TWI865891B - Oxide sintered body and its manufacturing method and sputtering target - Google Patents

Abstract

The oxide sintered body of the present invention contains tin, tantalum and niobium. The area ratio of the pores per unit area when observing the cross section of the oxide sintered body is 1% or less. The maximum circle equivalent diameter of the pores when observing the cross section of the oxide sintered body is 20 μm or less. The maximum Feret diameter of the pores when observing the cross section of the oxide sintered body is 50 μm or less. The relative density of the oxide sintered body measured based on the Archimedean method is preferably 99.6% or more. The bending strength of the oxide sintered body measured in accordance with JIS R1601 is preferably 180 MPa or more.

Description

Oxide sintered body and its manufacturing method and sputtering target

The present invention relates to an oxide sintered body and a method for manufacturing the same. In addition, the present invention relates to a sputtering target material including the oxide sintered body.

Tin oxide transparent conductive films are used in a wide range of applications, represented by display devices such as liquid crystal displays, plasma displays, and organic EL (Electro-Luminescence). Sputtering is known as one of the methods for forming tin oxide transparent conductive films. In the formation of conductive films using sputtering, if there are a large number of defects such as pinholes in the sputtering target, abnormal discharge will occur during sputtering, and particles will be generated during the sputtering process, and the target will crack or crack.

In order to prevent abnormal discharge from occurring during sputtering, the present applicant previously disclosed a method for manufacturing a sputtering target, which method comprises preparing an unsintered molded body having SnO ₂ as a main component and containing Nb ₂ O ₅ and Ta ₂ O ₅ , and sintering the molded body at 1550°C to 1650°C (see patent document 1). For the same purpose, the present applicant previously disclosed a sputtering target containing Ta ₂ O ₅ , Nb ₂ O ₅ , SnO ₂ as a remainder, and unavoidable impurities (see patent document 2). [Prior art document] [Patent document]

Patent document 1: Japanese Patent Publication No. 2007-131891 Patent document 2: Japanese Patent Publication No. 2008-248278

According to the technology described in Patent Documents 1 and 2, abnormal discharge and target cracking during the sputtering process can be suppressed. However, the performance of the display device using the tin oxide-based transparent conductive film is required to be further improved, and the tin oxide-based transparent conductive film is also required to be of higher quality. Therefore, the sputtering target used to manufacture the tin oxide-based transparent conductive film is also required to be of high quality with fewer abnormal discharge and target cracking during the sputtering process than before. Therefore, the present invention provides an oxide sintered body with fewer defects such as pinholes, and which is not prone to abnormal discharge and cracking when used as a sputtering target, and a method for manufacturing the same, as well as a sputtering target.

The present invention solves the above-mentioned problem by providing an oxide sintered body, which contains tin, tantalum and niobium. The area ratio of the pores per unit area when observing the cross section of the oxide sintered body is less than 1%.

Furthermore, the present invention provides a sputtering target comprising the above-mentioned oxide sintered body.

Furthermore, the present invention provides a method for manufacturing an oxide sintered body, The method comprises separately preparing a slurry of tin oxide, a slurry of tantalum oxide and a slurry of niobium oxide, Mixing the above slurries to prepare a mixed slurry, Applying a spray drying method to the above mixed slurry to produce a granulated product, Using the above granulated product to produce a molded body, Sintering the above molded body; The above slurry of tin oxide, the above slurry of tantalum oxide and the above slurry of niobium oxide each contain a dispersant in advance.

The present invention is described below based on a preferred embodiment. The present invention relates to an oxide sintered body and a sputtering target using the same. The oxide sintered body of the present invention is a sintered body of a plurality of metal oxides. Specifically, the oxide sintered body of the present invention contains tin element (hereinafter also referred to as "Sn"), tantalum element (hereinafter also referred to as "Ta"), and niobium element (hereinafter also referred to as "Nb") as metals. These metal elements exist in the sintered body in the form of oxides of each metal, or in the form of composite oxides of at least two metal elements selected from the three metal elements.

As described in the above-mentioned patent document 1, since _SnO2 is a difficult-to-sinter material, it has been difficult to produce a dense sintered body containing _SnO2 . Therefore, the sintered bodies containing _SnO2 known so far are prone to produce defective parts, namely pores. In contrast, one of the characteristics of the oxide sintered body of the present invention is that the existence of pores is greatly reduced. The pores are defective parts observed in the cross section of the oxide sintered body of the present invention. In this specification, the cross section of the oxide sintered body refers to the surface obtained by cutting the oxide sintered body by a prescribed method. The pores are open on the cross section and extend to the interior of the oxide sintered body. The pores include both through holes and bottomed holes. In this specification, the pore portion refers to a defect portion of a size confirmed to exist when a cross section of an oxide sintered body is observed with a microscope at a magnification of 200 times (observation field: 445.3 μm×634.6 μm).

