Silicon nitride sintered body and substrate for mounting electronic component

Abstract

To provide a silicon nitride sintered body in which orientation of β-type silicon nitride (β-Si3 N4) particles is controlled and thermal conductivity performance is further improved.SOLUTION: A silicon nitride sintered body has: a value KC1 of fracture toughness in a first direction parallel to a substrate plane of 5.5 MPa m1 / 2 or more; a value KC2 of fracture toughness in a second direction perpendicular to the substrate plane of 5.5 MPa m1 / 2 or more; a ratio KC1 / KC2 of the value KC1 in the first direction to the value KC2 in the second direction of 0.85 or more; and a thermal conductivity in the second direction of 103 W / mK or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, the increasing density and power output of electronic devices and semiconductor devices has led to an increase in the heat generation density of power modules. The temperature rise in power modules can cause malfunctions in components and cracks in insulated circuit boards. For this reason, ceramic substrates such as alumina and aluminum nitride, which have relatively high thermal conductivity, have been used for insulated circuit boards. However, alumina and aluminum nitride have the disadvantage of low mechanical strength. This has made it impossible to directly bond thick copper, which is subject to high thermal stress, to ceramic substrates, limiting the design of power modules. Specifically, the need to solder heat sinks, such as copper or aluminum, to the insulated circuit board increases the size of power modules, which is a problem. Therefore, silicon nitride (Si3N4) materials have attracted attention as insulated circuit boards. Compared to alumina and aluminum nitride, silicon nitride sintered compacts have higher strength and fracture toughness, making it possible to directly bond thick copper to insulated circuit boards, contributing to module miniaturization. Therefore, efforts are underway to develop silicon nitride sintered compacts with improved mechanical strength and thermal conductivity.

[0003] For example, Patent Document 1 discloses a method for producing a silicon nitride sintered substrate with improved mechanical properties and thermal conductivity. This method involves adding 1 to 15% by weight of a sintering aid (one or more elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb) to silicon nitride powder containing 0.1% or less by weight of Al, forming the resulting powder, and then firing the powder at a temperature of 1700 to 2300°C under a nitrogen gas pressure of 1 to 500 atmospheres. The silicon nitride sintered substrate obtained by this method is composed of 85 to 99% by weight of β-type silicon nitride grains, with the remainder being a grain boundary phase of oxide or oxynitride. The grain boundary phase contains 0.5 to 10 weight percent of one or more metal elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb. The grain boundary phase contains 1 weight percent or less of Al atoms, the porosity is 5 percent or less, and the microstructure of the sintered body contains 10 to 60 volume percent of beta-silicon nitride grains with a minor axis diameter of 5 μm or more. It is known that rare earth compounds and magnesium oxide can be added as sintering aids to obtain a silicon nitride sintered body substrate with high thermal conductivity, and that the thermal conductivity and mechanical strength can be improved by adjusting the mixing ratio and amount of these sintering aids.

[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 degree of orientation of β-type silicon nitride (β-Si3N4) particles. In Patent Document 2, silicon nitride powder containing 7% or less of β-type silicon nitride is used as a raw material, and the viscosity of the slurry is adjusted to 13,000 cps or more before forming a sheet compact. As a result, the intensity I of the X-ray diffraction peak of the (101) plane of the crystal structure of the β-type silicon nitride particles of the silicon nitride sintered substrate manufactured by this manufacturing method is 1. 101 and X-ray diffraction peak intensity of (210) plane of β-type silicon nitride I 210 Intensity ratio I 101 / I 210 As a result, the fracture toughness value K in the first direction parallel to the substrate plane of the silicon nitride sintered substrate wasC1 is the fracture toughness value K in the second direction perpendicular to the first direction C2 The decrease in fracture toughness relative to the temperature was suppressed, and a silicon nitride sintered substrate having isotropic fracture toughness in both directions was obtained. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 9-30866 [Patent Document 2] Japanese Patent Application Publication No. 2019-52072 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors reviewed the manufacturing method for conventional silicon nitride sintered bodies and focused on further controlling the degree of orientation of β-type silicon nitride (β-Si3N4) particles, with the aim of further improving the thermal conductivity performance of β-type silicon nitride particles in the substrate thickness direction.

