JP7723218B2 - Sintered oxide - Google Patents

Description

The present invention relates to an oxide sintered body containing an In-Ga-Zn based composite oxide.

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 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 used in place of conventional amorphous silicon.

In recent years, oxide semiconductors have been recognized as having the excellent characteristics of being able to combine high mobility (>10 cm ² /Vs) with extremely low off-leakage current (<10-22 A/μm), and are expected to be used as channel materials 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 of sputtering targets for depositing oxide semiconductor films are also increasing.

JP 2014-105124 A JP 2011-195406 A

However, the oxide sintered bodies disclosed in Patent Documents 1 and 2 were produced by first mixing _Ga2O3 powder and _{ZnO powder} and calcining the mixture to produce _{Ga2ZnO4 powder} , then pulverizing the _Ga2ZnO4 powder and mixing it with _In2O3 powder. However, these sintered bodies had the problem that sintering did not proceed sufficiently and the density did not increase. Furthermore, because _{Ga2ZnO4 powder} is very hard, when it is mixed with _{In2O3 powder} , the _ZrO2 used as a pulverizing medium for pulverizing _{the Ga2ZnO4 powder} is scraped off, resulting in the production of a large amount of impurities including Zr.

In consideration of the above problems, the present invention provides an oxide sintered body that has a high relative density and a significantly reduced content of impurities, including Zr.

The oxide sintered body of the present invention, which has been made to solve the above problems, is an oxide sintered body containing In, Ga, and Zn elements, and is characterized by including an _{In2Ga2ZnO7 crystal} phase and _{a Ga2ZnO4 crystal} phase, having a relative density of more than 100.0%, and having a Zr content of 100 mass ppm or less.
The oxide sintered body of the present invention is an oxide sintered body containing In, Ga, and Zn elements, and includes an _{In2Ga2ZnO7 crystal} phase and a _Ga2ZnO4 crystal phase _. The oxide sintered body has a relative density of more than 100.0% and _a Zr content of 100 mass ppm or less, so that the oxide sintered body has a high relative density and can significantly reduce the content of impurities including Zr.

The oxide sintered body of the present invention is an oxide sintered body containing In, Ga, and Zn elements.

Furthermore, the oxide sintered body of the present invention and a sputtering target material using _the same have an _{In2Ga2ZnO7 crystalline} phase and a _Ga2ZnO4 crystalline phase. The oxide sintered body of the present invention has a mottled mixture of _{the In2Ga2ZnO7 crystalline phase} and _{the Ga2ZnO4 crystalline} phase. Figure 2 is an SEM image of the surface of the oxide sintered body of the present invention observed using a scanning electron microscope, where the black region (A in Figure ₂ ) indicates the _Ga2ZnO4 crystalline phase and the whitish region (B in Figure ₂ ) indicates the _{In2Ga2ZnO7 crystalline} phase.

The SEM image shown in Figure 2 can be taken as follows: The cut surface obtained by cutting the oxide sintered body of the present invention is polished in stages using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. The mirror-finished cut surface is then thermally etched at 1100°C for 1 hour and observed using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), and an SEM image showing the grain boundaries of the cut surface is taken.

Furthermore, _{the In2Ga2ZnO7} phase and the _{Ga2ZnO4 phase} contained in the oxide sintered body of the present _invention and the sputtering target material made using the same can be confirmed by identifying peaks obtained by powder X-ray diffraction. Specifically, X-ray diffraction measurement is performed according to the following powder X-ray diffraction measurement conditions.

= Powder X-ray diffraction measurement conditions =
Radiation source: CuKα ray Tube voltage: 40 kV
・Tube current: 30mA
Scan speed: 5 deg/min
Step: 0.02 deg
Scan range: 2θ = 20 degrees to 80 degrees X-ray analysis software: PDXL2 Version 2.1.3.6

As a result of X-ray diffraction measurement, when the X-ray diffraction pattern matches with the X-ray diffraction pattern of ICDD (International Centre for Diffraction Data) card No. 38-1097 corresponding to the crystal structure of In ₂ Ga ₂ ZnO ₇ phase, it can be confirmed that the oxide sintered body of the present invention contains the In ₂ Ga ₂ ZnO ₇ phase. Furthermore, when the X-ray diffraction pattern matches with _the X-ray diffraction pattern of ICDD card No. 38-1240 corresponding to the crystal structure of Ga ₂ ZnO 4 phase, it can be confirmed that the oxide sintered body of the present invention contains the Ga ₂ ZnO ₄ phase.

