Method for producing oxide sintered body

Abstract

To provide a method for producing an oxide sintered body, in which a content of impurities is significantly reduced.SOLUTION: A method of the present invention for producing an oxide sintered body uses, as a raw material, an oxide containing two or more elements selected from In element, Ga element, and Zn element and satisfies the following conditions (a) to (c). An oxide having a purity of 6 N or more is used as the raw material. A grinding and mixing medium is formed of an oxide containing no element other than the elements selected as the raw material. Ultrapure water is used as a dispersion medium to form a slurry.SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

[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 become popular due to their 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 (<10-22A / 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 BEOL compatible processes in the semiconductor manufacturing process. Along with these expectations, the required properties 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 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-163441 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-202450 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 having a purity of 6N or higher. (b) The grinding and mixing media are formed from oxides that do not contain any elements other than the elements selected as the raw materials. (c) Using ultrapure water as a dispersion medium, the mixture is made into a slurry. This configuration makes it possible to produce an oxide sintered body with a significantly reduced content of impurities.

[0009] The raw material in (a) above is an oxide containing two or more elements selected from the group consisting of In, Ga, and Zn. Specifically, it may be two or three elements (In, Ga, and ZnO) selected from an oxide containing In (InO), an oxide containing Ga (GaO), or an oxide containing Zn (ZnO). 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 elements is 6N (99.9999 mass %) or higher. When the purity of each oxide used as a raw material is 6N or more, 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 is significantly reduced, and therefore 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, when two raw materials, an oxide containing In (In2O3) and an oxide containing Ga (Ga2O3), are selected, the grinding and mixing media are formed from an oxide containing no elements other than In and Ga. For example, the grinding and mixing media may be formed from In2O3, Ga2O3, or InGaO3, with media formed from In2O3 being preferred.

[0014] When two raw materials, an oxide containing In (In2O3) and an oxide containing Zn (ZnO), are selected, 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 In2O3, ZnO, or In2Zn3O6, with media formed from In2O3 being preferred.

[0015] When two raw materials, an oxide containing Ga (Ga2O3) and an oxide containing Zn (ZnO), are selected, the grinding and mixing media are formed from an oxide containing no elements other than Ga and Zn. For example, the grinding and mixing media may be formed from Ga2O3, ZnO, or Ga2ZnO4, with media formed from Ga2ZnO4 being preferred.

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

[0017] In (b), the phrase "the grinding / mixing media does not contain elements other than those selected as raw materials" means that the content of impurities contained in the grinding / mixing media is 100 mass ppm or less. Examples of impurities contained in the grinding / 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) above 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 ultrapure water 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 (d1). (d1) 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 Fig. 1, the metal mold in (d1) above is a molded body obtained by pouring a slurried raw material (hereinafter referred to as raw material slurry 1) into a molding frame 2 from above and draining the raw 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 (for example, 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 (d2). (d2) Slip casting is performed using a ceramic mold formed from an oxide that does not contain any 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 gets mixed in during slip casting, the purity of the molded body will not be reduced because the components of the molded body are the same as those of the ceramic mold.

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

[0026] When two types of oxides, an oxide containing In (In2O3) and an oxide containing Ga (Ga2O3), are selected as raw materials, the forming frame 2 and the lower forming die 3 for the ceramic forming die are formed from an oxide containing no elements other than In and Ga. For example, the forming frame 2 and the lower forming die 3 for the ceramic forming die are preferably formed from In2O3, Ga2O3, or InGaO3, and are particularly preferably formed from In2O3.

[0027] When an oxide containing In (In2O3) and an oxide containing Zn (ZnO) are selected as raw materials, the forming frame 2 and lower forming die 3 for the ceramic forming die are formed from an oxide containing no elements other than In and Zn. For example, the forming frame 2 and lower forming die 3 for the ceramic forming die are preferably formed from In2O3, ZnO, or In2Zn3O6, and are particularly preferably formed from In2O3.

