WO2025220265A1 - Sintered body, sputtering target, and method for manufacturing sintered body - Google Patents

Abstract

The present disclosure addresses the problem of providing: a sintered body containing indium, gallium, zinc, and oxygen, the sintered body having an IGZO homologous crystal phase as a main phase and suppressing the occurrence of cracks; and a method for manufacturing said sintered body. This sintered body contains indium, gallium, zinc, and oxygen, has an IGZO homologous crystal phase as a main phase, has a total crack length of 0.1 μm or less per 1 μm², and has a volume resistivity of 10 mΩ・cm or less.

Description

Sintered body, sputtering target, and method for producing sintered body

This disclosure relates to a sintered body, a sputtering target, and a method for manufacturing a sintered body.

Oxide thin films (also known as IGZO) composed of indium (In), gallium (Ga), zinc (Zn), and oxygen (O) are attracting attention as transparent conductive films and oxide semiconductors. IGZO thin films have the advantage of having higher mobility than a-Si (amorphous silicon), and are gradually being developed for use as display driving elements (TFTs) (Patent Documents 1-3). Since mobility tends to increase as the In composition ratio increases, active research has been conducted into regions with a high In composition ratio (high In) (Patent Document 4). Crystallinity tends to improve as the Zn composition ratio increases (Patent Document 5).

IGZO thin films are typically deposited using a sputtering target made of an IGZO sintered body. Because layered homologous crystal phases form in IGZO sintered bodies, which make grain growth more likely, it has been proposed to suppress grain growth by microwave sintering (Patent Document 6). Patent Document 7 describes how particles can be reduced by creating a sintered body with two or more types of homologous crystal phases.

Japanese Patent Application Laid-Open No. 2008-163441 JP 2008-163442 A WO 2009/142289 JP 2011-106003 A JP 2017-145510 A JP 2014-040348 A WO 2009/142289

Sintered bodies containing indium, gallium, zinc, and oxygen are prone to forming homologous crystalline phases, which have a layered structure, creating the problem of shear forces that can easily cause cracks within the crystal grains.

In view of the above problems, the present disclosure aims to provide a sintered body containing indium, gallium, zinc, and oxygen, in which the homologous crystalline phase is the main phase and in which cracking is suppressed, and a method for manufacturing the same.

In order to solve the above problems, the inventors conducted extensive research and discovered that by devising manufacturing methods, it is possible to obtain a sintered body in which the homologous crystalline phase is the main phase and in which cracking is suppressed.

That is, the gist of the present disclosure is as follows.
[1] A sintered body containing indium, gallium, zinc, and oxygen, having an IGZO homologous crystalline phase as the main phase, a total crack length of 0.05 μm or less per 1 μm ² , and a volume resistivity of 10 mΩ cm or less.
[2] The sintered body according to [1], having an average crystal grain size of 3 μm or less.
[3] The sintered body according to [1] or [2], having a volume resistivity of 5 mΩ cm or less.
[4] The sintered body according to any one of [1] to [3], wherein the coefficient of variation of volume resistivity is within 10%.
[5] The sintered body according to any one of [1] to [4], wherein the XRD diffraction peak intensity ratio (P _max /Q max ) is 3 or more, where P _max is the largest XRD diffraction peak intensity among the normalized XRD diffraction peak intensities of the IGZO homologous phase, and Q _{max is} the largest diffraction peak intensity among the normalized XRD diffraction peak intensities of other crystal phases excluding the IGZO homologous phase.
[6] The sintered body according to any one of [1] to [5], having a relative density of 95% or more.
[7] The sintered body according to any one of [1] to [6], having a bending strength of 200 MPa or more.
[8] The sintered body according to any one of [1] to [7], wherein the composition is in the following range in atomic ratio:
0.11≦In/(In+Ga+Zn)≦0.40 (1)
0.11≦Ga/(In+Ga+Zn)≦0.40 (2)
0.20≦Zn/(In+Ga+Zn)≦0.78 (3)
[9] A sputtering target comprising the sintered body according to any one of [1] to [8].
[10] The sputtering target according to [9], wherein the area of the sputtering surface is 176 cm ² or more, or the diameter of the sputtering surface is 150 mm or more.
[11] A method for producing a sintered body according to any one of [1] to [8], comprising mixing In ₂ O ₃ powder, Ga ₂ O ₃ powder, and ZnO powder, and hot pressing the resulting mixed powder under vacuum or an inert gas atmosphere at a maximum sintering temperature of 1000 to 1150°C and a press pressure of 150 kgf/cm ² or more.
[12] The method for producing a sintered body according to [11], wherein the pressing pressure is 125 kgf/cm ² or more in the temperature range from 900°C to the maximum sintering temperature.

According to the present disclosure, it is possible to provide a sintered body and a sputtering target that contain indium, gallium, zinc, and oxygen, have a homologous crystalline phase as the main phase, and suppress the occurrence of cracks.

