JP2006188392A - Oxide sintered compact, transparent electroconductive thin film, and element packaged with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide sintered compact which can be used for manufacturing an amorphous transparent electroconductive thin film having low specific resistance, smooth surface, and high light transmittance in the visible light region. <P>SOLUTION: The oxide sintered compact comprises indium (In), tungsten (W), zinc (Zn), and germanium (Ge), wherein the atomic number ratio of W to In is 0.004-0.023, the atomic number ratio of Zn to In is 0.004-0.032, and the atomic number ratio of Ge to In is 0.004-0.021, and has a specific resistance of ≤1 kΩ×cm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used for a display element such as a liquid crystal display (LCD) element and an organic electroluminescence (EL) element, an organic device such as an organic transistor, and an organic solar battery, and has a low film stress and a low specific resistance. The present invention relates to a crystalline transparent conductive thin film and an oxide sintered body used as a target material when the transparent conductive thin film is produced by a direct current sputtering method.

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 solar cell, a liquid crystal display element, and various other light receiving elements. In addition to being used as an electrode for electronic devices such as automobiles, as a heat-reflective film used for automobile window glass, window glass for buildings, various antistatic films, and as a transparent heating element for anti-fogging such as a freezer showcase It's being used.

The transparent conductive thin film includes a tin oxide (SnO ₂ ) film doped with antimony and fluorine, a zinc oxide (ZnO) film doped with aluminum and gallium, and an indium oxide (In ₂ O ₃ ) film doped with tin. Are widely used. In particular, an indium oxide film doped with tin, that is, an In ₂ O ₃ —Sn-based film is called an ITO (Indium Tin Oxide) film, and a transparent conductive thin film having a small specific resistance can be easily obtained. It is 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 a material having a low vapor pressure is used to form a film on a deposition target material (hereinafter simply referred to as “substrate”) or when precise film thickness control is required. Since the operation is very simple, it is widely used.

  In the sputtering method, a raw material having a target film component is generally used as a target. In this method, generally, a vacuum chamber using a vacuum apparatus and a target and a substrate are evacuated once, and then a rare gas such as argon is introduced, and the substrate is placed under a gas pressure of about 10 Pa or less. The anode is used as the anode, the target is used as the cathode, and glow discharge is generated between them to generate argon plasma. Then, argon cations in the plasma are collided with the target of the cathode, thereby repelling the target component particles and depositing the particles on the substrate to form a film.

  On the other hand, a transparent conductive thin film with a smooth surface is required for electrodes for LCDs and organic EL elements. In particular, in the case of an electrode of an organic EL element, an ultra-thin film of an organic compound is formed on the electrode. Therefore, the transparent conductive thin film is required to have excellent surface smoothness. In general, the surface smoothness greatly depends on the crystallinity of the film. Even if the composition is the same, the transparent conductive thin film (amorphous film) with an amorphous structure with no grain boundaries is more smooth than the transparent conductive thin film (crystalline film) with a crystalline structure. Is good. In fact, even in the case of an ITO film having a conventional composition, an amorphous ITO film obtained by performing sputtering at a substrate temperature of 150 ° C. or lower and a gas pressure of 1 Pa or higher by lowering the substrate temperature during film formation. However, the surface smoothness is excellent.

However, the specific resistance of the amorphous ITO film is limited to 6 × 10 ⁻⁴ Ωcm at the minimum, and in order to form a film with low surface resistance, it is necessary to form the film itself thickly. However, when the thickness of the ITO film is increased, a problem of coloring occurs.

  In addition, since the kinetic energy of the sputtered particles incident on the substrate is high, the temperature rises locally even when the substrate is not heated, and even with an ITO film formed at room temperature without heating the substrate, a fine crystalline phase and There is also a problem that a film composed of an amorphous phase may be obtained. This phenomenon is remarkable when the gas pressure in sputtering is low.

  If the fine crystal phase is partially formed, the surface smoothness is greatly affected. In addition, when the transparent conductive thin film is etched into a predetermined shape with a weak acid, only the crystal phase may remain unremoved, which is problematic. The presence of a fine crystal phase can be confirmed not only by X-ray diffraction but also by a transmission electron microscope or electron beam diffraction.

  Next, an organic EL element which is one of main application targets of the present invention will be described.

  The EL element uses electroluminescence, has high visibility because of self-emission, and is a completely solid element unlike a liquid crystal or plasma display panel. For this reason, EL elements have advantages such as excellent impact resistance, and are attracting attention as light-emitting elements in various display devices.

  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. Among these, the organic EL element 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). For this reason, research on practical application as a next-generation display element has been actively conducted.

  The configuration of the organic EL element is basically a laminate of an anode / light emitting layer / cathode, and a configuration in which a transparent anode is formed on a substrate using a glass plate or the like is usually employed. Since Ca or the like is used for the cathode and is not transparent, in this case, light emission is extracted from the substrate side (anode side).

  However, in recent years, attempts have been made to make the cathode transparent and to extract emitted light from the cathode side. This is because if the anode is made transparent together with the cathode, a transparent light emitting element as a whole can be obtained.

  When a transparent light emitting element is used as a whole, there are the following advantages. The first advantage is that an arbitrary color can be adopted as a background color, so that a colorful display can be obtained even during light emission, and the decorativeness can be improved. The second advantage is that when black is used as the background color, the contrast during light emission can be improved. The third advantage is that a color filter and a color conversion layer can be used on the light emitting element (on the side opposite to the substrate), so that the light emitting element can be used without considering the color filter and the color conversion layer. It can be manufactured. For this reason, for example, it is not necessary to consider forming a transparent electrode on a color filter or a color conversion layer inferior in heat resistance.

  Since the above advantages can be obtained by making the cathode transparent, attempts have been actively made to produce an organic EL device using a transparent cathode.

  For example, in an organic EL device described in JP-A-10-162959, an organic layer including an organic light emitting layer is interposed between an anode and a cathode, and the cathode is an electron injection metal layer and an amorphous transparent conductive material. And an electron injecting metal layer is in contact with the organic layer.

