JP5205696B2 - Gallium oxide based sintered body and method for producing the same - Google Patents

Description

  The present invention relates to a sputtering target used for forming a gallium oxide based transparent thin film by a sputtering method, a gallium oxide based sintered body used for the sputtering target, and a method for producing the same.

In a liquid crystal display, a plasma display, and a solar cell, a transparent conductive thin film is required, and an In ₂ O ₃ —SnO ₂ (ITO) film and a ZnO—Al ₂ O ₃ (AZO) film having a low specific resistance are used. It is used. These thin films are formed by a sputtering method using a sputtering target formed of a sintered body having the composition.

On the other hand, in addition to low specific resistance, a transparent conductive film made of a GaInO ₃ type crystal system that emphasizes characteristics such as transmittance (Patent Document 1), a natural superlattice homologous single crystal thin film made of GaInZnO ₄ (Patent Document 2), etc. Various transparent thin films have been developed according to the device application.

  These transparent thin films are expected to be used in applications other than conductive films, that is, optical devices, electronic devices, and X-ray optical devices.

  For these transparent thin films, in addition to sputtering, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and pulsed laser deposition (PLD) are widely known.

However, there have been almost no reports on gallium oxide-based sintered bodies including GaInM _x O _y (M is a positive divalent or higher-valent metal element) sintered body used for film formation.

Japanese Patent No. 3358893

Japanese Patent Laid-Open No. 2003-137692

  Generally, a CVD method or a sputtering method is used as a means for forming a transparent thin film. Among these, the sputtering method uses a sputtering target formed of a sintered body having a composition corresponding to the composition of the thin film.

  When film formation is performed by a sputtering method, abnormal discharge may occur. If abnormal discharge frequently occurs, the plasma discharge state becomes unstable, and stable film formation is not performed, which adversely affects the film characteristics.

  Further, a blackened product called nodule may be generated on the sputtering target. The presence of nodules causes abnormal discharge in sputtering, and further, the film deposition rate decreases and arcing causes particles to adhere to the thin film, which adversely affects the film characteristics such as the transmittance of the thin film.

  Furthermore, a crack and a crack may arise in a sputtering target during sputtering. There is a problem that arcing and nodules are generated from such cracks and cracks, and the yield of film formation is lowered.

  The present invention provides a sputtering target capable of suppressing the occurrence of such abnormal discharge, nodule and arcing, cracking and cracking during sputtering in the formation of a gallium oxide-based thin film, and a gallium oxide-based firing as a raw material thereof. The purpose is to provide ligation.

The gallium oxide based sintered body according to the present invention is represented by the formula GaInM _x O _y (M is a positive divalent or higher metal element, x is an integer from 1 to 3, and y is an integer from 4 to 8). The aggregate density is 95% or more in relative density, there is no Ga ₂ O ₃ insulating phase, and the average crystal grain size is 10 μm or less.

  The specific resistance is preferably 0.1 Ω · cm or less.

Such a gallium oxide-based sintered body has a particle size distribution of 1 μm or less in a slurry using a bead mill made of indium oxide powder, gallium oxide powder, and metal oxide powder each having a specific surface area of 3 to 15 m ² / g. After mixing and pulverizing until uniform, rapid dry granulation is performed using a spray dryer, etc., and the resulting granulated product is molded by cold isostatic pressing (CIP) , The oxygen flow rate to be introduced is set to 2 to 20 mL / min, the temperature rising rate in the temperature range of 600 to 1400 ° C. is set to 1 to 10 ° C./min, and the temperature is obtained by baking at 1200 to 1400 ° C. for 10 to 30 hours. .

  A sputtering target is produced by processing the obtained sintered body into a predetermined shape.

  When the gallium oxide-based sintered body according to the present invention is used, the generation of cracks and nodules in the sputtering target is suppressed during DC sputtering, and the occurrence of abnormal discharge is small. It becomes possible to form a film efficiently, inexpensively and with energy saving.

