JP2023022339A - Oxide sintered body and manufacturing method of oxide sintered body - Google Patents

Abstract

To provide an oxide sintered body that has relatively good plasma resistance and can be manufactured at relatively low cost.SOLUTION: The present invention relates to an oxide sintered body and a method for producing the oxide sintered body, wherein the oxide sintered body contains a conductive mayenite compound, has an average grain size in the range of 5 μm to 40 μm, and a relative density of 98% or more. The inventive manufacturing method of the oxide sintered body comprises the following steps: (1) a step of preparing a calcined powder containing calcium oxide and aluminum oxide in a ratio of 13:6 to 11:8 (molar ratio converted to CaO:Al2O3); (2) a step of placing the object to be processed containing the calcined powder in a container together with a reducing agent, and pressurizing the object to be processed with a press pressure of 50 kgf/cm2 or more; (3) a step of performing a heat treatment while maintaining the object to be processed at a temperature within a range of 1280°C to 1330°C under the reduced pressure in the container.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an oxide sintered body and a method for producing an oxide sintered body.

2. Description of the Related Art Conventionally, semiconductor manufacturing apparatuses have been used to manufacture semiconductors from wafers. In a semiconductor manufacturing apparatus, various processes such as film formation using various materials and etching are performed on wafers.

For example, in a wafer etching process, plasma of highly corrosive halogen gas such as chlorine gas or fluorine gas may be used. Such plasma can damage materials used in semiconductor manufacturing equipment. For this reason, plasma-resistant materials are used in equipment for such processes.

Oxide sintered bodies such as magnesium oxide (MgO) and yttrium oxide (Y ₂ O ₃ ) have been known as materials having good plasma resistance.

WO2012/157461

The plasma-resistant materials hitherto known, particularly MgO and Y ₂ O ₃ , are both difficult to sinter, and have the problem of high production costs for sintered bodies. Therefore, there is still a demand for an oxide sintered body that has plasma resistance and can be manufactured at a lower cost.

The present invention has been made in view of such problems, and the present invention provides an oxide sintered body that has relatively good plasma resistance and can be manufactured at a relatively low cost. The purpose is to Another object of the present invention is to provide a method for producing such an oxide sintered body.

In the present invention, an oxide sintered body,
containing a conductive mayenite compound,
The average crystal grain size is in the range of 5 μm to 40 μm,
An oxide sintered body having a relative density of 98% or more is provided.

Further, in the present invention, there is provided a method for producing an oxide sintered body,
(1) A step of preparing a calcined powder containing calcium oxide and aluminum oxide at a ratio of 13:6 to 11:8 (molar ratio converted to CaO:Al ₂ O ₃ );
(2) A step of placing the object to be treated containing the calcined powder in a container together with a reducing agent, and pressurizing the object to be treated with a press pressure of 50 kgf/cm ² or more;
(3) A step of holding the object to be treated in a range of 1280° C. to 1330° C. and performing heat treatment with the inside of the container being decompressed, wherein the press pressure applied to the object to be treated is From 3 hours before the completion of holding at temperature, it is reduced at a rate ranging from 20 kgf/cm ² /h to 60 kgf/cm ² /h on average, and is reduced to 0 (zero) by the completion of said holding. and,
A manufacturing method is provided, comprising:

The present invention can provide an oxide sintered body that has relatively good plasma resistance and can be manufactured at relatively low cost. Further, the present invention can provide a method for producing such an oxide sintered body.

BRIEF DESCRIPTION OF THE DRAWINGS It is the flowchart which showed typically an example of the manufacturing method of the oxide sintered compact by one Embodiment of this invention. 1 is a diagram schematically showing one configuration example of an apparatus used when heat-treating an object to be processed; FIG. FIG. 3 is a diagram schematically showing how the apparatus shown in FIG. 2 is used;

(Mayenite compound and conductive mayenite compound)
First, the mayenite compound and the conductive mayenite compound will be briefly described.

The mayenite compound has a typical composition represented by 12CaO.7Al ₂ O ₃ and has a characteristic crystal structure with three-dimensionally connected voids (cages) with a diameter of about 0.4 nm. The framework that makes up this cage is positively charged and forms 12 cages per unit cell. 1/6 of this cage is occupied with oxygen ions in order to satisfy the electroneutrality condition of the crystal. However, the caged oxygen ions have chemically different properties from the other oxygen ions that make up the framework, and for this reason the caged oxygen ions are specifically called free oxygen ions. . The mayenite compound is also expressed as [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴ +.2O ²⁻ .

Electrical conductivity is imparted to the mayenite compound when some or all of the free oxygen ions in the cage of the mayenite compound are replaced with electrons. This is because the electrons clathrated in the cage of the mayenite compound are not so constrained by the cage and can move freely in the crystal. A mayenite compound having such conductivity is particularly referred to as a conductive mayenite compound.

The conductive mayenite compound has an electron density of 1.0×10 ¹⁸ cm ⁻³ or more. The maximum electron density in conductive mayenite compounds is 2.3×10 ²¹ cm ⁻³ .

