Method for producing ceramic sintered body

Abstract

To provide a method for producing a ceramic sintered compact capable of preventing the surface waviness of the ceramic sintered compact.SOLUTION: Applying a hexagonal boron nitride powder to at least one surface of a green body containing a ceramic powder, the hexagonal boron nitride powder having a peak height ratio B / A of less than 0.02, where A is a height of an absorbance peak derived from hexagonal boron nitride near 800cm - 1 in an infrared absorbance spectrum, and B is a height of a highest absorbance peak in a range of 3100cm - 1 to 3800cm - 1; A method for producing a ceramic sintered body, comprising: a coating step of obtaining a green body having a hexagonal boron nitride layer; a laminating step of laminating a plurality of the green bodies each having a hexagonal boron nitride layer; and a firing step of firing the laminate to produce a laminate of a ceramic sintered body.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel method for producing a ceramic sintered body. [Background technology]

[0002] In recent years, ceramic sintered bodies have been widely used as substrates for semiconductor modules and structural components. For example, substrates for power element modules that mount high-power, high-heat-generating semiconductor elements are required to have high mechanical strength, high thermal conductivity, and high electrical insulation. Ceramic sintered bodies excel in these properties, and in recent years, ceramic sintered bodies have come to be widely used as substrates for power element modules.

[0003] Ceramic sintered bodies are produced by firing green bodies whose main component is ceramic powder. The green bodies are fired using an electric furnace or the like, but to reduce production costs, multiple green bodies are stacked and fired simultaneously. When firing multiple stacked green bodies, it is common to coat the surfaces of the green bodies with a separating material to facilitate separation of the sintered ceramic bodies after firing.

[0004] For example, Patent Document 1 describes a method for producing a ceramic sintered body in which ceramic powder is molded to produce green bodies, a slurry containing a separating material made of boron nitride (BN) is applied to the green bodies, the green bodies coated with the slurry are stacked, and the stacked green bodies are fired, thereby simultaneously firing a plurality of green bodies. Patent Document 2 also describes a method in which a slurry containing boron nitride powder, a dispersion medium, and a dispersant is applied to one side of a green body to form a separating material layer, and then the green bodies are stacked and fired, thereby simultaneously firing a plurality of green bodies. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-216577 [Patent Document 2] Japanese Patent Application Publication No. 2023-173138 Summary of the Invention [Problem to be solved by the invention]

[0006] If the green body has surface waviness, the surface waviness of the resulting ceramic sintered body will increase, causing a decrease in adhesion when a metal layer is formed on the ceramic sintered body by various metallization methods, etc. Therefore, an object of the present invention is to provide a manufacturing method that can prevent surface waviness of the ceramic sintered body. [Means for solving the problem]

[0007] In order to solve the above problems, the inventors conducted extensive research. Specifically, they believed that the formation of agglomerates between primary particles of hexagonal boron nitride had a negative effect on surface waviness. They then discovered that hexagonal boron nitride powder with a specific infrared absorption spectrum is less likely to form agglomerates, and that its use can prevent surface waviness.

[0008] That is, the present invention provides a ceramic powder-containing green body having a surface on which a fluorine-containing compound having a wavelength of 800 cm in an infrared absorption spectrum is applied. -1 The height A of the absorption peak due to hexagonal boron nitride near 3100 cm -1 ~3800cm -1 The method for producing a ceramic sintered body includes a coating step of applying hexagonal boron nitride powder having a peak height ratio B / A of less than 0.02 to the height B of the highest absorption peak in the range of 0.01 mg / cm2 to obtain a green body having a hexagonal boron nitride layer, a lamination step of stacking a plurality of green bodies having the hexagonal boron nitride layer, and a sintering step of firing the laminate to produce a laminate of ceramic sintered bodies. 2 ~0.6mg / cm 2Preferably, the hexagonal boron nitride powder has an average particle size D50 of 3 to 25 μm. Also, the ceramic is preferably silicon nitride.