The presence of pores in the oxide sintered body of the present invention is extremely low, that is, the area ratio of pores per unit area when observing the cross section of the oxide sintered body (hereinafter also referred to as "pore area ratio") is preferably 1% or less. Since the presence of pores is so low, the oxide sintered body of the present invention can effectively suppress abnormal discharge during sputtering when used as a sputtering target, for example. In addition, it can effectively prevent the generation of particles during sputtering and the cracking or cracking of the target. From the perspective of making these advantages more significant, the pore area ratio is preferably 0.9% or less, more preferably 0.8% or less, further preferably 0.7% or less, particularly preferably 0.6% or less, and particularly preferably 0.5% or less. The closer the value of the hole area ratio is to zero, the better. From this point of view, the hole area ratio is preferably more than 0% and less than 1%, more preferably 0.02% to 0.9%, further preferably 0.04% to 0.8%, further preferably 0.06% to 0.7%, particularly preferably 0.08% to 0.6%, and particularly preferably 0.1% to 0.5%. The method for determining the hole area ratio will be described in the embodiments described below. In addition, the method for setting the hole area ratio to a value below the above value is also described below.

One of the characteristics of the oxide sintered body of the present invention is that when the pores are observed in its cross section, the size of the pores is suppressed. Specifically, the maximum circular equivalent diameter of the pores when the cross section of the oxide sintered body is observed is extremely small, being 20 μm or less. By suppressing the size of the pores in this way, the oxide sintered body of the present invention can effectively suppress abnormal discharge during sputtering when used as a sputtering target, for example. Furthermore, it can effectively prevent the generation of particles during sputtering and the cracking or crazing of the target. From the viewpoint of making these advantages more significant, the maximum circular equivalent diameter of the pores is preferably 18 μm or less, more preferably 16 μm or less, further preferably 15 μm or less, particularly preferably 13 μm or less, and particularly preferably 12 μm or less. The closer the maximum circular equivalent diameter of the hole is to zero, the better. From this point of view, the maximum circular equivalent diameter of the hole is preferably greater than 0 μm and less than 20 μm, further preferably greater than 1 μm and less than 18 μm, more preferably greater than 2 μm and less than 16 μm, further preferably greater than 3 μm and less than 15 μm, particularly preferably greater than 4 μm and less than 13 μm, and particularly preferably greater than 5 μm and less than 12 μm. The method for determining the maximum circular equivalent diameter of the hole will be described in the embodiments described below. In addition, the method for setting the maximum circular equivalent diameter of the hole to less than the above value is also explained below.

In addition to the maximum circular equivalent diameter of the hole being less than the above value, the maximum Feret diameter of the hole of the oxide sintered body of the present invention is extremely small, less than 50 μm. The Feret diameter refers to the size of a rectangle circumscribed to the measurement object. By setting the maximum Feret diameter of the hole to less than the above value, the oxide sintered body of the present invention can effectively suppress abnormal discharge during sputtering when used as a sputtering target, for example. In addition, it can effectively prevent the generation of particles during sputtering and the cracking or cracking of the target. From the perspective of making these advantages more significant, the maximum Feret diameter of the hole is preferably 45 μm or less, more preferably 40 μm or less, further preferably 35 μm or less, particularly preferably 30 μm or less, particularly preferably 28 μm or less, and optimally 26 μm or less. The closer the maximum Feret diameter of the hole is to zero, the better. From this perspective, the maximum Feret diameter of the hole is preferably greater than 0 μm and less than 50 μm, further preferably 2 μm or more and 45 μm or less, more preferably 3 μm or more and 40 μm or less, further preferably 4 μm or more and 35 μm or less, particularly preferably 6 μm or more and 30 μm or less, particularly preferably 8 μm or more and 28 μm or less, and optimally 10 μm or more and 26 μm or less. The method for determining the maximum Feret diameter of the hole will be described in the following embodiments. In addition, the method for setting the maximum Feret diameter of the hole to a value below the above value will also be described below.

The oxide sintered body of the present invention preferably satisfies at least one of the above-mentioned (i) pore area ratio, (ii) maximum circle equivalent diameter, and (iii) maximum Feret diameter, and further preferably satisfies a combination of at least two of (i)-(iii), and more preferably satisfies all of (i)-(iii).

In addition to the above (i)-(iii), the oxide sintered body of the present invention is also characterized by a high relative density. Specifically, the relative density of the oxide sintered body of the present invention is preferably a high value of 99.6% or more. By showing such a high relative density, the oxide sintered body of the present invention is preferably used as a sputtering target and when sputtering is performed using the target, abnormal discharge during sputtering can be suppressed, so it is preferred. From this viewpoint, the relative density of the oxide sintered body of the present invention is preferably 99.8% or more, more preferably 100.0% or more, further preferably 100.2% or more, and even more preferably 100.3% or more. The upper limit of the relative density is not particularly limited, but is preferably 105% or less, further preferably 104% or less, more preferably 103% or less, and further preferably 102% or less. The oxide sintered body of the present invention having such a relative density can be suitably manufactured by the method described below. The relative density is measured according to the Archimedean method. The specific measurement method will be described in the embodiments described below.

