Method for producing oxide sintered body

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

Method for producing oxide sintered body

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

[0002] In the technical field of thin film transistors (hereinafter referred to as "TFTs") used in display devices such as flat panel displays (hereinafter referred to as "FPDs"), as FPDs become more highly functional, oxide semiconductors such as In-Ga-Zn composite oxides (hereinafter referred to as "IGZO") as shown in Patent Documents 1 and 2 are increasingly being put to practical use in place of conventional amorphous silicon.

[0003] In recent years, oxide semiconductors have been developed with high mobility (>10 cm ２ It has the excellent feature of being able to achieve both high voltage (V / Vs) and extremely low off-leakage current (<10-22 A / μm), and is expected to be used as a channel material for vertical FETs that can be integrated with Si-CMOS LSIs and highly integrated using a BEOL compatible process in the semiconductor manufacturing process. Along with these expectations, the required properties of 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 of these 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 25 ppm of Na as an impurity, and also lists Cd, Cu, Fe, K, Ni, Pb, etc. as impurities. The contents of these impurities other than Na are each 10 ppm or less, and the total content is 100 ppm or less.

[0005] JP 2008-163441 A JP 2010-202450 A

[0006] However, in recent years, the requirements for properties regarding impurities contained in oxide sintered bodies have become stricter, and further reduction in the content of impurities is being sought.

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

[0008] The method for producing an oxide sintered body of the present invention, which has been made to solve the above problems, is a method for producing an oxide sintered body using as a raw material an oxide containing two or more elements selected from the group consisting of In, Ga, and Zn, and satisfies the following (a) to (c): (a) The raw material 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 the raw materials. (c) Ultrapure water is used as the dispersion medium to form a slurry. This configuration makes it possible to produce an oxide sintered body with a significantly reduced impurity content.

[0009] The raw material in (a) is an oxide containing two or more elements selected from the group consisting of In, Ga, and Zn. Specifically, an oxide containing In (In ２ O ３ ), oxides containing Ga element (Ga ２ O ３ ), and two oxides containing Zn (ZnO) (In ２ O ３ and Ga ２ O ３ , In ２ O ３ and ZnO, Ga ２ O ３ and ZnO), and three types (In ２ O ３ , Ga ２ O ３ Furthermore, it may be a composite oxide containing two or more elements selected from the group consisting of In, Ga, and Zn.

[0010] The purity of the oxide containing two or more elements selected from the group consisting of In, Ga, and Zn is 6N (99.9999 mass%) or more. When the purity of each oxide used as a raw material is 6N or more, 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, Since the content of impurities such as Hg is significantly reduced, the content of impurities contained in the oxide sintered body produced 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 more, since the contents of Fe, Al, Si, Ni, and Cu can be significantly reduced.

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

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

[0013] That is, an oxide containing In element (In ２ O ３ ) and an oxide containing Ga element (Ga ２ O ３ When the above two types of grinding and mixing media are selected, the grinding and mixing media are formed from an oxide that does not contain any elements other than In and Ga. For example, the grinding and mixing media may be formed from an oxide that does not contain any elements other than In and Ga. ２ O ３ , Ga ２ O ３ , InGaO ３ Media formed from In ２ O ３ Preferably, the media is formed from

[0014] The raw material is an oxide containing In element (In ２ O ３ In the case where two types of materials are selected, that is, In and an oxide containing Zn (ZnO), the grinding and mixing media are formed from an oxide containing no elements other than In and Zn. For example, the grinding and mixing media may be formed from In ２ O ３ , ZnO, In ２ Zn ３ O ６ Media formed from In ２ O ３ Preferably, the media is formed from

[0015] The raw material is an oxide containing Ga element (Ga ２ O ３ When two types of materials are selected, that is, Ga and an oxide containing Zn (ZnO), the grinding and mixing media are formed from an oxide containing no elements other than Ga and Zn. ２ O ３ , ZnO, Ga ２ ZnO ４ and Ga ２ ZnO ４ Preferably, the media is formed from

[0016] The raw material is an oxide containing In element (In ２ O ３ ), oxides containing Ga element (Ga ２ O ３ In the case where three types of oxides are selected, namely, In, Ga, and Zn, the grinding and mixing media are formed from an oxide that does not contain any elements other than In, Ga, and Zn. ２ O ３ , Ga ２ ZnO ４ and Ga ２ ZnO ４ Preferably, the media is formed from

[0017] In addition, the above (b) that the grinding / mixing media "does not contain elements other than the elements selected as the raw materials" means that the content of impurities contained in the grinding / mixing media is 100 mass ppm or less. Here, examples of 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, and Hg.

