Silicon nitride sintered body, insulating circuit board, and semiconductor device.

Abstract

To provide a silicon nitride sintered body in which characteristic anisotropy such as thermal conductivity and bending strength is mitigated.SOLUTION: A silicon nitride sintered body is the silicon nitride sintered body that consists of a board with a RD direction and TD direction orthogonal to each other in a surface orthogonal relative to a ND direction of board thickness direction. In the silicon nitride sintered body, the RD direction is defined as a rolling direction of a green sheet of the silicon nitride sintered body, bending strength σx of the RD direction and bending strength σy of the TD direction orthogonal to the RD direction are 600 MPa or more respectively, and the ratio (|σy-σx| / σx) of a difference between the bending strength σx and the bending strength σy to the bending strength σx is 10% or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a silicon nitride sintered body, an insulating circuit board, and a semiconductor device. [Background technology]

[0002] In recent years, with the increasing density and power output of electronic devices and semiconductor devices, the heat density of power modules has also increased. Rising temperatures in power modules can cause malfunctions in components and cracking of the insulating circuit board. Therefore, ceramic substrates such as alumina and aluminum nitride, which have relatively high thermal conductivity, have been used for insulating circuit boards. However, alumina and aluminum nitride have the drawback of low mechanical strength. Consequently, thick copper, which experiences strong thermal stress, cannot be directly bonded to the ceramic substrate, limiting the structure of power modules. Specifically, the need to solder heat sinks (metal plates) made of copper or aluminum to the insulating circuit board leads to larger power modules, which is a problem. Therefore, silicon nitride (Si3N4) is attracting attention as an insulating circuit board material. Because silicon nitride sintered bodies have higher strength and fracture toughness compared to alumina and aluminum nitride sintered bodies, it becomes possible to directly bond thick copper to the insulating circuit board, contributing to the miniaturization of modules. Therefore, development is underway to improve both the mechanical strength and thermal conductivity of silicon nitride sintered bodies.

[0003] For example, Patent Document 1 discloses a method for manufacturing a silicon nitride sintered substrate with improved mechanical properties and thermal conductivity. In this manufacturing method, silicon nitride powder with an Al content of 0.1% by weight or less is mixed with a sintering aid consisting of one or more elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb in an amount of 1% to 15% by weight, molded, and then fired at a temperature of 1700°C to 2300°C under a nitrogen gas pressure of 1 atmosphere to 500 atmospheres. The silicon nitride sintered substrate obtained by this manufacturing method consists of 85% to 99% by weight of β-type silicon nitride grains and the remainder being a grain boundary phase of oxides or oxynitrides. Furthermore, the grain boundary phase contains 0.5% to 10% by weight of one or more metallic elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb. The Al atom content in the grain boundary phase is 1% by weight or less, the porosity is 5% or less, and the microstructure of the sintered body contains 10% to 60% by volume of β-type silicon nitride grains with a short axis diameter of 5 μm or more. In other words, it is known that in order to obtain a silicon nitride sintered substrate with high thermal conductivity, rare earth compounds and magnesium oxide are added as sintering aids, and the thermal conductivity and mechanical strength can be improved by adjusting the mixing ratio and amount of these additives. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-30866 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The β-type silicon nitride crystal grains, which are the main crystalline phase of silicon nitride sintered bodies, are known to be columnar crystal grains elongated in the c-axis direction. Therefore, silicon nitride sintered bodies do not consist of completely random crystal grain orientations, and often exhibit a crystal phase distribution in which the crystal grain orientation is biased in a particular direction, depending on the grain size, shape, and molding method of the raw materials. This bias in crystal grain orientation in silicon nitride sintered bodies causes anisotropy in properties such as thermal conductivity and bending strength. Specifically, β-type silicon nitride crystal grains are known to have anisotropy in thermal conductivity in the a-axis and c-axis directions, but bias in crystal grain orientation in a particular direction causes anisotropy in thermal conductivity in the silicon nitride sintered body. Furthermore, crystal grain orientation in a particular direction also affects the compounding of β-type silicon nitride crystal grains, resulting in anisotropy in mechanical strength due to changes in crack deflection and elongation. In particular, in processes such as doctor blade molding and extrusion molding, where shear forces are generated during molding, even a small amount of β-type silicon nitride crystal grains can cause the crystal grains to orient in the molding direction during slurry flow, leading to significant anisotropy between the molding direction and directions perpendicular to it. On the other hand, a similar anisotropy problem arises in reaction sintering methods using Si powder as a raw material. In sintering by reaction sintering, the exothermic reaction during nitriding can cause localized melting of Si or the β-conversion of silicon nitride, resulting in uneven properties of the sintered body. Therefore, it is common practice to control the nitriding reaction by adding silicon nitride powder as a diluent during raw material mixing. However, the added silicon nitride powder affects the crystal grain orientation of the sintered body, causing the crystal grains to preferentially orient in a specific direction. Such property anisotropy of silicon nitride sintered bodies can affect device design depending on the device's application, so it is desirable to mitigate it.

[0006] The inventors aimed to improve upon conventional silicon nitride sintered bodies by reviewing their manufacturing methods and focusing on controlling the texture structure of the silicon nitride sintered body, thereby suppressing the anisotropy of properties such as thermal conductivity and bending strength.

[0007] To solve the above problems, the present invention aims to provide a silicon nitride sintered body in which the anisotropy of properties such as thermal conductivity and bending strength is mitigated. Furthermore, the present invention also aims to provide an insulating circuit board and a semiconductor device using the silicon nitride sintered body. [Means for solving the problem]

[0008] One embodiment of the present invention is characterized in that the texture index J, which indicates the distribution state of the crystal orientation of each crystal grain obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD, is 1.2 to 1.7.

[0009] One embodiment of the present invention is a silicon nitride sintered body in which, when the substrate thickness direction is the ND direction, the crystal orientation distribution obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD is expressed in terms of Euler angles (φ1, Φ, φ2) according to Bunge's definition, and the maximum value of the density profile (MUD) in the range of φ2=0°, Φ=0°, φ1=0~60° is 1.0~1.6, and the maximum value of the density profile (MUD) in the range of φ2=0°, Φ=90°, φ1=0~180° is 2.0~7.0.