The oxide sintered body of the present invention is also characterized by high strength. Specifically, the bending strength of the oxide sintered body of the present invention is preferably a higher value of 180 MPa or more. By showing such a high bending strength, the oxide sintered body of the present invention is preferably used as a sputtering target, and when the target is used for sputtering, even if abnormal discharge occurs unexpectedly during the sputtering process, the target is unlikely to crack or crack, so it is preferred. From this viewpoint, the flexural strength of the oxide sintered body of the present invention is preferably 190 MPa or more, more preferably 200 MPa or more, further preferably 210 MPa or more, particularly preferably 220 MPa or more, particularly preferably 230 MPa or more, and most preferably 240 MPa or more. There is no particular restriction on the upper limit of the flexural strength, but it is preferably 300 MPa or less, further preferably 290 MPa or less, further preferably 280 MPa or less, and further preferably 270 MPa or less. The oxide sintered body of the present invention having such flexural strength can be suitably manufactured by the method described below. The flexural strength is measured in accordance with JIS R1601. The specific measurement method will be described in the embodiments described below.

Regarding the oxide sintered body of the present invention, from the viewpoint that DC (Direct Current) sputtering plating can be easily performed when the oxide sintered body is used as a sputtering target, it is preferable that the bulk resistivity is lower. From this viewpoint, the bulk resistivity of the oxide sintered body is preferably 10 Ω･cm or less. The bulk resistivity is measured in AUTO RANGE mode using Loresta (registered trademark) HP MCP-T410 (series 4-probe type ESP) manufactured by Mitsubishi Chemical Corporation. The measurement sites are set to 5 locations, namely, the center and four corners of the oxide sintered body, and the arithmetic mean of the measured values is set as the bulk resistivity of the sintered body.

As described above, the oxide sintered body of the present invention contains Sn, Ta and Nb as metal elements. From the viewpoint of improving the characteristics of the transparent conductive film formed by the oxide sintered body, the oxide sintered body of the present invention preferably contains SnO ₂ as a main component and contains Ta ₂ O ₅ and Nb ₂ O ₅ as auxiliary components. From the viewpoint of making this advantage more significant, the total amount of Ta ₂ O ₅ and Nb ₂ O ₅ in the oxide sintered body is preferably 1.15 mass% to 12.0 mass%, more preferably 3.5 mass% to 10 mass%, more preferably 4.0 mass% to 8.0 mass%, and more preferably 5.0 mass% to 7.0 mass%.

Regarding the ratio of Ta ₂ O ₅ to Nb ₂ O ₅ in the oxide sintered body of the present invention, from the viewpoint of improving the characteristics of the transparent conductive film formed from the oxide sintered body and the viewpoint of improving the sintered density of the oxide sintered body, the ratio is preferably 0.15 to 0.90, more preferably 0.15 to 0.60, more preferably 0.16 to 0.43, and even more preferably 0.17 to 0.33, expressed as a mass ratio of Nb ₂ O ₅ /Ta ₂ O ₅ .

Regarding the specific ratios of Sn, Ta, and Nb in the oxide sintered body of the present invention, it is preferred that Sn be 80 mass% or more and less than 100 mass% in terms of _SnO2 , it is preferred that Ta be more than 0 mass% and less than 10 mass% in terms of _Ta2O5 , and it is preferred that Nb be more than 0 _{mass %} and less than 10 mass% in terms of _Nb2O5 . Furthermore, it is preferred that Sn be 88 mass% or more and less than 98.85 mass% in terms of _SnO2 , it is preferred that Ta be 1 mass% or more and less than 8 mass% in terms of _Ta2O5 , and it is preferred that Nb be 0.15 mass% or more _and less than ₄ mass% in terms of _Nb2O5 . In particular, it is preferred that Sn is 90 mass % or more and 96.5 mass % or less as converted to SnO ₂ , it is preferred that Ta is 3 mass % or more and 7 mass % or less as converted to Ta ₂ O ₅ , and it is preferred that Nb is 0.5 mass % or more and 3 mass % or less as converted to Nb ₂ O _5. It is preferred that the oxide sintered body of the present invention contains Sn, Ta and Nb in such ratios, because the characteristics of the transparent conductive film formed from the oxide sintered body are improved. Furthermore, the respective ratios of SnO ₂ , Ta ₂ O ₅ , and Nb ₂ O ₅ are values on a mass basis including the amount of inevitable impurities contained in the oxide sintered body.

Next, a suitable method for producing the oxide sintered body of the present invention is described. The oxide sintered body of the present invention is produced by sintering raw material powders. Tin oxide powder, tantalum oxide powder and niobium oxide powder are used as raw material powders. As the tin oxide powder, _SnO2 powder is preferably used. As the tantalum oxide powder, _Ta2O5 powder is preferably used. As the niobium oxide powder, _{Nb2O5 powder} is preferably used. The usage ratio of each oxide powder is preferably adjusted in such _{a way that the ratio of SnO2, Ta2O5 and Nb2O5 contained in the target} oxide sintered _body becomes the above range.

