Method for manufacturing a silicon nitride substrate

Abstract

Provided is a method for manufacturing a silicon nitride substrate, capable of preventing a rapid nitriding reaction of silicon and providing a silicon nitride substrate with high heat dissipation and excellent mechanical properties through a uniform nitriding reaction. The method comprises: a first step of forming a composite powder by mixing a metal silicon powder and a silicon nitride powder and performing a fine pulverization treatment; a second step of forming a slurry for forming a sheet in which a sintering aid is dispersed in the composite powder by mixing the sintering aid and a dispersion medium in the composite powder; a third step of forming a sheet by performing molding on the slurry for forming a sheet; a fourth step of forming a debinding treatment sheet by performing debinding on a resin component by heating the sheet at 250-600°C; a fifth step of forming a nitriding treatment sheet by nitriding silicon contained in the sheet by heating the debinding treatment sheet at 1200-1500°C; and a sixth step of manufacturing a silicon nitride substrate by performing sintering on the nitriding treatment sheet. The composite powder is formed by adsorbing metal silicon particles and silicon nitride particles.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a silicon nitride substrate. More specifically, it relates to a method for manufacturing a silicon nitride substrate having high heat dissipation and excellent mechanical properties by using a composite powder formed by mixing metallic silicon powder and silicon nitride powder and then micronizing it as a silicon source, thereby preventing rapid nitriding reactions of silicon. Background Technology

[0002] In recent years, the demand for power devices has been increasing year by year. Specifically, with the widespread adoption of hybrid and electric vehicles, power devices are developing towards higher power, higher density, and higher temperature operation. To meet this development trend, the insulating substrates used in power devices are required to have high heat dissipation and excellent mechanical properties.

[0003] In other words, heat dissipation technology for the heat generated by semiconductor elements becomes extremely important in the insulating substrate used for power devices.

[0004] Aluminum nitride has been used as a material for insulating substrates with heat dissipation properties. Specifically, aluminum nitride is used as a material for heat-dissipating insulating substrates for power modules due to its excellent insulation and high thermal conductivity. However, aluminum nitride has lower mechanical properties in terms of strength and fracture toughness, and lacks reliability, thus limiting its applications.

[0005] On the other hand, silicon nitride sintered bodies are widely known as excellent structural ceramic materials that combine high strength and high toughness. Furthermore, silicon nitride sintered bodies are expected to exhibit extremely high thermal conductivity of 200-320 W / mK in their single-crystal state. Therefore, silicon nitride sintered bodies hold promise as materials for use as heat-dissipating insulating substrates.

[0006] However, in typical silicon nitride sintered bodies, the silicon nitride particles that make up the sintered body contain dissolved impurities such as oxygen. As a result, phonons responsible for heat conduction are scattered, leading to a thermal conductivity of only 20-80 W / mK for the silicon nitride sintered body, which is far lower than the theoretical value predicted for single crystals.

[0007] Based on this technical perspective, a method for manufacturing a dense silicon nitride substrate has been proposed that can be made from a raw material powder containing silicon powder and does not require removal of the modified layer after forming a sintered body (e.g., Patent Document 1). Specifically, Patent Document 1 describes a method for manufacturing a silicon nitride substrate, comprising: a raw material powder preparation step, preparing a predetermined raw material powder containing silicon powder, a rare earth element compound, and a magnesium compound; a wafer forming step, forming the raw material powder into a wafer shape to form a wafer; a nitriding step, heating the wafer in a nitrogen atmosphere to nitrid the silicon contained in the wafer; and a sintering step, sintering the wafer after the nitriding step in a nitrogen atmosphere.

[0008] Furthermore, a method for manufacturing a silicon nitride substrate with excellent thermal conductivity in the thickness direction has been proposed (for example, Patent Document 2). Specifically, Patent Document 2 describes a method for manufacturing a silicon nitride substrate, comprising: a step of mixing silicon powder, a sintering aid, and a dispersion medium to prepare a slurry; a step of forming a sheet from the slurry; a step of heat-treating the sheet in a nitrogen-containing atmosphere to nitride the silicon in the sheet to form silicon nitride; and a step of sintering the sheet containing silicon nitride to manufacture a silicon nitride substrate. Moreover, the step of forming silicon nitride included in the method for manufacturing a silicon nitride substrate described in Patent Document 2 is characterized by controlling the volatilization of the sintering aid and orienteding the silicon nitride particles along the direction of movement of the sintering aid, i.e., the thickness direction.

[0009] Furthermore, a manufacturing method has been proposed that enables the formation of a silicon nitride substrate with high separability without damage to the ceramic substrate (for example, Patent Document 3). Specifically, Patent Document 3 describes a silicon nitride substrate, which is a sintered body composed of a main phase composed of silicon nitride particles and a grain boundary phase composed of sintering aids. Its surface undulation is less than 1.0 μm, and it has the desired bending strength, thermal conductivity, and adhesion to metal plates. It also describes a manufacturing method that enables the formation of a silicon nitride substrate with high separability without damage to the ceramic substrate when separating each ceramic substrate from multiple stacked ceramic substrates after sintering.

[0010] Existing technical documents

[0011] Patent documents Patent Document 1: Japanese Invention Patent No. 5836522 Patent Document 2: Japanese Patent Application Publication No. 2022-027444 Patent Document 3: International Publication No. 2013 / 054852 Summary of the Invention The problem that the invention aims to solve However, the aforementioned prior art has the following problems that must be solved. Specifically, in the method described in Patent Document 1 for manufacturing a silicon nitride substrate from a raw material powder containing silicon powder, if a large amount of silicon powder is used, heat will be generated due to the rapid nitriding reaction of the silicon contained in the silicon powder. That is, in this method for manufacturing a silicon nitride substrate, in order to control the rapid heat generation of the silicon contained in the silicon powder used as a raw material powder, the nitriding reaction time must be set to a very long time. Furthermore, there is a problem that the rapid reaction may cause the metallic silicon to melt or remain unreacted.

[0012] To suppress the heat generated by silicon contained in silicon powder, which is used as a raw material powder, it is considered to use a mixed powder in which silicon powder and silicon nitride powder are mixed as a raw material for silicon nitride substrates. However, simply mixing silicon powder and silicon nitride powder does not produce a mixed powder in which the silicon powder and silicon nitride powder are uniformly mixed. Therefore, since the nitriding reaction of silicon contained in the raw material powder, i.e., silicon powder, is accompanied by heat, the nitriding reaction cannot be controlled. As a result, the method described in Patent Document 1, which enables the manufacture of silicon nitride substrates from raw material powder containing silicon powder, cannot use metallic silicon powder as a silicon source for silicon nitride substrates in large quantities.

[0013] Furthermore, in the manufacturing method of silicon nitride substrate described in Patent Documents 2-3, the silicon nitride in the wafer is nitrided and the sintering aid in the process of promoting the formation of silicon nitride is volatilized, and the silicon nitride particles are oriented along the thickness direction, without taking into account the heat generated by the rapid nitriding reaction of silicon powder.

[0014] As a result, silicon nitride substrates manufactured using conventional silicon nitride substrate manufacturing methods fail to fully meet the requirements from the perspectives of both manufacturing cost and the coexistence of thermal conductivity and mechanical properties.

[0015] Therefore, from the perspective of reducing the cost of raw material powder, even if the so-called reaction sintering method is adopted, using inexpensive silicon powder as raw material powder, nitriding the molded body in nitrogen gas and sintering it at high temperature, a method for manufacturing silicon nitride substrate is still needed, which has a nitriding process that can suppress the heat generated by the rapid nitriding reaction of silicon powder and make the silicon powder undergo a uniform nitriding reaction.

[0016] The present invention was made in view of the problems of the prior art mentioned above, and aims to provide a silicon nitride substrate that prevents the rapid nitriding reaction of silicon during the manufacturing process of the silicon nitride substrate, and has high heat dissipation and excellent mechanical properties through uniform nitriding reaction.

[0017] Methods for solving problems In view of these problems, the inventors conducted in-depth research and found that using a composite powder formed by mixing metallic silicon powder and silicon nitride powder and then micronizing it as the silicon source for a silicon nitride substrate can prevent rapid nitriding reaction and uneven reaction of silicon, thus completing the present invention.

[0018] That is, the method for manufacturing a silicon nitride substrate of the present invention, which advantageously solves the above-mentioned problems, is characterized by comprising: a first step of forming a composite powder by mixing metallic silicon powder and silicon nitride powder and performing micronization treatment; a second step of forming a slurry for sheet formation by mixing a sintering aid and a dispersion medium in the composite powder, wherein the sintering aid is dispersed in the composite powder; a third step of molding the slurry for sheet formation to form a sheet; a fourth step of heating the sheet at 250-600°C to degrease the resin component contained in the sheet to form a degreased sheet; a fifth step of heating the degreased sheet at 1200-1500°C to nitride the silicon contained in the degreased sheet to form a nitrided sheet; and a sixth step of forming a silicon nitride substrate from a silicon nitride sintered body formed by sintering the nitrided sheet; wherein the composite powder is formed by the adsorption of metallic silicon particles and silicon nitride particles.

[0019] It should be noted that the method for manufacturing the silicon nitride substrate of the present invention is more preferably implemented by means of the following methods to solve the problem: (a) The micronization process is carried out by any one or a combination thereof selected from air jet milling, ball milling, bead milling, planetary ball milling, vertical stirred ball milling and mechanochemical methods; (b) The average particle size D of the silicon metal particles S50 Relative to the average particle size D of the silicon nitride particles SN50 The ratio, i.e., the particle size ratio X, is 0.2-2.0; (c) In the first step, the silicon metal powder and the silicon nitride powder are contained in a molar ratio of 70:30 to 95:5, based on silicon nitride. (d) The silicon metal particles are uniformly dispersed on the surface of the silicon metal particles with microparticles composed of the sintering aid; (e) The sintering aid is a magnesium compound, which comprises one or more magnesium compounds selected from magnesium oxide, magnesium silicide and magnesium silicon nitride; (f) The sintering aid is the rare earth element compound, wherein the rare earth element comprises one or more elements selected from Y, Sc, La, Ce, Nd, Sm, Gd, Dy, Ho, Er and Yb; (g) The relative density of the sheet is 45% or more; (h) The thermal conductivity of the silicon nitride substrate, as measured by the xenon lamp flash method, is above 80 W / mK.

