TWI728073B - Pollinite sintered body, its manufacturing method and composite substrate - Google Patents

Abstract

The sintered sintered body of flatilite of the present invention is mainly composed of flatilite and contains silicon nitride or silicon carbide. It is preferable that the sintered body made of flatilite has a thermal expansion coefficient of less than 2.4 ppm/°C at 40 to 400°C, an open porosity of 0.5% or less, and an average crystal grain size of 1 μm or less.

Description

Pollinite sintered body, its manufacturing method and composite substrate

The present invention relates to a sintered body of calalite, its preparation method and a composite substrate.

Pollinite is known as a material with high heat resistance and a small coefficient of thermal expansion, and can be used as a material with high thermal shock resistance. In order to improve the mechanical properties of flatidite, it is also known that flatidite can be combined with silicon nitride or silicon carbide with high Young's modulus or strength (Patent Documents 1 and 2). Patent Document 1 discloses that rare earth oxides and silicon nitride or silicon carbide are added to a vermilionite with an average particle diameter of 1.2 μm and fired in the air to obtain a vermilionite sintered body with a relative density of 97 to 98%. Patent Document 2 discloses that silicon nitride or silicon carbide with an average particle size of 1 μm is added to a vermilionite with an average particle size of 3μm, and then sintered at atmospheric pressure in a nitrogen atmosphere to obtain a vermilionite sintered body with a high Young's modulus. .

In addition, Patent Document 3 discloses a composite substrate formed by directly bonding a functional substrate composed of lithium tantalate, lithium niobate, and the like and a support substrate made of sintered vermilionite as an acoustic wave device such as a surface acoustic wave device. In this elastic wave device, since the thermal expansion coefficient of the sintered vermilion stone of the support substrate is very small, 1.1 ppm/°C (40-400°C), the frequency-temperature dependence is greatly improved.

【Prior Technical Literature】

【Patent Literature】

Patent Document 1: Patent No. 3574560

Patent Document 2: Patent No. 4416191

Patent Document 3: International Patent Publication No. 2015/186571

When a functional substrate and a supporting substrate are joined in the manner of Patent Document 3, the surfaces of the two substrates are required to have a high degree of flatness. However, the relative density of the flatilite sintered body of Patent Document 1 is 97 to 98%, and there are several percentages of pores. Even if the surface of the sintered body is polished, high flatness cannot be obtained. In addition, in the flatilite sintered body of Patent Document 2, the flatilite raw material particles are 3 μm, and a sintering aid is added, so that the sintered particle size becomes larger than that of the flatilite raw material particles. Therefore, even if the polishing process is performed, a high degree of flatness cannot be obtained. In addition, if this sintered calalite is used as an elastic wave device, the sintered particle size becomes larger than the distance between the electrodes. In this case, the sound velocity of the composite substrate may change, resulting in a change in device characteristics.

In order to solve the above-mentioned problems, the main purpose of the present invention is to maintain the low thermal expansion coefficient of the flatilite sintered body, improve the rigidity and increase the flatness of the polishing surface.

The sintering system of plastolite of the present invention is a sintered body of plastolite containing silicon nitride or silicon carbide, which is mainly composed of plastinite, and has a thermal expansion coefficient of less than 2.4ppm/°C at 40~400°C and an open porosity of 0.5%. Hereinafter, the average crystal particle diameter (average particle diameter of sintered particles) is 1 μm or less. If you use this sintered glazeite Body, can maintain the low thermal expansion coefficient of the flatilite, improve the rigidity and increase the flatness of the polishing surface.

