Aluminum nitride sintered body and method for producing the same

Abstract

To provide an aluminum nitride sintered body having high thermal conductivity characteristics and reduced warpage of a substrate.SOLUTION: An aluminum nitride sintered body comprises aluminum nitride particles and a sintering aid phase. In the aluminum nitride sintered body, a thermal conductivity λ when converted to a thickness of 2.5 mm is 260 W / mK or more, and a warpage index value C1 indicating warpage of the entire substrate region is less than 0.20 μm / mm. The warpage index value C1 is calculated by C1=(Hmax-Hmin) / D1, using: a maximum height value Hmax (μm) and a minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square region of an entire surface of a substrate sample of the aluminum nitride sintered body; and a distance D1 (mm) of a diagonal line of the square region.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an aluminum nitride sintered body and a method for producing the same. [Background technology]

[0002] Aluminum nitride sintered body products are made of insulating materials with high thermal conductivity and have attracted attention as materials for high thermal conductivity substrates. Due to their excellent thermal conductivity, aluminum nitride sintered bodies are widely used as heat dissipation substrates for electronic components such as power transistor module substrates, light-emitting diodes, IC packages, and laser diodes in semiconductors and electronic devices where high temperatures can cause unstable operation. In recent years, aluminum nitride sintered body substrates have been widely used in electronic substrates for mobile applications, and higher heat dissipation capabilities are required. Therefore, various attempts have been made to improve the thermal conductivity of aluminum nitride sintered bodies.

[0003] For example, Patent Document 1 discloses an aluminum nitride sintered body and a method for producing the same. The aluminum nitride sintered body in Patent Document 1 has a high thermal conductivity of 260 W / m K or more by specifying the constituent components and content ratios of the grain boundary phase and the microstructure, specifically the average diameter, minimum diameter, maximum diameter, and number of aluminum nitride crystal grains. This method for producing an aluminum nitride sintered body includes the following steps: a molding step of mixing aluminum nitride powder having an average particle size of 1.5 μm or less with a sintering aid containing at least a Y compound powder and molding the mixture to obtain a green body; a degreasing step of degreasing the green body; a deoxidizing step of heat-treating the deoxidized green body in a non-oxidizing atmosphere or a reduced-pressure atmosphere at 1300°C to 1550°C to deoxidize it; a sintering step of heat-treating the deoxidized green body in a non-oxidizing atmosphere at 1800°C to 1950°C to obtain a primary sintered body having a thermal conductivity of 230 W / m·K or more; and a reducing step of heat-treating the primary sintered body in a weakly reducing atmosphere at 1750°C to 1900°C to obtain a high-thermal-conductivity aluminum nitride sintered body having a thermal conductivity of 260 W / m·K or more. In particular, in the sintering step, the deoxidized green body is heat-treated in a non-oxidizing atmosphere at 1800°C to 1950°C to obtain a primary sintered body having a thermal conductivity of 230 W / m·K or more. In the subsequent reduction process, the primary sintered body is heat-treated in a weakly reducing atmosphere at 1750°C to 1900°C to obtain an aluminum nitride sintered body with a thermal conductivity of 260 W / m·K or more (high thermal conductive aluminum nitride sintered body). In this reduction process, the grain boundary phase, which is a factor that inhibits thermal conductivity, is precipitated on the surface and removed, resulting in a final aluminum nitride sintered body with a thermal conductivity of 260 W / m·K or more. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-37691 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 provides an aluminum nitride sintered body having high thermal conductivity. Conventional aluminum nitride sintered bodies such as those disclosed in Patent Document 1 require high-temperature firing in a reducing atmosphere to achieve high thermal conductivity. However, it has been found that such conditions make the sintered body prone to deformation and warping (see, for example, Comparative Examples 1, 2, and 9 herein). Furthermore, when a conventional aluminum nitride sintered body is incorporated as a substrate into an electronic circuit, warping of the aluminum nitride sintered body substrate itself can adversely affect the densification of the circuit and the yield of the electronic circuit. Therefore, the inventors aimed to reduce warping of the substrate when the aluminum nitride sintered body is formed as a substrate while maintaining the high thermal conductivity of the aluminum nitride sintered body.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an aluminum nitride sintered body having high thermal conductivity and reduced substrate warpage, and a method for manufacturing the same. [Means for solving the problem]

[0007] (Section 1) An aluminum nitride sintered body according to one embodiment of the present invention is an aluminum nitride sintered body containing aluminum nitride particles and a sintering aid phase, The thermal conductivity λ when converted to a thickness of 2.5 mm is 260 W / mK or more, and The warpage index value C1 indicating the warpage of the entire substrate area is less than 0.20 μm / mm, The warpage index value C1 is calculated by using the maximum height value Hmax (μm) and the minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square area of ​​the entire surface of the substrate sample of the aluminum nitride sintered body, and the distance D1 (mm) of the diagonal of the square area, C1=(Hmax-Hmin) / D1 It is characterized in that it is calculated by the following formula.

[0008] (Section 2) An aluminum nitride sintered body according to a further embodiment of the present invention is preferably the aluminum nitride sintered body according to item 1, characterized in that the warpage index value C1 is 0.14 to 0.19 μm / mm.

[0009] (Section 3) An aluminum nitride sintered body according to a further embodiment of the present invention is more preferably the aluminum nitride sintered body according to item 1 or 2, wherein a second warpage index value C2 indicating warpage in a substrate corner region of the aluminum nitride sintered body is 0.17 to 0.35 μm / mm, The second warpage index value C2 is calculated by using a maximum height value Hmax (μm) and a minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square region including a corner on the surface of the substrate sample of the aluminum nitride sintered body, and a distance D2 (mm) between the diagonals of the square region, C2=(Hmax-Hmin) / D2 It is characterized in that it is calculated by the following formula.