The gallium oxide-based sintered body according to the present invention is represented by the formula GaInM _x O _y (M is a positive divalent or higher metal element, x is an integer of 1 to 3, and y is an integer of 4 to 8). In order to obtain such a sintered body, a raw material powder composed of gallium oxide (Ga ₂ O ₃ ) powder, indium oxide (In ₂ O ₃ ) powder, and metal oxide (MO) powder is mixed and pulverized, and then manufactured. After granulating and molding the obtained granulated product, the obtained molded body is sintered by firing at a predetermined temperature for a predetermined time. Here, as MO, magnesium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, etc. other than zinc oxide are mentioned.

  In order to solve the above-mentioned problems, the present inventor has analyzed the gallium oxide-based sintered body and intensively studied. As a result, in order to make the gallium oxide-based sintered body usable as a sputtering target, The knowledge that this matter is needed was obtained.

(1) The sintered body density is 95% or more by relative density,
(2) The specific resistance of the sintered body is 0.1 Ωcm or less,
(3) The average crystal grain size is 10 μm or less,
(4) The insulating phase of gallium oxide (Ga ₂ O ₃ ) is substantially absent.

  These will be specifically described.

(Sintered body density)
The sintered body density of the sintered body is preferably 95% or more in terms of relative density. Here, the true density is calculated by Equation 1, and the relative density is calculated from the actually measured sintered body density. In addition, the measured value of a sintered compact density is based on the Archimedes method.

Calculated true density = 100 / (Ga ₂ O ₃ blending ratio (mass%) / Ga ₂ O ₃ density + In ₂ O ₃ blending ratio (mass%) / In ₂ O ₃ density + MO blending ratio (mass%) ) / MO density) Equation 1
The higher the density of the sintered body, the less blackened product called nodules. This nodule is a lower oxide and has an adverse effect on the thin film such as transmittance.

  In order to make the relative density 95% or more, it is necessary to control the specific surface area of each raw material. If the specific surface area is too low, the particle size of the raw material becomes large and the packing density of the powder becomes high. However, since the particle size is large and the surface energy is small, the sintering driving force becomes small and high density cannot be achieved. On the contrary, when the specific surface area is too high, the packing density of the raw material becomes low, and the voids generated there cause low density. Therefore, in any case, the density of the sintered body is not increased, which causes generation of nodules.

  On the other hand, if the firing temperature is less than 1200 ° C., the relative density of the sintered body becomes low, causing nodule generation. On the other hand, when firing at a temperature exceeding 1400 ° C., a reaction occurs between the sintered body and the furnace, which is not preferable for production.

  Furthermore, if the firing time is 10 hours or more, a relative density of 95% or more can be achieved, but the firing time is preferably 10 to 30 hours. If the time is shorter than 10 hours, the molded body does not sinter sufficiently, and the relative density of the sintered body falls below 95%. On the other hand, if firing is performed for longer than 30 hours, the average crystal grain size of the sintered body increases, and the strength of the sintered body decreases as described later.

(Average crystal grain size)
When the average crystal grain size in the sintered body is large, the strength of the sintered body is lowered, which causes cracks in the sputtering target during sputtering. Therefore, the average crystal grain size is preferably 10 μm or less. In order to achieve a desired sintered body density and to make the average crystal grain size 10 μm or less, it is necessary to adjust the firing temperature and firing time. The average crystal grain size is measured by SEM observation after the fracture surface of the sintered body is mirror-polished and then grain boundaries are precipitated by thermal corrosion.

  In general, the average crystal grain size depends on the firing temperature and firing time. The lower the sintering temperature of the molded body and the shorter the firing time, the smaller the average crystal grain size of the obtained sintered body. In the case of a gallium oxide-based sintered body, preferable firing conditions for setting the relative density of the sintered body to 95% or more are a firing temperature: 1200 to 1400 ° C., and a firing time: 10 hours or more. Under these firing conditions, in order to set the sintered body density to 95% or more in terms of relative density and the average crystal grain size to 10 μm or less, the firing time needs to be 10 to 30 hours. If it is shorter than 10 h, the average crystal grain size is 10 μm or less, but the sintered compact density is less than 95% in terms of relative density. On the other hand, when firing is performed for more than 30 hours, the sintered body density exceeds 95% in terms of relative density, but the average crystal grain size exceeds 10 μm.

