyite structure is a main phase. In the oxide sintered body, the sintered density is preferably 6.5 g / cm ³ or more, and the average crystal grain size is preferably 5 μm or less.

  The sputtering target according to the present invention can be obtained by processing any one of the above oxide sintered bodies into a flat plate shape and bonding it to a cooling metal plate.

  The transparent conductive thin film according to the present invention is a transparent conductive thin film containing tungsten, zinc, and magnesium, with the balance being indium, oxygen, and unavoidable impurities, and the tungsten has an atomic ratio with respect to indium of 0.004 to 0.004. An amorphous transparent conductive thin film containing 0.033, zinc in an atomic ratio of 0.005 to 0.032 with respect to indium, and magnesium in an atomic ratio of 0.007 to 0.056 with respect to indium. is there.

In the transparent conductive thin film, the specific resistance is preferably 5 × 10 ⁻⁴ Ωcm or less, and the average surface roughness Ra (arithmetic average roughness) is preferably less than 1% of the film thickness, The transmittance of light having a wavelength of 400 nm is preferably 65% or more.

  Moreover, the transparent conductive thin film and a 3-5 nm metal thin film can be laminated to form a transparent conductive thin film having a smaller specific resistance. Examples of the metal thin film include silver, silver alloy, A thin film made of one or more metals selected from the group consisting of aluminum and aluminum alloys can be used.

  The organic device according to the present invention uses any one of the above transparent conductive thin films, and examples of the organic device include an organic EL element.

  The oxide sintered body according to the present invention is an oxide sintered body containing tungsten, zinc, and magnesium, with the balance being indium, oxygen, and inevitable impurities, and the tungsten has an atomic ratio of 0.1 to indium. 004 to 0.033, zinc is contained in a ratio of 0.005 to 0.032 in terms of atomic number with respect to indium, and magnesium is contained in a ratio of 0.007 to 0.056 in terms of atomic ratio with respect to indium. By performing sputtering using a sintered body, a transparent conductive thin film having a smooth surface, an amorphous structure, and a small specific resistance can be obtained without heating the substrate during film formation.

  Therefore, it is possible to provide an organic device in which defects such as dark spots are suppressed by using the transparent conductive thin film according to the present invention as an electrode.

  Furthermore, since the transparent conductive thin film also has good light transmittance, it is extremely useful for use as an electrode of an organic device for a display element such as an organic EL element.

  In order to solve the above-mentioned problems, the present inventor prepared transparent conductive thin films having various compositions by a sputtering method, and studied the crystal structure, electrical characteristics, and optical characteristics of the obtained transparent conductive thin films. As a result, it consists of indium, tungsten, zinc, magnesium and oxygen, tungsten is 0.004-0.033 in W / In atomic ratio, zinc is 0.005-0.032 in Zn / In atomic ratio, magnesium. When a sputtering target containing Mg / In at a ratio of 0.007 to 0.056 in terms of the number ratio of Mg / In is used, the obtained transparent conductive thin film has a smooth surface, is amorphous, and has a specific resistance. It has been found that it is small and suitable as a transparent conductive thin film of an organic EL element, and further, no nodules are observed during sputtering, and the present invention has been completed.

<Oxide sintered body>
The oxide sintered body according to the present invention is composed of indium, tungsten, zinc, magnesium and oxygen, tungsten is 0.004 to 0.033 in W / In atomic ratio, and zinc is 0 in Zn / In atomic ratio. 0.005 to 0.032, and magnesium is contained at a Mg / In atomic ratio of 0.007 to 0.056.

  In addition, the composition of the sputtering target produced from this oxide sintered compact and the transparent conductive thin film formed into a film using this sputtering target is substantially the same as the said oxide sintered compact.

  First, additive metal elements (tungsten, zinc, magnesium) of the oxide sintered body according to the present invention will be described.

