Composite ceramic materials and joints

Abstract

To provide a composite ceramic material and a conjugate capable of improving heat conductivity or bending strength.SOLUTION: A composite ceramic material includes silicon nitride particles and silicon carbide particles, wherein the silicon nitride particle includes 80% or over of β type silicon nitride, and a mean particle diameter of the silicon nitride particle is 0.1 μm or over and 10 μm or under in a cross section of the composite ceramic material. In the cross section, the silicon nitride particle having a particle diameter of 3-fold or over of the mean particle diameter has an area ratio of 35% or under to all the silicon nitride particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a composite ceramic material and a joined body. [Background technology]

[0002] Silicon nitride ceramics are used as materials for heat dissipation substrates because of their excellent properties, including heat dissipation and bending strength. As the development of high-capacity power devices and other elements progresses, heat generation increases, while the weight of the mounted equipment is also required. Therefore, high thermal conductivity and bending strength are desirable for materials for heat dissipation substrates. For this reason, silicon carbide, which has high thermal conductivity and bending strength, has been composited with silicon nitride. However, in such composite ceramic materials, the long diameter of the silicon nitride particles is large, exceeding 10 μm, which is disadvantageous in terms of bending strength. On the other hand, the proportion of silicon carbide is low, at less than 10% by mass, and the high thermal conductivity, one of silicon carbide's characteristics, is not fully utilized. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-34671 Summary of the Invention [Problem to be solved by the invention]

[0004] Embodiments of the present invention provide a composite ceramic material and a joined body that can improve thermal conductivity or bending strength. [Means for solving the problem]

[0005] The composite ceramic material of the embodiment includes: Multiple silicon nitride particles; Multiple and silicon carbide particles, wherein the silicon nitride particles contain 80% or more β-type silicon nitride, and in a cross section of the composite ceramic material, MultipleThe silicon nitride particles have an average particle size of 0.1 μm or more and 10 μm or less. In the cross section, all silicon carbide particles have an area ratio of 10% to 50% of all silicon nitride particles and all silicon carbide particles. In the cross section, silicon nitride particles having a particle size three times or more the average particle size occupy 35% or less of the area of ​​all silicon nitride particles. Composite ceramic materials are 2 Si 3 O 3 N 4 The composite ceramic material further comprises a grain boundary having a crystalline phase, and in the X-ray diffraction pattern, the Y relative to the peak intensity of silicon nitride and silicon carbide is 2 Si 3 O 3 N 4 The ratio of the maximum peak intensity of the type crystalline phase to that of the type crystalline phase is 15% or less. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a cross-sectional view showing a structural example of a composite ceramic material. FIG. [Figure 2] FIG. 1 is a perspective view illustrating a composite ceramic material. [Figure 3] FIG. 1 is a perspective view illustrating a composite ceramic material. [Figure 4] FIG. 2 is a schematic cross-sectional view illustrating a bonded body. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments will be described with reference to the drawings. Note that the drawings are schematic, and for example, the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc. may differ from the actual. Furthermore, in the embodiments, substantially identical components are assigned the same reference numerals, and descriptions thereof will be omitted.

[0008] FIG. 1 is a cross-sectional schematic diagram showing an example of the structure of a composite ceramic material according to an embodiment. As shown in FIG. 1, a composite ceramic material 110 according to an embodiment includes a crystal particle 10a, a crystal particle 10b, and grain boundaries 20 formed around the crystal particle 10a and the crystal particle 10b. In FIG. 1, the black portions represent the grain boundaries 20, the white particles represent the crystal particles 10a, and the gray particles represent the crystal particles 10b. A plurality of crystal particles 10a and a plurality of crystal particles 10b are present within the grain boundaries 20. The plurality of crystal particles 10, including the crystal particles 10a and the crystal particles 10b, may be separated from one another or may be partially in contact with one another. Some of the plurality of crystal particles 10 may be separated from one another, and other portions of the plurality of crystal particles 10 may be partially in contact with one another.

[0009] The crystal particles 10a are, for example, silicon nitride particles. The crystalline phase of the silicon nitride particles is preferably beta silicon nitride, and preferably does not contain alpha silicon nitride. The proportion of beta silicon nitride in the total silicon nitride observed on the measurement surface is called the beta silicon nitride ratio, and is expressed by Equation (1). X-ray diffraction of the composite ceramic material is measured, and from the diffraction pattern, the peak intensities of the (101) and (120) planes of beta silicon nitride, as well as the peak intensities of the (102) and (210) planes of alpha silicon nitride are read using the X-ray diffraction patterns of beta silicon nitride (e.g., PDF Card No. 01-073-3034) and alpha silicon nitride (e.g., PDF Card No. 01-078-2962), and these are then applied to the beta (101) intensity, beta (120) intensity, alpha (102) intensity, and alpha (210) intensity in Equation (1), respectively.

[0010]

number

[0011] If the beta phase ratio is lower than 80%, fewer particles grow into the columnar shape that is characteristic of beta silicon nitride, resulting in a decrease in thermal conductivity and strength. The higher the beta phase ratio, the better these properties improve; it is preferable for 90% or more of the silicon nitride to be beta silicon nitride, i.e., a beta phase ratio of 90% or more. It is even more preferable for all alpha silicon nitride to undergo a phase transition to beta silicon nitride, so that the silicon nitride contained in the composite ceramic material is 100% beta silicon nitride, i.e., a beta phase ratio of 100%. The beta phase ratio obtained from the measurement surface is the beta phase ratio of the composite ceramic material.