Regarding the particle size of each oxide powder, from the viewpoint of achieving sufficient dispersibility in the dispersion medium, the volume cumulative particle size D50 at the cumulative volume 50% measured by the laser diffraction scattering particle size distribution measurement method is preferably 0.3 μm to 1.2 μm, more preferably 0.4 μm to 1.1 μm, and further preferably 0.5 μm to 0.9 μm.

The results of the inventor's research have shown that in this manufacturing method, from the perspective of successfully manufacturing an oxide sintered body with suppressed pores, it is advantageous to prepare slurries of each oxide powder separately and mix the slurries to prepare a mixed slurry. The following is a detailed description of the procedure. First, prepare slurries of each oxide powder separately. As a dispersion medium for preparing the slurry, a liquid that can disperse each oxide powder can be used. As such a dispersion medium, for example, water and various organic solvents can be cited. As an organic solvent, for example, ethanol can be used. Among these dispersion media, water is preferably used from the perspective of economy and ease of handling. The ratio of the dispersing medium in the slurry is preferably set to 20% to 70% by mass relative to the mass of the oxide powder, more preferably 30% to 60% by mass, and further preferably 35% to 55% by mass. In this way, the oxide powder will be fully dispersed in the dispersing medium.

Regarding the concentration of the oxide powder in the slurry of each oxide powder, considering the dispersibility of the oxide powder in the dispersion medium, it is preferably 58 mass% to 84 mass%, more preferably 62 mass% to 77 mass%, and further preferably 64 mass% to 74 mass%. From the viewpoint of improving the dispersibility of each oxide powder contained in the slurry, it is better to mix a dispersant in each slurry. As a dispersant, an appropriate one can be used according to the type of oxide powder. For example, polycarboxylates such as ammonium polycarboxylate, sodium polycarboxylate and polycarboxylate amine salt; quaternary cationic polymers; non-ionic surfactants such as polyalkylene glycol; and cationic surfactants such as quaternary ammonium salts can be used. These dispersants can be used alone or in combination of two or more. Among these dispersants, polycarboxylates are preferred, and ammonium polycarboxylates are particularly preferred, in terms of higher dispersibility of oxide powder. The types of dispersants prepared in each slurry can be the same or different.

The concentration of the dispersant in each slurry can be appropriately selected according to the concentration and type of the oxide powder contained in the slurry. The concentration of the dispersant in the slurry is preferably set to 0.01 mass% to 0.04 mass% relative to the mass of the oxide powder, more preferably 0.015 mass% to 0.035 mass%, and further preferably 0.02 mass% to 0.03 mass%, so that the dispersion should be satisfactory. The concentration of the dispersant in each slurry can be the same or different.

A binder may also be mixed in each slurry. By mixing a binder, the strength of the granulated material can be made appropriate when the granulated material is obtained using the mixed slurry described later. As a binder, for example, various organic polymer materials can be used. As an organic polymer material, for example, polyvinyl alcohol, acrylic emulsion adhesive, etc. can be used. The concentration of the binder mixed in each slurry can be appropriately selected according to the concentration and type of the oxide powder contained in the slurry. The concentration of the binder in the slurry is preferably set to 0.2 mass% to 0.8 mass% relative to the mass of the oxide powder, more preferably 0.3 mass% to 0.7 mass%, and further preferably 0.4 mass% to 0.6 mass%, so that the strength of the granulated material can be appropriate. The concentration of the binder in each slurry can be the same or different.

The slurry is prepared by mixing the components constituting the slurry. From the viewpoint of fully dispersing the oxide powder in the dispersion medium, the mixing is preferably performed using a medium milling device such as a ball mill or a bead mill.

After preparing the slurries according to the above procedure, the slurries are then mixed to prepare a mixed slurry. The mixing ratio of the slurries is preferably adjusted so that the ratio of SnO ₂ , Ta ₂ O ₅ and Nb ₂ O ₅ contained in the target oxide sintered body is within the above range. In order to mix the slurries to obtain the mixed slurry, it is preferred to use a medium milling device such as a ball mill or a bead mill, but the method is not limited to this method.

Preparing slurries of various oxide powders and mixing the various slurries to obtain a mixed slurry has the following advantages. In this manufacturing method, as described later, it is preferred to use a mixed slurry and obtain granules by a spray drying method. In order to smoothly carry out the spray drying method, it is advantageous to increase the amount of dispersant prepared in the mixed slurry to reduce the viscosity of the mixed slurry. However, if the amount of dispersant prepared is increased, there is a tendency for the granules obtained by the spray drying method to be harder and difficult to crush. If a molded body for manufacturing an oxide sintered body obtained using such a granulated body is press-formed, the granules are difficult to crush during the pressurization process, resulting in defects in the molded body. If such a molded body is calcined, the resulting sintered body will be non-dense and will have defects. On the other hand, if the amount of dispersant added to the mixed slurry is reduced to make the granulated material easier to crush, the viscosity of the mixed slurry tends to increase, making it difficult to produce granulated materials with regular shapes. If a molded body using such granulated material is pressurized, defects are still likely to occur in the molded body, and the sintered body will be non-dense and will have defects. In contrast, the results of the inventor's research have shown that by adding a dispersant to the slurries of the oxide powders and mixing the slurries to obtain a mixed slurry, even if the amount of the dispersant added is reduced, the viscosity of the mixed slurry can be suppressed, and a mixed slurry with good dispersibility can be obtained. The sintered body made using this mixed slurry is a dense sintered body with the generation of defective parts suppressed.