[0010] One embodiment of the present invention is a silicon nitride sintered body characterized in that, when the substrate thickness direction is the ND direction, the area ratio of β-type silicon nitride crystal grains having a crystal orientation in which the inclination of the {1 0 -1 0} plane of the β-type silicon nitride crystal grains from the ND direction is within 70° in the pole figure obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD is 90 to 98% of all β-type silicon nitride crystal grains.

[0011] One embodiment of the present invention is a silicon nitride sintered body characterized in that, when the substrate thickness direction is the ND direction, the area ratio of β-type silicon nitride crystal grains having a crystal orientation such that the inclination of the {1 0 -1 0} plane of the β-type silicon nitride crystal grains from the ND direction is within 60° in the pole figure obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD is 80 to 94% of all β-type silicon nitride crystal grains.

[0012] One embodiment of the present invention is a silicon nitride sintered body characterized in that, when the substrate thickness direction is the ND direction, the area ratio of β-type silicon nitride crystal grains having a crystal orientation such that the inclination of the {1 0 -1 0} plane of the β-type silicon nitride crystal grains from the ND direction is within 50° in the pole figure obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD is 65 to 85% of all β-type silicon nitride crystal grains.

[0013] One embodiment of the present invention is a silicon nitride sintered body characterized in that, when the substrate thickness direction is the ND direction, the area ratio of β-type silicon nitride crystal grains having a crystal orientation such that the inclination of the {1 0 -1 0} plane of the β-type silicon nitride crystal grains from the ND direction is within 40° in the pole figure obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD is 50 to 75% of all β-type silicon nitride crystal grains.

[0014] One embodiment of the present invention is a silicon nitride sintered body characterized in that, when the substrate thickness direction is the ND direction, the area ratio of β-type silicon nitride crystal grains having a crystal orientation such that the inclination of the {1 0 -1 0} plane of the β-type silicon nitride crystal grains from the ND direction is within 30° in the pole figure obtained from the texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD is 30 to 52% of all β-type silicon nitride crystal grains.

[0015] One embodiment of the present invention is a silicon nitride sintered body characterized in that, when the substrate thickness direction is the ND direction, the intensity ratio I(002) / I(200) of the integrated intensity I(002) of the X-ray diffraction peak corresponding to the Miller index (002) plane of the β-type silicon nitride crystal grains in the ND direction, obtained by substrate surface analysis by X-ray diffraction, is 0.05 to 0.2.

[0016] A further embodiment of the silicon nitride sintered body of the present invention is characterized in that the ratio of the difference between the thermal conductivity λz in the substrate thickness direction and the thermal conductivity λx in the substrate forming direction (|λz-λx| / λx) to the thermal conductivity λx in the substrate forming direction is 6% or less.

[0017] A further embodiment of the silicon nitride sintered body of the present invention is further characterized in that the thermal conductivity λz in the substrate thickness direction and the thermal conductivity λx in the substrate molding direction are each 70 W / mK or higher.

[0018] A further embodiment of the present invention is a silicon nitride sintered body characterized in that the bending strength σx in the substrate forming direction and the bending strength σy in the direction perpendicular to the substrate forming direction within the substrate surface perpendicular to the substrate thickness direction are both 600 MPa or more, and the ratio of the difference between the bending strength σx and the bending strength σy (|σy-σx| / σx) to the bending strength σx is 10% or less.

[0019] A further embodiment of the silicon nitride sintered body of the present invention is further characterized in that, in a plane perpendicular to the substrate thickness direction, the ratio (|λx-λy| / λx) of the difference between the thermal conductivity λx in the substrate forming direction and the thermal conductivity λy in the direction perpendicular to the substrate forming direction, with respect to the thermal conductivity λx in the substrate forming direction, is 1.5% or less.

[0020] In a further form of the silicon nitride sintered body of the present invention, the bending strengths in two orthogonal directions in the plane orthogonal to the substrate thickness direction are each 600 MPa or more, and the ratio of the bending strengths in the two axial directions is 0.9 to 1.1. The two axial directions may be the molding direction and the direction orthogonal to the molding direction.

[0021] In a further form of the silicon nitride sintered body of the present invention, the silicon nitride sintered body further contains 92.5 to 97% by weight of Si3N4, 2.0 to 4.5% by weight of Y2O3, and 1.0 to 3.0% by weight of MgO in the raw material blending ratio.

[0022] An insulating circuit board according to an embodiment of the present invention includes the silicon nitride sintered body having the above characteristics and a metal plate joined to the surface of the silicon nitride sintered body. A semiconductor device according to an embodiment of the present invention includes the above insulating circuit board and a semiconductor element mounted on the metal plate of the insulating circuit board.

Advantages of the Invention

[0023] The silicon nitride sintered body of the present invention can improve property anisotropy by controlling the aggregate structure characteristics of β-type silicon nitride crystal grains by the EBSD method and / or by controlling the crystal characteristics by the X-ray diffraction method.

Brief Description of the Drawings

[0024] [Figure 1] A diagram showing band contrast images obtained by the EBSD method of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3. [Figure 2] A {1 0 -1 0} pole figure obtained by the EBSD method of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3. [Figure 3] A crystal orientation distribution diagram at φ2 = 0° obtained by the EBSD method of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3. [Figure 4]Figure 3 shows the density profiles of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3 in the range of φ2=0°, Φ=0°, and φ1=0~60° in the crystal orientation distribution. [Figure 5] Figure 3 shows the density profiles of the silicon nitride sintered bodies of Example 1, Example 2, Comparative Example 1, and Comparative Example 3 in the range of φ2=0°, Φ=90°, and φ1=0~180° in the crystal orientation distribution. [Figure 6] SEM image (magnification 5000) of pulverized β-type silicon nitride sintered powder in the manufacturing process of the silicon nitride sintered body of the present invention. [Figure 7] A schematic diagram showing a semiconductor device of one embodiment of the present invention. [Modes for carrying out the invention]

[0025] A silicon nitride sintered body according to one embodiment of the present invention has a substrate shape of a predetermined thickness and can be used as an electronic component mounting substrate for mounting electronic components, mainly by brazing (brazing or soldering) a metal plate such as a copper plate to the substrate surface. The thickness of the substrate is preferably 0.1 to 1.0 mm. Here, in the silicon nitride sintered body substrate, the substrate thickness direction is the ND or Z direction (normal direction to the substrate surface), the molding (or rolling) direction within the plane perpendicular to the ND direction (substrate surface) is the RD or X direction, and the direction perpendicular to the RD direction within the plane perpendicular to the ND direction (substrate surface) is the TD or Y direction.

