JP6637948B2 - IZO target and method for manufacturing the same - Google Patents

Description

  The present invention relates to an indium zinc oxide (IZO) target and a method for manufacturing the same. Further, the present invention relates to an indium zinc oxide (IZO) target and a film formation method using the same.

Sputtering targets made of a sintered body of indium zinc oxide (In ₂ O ₃ -ZnO: generally called IZO) are widely used for many electronic components such as a transparent conductive thin film of a liquid crystal display and a gas sensor. Have been. The IZO film has advantages such as a higher etching rate, less generation of particles, and an amorphous film than an ITO film which is a typical transparent conductive thin film. However, IZO has a problem that the bulk resistivity is higher than that of ITO and that the film resistance varies. For this reason, especially in the DC magnetron sputtering process, the discharge during the sputtering may become unstable.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 6-234565) discloses that a transparent conductive film having excellent conductivity can be obtained by doping IZO with an element having a valence of three or more positive valences, such as Sn. ing.

  Patent Document 2 (International Publication No. 2000/68456) provides an IZO sputtering target for forming a transparent conductive film capable of lowering the bulk resistance value by adding a very small amount of Sn and stably discharging in sputtering. The invention aiming at this is described. Specifically, there is described an IZO sputtering target for forming a transparent conductive film mainly containing In and Zn oxides, which contains 100 to 2000 ppm of Sn.

  Patent Literature 3 (Japanese Patent Application Laid-Open No. 2017-014534) describes that in the sputtering target described in Patent Literature 2, color unevenness easily occurs on the target surface, and it was necessary to polish the surface until the color unevenness disappeared. I have. Then, in order to eliminate color unevenness, it has been proposed that the content of Sn is set to be more than 2,000 ppm and 20,000 ppm or less (more than 2,000 ppm to 20,000 ppm).

JP-A-6-234565 International Publication No. 2000/68456 JP-A-2017-014534

  However, it has been found that when the IZO targets described in Patent Documents 1 to 3 are used, the film resistance of the sputtered film tends to depend on the oxygen concentration in the atmosphere during sputtering. More specifically, it has been found that when sputtering is performed using these IZO targets, the film resistance of the sputtered film tends to significantly increase as the oxygen concentration in the atmosphere during sputtering decreases. It was also found that the addition of Sn does not always reduce the bulk resistance. Depending on the application, sputtering under a low oxygen concentration and further under an oxygen-free condition is required. Therefore, it is desirable that the dependency of the film resistance on the oxygen concentration can be reduced. In particular, since organic EL, which has attracted attention in recent years, is sensitive to oxygen, it is necessary to form a film without introducing oxygen. Therefore, it is advantageous to obtain a sputtered film having a low film resistance even under a low oxygen concentration. .

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an IZO target in which the film resistance of a sputtered film is hardly affected by the oxygen concentration during sputtering. Another object of the present invention is to provide a method for manufacturing such an IZO target. Another object of the present invention is to provide a film formation method using the IZO target according to the present invention.

  The present inventors have conducted intensive studies to solve the above-mentioned problems, and found that an IZO target having a sintered body structure in which Sn segregated grains containing In and Sn are dispersed in a parent phase of IZO is effective. . Such an IZO target can be manufactured by adding ITO powder to the raw material powder of the IZO target. When a film was formed by using an IZO target having the structure as a sputtering target, it was found that the film resistivity was hardly changed by a change in oxygen concentration in a sputtering atmosphere. Although the oxygen concentration during sputtering often differs depending on the application to be used, the fact that the film resistivity hardly depends on the oxygen concentration in the sputtering atmosphere is advantageous in obtaining a sputtered film of stable quality.

  In one aspect of the present invention, which has been completed on the basis of the above findings, In / Sn and Zn are represented by atomic ratios of Zn / (In + Sn + Zn) = 0.030 to 0.250 and Sn / (In + Sn + Zn) = 0.002 to It is an IZO target having a total composition of 0.080 and a balance of O and unavoidable impurities, and a particle diameter of 200 nm or more containing In, Sn and O specified by FE-EPMA. This is an IZO target having a target structure in which Sn segregated grains are dispersed.

  In one embodiment, the IZO target according to the present invention contains In, Sn, and Zn in an atomic ratio so as to satisfy Sn / (In + Sn + Zn) = 0.10 to 0.030.

  In another embodiment, the IZO target according to the present invention contains In, Sn, and Zn so that the atomic ratio satisfies Zn / (In + Sn + Zn) = 0.040 to 0.200.

In still another embodiment of the IZO target according to the present invention, Sn segregated grains having a particle diameter of 200 nm or more are present in the target structure at a number density of 0.003 / μm ² or more.