Tungsten has the effect of increasing the crystallization temperature of the transparent conductive thin film and the effect of imparting conductivity to the transparent conductive thin film. As a result of increasing the crystallization temperature of the transparent conductive thin film by adding tungsten, the transparent conductive thin film tends to be amorphous. When the W / In atomic ratio is less than 0.004, the specific resistance of the transparent conductive thin film increases. Further, the transparent conductive thin film is crystallized, and the surface unevenness is increased. On the other hand, when it exceeds 0.033, the specific resistance of the transparent conductive thin film becomes 5 × 10 ⁻⁴ Ωcm or more.

  Further, tungsten has an effect of hindering the growth of crystal grains of the oxide sintered body in the oxide sintered body. If the W / In atomic ratio is 0.004 or more, the average crystal grain size of the oxide sintered body becomes very fine as 5 μm or less. When cracks occur in the sintered body during sputtering, nodules are likely to be generated in that portion, but the oxide sintered body of the present invention has a W / In atomic ratio of 0.004 to 0.033. The average crystal grain size becomes very small, and the bending strength of the oxide sintered body increases. For this reason, in the sputtering target produced from the oxide sintered compact of this invention, the crack of the sintered compact during sputtering which causes nodule generation hardly arises.

On the other hand, if the W / In atomic ratio exceeds 0.033, tungsten inhibits sintering, and the sintered density becomes less than 6.5 g / cm ³ . If the sintered density is low, it may cause nodules and the film forming speed during sputtering may be slow, which is not preferable for production.

  Zinc is added in the oxide sintered body for the purpose of imparting conductivity to the extent that direct current sputtering is possible and for raising the crystallization temperature. When the Zn / In atomic ratio of the oxide sintered body is less than 0.005, the specific resistance of the sintered body increases, so that the film formation rate becomes very low and the productivity deteriorates. Moreover, even if sputtering is performed, a transparent conductive thin film having a small specific resistance and being amorphous cannot be obtained. On the other hand, when the Zn / In atomic ratio exceeds 0.032, a transparent conductive thin film having excellent transmission characteristics cannot be obtained on the short wavelength side in the visible region (for example, near the wavelength of 400 nm).

  Magnesium contributes to the homogenization of the structure in the oxide sintered body. When a heterogeneous phase exists in the sintered body, it causes a decrease in the film forming speed. When the Mg / In atomic ratio of the oxide sintered body is less than 0.007, a fine phase containing a large amount of tungsten and zinc. Becomes a sintered body locally present in the bixbite phase. Since this fine phase has solid solution of tungsten and zinc in indium oxide, it is not as high a resistance phase as tungsten oxide and zinc oxide. For this reason, even if such a phase exists, the film forming speed does not decrease remarkably. However, this fine phase contains a large amount of tungsten and zinc, and the film forming speed is different from that of the main phase, bixbite phase, which may cause abnormal discharge during sputtering. When a Mg / In atomic ratio of 0.007 or more is added, such a fine phase cannot be seen because the solid solubility limit of tungsten and zinc in indium oxide increases. In consideration of stable production using a sputtering method, it is preferable that this heterogeneous phase does not exist. On the other hand, if the Mg / In atomic ratio of the oxide sintered body exceeds 0.056, the specific resistance of the transparent conductive thin film obtained by sputtering increases.

  Next, the crystal phase of the oxide sintered body according to the present invention will be described.

  In the oxide sintered body according to the present invention, it is preferable that there is no crystal phase due to the raw material powders of tungsten oxide, zinc oxide and magnesium oxide, and only the bixbite phase is constituted. The oxide sintered body composed only of the bixbite phase has a higher film formation rate by sputtering under the same conditions than the oxide sintered body in which the crystalline phase of the oxide caused by the raw material powder is detected. This is because the result is clearly faster. The reason why such a result was obtained is that the sputtering rate of the oxide crystal phase caused by the raw material is relatively slow, and the sputtering rate is slowed according to the ratio of the present. Therefore, a high deposition rate can be realized with a bixbite structure and a single-phase sintered body.