[0007] In order to solve the above problems, the object of the present invention is 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, and a method for manufacturing the silicon nitride sintered body. [Means for solving the problem]

[0008] A silicon nitride sintered body according to one embodiment of the present invention forms a substrate containing β-type silicon nitride particles, and is 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 in the substrate plane, is a negative value.

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

[0010] The silicon nitride sintered body of a further embodiment of the present invention more preferably has a fracture toughness value K C1 and fracture toughness value K C2 K C1 / K C2 is 0.85 or more.

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

[0012] In a further embodiment of the present invention, the silicon nitride sintered body has a thickness of 200,000 μm or less in a cross-sectional photograph taken of a cross section obtained by cutting the substrate vertically. 2 The region contains eight or more β-type silicon nitride particles each having 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.

[0013] The silicon nitride sintered body of a further embodiment of the present invention is more preferably characterized in that the arithmetic mean height Sa, which indicates the roughness of the substrate surface, is 0.8 μm or more.

[0014] One embodiment of the present invention provides a method for producing a silicon nitride sintered body, comprising the steps of: a mixing step of mixing silicon powder, rare earth oxide powder, and magnesium silicon nitride powder to produce a mixed powder so that the silicon nitride sintered body has a molar ratio of 85-95 mol % silicon nitride (Si3N4), 1-3 mol % rare earth oxide (RE2O3), and 4-12 mol % magnesium silicon nitride (MgSiN2); a forming step of forming the mixed powder 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 for a predetermined time to produce a silicon nitride sintered body.

[0015] In a further embodiment of the present invention, the method for producing a silicon nitride sintered body is more preferably carried out by using the silicon powder having a specific surface area of ​​5.0 m 2 / g or more, and D of the silicon powder 99.9 It is characterized by a diameter of 9.5 μm or less.

[0016] In a further embodiment of the method for producing a silicon nitride sintered body of the present invention, more preferably, the specific surface area of ​​the magnesium silicon nitride powder is 9.0 m 2 / g or more.

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

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

[0019] According to the silicon nitride sintered body and the method for producing the same of the present invention, the thermal conductivity in the thickness direction of the substrate is improved by controlling the long axes of the β-type silicon nitride particles to be aligned in the thickness direction of the substrate. [Brief explanation of the drawings]

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

[0021] [Figure 2] 10 is an SEM image of the substrate surface of the silicon nitride sintered body of Example 5 taken at a magnification of 2000 times.

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

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

[0024] [Figure 5] 1 is an 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] 1 is an X-ray diffraction pattern of the silicon nitride sintered body of Comparative Example 1.

[0027] [Figure 8] 10 is an X-ray diffraction pattern of the silicon nitride sintered body of Comparative Example 7.

[0028] [Figure 9] 1 is a photograph of a cross section of a substrate of the silicon nitride sintered body of Example 1.

[0029] [Figure 10] 10 is a photograph of a cross section of a substrate of the silicon nitride sintered body of Example 5.

[0030] [Figure 11] 1 is a photograph of a cross section of a substrate of a silicon nitride sintered body of Comparative Example 1.

[0031] [Figure 12] 1A is an exemplary image of a substrate cross section of a silicon nitride sintered body after a fracture toughness test, and FIG. 1B is a schematic diagram thereof, for explaining a method for measuring fracture toughness values ​​in a first direction and a second direction in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The silicon nitride sintered body according to one embodiment of the present invention is formed into a substrate shape of a predetermined thickness, and can be used as an electronic component mounting substrate, mainly by brazing (brazing or soldering) a metal plate such as a copper plate to the surface of the substrate, on which electronic components are mounted. 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 raw material powders of 85 to 95 mol % silicon, 1 to 3 mol % rare earth oxides, and 4 to 12 mol % magnesium silicon nitride, calculated as silicon nitride after complete nitridation of silicon. In this embodiment, the rare earth oxides can be selected from oxides of Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb, or a combination thereof.