[0010] (Section 4) An aluminum nitride sintered body according to a further embodiment of the present invention is more preferably the aluminum nitride sintered body according to any one of items 1 to 3, wherein a third warpage index value C3 indicating warpage in a substrate central region of the aluminum nitride sintered body is 0.10 to 0.29 μm / mm, The third warpage index value C3 is calculated by using a maximum height value Hmax (μm) and a minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square area located at the center of the surface of the substrate sample of the aluminum nitride sintered body, and a diagonal distance D3 (mm) of the square area, C3=(Hmax-Hmin) / D3 It is characterized in that it is calculated by the following formula.

[0011] (Section 5) An aluminum nitride sintered body according to a further embodiment of the present invention is preferably the aluminum nitride sintered body according to any one of items 1 to 4, characterized in that the thermal conductivity λ / warpage index value C1 is 1400 or more and 2000 or less.

[0012] (Section 6) An aluminum nitride sintered body according to a further embodiment of the present invention is preferably the aluminum nitride sintered body according to any one of items 1 to 5, characterized in that it is obtained by sintering 90 to 99.5% by weight of aluminum nitride and 0.5 to 10% by weight of yttrium oxide.

[0013] (Section 7) A method for producing an aluminum nitride sintered body according to one embodiment of the present invention includes the steps of: A method for producing an aluminum nitride sintered body according to any one of items 1 to 6, a mixing step of mixing an aluminum nitride raw material powder, a sintering aid, and an organic solvent to prepare a raw material mixture slurry; a molding step of molding the raw material mixture to obtain a molded body; a degreasing step of heating the compact in a degreasing temperature range under a dry air inflow or in a nitrogen atmosphere to perform a degreasing treatment; a deoxidation step of heating the degreased compact in a deoxidation temperature range in a nitrogen atmosphere to perform a deoxidation treatment; a sintering step of sintering the deoxidized compact in a nitrogen atmosphere within a sintering temperature range to produce an aluminum nitride precursor sintered body; a reduction firing step of embedding at least a portion of the aluminum nitride precursor sintered body with aluminum nitride powder to prepare an embedded structure, and heat-treating the embedded structure at 1850 to 1950°C in a weakly reducing atmosphere; a removing step of removing the aluminum nitride powder from the reduction-fired embedded structure to obtain an aluminum nitride sintered body; Including, The reduction firing step is carried out for 30 hours or more.

[0014] (Section 8) A further aspect of the method of the present invention is preferably the method of item 7, wherein the reduction firing step includes placing the aluminum nitride precursor sintered body in a graphite container, or a BN container or an AlN container in which carbon black or a carbon sheet has been placed, and embedding the aluminum nitride precursor sintered body in aluminum nitride powder until it can no longer be seen. [Effects of the Invention]

[0015] The present invention provides an aluminum nitride sintered body that has a high thermal conductivity of 260 W / mK or more and reduces warpage of the substrate. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram showing an example of a reduction firing step in one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a reduction firing step in conventional examples (Comparative Examples 1 and 2). [Figure 3] FIG. 1 is a schematic diagram showing the measurement ranges of warpage index values ​​C1, C2, and C3 on the substrate surface of an aluminum nitride sintered body. [Figure 4] (a) Images visually showing the results of measuring the three-dimensional shape of the aluminum nitride sintered body substrates of Example 1 and Comparative Example 1, where lighter colors indicate higher positions from the reference plane. DETAILED DESCRIPTION OF THE INVENTION

[0017] An aluminum nitride sintered body according to one embodiment of the present invention has a substrate shape of a predetermined thickness and can be used as a circuit board for mounting electronic components. The aluminum nitride sintered body is formed by sintering 90 to 99.5% by weight of aluminum nitride as the main raw material and 0.5 to 10% by weight of a sintering aid. The aluminum nitride sintered body is composed of a crystalline phase of aluminum nitride particles and a liquid phase of the sintering aid.

[0018] The sintering aid may be selected from the group consisting of oxides of rare earth elements Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb. In this embodiment, yttrium oxide (YO) is used as the sintering aid. It is known that adding rare earth oxides as sintering aids lowers the liquid phase formation temperature during sintering and densifies the crystal structure, resulting in both relatively high thermal conductivity and mechanical strength.

[0019] The aluminum nitride sintered body of this embodiment is characterized by its thermal conductivity characteristics, with a thermal conductivity λ of 260 W / mK or more when converted to a thickness of 2.5 mm. Furthermore, the aluminum nitride sintered body preferably has a thermal conductivity of 240 W / mK or more when converted to a thickness of 0.5 mm. The aluminum nitride sintered body of this embodiment preferably has a residual Y2O3 content of 0.1 wt% or less and a residual carbon (C element) content of 0.05 wt% or less. The Y2O3 content is more preferably 0.03 wt% or less. Furthermore, the carbon content is more preferably 0.03 wt% or less. The aluminum nitride sintered body of the present invention achieves both high thermal conductivity and reduced substrate warpage by controlling both the residual Y2O3 content and the carbon content in the sintered body.