[0020] The effects of the invention According to the present invention, by preventing rapid nitriding reactions of silicon, it is possible to manufacture silicon nitride substrates with high heat dissipation and excellent mechanical properties. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the various steps of the method for manufacturing a silicon nitride substrate according to the present invention.

[0022] Figure 2A These are SEM images of the metallic silicon particles and silicon nitride particles in the composite powder used in the manufacturing method of the silicon nitride substrate of the present invention before pulverization.

[0023] Figure 2B These are SEM images of the composite powder containing metallic silicon particles and silicon nitride particles after pulverization, used in the manufacturing method of the silicon nitride substrate of the present invention.

[0024] Figure 3 This is an EDS image of the metallic silicon particles and silicon nitride particles that make up the composite powder after they have been pulverized.

[0025] Figure 4 It is a magnified image of the EDS image of the metallic silicon particles and silicon nitride particles that make up the composite powder after they have been pulverized.

[0026] Figure 5 It is a SEM image of composite silicon particles, in which the surface of the metallic silicon particles constituting the composite powder is dispersed with microparticles composed of sintering aids.

[0027] Figure 6 This is an EDS image of composite silicon particles, in which the surface of the metallic silicon particles constituting the composite powder is dispersed with microparticles composed of sintering aids. Detailed Implementation

[0028] The embodiments of the present invention will now be described in detail. It should be noted that all accompanying drawings are illustrative and may differ from actual embodiments. Furthermore, the following embodiments illustrate apparatus or methods for embodying the technical concept of the present invention and are not intended to limit the structure to the following content. That is, various modifications can be made to the technical concept of the present invention within the scope of the claims.

[0029] [First Embodiment] The method for manufacturing the silicon nitride substrate according to the first embodiment will be described. Figure 1 This is a flowchart illustrating each step of the manufacturing method for the silicon nitride substrate according to this embodiment. For example... Figure 1As shown, the method for manufacturing a silicon nitride substrate according to this embodiment is characterized by comprising: a first step, forming a composite powder by mixing metallic silicon powder and silicon nitride powder and performing micronization treatment; a second step, forming a slurry for sheet formation by mixing a sintering aid and a dispersion medium in the composite powder, wherein the sintering aid is dispersed in the composite powder; a third step, molding the slurry for sheet formation to form a sheet; a fourth step, heating the sheet at 250-600°C to degrease the resin component contained in the sheet to form a degreased sheet; a fifth step, heating the degreased sheet at 1200-1500°C to nitride the metallic silicon contained in the degreased sheet to form a nitrided sheet; and a sixth step, sintering the nitrided sheet to form a silicon nitride substrate; wherein the composite powder is formed by the adsorption of metallic silicon particles and silicon nitride particles.

[0030] The following describes each step in the method for manufacturing the silicon nitride substrate according to this embodiment.

[0031] <First Process: The Process of Forming Composite Powder> The method for manufacturing a silicon nitride substrate according to this embodiment includes a composite powder forming process, in which composite powder is formed by the mechanochemical effect generated by mixing metallic silicon powder and silicon nitride powder and performing micronization treatment.

[0032] The composite powder forming process is the process of forming composite powders that serve as raw materials for manufacturing sintered silicon nitride wafers required for silicon nitride substrates.

[0033] That is, the composite powder forming process, which is the first step, is a process in which composite powder is formed by the mechanochemical effect generated by mixing metallic silicon powder and silicon nitride powder and performing micronization treatment, so as to serve as the raw material for manufacturing silicon nitride sintered bodies required for silicon nitride substrates.

[0034] Here, the mechanochemical effect refers to the effect of activating a substance by changing its binding state when mechanical energy is applied to it. The mechanochemical effect occurs when mechanical energy, such as impact, compression, shear, shear stress, and friction, is continuously applied to particles during the microparticle formation process, causing changes in the particle's crystal structure and activating its surface. This activation leads to a chemical reaction between the particle and the surrounding matter.

[0035] In conventional methods for manufacturing silicon nitride sintered bodies, it has been proposed to use only silicon nitride powder as the silicon supply source. However, due to the high cost of silicon nitride powder, using only silicon nitride powder as the silicon supply source leads to increased manufacturing costs. In contrast, in the silicon nitride substrate manufacturing method of this embodiment, metallic silicon particles can be used as the raw material for the silicon nitride sintered body, and the silicon nitride substrate is manufactured through a sintering reaction.

[0036] Furthermore, in the method for manufacturing a silicon nitride substrate according to this embodiment, silicon nitride powder is used as the silicon supply source for manufacturing the silicon nitride sintered body required for the silicon nitride substrate, in addition to metallic silicon powder.

[0037] That is, the method for manufacturing a silicon nitride substrate according to this embodiment is characterized in that a mixed powder of metallic silicon powder and silicon nitride powder is used as the silicon supply source of the silicon nitride sintered body, and a composite powder composed of metallic silicon and silicon nitride is used, which is formed by micronizing the mixed powder of metallic silicon powder and silicon nitride powder.

[0038] (Silicon metal powder and silicon nitride powder) In the method for manufacturing a silicon nitride substrate according to this embodiment, a mixed powder comprising metallic silicon powder and silicon nitride powder is used as the silicon supply source for manufacturing the silicon nitride sintered body required for the silicon nitride substrate. In the silicon supply source of the silicon nitride substrate contained in the mixed powder, the silicon nitride powder is preferably 20 mol% or less, more preferably 10 mol% or less. It is further preferably 5 mol% or less, as this can suppress the manufacturing cost of the silicon nitride substrate, and is therefore preferred.

[0039] That is, the metallic silicon contained in the mixed powder comprising metallic silicon powder and silicon nitride powder, which is the silicon supply source for manufacturing the silicon nitride sintered body required for manufacturing the silicon nitride substrate, is preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or less.

[0040] It should be noted that the molar concentration of silicon nitride in the mixed powder is a value calculated by converting the silicon content in the mixed powder to silicon nitride, that is, the value when 1 mol of silicon in the silicon powder is calculated as 1 / 3 mol. Specifically, for example, when the raw material powder, as a silicon supply source, contains 3 mol of silicon powder and 1 mol of silicon nitride powder, the content of silicon nitride powder in the silicon supply source contained in the raw material powder is 50 mol%.

[0041] The average particle size of the silicon metal particles constituting the silicon metal powder is 0.1-10.0 μm, preferably 2.0-5.0 μm. The average particle size of the silicon nitride particles constituting the silicon nitride powder is 1.0-25.0 μm, preferably 3.0-10.0 μm.

[0042] Here, before the mechanochemical effect produced by the micronization process used in the manufacturing method of the silicon nitride substrate of this embodiment is applied, the average particle size of the metallic silicon particles is 20.0-30.0 μm, while the average particle size of the silicon nitride particles is 40.0-50.0 μm.

[0043] It should be noted that the average particle size refers to the particle size at the 50% cumulative value of the particle size distribution measured by laser diffraction / scattering. Commercially available silicon nitride powder and silicon powder generally contain unavoidable impurities.

[0044] The oxygen content as an impurity in silicon nitride powder and metallic silicon powder varies depending on the properties of these powders. For example, it is about 1.2% by mass for silicon nitride powder and about 0.2% to a few% by mass for metallic silicon powder. The purity of the silicon nitride powder used in the method for manufacturing the silicon nitride substrate of this embodiment is preferably in the range of 98.0% or more and 99.99% or less, more preferably in the range of 99.0% or more and 99.90% or less. The purity of the silicon powder used in the method for manufacturing the silicon nitride substrate of this embodiment is preferably in the range of 99.0% or more, more preferably in the range of 99.5% or more.

[0045] In manufacturing a silicon nitride substrate, to improve the thermal conductivity of the silicon nitride substrate, it is preferable to reduce the amount of dissolved oxygen in the crystals of the silicon nitride sintered body. The silicon nitride substrate manufacturing method of this embodiment, since it employs reaction sintering and uses metallic silicon powder as the starting material, has a significant advantage in reducing oxygen content compared to the case where only silicon nitride is used as the silicon supply source. This is because, when silicon powder is used as the starting material, after the sheet forming process of molding the composite powder composed of metallic silicon powder and silicon nitride powder into a sheet shape, a nitriding process is performed on the sheet containing the composite powder. Furthermore, in the nitriding process, the nitriding reaction shown in the following reaction formula (1) is carried out.

[0046] 3Si + 2N2 = Si3N4 (1) The weight of the wafer containing the composite powder increases by approximately 70% due to the nitriding reaction. Therefore, the impurity oxygen content in the wafer containing the composite powder is relatively reduced. Thus, the method for manufacturing a silicon nitride substrate according to this embodiment, by using a composite powder composed of metallic silicon powder and silicon nitride powder as the silicon supply source, can reduce the oxygen content in the crystals of the silicon nitride sintered body compared to the case where only silicon nitride is used as the starting material.

[0047] That is, in the silicon nitride substrate manufacturing method of this embodiment, the wafer includes a composite powder composed of metallic silicon powder and silicon nitride powder as a silicon supply source. By performing a nitriding reaction on the wafer, the impurity oxygen content in the composite powder can be relatively reduced.

[0048] As a result, the influence of impurity oxygen content in the metallic silicon powder and silicon nitride powder constituting the composite powder becomes minor. Therefore, in the method for manufacturing a silicon nitride substrate according to this embodiment, a variety of metallic silicon powders can be used, ranging from low-grade metallic silicon powder with high impurity oxygen concentration to high-grade metallic silicon powder with low impurity oxygen content.

[0049] In particular, when it is necessary to reduce the impurity oxygen content in the silicon nitride substrate, it is preferable to use high-grade metallic silicon powder with low impurity oxygen concentration.