The electron density of the conductive mayenite compound is measured in two ways according to the electron density of the mayenite compound. When the electron density is less than 1.0×10 ¹⁸ cm ⁻³ to 3.0×10 ²⁰ cm ⁻³ , the electron density is obtained by measuring the diffuse reflection of the conductive mayenite compound powder and performing the Kubelka-Munk transformation of the absorption spectrum. It is calculated from the absorbance (Kuberka Munk transform value) at 0.8 eV (wavelength 443 nm). This method utilizes the proportional relationship between the electron density and the Kubelka-Munk transformation value. A method for creating a calibration curve will be described below.

Four samples with different electron densities are prepared, and the electron density of each sample is obtained from the signal intensity of electron spin resonance (ESR). The electron density measurable by ESR is about 1.0×10 ¹⁴ cm ⁻³ to 1.0×10 ¹⁹ cm ⁻³ . Plotting the Kubelka Munk value and the electron density determined by the ESR in logarithm yields a proportional relationship, which is used as a calibration curve. That is, in this method, the values are values obtained by extrapolating the calibration curve when the electron density is 1.0×10 ¹⁹ cm ⁻³ to 3.0×10 ²⁰ cm ⁻³ .

On the other hand, when the electron density is 3.0×10 ²⁰ cm ⁻³ to 2.3×10 ²¹ cm ⁻³ , the electron density is obtained by measuring the diffuse reflection of the conductive mayenite compound powder and applying the Kubelka-Munk transformation to the absorption spectrum. It is converted from the peak wavelength (energy). In that case, the following formula (1) is used:

n=(-(E _sp -2.83)/0.199) ^0.782 (1) Formula

Here, n is the electron density (cm ⁻³ ), and E _sp is the peak energy (eV) of the Kubelka-Munk-transformed absorption spectrum.

In addition, in the present application, the conductive mayenite compound includes calcium (Ca), aluminum (Al) and oxygen (O) as long as it has a C12A7 crystal structure composed of calcium (Ca), aluminum (Al) and oxygen (O). ) may be partially substituted with other atoms or atomic groups. For example, part of calcium (Ca) is magnesium (Mg), strontium (Sr), barium (Ba), lithium (Li), sodium (Na), chromium (Cr), manganese (Mn), cerium (Ce) , cobalt (Co), nickel (Ni) and copper (Cu). In addition, part of aluminum (Al) is silicon (Si), germanium (Ge), boron (B), gallium (Ga), titanium (Ti), manganese (Mn), iron (Fe), cerium (Ce) , praseodymium (Pr), scandium (Sc), lanthanum (La), yttrium (Y), europium (Eu), yttrium (Yb), cobalt (Co), nickel (Ni) and teribium (Tb) may be substituted with one or more atoms that are

Also, in the present application, the conductive mayenite compound has at least a portion of the free oxygen ions in the cage H ⁻ , H ₂ ⁻ , H ²⁻ , O ⁻ , O ₂ ⁻ , OH ⁻ , F ⁻ , Cl ⁻ , and It may be substituted with an anion such as S ^2- and an anion of nitrogen (N).

The ratio of calcium (Ca) and aluminum (Al) in _the conductive mayenite compound is preferably in the range of 13:6 to 11:8, preferably 12.5:6.5, in terms of molar ratio in terms of CaO: _Al2O3 . ~11:8 is more preferred, 12.3:6.7 to 11.5:7.5 is more preferred, and 12.2:6.8 to 11.8:7.2 is even more preferred. Preferably, about 12:7 is particularly preferred. When part of calcium (Ca) is substituted with other atoms, the number of moles of calcium and other atoms is regarded as the number of moles of calcium. When part of aluminum (Al) is substituted with other atoms, the number of moles of aluminum and other atoms is regarded as the number of moles of aluminum.

(Oxide sintered body according to one embodiment of the present invention)
In one embodiment of the present invention, an oxide sintered body,
containing a conductive mayenite compound,
The average crystal grain size is in the range of 5 μm to 40 μm,
An oxide sintered body having a relative density of 98% or more is provided.

As described above, the conventional plasma-resistant oxide sintered bodies have the problem that they are difficult to sinter and the manufacturing cost is high.

In contrast, the oxide sintered body according to one embodiment of the present invention is mainly composed of a conductive mayenite compound. For example, an oxide sintered body according to one embodiment of the present invention is substantially composed of a conductive mayenite compound. Conductive mayenite compounds can be sintered relatively easily. Therefore, in the oxide sintered body according to one embodiment of the present invention, manufacturing costs can be significantly suppressed.

Moreover, as will be described later, the oxide sintered body according to one embodiment of the present invention has relatively good plasma resistance.

Here, the reason why the oxide sintered body according to one embodiment of the present invention exhibits relatively good plasma resistance is considered as follows.

In general, plasma-induced degradation of oxide sintered bodies is considered to occur starting from defects such as crystal grain boundaries and pores. In this regard, the conductive mayenite compound contained in the oxide sintered body according to one embodiment of the present invention has an average crystal grain size in the range of 5 μm to 40 μm, and the crystal grains are relatively large. Also, the porosity is significantly suppressed.