[0026] The silicon nitride sintered body of this embodiment may be composed of a silicon nitride sintered body containing 1 to 5% by weight of rare earth oxide (first sintering aid), 1.0 to 3.5% by weight of magnesium compound (second sintering aid), and Si3N4 constituting the remainder. In other words, the silicon nitride sintered body of this embodiment is formed by molding and firing a slurry mixture of raw material powders obtained by mixing silicon nitride powder, rare earth oxide powder, and magnesium oxide powder in predetermined proportions. The silicon nitride sintered body may also be formed by a reaction sintering method using Si powder as the main raw material.

[0027] In this embodiment, the sintering aid is a combination of an oxide of a rare earth element (Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb) as the first sintering aid and magnesium oxide (MgO) or magnesium silicon nitride (MgSiN2) as the second sintering aid. In particular, by adding a Mg component together with the rare earth oxide as a sintering aid component, the liquid phase formation temperature during sintering can be lowered, and the sinterability can be improved. Furthermore, it is more preferable that the first sintering aid is 2.0 to 4.5% by weight of Y2O3 and the second sintering aid is 1.0 to 3.0% by weight of MgO. Previous knowledge has shown that by using Mg and Y as sintering aid components, the silicon nitride sintered body is densified, and as a result, relatively high thermal conductivity and mechanical strength can be achieved simultaneously. In this embodiment, MgO and Y2O3 were used as sintering aids. Furthermore, as an additional additive, an appropriate amount of hafnium oxide (HfO2) may be added to further promote the crystallization of the grain boundary phase. It has been found from past experience that the composition ratio of rare earth oxides within the range of 1 to 5% by weight does not significantly affect the properties of the silicon nitride sintered substrate; therefore, those skilled in the art can arbitrarily select the type and ratio of rare earth oxides.

[0028] The β-type silicon nitride crystal grains (or particles) constituting the substrate of the silicon nitride sintered body have an elongated hexagonal prismatic crystal structure with long and short axes. In this embodiment, the silicon nitride sintered body is designed to mitigate the anisotropy of its thermal conductivity and / or mechanical strength by controlling the random orientation of the β-type silicon nitride crystal grains.

[0029] The silicon nitride sintered body of this embodiment has texture characteristics within a specific range obtained from texture analysis of β-type silicon nitride crystal grains on the substrate surface by EBSD when the substrate thickness direction is the ND direction. In other words, the inventors have found that in silicon nitride sintered bodies having a texture structure within a specific range, the anisotropy of properties such as thermal conductivity and bending strength is relaxed. That is, by controlling the texture characteristics of β-type silicon nitride crystal grains in the silicon nitride sintered body, a desired silicon nitride sintered body with relaxed property anisotropy can be obtained.

[0030] EBSD (Electron Back-Scatter Diffraction) is a scanning electron microscope that measures the orientation of individual crystal grains or minute regions, enabling the analysis of the microscopic texture of silicon nitride sintered substrates. In particular, EBSD acquires orientation information for each crystal grain at a measurement depth of several tens of nanometers from the substrate surface, allowing for quantitative evaluation of the aggregate structure and its corresponding crystal orientation. In this embodiment, the following texture characteristics were used to control the anisotropy of the silicon nitride sintered body.

[0031] • Texture index J An Orientation Distribution Function (ODF) analysis was performed on the EBSD map obtained by the EBSD method to acquire a texture index J, which indicates the distribution state of the crystal orientation of each crystal grain. The texture index J indicates how strong the texture (texture, i.e., the state in which crystals are arranged in a specific orientation) of the sample is. It shows a value of 1 when the distribution state of crystal orientation is completely random, and an infinite value when all crystal orientations are the same (for example, a single crystal).

[0032] In ODF analysis, the spherical harmonics T by Bunge l mn Using the series expansion method with (g), the following series expansion is obtained:

number

number

[0033] • Density profiles (multiples of uniform density, MUD) using Euler angles (φ1, Φ, φ2) Texture analysis using the EBSD method includes a method of directly plotting the obtained crystal orientations in a three-dimensional space with Euler angles (φ1, Φ, φ2) as defined by Bunge as the coordinate axes. In this method, a single plotted point can definitively represent the crystal orientation, thus providing a precise representation of the crystal orientation. In this method, the crystal orientation is expressed in the form (hkl)[uvw], using the index of the crystal plane perpendicular to the ND direction (hkl) and the index of the crystal direction parallel to the RD direction [uvw], and the Euler angles corresponding to each crystal orientation are plotted in Euler space. In the case of a hexagonal crystal system such as β-Si3N4, the distribution of the {0 0 0 1} planes in Euler space, when the orientation distribution is taken in the section from φ1=0° to 60° at φ2=0° and Φ=0°, allows for a quantitative evaluation of the proportion of particles in β-Si3N4 whose long axis is oriented in the ND direction. Similarly, the distribution of the {1 0 -1 0} plane can be quantitatively evaluated as a density profile by taking the orientation distribution in the section from φ1=0° to 180° at φ2=0° and Φ=90°, and determining the proportion of β-Si3N4 particles whose long axis is oriented in the in-plane direction. Texture characteristics were evaluated by the maximum value of the density profile.

[0034] • Pole diagram Texture analysis using the EBSD method includes evaluation of a pole figure showing the distribution of crystal orientations of the {1 0 -1 0} plane of β-Si3N4 crystal grains in the RD-TD plane, which is a plane orthogonal to the ND direction. In the pole figure, areas with a high distribution density of the {1 0 -1 0} plane are represented in white, and areas with a low distribution density are represented in darker colors. Texture characteristics were quantitatively evaluated by the area ratio of β-type silicon nitride crystal grains having a crystal orientation tilted within a predetermined angular range from the ND direction of the {1 0 -1 0} plane of the β-type silicon nitride crystal grains in the pole figure. This area ratio is also called the cumulative relative frequency of the tilt angular range of the {1 0 -1 0} plane of β-Si3N4 crystal grains with respect to the ND direction.