[0018] The dispersion medium in (c) is preferably ultrapure water. Here, ultrapure water is water of high purity, and since the electrical resistivity of theoretically pure water (pure water) is 18.24 MΩ cm, it is preferable that the dispersion medium is as close as possible to this value, preferably 15.0 MΩ cm or more, more preferably 16.0 MΩ cm or more, even 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] This ultrapure water can be used as a dispersion medium and mixed with the raw materials to form a slurry. The ultrapure water is highly pure, and the purity of the raw materials is not reduced by impurities contained in the ultrapure water.

[0020] Furthermore, the method for producing an oxide sintered body of the present invention satisfies the following requirement (d1): (d1) Slip casting is performed using a metal mold. This configuration makes it possible to prevent impurities from being mixed into the oxide sintered body during slip casting.

[0021] As shown in Figure 1, the metal mold in (d1) above can obtain a molded body by pouring a slurried raw material (hereinafter referred to as raw material slurry 1) into a molding frame 2 from above and draining the material under reduced pressure through one or more drainage holes 4 provided in a lower molding die 3. The lower molding die 3 has a structure in which a water-permeable filter 5 (e.g., Gore-Tex (registered trademark) wet filter cloth, manufactured by Gore Japan Inc.) that prevents the raw material in the raw material slurry 1 from passing through is placed on the molding frame 2 via a sealing material 6.

[0022] Here, the molding frame 2 and the lower molding die 3 are made of metal, for example, aluminum, which is preferable because impurities are less likely to be mixed into the resulting molded body during slip casting.

[0023] Furthermore, the method for producing an oxide sintered body of the present invention satisfies the following requirement (d2): (d2) Slip casting is performed using a ceramic mold formed from an oxide containing no elements other than the elements selected as the raw materials. This configuration makes it possible to prevent impurities from being mixed into the oxide sintered body during slip casting.

[0024] If the ceramic mold in (d2) above is formed from an oxide that does not contain any elements other than the elements selected as the raw materials, even if part of the ceramic mold is mixed in during slip casting, the purity of the molded body will not be reduced because the components of the ceramic mold are the same as those of the molded body.

[0025] The structure of the ceramic forming mold in (d2) above is similar to the structure of the metal forming mold in (d1) above shown in FIG. 1, so detailed explanation will be omitted, but the forming frame 2 and the lower forming mold 3 are formed from the oxides described below.

[0026] The forming mold frame 2 and the forming lower mold 3 for the ceramic forming mold are made of an oxide containing In element (In ２ O ３ ) and an oxide containing Ga element (Ga ２ O ３When the two types of oxides are selected, the oxides are formed from oxides that do not contain elements other than In and Ga. For example, the forming mold frame 2 and the forming lower mold 3 for the ceramic forming mold are formed from oxides that do not contain In. ２ O ３ , Ga ２ O ３ , InGaO ３ Preferably, it is formed from In ２ O ３ It is particularly preferred that the polymer is formed from

[0027] The forming mold frame 2 and the forming lower mold 3 for the ceramic forming mold are made of an oxide containing In element (In ２ O ３ When two types of oxides are selected, that is, In and an oxide containing Zn (ZnO), the ceramic mold is formed from an oxide containing no elements other than In and Zn. For example, the molding frame 2 and the molding lower die 3 for the ceramic molding die may be formed from In ２ O ３ , ZnO, In ２ Zn ３ O ６ Preferably, it is formed from In ２ O ３ It is particularly preferred that the polymer is formed from

[0028] The forming mold frame 2 and the forming lower mold 3 for the ceramic forming mold are made of an oxide containing Ga element (Ga ２ O ３ When two types of oxides are selected, Ga and an oxide containing no elements other than Zn (ZnO), the ceramic molding die is formed of an oxide containing no elements other than Ga and Zn. ２ O ３ , ZnO, Ga ２ ZnO ４ Preferably, it is formed from Ga ２ ZnO ４ It is particularly preferred that the polymer is formed from