[0028] When two raw materials, an oxide containing Ga (Ga2O3) and an oxide containing Zn (ZnO), are selected, the forming frame 2 and the lower forming die 3 for the ceramic forming die are formed from an oxide containing no elements other than Ga and Zn. For example, the forming frame 2 and the lower forming die 3 for the ceramic forming die are preferably formed from Ga2O3, ZnO, or Ga2ZnO4, and particularly preferably formed from Ga2ZnO4.

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

[0030] In (b), the ceramic mold "does not contain elements other than those selected as raw materials" means that the ceramic mold contains impurities in an amount of 100 ppm or less. Examples of impurities that may be present 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, and Hg.

[0031] Furthermore, the method for producing an oxide sintered body of the present invention satisfies the following requirement (e). (e) After the surface of the oxide sintered body is ground, dry ice particles are sprayed onto the surface to perform surface treatment. With this configuration, the ejected dry ice particles collide with the surface of the oxide sintered body, thereby removing microcracks 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.In addition, since the dry ice particles are quickly vaporized, it is possible to prevent the dry ice particles from penetrating through the surface of the oxide sintered body.

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

[0033] Dry ice blasting conditions Average diameter of dry ice particles: 0.1-1mm Gas medium (N2) gauge pressure: 0.1~0.6Mpa ·Consumption rate: 20~100% Processing speed: 0.8~142.9mm / sec Nozzle temperature: ≥ 20℃ Processing angle: 0 degrees to 20 degrees Distance between target and blast nozzle: 10~140mm

[0034] Here, 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 refers to the feed rate at which the dry ice is pushed out. The "treatment speed" in the dry ice blasting conditions refers to the speed at which the blast nozzle is moved over the oxide sintered body. The "treatment angle" in the dry ice blasting conditions refers to 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 molding method.

[0039] First, as raw materials, In2O3 powder with a purity of 6N, Ga2O3 powder with a purity of 6N, and ZnO powder with a purity of 6N, which satisfy the above (a), are weighed out and placed in a pot. These are then pulverized and mixed, and ultrapure water that satisfies 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, in the dry milling, In2O3 powder, Ga2O3 powder, and ZnO powder are placed in a pot, along with Ga2ZnO4 balls (hereinafter referred to as GZO media) that satisfy the above (b) as milling and mixing media, and the pot is mixed using a ball mill to dry mill the In2O3 powder, Ga2O3 powder, and ZnO powder.

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

[0043] Then, the dry-milled In2O3 powder, Ga2O3 powder, and ZnO powder are placed in another pot with ultrapure water as a dispersant, and GZO media is added as a milling and mixing medium. The pot is then mixed to form a slurry. Alternatively, the mixture containing the dry-milled In2O3 powder, Ga2O3 powder, and ZnO powder can be left in the pot, and ultrapure water as a dispersant is added to the pot containing the dry-milled mixture, followed by mixing to form a slurry. Additives such as dispersants and binders can be added as needed.

[0044] On the other hand, in wet milling, 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 milling and mixing medium. The pot is then mixed in a ball mill to wet mill the In2O3 powder, Ga2O3 powder, and ZnO powder.

[0045] The raw material slurry containing the wet-milled In2O3 powder, Ga2O3 powder, and ZnO powder in the pot is filtered using a filter to separate it from the GZO media, thereby obtaining the raw material slurry.

[0046] Furthermore, if the pot, like the grinding and mixing media, is made of 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 that satisfies the above (d1) or a ceramic mold that satisfies the above (d2), and the ultrapure water that serves 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 to form the mold. A reduced pressure of greater than −700 mmHg is preferable. A vacuum pump or the like may also be used as a method for reducing the pressure. Furthermore, the reduced pressure drainage time is preferably approximately 30 minutes after the completion of the casting of the molded body. Here, if the reduced pressure drainage time is short, the molded body may be difficult to release from the molding frame 2, and cracks may occur. If the reduced pressure drainage time is too long, the molded body 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 body 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 kept under an oxygen-rich atmosphere, 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 method for producing an oxide sintered body 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. 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, etc.