[0009] In addition, in the present invention, the 800 cm -1 The height A of the absorption peak due to hexagonal boron nitride near 3100 cm -1 ~3800cm -1 The hexagonal boron nitride powder for separation materials may also be mentioned, in which the peak height ratio B / A to the height B of the highest absorption peak in the range of is less than 0.02. [Effects of the Invention]

[0010] According to the present invention, a ceramic sintered body having highly suppressed surface waviness can be easily obtained. DETAILED DESCRIPTION OF THE INVENTION

[0011] The method for producing a ceramic sintered body of the present invention is to apply a sintered ceramic powder to at least one surface of a green body containing ceramic powder, the sintered ceramic body being sintered with a sintered ceramic powder having ... -1 The height A of the absorption peak due to hexagonal boron nitride near 3100 cm -1 ~3800cm -1 The method includes a coating step of applying hexagonal boron nitride powder having a peak height ratio B / A of less than 0.02 to the height B of the highest absorption peak in the range of 1 / 2 to obtain a green body having a hexagonal boron nitride layer, a lamination step of laminating a plurality of green bodies having the hexagonal boron nitride layer, and a firing step of firing the laminate to produce a laminate of sintered ceramic bodies.

[0012] In the present invention, hexagonal boron nitride powder having a peak height ratio B / A of less than 0.02 is used as the separation material. By using such hexagonal boron nitride powder, surface waviness can be suppressed. The reason for this is not clear, but the inventors believe it to be as follows.

[0013] Generally, hexagonal boron nitride particles have functional groups such as OH groups and NH groups on the particle edge surfaces. In the infrared absorption spectrum, the NH groups have a peak intensity of 3350-3500 cm -1 Target contraction vibration in the range of 3530~3590cm -1 Asymmetric contraction vibrations were detected in the range of 3600–3750 cm -1 Therefore, hexagonal boron nitride powder composed of hexagonal boron nitride particles is detected in the range of 3100 cm -1 ~3800cm -1 Therefore, a peak is generally observed in the range of 800 cm due to hexagonal boron nitride. -1 The peak height A of the absorption peak near 3100 cm -1 ~3800cm -1 When the peak height ratio B / A is calculated relative to the height B of the highest absorption peak in this range, it is generally 0.02 or more.

[0014] On the other hand, the hexagonal boron nitride powder used in the present invention has a peak height ratio B / A of less than 0.02. -1 ~3800cm -1 This means that the peak in the range is small, i.e., the number of OH groups and NH2 groups is small. Hexagonal boron nitride particles generally have few surface functional groups, and it is thought that the interaction between hexagonal boron nitride particles is mainly due to the OH groups and NH2 groups on the particle edge faces. In the hexagonal boron nitride powder of the present invention, the number of OH groups and NH2 groups is small, so it is thought that the interaction between hexagonal boron nitride particles is suppressed and they are less likely to form aggregates.

[0015] As described above, it is believed that the presence of agglomerates when a hexagonal boron nitride layer is formed will have an adverse effect on surface waviness. However, in the present invention, it is believed that surface waviness can be suppressed by using a hexagonal boron nitride powder that is less likely to form agglomerates.

[0016] The infrared absorption spectrum of the hexagonal boron nitride powder of the present invention can be measured by the diffuse reflectance infrared method. -1~3800cm -1 The peak height of the peak with the largest height among these is defined as B. -1 The peak height of the absorption peak derived from hexagonal boron nitride near 3100 cm is defined as A. From these results, the peak height ratio B / A is calculated. The peak height ratio B / A is preferably 0.01 or less. -1 ~3800cm -1 If no peak is observed in this range, the powder has few OH groups and NH2 groups, and is a hexagonal boron nitride powder with a B / A ratio of less than 0.02 that can be used in the present invention.

[0017] The hexagonal boron nitride powder preferably has a D50 of 1.0 to 100 μm, more preferably 3.0 to 25.0 μm, and even more preferably 4.0 to 20.0 μm. By setting the D50 within this range, handleability is improved and the occurrence of surface waviness is easily prevented.

[0018] The hexagonal boron nitride powder preferably has a difference between D10 and D90 of 12 μm or less. A difference between D10 and D90 in this range means that the particle size of the individual particles in the hexagonal boron nitride powder is relatively uniform, which makes it easier to suppress surface waviness of the sintered body by making the boron nitride layer uniform.