In still another practical embodiment of the IZO target according to the present invention, Sn segregated grains having a particle diameter of 1000 nm or more are present in the target structure at a number density of 0.0003 / μm ² or more.

  In still another embodiment, the IZO target according to the present invention has a relative density of 90% or more.

  In still another embodiment, the IZO target according to the present invention has a bulk resistance of 0.3 mΩ · cm or more and less than 7.0 mΩ · cm.

  In still another embodiment of the IZO target according to the present invention, the Sn segregated particles have an average particle size of 450 nm or more and 9000 nm or less.

In another embodiment of the IZO target according to the present invention, Sn segregated grains having a particle diameter of 10,000 nm or more are present in the target structure at a number density of 0.0002 / μm ² or less.

  In still another embodiment, the IZO target according to the present invention further contains B so that the atomic ratio satisfies B / (In + Sn + Zn + B) = 0.036 or less.

In another aspect, the present invention is a method for producing an IZO target according to the present invention, comprising a step of sintering a mixture of ITO powder, In ₂ O ₃ powder, and ZnO powder.

  In one embodiment of the method for manufacturing an IZO target according to the present invention, each particle constituting the ITO powder contains In and Sn so that the atomic ratio satisfies 6 ≦ In / Sn ≦ 36.

In still another aspect, the present invention is a method for producing an IZO target according to the present invention, comprising a step of sintering a mixture of ITO powder, In ₂ O ₃ powder, ZnO powder, and B ₂ O ₃ powder.

  In another aspect, the present invention is a film forming method including a step of performing sputtering using the IZO target according to the present invention.

  In one embodiment of the film forming method according to the present invention, the step of performing sputtering is performed in an atmosphere gas having an oxygen concentration of 0.1 vol% or less.

  The IZO target according to the present invention has a characteristic that a change in film resistance obtained with respect to a change in oxygen concentration in a sputtering atmosphere is small. Therefore, a sputtered film of stable quality can be obtained regardless of the oxygen concentration. INDUSTRIAL APPLICABILITY The present invention is particularly useful for applications requiring film formation without introducing oxygen, such as organic EL.

7 shows an element mapping image of Example 3. 7 shows an element mapping image of Comparative Example 2. 8 shows an element mapping image of the Sn surface analysis result of Example 3 after smoothing. 13 shows an element mapping image after binarization of the Sn surface analysis result of Example 3.

(1. Overall composition)
In one embodiment of the IZO target according to the present invention, the atomic ratio of In, Sn and Zn is Zn / (In + Sn + Zn) = 0.030 to 0.250, Sn / (In + Sn + Zn) = 0.002 to 0.080. Is contained so as to satisfy the condition, and the balance has an entire composition composed of O and unavoidable impurities. The overall composition refers to the overall composition of the sintered body including Sn segregated grains dispersed in the structure of the sintered body.

  The reason why Zn / (In + Sn + Zn) is set to 0.030 or more is that by setting the amount of Zn to an appropriate range, a sputtered film having good conductivity can be obtained. Zn / (In + Sn + Zn) is preferably at least 0.030, and more preferably at least 0.040. Further, the reason why Zn / (In + Sn + Zn) is set to 0.250 or less is also that if the amount of Zn is too large, the conductivity of the sputtered film is deteriorated. Zn / (In + Sn + Zn) is preferably 0.250 or less, more preferably 0.200 or less.

  The reason why Sn / (In + Sn + Zn) is 0.002 or more is to significantly reduce the bulk resistance and significantly suppress the fluctuation of the film resistance due to the change in the oxygen concentration in the sputtering atmosphere. Sn / (In + Sn + Zn) is preferably at least 0.002, more preferably at least 0.005, and even more preferably at least 0.010. Further, the reason why Sn / (In + Sn + Zn) is set to 0.080 or less is that if added more, the density of the sintered body becomes too low, so that the bulk resistance is likely to be increased, and adverse effects on sputtering such as increase of particles are caused. This is because there is concern. Sn / (In + Sn + Zn) is preferably at most 0.065, more preferably at most 0.060, even more preferably at most 0.030.

  The unavoidable impurities are present in the raw material or inevitably mixed in the manufacturing process, and are originally unnecessary, but are trace amounts and do not significantly affect the characteristics of the sintered body. Therefore, it is an allowable impurity.