[0034] The β-type silicon nitride particles contained in the silicon nitride sintered body substrate have a crystal structure in the shape of an elongated hexagonal column with a long axis and a short axis. The silicon nitride sintered body of this embodiment has improved thermal conductivity in the thickness direction by controlling the β-type silicon nitride to be preferentially oriented in the thickness direction of the substrate. The properties of the silicon nitride sintered body of this embodiment are shown below.

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

[0036] The Lotgering factor f(hk0) is an index that represents the degree of orientation of each crystal grain that constitutes a polycrystalline body. 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 formulas 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) ρ is calculated using the diffraction intensity I in the 2θ range of 20 to 65 degrees in the X-ray diffraction spectrum of a non-oriented sample. It is calculated as the ratio of the sum of the diffraction intensities of the (hk0) plane, ΣI(hk0), to the sum of all diffraction intensities, ΣI(hkl), using Equation 2. Here, the diffraction intensity I is calculated from the X-ray diffraction spectrum of a reference sample (a non-oriented sample with the same composition as the target sample). ρ is calculated using the diffraction intensity I in the 2θ range of 20 to 65 degrees in the X-ray diffraction spectrum of a silicon nitride sintered sample. It is calculated as the ratio of the sum of the diffraction intensities of the (hk0) plane, ΣI(hk0), to the sum of all diffraction intensities, ΣI(hkl), using Equation 3. Here, h, k, and l are integers representing plane indices. If the crystal orientation of the obtained sample is random, the difference between ρ and ρ 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 non-oriented sample. In other words, a negative value for the Lotgering factor f(hk0) of the obtained sample indicates that the (00l) plane (i.e., the long axis) of the β-type silicon nitride grains is strongly oriented in the thickness direction.

[0037] In addition, as another index showing the degree of orientation of β-type silicon nitride particles in the substrate of the silicon nitride sintered body of this embodiment, the intensity I of the X-ray diffraction peak of the (101) plane of β-type silicon nitride of the silicon nitride sintered body is 101 and the intensity of the X-ray diffraction peak of the (210) plane of β-type silicon nitride I 210 Intensity ratio I 101 / I 210 In the silicon nitride sintered body of this embodiment, the intensity ratio I 101 / I 210 is 1.5 or more, and it is inferred that the long axis is oriented in the thickness direction.

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

[0039] In the silicon nitride sintered body of this embodiment, in a cross-sectional photograph taken of a cross section obtained by cutting the substrate perpendicular to the plane, 2 It was observed that the region contained 10 or more coarse β-silicon nitride particles with a major axis of 50 μm or more. Of these, it was observed that 8 or more coarse β-silicon nitride particles had 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 β-silicon nitride particles were oriented in the thickness direction of the plate.

[0040] That is, the silicon nitride sintered body of this embodiment contains a relatively large number of coarse grains having major axes of 50 μm or more, and the major axes of the β-type silicon nitride are preferentially oriented in the thickness direction of the substrate.

[0041] The silicon nitride sintered body of this embodiment has a thermal conductivity of 100 W / mK or more in the thickness direction of the substrate. The beta silicon nitride particles are rod-shaped, and the thermal conductivity in the long axis direction is approximately twice that in the short axis direction. Therefore, by aligning the beta particles in the thickness direction, the thermal conductivity in the thickness direction is significantly improved.

[0042] The silicon nitride sintered body of this embodiment is densified to a relative density of 98% or more. The silicon nitride sintered body of this embodiment has a fracture toughness value K C1 is 5.5 MPa m 1 / 2 or more, and the fracture toughness value K C2 is 5.5 MPa m 1 / 2 Furthermore, the fracture toughness value in the first direction, K C1 and the fracture toughness value in the second direction, K C2 Relative to K C1 / K C2is 0.85 or more. That is, in the silicon nitride sintered body, the columnar crystals are controlled to be aligned in the vertical direction, so that the mechanical strength (fracture toughness) of the substrate is exerted isotropically, and high mechanical strength (fracture toughness) is exerted in both the first direction and the second direction.