  Japanese Patent Application Laid-Open No. 2001-43980 describes an organic EL element that is devised so as to efficiently extract light from a cathode by making the cathode transparent and using a light-reflective metal film for the anode. .

  Here, each layer (electron injection metal layer, organic layer, hole injection transport layer, anode, cathode) constituting the organic EL element will be described.

  First, the electron injection metal layer is a metal layer that can inject electrons well into an organic layer including a light emitting layer. In order to obtain a transparent light-emitting element, the electron-injecting metal layer preferably has a light transmittance of 50% or more. For this purpose, the thickness of the layer needs to be an ultrathin film of about 0.5 nm to 20 nm. There is.

  Specifically, a metal having a work function of 3.8 eV or less and an electron injection property, such as Mg, Ca, Ba, Sr, Li, Yb, Eu, Y, and Sc, is used as the electron injection metal layer. And a metal layer having a thickness of 1 nm to 20 nm. The light transmittance is preferably 50% or more, and more preferably 60% or more.

  The organic layer is formed between the anode and the cathode and includes at least a light emitting layer. The organic layer may be a layer composed only of the light emitting layer, or may have a multilayer structure in which a hole injecting and transporting layer and the like are laminated together with the light emitting layer.

  In the organic EL element, the organic layer has the following functions: (1) a function that allows holes to be injected from the anode or the hole transport layer and an electron to be injected from the electron injection layer when an electric field is applied; 2) Transport function that moves injected charges (electrons and holes) by the force of an electric field, (3) Light emission function that provides a field for recombination of electrons and holes inside the light emitting layer, and connects this to light emission, etc. It has the function of

  The hole injection transport layer is a layer made of a hole transfer compound, and has a function of transferring holes injected from the anode to the light emitting layer. By interposing this hole injecting and transporting layer between the anode and the light emitting layer, many holes are injected into the light emitting layer with a lower electric field. In addition, electrons injected from the electron injection layer into the light emitting layer are accumulated near the interface in the light emitting layer due to an electron barrier existing at the interface between the light emitting layer and the hole injection transport layer. Thereby, the luminous efficiency of an organic EL element can be improved and the organic EL element excellent in the light emission performance is obtained.

  The anode is not particularly limited as long as it has a work function of 4.4 eV or more, preferably 4.8 eV or more, and a metal or a transparent conductive thin film having a work function of 4.8 eV or more, or a combination thereof. Are preferred.

  The anode is not necessarily transparent and may be coated with a black carbon layer or the like. Examples of metals suitable for the anode include Au, Pt, Ni, Ag, and Pd. Examples of the conductive oxide include In—Zn—O, In—Sn—O, ZnO—Al, and Zn—Sn—O. Examples of the stacked body include a stacked body of Au and In—Zn—O, a stacked body of Pt and In—Zn—O, and a stacked body of In—Sn—O and Pt.

Further, since the anode only needs to have a work function of 4.4 eV or more at the interface with the organic layer, the anode may be formed in two layers and a conductive film having a work function of 4.4 eV or less may be used on the side not in contact with the organic layer. Good. In this case, a metal such as Al, Ta, or W, or an alloy such as an Al alloy or Ta—W alloy can be used. Alternatively, a conductive polymer such as doped polyaniline or doped polyphenylene vinylene, an amorphous semiconductor such as a-Si, a-SiC, or aC can be used. Further, black semiconductor oxides such as Cr ₂ O ₃ , Pr ₂ O ₅ , NiO, Mn ₂ O ₅ , and MnO ₂ can also be used.

As described above, the cathode is preferably a transparent conductive layer and an amorphous film with excellent smoothness. In order to eliminate voltage drop and non-uniformity of light emission resulting therefrom, the specific resistance is preferably 5 × 10 ⁻⁴ Ωcm or less.

  However, it is impossible with conventional ITO materials to realize a stable transparent conductive thin film that has excellent surface smoothness and can remain amorphous even when subjected to the thermal history of the manufacturing process. there were. For this reason, it has been difficult to use conventional ITO materials for transparent electrodes of display elements such as organic EL displays and LCDs.

  As the amorphous film, indium oxide to which zinc is added is described in Patent Document 3 (Japanese Patent Laid-Open No. 7-235219). This publication introduces that Zn element is contained in an amount of 10 at% to 20 at% with respect to the sum of Zn element and In element, and exhibits stable amorphousness and high electrical conductivity.

  However, the film having the composition introduced here has a problem in that it has low light transmissivity with respect to light having a short wavelength side of visible light, particularly light having a wavelength near 400 nm.

  In consideration of improvement in productivity and reduction in manufacturing cost, it is preferable to employ a direct current sputtering method and perform high-speed film formation by applying high direct current power. However, depending on the type of element added to the sputtering target used for manufacturing the indium oxide thin film, arcing may occur when high DC power is applied, and in this case, high-speed film formation is impossible. In addition, when arcing occurs during film formation, it causes generation of particles and causes a decrease in product yield. Furthermore, if arcing occurs continuously, the film formation itself is hindered.

  Furthermore, depending on the sputtering target, when the integrated value of the input power increases, nodules (black projections on the target surface) are generated on the surface of the sputtering target, arcing occurs, and the film formation rate decreases. Problems occur.

  On the other hand, a sputtering target with a small arcing generation scale can be avoided by using a power source with an arcing suppression function. As a method for suppressing arcing in the power source, a DC pulsing method (a method in which a negative voltage applied to a target is periodically stopped and a low positive voltage is applied therebetween to neutralize charging on the target), an arc Cut-off circuit (a circuit that stops the power supply before it grows to complete arcing by detecting an increase in discharge current when arcing occurs, and restarts the power supply when the current flowing to the target has dropped sufficiently) (Non-patent document 1 ("Technology of transparent conductive film", Ohm Co., p.193-195)).

  However, these power supplies having an arcing suppression function are very expensive and increase the equipment cost. Moreover, even if these power supplies having an arcing suppression function are used, arcing cannot be completely suppressed with a conventional sputtering target such as a sputtering target using indium oxide described in Patent Document 3.

