Ceramic sintered body, method for producing the same, and silicon nitride powder

Abstract

To provide a ceramic sintered body having excellent workability.SOLUTION: A ceramic sintered body includes boron nitride and silicon nitride, wherein the ceramic sintered body has a total content of boron nitride and silicon nitride of 85-95 mass% and a number average value of silicon nitride particles having a particle size of 50 μm or over is 1 or under when observing its surface by using a scanning electron microscope in a visual field of 380 μm×500 μm.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a ceramic sintered body, a method for manufacturing the same, and silicon nitride powder.

Background Art

[0002] As a ceramic sintered body having excellent workability, a ceramic sintered body mainly composed of silicon nitride and boron nitride is known. For example, in Patent Document 1, as a ceramic sintered body for processing into a complex shape such as a nozzle, the total content of boron nitride and silicon nitride is 80 to 90% by mass, and the mass ratio of boron nitride to the total of boron nitride and silicon nitride is 35 to 45% by mass. A ceramic sintered body has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document Ⅰ

Summary of the Invention

Problems to be Solved by the Invention

[0004] Although a ceramic sintered body containing silicon nitride and boron nitride is easier to process than other ceramic sintered bodies, a corresponding load is applied to the tool for performing cutting. Therefore, wear and breakage of the tool may occur during processing, and the tool needs to be replaced each time. In order to suppress wear and breakage of the tool, it is effective to process the ceramic sintered body wet rather than dry. However, in wet processing, as described in Patent Document 1, there is a concern that oil and inorganic acid salts may adhere to the surface of the ceramic sintered body or penetrate into the internal pores.

[0005] Therefore, the present disclosure provides a ceramic sintered body having excellent workability. The present disclosure provides a silicon nitride powder suitably used as a sintering raw material for such a ceramic sintered body. The present disclosure provides a manufacturing method capable of manufacturing a ceramic sintered body having excellent workability.

Means for Solving the Problems

[0006] The present disclosure provides a ceramic sintered body containing boron nitride and silicon nitride, wherein the total content of boron nitride and silicon nitride is 85 to 95% by mass, and when the surface is observed with a scanning electron microscope (SEM), the number average value of silicon nitride particles having a particle diameter of 50 μm or more contained in a field of view of 380 μm × 500 μm is 1 or less.

[0007] In the above ceramic sintered body, the number of silicon nitride particles (coarse particles) having a particle diameter of 50 μm or more is sufficiently small. Therefore, even in dry processing, wear and breakage of the tools used for processing can be sufficiently suppressed. Further, during cutting, the falling off of coarse particles on the processed surface is suppressed, so that processing can be performed with high dimensional accuracy. Therefore, the above ceramic sintered body has excellent workability. However, the processing method is not limited to dry processing, and wet processing may also be used.

[0008] The number average value of particles having a particle diameter of 20 μm or more contained in the above field of view may be 5 or less. Thereby, wear and breakage of the tools used for cutting can be further suppressed. Further, such a ceramic sintered body can be processed with higher dimensional accuracy. Therefore, it has even more excellent workability.

[0009] The fluorine content of the above ceramic sintered body may be 50 ppm by mass or less. Such a ceramic sintered body having a low fluorine content can be suitably used as a member of a semiconductor manufacturing apparatus that requires high dimensional accuracy and purity.

[0010] The iron content of the above-mentioned ceramic sintered body may be 250 mass ppm or less. Such a ceramic sintered body can suppress the generation of black spots and thus has excellent appearance.

[0011] The boron nitride content of the above-mentioned ceramic sintered body may be 25 to 75 mass%, and the silicon nitride content may be 25 to 70 mass%. Such a ceramic sintered body can achieve a sufficient level of both workability and strength.

[0012] The present disclosure provides a method for manufacturing a ceramic sintered body, which includes a step of firing a mixture containing boron nitride powder, silicon nitride powder, and a sintering aid to obtain a ceramic sintered body, wherein the ratio of silicon nitride particles on a sieve with an opening size of 20 μm contained in the silicon nitride powder is 1 mass% or less, and the concentration ratio (O1 / O2) of the maximum value (O1) of the oxygen concentration measured in the temperature range of 1300°C or higher and less than 1450°C and the maximum value (O2) of the oxygen concentration measured in the temperature range of 1450°C or higher and less than 1550°C of the silicon nitride powder is 1.0 or more.

[0013] In the above manufacturing method, the ratio of silicon nitride particles on a sieve with an opening size of 20 μm contained in the silicon nitride powder is sufficiently reduced. Also, the silicon nitride powder has a large concentration ratio (O1 / O2). By using such silicon nitride powder, the number of coarse particles contained in the ceramic sintered body can be sufficiently reduced. Therefore, the ceramic sintered body obtained by this manufacturing method has excellent workability.

[0014] When the surface of the ceramic sintered body obtained by the above manufacturing method is observed with a scanning electron microscope, the average number of silicon nitride particles having a particle diameter of 50 μm or more contained in a field of view of 380 μm × 500 μm may be 1 or less.

[0015] The fluorine content of the silicon nitride powder may be 80 mass ppm or less. By using such silicon nitride powder, the fluorine content of the ceramic sintered body can be made sufficiently low. Such a ceramic sintered body is excellent in workability and has a sufficiently low fluorine content. Therefore, for example, it can be suitably used for members of semiconductor manufacturing equipment.