Furthermore, it is preferable for the oxide sintered body of the present invention and the sputtering target material made therefrom to have a relative density of over 100.0% in order to reduce the number of arcing events during sputtering. This is because an improved relative density reduces the volume resistivity of the oxide sintered body and the sputtering target material made therefrom, thereby suppressing charge concentration during sputtering. Furthermore, the formation of high-potential areas due to charge concentration and low-potential areas due to charge non-concentration during sputtering is suppressed, making it less likely that discharge will occur from high-potential areas to low-potential areas, thereby reducing the number of arcing events. It is more preferable for the oxide sintered body of the present invention to have a relative density of 100.5% or more, even more preferably 101.0% or more, particularly preferably 101.5% or more, even more particularly preferably 102.0% or more, even particularly preferably 102.5% or more, and even particularly preferably 103.0% or more. The upper limit of the relative density is not particularly limited, but is, for example, 105.0% or less.

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. Specifically, the mass of the target material in air is divided by the volume (mass of the target material in water/specific gravity of water at the measurement temperature), and the percentage of the theoretical density ρ (g/cm ³ ) based on the following formula (X) is taken as the relative density (unit: %).

(In the formula, C ₁ to C _i respectively represent the content (mass %) of the constituent substances of the target material, and ρ ₁ to ρ _i respectively represent the density (g/cm ³ ) of the constituent substances corresponding to C ₁ to C _i .)

The oxide sintered body of the present invention and the sputtering target material made using the same are considered to be composed of In ₂ O ₃ , Ga ₂ O ₃ , and ZnO. For example, the following:
C ₁ : mass% of In ₂ O ₃ in the oxide sintered body or target material
ρ ₁ : density of In ₂ O ₃ (7.18 g/cm ³ )
C ₂ : mass% of Ga ₂ O ₃ in the oxide sintered body or target material
ρ ₂ : density of Ga ₂ O ₃ (5.95 g/cm ³ )
_C3 : mass% of ZnO in the oxide sintered body or target material
ρ ₃ : density of ZnO (5.60 g/cm ³ )
By applying the above to the equation (X), the theoretical density ρ can be calculated.

The above-mentioned mass % of In ₂ O ₃ , mass % of Ga ₂ O ₃ , and mass % of ZnO can be determined from the analysis results of each element of the oxide sintered body or sputtering target material by ICP-OES analysis.

Furthermore, if the Zr content in the oxide sintered body of the present invention is 100 ppm by mass or less, the Zr-containing impurities contained in the oxide sintered body of the present invention are significantly reduced, and this is preferable. Furthermore, it is more preferable for the Zr content in the oxide sintered body of the present invention to be 50 ppm by mass or less, even more preferably 30 ppm by mass or less, particularly preferably 20 ppm by mass or less, even more particularly preferably 10 ppm by mass or less, even more particularly preferably 5 ppm by mass or less, even more particularly preferably 2 ppm by mass or less, even more particularly preferably 1 ppm by mass or less, and even more particularly preferably less than 1 ppm by mass.

The Zr content in the oxide sintered body of the present invention can be measured by adding nitric acid, perchloric acid, or hydrogen peroxide to the sintered body as needed, decomposing it by heating to form a solution, and then using an ICP optical emission spectrometer (Agilent Technologies: 720 ICP-OES) to measure the Zr concentration.

The oxide sintered body of the present invention is characterized in that the pinhole area ratio is 0.7% or less.
The oxide sintered body of the present invention is preferably a sputtering target material having a pinhole area ratio of 0.7% or less, in terms of forming a high-quality thin film. Furthermore, the oxide sintered body of the present invention is more preferably a pinhole area ratio of 0.6% or less, even more preferably 0.5% or less, particularly preferably 0.4% or less, and particularly preferably 0.3% or less. The lower limit of the pinhole area ratio is not particularly limited, but is, for example, 0.01% or more.

Here, the pinhole area ratio can be measured as follows: The surface of the oxide sintered body of the present invention is measured by evaluating the crystalline phase using a scanning electron microscope (SEM).

Specifically, the cut surface obtained by cutting the oxide sintered body of the present invention is polished in stages using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. Then, using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), BSE-COMP images of the mirror-finished cut surface are taken at 1000x magnification, randomly selecting 10 fields of view within an area of 87.5 μm x 125 μm, to obtain SEM images for the 10 fields of view.