Preparing slurries of various oxide powders and mixing the various slurries to obtain a mixed slurry also has the following other advantages. In the prior art, such as the technology described in the above-mentioned patent documents 1 and 2, when manufacturing an oxide sintered body containing multiple metal elements, the oxide powders of various metal elements are dispersed together in a dispersion medium to prepare the slurry. According to the research results of the inventors, if the slurry is prepared by this method, the dispersant formulated in the slurry preferentially acts on a specific oxide, and the dispersibility of the oxides in the dispersion medium varies. If the dispersibility varies, the state of the oxide powder in the granulated material manufactured by the slurry, such as the degree of crushability, is uneven, and therefore, there is a defect that pores are easily generated in the oxide sintered body finally obtained. The reason for the difference in dispersibility is that the interaction between the dispersant and each oxide powder varies depending on the type of oxide powder. Therefore, in this manufacturing method, in order to prevent the difference in dispersibility between oxides in the dispersion medium, a method is adopted in which each oxide powder is dispersed in the dispersion medium one by one instead of dispersing each oxide powder in the dispersion medium together, and the dispersant is mixed in the dispersion medium at this time. By adopting this method, the dispersant will surely act on each oxide powder, so the dispersibility of each oxide powder in the mixed slurry is not easy to produce differences.

After the mixed slurry is prepared, the mixed slurry is subjected to a spray drying method to produce granules. In the granulation by the spray drying method, in terms of the crushability of the granules, it is preferred to produce granules having a particle size of 30 μm to 60 μm, especially 35 μm to 55 μm, and especially 40 μm to 50 μm, as indicated by the volume cumulative particle size D50 at 50 volume % measured by the laser diffraction scattering particle size distribution measurement method. In terms of preventing the formation of pores when the granules are used to produce oxide sintered bodies, it is advantageous that the granules are easily crushed. In addition, the volume cumulative particle size D50 of the granulated material is the particle size measured without ultrasonic dispersion treatment.

After obtaining the granulated material, the granulated material is filled into a mold to produce a molded body. For example, a cold pressing method such as cold isostatic pressing can be used for molding. Regarding the pressure during molding, in terms of obtaining a dense molded body, it is preferably set to 600 kg/ ^cm2 or more and 1200 kg/ ^cm2 or less. After obtaining the molded body, a degreasing step can be performed on the molded body as needed. By performing a degreasing step on the molded body, organic substances contained in the molded body, such as dispersants and binders, can be removed. The degreasing step is performed by, for example, heating the molded body to a temperature of 500°C or more and 900°C or less in an atmospheric atmosphere.

After the molded body is obtained in this way, it is then calcined. The molded body can usually be calcined in an oxygen-containing atmosphere. In particular, calcination in an atmospheric atmosphere is simpler. The calcination temperature is preferably 1500°C to 1700°C, more preferably 1520°C to 1680°C, and further preferably 1550°C to 1650°C. The calcination time is preferably 1 hour to 100 hours, more preferably 2 hours to 50 hours, and further preferably 3 hours to 30 hours. The heating rate and the cooling rate are preferably independently 5°C/hour to 500°C/hour, more preferably 10°C/hour to 200°C/hour, and further preferably 20°C/hour to 100°C/hour.

The oxide sintered body obtained by the above method is dense and the formation of pores is suppressed. Therefore, the area ratio of the pores in the oxide sintered body is low, and the maximum circle equivalent diameter and the maximum Feret diameter are small.

The oxide sintered body thus obtained can be processed into a specified size by grinding or the like to make a sputtering target. The obtained sputtering target is joined to a backing plate to obtain a sputtering target. As the backing plate, for example, stainless steel, copper, and titanium can be used. For example, a low melting point solder such as indium can be used to join the target and the backing plate. The sputtering target thus obtained is suitable for manufacturing a sputtering film, such as a transparent conductive film. The sputtering film formed using the sputtering target can have the same composition as the sputtering target. The specific resistivity of the sputtering film is preferably a low resistance of 9 mΩ･cm or less. [Example]

The present invention is further described in detail below by using embodiments, but the scope of the present invention is not limited to these embodiments.