[0012] The crystal particles 10b are, for example, silicon carbide particles.

[0013] The composite ceramic material of the embodiment may contain other crystal phases in addition to the crystal grains 10a and the crystal grains 10b.

[0014] The composite ceramic material of this embodiment combines silicon nitride particles and silicon carbide particles to achieve both high thermal conductivity and high strength.

[0015] Ceramics using silicon nitride particles have high strength, but if the silicon nitride particles grow and the crystal grain size increases, for example, due to high-temperature sintering, this is advantageous in terms of thermal conductivity, but may result in a decrease in strength.

[0016] In contrast, in the composite ceramic material of the embodiment, by combining silicon nitride particles and silicon carbide particles, grain growth of the silicon nitride particles can be suppressed even when the composite ceramic is produced by high-temperature sintering. This allows for high strength. Furthermore, high-temperature sintering desorbs oxygen from the crystalline phase, increasing the amount of nitrogen-rich grain boundary phase. As a result, high thermal conductivity and high strength can be achieved at the same time.

[0017] The cross section of a composite ceramic material is observed using a scanning electron microscope (SEM-EDS) equipped with an energy dispersive X-ray spectrometer, for example, under conditions of an acceleration voltage of 15 kV and a probe current of 10 μA. The cross section may be a fracture surface formed by breaking the center of a sintered body, but more preferably, it is a cross section obtained by mirror-polishing the cut surface of a sintered body and then plasma-etching it with CH4 gas. When the composite ceramic material is incorporated into a bonded body, the composite ceramic material is removed from the bonded body, mirror-polished, and then plasma-etched with CH4 gas before observation. The observation magnification is set so that more than 500 crystal grains are present in the observation area. Therefore, the observation magnification depends on the size of the crystal grains. For example, if the average grain size of all grains is approximately 2 μm, the observation area is approximately 130 μm × approximately 95 μm, and the observation magnification is approximately 1000x. If the average particle size of all particles is about 0.4 μm, the observation area is about 15 μm × about 9 μm, and the observation magnification is about 10,000 times. If the average particle size of all particles is about 10 μm, the observation area is about 450 μm × about 270 μm, and the observation magnification is about 35 times. A plurality of observation areas adjusted in this manner, for example, three, are prepared, and the average particle size and other parameters are measured for each observation area, as described below. The average values ​​of the measurement results are used as the average particle size and area ratio of the composite ceramic material according to this embodiment.

[0018] The obtained observation images are analyzed using the image processing software ImageJ. Crystal grains 10a, 10b, and grain boundaries 20 are identified by binarizing the observation images. Silicon nitride particles and silicon carbide particles are distinguished from each other based on the results of SEM-EDS. By measuring the EDS mapping image of the cross-sectional image obtained by SEM observation, particles with a high nitrogen content are silicon nitride particles (crystal grains 10a), and particles with a high carbon content are silicon carbide particles (crystal grains 10b). Therefore, silicon nitride particles and silicon carbide particles can be distinguished from each other. Silicon nitride particles, for example, have a nitrogen content of 30 atomic % or more and a carbon content of 15 atomic % or less, while silicon carbide particles have a nitrogen content of 15 atomic % or less and a carbon content of 35 atomic % or more. Furthermore, assuming EDS analysis, the conductive coating on the observation cross section is preferably made of a material other than carbon, such as gold or platinum.

[0019] The particle size of each particle is defined as the diameter when the area of ​​each particle is assumed to be a circle, as calculated using ImageJ.

[0020] In the cross section, the average particle size of the silicon nitride particles calculated from multiple fields of view is preferably 0.1 μm or more and 10 μm or less. If the average particle size is less than 0.1 μm, thermal conduction is hindered at the grain boundaries, and the proportion of the grain boundary phase, which has low thermal conductivity, increases, resulting in a decrease in thermal conductivity. If the average particle size exceeds 10 μm, the surface area becomes large, making the material more susceptible to cracking and reducing strength.

[0021] In the cross section, silicon nitride particles having a particle size three times or more the average particle size of the silicon nitride particles preferably account for 35% or less of the area of ​​all silicon nitride particles. This reduces the number of coarse particles with a large surface area, thereby preventing a decrease in strength. It is more preferable that silicon nitride particles having a particle size three times or more the average particle size account for 20% or less of the area of ​​all silicon nitride particles. If the area ratio of silicon nitride particles having a particle size three times or more the average particle size exceeds 35% of all silicon nitride particles, the number of coarse particles with a large surface area will increase, resulting in a decrease in strength.

[0022] In the cross section, it is preferable that all silicon carbide particles account for 1% or more and 50% or less of the area of ​​all particles, including all silicon nitride particles and all silicon carbide particles. The presence of silicon carbide particles suppresses grain growth of silicon nitride particles and prevents an increase in the proportion of silicon nitride particles three times or more the average particle size, thereby maintaining high strength. Furthermore, the presence of silicon carbide particles, which have a higher thermal conductivity than silicon nitride particles, allows for high thermal conductivity to be achieved. This allows for both high thermal conductivity and high strength.