[0043] Next, a method for producing the silicon nitride sintered body of this embodiment will be described. The silicon nitride sintered body is produced by a reaction sintering method, which uses silicon powder as the starting material instead of silicon nitride powder, and heats the molded silicon powder in a nitrogen atmosphere to simultaneously nitride and densify the material. Generally, the reaction sintering method improves the thermal conductivity of the sintered body due to the high purity of the raw material, but it is said that raw material adjustment and sintering conditions for densification are difficult. Furthermore, in a typical reaction sintering method, silicon powder is converted into rod-shaped β-type silicon nitride particles, making it difficult to control their orientation in the plate thickness direction, and it is known that the orientation tends to become random.

[0044] According to this embodiment, the method for producing a silicon nitride sintered body mainly comprises the steps of: a mixing step of mixing a silicon raw material powder, a rare earth oxide powder, and a magnesium silicon nitride powder to produce a mixed powder so that the silicon nitride sintered body has a molar ratio of 85-95 mol% silicon nitride, 1-3 mol% rare earth oxide, and 4-12 mol% magnesium silicon nitride; a forming step of slurriing the mixed powder and forming 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 for a predetermined time to obtain a silicon nitride sintered body. Each step will be described in more detail below.

[0045] Silicon powder is prepared as a starting material. The silicon powder, organic solvent, and dispersant are pulverized in a ball mill until the specific surface area of ​​the silicon powder reaches 5.0 m 2 / g or more, D 99.9 The particle size is adjusted so that the diameter is 9.5 μm or less. Here, in the particle size distribution curve with the horizontal axis being particle diameter (μm) and the vertical axis being frequency (%), D 50The diameter (median diameter) is the particle diameter with a frequency of 50%, and D 99.9 The diameter is the particle diameter with a frequency of 99.9% (corresponding to the mode of distribution). After adjusting the particle size of the silicon powder, it is mixed with rare earth oxide powder and magnesium silicon nitride powder as sintering aids to produce a mixed powder. The specific surface area of ​​the magnesium silicon nitride powder is 9.0 m 2 / g or more is preferable. Here, the molar ratio is 85 to 95 mol % silicon, 1 to 3 mol % rare earth oxide, and 4 to 12 mol % magnesium silicon nitride, calculated as silicon nitride after silicon is completely nitrided. This mixed powder is thoroughly mixed in a ball mill, and then a binder, a plasticizer, and an organic solvent are added to form a slurry.

[0046] Next, the slurry is vacuum degassed to adjust the viscosity. The ratio of organic solvent contained 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 compact is produced using a doctor blade or the like.

[0047] The molded body is produced so that the inorganic filling rate is 47% or more. To achieve an inorganic filling rate of 47% or more, the specific surface area of ​​the silicon powder must be 9.0 m 2 / g or less (i.e., 5.0 to 9.0 m 2 It is preferable to adjust the crushing particle size so that the specific surface area of ​​the silicon powder is within the range of 9.0 m / g, and to set the proportion of organic solvent after degassing to 35 wt% or less. 2 If it is greater than / g, the proportion of fine silicon powder increases, which makes it easier for agglomeration to occur, resulting in poor packing properties. Also, if the proportion of organic solvent in the degassed slurry exceeds 35 wt%, the amount of organic solvent that volatilizes during sheet molding increases, resulting in greater drying shrinkage and the likelihood of fine bubbles forming within the molded body. The inorganic packing rate is measured as follows. The sheet molded body used for the measurement had a residual organic solvent 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 calculated. g (g / cm 3) was measured. The sheet molding used for the measurement was then subjected to a debindering treatment in the atmosphere at 500°C for 3 hours. The organic fraction Pi (%) was determined by measuring the weight after the debindering treatment, and the inorganic filling rate Fi (%) was calculated using the following equation 4. Fi=ρ g ×(1-Pi / 100) / ρ th ×100 (Formula 4) where ρ th is the theoretical density at the time of mill blending, and is a value calculated from the weight ratio of the raw material inorganic components.