In one embodiment, the IZO target according to the present invention further contains B such that B / (In + Sn + Zn + B) has an atomic ratio of 0.036 or less. B is derived, for example, from B ₂ O ₃ . Since B ₂ O ₃ has a low melting point of 450 ° C., a liquid phase is generated in the sintered body during sintering, so that the sinterability can be improved and the density can be increased. B / (In + Sn + Zn + B) is preferably 0.004 or more in order to exert the effect of improving sinterability in an advantageous manner, but if added too much, the bulk resistance greatly increases. Therefore, B / (In + Sn + Zn + B) = 0.036 or less It is preferred that

(2. Sn segregated grains)
In one embodiment, the IZO target according to the present invention is mainly composed of indium oxide (In ₂ O ₃ ) and a composite oxide of indium and zinc (Zn _k In ₂ O _{k + 3} , k = 2 to 7 (k is an integer)). Has a sintered body structure in which Sn segregated particles containing In, Sn, and O and having a particle size of 200 nm or more are dispersed. The parent phase may contain one or both oxides of indium oxide and zinc oxide. When a sputtering target having a sintered body structure in which Sn segregated particles having a particle diameter of 200 nm or more are dispersed in a matrix is used, the dependency of the sputtered film on the oxygen concentration in the sputtering atmosphere is reduced. For this reason, even if the oxygen concentration in the sputtering atmosphere changes depending on the application, a sputtered film having a stable film resistivity can be obtained.

In order to significantly exhibit the effect of improving conductivity and the effect of suppressing the change in film resistance due to the change in oxygen concentration in the sputtering atmosphere, Sn segregated grains having a particle diameter of 200 nm or more are sintered at a number density of 0.003 / μm ² or more. It is preferably present in the body structure, preferably present in the sintered body structure at a number density of 0.0045 / μm ² or more, and preferably present in the body structure at a number density of 0.01 / μm ² or more. More preferably, it is present in the sintered body structure. However, when the number density of Sn segregated particles having a particle diameter of 200 nm or more is excessive, the Sn concentration of each Sn segregated particle decreases when compared with the case where the atomic concentration of Sn in the target is the same. There is a possibility that the state becomes close to a state where Sn is diffused by being added as SnO ₂ , and it is difficult to obtain the original sputtering characteristics. Therefore, it is preferable that the Sn segregated particles having a particle diameter of 200 nm or more exist in the sintered body structure at a number density of 0.1 / μm ² or less, and the sintered body has a number density of 0.08 / μm ² or less. It is more preferably present in the structure, and even more preferably present in the structure of the sintered body at a number density of 0.04 / μm ² or less.

Further, in order to significantly exhibit the effect of improving the conductivity and the effect of suppressing the change in the film resistance due to the change in the oxygen concentration in the sputtering atmosphere, the Sn segregated particles having a particle diameter of 1000 nm or more have a number density of 0.0003 / μm ² or more. In the sintered body structure, it is preferable to be present in the sintered body structure with a number density of 0.001 pieces / μm ² or more, and it is preferable that the number density is 0.003 pieces / μm ² or more. More preferably, it exists in the sintered body structure at a number density. However, when the number density of the Sn segregated grains having a particle diameter of 1000 nm or more is excessive, sinterability is reduced, the density of the sintered body is reduced, the bulk resistance is increased, and there is a concern that particles may be caused. Therefore, 0.03 is the particle size 1000nm or more Sn polarized析粒pieces / [mu] m is preferably present in the sintered body structure ² in the following number density sintered body 0.026 pieces / [mu] m ² or less of number density It is more preferably present in the structure, and even more preferably present in the structure of the sintered body at a number density of 0.02 / μm ² or less.

Further, since excessively large Sn segregated particles may cause arcing, Sn segregated particles having a particle diameter of 10,000 nm or more are present in the sintered body structure at a number density of 0.0002 / μm ² or less. Preferably, it is present in the structure of the sintered body at a number density of 0.0001 / μm ² or less, and is present in the structure of the sintered body at a number density of 0.00005 / μm ² or less. Is more preferable.

  The average particle size of the Sn segregated particles is preferably 450 nm or more, more preferably 800 nm or more, and more preferably 900 nm or more, in order to significantly exert the effect of suppressing the change in the film resistance with respect to the oxygen concentration change in the sputtering atmosphere. Is even more preferred. If the average size of the Sn segregated grains is too large, the bulk resistance increases, and there is a possibility of causing arcing. Therefore, the average size is preferably 9000 nm or less, more preferably 6000 nm or less, and 3,000 nm or less. Is even more preferred.

