Silicon nitride sintered body and substrate for mounting electronic components

Abstract

To provide a silicon nitride sintered body with controlled orientation of β-type silicon nitride (β-Si3N4) grains and further improved thermal conductivity performance.SOLUTION: A silicon nitride sintered body comprises a substrate containing β-type silicon nitride grains, and contains, in a cross-sectional photograph of a cross section of the substrate formed by vertical scission to a plane surface, 10 or more β-type silicon nitride grains having a long axis of 50 μm or more in a region of 200,000 μm2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silicon nitride sintered body and a method for producing a silicon nitride sintered body. [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. The temperature rise 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 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.

[0004] Patent Document 2 discloses a silicon nitride sintered substrate and a method for manufacturing the same, which achieves thermal conductivity and mechanical strength by controlling the orientation of β-type silicon nitride (β-Si3N4) particles. In Patent Document 2, silicon nitride powder containing 7% or less β-type silicon nitride is used as a raw material, and a sheet molded body is formed after adjusting the viscosity of the slurry to 13,000 cps or more, thereby increasing the intensity of the X-ray diffraction peak of the (101) plane of the crystal structure of the β-type silicon nitride particles in the silicon nitride sintered substrate manufactured by this method. 101 The intensity of the X-ray diffraction peak I of the (210) plane of β-type silicon nitride 210 The intensity ratio I 101 / I 210 This is controlled to bring it closer to 1. As a result, the fracture toughness value K in the first direction parallel to the substrate plane of the silicon nitride sintered substrate is improved.C1 The fracture toughness value K in the second direction perpendicular to the first direction. C2 A silicon nitride sintered substrate was obtained that suppressed a relative decrease in fracture toughness and possessed isotropic fracture toughness in both directions. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-30866 [Patent Document 2] Japanese Patent Publication No. 2019-52072 [Overview of the project] [Problems that the invention aims to solve]

[0006] The inventors aimed to improve the thermal conductivity of β-type silicon nitride particles in the substrate thickness direction by reviewing the manufacturing method of conventional silicon nitride sintered bodies and focusing on further control of the orientation of β-type silicon nitride (β-Si3N4) particles.

[0007] To solve the above problems, the present invention aims to provide a silicon nitride sintered body in which the orientation of β-type silicon nitride (β-Si3N4) particles is controlled and the thermal conductivity performance in the substrate thickness direction is further improved, as well as a method for manufacturing a silicon nitride sintered body. [Means for solving the problem]

[0008] One embodiment of the present invention is a silicon nitride sintered body comprising a substrate containing β-type silicon nitride particles, characterized in that the Lotgering factor f(hk0), which indicates the degree of orientation of the (hk0) plane of the β-type silicon nitride particles on the substrate plane, is a negative value.

[0009] A further embodiment of the silicon nitride sintered body of the present invention is more preferably characterized by having a thermal conductivity of 100 W / mK or more in the substrate thickness direction.

[0010] A further form of the silicon nitride sintered body of the present invention preferably has a fracture toughness value K perpendicular to the thickness direction C1 and a fracture toughness value K in the thickness direction C2 and is characterized in that K C1 / K C2 is 0.85 or more.

[0011] A further form of the silicon nitride sintered body of the present invention preferably has, in a cross-sectional photograph taken of a cross-section obtained by cutting a substrate perpendicularly to the plane, 10 or more β-type silicon nitride particles having a major axis of 50 μm or more in a region of 200,000 μm 2 .

[0012] A further form of the silicon nitride sintered body of the present invention preferably has, in a cross-sectional photograph taken of a cross-section obtained by cutting a substrate perpendicularly, 8 or more β-type silicon nitride particles having a major axis of 50 μm or more and an inclination angle with respect to the normal of the substrate surface of 45 degrees or less in a region of 200,000 μm 2 .

[0013] A further form of the silicon nitride sintered body of the present invention preferably has an arithmetic mean height Sa indicating the roughness of the substrate surface of 0.8 μm or more.

[0014] A method for manufacturing a silicon nitride sintered body according to one form of the present invention includes, in a silicon nitride sintered body, a mixing step of mixing silicon powder, rare earth oxide powder, and magnesium silicon nitride powder so as to have a molar ratio of 85 to 95 mol% of silicon nitride (Si3N4), 1 to 3 mol% of rare earth oxide (RE2O3), and 4 to 12 mol% of magnesium silicon nitride (MgSiN2) to produce a mixed powder, a molding step of molding the mixed powder into a sheet shape to produce a molded body, a nitriding step of heating the molded body from a first temperature to a second temperature in a nitrogen atmosphere, and a densification step of firing the molded body at a third temperature and for a predetermined time in a nitrogen atmosphere to produce a silicon nitride sintered body.

[0015] A further embodiment of the present invention is a method for producing a silicon nitride sintered body, more preferably one in which the specific surface area of ​​the silicon powder is 5.0 m². 2 The D of the aforementioned silicon powder is 1 / g or more. 99.9 It is characterized by having a diameter of 9.5 μm or less.