[0050] Here, the silicon particles constituting the silicon powder can be silicon particles uniformly dispersed on the surface of the silicon particles by microparticles composed of sintering aids. That is, the silicon powder contains sintering aids. The sintering aids can be any silicon nitride contained in the wafer that serves as the precursor of the silicon nitride substrate, as long as its melting point is lower than that of the silicon nitride. They can be sintering aids used in the slurry formation process described later, such as rare earth element compounds or magnesium compounds. The particle size of the microparticles composed of the sintering aids is preferably 0.5 μm or less. By uniformly dispersing the microparticles composed of sintering aids on the surface of the silicon particles, the grain boundary energy of the silicon particles can be reduced, and the sinterability of the silicon nitride particles can be improved.

[0051] (Micronization process) In the composite powder formation step of the silicon nitride substrate manufacturing method of this embodiment, the composite powder is formed by micronizing a mixed powder consisting of metallic silicon powder and silicon nitride powder. The micronization process is performed by any one or a combination thereof, selected from air jet milling, ball milling, bead milling, planetary ball milling, vertical stirred ball milling, and mechanochemical methods.

[0052] For example, air jet milling is performed by ejecting compressed air or high-pressure steam or gas at a pressure of several atmospheres or higher from a nozzle. This jet of air accelerates silicon metal particles and silicon nitride particles, which are the raw material particles. The accelerated particles are then pulverized through collisions, impacts, and abrasive effects. Air jet milling is carried out using an air jet micro-pulverizer capable of applying this effect to silicon metal powder and silicon nitride powder to promote pulverization.

[0053] If an airflow mill is used to dry-mill silicon and silicon nitride particles, micro-powders with a particle size of 0.1-10.0 μm, preferably 1.0-5.0 μm, can be obtained. Airflow milling results in a lower temperature rise, making it suitable for pulverizing heat-sensitive substances. However, airflow milling has low energy efficiency; although it can produce micro-powders composed of silicon and silicon nitride particles, it consumes a lot of power and typically processes small quantities. Therefore, in addition to airflow milling, any one or a combination of other micro-powder processing methods, such as ball milling, bead milling, planetary ball milling, and vertical stirred ball milling, can also be used.

[0054] Types of airflow micronizers include: micronization type using jet airflow that generates horizontal swirling flow, airflow homogenization type using vertical swirling flow, Blaw-Knox or Trost airflow pulverization type based on the opposing collision of solid-gas mixed flow, method of causing solid-gas mixed jet flow to impact collision plate, and method of mixing solid-gas mixed flow in ultrasonic nozzle, etc.

[0055] In the composite powder formation step of the silicon nitride substrate manufacturing method of this embodiment, these methods can be appropriately selected. Furthermore, in the airflow milling process, which is frequently used in the composite powder formation step, not only can dry milling be achieved, but airflow can also be effectively utilized to achieve classification, or a high-performance airflow classification system can be directly connected to achieve the finest possible classification.

[0056] Thus, in the composite powder forming process, a composite powder that serves as the silicon source for a silicon nitride substrate is formed through the mechanochemical effect generated by micronizing a mixed powder of metallic silicon powder and silicon nitride powder. In other words, the composite powder forming process utilizes the mechanochemical or mechanical alloying reaction generated by micronizing a mixed powder of metallic silicon powder and silicon nitride powder to form a composite powder composed of metallic silicon powder and silicon nitride powder.

[0057] The composite powder is characterized in that it is formed by the adsorption of metallic silicon particles and silicon nitride particles. The composite particles constituting the composite powder formed by metallic silicon powder and silicon nitride powder may include metallic silicon particles coated with silicon nitride powder.

[0058] That is, the composite particles can use metallic silicon particles with a core particle located at the center of the composite particles as the base material. The composite particles have silicon nitride particles that cover all or part of the surface of the core particle, i.e., the metallic silicon particle, or adsorb onto all or part of the surface of the core particle, i.e., the metallic silicon particle.

[0059] The number of silicon nitride particles used to coat all or part of the surface of metallic silicon particles, or adsorbed on all or part of the surface of metallic silicon particles, is greater than the number of nuclei, i.e., metallic silicon particles.

[0060] Furthermore, the average particle size of the silicon nitride particles used to coat all or part of the surface of the metallic silicon particles can be smaller than the average particle size of the nucleus particles, i.e., the metallic silicon particles.

[0061] On the other hand, the composite particles constituting the composite powder formed from silicon metal powder and silicon nitride powder may include silicon nitride particles coated by silicon metal particles. That is, the composite particles may have a core particle, i.e., a silicon nitride particle, located at the center of the composite particles. The composite particles may have silicon metal particles coating all or part of the surface of the core particle, i.e., the silicon nitride particle, or adsorbed onto all or part of the surface of the core particle, i.e., the silicon nitride particle. The number of silicon metal particles used to coat all or part of the surface of the silicon nitride particle is greater than the number of core particles, i.e., silicon nitride particles.

[0062] Furthermore, the average particle size of the metallic silicon particles used to coat all or part of the surface of the silicon nitride particles can be smaller than the average particle size of the core particles, i.e., the silicon nitride particles.

[0063] Therefore, through the mechanochemical effect generated by micronizing a mixed powder of metallic silicon powder and silicon nitride powder, smaller silicon nitride particles can be adsorbed onto the surface of the metallic silicon particles, which have a larger particle size. As a result, the particles constituting the composite powder can form composite particles in which all or part of the surface of the metallic silicon particles located at the center of the composite particles are coated or adsorbed by silicon nitride particles.

[0064] Furthermore, through the mechanochemical effect generated by micronizing a mixed powder formed from silicon nitride powder and metallic silicon powder, smaller metallic silicon particles can be adsorbed onto the surface of silicon nitride with a larger particle size as the base material. As a result, composite particles constituting the composite powder can be formed in which all or part of the surface of the silicon nitride particle at the center of the composite particle is coated or adsorbed with metallic silicon particles. Alternatively, composite particles constituting the composite powder can be formed in which all or part of the surface of the silicon nitride particle at the center of the composite particle is adsorbed with metallic silicon particles.

[0065] Metallic silicon particles may be present on the surface of the composite particles constituting the composite powder. Furthermore, a layer of metallic silicon particles, formed by the aggregation of metallic silicon particles, may be formed on the surface of the composite particles constituting the composite powder. The metallic silicon particles present on the surface of the composite particles are nitrided in the nitriding process of the sheet containing the composite powder, described later, thereby becoming silicon nitride particles. Furthermore, all the metallic silicon particles present on the surface of the composite particles become silicon nitride. Ultimately, the composite powder is formed solely from silicon nitride particles.

[0066] Furthermore, silicon nitride particles may also be present on the surface of the composite particles constituting the composite powder. Further, metallic silicon particles may also be exposed from the surface of the composite particles constituting the composite powder. The metallic silicon particles exposed from the surface of the composite particles are nitrided in the nitriding process of the sheet containing the composite powder, described later, thereby becoming silicon nitride particles. Furthermore, all the metallic silicon particles present on the surface of the composite particles become silicon nitride. Ultimately, the composite powder is formed solely from silicon nitride particles.

[0067] <Second Process: Process of forming the slurry for sheet formation> The method for manufacturing a silicon nitride substrate according to this embodiment includes a slurry forming step, in which a sintering aid and a dispersion medium are mixed in the composite powder to form a slurry for sheet formation in which the sintering aid is dispersed in the composite powder. The slurry forming step is a step of forming a raw material slurry used to manufacture a sheet that serves as a precursor for a silicon nitride substrate.

[0068] In the slurry formation process, rare earth element compounds and magnesium compounds, acting as sintering aids, are added to the composite powder, and a dispersion medium is added for mixing to form a raw material slurry. The dispersion medium used for forming the raw material slurry can be water or an organic solvent, and an organic binder (organic binder) can be used as needed. The raw material slurry can be formed by adding the composite powder, sintering aid, dispersion medium, etc., and mixing them using conventional methods such as ball milling, bead milling, or planetary ball milling.

[0069] In the slurry forming process, the composite powder and sintering aid can be pre-mixed as a mixed powder, and then the mixed powder can be mixed with a dispersion medium, etc. Alternatively, in the slurry forming process, the composite powder and sintering aid can be weighed separately, and each powder of the composite powder and sintering aid can be fed into a ball mill or the like containing a dispersion medium, etc., and the mixed powder of the composite powder and sintering aid and the dispersion medium can be mixed simultaneously.

[0070] As described below, in the method for manufacturing a silicon nitride substrate according to this embodiment, a slurry for forming a wafer containing metallic silicon powder is formed, a degreased wafer-shaped body is obtained by removing the binder contained in the wafer formed by the slurry for forming a wafer, and after a nitriding process of nitriding the silicon contained in the degreased wafer-shaped body, a sintering process is performed to manufacture a silicon nitride substrate.

[0071] However, silicon nitride is difficult to sinter; it cannot be sintered on its own, thus it is impossible to obtain a silicon nitride sintered body with a dense structure. Therefore, in order to sinter silicon nitride and obtain a silicon nitride sintered body with a dense structure, sintering aids need to be added.

[0072] Furthermore, in order to improve the thermal conductivity of the silicon nitride sintered body, it is necessary to reduce the oxygen content of the dissolved oxygen in the silicon nitride particles contained in the silicon nitride sintered body, and to reduce the low thermal conductivity grain boundary glass phase constituting the silicon nitride sintered body. Therefore, in the silicon nitride substrate manufacturing method of this embodiment, by selecting a sintering aid in the slurry formation process, the high thermal conductivity of the silicon nitride substrate can be achieved.

[0073] Furthermore, in order to reduce the amount of dissolved oxygen in silicon nitride particles in the silicon nitride sintered body, it is preferable to use rare earth element compounds with high oxygen affinity and excellent oxygen-capturing ability in the grain boundary glass phase as sintering aids. In addition, in order to reduce the low thermal conductivity grain boundary glass phase in the silicon nitride sintered body, it is preferable to use magnesium compounds that can lower the melting point of the melt generated during heating, promote densification in the early stages of sintering, and evaporate and disperse during high-temperature sintering as sintering aids.