Next, the area of each SEM image occupied by pinholes with a circular equivalent diameter of 0.1 μm or greater is drawn and color-filled using Pictbear (Fenrir). Furthermore, particle analysis software (Sumitomo Metal Technology Co., Ltd.: Particle Analysis Version 3.0) is used to recognize and binarize the SEM image with the pinholes filled in. At this time, the conversion value is set so that one pixel is displayed in μm units.

Then, the pinhole and total areas are calculated using particle analysis software, and the percentage of pinholes relative to the total is calculated as the area ratio. The average area ratio obtained for each of the 10 SEM images is then used as the pinhole area ratio for the oxide sintered body of the present invention.

Furthermore, the average particle size of the In ₂ Ga ₂ ZnO ₇ phase contained in the oxide sintered body of the present invention is preferably 6.0 μm or less in terms of high bending strength. The average particle size of the In ₂ Ga ₂ ZnO ₇ phase is more preferably 5.5 μm or less, even more preferably 5.0 μm or less, particularly preferably 4.5 μm or less, even more particularly preferably 4.0 μm or less, and even more particularly preferably 3.5 μm or less. On the other hand, the average particle size of the In ₂ Ga ₂ ZnO ₇ phase is preferably 1.0 μm or more, more preferably 2.0 μm or more, and particularly preferably 3.0 μm or more.

The average particle size of the In ₂ Ga ₂ ZnO ₇ phase contained in the oxide sintered body of the present invention, that is, the diameter of an equivalent circle with respect to area, can be calculated by image processing of an SEM image taken using a scanning electron microscope.

Specifically, the cut surface obtained by cutting the oxide sintered body of the present invention is polished in stages using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. The mirror-finished cut surface is then thermally etched at 1100°C for 1 hour and observed using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation). BSE-COMP images are taken at 1000x magnification within a range of 87.5 μm x 125 μm, randomly selected from 10 fields of view, to obtain SEM images for the 10 fields of view.

The obtained SEM image was plotted along the grain boundaries of _{the In2Ga2ZnO7 phase using} image processing software ImageJ. After all plotting was completed, particle analysis was performed to obtain the area of each particle. The area-equivalent circle diameter was then calculated from the area of each particle. This was performed on 10 SEM images, and the average of the calculated equivalent circle diameters of all particles was taken as the equivalent circle diameter _of the _{In2Ga2ZnO7 phase} .

The average particle size of the _{Ga2ZnO4 phase} contained in the oxide sintered body of the present invention is preferably 1.0 _μm or more and 4.5 μm or less in terms of reducing abnormal discharge, more preferably 1.5 μm or more and 4.0 μm or less, and even more preferably 2.0 μm or more _and 3.5 μm or less.

The average particle size of the Ga ₂ ZnO ₄ phase contained in the oxide sintered body of the present invention, i.e., the area circle equivalent diameter, can be calculated by image processing of an SEM image taken using a scanning electron microscope, similar to the average particle size of the In ₂ Ga ₂ ZnO ₇ phase.

Specifically, the obtained SEM image was plotted along the grain boundaries of the _{Ga2ZnO4 phase} using image processing software ImageJ. After all plotting was completed, particle analysis was performed to obtain the area of each particle. The equivalent area diameter was then calculated from the obtained area of each particle. This was performed on 10 SEM images, and the average of the calculated equivalent area diameters of all particles was taken as the equivalent area diameter of the _{Ga2ZnO4 phase} .

The oxide sintered body of the present invention is characterized in that the atomic ratio of the In element, the Ga element, and the Zn element satisfies the following formula:
0.15<In/(In+Ga+Zn)<0.35
0.4<Ga/(In+Ga+Zn)<0.6
0.15<Zn/(In+Ga+Zn)<0.35
The oxide sintered body of the present invention is preferable because the atomic ratios of the In element, Ga element, and Zn element satisfy all of the above three formulas, and therefore the oxide sintered body of the present invention contains the In ₂ Ga ₂ ZnO ₇ phase and the Ga ₂ ZnO ₄ phase in an optimal ratio.

It is more preferable that In/(In+Ga+Zn) be 0.17<In/(In+Ga+Zn)<0.33, and even more preferable that In/(In+Ga+Zn) be 0.2<In/(In+Ga+Zn)<0.3.