In the present invention, the particle size and number density of Sn segregated particles are measured by the following methods. An FE-EPMA (field emission electron probe microanalyzer) is used as a measuring instrument. In the examples, JXA-8500F (FE-EPMA manufactured by JEOL Ltd.) was used.
Measurement sample: The sputtering target is cut perpendicularly to the sputtering surface, the section is mirror-polished, and a half-thick portion is observed.
Observation method: Using the surface analysis function attached to FE-EPMA, surface analysis is performed under the following conditions.
・ Acceleration voltage: 15.0 kV
・ Irradiation current: 1.0 to 2.5 × 10 ^-7 A
-Magnification: 2000 times-Measurement method: Beam scan-Beam diameter (μm): 0
-Measurement time (ms): 5
・ Integration: 1
Measurement elements and spectral crystals: In (PETH), Zn (LIFH), Sn (PETH), O (LDE1)
・ Measurement visual field (per visual field): 50 μm × 50 μm
・ Pixel: 256 × 256

When the surface analysis is performed by the above procedure and the element mapping image is displayed in gray scale, the measurement data of FIG. 1 (Example 3) and FIG. 2 (Comparative Example 2) are obtained. Although Lv can be manually operated, Lv that is automatically calculated mechanically is used as it is. In Example 3, a portion where Sn is segregated in the form of coarse particles (the lightest part in the element mapping image of Sn) is seen, whereas in Comparative Example 4, coarse segregation is not seen. In Comparative Example 4, Sn segregated grains were not observed because Sn diffused into In ₂ O ₃ grains when SnO ₂ powder was used as a raw material, resulting in a concentration below the lower detection limit of FE-EPMA. Conceivable. On the other hand, although the present invention is not intended to be limited, it is expected that Sn is not diffused when coarse ITO powder is added, but the driving force for diffusion depends on the concentration gradient. It is considered that between the SnO ₂ powder and the ITO powder, the Sn concentration of the ITO powder is lower, so that the Sn is less likely to diffuse into the surroundings of the ITO powder.

  From the obtained gray scale image of Sn, the particle diameter of each Sn segregated particle and the number density of the Sn segregated particle are measured using a particle measurement function. The following is an execution procedure using analysis software attached to JXA-8500F, but similar image processing software may be used. First, a smoothing filter is executed from the filter item. FIG. 3 shows an example of the third embodiment. Next, binarization is performed. The threshold value in the binarization is manually set so that the shape of the Sn segregated grains during the surface analysis can be captured without excess or deficiency. , A threshold is set. FIG. 4 shows an example of the third embodiment.

Thereafter, labeling of the binarized image is performed. In this software, the selection items of the labeling process are “3-connected” and “the outer peripheral particles are not labeled”. Subsequently, the labeling image is measured, and the circle equivalent diameter of each Sn segregated grain is mechanically calculated. The circle equivalent diameter of each Sn polarized析粒as the particle size of the Sn-polarized析粒, particle size 200nm or more, 1000 nm or more and 10000nm more number of particles was counted, respectively, determine the number of particles present in 2500 [mu] m ² is measured field of view, the number Is divided by the measurement visual field area to obtain a number density (pieces / μm ² ). Further, the average particle size of the Sn segregated particles is determined from the circle equivalent diameter of each Sn segregated particle calculated mechanically. The above procedure is performed in five or more measurement visual fields, and the average value is used as the measurement result.

(3. Bulk resistivity)
The bulk resistivity of the IZO target according to one embodiment of the present invention can be significantly lower than that of the conventional IZO target because the Sn segregated grains are dispersed in the structure. Specifically, the IZO target according to the present invention, in one embodiment, can have a bulk resistivity of less than 7.0 mΩ · cm. The bulk resistivity of the IZO target according to the present invention is preferably 3.0 mΩ · cm or less, more preferably 2.0 mΩ · cm or less. Although the lower limit of the bulk resistivity is not limited, the bulk resistivity of the IZO target according to the present invention is usually 0.3 mΩ · cm or more, and typically 0.5 mΩ · cm, due to the material limit of IZO. That is all.

In the present invention, the bulk resistivity of the target is measured by a four-probe method using a resistivity meter. Since there is an altered layer with a small amount of Zn on the surface of the sintered body, the sintered body is ground by 0.5 mm and finished to # 400 with abrasive paper. In the examples, the measurement was performed with the following apparatus.
Resistivity measuring device: Model FELL-TC-100-SB- # 5 + (manufactured by NPS Corporation)
Measurement jig RG-5

(4. Relative density)
It is preferable that the relative density of the target is high in order to perform stable sputtering with little arcing. In one embodiment, the IZO target according to the present invention has a relative density of 90% or more. The relative density is preferably at least 92%, more preferably at least 95%, even more preferably at least 96%, for example, 90 to 99%. The relative density is determined by the ratio of the Archimedes density to the reference density determined by the composition.