The method for preparing the flatilite sintered body of the present invention includes (a) mixing 60 to 90% by volume of flatilite powder with an average particle size of 0.1 to 1 μm and 10 to 40% by volume of silicon nitride powder with an average particle size of 0.1 to 1 μm. 100% by volume to obtain mixed raw material powder, or mix 70~90% by volume of vermilionite powder with an average particle size of 0.1~1μm and 10-30% by volume of silicon carbide powder with an average particle size of 0.1~1μm, totaling 100% by volume, The step of obtaining mixed raw material powder; and (b) forming the above-mentioned mixed raw material powder into a shaped body of a predetermined shape, which ^{is hot-pressed at a pressure of 20 to 300 kgf/cm 2} and a sintering temperature of 1350 to 1450°C (maximum temperature) The step of firing to obtain a sintered body of vermilionite. This production method is suitable for the production of the sintered sintered body of vermilionite of the present invention. In addition, the average particle size of the powder was measured by the laser diffraction method (the same applies below).

The composite substrate of the present invention is a composite substrate in which a functional substrate and a support substrate are joined, and the support substrate is the above-mentioned sintered body of calalite. Since the polished surface of this composite substrate, which is a support substrate, of the sintered sintered vermilionite has high flatness, it can be well bonded to a functional substrate. In addition, when this composite substrate is used in a surface acoustic wave device, the frequency-temperature dependence can be greatly improved. Furthermore, even in optical waveguide elements, LED elements, and switching elements, the support substrate has a small coefficient of thermal expansion, so performance can be improved.

10‧‧‧Composite substrate

12‧‧‧Piezoelectric substrate

14‧‧‧Support substrate

30‧‧‧Electronic components

32、34‧‧‧IDT electrode

36‧‧‧Reflective electrode

The first figure is the manufacturing process drawing of the sintered body of flatilite.

FIG. 2 is a perspective view of the composite substrate 10.

FIG. 3 is a perspective view of the electronic component 30 manufactured using the composite substrate 10.

Fig. 4 is an SEM image of the polished surface of the sintered body of vermilionite in Experimental Example 3, (a) the original data, and (b) the data after the binarization process.

The following describes the embodiments of the present invention, but they cannot be used to limit the present invention. Without departing from the spirit and scope of the present invention defined by the appended claims, those skilled in the art can make various changes based on common knowledge. , Improve.

The flatilite sintered system of this embodiment is mainly composed of flatilite and contains silicon nitride or silicon carbide. The main component refers to the component with the largest volume in the sintered body. It is preferable that the sintered body made of flatilite has a thermal expansion coefficient of less than 2.4 ppm/°C at 40 to 400°C, an open porosity of 0.5% or less, and an average crystal grain size of 1 μm or less. Although the sintered body of flatilite contains silicon nitride or silicon carbide, which has a higher coefficient of thermal expansion than that of flatilite, it can still maintain a low coefficient of thermal expansion. In addition, since the sintered body made of plastinite contains silicon nitride or silicon carbide with a higher Young's modulus than that of plastinite, its rigidity is higher than that of plastinite alone. In addition, the open porosity of the sintered balsamite is 0.5% or less, contains almost no pores, has an average particle size of 1 μm or less, and the flatness of the polished surface (polished surface) is improved.

It is preferable that the sintered body of vernilite of the present embodiment has 10 or less pores with a maximum length of 1 μm or more per an area of 100 μm×100 μm. If the number of pores is 10 or less, the flatness of the polished surface becomes higher. The number of pores is preferably 3 or less, more preferably 0.

It is preferable that the sintered body of vernilite of the present embodiment has a Young's modulus of 160 GPa or more and a 4-point bending strength of 220 MPa or more. Due to silicon nitride or carbonization The Young's modulus or strength of silicon is higher than that of flatidite. By adjusting the addition ratio of flatidite, the Young's modulus of the flatidite-based sintered body can reach 160GPa or more, and the 4-point bending strength can be 220MPa or more.

It is preferable that the average roughness Ra of the center of the polished surface of the vernilite sintered body of this embodiment is 1.5 nm or less. As a composite substrate used for elastic wave devices, it is known to be made by joining a functional substrate and a support substrate. Therefore, a sintered sintered calalite with a polishing surface Ra of 1.5 nm or less is used as a support substrate to make the support substrate and the functional substrate The bonding is good. For example, the actual bonding area ratio (joining area ratio) in the bonding interface is 80% or more (preferably 90% or more). The center average roughness Ra of the polished surface is 1.1 nm or less, more preferably 1.0 nm or less, and most preferably 0.8 nm or less.