[0020] Furthermore, the aluminum nitride sintered body can be configured as a substrate having a three-dimensional shape with reduced warpage compared to conventional sintered bodies. To quantitatively evaluate the three-dimensional shape of this substrate, three-dimensional shape measurement can be performed using an optical measuring instrument with a camera optical system. The optical measuring instrument uses (preferably two or more) camera optical systems to precisely scan a specified square area (a square range) on the substrate surface to obtain three-dimensional data on the surface shape, including unevenness, waviness, warpage, etc. of the substrate surface. This three-dimensional data is a collection of height information (height value or z coordinate) at measurement positions (x, y coordinates) on a plane and can be expressed as a three-dimensional map. The height value is the relative height with respect to a reference plane (H = 0) automatically set by software as a plane on which the entire substrate is as horizontal as possible. The maximum height value Hmax is the maximum value of this relative height, and the minimum height value Hmin is the minimum value of this relative height. The difference ΔH between the maximum height value Hmax and the minimum height value Hmin was used to evaluate the amount of warpage of the substrate. It is expected that the larger the square area to be measured, the larger the amount of warpage (ΔH). Therefore, the warpage index value C was calculated by dividing this amount of warpage (ΔH) by the diagonal line D of the square area. The warpage index value C was then used to evaluate the warpage of the substrate. In this embodiment, the warpage index value C1 for the entire substrate area, the warpage index value C2 for the corner areas, and the warpage index value C3 for the central area were evaluated. Figure 3 is a schematic diagram showing the evaluation ranges of the warpage index values ​​C1, C2, and C3. Note that the surface roughness of the substrate itself is extremely small compared to the amount of warpage and can therefore be ignored.

[0021] The aluminum nitride sintered body has a warpage index value C1 of less than 0.20 μm / mm, which indicates the warpage of the entire substrate region. The warpage index value C1 is more preferably 0.14 to 0.19 μm / mm. Here, the warpage index value C1 is calculated by using the maximum height value Hmax (μm) and the minimum height value Hmin (μm) obtained by optical three-dimensional shape measurement of a square region (a square range with one side of 50 mm) of the entire surface of a substrate sample of the aluminum nitride sintered body fabricated to a predetermined size (a square with a thickness of 0.5 mm and sides of 50.8 mm), and the distance D1 (mm) between the diagonals of the square region, C1=(Hmax-Hmin) / D1 It was calculated by:

[0022] The aluminum nitride sintered body has a second warpage index value C2 of 0.17 to 0.35 μm / mm, which indicates the warpage in the corner regions of the substrate. Here, the second warpage index value C2 is calculated by using the maximum height value Hmax (μm) and the minimum height value Hmin (μm) obtained by optical three-dimensional shape measurement of a square region (a square range with one side of 25 mm) including the corners of the surface of a substrate sample of the aluminum nitride sintered body fabricated to a predetermined size (a square with a thickness of 0.5 mm and a side length of 50.8 mm) and the diagonal distance D2 (mm) of the square region, C2=(Hmax-Hmin) / D2 It was calculated by:

[0023] The aluminum nitride sintered body has a third warpage index value C3 of 0.10 to 0.29 μm / mm, which indicates the warpage in the substrate central region. Here, the third warpage index value C3 is calculated by using the maximum height value Hmax (μm) and the minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square region (a square range with one side of 25 mm) located at the center of the surface of a substrate sample of the aluminum nitride sintered body fabricated to a predetermined size (a square with a thickness of 0.5 mm and sides of 50.8 mm) and the diagonal distance D3 (mm) of the square region, C3=(Hmax-Hmin) / D3 It was calculated by:

[0024] As described below, the aluminum nitride sintered body manufactured by the conventional manufacturing method (Comparative Example 9) had a first warpage index value C1 of approximately 0.30 μm / mm, a second warpage index value C2 of approximately 0.55 μm / mm, and a third warpage index value C3 of approximately 0.41 μm / mm. In contrast, the aluminum nitride sintered body of the present invention had a first warpage index value C1 of 0.14 to 0.19 μm / mm, a second warpage index value C2 of 0.17 to 0.35 μm / mm, and a third warpage index value C3 of 0.10 to 0.29 μm / mm. In other words, the aluminum nitride sintered body of the present invention exhibited reduced substrate warpage over the entire substrate region, corner regions, and central region compared to the aluminum nitride sintered body manufactured by the conventional manufacturing method. Furthermore, the thermal conductivity λ / warpage index value C1 was used as an index showing compatibility between the first warpage index value C1 and the thermal conductivity λ. As will be described later, the aluminum nitride sintered body produced by a conventional method (Comparative Example 9) has a λ / C1 of approximately 900, whereas the aluminum nitride sintered body of the present invention has a λ / C1 of 1400 to 2000. Therefore, the aluminum nitride sintered body of the present invention is characterized by having a high thermal conductivity of 260 W / mK or more and by reducing warpage of the substrate compared to conventional products.

[0025] Next, a method for producing an aluminum nitride sintered body according to this embodiment will be described. The method for producing an aluminum nitride sintered body mainly includes a mixing step of mixing an aluminum nitride raw material powder, a sintering aid, and an organic solvent to prepare a slurry of the raw material mixture; a molding step of molding the raw material mixture to obtain a molded body; a degreasing step of heating the molded body in a degreasing temperature range under a dry air inflow or in a nitrogen atmosphere to degreasing; a deoxidizing step of heating the degreased molded body in a deoxidizing temperature range in a nitrogen atmosphere to deoxidize; a sintering step of sintering the deoxidized molded body in a sintering temperature range in a nitrogen atmosphere to produce an aluminum nitride precursor sintered body; a reduction-firing step of embedding the aluminum nitride precursor sintered body in aluminum nitride powder to produce an embedded structure, and then heat-treating the embedded structure in a weakly reducing atmosphere at 1850 to 1950°C for 30 hours or more; and a removal step of removing the aluminum nitride powder from the reduced-fired embedded structure to obtain an aluminum nitride sintered body. Each step will be described in detail below. In this specification, "embedded" does not only mean that the aluminum nitride precursor sintered body is completely covered with aluminum nitride powder (the outer peripheral surface of the aluminum nitride precursor sintered body is completely surrounded by aluminum nitride powder), but also that the aluminum nitride precursor sintered body is mostly covered with aluminum nitride powder to the extent that part of the outer peripheral surface is visible.