[0029] The forming mold frame 2 and the forming lower mold 3 for the ceramic forming mold are made of an oxide containing In element (In ２ O ３ ), oxides containing Ga element (Ga２ O ３ In the case where three types of oxides are selected, namely, In, Ga, and an oxide containing Zn (ZnO), the molding frame 2 and the molding lower die 3 for the ceramic molding die are formed from an oxide containing no elements other than In, Ga, and Zn. ２ O ３ , Ga ２ ZnO ４ Preferably, it is formed from Ga ２ ZnO ４ It is particularly preferred that the polymer is formed from

[0030] In addition, the above (b) that the ceramic molding die "does not contain elements other than the elements selected as the raw materials" means that the content of impurities contained in the ceramic molding die is 100 ppm or less. Examples of impurities contained in the ceramic forming 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, and Hg.

[0031] Furthermore, the method for producing an oxide sintered body of the present invention satisfies the following (e): (e) After grinding the surface of the oxide sintered body, dry ice particles are sprayed onto the surface to perform surface treatment. With this configuration, the sprayed dry ice particles collide with the surface of the oxide sintered body, thereby removing microcracked portions present on the surface of the oxide sintered body and also removing processing chips, dust, and dirt present on the surface of the oxide sintered body. Furthermore, since the dry ice particles quickly vaporize, penetration of the dry ice particles through the surface of the oxide sintered body can be suppressed.

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

[0033] Dry ice blasting conditions: Average particle size of dry ice particles: 0.1 to 1 mm Gas medium (N ２ ) Gauge pressure: 0.1 to 0.6 MPa Wear rate: 20 to 100% Processing speed: 0.8 to 142.9 mm / sec Nozzle temperature: ≧20°C Processing angle: 0 to 20 degrees Distance between target and blast nozzle: 10 to 140 mm

[0034] The dry ice particles sprayed from the blast nozzle are crushed and pulverized dry ice, and their shape does not have to be spherical, and they may be irregular. The size of the dry ice particles is not particularly limited as long as they can be sprayed together with the gas medium. The average particle size of the dry ice particles is preferably 0.1 to 1 mm.

[0035] 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 of ejecting the dry ice particles and gas medium can be carried out in the same manner as general shot blasting, by simply mixing the dry ice particles with the gas medium that is ejected at a predetermined pressure.

[0037] The "wear rate" in the dry ice blasting conditions indicates the feed rate at which the dry ice is pushed out. The "treatment speed" in the dry ice blasting conditions indicates the speed at which the blast nozzle is moved over the oxide sintered body. The "treatment angle" in the dry ice blasting conditions indicates the angle of the blast nozzle with respect to the surface of the oxide sintered body. When the blast nozzle is positioned perpendicular to the surface of the oxide sintered body, the treatment angle is 0 degrees, and when the blast nozzle is positioned parallel to the surface of the oxide sintered body, the treatment angle is 90 degrees.

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

[0039] First, as a raw material, In with a purity of 6N that satisfies the above (a) is used. ２ O ３ Powder, 6N purity Ga ２ O ３ The powder and ZnO powder with a purity of 6N are weighed and placed in a pot, and these are pulverized and mixed. 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, Hg, etc. is significantly reduced. A dispersant may be added when forming the slurry.

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

[0041] Specifically, the dry grinding is carried out by adding In ２ O ３ Powder, Ga ２ O ３ powder, and ZnO powder, and a grinding and mixing medium that satisfies the above (b). ２ ZnO ４ By placing balls (hereinafter referred to as GZO media) in the pot and mixing the pot in a ball mill, In ２ O ３ Powder, Ga ２ O ３ The powder and ZnO powder are dry-milled.

[0042] The dry-ground In in the pot ２ O ３ Powder, Ga ２ O ３ The mixture containing the powder and ZnO powder was separated from the GZO media using a filter, and the dry-milled In ２ O ３Powder, Ga ２ O ３ A mixture containing the powder and ZnO powder is obtained.