(Sintered body resistivity)
In the sputtering target, the specific resistance is important. When the specific resistance of the sputtering target is high, the heat conduction is deteriorated, so that thermal stress is generated in the sputtering target and cracks are likely to occur. For this reason, the one where the specific resistance of the sintered compact used for a sputtering target is small is preferable. In addition, by using a sintered body having a small specific resistance as a sputtering target, the current and voltage during film formation are reduced, and a reduction in damage to the film and energy saving are also expected. The specific resistance is preferably 0.1 Ω · cm or less. The specific resistance of the sintered body is measured by a four-end needle method.

  When the sintered body density is low, the specific resistance of the sintered body is high, and by setting the relative density to 95% or more, the specific resistance of the sintered body is 0.1 Ω · cm or less.

(With or without insulation phase)
If an insulating phase of gallium oxide (Ga ₂ O ₃ ) is present in the sintered body, it will cause abnormal discharge in sputtering, so it is preferable that it does not exist. The presence or absence of the Ga ₂ O ₃ insulating layer is caused by the raw material grinding conditions and the granulation method. In order to produce a sintered body in which this phase does not exist, it is necessary to adjust the specific surface area of the raw material, and to perform a granulation method using rapid drying such as a spray dryer.

That is, after the raw material powder is mixed and pulverized in a ball mill, dried by natural drying, and pulverized, molded, and sintered, a phase in which Ga ₂ O ₃ of several tens to 100 μm is bent is generated, which is an abnormal discharge. Cause the occurrence of Note that the presence of an insulating phase of gallium oxide (Ga ₂ O ₃ ) is determined by X-ray diffraction.

  By providing the sintered body with these conditions, it is possible to obtain a sputtering target with less generation of cracks and abnormal discharge over the long term.

  Next, each factor affecting the gallium oxide-based sintered body in the manufacturing process of the gallium oxide-based sintered body will be described below.

[Raw material powder]
As the Ga ₂ O ₃ powder, In ₂ O ₃ powder, and MO powder, which are raw materials for obtaining the gallium oxide sintered body of the present invention, a powder having a specific surface area of 3 to 15 m ² / g is used. When the specific surface area is less than 3 m ² / g, the packing density of the powder becomes high, but since the particle size is large and the surface energy is small, the sintering driving force becomes small and the sintered body cannot be made high density. On the other hand, if it is larger than 15 m ² / g, the packing density of the raw material becomes low, and the voids generated there cause a reduction in the density of the sintered body.

[mixture]
First, the raw material powder is mixed. For mixing, a wet or dry ball mill, vibration mill, bead mill, or the like can be used. In order to obtain uniform and fine crystal grains and vacancies, a bead mill mixing method is most preferable because the crushing efficiency of the aggregates is high in a short time and the additive is well dispersed.

  The pulverization and mixing time by the bead mill varies depending on the size of the apparatus and the amount of slurry to be processed, but is adjusted so that the particle size distribution in the slurry is uniform to 1 μm or less.

  When the treatment time is short, the raw material powder cannot be uniformly mixed and pulverized, so that voids are generated in the sintered body, leading to a decrease in relative density. On the other hand, even if the thickness is adjusted to 1 μm or less, fine particles are present when pulverized and mixed for a long period of time, the raw material packing density is lowered, and the relative density of the sintered body is lowered.

  When mixing, an arbitrary amount of binder is added and mixed at the same time. As the binder, polyvinyl alcohol, vinyl acetate, or the like can be used.