Here, the bixbyite structure is a crystal structure of indium oxide (In ₂ O ₃ ) and is also referred to as a rare earth oxide C type (see “Technology of Transparent Conductive Film”, Ohm, p. 82). . Cations such as tungsten, zinc, and germanium are substituted with indium ions in indium oxide having a bixbyite structure to form a solid solution. In ₂ O ₃ may take a corundum type structure in addition to the bixbyite type structure.

<Manufacture of oxide sinter>
The oxide sintered body according to the present invention can be manufactured, for example, as follows. First, indium oxide powder having an average particle size of 0.1 to 3 μm or less, tungsten oxide powder, magnesium oxide powder, and zinc oxide powder are prepared at a predetermined ratio, put into a resin pot together with water, and mixed in a wet ball mill. A slurry is obtained. At this time, it is preferable to use a hard ZrO ₂ ball mill in order to avoid mixing impurities into the slurry as much as possible. The mixing time is preferably 10 to 30 hours. If it is shorter than 10 hours, the raw material powder is not sufficiently pulverized, and it may be difficult to stably obtain a high-density target having a bixbite type indium oxide crystal phase as a main phase. When the length is long, overgrinding occurs, and the particles are strongly aggregated. Similarly, it may be difficult to stably obtain a high-density target. After mixing, the slurry is taken out, filtered, dried and granulated.

The granulated powder (average particle size of about 25 to 100 μm) granulated as described above is subjected to a pressure of 196 MPa to 490 MPa ( ² ton / cm ^{2 to 5} ton / cm ² ) with a cold isostatic pressure (CIP) press. Mold. When the pressure is lower than 196 MPa ( ² ton / cm ² ), the density of the molded body does not increase, and it is difficult to obtain a high-density target. When the pressure exceeds 490 MPa (5 ton / cm ² ), the density of the molded body is increased. However, adjustment of conditions such as processes and equipment for obtaining the pressure becomes excessive, and the manufacturing cost increases.

Next, in the atmosphere obtained by introducing oxygen into the sintering furnace at a rate of 10 L / min per 0.01 m ^{3 of} the furnace volume, the obtained molded body was heated at a temperature of 1200 to 1500 ° C. and 10 to 10 ° C. Sinter for 30 hours. If the temperature is lower than 1200 ° C, it is difficult to stably obtain a high-density target. If the temperature exceeds 1500 ° C, not only the crystal grain size increases, but also the reaction with the hearth plate may occur. When the treatment time is shorter than 10 hours, it is difficult to stably obtain a high-density target, and when it exceeds 30 hours, the crystal grain size becomes large.

  The temperature increase rate when performing the sintering at 1200 to 1500 ° C. is about 0.5 ° C./min up to 750 ° C. and about 1 ° C./min from 750 ° C. to the predetermined sintering temperature. Is preferred. Thus, the reason why it is preferable to slow the temperature rising rate is to make the temperature distribution in the furnace uniform. Further, after the sintering treatment is completed, it is preferable to lower the temperature at about 1 ° C./min in order to stop the introduction of oxygen and prevent the sintered body from cracking due to thermal shock.

  In addition, when a different oxide phase exists in oxide sintered compact, abnormal discharge will occur easily. Furthermore, when the foreign oxide phase is a high resistance material, if a large amount of DC power is applied, the foreign oxide phase is likely to be charged and the frequency of arcing during film formation increases, so the DC power is increased. Even if it is added, it is difficult to obtain a high deposition rate. However, when there is no foreign oxide phase in the oxide sintered body and all the added elements are dissolved in the indium sites, the possibility of such a phenomenon is reduced. In the oxide sintered body of the present invention, indium oxide, tungsten oxide, magnesium oxide and zinc oxide having an average particle diameter of 0.1 to 3 μm are used as raw material powders, and then fully mixed and pulverized, so that all additions are made. An element can be replaced with an In site. When the average particle diameter of the raw material powder is less than 0.1 μm, it becomes easy to dissolve, but the aggregation of the raw material powder becomes strong and it is difficult to achieve high density. On the other hand, when the average particle diameter of the raw material powder exceeds 3 μm, it is difficult to perform appropriate pulverization in the pulverization step, and there is a concern that coarse raw material powder exists in the granulated powder. As a result, if the raw material powder is non-uniformly dispersed, sintering cannot be performed uniformly, and high density cannot be achieved. In addition, if coarse raw material powder exists in the granulated powder, diffusion of atoms in the coarse raw material powder does not proceed even if the sintering process is performed, and there is a foreign oxide phase in the oxide sintered body. The problem of end up occurs.