[0048] The resulting sheet-like compact was then debindered in a dry air atmosphere at approximately 500 to 800°C. It was then heated in a vacuum to approximately 1000°C (first temperature) in a furnace, and then placed in a pressurized nitrogen atmosphere, where it was heated from approximately 1000°C to approximately 1350°C (second temperature). The compact was then nitrided by gradually increasing the temperature from the first temperature to the second temperature (e.g., at 1°C / min) in the pressurized nitrogen atmosphere. The furnace was then placed in a higher-pressure pressurized nitrogen atmosphere, and the temperature was increased from the second temperature to a third temperature of approximately 1750 to 2000°C (preferably 1900°C). After the temperature increase, the nitrided compact was sintered by holding it at the third temperature for a long period of time (e.g., approximately 8 hours), whereby the compact was sufficiently densified and a silicon nitride sintered body was produced.

[0049] The above-described process allows the production of sintered silicon nitride in which β-type silicon nitride particles are preferentially oriented in the thickness direction of the substrate. Specifically, the use of magnesium silicon nitride and minimal addition of yttrium oxide (i.e., 1-3 mol% rare earth oxide) in the manufacturing process reduces the amount of oxygen in the compact, which is thought to enhance the reduction properties during the nitriding and densification processes. This enhanced reduction reduces the silicon oxide film on the surface of the silicon powder, causing SiO(g) to volatilize in the thickness direction. Furthermore, the reduction reaction SiO(g) + CO(g) → Si(g) + CO2(g) is promoted, and the generated Si(g) undergoes the reaction 3Si(g) + 2N2(g) → β-Si3N4 within the porous body before densification, resulting in the precipitation of β-Si3N4 in the thickness direction within the pores. Furthermore, increasing the heat treatment temperature results in a silicon nitride substrate in which β-type silicon nitride particles are preferentially oriented in the thickness direction, with β-Si3N4 precipitated in the pores as nuclei. The elongation of the β-type silicon nitride particles in the thickness direction increases the thermal conductivity, which is thought to improve the heat dissipation properties of the insulating substrate.

[0050] The above-described steps are merely examples and are not intended to limit the scope of the present invention. For example, the method for forming the slurry is not limited to the doctor blade method, and the slurry may be pressure-molded into a sheet by extrusion molding, casting, or other methods. [Example]

[0051] The present invention will be described in more detail below based on examples and comparative examples, but the present invention should not be construed as being limited by the following examples.

[0052] The silicon nitride sintered bodies according to Examples 1 to 20 and Comparative Examples 1 to 8 were produced under the following conditions and procedures.

[0053] Silicon powder and sintering aid powder with predetermined powder properties were prepared. An appropriate amount of silicon powder was placed in a ball mill, and the silicon powder, organic solvent, and dispersant were pulverized in the ball mill to measure the specific surface area and D of the silicon powder.99.9 The particle size was adjusted until the diameter reached the specified value. Here, the compounding ratio of each sample and the D of the silicon powder 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. A binder (polyvinyl butyral), a plasticizer (dioctyl adipate), and an organic solvent (a mixed solvent of toluene and ethanol) were then added to form a slurry. The viscosity of the slurry was adjusted by vacuum degassing. The organic solvent content of the degassed slurry was set to 35 wt% or less, and the viscosity of the slurry was set to 15,000–25,000 cps. The viscosity of the slurry was measured using a TVC-7 viscometer manufactured by Toki Sangyo Co., Ltd. Specifically, a spindle was rotated in the slurry, and the viscosity was calculated from the resistance. Sheet-shaped compacts were then fabricated using a doctor blade at a molding speed of 200 mm / min or higher. The inorganic filling ratio Fi (%) of each sheet-shaped compact was then measured. The surface of the resulting sheet-like compact was sprayed with BN as a release agent to prepare 20 laminates per block. The laminates were debindered at 500°C in dry air, then placed in a furnace and heated to approximately 1000°C in a vacuum. The temperature was then increased at 1°C / min to approximately 1350°C in a nitrogen atmosphere pressurized at 0.2 MPa. The temperature was then increased from approximately 1350°C to approximately 1900°C in a nitrogen atmosphere pressurized at 0.9 MPa, and sintered at approximately 1900°C for approximately 8 hours. After sintering, the laminate substrate was separated, and the sintered surface was honed by blasting alumina abrasive grains (average particle size: 50 μm) at a honing pressure of 0.4 MPa to obtain a 190 mm x 140 mm silicon nitride sintered body with a thickness of 0.35 mm.