[Quick drying granulation]
Next, granulated powder is obtained from the raw material powder slurry. In granulation, it is preferable to perform rapid drying granulation. As an apparatus for rapid drying granulation, a spray dryer is widely used. The specific drying conditions are determined by various conditions such as the slurry concentration of the slurry to be dried, the temperature of hot air used for drying, the air volume, etc., and therefore, it is necessary to obtain optimum conditions in advance. When natural drying is performed, the sedimentation rate varies depending on the difference in specific gravity of the raw material powder, so that separation of Ga ₂ O ₃ powder, In ₂ O ₃ powder, and ZnO powder occurs, and uniform granulated powder cannot be obtained. When a sintered body is produced using this non-uniform granulated powder, a Ga ₃ O ₃ phase that is an insulating phase is present, which causes abnormal discharge in sputtering.

[Molding]
The granulated powder is molded at a pressure of 1 ton / cm ² or more by a die press or cold isostatic press (CIP) to obtain a molded body.

[Baking method]
As a sintering method for obtaining the gallium oxide-based sintered body of the present invention, a pressure sintering method such as hot pressing, oxygen pressing, hot isostatic pressing, etc. can be adopted in addition to the atmospheric pressure sintering method. it can. However, it is preferable to employ a normal pressure sintering method from the viewpoints of reducing manufacturing costs, possibility of mass production, and easy production of large sintered bodies.

[Baking atmosphere]
In the atmospheric pressure sintering method, the compact is usually fired and sintered in the atmosphere. In order to further increase the density of the sintered body, oxygen is introduced and sintered in the temperature raising process. However, oxygen deficiency is suppressed by introduction of oxygen, and the specific resistance of the sintered body may be increased. Therefore, the oxygen flow rate when introducing oxygen is preferably 2 to 20 L / min. When the metal oxide (MO) added to the sintered body is an easily evaporated oxide, for example, when it is ZnO, if the oxygen flow rate during sintering is less than 2 L / min, the evaporation suppression of the metal oxide is performed. (Density increase) The effect is reduced, and the density of the sintered body is lowered. On the other hand, if it exceeds 20 L / min, the inside of the sintering furnace is cooled by the flow rate, and soaking is reduced.

[Baking temperature]
A baking temperature shall be 1200-1400 degreeC. The firing time is 10 to 30 hours. When the firing temperature is less than 1200 ° C., the relative density of the sintered body cannot be 95% or more. On the other hand, when the firing temperature exceeds 1400 ° C. or the firing time exceeds 30 hours, the average crystal grain size increases due to remarkable crystal grain growth, and coarse pores are generated, resulting in a decrease in sintered body strength and abnormal discharge. Cause.

  Furthermore, the temperature rising rate during sintering needs to be 1 to 10 ° C./min in the temperature range of 600 to 1400 ° C. The temperature range of 600 to 1400 ° C. is the range in which the sintering proceeds most. When the rate of temperature increase in this temperature range is slower than 1 ° C./min, the crystal grain growth becomes remarkable and high density is achieved. I can't. On the other hand, when the rate of temperature rise is faster than 10 ° C./min, the heat uniformity in the sintering furnace is lowered, and as a result, the amount of shrinkage during sintering occurs and the sintered body may be cracked. .

By controlling the various conditions in the production process of the sintered body as described above, the sintered body density is 95% or more in relative density, the specific resistance is 0.1 Ωcm or less, and the average crystal grain size is 10 μm or less. And a gallium oxide-based sintered body substantially free of a gallium oxide (Ga ₂ O ₃ ) phase can be obtained.

  By processing such a gallium oxide-based sintered body into a predetermined shape, it is possible to obtain a sputtering target that can be used for film formation of a gallium oxide-based transparent thin film and that does not generate nodules, abnormal discharge, and cracks. it can.

[Example 1]
The In ₂ O ₃ powder having a specific surface area of 10.5 m ² / g and the Ga ₂ O ₃ powder having a specific surface area of 11.2 m ² / g are each 25 mol%, and the ZnO powder having a specific surface area of 8.5 m ² / g is 50 mol%. And mixed and pulverized with a bead mill until the particle size distribution of each raw material powder became 1 μm or less. When mixing and pulverizing, 1% by mass of polyvinyl alcohol was added as a binder.

  The specific surface area was measured with Macsorb HM model-1208 manufactured by Mountec Co., Ltd.