[0016] A further embodiment of the present invention is a method for producing a silicon nitride sintered body, more preferably wherein the specific surface area of ​​the silicon magnesium nitride powder is 9.0 m². 2 It is characterized by being 1 / g or more.

[0017] A further embodiment of the present invention is a method for producing a silicon nitride sintered body, more preferably characterized in that the molded body is produced by a sheet molding method.

[0018] A further embodiment of the present invention, a method for producing a silicon nitride sintered body, is more preferably characterized in that the inorganic filling rate of the molded body is 47% or more. [Effects of the Invention]

[0019] According to the silicon nitride sintered body and its manufacturing method of the present invention, the thermal conductivity in the thickness direction of the substrate is improved by controlling the alignment of the long axis of the β-type silicon nitride particles with the thickness direction of the substrate. [Brief explanation of the drawing]

[0020] [Figure 1] SEM image of the substrate surface of the silicon nitride sintered body of Example 1, taken at a magnification of 2000x.

[0021] [Figure 2] SEM image of the substrate surface of the silicon nitride sintered body of Example 5, taken at 2000x magnification.

[0022] [Figure 3] SEM image of the substrate surface of the silicon nitride sintered body of Comparative Example 1, taken at a magnification of 2000x.

[0023] [Figure 4]X-ray diffraction pattern of the silicon nitride sintered body of Example 1.

[0024] [Figure 5] X-ray diffraction pattern of the silicon nitride sintered body of Example 5.

[0025] [Figure 6] X-ray diffraction pattern of the silicon nitride sintered body of Example 12.

[0026] [Figure 7] X-ray diffraction pattern of the silicon nitride sintered body of Comparative Example 1.

[0027] [Figure 8] X-ray diffraction pattern of the silicon nitride sintered body of Comparative Example 7.

[0028] [Figure 9] Observation photograph of the cross-section of the silicon nitride sintered substrate of Example 1.

[0029] [Figure 10] Observation photograph of the cross-section of the silicon nitride sintered substrate of Example 5.

[0030] [Figure 11] Observation photograph of the cross-section of the silicon nitride sintered substrate of Comparative Example 1.

[0031] [Figure 12] (a) an illustrative image of a cross-section of a silicon nitride sintered body substrate after a fracture toughness test, and (b) a schematic diagram thereof, for explaining the method of measuring fracture toughness values ​​in the first and second directions in the present invention. [Modes for carrying out the invention]

[0032] 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.

[0033] The silicon nitride sintered body of this embodiment is a sintered body composed of 85 to 95 mol% silicon (calculated as silicon nitride after complete silicon nitriding), 1 to 3 mol% rare earth oxide, and 4 to 12 mol% magnesium silicon nitride as raw material powders. In this embodiment, the rare earth oxide can be selected from oxides of Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb, or combinations thereof.

[0034] The β-type silicon nitride particles contained in the silicon nitride sintered substrate have an elongated hexagonal prismatic crystal structure with long and short axes. In this embodiment, the silicon nitride sintered substrate is designed to preferentially orient β-type silicon nitride in the thickness direction of the substrate, thereby improving thermal conductivity in the thickness direction. The characteristics of the silicon nitride sintered substrate in this embodiment are shown below.

[0035] The silicon nitride sintered body of this embodiment is configured such that the Lotgering factor f(hk0), which indicates the degree of orientation of the (hk0) plane of β-type silicon nitride on the substrate surface, is a negative value.

[0036] The Lotgering factor f(hk0) is an index that represents the degree of orientation of each crystal grain constituting a polycrystalline material. The value of the Lotgering factor f(hk0) is calculated using the integrated intensity of each diffraction peak of X-rays diffracted from the target crystal plane, according to the following equations 1 to 3. f(hk0)=(ρ−ρ0) / (1−ρ0) (Equation 1) ρ0=ΣI0(hk0) / ΣI0(hkl) (Equation 2) ρ = ΣI(hk0) / ΣI(hkl) (Equation 3) ρ0 is calculated using the diffraction intensity I0 of the X-ray diffraction spectrum of the unoriented sample in the range of 2θ from 20 to 65 degrees, and is obtained by Equation 2 as the ratio of the total diffraction intensity ΣI0(hk0) of the (hk0) plane to the sum of all diffraction intensities ΣI0(hkl). Here, the diffraction intensity I0 is calculated from the X-ray diffraction spectrum of the reference sample (an unoriented sample having the same composition as the target sample). Furthermore, ρ is calculated using the diffraction intensity I of the X-ray diffraction spectrum of the silicon nitride sintered body sample in the range of 2θ from 20 to 65 degrees, and is obtained by Equation 3 as the ratio of the total diffraction intensity ΣI(hk0) of the (hk0) plane to the sum of all diffraction intensities ΣI(hkl). Note that h, k, and l are integers and represent plane indices. If the crystal orientation of the obtained sample is random, the difference between ρ and ρ0 is small, and according to Equation 1, f(hk0) will be close to zero. If f(hk0) is a negative value (ρ<ρ0), it means that the obtained sample has a lower degree of orientation of the (hk0) plane than the unoriented sample. In other words, a negative value for the Lot-Gering factor f(hk0) of the obtained sample indicates that the (00l) plane (i.e., the long axis) of the β-type silicon nitride particles is strongly oriented in the thickness direction.