Therefore, it is believed that the oxide sintered body according to one embodiment of the present invention has fewer defects such as grain boundaries and pores, and as a result, relatively good plasma resistance can be obtained.

In one embodiment of the present invention, the reason why the average crystal grain size is 40 μm or less is to suppress a decrease in the strength of the sintered body. Further, by setting the average crystal grain size to 40 μm or less, it is possible to enhance the thermal shock resistance of the sintered body.

By the way, in general, in the process of manufacturing an oxide sintered body, if crystal grains are to be grown large, pores tend to be incorporated into the structure. Therefore, the relative density of the resulting sintered body tends to decrease.

However, in one embodiment of the present invention, during the firing of the oxide sintered body, the step of pressurizing the object to be treated with a press pressure of 50 kgf/cm ² or more and releasing the press pressure applied to the object to be treated and the step of Due to such a characteristic process, in one embodiment of the present invention, it is possible to significantly prevent pores from remaining in the sintered body and to grow large crystal grains. That is, it is possible to obtain an oxide sintered body having large crystal grains while suppressing a decrease in relative density.

Owing to the features described above, an embodiment of the present invention can provide an oxide sintered body that has relatively good plasma resistance and can be manufactured at relatively low cost.

(Other characteristics of oxide sintered body according to one embodiment of the present invention)
The oxide sintered body according to one embodiment of the present invention has an average grain size in the range of 5 μm to 40 μm as described above.

The average grain size is preferably 10 μm or more, more preferably 15 μm or more.

In the present application, the average crystal grain size of the oxide sintered body can be determined by image processing. Specifically, the average crystal grain size can be calculated by importing an SEM photograph (1000 times) of the oxide sintered body into image processing software and averaging the grain size of each grain.

Also, the oxide sintered body according to one embodiment of the present invention has a relative density of 98% or more. The relative density is preferably 98.5% or higher, more preferably 99.0% or higher.

The oxide sintered body according to one embodiment of the present invention may have a thickness of 8 mm or more.

As described above, conventional plasma-resistant oxide sintered bodies are difficult to sinter, and therefore it is difficult to produce thick sintered bodies. However, with the oxide sintered body according to one embodiment of the present invention, a relatively thick sintered body can be produced relatively easily and at low cost.

The thickness of the sintered body is, for example, 10 mm or more, and may be 15 mm or more.

Further, the oxide sintered body according to an embodiment of the present invention may contain alkali metal impurities in an amount of 1000 ppm or less by weight. In addition, in the oxide sintered body according to one embodiment of the present invention, main alkali metal impurities include, for example, sodium and lithium.

In addition, the oxide sintered body according to one embodiment of the present invention can change the conductivity relatively easily by finely adjusting the manufacturing conditions, and can produce sintered bodies with various conductivities. can.

Conductivity ranges, for example, from 400 S/cm to 600 S/cm.

(Method for producing oxide sintered body according to one embodiment of the present invention)
Next, an example of a method of manufacturing an oxide sintered body according to an embodiment of the present invention having the characteristics described above will be described. However, the manufacturing method shown below is merely an example, and it is obvious to those skilled in the art that the oxide sintered body according to one embodiment of the present invention can be manufactured by other methods.

FIG. 1 schematically shows a flow of a method for producing an oxide sintered body according to an embodiment of the present invention (hereinafter referred to as "first production method").

As shown in FIG. 1, the first manufacturing method includes:
(1) A step of preparing calcined powder containing calcium oxide and aluminum oxide at a ratio of 13:6 to 11:8 (molar ratio converted to CaO:Al ₂ O ₃ ) (S110);
(2) a step of placing the object to be treated containing the calcined powder in a container together with a reducing agent and pressurizing the object to be treated with a press pressure of 50 kgf/cm ² or more (S120);
(3) A step of holding the object to be treated in a range of 1280° C. to 1330° C. and performing heat treatment with the inside of the container being decompressed, wherein the press pressure applied to the object to be treated is From 3 hours before completion of holding at temperature, it is reduced at a rate ranging from 20 kgf/cm ² /h to 60 kgf/cm ² /h on average, and is reduced to 0 (zero) by the completion of said holding. (S130);
have

Each step will be described in detail below.

(Step S110)
First, calcined powder for the object to be processed, which is used after step S120, is prepared.

In the present application, "calcined powder" means mixed powder containing calcium oxide and aluminum oxide prepared by heat treatment. The "calcined powder" is prepared so that the molar ratio of calcium (Ca) and aluminum (Al) is 13:6 to 11:8 in terms of CaO:Al ₂ O ₃ .

In particular, the ratio of calcium (Ca) and aluminum (Al) is preferably in the range of 12.5:6.5 to 11:8 in terms of CaO:Al ₂ O ₃ molar ratio, and 12.3 :6.7 to 11.5:7.5, more preferably 12.2:6.8 to 11.8:7.2. Ideally, the molar ratio of calcium oxide to aluminum oxide is about 12:7.

The calcined powder can be prepared, for example, as follows.