Japanese Patent Laid-Open No. 10-162959

JP 2001-43980 A

JP 7-235219 A

“Transparent conductive film technology”, Ohm, p. 82, p. 193-195

  The present invention has been made in view of such problems, and it is possible to produce an amorphous transparent conductive thin film having a small specific resistance, a smooth film surface, and a high light transmittance in the visible light region. An object of the present invention is to provide an oxide sintered body. It is another object of the present invention to provide a sputtering target in which arcing does not occur even when high DC power is applied in a film formed by a DC sputtering method using a power source having no arcing suppression function, and a thin film to be formed is less likely to crack. And

  The oxide sintered body according to the present invention is made of indium, tungsten, zinc, and germanium. Tungsten is a W / In atomic ratio of 0.004 to 0.023, and zinc is a Zn / In atomic ratio of 0. A ratio of 0.004 to 0.032, germanium is contained in a Ge / In atomic ratio of 0.004 to 0.021, and a specific resistance is 1 kΩcm or less.

The specific resistance of the oxide sintered body is preferably 1 × 10 ⁻¹ Ωcm or less because the film formation rate when used as a sputtering target is improved, and the oxide sintered body is preferably It is also preferable that the indium oxide crystal phase having a bixbyite structure is a main phase and does not substantially contain a tungsten oxide crystal phase, a zinc oxide crystal phase, or a germanium oxide crystal phase because the film forming speed is improved. Furthermore, setting the sintered density of the oxide sintered body to 6.5 g / cm ³ or more reduces the generation amount of nodules (black projections on the target surface), reduces arcing, and increases the film formation rate. This is preferable because it is less likely to cause a problem such as reduction.

  The oxide sintered body according to the present invention can be made into a sputtering target by processing it into a flat plate shape and bonding it to a cooling metal plate.

The transparent conductive thin film according to the present invention is made of indium, tungsten, zinc, and germanium, tungsten is a W / In atomic ratio of 0.004 to 0.023, and zinc is Zn / In atomic ratio of 0.00. A ratio of 004 to 0.032, germanium is contained in a ratio of 0.004 to 0.021 in terms of Ge / In atomic ratio, a specific resistance is 5 × 10 ⁻⁴ Ωcm or less, and the film quality is amorphous. It is characterized by quality. Further, the transparent conductive thin film according to the present invention preferably has a surface roughness (arithmetic average roughness Ra) of less than 1% with respect to the film thickness, and a transmittance of light having a wavelength of 400 nm is 65% or more. It is preferable that

  The transparent conductive thin film according to the present invention can be obtained by performing sputtering with a sputtering target using the oxide sintered body according to the present invention. In addition, the sputtering apparatus to be used may not have an arcing suppression function, and the transparent conductive thin film according to the present invention is subjected to a direct current sputtering method with a sputtering target using the oxide sintered body according to the present invention. But you can get it.

  By using the transparent conductive thin film according to the present invention as a cathode, a top emission type organic EL device can be obtained. Further, the transparent conductive thin film according to the present invention is formed on a resin film, and the transparent conductive thin film is formed. Can be used as a cathode and / or an anode to form a flexible organic EL device.

The method for producing an oxide sintered body according to the present invention includes an In ₂ O ₃ powder, a WO ₃ powder, a ZnO powder and a GeO ₂ powder having an average particle diameter of 1 μm or less, and tungsten having a W / In atomic ratio of 0.00. Formulated so that the ratio of 004 to 0.023, the ratio of zinc to 0.004 to 0.032 in terms of the Zn / In atomic ratio, and the ratio of germanium to 0.004 to 0.021 in terms of the Ge / In atomic ratio. And mixing to obtain a mixed powder; granulating the obtained mixed powder to an average particle size of 20 to 150 μm to obtain a granulated powder; A process of obtaining a compact by applying a pressure of ² to 5 ton / cm ^{2 with} a hydraulic press, and introducing oxygen into the sintering furnace at a rate of 50 to 250 L / min per furnace volume 0.1 m ³ , temperature: The molded body is sintered at 1200 to 1500 ° C. for 10 to 40 hours. And obtaining an oxide sintered body, characterized by having a.

  In addition, it is preferable that the mixing time in the process of obtaining the said mixed powder is 10 to 30 hours.

  Moreover, in the said sintering, the temperature increase rate until it reaches a sintering temperature is preferably 0.5 to 3 ° C./min, and the cooling rate after sintering is about 1000 ° C. after the introduction of oxygen is stopped. Is preferably 0.1 to 1 ° C./min.

By using the oxide sintered body according to the present invention as a sputtering target, an amorphous transparent conductive thin film having low specific resistance, excellent surface smoothness, and excellent light transmittance in the visible light region is produced. be able to. Also, high-speed film formation is possible. Furthermore, when the sintered density of the oxide sintered body according to the present invention is set to 6.5 g / cm ³ or more, a large direct current can be formed in an inexpensive direct current sputtering method equipped with a direct current power source having no arcing suppression function. Even if power is turned on, arcing can be made difficult to occur.

  The inventor of the present invention uses an oxide sintered body containing indium, tungsten, zinc and germanium in a predetermined atomic ratio and having a specific resistance of 1 kΩcm or less as a sputtering target. The present inventors have found that an amorphous transparent conductive thin film having excellent properties and visible light region transparency can be produced, and that high-speed film formation is possible. Further, it has also been found that when the sputtering target is used, arcing does not occur even when high power is applied in film formation using an inexpensive DC sputtering apparatus equipped with a DC power supply having no arcing suppression function. The present invention has been completed based on these findings.

1. Oxide Sintered Body The oxide sintered body of the present invention contains indium, tungsten, zinc, and germanium, the tungsten content is 0.004 to 0.023 in terms of W / In atomic ratio, and the zinc content The Zn / In atomic ratio is 0.004 to 0.032, the germanium content is Ge / In atomic ratio is 0.004 to 0.021, and the specific resistance is 1 kΩcm or less. . The sintered body preferably has a bixbite type indium oxide as a main phase.

  When a transparent conductive thin film is produced by a sputtering method using a sputtering target produced from the oxide sintered body, it has a high crystallization temperature exceeding 200 ° C., is amorphous, and has a low specific resistance. A conductive thin film can be obtained.

  The reason why the proportions of tungsten, zinc and germanium in the oxide sintered body are limited as described above is as follows.