[0037] Furthermore, as another indicator of the degree of orientation of β-type silicon nitride particles in the silicon nitride sintered substrate of this embodiment, the intensity of the X-ray diffraction peak of the (101) plane of β-type silicon nitride in the silicon nitride sintered body is I 101 And the intensity of the X-ray diffraction peak I of the (210) plane of β-type silicon nitride 210 The intensity ratio I 101 / I 210 Examples include the silicon nitride sintered body of this embodiment, where the strength ratio is I 101 / I 210 However, since it is 1.5 or higher, orientation towards the thickness direction of the long axis is inferred.

[0038] Furthermore, in the silicon nitride sintered body of this embodiment, the arithmetic mean height Sa, which indicates the roughness of the substrate surface, is 0.8 μm or more. Since β-type silicon nitride particles are columnar particles, when the long axis of the β-type silicon nitride particles is preferentially oriented in the thickness direction of the plate, the particle tips protrude from the substrate surface, resulting in an arithmetic mean height Sa of 0.8 μm or more, which is a relatively high value.

[0039] Furthermore, in the silicon nitride sintered body of this embodiment, in the cross-sectional photograph taken of a cross-section obtained by cutting the substrate perpendicular to the plane, 200,000 μm 2 Within this region, it was observed that there were 10 or more coarse particles of β-type silicon nitride with a major axis of 50 μm or more. Among these, it was observed that there were 8 or more coarse particles of β-type silicon nitride with a major axis of 50 μm or more and an inclination angle of 45 degrees or less with respect to the normal to the substrate surface. In other words, microscopic analysis showed that the major axes of many of the coarse particles of β-type silicon nitride were oriented in the direction of the plate thickness.

[0040] In other words, the silicon nitride sintered body of this embodiment contains a relatively large amount of coarse particles having a long axis of 50 μm or more, and the long axis of β-type silicon nitride is preferentially oriented in the thickness direction of the substrate.

[0041] Furthermore, in the silicon nitride sintered body of this embodiment, the thermal conductivity in the thickness direction of the substrate is 100 W / mK or higher. That is, the shape of the β-type silicon nitride particles is rod-shaped, and the thermal conductivity in the long axis direction is approximately twice that in the short axis direction. Therefore, by aligning the β particles in the thickness direction of the plate, the thermal conductivity in the thickness direction of the plate is greatly improved.

[0042] Furthermore, the silicon nitride sintered body of this embodiment is densified to a relative density of 98% or higher. In the silicon nitride sintered body of this embodiment, the fracture toughness value K in the first direction parallel to the substrate plane is C1 5.5 MPa·m 1 / 2 The above is the value of fracture toughness K in the second direction perpendicular to the substrate plane. C2 5.5 MPa·m 1 / 2 That concludes the explanation. Furthermore, the fracture toughness value K in the first direction is also included. C1 and the value of fracture toughness K in the second direction C2 The ratio of K C1 / K C2The ratio is 0.85 or higher. In other words, in the silicon nitride sintered body, the columnar crystals are controlled to be aligned in the vertical direction, resulting in isotropically exhibited mechanical strength (fracture toughness) of the substrate, and high mechanical strength (fracture toughness) is exhibited in both the first and second directions.

[0043] Next, a method for manufacturing the silicon nitride sintered body of this embodiment will be described. The manufacturing method for the silicon nitride sintered body does not use silicon nitride powder as a starting material, but rather silicon powder as a starting material, and the molded silicon powder is heated in a nitrogen atmosphere to perform nitriding and densification simultaneously using a reaction sintering method. In general, the reaction sintering method improves the thermal conductivity of the sintered body because of the high purity of the raw materials, but it is said to be difficult to adjust the raw materials and firing conditions for densification. Furthermore, in general reaction sintering methods, since silicon powder is converted into rod-shaped β-type silicon nitride particles, it is difficult to control their orientation in the thickness direction of the plate, and it is known that the orientation tends to be random.

[0044] According to this embodiment, the method for producing a silicon nitride sintered body mainly comprises a mixing step of mixing silicon raw material powder, rare earth oxide powder, and magnesium silicon nitride powder to produce a mixed powder such that the molar ratio of silicon nitride is 85 to 95 mol%, rare earth oxide is 1 to 3 mol%, and magnesium silicon nitride is 4 to 12 mol% in the silicon nitride sintered body; a molding step of forming the mixed powder into a slurry and shaping it into a sheet to produce a molded body; a nitriding step of heating the molded body from a first temperature to a second temperature in a nitrogen atmosphere; and a densification step of firing the molded body in a nitrogen atmosphere at a third temperature and for a predetermined time to obtain a silicon nitride sintered body. Each step will be described in more detail below.