[0016] The iron content of the silicon nitride powder may be 300 mass ppm or less. By using such silicon nitride powder, the black spots generated in the ceramic sintered body can be reduced. Thereby, a ceramic sintered body excellent in appearance can be manufactured.

[0017] The present disclosure provides a silicon nitride powder in which the ratio of silicon nitride particles on a sieve with an opening of 20 μm is 1 mass% or less, and the concentration ratio (O1 / O2) of the maximum value (O1) of the oxygen concentration measured in the temperature range of 1300 °C or higher and less than 1450 °C and the maximum value (O2) of the oxygen concentration measured in the temperature range of 1450 °C or higher and less than 1550 °C is 1.0 or more. By using this silicon nitride powder as a sintering raw material, the formation of coarse particles can be suppressed. Therefore, it can be suitably used as a sintering raw material for a ceramic sintered body having excellent workability.

[0018] In the particle size distribution of the silicon nitride powder, D90 may be 5 μm or less, and the ratio of D100 to D90 may be 3.5 or less. When such silicon nitride powder is used as a sintering raw material, the number of coarse particles contained in the ceramic sintered body can be further reduced. Therefore, a ceramic sintered body having further excellent workability can be obtained.

Advantages of the Invention

[0019] A ceramic sintered body having excellent workability can be provided. A silicon nitride powder suitably used as a sintering raw material for such a ceramic sintered body can be provided. A manufacturing method capable of manufacturing a ceramic sintered body having excellent workability can be provided.

Brief Description of the Drawings

[0020]

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Modes for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as appropriate. However, the following embodiments are examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content.

[0022] FIG. 1 is a perspective view of a ceramic sintered body according to an embodiment. The ceramic sintered body 10 may contain boron nitride, silicon nitride, and a sintering aid. The total content of boron nitride and silicon nitride in the ceramic sintered body 10 is 85 to 95% by mass, and may be 90 to 95% by mass. Thereby, workability and strength can be achieved at a high level. The total content of boron nitride and silicon nitride in the ceramic sintered body 10 can be determined by X-ray diffraction.

[0023] The content of boron nitride in the ceramic sintered body 10 may be 25 to 75% by mass, and may also be 30 to 70% by mass. The content of silicon nitride in the ceramic sintered body 10 may be 25 to 70% by mass, and may also be 30 to 65% by mass. Such a ceramic sintered body has excellent heat resistance, excellent workability, and high strength. Since the ceramic sintered body 10 contains boron nitride and silicon nitride as main components, it can also be called a composite ceramic sintered body.

[0024] The mass ratio of boron nitride to the total of boron nitride and silicon nitride contained in the ceramic sintered body 10 may be 30 to 75% by mass, may be 35 to 70% by mass, and may also be 35 to 50% by mass. Thereby, while maintaining excellent workability, the relative density can be increased to sufficiently increase the strength and elastic modulus.

[0025] In addition to boron nitride and silicon nitride, the ceramic sintered body 10 may contain sub-components derived from a sintering aid. Examples of the sub-components include alkaline earth oxides such as magnesium oxide and calcium oxide, rare earth oxides such as aluminum oxide, silicon oxide, and yttrium oxide, and composite oxides such as spinel. Further, it may contain a glassy grain boundary phase generated by the reaction of a sintering aid and an oxide when manufacturing the ceramic sintered body 10.

[0026] The relative density of the ceramic sintered body 10 may be 76 to 98%, and may be 79 to 95% from the viewpoint of achieving both sufficient flexural strength and excellent workability at a high level. The relative density can be measured by the Archimedes method.

[0027] FIG. 2 is a diagram schematically showing silicon nitride particles included in an observation image of the surface of a ceramic sintered body by a scanning electron microscope (SEM). The SEM observation image of the present embodiment is an image obtained by magnifying the surface of the ceramic sintered body 250 times. In FIG. 2, one silicon nitride particle 20 is shown for the sake of explanation, and other particles are not drawn. The particle diameter L1 of the silicon nitride particle 20 is measured in an image magnified 250 times as shown in FIG. 2. Specifically, two points on the outer edge of the silicon nitride particle 20 are selected so that the distance therebetween is maximized. The length of the line segment connecting these two points becomes the particle diameter L1. In this specification, a silicon nitride particle having this particle diameter L1 of 50 μm or more is referred to as a coarse particle.

[0028] In the ceramic sintered body of the present embodiment, the number average value of coarse particles included in a field of view of 380 μm × 500 μm is 1 or less. Here, the number average value is obtained as the number average value of coarse particles included in each of at least 15 arbitrarily selected fields of view (380 μm × 500 μm). From the viewpoint of improving the reliability of the number average value, the fields of view are preferably selected uniformly from the entire surface of the ceramic sintered body. For example, in the case of a hexahedral sintered body as shown in FIG. 1, it is preferable to select 2 to 3 fields of view from each of the respective surfaces (two surfaces parallel to the X - Y plane, two surfaces parallel to the Y - Z plane, and two surfaces parallel to the Z - X plane). The number of coarse particles is measured in each selected field of view, and at least 15 measurement values are obtained. The arithmetic average value of these measurement values becomes the number average value of coarse particles.

[0029] When only a part of the coarse particles is shown in the visual field, select two points on the outer edge so that the distance between them is maximized in the shown part, and assume that the length of the line segment connecting the two points is the particle diameter L1, and then measure. If this measured value is 50 μm or more, it is counted as one coarse particle. On the other hand, if this measured value is less than 50 μm, it is not counted as a coarse particle.