[Example 1] Prepare _SnO2 powder with a particle size D50 of 0.7 μm, _{Ta2O5 powder} with a particle size D50 of 0.6 μm, and _{Nb2O5 powder} with a particle size D50 of 0.9 μm. The particle size D50 is measured using a particle size distribution measuring device MT3300EXII manufactured by MicrotracBEL Co., Ltd. Water is used as a dispersion medium. The refractive index of the measured substance is set to 2.20. Each oxide powder is placed separately in a crucible, and 0.5 mass% of polyvinyl alcohol, 0.02 mass% of ammonium polycarboxylate, and 50 mass% of water are added relative to the mass of each oxide powder, and mixed using a ball mill for 20 hours to prepare each slurry. The prepared slurries were mixed and mixed for 60 minutes using a ball mill to obtain a mixed slurry. The mixing ratio of each slurry was 96.5 mass % for SnO ₂ , 3.0 mass % for Ta ₂ O ₅ , and 0.5 mass % for Nb ₂ O ₅ relative to the total of each powder.

The mixed slurry is supplied to a spray drying device, and spray drying is performed under the conditions of an atomizer speed of 14000 rpm, an inlet temperature of 200°C, and an outlet temperature of 80°C to obtain granules. The particle size D50 of the granules is 45 μm. The obtained granules are filled into a mold of 158 mm×640 mm, and pressed under a pressure of 800 kg/ ^cm2 to obtain a molded body. The obtained molded body is heated at 750°C for 6 hours in an atmospheric atmosphere for degreasing. The degreased molded body is calcined to produce a sintered body. The calcination was carried out in an atmosphere with an oxygen concentration of 20 vol%, at a calcination temperature of 1600°C, a calcination time of 8 hours, a heating rate of 50°C/h, and a cooling rate of 50°C/h. The sintered body obtained in this way was cut to obtain an oxide sintered body with a width of 100 mm, a length of 240 mm, a thickness of 8 mm, and a surface roughness Ra of 1.0 μm. A #170 grindstone was used in the cutting process.

[Examples 2 and 3] The powders were mixed so that the ratio of each powder relative to the total of _SnO2 powder, _{Ta2O5 powder} and _{Nb2O5 powder} was as shown in Table 1. Except for this, an oxide sintered body was obtained in the same manner as in Example 1.

[Comparative Example 1] Prepare the same _SnO2 powder, _{Ta2O5 powder} and _Nb2O5 powder as in Example 1. Weigh each powder so that _SnO2 is 94 mass%, _Ta2O5 is 5 mass% and _{Nb2O5 is} 1 mass% relative to the total of each powder, and dry mix for 21 hours. Add ₆ mass% of a 4 mass% polyvinyl alcohol aqueous solution relative to the mixed powder. After mixing the polyvinyl alcohol and the mixed powder using a mortar, pass the mixture through a _5.5 mesh sieve to obtain a mixed powder for molding. Except for this, an oxide sintered body is obtained in the same manner as in Example 1.

[Comparative Example 2] Prepare the same _SnO2 powder, _{Ta2O5 powder} and _Nb2O5 powder as in Example 1. Put all the powders into a _crucible , add 0.5 mass% of polyvinyl alcohol, 0.02 mass% of ammonium polycarboxylate and 50 mass% of water relative to the total amount of the powders, and mix them for 20 hours using a ball mill to prepare a mixed slurry. Regarding the ratio of each powder in the mixed slurry, relative to the total of each powder, _SnO2 is set to 94 mass%, _Ta2O5 is set to 5 mass%, _{and Nb2O5} is set to 1 mass%. Except for this, an oxide sintered body is obtained in the same manner as in Example ₁ .

[Comparative Example 3] In this comparative example, the concentration of the dispersant used in Example 2, i.e., 0.02 mass % of ammonium polycarboxylate, was increased to 0.05 mass %. Other than this, an oxide sintered body was obtained in the same manner as in Example 2.

[Evaluation] The pore area ratio, maximum circle equivalent diameter, maximum Feret diameter, relative density, and bending strength of the oxide sintered bodies obtained in the embodiments and comparative examples were measured by the following method. In addition, the oxide sintered bodies obtained in the embodiments and comparative examples were used to manufacture sputtering targets, and the degree of abnormal discharge and the degree of target cracking during sputtering using the targets were evaluated by the following method. The above results are shown in Table 1 below.

[Area ratio of hole, maximum circle equivalent diameter and maximum Feret diameter] (1) Preparation of cross section of oxide sintered body Use sandpaper #180, #400, #800, #1000 and #2000 to grind the cross section of the oxide sintered body in stages, and finally polish it to a mirror surface. (2) Determination of pore area ratio, maximum circular equivalent diameter, and maximum Feret diameter Using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), a BSE (Back Scattered Electron)-COMP image (hereinafter also referred to as "SEM image") in the range of 445.3 μm × 634.6 μm was taken at a magnification of 200 times for the cross section of the oxide sintered body. The SEM image was tracked using particle analysis software ("Particle Analysis Version 3.0", manufactured by Sumitomo Metal Technology Co., Ltd.) and image identification was performed using a scanner. The image was binarized. At this time, the conversion value was set to display 1 pixel in μm. Next, the area and the sum of the areas of all the holes captured in the SEM image are calculated. The percentage of the sum of the hole areas relative to the field of view area (445.3 μm×634.6 μm) is calculated. The arithmetic mean of the percentages measured using 10 different SEM images is calculated, and the arithmetic mean is set as the hole area ratio of the present invention. In addition, the circular equivalent diameter of the hole is calculated based on the hole area measured in the process of calculating the hole area ratio. The maximum value of all the circular equivalent diameters measured using 10 different SEM images is set as the maximum circular equivalent diameter of the hole. Different from the above operation, all the holes captured in the SEM image are taken as the object, and the horizontal Feret diameter (μm) is calculated based on the total number of pixels in the horizontal direction, and the vertical Feret diameter (μm) is calculated based on the total number of pixels in the vertical direction. The maximum value of all horizontal Feret diameters and vertical Feret diameters measured in 10 different SEM images is set as the maximum Feret diameter of the hole.