[0023] In the cross section, it is preferable that the silicon carbide particles have an average aspect ratio of 2 or less and an average particle size of 0.1 μm to 10 μm. As with the silicon nitride particles described above, if the average particle size of the silicon carbide particles is less than 0.1 μm, the thermal conductivity decreases, and if it exceeds 10 μm, the strength decreases. Therefore, by keeping the particle size within the above range, both high thermal conductivity and high strength can be achieved.

[0024] The aspect ratio of silicon carbide particles is defined as the ratio of the maximum Feret diameter to the minimum Feret diameter, calculated using ImageJ for each particle.

[0025] The grain boundary 20 contains yttrium, silicon, oxygen, and nitrogen. For example, the grain boundary 20 contains a Y2Si3O3N4-type crystalline phase. The Y2Si3O3N4-type crystalline phase refers to a crystal having the same crystalline structure as that of Y2Si3O3N4. Here, the same crystalline structure refers to the same crystal system, space group, and positional relationship of the constituent atoms, but the interatomic distances or lattice constants do not necessarily have to be the same. Furthermore, the elements contained in the crystalline phase are not important. In other words, the composition of the Y2Si3O3N4-type crystalline phase may be the same as or different from that of the Y2Si3O3N4 crystal.

[0026] In the X-ray diffraction pattern of the composite ceramic material, it is preferable that the ratio of the maximum peak intensity of the Y2Si3O3N4 type crystalline phase to the peak intensity of silicon nitride and silicon carbide is 1% or more and 15% or less, as expressed by formula (2). This results in a high thermal conductivity because there is more crystalline phase with a higher thermal conductivity than the grain boundary phase composed of a glass phase.

[0027] The conditions for measuring the X-ray diffraction pattern are set, for example, as follows: An X-ray diffractometer, such as a Smart-Lab manufactured by Rigaku Corporation, is used to perform X-ray diffraction using the focusing method (reflection method, Bragg-Brendano method). For X-ray diffraction, an arbitrary cross section of the composite ceramic material is used as the measurement surface. The measurement surface is polished so that the surface roughness Ra is 0.05 μm or less. A Cu target (Cu-Kα) is used for measurement. The tube voltage is set to 45 kV. The tube current is set to 200 mA. The scanning speed is set to 2.0 to 20.0° / min. The incident parallel slit is set to 5 degrees, the longitudinal limiting slit is 10 mm, the receiving slit is 20 mm, and the receiving parallel slit is 5 degrees. The scanning range (2θ) is set to 10° to 80°, and measurements are performed in 0.01° increments.

[0028] When X-ray diffraction analysis is performed on a sample of composite ceramic material, crystalline phases other than silicon nitride and silicon carbide, contained in the grain boundary phase, are also detected. The crystalline phase is Y2Si3O3N4, and as shown in equation (2), the peak intensity ratio of Y2Si3O3N4 can be obtained by normalizing the intensity of its maximum peak by the intensities of the four peaks of the above-mentioned beta and alpha silicon nitrides (if alpha silicon nitride is not present, the alpha (102) intensity and alpha (210) intensity are 0) and the intensity of the maximum peak of silicon carbide.

[0029]

number

[0030] The Y2Si3O3N4 type crystalline phase may further contain magnesium. The concentration of magnesium in the grain boundary phase containing the Y2Si3O3N4 type crystalline phase is preferably 0.01 atomic % or more. The inclusion of magnesium is advantageous for good grain growth of silicon nitride.

[0031] Next, a first example of a method for producing the composite ceramic material of this embodiment will be described. The first example of a method for producing the composite ceramic material includes a mixing step, a molding step, and a sintering step.

[0032] In the mixing process, the first raw material, the second raw material, and the auxiliary agent are mixed to form a mixed powder. These can be mixed using, for example, a planetary ball mill. By using a planetary ball mill, coarse particles contained in the first raw material, the second raw material, and the auxiliary agent can be pulverized, thereby improving the uniformity of the particle size of the mixed powder.

[0033] Examples of the first raw material include powders of silicon or silicon nitride.

[0034] An example of the second raw material is a powder of silicon carbide or the like. carbonization The average particle size of the silicon powder is preferably 100 nm or less, but may be on the order of several μm. carbonization The silicon powder may have a cubic or hexagonal crystal structure.

[0035] Examples of the auxiliary agent include magnesium oxide and yttrium oxide. These auxiliary materials may be used alone or in combination. The auxiliary agent reacts with the surface oxide film of silicon or silicon carbide during firing to promote grain growth of silicon nitride or silicon carbide, ultimately remaining as a glass phase at the grain boundaries 20 together with a Y2Si3O3N4 crystalline phase.

[0036] The mixed powder is preferably formed by mixing 88.5% by mass to 96.5% by mass of silicon nitride and silicon carbide, 1% by mass to 3.5% by mass of magnesium oxide, and 2.5% by mass to 8% by mass of yttrium oxide, so that the total amount is 100% by mass. If the amount of auxiliary agent is too small, grain growth of silicon nitride and silicon carbide becomes difficult, while if the amount is too large, the grain boundary phase increases, reducing the thermal conductivity and bending strength of the composite ceramic material.

[0037] In the compacting process, the mixed powder is compressed and compacted by uniaxial pressing, and then the compact is subjected to cold isostatic pressing (CIP).