[0045] Prepare silicon powder as the starting material. Grind the silicon powder, organic solvent, and dispersant in a ball mill until the specific surface area of ​​the silicon powder reaches 5.0 m². 2 / g or more, D 99.9 Particle size adjustment is performed so that the diameter is 9.5 μm or less. Here, in the particle size distribution curve with particle size (μm) on the horizontal axis and frequency (%) on the vertical axis, D 50The diameter (median diameter) is the diameter of the particles that account for 50% of the frequency, D 99.9 The diameter is the particle size corresponding to the mode of the distribution (99.9% frequency). After adjusting the particle size of the silicon powder, a mixed powder is prepared by mixing rare earth oxide powder and magnesium silicon nitride powder as sintering aids. The specific surface area of ​​the magnesium silicon nitride powder is 9.0 m². 2 It is preferable that the amount is 1 / g or more. Here, in terms of molar ratio, 85-95 mol% silicon, 1-3 mol% rare earth oxide, and 4-12 mol% magnesium silicon nitride are mixed, based on silicon nitride after silicon has been completely nitrided. This mixed powder is thoroughly mixed in a ball mill, and then a binder, plasticizer, and organic solvent are added to form a slurry.

[0046] Next, the slurry is degassed under vacuum and its viscosity is adjusted. The proportion of organic solvent in the degassed slurry is set to 35 wt% or less, and the viscosity of the slurry is set to 15,000 to 25,000 cps. Then, a sheet-like molded body is produced using a doctor blade or the like.

[0047] The molded body is manufactured so that the inorganic filling rate is 47% or higher. To achieve an inorganic filling rate of 47% or higher in the molded body, the specific surface area of ​​the silicon powder must be 9.0 m². 2 / g or less (i.e., 5.0-9.0m) 2 It is preferable to adjust the particle size of the pulverizer so that it is within the range of / g, and to keep the proportion of organic solvent after defoaming at 35 wt% or less. The specific surface area of ​​the silicon powder is 9.0 m². 2 When the value exceeds / g, the proportion of fine silicon powder increases, making aggregation more likely and resulting in poor packing performance. Furthermore, if the proportion of organic solvent in the slurry after degassing exceeds 35 wt%, a large amount of organic solvent volatilizes during sheet molding, leading to increased drying shrinkage and the formation of fine bubbles within the molded body. The inorganic packing rate was measured as follows: The sheet molded body used for measurement had a residual organic solvent content of 0.1 wt% or less. The volume and weight of the sheet molded body were measured, and the green density ρ of the molded body was determined. g (g / cm 3The organic fraction Pi (%) was measured. Subsequently, the sheet molded body used for measurement was subjected to a debinding treatment in air at 500°C / 3h. The organic fraction Pi (%) was determined by measuring the weight after the debinding treatment, and the inorganic filling rate Fi (%) was calculated using Equation 4 below. Fi = ρ g ×(1-Pi / 100) / ρ th ×100 (Formula 4) Here ,ρ th This is the theoretical density when milled, and is a value calculated from the weight ratio of inorganic components in the raw materials.

[0048] Next, the prepared sheet-like molded body was debindered in a dry air atmosphere of approximately 500-800°C. After that, it was heated in a furnace under vacuum to approximately 1000°C (first temperature), then the atmosphere was changed to a nitrogen pressurized atmosphere, and the temperature was raised from approximately 1000°C to approximately 1350°C (second temperature). At this time, nitriding of the molded body can be performed by gradually raising the temperature from the first temperature to the second temperature (for example, 1°C / min) in a nitrogen pressurized atmosphere. Then, the atmosphere inside the furnace was changed to a higher pressure nitrogen pressurized atmosphere, and the temperature was raised from the second temperature to the third temperature of approximately 1750-2000°C (preferably 1900°C). After the temperature rise, the temperature was maintained at the third temperature for a long period of time (for example, approximately 8 hours), thereby firing the nitrided molded body and sufficiently densifying the molded body to produce a silicon nitride sintered body.

[0049] By following the process described above, it is possible to manufacture a silicon nitride sintered body in which β-type silicon nitride particles are preferentially oriented in the thickness direction of the substrate. In other words, it can be considered that the reducing properties in the nitriding and densification processes are enhanced by suppressing the amount of oxygen in the molded body through the use of magnesium silicon nitride and minimizing the amount of yttrium oxide added (i.e., using 1-3 mol% rare earth oxides) in the manufacturing method. When the reducing properties are enhanced in this way, the silicon oxide film on the surface of the silicon powder is reduced, and SiO(g) volatilizes in the thickness direction of the plate. Furthermore, the reduction reaction SiO(g) + CO(g) → Si(g) + CO2(g) is promoted, and the generated Si(g) undergoes the reaction process 3Si(g) + 2N2(g) → β-Si3N4 in the porous body before densification, and it is thought that β-Si3N4 precipitates in the thickness direction within the pores. Furthermore, as the heat treatment temperature increases, a silicon nitride substrate is obtained in which β-type silicon nitride particles are preferentially oriented in the thickness direction, with β-Si3N4 precipitated in the thickness direction within the pores as nuclei. It is thought that the extension of the β-type silicon nitride particles in the thickness direction increases the thermal conductivity, improving the heat dissipation performance as an insulating substrate.