[0026] In the mixing process, an appropriate amount of aluminum nitride raw material powder and an appropriate amount of sintering aid powder are prepared. The aluminum nitride raw material powder, which is the main raw material, is preferably a high-purity fine powder with few metal impurities and a low oxygen content. The sintering aid can be selected from the group of oxides of rare earth elements Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb, but is preferably Y2O3. In the manufacturing method of this embodiment, 90 to 99.5 wt% of aluminum nitride raw material powder and 0.5 to 10 wt% of Y2O3 are blended. The prepared raw materials (aluminum nitride and sintering aid) are charged into a grinding mixer such as a ball mill, and an organic solvent, dispersant, organic binder, and / or plasticizer are added. The mixed materials are thoroughly ground and mixed for a predetermined time. The organic solvent is, for example, a solvent prepared by blending toluene and ethanol in a predetermined ratio. The amount of organic solvent is approximately 30 to 70 parts by weight per 100 parts by weight of the aluminum nitride raw material powder. The dispersant is, for example, a polycarboxylic acid surfactant. However, these organic solvents and dispersants can be selected arbitrarily. The organic binder is, for example, polyvinyl butyral resin or acrylic resin. The amount added is about 3 to 10 parts by weight per 100 parts by weight of the raw material powder. The plasticizer is, for example, dibutyl phthalate (DBP). The amount added is about 1 to 5 parts by weight per 100 parts by weight of the raw material powder. Then, a slurry-like raw material mixture in which the raw materials are sufficiently dispersed and mixed is obtained. Note that additional additives may be added to the mixture of aluminum nitride raw material powder and sintering aid powder.

[0027] In the molding step, the obtained slurry-like raw material mixture is molded into a shape having a predetermined size and thickness by any method such as press molding, casting, or doctor blade molding to produce a molded body.

[0028] In the debinding step, the compact is placed in a debinding oven and heated for at least about one hour in a debinding temperature range under a dry air inflow or a nitrogen atmosphere (although this is not a limitation), thereby removing organic components such as the added organic binder. The debinding temperature range is preferably about 400 to 600°C (so as not to sinter the compact). More preferably, the compact is placed in a BN (boron nitride) case and heated for four hours under a dry air inflow at about 500°C or in a nitrogen atmosphere at about 600°C, thereby properly debinding the organic components.

[0029] In the deoxidation step, the degreased compact is placed in a sintering furnace and heated in a nitrogen atmosphere within a deoxidation temperature range for 10 to 20 hours to deoxidize the compact. The deoxidation temperature range is preferably 1500 to 1650°C. More preferably, the degreased compact is placed inside a sealed BN case, and the case is placed in a sintering furnace for heat treatment.

[0030] In the sintering step, the deoxidized compact is heated and sintered in a sintering furnace in a nitrogen atmosphere within a sintering temperature range for 2 to 20 hours to produce an aluminum nitride precursor sintered body. The sintering temperature range is preferably 1750 to 1900°C. More preferably, the sintering step is carried out continuously without removing the deoxidized compact from the sintering furnace. The produced aluminum nitride precursor sintered body is then removed from the sintering furnace.

[0031] In the reduction-sintering process, as shown in FIG. 1, the prepared aluminum nitride precursor sintered body is placed in a graphite (C) container, or a BN or AlN container containing carbon black or a carbon sheet. The precursor sintered body is completely embedded in aluminum nitride powder until it is no longer visible, thereby producing an embedded structure made of aluminum nitride powder. At this time, it is preferable that all outer surfaces of the aluminum nitride precursor sintered body are surrounded by aluminum nitride powder. The container containing the embedded structure is then sealed and placed in a sintering furnace. The aluminum nitride powder used for embedding is preferably a powder with an oxygen content of 1% by weight or less. The resulting mixture is then heated at 1850 to 1950°C for 30 hours or more to perform reduction-sintering. The reduction-sintering time may be 30 hours or more, but is preferably 30 to 100 hours. The graphite (carbon) or carbon black functions as a weakly reducing atmosphere source, thereby creating a weakly reducing atmosphere inside the sintering furnace. Nitrogen gas may be introduced into this reduction-sintering process. Alternatively, instead of introducing graphite (carbon) or carbon black, CO gas, which is a reducing gas, may be introduced to create a weakly reducing atmosphere.

