Method for manufacturing oxide sintered bodies

Abstract

The method for producing an oxide sintered body according to the present invention uses, as a raw material, an oxide including two or more elements selected from In, Ga, and Zn, the method satisfying (a) to (c). (a) An oxide having a purity of 6N or more is used as the raw material. (b) The medium for pulverization and mixing is formed from an oxide including no element other than the elements selected as the raw material. (c) Slurry is obtained by using ultrapure water as a dispersion medium.

Description

[Technical Field]

[0001] The present invention relates to a method for producing an oxide sintered body using an oxide containing two or more elements selected from In, Ga, and Zn as a raw material. [Background technology]

[0002] In the field of thin-film transistors (hereinafter referred to as "TFTs") used in display devices such as flat panel displays (hereinafter referred to as "FPDs"), with the increasing functionality of FPDs, oxide semiconductors, such as In-Ga-Zn composite oxides (hereinafter referred to as "IGZO") as shown in Patent Documents 1 and 2, are being put into practical use as a replacement for conventional amorphous silicon.

[0003] Furthermore, in recent years, oxide semiconductors have shown high mobility (>10cm). 2 It possesses the excellent characteristic of being able to achieve both a low Vs (Vs) and extremely low off-leak current (<10-22 A / μm), and is expected to be used as a channel material for vertical FETs that can be mixed with Si-CMOS LSIs and highly integrated using BEOL-compatible processes in semiconductor manufacturing. Along with these expectations, the required characteristics for sputtering targets for depositing oxide semiconductor films are also increasing.

[0004] The oxide sintered body disclosed in Patent Document 1 contains Fe, Al, Si, Ni, and Cu as impurities, and it is disclosed that the content of each is 10 ppm or less, but the total content of the impurities is not disclosed. Furthermore, the oxide sintered body disclosed in Patent Document 2 contains Na at a content of 25 ppm as an impurity, and also lists Cd, Cu, Fe, K, Ni, Pb, etc. as impurities. The content of these impurities other than Na is 10 ppm or less each, and the total content is 100 ppm or less. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-163441 [Patent Document 2] Japanese Patent Publication No. 2010-202450 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, in recent years, the requirements for impurities in oxide sintered bodies have become even stricter, and further reductions in impurity content are needed.

[0007] In view of the above problems, the present invention provides a method for producing an oxide sintered body that can produce an oxide sintered body with a significantly reduced impurity content. [Means for solving the problem]

[0008] The present invention, which was developed to solve the above problems, is a method for producing an oxide sintered body using an oxide containing two or more elements selected from In, Ga, and Zn as raw materials, and satisfies the following (a) to (c). (a) The raw material used is an oxide with a purity of 6N or higher. (b) The grinding and mixing media is formed from an oxide that does not contain any elements other than the elements selected as raw materials. (c) Use ultrapure water as the dispersion medium to form a slurry. This configuration makes it possible to manufacture oxide sintered bodies with a significantly reduced impurity content.

[0009] The raw material in (a) above is an oxide containing two or more elements selected from In, Ga, and Zn. Specifically, it may be two selected from oxides containing In (In2O3), oxides containing Ga (Ga2O3), and oxides containing Zn (ZnO) (In2O3 and Ga2O3, In2O3 and ZnO, Ga2O3 and ZnO), or three selected from these (In2O3, Ga2O3, and ZnO). Furthermore, it may be a composite oxide containing two or more elements selected from In, Ga, and Zn.

[0010] Furthermore, the purity of the oxide containing two or more elements selected from In, Ga, and Zn is 6N (99.9999 mass%) or higher. If the purity of each oxide used as a raw material is 6N or higher, the content of impurities such as Fe, Al, Si, Ni, Cu, Li, Be, B, F, Na, Mg, P, K, Ca, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Cs, Ba, Tl, Pb, Bi, Th, U, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg is significantly reduced, and therefore the content of impurities in oxide sintered bodies manufactured from these raw materials can also be significantly reduced. In particular, it is preferable that the purity of each oxide used as a raw material is 6N or higher, as this allows for a significant reduction in Fe, Al, Si, Ni, and Cu.

[0011] In this specification, the elements H, He, C, N, O, Ne, S, Cl, Ar, Br, Kr, Tc, I, Xe, Pm, Po, At, Rn, Fr, Ra, and actinides are excluded from the group of impurity elements. Furthermore, elements whose analytical values ​​are below the detection limit are considered not to be present.

[0012] The grinding and mixing media in (b) above is formed from an oxide that does not contain any elements other than the elements selected as raw materials.

[0013] In other words, when two types of oxides are selected as raw materials, namely an oxide containing the element In (In2O3) and an oxide containing the element Ga (Ga2O3), the grinding and mixing media is formed from an oxide that does not contain any elements other than In and Ga. For example, the grinding and mixing media may be a media formed from In2O3, Ga2O3, or InGaO3, with a media formed from In2O3 being preferred.

[0014] When two types of oxides are selected as raw materials—an oxide containing the element In (In2O3) and an oxide containing the element Zinc (ZnO)—the grinding and mixing media is formed from oxides that do not contain any elements other than In and Zinc. For example, the grinding and mixing media may be formed from In2O3, ZnO, or In2Zn3O6, with media formed from In2O3 being preferred.