Here, the reference density is obtained by performing a component analysis of the sputtering target and converting the atomic ratio (at%) of In, Zn, Sn, and B with respect to a total of 100 at% of In, Zn, Sn, and B obtained by the analysis. It is calculated using the oxide weight ratio (% by weight) obtained as described above and the elemental densities of In ₂ O ₃ , ZnO, SnO ₂ and B ₂ O ₃ . Specifically, the simplex density of In ₂ O ₃ is 7.18 (g / cm ³ ), the simplex density of ZnO is 5.61 (g / cm ³ ), and the simplex density of SnO ₂ is 6.95 (g / cm ³ ). cm ³ ), the density of B ₂ O ₃ alone as 1.85, the weight ratio of In ₂ O ₃ as W _In2O3 (weight%), the weight ratio of _ZnO as W _ZnO (weight%), and the weight ratio of SnO ₂ as W _SnO2 (% by weight), the weight ratio of B ₂ O ₃ as W _{B2 O3,} the reference density ^{(g / cm 3) = (} 7.18 × W In2O3 + 5.61 × W ZnO + 6.95 × W SnO2 + 1.85 × _WB2O3 ) / 100. However, when B is not added, the calculation is performed with _{WB2O3 set} to 0.

This relative density is based on a reference density calculated on the assumption that the sputtering target is a mixture of In ₂ O ₃ , ZnO and SnO ₂ , and the true value of the density of the target sputtering target is Since the density may be higher than the above-mentioned reference density, the relative density here may exceed 100%.

(5. Manufacturing method)
Next, a preferred example of the method for manufacturing an IZO target according to the present invention will be described step by step.

(5-1 Preparation of ITO powder)
First, a powder (ITO powder) of an oxide sintered body composed of Sn, In, O and unavoidable impurities is prepared. The ITO powder can be obtained by producing an ITO sintered body by a known method and pulverizing it. Alternatively, in order to facilitate the pulverization, the mixed powder of In ₂ O ₃ and SnO ₂ may be sintered (called calcination) and then pulverized.

  ITO powder is finally the raw material of the Sn segregated particles described above in the sintered body. Regarding the composition of each particle constituting the ITO powder, the atomic ratio of In to Sn is preferably 6 ≦ In / Sn, more preferably 7 ≦ In / Sn, for improving the conductivity. , 9 ≦ In / Sn. In addition, since the conductivity of the ITO powder decreases even if the amount of Sn is too small, the atomic ratio of In to Sn is preferably In / Sn ≦ 36, and more preferably In / Sn ≦ 25. It is still more preferable that In / Sn ≦ 15.

The ITO sintered body can be manufactured by pulverizing and mixing SnO ₂ powder and In ₂ O ₃ powder at a predetermined compounding ratio and then sintering. It is preferable to use SnO ₂ powder and In ₂ O ₃ powder as raw materials having a high purity, for example, a purity of 99% by mass or more, and more preferably 99.9% by mass or more from the viewpoint of preventing unexpected defects. . The average particle size of the raw material powder can be, for example, 0.5 μm to 2.5 μm. Here, when referring to the average particle diameter of the powder in this specification, it refers to the median diameter (D50) when the cumulative distribution of the particle diameter is obtained on a volume basis by a laser diffraction / scattering method. There are various pulverization and mixing methods, and wet pulverization and mixing using a wet medium stirring mill such as a bead mill can be suitably used. In the case of wet pulverization and mixing, the uniformity of the slurry can be improved by adding a dispersant as appropriate. Other methods may be used as long as the purpose of uniform mixing of the raw materials can be realized.

  Press molding is performed on the mixed powder obtained after the pulverization and mixing. The press molding is performed by filling the mixed powder into a mold and maintaining a pressure of, for example, 30 to 60 MPa for 1 to 3 minutes. Prior to press molding, granulation may be performed as necessary. By improving the fluidity of the powder by granulation, the powder can be uniformly filled in a mold at the time of press molding in the next step, and a homogeneous molded body can be obtained. There are various methods for granulation. One method for obtaining granulated powder suitable for press molding is a method using a spray-type drying device (spray dryer). Further, by adding a binder such as polyvinyl alcohol (PVA) to the slurry and including the binder in the granulated powder, the strength of the molded body can be improved. In addition, cold isostatic pressing (CIP) may be performed after press molding.

  The sintering of the compact can be performed in an oxygen atmosphere using an electric furnace. It is preferable that the sintering is performed at a sintering temperature of 1300 to 1600 ° C. In order to obtain a high-density sintered body, the sintering temperature is preferably 1300 ° C. or higher. In addition, the sintering temperature is preferably 1600 ° C. or less from the viewpoint of preventing a reduction in sintering density and a composition deviation due to volatilization of tin oxide. When the molded body contains a binder, a binder removal step may be introduced as needed during the heating up to the sintering temperature.

  The holding time at the sintering temperature is appropriately selected depending on the size of the compact, but generally less than 5 hours, the sintering does not proceed sufficiently, the density of the sintered body does not become sufficiently high, or the sintered body is warped. Or If the holding time exceeds 30 hours, unnecessary energy and time-consuming waste occurs, which is not preferable in production.