[0043] Then, in a separate pot, dry-ground In ２ O ３ Powder, Ga ２ O ３ The powder, ZnO powder, and ultrapure water as a dispersion medium are added, and GZO media are further added as a grinding and mixing medium. The pot is then mixed to form a slurry. ２ O ３ Powder, Ga ２ O ３ Alternatively, the mixture containing the powder and the ZnO powder may be left in the pot, and ultrapure water may be added as a dispersion medium to the pot containing the dry-milled mixture, and the mixture may be mixed to form a slurry. Additives such as a dispersant and a binder may be added as needed.

[0044] On the other hand, wet grinding is carried out by adding In ２ O ３ Powder, Ga ２ O ３ In powder, ZnO powder, and ultrapure water as a dispersion medium were added, and GZO media were added as a grinding and mixing medium. The pot was then mixed in a ball mill to produce In. ２ O ３ Powder, Ga ２ O ３ The powder and ZnO powder are wet-milled.

[0045] The wet-ground In in the pot ２ O ３ Powder, Ga ２ O ３ The raw slurry containing the powder and ZnO powder is filtered using a filter to separate it from the GZO media, thereby obtaining the raw slurry.

[0046] Furthermore, if the pot, like the grinding and mixing media, is formed from an oxide that does not contain any elements other than those selected as raw materials, even if part of the pot is scraped off when the raw materials are ground and mixed, the incorporation of impurities such as Al and Si can be suppressed.

[0047] The raw material slurry thus obtained is poured into a metal mold satisfying the above (d1) or a ceramic mold satisfying the above (d2), and the ultrapure water serving as the dispersion medium is removed to obtain a compact.

[0048] Specifically, the obtained raw material slurry is degassed and poured into a metal mold satisfying the above (d1) or a ceramic mold satisfying the above (d2). The pressure is then reduced on the lower mold surface side of the filter 5 shown in FIG. 1 , and the water in the raw material slurry is drained under reduced pressure from the filter surface side, thereby forming the molded product. A reduced pressure of greater than −700 mmHg is preferred. A vacuum pump or the like may also be used as a method of reducing the pressure. Furthermore, the reduced pressure drainage time is preferably approximately 30 minutes after the completion of the casting of the molded product. Here, if the reduced pressure drainage time is short, the molded product may be difficult to release from the molding frame 2, and cracks may occur. Furthermore, if the reduced pressure drainage time is too long, the molded product may be released from the molding frame 2 during the reduced pressure drainage, and air is sucked through the gaps, causing only the released portion of the molded product to dry rapidly, making it more susceptible to cracks.

[0049] The resulting compact is fired to obtain a fired body. When firing the compact, the inside of the firing furnace is placed under an atmosphere of high oxygen concentration, which can prevent light elements such as H, C, and N from being mixed into the fired body.

[0050] The resulting sintered body is then cut into a desired shape to obtain the oxide sintered body of the present invention.

[0051] The method for producing a sputtering target of the present invention is characterized in that the oxide sintered body produced by the method for producing an oxide sintered body of the present invention described above is joined to a substrate.

[0052] The sputtering target of the present invention can be obtained by joining, i.e., bonding, the oxide sintered body produced by the oxide sintered body production method of the present invention to a substrate using solder (e.g., In metal). The substrate can be made of Cu, Al, Ti, or stainless steel. The bonding material can be a bonding material used for bonding conventional ITO target materials, such as In metal. 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 of the present invention to the substrate is not particularly limited, but examples include low-melting-point solders such as In metal, In—Sn metal, or In alloy metal in which trace metal components are added to In. The melting point of the low-melting-point solder is 150 to 200° C., so when filling the 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. The surface of the oxide sintered body is subjected to the surface treatment by dry ice blasting, in which dry ice particles are sprayed, according to the above-mentioned dry ice blasting conditions, as shown in (e) above.

[0055] The oxide sintered body bonded to the substrate in this manner is subjected to dry ice blasting to obtain the sputtering target of the present invention.