Tungsten contributes to improving the conductivity of the transparent conductive thin film and increasing the crystallization temperature. When the W / In atomic ratio of the oxide sintered body is less than 0.004, the specific resistance becomes larger than 5 × 10 ⁻⁴ Ωcm. Further, the crystallization temperature of the obtained transparent conductive thin film is not sufficiently high, and when the film is formed by sputtering, a transparent conductive thin film containing a crystal phase is obtained. On the other hand, when the W / In atomic ratio of the oxide sintered body exceeds 0.023, the obtained transparent conductive film is amorphous, but the specific resistance becomes larger than 5 × 10 ⁻⁴ Ωcm. .

  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 increasing the crystallization temperature of the film. If the Zn / In atomic ratio of the oxide sintered body is less than 0.004, the specific resistance of the sintered body increases, so the film forming speed becomes very low, the productivity is inferior, and the amorphous body is amorphous. The transparent conductive thin film 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 range (for example, near the wavelength of 400 nm).

  Germanium contributes to the improvement of conductivity. When the Ge / In atomic ratio of the oxide sintered body is less than 0.004, there is no effect of reducing the specific resistance of the transparent conductive thin film by adding Ge, and when the Ge / In atomic ratio exceeds 0.021. On the contrary, the specific resistance of the transparent conductive thin film obtained becomes large.

2. Production Method of Oxide Sintered Body and Sputtering Target The oxide sintered body containing indium, tungsten and zinc of the present invention can be produced as follows.

In ₂ O ₃ powder, WO ₃ powder, ZnO powder and GeO ₂ powder having an average particle size of 1 μm or less are used as raw material powders. In ₂ O ₃ powder, WO ₃ powder, ZnO powder and GeO ₂ powder are prepared at a predetermined ratio, put into a resin pot together with water, a dispersant and a binder, and mixed in a wet ball mill to form a slurry. At this time, it is preferable to use hard ZrO ₂ balls in order to avoid mixing impurities in the slurry as much as possible. The mixing time is preferably 10 hours to 30 hours. When the time is shorter than 10 hours, the raw material powder is not sufficiently pulverized, and it becomes difficult to obtain a sintered body having a bixbite type indium oxide crystal phase as a main phase. In addition, if there is a raw material powder that is not sufficiently pulverized, diffusion during sintering is not sufficiently performed, and a raw material powder having a large specific resistance is present in the sintered body, and arcing is likely to occur. . On the other hand, if it is longer than 30 hours, it is excessively pulverized and the particles are strongly agglomerated, making it difficult to stably obtain a high-density target. After mixing, the slurry is taken out and spray-dried using a spray dryer to obtain granulated powder.

The granulated powder granulated to an average particle size of about 20 μm to 150 μm is molded by applying a pressure of ² to 5 ton / cm ² with a cold isostatic press. As the molding press, a cold isostatic press is preferable because a uniform molded body can be obtained. When the pressure is lower than ² ton / cm ² , the density of the molded body does not increase and it is difficult to obtain a high-density target. On the other hand, when the density is higher than 5 ton / cm ² , the density of the molded body can be increased, but the facilities and the like become large and the manufacturing cost increases.

Next, in an atmosphere obtained by introducing oxygen into the sintering furnace at a rate of 100 L / min per 0.1 m ^{3 of} the furnace internal volume, the obtained molded body was subjected to temperature: 1200 to 1500 ° C. and time: 10 In about 40 hours, heat treatment is performed and sintering is performed.

When the amount of oxygen introduced is less than 50 L / min per 0.1 m ³ of the furnace volume, the tungsten oxide and zinc oxide are thermally dissociated to increase evaporation, making it difficult to obtain a high-density sintered body. If it exceeds 250 L / min, temperature variation in the furnace becomes large, and stable production of a high-density sintered body becomes difficult.

Moreover, since it is difficult to stably obtain a high-density target when the heat treatment temperature is lower than 1200 ° C., it is not preferable. When the heat treatment temperature is higher than 1500 ° C., sublimation of WO _{3 in} the raw material occurs and sputtering is performed. This is not preferable because it affects the composition of the target.

  The heating rate during the heat treatment is preferably about 0.5 to 3.0 ° C./min. In cooling after sintering by heat treatment, oxygen introduction is stopped and the temperature is lowered to about 1000 ° C. at 1 ° C./min. Is preferred. Slowing the temperature rise is necessary to make the temperature distribution in the furnace uniform, and performing the temperature drop to about 1000 ° C. at 1 ° C./min in order to prevent the target from cracking due to thermal shock. is necessary.

  The obtained oxide sintered body containing indium, tungsten and zinc is processed into a desired shape (the thickness is usually about 3 to 10 mm because it is used as a sputtering target), and the surface to be sputtered is polished with a cup grindstone or the like. .

  The oxide sintered body processed as described above is bonded to a cooling plate made of pure copper or molybdenum with an In-based brazing material having a melting point of 120 to 200 ° C. to obtain a sputtering target. At this time, in order to improve wettability with the backing plate and prevent diffusion of the backing plate material, a metallized film may be formed on the bonding surface of the sputtering target by sputtering or vapor deposition.

3. Sputtering target Although the sputtering target which concerns on this invention can be manufactured as mentioned above, the characteristic etc. are demonstrated below.

The film formation speed during direct current sputtering depends on the specific resistance of the sputtering target, and the film formation speed increases as the specific resistance decreases. Therefore, even when the oxide sintered body containing indium, tungsten, zinc and germanium according to the present invention is used for a sputtering target, the specific resistance of the sputtering target is small in order to realize a high film formation rate. More specifically, the specific resistance is required to be 1 kΩcm or less, and preferably 1 × 10 ⁻¹ Ωcm or less.

  Moreover, in the sputtering target which concerns on this invention, it is preferable that the crystal phase resulting from tungsten oxide, zinc oxide, and germanium oxide which are raw material powder does not exist, and is comprised only by the bixbite phase. When the specific resistance is the same, the oxide sintered body composed only of the bixbite phase is sputtered 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 film forming speed by is clearly fast. 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.