[0015] When two types of oxides are selected as raw materials, one containing Ga (Ga2O3) and the other containing Zn (ZnO), the grinding and mixing media is formed from oxides that do not contain any elements other than Ga and Zn. For example, the grinding and mixing media may be made from Ga2O3, ZnO, or Ga2ZnO4, with Ga2ZnO4 being preferred.

[0016] When three types of oxides are selected as raw materials—an oxide containing the element In (In2O3), an oxide containing the element Ga (Ga2O3), and an oxide containing the element Zn (ZnO)—the grinding and mixing media is formed from oxides that do not contain elements other than In, Ga, and Zn. For example, the grinding and mixing media may be a media formed from In2O3 or Ga2ZnO4, and a media formed from Ga2ZnO4 is preferred.

[0017] In addition, the statement that the grinding and mixing media in (b) above "do not contain elements other than the elements selected as the raw materials" indicates that the content of impurities contained in the grinding and mixing media is 100 mass ppm or less. Here, examples of the impurities contained in the grinding and mixing media include Li, Be, B, F, Na, Mg, Al, Si, P, K, Ca, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Cs, Ba, Tl, Pb, Bi, Th, U, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, etc.

[0018] The dispersion medium in (c) above is preferably ultrapure water. Here, ultrapure water is high-purity water, and since the electrical resistivity of theoretical pure water (pure water) is 18.24 MΩ·cm, it is preferably a value that approaches this value as closely as possible, preferably 15.0 MΩ·cm or more, more preferably 16.0 MΩ·cm or more, still more preferably 17.0 MΩ·cm or more, particularly preferably 17.5 MΩ·cm or more, and even more particularly preferably 18.0 MΩ·cm or more.

[0019] It is preferable to use such ultrapure water as the dispersion medium, mix it with the raw materials, and form a slurry. Ultrapure water is of high purity, and the purity of the raw materials will not be reduced by the impurities contained in the ultrapure water.

[0020] Moreover, the method for producing the oxide sintered body of the present invention satisfies the following (d1). (d1) Casting molding is performed using a metal molding die. With this configuration, it is possible to make it difficult for impurities to mix into the oxide sintered body during casting molding.

[0021] As shown in Figure 1, the metal mold described in (d1) above allows for the production of a molded body by injecting a slurry of raw materials (hereinafter referred to as raw material slurry 1) into the mold frame 2 from above and draining the water under reduced pressure through one or more drainage holes 4 provided in the lower mold 3. The lower mold 3 has a structure in which a water-permeable filter 5 (for example, GORE-TEX® wet filter cloth, manufactured by Gore Japan Co., Ltd.) that prevents the raw materials in the raw material slurry 1 from passing through is placed on the lower mold 3, and the mold frame 2 is placed on top of it via a sealing material 6.

[0022] Here, the molding mold 2 and the lower molding mold 3 are made of metal, and it is preferable that they be made of aluminum, for example, as this makes it less likely for impurities to be mixed into the molded product obtained during the casting process.

[0023] Furthermore, the method for producing the oxide sintered body of the present invention satisfies the following (d2). (d2) The material is cast using a ceramic mold made from an oxide that does not contain any elements other than those selected as raw materials. This configuration makes it difficult for impurities to be mixed into the oxide sintered body during the casting process.

[0024] If the ceramic mold in (d2) above is made from an oxide that does not contain any elements other than the elements selected as raw materials, then even if a part of the ceramic mold is mixed in during the casting process, it will not reduce the purity of the molded body because it is the same as the components of the molded body.

[0025] Furthermore, since the structure of the ceramic mold in (d2) above is similar to the structure of the metal mold in (d1) shown in Figure 1, a detailed explanation will be omitted. However, the molding frame 2 and the lower molding mold 3 are formed from the oxides described below.

[0026] When two types of oxides are selected as raw materials for a ceramic mold, namely an oxide containing In (In2O3) and an oxide containing Ga (Ga2O3), the mold frame 2 and lower mold 3 are formed from oxides that do not contain elements other than In and Ga. For example, the mold frame 2 and lower mold 3 for a ceramic mold are preferably formed from In2O3, Ga2O3, or InGaO3, and are particularly preferably formed from In2O3.

[0027] When two types of oxides are selected as raw materials for a ceramic mold, namely an oxide containing In (In2O3) and an oxide containing Zn (ZnO), the mold frame 2 and lower mold 3 are formed from oxides that do not contain elements other than In and Zn. For example, the mold frame 2 and lower mold 3 for a ceramic mold are preferably formed from In2O3, ZnO, or In2Zn3O6, and are particularly preferably formed from In2O3.

[0028] When two types of oxides are selected as raw materials for a ceramic mold, namely an oxide containing Ga (Ga2O3) and an oxide containing Zn (ZnO), the mold frame 2 and lower mold 3 are formed from oxides that do not contain elements other than Ga and Zn. For example, the mold frame 2 and lower mold 3 for a ceramic mold are preferably formed from Ga2O3, ZnO, or Ga2ZnO4, and are particularly preferably formed from Ga2ZnO4.