[0019] The D10, D50 and D90 of the hexagonal boron nitride powder are the particle sizes at which the cumulative volume is 10%, 50% and 90%, respectively, on the particle size distribution curve determined by laser diffraction / scattering method.

[0020] The average aspect ratio of the hexagonal boron nitride powder is preferably 5 or more, more preferably 7 or more. There is no particular upper limit to the average aspect ratio of the hexagonal boron nitride powder, but it can be, for example, 30 or less, particularly 20 or less. The average aspect ratio of the hexagonal boron nitride powder can be determined by randomly selecting 100 different hexagonal boron nitride primary particles from an image observed under a scanning electron microscope at 1000x magnification, measuring the length and thickness of the major axis of the hexagonal boron nitride primary particles, calculating the aspect ratio of each (major axis length / thickness length), and averaging the values.

[0021] The method for producing the hexagonal boron nitride powder used in the present invention is not particularly limited, but can be obtained, for example, by mixing an oxygen-containing boron compound, a carbon source having a sulfur concentration of 1,000 to 10,000 ppm, and an oxygen-containing calcium compound in such a ratio that the B contained in the oxygen-containing boron compound and the C contained in the carbon source are 0.75 to 0.85 in terms of B / C (element ratio), and the oxygen-containing calcium compound is 10 to 15 parts by mass, calculated as CaO on a Ca basis, per 100 parts by mass of the total amount of the oxygen-containing boron compound in terms of B2O3 on a B basis and the carbon source in terms of C, and heating the mixture in a nitrogen atmosphere at 1,450 to 1,550°C for four hours or more and at 1,650 to 2,100°C for two hours or more to reduce and nitride it, removing by-products other than boron nitride present in the reaction product by acid washing, and further calcining the mixture in an inert gas atmosphere at 1,600 to 1,800°C for four hours or more.

[0022] Another method for producing the boron-containing compound includes mixing an oxygen-containing boron compound, a carbon source containing less than 1000 ppm sulfur, and an oxygen-containing calcium compound in a ratio of 0.75 to 0.85 (B / C ratio) of the boron compound to the carbon source, and in a ratio of 10 to 15 parts by mass of the calcium compound (CaO equivalent) per 100 parts by mass of the combined total of the boron compound (B2O3 equivalent) and the carbon source (C equivalent), heating the mixture under a nitrogen atmosphere at 1450 to 1550°C for at least 4 hours and then at 1650 to 2100°C for at least 2 hours to reduce and nitride the reaction product, followed by removing by-products other than boron nitride by acid washing. Examples of such a production method include the method described in Comparative Example 1 of WO2018 / 101241.

[0023] The method for applying the hexagonal boron nitride powder in the application step of the present invention is not particularly limited. For example, it may be a wet application method in which a hexagonal boron nitride slurry in which hexagonal boron nitride powder is dispersed in a dispersion medium is applied onto the green body and then the solvent is removed by drying, or it may be a dry application method in which the hexagonal boron nitride powder is applied onto the green body using a sieve or the like.

[0024] An example of the wet coating method is a method in which a hexagonal boron nitride slurry containing hexagonal boron nitride powder and a dispersion medium is applied using a spray coater. The dispersion medium is not particularly limited, but examples include lower alcohols such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, and water. These dispersion mediums may be used alone or in combination of two or more. The amount of dispersion medium in the hexagonal boron nitride slurry can be determined appropriately depending on the application conditions to the green body, but can be, for example, 200 to 10,000 parts by mass, preferably 1,000 to 5,000 parts by mass, per 100 parts by mass of hexagonal boron nitride powder. The hexagonal boron nitride slurry may contain components other than the hexagonal boron nitride powder and the dispersion medium, as long as the effects of the present invention are not impaired. A green body having a hexagonal boron nitride layer can be obtained by applying the hexagonal boron nitride slurry to the green body and then drying it to remove the dispersion medium. Drying can be carried out by leaving the green body at a temperature of about 30 to 150°C, for example.

[0025] Examples of the dry coating method include coating using a sieve and coating by a method in which powder is deposited on the surface of a rotating roller and then peeled off from the roller and scattered.