[0074] Therefore, in the slurry forming process, rare earth element compounds and magnesium compounds can preferably be used as sintering aids. The rare earth element compounds and magnesium compounds used as sintering aids can be prepared together with the composite powder used as a silicon source as raw materials for the raw slurry.

[0075] The amount of rare earth element compound added is as follows: When converting silicon in the raw material powder to silicon nitride, it is preferable to add the rare earth element compound in such a way that the raw material powder contains 1.0 mol% or more and 7.0 mol% or less of rare earth element compound as oxides. The amount of rare earth element compound added (molar concentration) refers to the molar concentration of rare earth element compound in the three components of the composite powder, the rare earth element compound, and the magnesium compound, which serve as the silicon supply source, and the same applies to the following description.

[0076] Rare earth element compounds have a high affinity for oxygen and excellent ability to capture oxygen from the grain boundary glass phase that constitutes the silicon nitride substrate. Therefore, when the amount of rare earth element compound added is less than 1.0 mol%, it cannot capture oxygen in the grain boundary glass phase, leading to an increase in the amount of dissolved oxygen in the silicon nitride particles and a decrease in the thermal conductivity of the silicon nitride substrate, which is therefore not preferred. Furthermore, when the amount of rare earth element compound added is greater than 7.0 mol%, the amount of low thermal conductivity grain boundary phase containing rare earth element compounds increases, which may lead to a decrease in the thermal conductivity of the silicon nitride substrate.

[0077] In particular, when the silicon in the metallic silicon powder is converted into silicon nitride, it is more preferable to add the rare earth element compound in such a way that the raw material slurry contains 1.5 mol% or more and 5.0 mol% or less of rare earth element compound in terms of oxide content, and even more preferably to add the rare earth element compound in such a way that the rare earth element compound contains 2.0 mol% or more and 4.0 mol% or less of rare earth element compound.

[0078] In rare earth element compounds, preferably, the rare earth element contained in the compound includes one or more elements selected from Y, Sc, La, Ce, Nd, Sm, Gd, Dy, Ho, Er, and Yb. Rare earth element oxides can be cited as examples of rare earth element compounds. Specifically, yttrium oxide, cerium oxide, ytterbium oxide, or scandium oxide are preferred as rare earth element compounds. The rare earth element compound is not limited to one type; two or more rare earth element compounds can be used simultaneously.

[0079] The amount of magnesium compound added is: when converting silicon in the composite powder to silicon nitride, it is preferred to contain 8.0 mol% or more and 15.0 mol% of magnesium compound in terms of oxide conversion. The content (molar concentration) of magnesium compound refers to the molar concentration of magnesium compound among the three components in the composite powder: silicon supply source, rare earth element compound, and magnesium compound.

[0080] When silicon nitride sintered bodies are manufactured by adding only rare earth element compounds as sintering aids, densification requires sintering in a high nitrogen pressure environment of approximately 10 MPa and at ultra-high temperatures of up to 2000 °C. This necessitates the use of specialized sintering furnaces, thus increasing process costs. Furthermore, sintering the silicon nitride body at ultra-high temperatures leads to significant grain growth in the constituent particles, resulting in a decrease in the mechanical properties of the silicon nitride sintered body.

[0081] From this technical perspective, in order to achieve high strength and high toughness in the silicon nitride sintered body by promoting densification during post-sintering, it is preferable to add a magnesium compound as a sintering aid along with a rare earth element compound. By adding the magnesium compound, magnesium ions become modifying ions for the oxynitride glass generated during heating, reducing the viscosity of the oxynitride glass and promoting the densification of the silicon nitride sintered body structure. Furthermore, the magnesium compound evaporates and disperses during sintering, reducing the amount of residual grain boundary phase.

[0082] When the amount of magnesium compound added is less than 8.0 mol%, the magnesium will volatilize before sintering shrinkage, making it impossible to obtain a dense silicon nitride sintered body. Furthermore, when the amount of magnesium compound added is more than 15.0 mol%, a large amount of magnesium will remain even after the sintering process, potentially hindering the thermal conductivity of the sintered body. Therefore, when converting silicon in the composite powder to silicon nitride, it is preferable to add the magnesium compound in an oxide-based manner, containing 8.0 mol% or more but less than 15.0 mol%.

[0083] As magnesium compounds, for example, magnesium silicides, fluorides, borides, nitrides, and their ternary compounds can be used. In particular, considering ease of operation, stability during the process, and the absence of harmful substances, it is preferable that the magnesium compound added to the raw material powder comprises one or more magnesium compounds selected from magnesium oxide (MgO), magnesium silicide (Mg₂Si), or magnesium silicon nitride (MgSiN₂). Furthermore, more preferably, the magnesium compound added to the raw material powder is one or more magnesium compounds selected from magnesium oxide (MgO), magnesium silicide (Mg₂Si), or magnesium silicon nitride (MgSiN₂).

[0084] The slurry raw material formed in the slurry forming process described above is a mixed powder consisting of composite powder as a silicon supply source, rare earth element compounds, and magnesium compounds. Alternatively, instead of weighing and mixing the individual powders in the raw material powder, the raw material slurry can be mixed and pulverized together with other components contained in the raw material slurry during the slurry forming process.

[0085] In the slurry forming process, there are no particular limitations on the type, amount, or method of adding the dispersion medium, organic binder, and dispersant when preparing the raw material slurry for forming sheets. They can be selected arbitrarily according to the method of forming sheets.

[0086] The following describes specific conditions for adding sintering aids, dispersion media, and organic binders to composite powders in the slurry forming process to form raw material slurry.

[0087] Weigh the composite powder and sintering aid. Prepare a grinding vessel, such as a ball mill, containing 0.5-2 wt% dispersant and 30-70 wt% organic solvent relative to the total amount of composite powder and sintering aid. Add the composite powder and sintering aid to the grinding vessel equipped with the grinding apparatus containing the dispersant. Examples of grinding apparatus include air jet mills, ball mills, planetary ball mills, and vertical stirred ball mills. Sorbitan ester or polyoxyalkylene dispersant can be used. Ethanol or toluene can be used as the organic solvent for the dispersion medium. It should be noted that a dispersion medium can also be used without adding a dispersant. The raw material powder can be mixed and pulverized using a ball mill.

[0088] The time for mixing and pulverizing varies depending on the function of the grinding equipment used, the amount of composite powder as the starting material, and the amount of sintering aid, and is therefore not particularly limited. However, it is preferable to select a time that allows for sufficient pulverization and mixing of the composite powder and sintering aid. The mixing and pulverizing time is preferably 6 hours or more and 48 hours or less, more preferably 12 hours or more and 24 hours or less.

[0089] If the mixing and pulverizing time is less than 6 hours, the sintering aid cannot be uniformly mixed into the raw material slurry, resulting in in-plane unevenness on the nitrided sheet after sintering, which is therefore undesirable. On the other hand, if the mixing and pulverizing time exceeds 48 hours, which is too long, even if the composite powder and sintering aid are mixed and pulverized, their mixing state will not change significantly, and impurities may be introduced from the grinding balls or grinding jar.

[0090] It should be noted that in the slurry forming process, after the composite powder and sintering aid are mixed and pulverized, the dispersion medium contained in the raw material slurry can be removed as needed.

[0091] Furthermore, after pulverization and mixing, an organic binder (organic binder) of 5-30 wt% or less can be added and mixed again to produce a slurry for sheet formation. There are no particular limitations on the organic binder; for example, PVB-based (polyvinyl butyral) resins, ethyl cellulose-based resins, or acrylic resins are preferred.

[0092] Regarding the mixing time after adding the organic binder, it varies depending on the performance of the mixing device such as the grinding device, so there is no particular limitation. However, it is preferred to be 1 hour or more and 24 hours or less, and more preferably 6 hours or more and 12 hours or less.

[0093] This is because when the mixing time is less than 1 hour, cracks may occur in the resulting sheet when the organic binder and raw material powder are not uniformly mixed before sheet forming, which is therefore undesirable. Furthermore, even with mixing times longer than 24 hours, the mixing state of the organic binder and raw material powder does not change significantly; therefore, from a production point of view, a mixing time of 24 hours or less is preferred.

[0094] After adding an organic binder and mixing, the viscosity of the slurry is adjusted by vacuum degassing, thus forming a sheet-forming slurry. In this way, the sheet-forming slurry formed in the second step can be coated onto a sheet-forming substrate using a sheet forming machine, and the sheet can be formed in the next step, the sheet forming process.

[0095] Here, the viscosity of the slurry for sheet formation is 100-200 cps before vacuum degassing and 6000-7000 cps after vacuum degassing. As a result, the slurry for sheet formation after vacuum degassing becomes a slurry suitable for forming sheets.

[0096] <Third Process: Sheet Forming Process> The method for manufacturing a silicon nitride substrate according to this embodiment includes a sheet forming step, which involves molding the sheet-forming slurry to form a sheet. The sheet forming step is a process of molding a sheet-forming slurry having a specified composition and a specified viscosity into a sheet shape to form a sheet. The sheet-shaped formed body is a green sheet.

[0097] Specifically, as described above, after mixing the composite powder, sintering aid and dispersion medium using a ball mill or planetary ball mill, removing the dispersion medium as needed, and adding an organic binder, the sheet forming slurry is molded into sheets to form sheets.

[0098] The method of forming a sheet from a sheet-forming slurry containing raw material composite powder, sintering aid, dispersion medium and binder is not particularly limited as long as the method can form a sheet from the sheet-forming slurry. For example, die forming, sheet forming, extrusion forming, cold isostatic pressing (CIP forming) and the like can be used.

[0099] The shape and size of the sheet formed in the sheet forming process are not particularly limited, and can be set to any shape and thickness according to the required shape and thickness when used as a silicon nitride substrate. For example, the thickness of the sheet formed in the sheet forming process is preferably 0.05-2.5 mm, more preferably 0.25-1.0 mm. It should be noted that in the sheet forming process, the obtained sheet can be cut into the specified size using a punching machine or the like as needed.