<Sputtering target>
About the obtained oxide sintered body, the surface to be sputtered is polished with a cup grindstone or the like, processed to a thickness of about 3 to 10 mm, and bonded to a cooling metal plate (backing plate) such as an indium alloy. Thus, a sputtering target can be obtained.

<Sputtering film formation>
The transparent conductive thin film according to the present invention uses the sputtering target of the present invention, for example, the distance between the target substrates at the time of sputtering is 50 to 100 mm, the sputtering gas pressure is 0.5 to 1.5 Pa, and the direct current magnetron sputtering. It can be obtained by forming a film by the method.

  As for the distance between the target substrates, when the distance between the target substrates is shorter than 50 mm, the kinetic energy of the sputtered particles deposited on the substrate increases, so that the substrate receives a great deal of damage, resulting in a lower oxide or the like. The specific resistance of the transparent conductive thin film is increased. In addition, the film thickness becomes non-uniform and the film thickness distribution becomes worse. When the distance between the target substrates is longer than 100 mm, the film thickness distribution is improved, but the kinetic energy of the sputtered particles deposited on the substrate becomes too low, and the densification due to diffusion is less likely to occur on the substrate. Only a thin film can be obtained, which is not preferable.

  With respect to the sputtering gas pressure, if the sputtering gas pressure is lower than 0.5 Pa, the kinetic energy of the sputtered particles deposited on the substrate increases, so that the substrate is greatly damaged and becomes a lower oxide or the like. The specific resistance of the conductive thin film increases. When the sputtering gas pressure is higher than 1.5 Pa, not only the film formation rate is slowed, but also the kinetic energy of the sputtered particles deposited on the substrate becomes too low, and densification due to diffusion does not occur on the substrate, resulting in low density. Only a transparent conductive thin film can be obtained, which is not preferable.

<Transparent conductive thin film>
The transparent conductive thin film of the present invention is composed of indium, tungsten, zinc, magnesium and oxygen, and tungsten is 0.004 to 0.033 in W / In atomic ratio and zinc is 0.005 in Zn / In atomic ratio. -0.032, and magnesium is contained at a ratio of 0.007 to 0.056 in terms of Mg / In atomic ratio. As described above, the composition of the transparent conductive thin film obtained by the sputtering film formation is substantially the same as that of the sintered body.

The transparent conductive thin film of the present invention is completely amorphous and has a smooth surface, and the average roughness (Ra) of the surface is less than 1% of the film thickness. Furthermore, the transparent conductive thin film of the present invention exhibits a specific resistance of 5 × 10 ⁻⁴ Ωcm or less even when formed without heating.

  For this reason, the transparent conductive thin film according to the present invention can be formed as an electrode even on an organic light emitting layer that is inferior in heat resistance, and the top that can efficiently extract light from the cathode that is the top electrode. It can contribute to the realization of an emission type organic EL element. Further, even if the film is formed without heating the substrate, the specific resistance is small and the surface is smooth as described above. Therefore, the transparent conductive thin film according to the present invention uses a resin film substrate. It can also be used as the cathode and / or anode of a conventional flexible transparent organic EL device, and has an extremely high industrial value.