[0026] Sieving is a method of coating hexagonal boron nitride particles, which can remove agglomerates. Therefore, controlling the sieving conditions makes it easy to coat the powder as single particles, not just for the hexagonal boron nitride powder of the present invention. However, since the hexagonal boron nitride powder of the present invention has few agglomerates, this method can be easily performed without controlling the sieving conditions. The mesh size of the sieve used may be determined appropriately depending on the primary particle size of the boron nitride particles to be coated. The distance between the sieve and the green body is not particularly limited, but is preferably 1 mm or more and 500 mm or less, and more preferably 10 mm or more and 300 mm or less, in order to facilitate uniform and efficient coating of boron nitride.

[0027] Another preferred method is the electrostatic screen method, in which a voltage is applied between the sieve and the green body. With the electrostatic screen method, an electric field is generated between the sieve and the green body by applying a voltage, and the hexagonal boron nitride particles reach the green body along the electric field, making it easy to achieve a uniform coating. Coating using this electrostatic screen method can be performed using commercially available devices such as an electrostatic screen duster. An example of such a device is the electrostatic screen duster (Berg Industrial Co., Ltd.). The direction of the voltage between the sieve and the green body is not particularly limited, and the green body side may be positive or negative. The voltage between the sieve and the green body is not particularly limited, but from the viewpoint of facilitating the generation of a stable electric field, it is preferably 0.1 kV to 20 kV, and more preferably 1 kV to 10 kV.

[0028] In the electrostatic screening method, the hexagonal boron nitride powder on the sieve may be electrically charged. By charging the hexagonal boron nitride powder, the aggregation of the hexagonal boron nitride particles is more easily suppressed due to electrical repulsion. The hexagonal boron nitride powder may be positively or negatively charged.

[0029] The method for charging the hexagonal boron nitride powder is not particularly limited, and can be carried out by a known method. A simple method includes, for example, charging by friction between powders or between a powder and an apparatus, and the hexagonal boron nitride powder can be charged by placing the hexagonal boron nitride powder on a sieve and rubbing it with another object, or by rubbing the hexagonal boron nitride powder with something that can hold the powder, such as a sponge, against a SUS plate, aluminum plate, or the like. The powder can also be rubbed against the mesh part of a sieve or the side of the sieve-over-sieve container.

[0030] As a method for adhering powder to the surface of a rotating roller and then peeling the powder off the roller and scattering it, for example, an apparatus equipped with a roller at the bottom opening of a powder box containing the powder can be used. In this apparatus, hexagonal boron nitride powder is charged into the powder box, and the roller is rotated to adhere the hexagonal boron nitride powder to the roller surface, while the hexagonal boron nitride powder is peeled off from the roller surface facing the green body placed below the roller, thereby applying the hexagonal boron nitride powder to the green body. There are no particular limitations on the method for peeling the hexagonal boron nitride powder from the roller surface, and known methods can be used, such as physical action or corona discharge. The use of the hexagonal boron nitride powder of the present invention makes it easier to adhere hexagonal boron nitride single particles to the roller surface and reduces agglomerates in the hexagonal boron nitride layer. Examples of devices for applying boron nitride powder in this manner include the Nikka K-VII Spray (Nikka Co., Ltd.), which uses a brush roller to remove the powder as a physical action, and the Nikka K-III Spray (Nikka Co., Ltd.), which uses corona discharge to remove the powder.

[0031] In the manufacturing method of the present invention, the amount of hexagonal boron nitride powder to be applied to the green body is not particularly limited, but the amount of hexagonal boron nitride in the hexagonal boron nitride layer is preferably 0.01 mg / cm. 2 ~1.0mg / cm 2 It is preferable to set the density to 0.05 mg / cm 2 ~0.7mg / cm 2 More preferably, it is 0.1 mg / cm 2 ~0.6mg / cm 2 It is more preferable that the hexagonal boron nitride layer has a too small amount of hexagonal boron nitride, which limits its effectiveness as a separator. If the hexagonal boron nitride layer has a too large amount of hexagonal boron nitride, a large amount of hexagonal boron nitride powder will remain on the sintered body obtained by firing the green body. If a large amount of hexagonal boron nitride powder remains, this may adversely affect the bondability with copper and the heat cycle characteristics when the sintered body is used as a heat dissipation substrate or the like.