[0038] When silicon powder is used as the first raw material, the compact may be subjected to a nitriding treatment. For example, the silicon is converted to silicon nitride by heat treatment at a temperature of 1300°C to 1450°C for 2 hours to 8 hours in a nitrogen atmosphere at 1 atmosphere pressure. Note that the same applies when carbon is used instead of silicon carbide, but the carbon does not react with silicon during the nitriding treatment.

[0039] In the sintering step, the compact is sintered by heat treatment at a temperature of 1800°C to 2000°C for 12 to 72 hours in a nitrogen atmosphere at a pressure of 7.5 to 10 atmospheres. The nitrogen atmosphere at a pressure of 7.5 to 10 atmospheres can suppress evaporation of silicon nitride. When nitriding is performed before the sintering step, it is preferable to perform the sintering step immediately after the compact without exposing it to the atmosphere. When carbon is used instead of silicon carbide, part of the silicon nitride reacts with the carbon in the sintering step to produce silicon carbide.

[0040] The sintered body obtained in the sintering step is cut into a desired shape.

[0041] The thermal conductivity of the manufactured composite ceramic material is measured in accordance with JIS-R-1611, which corresponds to ISO18755 (2005). The thermal conductivity is measured by the laser flash method using a Netsch flash analyzer LFA 467 HyperFlash.

[0042] The bending strength of the manufactured composite ceramic material is measured by a three-point bending strength test in accordance with JIS-R-1601. JIS-R-1601 corresponds to ISO14704 (2000). The three-point bending strength test is performed using a Shimadzu Autograph AG-X (100kN). The load cell is set to 1kN, the test speed is 0.5mm / min, the indenter radius and support radius are both R2, and the distance between supports is 30mm, and the test is performed at room temperature.

[0043] The composite ceramic material of the embodiment has a thermal conductivity of 70 W / (m·K) or more. The upper limit of the thermal conductivity is not particularly limited, but is, for example, 250 W / (m·K) or less.

[0044] The composite ceramic material of the embodiment has a bending strength of 500 MPa or more. The upper limit of the bending strength is not particularly limited, but is, for example, 1100 MPa or less.

[0045] The method for producing the composite ceramic material is not limited to the first example of production, but a second example of production method for the composite ceramic material will be described below.

[0046] The second manufacturing method example includes a mixing step and a sintering step.

[0047] In the mixing process, the first raw material, the second raw material, and the auxiliary agent are mixed to form a mixed powder. These can be mixed using, for example, a planetary ball mill. By using a planetary ball mill, coarse particles contained in the first raw material, the second raw material, and the auxiliary agent can be pulverized, thereby improving the uniformity of the particle size of the mixed powder.

[0048] An example of the first raw material is powder of silicon nitride, etc. The explanation of the second raw material and auxiliary agent can be appropriately cited from the explanation of the first example of the manufacturing method.

[0049] The mixed powder is preferably formed by mixing 88.5% by mass to 96.5% by mass of silicon nitride and silicon carbide, 1% by mass to 3.5% by mass of magnesium oxide, and 2.5% by mass to 8% by mass of yttrium oxide, so that the total amount is 100% by mass. If the amount of auxiliary agent is too small, grain growth of silicon nitride and silicon carbide becomes difficult, while if the amount is too large, the grain boundary phase increases, reducing the thermal conductivity and bending strength of the composite ceramic material.

[0050] In the sintering process, heat treatment is performed using spark plasma sintering (SPS) at a temperature of 1800°C to 2000°C, a press pressure of 20 MPa or more, and a nitrogen atmosphere pressure of atmospheric pressure to 10 atmospheres. If the temperature is less than 1800°C or more than 2000°C, the press pressure is less than 20 MPa, and the atmosphere pressure is less than atmospheric pressure, there are problems such as not achieving high density or not causing a phase transition to high-performance β-type silicon nitride. The treatment time is not particularly limited, but for example, it can be 3 minutes. End Less than 72 hours. 3 minutes less than If the first raw material is silicon nitride, there are problems such as failure to achieve high density or failure to undergo a phase transition to high-performance beta-type silicon nitride. If the time exceeds 72 hours, decomposition may occur, resulting in failure to sinter. The above heat treatment allows the mixed powder to be sintered under pressure, eliminating the need for a molding process. Furthermore, using silicon nitride as the first raw material eliminates the need for a nitriding process. If carbon is used instead of silicon carbide, this heat treatment will cause a portion of the silicon nitride to react with the carbon to produce silicon carbide. Hot pressing may also be used instead of SPS.

[0051] The sintered body obtained by the SPS may then be subjected to a second heat treatment, for example, at 1900°C to 2000°C for 12 to 72 hours in a nitrogen atmosphere at 7.5 to 10 atmospheres. The nitrogen atmosphere at 7.5 to 10 atmospheres can suppress evaporation of silicon nitride.

[0052] The sintered body obtained in the sintering step is cut into a desired shape.

[0053] By using the second manufacturing method example, in the cross section, silicon carbide particles having a particle size three times or more the average particle size of the silicon carbide particles can be made to account for 10% or less of the area of ​​all silicon carbide particles. This reduces the number of coarse particles with a large surface area, making it possible to suppress a decrease in strength. carbonization Silicon particles are all carbonization If the area ratio of the silicon carbide particles exceeds 10%, the number of coarse particles with a large surface area increases, resulting in a decrease in strength.It is more preferable that the area ratio of silicon carbide particles having a particle size three times or more the average particle size is 1% or less of all silicon carbide particles.