[0100] The relative density of the sheet obtained in the sheet forming process is preferably 45% or more, more preferably 50% or more. If the sheet formed in the sheet forming process is cut into a specified size, the relative density of the cut sheet is preferably 45% or more.

[0101] In the wafer forming process, the relative density of the formed wafer can be adjusted by the amount of raw material powder (solid concentration) contained in the wafer forming slurry formed in the wafer forming slurry forming process and the amount of binder added to the slurry. Here, since the relative density of the wafer formed in the wafer forming process is 45% or more, the porosity of the wafer can be sufficiently reduced, thereby resulting in a higher sintering density of the silicon nitride substrate obtained after the subsequent sintering process, which is preferred.

[0102] There is no particular upper limit to the relative density of the sheet formed in the sheet forming process. To increase the relative density of the sheet, it is necessary to increase the solids concentration of the sheet forming slurry by reducing the amount of binder or the like used in the sheet forming slurry forming process. If the solids concentration of the sheet forming slurry increases, cracks or other defects may occur in the sheet formed from that slurry, making its operation difficult. Therefore, the relative density of the sheet obtained in the sheet forming process is preferably 65% ​​or less, more preferably 60% or less.

[0103] <Fourth step: Degreasing process to form degreased tablets> Furthermore, the method for manufacturing the silicon nitride substrate according to this embodiment includes a degreasing step, wherein the wafer is heated at 250-600°C to remove the resin components (binders) contained in the wafer, thereby forming a degreased wafer. In the degreasing step, the resin components (binders, etc.) contained in the wafer can be completely removed by heating the wafer formed in the wafer forming step in an atmosphere of an inert gas such as air or nitrogen, or a mixture thereof. The residual carbon content contained in the wafer is 0.01% or less.

[0104] In the fourth process, the temperature of the heated sheet can be appropriately set according to the planar shape of the sheet, the thickness of the sheet, and the amount of binder as a resin component contained in the sheet.

[0105] <Fifth step: Nitriding process to form nitrided sheets> The method for manufacturing a silicon nitride substrate according to this embodiment includes a nitriding step, wherein the degreased wafer is heated at 1200-1500°C to nitride the silicon contained in the degreased wafer to form a nitrided wafer. In the nitriding step, by heating the wafer formed in the wafer forming step in an inert gas atmosphere such as nitrogen, all the constituent components, namely the metallic silicon powder, contained in the degreased wafer can be nitrided after obtaining the degreased wafer.

[0106] The wafer formed in the wafer forming process comprises a composite powder formed from metallic silicon powder and silicon nitride powder. The composite particles constituting the composite powder include metallic silicon particles coated with silicon nitride particles. Further, in the composite particles, silicon nitride particles are adsorbed on all or part of the surface of the core particle, i.e., the metallic silicon particle, located at the center of the composite particle.

[0107] On the other hand, the composite particles constituting the composite powder include composite particles in which metallic silicon particles are adsorbed onto silicon nitride particles, and the metallic silicon particles can be exposed from the composite particles. It includes silicon nitride particles coated with metallic silicon particles. Further, in the composite particles, the metallic silicon particles are adsorbed onto all or part of the surface of the core particle, i.e., the silicon nitride particle, located at the center of the composite particle.

[0108] Furthermore, the composite particles constituting the composite powder include composite particles in which metallic silicon particles are adsorbed onto silicon nitride particles, and the metallic silicon particles can be exposed from the composite particles.

[0109] In the nitriding process, the silicon metal particles present on the surface of the composite particles are nitrided to become silicon nitride particles. Furthermore, all the silicon metal particles present on the surface of the composite particles become silicon nitride. Additionally, in the nitriding process, the silicon metal particles exposed from the surface of the composite particles are nitrided to become silicon nitride particles. Again, all the silicon metal particles exposed from the surface of the composite particles become silicon nitride.

[0110] Ultimately, the silicon source contained in the wafer formed in the wafer forming process, which serves as the raw material for the silicon nitride substrate, is formed from the silicon nitride powder initially prepared and the silicon nitride powder generated by the nitriding reaction.

[0111] Furthermore, before starting the fifth step of the nitriding process, it is necessary to remove the gases present in the furnace that are part of the silicon nitriding reaction used for degreasing the wafers. To do this, the furnace can be depressurized and evacuated first, then nitrogen can be supplied to the furnace before starting the nitriding process. The pressure at which the furnace is depressurized and evacuated before supplying nitrogen is not particularly limited; for example, it is preferable to depressurize to below 1.0 Pa, and more preferably to evacuate to below 0.1 Pa.

[0112] The heating temperature for the degreasing treatment of the tablets in the nitriding process is not particularly limited, but is preferably 600°C or higher and 1500°C or lower, more preferably 1000°C or higher and 1480°C or lower. The treatment time for the degreasing treatment of the tablets in the nitriding process is preferably within the range of 1 hour or higher and 20 hours or lower, and more preferably within the range of 5 hours or higher and 15 hours or lower.

[0113] When the heating temperature of the degreased wafer in the nitriding process is above 1000°C, or the processing time of the nitriding process is above 1 hour, it is preferred because there will be no unreacted silicon powder remaining in the degreased wafer, and the sintering process of the degreased wafer will not result in a silicon nitride sintered body with a dense structure.

[0114] On the other hand, when the nitriding reaction is carried out at a temperature of 1480°C or below during the nitriding process, or when the nitriding process takes less than 15 hours, the sintering aid component contained in the degreased sheet volatilizes, resulting in insufficient sintering aid content during the sintering process. As a result, even if the degreased sheet is sintered, it is not difficult to obtain a silicon nitride sintered body with a dense structure, which is therefore preferable.

[0115] In the nitriding process, there are no particular limitations on the method of heating the degreased sheet. For example, the degreased sheet can be stacked between hexagonal boron nitride (BN) powder or hexagonal boron nitride (BN) plates for demolding, and then carried out in a vacuum / pressurized atmosphere furnace composed of graphite insulation material and a graphite heater. Here, hexagonal boron nitride powder (h-BN) is a white powder with a scaly crystal structure similar to graphite, and is a material with excellent thermal conductivity, heat resistance, corrosion resistance, electrical insulation, and lubrication / demolding properties.

[0116] The vacuum / pressurized atmosphere furnace used for the nitriding treatment of the degreased sheets can be, for example, a sealed box furnace. By using such a vacuum / pressurized atmosphere furnace, the gases generated inside the furnace can be vented outside the furnace.

[0117] Furthermore, by using a closed-box furnace, which is one of the vacuum / pressurized atmosphere furnaces, for example, when performing the binder removal process to remove the organic binder used in the molding of the wafer, the binder removal process, the nitriding process, and then the sintering process can be performed using one of the aforementioned furnaces. Thus, in the nitriding process included in the silicon nitride substrate manufacturing method of this embodiment, the productivity of the silicon nitride substrate can be improved by using a vacuum / pressurized atmosphere furnace.

[0118] Furthermore, during the nitriding of the degreased wafer containing composite powder, the degreased wafer does not undergo dimensional changes, but its weight increases. Therefore, the relative density of the degreased wafer after nitriding increases by about 15% compared to the degreased wafer before nitriding, making it easier to densify the silicon nitride wafer in the next process, namely the sintering process.

[0119] Furthermore, the increased relative density of the degreased wafer after nitriding has the following advantages: in the next step, the sintering process, the sintering time of the silicon nitride wafer can be shortened, and excessive grain growth that adversely affects mechanical properties can be prevented. Therefore, in the silicon nitride substrate manufacturing method of this embodiment, since reaction sintering is utilized, it has excellent characteristics from the perspective of achieving high thermal conductivity of the silicon nitride substrate.

[0120] <Sixth Process: Sintering of the Nitrided Sheets> The method for manufacturing a silicon nitride substrate according to this embodiment includes a sintering process, in which a silicon nitride substrate is formed by sintering the silicon nitride sintered body formed by sintering the nitride-treated sheet.

[0121] That is, the sintering process, as the final step, is a process of sintering the nitrided wafer formed after the nitriding process in a nitrogen atmosphere. Furthermore, in the sintering process, the nitrided wafer becomes the final product, namely the silicon nitride substrate.

[0122] The heating temperature of the nitrided sheet in the sintering process is not particularly limited, as long as it can densify the structure of the nitrided sheet. For example, heating at 1700-1950°C is preferred, and heating at 1750-1900°C is more preferred. In the sintering process, the sintering time of the nitrided sheet in a nitrogen atmosphere is preferably 1-48 hours, and more preferably 5-24 hours.

[0123] If the sintering temperature of the nitrided wafer in the sintering process is below 1700°C, or the sintering time is less than 1 hour, the microstructure of the nitrided wafer cannot be sufficiently densified, which is therefore not preferred. On the other hand, if the heating temperature of the sintering process is above 1950°C, or the sintering time exceeds 48 hours, the particles constituting the nitrided wafer may undergo excessive grain growth, resulting in a decrease in the strength of the silicon nitride substrate obtained after sintering the nitrided wafer, which is also not preferred.

[0124] Preferably, the sintering process is performed by heating under a nitrogen atmosphere. The pressure of the nitrogen atmosphere used in the sintering process is not particularly limited; for example, preferably, heating is performed at a pressure that prevents the silicon nitride generated in the nitriding process from decomposing, depending on the heating temperature of the sintering process. Specifically, preferably, the pressure of the nitrogen atmosphere is set to 0.1 MPa or higher, more preferably 0.9 MPa or higher. However, if the pressure of the nitrogen atmosphere is too high, a special furnace with high pressure resistance is required; therefore, for example, the pressure of the nitrogen atmosphere is preferably 1 MPa or lower, more preferably 0.92 MPa or lower.

[0125] By performing a sintering process, a silicon nitride substrate with a relative density of 95% or higher can be obtained. As a result, the silicon nitride substrate obtained after the sintering process can become a dense silicon nitride substrate without a modified layer. Therefore, the silicon nitride substrate obtained after the sintering process, in its unprocessed state, has a thermal conductivity of 85 W / mK or higher, preferably 120 W / mK or higher, as measured by laser scintillation.