[0029] When three types of oxides are selected as raw materials for a ceramic mold, the mold frame 2 and the lower mold 3 are formed from oxides that do not contain elements other than In, Ga, and Zn, such as an oxide containing In (In2O3), an oxide containing Ga (Ga2O3), and an oxide containing Zn (ZnO). For example, the mold frame 2 and the lower mold 3 for a ceramic mold are preferably formed from In2O3 and Ga2ZnO4, and are particularly preferably formed from Ga2ZnO4.

[0030] Furthermore, the statement that the ceramic mold in (b) above "does not contain elements other than the elements selected as raw materials" means that the amount of impurities contained in the ceramic mold is 100 ppm or less. Examples of impurities contained in the ceramic mold include Li, Be, B, F, Na, Mg, Al, Si, P, K, Ca, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Cs, Ba, Tl, Pb, Bi, Th, U, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, etc.

[0031] Furthermore, the method for producing the oxide sintered body of the present invention satisfies the following (e). (e) After grinding the surface of the oxide sintered body, surface treatment is performed by spraying dry ice particles. With this configuration, the ejected dry ice particles collide with the surface of the oxide sintered body, removing microcracks on the surface, as well as processing debris, dust, and other contaminants. Furthermore, since the dry ice particles vaporize immediately, it is possible to prevent them from penetrating the surface of the oxide sintered body.

[0032] The dry ice blasting conditions for spraying dry ice particles are as follows:

[0033] =Dry Ice Blast Conditions= • Average particle size of dry ice particles: 0.1~1mm • Gauge pressure of the gas medium (N2): 0.1~0.6 MPa ·Consumption rate: 20~100% Processing speed: 0.8~142.9 mm / sec • Nozzle temperature: ≥20℃ • Processing angle: 0 to 20 degrees • Distance between target and blast nozzle: 10-140mm

[0034] Here, the dry ice particles ejected from the blast nozzle are crushed and broken down dry ice, and their shape does not have to be spherical; it can be amorphous. Furthermore, the size of the dry ice particles is not particularly limited, as long as they are small enough to be ejected together with the gas medium. The average particle size of the dry ice particles is preferably 0.1 to 1 mm.

[0035] Furthermore, the gas medium used to eject the dry ice particles is not particularly limited as long as it does not affect the surface of the oxide sintered body of the present invention. For example, air, nitrogen, or other inert gases can be used. The gauge pressure of the gas medium is preferably 0.1 to 0.6 MPa.

[0036] Furthermore, the method for ejecting the dry ice particles and gas medium can be carried out in the same way as general shot blasting, by mixing the dry ice particles with the gas medium ejected at a predetermined pressure and then ejecting them.

[0037] In the above dry ice blasting conditions, "consumment rate" refers to the feed rate at which the dry ice is pushed out. In addition, "processing speed" refers to the speed at which the blast nozzle is moved over the oxide sintered body. Furthermore, "processing angle" refers to the angle of the blast nozzle with respect to the surface of the oxide sintered body. When the blast nozzle is perpendicular to the surface of the oxide sintered body, the processing angle is 0 degrees, and when the blast nozzle is parallel to the surface of the oxide sintered body, the processing angle is 90 degrees.

[0038] As an example of a method for producing an oxide sintered body according to the present invention, the above (a) to (e) will be further explained based on a filtration molding method.

[0039] First, as raw materials, In2O3 powder, Ga2O3 powder, and ZnO powder with a purity of 6N, all satisfying the above (a), are weighed and placed in a pot. These are then crushed and mixed, and ultrapure water satisfying the above (c) is added as a dispersion medium to form a slurry, thereby obtaining a raw material slurry. Since the purity of each oxide used as a raw material is 6N or higher, the content of impurities such as Fe, Al, Si, Ni, Cu, Li, Be, B, F, Na, Mg, P, K, Ca, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Cs, Ba, Tl, Pb, Bi, Th, U, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg is significantly reduced. A dispersant may be added when forming the slurry.

[0040] The method for grinding and mixing the raw materials may be dry grinding or wet grinding.

[0041] Specifically, dry grinding involves placing In2O3 powder, Ga2O3 powder, and ZnO powder, along with Ga2ZnO4 balls (hereinafter referred to as GZO media) that satisfy the above (b) as a grinding and mixing medium, into a pot and mixing the contents of the pot with a ball mill to dry grind the In2O3 powder, Ga2O3 powder, and ZnO powder.

[0042] The mixture containing the dry-ground In2O3 powder, Ga2O3 powder, and ZnO powder in the pot is separated from the GZO media using a filter to obtain the mixture containing the dry-ground In2O3 powder, Ga2O3 powder, and ZnO powder.

[0043] Subsequently, dry-ground In2O3 powder, Ga2O3 powder, and ZnO powder are placed in another pot along with ultrapure water as a dispersion medium. GZO media is then added as a grinding and mixing medium, and the contents of the pot are mixed to form a slurry. Alternatively, the mixture containing the dry-ground In2O3 powder, Ga2O3 powder, and ZnO powder may be left in the pot and ultrapure water as a dispersion medium is added to the pot containing the dry-ground mixture and mixed to form a slurry. Additives such as dispersants and binders may be added as needed.

[0044] On the other hand, in wet grinding, In2O3 powder, Ga2O3 powder, and ZnO powder are placed in a pot along with ultrapure water as a dispersion medium, and GZO media is added as a grinding and mixing medium. The pot is then mixed in a ball mill to wet grind the In2O3 powder, Ga2O3 powder, and ZnO powder.