[0054] By using the second manufacturing method, the ratio of the maximum peak intensity of the Y2Si3O3N4-type crystalline phase to the four peak intensities of silicon nitride and the maximum peak intensity of silicon carbide in the X-ray diffraction pattern of the composite ceramic material 110 can be reduced to 1% or less, as shown in formula (2). By performing SPS heat treatment before the high-temperature, high-pressure heat treatment used in the first manufacturing method, it is possible to reduce the grain boundary phase, which is a crystalline phase but has lower thermal conductivity and strength than silicon nitride or silicon carbide, thereby improving thermal conductivity and strength. SPS is more effective at reducing the grain boundary phase than high-temperature, high-pressure heat treatment because the grain boundary phase is pushed to the surface of the sintered body by the press pressure during sintering.

[0055] In the composite ceramic material 110 formed using the second manufacturing example, the c-axes of silicon nitride particles having a particle size at least three times the average particle size of the silicon nitride particles are preferably aligned. Orientation can be evaluated, for example, by measuring X-ray diffraction on the surface of a sintered body subjected to SPS. The surface of the sintered body measured by X-ray diffraction is referred to as the measurement surface. The diffraction pattern obtained from the measurement surface is compared with the X-ray diffraction pattern of β-silicon nitride (e.g., PDF card No. 01-073-3034), and the peak intensities of the (002) and (320) planes of the β-silicon nitride particles are read. The orientation value calculated using the following formula (3) can be used to determine the direction of the c-axes of the β-silicon nitride particles relative to the measurement surface. The smaller this value, the closer the c-axes of the silicon nitride particles are to being parallel to the measurement surface. It is preferable that the c-axes of the silicon nitride particles obtained from at least one measurement surface of the sintered body be non-perpendicular (≠±90°) to the measurement surface, preferably within ±45°, or even approximately parallel. "Approximately parallel" includes not only the parallel direction but also a state within ±20 degrees from the parallel direction. Furthermore, the value indicating the orientation obtained by formula (3) is preferably less than 0.5.

[0056]

number

[0057] Since silicon nitride particles have high thermal conductivity in the c-axis direction, the thermal conductivity can be improved by orienting the c-axis of the silicon nitride particles.

[0058] 2 and 3 are perspective views illustrating composite ceramic materials according to the embodiments. For example, as shown in FIGS. 2 and 3, the composite ceramic material 110 is a substrate. The substrate may have any shape. As described above, the composite ceramic material of the embodiment has high thermal conductivity and high bending strength. Therefore, the composite ceramic material of the embodiment can be suitably used as a substrate. Alternatively, the composite ceramic material of the embodiment may be a bearing or the like.

[0059] FIG. 4 is a schematic cross-sectional view illustrating the bonded body of the embodiment. 4, the bonded body 210 of the embodiment includes a first metal part 31 and a composite ceramic material 110. In this example, the composite ceramic material 110 is used as a substrate.

[0060] The first metal part 31 is joined to the composite ceramic material 110. For example, a joint 41 is provided between the first metal part 31 and the composite ceramic material 110. The first metal part 31 may be joined directly to the composite ceramic material 110 without the joint 41 being interposed therebetween.

[0061] In the example shown in FIG. 4 , the bonded body 210 further includes a second metal part 32 and a semiconductor element 50. The semiconductor element 50 is bonded to the first metal part 31. The first metal part 31 is located between the composite ceramic material 110 and the semiconductor element 50. For example, a bonding part 42 is provided between the semiconductor element 50 and the first metal part 31. The semiconductor element 50 may be bonded directly to the first metal part 31 without the bonding part 42.

[0062] The second metal part 32 is joined to the composite ceramic material 110. The composite ceramic material 110 is located between the first metal part 31 and the second metal part 32. For example, a joint part 43 is provided between the second metal part 32 and the composite ceramic material 110. The second metal part 32 may be joined directly to the composite ceramic material 110 without the joint part 43. The second metal part 32 functions as, for example, a heat sink.

[0063] The first metal portion 31 and the second metal portion 32 include, for example, at least one selected from the group consisting of copper and aluminum. The joint portions 41 to 43 include, for example, at least one selected from the group consisting of silver and copper. The joint portions 41 to 43 may further include at least one selected from the group consisting of titanium, hafnium, zirconium, niobium, silicon, magnesium, indium, tin, and carbon. The semiconductor element 50 includes, for example, a diode, a MOSFET, or an IGBT.

[0064] The bonding portions 41 to 43 preferably contain an active metal. For example, when the first metal portion 31 and the second metal portion 32 contain copper, the active metal is at least one selected from the group consisting of titanium, hafnium, zirconium, and niobium. The bonding portions 41 to 43 preferably contain silver, copper, and at least one selected from the group consisting of titanium, hafnium, zirconium, and niobium.

[0065] When the first metal portion 31 and the second metal portion 32 contain aluminum, the active metal is at least one selected from the group consisting of silicon and magnesium. Preferably, the bonding portions 41 to 43 contain at least one selected from the group consisting of silver, copper, silicon, and magnesium.