It is preferable that the sintered sintered body made of balsamite of this embodiment has a thermal expansion coefficient of 2.0 ppm/°C or less at 40 to 400°C. The composite substrate formed by using the sintered body of calalite as the supporting substrate is applied to the elastic wave device. When the temperature of the elastic wave device rises, the functional substrate has thermal expansion smaller than the original thermal expansion, which can improve the frequency-temperature dependence of the elastic wave device. The coefficient of thermal expansion at 40 to 400°C is preferably 1.8 ppm/°C or less.

When the flatilite sintered body of this embodiment contains silicon nitride, the flatilite phase is preferably 60-90% by volume, and the silicon nitride phase is 10-40% by volume. When silicon carbide is contained, the flatilite phase is preferred. It is 70~90% by volume, and the silicon carbide phase is 10~30% by volume. With this combination ratio, the characteristics such as the number of pores or Young's modulus, the average roughness of the center of the polished surface Ra, and the coefficient of thermal expansion at 40 to 400°C are good. The volume% of each phase is obtained in the following manner. That is, for the polished surface of the sintered sintered body of calalite in this embodiment, image observation and assembly were performed with a SEM reflection electron microscope. Component analysis, the area ratio of each phase is obtained by the ratio of vernixite in the image, which is expediently used as the volume ratio (vol%) of each phase.

Next, an embodiment of the method for producing the sintered sintered body of vermilionite according to the present invention will be described. Referring to Fig. 1, the production of the sintered body includes (a) the steps of preparing a mixed raw material powder, and (b) the step of producing the sintered body of calalite.

Step (a): Preparation of mixed raw material powder

It is preferable to use a powder with high purity and a small average particle size as the raw material of flatilite. The purity is preferably 99.0% or more, more preferably 99.5% or more, and most preferably 99.8% or more. The unit of purity is mass %. In addition, the average particle diameter (D50) is preferably 1 μm or less, more preferably 0.1 to 1 μm. The raw material of flatilite can be commercially available, or it can be made of high-purity magnesia, alumina, and silica powder. For the production method of flatilite raw material, the method described in Patent Document 3 can be referred to. The silicon nitride raw material or the silicon carbide raw material preferably uses a powder with a small average particle size. The average particle size is preferably 1 μm or less, more preferably 0.1 to 1 μm. When preparing the mixed raw material powder of flatidite raw material and silicon nitride raw material, for example, weigh 60~90% by volume of flatidite raw material and 10~40% by volume of silicon nitride raw material for a total of 100% by volume, and mix with a mixer such as a ball mill , If necessary, dry with a spray dryer to obtain mixed raw material powder. In addition, when preparing the mixed raw material powder of flatilite raw material and silicon carbide raw material, for example, weighing 70-90% by volume of flatilite raw material and 10-30% by volume of silicon carbide raw material, a total of 100% by volume, and mixing with a mixer such as a ball mill , If necessary, dry with a spray dryer to obtain mixed raw material powder.

Step (b): Production of sintered body

The mixed raw material powder obtained in step (a) forms a molded body of a predetermined shape. The molding method is not particularly limited, and general molding methods can be used. E.g, The mixed raw material powder is directly pressed into a mold. In press molding, spray drying can be used to form pellets, and the moldability becomes good. In addition, organic adhesives are added to make bad soil, extruded to form, and make mud to form flakes. These procedures must remove the organic adhesive before or during the firing step. In addition, CIP (cold hydrostatic pressure) high pressure forming can also be used.