[0054] For each of the prepared samples of Examples 1 to 20 and Comparative Examples 1 to 8, the crystalline phase of each sample was identified by X-ray diffraction measurement, and the X-ray diffraction pattern was analyzed to obtain the integrated intensity of each diffraction peak, the Lotgering factor f(hk0), and the intensity ratio I 101 / I 210 In addition, for each sample, the β-type silicon nitride particles were observed on the vertical cross section, and the particle size was measured at 200,000 μm.2 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 were calculated. Furthermore, the relative density, arithmetic mean height Sa, thermal conductivity (W / mK), fracture toughness (MPa m 1 / 2 ) was measured. The measurements were carried out under the following conditions:

[0055] X-ray diffraction measurement and analysis The X-ray diffraction intensity of each sample was measured by powder X-ray diffraction using Cu-Kα radiation using an Ultima IV model manufactured by Rigaku Corporation. Individual pieces cut to 10 mm x 10 mm were used for the measurements. The substrate surface after honing was used as the measurement surface. The measurement conditions were as follows: Sampling width: 0.02 degrees Scan speed: 10 degrees / min Divergence slit: 2 / 3 degrees Divergence vertical slit: 10 mm Scattering slit: 8 mm 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 on the substrate plane, the integrated intensity of the diffraction peaks corresponding to the Miller indices (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 101 / I 210 was derived.

[0056] Observation method for β-type silicon nitride particles on a vertical cross section Using individual pieces cut to 10 mm x 10 mm, the pieces were embedded in epoxy resin and the vertical cross section of the substrate was observed. The observation surface was prepared using the following procedure. The surface was flattened using #800 diamond polishing paper, and then polished with diamond slurry in the order of 15 μm, 6 μm, and 1 μm until the polishing scratches from each previous process were removed, followed by a final polish with a 50 nm alumina slurry to obtain a mirror surface. After mirror polishing, CF4 plasma etching was performed to create the observation surface. The observation surface was then observed using a laser microscope VKX-150 manufactured by Keyence Corporation at a 20x objective lens magnification, and the cross section was photographed. The cross section photograph was then image processed to obtain a 200,000 μm area. 2 In the cross-sectional photograph of the sample, the number of coarse β-silicon nitride particles with a major axis of 50 μm or more and the number of coarse particles with an inclination of 45 degrees or less with respect to the normal to the substrate surface were counted.

[0057] Relative density The density of the sintered body was calculated from the theoretical density calculated from the raw material composition (Equation 5). The density of the sintered body was measured by the Archimedes method using pure water. Relative density (%) = (sintered density / theoretical density) × 100 (Equation 5)

[0058] Arithmetic mean height Sa The surface roughness Sa of the substrate surface after honing was measured in an area of ​​500 μm×500 μm using a laser microscope VKX-150 manufactured by Keyence Corporation. The measurement conditions were as follows: Objective lens magnification: x20 Image correction: Automatic surface tilt correction Filter type: Gaussian S-filter: 2 μm F-Operation: None L-filter: 0.2 mm End effect correction: Yes

[0059] Thermal conductivity The flash method was used to measure the thermal conductivity of the substrate in the thickness direction. A thermal conductivity measuring device LFA467 manufactured by NETZSCH Geratebau GmbH was used for the measurements. 10mm x 10mm pieces were cut from the substrate for the measurements. A gold sputtering film was formed on both sides of the piece to reduce the transmission of flash light, and graphene spray was used on both sides of the piece to uniformly absorb pulsed light, followed by a blackening treatment. When calculating the thermal conductivity, a value of 0.68J / (g·K) was used as the specific heat of the resulting sintered body.