This is an image analysis diagram (for reference) used when analyzing the cracks. This is an image (for reference) of a sintered body (single phase) after binarization processing.

The present disclosure will be described below using specific embodiments, but the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications to the configurations may be made as appropriate within the scope of the gist of the present disclosure.

The sintered body according to an embodiment of the present disclosure contains indium, gallium, zinc, and oxygen. A sintered body having such a composition is sometimes referred to as an IGZO sintered body. IGZO is an abbreviation derived from the initial letters of each of the constituent elements: indium (In), gallium (Ga), zinc (Zn), and oxygen (O). IGZO thin films are used as transparent conductive films and oxide semiconductors, and are used as driving elements (TFTs) for displays and the like due to their excellent properties, such as higher mobility than a-Si.

IGZO thin films can usually be formed using the sputtering method. A sputtering target made of IGZO sintered body (sometimes referred to as an IGZO sputtering target) is placed in a vacuum chamber, and argon ions generated by glow discharge are collided with the sputtering target at high speed. The ejected atoms are deposited on an opposing glass substrate, etc., to form a thin film with roughly the same composition as the sputtering target.

IGZO sputtering targets are made from sintered bodies made by sintering raw material powders. During sintering, the raw material oxides containing In, Ga, and Zn react to form a homologous crystalline phase. While the homologous crystalline phase is a stable phase, its layered structure makes it susceptible to shear forces, resulting in cracks. Cracks can cause arcing during sputtering and can also cause target cracking during high-power sputtering, so it is desirable to reduce them as much as possible.

The IGZO sintered body according to this embodiment has an IGZO homologous phase as its main phase. The IGZO homologous phase is a homologous crystalline phase represented by (In,Ga) _{2O3 (} ZnO) _m (m = 0.5 or an integer from 1 to 20), and in particular a homologous crystalline phase represented by (In,Ga) _2O3 ( _ZnO ) _m (m = 1, 2, ₃ , ₄ ). In addition to the IGZO homologous phase, the IGZO sintered body may also contain other crystalline phases such as _{a ZnGa2O4} phase, an _In2O3 phase, a β- _GaInO3 phase, and _{an In2Zn7O10 phase} .

The IGZO sintered body is analyzed by XRD (X-ray diffraction), and each crystalline phase is identified by ICSD (Crystal Structure Database). When the largest XRD diffraction peak intensity among the normalized XRD diffraction peak intensities of the IGZO homologous phase is defined as P _max and the largest XRD diffraction peak intensity among the normalized XRD diffraction peak intensities of the other crystalline phases excluding the IGZO homologous phase is defined as Q _max , if the XRD diffraction peak intensity ratio (P _max /Q _max ) is at least 1, the IGZO homologous crystalline phase is determined to be the main phase.

Normalized XRD diffraction peak intensity refers to the XRD diffraction peak intensity obtained by subtracting the "background intensity" from the XRD diffraction peak intensity of each crystalline phase (crystal plane), where the average intensity at X-ray diffraction angles 2θ = 40° to 41° is taken as the "background intensity." If a peak derived from a crystalline phase is present in the above angle range, a range of Δ2θ = 1° within the range of 2θ = 20° to 50°, where no peak derived from a crystalline phase is present, is selected, and the average intensity thereof is taken as the background. If the X-ray diffraction peak intensity after normalization is 0 (zero) or less, the diffraction peak intensity is considered to be zero.

A thin film in a composition range in which the IGZO homologous crystalline phase is the main phase exhibits excellent properties as a TFT channel layer, such as high mobility and low carrier concentration. In this embodiment, the XRD diffraction peak intensity ratio (P _max /Q _max ) is more preferably 3 or more, even more preferably 5 or more, and particularly preferably 10 or more. Furthermore, as long as the XRD diffraction peak intensity ratio (P _max /Q _max ) is at least 1 or more, In, Ga, and Zn can be substituted with other elements as necessary.

Cracks can cause arcing during sputtering and can also cause cracks or fractures in the sputtering target, so it is desirable to reduce them as much as possible. In the IGZO sintered body according to this embodiment, the total length of the cracks is 0.05 μm or less per 1 μm ^2. This prevents adverse effects of cracks during sputtering and the occurrence of cracks or fractures in the target. Preferably, the total length of the cracks is 0.03 μm or less per 1 μm ² , and more preferably 0.02 μm or less. There is no particular need to limit the lower limit of the total crack length, but it is 0.000 μm or more per 1 μm ² .

In this embodiment, the average crystal grain size of the sintered body is preferably 3 μm or less. The IGZO homologous phase is prone to grain growth, and as the crystal grains become coarse, cracks are more likely to occur. Furthermore, as mentioned above, when the layered IGZO homologous phase is the main phase, cracks are likely to occur due to shear force, but the occurrence of cracks can be suppressed by reducing the grain size. Furthermore, since grain growth can lead to a decrease in flexural strength, a fine crystal grain size is preferred. The average crystal grain size is preferably 2 μm or less.