[0045] The raw material slurry containing wet-ground In2O3 powder, Ga2O3 powder, and ZnO powder in the pot is separated from the GZO media by filtering using a filter to obtain the raw material slurry.

[0046] Furthermore, if the pot is formed from an oxide that does not contain elements other than those selected as raw materials, similar to the grinding and mixing media, then even if a part of the pot is scraped off during the grinding and mixing of the raw materials, the inclusion of impurities such as Al and Si can be suppressed.

[0047] The raw material slurry obtained in this way is poured into a metal mold that satisfies (d1) above, or a ceramic mold that satisfies (d2) above, and a molded body is obtained by removing the ultrapure water which is the dispersion medium.

[0048] Specifically, the obtained raw material slurry is degassed and injected into a metal mold satisfying (d1) above, or a ceramic mold satisfying (d2) above. The lower mold surface of the filter 5 shown in Figure 1 is then depressurized, and the water in the raw material slurry is drained from the filter surface side under reduced pressure to form the product. A reduced pressure of more than -700 mmHg is preferable. A vacuum pump or the like may be used as the method for reducing the pressure. Furthermore, the depressurization drainage time is preferably about 30 minutes after the completion of material deposition of the molded body. If the depressurization drainage time is too short, the molded body may become difficult to release from the molding frame 2, and cracks may occur. Conversely, if the depressurization drainage time is too long, the molded body may release from the molding frame 2 during depressurization drainage, air may be sucked in through the gap, and only the released portion of the molded body may dry rapidly, making it prone to cracking.

[0049] A fired body is obtained by firing the resulting molded body. When firing the molded body, creating a high-concentration oxygen atmosphere inside the firing furnace can suppress the incorporation of light elements such as H, C, and N into the fired body.

[0050] Then, by cutting the resulting fired body into an arbitrary shape, the oxide sintered body of the present invention can be obtained.

[0051] Furthermore, the method for manufacturing a sputtering target according to the present invention is characterized in that an oxide sintered body manufactured by the method for manufacturing an oxide sintered body according to the present invention described above is joined to a substrate.

[0052] A sputtering target of the present invention can be obtained by joining, i.e., bonding, an oxide sintered body produced by the method for producing an oxide sintered body of the present invention to a substrate using solder (e.g., In metal). Examples of substrates include Cu, Al, Ti, or stainless steel. As the bonding material, a bonding material used for bonding conventional ITO target materials, such as In metal, can be used. The bonding method is also the same as the bonding method for conventional ITO target materials.

[0053] Here, the material of the solder used to join the oxide sintered body and the substrate of the present invention is not particularly limited, but examples include low-melting-point solders such as In metal, In-Sn metal, or In alloy metal obtained by adding a small amount of metal component to In. The melting point of such low-melting-point solder is 150 to 200°C, so when filling with solder, the solder is heated to 150 to 300°C to melt it.

[0054] Then, the oxide sintered body bonded to the substrate is subjected to dry ice blasting. Surface treatment by dry ice blasting, in which dry ice particles are ejected from the surface of the oxide sintered body as described in (e) above, is carried out according to the dry ice blasting conditions described above.

[0055] The sputtering target of the present invention can be obtained by dry ice blasting the oxide sintered body bonded to the substrate in this manner.

[0056] Furthermore, the oxide sintered body of the present invention is an oxide sintered body containing two or more elements selected from In, Ga, and Zn, characterized in that the total content of the elements in groups A and B below, as determined by GDMS analysis, is 10 ppm by mass or less, and the total content of the elements in group B is 1 ppm by mass or less. Group A: Li, Be, B, F, Na, Mg, Al, Si, P, K, Ca, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Cs, Ba, Tl, Pb, Bi, Th, U Group B: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg However, if the content is below the detection limit of GDMS analysis, it will be considered as 0 ppm by mass.

[0057] Elements belonging to Group A and Group B are treated as impurities contained in the oxide sintered body of the present invention. Here, Group A is a group of elements mainly selected from alkali metals, alkaline earth metals, poor metals, nonmetals, and actinides. Since these elements belonging to Group A may adversely affect the properties of the oxide semiconductor film formed by the oxide sintered body of the present invention, it is preferable to have a low content. Group B is a group of elements mainly selected from transition metals and lanthanides. Since these elements belonging to Group B may adversely affect the properties of the oxide semiconductor film formed by the oxide sintered body of the present invention, it is preferable to have a low content. In particular, since elements belonging to Group B are more likely to adversely affect the properties of the oxide semiconductor film formed by the oxide sintered body of the present invention than elements belonging to Group A, it is especially preferable to reduce their content.

[0058] It is preferable that the total content of elements in groups A and B as determined by GDMS analysis is 10 ppm by mass or less, and the total content of elements in group B is 1 ppm by mass or less, in order to produce high-performance TFTs. Furthermore, it is more preferable that the total content of elements in groups A and B as determined by GDMS analysis is 8 ppm by mass or less, even more preferable that it is 6 ppm by mass or less, particularly preferable that it is 5 ppm by mass or less, even more preferable that it is 4.9 ppm by mass or less, even more preferable that it is 4.8 ppm by mass or less, and also particularly preferable that it is 4.5 ppm by mass or less. Furthermore, it is more preferable that the total content of elements in group B as determined by GDMS analysis is 0.9 ppm by mass or less, even more preferable that it is 0.8 ppm by mass or less, particularly preferable that it is 0.7 ppm by mass or less, even more preferable that it is 0.6 ppm by mass or less, even more preferable that it is 0.5 ppm by mass or less, and also particularly preferable that it is 0.4 ppm by mass or less.