[0056] The oxide sintered body of the present invention is an oxide sintered body containing two or more elements selected from In, Ga, and Zn, and is characterized in that the total content of elements in the following 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: 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, when the content is less than the detection limit of GDMS analysis, it is considered to be 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. These elements belonging to Group A may have an adverse effect on the properties of the oxide semiconductor film formed using the oxide sintered body of the present invention, so it is preferable that the content thereof is small. Furthermore, Group B is a group of elements mainly selected from transition metals and lanthanides. These elements belonging to Group B may also have an adverse effect on the properties of the oxide semiconductor film formed using the oxide sintered body of the present invention, so it is preferable that the content thereof is small. In particular, elements belonging to Group B are more likely to have an adverse effect on the properties of the oxide semiconductor film formed using the oxide sintered body of the present invention than elements belonging to Group A, so it is preferable that the content thereof is particularly small.

[0058] It is preferable that the total content of the elements of Group A and Group B as determined by GDMS analysis is 10 mass ppm or less and the total content of the elements of Group B is 1 mass ppm or less, in order to manufacture high-performance TFTs. Furthermore, it is more preferable that the total content of the elements of Group A and Group B as determined by GDMS analysis is 8 mass ppm or less, even more preferably 6 mass ppm or less, particularly preferably 5 mass ppm or less, more particularly preferably 4.9 mass ppm or less, even particularly preferably 4.8 mass ppm or less, and even particularly preferably 4.5 mass ppm or less. Furthermore, it is more preferable that the total content of the elements of Group B as determined by GDMS analysis is 0.9 mass ppm or less, even more preferably 0.8 mass ppm or less, particularly preferably 0.7 mass ppm or less, more particularly preferably 0.6 mass ppm or less, even particularly preferably 0.5 mass ppm or less, and even particularly preferably 0.4 mass ppm 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 using a sample as a cathode in an Ar atmosphere, the sample surface is sputtered in the plasma, and the ionized constituent elements are measured using a mass spectrometer. Furthermore, GDMS analysis can measure the chemical components contained in a metal material with higher accuracy than ICP-AES analysis. 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] The oxide sintered body of the present invention is also characterized by having a relative density of 95% or more. The oxide sintered body of the present invention exhibits a high relative density, and the relative density is preferably 95% or more. When sputtering is performed using a sputtering target material using the oxide sintered body of the present invention exhibiting such a high relative density, it is preferable because it becomes possible to suppress the generation of particles.

[0061] The oxide sintered body of the present invention preferably has a relative density of 97% or more, even more preferably 98% or more, particularly preferably 99% or more, more particularly preferably 99.5% or more, even more particularly preferably 99.7% or more, still more particularly preferably 99.9% or more, even more preferably 100% or more, and particularly preferably more than 100%.

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

[0063] The oxide sintered body of the present invention is also characterized in that it has a bulk resistance of 100 mΩ cm or less. The oxide sintered body of the present invention exhibits a low bulk resistance, and it is preferable that the bulk resistance is 100 mΩ cm or less. By using a sputtering target material using the oxide sintered body of the present invention that exhibits such a low bulk resistance, DC sputtering becomes possible, which is preferable.

[0064] The oxide sintered body of the present invention more preferably has a bulk resistance of 50 mΩ cm or less, even more preferably 40 mΩ cm or less, particularly preferably 30 mΩ cm or less, more particularly preferably 25 mΩ cm or less, even more particularly 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, still more preferably 5 mΩ cm, still more preferably 3.5 mΩ cm, and particularly preferably 1.5 mΩ cm.

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

[0066] The oxide sintered body of the present invention is also characterized in that it has a crystal grain size of 30 μm or less. The oxide sintered body of the present invention exhibits a small crystal grain size, and the crystal grain size is preferably 30 μm or less. The oxide sintered body of the present invention is preferred in that the small crystal grain size can increase its density and strength and reduce its resistance.

[0067] The oxide sintered body of the present invention preferably has a crystal grain size of 20 μm or less, even more preferably 15 μm or less, particularly preferably 12 μm or less, more particularly preferably 10.3 μm or less, even more particularly preferably 10 μm or less, still more 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, still more preferably 4.0 μm or less, and particularly preferably 3.0 μm or less. Furthermore, the smaller the crystal grain size, the better, and although there is no particular lower limit, it is usually 0.1 μm or more.