The sintered body according to this embodiment has a volume resistivity of 10 mΩ·cm or less. The lower the volume resistivity of a sputtering target made of an IGZO sintered body, the more stable the sputtering becomes. Since grain growth is likely to occur when the IGZO homologous crystal phase is present, the use of "microwave sintering" to suppress grain growth has been investigated. However, this sintering method makes it difficult to obtain a sintered body with low resistivity. According to the present disclosure, it is possible to obtain a sintered body with low resistivity while suppressing grain growth. The volume resistivity is more preferably 5 mΩ·cm or less, and even more preferably 1 mΩ·cm or less.

The sintered body according to this embodiment preferably has an in-plane coefficient of variation of volume resistivity of 10% or less. In a sputtering target made of an IGZO sintered body, the smaller the coefficient of variation of volume resistivity, the more stable the sputtering becomes. As mentioned above, the IGZO homologous phase has the property of being prone to grain growth, but in conventional manufacturing methods, suppressing grain growth causes fluctuations in volume resistivity and its variation. According to the present disclosure, it is possible to suppress grain growth while keeping the coefficient of variation of volume resistivity small. More preferably, it is 5% or less.

The coefficient of variation of the volume resistivity is calculated from the following formula.
Coefficient of variation (CV) [%] = (standard deviation) / (arithmetic mean value) × 100
Regarding the measurement locations and number of measurement points for volume resistivity, when the area of the sintered body is S ^cm2 and the peripheral length is L cm, the interval between measurement points is set to (L ^1/2 )/1.5 (cm) or more, and the number of measurement points is set to the smallest number (positive number) equal to or greater than the number calculated from 3 × S/L, the volume resistivity at each measurement point is measured, and the arithmetic mean value and standard deviation are calculated. Note that if it is not possible to take the number of measurement points specified in the above formula, the maximum number of measurable points is measured.

The sintered body according to this embodiment preferably has a relative density of 95% or higher. The higher the relative density of a sputtering target made of an IGZO sintered body, the more effectively it can suppress the generation of particles and the like during sputtering. Since IGZO homologous crystal phases tend to cause grain growth, lowering the sintering temperature to suppress grain growth has been investigated. However, this low-temperature sintering makes it difficult to obtain a high-density sintered body. According to the present disclosure, it is possible to obtain a high-density sintered body while suppressing grain growth. The relative density is more preferably 97% or higher, and even more preferably 98% or higher.

The sintered body according to this embodiment preferably has a flexural strength of 200 MPa or more. In particular, when an IGZO homologous crystalline phase is present, there is a problem in that cracks occur due to grain growth, making it easy for the flexural strength to decrease. According to the present disclosure, grain growth can be suppressed, thereby suppressing the occurrence of cracks and the decrease in flexural strength. A flexural strength of 230 MPa or more is more preferable. In particular, by increasing the strength of the sintered body, cracks during sputtering can be suppressed, allowing sputtering to be performed at high power.

The sintered body according to this embodiment contains indium, gallium, and zinc, and the content of each element is not particularly limited. However, in order to make the IGZO homologous phase the main phase, it is preferable that the content ratios of indium, gallium, and zinc satisfy the following formulas (1) to (3). In the formulas, In, Ga, and Zn represent the atomic ratios of each element contained in the sintered body. Furthermore, other elements may be added or substituted as necessary.
0.11≦In/(In+Ga+Zn)≦0.40 (1)
0.11≦Ga/(In+Ga+Zn)≦0.40 (2)
0.20≦Zn/(In+Ga+Zn)≦0.78 (3)
More preferably, the following formulas (4) to (6) are satisfied.
0.15≦In/(In+Ga+Zn)≦0.35 (4)
0.15≦Ga/(In+Ga+Zn)≦0.35 (5)
0.20≦Zn/(In+Ga+Zn)≦0.70 (6)

The sintered body of this embodiment can be used as a PVD (physical vapor deposition) material, for example, a sputtering target, a vacuum deposition material, an ion plating material, etc. When used as a sputtering target, it can be formed into a disk-shaped, rectangular, or cylindrical shape, and can be bonded to a backing plate using a bonding material. When used as a sputtering target, its thickness can be 20 mm or less, preferably 3.0 to 15 mm, and more preferably 3.0 to 12 mm. It is preferable that the area of the sputtered surface is 176 cm ² or more, or the diameter of the sputtered surface is 150 mm or more. It is difficult to achieve large sizes of 176 cm ² or more or a diameter of 150 mm or more using HIP (hot isostatic pressing) sintering or SPS (spark plasma sintering).