Furthermore, it is more preferable that Ga/(In+Ga+Zn) be 0.42<Ga/(In+Ga+Zn)<0.58, and even more preferable that Ga/(In+Ga+Zn) be 0.45<Ga/(In+Ga+Zn)<0.55.

Furthermore, it is more preferable that Zn/(In+Ga+Zn) is 0.17<Zn/(In+Ga+Zn)<0.33, and even more preferable that 0.2<Zn/(In+Ga+Zn)<0.3.

Here, the atomic ratios of In, Ga, and Zn elements in the oxide sintered body of the present invention can be measured by measuring the respective concentrations of In, Ga, and Zn elements using an ICP optical emission spectrometer (Agilent Technologies: 720 ICP-OES), and the atomic ratios can be calculated from the measured concentrations.

The oxide sintered body of the present invention is characterized in that it has a bending strength of 150 MPa or more.
The oxide sintered body of the present invention exhibits such high bending strength, and when it is used as a sputtering target material for sputtering, even if an unintended abnormal discharge occurs during sputtering, the target material is less likely to break or crack, which is preferable. The oxide sintered body of the present invention preferably has a bending strength of 160 MPa or more, more preferably 165 MPa or more, and particularly preferably 170 MPa or more. The upper limit of the bending strength is not particularly limited, but is, for example, 250 MPa or less. A specific method for measuring bending strength will be described later.

The sputtering target material of the present invention is characterized by including the oxide sintered body of the present invention described above.
The sputtering target material of the present invention contains the oxide sintered body of the present invention described above, and therefore the number of arcing occurrences can be significantly reduced, and the generation of particles can be further suppressed, allowing a high-quality oxide semiconductor film to be formed with a high yield. In addition, the inclusion of impurities containing Zr in the oxide semiconductor film can be significantly reduced.

Furthermore, as an example of a method for producing the oxide sintered body of the present invention, a filtration molding method will be described below.

First, _{the raw materials In2O3 powder} , _{Ga2O3 powder} , and ZnO powder are weighed and placed in a pot. They are then pulverized and mixed, and an organic additive and a dispersion medium are added to obtain a mixture slurry. Examples of the organic additive include known binders and dispersants. The dispersion medium is not particularly limited, and can be selected from water, alcohol, etc. depending on the application.

Here, the grinding and mixing method may be dry grinding or wet grinding.

Specifically, in the dry grinding, In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder, and Ga ₂ ZnO _balls (hereinafter referred to as GZO media) as grinding media are placed in a pot, and the pot is mixed in a ball mill to dry grind the In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder.

The mixture containing the dry-milled In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder in the pot is separated from the GZO media using a filter to obtain a mixture containing the dry-milled In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder.

Then, _the dry-milled _In2O3 powder, _Ga2O3 powder, and _ZnO powder, along with an organic additive (e.g., a dispersant) and a dispersion medium (e.g., water) are placed in another pot, and GZO media is added as a grinding medium. The pot is then mixed to form a slurry. Alternatively, instead of removing the mixture containing _the dry-milled _In2O3 powder, _Ga2O3 powder, and _ZnO powder from the pot, an organic additive (e.g., a dispersant) and a dispersion medium (e.g., water) may be added to the pot containing the dry-milled mixture and mixed to form a slurry.

On the other hand, in wet grinding, _In2O3 powder, _Ga2O3 powder, _ZnO powder, _an organic additive (e.g., a dispersant), and a dispersion medium (e.g., water) are placed in a pot, and GZO media is further added as grinding media. The pot is then mixed in a ball mill to wet grind _{the In2O3} powder, _{Ga2O3 powder} , and ZnO powder.

The mixture slurry containing the wet-milled In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder in the pot is filtered using a filter to separate it from the GZO media, thereby obtaining the mixture slurry.

The resulting mixture slurry is poured into a mold and the dispersion medium is removed to obtain a molded body. Examples of molds include metal molds, plaster molds, and resin molds.

The resulting molded body is fired to obtain a fired body. When the molded body is fired, _{an In2Ga2ZnO7 phase and a Ga2ZnO4} phase are formed. When the firing temperature of the molded body is higher than 1400°C and lower than 1530°C, an oxide sintered body with high density and high strength can be obtained. The resulting fired body is then cut into any shape to obtain the oxide sintered body of the present invention.

As another example of a method for producing the oxide sintered body of the present invention, the CIP molding method will be described below.

First, the process of pulverizing and mixing the raw materials In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder to obtain a mixed slurry is the same as the process of the filtration-type molding method described above, so a description thereof will be omitted.