[0050] The process described above is merely an example and does not limit the present invention. For example, the slurry molding method is not limited to the doctor blade method; the slurry may be pressure-molded into a sheet molded body by methods such as extrusion molding or casting. [Examples]

[0051] 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.

[0052] The silicon nitride sintered bodies in Examples 1-20 and Comparative Examples 1-8 were prepared under the following conditions and procedures.

[0053] Silicon powder having predetermined powder properties and sintering aid powder were prepared. An appropriate amount of silicon powder was placed in a ball mill, and the silicon powder, organic solvent, and dispersant were ground in the ball mill, and the specific surface area and D of the silicon powder were measured.99.9 The particle size was adjusted until the diameter value reached a predetermined value. Here, the blending composition ratio for each sample, as well as the D content of the silicon powder, were determined. 99.9 Diameter, D 50 The diameter and specific surface area values ​​are shown in Table 1. After adjusting the particle size of the silicon powder, a sintering aid was added and the mixture was mixed in a ball mill for 1 hour. Then, a binder (polyvinyl butyral), a plasticizer (dioctyl adipate), and an organic solvent (a mixed solvent of toluene and ethanol) were added to form a slurry. The slurry was degassed under vacuum and its viscosity was adjusted. The proportion of organic solvent in the degassed slurry was set to 35 wt% or less, and the viscosity of the slurry was set to 15,000 to 25,000 cps. The viscosity of the slurry was measured using a TVC-7 viscometer manufactured by Toki Sangyo Co., Ltd. Specifically, the viscosity was calculated from the resistance force when the spindle was rotated in the slurry. Then, sheet-like molded bodies were produced using a doctor blade with a molding speed of 200 mm / min or more. Next, the inorganic filling rate Fi (%) of the sheet-like molded bodies of each sample was measured. BN was spray-coated onto the surface of the fabricated sheet-like molded body as a release agent, and a laminate of 20 sheets per block was prepared. The laminate was debindered in dry air at 500°C, then placed in a furnace and heated to approximately 1000°C in a vacuum, and then heated to approximately 1350°C at a rate of 1°C / min in a nitrogen pressurized atmosphere of 0.2 MPa. Next, the atmosphere was changed to a nitrogen pressurized atmosphere of 0.9 MPa, and the temperature was raised from approximately 1350°C to approximately 1900°C, where firing was performed for approximately 8 hours. After firing, the laminated substrate was separated, and the sintered surface was honed by spraying alumina abrasive grains (average particle size ~50 μm) at a honing pressure of 0.4 MPa to obtain a silicon nitride sintered body with a plate thickness of 0.35 mm and a size of 190 mm × 140 mm.

[0054] For each of the prepared samples in Examples 1-20 and Comparative Examples 1-8, the crystalline phase of each sample was identified by X-ray diffraction measurement, and the X-ray diffraction pattern was analyzed to determine the integrated intensity of each diffraction peak, the Lotgering factor f(hk0), and the intensity ratio I. 101 / I 210 The following was derived. In addition, for each sample, the β-type silicon nitride particles in the vertical cross-section were observed, and the 200,000 μm2 Within the specified region, we determined the number of coarse particles with a major axis of 50 μm or more, and the number of coarse particles with an inclination angle of 45 degrees or less relative to the normal to the substrate surface. Furthermore, for each sample, we determined the relative density, arithmetic mean height Sa, thermal conductivity (W / mK), and fracture toughness (MPa·m). 1 / 2 The following measurements were taken. All measurements were performed under the following conditions.

[0055] • 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 10 mm × 10 mm were used for measurement. The surface of the substrate after honing was used as the measurement surface. The measurement conditions were as follows: Sampling width: 0.02 degrees Scan speed: 10 degrees / minute Divergence slit: 2 / 3 degrees Divergent vertical slit: 10mm Scattering slit: 8mm Light-receiving slit: Open Tube voltage / current: 40kV / 40mA Detector: Semiconductor detector In the X-ray diffraction pattern of the substrate plane obtained by X-ray incidence onto the substrate plane, the integrated intensity of the diffraction peak corresponding to the Miller index (hkl) of β-type silicon nitride particles was calculated. Based on the calculated peak intensities, the Lotgering factor f(hk0) and the intensity ratio I were calculated. 101 / I 210 This was derived.

[0056] Method for observing β-type silicon nitride particles in a vertical cross-section. Using 10mm x 10mm pieces, the pieces were embedded in epoxy resin, and the cross-section perpendicular to the substrate was observed. The observation surface was prepared using the following procedure: The surface was flattened with #800 diamond abrasive paper, and then polished with diamond slurry in the order of 15μm, 6μm, and 1μm until polishing scratches from each preceding step were removed. A mirror surface was obtained by finishing with a 50nm alumina slurry. After mirror polishing, plasma etching with CF4 was performed to create the observation surface. Then, using a laser microscope VKX-150 manufactured by Keyence Corporation, the observation surface was observed with an objective lens magnification of 20x, and photographs of the cross-section were taken. Image processing of the cross-sectional photographs was performed, and the region was 200,000μm. 2 In the cross-sectional photograph, the number of coarse particles with a major axis of 50 μm or more among the β-type silicon nitride particles, and further, the number of coarse particles whose inclination with respect to the normal to the substrate surface is 45 degrees or less, were measured.