[0032] FIG. 2 is a schematic diagram showing a conventional reduction-sintering process. In the conventional reduction-sintering process, an aluminum nitride precursor is placed in a graphite container and sintered in a weakly reducing atmosphere, thereby reducing the aluminum nitride precursor. As a result, the sintering aid components are precipitated on the substrate surface and removed from the aluminum nitride precursor. However, in the conventional reduction-sintering process, the auxiliary components are discharged solely through the atmosphere, which is inefficient. Furthermore, it has been pointed out that the carbon component from the graphite container easily flows into the aluminum nitride precursor. In contrast, in the present invention, as shown in FIG. 1, the aluminum nitride precursor is embedded in aluminum nitride powder during the reduction-sintering process, thereby more effectively controlling the amount of auxiliary components discharged and the amount of carbon component inflowing. As a result, high thermal conductivity and reduced substrate warpage are achieved. In particular, in addition to the discharge of auxiliary components by atmosphere control, the adsorption of auxiliary components in the aluminum nitride precursor sintered body by aluminum nitride powder further promotes the discharge of auxiliary components. Furthermore, since the aluminum nitride precursor sintered body does not come into direct contact with the graphite container, the incorporation of carbon (C) components from the graphite container is suppressed. Therefore, although the aluminum nitride precursor sintered body is completely covered with aluminum nitride powder in Figure 1, by covering the aluminum nitride precursor sintered body with aluminum nitride powder to the extent that the inflow of carbon (C) components is suppressed, it is possible to achieve both high thermal conductivity and reduced warpage of the substrate.

[0033] Finally, in the removal step, the aluminum nitride powder is removed from the reduction-fired embedded structure, thereby obtaining the aluminum nitride sintered body of the present invention.

[0034] Furthermore, when the aluminum nitride sintered body manufactured by the manufacturing method of this embodiment is identified by crystalline phase X-ray diffraction, it may have diffraction peaks of the AlN crystalline phase as well as diffraction peaks of rare earth compounds (e.g., Y2O3, YAM, etc.) used as sintering aids.

[0035] The present invention will be described in more detail below based on examples and comparative examples, but the present invention should not be construed as being limited by the following examples.

[0036] The aluminum nitride sintered bodies according to Examples 1 to 19 and Comparative Examples 1 to 9 were produced under the following conditions and procedures. Comparative Example 9 was produced under almost the same conditions as Example 1 of Patent Document 1.

[0037] The specified amounts of aluminum nitride raw material powder and sintering aid powder were prepared. The aluminum nitride raw material powder was manufactured by the reduction-nitridation method and had an average particle size (D50) of approximately 1.0 μm and an oxygen content of 1 wt% or less. The sintering aid used was Y2O3 powder with an average particle size (D50) of approximately 1.2 μm.

[0038] For Examples 1-7, 9-19, and Comparative Examples 1-9, a predetermined amount of Y2O3 powder, approximately 0.5 parts by weight of a dispersant, and approximately 60 parts by weight of a mixed solvent of toluene and ethanol were added to 100 parts by weight of aluminum nitride powder, and the mixture was ground and mixed using a ball mill equipped with a resin container and alumina balls. 3.5 parts by weight of an acrylic binder was further added to the ground mixture, and the mixture was stirred and mixed using a ball mill until the dissolved binder solution and the ground mixture were completely mixed, after which a slurry was produced. The raw material mixture was then molded to a predetermined size and thickness using a press molding method. Specifically, in the press molding method, the mixed and ground slurry was dried and granulated using a spray dryer to obtain AlN granules. The AlN granules were then press molded to obtain a substrate-like molded body having a predetermined size and thickness.

[0039] On the other hand, Example 8 differs from the above in the process from mixing to molding, since it uses a sheet molding method. A predetermined amount of Y2O3 powder, approximately 0.8 parts by weight of a surfactant dispersant, and approximately 25 parts by weight of a toluene-ethanol mixed solvent were added to 100 parts by weight of aluminum nitride powder, and the mixture was ground and mixed using a ball mill equipped with a resin container and alumina balls. A dissolved binder solution consisting of approximately 8 parts by weight of polyvinyl butyral as a binder, approximately 3.5 parts by weight of dibutyl phthalate as a plasticizer, and approximately 25 parts by weight of a toluene-ethanol mixed solvent was then added to the ground mixture. The dissolved binder solution and the ground mixture were then mixed using a ball mill until completely mixed, after which a slurry was prepared. The slurry was then heated and left in a vacuum to degas and volatilize the solvent, adjusting the viscosity at 25°C to 20,000 cps. A plate-shaped green sheet was then obtained from the prepared slurry using a doctor blade method. The final drying temperature in the doctor blade molding device was set to 120° C. The obtained green sheet was cut into a predetermined size by die pressing to obtain a substrate-like molded product having a predetermined size and thickness.

[0040] Next, the prepared compact was placed in a BN housing and heated in a nitrogen atmosphere at approximately 600°C for 4 hours to perform a degreasing treatment to remove organic components such as binders. The degreasing compact was placed on a BN bottom plate, and BN side and top plates were attached to the bottom plate to assemble a closed housing. The housing containing the compact was then placed in a sintering furnace and heated in a nitrogen atmosphere at 1500-1650°C for 10-20 hours to perform a deoxidation treatment on the compact. For Examples 1-19 and Comparative Examples 1-4 and 6-9, the deoxidized compact was sintered by heating in a nitrogen atmosphere at 1750-1900°C for 2-20 hours without removing it from the sintering furnace to obtain an aluminum nitride precursor sintered body. For Comparative Example 5, the sintering step was not performed, and the compact was removed from the sintering furnace and proceeded to the subsequent reduction sintering step. For Comparative Example 6, the reduction sintering step was not performed, and the compact was removed from the sintering furnace to complete the process.