[0126] Furthermore, the sintered silicon nitride wafer obtained after the sintering process becomes a silicon nitride substrate manufactured by the silicon nitride substrate manufacturing method of this embodiment. This silicon nitride substrate can be a silicon nitride substrate with β-phase silicon nitride as the main component and containing rare earth elements. The rare earth elements contained in the silicon nitride substrate can be in an elemental state or can form compounds with other substances. In this case, the silicon nitride substrate preferably contains 1.0 mol% or more and 4.0 mol% or less of rare earth elements when converted to oxides. Furthermore, the amount of magnesium in the silicon nitride substrate that has undergone the sintering process is preferably 2.0 mol% or less when converted to oxides. When the silicon nitride substrate that has undergone the sintering process contains magnesium, the magnesium can be in an elemental state or can form compounds with other substances.

[0127] The thickness of the silicon nitride substrate used as the sintered silicon nitride wafer is not particularly limited and can be any thickness. However, for example, when used as a heat-dissipating insulating substrate for semiconductor devices or electronic devices, a thickness of 0.05 mm or more and 2.5 mm or less is preferred. It should be noted that the thickness of the silicon nitride substrate obtained after the sintering process can be selected by adjusting the thickness of the wafer formed in the wafer forming process.

[0128] Therefore, in the silicon nitride substrate manufacturing method of this embodiment, a composite powder containing silicon nitride particles coated with metallic silicon particles is used as the silicon source constituting the silicon nitride substrate. Thus, the silicon nitride substrate manufacturing method of this embodiment does not generate heat due to the rapid nitriding reaction of the metallic silicon particles contained in the metallic silicon powder, and the nitriding reaction proceeds uniformly.

[0129] That is, the method for manufacturing a silicon nitride substrate in this embodiment can use metallic silicon as the silicon source contained in the wafer constituting the silicon nitride substrate, and manufacture a silicon nitride substrate containing silicon nitride obtained by nitriding the metallic silicon.

[0130] As explained above, the silicon nitride substrate manufacturing method according to the first embodiment prevents the heat generated by the rapid nitriding reaction of silicon contained in the metallic silicon powder, allowing the silicon to undergo a uniform nitriding reaction, thereby enabling the manufacture of a silicon nitride substrate with high heat dissipation and excellent mechanical properties. In other words, the silicon nitride substrate manufacturing method of the first embodiment can manufacture a silicon nitride substrate with a thermal conductivity of 80 W / mK or higher as measured by laser scintillation. Furthermore, it is possible to provide a high thermal conductivity silicon nitride substrate manufactured by the silicon nitride substrate manufacturing method of the first embodiment and its application products.

[0131] [Second Embodiment] The manufacturing method of the silicon nitride substrate according to the second embodiment will be described. Based on the above embodiment, the manufacturing method of the silicon nitride substrate according to this embodiment is characterized in that the average particle size D of the metallic silicon particles is... S50 Relative to the average particle size D of the silicon nitride particles SN50 The ratio, i.e., the particle size ratio X, is 0.2-2.0. Hereinafter, the characteristic parts of the method for manufacturing the silicon nitride substrate according to this embodiment will be described.

[0132] The first step in the method for manufacturing a silicon nitride substrate according to this embodiment, namely the step of forming composite powder, is characterized in that the average particle size D of the metallic silicon particles is... S50 Relative to the average particle size D of silicon nitride particles SN50 The ratio, i.e., the particle size ratio X, is 0.2-2.0.

[0133] That is, the method for manufacturing silicon nitride substrate in this embodiment specifies the conditions for achieving metal silicon-silicon nitride particles formed by coating or adsorbing silicon nitride particles with silicon nitride particles as the base material, for the composite particles constituting the silicon source, i.e., composite powder contained in the sintered silicon nitride sheet.

[0134] Furthermore, the method for manufacturing a silicon nitride substrate in this embodiment specifies conditions for achieving metal-silicon nitride particles formed by coating or adsorbing silicon nitride particles with metal silicon particles as the base material, in the composite particles constituting the silicon source, i.e., the composite powder, contained in the sintered silicon nitride wafer. In other words, the morphology is that silicon nitride particles are adsorbed around metal silicon particles, and a structure opposite to the structure of the aforementioned composite particles can also be formed.

[0135] In other words, in the method for manufacturing a silicon nitride substrate according to this embodiment, the structure of the composite particles constituting the silicon source, i.e., the composite powder, contained in the sintered silicon nitride wafer can be appropriately selected based on the average particle size of the silicon nitride particles used as raw materials for the composite powder before imparting the mechanochemical effect generated by the micronization process, the average particle size of the metallic silicon particles, the micronization process conditions, and the nitriding reaction conditions.

[0136] Composite powders are formed by mixing metallic silicon powder with silicon nitride powder and imparting the resulting mechanochemical effects through micronization. Furthermore, the micronization process is selected from any one of air jet milling, ball milling, planetary ball milling, and vertical stirred ball milling, or a combination thereof.

[0137] From this technical perspective, the method for manufacturing a silicon nitride substrate according to this embodiment, in its first step, controls the particle size D of the metallic silicon particles constituting the metallic silicon powder. S50 The particle size D of silicon nitride that constitutes silicon nitride powder SN50 This results in composite microparticles in which the entire surface of the parent material, i.e., silicon nitride particles, is uniformly coated with metallic silicon particles, or metallic silicon particles are adsorbed on all or part of the surface of silicon nitride particles.

[0138] Furthermore, in the silicon nitride substrate manufacturing method of this embodiment, in its first step, the particle size D of the metallic silicon particles constituting the metallic silicon powder is controlled. S50 The particle size D of silicon nitride that constitutes silicon nitride powder SN50 This results in the formation of composite microparticles where the entire surface of the nucleus particles or the parent material, i.e., the metallic silicon particles, is uniformly coated with silicon nitride particles, or where silicon nitride particles are adsorbed onto all or part of the surface of the metallic silicon particles.

[0139] In the silicon nitride substrate manufacturing method of this embodiment, the average particle size D of the metallic silicon particles is... S50 Relative to the average particle size D of silicon nitride particles SN50The ratio, i.e. the particle size ratio X, can be expressed by the following formula (1).

[0140] Particle size ratio X = Average particle size D of metallic silicon particles S50 / Average particle size D of silicon nitride particles SN50 (1) The particle size ratio X can be set by comprehensively considering the particle size of the metallic silicon particles and the particle size of the silicon nitride particles contained in the composite microparticles. If the particle size ratio X is 0.2 or higher, it is preferable because silicon nitride particles can be adsorbed on the surface of the core particles, i.e., the metallic silicon particles, that constitute the composite powder microparticles.

[0141] If the particle size ratio X is 2.0 or less, it is preferable because the silicon nitride particles are not adsorbed on the surface of the core particles that constitute the composite powder microparticles, namely the metallic silicon particles, and the silicon nitride particles are not fixed to each other.

[0142] It should be noted that the particle size ratio X can be appropriately set according to the particle size of the metallic silicon particles constituting the composite powder, the particle size of the silicon nitride particles, and the micro-pulverization process used for micro-pulverization, selected from any one or a combination thereof, such as air jet milling, ball milling, planetary ball milling, and vertical stirred ball milling.

[0143] Thus, according to the silicon nitride substrate manufacturing method of this embodiment, the average particle size D of the silicon nitride particles is set as the silicon source constituting the silicon nitride substrate. SN50 Relative to the average particle size D of metallic silicon particles S50 The ratio, or particle size ratio X, allows silicon metal particles and silicon nitride particles to adsorb each other. Furthermore, by setting the average particle size D of the silicon nitride particles... SN50 Relative to the average particle size D of metallic silicon particles S50 The ratio of particle size to particle size, X, can form a composite powder containing silicon nitride particles coated with metallic silicon particles.

[0144] Furthermore, by setting the average particle size D of the silicon nitride particles SN50 Relative to the average particle size D of metallic silicon particles S50 The ratio of particle size to particle size, X, can form a composite powder containing metallic silicon particles coated or adsorbed by silicon nitride particles.

[0145] Therefore, in the silicon nitride substrate manufacturing method of this embodiment, there is no heat generated by the rapid nitriding reaction of the exposed metal silicon particles from the silicon nitride particles adsorbed on the surface of the core particles constituting the composite powder microparticles, thereby the nitriding reaction can be carried out uniformly on the entire surface of the metal silicon particles.

[0146] In the silicon nitride substrate manufacturing method of this embodiment, there is no heat generated by the rapid nitriding reaction of the metal silicon particles adsorbed on the surface of the core particles, i.e., silicon nitride particles, which constitute composite powder microparticles, thereby the nitriding reaction can be carried out uniformly on the entire surface of the metal silicon particles adsorbed on the surface of silicon nitride particles.

[0147] That is, the method for manufacturing a silicon nitride substrate in this embodiment can use metallic silicon as the silicon source contained in the wafer constituting the silicon nitride substrate, and manufacture a silicon nitride substrate containing silicon nitride obtained by the nitriding reaction of metallic silicon particles.

[0148] As explained above, the silicon nitride substrate manufacturing method according to the second embodiment prevents the heat generated by the rapid nitriding reaction of the silicon particles contained in the silicon powder, and allows the silicon to undergo a uniform nitriding reaction, thereby enabling the manufacture of a silicon nitride substrate with high heat dissipation and excellent mechanical properties.

[0149] [Other Implementation Methods] The present invention has been described above with reference to embodiments, but the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention. Furthermore, systems or apparatuses that combine the individual features included in the various embodiments in any manner are also included within the scope of the present invention.

[0150] [Example] The effects of the present invention will be specifically described below based on the embodiments, but the present invention is not limited to these embodiments.

[0151] <Example 1 of the Invention> A silicon nitride substrate was manufactured using the silicon nitride substrate manufacturing method of the present invention as follows. Furthermore, various characteristics of the silicon nitride substrate obtained using the silicon nitride substrate manufacturing method of the present invention were evaluated.