[0060] Fracture toughness The fracture toughness of each sample was measured using a Vickers hardness tester HV-120 manufactured by Mitutoyo Corporation in accordance with JIS-R1607. Specifically, the cross section of the substrate cut along the thickness direction was mirror-polished, and an indentation with diagonal lengths a1 and a2 was made on the mirror-polished surface near the center of the thickness direction of the mirror-polished surface, as shown in Figures 12(a) and 12(b). The diagonal lengths a1 and a2 of the indentation and the lengths c1 and c2 of the crack generated from the apex of the indentation were measured, and the fracture toughness value K was calculated from the indentation load, diagonal length of the indentation, crack length, and elastic modulus. C According to JIS-R1607, the fracture toughness value KC is calculated by 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: Elastic modulus P: Indentation 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 is the fracture toughness value K in the first direction (parallel to the substrate plane). C1 , fracture toughness value K in the second direction (direction perpendicular to the substrate plane) C2Specifically, the crack length generated in the direction parallel to the substrate plane is defined as c1, and C in Equation 6 is set to c1 / 2, so that K C1 In addition, the crack length that occurred in the direction perpendicular to c1 (thickness direction of the substrate) is defined as c2, and by changing C in Equation 6 to c2 / 2, K C2 The thickness of the test piece was 0.35 mm, and the indentation load P was 10 kgf.

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

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] Examples 1 to 20 consisted of raw material powders with a molar ratio of 85 to 95 mol % silicon (calculated as silicon nitride), 1 to 3 mol % rare earth oxide, and 4 to 12 mol % magnesium silicon nitride. Here, in Examples 1 to 14, yttrium oxide (YO) was selected as the rare earth oxide (RE2O3). In Examples 15 to 20, La2O3, Sm2O3, Gd2O3, Dy2O3, Er2O3, and Yb2O3 were selected as the rare earth oxide (RE2O3). Then, the D of the silicon powder, which was the starting material, 99.9 The diameter is 8.0 to 9.5 μm (less than 9.5 μm) and the specific surface area is 5.0 to 8.0 m 2 / g(5.0m 2 / g or more and 9.0m 2 / g or less). 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 the magnesium silicon nitride was 3 mol % (less than 4 mol %). Comparative Example 4 is a sample in which the D of the silicon powder, which is the starting material, 99.9 The diameter is 12.3 μm (larger than 9.5 μm) and the specific surface area is 4.3 m 2 / g(5.0m 2 Comparative Example 5 is a sample in which the specific surface area of ​​the silicon powder used as the starting material is 9.9 m 2 / g(9.0m 2 Comparative Example 6 is a sample containing 0.9 mol % (less than 1 mol %) of yttrium oxide. Comparative Example 7 is a sample containing 12.7 mol % (more than 12 mol %) of magnesium silicon nitride and D 99.9 The sample had a diameter of 10.1 μm (larger than 9.5 μm). Comparative Example 8 was a sample with 0.5 mol % (less than 4 mol %) of magnesium silicon nitride. In Comparative Examples 4, 5, and 7, due to the characteristics of the silicon powder, the inorganic filling rate of the molded body produced in the molding process was less than 47%. Note that, in Comparative Examples 1 to 3, 6, and 8, measurement of the inorganic filling rate of the molded body was omitted, but since the silicon powder characteristics and manufacturing conditions were similar, it is estimated that the inorganic filling rate would be 47% or more, as in the Examples.