By grinding the obtained ITO sintered body, ITO powder is obtained. Examples of the pulverizing method include a combination of a pestle and a mortar, a hammer mill, and a pod mill. Among them, a pod mill is preferable from the viewpoint of productivity. Further, it is more preferable to further reduce the size by a wet bead mill or the like. To remove coarse particles of the ITO powder, sieving is performed. For example, a sieve having an opening of 150 μm or less can be used. The average particle size (D50) of the ITO powder after sieving is preferably 10 μm or less, more preferably 5 μm or less. The average particle size of the ITO powder before mixing with the In ₂ O ₃ powder and ZnO powder is preferably 0.4 μm or more, more preferably 0.9 μm or more.

(5-2 Production of IZO target)
The IZO target according to the present invention is obtained by pulverizing and mixing In ₂ O ₃ powder, ZnO powder, and the above-obtained ITO powder such that Zn / (In + Sn + Zn) and Sn / (In + Sn + Zn) have a predetermined atomic ratio. It can be manufactured later by sintering. Further, B ₂ O ₃ powder may be added as needed. Sintering may be performed after calcination. A specific procedure will be described as an example. First, In ₂ O ₃ powder, ZnO powder, and, if necessary, B ₂ O ₃ powder are weighed at a predetermined mixing ratio, and then finely pulverized and mixed. In order to mix the ITO powder uniformly without pulverization as much as possible, 5 to 10 minutes before stopping the pulverization and mixing of the In ₂ O ₃ powder, ZnO powder and, if necessary, the B ₂ O ₃ powder, It is preferable to mix as it is. The raw material In ₂ O ₃ powder, ZnO powder, and B ₂ O ₃ powder to be added as needed are of high purity, for example, those having a purity of 99% by mass or more, and more preferably 99.9% by mass or more. This is preferable from the viewpoint of preventing unexpected defects. Examples of the mixing method include a method of performing wet pulverization and mixing using a wet medium stirring mill such as a bead mill. In the case of wet pulverization and mixing, the uniformity of the slurry can be increased by adding a dispersant as appropriate. Other methods may be used as long as the purpose of uniform mixing of the raw materials can be realized.

  In order to improve the sinterability, the mixed powder after the fine pulverization and mixing preferably has an average particle size of 2 μm or less, more preferably 1.5 μm or less. The average particle size of the mixed powder after the fine pulverization and mixing is preferably 0.3 μm or more, more preferably 0.5 μm or more, since excessive pulverization increases the amount of contamination from beads and the like. The above is the average particle size including the ITO powder.

  Press molding is performed on the mixed powder after the pulverization and mixing. The press molding is performed by filling the mixed powder into a mold and maintaining a pressure of, for example, 30 to 60 MPa for 1 to 3 minutes. The compact obtained by press molding may be further pressed at 140 to 200 MPa by a hydrostatic press (CIP). Thereby, a more uniform and high-density molded article can be obtained.

  Prior to press molding, granulation may be performed as necessary. By improving the fluidity of the powder by granulation, the powder can be uniformly filled in a mold at the time of press molding in the next step, and a homogeneous molded body can be obtained. There are various methods for granulation. One method for obtaining granulated powder suitable for press molding is a method using a spray-type drying device (spray dryer). Further, by adding a binder such as polyvinyl alcohol (PVA) to the slurry and including the binder in the granulated powder, the strength of the molded body can be improved.

  The sintering of the compact can be performed in an oxygen atmosphere using an electric furnace. The sintering temperature is preferably set to 1300 to 1500 ° C. for sintering. In order to obtain a high-density sintered body, the sintering temperature is preferably 1300 ° C. or higher. Further, the sintering temperature is preferably 1500 ° C. or less from the viewpoint of preventing a reduction in sintering density and a composition deviation due to volatilization of zinc oxide. When the molded body contains a binder, a binder removal step may be introduced as needed during the heating up to the sintering temperature.

  The holding time at the sintering temperature is appropriately selected depending on the size of the compact, but if it is shorter than 5 hours, the sintering does not proceed sufficiently, the density of the sintered body does not become sufficiently high, or the sintered body warps. I do. If the holding time exceeds 30 hours, unnecessary energy and time-consuming waste occurs, which is not preferable in production.

  The obtained IZO sintered body is processed into a desired shape by a processing machine such as a surface grinder, a cylindrical grinder, and a machining machine, whereby a sputtering target can be manufactured. There is no particular limitation on the shape of the sputtering target. For example, the shape may be a disk, a rectangle, a cylinder, or the like. The sputtering target may be used by bonding with a backing plate and a bonding material as needed.

