Silicon nitride sintered body and method for producing silicon nitride sintered body

Abstract

Provided is a silicon nitride sintered body in which the orientation of β-type silicon nitride (β-Si3N4) particles is controlled and the thermal conductivity performance is further improved. The silicon nitride sintered body forms a substrate containing β-type silicon nitride particles, and the Lotgering factor f(hk0), which indicates the orientation degree of the (hk0) plane of the β-type silicon nitride particles on the substrate plane, is a negative value.

Description

Technical Field

[0001] The present invention relates to a silicon nitride sintered body and a method for manufacturing the silicon nitride sintered body.

Background Art

[0002] In recent years, with the increasing density and high power of electronic devices and semiconductor devices, the heat generation density of power modules has been increasing. The temperature rise of the power module causes factors such as malfunction of elements and cracking of the insulating circuit board. Therefore, ceramic substrates such as alumina and aluminum nitride, which are materials with relatively high thermal conductivity, have been used for the insulating circuit board. However, alumina and aluminum nitride have the disadvantage of low mechanical strength. Therefore, it has not been possible to directly bond thick copper to the ceramic substrate where strong thermal stress is applied, which has restricted the structure of the power module. Specifically, since it is necessary to solder a heat sink such as copper or aluminum to the insulating circuit board, the problem is that the power module becomes larger. Therefore, silicon nitride (Si 3 N 4 ) material has been attracting attention as an insulating circuit board. Since the silicon nitride sintered body has higher strength and fracture toughness than alumina and aluminum nitride sintered bodies, it is possible to directly bond thick copper to the insulating circuit board, contributing to the miniaturization of the module. Therefore, the development of a silicon nitride sintered body with improved thermal conduction performance as well as mechanical strength has been carried out.

[0003] For example, Patent Document 1 discloses a method for manufacturing a silicon nitride sintered body substrate with improved mechanical properties and thermal conductivity. In this manufacturing method, a sintering aid of one or more elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb is added to silicon nitride powder with an Al content of 0.1 wt% or less in the range of 1 wt% or more and 15 wt% or less, and after molding, it is fired at a temperature of 1700 °C or more and 2300 °C or less under a nitrogen gas pressure of 1 atm or more and 500 atm or less. The silicon nitride sintered body substrate obtained by this manufacturing method is composed of β-type silicon nitride grains of 85 wt% or more and 99 wt% or less and the balance being a grain boundary phase of an oxide or oxynitride. Further, the grain boundary phase contains one or more metal elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb in the range of 0.5 wt% or more and 10 wt% or less. And the Al atom content in the grain boundary phase is 1 wt% or less, the porosity is 5% or less, and the proportion of β-type silicon nitride grains having a minor axis diameter of 5 μm or more in the microstructure of the sintered body is 10 vol% or more and 60 vol% or less. That is, in order to obtain a high thermal conductivity silicon nitride sintered body substrate, it is known that rare earth compounds or magnesium oxide can be added as a sintering aid, and the thermal conductivity and mechanical strength can be improved by their mixing ratio and addition amount.

[0004] Patent Document 2 discloses a silicon nitride sintered body substrate and a method for manufacturing the same, in which the thermal conductivity and mechanical strength are realized by controlling the orientation degree of β-type silicon nitride (β-Si 3 N 4 ) particles. In Patent Document 2, silicon nitride powder containing 7% or less of β-type silicon nitride is used as a raw material, and after adjusting the viscosity of the slurry to 13000 cps or more, a sheet molded body is formed. Thus, 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 body substrate by this manufacturing method 101 and the intensity I of the X-ray diffraction peak of the (210) plane of β-type silicon nitride 210 and the intensity ratio I of them 101 / I 210It is controlled to be 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 body substrate C1 is suppressed from relatively decreasing with respect to the fracture toughness value K in the second direction perpendicular to the first direction C2 , and a silicon nitride sintered body substrate having isotropic fracture toughness in both directions is obtained.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] The inventors reviewed the manufacturing method of conventional silicon nitride sintered bodies and focused on further controlling the orientation degree of β-type silicon nitride (β-Si 3 N 4 ) particles, and made it an issue to further improve the heat conduction performance of β-type silicon nitride particles in the substrate thickness direction.