[0066] When the first metal portion 31 and the second metal portion 32 contain copper, titanium is particularly preferable as the active metal. Titanium reacts with silicon nitride to form titanium nitride, thereby increasing the bonding strength.

[0067] By using the composite ceramic material 110 of the embodiment for the bonded body 210, the thermal conductivity and bending strength of the bonded body 210 can be improved. Furthermore, by using the composite ceramic material 110 with excellent thermal conductivity for a substrate, for example, the heat dissipation performance of the substrate can be improved. In addition, the composite ceramic material 110 has excellent bending strength. Therefore, the substrate can be made thinner while maintaining its strength. This further improves the heat dissipation performance of the substrate.

[0068] According to the embodiments described above, it is possible to provide a composite ceramic material and a joined body that can improve thermal conductivity and bending strength.

[0069] The embodiments of the present invention have been described above with reference to specific examples. However, the embodiments of the present invention are not limited to these specific examples. For example, the specific configurations of each element, such as the composite ceramic material, the metal part, the joint, and the semiconductor element, are within the scope of the present invention as long as a person skilled in the art can implement the present invention in a similar manner and obtain similar effects by appropriately selecting them from known ranges.

[0070] Furthermore, any combination of two or more elements of each specific example within the scope of technical feasibility is also included within the scope of the present invention as long as it includes the gist of the present invention.

[0071] In addition, all composite ceramic materials and joined bodies that can be implemented by a person skilled in the art by appropriately modifying the design based on the composite ceramic material and joined body described above as the embodiments of the present invention also fall within the scope of the present invention, as long as they include the gist of the present invention.

[0072] In addition, within the scope of the concept of the present invention, a person skilled in the art may come up with various modifications and alterations, and it will be understood that these modifications and alterations also fall within the scope of the present invention. [Example]

[0073] The present invention will be described below with reference to examples.

[0074] (Examples 1 to 3) Si powder, SiC powder, MgO powder, and Y2O3 powder were placed in a pot, balls and ethanol were added, and then a planetary ball mill was used to set the rotation speed at 300 to 600 rpm and knead for 60 to 180 minutes to form a slurry. The resulting slurry was then distilled and dried to prepare the raw material powder. powderAfter uniaxial press molding, the material was subjected to CIP treatment, nitriding treatment at 1450°C for 4 hours in a nitrogen atmosphere at atmospheric pressure, and then sintering at 1800-2000°C for 12-72 hours in a nitrogen atmosphere at 7.5 atmospheres to form a composite ceramic material comprising silicon nitride and silicon carbide. In this way, the average particle size of the silicon nitride and the proportion of coarse particles in the silicon nitride were adjusted by appropriately adjusting the rotation speed and time of the planetary ball mill and the sintering temperature and time.

[0075] After processing the composite ceramic material, the thermal conductivity and strength were measured. One side of the sample used for measuring thermal conductivity was mirror-finished, followed by plasma etching to create a sample for cross-sectional observation. This sample was gold-coated, and the cross-sectional image shown in Figure 1 was obtained using SEM-EDS, for example, in Example 3. In this figure, the black areas represent the grain boundary phase, the white particles represent silicon nitride particles, and the gray particles represent silicon carbide particles.

[0076] (Comparative Examples 1, 3, and 5) Silicon nitride ceramic materials were formed in Comparative Example 1 by the same method as Example 1, Comparative Example 3 by the same method as Example 2, and Comparative Example 5 by the same method as Example 3, except that no SiC powder was added.

[0077] (Comparative Examples 2 and 4) In Comparative Example 2, compared to Example 1, the kneading conditions using the planetary ball mill were changed to increase the rotation speed and extend the milling time, and the sintering conditions were changed to decrease the temperature and shorten the time, but a composite ceramic material was formed using the same method as in Example 1. In Comparative Example 4, compared to Example 2, the kneading conditions using the planetary ball mill were changed to decrease the rotation speed and shorten the milling time, and the sintering conditions were changed to increase the temperature and lengthen the time, but a composite ceramic material comprising silicon nitride and silicon carbide was formed using the same method as in Example 2.

[0078] After processing the composite ceramic material, the thermal conductivity and strength were measured. One side of the sample used for measuring thermal conductivity was mirror-finished, and then plasma etching was performed to create a sample for cross-sectional observation. After gold vapor deposition on this sample, a cross-sectional image was obtained using SEM-EDS.

[0079] The results of particle analysis of cross-sectional images of Examples 1 to 3 and Comparative Examples 1 to 5, performed using ImageJ as described above, as well as the results of thermal conductivity and strength, are shown in Tables 1 to 3. Table 1 shows the property results of Example 1 and Comparative Examples 1 and 2. Table 2 shows the property results of Example 2 and Comparative Examples 3 and 4. Table 3 shows the property results of Example 3 and Comparative Example 5. In the tables, coarse particles refer to particles having a particle size three times or more the average particle size.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] The evaluation and analysis of Examples 1 to 3 revealed that the average particle size of the silicon nitride particles was within the range of 0.1 to 10 μm, and that silicon nitride particles with a particle size three times larger than the average particle size accounted for 35% or less of the total silicon nitride particles. The average aspect ratio of the silicon carbide particles was 2 or less, the average particle size of the silicon carbide particles was within the range of 0.1 μm to 10 μm, and the area ratio of all silicon carbide particles was within the range of 10% to 50% of the total silicon nitride particles and all silicon carbide particles. The grain boundary phase contained a Y2Si3O3N4-type crystalline phase, the maximum peak intensity ratio of which was within the range of 1 to 10% relative to silicon nitride and silicon carbide, and the grain boundary phase contained Mg at a ratio of 0.01 atomic % or more.