  When used as a transparent conductive thin film, it may be desired to further reduce the specific resistance. In this case, the specific resistance can be further reduced by laminating the transparent conductive thin film according to the present invention and a metal thin film such as silver, silver alloy, aluminum or aluminum alloy. However, as long as it functions as a transparent conductive thin film, the transmittance in the visible light region is desirably 90% or more. Therefore, the thickness of the metal thin film is preferably 3 to 5 nm. When the metal thin film is thicker than 5 nm, the resistance value is lowered, but the light transmittance is deteriorated. On the other hand, if the thickness is less than 3 nm, the continuity of the metal thin film is lost, and the effect of laminating the metal thin film cannot be fully exhibited.

<Manufacture of oxide sinter>
(Examples 1 to 3, Comparative Examples 1 and 2)
As raw materials, In ₂ O ₃ powder (purity 99.99 mass%) with an average particle diameter of 0.1 μm to ₃ μm, WO ₃ powder (purity 99.99 mass%) with an average particle diameter of 0.1 μm to ₃ μm, average particle diameter MgO powder (purity 99.99 mass%) of 0.1 μm to 3 μm and ZnO powder (purity 99.99 mass%) having an average particle size of 0.1 μm to 3 μm were used.

Each powder was mixed in a predetermined amount, put into a resin pot together with pure water, a dispersant, and a binder, and mixed for 20 hours using a wet ball mill using a hard ZrO ₂ ball mill to obtain a mixed slurry. Then, the mixed slurry was taken out, filtered, dried and granulated. The obtained granulated powder was molded by a cold isostatic press while applying a pressure of 294 MPa (3 ton / cm ² ).

Next, the obtained molded body was sintered at 1200 ° C. for 30 hours in an atmosphere obtained by introducing oxygen into the sintering furnace at a rate of 10 L / min per 0.01 m ^{3 of} the furnace volume. At this time, the temperature was raised from 750 ° C. at 0.5 ° C./min and from 750 ° C. to 1200 ° C. at 1 ° C./min. After completion of the sintering, oxygen introduction was stopped, the temperature was lowered from 1200 ° C. to 1000 ° C. at 10 ° C./min, kept at 1000 ° C. for 3 hours, and then allowed to cool. As described above, an oxide sintered body was obtained.

  The end material of the obtained oxide sintered body was pulverized, and powder X-ray diffraction measurement was performed with an X-ray diffractometer (M18XHF22, manufactured by Mac Science). A local analysis by EPMA was also performed.

  Moreover, the sintered density of the obtained oxide sintered body was determined by Archimedes method. Regarding the measurement of the crystal grain size of the obtained oxide sintered body, the surface of the obtained oxide sintered body was polished, then subjected to thermal etching at 1100 ° C., and observed with a scanning electron microscope (SEM). The average particle size was determined.

  For Examples 1 to 3 and Comparative Examples 1 and 2, the sintering temperature and the composition of the obtained oxide sintered body (indicated by the atomic ratio of tungsten, magnesium and zinc to indium), the sintering density and the average grain size The diameter is shown in Table 1.

As for the sintered density, in Comparative Example 2 in which the W / In atomic ratio is 0.036 and exceeds the upper limit of 0.033 which is the upper limit of the W / In atomic ratio of the present invention, the sintered density is 6 It is less than 0.5 g / cm ^3, and it can be seen that as the amount of W increases, the sinterability deteriorates. As for the average particle diameter, the effect of the W amount is large, the W / In atom number ratio is 0.003, and is less than 0.004 which is the lower limit value of the W / In atom number ratio of the present invention. Then, although there is no problem in terms of the sintered density, the average particle size is 6.1 μm, which is larger than 5 μm, and it is considered that there is a problem in terms of strength of the sintered body. When sputtering was actually performed using the sintered body of Comparative Example 1 as a target, sintering cracks occurred during sputtering. As can be seen from Table 1, the average particle size increases as the amount of W decreases.