First, a mixed powder is prepared. The mixed powder contains at least raw materials serving as a calcium oxide source and an aluminum oxide source.

For example, the mixed powder may contain calcium aluminate, or the mixed powder may contain at least two selected from the group consisting of a calcium compound, an aluminum compound, and calcium aluminate.

The mixed powder may contain, for example, a calcium compound and an aluminum compound. The mixed powder may also contain, for example, a calcium compound and calcium aluminate. The mixed powder may also contain, for example, an aluminum compound and calcium aluminate. The mixed powder may also contain, for example, a calcium compound, an aluminum compound, and calcium aluminate. Furthermore, the mixed powder may be, for example, a mixed powder containing only calcium aluminate.

As a representative example, step S110 will be described below assuming that the mixed powder contains at least a raw material A serving as a calcium oxide source and a raw material B serving as an aluminum oxide source.

Raw material A includes calcium carbonate, calcium oxide, calcium hydroxide, calcium hydrogen carbonate, calcium sulfate, calcium metaphosphate, calcium oxalate, calcium acetate, calcium nitrate, and calcium halide. Among these, calcium carbonate, calcium hydroxide, and calcium oxide are preferred.

Examples of raw material B include aluminum hydroxide, aluminum oxide, aluminum sulfate, aluminum nitrate, and aluminum halide. Among these, aluminum oxide and aluminum hydroxide are preferred. Aluminum oxide (alumina) includes α-alumina, γ-alumina, δ-alumina and the like, and α-alumina is preferred.

In addition, it is preferable that the raw material A and the raw material B have a low content of alkali metal impurities. This makes it possible to reduce the amount of alkali metal impurities contained in the calcined powder and the object to be processed. In addition, the plasma resistance of the finally obtained sintered body can be further enhanced.

The content of alkali metal impurities is, for example, 1000 ppm or less by weight. The content of alkali metal impurities is preferably 100 ppm or less by weight, more preferably 10 ppm or less by weight.

In this application, the major alkali metal impurities are sodium and lithium.

Next, the mixed powder containing raw material A and raw material B is heat-treated. As a result, a calcined powder containing calcium oxide and aluminum oxide is obtained. As described above, the molar ratio of calcium oxide to aluminum oxide in the calcined powder is in the range of 13:6 to 11:8.

The heat treatment temperature is in the range of approximately 500.degree. C. to 1270.degree.

However, precisely, the temperature of the heat treatment varies depending on the raw material A and the raw material B used.

For example, when calcium oxide is used as raw material A and aluminum oxide is used as raw material B, the heat treatment temperature is, for example, in the range of 500°C to 1270°C. In addition, when calcium carbonate is selected as raw material A, the temperature at which calcium carbonate decomposes into calcium oxide and carbon dioxide is about 900°C, so the heat treatment temperature of the mixed powder must be at least 900°C or higher. Similarly, when calcium hydroxide is selected as raw material A, the temperature at which calcium hydroxide decomposes into calcium oxide and water is 450° C. to 500° C. Therefore, the heat treatment temperature of the mixed powder is at least 500° C. or higher. There is a need. Other compounds can also be considered in the same way.

If the heat treatment temperature of the mixed powder containing raw material A and raw material B is too high, sintering proceeds and pulverization becomes difficult. The heat treatment temperature is preferably in the range of 700°C to 1250°C, more preferably in the range of 900°C to 1200°C, even more preferably in the range of 950°C to 1150°C, further preferably 1000°C to 1100°C. is most preferably in the range of

The heat treatment may be performed in air, in an oxygen-containing atmosphere (for example, an oxygen gas atmosphere), in an inert gas atmosphere, or in a vacuum atmosphere.

The calcined powder obtained after the heat treatment is usually in the form of partially sintered powder or lumps. Therefore, pulverization treatment may be carried out as necessary.

A ball mill or the like, for example, is used for the pulverization treatment (coarse pulverization). An automatic mortar may be used. In a dry ball mill, pulverization may be performed to an average particle size of about 1 μm to 100 μm. In a dry ball mill, for example, an alcohol represented by C _n H _2n+1 OH (where n is an integer of 3 or more) (eg, isopropyl alcohol) is used as a grinding aid.

Here, the "average particle size" of the powder after pulverization means a value obtained by measurement by a laser diffraction scattering method.

If you want to obtain a finer and more uniform powder, for example, a wet ball mill or a circulation system using an alcohol (eg, isopropyl alcohol) represented by C _n H _2n+1 OH (n is an integer of 3 or more) as a solvent By using a bead mill or the like, the average particle size of the powder can be reduced to 0.5 μm to 50 μm.

A calcined powder is prepared by the above steps.

(Step S120)
Next, the object to be processed containing the calcined powder obtained in step S110 is placed in a sealable container.

Powdery calcined powder may be used as it is as the object to be processed. Alternatively, a compact containing calcined powder may be used as the object to be processed.

