JP7764280B2 - Composite ceramic materials and joints - Google Patents

Description

Embodiments of the present invention relate to composite ceramic materials and joined bodies.

Silicon nitride ceramics are used as materials for heat dissipation substrates because they exhibit excellent properties such as 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 equipment on which they are mounted is also required. Therefore, it is desirable for materials for heat dissipation substrates to have high thermal conductivity and bending strength. For this reason, silicon carbide, which has high thermal conductivity and bending strength, is being combined with silicon nitride. However, in such composite ceramic materials, the long diameter of the silicon nitride particles is large, at 10 μm or more, which is disadvantageous in terms of bending strength. Meanwhile, the proportion of silicon carbide is low, at less than 10% by mass, and the high thermal conductivity, one of silicon carbide's properties, is not fully utilized.

Japanese Patent Application Publication No. 8-34671

Embodiments of the present invention provide composite ceramic materials and joined bodies that can improve thermal conductivity or bending strength.

A composite ceramic material according to an embodiment comprises a plurality of silicon nitride particles and a plurality of silicon carbide particles, wherein the silicon nitride particles contain 80% or more β-type silicon nitride, and the average particle size of the plurality of silicon nitride particles is 0.1 μm or more and 10 μm or less in a cross section of the composite ceramic material. In the cross section, all silicon carbide particles account for 10% or more and 50% or less of the area 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 account for 35% or less of the area of all silicon nitride particles. The composite ceramic material further comprises grain boundaries having a Y2Si3O3N4 _crystalline phase , and in an X-ray diffraction pattern of the composite ceramic material, the ratio of the maximum peak intensity of the Y2Si3O3N4 crystalline phase to the peak intensities _{of silicon} nitride _{and silicon carbide is} 15 % _or less .

1 is a cross-sectional view showing a structural example of a composite ceramic material. FIG. FIG. 1 is a perspective view illustrating a composite ceramic material. FIG. 1 is a perspective view illustrating a composite ceramic material. FIG. 2 is a schematic cross-sectional view illustrating a bonded body.

Embodiments will be described below 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 situation. Furthermore, in the embodiments, substantially identical components are designated by the same reference numerals, and their description will be omitted.

Figure 1 is a cross-sectional schematic diagram showing an example structure of a composite ceramic material according to an embodiment. As shown in Figure 1, the composite ceramic material 110 according to an embodiment includes a crystal grain 10a, a crystal grain 10b, and grain boundaries 20 formed around the crystal grain 10a and the crystal grain 10b. In Figure 1, the black portions represent the grain boundaries 20, the white particles represent the crystal grains 10a, and the gray particles represent the crystal grains 10b. Multiple crystal grains 10a and multiple crystal grains 10b exist within the grain boundaries 20. Multiple crystal grains 10, including crystal grains 10a and 10b, may be separated from one another or may be partially in contact with one another. Some of the multiple crystal grains 10 may be separated from one another, and other portions of the multiple crystal grains 10 may be partially in contact with one another.

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 fraction, and is expressed by formula (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) as references. These are then applied to the beta(101) intensity, beta(120) intensity, alpha(102) intensity, and alpha(210) intensity in formula (1), respectively.

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 properties. The higher the beta phase ratio, the better these properties improve, and 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 100% of the silicon nitride contained in the composite ceramic material is 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.

Crystal particles 10b are, for example, silicon carbide particles.

The composite ceramic material of the embodiment may contain crystalline phases other than crystal grains 10a and 10b.

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

Ceramics using silicon nitride particles have high strength, but if the silicon nitride particles grow and the crystal grain size increases, for example through high-temperature sintering, this may have an advantage in terms of thermal conductivity but may result in a decrease in strength.

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 to be achieved. Furthermore, high-temperature sintering causes oxygen to be released 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.

The cross section of the 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 an irradiation current of ₁₀ μA. The cross section may be a fracture surface formed by breaking the center of the sintered body, but more preferably is a cross section obtained by mirror-polishing the cut surface of the 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 500 or more 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 about 2 μm, the observation area is about 130 μm × about 95 μm, and the observation magnification is about 1000x. If the average grain size of all grains is about 0.4 μm, the observation area is about 15 μm × about 9 μm, and the observation magnification is about 10,000x. If the average grain size of all grains is about 10 μm, the observation area is about 450 μm × about 270 μm, and the observation magnification is about 35x. Multiple observation areas adjusted in this way, for example, three, are prepared, and the average grain 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 grain size and area ratio of the composite ceramic material according to this embodiment.