[0041] For Examples 1 to 19 and Comparative Examples 3 to 5, 7, and 8, the obtained aluminum nitride precursor sintered body was placed in a graphite container, or a BN or AlN container containing carbon black or a carbon sheet. As shown in FIG. 1, the aluminum nitride precursor sintered body was embedded in AlN powder until it was no longer visible, and then sealed in the BN or AlN container. Aluminum nitride powder containing 1 wt. % or less of oxygen was used as the embedding AlN powder in each example. The sample was then heated at 1780 to 1950°C for 5 to 100 hours for reduction and sintering. In this manner, samples for Examples 1 to 19 and Comparative Examples 3 to 5 were prepared. For Comparative Examples 1, 2, and 9, the obtained aluminum nitride precursor sintered body was placed in a graphite container or a BN container containing carbon black, and then sealed in the container. The sample was then heated at 1950°C for 70 hours in Comparative Examples 1 and 2, and at 1850°C for 12 hours in Example 9 for reduction and sintering. In this manner, samples of Comparative Examples 1, 2, and 9 were prepared.

[0042] For each of the prepared samples of Examples 1 to 19 and Comparative Examples 1 to 9, the diffraction patterns obtained by X-ray diffraction measurement and the diffraction peaks of the AlN crystal phase were identified to confirm that an aluminum nitride sintered body was obtained.

[0043] The prepared samples of Examples 1 to 19 and Comparative Examples 1 to 9 were subjected to the following evaluations of various characteristics.

[0044] (i) Thermal conductivity The aluminum nitride sintered body was cut into pieces measuring 10 mm x 10 mm x 0.5 mm thick, and a gold sputtering film of approximately 100 nm was formed on both sides of each piece. Then, graphene was sprayed onto both sides of each piece, with the graphene coating amount being approximately 0.1 mg / mm. 2The samples were subjected to a uniform blackening treatment to achieve a uniform blackening temperature. Using a thermal diffusivity measurement device (Model LFA467) manufactured by Netsch Japan Co., Ltd., measurements were taken three times at a voltage of 250 V and a pulse width of 30 μs. The average value was used as the thermal diffusivity. The measured thermal diffusivity was multiplied by the density and specific heat of the sintered body, measured using the Archimedes method, to determine the thermal conductivity of the 0.5 mm thick sample. Furthermore, aluminum nitride sintered bodies exhibit a tendency for their thermal conductivity to decrease with increasing temperature. The laser flash method calculates thermal diffusivity from the time it takes for the sample to heat up, resulting in a measurement that includes a decrease in thermal diffusivity due to the increase in sample temperature. For example, a thinner sample will experience a greater temperature increase than a thicker sample, resulting in a lower measured thermal diffusivity. Therefore, the table below shows the thermal diffusivity data for the same sample measured at a thickness of 2.5 mm, followed by measurements after polishing to thicknesses of 1.5, 1.0, 0.75, and 0.5 mm. Table 1 clearly shows that the thermal conductivity is lower for thinner samples. The obtained thermal conductivity was used to calculate the multiplication factor for each thickness to convert it to a thickness of 2.5 mm T. Specifically, the thermal conductivity value of the 0.5 mm T sample was multiplied by 1.10 to calculate the thermal conductivity λ converted to a thickness of 2.5 mm T. [Table 1]

[0045] (ii) Y2O3 content A scanning X-ray fluorescence analyzer, model "Primus IV" manufactured by Rigaku Corporation, was used. The aluminum nitride sintered body produced was cut into a piece of 50.8 mm x 50.8 mm, and the Al and Y contents were measured at five points, the center and four corners of the substrate. The Y2O3 content was calculated using a calibration curve, and the average value was taken as the Y2O3 content.

[0046] (iii) Carbon content The produced aluminum nitride sintered body was cut into a piece of 50.8 mm x 50.8 mm, and a total of five points, the center and four corners of the substrate, were measured using a high-frequency heating combustion-infrared absorption method in an oxygen atmosphere using an EMIA-Pro manufactured by Horiba, Ltd., and the average value was taken as the carbon content.

[0047] (iv) Warpage index values ​​C1, C2, C3 The fabricated 0.5 mm thick aluminum nitride sintered substrate was cut into a 50.8 mm x 50.8 mm piece. A 50 mm square area, excluding the edge (0.4 mm), was optically scanned using a Keyence Corporation OneShot 3D Shape Measuring Instrument (Model: VR-6000). The entire surface was measured, and height data and image data were acquired. In the image data, lighter colors visually indicate higher relative positions. The warpage index values ​​C1, C2, and C3 were calculated using an analysis application. First, to calculate the warpage index value C1, a reference plane was set (tilt correction) across the entire substrate surface, and then a surface measurement (flatness) was performed across the entire substrate surface. The difference ΔH between the maximum height value Hmax and the minimum height value Hmin was calculated. The resulting difference ΔH was divided by the diagonal length (71.84 mm) of the 50.8 mm square area to calculate the warpage index value C1. Second, to calculate the warpage index value C2, a reference plane was set (tilt correction) across the entire substrate, and then surface measurements (flatness) were performed on each of the four 25 mm square areas at the corners of the substrate. The average difference between the maximum height value Hmax and the minimum height value Hmin was calculated, resulting in a difference ΔH. The resulting difference ΔH was divided by the diagonal length of the 25 mm square area (35.36 mm) to calculate the warpage index value C2. Third, to calculate the warpage index value C3, a reference plane was set (tilt correction) across the entire substrate, and then surface measurements (flatness) were performed on a 25 mm square area at the center of the substrate. The difference ΔH between the maximum height value Hmax and the minimum height value Hmin was calculated. The resulting difference ΔH was divided by the diagonal length of the 25 mm square area (35.36 mm) to calculate the warpage index value C3.

[0048] Table 2 shows the conditions for each sample of Examples 1 to 19 and Reference Examples 1 to 9 and the results of various measurements on the properties of the sintered bodies.