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

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

[0070] The oxide sintered body of the present invention preferably has a bending strength of 55 MPa or more, even more preferably 60 MPa or more, particularly preferably 70 MPa or more, more particularly preferably 80 MPa or more, even more particularly preferably 90 MPa or more, still more particularly preferably 100 MPa or more, even more preferably 120 MPa or more, even more preferably 140 MPa or more, and particularly preferably 150 MPa or more.

[0071] Here, the flexural strength of the oxide sintered body of the present invention is measured in accordance with JIS R 1601. A specific method for measuring the flexural strength will be described later.

[0072] 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 obtained by joining, i.e., bonding, the oxide sintered body of the present invention to a substrate.

[0073] In this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number), it also means "preferably larger than X" or "preferably smaller than Y".

[0074] The method for producing an oxide sintered body of the present invention produces an oxide sintered body with a significantly reduced content of impurities.

[0075] 1 is an explanatory diagram showing the structure of a mold used in slip casting according to the present invention. 2 is a table showing the contents of impurities contained in the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 4.

[0076] The oxide sintered body according to the embodiment of the present invention will be further described below with reference to the following examples. However, the present invention is not limited to the following examples.

[0077] (Example 1) As a raw material, In with a purity of 6N (99.9999 mass%) was used. ２ O ３Ga powder (median diameter D50 = 0.6 μm) with a purity of 6N (99.9999 mass%) ２ O ３ Powder (median diameter D50 = 1.5 μm) with a purity of 6N (99.9999 mass%) and ZnO powder (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, and placed in a pot. 0.6 mass% of ammonium polycarboxylate was added as a dispersant with respect to the total mass of each powder, and 20 mass% of ultrapure water was added as a dispersion medium with respect to the total mass of each powder. Ga was added as a grinding and mixing medium. ２ ZnO ４ The mixture was pulverized and mixed in a ball mill using balls (GZO media) for 24 hours to obtain a raw material slurry.

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

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

[0080] Next, the obtained compact was fired in an oxygen atmosphere at a firing temperature of 1500°C for 10 hours at a temperature increase rate of 300°C / h and a temperature decrease rate of 50°C / h to obtain a fired body. The fired body was then cut using a #170 grindstone to a width of 210 mm, a length of 710 mm, and a thickness of 6 mm to obtain an oxide sintered body according to Example 1.

[0081] Then, the oxide sintered body according to Example 1 was joined to a substrate with In solder, and the surface of the oxide sintered body was subjected to a surface treatment according to the following dry ice blasting conditions, thereby obtaining a sputtering target according to Example 1.

[0082] Dry ice blasting conditions: Average particle size of dry ice particles: 0.3 mm Gas medium (N ２) Gauge pressure: 0.3 MPa Wear rate: 70% Processing speed: 20.0 mm / sec Nozzle temperature: 25°C Processing angle: 0 degrees Distance between target and blast nozzle: 30 mm

[0083] (Example 2) In Example 2, the same manufacturing method as in Example 1 was carried out, except that the powders were 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 carried out, except that the powders were 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 carried out, except that the powders were 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 grinding and mixing media was ZrO ２ Except for the change, the same production method as in Example 1 was carried out, 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 grinding and mixing media was Al ２ O ３ Except for the change, the same production method as in Example 1 was carried out, and an oxide sintered body and a sputtering target according to Comparative Example 2 were obtained.

[0088] (Comparative Example 3) In Comparative Example 3, the same production 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, and an oxide sintered body and a sputtering target according to Comparative Example 3 were obtained.

[0089] Comparative Example 4 In Comparative Example 4, the raw material slurry according to Example 1 was dried with a spray dryer to obtain granulated powder. ２ The press-molded body was then vacuum-packed under a surface pressure of 1.0 tf / cm ２ A CIP molded body was obtained by CIP molding under the conditions of

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

[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 following physical properties were measured for the oxide sintered bodies and sputtering targets obtained in Examples 1 to 4 and Comparative Examples 1 to 4. The measured physical property values ​​and the measurement methods for the physical property values ​​are shown below, and the measurement results are shown in Table 1 and FIG.