[Relative density] Relative density is measured based on the Archimedean method. Specifically, the mass of the oxide sintered body in air is divided by the volume (mass of the sintered body in water/specific gravity of water at the measurement temperature), and the value of the percentage relative to the theoretical density ρ (g/cm ³ ) calculated based on the following formula (1) is set as the relative density (unit: %). ρ＝{(C ₁ /100)/ρ ₁ ＋(C ₂ /100)/ρ ₂ ＋(C ₃ /100)/ρ ₃ } ^-1 (1) In formula (1), C ₁ to C ₃ respectively represent the content (mass %) of the constituent substances of the target material, and ρ ₁ to ρ ₃ represent the density (g/cm ³ ) of each constituent substance corresponding to C ₁ to C ₃ . In the case of the present invention, the contents (mass %) of the constituent substances of the target are taken as SnO ₂ , Ta ₂ O ₅ , and Nb ₂ O ₅ , for example, C1: mass % of SnO ₂ in the target ρ1: density of SnO ₂ (6.95 g/cm ³ ) C2: mass % of Ta ₂ O ₅ in the target ρ2: density of Ta ₂ O ₅ (8.74 g/cm ³ ) C3: mass % of Nb ₂ O ₅ in the target ρ3: density of Nb ₂ O ₅ (4.47 g/cm ³ ) These can be applied to formula (1) to calculate the theoretical density ρ. Furthermore, the mass % of SnO ₂ , the mass % of Ta ₂ O ₅ and the mass % of Nb ₂ O ₅ can be obtained based on the analysis results of each element of the target material obtained by ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer).

[Bending strength] Autograph (registered trademark) AGS-500B manufactured by Shimadzu Corporation was used. The test specimens (total length 36 mm or more, width 4.0 mm, thickness 3.0 mm) cut from the oxide sintered body were used as the test objects, and the three-point bending strength test method of JIS R1601 was used for the test.

[Occurrence of abnormal discharge and degree of target cracking] A sputtering target was prepared using the oxide sintered bodies obtained in the examples and comparative examples, and the target was mounted in a DC magnetron sputtering device for sputtering. The sputtering conditions were as follows. ･Ultimate vacuum degree: 3×10 ^-6 Pa ･Sputtering pressure: 0.4 Pa ･Oxygen partial pressure: 1×10 ^-3 Pa ･Power input time: 2 W/cm ² ･Duration: 25 hours The number of arcs generated during sputtering under the above conditions was measured using an arc counter attached to the power supply. μArc Moniter MAM Genesis MAM Data Collector Version 2.02 (manufactured by LANDMARK TECHNOLOGY) was used as the arc counter. The evaluation criteria were as follows. A: The number of arcing is less than 5 times. B: The number of arcing is more than 5 times and less than 30 times. C: The number of arcing is more than 30 times. During the sputtering process under the above conditions, visual observation was used to evaluate whether the target was cracked.

[Table 1] SnO ₂ (mass%) Ta ₂ O ₅ (mass%) Nb ₂ O ₅ (mass %) Hole area ratio (%) Maximum circle equivalent diameter of hole (μm) Maximum Feret diameter of the hole (μm) Relative density(%) Flexural strength (MPa) Abnormal discharge level Degree of rupture Embodiment 1 96.5 3 0.5 0.54 12.5 26.5 100.3 235 A without Embodiment 2 94 5 1 0.49 11.9 25.5 100.5 241 A without Embodiment 3 90 7 3 0.61 13.2 28.1 100.2 229 A without Comparison Example 1 94 5 1 2.03 21.1 56.0 99.0 170 C have Comparison Example 2 94 5 1 2.31 25.7 61.1 98.8 163 C have Comparison Example 3 94 5 1 1.25 20.5 52.3 99.3 176 B have

According to the results shown in Table 1, when the oxide sintered bodies obtained in each embodiment are used as sputtering targets, abnormal discharge is less likely to occur during sputtering, and the target is less likely to break, compared with the case where the oxide sintered bodies obtained in the comparative examples are used as sputtering targets. In contrast, in comparative example 1, in which the spray drying method is not used to produce the calcined molded body, the molded body cannot be made dense, and a large number of pores are generated in the oxide sintered body produced from the molded body. In comparative example 2, in which slurry is not prepared for each raw material powder, the granulated material is uneven, the molded body cannot be made dense, and a large number of pores are generated in the oxide sintered body produced from the molded body. In Comparative Example 3, where the amount of dispersant was greater than that in Comparative Example 2, the granulated product was uniform but hard and difficult to crush, so the compact could not be made dense, and a large number of pores were generated in the oxide sintered body produced from the compact. [Industrial Applicability]