[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. As shown in (e) above, the surface of the oxide sintered body is subjected to surface treatment by dry ice blasting, in which dry ice particles are sprayed, according to the above dry ice blasting conditions.

[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 the group consisting of 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, if 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 a negative 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 of these elements belonging to Group A is low. Furthermore, Group B is a group of elements mainly selected from transition metals and lanthanides. These elements belonging to Group B may also have a negative 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 of these elements is low. In particular, elements belonging to Group B are more likely to have a negative 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 of these elements is particularly low.

[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 preferable that it is 6 mass ppm or less, particularly preferable that it is 5 mass ppm or less, even more particularly preferable that it is 4.9 mass ppm or less, even more particularly preferable that it is 4.8 mass ppm or less, and even more particularly preferable that it is 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 that it is 0.8 mass ppm or less, particularly preferably that it is 0.7 mass ppm or less, even more particularly preferable that it is 0.6 mass ppm or less, even more particularly preferable that it is 0.5 mass ppm or less, and even more particularly preferable that it is 0.4 mass ppm or less.

[0059] Here, the total content of elements in groups A and 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 the 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 metal materials with higher accuracy than ICP-AES analysis. The total content of elements in groups A and 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 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 is 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 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 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 the bulk resistance is preferably 100 mΩ cm or less. The use of a sputtering target material using the oxide sintered body of the present invention exhibiting such low bulk resistance is preferable in that DC sputtering becomes possible.

[0064] The oxide sintered body of the present invention preferably has a bulk resistivity 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 especially 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 characterized in that the crystal grain size is 30 μm or less. The oxide sintered body of the present invention has 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, even 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, 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, 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 characterized in that it has a bending strength of 50 MPa or more. The oxide sintered body of the present invention exhibits a high value of flexural strength, and the flexural strength is preferably 50 MPa or more. When sputtering is performed using a sputtering target material using the oxide sintered body of the present invention exhibiting such high flexural strength, even if an abnormal discharge unintentionally occurs during sputtering, the sputtering target material is less likely to crack, 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, even more particularly preferably 80 MPa or more, even more particularly preferably 90 MPa or more, still 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 bending strength of the oxide sintered body of the present invention is measured in accordance with JIS R 1601. The specific method for measuring the bending 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 includes the meaning "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 includes the meaning "preferably larger than X" or "preferably smaller than Y." [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0075] [Figure 1] FIG. 2 is an explanatory diagram showing the structure of a mold used in slip casting according to the present invention. [Figure 2] 1 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. BEST MODE FOR CARRYING OUT THE INVENTION

[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 raw materials, In2O3 powder (median diameter D50 = 0.6 μm) with a purity of 6N (99.9999 mass%), Ga2O3 powder (median diameter D50 = 1.5 μm) with a purity of 6N (99.9999 mass%), and ZnO powder (median diameter D50 = 0.8 μm) with a purity of 6N (99.9999 mass%) were weighed out so that the atomic ratio of In, Ga, and Zn was In:Ga:Zn = 1:1:1. The powders were placed in a pot, and 0.6 mass% of ammonium polycarboxylate was added as a dispersant and 20 mass% of ultrapure water was added as a dispersion medium. The mixture was milled and mixed for 24 hours in a ball mill using Ga2ZnO4 balls (GZO media) as milling and mixing media 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 diameter 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 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 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 carried out, 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 carried out except that the grinding and mixing media was changed to Al2O3, 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 raw material slurry was poured into a gypsum mold, the dispersion medium was drained, and a molded body was obtained. Except for this, a manufacturing method similar to that of Example 1 was carried out, 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. The obtained granulated powder was then subjected to a surface pressure of 0.5 tf / cm 2 The pressed product 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.

[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 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 Comparative Example 4.