The slurry thus produced was taken out and rapidly dried and granulated using a spray dryer under conditions of a slurry supply rate of 140 ml / min, a hot air temperature of 140 ° C. and a hot air volume of 8 Nm ³ / min, and the granulated product was subjected to cold isostatic pressing. Was molded at a pressure of 3 ton / cm ² to obtain a disk-shaped molded body having a diameter of 100 mm and a thickness of 8 mm.

  Next, this molded body is heated in the atmosphere at a rate of 0.5 ° C./min up to 600 ° C., and oxygen gas is introduced at a flow rate of 10 L / min, while 1 ° C. up to 600-800 ° C. The temperature was increased at a rate of 3 ° C./min at a rate of 3 ° C./min. Thereafter, holding was performed at 1300 ° C. for 20 hours to obtain a sintered body.

After calculating the density of the obtained sintered body from the weight and geometric dimensions of the sintered body, a part of the sintered body is cut, the cut portion is mirror-polished, and then thermally corroded, and observed by SEM. The average crystal grain size was measured by (manufactured by Hitachi High-Technologies Corporation, using S-800). From the X-ray diffraction results (manufactured by Rigaku Corporation, using rad-RVB), it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected.

  Further, the obtained sintered body was processed into a disk shape having a diameter of 75 mm and a thickness of 6 mm to produce a sputtering target. Using this target, the number of abnormal discharges during DC magnetron sputtering and the presence or absence of cracks were examined. The sputtering conditions were fixed at an input power of 200 W and an Ar gas pressure of 0.3 Pa. And the frequency | count of abnormal discharge which generate | occur | produces per 10 minutes after 10-hour progress from the start of experiment was measured. The obtained results are shown in Table 1.

[Example 2]
In ₂ O ₃ powder with a specific surface area of _{^{3.5m 2 / g, Ga 2 O}} 3 powder having a specific surface area of 4.0 m ² / g, except for using ZnO powder having a specific surface area of 3.1m ² / g, carried Measurements and tests similar to Example 1 were performed. The results are shown in Table 1.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 3]
In ₂ O ₃ powder having a specific surface area of _{^{14.5m 2 / g, Ga 2 O}} 3 powder having a specific surface area of 14.6 m ² / g, except for using ZnO powder having a specific surface area of 14.9m ² / g, Example In the same manner as in No. 1, a sintered body was obtained.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 4]
A sintered body was obtained in the same manner as in Example 1 except that the sintering temperature was 1200 ° C. and the sintering time was 10 h.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 5]
A sintered body was obtained in the same manner as in Example 1 except that the sintering temperature was 1400 ° C. and the sintering time was 30 h.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 6]
A sintered body was obtained in the same manner as in Example 1 except that the oxygen flow rate during sintering was 20 L / min.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 7]
A sintered body was obtained in the same manner as in Example 1 except that the oxygen flow rate during sintering was 2 L / min.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 8]
A sintered body was obtained in the same manner as in Example 1 except that the temperature was raised at 1 ° C./min in the temperature range of 600 to 1300 ° C.

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Example 9]
A sintered body was obtained in the same manner as in Example 1 except that the temperature was increased at a rate of 1 ° C./min from 600 to 800 ° C., and further at a rate of 10 ° C./min in the temperature range of 800 to 1300 ° C. .

From the X-ray diffraction result of the obtained sintered body, it was found that the crystal structure of this sintered body was InGaZnO ₄ . From the X-ray diffraction results, no diffraction peak due to Ga ₂ O ₃ was detected. Moreover, the same measurement and test as Example 1 were performed about the obtained sintered compact. The results are shown in Table 1.

[Comparative Example 1]
In ₂ O ₃ powder having a specific surface area of _{^{2.5m 2 / g, Ga 2 O}} 3 powder having a specific surface area of 0.9 m ² / g, except for using ZnO powder having a specific surface area of 2.2 m ² / g Example 1 In the same manner, a sintered body was obtained.

When the particle size distribution of the slurry after mixing and pulverization by the bead mill was measured, the particle size distribution of the slurry was 10 μm at the maximum even though the rotation speed and mixing / pulverization time in the bead mill were the same as in Example 1. Met.