A method for manufacturing a sintered body, particularly a sputtering target, according to this embodiment will now be described. However, the manufacturing conditions, etc. below are not limited to the disclosed scope, and it is clear that some omissions and modifications may be made. Furthermore, detailed descriptions of well-known manufacturing processes and processing operations will be omitted to avoid unnecessarily obscuring the disclosed manufacturing method.

(1. Raw material powder)
As raw material powders, indium oxide (In ₂ O ₃ ) powder, gallium oxide (Ga ₂ O ₃ ) powder, and zinc oxide (ZnO) powder are prepared. It is preferable to use In ₂ O ₃ powder with a median diameter (D50): 0.5 to 3.0 μm and a specific surface area: 4.0 to 10 m ² /g, Ga ₂ O ₃ powder with a median diameter (D50): 0.5 to 4.0 μm and a specific surface area: 6.0 to 30 m ² /g, and ZnO powder with a median diameter (D50): 0.1 to 2.0 μm and a specific surface area: 2.0 to 20 m ² /g. Furthermore, it is preferable to use raw material powders with a purity of 99.9% by mass or higher. The raw material powders may be calcined.

(2. Mixing and grinding process)
The above raw material powders are weighed out to achieve the desired composition ratio (content ratio of the sintered body), and mixed and pulverized. There are various pulverization methods depending on the desired particle size and the material to be pulverized, but wet or dry ball mills, vibration mills, bead mills, etc. can be used. To obtain uniform and fine crystal particles, the bead mill mixing method is preferred, as it has high efficiency in breaking down agglomerates in a short time and also ensures good dispersion of additives. After pulverization, the median diameter (D50) is preferably 0.1 to 1.0 μm, and the specific surface area is preferably 10.0 to 30.0 m ² /g.

(3. Sintering process)
Next, the mixed powder is sintered. Conventionally, sintering has been performed in air or an oxygen gas atmosphere at approximately 1400 to 1600°C. However, as the sintering temperature increases, grain growth occurs, reducing the flexural strength. Furthermore, the volume resistivity increases, which can lead to abnormal discharges and particle generation during sputtering, making stable sputtering difficult. Stabilizing sputtering is particularly important when using larger targets and attempting to deposit a uniform film.

In the present disclosure, sintering is performed in a vacuum or in an inert gas (argon, nitrogen, etc.) atmosphere to generate oxygen deficiencies in the sintered body and reduce the volume resistivity. Sintering in an inert gas atmosphere is preferable to a vacuum in order to suppress ZnO sublimation. On the other hand, if sintering is performed in an inert gas atmosphere without pressure (atmospheric pressure), In ₂ O ₃ and Ga ₂ O ₃ are reduced, which inhibits the density improvement of the sintered body and may contaminate the inside of the device. Therefore, pressure sintering, which can suppress reduction to some extent, is preferred, and hot press sintering is particularly preferred from the viewpoint of productivity.

(3-1. Sintering holding temperature)
The maximum sintering temperature in the sintering process is set to 1000°C to 1150°C. Conventionally, sintering was performed at 1400 to 1600°C, but by setting the temperature to 1150°C or below, grain growth can be suppressed and bending strength can be improved. If the maximum sintering temperature is set too high, _In2O3 or _Ga2O3 may react with carbon, which is a sintering device component, and be reduced, so it is set to 1150° _C or below. On the other hand, if _the maximum sintering temperature is set too low, the density of the sintered body will not increase, so it is set to 1000°C or above.

(3-2. Pressing pressure)
The pressing pressure at the maximum sintering temperature in pressure sintering is preferably 150 kgf/cm ² or more. When sintering is performed in a vacuum or inert gas atmosphere, In ₂ O ₃ or Ga ₂ O ₃ may be reduced, but this reduction can be suppressed by performing hot pressing at a pressing pressure of 150 kgf/cm ² or more. There is no particular upper limit to the pressing pressure, but in view of the strength of the members used in hot pressing, it is preferable to set it to 400 kgf/cm ² or less.

(3-3. Sintering holding time)
The holding time at the maximum sintering temperature can be set to 2 to 50 hours. By controlling the holding time within this range, it is possible to increase the density of the sintered body while maintaining productivity.

(3-4. Temperature Rise Rate)
In the temperature range from 700°C to the maximum sintering temperature, the temperature rise rate is preferably 0.1 to 5.0°C/min, and more preferably 0.3 to 3.0°C/min. In the above-mentioned predetermined temperature range, a temperature rise rate exceeding 5.0°C/min is undesirable from the viewpoint of process stability during mass production, and a temperature rise rate below 0.1°C/min is undesirable from the viewpoint of reduced productivity. However, the temperature rise rate outside the above-mentioned predetermined temperature range is not limited, and any temperature rise rate can be adopted.