A compact can be produced by compression molding the calcined powder. The molding pressure of the calcined powder is preferably in the range of 150 MPa to 300 MPa, for example. If the molding pressure exceeds 300 MPa, the molded body may crack. Moreover, when the compacting pressure is less than 150 MPa, the relative density of the finally obtained sintered body may decrease.

The object to be processed placed in the container is then pressurized from above and below.

The press pressure at this time is 50 kgf/cm ² or more. If the pressing pressure is less than 50 kgf/cm ² , grain growth is not promoted in the subsequent step S130, making it difficult to obtain an average crystal grain size of 5 μm or more.

A reducing agent is further installed in the container.

Ti members and/or Ca sources are used as reducing agents.

The Ti member may be in the form of Ti plate, Ti foil, and Ti powder, for example.

The Ca source may also be in the form of _CaH2 powder, for example.

In addition to the Ti member and/or Ca source, an aluminum (Al) vapor source and a carbon monoxide (CO) source may be installed under the treatment environment.

Among these, as the Al vapor source, for example, aluminum powder, aluminum foil, aluminum plate, and the like may be used. Also, as the CO source, for example, a carbon (C) member such as a carbon plate and a carbon container may be used.

(Step S130)
Next, the inside of the container is decompressed. Further, the object to be treated is heated while being pressurized to be heat-treated. For example, the pressure inside the container is reduced to 30 Pa or less. The pressure inside the container is preferably reduced to 10 Pa or less.

The heat treatment temperature of the object to be processed (hereinafter also referred to as "firing temperature") is in the range of 1280.degree. C. to 1330.degree. The firing temperature is preferably in the range of 1290°C to 1320°C.

The heat treatment time of the object to be processed (hereinafter also referred to as “firing time”) varies depending on the firing temperature, but is, for example, in the range of 14 hours to 100 hours. The firing time is preferably in the range of 24 hours to 96 hours.

By heat-treating the object to be treated, calcium oxide and aluminum oxide (and calcium aluminate if included) in the calcined powder react to form a non-conductive mayenite compound. Also, it is reduced by a reducing agent to form a conductive mayenite compound.

Here, in the first manufacturing method, the press pressure applied to the object to be processed is gradually weakened from the point of time 3 hours before the completion of holding at the firing temperature, and the press pressure reaches the firing temperature at the latest. By the end of the hold, it drops to 0 (zero).

Assuming that the average value of this press pressure decrease rate is called "press pressure decrease rate v", the press pressure decrease rate v is in the range of 20 kgf/cm ² /h to 60 kgf/cm ² /h. The higher the press pressure decrease speed v, the faster the press pressure applied to the object to be processed decreases. That is, the object to be processed is more quickly released from the pressure application state.

When the press pressure applied to the object to be processed is released in this manner, large grains having an average crystal grain size of 5 μm or more are formed in the finally obtained oxide sintered body.

In particular, the press pressure reduction rate v is preferably in the range of 20 kgf/cm ² /h to 60 kgf/cm ² /h.

After step S130, a dense sintered body having a relative density of 98% or more is manufactured. The relative density of the sintered body is preferably 99% or more. The higher the relative density, the less likely the sintered body will break against impact and thermal stress.

Further, by reducing the amounts of impurities contained in the raw materials A and B used in the calcined powder described above, alkali metal impurities contained in the sintered body can be significantly suppressed. For example, the amount of alkali metal impurities contained in the sintered body is 1000 ppm or less by weight.

As described above, the oxide sintered body obtained by the first production method has a large average crystal grain size, a high relative density, and a small amount of impurities, and therefore has good plasma resistance.

Moreover, in the first manufacturing method, a relatively large sintered body can be manufactured relatively easily. For example, the resulting sintered body may have a thickness of 8 mm or more.

FIG. 2 schematically shows a configuration diagram of an apparatus used in steps S120 to S130.

As shown in FIG. 2, this device 100 has a pressure member 110 and a heating chamber 180 .

The pressing member 110 has a tubular member 120 and a pressing member 130 .

The object to be processed is pressurized within the pressurizing member. The cylindrical member is preferably a member made of a material containing carbon (for example, carbon, SiC, etc.), and more preferably a member made of carbon.

In the present invention, the tubular member is not limited to a tubular shape, and may be box-shaped, for example. Further, the cross section of the cylindrical member is not limited to square, circular, or the like, and may conform to the shape of the sintered body to be manufactured.

Further, the material of the pressing member 130 is not particularly limited. The pressing member 130 is preferably a member containing carbon (such as carbon or SiC), and more preferably a member made of carbon. Therefore, the object to be processed is preferably pressurized within a pressurizing member containing carbon, and more preferably pressurized within a pressurizing member made of carbon. In particular, the object to be processed is preferably pressurized inside a tubular member containing carbon, and more preferably pressurized inside a tubular member made of carbon.

Cylindrical member 120 has a side surface 122 and a bottom surface 124 and an interior space 126 surrounded by the side surface 122 and the bottom surface 124 . More specifically, interior space 126 is defined by inner side wall 128 and inner bottom wall 129 .