Next, the obtained molded body is fired to produce a flatilite sintered body. At this time, the sintered particles are maintained in a fine state, and the discharge of pores during sintering can improve the flatness of the surface of the sintered sintered body. This method is very effective for hot pressing. Compared with normal temperature sintering, the use of this hot pressing method can improve the densification of the fine particle state at low temperatures, and suppress the common large air pores in normal temperature sintering. The firing temperature during hot pressing is preferably 1350 to 1450°C, more preferably 1375 to 1425°C. In addition, the pressure during hot pressing is preferably 20 to 300 kgf/cm ² . In particular, the low pressure can miniaturize the hot press fixture and prolong its life. The holding time of the firing temperature (maximum temperature) can be selected for an appropriate and appropriate time in consideration of the shape or size of the molded body, the characteristics of the heating furnace, and the like. Specifically, the preferred holding time is, for example, 1 to 12 hours, and more preferably 2 to 8 hours. The firing environment is not particularly limited, and the environment during the hot pressing can be an inert gas environment such as general nitrogen and argon. The heating rate or cooling rate can be appropriately and appropriately set in consideration of the shape or size of the molded body, the characteristics of the heating furnace, and the like. For example, it can be set in the range of 50 to 300°C/hr.

Next, an embodiment of the composite substrate of the present invention will be described. The composite substrate of the present embodiment is formed by joining a functional substrate and a support substrate made of the above-mentioned flatilite sintered body. The composite substrate can increase the bonding area of the two substrates to have good bonding characteristics. The functional substrate is not particularly limited. For example, it is selected from lithium tantalate, lithium niobate, gallium nitride, silicon dioxide, and the like. Bonding method is more Best for direct bonding. In the case of direct bonding, the bonding surfaces of the functional substrate and the support substrate are separately polished and then activated, and the two bonding surfaces are pressed against the two substrates in a state where they face each other. To activate the bonding surface, for example, the bonding surface is irradiated with an inert gas (argon, etc.) ion beam, plasma, or neutral atom beam. The thickness ratio of the functional substrate and the support substrate (functional substrate thickness/support substrate thickness) is preferably 0.1 or less. Figure 2 shows an example of a composite substrate. The composite substrate 10 is formed by directly bonding the piezoelectric substrate 12 as a functional substrate and the supporting substrate 14 together.

The composite substrate of this embodiment can be used as an electronic component. This electronic component can be selected from LED components, optical waveguide components, switching components, etc. on elastic wave components (surface acoustic wave components or Lamb waves, thin film resonators (FBAR)). When the elastic wave element uses the above-mentioned composite substrate, since the thermal expansion coefficient of the sintered sintered body of calalite as the supporting substrate is very small and less than 2.4 ppm/°C (40 to 400°C), the frequency temperature dependence can be greatly improved. FIG. 3 shows an example of an electronic component 30 manufactured using the composite substrate 10. The electronic component 30 is a One Port SAW resonator, that is, a surface acoustic wave component. First, a plurality of patterns of electronic components 30 are formed on the piezoelectric substrate 12 of the composite substrate 10 using general photoetching, and then the electronic components 30 are cut out one by one. The electronic component 30 uses a photoetching technique to form IDT (Interdigital Transducer) electrodes 32 and 34 and a reflective electrode 36 on the surface of the piezoelectric substrate 12.

The above-mentioned embodiments cannot be used to limit the present invention, and the technical scope of the present invention describes the present invention, and is not limited to the present invention.

[Examples]

1. Production of mixed raw material powder

3mm)，在使用純水之球磨機中進行70小時粉碎，以製作平均粒徑0.5~0.6μm的菫青石粉碎物。將所獲得的泥漿在大氣下，以110℃進行乾燥，藉由篩選乾燥物獲得菫青石粉末。依表一中實驗例1~9的原料粉末組成比例，秤量菫青石原料與氮化矽原料或碳化矽原料，藉由使用