  The crystal structure of the oxide sintered bodies obtained in Examples 1 to 3 and Comparative Examples 1 and 2, the distribution state of the additive elements in the oxide sintered bodies, and the presence or absence of an extraneous oxide phase, The results of investigation using an analyzer (EPMA) and an X-ray diffractometer (XRD) were as follows. As for the diffraction peak in the X-ray diffraction measurement of the oxide sintered body, only the diffraction peak due to the indium oxide crystal phase having a bixbite type structure was observed. In addition, as a result of X-ray diffraction measurement, it was also confirmed that there was no crystalline phase of tungsten oxide, zinc oxide, or magnesium oxide. Furthermore, local analysis by EPMA confirmed that tungsten, zinc, and magnesium were uniformly dispersed and dissolved in the indium oxide crystal phase in each oxide sintered body.

<Film formation>
(Examples 4-8, Comparative Examples 3-8)
Examples 4 to 8 and the comparison were made in the same manner as in Example 1 except that the composition of In ₂ O ₃ powder, WO ₃ powder, MgO powder and ZnO powder to be mixed was changed and the composition was changed from Example 1. The oxide sintered bodies of Examples 3 to 8 were obtained. And the sputter | spatter surface of each oxide sintered compact was polished with the cup grindstone, it processed into diameter 152mm and thickness 5mm, and it bonded together to the backing plate using the indium-type alloy, and was set as the sputtering target.

The DC magnetron sputtering apparatus used in Examples 4 to 8 and Comparative Examples 3 to 8 is shown in FIG. The sputtering target 2 was attached to the cathode for the non-magnetic target of the DC magnetron sputtering apparatus, and a # 7059 glass substrate 4 having a thickness of 1.1 mm was attached to the opposite surface of the sputtering target 2. The atmosphere is Ar + O ₂ , the total pressure is 0.6 Pa, O ₂ / (Ar + O ₂ ) × 100 = 2.5%, sputtering is performed with the distance between the target substrates being 70 mm, A transparent conductive thin film having a thickness of 200 nm was formed. The substrate was not heated.

  About the case where it sputter | spatterred using the oxide sintered compact of Example 4, 5 and Comparative Example 3, 4, the film-forming speed | rate was calculated | required from the film-forming time and the film thickness. Table 2 shows the composition of the oxide sintered body, the sintered density, and the film formation rate for Examples 4 and 5 and Comparative Examples 3 and 4. The film thickness is marked on the glass substrate 4 with magic ink, the magic ink marked after the film formation and the film deposited on the glass substrate 4 are removed with acetone, and the resulting step is measured with a contact-type surface shape measuring instrument ( Dektak3ST).

  The surface smoothness of the transparent conductive thin films according to Examples 6 to 8 and Comparative Examples 3 to 8 was evaluated by measuring average roughness (Ra) with an atomic force microscope. The specific resistance was measured by a four-end needle method. Moreover, the composition of the transparent conductive thin film was measured by EPMA. Furthermore, the light transmittance at 400 nm including the substrate was measured with a spectrophotometer (manufactured by Hitachi, Ltd., U-4000). Table 3 shows the composition, specific resistance, average roughness (Ra), and light transmittance at a wavelength of 400 nm of the transparent conductive thin films according to Examples 6 to 8 and Comparative Examples 5 to 8.

  The crystallinity was also evaluated with an X-ray diffractometer (XRD).

  The oxide sintered bodies of Examples 4 and 5 have Zn / In atomic ratios of 0.009 and 0.032, respectively, and are larger than 0.005 which is the lower limit value of the range of the present invention. Therefore, the film formation rates by sputtering were 55 nm / min and 52 nm / min, respectively, and increased to the same level as the ITO film formation rate (about 50 nm / min).

  On the other hand, the oxide sintered body of Comparative Example 3 has a Zn / In atomic ratio of 0.004, which is lower than 0.005, which is the lower limit value of the range of the present invention. The conductivity of the body is considered bad. Therefore, the film formation rate by sputtering is as small as 29 nm / min, which is only about 60% of the film formation rate of ITO, and nodules are generated during sputtering, resulting in an unfavorable production result.