In particular, tubular member 120 may have a generally cylindrical or prismatic configuration. In the former case, the bottom surface 124 is substantially circular, and in the latter case, the bottom surface 124 is substantially polygonal. The internal space 126 may have a substantially cylindrical or prismatic shape. In the former case, the inner bottom wall 129 will be substantially circular, and in the latter case the inner bottom wall 129 will be substantially polygonal.

The pressing member 130 has a tip 135 that can be inserted into the interior space 126 of the tubular member 120 with a predetermined pressing pressure. FIG. 2 shows a state before the pressing member 130 is inserted into the inner space 126 of the tubular member 120. As shown in FIG.

Note that the pressure member 110 may be configured by a commercially available hot press device.

Heating chamber 180 has a structure that accommodates pressure member 110 . The heating chamber 180 has a gas inlet 182 and an exhaust port 184, and can control internal pressure (degree of vacuum) and atmosphere. Moreover, the heating chamber 180 may have a heating structure capable of heating the pressure member 110 . For example, there is a structure in which a heating element is provided between the heating chamber 180 and the tubular member 120 . However, if the pressing member 110 itself has a heating mechanism, the heating structure of the heating chamber 180 can be omitted.

FIG. 3 shows an example of how the device 100 is used.

As shown in FIG. 3, when using the apparatus 100, first, one or more carbon plates 140 are placed on the lower surface of the inner space 126 of the cylindrical member 120 of the pressure member 110, that is, on the inner bottom wall 129. Installed. However, installation of the carbon plate 140 is optional.

Next, a first member 142 is placed on the carbon plate 140 .

The first member 142 has a reducing agent such as a Ti and/or Ca source. For example, the first member 142 may be composed of Ti powder, Ti plate, or Ti foil. Alternatively, the first member 142 may be _CaH2 powder. Alternatively, the first member 142 may have a Ti source and _CaH2 powder.

Next, an object 145 to be processed is installed in the inner space 126 of the cylindrical member 120 so as to cover the first member 142 . The object 145 to be processed has calcined powder containing calcium oxide and aluminum oxide, as described above.

The object to be processed 145 is installed in the internal space 126 in a state where it is coated (preferably entirely coated) with a coating member (for example, alumina (aluminum oxide) or the like) having a large number of fine through-holes. can be In this case, it becomes easy to recover the product after the heat treatment.

Next, if necessary, a second member 147 is installed in the internal space 126 of the cylindrical member 120 so as to cover the object 145 to be processed.

A second member 147 has a reducing agent such as a Ti and/or Ca source. For example, the second member 147 may be composed of Ti powder, Ti plate, or Ti foil. Alternatively, the second member 147 may be _CaH2 powder. Alternatively, the second member 147 may have a Ti source and _CaH2 powder. The second member 147 may be the same member as the first member 142 .

Next, one or more second carbon plates 150 are placed on the second member 147 . However, installation of the second carbon plate 150 is optional.

Next, the tip 135 of the pressing member 130 is inserted into the inner space 126 of the tubular member 120 . Further, by applying a load to the pressing member 130 from above, a predetermined pressing pressure is applied to each member in the internal space 126 via the tip 135 of the pressing member 130 .

As mentioned above, the press pressure is 50 kgf/cm ² or more.

Next, the assembly 160 including the pressure member 110 configured in this way is installed inside the heating chamber 180 .

Next, using gas inlet 182 and exhaust port 184 of heating chamber 180, the interior of heating chamber 180 is decompressed to a predetermined pressure.

For example, the pressure inside the heating chamber 180 can be reduced by connecting the exhaust port 184 to an exhaust device such as a vacuum pump and operating the exhaust device. For example, the internal pressure of heating chamber 180 is 30 Pa or less. The internal pressure is preferably 10 Pa or less.

A predetermined gas may then be introduced at a predetermined concentration via the gas inlet 182 .

Next, the inside of heating chamber 180 is heated to a predetermined temperature, and assembly 160 is heated. The firing temperature for the assembly 160 ranges from 1280° C. to 1330° C., as previously described.

The firing time varies depending on the firing temperature and the mass of the object 145 to be processed, but is in the range of 24 hours to 96 hours, for example.

When the assembly 160 is heated, carbon monoxide gas is generated from the pressure member 110 made of carbon and the carbon plates 140 and 150 .

Also, due to the presence of the first member 142 and the second member 147, the object 145 to be processed is surrounded by a reducing agent such as Ti and/or Ca. For example, if _CaH2 powder is used for the first member 142 and/or the second member 147, the _CaH2 powder will decompose to produce Ca vapor.

As a result, the interior of the heating chamber 180, particularly the interior space 126 of the tubular member 120, becomes a strong reducing atmosphere. Therefore, a conductive mayenite compound is generated from the object 145 to be processed.

Here, as described above, the press pressure applied to the object 145 to be processed is gradually weakened three hours before the holding at the firing temperature is completed. The press pressure decrease rate v is in the range of 20 kgf/cm ² /h to 60 kgf/cm ² /h as described above.

Therefore, the press pressure becomes 0 (zero) before or at the time when the holding at the firing temperature is completed.