[0084] On the other hand, evaluation and analysis of Comparative Examples 1, 3, and 5 revealed that no silicon carbide was contained, and silicon nitride particles having a particle size three times or more the average particle size accounted for 35% or more of the area of ​​all silicon nitride particles, and the grain boundary phase contained Mg, but no Y2Si3O3N4-type crystal phase was present. Furthermore, evaluation and analysis of Comparative Examples 2 and 4 revealed that silicon nitride particles having a particle size three times or more the average particle size accounted for 35% or less of the area of ​​all silicon nitride particles, but the average particle size of the silicon nitride particles was outside the range of 0.1 to 10 μm. Furthermore, it can be seen that Examples 1 to 3 are able to achieve both high thermal conductivity and high strength compared to Comparative Examples 1 to 5.

[0085] (Examples 4 and 5) Si3N4 powder, SiC powder, MgO powder, and Y2O3 powder were placed in a pot, balls and ethanol were added, and then the mixture was kneaded in a planetary ball mill in the same manner as in Examples 1 to 3 to form a slurry. The obtained slurry was distilled and dried to prepare a raw material powder. powder In a nitrogen atmosphere with atmospheric pressure, a pressure of 100 MPa, a temperature of 1800°C, and 3 minutes End The composite ceramic material of Example 4 containing silicon nitride and silicon carbide was obtained by performing a heat treatment by SPS for 72 hours or less.

[0086] The sintered body obtained in Example 4 was further heat-treated in a nitrogen atmosphere having a pressure of 7.5 atmospheres at a temperature of 1900°C for more than 3 minutes and not more than 72 hours to obtain a composite ceramic material of Example 5 comprising silicon nitride and silicon carbide.

[0087] After processing the composite ceramic material, the thermal conductivity and strength were measured. One side of the sample used for measuring thermal conductivity was mirror-finished, and then plasma etching was performed to create a sample for cross-sectional observation. After gold vapor deposition on this sample, a cross-sectional image was obtained using SEM-EDS.

[0088] (Comparative Example 6) Si3N4 powder, SiC powder, MgO powder, and Y2O3 powder were placed in a pot, balls and ethanol were added, and then the mixture was kneaded in a planetary ball mill in the same manner as in Examples 4 and 5 to form a slurry. The obtained slurry was distilled and dried to prepare a raw material powder. powder The composite ceramic material of Comparative Example 6 comprising silicon nitride and silicon carbide was obtained by heat treatment using SPS under a nitrogen atmosphere at atmospheric pressure, a pressure of 100 MPa, a temperature of 1700°C, and a time of 3 minutes.

[0089] After processing the above ceramics, the thermal conductivity and strength were measured. One side of the sample used for measuring thermal conductivity was mirror-finished, and then plasma etching was performed to create a sample for cross-sectional observation. After gold vapor deposition on this sample, a cross-sectional image was obtained using SEM-EDS.

[0090] The particle analysis of the cross-sectional images of Examples 4 and 5 and Comparative Example 6 was performed using ImageJ using the method described above. The results of the measurement of the orientation value expressed by the above formula (3), the thermal conductivity, and the strength are shown in Table 4.

[0091] [Table 4]

[0092] The evaluation and analysis results for Examples 4 and 5 showed that the average particle size of the silicon nitride particles was within the range of 0.1 to 10 μm, and that silicon nitride particles having a particle size three times or more the average particle size accounted for 35% or less of the total silicon nitride particles. The average aspect ratio of the silicon carbide particles was 2 or less, the average particle size of the silicon carbide particles was within the range of 0.1 to 10 μm, and that silicon carbide particles having a particle size three times or more the average particle size of the silicon carbide particles accounted for 10% or less of the total silicon carbide particles. The area ratio of all silicon carbide particles to all silicon nitride particles and all silicon carbide particles was within the range of 10% to 50% of the total silicon carbide particles. The grain boundary phase contained a Y2Si3O3N4-type crystalline phase, the maximum peak intensity ratio of which was 1% or less relative to silicon nitride and silicon carbide, and the grain boundary phase contained Mg at a ratio of 0.01 atomic % or more. The value representing the c-axis orientation of the silicon nitride particles, expressed by the above formula (3), was less than 0.5. This indicated that the c-axes of the silicon nitride particles of Examples 4 and 5 were oriented. Furthermore, X-ray diffraction analysis of all of Examples 1-5 and Comparative Examples 1-5 showed that the crystalline phase of the silicon nitride was 100% β-type silicon nitride.