[0035] The silicon nitride sintered body of this embodiment has the following specific texture characteristics with respect to the texture index J. The texture index J, which indicates the distribution state of the crystal orientation of each crystal grain, is 1.2 to 1.7, preferably 1.2 to 1.64, more preferably 1.2 to 1.58, and even more preferably 1.2 to 1.53.

[0036] The silicon nitride sintered body of this embodiment has the following unique texture characteristics with respect to its density profile. The density profile is visually illustrated by the crystal orientation distribution diagram in Figure 3. The maximum value of the density profile (MUD) in the range of φ2=0°, Φ=0°, and φ1=0~60° is 1.0~1.6, preferably 1.0~1.53, more preferably 1.06~1.50, and even more preferably 1.14~1.50, and the maximum value of the density profile in the range of φ2=0°, Φ=90°, and φ1=0~180° is 2.0~7.0, preferably 2.0~6.38, more preferably 2.1~6.38, and even more preferably 2.10~4.26.

[0037] The silicon nitride sintered body of this embodiment is illustrated by the pole diagram in Figure 2 and has the following unique texture characteristics based on quantitative evaluation of the pole diagram. The area ratio of β-type silicon nitride crystal grains having a crystal orientation in which the inclination of the {1 0 -1 0} plane from the ND direction is within 70° is 90 to 98% of all β-type silicon nitride crystal grains, preferably 91 to 98%, more preferably 91.4 to 97.8%, and even more preferably 94.9 to 97.8%. The area ratio of β-type silicon nitride crystal grains having a crystal orientation in which the inclination of the {1 0 -1 0} plane from the ND direction is within 60° is 80 to 94% of all β-type silicon nitride crystal grains, preferably 81 to 94%, more preferably 81.3 to 93.3%, and even more preferably 85.7 to 93.3%. The area percentage of β-type silicon nitride crystal grains having a crystal orientation in which the inclination of the {1 0 -1 0} plane from the ND direction is within 50° is 65-85%, preferably 67-84%, more preferably 67.5-83.1%, and even more preferably 70.2-83.1% of all β-type silicon nitride crystal grains. The area percentage of β-type silicon nitride crystal grains having a crystal orientation in which the inclination of the {1 0 -1 0} plane from the ND direction is within 40° is 50-75%, preferably 51-73%, more preferably 51.8-72.1%, and even more preferably 51.8-68.1% of all β-type silicon nitride crystal grains. The area percentage of β-type silicon nitride crystal grains having a crystal orientation such that the inclination of the {1 0 -1 0} plane of the β-type silicon nitride crystal grain from the ND direction is within 30° is 30 to 52%, preferably 33 to 52%, more preferably 34.1 to 51.1%, and even more preferably 34.1 to 48.3% of all β-type silicon nitride crystal grains.

[0038] In other words, the silicon nitride sintered body of this embodiment has the above-mentioned texture characteristics and thus possesses a texture structure in which β-type silicon nitride crystal grains are randomly oriented.

[0039] The silicon nitride sintered body of this embodiment has the following thermal conductivity characteristics in relation to the texture characteristics described above. The thermal conductivity λx in the substrate forming direction (RD direction), the thermal conductivity λy in the direction perpendicular to the substrate forming direction (TD direction), and the thermal conductivity λz in the substrate thickness direction (ND direction) are all 70 W / mK or higher. The ratio of the difference between the thermal conductivity λz in the substrate thickness direction and the thermal conductivity λx (|λz-λx| / λx) to the thermal conductivity λx is 6% or less. Also, the ratio of the difference between the thermal conductivity λx and the thermal conductivity λy (|λx-λy| / λx) to the thermal conductivity λx is within 1.5%. This means that the ratio of the difference in thermal conductivity in any two orthogonal axial directions within a plane perpendicular to the substrate thickness direction is within 1.5%. This is because the difference between the thermal conductivity λx and the thermal conductivity λy is greatest within that plane. In other words, the silicon nitride sintered body of this embodiment has high thermal conductivity characteristics with a thermal conductivity of 70 W / mK or higher, and furthermore, its characteristic anisotropy is reduced to 6% or less.

[0040] The silicon nitride sintered body of this embodiment has the following mechanical strength characteristics in relation to the texture characteristics described above. The bending strength σx in the substrate forming direction (RD direction) and the bending strength σy in the direction perpendicular to the substrate forming direction (TD direction) are both 600 MPa or more. Furthermore, the ratio of the difference between bending strength σx and bending strength σy (|σx-σy| / σx) to bending strength σx is within 10%. This means that the ratio of bending strengths in any two orthogonal axial directions within a plane perpendicular to the substrate thickness direction is 0.9 to 1.1. This is because the difference between bending strength σx and bending strength σy is maximized within that plane. In other words, the silicon nitride sintered body of this embodiment has high mechanical strength characteristics of 600 MPa or more in bending strength, and furthermore, its characteristic anisotropy is reduced to 10% or less.

[0041] Therefore, the silicon nitride sintered body of this embodiment achieves both a thermal conductivity of 70 W / mK or higher and a bending strength of 600 MPa or higher, and furthermore, it is possible to suppress the anisotropy of its properties to 6% or less and 10% or less, respectively.

[0042] Furthermore, the silicon nitride sintered body of this embodiment was also analyzed by substrate surface analysis using X-ray diffraction. Specifically, it was found that the silicon nitride sintered body has the following crystal structure characteristics in relation to the texture characteristics described above. When the substrate thickness direction is the ND direction, the intensity ratio I(002) / I(200) of the integrated intensity I(002) of the X-ray diffraction peak corresponding to the Miller index (002) plane of the β-type silicon nitride crystal grains in the ND direction, obtained by substrate surface analysis using X-ray diffraction, is 0.05 to 0.2.