[0032] The ceramic powder used in the green body of the present invention is not particularly limited as long as it is a ceramic powder used as a raw material for a ceramic sintered body, and examples thereof include silicon nitride, aluminum nitride, titanium nitride, aluminum oxide, titanium oxide, and zirconium oxide. These ceramic powders can be used alone or in combination of two or more. From the viewpoint of obtaining a ceramic sintered body having excellent insulating properties and high thermal conductivity and being used in applications where suppression of surface waviness is particularly important, silicon nitride powder, aluminum nitride powder, aluminum oxide powder, and a mixed powder of aluminum oxide and zirconium oxide are preferred, and silicon nitride powder is more preferred.

[0033] From the viewpoint of sinterability, the specific surface area of ​​the ceramic powder is preferably 1 m 2 / g or more, especially 2m 2 / g or more, especially 5m 2 / g or more, especially 7m 2 / g or more, and the upper limit is preferably 20m 2 / g or less, especially 15m 2 The specific surface area of ​​the ceramic powder is the BET specific surface area measured by the BET single-point method using nitrogen gas adsorption.

[0034] The green body may contain, in addition to the ceramic powder, a sintering aid, a binder resin, and the like.

[0035] The sintering aid can be any sintering aid commonly used for sintering ceramic powders, and examples include yttria, magnesia, ceria, silica, and calcia. In particular, when the ceramic powder contains silicon nitride powder, carbonitride compounds such as Y2Si4N6C, Yb2Si4N6C, Ce2Si4N6C, and MgSi4N6C, and nitride compounds such as MgSiN2 may be used as sintering aids. The amount of sintering aid in the green body is preferably 1 to 20 parts by mass, and more preferably 3 to 10 parts by mass, per 100 parts by mass of the ceramic powder.

[0036] The binder resin is not particularly limited, but examples thereof include polyvinyl alcohol, polyvinyl butyral, methyl cellulose, alginic acid, polyethylene glycol, carboxymethyl cellulose, ethyl cellulose, acrylic resin, etc. The content of the binder resin in the green body is preferably 1 to 40 parts by mass, more preferably 5 to 30 parts by mass, per 100 parts by mass of the ceramic powder.

[0037] The method for producing the green body is not particularly limited, and the green body may be produced by press molding using a powder obtained by dry mixing the constituent components of the green body, or by wet mixing the constituent components of the green body to produce a slurry for granule production, which is then dried using a spray dryer or the like to produce granules.

[0038] Alternatively, the green body may be produced by wet-mixing the constituent components to prepare a green body molding slurry, and then molding the green body molding slurry into a sheet. The green body molding slurry may be prepared, for example, by weighing out the components in predetermined amounts and stirring and mixing them so that the ceramic powder is dispersed in the dispersion medium. Examples of dispersion devices used for stirring and mixing include ultrasonic dispersion devices, bead mills, ball mills, roll mills, homomixers, ultramixers, disperser mixers, homomixers, through-type high-pressure dispersion devices, collision-type high-pressure dispersion devices, porous high-pressure dispersion devices, clump-removal type high-pressure dispersion devices, (collision + through-type) high-pressure dispersion devices, and ultra-high-pressure homogenizers. After stirring and mixing, the green body slurry may be filtered, if necessary, to remove clumps.

[0039] The method for producing a green body from the green body molding slurry is not particularly limited, and known molding methods can be used, but molding by a doctor blade method is preferred from the viewpoint of good sheet thickness uniformity, etc. The obtained green body can be processed into an appropriate size and any shape. For example, it is generally processed into a roughly rectangular parallelepiped shape with a side length of 100 mm to 2000 mm and a thickness of 0.3 mm to 1.2 mm. Note that after molding into a size larger than that used for firing, cutting can be performed to obtain the desired shape. Cutting can be performed before or after drying, which will be described later.

[0040] When obtaining a green body from the green body molding slurry, it is preferable to carry out a drying step as necessary. The drying step is a step of further removing the dispersion medium from the green body, which makes it easier to subsequently sinter the green body. For example, when the dispersion medium is water, the drying step can be carried out by leaving the green body at a temperature of about 30°C to 150°C, and it is preferable to dry the green body so that the water content is 10% or less.