[0007] In order to solve the above problems, an object of the present invention is to control the orientation of β-type silicon nitride (β-Si 3 N 4 ) particles and provide a silicon nitride sintered body with further improved heat conduction performance in the substrate thickness direction, and a method for manufacturing a silicon nitride sintered body.

Means for Solving the Problems

[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) indicating the orientation degree of the (hk0) plane of the β-type silicon nitride particles on the substrate plane is a negative value.

[0009] A further form of the silicon nitride sintered body 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] A further form of the silicon nitride sintered body of the present invention is more preferably the fracture toughness value K perpendicular to the thickness direction C1 and the fracture toughness value K in the thickness direction C2 and has K C1 / K C2 is 0.85 or more.

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

[0012] A further form of the silicon nitride sintered body of the present invention is more preferably in a cross-sectional photograph taken of a cross-section obtained by cutting the substrate vertically, in a region of 200,000 μm 2 contains 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.

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

[0014] A method for manufacturing a silicon nitride sintered body according to one form of the present invention is a silicon nitride sintered body in which silicon nitride (Si 3 N 4 ) 85 to 95 mol%, rare earth oxide (RE 2 O 3 ) 1 to 3 mol% and magnesium silicon nitride (MgSiN 2)A mixing step of producing a mixed powder by mixing silicon powder, rare earth oxide powder, and magnesium silicon nitride powder so as to have a molar ratio of 4 to 12 mol%, 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, characterized by including these steps.

[0015] In a method for producing a silicon nitride sintered body according to a further aspect of the present invention, more preferably, the specific surface area of the silicon powder is 5.0 m 2 / g or more, and the D 99.9 iameter of the silicon powder is 9.5 μm or less.

[0016] In a method for producing a silicon nitride sintered body according to a further aspect 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] In a method for producing a silicon nitride sintered body according to a further aspect of the present invention, more preferably, the molded body is produced by a sheet molding method.

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

Advantages of the Invention

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

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0032] The silicon nitride sintered body according to one embodiment of the present invention has a substrate shape with a predetermined thickness, and mainly, a metal plate such as a copper plate is brazed (brazed or soldered) to the substrate surface and can be used as a substrate for mounting electronic components for mounting electronic components. The thickness of the substrate is preferably 0.1 to 1.0 mm.

[0033] The silicon nitride sintered body of the present embodiment is a sintered body composed of, as raw material powders, 85 to 95 mol% of silicon in terms of silicon nitride after complete nitridation of silicon, 1 to 3 mol% of rare earth oxide, and 4 to 12 mol% of magnesium silicon nitride. In the present 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 substrate of the silicon nitride sintered body have an elongated hexagonal columnar crystal structure having a major axis and a minor axis. The silicon nitride sintered body of the present embodiment is controlled so that β-type silicon nitride is preferentially oriented in the thickness direction of the substrate, thereby improving the thermal conductivity in the thickness direction. The characteristics of the silicon nitride sintered body of the present embodiment are shown below.

[0035] The silicon nitride sintered body of the present embodiment is configured such that the Lotgering factor f(hk0) indicating the degree of orientation of the (hk0) plane of β-type silicon nitride in the substrate plane has a negative value.

[0036] The Lotgering factor f(hk0) is an index representing the degree of orientation of each crystal grain constituting the polycrystal. The value of the Lotgering factor f(hk0) is calculated by the following formulas 1 to 3 using the integrated intensity of each diffraction peak of the X-ray diffracted from the target crystal plane. f(hk0)=(ρ-ρ 0 ) / (1-ρ 0 ) (Formula 1) ρ 0 =ΣI 0 (hk0) / ΣI 0 (hkl) (Formula 2) ρ=ΣI(hk0) / ΣI(hkl) (Equation 3) ρ 0 is the diffraction intensity I in the 2θ range from 20 degrees to 65 degrees in the X-ray diffraction spectrum of a non-oriented sample 0 The sum of all the diffraction intensities, ΣI 0 The sum of the diffraction intensities of the (hk0) plane relative to the (hkl) plane ΣI 0 It is calculated as a ratio of (hk0) by Equation 2. Here, the diffraction intensity I 0 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 degrees to 65 degrees in the X-ray diffraction spectrum of a silicon nitride sintered sample, and is found from Equation 3 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). Note that h, k, and l are integers and represent plane indices. If the crystal orientation of the obtained sample is random, ρ and ρ 0 The difference between the two is small, and according to Equation 1, f(hk0) is close to zero. If f(hk0) is a negative value (ρ<ρ 0 ), this means that the obtained sample has a lower degree of orientation of the (hk0) plane than the non-oriented sample. In other words, the Lotgering factor f(hk0) of the obtained sample is a negative value, which 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 210include. In the silicon nitride sintered body of this embodiment, the strength ratio I 101 / I 210 is 1.5 or more, and the orientation of the long axis in the plate thickness direction is presumed.