[0059] Here, the total content of elements in Group A and Group B, the total content of elements in Group A, and the total content of elements in Group B are measured using GDMS analysis. GDMS analysis is a method in which a glow discharge is generated with the sample as the cathode in an Ar atmosphere, the sample surface is sputtered in the plasma, and the ionized constituent elements are measured with a mass spectrometer. Furthermore, GDMS analysis can measure the chemical components contained in metallic materials with higher accuracy than ICP-AES analysis. Note that the total content of elements in Group A and Group B is the sum of the total content of elements in Group A and the total content of elements in Group B.

[0060] Furthermore, the oxide sintered body of the present invention is characterized by having a relative density of 95% or more. The oxide sintered body of the present invention exhibits a high relative density, preferably 95% or higher. When sputtering is performed using a sputtering target material made from the oxide sintered body of the present invention exhibiting such a high relative density, it is preferable because it is possible to suppress the generation of particles.

[0061] The oxide sintered body of the present invention is more preferably 97% or higher, even more preferably 98% or higher, particularly preferably 99% or higher, even more preferably 99.5% or higher, even more preferably 99.7% or higher, also particularly preferably 99.9% or higher, even more preferably 100% or higher, and especially preferably over 100%.

[0062] Here, the relative density of the oxide sintered body of the present invention and the sputtering target material using the same are measured based on the Archimedes method. The specific method for measuring this relative density will be described later.

[0063] Furthermore, the oxide sintered body of the present invention is characterized by having a bulk resistance of 100 mΩ·cm or less. The oxide sintered body of the present invention exhibits a low bulk resistance, preferably 100 mΩ·cm or less. Using a sputtering target material made from such a low bulk resistance oxide sintered body of the present invention is preferable because it enables DC sputtering.

[0064] The oxide sintered body of the present invention is more preferably 50 mΩ·cm or less in bulk resistance, even more preferably 40 mΩ·cm or less, particularly preferably 30 mΩ·cm or less, even more preferably 25 mΩ·cm or less, even more preferably 20 mΩ·cm or less, also particularly preferably 18.5 mΩ·cm, even more preferably 15 mΩ·cm, even more preferably 10 mΩ·cm, even more preferably 5 mΩ·cm, even more preferably 3.5 mΩ·cm, and especially preferably 1.5 mΩ·cm.

[0065] Here, the bulk resistance of the oxide sintered body of the present invention is measured by the DC four-probe method. The specific method for measuring this bulk resistance will be described later.

[0066] Furthermore, the oxide sintered body of the present invention is characterized by having a crystal grain size of 30 μm or less. The oxide sintered body of the present invention exhibits a small crystal grain size, preferably 30 μm or less. The oxide sintered body of the present invention is preferable because its small crystal grain size increases its density and strength and reduces its resistance.

[0067] The oxide sintered body of the present invention is more preferably 20 μm or less in crystal grain size, even more preferably 15 μm or less, particularly preferably 12 μm or less, even more preferably 10.3 μm or less, even more preferably 10 μm or less, also particularly preferably 8.0 μm or less, even more preferably 7.0 μm or less, even more preferably 6.0 μm or less, even more preferably 5.0 μm or less, even more preferably 4.0 μm or less, and especially preferably 3.0 μm or less. Furthermore, the smaller the crystal grain size, the better. There is no lower limit, but it is usually 0.1 μm or more.

[0068] Here, the grain size of the oxide sintered body of the present invention can be calculated by image processing of SEM images taken using a scanning electron microscope. The specific method for measuring the grain size will be described later.

[0069] Furthermore, the oxide sintered body of the present invention is characterized by having a flexural strength of 50 MPa or more. The oxide sintered body of the present invention exhibits a high flexural strength, preferably 50 MPa or higher. When sputtering is performed using a sputtering target material made of the oxide sintered body of the present invention, which exhibits such high flexural strength, it is preferable that cracks are less likely to occur in the sputtering target material even if an unintended abnormal discharge occurs during sputtering.

[0070] The oxide sintered body of the present invention is more preferably 55 MPa or higher, even more preferably 60 MPa or higher, particularly preferably 70 MPa or higher, even more preferably 80 MPa or higher, even more preferably 90 MPa or higher, particularly preferably 100 MPa or higher, even more preferably 120 MPa or higher, even more preferably 140 MPa or higher, and especially preferably 150 MPa or higher.

[0071] Here, the flexural strength of the oxide sintered body of the present invention is measured in accordance with JIS R1601. The specific method for measuring this flexural strength will be described later.

[0072] Furthermore, the sputtering target of the present invention is made of the oxide sintered body of the present invention. The sputtering target of the present invention is formed by joining, i.e., bonding, an oxide sintered body and a substrate according to the present invention.