  The oxide sintered body of Comparative Example 4 has an Mg / In atomic ratio of 0.006, which is lower than 0.007, which is the lower limit of the range of the present invention. Therefore, although the sintered density is about the same as in Examples 4 and 5, the film forming rate is about 15% lower than in Examples 4 and 5.

The oxide sintered body of Comparative Example 5 has a W / In atomic ratio of 0.041, which exceeds 0.033, which is the upper limit of the range of the present invention, and has a sintered density of 6.41 g / cm. ³ and smaller. Therefore, the film formation rate was as low as 31 nm / min, and nodules were also generated.

  The oxide sintered body of Comparative Example 6 has a W / In atomic ratio of 0.003, which is lower than 0.004, which is the lower limit of the range of the present invention. For this reason, the sintered compact was cracked during sputtering, and nodules were also generated.

The transparent conductive thin film according to Examples 6 to 8 within the scope of the present invention has a specific resistance of 3.7 to 4.8 × 10 ⁻⁴ Ωcm and a favorable value of 5 × 10 ⁻⁴ Ωcm or less. Specific resistance is shown. The transparent conductive thin films according to Examples 6 to 8 were formed without heating the substrate.

  In addition, the transparent conductive thin films according to Examples 6 to 8 within the scope of the present invention have an average surface roughness (Ra) of 0.31 to 0.43 nm and 0.16 to 0.46 with respect to the film thickness. It was 0.22% and was excellent in smoothness.

On the other hand, the transparent conductive thin film according to Comparative Example 3 has a Zn / In atomic ratio of 0.004, which is lower than 0.005, which is the lower limit of the range of the present invention. For this reason, the specific resistance of the transparent conductive thin film is increased to 9 × 10 ⁻⁴ Ωcm, which is unsuitable as an electrode. Moreover, it was not amorphous in the evaluation by an X-ray diffractometer (XRD).

The transparent conductive thin film according to Comparative Example 5 has a W / In atomic ratio of 0.041, which exceeds 0.033, which is the upper limit of the range of the present invention. Therefore, the specific resistance of the transparent conductive thin film is as large as 14 × 10 ⁻⁴ Ωcm, which is unsuitable as an electrode.

The transparent conductive thin film according to Comparative Example 6 has a W / In atomic ratio of 0.003, which is lower than 0.004 which is the lower limit value of the range of the present invention. For this reason, the specific resistance was 5.9 × 10 ⁻⁴ Ωcm, exceeding 5 × 10 ⁻⁴ Ωcm, resulting in an unsuitable electrode. Further, the crystallization temperature was lowered, the transparent conductive thin film was crystallized during sputtering, the surface was uneven, and the average surface roughness (Ra) was 4 nm. Since the film thickness was 200 nm, the average roughness (Ra) of the surface was 2% with respect to the film thickness, exceeding 1%.

  For comparison, the same measurement was performed on the ITO film, but the average roughness (Ra) was 4.2 nm, indicating an average roughness (Ra) exceeding 1% with respect to the film thickness of 200 nm. It was.

  The transparent conductive thin film according to Comparative Example 7 has a Zn / In atomic ratio of 0.035, which exceeds 0.032 which is the upper limit of the range of the present invention. For this reason, the transmittance of light having a wavelength of 400 nm was as small as 58%, which was 60% or less.

The transparent conductive thin film according to Comparative Example 8 has an Mg / In atomic ratio of 0.058, which exceeds the upper limit of 0.056 in the range of the present invention. Therefore, the specific resistance was 7.8 × 10 ⁻⁴ Ωcm, which was larger than 5 × 10 ⁻⁴ Ωcm.

  In any of the transparent conductive thin films according to Examples 4 to 8 within the scope of the present invention, no crystal peak was observed and the film was amorphous.

(Example 9, Comparative Example 9)
Example 9 and Comparative Example 9 attempted to laminate a transparent conductive thin film having the same composition as that of Example 6 within the scope of the present invention and an Ag film for the purpose of further reducing the resistance.