(3-5. Rebate measures)
In the temperature range of 900°C or higher, it is desirable to keep the pressing pressure at 125 kgf/ ^cm2 or higher during heating, temperature holding, and temperature reduction. If the pressing pressure is 125 kgf/ ^cm2 or lower in the temperature range of 900°C or higher, _{In2O3 and Ga2O3} will react with carbon in the sintered component and be reduced, which may cause _a decrease in density, compositional deviation, or damage to the component.

(3-6. Temperature fall rate)
In the temperature range from the maximum sintering temperature to 600°C, the temperature drop rate is preferably 10°C/min or less. By setting the temperature drop rate to 10°C/min or less, cracking of the sintered body due to thermal stress can be suppressed. Here, the temperature range in which the temperature drop rate is 10°C/min or less is set to 600°C or higher because sintered bodies at 600°C or higher tend to experience large thermal stress when cooled. However, the temperature drop rate outside the above-mentioned predetermined temperature range is not particularly limited, and any temperature drop rate can be adopted.

Furthermore, if pressure is continued to be applied in a temperature range of 600°C or less, internal stress will build up, which may cause cracks in the sintered body. Therefore, when the temperature is lowered to 600°C or less, it is preferable that the pressure be 50 kgf/cm2 or ^less , and in particular that no pressure be applied at all.

(4. Finishing Process)
The sintered body obtained through the above sintering process can be processed into a desired shape using a processing machine such as a surface grinder, a cylindrical grinder, or a machining device, as needed. The shape of the sputtering target is not particularly limited, and it can be a flat disk, a rectangle, a cylinder, or the like. Furthermore, the sputtering target can be bonded to a backing plate as needed.

The following description is based on examples and comparative examples. Please note that these examples are merely examples and are not intended to limit the scope of the present invention. In other words, the present invention is limited only by the scope of the claims, and includes various modifications other than the examples included in this disclosure.

The evaluation methods used in the examples and comparative examples are as follows. Since sputtering targets are processed by grinding, polishing, etc., the surface of the sintered body after polishing is in substantially the same condition as the sputtering surface of the sputtering target. Various evaluations were also performed on a representative portion (sample) of the sintered body. If the various physical properties of the representative sample fall within the ranges of this disclosure, the sintered body is encompassed by the present invention. In other words, even if a unique, exceptional, or partial sample that is not representative of the sintered body is measured and falls outside the range of this disclosure, if the various physical properties of the representative sample fall within the ranges of this disclosure, the sintered body is encompassed by the present invention as long as it exhibits the effects of the present invention.

(Composition analysis)
The composition of the sintered body was analyzed using the following equipment.
Equipment: SPS3500DD manufactured by SII
Method: ICP-OES (inductively coupled plasma optical emission spectroscopy)

(Crystalline Phase Analysis)
The crystal phase analysis was carried out using the following equipment.
Principle: X-ray diffraction method Equipment: Rigaku Ultima IV
Tube: Cu-Kα ray Tube voltage: 40 kV
Tube current: 30mA
Measurement method: 2θ-θ reflection method Measurement range (2θ): 20 to 90°
Scan speed: 8°/min
Sampling interval: 0.02°
Divergence slit: 1°
Divergence vertical limit slit: 10 mm
Scattering slit: 8 mm
Receiving slit: Open state Goniometer: Horizontal type for sample Sample measurement location: Sputtered surface side

(About cracks)
The cross sections (planes parallel to the plane corresponding to the sputtered surface) of the center and end (3 cm inside from the outer periphery) of the sintered body were observed using a backscattered electron image (magnification: 2000 times) of an FE-EPMA (field emission electron probe microanalyzer), and an arbitrary number of images were taken.
Equipment used: JXA-8500 (JEOL)
Acceleration voltage: 15.0 kV
Beam current: 2.0×10 ⁻⁸

The captured images were analyzed using ImageJ (image processing software). A reference diagram for ImageJ analysis is shown in Figure 1 (left: SEM micrograph, right: ImageJ image analysis diagram). As shown in Figure 1, analysis using ImageJ makes it possible to count the frequency (vertical axis) of the brightness (horizontal axis) of the captured image: n (range = 0 to 255). Note that in backscattered electron images, heavier elements are displayed in brighter colors, and lighter elements are displayed in darker colors.

For the single-phase structure, three images were selected in which the brightness (n _max ) with the highest frequency was 160≦n _max ≦180, and among the brightnesses with a frequency of 1/10 or more of the frequency of n _max , the darkest brightness (n _1/10 ) was n _max -20≦n _1/10 ≦n _max -15. Then, n _def was set so that n _1/10 -n _def = 5, and the images were binarized so that values below n _def were black and values above n _def were white (see Figure 2). To distinguish them from pores, black areas with a long side/short side of 3 or more were considered cracks, and their lengths were measured. The total length of the lines divided by the field area was taken as the crack length per 1 μm ² , and the average of the crack lengths per 1 μm ² of the three images was taken as the total crack length.