[0057] • Relative density The density of the sintered body was calculated from the theoretical density obtained from the raw material mixing ratio (Equation 5). The density of the sintered body was measured using the Archimedes method with pure water. Relative density (%) = (Sintered body density / Theoretical density) × 100 (Equation 5)

[0058] • Arithmetic mean height Sa The surface roughness Sa of a 500 μm × 500 μm area of ​​the substrate surface after honing was measured using a VKX-150 laser microscope manufactured by Keyence Corporation. The measurement conditions were as follows: Objective lens magnification: ×20 Image correction: Automatic tilt correction Filter type: Gaussian S-filter: 2μm F-Operation: None L-filter: 0.2mm End effect correction: Yes

[0059] • Thermal conductivity The flash method was used to measure the thermal conductivity in the thickness direction of the substrate. A NETZSCH Geratebau GmbH LFA467 thermal conductivity measuring instrument was used for the measurement. Individual pieces cut from the substrate to 10 mm x 10 mm were used for the measurement. To suppress the transmission of flash light, a gold sputtered film was formed on both sides of the individual pieces, and to uniformly absorb the pulsed light, a blackening treatment was performed using graphene spray on both sides of the individual pieces. When calculating the thermal conductivity, a specific heat value of 0.68 J / (g·K) was used for the obtained sintered body.

[0060] • Fracture toughness The fracture toughness of each sample was measured according to JIS-R1607 using a Vickers hardness tester HV-120 manufactured by Mitutoyo Corporation. Specifically, the cross-section of the substrate, cut along the thickness direction, was mirror-polished, and as shown in Figures 12(a) and (b), indentations with diagonal lengths a1 and a2 were formed on the mirror-polished surface near the center in the thickness direction of the mirror-polished surface. The diagonal lengths a1 and a2 of the resulting indentations and the crack lengths c1 and c2 originating from the apex of the indentations were measured, and the fracture toughness value K was calculated from the indentation load, the diagonal lengths of the indentations, the crack lengths, and the elastic modulus. C The following was determined. According to JIS-R1607, the fracture toughness value KC is calculated using the following formula. K C = 0.026 × E 1 / 2 ×P 1 / 2 ×a / C 3 / 2 (Formula 6) C=((c1 / 2+c2 / 2) / 2) / 2 (Equation 7) a=((a1 / 2+a2 / 2) / 2) / 2 (formula 8) E: Modulus of elasticity P: Compression load a: Half the average diagonal length of the indentation. C: Half the average crack length In contrast, in this embodiment, the fracture toughness value K C The fracture toughness value K in the first direction (direction parallel to the substrate plane) C1 , fracture toughness value K in the second direction (direction perpendicular to the substrate plane) C2The evaluation was performed separately. Specifically, by setting the length of the crack that occurred in a direction parallel to the substrate plane as c1, and setting C in Equation 6 to c1 / 2, K C1 The following was calculated. Furthermore, by setting the length of the crack that occurred in the direction perpendicular to c1 (the thickness direction of the substrate) to c2, and setting C in equation 6 to c2 / 2, K C2 The following calculation was performed. The thickness of the test specimen was set to 0.35 mm, and the indentation load P was set to 10 kgf.