[0030] From the viewpoint of further improving the workability of the ceramic sintered body 10, the number average value of coarse particles having a particle diameter of 50 μm or more may be 0.6 or less, may be 0.2 or less, or may be 0. Similarly, from the same viewpoint, the number average value of silicon nitride particles having a particle diameter of 20 μm or more contained in the above visual field may be 5 or less, may be 3 or less, or may be 1 or less. The ceramic sintered body 10 may not contain silicon nitride particles having a particle diameter of 20 μm or more.

[0031] The fluorine content of the ceramic sintered body 10 may be 50 mass ppm or less, may be 10 mass ppm or less, or may be 0 mass ppm. Such a ceramic sintered body 10 has excellent workability and a sufficiently low fluorine content, so it can be suitably used as a member of a semiconductor manufacturing apparatus.

[0032] The iron content of the ceramic sintered body 10 may be 250 mass ppm or less, may be 200 mass ppm or less, may be 100 mass ppm or less, or may be 0 mass ppm or less. Such a ceramic sintered body 10 has excellent workability and has an excellent appearance because the generation of black spots is sufficiently suppressed.

[0033] From the viewpoint of improving reliability, the flexural strength of the ceramic sintered body 10 may be 100 MPa or more, may be 200 MPa or more, or may be 300 MPa or more. The flexural strength in this specification is the three-point bending strength measured using a commercially available universal testing machine in accordance with JIS R1601:2008. The flexural strength may be, for example, 100 to 400 MPa.

[0034] The elastic modulus of the ceramic sintered body 10 may be 25 GPa or more, and may be 60 GPa or more, from the viewpoint of improving processing accuracy. The elastic modulus in this specification is measured using a commercially available universal testing machine in accordance with JIS R1601:1995. The elastic modulus is, for example, 25 to 100 GPa.

[0035] The density of the ceramic sintered body 10 may be 1.9 to 2.8 g / cm 3 and may be 2.0 to 2.7 g / cm 3 This enables both good machinability and wear resistance.

[0036] The shape of the ceramic sintered body is not limited to the shape shown in FIG. 1. For example, it may be a disc shape or a ring shape. Whatever the shape, at least 15 fields of view should be selected evenly from the entire surface.

[0037] The ceramic sintered body 10 of this embodiment is excellent in workability. Therefore, even in dry machining, wear and breakage of the tools used in cutting can be sufficiently suppressed. As a result, it has excellent dimensional accuracy, and impurities such as oil and inorganic acid salts associated with wet machining can also be sufficiently reduced. Therefore, it can be suitably used as a ceramic sintered body for members of semiconductor manufacturing equipment.

[0038] An example of the manufacturing method of the ceramic sintered body will be described below. The manufacturing method of this example has a step of firing a mixture (sintering raw material) containing boron nitride powder, silicon nitride powder, and a sintering aid to obtain a ceramic sintered body.

[0039] The silicon nitride powder contained in the above mixture has a ratio of silicon nitride particles on a sieve with an opening of 20 μm of 1 mass% or less. By using such silicon nitride particles, the number of coarse particles contained in the ceramic sintered body can be sufficiently reduced. From the same viewpoint, the ratio may be 0.1 mass% or less, may be 0.05 mass% or less, or may be 0.02 mass% or less. Such silicon nitride powder can be obtained by pulverizing and / or sieving the silicon nitride powder obtained by a normal method.

[0040] The average particle size (D50) of the silicon nitride powder (raw material powder) before pulverization and / or sieving may be 0.5 to 3.0 μm. Using the silicon nitride powder in this range, the ratio of silicon nitride particles on a sieve with an opening of 20 μm is adjusted by pulverization and / or sieving. Thereby, it becomes easier to adjust D50, D90, etc.

[0041] The total oxygen content of the silicon nitride powder before pulverization may be 0.8 to 2.2 mass%. When the total oxygen content is within this range and the average particle size (D50) of the silicon nitride powder before pulverization is 0.5 to 3.0 μm, it becomes easier to adjust the concentration ratio (O1 / O2) of the silicon nitride powder used as a sintering raw material to, for example, 1.0 or more, preferably 1.3 or more, as described below. Note that the total oxygen content of the silicon nitride powder used as a sintering raw material may be adjusted, for example, by the oxygen content of the raw material silicon powder used in the firing process when manufacturing the silicon nitride powder, or may be adjusted by the components of the atmosphere in the sintering process. When the oxygen content of the silicon powder is high, for example, the oxygen content contained in the silicon powder can be reduced by using a pretreatment liquid containing hydrofluoric acid.

[0042] For the measurement of the maximum oxygen concentration (O1) and the maximum oxygen concentration (O2), an oxygen and nitrogen analyzer (trade name: EMGA-920) manufactured by Horiba, Ltd. can be used. A commercially available oxygen and nitrogen analyzer is used. The measurement procedure is as follows. The sample for measurement is heated from 20°C to 2000°C at a heating rate of 8°C / second in an atmosphere of helium gas. The oxygen desorbed as the temperature rises is detected by the infrared absorption method. At the beginning of heating, the oxygen bound to the surface of the silicon nitride powder desorbs. When further heated to the temperature at which silicon nitride decomposes, the oxygen inside the silicon nitride powder desorbs.