[0152] As the silicon metallic powder, a powder with a purity of 99.0%, an average particle size of 25.0 μm, and an oxygen impurity content of 0.40% by mass was prepared. As the silicon nitride powder, β-silicon nitride powder (manufactured by Shinano Electric Manufacturing Co., Ltd.) with a purity of 99.0% and an average particle size of 40.0 μm was prepared. The oxygen impurity content of the silicon metallic powder was determined using a nitrogen / oxygen simultaneous analysis apparatus (Horiba Manufacturing Co., Ltd., model: EMGA-20E).

[0153] (Composite formation process: Powder preparation) As an apparatus required for mixing metallic silicon powder and β-silicon nitride powder to form a metallic silicon-silicon nitride composite, an air jet milling apparatus (Kurimoto Iron Works Co., Ltd. model: KJ-25) was prepared. After weighing and mixing metallic silicon powder and silicon nitride powder in a prescribed ratio, the aforementioned air jet milling apparatus was used to mix the metallic silicon powder and β-silicon nitride powder to form a metallic silicon-silicon nitride composite. Thus, the composite powder manufactured in Invention Example 1 is designated as Powder Type No. 1.

[0154] The manufacturing conditions for powder type No. 1 are as follows: rotor speed: 12000 rpm, nozzle pressure: 0.60 MPa; pulverizing of silicon metal powder and β-silicon nitride powder; and synthesis of a composite powder composed of silicon metal and silicon nitride. The formation conditions of the composite powder are adjusted so that the average particle size of the particles constituting the silicon metal and silicon nitride composite powder is 2.0-3.0 μm.

[0155] Table 1 shows the formation conditions of composite powder composed of metallic silicon and silicon nitride, namely powder type No. 1.

[0156] [Table 1]

[0157] (Preparation of slurry for sheet formation) Next, a substrate forming slurry is prepared, which includes the composite powder (powder type No. 1) used in Example 1 of the Invention, a sintering aid, a dispersion, and a binder. The amounts of the composite powder (powder type No. 1), rare earth compound, magnesium compound, dispersion, and binder used in Example 1 for manufacturing the silicon nitride substrate are shown in Table 2.

[0158] As shown in Table 2, magnesium oxide powder (manufactured by Kyowa Chemical Industry Co., Ltd.) with an average particle size of 0.5 μm or magnesium silicon nitride powder with an average particle size of 1.0 μm was used as the sintering aid contained in the slurry for sheet formation, which includes raw material composite powder, sintering aid, dispersion medium and binder. Furthermore, yttrium oxide powder (manufactured by Shin-Etsu Chemical Industry Co., Ltd.) with an average particle size of 1.5 μm was used as the rare earth element compound.

[0159] Table 2 only shows the proportions of magnesium compounds and rare earth element compounds; the rest is silicon powder, i.e., powder type No. 1.

[0160] The molar ratios shown in Table 2 are the molar ratios assuming that silicon (Si) is completely nitrided to silicon nitride (Si3N4), converting silicon to silicon nitride, and converting magnesium compounds to magnesium oxide (MgO).

[0161] [Table 2]

[0162] Using ethanol as the dispersion medium, the prepared powder No. 1 was pulverized and mixed for 24 hours using a silicon nitride ball mill in a resin tank and with silicon nitride balls. Ethanol, pre-weighed to a slurry concentration of 50 wt%, was added to the resin tank. After pulverizing and mixing the composite powder, 14.3 wt% of an organic binder, i.e., a resin binder (Sekisui Chemicals, trade name "Esurek"), was added, and the mixture was mixed for another 24 hours.

[0163] Then, the viscosity was adjusted using a vacuum degassing machine (manufactured by Yingxing Co., Ltd.) to prepare a coating slurry. The viscosity of the viscosity-adjusted coating slurry was adjusted to 300 mPa·s.

[0164] (Forming of the sheet) The slurry for forming a sheet, after viscosity adjustment, was used to form a sheet with a thickness of 0.4 mm using a doctor blade coating machine (manufactured by Sansho Kogyo Co., Ltd.). After forming the sheet with the slurry, the formed sheet was cut into 50×50×0.4 mm pieces, and the relative density of the sheet was evaluated.

[0165] The relative density of the sheets was evaluated by length measurement. The results showed that the relative density of the obtained sheets was 60%-70%.

[0166] (Manufacturing of degreased tablets) The sheets manufactured in the sheet forming process are formed and evaluated. Then, boron nitride powder (hereinafter also referred to as "BN powder") is coated onto the surface of the sheets. Twelve degreased sheets coated with BN powder are stacked as a group and placed in a boron nitride container (hereinafter also referred to as "BN crucible"). Then, the BN crucible containing the twelve degreased sheets coated with BN powder is placed in a box furnace (manufactured by Motoyama Corporation, model: DC-6060) and heated at 600°C for 60 hours in an atmospheric atmosphere to perform a binder removal process. That is, by degreasing the resin component binder contained in the sheets formed from the sheet forming slurry, degreased sheets are obtained.

[0167] (Manufacturing of nitride sheets) The BN crucible containing the degreased sheet was placed in a vacuum / pressurized atmosphere furnace (Shimadzu Corporation model: PVLgr10 VESTA). The furnace pressure was first reduced to 10. －1 The pressure was increased to 0.1 MPa, and then nitrogen gas was introduced into the furnace. Nitriding was carried out at 1480 °C for 8 hours in a nitrogen atmosphere of 0.1 MPa. 99.9% by volume nitrogen was used as the nitrogen gas.

[0168] The degreased tablet obtained in this way was used as the nitrided tablet in Manufacturing Example 1. In Example 1, the heating rate used to obtain the nitrided tablet was set to 0.2°C / min.

[0169] (Sintering of nitride sheets) Next, as a post-sintering step, the nitrided sheet that had undergone nitriding treatment in the nitriding process was sintered under specified conditions for the sample of Manufacturing Example 1. The sintered nitrided sheet of Manufacturing Example 1 was used as the silicon nitride substrate of Invention Example 1. X-ray diffraction (Rigaku Corporation, Model: Mini Flex600) was performed on the silicon nitride substrate obtained in Invention Example 1. The X-ray diffraction results are shown in Table 3. As shown in Table 3, it is clear that no residual silicon was detected in the silicon nitride substrate.

[0170] It should be noted that the sintering of the nitrided sheets is carried out using the same vacuum / pressurized atmosphere furnace as the nitriding process. Similarly, the stacked nitrided sheets are placed in a BN crucible, and then the BN crucible is placed in a vacuum / heated atmosphere furnace for the process.

[0171] <Determination and Evaluation of Various Properties of Silicon Nitride Substrates> After sintering the silicon nitride wafer, the sintered silicon nitride wafer is taken out of the BN crucible and the BN powder and other adhering materials on the surface are removed using a sandblasting device (made by Fuji Seisakusho). As the final product, a silicon nitride substrate is made.

[0172] The microstructure of the silicon nitride substrate thus manufactured was observed and evaluated. Furthermore, various properties of the silicon nitride substrate were measured. Specifically, the microstructure of the silicon nitride substrate was observed, and its relative density, thermal conductivity, and mechanical properties (three-point bending strength and fracture toughness) were measured. The results and evaluations of the various properties of the silicon nitride substrate are shown in Table 3.

[0173] (Organizational observation) The silicon nitride substrate manufactured in Example 1 was subjected to microstructural observation. The microstructure of the silicon nitride substrate was observed by grinding a cross-section of the substrate and using a scanning electron microscope (SEM) (manufactured by Nippon Electron Ltd., model: JSM-IT210). Table 3 shows the SEM observation results of the cross-section of the silicon nitride substrate manufactured in Example 1. It should be noted that the evaluation of the microstructure observation is as follows.

[0174] 〇: Sintered bodies that allow for microstructural observation -: Sintered bodies that have become low-density due to melting and whose microstructure has not been observed. Figure 2 shows a cross-sectional SEM image of the silicon nitride substrate manufactured in Example 1 of the invention. Figure 2 is an SEM image of the microparticles of the composite powder used in the manufacturing method constituting the silicon nitride substrate. Figure 2A These are SEM images of the metallic silicon particles and silicon nitride particles that make up the composite powder before they are pulverized. Figure 2B These are SEM images of the metallic silicon particles and silicon nitride particles that make up the composite powder after they have been pulverized.

[0175] As shown in Figure 2, the composite powder obtained by the mechanochemical effect produced by micronization shows that the particle size of the composite particles constituting the composite powder is smaller compared with that before the composite powder synthesis (before the mechanochemical effect).

[0176] Next, after observing the cross-section of the silicon nitride substrate manufactured in Example 1 using SEM, the elements contained in the silicon nitride substrate were identified using energy dispersive X-ray spectroscopy (EDS). Figure 3-4 This refers to a two-dimensional image obtained by distinguishing element distributions by color based on element peak information detected using EDS in Example 1 of the invention. Figure 3 This is an EDS image of the metallic silicon particles and silicon nitride particles that make up the composite powder after they have been pulverized. Figure 4 It is a magnified image of the EDS image of the metallic silicon particles and silicon nitride particles that make up the composite powder after they have been pulverized.

[0177] like Figure 3-4 As shown, nitrogen is clearly distributed on a portion of the surface of the composite particles constituting the composite powder. This confirms that silicon nitride particles are bonded to the surface of metallic silicon particles and thus composited.

[0178] Furthermore, Figure 5 The diagram shows a composite silicon particle, which is a metallic silicon particle constituting the composite powder used in Example 1 of the invention. The composite silicon particle is manufactured with microparticles composed of a sintering aid (magnesium compound) dispersed on the surface of the metallic silicon particle, and an SEM image of the composite silicon particle is shown. Figure 6 EDS image showing composite silicon particles in which the surface of metallic silicon particles constituting the composite powder is dispersed with microparticles composed of sintering aids.

[0179] like Figure 5-6 As shown, it can be clearly seen that microparticles composed of sintering aids are uniformly dispersed on the surface of metallic silicon particles.

[0180] By using these metallic silicon particles as a component of the composite powder, and combining them with the addition of sintering aids for manufacturing slurry for wafer formation, the sinterability of the silicon nitride particles contained in the wafer can be further improved.