The multiple observation images obtained are analyzed using the image processing software ImageJ. Crystal grains 10a, 10b, and grain boundaries 20 are defined 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 through 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), making it possible to distinguish between silicon nitride particles and silicon carbide particles. 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 will be performed, the conductive coating on the observation cross-section is preferably made of a material other than carbon, such as gold or platinum.

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

In the above 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, not only will heat conduction be hindered at the grain boundaries, but the proportion of grain boundary phases with low thermal conductivity will increase, resulting in a decrease in thermal conductivity. Furthermore, if the average particle size exceeds 10 μm, the surface area will be too large, making the material more susceptible to cracking and reducing strength.

In the above cross section, it is preferable that 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. This reduces the number of coarse particles with large surface areas, 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 large surface areas will increase, resulting in a decrease in strength.

In the above cross section, it is preferable that all silicon carbide particles have an area ratio of 1% to 50% 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 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, makes it possible to achieve high thermal conductivity. This allows for both high thermal conductivity and high strength to be achieved.

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

The aspect ratio of silicon carbide particles is determined by calculating the maximum and minimum Feret diameters of each particle using ImageJ, and then calculating the ratio of the maximum Feret diameter to the minimum Feret diameter.

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 crystal system, space group, _and positional relationship of the constituent atoms being the same, but the _interatomic distance or _lattice constant 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 the composition of the _{Y2Si3O3N4 crystal} .

In the X-ray diffraction pattern of the composite ceramic material, the ratio of the maximum peak intensity of the _Y2Si3O3N4 type crystalline phase to the peak intensities of silicon _nitride and _{silicon carbide} is preferably 1% or more and 15% or less, as expressed by formula (2). This results in a high thermal conductivity because there is a large amount of crystalline phase with a higher thermal conductivity than the grain boundary phase composed of a glass phase.

The conditions for measuring the X-ray diffraction pattern are set, for example, as follows: An X-ray diffractometer, such as a Rigaku Corporation Smart-Lab, 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 to a surface roughness Ra of 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 set to 10 mm, the receiving slit is set to 20 mm, and the receiving parallel slit is set to 5 degrees. The scanning range (2θ) is set to 10° to 80°, and measurements are taken in 0.01° increments.

X-ray diffraction analysis of a composite ceramic material sample detects a crystalline phase other than silicon _nitride and silicon carbide contained in the grain boundary phase. The crystalline phase is _Y2Si3O3N4 , and as shown in formula ( ₂ ), the peak intensity ratio of _Y2Si3O3N4 can be obtained by normalizing the maximum peak intensity of the crystalline phase by the intensities of the four peaks of β- and α-silicon nitrides (if α-silicon nitride is not present, the α _{( 102} ) and α( _{210 )} intensities are 0) and the maximum peak intensity of silicon carbide.

_{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 .

Next, we will explain a first example manufacturing method for the composite ceramic material of this embodiment. The first example manufacturing method for the composite ceramic material includes a mixing process, a molding process, and a sintering process.

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.

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

Examples of the second raw material include powder of silicon carbide. The average particle size of the silicon carbide powder is preferably 100 nm or less, but may be on the order of several micrometers. The silicon carbide powder may have a cubic or hexagonal crystal structure.

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, and ultimately remains as a glass phase at the grain boundaries ₂₀ together with _{a Y2Si3O3N4 crystalline} phase.

The mixed powder is preferably formed by mixing 88.5% by mass or more and 96.5% by mass or less of silicon nitride and silicon carbide, 1% by mass or more and 3.5% by mass or less of magnesium oxide, and 2.5% by mass or more and 8% by mass or less of yttrium oxide, so that the total amount is 100% by mass. If the amount of auxiliary agent is too small, grain growth of the 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.

In the molding process, the mixed powder is compressed and molded using a uniaxial press, and then the compact is subjected to cold isostatic pressing (CIP).

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 to 8 hours in a nitrogen atmosphere at 1 atmosphere pressure. The same applies when carbon is used instead of silicon carbide, but the carbon does not react with the silicon during the nitriding treatment.