[0043] The maximum oxygen concentration (O1) is the maximum value of the oxygen concentration detected in the temperature range of 1300°C or higher and less than 1450°C. The maximum oxygen concentration (O2) is the maximum value of the oxygen concentration detected in the temperature range of 1450°C or higher and less than 1550°C. The ratio of the maximum oxygen concentration (O1) to the maximum oxygen concentration (O2) (concentration ratio: O1 / O2) is, for example, 1.0 or higher, preferably 1.3 or higher. By being in such a range, the formation of coarse particles can be suppressed. The reason is speculated as follows.

[0044] The oxygen detected in the temperature range of 1300°C or higher and less than 1450°C is considered to be mainly the oxygen present on the surface of the silicon nitride powder. On the other hand, the oxygen detected in the temperature range of 1450°C or higher and less than 1550°C is considered to be mainly the oxygen inside (inside from the surface) of the silicon nitride powder. When the ratio of the oxygen inside the silicon nitride powder is large, it tends to aggregate and coarsen during sintering. Therefore, if the concentration ratio (O1 / O2) is in the above range, it is considered that the ratio of the surface oxygen becomes high and the formation of coarse particles during sintering can be suppressed.

[0045] If silicon nitride powder is pulverized, oxygen that was present inside the silicon nitride particles appears on the surface. As a result, the concentration ratio (O1 / O2) can be increased. Therefore, the size of the silicon nitride powder (raw material powder) before pulverization may be set on the premise of pulverization. When the average particle diameter (D50) of the silicon nitride powder before pulverization is 0.5 to 3.0 μm, the pulverization time by a ball mill may be several hours. The pulverization time by a ball mill may be, for example, 3 to 6 hours.

[0046] The iron content of the silicon nitride powder used as a sintering raw material may be 300 mass ppm or less, and may also be 250 mass ppm or less. By using such a silicon nitride powder with a low iron content, the generation of black spots can be suppressed, and a ceramic sintered body having an excellent appearance can be obtained. The iron content can be adjusted by acid treatment. Examples of the acid used for the acid treatment include hydrofluoric acid, hydrochloric acid, nitric acid, and sulfuric acid. More iron can be removed by increasing the acid concentration. In order to sufficiently remove the iron oxide film on the surface of the silicon nitride particles, it is preferable to perform acid treatment with hydrofluoric acid. The acid concentration of the acid used for the acid treatment may be 5 to 15 mass%.

[0047] The fluorine content of the silicon nitride powder used as a sintering raw material may be 80 mass ppm or less, may be 60 mass ppm or less, and may even be 10 mass ppm or less. By using such a silicon nitride powder, the fluorine content in the ceramic sintered body can be made sufficiently small. When performing acid treatment of the silicon nitride powder using hydrofluoric acid, a defluorination treatment by heating may be performed after the acid treatment. By performing the defluorination treatment by heating, the fluorine content can be reduced. The heating conditions can be set as appropriate, and may be, for example, 1000 to 1500 °C for 3 to 10 hours. By setting more severe heating conditions, the fluorine content of the silicon nitride powder can be reduced.

[0048] From the perspective of promoting liquid-phase sintering while suppressing excessive grain growth, the total oxygen content of the silicon nitride powder used as the sintering raw material may be 0.5 to 2.5% by mass, or may be 1.3 to 2.0% by mass. The total oxygen content of the silicon nitride powder can be determined as the integrated value when measuring the maximum oxygen concentration (O1) and the maximum oxygen concentration (O2). That is, it can be measured under the same conditions as when measuring the maximum oxygen concentration (O1) and the maximum oxygen concentration (O2) using an oxygen-nitrogen analyzer (trade name: EMGA-920) manufactured by Horiba, Ltd.

[0049] From the perspective of sufficiently suppressing abnormal grain growth and reducing coarse particles contained in the ceramic sintered body, the average particle size (D50) of the silicon nitride powder may be 0.3 to 2 μm or less, and may be 0.4 to 1.5 μ in m It may be, and may be 0.5 to 1.0 μm.

[0050] The particle size distribution in the present disclosure is measured in accordance with the method described in JIS Z 8825:2013 "Particle Size Analysis - Laser Diffraction / Scattering Method". In the cumulative distribution of the number-based particle size distribution measured in this way, the particle size when the integrated value from the small particle size reaches 50% of the whole is the average particle size (D50). In this cumulative distribution, the particle size when the integrated value from the small particle size reaches 90% of the whole is D90, and the particle size when the integrated value from the small particle size reaches 100% of the whole is D100. For the measurement of the particle size distribution, Microtrac (manufactured by Nikkiso Co., Ltd., trade name: MT3300EXII) can be used.

[0051] D90 in the particle size distribution of the silicon nitride powder is 5 μm or less, and the ratio of D100 to D90 may be 3.5 or less. Since such silicon nitride powder has sufficiently reduced large-sized particles, the coarse particles in the ceramic sintered body can be sufficiently reduced. Also, D10 in the particle size distribution of the silicon nitride powder may be 0.2 to 0.6 μm. D100 may be 3 to 10 μm.

[0052] The α-phase ratio of the silicon nitride powder (the relative ratio of α-Si3N4 to the whole Si3N4) may be 80% or more, and may also be 85% or more. By using the silicon nitride powder having such an α-phase ratio, abnormal grain growth during firing can be suppressed, and coarsening of the silicon nitride particles can be suppressed. The α-phase ratio of the silicon nitride powder can be determined by the diffraction line intensity of X-ray diffraction.