[0049] [Table 2]

[0050] According to Table 2, the Y2O3 content in the sintered compacts of Examples 1 to 19 and Comparative Examples 1 and 2 was 0.10 wt% or less, while it was 0.4 wt% or more in Comparative Examples 3 to 9. In particular, the Y2O3 content in the sintered compacts of Examples 1 to 19 was 0.03 wt% or less, while the Y2O3 content in the sintered compacts of Comparative Examples 1 and 2 was 0.04 wt% or more, and 0.4 wt% or more in Comparative Examples 3, 7, and 8. The Y2O3 content in Examples 1 to 19, which underwent reduction firing for 30 hours or more under embedded conditions, was lower than the Y2O3 content in Comparative Examples 1 and 2, which underwent reduction firing for 70 hours without embedding. This indicates that the aluminum nitride powder embedding treatment and reduction firing for 30 hours or more effectively expels auxiliary components from the sintered compact compared to reduction firing without embedding. Furthermore, when comparing the samples prepared under embedding conditions, the treatment time of the reduction firing step was 30 hours or more in Examples 1 to 19, whereas the treatment time of the reduction firing step was 20 hours or less (5, 10, 20 hours) in Comparative Examples 3, 7, and 8, but the Y2O3 contents were relatively high in Comparative Examples 3, 7, and 8. This indicates that a treatment time of about 20 hours is insufficient to remove Y2O3.

[0051] Furthermore, in Examples 1 to 19, the carbon content in the sintered body was 0.03 wt % or less, whereas in Comparative Examples 1 and 2, the carbon content in the sintered body was 0.08 wt % or more. This indicates that the inflow of carbon into the sintered body is suppressed by embedding the precursor sintered body in aluminum nitride powder and reducing and firing it.

[0052] That is, as shown in Table 2, in Examples 1 to 19, the Y2O3 content in the sintered body was controlled to 0.10% by weight or less, and the carbon content in the sintered body was controlled to 0.05% by weight or less.

[0053] According to Table 2, Examples 1 to 19 and Comparative Examples 1, 2, 8, and 9 exhibit high thermal conductivities λ (2.5T equivalent) of 260 W / mK or more, whereas Comparative Examples 3 to 6 exhibit thermal conductivities λ (2.5T equivalent) of less than 250 W / mK. Comparative Examples 3, 4, and 6 did not undergo an appropriate reduction firing step, and therefore it can be said that the auxiliary components were not sufficiently discharged. Specifically, Comparative Example 3 had a short treatment time for the reduction firing step, and Comparative Example 4 had a low treatment temperature for the reduction firing step. Comparative Example 6 did not undergo a reduction firing step. Furthermore, Comparative Example 5 did not undergo a sintering step.

[0054] Next, the warpage characteristics of the sintered bodies of the examples and comparative examples will be described. Figure 4 is an image visually showing the results of three-dimensional shape measurement of an aluminum nitride sintered body substrate, with Figure 4(a) being the image of Example 1 and Figure 4(b) being the image of Comparative Example 1. In the shading of the image, lighter colors indicate higher positions from the reference plane. Comparing Figures 4(a) and 4(b), it can be visually confirmed that Example 1 has more uniform shading than Comparative Example 1, and that the difference in height of the substrate surface is smaller (smaller warpage). Then, by analyzing data related to the images, the warpage of the substrate was quantitatively evaluated.

[0055] Table 3 shows the conditions for each sample of Examples 1 to 19 and Comparative Examples 1 to 9, as well as the results of various measurements on the warpage characteristics and thermal conductivity characteristics of the sintered bodies.

[0056] [Table 3]

[0057] In Examples 1 to 19 and Comparative Example 6, the warpage index value C1 was less than 0.20 μm / mm, while in Comparative Examples 1 to 5 and 7 to 9, the warpage index value C1 was 0.22 μm / mm or more. In particular, in Examples 1 to 19, the warpage index value C1 was 0.14 to 0.19 μm / mm. In Comparative Example 6, the warpage index value C1 was less than 0.20 μm / mm because a reduction firing process was not performed. However, in Comparative Example 6, the thermal conductivity λ was less than 260 W / mK, and high thermal conductivity and reduced substrate warpage were not achieved at the same time. On the other hand, in Comparative Examples 1, 2, and 9, the warpage index value C1 was relatively large due to the reduction firing process without embedding. Furthermore, in Comparative Examples 3, 7, and 8, the treatment time of the reduction firing process under embedding was shorter (less than 30 hours) compared to the Examples, resulting in a relatively large warpage index value C1. In Comparative Example 4, the treatment temperature of the reduction firing step under embedding is low (less than 1850° C.), and therefore the warpage index value C1 is relatively large compared to the Examples.

[0058] In Examples 1 to 19 and Comparative Example 6, the warpage index value C2 was less than 0.40 μm / mm, while in Comparative Examples 1 to 5 and 7 to 9, the warpage index value C2 was 0.41 μm / mm or more. In particular, in Examples 1 to 19, the warpage index value C2 was 0.17 to 0.35 μm / mm. In Comparative Example 6, the warpage index value C2 was less than 0.40 μm / mm because a reduction firing process was not performed. However, in Comparative Example 6, the thermal conductivity λ was less than 260 W / mK, and high thermal conductivity and reduced substrate warpage were not achieved at the same time. On the other hand, in Comparative Examples 1 and 2, the warpage index value C2 was relatively large due to the reduction firing process without embedding. Furthermore, in Comparative Examples 3, 7, and 8, the treatment time of the reduction firing process under embedding was shorter (less than 30 hours) than in the Examples, resulting in a relatively large warpage index value C2. In Comparative Example 4, the treatment temperature of the reduction firing step under embedding is low (less than 1850° C.), and therefore the warpage index value C2 is relatively large compared to the Examples.