(6. Film formation)
In one aspect, the present invention provides a film forming method including a step of performing sputtering using the IZO target according to the present invention. The IZO target according to the present invention has a characteristic that a change in film resistance obtained with respect to a change in oxygen concentration in a sputtering atmosphere is small. Therefore, using the IZO target according to the present invention makes it possible to obtain a sputtered film of stable quality regardless of the oxygen concentration. In one embodiment, the oxygen concentration in the atmosphere gas at the time of sputtering is 2 vol% or less. In another embodiment, the oxygen concentration in the atmosphere gas at the time of sputtering is 1 vol% or less. In yet another embodiment, the oxygen concentration in the atmosphere gas at the time of sputtering is 0.5 vol% or less. In yet another embodiment, the oxygen concentration in the atmosphere gas at the time of sputtering is 0.1 vol% or less. In yet another embodiment, the oxygen concentration in the atmosphere gas at the time of sputtering is 0 vol%. An atmosphere gas at the time of sputtering may be a mixed gas of Ar and oxygen.

  Hereinafter, Examples of the present invention are shown together with Comparative Examples, but these Examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention.

<1. Preparation of ITO powder>
SnO ₂ powder and In ₂ O ₃ powder and _{SnO 2: In 2 O 3 =} 10: 90 ( however, Example 16 SnO _2: In ₂ O ₃ = 15: 80, Example 17 SnO _2: an In ₂ O ₃ = 5: 95) and then wet-milled and mixed (using ZrO ₂ beads). Granulation was performed by adding polyvinyl alcohol (PVA) as a binder to the slurry obtained by the wet pulverization and mixing to obtain a granulated powder. The granulated powder was press-formed at Φ280 mm × 20 mmt at 30 MPa, and sintered at 1500 ° C. for 20 hours in an electric furnace in an oxygen atmosphere to produce an ITO sintered body. The obtained ITO sintered body was pulverized with a pestle and a mortar, pulverized with a pod mill, further finely pulverized with a ball mill, and sieved with a sieve having an opening of 150 μm to obtain ITO powder. The average particle size of the ITO powder was sieved and adjusted according to the test number.

<2. Production of sintered body>
In ₂ O ₃ powder, ZnO powder, SnO ₂ powder, and B ₂ O ₃ powder were prepared according to the test numbers described in Table 1-1. Next, these were pulverized and mixed by wet pulverization (using ZrO ₂ beads). Five minutes before the stop of the pulverization and mixing, the previously prepared ITO powder was added so that the metal atomic ratio finally becomes as shown in Table 1-1. The average particle size of the slurry (mixed powder) after the pulverization and mixing was in the range of 0.3 to 0.8 μm in each of the test examples. Granulation was performed by adding PVA to the slurry after the pulverization and mixing, and a granulated powder was obtained. However, in the test examples in which “calcination” is “present” in the table, In ₂ O ₃ powder, ZnO powder, and ITO powder were mixed such that the metal atomic ratios described in Table 1-1 were satisfied. Mix before pulverization, pre-sinter in air at 1300 ° C for 5 hours, crush the resulting mass with a pestle and mortar, and use a ball mill to reduce the average particle size to 0.3-0.8 μm. Wet pulverization. PVA was added to the obtained slurry and granulated to obtain granulated powder.

  Thereafter, in each test example, the granulated powder was press-molded at Φ280 mm × 20 mmt at 30 MPa, cold isostatically pressed at 140 MPa, and formed into a molded body. Sintered. In addition, as a result of analyzing the component composition of the sintered body, it was confirmed that the composition ratio was equivalent to the mixing ratio of the raw material powder.

  The average particle size of the powder refers to the median diameter (D50) when the cumulative distribution of the particle size is determined on a volume basis by a laser diffraction / scattering method using LA-960 manufactured by Horiba, Ltd.

<3. Average particle size of Sn segregated particles>
The average particle size of the Sn segregated particles dispersed in the structure of the sintered body according to each test example obtained by the above manufacturing method was measured by the method described above. The results are shown in Table 1-2.

<4. Number density of Sn segregated grains>
With respect to the sintered bodies according to the respective test examples obtained by the above manufacturing method, the number density of Sn segregated grains dispersed in the structure was measured by the method described above. The results are shown in Table 1-2.

<5. Bulk resistivity>
With respect to the sintered bodies according to the respective test examples obtained by the above-described production methods, the bulk resistivity was measured at room temperature by a four-probe method using the following apparatus.
Resistivity measuring device: Model FELL-TC-100-SB- # 5 + (manufactured by NPS Corporation)
Measuring jig: RG-5
The results are shown in Table 1-2.

<6. Relative density>
The densities of the sintered bodies according to the respective test examples obtained by the above-described production methods were measured by the Archimedes method, and the ratio (%) to the reference density determined by the composition was determined, and the relative density was determined.