[0093] <GDMS Analysis> The contents of impurities (elements of Group A and Group B) contained in the oxide sintered bodies 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 glow discharge is generated using a sample as a cathode in an Ar atmosphere, the sample surface is sputtered in the plasma, and the ionized constituent elements are measured using a mass spectrometer. Note that "N.D." in Figure 2 indicates a case where the content is below the detection limit of GDMS analysis, and the content is considered to be 0 ppm by mass.

[0094] <Relative Density> The relative density of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 4 was measured based on the Archimedes method. Specifically, the mass of the target material in air was divided by the volume (mass of the target material in water / specific gravity of water at the measurement temperature) to obtain the theoretical density ρ (g / cm) based on the following formula (X): ３ The percentage of the density (unit: %) was taken as the relative density.

[0095]

[0096] (C in the formula １ ~C ｉ indicates the content (mass%) of the constituent substances in the target material, and ρ １ ~ρ ｉ is C １ ~C ｉ The density (g / cm) of each constituent material corresponding to ３ ) indicates.

[0097] The oxide sintered body of the present invention and the sputtering target material made using the same are composed of In. ２ O ３ , Ga ２ O ３ , ZnO, for example, as follows: C １ : In of oxide sintered body or target material ２ O ３ Mass% of ρ １ :In ２ O ３ Density (7.18 g / cm ３ ) C ２ : Ga of oxide sintered body or target material ２ O ３ Mass% of ρ ２ : Ga ２ O ３ Density (5.95 g / cm ３ ) C ３ ρ: mass% of ZnO in the oxide sintered body or target material ３ : Density of ZnO (5.60 g / cm ３ ) was applied to equation (X) to calculate the theoretical density ρ.

[0098] In addition, the above-mentioned In ２ O ３ %, by mass of Ga２ O ３ The mass % of ZnO and the mass % of ZnO were determined from the analysis results of each element of the oxide sintered body or sputtering target material by ICP-OES analysis.

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

[0100] <Crystal Grain Size Measurement> The crystal grain size, i.e., the equivalent circle diameter, of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 4 was measured by measuring the equivalent circle diameter of each crystal phase from SEM images of the surface of the oxide sintered body taken with a scanning electron microscope. Specifically, the cut surface obtained by cutting the oxide sintered body of the present invention was polished in stages using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. Next, the cut surface was polished with an etching solution (nitric acid (60 to 61 mass % aqueous solution, manufactured by Kanto Chemical Co., Inc.), hydrochloric acid (35.7 to 37.0 mass % aqueous solution, manufactured by Kanto Chemical Co., Inc.), and pure water in a volume ratio of HCl:H at 40°C. ２ O: HNO ３ The cut surface was then observed using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), and BSE-COMP images of 10 fields of view were taken at random at 1000x magnification and within an area of ​​87.5 μm × 125 μm, to obtain SEM images of the 10 fields of view.

[0101] The obtained SEM image was plotted along the grain boundaries of each crystalline phase using 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. Then, the equivalent area circle diameter was calculated from the obtained area of ​​each particle. This was performed on 10 SEM images, and the arithmetic mean value of the calculated equivalent area circle diameters of all particles was taken as the equivalent area circle diameter of the crystalline phase in each oxide sintered body. The obtained equivalent area circle diameter was taken as the crystal grain size in each oxide sintered body.

[0102] <Flexural Strength> The flexural strength of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 4 was measured in accordance with JIS standard: JIS-R-1601 (Flexural Strength Test Method for Fine Ceramics) using an Autograph (registered trademark) AGS-500B manufactured by Shimadzu Corporation. Specifically, using test pieces (total length 36 mm or more, width 4.0 mm, thickness 3.0 mm) cut out from each oxide sintered body, the flexural strength was measured according to the three-point bending strength measurement method of JIS-R-1601.

[0103]

[0104] As shown in Figure 2, the Zr content of the oxide sintered bodies according to Examples 1 to 4 was less than 1 mass ppm, and therefore the inclusion of impurities was reduced. On the other hand, the Zr content of the oxide sintered body according to Comparative Example 1 was 20 mass ppm or more, and therefore ZrO ２ It is believed that Zr was mixed in from the grinding and mixing media due to the use of balls made of the material.