[0043] Next, a method for producing the silicon nitride sintered body of this embodiment will be described. The method for producing the silicon nitride sintered body mainly includes the steps of: generating a silicon nitride ingot with a β ratio of 70 to 90%; crushing the silicon nitride ingot to produce β-type silicon nitride powder having a specific surface area and average particle diameter within a predetermined range; mixing the β-type silicon nitride powder, rare earth oxide powder, and magnesium oxide powder (or silicon magnesium nitride powder) in a predetermined mixing ratio, and adding a solvent to form a slurry; molding the slurry into a sheet molded body of a predetermined thickness; and sintering the sheet molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body. Each step will be described in detail below.

[0044] First, β-type silicon nitride powder was synthesized by direct nitriding. Metallic silicon powder and magnesium oxide powder in an amount of 0.2 wt% to 1.0 wt% relative to the metallic silicon powder were mixed, and a nitriding reaction was carried out at a temperature of 1350°C or higher to obtain silicon nitride ingots with a β-ratio of 70 to 90%. The obtained ingots were coarsely and finely ground to obtain a material that does not contain columnar particles with a short axis diameter of 2 μm or more and has a specific surface area of ​​6.0 to 11.0 m². 2The specific surface area and average particle size D50 were adjusted to a range of 0.5 μm to 1.5 μm / g. This specific surface area and average particle size D50 were adjusted by the grinding time. After grinding, the powder was acid-washed and water-washed to adjust it to a powder with an oxygen content of 0.8% or less and a surface fluorine content of 800 ppm or less. The adjusted β-type silicon nitride powder contains trace amounts of whiskers, but does not contain columnar particles with a short axis diameter of 2 μm or more, and is predominantly composed of polygonal particles (see Figure 6). As a result, it is possible to obtain a sintered body in which no specific crystal planes are oriented during molding and which remains relatively unoriented even after sintering.

[0045] 2-4.5% by weight of rare earth oxide powder (preferably yttrium oxide powder) and 1.0-3.0% by weight of magnesium oxide powder (or magnesium silicon nitride powder) were wet-mixed in a mixed solvent of toluene and ethanol using a φ10 silicon nitride boulder and a nylon pot mill. In the wet mixing, an appropriate amount of dispersant may be added, and typically, a polycarboxylic acid-based or amine-based dispersant is added at a concentration of 0.2 mg / m² relative to the surface area of ​​the raw material powders. 2 From 1.5 mg / m² 2 It is added within the specified range. The remaining β-type silicon nitride powder is placed in the mill and mixed for 12 to 24 hours. After that, a binder, plasticizer, and organic solvent are added to form a slurry. For preparing the slurry used for molding, wet mixing using an organic solvent is preferable in order to improve productivity and suppress the increase in oxygen content during mixing. As a specific example, a dispersant, an organic solvent mixed with toluene and ethanol is added to the raw material powder and prepared by a commonly used mixing and grinding method. Then, the mixture is uniformly mixed and the particle size is adjusted using methods such as a ball mill, bead mill, or vibrating mill. The slurry is degassed and its viscosity adjusted in a vacuum until it is viscous enough to form a green sheet. As for the materials of the mill and media used in the mixing and grinding method, resins such as urethane and nylon, or ceramics such as silicon nitride and zirconium oxide can be used, but in order to prevent the inclusion of impurities in the slurry, it is preferable to use resin or silicon nitride as the material.

[0046] The rare earth oxide powder can be selected from oxides of Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb, or combinations thereof. Preferably, the rare earth oxide powder is yttrium oxide (Y2O3).

[0047] Furthermore, the β-type silicon nitride powder has a specific surface area of ​​11.0 m². 2 The particle size is small, less than 1 / g, and densification is not sufficient if only rare earth oxides are used as sintering aids. Therefore, it is desirable to use magnesium compounds such as magnesium oxide (MgO) or magnesium silicon nitride (MgSiN2) and rare earth oxides such as Yb2O3 or Y2O3 as sintering aids. Magnesium compounds form low-melting-point liquid-phase compounds, which promotes densification and has the effect of lowering the firing temperature and shortening the firing time. In addition, rare earth oxides have a high affinity for oxygen, which reduces the amount of dissolved oxygen in silicon nitride particles and has the effect of increasing thermal conductivity.

[0048] In the molding process, the high-viscosity slurry, after viscosity adjustment by vacuum degassing, is formed into a sheet, and a green sheet of a predetermined thickness is obtained by the doctor blade method. The thickness of the green sheet can be changed as appropriate depending on the required thickness of the sintered body, but it is usually in the range of 0.1 to 1.3 mm. The molded green sheet is processed into the desired shape by a die press or cutting machine to obtain a molded body. In this molding process, the direction in which the doctor blade moves relative to the molded body and rolls it is determined as the molding direction (RD direction) of the silicon nitride sintered body.

[0049] A block body is prepared by stacking 15 to 30 molded bodies by spraying the surface of the molded body obtained in the molding process with boron nitride powder, which is a mold release agent. This block body is placed inside a boron nitride sheath and degreased in dry air at a temperature range of 500 to 600°C. The atmosphere during degreasing may also be nitrogen or vacuum. By firing the degreased block body at a high temperature for a predetermined time, a silicon nitride sintered body, the final target product of this manufacturing method, is obtained. The firing process is carried out in a firing furnace in a non-oxidizing (nitrogen) atmosphere at a temperature range of approximately 1750 to 2000°C. Furthermore, in order to prevent the volatilization of Si3N4 and sintering aids (e.g., MgO), it is preferable to perform pressurized firing at a pressure of 5 atmospheres or more.

[0050] By following the process described above, a silicon nitride sintered substrate with unique texture characteristics can be obtained.

[0051] Furthermore, in a second embodiment, the silicon nitride sintered body may be formed by a reaction sintering method using Si powder as the main raw material. Similar to the above manufacturing method, a silicon nitride ingot is crushed to produce β-type silicon nitride powder having a specific surface area and average particle diameter within a predetermined range. Then, by adding the produced β-type silicon nitride powder to the Si powder as a diluent during raw material mixing, a silicon nitride sintered body substrate having the above texture characteristics can be obtained. The amount of β-type silicon nitride powder is preferably 3 to 10% by weight.