In the sintering process, 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. A nitrogen atmosphere of 7.5 to 10 atmospheres prevents silicon nitride from evaporating. If nitriding is performed before the sintering process, it is preferable to perform the sintering process immediately without exposing the compact to the atmosphere. If carbon is used instead of silicon carbide, part of the silicon nitride reacts with the carbon during the sintering process to produce silicon carbide.

The sintered body obtained through the sintering process is cut into the desired shape.

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

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). A Shimadzu Autograph AG-X (100 kN) is used for the three-point bending strength test. The load cell is set to 1 kN, the test speed is 0.5 mm/min, the indenter radius and support base radius are both R2, and the distance between supports is 30 mm. The test is performed at room temperature.

The thermal conductivity of the composite ceramic material of this embodiment is 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.

The flexural strength of the composite ceramic material of this embodiment is 500 MPa or more. The upper limit of the flexural strength is not particularly limited, but is, for example, 1100 MPa or less.

The manufacturing method for the composite ceramic material is not limited to the first manufacturing example. Below, a second manufacturing example for the composite ceramic material is described.

The second manufacturing method example includes a mixing process and a sintering process.

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.

An example of the first raw material is powder such as silicon nitride. The explanation of the second raw material and auxiliary agents can be found in the explanation of the first manufacturing method example, as appropriate.

The mixed powder is preferably formed by mixing 88.5% by mass or more and 96.5% by mass or less of silicon nitride and silicon carbide, 1% by mass or more and 3.5% by mass or less of magnesium oxide, and 2.5% by mass or more and 8% by mass or less of yttrium oxide, so that the total amount is 100% by mass. If the amount of auxiliary agent is too small, grain growth of the 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.

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, problems such as failure to densify or failure to undergo phase transition to high-performance β-type silicon nitride may occur. The treatment time is not particularly limited, but is, for example, 3 minutes to 72 hours. If it is less than 3 minutes, problems such as failure to densify or failure to undergo phase transition to high-performance β-type silicon nitride may occur. If it exceeds 72 hours, decomposition may occur and sintering may not occur. This 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 causes a portion of the silicon nitride to react with the carbon to produce silicon carbide. Alternatively, hot pressing may be used instead of SPS.

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

The sintered body obtained through the sintering process is cut into the desired shape.

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, thereby suppressing a decrease in strength. If the area ratio of silicon carbide particles having a particle size three times or more the average particle size to all 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.

By using the second manufacturing method, the ratio of the maximum peak intensity of the Y2Si3O3N4 crystalline phase to the intensities of the four _{silicon nitride} peaks and the maximum _silicon carbide peak can be reduced to 1% or less in the X-ray diffraction pattern of the composite ceramic material ₁₁₀ , 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.

In the composite ceramic material 110 formed using the second manufacturing method, 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 read by referring to 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 confirm 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 degrees) to the measurement surface, preferably at an angle within ±45 degrees, or even approximately parallel. "Approximately parallel" includes not only the parallel direction but also a state within ±20 degrees of the parallel direction. Furthermore, the value indicating the orientation calculated by formula (3) is preferably less than 0.5.

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

2 and 3 are perspective views illustrating the composite ceramic material according to the embodiment.
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.

FIG. 4 is a schematic cross-sectional view illustrating the bonded body of the embodiment.
4, the joined 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.

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 also be joined directly to the composite ceramic material 110 without the joint 41.

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.

The second metal portion 32 is bonded to the composite ceramic material 110. The composite ceramic material 110 is located between the first metal portion 31 and the second metal portion 32. For example, a bonding portion 43 is provided between the second metal portion 32 and the composite ceramic material 110. The second metal portion 32 may be bonded directly to the composite ceramic material 110 without the bonding portion 43. The second metal portion 32 functions, for example, as a heat sink.

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 41-43 include, for example, at least one selected from the group consisting of silver and copper. The joint portions 41-43 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.

The joints 41-43 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 joints 41-43 preferably contain silver, copper, and at least one selected from the group consisting of titanium, hafnium, zirconium, and niobium.

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. It is preferable that the bonding portions 41 to 43 contain at least one selected from the group consisting of silver, copper, silicon, and magnesium.