5mm氧化鋁圓石的球磨機混合，利用噴霧乾燥製作混合原料粉末。此外，氮化矽原料可為市售平均粒徑0.8μm，純度97%以上的粉末，碳化矽原料可為市售平均粒徑0.5μm，純度97%以上的粉末。 First, use commercially available high-purity magnesia, alumina, and silica powders with an average particle size of 1 μm or less and a purity of 99.9% or more to make the raw material of flamite. In other words, the powders are weighed and mixed for the purpose of forming the flatilite composition, and heated at 1400° C. for 5 hours in an atmospheric environment to obtain coarse flatilite particles. For the obtained coarse particles of glazeite, alumina was used as the cobblestone (

3mm), pulverized in a ball mill using pure water for 70 hours to produce pulverized glazeite with an average particle diameter of 0.5 to 0.6 μm. The obtained slurry was dried at 110° C. under the atmosphere, and the dried product was sieved to obtain flaxite powder. According to the composition ratio of the raw material powder in Experimental Examples 1-9 in Table 1, weigh the calalite raw material and the silicon nitride raw material or silicon carbide raw material by using

The 5mm alumina pebbles are mixed with a ball mill and spray-dried to produce mixed raw material powder. In addition, the silicon nitride raw material can be a commercially available powder with an average particle size of 0.8 μm and a purity of more than 97%, and the silicon carbide raw material can be a commercially available powder with an average particle size of 0.5 μm and a purity of more than 97%.

2. Production of sintered body of plastinite

100mm厚度25mm的成形體。將各成形體置於石墨製的模具中，使用熱壓爐，在200kgf/cm²壓力下，以1375~1425℃燒成溫度(最高溫度)進行5小時燒成，以製作菫青石質燒結體。各實驗例的燒成溫度如表一所示。燒成環境為氬氣環境，升溫速度為100℃/hr，降溫速度為200℃/hr，降溫時從1200℃以下退火。此外，實驗例10僅使用菫青石粉末，以相同條件製作成形體，使用熱壓爐，在壓力200kgf/cm²下，以1425℃燒成溫度(最高溫度)，進行5小時燒成，以製作單獨菫青石的燒結體。 The mixed raw material powders of experimental examples 1 to 9 were pressure-formed ^{with a 50kgf/cm 2 uniaxial mold to obtain}

A molded body with a thickness of 100mm and a thickness of 25mm. Place each molded body in a graphite mold and use a hot-press furnace to fire at a sintering temperature (maximum temperature) of 1375 to 1425°C for 5 hours under a pressure of ^{200 kgf/cm 2 to produce a sintered body of vermilionite} . The firing temperature of each experimental example is shown in Table 1. The firing environment is an argon atmosphere, the temperature rise rate is 100°C/hr, the temperature drop rate is 200°C/hr, and the annealing is carried out from 1200°C or lower when the temperature is lowered. In addition, experimental example 10 uses only vermilionite powder to produce a molded body under the same conditions, using a hot press furnace, at a pressure of 200 kgf/cm ² and a sintering temperature of 1425°C (maximum temperature) for 5 hours to produce A sintered body of glazeite alone.

3. Characteristic evaluation

Test pieces (4×3×40 mm anti-bending rods) were sliced from the vermilion sintered bodies of Experimental Examples 1 to 10 for evaluation tests. In addition, the polished surface of the sintered body can be processed into a mirror surface by polishing one surface of a 4×3×10 mm test piece. Use 3μm diamond particles, 0.5μm diamond particles for grinding in sequence, and finally with diamond particles below 0.1μm for final grinding and modification. The evaluation of the characteristics is as follows.

(1) Crystalline phase

The sintered body is pulverized, and the crystal phase is measured with an X-ray diffraction apparatus. The measurement conditions are CuKα, 50kV, 300mA, 2θ=5-70°. A rotating counter-cathode X-ray diffractometer (RINT manufactured by Rigaku Electrode) was used.

(2) Composition of sintered body

The polished surface of the sintered body was observed by reflection electron imaging and composition analysis by SEM, and the area ratio of the vermilion phase to other crystalline phases was obtained from the image contrast ratio, which was used as the volume ratio of the sintered body. Figure 4 shows the ground surface An example of SEM image. Figure 4 is an SEM image of the polished surface of the sintered body of vermilionite in Experimental Example 3. (a) is the original data, and (b) is the data after the binarization process. In Figure 4(a), the black part is the calalite phase, and the white part is the silicon nitride phase.