Furthermore, in the sputtering target according to the present invention, it is desirable that the sintered density is 6.5 g / cm ³ or more. If the sputtering target has a sintered density of 6.5 g / cm ³ or more, the generation amount of nodules (black projections on the target surface) is small, and problems such as arcing and a decrease in film formation rate are unlikely to occur.

Even in the sputtering target according to the present invention, when the sintering density is lowered, nodules (referred to as black projections on the target surface) are generated in the vicinity of erosion during sputtering for a long time, and arcing occurs during film formation. It becomes easy. If the film is formed in such a state, a transparent conductive thin film having a small specific resistance cannot be obtained. The susceptibility of nodules is related to the sintered density, and setting the sintered density to 6.5 g / cm ³ or more is effective in suppressing nodules and arcing when sputtering is performed for a long time. is there.

  When the sputtering method is performed, the element or particles are sputtered off from the surface by sputtering, and the appearance is scraped off as an appearance. At this time, vacancies existing in the sputtering target are, The vacancies coming out on the surface and coming out on the surface form recesses on the surface. In the recesses on the surface, the sputtered elements or particles adhere to and deposit on the walls of the recesses and grow to form nodules. The lower the sintering density, the more concave portions on the surface, and thus more nodules. When this nodule grows, plasma concentrates during discharge, and arcing occurs and the film formation rate decreases, leading to deterioration of film characteristics. The amount of nodules generated on the target surface, and the cumulative input power at which arcing and film deposition rate start to decrease greatly depend on the sintering density. The higher the sintering density, the smaller the amount of nodules and the occurrence of arcing. In addition, the integrated input power value at which the film formation rate starts to decrease increases.

Therefore, when the sintered density is low (for example, 4 to 6.4 g / cm ³ ), the integrated input power value at which the occurrence of arcing and the decrease in the film formation rate starts is small.

4). Transparent conductive thin film By carrying out sputtering method or ion plating method using the sputtering target according to the present invention, the specific resistance is 5 × 10 ⁻⁴ Ωcm or less, and the visible light region, particularly on the short wavelength side. An amorphous transparent conductive thin film having a large transmittance can be produced. Further, the surface roughness (Ra) of the thin film is less than 1% with respect to the film thickness. In addition, the composition of the formed transparent conductive thin film is substantially the same as the sputtering target used.

  The method for producing a transparent conductive thin film is preferably formed using the sputtering target of the present invention, with the distance between the target substrates during sputtering being 60 mm to 150 mm, and the sputtering gas pressure being 0.5 Pa to 1.5 Pa. .

  When the distance between the target substrates is shorter than 60 mm, the kinetic energy of the sputtered particles deposited on the substrate increases, and the damage to the substrate increases. For this reason, specific resistance will become large. If the distance between the target substrates is longer than 150 mm, the kinetic energy of the sputtered particles deposited on the substrate becomes too low, and densification due to solid phase diffusion inside the oxide film deposited on the substrate does not occur, and the transparent conductive material with low density Only a thin film can be obtained, which is not preferable.

  On the other hand, when the sputtering gas pressure is lower than 0.5 Pa, the kinetic energy of the sputtered particles deposited on the substrate increases, and the damage to the substrate increases. For this reason, the specific resistance of the film itself is increased. When the sputtering gas pressure is higher than 1.5 Pa, the kinetic energy of the sputtered particles deposited on the substrate becomes too low, and densification due to solid phase diffusion inside the oxide film deposited on the substrate does not occur, and the transparent conductive material with low density. Only a thin film is obtained, which is not preferable.

The transparent conductive thin film of the present invention produced under the preferable conditions described above has a small specific resistance of 5 × 10 ⁻⁴ Ωcm or less. Moreover, since it is an amorphous structure, the surface is smooth. Furthermore, since it has a high crystallization temperature exceeding 200 ° C., even if it is heated below 200 ° C., their properties do not change. Therefore, it is easy to stably produce an amorphous film even by a sputtering method in which the substrate is susceptible to heat from plasma. In addition, the characteristics are stable even if a heating process of less than 200 ° C. is included in the manufacturing process after film formation. Furthermore, since the transmittance of visible light, particularly light on the short wavelength side (for example, light with a wavelength of 400 nm) is large, the light emitting element using the transparent conductive thin film of the present invention emits blue, green and red uniformly. Can be made. This makes it possible to manufacture a high-quality display.

  Although the transparent conductive thin film of the present invention has an amorphous structure, this amorphous structure includes a case where there are microcrystals of such a size and amount that a crystal phase is not detected by X-ray diffraction. Even if there is such a fine crystal, the surface roughness (Ra) is less than 1% with respect to the film thickness, and the same effect can be obtained.

  As described above, the transparent conductive thin film of the present invention has a small specific resistance, a smooth surface, a high crystallization temperature exceeding 200 ° C., and a light in the visible light region, particularly a short wavelength side ( For example, the transmittance of light having a wavelength of 400 nm is large. Therefore, it is useful for display devices, and is particularly suitable for application to organic EL elements, inorganic EL elements, liquid crystal elements, touch panels, and the like.

  Further, when depositing the transparent conductive thin film according to the present invention, it is not necessary to heat the substrate. Therefore, according to the present invention, the transparent conductive thin film having a small specific resistance is formed on the substrate that is weak against heat such as resin. Can be deposited. Therefore, a transparent conductive thin film as a cathode can be formed on the organic light emitting layer. Therefore, the transparent conductive thin film according to the present invention is useful for realizing a top emission type organic EL device capable of efficiently extracting light from the cathode which is the upper surface electrode. For example, a TFT (thin- It can be used as a cathode of an organic light emitting layer in a top emission type organic EL device using a film transistor) substrate.

  Furthermore, even if the substrate is a soft resin film substrate having poor heat resistance, it is not necessary to heat the substrate, so that a transparent electrode having a small specific resistance can be formed without deforming the substrate. Therefore, the transparent conductive thin film of the present invention can be used as a transparent electrode formed on a resin film substrate, for example, as a cathode and / or an anode of a flexible transparent organic EL element using the resin film substrate. Can be used.