<7. Sputtering test>
The sintered body according to each of the test examples obtained by the above-described manufacturing method was machined to finish a disk-shaped sputtering target having a diameter of 8 inches and a thickness of 5 mm. The cylindrical shape was finished by cylindrical grinding and lathing. Next, sputtering was performed using this sputtering target. The sputtering conditions were as follows. The sputtering test was performed twice while changing the oxygen concentration in the atmosphere. Note that heating of the substrate during sputtering and annealing after sputtering were not performed.
Sputter power: 1 W / cm ²
Gas pressure: 0.5 Pa (abs)
Atmosphere: (1) Ar containing 0 vol% oxygen: gas pressure 0.5 Pa (abs)
(2) Ar containing 2 vol% of oxygen: gas pressure 0.5 Pa (abs)
Film thickness: 1000Å
The film resistivity of the obtained sputtered film was measured by a four-probe method using a model FELL-TC-100-SB- # 5 + thin film resistivity meter manufactured by NPS Corporation. The results are shown in Table 1-2.

Comparative Examples 4 and 5 are examples in which neither SnO ₂ nor ITO was added to the raw material, and the film resistance varied greatly with changes in the oxygen concentration in the sputtering atmosphere.
Comparative Examples 1 to 3 are examples in which SnO ₂ was added to the raw material. The film resistance varied greatly with changes in the oxygen concentration in the sputtering atmosphere, and the bulk resistivity was also large. It was shown that the addition of SnO ₂ did not directly lead to a decrease in bulk resistance.
Examples 1 to 21 are examples in which ITO was added to the raw material. Since the composition and the size of the Sn segregated grains dispersed in the structure of the target were appropriate, the bulk resistivity was reduced. Further, there was little change in the film resistivity with respect to the change in the oxygen concentration in the sputtering atmosphere.
In Example 18, since the proportion of Sn in the entire composition of the target was large, the relative density was lower and the bulk resistivity was higher than in the other examples. In Example 19, since the average particle diameter of the Sn segregated particles dispersed in the structure of the target was large, the bulk resistivity was large as compared with the other examples.

Claims (15)

  In, Sn, and Zn are contained in atomic ratios such that Zn / (In + Sn + Zn) = 0.030 to 0.250 and Sn / (In + Sn + Zn) = 0.002 to 0.080, and the balance is O and inevitable. An IZO target having an overall composition composed of impurities and having a target structure in which Sn segregated grains having a particle diameter of 200 nm or more and containing In, Sn, and O specified by FE-EPMA are dispersed.   The IZO target according to claim 1, wherein In, Sn, and Zn are contained so as to satisfy Sn / (In + Sn + Zn) = 0.10 to 0.030 in atomic ratio.   3. The IZO target according to claim 1, wherein In, Sn, and Zn are contained in an atomic ratio such that Zn / (In + Sn + Zn) = 0.040 to 0.200 is satisfied. 4. The IZO target according to any one of claims 1 to 3, wherein Sn segregated particles having a particle size of 200 nm or more are present in the target structure at a number density of 0.003 / μm ² or more. The IZO target according to any one of claims 1 to 4, wherein Sn segregated particles having a particle diameter of 1000 nm or more are present in the target structure at a number density of 0.0003 / μm ² or more.   The IZO target according to any one of claims 1 to 5, wherein the relative density is 90% or more.   The IZO target according to claim 1, having a bulk resistance of 0.3 mΩ · cm or more and less than 7.0 mΩ · cm.   The IZO target according to any one of claims 1 to 7, wherein an average particle size of the Sn segregated particles is 450 nm or more and 9000 nm or less. The IZO target according to any one of claims 1 to 8, wherein Sn segregated particles having a particle diameter of 10,000 nm or more are present in the target structure at a number density of 0.0002 / μm ² or less.   The IZO target according to any one of claims 1 to 9, further containing B so as to satisfy B / (In + Sn + Zn + B) = 0.036 or less in atomic ratio. ITO powder, In ₂ O ₃ powder and IZO target manufacturing method according to any one of claims 1 to 10 the mixture comprising the step of sintering of ZnO powder.   The method for producing an IZO target according to claim 11, wherein each particle constituting the ITO powder contains In and Sn so that the atomic ratio satisfies 6 ≦ In / Sn ≦ 36. ITO powder, In ₂ O ₃ powder, IZO target manufacturing method according to claim 10 including the step of sintering a mixture of ZnO powder and B ₂ O ₃ powder.   A film forming method comprising a step of performing sputtering using the IZO target according to claim 1.   The method according to claim 14, wherein the sputtering is performed in an atmosphere gas having an oxygen concentration of 0.1 vol% or less.