According to the present invention, an oxide sintered body having fewer pores or smaller pores even if present, and which is less prone to abnormal discharge and cracking when used as a sputtering target, and a method for manufacturing the same, and a sputtering target can be provided. If the oxide sintered body of the present invention is used for sputtering, compared with the case of using the previous oxide sintered body, abnormal discharge or cracking during sputtering can be suppressed and film formation can be achieved, so the generation of excess defective products can be suppressed, and the generation of waste can be reduced. In other words, the energy cost of processing such waste can be reduced. This is closely related to achieving sustainable management and effective utilization of natural resources, as well as decarbonization (carbon neutralization).

Claims (12)

An oxide sintered body contains 80 mass % or more and less than 100 mass % of a tin element calculated as _SnO2 , more than 0 mass % and less than 10 _mass % of a tantalum element calculated as _Ta2O5 , and more than 0 mass % and less than 10 mass % of a niobium element calculated as _Nb2O5 , wherein an area ratio of pores per unit area in cross _- sectional observation of the oxide sintered body is less than 1%, and the area ratio of pores per unit area is a value calculated as a percentage of the total area of pores relative to a field of view area (445.3 μm×634.6 μm) with respect to all pores captured in an SEM image. An oxide sintered body containing 80 mass % or more and less than 100 mass % of a tin element in terms of _SnO2 , more than 0 mass % and less than 10 mass % of a tantalum element in terms of _Ta2O5 , and more than ₀ mass % and less than 10 mass % of a niobium _element in terms of _Nb2O5 , wherein the maximum circle equivalent diameter of a pore portion in cross-sectional observation of the oxide sintered body is less than 20 μm. An oxide sintered body containing 80 mass % or more and less than 100 mass % of a tin element in terms of _SnO2 , more than 0 mass % and less than 10 mass % of a tantalum element in terms of _Ta2O5 , and more than ₀ mass % and less than 10 mass % of a niobium _element in terms of _Nb2O5 , wherein the maximum Feret diameter of a pore portion in cross-sectional observation of the oxide sintered body is less than 50 μm. An oxide sintered body containing 80 mass % or more and less than 100 mass % of a tin element in terms of SnO ₂ , more than 0 mass % and less than 10 mass % of a tantalum element in terms of Ta ₂ O _{5 ,} and ₅ converted to more than 0 mass % and less than 10 mass % of niodium element, the area ratio of pores per unit area in cross-section observation of the above-mentioned oxide sintered body is less than 1%, the maximum circle equivalent diameter of the above-mentioned pores is less than 20 μm, the maximum Feret diameter of the above-mentioned pores is less than 50 μm, and the area ratio of pores per unit area is the percentage of the total area of pores relative to the field of view area (445.3 μm×634.6 μm) with respect to all pores photographed in the SEM image. An oxide sintered body as claimed in any one of claims 1 to 4, wherein the relative density measured based on the Archimedean method is 99.6% or more. An oxide sintered body as claimed in any one of claims 1 to 4, wherein the bending strength measured in accordance with JIS R1601 is 180 MPa or more. The oxide sintered body of any one of claims 1 to 4 contains 90 mass % to 96.5 mass % of tin element in terms of _SnO2 , 3 mass % to 7 mass % of tantalum element in terms of _Ta2O5 , and 0.5 mass % to ₃ mass % of niobium _element in terms of _Nb2O5 . The oxide sintered body according to any one of claims 1 to 4, wherein the ratio of Ta ₂ O ₅ to Nb ₂ O ₅ expressed as a mass ratio of Nb ₂ O ₅ /Ta ₂ O ₅ is 0.15 or more and 0.90 or less. A sputtering target comprising an oxide sintered body as described in any one of claims 1 to 4. A method for manufacturing a sputtering film, which uses a sputtering target as described in claim 9. A method for producing a sputtering target of an oxide sintered body as claimed in any one of claims 1 to 4, comprising preparing a slurry of tin oxide, a slurry of tantalum oxide and a slurry of niobia oxide separately, mixing the slurries to prepare a mixed slurry, spray drying the mixed slurry to produce granules, using the granules to produce a body, The formed body is sintered; the above-mentioned tin oxide slurry, the above-mentioned tantalum oxide slurry and the above-mentioned niobium oxide slurry respectively contain dispersants in advance, and the mass of the above-mentioned dispersants relative to the mass of the oxide powders respectively contained in the above-mentioned tin oxide slurry, the above-mentioned tantalum oxide slurry and the above-mentioned niobium oxide slurry is 0.01 mass% or more and 0.04 mass% or less. The manufacturing method of claim 11, wherein the dispersant is a polycarboxylate.