[1. Experimental example investigating the effect of oxide sinter properties on film deposition rate and transparent conductive thin film properties]
(Examples 1-7)
In ₂ O ₃ powder, WO ₃ powder, ZnO powder and GeO ₂ powder having an average particle size of 1 μm or less were used as raw material powders. In ₂ O ₃ powder, WO ₃ powder and ZnO powder were prepared at a predetermined ratio, put into a resin pot together with water, a dispersant and a binder, and mixed by a wet ball mill. At this time, hard ZrO ₂ balls were used, and the mixing time was 18 hours. After mixing, the slurry was taken out, filtered, dried and granulated. The obtained granulated powder was molded by applying a pressure of 3 ton / cm ² with a cold isostatic press.

Next, the obtained molded body was sintered as follows. Sintering was performed at 1300 ° C. for 20 hours in an atmosphere in which oxygen was introduced into the sintering furnace at a rate of 100 L / min per 0.1 m ^{3 of the} furnace volume. At this time, the temperature was raised at 1 ° C./min, and when cooling after sintering, the introduction of oxygen was stopped and the temperature was lowered to 1000 ° C. at 1 ° C./min.

  The milled end of the obtained oxide sintered body was pulverized and subjected to powder X-ray diffraction measurement with an X-ray diffractometer (M18XHF22, manufactured by MacScience Co.), resulting from a bixbite type indium oxide crystal phase. Only diffraction peaks were observed. Further, according to local analysis by EPMA, in each of the obtained oxide sintered bodies, there is a crystal phase of indium oxide, but there is no crystal phase of tungsten oxide, zinc oxide, or germanium oxide. It was confirmed that zinc and germanium were dissolved in indium.

  Next, each oxide sintered body containing indium, tungsten, zinc, and germanium was processed into a size of 152 mm in diameter and 5 mm in thickness, and the sputtering surface was polished with a cup grindstone (# 140 manufactured by Nitrex). When measured with a contact-type surface roughness meter (Surfcom E-MD-S75A manufactured by Tokyo Seimitsu), the maximum height Rz was all 0.3 μm or less. Moreover, the specific resistance was measured with respect to the sputtering surface of the oxide sintered body using a four-end needle method resistivity meter Loresta EP (manufactured by Dia Instruments, MCP-T360 type). The measurement results are shown in Table 1.

  As can be seen from the results shown in Table 1, the oxide sintered bodies of Examples 1 to 7 have a W / In atomic ratio of 0.004 to 0.022 and a Zn / In atomic ratio of 0.005 to 0. 0.032, the Ge / In atomic ratio is 0.004 to 0.020, the specific resistance is 0.004 to 0.015 Ωcm, and both the composition and the specific resistance are oxide sintered bodies within the scope of the present invention. It was.

  Next, the oxide sintered body processed and polished as described above was bonded to a backing plate made of oxygen-free copper to obtain a sputtering target. Metal indium was used for bonding.

Next, sputtering was performed using this sputtering target to produce a transparent conductive thin film. The sputtering target was attached to the cathode for a non-magnetic target of a direct current magnetron sputtering apparatus (SPF503K, manufactured by Tokki Co., Ltd.) equipped with a direct current power supply having no arcing suppression function, and a glass substrate was disposed at a position facing the sputtering target. In order to measure the film thickness, a part of the sputtering target directly above the center of the glass substrate was marked with magic ink. The target-substrate distance was 80 mm. Then, 4% of O ₂ gas is mixed with pure Ar gas to be introduced, the gas pressure is set to 0.8 Pa, DC plasma is generated with a DC power of 160 W, and the substrate remains stationary facing the sputtering target. Sputtering was performed for 30 minutes without heating.

  After film formation, the marked magic ink and the film deposited thereon are removed with acetone, and the resulting step is measured with a contact-type surface shape measuring instrument (Dektak 3ST, manufactured by Nippon Vacuum Technology Co., Ltd.). It was measured. The film formation rate was calculated from the film thickness / film formation time. Table 1 shows the calculated film formation rates.

  Further, in order to investigate the electrical and optical characteristics of the transparent conductive thin film, a film thickness of about 150 nm is obtained in accordance with a predetermined film formation speed in the same manner as described above, except that no marking is performed with magic ink. A transparent conductive thin film was prepared.

  Next, specific resistance, surface roughness Ra, and light transmittance at a wavelength of 400 nm were measured for the produced transparent conductive thin film. The specific resistance was calculated by measuring the surface resistance of the transparent conductive thin film by the four-end needle method. The surface roughness Ra of the transparent conductive thin film was measured with an atomic force microscope (manufactured by Digital Instruments, NS-III, D5000 system). The light transmittance including the substrate was measured with a spectrophotometer (manufactured by Hitachi, Ltd., U-4000). Table 1 shows the measurement results.

  Whether or not the produced transparent conductive thin film was amorphous was confirmed by a transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, HF2200). The transparent conductive thin films of Examples 1 to 7 were all amorphous. Met.

As can be seen from Table 1, the oxide sintered bodies according to Examples 1 to 7 have compositions within the scope of the present invention, and the specific resistance is as small as 0.004 to 0.015 Ωcm. It is in the range of. For this reason, the film-forming speed | rate by the sputtering method using the oxide sintered compact which concerns on Examples 1-7 is as high as 45-55 nm / min. Moreover, the characteristic of the obtained transparent conductive thin film has a specific resistance as small as 3.3 × 10 ^{−4 to} 4.8 × 10 ⁻⁴ Ωcm, and a surface roughness Ra as 0.3 to 0.5 nm. It is small and excellent in smoothness. Furthermore, the transmittance of light having a wavelength of 400 nm is as large as 65 to 70%, and the light transmittance is good in the visible light region.

  Moreover, even if the transparent conductive thin film which concerns on Examples 1-7 was heated at 200 degreeC in nitrogen, the amorphousness was maintained and the deterioration of electroconductivity was not seen. Therefore, even when the sputtering method in which the substrate easily receives heat from the plasma is used, it is considered that the amorphous film can be stably obtained by using the oxide sintered body according to Examples 1 to 7. It is done. Moreover, even if a 200 degreeC heating process is included in the manufacturing process after film | membrane formation, it is thought that the characteristic of the transparent conductive thin film which concerns on Examples 1-7 is stable.