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

[0068] Table 1 shows the structural characteristics of each sample of silicon nitride sintered body of Examples 1 to 14 and Comparative Examples 1 to 8. According to Table 1, in Examples 1 to 14, the Lotgering factor f(hk0), which indicates the degree of orientation of the (hk0) plane of the β-type silicon nitride particles, was a negative value, and the intensity ratio I 101 / I 210 is 1.5 or more. In other words, it can be seen that the orientation of β-type silicon nitride is dominant 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 is less than 1.0. Table 1 also shows that in Examples 1 to 14, the arithmetic mean height Sa, which indicates the roughness of the substrate surface, is 0.8 μm or more. On the other hand, in Comparative Examples 1 to 8, except for Comparative Example 6, the arithmetic mean height Sa is less than 0.8 μm. Furthermore, as shown in Table 1 and FIGS. 9 and 10, according to the image analysis results of the photographed substrate cross-sectional images, in Examples 1 to 14, the arithmetic mean height Sa was less than 0.8 μm. 2 In the cross-sectional photograph of the sample, it was shown that the sample contained 10 or more coarse β-silicon nitride particles with a major axis of 50 μm or more, and among the coarse particles, 7 or more β-silicon nitride particles had 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 FIG. 11, the sample contained 10 or more coarse β-silicon nitride particles with a major axis of 50 μm or more, and among the coarse particles, 7 or more β-silicon nitride particles had an inclination angle of 45 degrees or less with respect to the normal to the substrate surface. 2 In the cross-sectional photograph, there were eight or less coarse β-silicon nitride particles with a major axis of 50 μm or more, and six or less of the coarse particles were β-silicon nitride particles with an inclination angle of 45 degrees or less relative to the normal to the substrate surface.

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

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

[0071] Table 3 shows the thermal conductivity and physical strength of each sample of silicon nitride sintered body 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. This indicates that in the crystal structure of the silicon nitride sintered body, the preferred 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 thermal conductivity. Furthermore, according to Table 3, in Examples 1 to 14, the fracture toughness value K in the first direction parallel to the substrate plane was 100 W / mK or more. C1 is 5.5 MPa m 1 / 2 or more, and the fracture toughness value K C2 is 5.5 MPa m 1 / 2 Furthermore, in Examples 1 to 14, the fracture toughness values ​​K C1 and the fracture toughness value in the second direction, K C2 Relative to K C1 / K C2 The ratio K was 0.85 to 1.2, which indicated that the mechanical strength (fracture toughness) of the substrate was isotropically exhibited. C1 / K C2 is approximately 0.8, and the fracture toughness value K C2 was found to be significantly larger.

[0072] Table 4 shows the thermal conductivity and physical strength of each sample of the silicon nitride sintered body 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. Also, according to Table 4, in Examples 15 to 20, the fracture toughness value K in the first direction parallel to the substrate plane was 100 W / mK or more. C1 is 5.5 MPa m 1 / 2 or more, and the fracture toughness value K C2 but 5.5 MPa m 1 / 2 Approximately equal to or 5.5 MPa m 1 / 2 Furthermore, in Examples 15 to 20, the fracture toughness values ​​K C1 and the fracture toughness value in the second direction, K C2 Relative to K C1 / KC2 was 0.85 to 1.2, which indicated that the mechanical strength (fracture toughness) of the substrate was exerted isotropically.

[0073] The present invention is not limited to the above-described embodiments, and can be implemented in various forms within the technical scope of the present invention.

Claims

1. The fracture toughness value K in the first direction parallel to the substrate plane Ｃ１ is 5.5 MPa m １／２ That's all, The fracture toughness value K in the second direction perpendicular to the substrate plane Ｃ２ is 5.5 MPa m １／２ That's all, The fracture toughness value K in the first direction Ｃ１ and the fracture toughness value K in the second direction Ｃ２ Relative to K Ｃ１ / K Ｃ２ is 0.85 or more, and A silicon nitride sintered body having a thermal conductivity in a second direction of 103 W / mK or more.

2. 2. The silicon nitride sintered body according to claim 1, wherein the arithmetic mean height Sa, which indicates the roughness of the substrate surface, is 0.8 μm or more.

3. 2. The silicon nitride sintered body according to claim 1, wherein β-type silicon nitride particles having a major axis of 50 μm or more are preferentially oriented in the second direction.

4. The silicon nitride sintered body according to any one of claims 1 to 3, a metal plate brazed to the surface of the silicon nitride sintered body; An electronic component mounting substrate comprising:

Images