As described above, the resulting mixture slurry is spray-dried to obtain a dry powder. The resulting dry powder is then filled into a mold and pressed into a compact.

Next, the obtained compact is fired to obtain a fired body. When the compact is fired, _{an In2Ga2ZnO7 phase and a Ga2ZnO4} phase are formed. When the firing temperature of the compact is higher than 1400°C and lower than 1530°C, an oxide sintered body with high density and high strength can be obtained. The obtained fired body is then cut into any shape to obtain the oxide sintered body of the present invention.

The above-described method for producing an oxide sintered body of the present invention does _not include a step of grinding and mixing _Ga2O3 powder and ZnO powder and calcining them to form a calcined body made of crystalline _{Ga2ZnO4 .} Therefore, the calcined powder does not contain crystalline _{Ga2ZnO4 ,} which has extremely hard properties, and even if grinding media made of _ZrO2 are used, the content of impurities including Zr in the obtained oxide sintered body of the present invention can be significantly reduced. Furthermore, by using grinding media made of _Ga2ZnO4 instead of grinding media made _{of ZrO2} , the content of impurities including Zr in the obtained oxide sintered body of the present invention can be further reduced.

The sputtering target material of the present invention can be obtained by bonding the oxide sintered body of the present invention obtained by the above-described method for producing an oxide sintered body of the present invention to a substrate. Examples of the substrate include 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.

The method for producing a film of the present invention is characterized in that a thin film is formed on a substrate by sputtering using the sputtering target material of the present invention.
By performing sputtering using the sputtering target material of the present invention to form a thin film on a substrate, it is possible to form a high quality thin film with a high yield.

Specifically, by performing sputtering using the sputtering target material of the present invention, a high-quality thin film, such as an oxide semiconductor film, can be formed on a substrate. Examples of the substrate include a glass substrate, a resin substrate, and a silicon substrate.

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," as well as "preferably greater 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 greater than X" or "preferably less than Y."

The oxide sintered body of the present invention has a high relative density and significantly reduces the content of impurities, including Zr.

1 is a table listing the physical property values and measurement results of oxide sintered bodies according to Examples 1 to 4 of the present invention and Comparative Examples 1 to 5. 1 is an SEM image of the surface of an oxide sintered body according to the present invention, observed using a scanning electron microscope.

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

Example 1
_In2O3 powder (median diameter D50 0.6 μm), _{Ga2O3 powder} (median diameter D50 1.5 μm), and ZnO powder (median diameter D50 0.8 μm) were weighed so that the atomic ratio of In to Ga to Zn _was In:Ga:Zn = 1:2:1, placed in a pot, and dry-mixed in a ball mill using grinding media (GZO media) for 24 hours to obtain a mixed raw material powder. Note that after grinding and mixing, the mixed raw material powder was not calcined.

Here, the median diameter D50 of each powder was measured using a particle size distribution analyzer MT3300EXII manufactured by Microtrackbell Corporation. Water was used as the solvent for the measurement sample. The refractive index of the measurement material was set to 2.20.

Next, 0.2% by mass of acrylic emulsion binder relative to the mixed raw material powder was added to the pot as a binder, 0.6% by mass of ammonium polycarboxylate relative to the mixed raw material powder as a dispersant, and 20% by mass of water relative to the mixed raw material powder as a dispersant.The mixture was then ball milled using grinding media (GZO media) for 24 hours to obtain a mixed slurry.

The mixture slurry obtained in this way was poured into an aluminum mold, the dispersion medium was drained, and a molded body was obtained.

The resulting compact was then fired in an air atmosphere at a firing temperature of 1410°C for 10 hours at a heating rate of 300°C/h and a cooling rate of 50°C/h to obtain a fired body. The fired body was then machined to a width of 210 mm, length of 710 mm, and thickness of 6 mm to obtain the oxide sintered body according to Example 1. A #170 grinding wheel was used for the cutting process.

Example 2
In Example 2, the same manufacturing method as in Example 1 was carried out except that the firing temperature was changed to 1450°C, and an oxide sintered body according to Example 2 was obtained.

Example 3
In Example 3, the same manufacturing method as in Example 1 was carried out except that the firing temperature was changed to 1500°C, and an oxide sintered body according to Example 3 was obtained.