[0061] Tables 1 and 3 show the conditions and various measurement results for each sample in Examples 1 to 14 and Reference Examples 1 to 8. Tables 2 and 4 show the conditions and various measurement results for each sample in Examples 15 to 20. Figures 1 to 3 show illustrative SEM images of the substrate surface of the samples in Examples 1 and 5 and Comparative Example 1, taken at 2000x magnification. Figures 4 to 8 show illustrative X-ray diffraction patterns of Examples 1, 5, 12 and Comparative Examples 1 and 7. In the X-ray diffraction patterns, the Miller index (hkl) is indicated for each diffraction peak of the β-type silicon nitride particles. Figures 9 to 11 show illustrative cross-sectional images of Examples 1 and 5 and Comparative Example 1.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] Examples 1-20 consist of raw material powders in molar ratios of 85-95 mol% silicon (equivalent to silicon nitride), 1-3 mol% rare earth oxide, and 4-12 mol% magnesium silicon nitride. In Examples 1-14, yttrium oxide (Y2O3) was selected as the rare earth oxide (RE2O3). In Examples 15-20, La2O3, Sm2O3, Gd2O3, Dy2O3, Er2O3, and Yb2O3 were selected as the rare earth oxide (RE2O3), respectively. The starting material is silicon powder D 99.9 The diameter is 8.0 to 9.5 μm (9.5 μm or less), and the specific surface area is 5.0 to 8.0 m². 2 / g(5.0m 2 / g or more and 9.0m 2 (less than / g). In addition, in Examples 1 to 20, the inorganic filling rate of the molded body produced in the molding process was 47% or more. On the other hand, Comparative Examples 1 and 2 are samples in which magnesium oxide was used as the raw material powder instead of magnesium silicon nitride. Comparative Example 3 is a sample in which magnesium silicon nitride was 3 mol% (less than 4 mol%). Comparative Example 4 is a sample in which the starting material silicon powder was D 99.9 The diameter is set to 12.3 μm (larger than 9.5 μm), and the specific surface area is set to 4.3 m². 2 / g(5.0m 2 The sample was less than 1 / g. Comparative Example 5 is a sample in which the specific surface area of ​​the starting material, silicon powder, was 9.9 m². 2 / g(9.0m 2 Comparative Example 6 is a sample in which yttrium oxide was present at 0.9 mol% (less than 1 mol%). Comparative Example 7 is a sample in which magnesium silicon nitride was present at 12.7 mol% (greater than 12 mol%), and D 99.9 The sample had a diameter of 10.1 μm (larger than 9.5 μm). Comparative Example 8 was a sample containing 0.5 mol% (less than 4 mol%) magnesium silicon nitride. In Comparative Examples 4, 5, and 7, due to the properties of the silicon powder, the inorganic filling rate of the molded bodies produced in the molding process was less than 47%. In Comparative Examples 1-3, 6, and 8, the measurement of the inorganic filling rate of the molded bodies was omitted, but since the silicon powder properties and manufacturing conditions were similar, it is presumed that the inorganic filling rate would be 47% or more, similar to the examples.

[0067] In the SEM images (2000x magnification) of the substrate surface of the silicon nitride sintered body shown in Figures 1-3, rod-shaped β-type silicon nitride particles can be observed. In particular, in Figures 1 and 2, corresponding to Examples 1 and 5, the cross-section in the short-axis direction of the β-type silicon nitride particles, whose long axes are aligned in the thickness direction of the substrate, can be observed. Furthermore, in the X-ray diffraction patterns shown in Figures 4-8, diffraction peaks were confirmed at 2θ, corresponding to the (110), (200), (101), (120), (201), and (301) planes of the β-type silicon nitride particles.

[0068] Table 1 shows the structural characteristics of each sample of silicon nitride sintered bodies, Examples 1-14 and Comparative Examples 1-8. According to Table 1, in Examples 1-14, the Lotgering factor f(hk0), which indicates the degree of orientation of the (hk0) plane of β-type silicon nitride particles, shows a negative value, and the intensity ratio I 101 / I 210 The value is 1.5 or higher. This indicates that the orientation of β-type silicon nitride is predominant in the thickness direction of the substrate. In contrast, in Comparative Examples 1 to 8, the Lotgering factor f(hk0) is a positive value, and the intensity ratio I 101 / I 210 The values ​​are less than 1.0. Table 1 also shows that in Examples 1-14, the arithmetic mean height Sa, which indicates the roughness of the substrate surface, is 0.8 μm or greater. On the other hand, in Comparative Examples 1-8, except for Comparative Example 6, the arithmetic mean height Sa is less than 0.8 μm. Furthermore, as shown in Table 1 and Figures 9 and 10, according to the image analysis results of the captured substrate cross-sectional images, in Examples 1-14, the region 200,000 μm 2 The cross-sectional photograph showed that it contained 10 or more coarse β-type silicon nitride particles with a long axis of 50 μm or more, and of those coarse particles, it contained 7 or more β-type silicon nitride particles with an inclination angle of 45 degrees or less with respect to the normal to the substrate surface. On the other hand, in Comparative Examples 1 to 8, as shown in Table 1 and Figure 11, the region was 200,000 μm. 2 In the cross-sectional photograph, there were 8 or fewer coarse β-type silicon nitride particles with a long axis of 50 μm or more, and of those coarse particles, there were 6 or fewer β-type silicon nitride particles with an inclination angle of 45 degrees or less with respect to the normal to the substrate surface.

[0069] Table 2 shows the structural characteristics of each sample of silicon nitride sintered bodies in Examples 15-20. In Examples 15-20, the Lotgering factor f(hk0), which indicates the degree of orientation of the (hk0) plane of β-type silicon nitride particles, shows a negative value. In Examples 15, 16, and 20, the intensity ratio I 101 / I 210 The intensity ratio was 1.1 or higher, and in Examples 17-19, the intensity ratio was 101 / I 210 The value is 1.5 or higher. Furthermore, Table 2 shows that in Examples 15-20, the arithmetic mean height Sa, which indicates the roughness of the substrate surface, is 0.8 μm or higher. In addition, as shown in Table 2, according to the image analysis results of the captured substrate cross-sectional images, in Examples 15-20, the region is 200,000 μm. 2 The cross-sectional photograph showed that it contained 10 or more coarse β-type silicon nitride particles with a long axis of 50 μm or more. Furthermore, according to Table 2, with the exception of Example 20, where the rare earth oxide was Yb2O3, it was shown that among the coarse particles, there were 8 or more β-type silicon nitride particles with an inclination angle of 45 degrees or less with respect to the normal to the substrate surface. In Example 20, 7 β-type silicon nitride particles with an inclination angle of 45 degrees or less were confirmed. In other words, it was shown that Examples 1 to 20 contained at least 7 β-type silicon nitride particles with an inclination angle of 45 degrees or less with respect to the normal to the substrate surface among the coarse particles.