[0073] In this specification, when "X~Y" (where X and Y are any numbers) is used, unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as the meaning of "preferably greater than X" or "preferably less than Y." Similarly, when "greater than or equal to X" (where X is any number) or "less than or equal to Y" (where Y is any number) is used, it also includes the meaning of "preferably greater than X" or "preferably less than Y." [Effects of the Invention]

[0074] The present invention provides a method for producing an oxide sintered body with a significantly reduced impurity content. [Brief explanation of the drawing]

[0075] [Figure 1] This is an explanatory diagram showing the structure of a mold used in the casting process according to the present invention. [Figure 2] This table shows the impurity content in the oxide sintered bodies of Examples 1-4 and Comparative Examples 1-4. [Best Mode for Carrying Out the Invention]

[0076] The oxide sintered body according to embodiments of the present invention will be further described below with reference to the following examples. However, the following examples are not intended to limit the present invention.

[0077] (Example 1) As raw materials, In2O3 powder with a purity of 6N (99.9999 mass%) (median diameter D50 = 0.6 μm), Ga2O3 powder with a purity of 6N (99.9999 mass%) (median diameter D50 = 1.5 μm), and ZnO powder with a purity of 6N (99.9999 mass%) (median diameter D50 = 0.8 μm) were weighed so that the mixing ratio of each powder was such that the atomic ratio of In, Ga, and Zn was In:Ga:Zn = 1:1:1. The mixture was placed in a pot, and 0.6 mass% of ammonium polycarboxylate relative to the total mass of each powder was added as a dispersant, and 20 mass% of ultrapure water relative to the total mass of each powder was added as a dispersion medium. Using Ga2ZnO4 balls (GZO media) as a grinding and mixing medium, the mixture was ground and mixed in a ball mill for 24 hours to obtain a raw material slurry.

[0078] Here, the median diameter D50 of each powder was measured using a particle size distribution analyzer MT3300EXII manufactured by Microtrac Bell Co., Ltd. Water was used as the solvent for the measurement samples. The refractive index of the measured substances was set to 2.20.

[0079] The raw material slurry obtained in this way was poured into an aluminum mold, the dispersion medium was drained, and a molded body was obtained.

[0080] Next, the obtained molded body was fired in an oxygen atmosphere at a firing temperature of 1500°C for 10 hours, with a heating rate of 300°C / h and a cooling rate of 50°C / h to obtain a fired body. The obtained fired body was then machined using a #170 grinding wheel to obtain an oxide sintered body according to Example 1, with dimensions of 210 mm in width, 710 mm in length, and 6 mm in thickness.

[0081] Then, the oxide sintered body according to Example 1 was joined to the substrate with In solder, and the surface of the oxide sintered body was surface-treated according to the dry ice blasting conditions described below to obtain the sputtering target according to Example 1.

[0082] =Dry Ice Blast Conditions= • Average particle size of dry ice particles: 0.3 mm • Gauge pressure of gas medium (N2): 0.3 MPa ·Consumption rate: 70% Processing speed: 20.0 mm / sec • Nozzle temperature: 25℃ • Processing angle: 0 degrees • Distance between target and blast nozzle: 30mm

[0083] (Example 2) In Example 2, the same manufacturing method as in Example 1 was followed, except that the mixing ratio of each powder was weighed so that the atomic ratio of In, Ga, and Zn was In:Ga:Zn = 2:1:1, and an oxide sintered body and a sputtering target according to Example 2 were obtained.

[0084] (Example 3) In Example 3, the same manufacturing method as in Example 1 was followed, except that the mixing ratio of each powder was weighed so that the atomic ratio of In, Ga, and Zn was In:Ga:Zn = 1:2:1, and an oxide sintered body and a sputtering target according to Example 3 were obtained.

[0085] (Example 4) In Example 4, the same manufacturing method as in Example 1 was followed, except that the mixing ratio of each powder was weighed so that the atomic ratio of In, Ga, and Zn was In:Ga:Zn = 1:1:2, and an oxide sintered body and a sputtering target according to Example 4 were obtained.

[0086] (Comparative Example 1) In Comparative Example 1, the same manufacturing method as in Example 1 was carried out, except that the grinding and mixing media was changed to ZrO2, and an oxide sintered body and a sputtering target according to Comparative Example 1 were obtained.

[0087] (Comparative Example 2) In Comparative Example 2, the same manufacturing method as in Example 1 was followed, except that the grinding and mixing media was changed to Al2O3, to obtain the oxide sintered body and sputtering target according to Comparative Example 2.

[0088] (Comparative Example 3) In Comparative Example 3, the same manufacturing method as in Example 1 was carried out, except that the raw material slurry was poured into a gypsum mold, the dispersion medium was drained, and a molded body was obtained, thereby obtaining the oxide sintered body and sputtering target according to Comparative Example 3.

[0089] (Comparative Example 4) In Comparative Example 4, the raw material slurry from Example 1 was dried with a spray dryer to obtain granulated powder. Furthermore, the obtained granulated powder was subjected to a surface pressure of 0.5 tf / cm². 2 The product is press-formed under these conditions, and the press-formed body is then vacuum-packed, with a surface pressure of 1.0 tf / cm². 2 A CIP molded body was obtained by CIP molding under these conditions.