[0181] (Determination of relative density) The relative density of the silicon nitride substrate manufactured in Example 1 of the Invention was measured. The relative density of the silicon nitride substrate was determined by phase identification using X-ray diffraction and performed according to the Archimedes method. Table 3 shows the results of the relative density measurement of the silicon nitride substrate manufactured in Example 1 of the Invention.

[0182] (Determination of thermal conductivity) The thermal conductivity of the silicon nitride substrate manufactured in Example 1 of the Invention was measured. The thermal conductivity of the silicon nitride substrate was specifically measured as follows: The manufactured silicon nitride substrate was cut into 10mm square pieces, and gold plating (Sanyu Electronics Co., Ltd. model: SC-701AT) was applied to the surface. The thermal conductivity was measured using a xenon lamp flash method (NETZSCH Japan Co., Ltd. model: LFA467). Table 3 shows the measurement results of the thermal conductivity of the silicon nitride substrate manufactured in Example 1 of the Invention.

[0183] (Determination of mechanical properties) The mechanical properties of the silicon nitride substrate manufactured in Example 1 of the Invention were measured. Three-point bending strength and fracture toughness were selected as the mechanical properties of the silicon nitride substrate. The mechanical properties of the silicon nitride substrate were measured in the following manner. Specifically, the three-point bending strength (ISO 23242:2020) and fracture toughness (ISO 21113:2018) of the manufactured silicon nitride substrate were measured and evaluated according to ISO standards. Table 3 shows the measurement results of the mechanical properties of the silicon nitride substrate manufactured in Example 1 of the Invention.

[0184] [Table 3]

[0185] First, as shown in Figure 2, the silicon nitride substrate was cross-sectionally ground, and the phase composition of the silicon nitride substrate was identified by X-ray diffraction based on scanning electron microscopy (SEM) images. It was confirmed that silicon nitride was obtained from the metallic silicon powder used in Example 1 of the Invention. The SEM observation results also confirmed that the pores were few and the structure was bimodal.

[0186] Furthermore, SEM observation of the cross-section of the silicon nitride substrate manufactured in Example 1 confirms that there is no altered layer.

[0187] The measurement results of the silicon nitride substrate shown in Table 3 clearly indicate that the silicon nitride substrate produced in Example 1 of the Invention is a dense body with a relative density of 99% or more and a thermal conductivity of about 80 W / mK.

[0188] <Invention Examples 2-24, Comparative Examples 1-16> Except for changing the raw materials (powder type, magnesium compound), raw material composition, formation conditions of the composite as powder type, heating rate during degreasing treatment of the sheet, and sintering conditions, silicon nitride substrates of Invention Examples 2-24 and Comparative Examples 1-16 were manufactured in the same manner as Invention Example 1.

[0189] Specifically, powder type No. 2-10, with modified manufacturing conditions, was used as the powder type constituting the silicon nitride substrate manufactured in Examples 2-24. Silicon nitride magnesium powder was used as the magnesium compound contained in the sheet forming slurry. In Examples 2-24, the heating rate used during the nitriding treatment of the degreased sheet was 0.2-1.0 °C / min.

[0190] Tables 1-5 show the raw materials, composite formation conditions, sheet formation conditions, nitriding treatment conditions, and sintering conditions for the silicon nitride substrates manufactured in Invention Examples 2-24 and Comparative Examples 1-16.

[0191] It can be confirmed that the silicon nitride substrate produced in Example 17 is a dense body with a relative density of 99% or more and a thermal conductivity of 121 W / mK.

[0192] [Table 4]

[0193] [Table 5]

[0194] As shown in Tables 1-5, when the proportion of metallic silicon powder in the composite powder constituting the silicon nitride sintered body is increased (Table 1, Powder Type No. 9, Comparative Examples 9-12), the heat generated due to the rapid nitriding reaction of silicon cannot be suppressed. Therefore, in the sintering process included in the manufacturing process of the silicon nitride sintered body, the rate of temperature rise of the sintering temperature of the nitride sheet cannot be increased. As a result, the silicon nitride sintered body obtained through the sintering process melts due to heat generation.

[0195] On the other hand, when the proportion of silicon nitride powder in the composite powder constituting the silicon nitride sintered body is increased (Table 1, Powder Type No. 10, Comparative Examples 13-16), the heat generated due to the rapid nitriding reaction of silicon can be suppressed because the proportion of metallic silicon powder is relatively small. Therefore, in the sintering process included in the manufacturing process of the silicon nitride sintered body, the rate of temperature rise of the sintering temperature of the nitride sheet can be increased. As a result, the silicon nitride sintered body obtained through the sintering process contains more oxygen internally, thereby reducing its thermal conductivity.

[0196] <Invention Examples 25-48, Comparative Examples 17-24> Except for changing the raw materials (powder type, magnesium compound), raw material composition, formation conditions of the composite as powder type, heating rate during degreasing of the sheet, and sintering conditions, silicon nitride substrates of Invention Examples 25-48 and Comparative Examples 17-24 were manufactured in the same manner as in Invention Example 1.

[0197] Specifically, powder type No. 11-18, with modified manufacturing conditions, was used as the powder type constituting the silicon nitride substrate manufactured in Examples 25-48. Magnesium oxide powder was used as the magnesium compound contained in the sheet forming slurry.

[0198] In Invention Examples 25-48, the heating rate used when nitriding the degreased wafers was 0.2-1.0 °C / min. Tables 1 and 7-8 show the raw materials, composite formation conditions, wafer formation conditions, nitriding conditions, and sintering conditions of the silicon nitride substrates manufactured in Invention Examples 25-48 and Comparative Examples 17-24.

[0199] [Table 6]

[0200] [Table 7]

[0201] [Table 8]

[0202] Based on these experimental data, a composite powder composed of silicon metal powder and silicon nitride powder is formed by micronizing the mixed powder. The silicon nitride substrate manufactured using this composite powder has a thermal conductivity of approximately 80 W / mK or higher, with the highest thermal conductivity exceeding 120 W / mK.

[0203] As a result, a composite powder consisting of silicon metal powder and silicon nitride powder is formed by micronizing the mixed powder, and the silicon nitride substrate manufactured using the composite powder clearly has high heat dissipation properties.

[0204] Furthermore, the silicon nitride substrate manufactured using this composite powder composed of metallic silicon and silicon nitride exhibits excellent mechanical properties due to the good evaluation results of the three-point bending strength and fracture toughness measurements, which indicate mechanical properties.

[0205] Thus, the method for manufacturing the silicon nitride substrate of the present invention uses a composite powder composed of metallic silicon and silicon nitride, wherein the metallic silicon and silicon nitride is composed of a mixture of metallic silicon powder and silicon nitride powder. Therefore, the silicon nitride particles adsorbed on the metallic silicon particles exist uniformly in the composite powder without agglomeration, thereby preventing the exposed metallic silicon particles from undergoing a rapid nitriding reaction. Furthermore, the metallic silicon particles coated with silicon nitride particles undergo a uniform nitriding reaction.

[0206] That is, the composite powder contains metallic silicon particles as core particles, and the metallic silicon particles exposed from the silicon nitride particles covering the surface of the metallic silicon particles become silicon nitride particles through a nitriding reaction. As a result, after the nitriding reaction is completed, the composite powder becomes a silicon source powder consisting only of silicon nitride particles.

[0207] In other words, the method for manufacturing a silicon nitride substrate according to the present invention can reduce the manufacturing cost of the silicon nitride substrate by using a large amount of metallic silicon powder as the silicon source for the sintered silicon nitride wafer. Thus, it is clear that the method for manufacturing a silicon nitride substrate according to the present invention satisfies these requirements from the perspectives of both manufacturing cost and the thermal conductivity and mechanical properties of the manufactured silicon nitride substrate.

[0208] Industrial availability According to the present invention, since silicon nitride substrates with high heat dissipation and excellent mechanical properties can be manufactured by preventing rapid nitriding reactions of silicon, it is of great industrial use and contributes to the development of semiconductor-related industries.

Claims

1. A method for manufacturing a silicon nitride substrate, characterized in that, include: The first step involves mixing metallic silicon powder and silicon nitride powder and then performing micro-pulverization to form a composite powder. The second step involves mixing a sintering aid and a dispersion medium into the composite powder to form a slurry for forming sheets in which the sintering aid is dispersed in the composite powder. The third step is to mold the slurry used for forming the sheet into a sheet; The fourth step involves heating the tablet at 250-600℃ to degrease the resin components contained in the tablet to form a degreased tablet. The fifth step involves heating the degreased tablets at 1200-1500℃ to nitrify the silicon contained in the degreased tablets to form nitrided tablets. The sixth step involves forming a silicon nitride substrate from the silicon nitride sintered body formed by sintering the nitride-treated wafer. The composite powder is formed by the adsorption of metallic silicon particles and silicon nitride particles.

2. The method for manufacturing a silicon nitride substrate according to claim 1, characterized in that, The micronization process is carried out by any one or a combination thereof selected from air jet milling, ball milling, bead milling, planetary ball milling, vertical stirred ball milling, and mechanochemical methods.

3. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, The average particle size D of the metallic silicon particles S50 Relative to the average particle size D of the silicon nitride particles SN50 The ratio, i.e., the particle size ratio X, is 0.2-2.

0.

4. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, In the first step, the silicon metal powder and the silicon nitride powder are contained in a molar ratio of 70:30 to 95:5, based on silicon nitride.

5. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, The surface of the silicon metal particles is uniformly dispersed with microparticles composed of the sintering aid.

6. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, The sintering aid is a magnesium compound, which includes one or more magnesium compounds selected from magnesium oxide, magnesium silicide, and magnesium silicon nitride.

7. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, The sintering aid is the rare earth element compound, which contains one or more elements selected from Y, Sc, La, Ce, Nd, Sm, Gd, Dy, Ho, Er, and Yb.

8. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, The relative density of the sheet is above 45%.

9. The method for manufacturing a silicon nitride substrate according to claim 1 or 2, characterized in that, The thermal conductivity of the silicon nitride substrate, measured by the xenon lamp flash method, is above 80 W / mK.

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