[0052] Figure 7 is a schematic diagram illustrating an insulating circuit board 11 constructed using the silicon nitride sintered body of the above embodiment, and a semiconductor device 10 equipped with the insulating circuit board 11. The insulating circuit board 11 comprises a silicon nitride sintered body 13 formed as an insulating substrate, and a metal plate 15 as a conductor (circuit) bonded to the surface of the silicon nitride sintered body 13. In the illustrated Figure 7, the metal plate 15 is bonded to both the upper and lower surfaces of the silicon nitride sintered body 13 via a bonding layer. Here, the metal plate 15 is preferably a copper plate. Furthermore, the bonding layer is preferably a solder material such as Ag nanoparticles. The semiconductor device 10 comprises the insulating circuit board 11 and a semiconductor element 17 mounted on the metal plate 15 of the insulating circuit board 11. The semiconductor element 17 is mounted by solder paste or the like. In other words, the semiconductor device 10 of this embodiment can exhibit the characteristics of the silicon nitride sintered body 13 with improved characteristic anisotropy as a semiconductor device product. [Examples]

[0053] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0054] The silicon nitride sintered bodies in Examples 1-8 and Comparative Examples 1-3 were prepared under the following conditions and procedures. In Examples 1-8 and Comparative Example 3, they were synthesized from high-purity metallic silicon powder by direct nitriding. silicon nitrideBeta-type silicon nitride powder was prepared by crushing and washing ingots. The specific surface area and average particle size of the beta-type silicon nitride powder were measured to confirm its properties. Next, in Examples 1-7 and Comparative Example 3, appropriate amounts of MgO powder and Y2O3 powder were added to the beta-type silicon nitride powder according to the blending composition ratio of each powder. Furthermore, in Example 7, an appropriate amount of HfO2 powder was added. In Example 8, appropriate amounts of the prepared beta-type silicon nitride powder, MgSiN2 powder, and Y2O3 powder were added to the metallic silicon powder according to the blending composition ratio of each powder. In Comparative Examples 1 and 2, appropriate amounts of MgO powder and Y2O3 powder were added to the metallic silicon powder according to the blending composition ratio of each powder. 0.3 mg / m³ of a polycarboxylic acid-based surfactant dispersant was added to 100 parts by weight of this mixture. 2 Then, approximately 50 parts by weight of a mixed solvent of toluene and ethanol was added, and the mixture was crushed and mixed using silicon nitride pebbles. Subsequently, 18 parts by weight of polyvinyl butyral as a binder, 6 parts by weight of dioctyl adipicate as a plasticizer, and approximately 20 parts by weight of the mixed solvent of toluene and ethanol were added, and the mixture was stirred and mixed with a ball mill until the binder was completely dissolved and mixed, and a slurry was prepared. The slurry was then left in a vacuum to degas and volatilize, and the viscosity was adjusted. Next, a sheet molded body was obtained from the prepared slurry by the doctor blade method. The molding direction of the doctor blade was defined as the substrate molding direction X. The obtained sheet molded body was die-cut into a shape of 260 mm x 200 mm by die press processing. Subsequently, boron nitride powder was sprayed onto the surface of the die-cut sheet as a release agent, and 25 laminates per block were prepared, placed in a boron nitride sheath, and heated in dry air at 500°C for approximately 4 hours to remove organic components such as binders. Then, the sheet molded body was heated at 1860°C for 4 hours in a nitrogen atmosphere of 9 atmospheres to obtain a silicon nitride substrate laminate. The substrates of the silicon nitride laminate were separated, the top and bottom substrates were removed, and the outer edges of the remaining 23 substrates were broken with a laser. The boron nitride powder remaining on the substrate surface and the droplets attached by the laser processing were removed by honing to obtain a silicon nitride sintered substrate measuring 190 mm × 140 mm × 0.32 mm.

[0055] During the preparation of each sample, the specific surface area, particle size D50, fluorine content, and oxygen content of the β-type silicon nitride powder were measured. Then, for each prepared sample, texture analysis was performed using the EBSD method to obtain the texture index J, crystal orientation distribution at φ2=0°, maximum density profile, pole figure, and area ratio in the pole figure. Furthermore, structural analysis was performed on each prepared sample using X-ray diffraction to obtain the intensity ratio I(002) / I(200). For each prepared sample, the thermal conductivity λx in the substrate molding direction, the thermal conductivity λy in the direction perpendicular to the substrate molding direction, and the thermal conductivity λz in the substrate thickness direction were measured. Additionally, the bending strength σx in the substrate molding direction and the bending strength σy in the direction perpendicular to the substrate molding direction were measured for each prepared sample.

[0056] The various measurements and evaluations were performed under the following conditions.

[0057] • Specific surface area of ​​β-type silicon nitride powder The specific surface area was measured using the BET single-point method. The measuring device used was a Monosorb, model MS-21, manufactured by Quantachrome.

[0058] • Particle size D50 of β-type silicon nitride powder Measurements were performed using the SALD-2000 laser diffraction particle size distribution analyzer manufactured by Shimadzu Corporation. Sodium hexametaphosphate was used as the dispersant, with a refractive index of 2.4.

[0059] • Fluorine content of β-type silicon nitride powder The measurements were performed using the Dionex Integrion RFIC ion chromatograph manufactured by Thermo Fisher Scientific K.K. and the AQF-2100H automated sample combustion system manufactured by Nitto Seiko Analytech Co., Ltd., according to the thermal hydrolysis separation-ion chromatography method described in JIS R 1603 (2018).

[0060] • Oxygen content of β-type silicon nitride powder Measurements were performed using the EMGA-920 from Horiba, Ltd., employing the inert gas fusion-nondispersive infrared absorption method.

[0061] • Collective tissue analysis using EBSD method The crystal orientation of each sample was measured using the EBSD method with an Oxford Instruments C-Nano. The substrate surface was polished to a mirror finish using the following method. First, the surface was flattened with a #600 diamond polishing pad. Then, intermediate polishing was performed using diamond slurry in the order of 15 μm, 6 μm, and 1 μm. For the final polishing, a mirror finish was obtained by polishing with a 50 nm alumina slurry followed by polishing with 40 nm colloidal silica. After the final polishing, ultrasonic cleaning was performed using acetone and ethanol, and the surface roughness Sa in a 100 μm × 140 μm area (objective lens magnification 100x) was 0.01 μm or less using a laser microscope. The sample coordinate system was set so that the thickness direction of the substrate after mirror finishing was the Z direction (ND direction), the substrate forming direction was the X direction (RD direction), and the direction orthogonal to the substrate forming direction was the Y direction (TD direction). Under the conditions of an acceleration voltage of 15kV and a step size of 0.21μm, a sample of 11000μm was produced. 2 EBSD mapping was performed on the region. The obtained EBSD maps were analyzed using Oxford Instruments' EBSD analysis tool AZtecCrystal to perform orientation distribution function analysis, etc., and the crystal orientation distribution map at texture index J and φ2=0°, the maximum value of the density profile, the maximum value, the pole figure, and the area ratio in the pole figure were obtained.