[0053] As the boron nitride powder, for example, the one having an average particle diameter (D50) of 5.0 μm can be used. The boron nitride powder may be amorphous or crystallized. When using the crystallized hexagonal boron nitride (h-BN) powder, anisotropy is likely to occur in the ceramic sintered body due to the flaky shape of the boron nitride particles. Therefore, the boron nitride powder may be an amorphous boron nitride powder that is not crystallized. When the boron nitride powder is amorphous, it is preferable that the graphitization index (GI) determined in the following manner is 5.0 or more.

[0054] The graphitization index (GI: Graphitization Index) is calculated and obtained by the following formula for the integral intensity ratio, that is, the area ratio of the (100) plane, (101) plane and (102) plane of the X-ray diffraction pattern. GI = [area{(100)+(101)}] / [area(102)]

[0055] When the boron nitride particles are completely crystallized, the GI is said to be 1.60. However, in the case of a highly crystalline and flaky-shaped hexagonal boron nitride powder with sufficiently grown particles, the GI is even smaller because the particles are likely to be oriented. That is, the GI is an index of the crystallinity of the flaky-shaped hexagonal boron nitride powder, and the lower this value, the higher the crystallinity. The boron nitride powder with a GI of 5.0 or more has a low crystallinity of the primary particles of boron nitride. Therefore, the anisotropy of the ceramic sintered body using such a boron nitride powder can be reduced. The GI can be controlled by the crystallization temperature.

[0056] The measurement of GI can be performed, for example, using "D8 ADVANCE Super Speed" (manufactured by Bruker AXS). As a pretreatment for the measurement, if necessary, boron nitride powder is pulverized using an agate mortar or the like. Then, the boron nitride powder is press-molded to produce a molded body. X-rays are irradiated so as to be symmetric with respect to the normal of the plane in the in-plane direction of the molded body. As the X-ray source for the measurement, CuKα rays are used, the tube voltage is 45 kV, and the tube current is 360 mA.

[0057] From the viewpoint of suppressing the decrease in the reaction sites with the sintering aid and promoting liquid-phase sintering, the lower limit of the total oxygen content of the boron nitride powder may be 1.0 mass%. The upper limit of the total oxygen content of the boron nitride powder may be 3.0 mass% from the viewpoint of ease of acquisition, and may be 2.6 mass%. The total oxygen content of the boron nitride powder can be measured using an oxygen-nitrogen analyzer (trade name: EMGA-920) manufactured by Horiba, Ltd.

[0058] As the sintering aid, oxide-based ones can be used. For example, Y2O 3、 MgO, Al2O3, etc. can be mentioned. Silicon nitride powder, boron nitride powder, and a sintering aid are blended to prepare a mixture. The mass ratio of boron nitride to the total of boron nitride powder and silicon nitride powder in the mixture may be 30 to 75 mass%, may be 35 to 70 mass%, or may be 35 to 50 mass%. Thus, a ceramic sintered body having excellent heat resistance, excellent workability, and high strength can be obtained.

[0059] The total content of boron nitride powder and silicon nitride powder in the mixture may be 85 to 95 mass%, or may be 90 to 95 mass%. Thus, the content of the sintering aid can be adjusted to an appropriate range, and a ceramic sintered body having high levels of workability and strength can be manufactured.

[0060] The preparation of the mixture may be carried out by dry grinding and dry mixing, or may be carried out by wet grinding and wet mixing using a ball mill or the like. Further, an apparatus having a high dispersing power such as a bead mill may be used. The liquid medium used for wet grinding and wet mixing may be an organic solvent, for example, alcohols. In order to further improve the formability, an organic binder may be blended at a ratio of 3% by mass or less based on the solid content, and granulation may be performed by a spray dryer.

[0061] The obtained mixture may be fired by hot pressing. Further, a molded body having a predetermined shape may be produced by a mold and / or CIP, and the molded body may be fired. The shape of the molded body is not particularly limited.

[0062] The hot pressing is carried out, for example, by heating to a temperature range of 1650 to 1850°C while applying a pressure of 10 to 30 MPa in an inert gas atmosphere. The holding time in this temperature range may be 1 to 10 hours. When firing the molded body, it is fired at normal pressure (atmospheric pressure) in an inert atmosphere. The firing temperature may be, for example, 1650 to 1850°C, or may be 1700 to 1800°C. Thereby, it is possible to obtain a sufficiently densified ceramic sintered body while suppressing the decomposition of silicon nitride. The time for maintaining the above-mentioned firing temperature may be 1 to 10 hours, or may be 2 to 8 hours. When using the granulated mixture, it may be heated to a temperature range of 400 to 600°C for degreasing before the above-mentioned firing.

[0063] In this way, the ceramic sintered body 10 can be obtained. Since the ceramic sintered body 10 has excellent workability, it can be processed by dry processing. Although it is also possible to process by wet processing, there is a tendency for oil components and organic and inorganic acid salts contained in a coolant or the like during processing to adhere to the surface of the ceramic sintered body 10 or penetrate into the internal pores. It is difficult to completely remove these components by washing or the like. If such components remain on the surface or inside of the ceramic sintered body, there is a concern that they may react with molten metal or be mixed in as impurities when used as a member of a semiconductor manufacturing apparatus or the like. Therefore, the ceramic sintered body 10 that can be processed by dry processing can be preferably used for various applications in terms of reducing the mixing of impurities.