[0105] The Al content of the oxide sintered bodies according to Examples 1 to 4 was 1 mass ppm or less, so that it was possible to reduce the inclusion of impurities containing Al. On the other hand, the Al content of the oxide sintered body according to Comparative Example 2 was 20 mass ppm or more, so that it was possible to reduce the inclusion of Al as a grinding / mixing medium. ２ O ３ It is believed that Al was mixed in from the grinding and mixing media due to the use of balls made of Al.

[0106] The total content of impurities (elements of groups A and B) contained in the oxide sintered bodies according to Examples 1 to 4 was 5 ppm by mass or less, which enabled the impurities to be reduced. On the other hand, the total content of impurities (elements of groups A and B) contained in the oxide sintered bodies according to Comparative Examples 1 to 4 was 20 ppm by mass or more. For example, the total content of impurities (elements of groups A and B) contained in the oxide sintered body according to Comparative Example 3 was 20 ppm by mass or more, which suggests that impurities were mixed in from the mold due to the use of a gypsum mold. Furthermore, the total content of impurities (elements of groups A and B) contained in the oxide sintered body according to Comparative Example 4 was 20 ppm by mass or more, which suggests that impurities were mixed in 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) contained in the oxide sintered bodies according to Examples 1 to 4 was 1 ppm by mass or less, and therefore the content of impurities could be reduced. On the other hand, the total content of impurities (elements of group B) contained in the oxide sintered bodies according to Comparative Examples 1, 2, and 4 exceeded 1 ppm by mass.

[0108] The inventions disclosed in this specification include, in addition to the configurations of each invention and embodiment, those specified by changing these partial configurations to other configurations disclosed in this specification, to the extent applicable, or those specified by adding other configurations disclosed in this specification to these configurations, or those specified as higher-level concepts specified by deleting these partial configurations to the extent that partial effects can be obtained.

[0109] The method for producing an oxide sintered body according to the present invention significantly reduces the content of impurities, and is therefore suitable as a method for producing a high-purity oxide sintered body and a sputtering target. Furthermore, the oxide sintered body and sputtering target according to the present invention can suppress the occurrence of arcing compared to conventional sputtering targets, thereby reducing the occurrence of defective products. This leads to the achievement of sustainable management and efficient use of natural resources, and decarbonization (carbon neutrality).

[0110] REFERENCE SIGNS LIST 1 raw material slurry 2 molding mold 3 molding lower mold 4 drain hole 5 filter 6 sealing material

Claims

1. A method for producing an oxide sintered body using an oxide containing two or more elements selected from the group consisting of In, Ga, and Zn as a raw material, which satisfies the following (a) to (c): (a) The raw material is an oxide with a purity of 6N or higher. (b) The grinding and mixing media is made of an oxide that does not contain any elements other than the elements selected as the raw materials. (c) Ultrapure water is used as a dispersion medium to form a slurry.

2. A method for producing an oxide sintered body according to claim 1, which satisfies the following (d1): (d1) Slip molding is performed using a metal mold.

3. A method for producing an oxide sintered body according to claim 1, which satisfies the following (d2): (d2) Slip casting is performed using a ceramic mold formed from an oxide that does not contain any elements other than the element selected as the raw material.

4. A method for producing an oxide sintered body according to any one of claims 1 to 3, which satisfies the following (e): (e) After the surface of the oxide sintered body is ground, dry ice particles are blasted onto the surface for surface treatment.

5. A method for producing a sputtering target, comprising bonding an oxide sintered body produced by the method for producing an oxide sintered body according to any one of claims 1 to 3 to a substrate.

6. An oxide sintered body containing two or more elements selected from In, Ga, and Zn, characterized in that the total content of elements in the following 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. 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, when the content is less than the detection limit of GDMS analysis, it is regarded as 0 ppm by mass.

7. The oxide sintered body according to claim 6, characterized in that the relative density is 95% or more.

8. The oxide sintered body according to claim 6, characterized in that the bulk resistance is 100 mΩ·cm or less.

9. The oxide sintered body according to claim 6, characterized in that the crystal grain size is 30 μm or less.

10. The oxide sintered body according to claim 6, characterized in that the flexural strength is 50 MPa or more.

11. A sputtering target comprising the oxide sintered body according to any one of claims 6 to 10.

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