[0041] In the lamination process, multiple green bodies are stacked to form a laminate with a boron nitride layer between adjacent green bodies. The number of stacked green bodies can be any number, ranging from several to several tens of green bodies.

[0042] When the green bodies contain organic components such as binders, it is preferable to degrease the green body laminate prior to firing. The degreasing temperature for degreasing the green body laminate is preferably 300°C to 1200°C, more preferably 400°C to 1000°C. The degreasing of the green body laminate is typically carried out in an atmosphere of an oxidizing gas such as oxygen or air, a reducing gas such as hydrogen, an inert gas such as argon or nitrogen, carbon dioxide, or a mixture of these, or in a humidified gas atmosphere containing a mixture of these gases and water vapor. The degreasing time at the above degreasing temperature can be appropriately selected depending on the type and amount of organic components such as binders used in the green bodies, and the degreasing atmosphere, but is typically 30 minutes to 12 hours, preferably 2 hours to 10 hours. In the firing step, the laminate is fired to produce a laminate of sintered ceramic bodies. The firing conditions are not particularly limited, and the firing may be carried out under known firing conditions for obtaining sintered ceramic bodies.

[0043] For example, when the ceramic of the ceramic powder is silicon nitride or aluminum nitride, firing is preferably carried out in an inert gas atmosphere. An inert gas atmosphere refers to, for example, a nitrogen atmosphere or an argon atmosphere. The firing pressure is not particularly limited, but because high pressures increase the cost of equipment, for example, firing is carried out at a pressure of 10 MPa·G or less, more preferably 3 MPa·G or less, and even more preferably 1 MPa·G or less. Furthermore, when the ceramic of the ceramic powder is silicon nitride, low pressures may cause silicon nitride to decompose during firing, so a firing pressure of 0 MPa·G or more is preferred. The firing temperature is not particularly limited as long as the desired sintering reaction proceeds. For example, when the ceramic of the ceramic powder is silicon nitride, it can be, for example, 1200°C to 2000°C, more preferably 1500°C to 1900°C. The firing time is not particularly limited as long as the desired sintering reaction proceeds, but for example, when the ceramic of the ceramic powder is silicon nitride, it is generally about 3 to 20 hours.

[0044] After the firing step, the ceramic sintered body is separated from the stack of ceramic sintered bodies to obtain a ceramic sintered body. Since the separator layer is provided between adjacent ceramic sintered bodies in the stack of ceramic sintered bodies, the ceramic sintered body can be easily separated from the stack of ceramic sintered bodies.

[0045] Boron nitride powder may remain on the surface of the ceramic sintered body separated from the laminate. Therefore, it is preferable to remove the boron nitride powder remaining on the surface of the ceramic sintered body after separating it from the laminate. For example, it is preferable to subject the ceramic sintered body separated from the laminate to honing using free abrasive grains. In this case, it is preferable to use alumina abrasive grains with an average particle size of 10 to 100 μm as the free abrasive grains. Furthermore, after honing, the ceramic sintered body may be ultrasonically cleaned or washed with a spray of water to remove the alumina abrasive grains and boron nitride powder. It is preferable that no boron nitride particles are observed on the surface of the ceramic sintered body when observed with a scanning electron microscope. Polishing may or may not be performed after honing.

[0046] The ceramic sintered body separated from the laminate is cut mechanically or by laser, as required, to obtain a ceramic sintered body of a desired size and shape.

[0047] The manufacturing method of the present invention makes it possible to obtain a ceramic sintered body with highly suppressed surface waviness. For example, it is possible to easily obtain a silicon nitride sintered body with an arithmetic mean waviness Wa of 0.20 μm or less.

[0048] The ceramic sintered body obtained by the manufacturing method of the present invention can be used for any purpose, including, but not limited to, substrates that require a high degree of suppression of surface waviness. Specific examples include various heat dissipation substrates, power module substrates (for automobiles, electric railways, and high-power semiconductors), high-frequency circuit boards, LED packages, and optical pickup submounts (for DVDs and CDs). [Example]

[0049] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples. The measurements of the various items in the examples and comparative examples were performed by the following methods.