Example 4
In Example 4, the grinding media was changed to ZrO ₂ and the firing temperature was changed to 1450 ° C., but the same manufacturing method as in Example 1 was carried out to obtain an oxide sintered body according to Example 4.

(Comparative Example 1)
In Comparative Example 1, the same manufacturing method as in Example 1 was carried out except that the firing temperature was changed to 1400°C, and an oxide sintered body according to Comparative Example 1 was obtained.

(Comparative Example 2)
In Comparative Example 2, the same manufacturing method as in Example 1 was carried out except that the firing temperature was changed to 1530°C, and an oxide sintered body according to Comparative Example 2 was obtained.

(Comparative Example 3)
_Ga2O3 powder (median diameter _D50 : 1.5 μm) and ZnO powder (median diameter D50: 0.8 μm) were weighed out so that _{the Ga2O3} :ZnO ratio was 1:1 (the atomic ratio of Ga to Zn was Ga:Zn = 2:1), and the mixture was milled and mixed in a ball mill using water as a dispersion medium and milling media ( _ZrO2 balls) for 6 hours to obtain a _Ga2O3 - _ZnO mixed powder slurry. The resulting _Ga2O3 - _ZnO mixed powder slurry was then dried using a spray dryer to obtain a _Ga2O3 - _ZnO granulated powder. Furthermore, the obtained Ga ₂ O ₃ —ZnO granulated powder was placed in an alumina crucible and calcined in an air atmosphere at a calcination temperature of 900° C. for 5 hours to obtain a calcined powder containing crystalline Ga ₂ ZnO ₄ .

The obtained calcined powder (containing _{crystalline Ga2ZnO4} ) and _In2O3 powder (median diameter D50 of 0.6 μm) were weighed to a _Ga2ZnO4 : _In2O3 = 2: ₁ (atomic ratio of In, Ga, and Zn: In:Ga _{: Zn} = 1:2:1), and were pulverized and mixed in a ball mill using water as a dispersion medium and grinding media ( _ZrO2 balls) for 6 hours to obtain _{a Ga2ZnO4} - _{In2O3 mixed} powder slurry. Next, the obtained _Ga2ZnO4 - _In2O3 mixed powder slurry was dried using _a spray dryer to obtain _{a Ga2ZnO4 - In2O3 granulated} powder.

The Ga ₂ ZnO ₄ —In ₂ O ₃ granulated powder thus obtained was press-molded under a surface pressure of 0.5 tf/cm ² , and then CIP-molded under a surface pressure of 1.5 tf/cm ² to obtain a green body.

Next, the obtained compact was fired in an air atmosphere at a firing temperature of 1450°C for 10 hours at a heating rate of 300°C/h and a cooling rate of 50°C/h to obtain a fired body. The fired body was then cut 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 3. A #170 grinding wheel was used for the cutting. _{The In2O3} powder, _Ga2O3 powder, and ZnO powder used in Comparative Example 3 were _the same as those used in Example 1.

(Comparative Example 4)
In Comparative Example 4, the same manufacturing method as in Comparative Example 3 was carried out except that the firing temperature was changed to 1500°C, and an oxide sintered body according to Comparative Example 4 was obtained.

(Comparative Example 5)
In ₂ O ₃ powder (median diameter D50: 0.6 μm), Ga ₂ O ₃ powder (median diameter D50: 1.5 μm), and ZnO powder (median diameter D50: 0.8 μm) were weighed out so that the mixing ratio of each powder was such that the atomic ratio of In to Ga to Zn was In:Ga:Zn = 1:2:1, and placed in a pot. The mixture was then dry-mixed in a ball mill using grinding media (ZrO ₂ balls) for 24 hours to obtain a mixed raw material powder.

The obtained mixed raw material powder was placed in an alumina crucible and calcined in an air atmosphere at a calcination temperature of 900° C. for 5 hours to obtain a calcined powder containing crystalline Ga ₂ ZnO ₄ .

Next, 0.2% by mass of an acrylic emulsion binder relative to the calcined powder was added to the pot as a binder, 0.6% by mass of ammonium polycarboxylate relative to the calcined powder as a dispersant, and 20% by mass of water relative to the calcined powder as a dispersion medium, and the mixture was mixed in a ball mill using grinding media ( _ZrO2 balls) for 24 hours to obtain a mixture slurry.

The mixture slurry obtained in this way was poured into an aluminum mold, the dispersion medium was drained, and a molded body was obtained.