(3) Bulk density, open porosity

Measure the bulk density and open porosity by the Archimedes method using pure water using an anti-folding rod.

(4) Relative density

The calculated density of the sintered body is calculated from the composition of the sintered body and the density of each component, and the ratio of the measured bulk density to the calculated density is taken as the relative density. In the present invention, pansy bluestone density 2.505g / cm ^3, a silicon nitride density of 3.20g / cm ^3, silicon carbide density of 3.21g / cm ^3. The density of silicon nitride and silicon carbide used in the present invention does not consider the influence of impurity oxygen in the raw material.

(5) Bending strength

According to JIS R1601, the 4-point bending strength is measured. The shape of the test piece is a 3×4×40 mm anti-folding rod or a half-length anti-folding rod.

(6) Young's modulus

According to the JIS R1602 standard, it is measured by the static torsion method. The shape of the test piece is a 3×4×40 mm anti-folding rod.

(7) Thermal expansion coefficient (40~400℃)

According to the JIS R1618 standard, the measurement is carried out by the pressure bar differential method. The shape of the test piece is a 3×4×20 mm anti-folding rod.

(8) Number of stomata

The polished surface of the completed sintered body was observed by SEM, and the number of pores with a maximum length of 1 μm or more per 100 μm×100 μm was counted.

(9) Surface flatness (Ra)

With respect to the polished surface of the sintered body completed as described above, the centrality average roughness Ra was measured using AFM. The measurement range is 10μm×10μm.

(10) Average particle size of sintered particles

For the polished surface of the sintered body completed above, thermal etching was performed at 1200 to 1400°C for 2 hours, the size of 200 or more sintered particles was measured by SEM, and the average particle size was calculated by linear analysis. The linear analysis coefficient is 1.5, and the length measured by SEM is multiplied by 1.5 as the average particle size.

(11) Joinability

Discs with a diameter of 100 mm and a thickness of 600 μm were cut from the sintered bodies of Experimental Examples 1-10. After grinding and processing the disc according to the above method, the surface is cleaned to remove particles or pollutants. Next, the disc is used as a supporting substrate, and the supporting substrate and the functional substrate are directly bonded to obtain a composite substrate. In other words, firstly, the bonding surfaces of the supporting substrate and the functional substrate are activated with an argon ion beam, and then the two bonding surfaces are faced to each other and pressed at 10 tonf to obtain a bonded composite substrate. As a functional substrate, a lithium tantalate (LT) substrate and a lithium niobate (LN) substrate can be used. The bonding property is evaluated through infrared images. A bonding area of 90% is considered "best", 80% or more and 90% or less is "good", and 80% or less is "not good".

4. Evaluation results

Compared with the sintered body of pure vermilionite of Experimental Example 10, the sintered body of vermilionite of Experimental Examples 1 to 9 containing silicon nitride or silicon carbide has increased flexural strength and Young's modulus. The Young's modulus is increased to more than 160 GPa, and the 4-point bending strength is more than 220 MPa. In addition, the sintered bodies of vermilionite of Experimental Examples 1 to 4 and 6 to 8 have a thermal expansion coefficient of less than 2.4 ppm/°C at 40 to 400°C (Experimental Examples 1 to 4 with silicon nitride added are 1.4 to 1.8 ppm/°C) , The experimental examples 6 to 8 where silicon carbide was added were 1.8 to 2.3 ppm/°C). Although it was slightly increased compared with the sintered vermilionite alone of experimental example 10, the coefficient of thermal expansion was still low. In addition, the open porosity of the vermilionite sintered bodies of Experimental Examples 1 to 4 and 6 to 8 was less than 0.1%, the average crystal grain size was 1 μm or less, and the center average roughness Ra of the polished surface was 1.1 nm or less. Therefore, the bonding performance between the discs cut out of the sintered bodies of vermilionite and the functional substrate in the experimental examples 1 to 3, 6, and 7 is the "best" which is 90% or more of the bonding area of the two. According to the experimental examples 4, 8 When the disc cut out of the sintered plastinite body is directly bonded to the functional substrate, the bonding performance is "good", which is 80% or more and 90% or less of the bonding area. In addition, when the average center roughness Ra of the polished surface becomes this low value, it contributes to reducing the number of pores to 3 or less. In addition, one of the reasons why the average particle size of Experimental Examples 1 to 9 became 1 μm or less was that the rare earth oxide sintering aid was not used for sintering.