[0062] • X-ray diffraction measurement and analysis The X-ray diffraction intensity of each sample was measured using powder X-ray diffraction with Cu-Kα rays, employing a Rigaku Corporation Ultima IV X-ray analyzer. Individual pieces cut to 15 mm × 15 mm were used for measurement. The substrate surface was polished to a thickness of 20 μm or more with a #600 diamond polishing pad, and the measurement surface was defined as the surface roughness Sa of 0.6 μm or less within a 100 μm × 140 μm area (objective lens magnification 100x) measured with a laser microscope. The X-ray diffraction measurement conditions were as follows: Scanning range: from 10 degrees to 85 degrees Sampling width: 0.02 degrees Scanning speed: 10 degrees / minute Divergence slit: 2 / 3 degrees Vertical divergence slit: 10 mm Scattering slit: 8 mm Receiving slit: open Tube voltage / current: 40 kV / 40 mA Detector: semiconductor detector In the X-ray diffraction pattern of the substrate plane obtained by X-ray incidence on the substrate plane, the integrated intensities of the diffraction peaks corresponding to the Miller indices (002) and (200) of β-type silicon nitride particles were calculated using analysis software.

[0063] · Thermal conductivity For the measurement method of the thermal conductivity in various directions of the substrate, the flash method was adopted. For the measurement, a thermal conductivity measurement device LFA467 manufactured by NETZSCH Geratebau GmbH was used. For the measurement, specimens cut into 10 mm × 10 mm from the substrate were used. To suppress the transmission of the flash light, a gold sputter film of about 100 nm was formed on both sides of the specimen. To uniformly absorb the pulsed light, graphene spray was used on both sides of the specimen, and a uniform blackening treatment was performed so that the graphene coating amount was about 0.1 mg / mm 2 was achieved. For the measurement of the thermal conductivity in the X and Y directions, a sample holder for in-plane measurement was used. When calculating the thermal conductivity, a value of 0.68 J / (g·K) was used as the specific heat of the obtained sintered body.

[0064] · Three-point bending strength The measuring device is of the type AG-IS manufactured by Shimadzu Corporation. The measurement conditions are a crosshead speed of 0.5 mm / minute and a distance between supports of 30 mm. The size of the test piece is 20 mm in width and 0.3 - 0.4 mm in thickness. For the bending strength σx in the X direction, the test was carried out with the test jig arranged in a direction perpendicular to the forming direction (the direction of the distance between the supports of the support tool coincides with the X direction). For the bending strength σy in the Y direction, the test was carried out with the test jig arranged in a direction parallel to the forming direction (the direction of the distance between the supports of the support tool coincides with the Y direction).

[0065] Tables 1 and 2 show the conditions and various measurement results for each sample in Examples 1-8 and Reference Examples 1-3. Table 1 mainly shows the preparation conditions for each sample, and Table 2 shows various characteristics. Figure 1 shows representative band contrast images of Examples 1 and 2 and Comparative Examples 1 and 3 obtained by EBSD. Figure 2 shows representative pole figures of Examples 1 and 2 and Comparative Examples 1 and 3 obtained by EBSD. Figure 3 shows representative crystal orientation distribution diagrams of Examples 1 and 2 and Comparative Examples 1 and 3 at φ2=0°. Figure 4 shows representative density profiles of Examples 1 and 2 and Comparative Examples 1 and 3 in the range of φ2=0°, Φ=0°, and φ1=0-60°. Figure 5 shows representative density profiles of Examples 1 and 2 and Comparative Examples 1 and 3 in the range of φ2=0°, Φ=90°, and φ1=0-180°.

[0066] [Table 1]

[0067] [Table 2]

[0068] According to Table 1, Examples 1-7 range from 6.0 to 11.0 m 2 The product was formed using β-type silicon nitride powder as the main raw material, with a specific surface area of ​​0.5 μm to 1.5 μm and an average particle size D50 of 0.5 μm to 1.5 μm. On the other hand, Example 8 uses metallic silicon powder as the main raw material, but with β-type silicon nitride powder within the above range added as a diluent. In contrast, Comparative Examples 1 and 2 use metallic silicon powder as the main raw material without a diluent. Comparative Example 3 is 5.0 m 2 It was formed primarily from β-type silicon nitride powder with a specific surface area of ​​1 / g and an average particle size D50 of 2.0 μm.

[0069] As shown in Table 2, the texture index J is 1.2 to 1.7 for Examples 1 to 8, while it is greater than 1.7 for Comparative Examples 1 to 3. This indicates that the crystal grains in Examples 1 to 8 are oriented in a more random manner than in Comparative Examples 1 to 3. Furthermore, in Examples 1 to 8, the maximum value of the density profile in the range of φ2=0°, Φ=0°, and φ1=0 to 60° is 1.0 to 1.6, and the maximum value of the density profile in the range of φ2=0°, Φ=90°, and φ1=0 to 180° is 2.0 to 7.0, whereas Comparative Examples 1 to 3 show values ​​outside these ranges. In other words, Examples 1 to 8 and Comparative Examples 1 to 3 can also be differentiated in terms of texture characteristics by the maximum value of the density profile.

[0070] Furthermore, as shown in the pole diagram of Figure 2, in Examples 1 and 2, the white areas are dispersed, indicating that the crystal orientation of the β-Si3N4 crystal grains is dispersed over a wide area. On the other hand, in Comparative Example 1, the distribution in the Z direction (intersection of the X and Y axes) is extremely small, indicating that the {0 0 0 1} plane of the β-Si3N4 crystal grains is preferentially oriented in the Z direction (ND direction). In Comparative Example 3, the distribution of the {1 0 -1 0} plane in the Y direction is large, indicating that the {0 0 0 1} of β-Si3N4 is preferentially oriented in the X direction.