[0091] Then, the oxide sintered body according to Comparative Example 4 was bonded 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 "ND" in FIG. 2 indicates a case where the content was below the detection limit of GDMS analysis, and the content was 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]

number

[0096] (C1~C in the formula i indicates the content (mass%) of the constituent substances of the target material, and ρ1 to ρ i is C1~C i The density of each constituent material (g / cm 3 ) indicates.

[0097] The oxide sintered body of the present invention and the constituent materials of the sputtering target material using the same are considered to be In2O3, Ga2O3, and ZnO, and for example, C1: mass% of In2O3 in oxide sintered body or target material ρ1: Density of In2O3 (7.18 g / cm 3 ) C2: mass% of Ga2O3 in the oxide sintered body or target material ρ2: density of Ga2O3 (5.95 g / cm 3 ) C3: mass% of ZnO in oxide sintered body or target material ρ3: Density of ZnO (5.60 g / cm 3 ) The theoretical density ρ was calculated by applying to equation (X).

[0098] The mass % of In2O3, mass % of Ga2O3, and mass % of ZnO described above were determined from the results of analysis 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 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 test method for conductive plastics by the four-point probe method).

[0100] <Crystal grain size measurement> The crystal grain size, i.e., the equivalent circle diameter, of each crystalline phase in the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 4 was measured 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 stepwise using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. Next, the cut surface was immersed in an etching solution (a mixture of nitric acid (60 to 61% by mass aqueous solution, manufactured by Kanto Chemical Co., Inc.), hydrochloric acid (35.7 to 37.0% by mass aqueous solution, manufactured by Kanto Chemical Co., Inc.), and pure water in a volume ratio of HCl:HO:HNO = 1:1:0.08) at 40°C for 2 minutes for etching treatment. The cut surface was then observed using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), and 10 randomly selected BSE-COMP images were taken at a magnification of 1000x within a range of 87.5 μm x 125 μm, to obtain SEM images for the 10 fields of view.

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

[0102] <Diverse bending strength> The bending 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 (Bending strength test method for fine ceramics) using an Autograph (registered trademark) AGS-500B manufactured by Shimadzu Corporation. Specifically, the bending strength was measured according to the three-point bending strength measurement method of JIS-R-1601 using test pieces (total length 36 mm or more, width 4.0 mm, thickness 3.0 mm) cut out from each oxide sintered body.

[0103] [Table 1]

[0104] 2, the Zr content of the oxide sintered bodies according to Examples 1 to 4 was less than 1 ppm by mass, which enabled the reduction of impurities. On the other hand, the Zr content of the oxide sintered body according to Comparative Example 1 was 20 ppm by mass or more, which suggests that Zr was mixed in from the grinding and mixing media, which were made of ZrO2 balls.

[0105] The Al content of the oxide sintered bodies according to Examples 1 to 4 was 1 ppm by mass or less, which enabled the reduction of impurities containing Al. On the other hand, the Al content of the oxide sintered body according to Comparative Example 2 was 20 ppm by mass or more, which is thought to be due to the use of balls made of Al2O3 as grinding and mixing media, which resulted in the contamination of Al from the grinding and mixing media.

[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 used for the gypsum molding. 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, which enabled the content of impurities to 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. [Industrial Applicability]

[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). [Explanation of symbols]

[0110] 1...Raw material slurry 2...Molding frame 3…Bottom mold for molding 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 In, Ga, and Zn as a raw material, A method for producing an oxide sintered body, which satisfies the following (a) to (c): (a) The raw material is an oxide having a purity of 6N or higher. (b) The grinding and mixing media are formed from oxides that do not contain any elements other than the elements selected as the raw materials. (c) Using ultrapure water as a dispersion medium, a slurry is formed.

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

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

4. The 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 sprayed onto the surface to perform 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 element, Ga element, and Zn element, An oxide sintered body characterized in that the total content of elements of the following groups A and B, as determined by GDMS analysis, is 10 ppm by mass or less, and the total content of elements of 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, the content is considered to be 0 ppm by mass.

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

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

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

10. 7. The oxide sintered body according to claim 6, wherein 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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