(Comparative Examples 1-7)
In Examples 1 to 7, In ₂ O ₃ powder, WO ₃ powder, ZnO powder and GeO ₂ powder having an average particle diameter of 1 μm or less were used as raw material powders, while in Comparative Examples 1 to 7, the average particle diameter was 3 ˜5 μm In ₂ O ₃ powder, WO ₃ powder, ZnO powder and GeO ₂ powder were used as raw material powders. Moreover, in Examples 1-7, the time for mixing the raw material powder in the wet ball mill was 18 hours, whereas in Comparative Examples 1-7, the time was shortened to 5 hours. The other conditions were the same as those in Examples 1 to 7, and an oxide sintered body containing indium, tungsten, zinc, and germanium was produced and used as samples of Comparative Examples 1 to 7.

In the same manner as in Examples 1 to 7, powder X-ray diffraction and measurement by EPMA (manufactured by Shimadzu Corporation, EPMA-2300) were performed, and the obtained oxide sintered body had a crystalline phase of WO ₃ , ZnO and GeO ₂ Furthermore, it was confirmed that the oxide sintered body contained tungsten, zinc, and germanium in an atomic ratio with respect to indium at a ratio shown in Table 2.

  Similarly to Examples 1 to 7, the specific resistance of the oxide sintered bodies of Comparative Examples 1 to 7 was determined using a four-end needle method resistivity meter Loresta EP (manufactured by Dia Instruments, MCP-T360 type). It was measured.

  Next, the oxide sintered body was polished and processed by the same method as in Examples 1 to 7, and bonded to a backing plate made of oxygen-free copper to obtain a sputtering target. And the transparent conductive thin film was produced by sputtering method using this sputtering target, and the film-forming speed | rate was measured like Example 1-7. Table 2 shows the composition and specific resistance of the oxide sintered bodies of Comparative Examples 1 to 7 and the measurement results of the film formation rate when using the sputtering target prepared from the oxide sintered bodies of Comparative Examples 1 to 7. Show.

  As can be seen from Table 2, the oxide sintered bodies of Comparative Examples 1 to 7 have a W / In atomic ratio of 0.005 to 0.023 and a Zn / In atomic ratio of 0.004 to 0.032. The Ge / In atomic ratio is 0.004 to 0.021 and the composition is within the range of the oxide sintered body according to the present invention, but the specific resistance is as large as 11000 Ωcm to 30000 Ωcm, and the oxide according to the present invention. It was an oxide sintered body that exceeded the upper limit (1 kΩcm = 1000 Ωcm) of the specific resistance of the sintered body and deviated from the range of the oxide sintered body according to the present invention. For this reason, the film formation rate is as low as 20 to 29 nm / min.

(Comparative Examples 8 and 9)
In Comparative Examples 8 and 9, the composition was changed from that of Examples 1 to 7, but the raw material powder was similar to Examples 1 to 7, In ₂ O ₃ powder having an average particle size of 1 μm or less, WO ₃ powder, ZnO powder and GeO ₂ powder were used as raw material powders, and the time for mixing the raw material powders with a wet ball mill was 18 hours as in Examples 1 to 7, and the other production conditions were the same as in Examples 1 to 7. Thus, an oxide sintered body was produced.

  Next, the sputtering target was produced from the obtained oxide sintered compact by the method similar to Examples 1-7, and the transparent conductive thin film was produced by sputtering method using this sputtering target. And the specific resistance, surface roughness Ra, and the transmittance | permeability of the light of wavelength 400nm were measured about the produced transparent conductive thin film by the method similar to Examples 1-7. Table 3 shows the measurement results.

(Comparative Examples 10 and 11)
In Comparative Example 10, a transparent conductive thin film made of ITO (In ₂ O ₃ -10% by mass SnO ₂ ), which is a well-known material, was prepared by a well-known method, and the transparent thin film was formed by the same method as in Examples 1 to 7. The conductive thin film was measured for specific resistance, surface roughness Ra, and light transmittance at a wavelength of 400 nm. Table 3 shows the measurement results.

In Comparative Example 11, a transparent conductive thin film made of IZO (In ₂ O ₃ -10 mass% ZnO) proposed in Patent Document 3 was prepared by a known method, and the same method as in Examples 1 to 7 was used. The transparent conductive thin film was measured for specific resistance, surface roughness Ra, and light transmittance at a wavelength of 400 nm. Table 3 shows the measurement results.

As can be seen from Table 3, in the oxide sintered body according to Comparative Example 8, the contents of tungsten, zinc, and germanium are all below the lower limit of the range of the present invention. For this reason, the characteristics of the obtained transparent conductive thin film are large, such as a specific resistance of 15.1 × 10 ⁻⁴ Ωcm, and a surface roughness Ra of 1.8 nm, which is inferior in smoothness.

In the oxide sintered body according to Comparative Example 9, the contents of tungsten, zinc, and germanium all exceed the upper limit of the range of the present invention. Therefore, the characteristics of the obtained transparent conductive thin film are 1.1 nm for the surface roughness Ra, 0.7% with respect to the film thickness, and less than 1%, but 18% for the specific resistance. .2 × 10 ⁻⁴ Ωcm, and the transmittance of light with a wavelength of 400 nm is as small as 60%.

The oxide sintered body according to Comparative Example 10 is a transparent conductive thin film made of ITO (In ₂ O ₃ -10 mass% SnO ₂ ), which is a well-known material, and the composition is an oxide sintered body according to the present invention. Is different. For this reason, the characteristics of the obtained transparent conductive thin film have a large specific resistance of 6.5 × 10 ⁻⁴ Ωcm and a surface roughness Ra of 2.5 nm, which is inferior in smoothness.

The oxide sintered body according to Comparative Example 11 is a transparent conductive thin film made of IZO (In ₂ O ₃ -10% by mass ZnO) proposed in Patent Document 3, and the composition is an oxide according to the present invention. Different from sintered body. For this reason, although the characteristic of the obtained transparent conductive thin film has favorable specific resistance and surface roughness Ra, the transmittance | permeability of light with a wavelength of 400 nm is as small as 61%.