[0071] As shown in Table 2, it was found that the texture characteristics were differentiated between Examples 1-8 and Comparative Examples 1-3 by the area ratio of β-type silicon nitride crystal grains that quantitatively demonstrate the characteristics of the pole figure. Specifically, in Examples 1-8, the area ratio of β-type silicon nitride crystal grains having a crystal orientation in which the tilt of the {1 0 -1 0} plane from the ND direction is within 70° was 90-98% for all β-type silicon nitride crystal grains, whereas in Comparative Examples 1-3 it was outside this range. In Examples 1-8, the area ratio of β-type silicon nitride crystal grains having a crystal orientation in which the tilt of the {1 0 -1 0} plane from the ND direction is within 60° was 80-94% for all β-type silicon nitride crystal grains, compared to outside this range in Comparative Examples 1-3. In Examples 1-8, the area percentage of β-type silicon nitride crystal grains having a crystal orientation in which the tilt of the {1 0 -1 0} plane from the ND direction is within 50° is 65-85% for all β-type silicon nitride crystal grains, whereas in Comparative Examples 1-3 it is outside this range. In Examples 1-8, the area percentage of β-type silicon nitride crystal grains having a crystal orientation in which the tilt of the {1 0 -1 0} plane from the ND direction is within 40° is 50-75% for all β-type silicon nitride crystal grains, whereas in Comparative Examples 1-3 it is outside this range. In Examples 1-8, the area percentage of β-type silicon nitride crystal grains having a crystal orientation in which the tilt of the {1 0 -1 0} plane from the ND direction is within 30° is 30-52% for all β-type silicon nitride crystal grains, compared to outside this range in Comparative Examples 1-3.

[0072] As shown in Table 2, in Examples 1-8 and Comparative Examples 1-3, the thermal conductivity λx, λy, and λz are each 70 W / mK or higher. Furthermore, the ratio λz / λx, which is the ratio of the thermal conductivity λx in the substrate molding direction to the thermal conductivity λz in the substrate thickness direction, is 0.96-1.06 in Examples 1-8, while it is outside this range in Comparative Examples 1-3. In other words, the ratio of the difference between the thermal conductivity λz and the thermal conductivity λx (|λz-λx| / λx) to the thermal conductivity λx is 6% or less in Examples 1-8, while it is 10% or more in Comparative Examples 1-3. Note that in Examples 1-7, the difference ratio is 5% or less. In addition, the ratio λy / λx, which is the ratio of the thermal conductivity λx in the substrate molding direction to the thermal conductivity λy in the direction orthogonal to it, is 0.99-1.00 in Examples 1-8, while it is outside this range in Comparative Examples 1-3. In other words, the ratio of the difference between the thermal conductivity λy and the thermal conductivity λx (|λy-λx| / λx) to the thermal conductivity λx is 1.5% or less in Examples 1 to 8, while it is 1.9% or more in the comparative examples. That is, the characteristic anisotropy of the thermal conductivity is significantly reduced in Examples 1 to 8 compared to Comparative Examples 1 to 3.

[0073] As shown in Table 2, in Examples 1-8 and Comparative Examples 2 and 3, the bending strength σx in the substrate forming direction and the bending strength σy in the direction perpendicular to the substrate forming direction are both 600 MPa or higher. In Comparative Example 1, the bending strengths σx and σy are less than 600 MPa and do not meet the standard strength. Furthermore, the ratio of bending strength σx to bending strength σy, σy / σx, is between 0.9 and 1.1 in Examples 1-8, while it is outside this range in Comparative Examples 2 and 3. In other words, the ratio of the difference between bending strength σx and bending strength σy (|σy-σx| / σx) to bending strength σx is 10% or less in Examples 1-8, while it is greater than 10% in Comparative Examples 2 and 3. That is, Examples 1-8 have the desired bending strength, while the anisotropy of the mechanical strength characteristics is significantly reduced compared to Comparative Examples 2 and 3.

[0074] Furthermore, as shown in Table 2, the intensity ratio I(002) / I(200) of the integrated intensity I(002) to the integrated intensity I(200) of the X-ray diffraction peaks is between 0.05 and 0.2, whereas in Comparative Examples 2 and 3 it is outside this range. In other words, it is possible to differentiate Examples 1 to 8 from Comparative Examples 1 to 3 by structural analysis using X-ray diffraction.

[0075] The present invention is not limited to the embodiments described above, and can be implemented in various forms as long as they fall within the technical scope of the present invention. [Explanation of Symbols]

[0076] 10 Semiconductor Devices 11 Insulated circuit board 13. Silicon nitride sintered body 15 metal plate 17 Semiconductor devices

Claims

1. A silicon nitride sintered body comprising a substrate having mutually orthogonal RD and TD directions in a plane perpendicular to the ND direction in the substrate thickness direction, wherein the RD direction is defined as the rolling direction of the green sheet of the silicon nitride sintered body, The bending strength σx in the RD direction and the bending strength σy in the TD direction perpendicular to the RD direction are each 600 MPa or more, and the ratio of the difference between the bending strength σx and the bending strength σy (|σy - σx| / σx) to the bending strength σx is 10% or less. The ratio of the difference between the thermal conductivity λz in the substrate thickness direction and the thermal conductivity λx in the RD direction (|λz - λx| / λx) to the thermal conductivity λx in the RD direction is 6% or less. A silicon nitride sintered body characterized in that the intensity ratio I(002) / I(200) of the integrated intensity I(002) of the X-ray diffraction peak corresponding to the Miller index (002) plane in the ND direction, obtained by X-ray diffraction, and the integrated intensity I(200) of the X-ray diffraction peak corresponding to the Miller index (200) plane is 0.05 to 0.

2.

2. An insulating circuit board comprising the silicon nitride sintered body described in claim 1 and a metal plate bonded to the surface of the silicon nitride sintered body.

3. A semiconductor device comprising an insulating circuit board as described in claim 2, and a semiconductor element mounted on a metal plate of the insulating circuit board.

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