When the first metal portion 31 and the second metal portion 32 contain copper, titanium is particularly preferred as the active metal. Titanium reacts with silicon nitride to form titanium nitride, which can increase the bonding strength.

By using the composite ceramic material 110 of the embodiment in the joined body 210, the thermal conductivity and bending strength of the joined body 210 can be improved. Furthermore, by using the composite ceramic material 110, which has excellent thermal conductivity, in the substrate, the heat dissipation properties of the substrate can be improved, for example. 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 properties of the substrate.

The embodiments described above provide composite ceramic materials and bonded bodies that can improve thermal conductivity and bending strength.

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, metal parts, joints, and semiconductor elements, 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 within the known range.

Furthermore, any combination of two or more elements of each specific example, to the extent technically possible, is also included within the scope of the present invention, as long as it encompasses the gist of the present invention.

In addition, all composite ceramic materials and joined bodies that can be implemented by a person skilled in the art through appropriate design modifications based on the composite ceramic materials and joined bodies described above as 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.

In addition, within the scope of the concept of this invention, a person skilled in the art may conceive of various modifications and alterations, and it is understood that these modifications and alterations also fall within the scope of this invention.

The present invention will be explained below with reference to examples.

Examples 1 to 3
Si powder, SiC powder, _MgO powder, and _Y2O3 powder were placed in a pot, balls and ethanol were added, and the mixture was kneaded for 60 to 180 minutes using a planetary ball mill at a rotation speed of 300 to 600 rpm to form a slurry. The resulting slurry was then distilled and dried to prepare a raw material powder. The raw material powder was uniaxially press-molded, then subjected to CIP treatment, nitriding at 1450°C for 4 hours in a nitrogen atmosphere at atmospheric pressure, and sintering at 1800°C to 2000°C for 12 to 72 hours in a nitrogen atmosphere at 7.5 atmospheres to form a composite ceramic material containing silicon nitride and silicon carbide. The average particle size of the silicon nitride and the proportion of coarse particles were adjusted by appropriately adjusting the rotation speed and time of the planetary ball mill and the sintering temperature and time.

After processing the above 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 applying a gold coating to this sample, the cross-sectional image shown in Figure 1 for Example 3 was obtained using SEM-EDS. In this image, the black areas represent the grain boundary phase, the white particles represent silicon nitride particles, and the gray particles represent silicon carbide particles.

(Comparative Examples 1, 3, and 5)
The silicon nitride ceramic materials for Comparative Example 1 were formed in the same manner as in Example 1, Comparative Example 3 in the same manner as in Example 2, and Comparative Example 5 in the same manner as in Example 3, except that no SiC powder was added.

(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.

After processing the above 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 etched to create a sample for cross-sectional observation. Gold was vapor-deposited on this sample, and a cross-sectional image was obtained using SEM-EDS.

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

As a result of evaluation and analysis of Examples 1 to 3, the average particle size of the silicon nitride particles was within the range of 0.1 to 10 μm, and the 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, the average particle size of the silicon carbide particles was within the range of 0.1 μm to 10 μm, and 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 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.

On the other hand, evaluation and analysis of Comparative Examples 1, 3, and 5 showed that no silicon carbide was contained, 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 showed 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 can achieve both high thermal conductivity and high strength compared to Comparative Examples 1 to 5.

(Examples 4 and 5)
_Si3N4 powder, SiC powder, MgO powder, and _Y2O3 powder were placed in a pot, _balls and _ethanol were added, and the mixture was kneaded using a planetary ball mill in the same manner as in Examples 1 to 3 to form a slurry. The resulting slurry was distilled and dried to prepare a raw material powder. The raw material powder was subjected to a heat treatment by SPS in a nitrogen atmosphere at atmospheric pressure, at a pressure of 100 MPa, at a temperature of 1800°C, for a time period of 3 minutes to 72 hours, to obtain the composite ceramic material of Example 4 comprising silicon nitride and silicon carbide.

The sintered body obtained in Example 4 was further heat-treated in a nitrogen atmosphere at 7.5 atmospheres at 1900°C for more than 3 minutes and not more than 72 hours to obtain the composite ceramic material of Example 5, which comprises silicon nitride and silicon carbide.

After processing the above 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 etched to create a sample for cross-sectional observation. Gold was vapor-deposited on this sample, and a cross-sectional image was obtained using SEM-EDS.