[0050] (1) Evaluation of waviness of silicon nitride substrate The surface waviness of the ceramic sintered body was measured using a surface roughness meter to measure the filtered centerline waviness, and the arithmetic mean waviness Wa, that is, the arithmetic mean of the absolute values ​​of the deviations from the average surface height, was used. The measurement conditions were an evaluation length of 4 mm, a measurement speed of 0.3 mm / s, and a cutoff value of 0.8 mm.

[0051] (2) Measurement of D10, D50, and D90 of hexagonal boron nitride powder Hexagonal boron nitride powder was dispersed in pure water and dispersed for 30 seconds at 300W using an ultrasonic homogenizer (Nippon Seiki Seisakusho: US-600T). The suspension was then subjected to wet measurement using a particle size distribution analyzer (Microtrac: MT3300EXII) equipped with a standard sample circulator (Microtrac: SDC). The D10, D50, and D90 of the hexagonal boron nitride powder were determined from the volume-based particle size distribution obtained.

[0052] (3) Measurement of infrared absorption spectrum of hexagonal boron nitride powder The infrared absorption spectrum of hexagonal boron nitride powder was measured by diffuse reflectance infrared spectroscopy using an Agilent Technologies FTS-3000. The sample was pretreated by drying at 200°C under reduced pressure for 2 hours. The sample was packed into a measuring cup and measured. The resolution was 4 cm. -1 , measurement range is 400~4000cm -1 The number of measurements was 64. From the results obtained, it was found that the hexagonal boron nitride powder -1 The height A of the absorption peak due to hexagonal boron nitride near 3100 cm -1 ~3800cm -1 The peak height ratio B / A was calculated from the height B of the highest absorption peak in the range.

[0053] The silicon nitride substrate was manufactured using the following raw materials containing silicon nitride powder and a sintering aid.

[0054] <Silicon nitride powder> ·Beta conversion rate: 99% ·Average particle size D50: 0.9μm <Sintering aid> Yttria (manufactured by Shin-Etsu Chemical Co., Ltd.) Magnesia (manufactured by Ube Materials Co., Ltd.) <Binders and dispersants> Binder resin: Acrylic resin (manufactured by Fujikura Kasei Co., Ltd.) Dispersant: Cerna D735 (manufactured by Chukyo Yushi Co., Ltd.)

[0055] <Hexagonal boron nitride powder> B1: Hexagonal boron nitride powder produced by the following method 195 g of boron oxide (oxygen-containing boron compound), 82 g of carbon black (carbon source) with a sulfur concentration of 100 ppm, and 49.4 g of calcium oxide (oxygen-containing calcium compound) were mixed using a ball mill. The B / C (element ratio) ratio of the B contained in the oxygen-containing boron compound to the C contained in the carbon source of this mixture was 0.82, and the amount of the oxygen-containing calcium compound, calculated as CaO on a Ca basis, per 100 parts by mass of the total amount of the oxygen-containing boron compound in B-based B2O3 equivalent and the carbon source in C-based C equivalent was 10.5 parts by mass. 100 g of this mixture was nitrided in a graphite Tammann furnace under a nitrogen gas atmosphere by holding it at 1450°C for 6 hours and then at 1850°C for 2 hours. Next, the by-product-containing boron nitride was crushed and placed in a container, and hydrochloric acid (7% by mass HCl) was added in an amount five times the amount of the by-product-containing boron nitride, followed by stirring at 700 rpm for 24 hours. After the acid washing, the acid was filtered, and the boron nitride obtained by filtration was dispersed in pure water in the same amount as the acid used, and then filtered again. This operation was repeated six times, and then the resultant was vacuum dried at 200°C for six hours. B2: Hexagonal boron nitride powder obtained in the same manner as B1, except that the nitriding temperature was 1500°C for 8 hours and 1900°C for 4 hours. B3: Hexagonal boron nitride powder obtained in the same manner as B1, except that the nitriding temperature was 1500°C for 8 hours and 1950°C for 8 hours. B4: Hexagonal boron nitride powder obtained in the same manner as B1, except that the nitriding temperature was 1500°C for 8 hours and 1970°C for 12 hours. B5: Hexagonal boron nitride powder obtained in the same manner as B2, except that the sulfur concentration was set to 3500 ppm.