Through these steps, grain growth is promoted during the firing process of the object 145 to be processed, and a sintered body containing grains with a large average crystal grain size is manufactured.

After that, after the assembly 160 is cooled to room temperature, the assembly 160 is taken out from the heating chamber 180 and the sintered body is recovered from the assembly 160 .

A sintered compact can be produced from the object 145 to be treated by performing heat treatment using such an apparatus 100 .

It should be obvious to those skilled in the art that the apparatus 100 described above is merely an example, and that other apparatuses may be used to heat-treat the object to be processed.

Examples of the present invention will be described below. Here, Examples 1 to 10 are examples, and Examples 21 to 28 are comparative examples.

(Example 1)
A sintered body composed of a conductive mayenite compound was produced by the following method.

(Preparation of calcined powder)
First, 313.5 g _{of calcium carbonate (CaCO 3 ,} manufactured by _Kojundo Chemical Co., Ltd., catalog code CAH08PB) powder and , and 186.5 g of aluminum oxide (α-Al ₂ O ₃ , manufactured by Kojundo Chemical Co., Ltd., catalog code ALO14PB) powder.

Next, this mixed powder was heated to 1000° C. at a rate of temperature increase of 300° C./hour in the air, and held at 1000° C. for 12 hours. Thereafter, this was cooled to room temperature at a cooling rate of 300°C/hour.

As a result, about 362 g of white powder (hereinafter referred to as powder "A1") was obtained. When the particle size of the obtained powder A1 was measured by a laser diffraction scattering method (SALD-2100, manufactured by Shimadzu Corporation), the average particle size was 10 μm.

Next, 330 g of powder A1, 3 kg of zirconia balls with a diameter of 5 mm, and 1 ml of industrial EL grade isopropyl alcohol as a grinding aid are placed in a 7-liter zirconia container, and a zirconia lid is placed on the container. Then, ball mill pulverization treatment was performed at a rotation speed of 72 rpm for 10 hours.

As a result, a white powder (hereinafter referred to as powder "B1") was obtained. As a result of X-ray diffraction analysis, the obtained powder B1 has calcium oxide (CaO) and aluminum oxide (Al ₂ O ₃ ) as main crystals, with a slight amount of calcium aluminate (CaO.Al ₂ O ₃ , 3CaO.Al ₂ O ₃ , CaO.2Al ₂ O ₃ ). Moreover, it was found that the average particle size of the powder B1 obtained by the above laser diffraction scattering method was 2.0 μm.

(Production of oxide sintered body)
Next, the powder B1 was used as an object to be treated and heat-treated to produce an oxide sintered body.

The apparatus 100 as shown in FIG. 2 was used for the heat treatment of the powder B1. The inner bottom wall 129 of tubular member 120 is circular and measures approximately 60 mm in diameter.

In the internal space 126 of the tubular member 120, the members were installed in the following order from the bottom:
Two carbon plates 140 (diameter 59 mm x thickness 5 mm)
Alumina cloth (cloth containing about 50% by weight of alumina powder) (manufactured by Tanaka Paper Industry Co., Ltd., MA-80)
Ti plate (diameter 59 mm x thickness 0.5 mm) as first member 142
Object to be treated 145: The object to be treated 145 is a Ti plate (diameter 59 mm x thickness 0.5 mm) as a second member 147 arranged in a state of being covered with the alumina cloth.
Alumina cloth (cloth containing about 50% by weight of alumina powder) (manufactured by Tanaka Paper Industry Co., Ltd., MA-80)
Four carbon plates 150 (diameter 59 mm x thickness 5 mm).

Next, this assembly was installed in the heating chamber 180 while a pressing pressure of 50 kg/cm ² was applied to the object to be processed by the pressing member 130 .

The pressure inside the heating chamber 180 was reduced to about 10 Pa using a rotary pump. In this state, the inside of the heating chamber 180 was heated, and the object to be processed was heat-treated.

The heat treatment was carried out by heating the assembly to 1300°C at a heating rate of 300°C/hour, holding at this temperature for 48 hours, and then cooling the assembly to room temperature at a cooling rate of 300°C/hour. .

In addition, the press pressure on the object to be treated was lowered to zero at a rate of 20 kgf/cm ² /h after 45 hours had passed since the temperature reached 1300°C.

When the object to be treated was collected after this treatment, a black substance with a black surface (hereinafter referred to as black substance “C1”) was obtained. The black substance C1 did not adhere to other members and was collected relatively easily.

No deformation such as warpage or swelling was observed in the black material C1. The dimensions were 60 mm diameter by 8.4 mm thick.

(analysis)
A sample for electron density measurement was taken from the black material C1. The black material C1 was coarsely pulverized using an alumina automatic mortar, and the sample was collected from the portion corresponding to the central portion of the black material C1 among the obtained coarse powders.

X-ray diffraction analysis of the sample obtained showed that this sample had only the C12A7 structure. Further, the electron density obtained from the peak position of the light diffuse reflectance spectrum of the obtained powder was 1.8×10 ²¹ cm ⁻³ , and the variation depending on the location was not remarkable.