[2. Experimental example investigating the effect of sintered density on arcing and nodule generation]
(Examples 8-11, Comparative Examples 12-15)
In the manufacturing conditions of Example 2, the temperature at the time of sintering the molded body obtained by cold isostatic pressing was set to 1400 ° C., the sintering time was varied from 1 to 30 hours, and the other manufacturing conditions were as in Example 2. Similar to the production conditions, oxide sintered bodies having various sintered densities were produced. As in Example 2, the composition was W / In atomic ratio = 0.007, Zn / In atomic ratio = 0.020, Ge / In atomic ratio = 0.014, and the sintered density was 5. It became 1-7.0g / cm < ³ >. When the average value of 100 crystal grain sizes in the oxide sintered body was determined from observation of the fracture surface of the oxide sintered body by a scanning electron microscope, any one of Examples 8 to 11 and Comparative Examples 12 to 15 was obtained. The average value of the crystal grain size was 7 to 9 μm.

Next, the sputtering target using the oxide sintered bodies according to Examples 8 to 11 and Comparative Examples 12 to 15 was attached to the nonmagnetic target cathode of the direct current magnetron sputtering apparatus, and film formation was performed by the sputtering method. The distance between the target substrates was 80 mm, and 4% of O ₂ gas was introduced into Ar gas having a purity of 99.9999% by mass, and the gas pressure was set to 0.8 Pa to generate DC plasma. The direct current power was increased from 150 W to 800 W in increments of 50 W, each power was deposited for 1 hour, and the direct current power when cracks began to enter the sputtering target was determined. The results are shown in Table 4.

As shown in Table 4, if the sintered body density of the sputtering target is 6.5 g / cm ³ or more (Examples 8 to 11), cracks do not occur even when DC power is applied up to 800 W. The film could be stably formed. In order to increase the productivity of the transparent conductive thin film, it is necessary to apply as high an electric power as possible to the target and to produce the film at a high film formation rate. However, the sintered body density is 6.5 g / cm ³ or more. In the case of a sputtering target, it is considered that a film can be formed by applying high power to the target.

On the other hand, when the sintered compact density of the sputtering target was less than 6.5 g / cm ³ (Comparative Examples 12 to 15), cracks occurred in the sputtering target before increasing the DC power to 800 W. . It was observed that nodule was generated in the crack part when the crack was generated in the sputtering target. Further, when the film was formed continuously after the occurrence of cracks, a decrease in the film formation rate, the occurrence of arcing, and an increase in the specific resistance of the obtained film were observed. Therefore, a sputtering target having a sintered body density of less than 6.5 g / cm ³ (Comparative Examples 12 to 15) cannot be used for manufacturing a transparent conductive thin film.

  In addition, Examples 8-11 and Comparative Examples 12-15 have the same composition as Example 2 (W / In atomic ratio = 0.007, Zn / In atomic ratio = 0.020, Ge / In atomic number The ratio was measured for a sputtering target having a ratio = 0.014). Even when an oxide sintered body having the same composition as in Example 1 and Examples 3 to 8 was used, the same result was obtained. .

  The transparent conductive thin film according to the present invention can be used not only as an organic EL element but also as an inorganic EL element, a transparent electrode for LCD (Liquid Crystal Display), electronic paper, and a touch panel.

Claims (11)

  It consists of indium, tungsten, zinc, germanium, tungsten is a W / In atomic ratio of 0.004-0.023, zinc is a Zn / In atomic ratio of 0.004-0.032, germanium is An oxide sintered body containing a Ge / In atomic ratio of 0.004 to 0.021 and having a specific resistance of 1 kΩcm or less. 2. The oxide sintered body according to claim 1, wherein the specific resistance is 1 × 10 ⁻¹ Ωcm or less.   3. The oxide firing according to claim 1, wherein the main phase is an indium oxide crystal phase having a bixbyite structure and substantially does not include a tungsten oxide crystal phase, a zinc oxide crystal phase, or a germanium oxide crystal phase. Union. 4. The oxide sintered body according to claim 1, wherein the sintered density is 6.5 g / cm ³ or more.   The sputtering target which processed the oxide sintered compact in any one of Claims 1-4 into the flat form, and bonded together to the metal plate for cooling. It consists of indium, tungsten, zinc, germanium, tungsten is a W / In atomic ratio of 0.004-0.023, zinc is a Zn / In atomic ratio of 0.004-0.032, germanium is A transparent conductive material comprising a Ge / In atomic ratio of 0.004 to 0.021, a specific resistance of 5 × 10 ⁻⁴ Ωcm or less, and an amorphous film. Thin film.   7. The transparent conductive thin film according to claim 6, wherein the surface roughness (Ra) is less than 1% with respect to the film thickness.   The transparent conductive thin film according to claim 6 or 7, wherein the transmittance of light having a wavelength of 400 nm is 65% or more.   A top emission type organic EL device, wherein the transparent conductive thin film according to claim 6 is used as a cathode.   A flexible organic EL device comprising the transparent conductive thin film according to any one of claims 6 to 8 formed on a resin film, and the transparent conductive thin film being used as a cathode and / or an anode. In ₂ O ₃ powder, WO ₃ powder, ZnO powder and GeO ₂ powder having an average particle diameter of 1 μm or less, tungsten is a ratio of 0.004 to 0.023 in terms of W / In atomic ratio, and zinc is a Zn / In atom. A step of preparing a mixed powder by mixing and mixing germanium so as to have a ratio of 0.004 to 0.032 in terms of the number ratio and a ratio of 0.004 to 0.021 in terms of the Ge / In atomic ratio. The obtained mixed powder is granulated to an average particle size of 20 to 150 μm to obtain a granulated powder, and a pressure of ² to 5 ton / cm ² is applied to the obtained granulated powder by a cold isostatic press. The step of obtaining a molded body and the above molding at a temperature of 1200 to 1500 ° C. and a time of 10 to 40 hours while introducing oxygen into the sintering furnace at a rate of 50 to 250 L / min per 0.1 m ^{3 of} the furnace volume. And sintering the body to form an oxide sintered body. Method for manufacturing the oxide sintered body according to claim.