The resulting compact was then fired in an air atmosphere at a firing temperature of 1430°C for 10 hours at a heating rate of 300°C/h and a cooling rate of 50°C/h to obtain a fired body. The fired body was then machined to a width of 210 mm, length of 710 mm, and thickness of 6 mm to obtain the oxide sintered body according to Comparative Example 5. A #170 grinding wheel was used for the cutting process.

The following physical properties were measured for the oxide sintered bodies obtained in Examples 1 to 4 and Comparative Examples 1 to 5. The measured physical properties and the methods for measuring them are shown below, and the measurement results are shown in Figure 1.

<Elemental analysis>
Nitric acid, perchloric acid, or hydrogen peroxide was added to the sample as needed, and the sample was decomposed by heating to form a solution, and the concentrations of each element (In, Ga, Zn, and Zr) were measured using an ICP optical emission spectrometer (Agilent Technologies: 720 ICP-OES).

<Relative density>
The relative densities of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 were measured by 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), and the percentage of this value relative to the theoretical density ρ (g/cm ³ ) based on the above formula (X) was taken as the relative density (unit: %).

<Crystal grain size measurement>
The crystal grain sizes, i.e., the area circle equivalent diameters, of the In ₂ Ga ₂ ZnO ₇ phase and the Ga ₂ ZnO ₄ phase were measured from SEM images of the surfaces of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 taken using a scanning electron microscope. Specifically, the cut surfaces obtained by cutting the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 were polished in stages using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. Next, the mirror-finished cut surfaces were thermally etched at 1100°C for 1 hour and observed using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation). BSE-COMP images were taken at 1000x magnification in a range of 87.5 μm × 125 μm, randomly selected from 10 fields of view, to obtain SEM images for the 10 fields of view.

Furthermore, the obtained SEM image was plotted along the grain boundaries of the In ₂ Ga ₂ ZnO ₇ phase using image processing software ImageJ, and after all plotting was completed, particle analysis was performed to obtain the area of each particle. The equivalent area circle diameter was then calculated from the area of each obtained particle. This was performed on 10 SEM images, and the average value of the calculated equivalent area circle diameters of all particles was taken as the equivalent area circle diameter of the In ₂ Ga ₂ ZnO ₇ phase. Next, the obtained SEM image was plotted along the grain boundaries of the Ga ₂ ZnO ₄ phase using image processing software ImageJ, and the equivalent area circle diameter was calculated from the area of each particle obtained by similarly performing particle analysis. This was performed on 10 SEM images, and the average value of the calculated equivalent area circle diameters of all particles was taken as the equivalent area circle diameter of the Ga ₂ ZnO ₄ phase.

Identifying crystalline phases by X-ray diffraction
The crystalline phases of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 were identified by X-ray diffraction using SmartLab (registered trademark) manufactured by Rigaku Corporation under the above-mentioned powder X-ray diffraction measurement conditions.

<Diverse bending strength>
The flexural strength of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 was measured in accordance with JIS standard JIS-R-1601 (Testing method for bending strength of fine ceramics) using an Autograph (registered trademark) AGS-500B manufactured by Shimadzu Corporation. Specifically, the flexural strength was measured according to the three-point bending strength measurement method of JIS-R-1601 (Testing method for bending strength of fine ceramics) using test pieces (total length 36 mm or more, width 4.0 mm, thickness 3.0 mm) cut out from the oxide sintered bodies.

<Pinhole area ratio>
The pinhole area ratios of the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 were measured by evaluating the crystalline phase of the surface of the oxide sintered body using a scanning electron microscope. Specifically, the cut surface obtained by cutting the oxide sintered body was polished in stages using emery paper #180, #400, #800, #1000, and #2000, and finally buffed to a mirror finish. Then, BSE-COMP images of the mirror-finished cut surface were taken at random in 10 fields of view within a range of 87.5 μm × 125 μm at 1000x magnification using a scanning electron microscope (SU3500, manufactured by Hitachi High-Technologies Corporation), and SEM images of the 10 fields of view were obtained.

Next, the area occupied by pinholes with a circle-equivalent diameter of 0.1 μm or more in each SEM image was drawn and color-filled using Pictbear (manufactured by Fenrir Corporation). Furthermore, particle analysis software (manufactured by Sumitomo Metal Technology Co., Ltd.: Particle Analysis Version 3.0) was used to recognize and binarize the SEM images with the pinholes filled in. The conversion value was set so that one pixel was displayed in μm units. The particle analysis software then calculated the pinhole and total areas, and the percentage of pinholes relative to the total was determined as the area ratio. The average area ratio obtained for each of the 10 SEM images was then used to determine the pinhole area ratio for the oxide sintered body.