  In Example 9, a transparent conductive thin film having the same composition as in Example 6 and having a thickness of 75 nm was prepared in the same manner, and an Ag layer was formed to 5 nm, and a transparent conductive thin film having the same composition was further formed to a thickness of 75 nm. It is only a stack. In Comparative Example 9, a 7-nm thick Ag layer was formed on a 75-nm thick transparent conductive thin film having the same composition as that of Example 6 and similarly manufactured, and a 75-nm thick transparent conductive thin film having the same composition was further formed. It is only a stack. With respect to the laminated films according to Example 9 and Comparative Example 9, the specific resistance and the transmittance of light having a wavelength of 550 nm were measured by the same method as described above. The results are shown in Table 4 below.

The specific resistance value of the transparent conductive thin film according to Example 6 is 3.7 × 10 ⁻⁴ Ωcm, whereas in Example 9 in which a 5 nm Ag layer is provided, the specific resistance value is 6 × 10 ^{− 5} Ωcm, which is about 1/6 that of Example 9. In Example 9, the transmittance of light with a wavelength of 550 nm was 93%, which exceeded 90%, and the light transmittance showed a good result.

On the other hand, Comparative Example 9 provided with a 7 nm Ag layer had a specific resistance of 4 × 10 ⁻⁵ Ωcm, which was lower than that of Example 6, but the transmittance of light having a wavelength of 550 nm was 87%. Compared to 9, it was about 6% smaller and less than 90%.

It is the schematic of the DC magnetron sputtering apparatus used in Examples 4-9 and Comparative Examples 3-9.

Explanation of symbols

1 Vacuum chamber 2 Target 3 DC power supply 4 Glass substrate 5 Supply pipe 6 Magnet

Claims (13)

  An oxide sintered body containing tungsten, zinc, and magnesium, the balance being indium, oxygen, and inevitable impurities, wherein tungsten is an atomic ratio with respect to indium of 0.004 to 0.033, and zinc is an atom with respect to indium An oxide sintered body containing 0.005 to 0.032 in terms of number ratio and 0.007 to 0.056 in terms of number ratio of magnesium to indium.   2. The oxide sintered body according to claim 1, wherein the main phase is an indium oxide crystal phase having a bixbyite structure. The oxide sintered body according to claim 1 or 2, wherein the sintered density is 6.5 g / cm ³ or more.   The oxide sintered body according to claim 1, wherein the average crystal grain size is 5 μm or less.   A sputtering target, wherein the oxide sintered body according to claim 1 is processed into a flat plate shape and bonded to a cooling metal plate.   A transparent conductive thin film containing tungsten, zinc, and magnesium, the balance being indium, oxygen, and inevitable impurities, wherein tungsten is an atomic ratio with respect to indium of 0.004 to 0.033, and zinc is an atomic number with respect to indium An amorphous transparent conductive thin film containing 0.005 to 0.032 in terms of ratio and 0.007 to 0.056 in terms of the atomic ratio of magnesium to indium. The transparent conductive thin film according to claim 6, which has a specific resistance of 5 × 10 ⁻⁴ Ωcm or less.   The transparent conductive thin film according to claim 6 or 7, wherein the average roughness (Ra) of the surface is less than 1% of the film thickness.   The transparent conductive thin film according to any one of claims 6 to 8, wherein the transmittance of light having a wavelength of 400 nm is 65% or more.   A transparent conductive thin film formed by laminating the transparent conductive thin film according to claim 6 and a metal thin film of 3 to 5 nm.   The transparent conductive thin film according to claim 10, wherein the metal thin film is a thin film made of one or more metals selected from the group consisting of silver, silver alloy, aluminum, and aluminum alloy.   The organic device using the transparent conductive thin film in any one of Claims 6-11.   The organic electroluminescent element using the transparent conductive thin film in any one of Claims 6-11.

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