[0090] Next, the obtained CIP molded body was fired in an air atmosphere at a firing temperature of 1500°C for 10 hours, with a heating rate of 300°C / h and a cooling rate of 50°C / h to obtain a fired body. The obtained fired body was then machined using a #170 grinding wheel to obtain an oxide sintered body according to Comparative Example 4, with dimensions of 210 mm in width, 710 mm in length, and 6 mm in thickness.

[0091] Then, the oxide sintered body according to Comparative Example 4 was joined to a substrate to obtain a sputtering target according to Comparative Example 4. Note that the surface of the oxide sintered body according to Comparative Example 4 was not subjected to surface treatment by dry ice blasting.

[0092] The oxide sintered bodies and sputtering targets obtained in Examples 1-4 and Comparative Examples 1-4 were then subjected to the following physical properties. The measured physical properties and the methods used to measure them are shown below, along with the measurement results in Table 1 and Figure 2.

[0093] <GDMS analysis> The contents of impurities (elements in Group A and Group B) contained in the oxide sintered compacts according to Examples 1 to 4 and Comparative Examples 1 to 4 were measured using GDMS analysis. GDMS analysis is a method in which a sample is used as a cathode to generate a glow discharge in an Ar atmosphere, the sample surface is sputtered in a plasma, and the ionized constituent elements are measured with a mass spectrometer. In FIG. 2, "N.D." indicates a case where the value is less than the detection limit of GDMS analysis, and the content is regarded as 0 mass ppm.

[0094] 〈Relative density〉 The relative densities of the oxide sintered compacts according to Examples 1 to 4 and Comparative Examples 1 to 4 were measured based on the Archimedes method. Specifically, the air mass of the target material was divided by the volume (the underwater mass of the target material / the specific gravity of water at the measurement temperature), and the percentage value with respect to the theoretical density ρ (g / cm 3 ) was taken as the relative density (unit: %).

[0095]

Equation

[0096] (In the formula, C1 to C i each represent the content (mass %) of the constituent substances of the target material, and ρ1 to ρ i represent the densities (g / cm i ) of the respective constituent substances corresponding to C1 to C 3 ).)

[0097] The constituent substances of the oxide sintered compact of the present invention and the sputtering target material using the same are considered to be In2O3, Ga2O3, and ZnO. For example, as follows, C1: Mass % of In2O3 in the oxide sintered compact or the target material ρ1: Density of In2O3 (7.18 g / cm 3 ) C2: Mass % of Ga2O3 in the oxide sintered compact or the target material ρ2: Density of Ga2O3 (5.95 g / cm 3 ) C3: Mass % of ZnO in the oxide sintered compact or the target material ρ3: Density of ZnO (5.60 g / cm³) 3 ) By applying this to equation (X), the theoretical density ρ was calculated.

[0098] The mass percentages of In2O3, Ga2O3, and ZnO mentioned above were determined from the analysis results of each element of the oxide sintered body or sputtering target material by ICP-OES analysis.

[0099] <Bulk resistance> The bulk resistance of the oxide sintered bodies in Examples 1-4 and Comparative Examples 1-4 was measured using a Loresta®-GX MCP-T700 low-resistivity resistivity meter manufactured by Nitto Seiko Analytech Co., Ltd., in accordance with the measurement method of JIS-K-7194 (Resistivity test method for conductive plastics using the four-probe method).

[0100] <Crystal grain size measurement> The crystal grain size, i.e., the area circle equivalent diameter, of the oxide sintered bodies in Examples 1-4 and Comparative Examples 1-4 was determined by measuring the area circle equivalent diameter of each crystal phase from SEM images taken of the surface of the oxide sintered body using a scanning electron microscope. Specifically, the cut surface obtained by cutting the oxide sintered body of the present invention was polished stepwise using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. Next, the cut surface was etched by immersion for 2 minutes in an etching solution at 40°C (a mixture of nitric acid (60-61% by mass aqueous solution, manufactured by Kanto Chemical Co., Ltd.), hydrochloric acid (35.7-37.0% by mass aqueous solution, manufactured by Kanto Chemical Co., Ltd.), and pure water in a volume ratio of HCl:H2O:HNO3 = 1:1:0.08). The cross-section was then observed using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), and 10 randomly selected BSE-COMP images were captured in an area of ​​87.5 μm × 125 μm at a magnification of 1000x, obtaining SEM images for all 10 fields.

[0101] The obtained SEM images were plotted along the grain boundaries of each crystalline phase using the image processing software ImageJ (provided by the National Institutes of Health). After all plotting was completed, particle analysis was performed (Analyze → Analyze Particles) to obtain the area of ​​each particle. Subsequently, the area circle equivalent diameter was calculated from the obtained area of ​​each particle. This was performed for 10 fields of view of the SEM images, and the arithmetic mean value of the area circle equivalent diameters of all calculated particles was taken as the area circle equivalent diameter of the crystalline phase in each oxide sintered body. The obtained area circle equivalent diameter was taken as the grain size in each oxide sintered body.

[0102] <Diverse bending strength> The flexural strength of the oxide sintered bodies in Examples 1-4 and Comparative Examples 1-4 was measured using a Shimadzu Autograph® AGS-500B in accordance with JIS standard JIS-R-1601 (Bending strength test method for fine ceramics). Specifically, test pieces (total length 36 mm or more, width 4.0 mm, thickness 3.0 mm) cut from each oxide sintered body were used to measure the three-point bending strength according to the measurement method of JIS-R-1601.