(Comparative Example 6)
_Si3N4 powder, SiC powder, _MgO powder, and _Y2O3 powder were placed in a pot, _balls and ethanol were added, and the mixture was kneaded using a planetary ball mill to form a slurry in the same manner as in Examples 4 and 5. The resulting slurry was distilled and dried to prepare a raw material powder. The raw material powder was subjected to a heat treatment by SPS under a nitrogen atmosphere at atmospheric pressure, at a pressure of 100 MPa, at a temperature of 1700°C, and for 3 minutes, to obtain a composite ceramic material comprising silicon nitride and silicon carbide of Comparative Example 6.

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 etched to create a sample for cross-sectional observation. Gold was vapor-deposited on this sample, and a cross-sectional image was obtained using SEM-EDS.

Table 4 shows the results of particle analysis of cross-sectional images of Examples 4 and 5 and Comparative Example 6 performed using ImageJ using the method described above, as well as the values indicating the orientation expressed by formula (3) above, and the measurement results of thermal conductivity and strength.

As a result of evaluation and analysis of Examples 4 and 5, the average particle size of the silicon nitride particles was within the range of 0.1 to 10 μm, and the 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, the average particle size of the silicon carbide particles was within the range of 0.1 to 10 μm, and the 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 area of all silicon carbide particles. The area ratio of all silicon carbide particles was within the range of 10% to 50% of all silicon nitride particles and all silicon carbide particles. The grain boundary phase contained a Y ₂ Si ₃ O ₃ N ₄ 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 represented 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.

On the other hand, as a result of evaluation and analysis of Comparative Example 6, the average particle size of the silicon nitride particles was in the range of 0.1 to 10 μm, and the silicon nitride particles having a particle size three times or more of the average particle size had an area ratio of 35% or less relative to the total silicon nitride particles. The average aspect ratio of the silicon carbide particles was 2 or less, and the silicon carbide particles having a particle size three times or more of the average particle size of silicon carbide had an area ratio of 10% or less relative to the total silicon carbide particles, but the average particle size was 0.1 μm or less. All silicon carbide particles had an area ratio of 10% to 50% relative to all silicon nitride particles and all silicon carbide particles. The grain boundary phase contained a Y ₂ Si ₃ O ₃ N ₄ 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, and its ratio was 0.01 atomic % or more. The value representing the c-axis orientation of the silicon nitride particles, as expressed by the above formula (3), was 0.5 or more. However, as a result of X-ray diffraction, the silicon nitride crystalline phase was not solely the required β-type silicon nitride, but contained 21% α-type silicon nitride, so the thermal conductivity and strength were significantly low. Furthermore, it can be seen that Examples 4 and 5 can achieve both high thermal conductivity and high strength compared to Comparative Example 6.

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 containing 80% or more beta-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 or more and 10 μm or less. 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 an area ratio of 35% or less of all silicon nitride particles, and it was found that both high thermal conductivity and high strength can be achieved.

While 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 may be embodied in a variety of other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their variations are within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

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 (13)

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 ;}
A composite ceramic material, wherein in an 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. 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. 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. 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. 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 composite ceramic material according to claim 1 , wherein a ratio of the _maximum peak intensity of _{the Y2Si3O3N4 type} crystal phase is 1% or _less . 7. The composite ceramic material according to claim 1, wherein a value indicating the c-axis orientation of the silicon nitride particles having a particle size three times or more the average particle size of the plurality of silicon nitride particles, calculated by the following formula ( 3 ) using an X-ray diffraction pattern of a measurement surface of the composite ceramic material , is less than 0.5 :
4. The composite ceramic material according to claim 1 , wherein a ratio of the maximum peak intensity of _{the Y2Si3O3N4 type} crystal _phase is 1% or more and 15% or _less . 9. The composite ceramic material according to claim 6 _, wherein _{the Y2Si3O3N4 type} crystal phase contains 0.01 atomic _% or more of magnesium. 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: the substrate and the first metal portion are joined via a first joining portion,
the first metal portion includes copper,
11. The bonded body of claim 10 , wherein the first bonded portion comprises silver, copper, and at least one selected from the group consisting of titanium, hafnium, zirconium, niobium, silicon, magnesium, indium, tin, and carbon. 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. 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.