[0064] As described above, several embodiments have been described, but the present disclosure is not limited to the above embodiments at all. For example, since the ceramic sintered body 10 is easy to process and can be processed with high dimensional accuracy, it is not limited to being a member of a semiconductor manufacturing apparatus and can be used for various applications.

Example

[0065] The content of the present disclosure will be described in more detail with reference to Examples and Comparative Examples, but the present disclosure is not limited to the following examples.

[0066] [Preparation of Ceramic Sintered Body] (Example 1) Commercially available silicon nitride powder (α conversion rate: 84.7%, average particle diameter D50: 0.91 μm, total oxygen content: 1.512 mass%) was prepared as a raw material powder. In order to adjust to a desired particle size distribution, this raw material powder was pulverized by a ball mill and sieved using a sieve. In this way, silicon nitride powder A as a sintering raw material was prepared. The particle size distribution, α conversion rate, fluorine content, total oxygen content, oxygen concentration ratio, Fe content, and Al content of the silicon nitride powder A were measured by the following procedure. Since the silicon nitride powder used in Example 1 had a low Fe content, acid treatment was not performed.

[0067] To measure the particle size distribution of silicon nitride powder A, 2 ml of a 20 mass% aqueous solution of sodium hexametaphosphate and 200 ml of pure water were mixed to prepare a mixed solvent. 60 mg of a measurement sample of silicon nitride powder A was introduced into this mixed solvent. Then, mixing and dispersion were carried out for 3 minutes using an ultrasonic homogenizer (manufactured by Nippon Seiki Co., Ltd., product name: US-300). Thereafter, using a Microtrac (manufactured by Nikkiso Co., Ltd., product name: MT3300EXII), the particle size distribution based on the number was measured. Pure water was used as the solvent in the circulator of the Microtrac. Using this pure water, the concentration of silicon nitride powder A in the measurement sample was adjusted. In the cumulative distribution of the particle size distribution, the particle sizes at which the cumulative value based on the number from the small particle size became 10%, 50%, 90%, and 100% were determined, respectively. These results are shown in Table 1 as D10, D50, D90, and D100, respectively.

[0068] Using a sieve with an opening of 20 μm, 10 g of silicon nitride powder A was sieved. The mass ratio of the silicon nitride powder remaining on the sieve is shown in Table 1 as "ratio on the sieve".

[0069] The α-phase conversion rate of silicon nitride powder A was measured by the following procedure. Using an X-ray diffractometer (manufactured by Rigaku, device name: Ultima IV), X-ray diffraction of the silicon nitride powder was performed using CuKα radiation. For the α-phase, the diffraction line intensity I a102 of the (102) plane and the diffraction line intensity I a210 of the (210) plane were used. For the β-phase, the diffraction line intensity I b101 of the (101) plane and the diffraction line intensity I b210 of the (210) plane were used. Using these diffraction line intensities, the α-phase conversion rate was calculated by the following formula. The results were as shown in Table 1. α-phase conversion rate (%) = (I a102 + I a210 ) / (I a102 + I a210 + I b101 + I b210 ) × 100

[0070] The fluorine content of silicon nitride powder A was measured as follows. Silicon nitride powder A was heated using an automatic sample combustion apparatus (manufactured by Mitsubishi Chemical Corporation, apparatus name: AQF-2100H type), and the generated gas was dissolved in water. The fluorine dissolved in water was measured using an ion chromatograph (manufactured by Thermo Fisher Scientific, apparatus name: ICS-2100). Based on this measured value, the fluorine content of silicon nitride powder A was calculated. The results were as shown in Table 1.

[0071] For the measurement of the total oxygen amount, maximum oxygen concentration (O1), and maximum oxygen concentration (O2) of silicon nitride powder A, an oxygen-nitrogen analyzer (manufactured by Horiba, Ltd., apparatus name: EMGA-920) was used. The concentration ratio (O1 / O2) was calculated from the measured values of the maximum oxygen concentration (O1) and the maximum oxygen concentration (O2). The Fe and Al contents of silicon nitride powder A were analyzed by the following procedure. A briquette of silicon nitride powder was formed to prepare a measurement sample. The Fe and Al contents of the measurement sample were measured using a fluorescence X-ray (XRF) analyzer (manufactured by Rigaku Corporation, product name: PrimusII). The results were as shown in Table 1.

[0072] As the boron nitride powder, an amorphous one was used. The total oxygen amount of the boron nitride powder was 1.60% by mass, and the GI was 5.0 or more. As the sintering aid, aluminum oxide and yttrium oxide were used. The ratio of aluminum oxide to the total sintering aid was 24% by mass.

[0073] Silicon nitride powder A, boron nitride powder, and a sintering aid were blended to obtain a blend. The mass ratio of the boron nitride powder to the total of the boron nitride powder and the silicon nitride powder was 35% by mass.

[0074] The above-mentioned formulations were mixed to prepare a mixture. The mixture was hot-pressed under a nitrogen atmosphere to produce a ceramic sintered body. The hot pressing was carried out by maintaining the temperature at 1700 °C for 3 hours while applying a pressure of 18 MPa. The content ratios of silicon nitride, boron nitride, and components derived from the sintering aid in the ceramic sintered body were the same as the blending ratios of the respective raw materials.