In the case of a structure containing multiple crystalline phases, three images were arbitrarily selected such that the brightness (n1) at which the frequency of the portion corresponding to the brightest crystalline phase (the phase with a high proportion of _{In2O3 phase} ) was greatest was 200≦n1≦220, and the brightness (n2) at which the frequency of the portion corresponding to the darkest crystalline phase (the phase with a low proportion of _{In2O3 phase} ) was greatest was 115≦n2≦135. Among the brightnesses whose frequency was 1/10 or more of the frequency of n2, the darkest brightness was defined as n1 _/10 , and _ndef was set so that n1 _/10 - _ndef = 5. The images were binarized so that brightnesses below _ndef were black and brightnesses above _ndef were white. To distinguish from pores, black portions with a long side/short side length of 3 or more were considered cracks, and their lengths were measured. The total length of the lines divided by the area of the field of view is taken as the crack length per 1 ^μm2 , and the average value of the crack lengths per unit area of the three sheets is taken as the total crack length.

(Regarding average crystal grain size)
A sample for observation was cut out from the sintered body, and the surface of the cut sample (the surface corresponding to the sputtered surface) was mirror-polished. A structural photograph of the mirror-polished sample surface was taken in five fields of view at a magnification of 5000 times using a scanning electron microscope (SEM). Next, three lines (hereinafter referred to as lines 1, 2, and 3) were drawn on the photographed image so that each line intersected 10 or more crystal grains. The length of each line and the number of intersections with the grain boundaries were determined. The grain boundaries at the start and end points of the lines were not included. Based on the measured length of the lines and the number of intersections, the crystal grain size in one field of view was calculated using the following formula:
Grain size in one field of view = (length of line 1/number of intersections between line 1 and grain boundaries + length of line 2/number of intersections between line 2 and grain boundaries + length of line 3/number of intersections between line 3 and grain boundaries) ÷ 3
The crystal grain size was then calculated for each of the five fields of view using the above formula, and the arithmetic mean value of the five fields of view was taken as the average crystal grain size. However, when the number of particles intersected by each straight line within the field of view was less than 10, a magnification of 2000x or 1000x was used. The equipment and measurement conditions used were as follows:
Equipment used: JXA-8500F (JEOL)
Acceleration voltage: 15.0 kV
Beam current: 5.0×10 ⁻⁸ A

(Volume resistivity)
The surface of a sintered body having a diameter of 180 mm was polished, and the volume resistivity was measured at 13 random points on the polished surface spaced at intervals of 5.0 cm or more, and the arithmetic mean value and standard deviation of the 13 points were calculated. The following equipment was used for the measurement.
Equipment: NPS resistivity measuring instrument Σ-5+
Method: Constant current application method Method: DC 4-probe method Measurement temperature: Room temperature (20 to 25°C)

(Regarding relative density)
The relative density was calculated using the following formula.
Relative density (%) = Archimedes density / calculated density × 100
Archimedes density: The upper and lower surfaces of the sintered body were ground to a thickness of 1 mm, and the outer peripheral surface was ground to a thickness of 5 mm to prepare a measurement sample, and the Archimedes density was calculated using the Archimedes method.
Calculated density: The sintered body was subjected to a component analysis, and the oxide mass ratio (mass%) was calculated by converting the atomic ratio (at%) of each of In, Ga, and Zn relative to the total of 100 at% of the constituent _elements In, Ga, and Zn. The calculated density was then calculated using the theoretical densities of _In2O3 , _{Ga2O3 ,} and ZnO shown below.
Calculated density (g/cm ³ )=(W1+W2+W3)/(W1/d1+W2/d2+W3/d3)
W1: Mass ratio of _In2O3 (mass _% )
W2: Mass ratio of _Ga2O3 (mass _% )
W3: ZnO mass ratio (mass%)
Theoretical density:
d1: 7.18 g/cm ³ (theoretical density of In ₂ O ₃ )
d2: 5.95 g/cm ³ (theoretical density of Ga ₂ O ₃ )
d3: 5.61 g/cm ³ (theoretical density of ZnO)

(Regarding bending strength)
A sample was cut out from the sintered body, and the surface of the cut sample (the surface corresponding to the sputtered surface) was polished. The flexural strength of the polished surface was measured in accordance with JIS R 1601:2008.
Test method: Three-point bending test Support distance: 30 mm
Sample size: 3 x 4 x 40 mm
Head speed: 0.5 mm/min
The number of test pieces was set to 10, and the average value was calculated.