[0093] On the other hand, the evaluation and analysis of Comparative Example 6 showed that the average particle size of the silicon nitride particles was within the range of 0.1 to 10 μm, and that silicon nitride particles having a particle size three times or more the average particle size accounted for 35% or less of the area of ​​all silicon nitride particles. The average aspect ratio of the silicon carbide particles was 2 or less, and silicon carbide particles having a particle size three times or more the average particle size of silicon carbide accounted for 10% or less of the area of ​​all silicon carbide particles, but the average particle size was 0.1 μm or less. All silicon carbide particles accounted for 10% to 50% of the area of ​​all silicon nitride particles and all silicon carbide particles. The grain boundary phase contained a Y2Si3O3N4-type crystalline phase, the maximum peak intensity ratio of which was 1% or less relative to silicon nitride and silicon carbide, and the grain boundary phase contained Mg at a ratio of 0.01 atomic % or more. The value indicating the c-axis orientation of the silicon nitride particles, as expressed by the above formula (3), was 0.5 or more. However, X-ray diffraction results showed that the silicon nitride crystalline phase was not solely beta silicon nitride, as required, but contained 21% alpha silicon nitride, resulting in significantly low thermal conductivity and strength. Furthermore, it can be seen that Examples 4 and 5 are able to achieve both high thermal conductivity and high strength compared to Comparative Example 6.

[0094] From the above, it was found that the composite ceramic material of the example is a composite ceramic material comprising silicon nitride particles and silicon carbide particles, the silicon nitride particles contain 80% or more β-type silicon nitride, and the average particle size of the silicon nitride particles in the cross section of the composite ceramic material is 0.1 μm to 10 μm. In the cross section, silicon nitride particles having a particle size three times or more the average particle size of the silicon nitride particles account for 35% or less of the area of ​​all silicon nitride particles, and it was found that both high thermal conductivity and high strength can be achieved.

[0095] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0096] 10a...crystal grain, 10b...crystal grain, 20...grain boundary, 31...first metal portion, 32...second metal portion, 41-43...joint portion, 50...semiconductor element, 110...composite ceramic material, 210...jointed body.

Claims

1. A composite ceramic material comprising a plurality of silicon nitride particles and a plurality of silicon carbide particles, The silicon nitride particles contain 80% or more of β-type silicon nitride, In a cross section of the composite ceramic material, the average particle size of the plurality of silicon nitride particles is 0.1 μm or more and 10 μm or less, In the cross section, all of the silicon carbide particles have an area ratio of 10% or more and 50% or less of all of the silicon nitride particles and all of the silicon carbide particles, In the cross section, the silicon nitride particles having a particle size three times or more the average particle size of the plurality of silicon nitride particles have an area ratio of 35% or less relative to all the silicon nitride particles in the cross section, further comprising grain boundaries having a Y2Si3O3N4 type crystalline phase; In the X-ray diffraction pattern of the composite ceramic material, the ratio of the maximum peak intensity of the Y 2 Si 3 O 3 N 4 type crystal phase to the peak intensities of silicon nitride and silicon carbide is 15% or less.

2. the average particle size of the plurality of silicon nitride particles is 0.1 μm or more and 1.0 μm or less; 2. The composite ceramic material according to claim 1, wherein in the cross section, the silicon nitride particles having a particle size three times or more the average particle size of the plurality of silicon nitride particles have an area ratio of 20% or less relative to all the silicon nitride particles.

3. 3. The composite ceramic material according to claim 1, wherein the silicon carbide particles have an average aspect ratio of 2 or less and an average particle size of 0.1 μm or more and 10 μm or less in the cross section.

4. 4. The composite ceramic material according to claim 1, wherein, in the cross section, the silicon carbide particles having a particle size three times or more the average particle size of the plurality of silicon carbide particles have an area ratio of 10% or less relative to all the silicon carbide particles in the cross section.

5. 5. The composite ceramic material according to claim 4, wherein, in the cross section, the silicon carbide particles having a particle size three times or more the average particle size of the plurality of silicon carbide particles have an area ratio of 1% or less relative to all the silicon carbide particles in the cross section.

6. The Y ２ Si ３ O ３ N ４ 6. The composite ceramic material according to claim 1, wherein the ratio of the maximum peak intensity of the type crystal phase is 1% or less.

7. A composite ceramic material described in any one of claims 1 to 6, wherein the value indicating the c-axis orientation of the silicon nitride particles having a particle size that is three or more times the average particle size of the plurality of silicon nitride particles, calculated using the X-ray diffraction pattern of the measurement surface of the composite ceramic material by the following formula (3), is less than 0.

5. [Equation 1]

8. The Y ２ Si ３ O ３ N ４ 4. The composite ceramic material according to claim 1, wherein the ratio of the maximum peak intensity of the type crystal phase is 1% or more and 15% or less.

9. The Y ２ Si ３ O ３ N ４ 9. The composite ceramic material according to claim 6, wherein the type crystalline phase contains 0.01 atomic % or more of magnesium.

10. A substrate using the composite ceramic material according to any one of claims 1 to 9; a first metal portion bonded to the substrate; A joint body comprising:

11. the substrate and the first metal portion are joined via a first joining portion, the first metal portion includes copper, The first bonding portion is made of silver, copper, titanium, hafnium, zirconium, niobium, silicon, and at least one selected from the group consisting of silicon, magnesium, indium, tin, and carbon.

12. Further comprising a second metal part bonded to the substrate, The bonded body according to claim 10 or 11, wherein the substrate is located between the first metal part and the second metal part.

13. further comprising a semiconductor element bonded to the first metal portion; The bonded body according to claim 10 , wherein the first metal portion is located between the substrate and the semiconductor element.

Images