[0075] (Example 2) A ceramic sintered body was produced in the same manner as in Example 1, except that the mass ratio of boron nitride powder to the total of boron nitride powder and silicon nitride powder was changed to 70% by mass, and the hot pressing conditions were changed to 1800 °C. (Example 3) A ceramic sintered body was produced in the same manner as in Example 1, except that the hot pressing conditions were changed to 1750 °C.

[0076] (Example 4) Commercially available silicon nitride powder (α-phase conversion rate: 85.7%, average particle size D50: 2.52 μm, total oxygen content: 1.089% by mass) was prepared as a raw material powder. To adjust to the desired particle size distribution, this raw material powder was pulverized by a ball mill and sieved using a sieve. In this way, silicon nitride powder B as a sintering raw material was prepared. The measurements of silicon nitride powder B were carried out in the same manner as in Example 1. The results are shown in Table 1. A ceramic sintered body was produced in the same manner as in Example 1, except that this silicon nitride powder B was used as the sintering raw material. Since the silicon nitride powder used in Example 4 had a low Fe content, acid treatment was not performed.

[0077] (Example 5) A ceramic sintered body was produced in the same manner as in Example 4, except that the hot pressing conditions were changed to 1650 °C.

[0078] (Example 6) Commercially available silicon nitride powder (α conversion rate: 91.4%, average particle size D50: 1.18 m, total oxygen content: 1.116 mass%) was prepared as the raw material powder. To adjust to the desired particle size distribution, this raw material powder was pulverized by a ball mill and sieved using a sieve. Thereafter, acid treatment with hydrofluoric acid was performed so that the Fe content shown in Table 2 was obtained. Thereafter, as a defluorination treatment, heating was performed at 1100 ° C for 3 hours. In this way, silicon nitride powder C as a sintering raw material was prepared. Each measurement of the silicon nitride powder C was performed in the same manner as in Example 1. The results are shown in Table 2.

[0079] A ceramic sintered body was produced in the same manner as in Example 1 except that the silicon nitride powder C thus obtained was used as a sintering raw material. The evaluation results of the silicon nitride powder were as shown in Table 2.

[0080] (Example 7) A ceramic sintered body was produced in the same manner as in Example 6 except that the hot press conditions were changed to 1725 ° C.

[0081] (Example 8) A ceramic sintered body was produced in the same manner as in Example 6 except that the hot press conditions were changed to 1650 ° C.

[0082] (Comparative Example 1) A ceramic sintered body was produced in the same manner as in Example 1 except that commercially available silicon nitride powder (α conversion rate: 91.24%, average particle size D50: 0.92 μm, total oxygen content: 0.752 mass%) was used as a sintering raw material without pulverization and sieving. The concentration ratio (O1 / O2) of this silicon nitride powder D was 1.0, different from Examples 6 to 8. The other evaluation results of the silicon nitride powder D were as shown in Table 2.

[0083] (Comparative Example 2) Commercially available silicon nitride powder (α - conversion rate: 91.2%, average particle size D50: 0.92 μm, total oxygen content: 0.752 mass%) was prepared as a raw material powder. To adjust it to the desired particle size distribution, this raw material powder was pulverized by a ball mill and sieved using a sieve. Then, acid treatment with hydrofluoric acid was performed to obtain the Fe content shown in Table 2. After that, as a defluorination treatment, heating was carried out at 1300 °C for 6 hours. In this way, silicon nitride powder E as a sintering raw material was prepared. Each measurement of silicon nitride powder E was carried out in the same manner as in Example 1. The results are shown in Table 2.

[0084] A ceramic sintered body was produced in the same manner as in Example 1 except that the thus - obtained silicon nitride powder E was used. The evaluation results of the silicon nitride powder were as shown in Table 2.

[0085] [Evaluation of Ceramic Sintered Body] The evaluation of the ceramic sintered bodies obtained in each example and each comparative example was carried out as follows.

[0086] [Evaluation of Ceramic Sintered Body] [Evaluation of the Number of Coarse Particles] Fifteen locations were arbitrarily selected from a ring - shaped ceramic sintered body, and SEM observation of the surface (magnification: 250 times) was performed. The fifteen locations were selected as evenly as possible from the entire surface so that the selected positions would not be concentrated.

[0087] Figures 3 to 10 are SEM photographs of the surfaces of the ceramic sintered bodies of Examples 1 to 8. Figures 11 and 12 are SEM photographs of the surfaces of the ceramic sintered bodies of Comparative Example 1 and Comparative Example 2. In the SEM photographs of two locations of each ceramic sintered body shown in Figures 3 to 12, the number of 250 coarse particles was counted in the images as shown in these photographs.

[0088] In a field of 380 μm × 500 μm, the number of silicon nitride particles with a particle diameter of 50 μm or more was measured. The measurement was performed at 15 locations in each example and each comparative example. Then, the arithmetic mean value of the number detected in each field was determined. Also, in the same field, the number of silicon nitride particles with a particle diameter of 20 μm or more was measured. And, in the same manner as in the case of silicon nitride particles with a particle diameter of 50 μm or more, the arithmetic mean value of the number of silicon nitride particles with a particle diameter of 20 μm or more was determined. These results were rounded off to the nearest whole number and shown in Table 1 and Table 2. In Table 1 and Table 2, the average value of the number of silicon nitride particles with a particle diameter of 50 μm or more was shown in the column of "Number of particles (≥50)", and the average value of the number of silicon nitride particles with a particle diameter of 20 μm or more was shown in the column of "Number of particles (≥20)".