[0070] From the above results, it can be inferred that in the silicon nitride sintered bodies of Examples 1 to 20, the long axis of β-type silicon nitride is preferentially oriented in the thickness direction of the substrate compared to the comparative example sample. Furthermore, it was found that in the silicon nitride sintered bodies of Examples 1 to 20, a relatively large number of coarse particles of β-type silicon nitride with a long axis of 50 μm or more were formed compared to the comparative example sample, and that the coarse particles were preferentially aligned in the thickness direction of the substrate (within 45 degrees of the normal). In other words, the silicon nitride sintered body of the present invention is characterized by crystal growth such that the β-type silicon nitride particles become coarser in the thickness direction of the plate.

[0071] Table 3 shows the thermal conductivity and physical strength of each sample of the silicon nitride sintered bodies of Examples 1 to 14 and Comparative Examples 1 to 8. According to Table 3, in Examples 1 to 14, the thermal conductivity in the thickness direction of the substrate was 100 W / mK or more. On the other hand, in Comparative Examples 1 to 8, the thermal conductivity was less than 100 W / mK. That is, it can be seen that in the crystal structure of the silicon nitride sintered body, the preferential orientation of the long axes of the β-type silicon nitride particles in the thickness direction of the substrate and the coarsening of the β-type silicon nitride particles contribute to the improvement of the thermal conductivity. Further, according to Table 3, in Examples 1 to 14, the fracture toughness value K C1 in the first direction parallel to the substrate plane was 5.5 MPa·m 1 / 2 or more, and the fracture toughness value K C2 in the second direction perpendicular to the substrate plane was 5.5 MPa·m 1 / 2 or more. Furthermore, in Examples 1 to 14, the ratio K C1 of the fracture toughness value K C2 in the first direction to the fracture toughness value K C1 in the second direction, K C2 / K C1 / K C2 was 0.85 to 1.2, indicating that the mechanical strength (fracture toughness) of the substrate was exhibited isotropically. In contrast, in Comparative Examples 1 to 8, the ratio K C2 / K

[0072] Table 4 shows the thermal conductivity and physical strength of each sample of the silicon nitride sintered bodies of Examples 15 to 20. According to Table 4, in Examples 15 to 20, the thermal conductivity in the thickness direction of the substrate was 100 W / mK or more. Further, according to Table 4, in Examples 15 to 20, the fracture toughness value K C1 in the first direction parallel to the substrate plane was 5.5 MPa·m 1 / 2 or more, and the fracture toughness value K C2 in the second direction perpendicular to the substrate plane was approximately equal to 5.5 MPa·m 1 / 2 or 5.5 MPa·m 1 / 2 or more. Furthermore, in Examples 15 to 20, the ratio K C1 of the fracture toughness value K C2 in the first direction to the fracture toughness value K C1 / KC2 The values ​​ranged from 0.85 to 1.2, indicating that the mechanical strength (fracture toughness) of the substrate was exhibited isotropically.

[0073] 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.

Claims

1. The substrate contains β-type silicon nitride particles, In a cross-sectional photograph taken of a substrate cut perpendicular to a plane, 200,000 μm ２ Within this region, there are 10 or more β-type silicon nitride particles with a long axis of 50 μm or more. A silicon nitride sintered body characterized in that the intensity ratio I101 / I210 of the intensity I101 of the X-ray diffraction peak of the (101) plane of β-type silicon nitride and the intensity I210 of the X-ray diffraction peak of the (210) plane of β-type silicon nitride are 1.5 or greater.

2. The substrate contains β-type silicon nitride particles, In a cross-sectional photograph taken of a substrate cut perpendicular to a plane, 200,000 μm ２ Within this region, there are seven or more β-type silicon nitride particles whose major axis is 50 μm or longer and whose inclination angle with respect to the normal to the substrate surface is 45 degrees or less. A silicon nitride sintered body characterized in that the intensity ratio I101 / I210 of the intensity I101 of the X-ray diffraction peak of the (101) plane of β-type silicon nitride and the intensity I210 of the X-ray diffraction peak of the (210) plane of β-type silicon nitride are 1.5 or greater.

3. The silicon nitride sintered body according to claim 1 or 2, characterized in that the arithmetic mean height Sa indicating the surface roughness of the substrate is 0.8 μm or more.

4. A silicon nitride sintered body according to claim 1 or 2, characterized in that the thermal conductivity in the substrate thickness direction is 100 W / mK or more.

5. A substrate for mounting electronic components, comprising a silicon nitride sintered body according to claim 1 or 2, and a metal plate brazed to the surface of the silicon nitride sintered body.

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