Example 1
_{In2O3 powder} , _{Ga2O3 powder} , and ZnO powder were prepared, weighed, mixed, and pulverized to obtain a powder with a median diameter _D50 of 0.64 μm and a specific surface area of 11.7 ^m2 /g. Next, this mixed powder was filled into a carbon die and hot-pressed under an argon atmosphere at a maximum sintering temperature of 1150°C, a pressure of 250 kgf/ ^cm2 , and a holding time of 5 hours to produce a sintered body with a diameter of 180 mm. The heating rate from 700°C to the maximum sintering temperature was 3°C/min, and the cooling rate from the maximum sintering temperature to 600°C was 5°C/min.

The physical properties of the sintered body obtained in Example 1 were measured, and good results were obtained, including a total crack length of 0.002 μm/μm ² , an average crystal grain size of 1.2 μm, a relative density of 98.6%, a volume resistivity of 0.6 mΩ·cm, a coefficient of variation of volume resistivity of 4.7%, and a flexural strength of 262.6 MPa. The sintered body had an IGZO homologous crystal phase of InGaZnO ₄ as its main phase. The results are shown in Table 1.

Example 2
A sintered body was produced using the same manufacturing method and conditions as in Example 1, except for the different composition. Measurement of the physical properties of the sintered body obtained in Example 2 showed good results, including a total crack length of 0.019 μm/μm ² , an average crystal grain size of 1.6 μm, a relative density of 99.1%, a volume resistivity of 0.6 mΩ·cm, a coefficient of variation of volume resistivity of 8.3%, and a flexural strength of 241.3 MPa. The sintered body had an IGZO homologous crystal phase of InGaZn ₂ O ₅ as its main phase.

Example 3
A sintered body was produced using the same manufacturing method and conditions as in Example 1, except for the different composition. Measurement of the physical properties of the sintered body obtained in Example 3 showed good results, including a crack length of 0.010 μm/μm ² , an average crystal grain size of 1.3 μm, a relative density of 98.7%, a volume resistivity of 0.8 mΩ·cm, a coefficient of variation of volume resistivity of 2.8%, and a flexural strength of 260.0 MPa. The sintered body had an IGZO homologous crystal phase of InGaZn ₄ O ₇ as its main phase.

Example 4
A sintered body was produced using the same manufacturing method and conditions as in Example 1, except for the different composition. Measurement of the physical properties of the sintered body obtained in Example 3 showed good results, including a total crack length of 0.003 μm/μm ² , an average crystal grain size of 0.7 μm, a relative density of 98.9%, a volume resistivity of 0.8 mΩ·cm, a coefficient of variation of volume resistivity of 4.6%, and a flexural strength of 279.9 MPa. The sintered body had an IGZO homologous crystal phase of InGaZn ₃ O ₆ as the main phase, with an In ₂ Zn ₇ O ₁₀ phase present.

(Comparative Example 1)
_In2O3 powder, _{Ga2O3 powder} , and ZnO powder were prepared, weighed, mixed, and pulverized to obtain the _desired composition shown in Table 1, resulting in a powder with a median diameter _D50 of 0.64 μm and a specific surface area of 11.7 ^m2 /g. Next, this mixed powder was filled into a die and uniaxially compacted at a pressure of 785 kfg/ ^cm2 and a holding time of 1 minute, followed by CIP compaction at a pressure of 1795 kgf/ ^cm2 and a holding time of 1 minute. The resulting compact was then pressurelessly sintered in an oxygen atmosphere at a maximum sintering temperature of 1350°C and a holding time of 20 hours to produce a sintered body with a diameter of 180 mm. Measurement of the physical properties of the sintered body obtained in Comparative Example 1 revealed that the total crack length was 0.111 μm/μm ² , the average crystal grain size was 8.3 μm, the volume resistivity was 70 mΩ·cm, and the flexural strength was 77.1 MPa, which was not the desired result. Note that the sintered body had an IGZO homologous crystal phase of InGaZnO ₄ as its main phase.

(Comparative Example 2)
_In2O3 powder, _{Ga2O3 powder} , and ZnO powder were prepared, weighed, mixed, and pulverized to obtain the _desired composition shown in Table 1, resulting in a powder with a median diameter _D50 of 0.24 μm and a specific surface area of 11.45 ^m2 /g. Next, this mixed powder was filled into a die and uniaxially compacted at a pressure of 785 kfg/ ^cm2 and a holding time of 1 minute, followed by CIP compaction at a pressure of 1795 kgf/ ^cm2 and a holding time of 1 minute. The resulting compact was then pressurelessly sintered in air at a maximum sintering temperature of 1400°C and a holding time of 20 hours to produce a sintered body with a diameter of 180 mm. Measurement of the physical properties of the sintered body obtained in Comparative Example 2 revealed that the total crack length was 0.118 μm/μm ² , the average crystal grain size was 8.3 μm, the volume resistivity was 41.7 mΩ·cm, and the coefficient of variation of the volume resistivity was 13.29%, which was not the desired result. The sintered body had an IGZO homologous crystal phase of InGaZn ₂ O ₅ as its main phase.