[0089] <Density> The density of each ceramic sintered body was measured by the Archimedes method. The results were as shown in Table 1 and Table 2.

[0090] <Flexural strength> Each ceramic sintered body was processed into a predetermined shape to prepare a test piece for measurement. Using a commercially available universal testing machine (manufactured by Shimadzu Corporation, apparatus name: Autograph AG2000D), the three-point flexural strength was measured in accordance with JIS R 1601:2008. The three-point flexural strength was defined as the strength when a load was applied in a direction parallel to the pressing direction of the hot press. The results were as shown in Table 1 and Table 2.

[0091] <Elastic modulus> Each ceramic sintered body was processed into a predetermined shape to prepare a test piece for measurement. Using a commercially available universal testing machine (manufactured by Shimadzu Corporation, apparatus name: Autograph AG2000D), the elastic modulus was measured in accordance with JIS R1601:1995. The elastic modulus was defined as the elastic modulus when a load was applied in a direction parallel to the pressing direction of the hot press. The results were as shown in Table 1 and Table 2.

[0092] <Shore hardness> Each ceramic sintered body was processed into a predetermined shape to prepare a test piece for measurement. Using a commercially available Shore hardness tester (manufactured by Shimadzu Corporation, device name: Shore hardness tester type D), the Shore hardness was measured in accordance with JIS Z 2246:2000. The Shore hardness was defined as the strength when a load was applied in a direction parallel to the pressing direction of the hot press. The results were as shown in Tables 1 and 2.

[0093] <Evaluation of workability> At the end of each ceramic sintered body, grooves were formed using drill-shaped tools (φ = 2.5 mm, 1 mm) along the thickness direction (the pressing direction of the hot press). After forming the grooves, the presence or absence of wear and loss of the drill-shaped tools was visually evaluated according to the following criteria. The results were as shown in Tables 1 and 2. A: No loss of the tool occurred, and the wear of the tool was also small. B: No loss of the tool occurred, but the wear of the tool was large. C: Loss of the tool occurred.

[0094]

Table 1

[0095]

Table 2

[0096] The workability of Examples 1 to 5 was evaluated as "A", and the workability of Examples 6 to 8 was evaluated as "B". In contrast, the workability of Comparative Examples 1 and 2 containing coarse particles of silicon nitride with a particle size exceeding 50 μm was evaluated as "C". Also, from the comparison between Examples 1 to 5 and Examples 6 and 7, it was confirmed that the fewer the number of silicon nitride particles with a particle size exceeding 20 μm, the better the workability.

Industrial applicability

[0097] According to the present disclosure, it is possible to provide a ceramic sintered body having excellent workability. It is possible to provide a manufacturing method capable of manufacturing a ceramic sintered body having excellent workability.

Explanation of reference numerals

[0098] 10... ceramic sintered body, 20... silicon nitride particles.

Claims

1. A ceramic sintered body containing boron nitride and silicon nitride, wherein the total content of the boron nitride and the silicon nitride is 85 to 95% by mass, the content of the boron nitride is 25 to 75% by mass, and the content of the silicon nitride is 25 to 70% by mass, A ceramic sintered body, wherein when the surface is observed with a scanning electron microscope, the average number of silicon nitride particles having a particle diameter of 50 μm or more contained in a field of view of 380 μm × 500 μm is 1 or less.

2. The ceramic sintered body according to claim 1, wherein the average number of silicon nitride particles having a particle diameter of 20 μm or more contained in the field of view is 5 or less.

3. The ceramic sintered body according to claim 1 or 2, wherein the fluorine content is 50 mass ppm or less.

4. The ceramic sintered body according to any one of claims 1 to 3, wherein the iron content is 250 mass ppm or less.

5. A method for producing a ceramic sintered body, comprising a step of firing a mixture containing boron nitride powder, silicon nitride powder, and a sintering aid to obtain a ceramic sintered body, wherein the ratio of silicon nitride particles on a sieve with an opening of 20 μm contained in the silicon nitride powder is 1% by mass or less, The maximum value (O １ ) of the oxygen concentration measured in the temperature range of 1300 °C or higher and less than 1450 °C of the silicon nitride powder, and the maximum value (O ２ ) of the oxygen concentration measured in the temperature range of 1450 °C or higher and less than 1550 °C, the concentration ratio (O １ / O ２ ) is 1.0 or more, A method for producing a ceramic sintered body, wherein the content of boron nitride in the ceramic sintered body is 25 to 75% by mass, and the content of silicon nitride is 25 to 70% by mass.

6. The ratio of silicon nitride particles on a sieve with an opening of 20 μm is 1% by mass or less, The maximum value of the oxygen concentration (O １ ), measured in the temperature range of 1300 °C or higher and less than 1450 °C, and the maximum value of the oxygen concentration (O ２ ), measured in the temperature range of 1450 °C or higher and less than 1550 °C, have a concentration ratio (O １ / O ２ ) of 2.0 or higher, and the α conversion rate is 84.7% or more, A silicon nitride powder having a D90 in the particle size distribution of 5 μm or less and a ratio of D100 to D90 of 3.5 or less.

7. The silicon nitride powder according to claim 6, wherein D100 is 3 to 10 μm and the total oxygen content is 0.5 to 2.5% by mass.

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