[0059] In Examples 1 to 19 and Comparative Example 6, the warpage index value C3 was less than 0.35 μm / mm, while in Comparative Examples 1 to 5 and 7 to 9, the warpage index value C3 was 0.37 μm / mm or more. In particular, in Examples 1 to 19, the warpage index value C3 was 0.10 to 0.29 μm / mm. In Comparative Example 6, the warpage index value C3 was less than 0.35 μm / mm because a reduction firing process was not performed. However, in Comparative Example 6, the thermal conductivity λ was less than 260 W / mK, and high thermal conductivity and reduced substrate warpage were not achieved at the same time. On the other hand, in Comparative Examples 1 and 2, the warpage index value C3 was relatively large due to the reduction firing process without embedding. Furthermore, in Comparative Examples 3, 7, and 8, the treatment time of the reduction firing process under embedding was shorter (less than 30 hours) than in the Examples, resulting in a relatively large warpage index value C3. In Comparative Example 4, the treatment temperature of the reduction firing step under embedding is low (less than 1850° C.), and therefore the warpage index value C3 is relatively large compared to the Examples.

[0060] To evaluate the relationship between thermal conductivity and substrate warpage, λ / C1 was calculated for each sample. In Examples 1 to 19, λ / C1 was 1300 or higher, while in Comparative Examples 1 to 9, it was less than 1220. In particular, in Examples 1 to 19, λ / C1 was 1400 to 2000. In other words, Examples 1 to 19 achieved both high thermal conductivity of 260 W / mK or higher and reduced substrate warpage.

[0061] The present invention is not limited to the above-described embodiments, and can be implemented in various forms within the technical scope of the present invention.

Claims

1. An aluminum nitride sintered body containing aluminum nitride particles and a sintering aid phase, The thermal conductivity λ when converted to a thickness of 2.5 mm is 260 W / mK or more, and The warpage index value C1 indicating the warpage of the entire substrate region is less than 0.20 μm / mm, The warpage index value C1 is calculated by using a maximum height value Hmax (μm) and a minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square region of the entire surface of the substrate sample of the aluminum nitride sintered body, and a distance D1 (mm) of the diagonal of the square region, C1=(Hmax-Hmin) / D1 An aluminum nitride sintered body characterized by being calculated by the following formula.

2. 2. The aluminum nitride sintered body according to claim 1, wherein the warpage index value C1 is 0.14 to 0.19 μm / mm.

3. a second warpage index value C2 indicating warpage in a substrate corner region of the aluminum nitride sintered body is 0.17 to 0.35 μm / mm; The second warpage index value C2 is calculated by using a maximum height value Hmax (μm) and a minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square region including a corner of the surface of the substrate sample of the aluminum nitride sintered body, and a distance D2 (mm) between the diagonals of the square region, C2=(Hmax-Hmin) / D2 2. The aluminum nitride sintered body according to claim 1, wherein the sintered body is calculated by the following formula:

4. a third warpage index value C3 indicating the warpage of the substrate central region of the aluminum nitride sintered body is 0.10 to 0.29 μm / mm; The third warpage index value C3 is calculated by using a maximum height value Hmax (μm) and a minimum height value Hmin (μm) obtained by three-dimensional shape measurement of a square region located at the center of the surface of the substrate sample of the aluminum nitride sintered body, and a distance D3 (mm) between the diagonals of the square region: C3=(Hmax-Hmin) / D3 2. The aluminum nitride sintered body according to claim 1, wherein the sintered body is calculated by the following formula:

5. 2. The aluminum nitride sintered body according to claim 1, wherein the thermal conductivity λ / warpage index value C1 is 1,400 or more and 2,000 or less.

6. 2. The aluminum nitride sintered body according to claim 1, which is obtained by sintering 90 to 99.5% by weight of aluminum nitride and 0.5 to 10% by weight of yttrium oxide.

7. A method for producing the aluminum nitride sintered body according to any one of claims 1 to 6, comprising the steps of: a mixing step of mixing an aluminum nitride raw material powder, a sintering aid, and an organic solvent to prepare a raw material mixture slurry; a molding step of molding the raw material mixture to obtain a molded body; a degreasing step of heating the compact in a degreasing temperature range under a dry air inflow or in a nitrogen atmosphere to perform a degreasing treatment; a deoxidation step of heating the degreased compact in a deoxidation temperature range in a nitrogen atmosphere to perform a deoxidation treatment; a sintering step of sintering the deoxidized compact in a nitrogen atmosphere within a sintering temperature range to produce an aluminum nitride precursor sintered body; a reduction firing step of embedding at least a portion of the aluminum nitride precursor sintered body with aluminum nitride powder to form an embedded structure, and heat-treating the embedded structure at 1850 to 1950°C in a weakly reducing atmosphere; a removing step of removing the aluminum nitride powder from the reduction-fired embedded structure to obtain an aluminum nitride sintered body; Including, A method for producing an aluminum nitride sintered body, characterized in that the reduction firing step is carried out for 30 hours or more.

8. 8. The method according to claim 7, wherein the reduction firing step includes placing the aluminum nitride precursor sintered body in a graphite container, or a BN container or an AlN container in which carbon black or a carbon sheet is placed, and embedding the aluminum nitride precursor sintered body in aluminum nitride powder until the aluminum nitride precursor sintered body is no longer visible.

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