Thus, it was confirmed that the black substance C1 was composed of the conductive mayenite compound.

The black material C1 is hereinafter referred to as "Sample 1".

(Examples 2 to 10)
An oxide sintered body was produced in the same manner as in Example 1.

However, in Examples 2 to 10, sintered bodies were produced under conditions different from those in Example 1. The manufacturing conditions for the sintered body are shown in Table 1 below.

The sintered bodies obtained in Examples 2 to 10 are hereinafter referred to as "Sample 2" to "Sample 10", respectively.

As a result of the same evaluation as in Example 1, it was confirmed that Samples 2 to 10 were all composed of a conductive mayenite compound.

(Examples 21 to 28)
An oxide sintered body was produced in the same manner as in Example 1.

However, in Examples 21 to 28, materials different from those in Example 1 were used as raw materials for preparing the calcined powder. Specifically, α-Al ₂ O ₃ manufactured by Junsei Chemical Co., Ltd., product number 32015jis_J-2 was used as aluminum oxide, and calcium carbonate manufactured by Junsei Chemical Co., Ltd., product number 43260jis-2 was used as calcium carbonate. .

In Examples 21 to 28, sintered bodies were produced under conditions different from those in Example 1. The manufacturing conditions for the sintered body are shown in Table 1 below.

The sintered bodies obtained in Examples 21 to 28 are hereinafter referred to as "Sample 21" to "Sample 28", respectively.

As a result of the same evaluation as in Example 1, it was confirmed that Samples 21 to 28 were all composed of a conductive mayenite compound.

（サンプルの特性評価）
各サンプルを用いて、以下の評価を実施した。

(Sample characterization)
The following evaluations were carried out using each sample.

(Measurement of average grain size)
An SEM image of each sample was taken at 1000x. The obtained SEM image was loaded into image processing software (WinROOF: manufactured by Mitani Shoji Co., Ltd.) and binarized. The grain size of each grain was averaged to calculate the average crystal grain size.

(Measurement of relative density)
The relative density of each sample was measured by the Archimedes method.

(Measurement of impurity concentration)
The amount of alkali metal impurities contained in each sample was measured by ICP emission spectrometry.

(Conductivity measurement)
The conductivity of each sample was measured by the 4-terminal (electrode) method.

(Bending strength test)
The flexural strength of each sample was evaluated by a 4-point bending test. The dimensions of the test piece were 4 mm in width, 3 mm in height, and 50 mm in length, and the test was conducted in accordance with JIS R1601.

(Evaluation of plasma resistance)
Each sample was exposed to plasma gas and evaluated for plasma resistance.

_CF4 gas was used as the plasma gas. The plasma power was 350 W and the pressure was 10 Pa. The test time was 130 minutes. After testing, the samples were evaluated for etch rate.

Table 2 below summarizes the test results obtained for each sample.

表２から、サンプル１～サンプル１０では、サンプル２１～２８に比べて、エッチング速度が有意に抑制されており、耐プラズマ性が良好であることがわかった。

From Table 2, it was found that Samples 1 to 10 had significantly lower etching rates than Samples 21 to 28, and had good plasma resistance.

For comparison, similar tests were performed using commercially available MgO and Y ₂ O ₃ test pieces. As a result, the MgO test piece had an etching rate of 37.6 nm/h. Also, the etching rate of the Y ₂ O ₃ test piece was 54.7 nm/h.

From this, it was found that Samples 1 to 10 had good plasma resistance comparable to that of MgO and Y ₂ O ₃ .

100 device 110 pressure member 120 cylindrical member 122 side surface 124 bottom surface 126 internal space 128 inner side wall 129 inner bottom wall 130 pressing member 135 tip 140 carbon plate 142 first member 145 object to be processed 147 second member 150 second Carbon plate 160 Assembly 180 Heating chamber 182 Gas inlet 184 Exhaust port

Claims (4)

An oxide sintered body,
containing a conductive mayenite compound,
The average crystal grain size is in the range of 5 μm to 40 μm,
An oxide sintered body having a relative density of 98% or more. The oxide sintered body is composed of a conductive mayenite compound,
2. The oxide sintered body according to claim 1, wherein the content of alkali metal impurities is 1000 ppm or less by weight. 3. The oxide sintered body according to claim 1, having a thickness of 8 mm or more. A method for producing an oxide sintered body,
(1) A step of preparing a calcined powder containing calcium oxide and aluminum oxide at a ratio of 13:6 to 11:8 (molar ratio converted to CaO:Al ₂ O ₃ );
(2) A step of placing the object to be treated containing the calcined powder in a container together with a reducing agent, and pressurizing the object to be treated with a press pressure of 50 kgf/cm ² or more;
(3) A step of holding the object to be treated in a range of 1280° C. to 1330° C. and performing heat treatment with the inside of the container being decompressed, wherein the press pressure applied to the object to be treated is From 3 hours before the completion of holding at temperature, it is reduced at a rate ranging from 20 kgf/cm ² /h to 60 kgf/cm ² /h on average, and is reduced to 0 (zero) by the completion of said holding. and,
A manufacturing method.

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