After measuring the density of the obtained sintered body, a part of the sintered body was cut, and the cut surface was mirror-polished and thermally corroded, and the average crystal grain size was measured by SEM observation. From the X-ray diffraction results, it was found that this sintered body was composed of an InGaZnO ₄ phase and a Ga ₂ O ₃ phase.

  Further, the obtained sintered body was processed into a disk shape having a diameter of 75 mm and a thickness of 6 mm to produce a sputtering target. Using this target, the number of abnormal discharges during DC magnetron sputtering and the presence or absence of cracks were examined. The sputtering conditions were fixed at an input power of 200 W and an Ar gas pressure of 0.3 Pa. And the frequency | count of abnormal discharge which generate | occur | produces per 10 minutes after 10-hour progress from the start of experiment was measured. The obtained results are shown in Table 1.

[Comparative Example 2]
In ₂ O ₃ powder having a specific surface area of _{^{15.5m 2 / g, Ga 2 O}} 3 powder having a specific surface area of 16.3 m ² / g, except for using ZnO powder having a specific surface area of 15.8 m ² / g Example 1 In the same manner, a sintered body was obtained.

After measuring the density of the obtained sintered body, a part of the sintered body was cut, and the cut surface was mirror-polished and thermally corroded, and the average crystal grain size was measured by SEM observation. From the X-ray diffraction results, it was found that this sintered body was composed only of InGaZnO ₄ phase.

  Moreover, after measuring the density of the obtained sintered compact, the same measurement and test as Example 1 were performed about the sintered compact. The results are shown in Table 1.

[Comparative Example 3]
A sintered body was obtained in the same manner as in Example 1 except that the sintering temperature was 1200 ° C. and the sintering time was 5 h.

After measuring the density of the obtained sintered body, a part of the sintered body was cut, and the cut surface was mirror-polished and thermally corroded, and the average crystal grain size was measured by SEM observation. From the X-ray diffraction results, it was found that this sintered body was composed only of InGaZnO ₄ phase.

  Moreover, after measuring the density of the obtained sintered compact, the same measurement and test as Example 1 were performed about the sintered compact. The results are shown in Table 1.

[Comparative Example 4]
A sintered body was obtained in the same manner as in Example 1 except that the sintering temperature was 1400 ° C. and the sintering time was 35 h.

After measuring the density of the obtained sintered body, a part of the sintered body was cut, and the cut surface was mirror-polished and thermally corroded, and the average crystal grain size was measured by SEM observation. From the X-ray diffraction results, it was found that this sintered body was composed only of InGaZnO ₄ phase.

  Moreover, after measuring the density of the obtained sintered compact, the same measurement and test as Example 1 were performed about the sintered compact. The results are shown in Table 1.

[Comparative Example 5]
The specific surface area was 10.5 m ² / g In ₂ O ₃ powder, the specific surface area 11.2 m ² / g Ga ₂ O ₃ powder was 25 mol%, and the specific surface area 8.5 m ² / g ZnO powder was 50 mol%. The mixture was mixed and pulverized with a bead mill until the particle size distribution of each raw material powder became 1 μm or less. At this time, 1% by mass of polyvinyl alcohol was added as a binder.

The slurry thus prepared was taken out, naturally dried in a high-temperature bath, and pulverized to 300 μm or less. This granulated product was molded by a cold isostatic press at a pressure of 3 ton / cm ² to obtain a disk-shaped molded body having a diameter of 100 mm and a thickness of 8 mm.

  Next, this molded body was sintered in the same manner as in Example 1 to obtain a sintered body.

After measuring the density of the obtained sintered body, a part of the sintered body was cut, and the cut surface was mirror-polished and thermally corroded, and the average crystal grain size was measured by SEM observation. From the X-ray diffraction results, it was found that this sintered body was composed of an InGaZnO ₄ phase and Ga ₂ O ₃ .

  Moreover, after measuring the density of the obtained sintered compact, the same measurement and test as Example 1 were performed about the sintered compact. The results are shown in Table 1.