Arcing evaluation
Using the oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5, sputtering was carried out under the following sputtering conditions, and the number of times arcing occurred was measured.

=Sputtering conditions=
Equipment: DC magnetron sputtering equipment, exhaust system cryopump, rotary pump. Ultimate vacuum: 3×10 ⁻⁶ [Pa]
Sputtering pressure: 0.4 [Pa]
Oxygen partial pressure: 1 × 10 ⁻³ [Pa]
・Input power time: 2W/ ^cm2
Duration: 10 hours

The number of arcing occurrences was measured using an arcing counter (model: μArc Monitor MAM Genesis MAM Data Collector Ver. 2.02 (manufactured by LANDMARK TECHNOLOGY)) and evaluated as follows.
A: Very few (less than 200 times)
B: Low (more than 200 times but less than 250 times)
C: Somewhat high (more than 250 times and less than 300 times)
D: Very often (over 300 times)

As shown in Figure 1, the oxide sintered bodies of Examples 1 to 4 were able to reduce the number of arcing occurrences when the relative density was above 100.0%.

The oxide sintered bodies of Examples 1 to 4 had a Zr content of 100 ppm by mass or less, which reduced the amount of Zr-containing impurities. Furthermore, the oxide sintered bodies of Examples 1 to 3 had a particularly low incidence of arcing when the Zr content was less than 1 ppm by mass.

The oxide sintered bodies of Examples 1 to 4 were able to reduce the number of arcing occurrences when the pinhole area ratio was 0.7% or less.

The oxide sintered bodies of Examples 1 to 4 were able to reduce the number of arcing occurrences when their flexural strength was 150 MPa or more.

The oxide sintered bodies according to Examples 1 to 4 and Comparative Examples 1 to 5 were confirmed to be composed of two crystalline phases, an In ₂ Ga ₂ ZnO _7- phase and a Ga ₂ ZnO _4- phase, from the results of X-ray diffraction measurement.

The inventions disclosed in this specification include, in addition to the configurations of each invention and embodiment, to the extent applicable, those specified by changing these partial configurations to other configurations disclosed in this specification, or those specified by adding other configurations disclosed in this specification to these configurations, or those larger concepts specified by removing these partial configurations to the extent that partial effects are obtained.

The oxide sintered body of the present invention has a high relative density and a significantly reduced content of impurities, including Zr, making it suitable as a sputtering target material. Furthermore, the oxide sintered body of the present invention can suppress arcing compared to conventional sputtering targets, thereby reducing the occurrence of defective products. This will lead to the sustainable management and efficient use of natural resources, and the achievement of decarbonization (carbon neutrality).

Claims (7)

An oxide sintered body containing In, Ga, and Zn elements,
the atomic ratio of the In element, the Ga element, and the Zn element satisfies the following formula:
0.15<In/(In+Ga+Zn)<0.35
0.4<Ga/(In+Ga+Zn)<0.6
0.15<Zn/(In+Ga+Zn)<0.35
The peaks obtained by powder X-ray diffraction were identified and confirmed to contain an In ₂ Ga ₂ ZnO ₇ crystalline phase and a Ga ₂ ZnO ₄ crystalline phase,
The relative density , which is a percentage value of the theoretical density ρ (g/cm ³ ) based on the following formula (X), is more than 100.0%,
An oxide sintered body having a Zr content of less than 1 ppm by mass.
(In the formula, C ₁ to C _i respectively represent the content (mass %) of the constituent substances of the target material, and ρ ₁ to ρ _i respectively represent the density (g/cm ³ ) of the constituent substances corresponding to C ₁ to C _i .) The oxide sintered body according to claim 1, characterized in that the pinhole area ratio is 0.7% or less. The oxide sintered body according to claim 1 or 2, characterized in that the relative density is 100.5% or more. The oxide sintered body according to claim 1 or 2, characterized in that the relative density is 101.0% or more. The oxide sintered body according to claim 1 or 2, characterized in that the oxide sintered body has a flexural strength of 150 MPa or more. A sputtering target material comprising the oxide sintered body according to claim 1 or 2. A method for producing a film, comprising sputtering the sputtering target material according to claim 6 to form a thin film on a substrate.