[0103] [Table 1]

[0104] As shown in Figure 2, the Zr content of the oxide sintered bodies in Examples 1 to 4 was less than 1 ppm by mass, indicating that the inclusion of impurities was reduced. On the other hand, the Zr content of the oxide sintered body in Comparative Example 1 was 20 ppm by mass or more, suggesting that Zr was introduced from the ZrO2 balls used as the grinding and mixing media.

[0105] The Al content of the oxide sintered bodies in Examples 1 to 4 was 1 ppm by mass or less, indicating that the inclusion of Al-containing impurities was reduced. On the other hand, the Al content of the oxide sintered body in Comparative Example 2 was 20 ppm by mass or more, suggesting that Al was introduced from the Al2O3 balls used as the grinding and mixing media.

[0106] The total content of impurities (elements of group A and group B) in the oxide sintered bodies of Examples 1 to 4 was 5 ppm by mass or less, indicating that the presence of impurities was reduced. On the other hand, the total content of impurities (elements of group A and group B) in the oxide sintered bodies of Comparative Examples 1 to 4 was 20 ppm by mass or more. For example, the total content of impurities (elements of group A and group B) in the oxide sintered body of Comparative Example 3 was 20 ppm by mass or more, suggesting that impurities were introduced from the mold used due to the use of a gypsum mold. Furthermore, the total content of impurities (elements of group A and group B) in the oxide sintered body of Comparative Example 4 was 20 ppm by mass or more, suggesting that impurities were introduced when the raw material slurry was dried with a spray dryer to form granulated powder.

[0107] Furthermore, the total content of impurities (elements of group B) in the oxide sintered bodies of Examples 1 to 4 was 1 ppm by mass or less, indicating that the presence of impurities was reduced. On the other hand, the total content of impurities (elements of group B) in the oxide sintered bodies of Comparative Examples 1, 2, and 4 was greater than 1 ppm by mass.

[0108] The inventions disclosed herein include, in addition to the configurations of each invention and embodiment, those specified by modifying these partial configurations to other configurations disclosed herein to the extent applicable, or those specified by adding other configurations disclosed herein to these configurations, or those specified by deleting these partial configurations to the extent that partial effects are obtained, resulting in broader conceptualizations. [Industrial applicability]

[0109] The method for producing oxide sintered bodies according to the present invention significantly reduces the content of impurities, making it suitable as a method for producing high-purity oxide sintered bodies and sputtering targets. Furthermore, the oxide sintered bodies and sputtering targets according to the present invention can suppress arcing compared to conventional sputtering targets, thereby reducing the occurrence of defective products. This contributes to the sustainable management and efficient use of natural resources, as well as achieving decarbonization (carbon neutrality). [Explanation of Symbols]

[0110] 1… Raw material slurry 2…Molding mold 3…Bottom mold for molding 4…Drainage holes 5…Filter 6…Sealant

Claims

1. A method for manufacturing a sputtering target material consisting of an oxide sintered body made from an oxide containing two or more elements selected from In, Ga, and Zn, A method for manufacturing a sputtering target material that satisfies the following conditions (a) to (d1). (a) The raw material used is an oxide with a purity of 6N or higher. (b) The grinding and mixing media is formed from an oxide that does not contain any elements other than the elements selected as raw materials. (c) Use ultrapure water as the dispersion medium to form a slurry. (d1) The product is cast using a metal mold.

2. A method for producing a sputtering target material comprising an oxide sintered body made from an oxide containing two or more elements selected from In, Ga, and Zn, A method for manufacturing a sputtering target material that satisfies the following conditions (a) to (d2). (a) The raw material used is an oxide with a purity of 6N or higher. (b) The grinding and mixing media is formed from an oxide that does not contain any elements other than the elements selected as raw materials. (c) Use ultrapure water as the dispersion medium to form a slurry. (d2) The material is cast using a ceramic mold made from an oxide that does not contain any elements other than the element selected as the raw material.

3. A method for manufacturing a sputtering target material according to claim 1 or 2, which satisfies (e) below. (e) After grinding the surface of the oxide sintered body, surface treatment is performed by spraying dry ice particles.

4. A method for manufacturing a sputtering target, characterized in that a sputtering target material manufactured by the method for manufacturing a sputtering target material described in claim 1 or 2 is joined to a substrate.

5. A sputtering target material comprising an oxide sintered body containing two or more elements selected from In, Ga, and Zn, A sputtering target material characterized in that the total content of elements in groups A and B below, as determined by GDPM analysis, is 10 ppm by mass or less, and the total content of elements in group B is 1 ppm by mass or less. Group A: Li, Be, B, F, Na, Mg, Al, Si, P, K, Ca, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Cs, Ba, Tl, Pb, Bi, Th, U Group B: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg However, if the content is below the detection limit of GDPM analysis, it will be considered as 0 ppm by mass.

6. The sputtering target material according to claim 5, characterized in that its relative density is 95% or more.

7. The sputtering target material according to claim 5, characterized in that the bulk resistance is 100 mΩ·cm or less.

8. The sputtering target material according to claim 5, characterized in that the crystal grain size is 30 μm or less.

9. The sputtering target material according to claim 5, characterized in that it has a bending strength of 50 MPa or more.

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