In addition, Experimental Examples 1 to 4 and 6 to 8 correspond to Examples of the present invention, and Experimental Examples 5, 9, and 10 correspond to Comparative Examples. This experimental example cannot be used to limit the present invention.

The present invention is based on claiming the priority of Japanese Patent Application No. 2016-058969 filed on March 23, 2016 and Japanese Patent Application No. 2017-033437 filed on February 24, 2017, the contents of which are cited in the specification of the present invention .

Claims (11)

A sintered sintered sintered body made of stigmaite, comprising silicon nitride or silicon carbide as its main component, wherein the thermal expansion coefficient of the sintered sintered body at 40 to 400°C is less than 2.4ppm/°C, The open porosity is 0.5% or less, and the average crystal grain size is 1 μm or less (but not including 1 μm). According to the first item of the scope of the patent application, the sintered body has a thermal expansion coefficient of 1.7 ppm/°C at 40 to 400°C. The sintered sintered body described in item 1 of the scope of patent application, wherein the average crystal grain size of the sintered sintered body is 0.61 μm or less. According to the first item of the patent application, the number of pores with a maximum length of 1 μm or more is 10 or less per 100 μm×100 μm polished surface. The sintered body of flatilite according to any one of items 1 to 4 in the scope of the patent application, wherein the Young's modulus is 160 GPa or more. According to the sintered body described in any one of items 1 to 4 in the scope of the patent application, the 4-point bending strength is 220 MPa or more. According to the sintered body of flatilite according to any one of items 1 to 4 in the scope of the patent application, the center average roughness Ra of the polished surface is 1.5 nm or less. As described in any one of items 1 to 4 in the scope of the patent application, the sintered body of flatilite contains silicon nitride. The polished surface is imaged and analyzed with a SEM reflection electron microscope, and the image of the flax When the ratio of bluestone is obtained, the area ratio of the bluestone phase and the silicon nitride phase is 60~90% by volume, and the silicon nitride phase has 10-40% by volume. As described in any one of items 1 to 4 of the scope of patent application, the sintered body contains silicon carbide. The polished surface is imaged and analyzed with a SEM reflection electron microscope, and the image of the sintered body When obtaining the area ratio of the bluestone phase to the silicon carbide phase, the bluestone phase has 70 to 90% by volume, and the silicon nitride phase has 10 to 30% by volume. A method for preparing a flatilite sintered body, comprising: (a) mixing 60~90% by volume of flatilite powder with an average particle size of 0.1~1μm and 10~40% by volume of silicon nitride powder with an average particle size of 0.1~1μm, a total of 100 Volume%, obtain mixed raw materials, or mix 70~90% by volume of vernix powder with an average particle size of 0.1~1μm and 10-30% by volume of silicon carbide powder with an average particle size of 0.1~1μm, a total of 100% by volume, to obtain a mixed raw material Step; and (b) forming the mixed raw materials to form a shaped body of a predetermined shape, and the shaped body ^{is hot-pressed and fired at a pressure of 20~300kgf/cm 2} and a firing temperature of 1350~1450°C to obtain a pansy The steps of the bluestone sintered body. A composite substrate is a composite substrate formed by joining a functional substrate and a supporting substrate, wherein the supporting substrate is the sintered body of flatilite described in any one of the scope of patent application 1-9.

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