(Comparative Example 3)
_In2O3 powder, _{Ga2O3 powder} , and ZnO powder were prepared, weighed, mixed, and pulverized to obtain the _desired composition shown in Table 1, resulting in a powder with a median diameter _D50 of 0.64 μm and a specific surface area of 11.7 ^m2 /g. This mixed powder was then filled into a die and uniaxially compacted at a pressure of 785 kfg/ ^cm2 and a holding time of 1 minute. It was then subjected to CIP compaction at a pressure of 1795 kgf/ ^cm2 and a holding time of 1 minute. The resulting compact was microwave sintered in air at a maximum sintering temperature of 1400°C and a holding time of 30 minutes to produce a sintered body with a diameter of 30 mm. The sintered body obtained in Comparative Example 3 exhibited cracks. This is believed to be due to high temperatures being applied to a portion of the sintered body during sintering, resulting in large temperature variations within the sintered body.

Since it was not possible to obtain a sample of sufficient size for the sintered body obtained in Comparative Example 3, it was not possible to measure the XRD, bending strength, or coefficient of variation of volume resistivity. The volume resistivity varied significantly, reaching 11 mΩ cm at low points, but exceeding the upper limit of measurement at high points. When the grain size was measured at the points with low volume resistivity, the average crystal grain size was 3.55 μm and the total length of the cracks was 0.052 μm, which was not the desired result.
Since microwave sintering has a short sintering time, it is thought that the temperature unevenness within the sintered body becomes large, resulting in non-uniform volume resistivity and grain size.

(Comparative Example 4)
Except for the different composition and sintering temperature, a sintered body was produced using the same manufacturing method and conditions as in Example 1. Measurement of the physical properties of the sintered body obtained in Comparative Example 4 revealed that an _{In2O3 phase} was present in addition to the IGZO homologous crystal phase of _InGaZnO4 , and the desired results were not obtained.

According to this disclosure, it is expected that particles generated during sputtering can be suppressed, potentially improving product yields. Improving product yields will lead to a stable supply of products and reduced loss of metal raw materials, which are limited resources. Therefore, this disclosure may contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster technological innovation," and Goal 12, "Ensure sustainable consumption and production patterns." The sintered body and sputtering target according to this disclosure are useful for forming IZO thin films as transparent conductive films and oxide semiconductor films.

The present disclosure provides a sintered body containing indium, gallium, zinc, and oxygen, in which the IGZO homologous crystalline phase is the main phase and cracking is suppressed, and a method for manufacturing the same. The sintered body and sputtering target according to the present disclosure are useful for forming IGZO thin films as transparent conductive films and oxide semiconductor films.

Claims (12)

A sintered body containing indium, gallium, zinc, and oxygen, having an IGZO homologous crystalline phase as a main phase, a total crack length of 0.05 μm ^or less per 1 μm2, and a volume resistivity of 10 mΩ cm or less. The sintered body according to claim 1, having an average crystal grain size of 3 μm or less. The sintered body according to claim 1, having a volume resistivity of 5 mΩ·cm or less. The sintered body according to claim 1, wherein the coefficient of variation of volume resistivity is within 10%. 2. The sintered body according to claim 1, wherein the XRD diffraction peak intensity ratio (P _{max /} Q _max ) is 3 or more, where P _max is the largest XRD diffraction peak intensity among the normalized XRD diffraction peak intensities of the IGZO homologous phase and Q _max is the largest XRD diffraction peak intensity among the normalized XRD diffraction peak intensities of other crystal phases excluding the IGZO homologous phase. The sintered body according to claim 1, having a relative density of 95% or more. The sintered body according to claim 1, having a flexural strength of 200 MPa or more. 2. The sintered body according to claim 1, wherein the composition is in the following range in atomic ratio:
0.11≦In/(In+Ga+Zn)≦0.40 (1)
0.11≦Ga/(In+Ga+Zn)≦0.40 (2)
0.20≦Zn/(In+Ga+Zn)≦0.78 (3) A sputtering target comprising the sintered body according to any one of claims 1 to 8. 10. The sputtering target according to claim 9, wherein the area of the sputtering surface is 176 cm ^{<2 >} or more, or the diameter of the sputtering surface is 150 mm or more. A method for producing a sintered body according to any one of claims 1 to 8, comprising mixing _{In2O3 powder} , _{Ga2O3 powder} , and ZnO powder, and hot pressing the resulting mixed powder under vacuum or an inert gas atmosphere at a maximum sintering temperature of 1000 to 1150°C and a press pressure at the maximum sintering temperature of 150 kgf/cm2 or ^more . The method for producing a sintered body according to claim 11, wherein the pressing pressure is 125 kgf/cm ² or more in the temperature range from 900°C to the maximum sintering temperature.