[0056] In addition, for all of the hexagonal boron nitride powders B1 to B5, the difference between D90 and D10 was 12 μm or less.

[0057] Example 1 (Preparation of green bodies) 100 parts by weight of silicon nitride powder, 5 parts by weight of yttria, 3 parts by weight of magnesia, 0.5 parts by weight of dispersant, and 22 parts by weight of binder were weighed and mixed in a ball mill using water as a solvent and a resin pot and silicon nitride balls for 48 hours. Next, a vacuum defoamer (manufactured by Sayama Riken Co., Ltd.) was used to defoam and adjust the viscosity to produce a raw material slurry. The raw material slurry was then molded into a sheet with a width of 750 mm and a thickness of 420 μm using a doctor blade method. The resulting molded body was dried in air at 40°C to evaporate the solvent, and then cut to a size of 200 mm x 268 mm on the main surface to obtain a green body (green sheet). (Coating process) Hexagonal boron nitride powder B1 was filled into the powder supply box of an electrostatic screen sieving machine (manufactured by Berg Kogyo Co., Ltd.), and a voltage of 3 kV was applied between the electrostatic screen and the green body to generate an electrostatic field. The boron nitride powder was then released into the electrostatic field and applied to the green body, yielding a green body with a boron nitride layer. The amount of hexagonal boron nitride powder applied was 0.2 mg / cm. 2 In the same manner, hexagonal boron nitride powder was applied to one side of a total of 10 green bodies. (Lamination process) Ten green bodies having the boron nitride layer were stacked together so that the surface of one green body having the boron nitride layer was in contact with the surface of another green body not having the boron nitride layer, to produce a stack with a separator layer provided between adjacent green bodies. (Firing process) The laminate was degreased by holding it in an air atmosphere at 400°C for 5 hours. It was then fired in a nitrogen atmosphere at 1830°C for 9 hours under a pressure of 0.8 MPa·G. After firing, the laminate was removed and 10 silicon nitride sintered bodies were separated from the laminate. The silicon nitride sintered bodies were easily separated. (evaluation) All 10 of the resulting silicon nitride sintered bodies were evaluated for waviness. The evaluation results for the ceramic sintered body with the largest Wa value are shown in Table 1. Note that the separability in Table 1 indicates whether or not the 10 silicon nitride sintered bodies could be easily separated from the laminate after the firing process.

[0058] <Examples 2 to 4, Comparative Example 1> Silicon nitride sintered bodies were obtained and evaluated in the same manner as in Example 1, except that the hexagonal boron nitride powder used was changed as shown in Table 1.

[0059] [Table 1]

Claims

1. At least one surface of the green body containing ceramic powder is coated with a material having a wavelength of 800 cm in the infrared absorption spectrum. －１ The height A of the absorption peak due to hexagonal boron nitride in the vicinity of 3100 cm －１ ~3800cm －１ a coating step of applying a hexagonal boron nitride powder having a peak height ratio B / A of less than 0.02 to the height B of the highest absorption peak in the range of a lamination step of laminating a plurality of green bodies each having a hexagonal boron nitride layer; a firing step of firing the laminate to produce a laminate of ceramic sintered bodies; Including, A method for manufacturing a ceramic sintered body.

2. In the green body having the hexagonal boron nitride layer, the amount of hexagonal boron nitride in the hexagonal boron nitride layer is 0.01 mg / cm ２ ~0.6 mg / cm ２ The method for producing a ceramic sintered body according to claim 1, wherein

3. 3. The method for producing a ceramic powder according to claim 1, wherein the hexagonal boron nitride powder has a D50 of 3 to 25 μm.

4. 3. The method for producing a ceramic sintered body according to claim 1, wherein the ceramic is silicon nitride.

5. 800 cm in the infrared absorption spectrum －１ The height A of the absorption peak due to hexagonal boron nitride in the vicinity of 3100 cm －１ ~3800cm －１ The hexagonal boron nitride powder for separation materials has a peak height ratio B / A of less than 0.02 with respect to the height B of the highest absorption peak in the range of 1.

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