[Comparative Example 6]
Sintering was performed in the same manner as in Example 1 except that the temperature was increased from 600 to 800 ° C. at a rate of 1 ° C./min, and further in the temperature range of 800 to 1300 ° C., at a rate of 12 ° C./min. During the sintering, cracks occurred in the sintered body.

  If the heating rate in the vicinity of the sintering temperature is faster than 10 ° C./min, the sintered body is not necessarily broken, but cracks are likely to occur.

Examples 1 to 9 are examples in which the specific surface areas of Ga ₂ O ₃ , In ₂ O ₃ , and ZnO are within the scope of the present invention. As can be seen from Table 1, the sintered body density of the obtained gallium oxide-based sintered body is 95 to 98% or more in relative density. In addition, the maximum resistivity of the sintered body is 0.08 Ω · cm. Furthermore, gallium oxide (Ga ₂ O ₃ ) does not exist in the obtained sintered body.

On the other hand, Comparative Example 1 and Comparative Example 2 are examples in which the specific surface areas of Ga ₂ O ₃ , In ₂ O ₃ and ZnO are outside the scope of the present invention. Therefore, in Comparative Example 1, all the sintered body density, average crystal grain size, and specific resistance values of the sintered body did not satisfy the requirements, and a Ga ₂ O ₃ phase was also observed. For this reason, cracks and abnormal discharge occurred. In Comparative Example 2, the sintered body density and specific resistance of the sintered body did not satisfy the requirements, and cracks and abnormal discharge occurred.

  Comparative Example 3 and Comparative Example 4 are examples in which the sintering conditions are outside the scope of the present invention. Therefore, in Comparative Example 3, the sintered body density and specific resistance do not satisfy the requirements and abnormal discharge occurs, and in Comparative Example 4, the crystal grain size does not satisfy the requirements and the gallium oxide-based sintered body is applied. The above-mentioned requirements were not met, and cracks and abnormal discharges were observed.

In Comparative Example 5, since granulation was performed by natural drying, the sintered body density and specific resistance were not satisfied, and a Ga ₂ O ₃ phase was also present. Accordingly, cracks and abnormal discharge were observed.

Claims (4)

After mixing and pulverizing raw material powder consisting of indium oxide powder, gallium oxide powder, and metal oxide powder having a specific surface area of 3 to 15 m ² / g until the particle size distribution in the slurry is all uniform at 1 μm or less by a bead mill. Then, after rapid drying granulation, the obtained granulated product was molded by cold isostatic pressing, and the resulting molded product was subjected to 600 at a normal pressure sintering method with an oxygen flow rate of 2 to 20 mL / min. It is obtained by heating at a rate of temperature rise in the temperature range of ˜1400 ° C. as 1 to 10 ° C./min and firing at 1200 to 1400 ° C. for 10 to 30 hours,
GaInM _x O _y (M is a divalent or higher-valent metal element, x is an integer of 1 to 3, y is an integer of 4 to 8), and the sintered body density is 95% or more in terms of relative density, A gallium oxide-based sintered body having no Ga ₂ O ₃ insulating phase and an average crystal grain size of 10 μm or less.   The gallium oxide-based sintered body according to claim 1, wherein the specific resistance is 0.1 Ω · cm or less. A sputtering target obtained by processing into a predetermined shape gallium oxide based sintered body according to claim 1 or 2. After mixing and pulverizing raw material powder consisting of indium oxide powder, gallium oxide powder, and metal oxide powder having a specific surface area of 3 to 15 m ² / g until the particle size distribution in the slurry is all uniform at 1 μm or less by a bead mill. Then, after rapid drying granulation, the obtained granulated product was molded by cold isostatic pressing, and the resulting molded product was subjected to 600 at a normal pressure sintering method with an oxygen flow rate of 2 to 20 mL / min. The temperature rise rate in a temperature range of ˜1400 ° C. is raised as 1 to 10 ° C./min, and sintered at 1200 to 1400 ° C. for 10 to 30 hours to obtain a sintered body. Of manufacturing a gallium oxide sintered body.