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

[0039] And 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, in a region of 200,000 μm 2 it was observed that 10 or more coarse particles of β-type silicon nitride having a long axis of 50 μm or more were included. Among them, it was observed that 8 or more coarse particles of β-type silicon nitride having a long axis of 50 μm or more and an inclination angle with respect to the normal of the substrate surface of 45 degrees or less were included. That is, in the analysis using a microscope, it was shown that the long axes of a large number of coarse particles of β-type silicon nitride were oriented in the plate thickness direction.

[0040] That is, the silicon nitride sintered body of this embodiment contains a relatively large number 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] And in the silicon nitride sintered body of this embodiment, the thermal conductivity in the thickness direction of the substrate is 100 W / mK or more. That is, the shape of the β-type silicon nitride particles is rod-shaped, and the thermal conductivity in the long axis direction is about twice that in the short axis direction. Therefore, by aligning the β particles in the plate thickness direction, the thermal conductivity in the plate thickness direction is greatly improved.

[0042] Also, the silicon nitride sintered body of this embodiment is densified to a relative density of 98% or more. And in the silicon nitride sintered body of this embodiment, the value K of the fracture toughness in the first direction parallel to the substrate plane C1is 5.5 MPa·m 1 / 2 or more, and the value K of the fracture toughness in the second direction perpendicular to the substrate plane C2 is 5.5 MPa·m 1 / 2 or more. Further, the value K of the fracture toughness in the first direction C1 and the value K of the fracture toughness in the second direction C2 The ratio K C1 / K C2 is 0.85 or more. That is, in the silicon nitride sintered body, by controlling the columnar crystals to be aligned in the longitudinal direction, the mechanical strength (fracture toughness) of the substrate is exhibited isotropically, and high mechanical strength (fracture toughness) is exhibited in both the first direction and the second direction.

[0043] Subsequently, a method for manufacturing the silicon nitride sintered body of the present embodiment will be described. The method for manufacturing the silicon nitride sintered body is not using silicon nitride powder as a starting material, but using silicon powder as a starting material, heating the formed silicon powder in a nitrogen atmosphere, and performing reaction sintering in which nitridation and densification are performed simultaneously. Generally, in the reaction sintering method, since the raw material purity is high, the thermal conductivity of the sintered body is improved, but it is said that it is difficult to adjust the raw material and firing conditions for densification. In addition, in a general reaction sintering method, since it is difficult to control the orientation of silicon powder to convert into rod-shaped β-type silicon nitride particles in the plate thickness direction, it is known that the orientation tends to be random.

[0044] According to the present embodiment, the method for manufacturing a silicon nitride sintered body mainly includes, in the silicon nitride sintered body, a mixing step of mixing silicon raw material 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, 1 to 3 mol% of rare earth oxide, and 4 to 12 mol% of magnesium silicon nitride to produce a mixed powder, a forming step of slurrying the mixed powder and forming it into a sheet shape to produce a formed body, a nitriding step of heating the formed body from a first temperature to a second temperature in a nitrogen atmosphere, and a densification step of firing the formed body at a third temperature and a predetermined time in a nitrogen atmosphere to obtain a silicon nitride sintered body. Hereinafter, each step will be described more specifically.

[0045] Prepare silicon powder as a starting material. Grind the silicon powder, an organic solvent, and a dispersant with a ball mill so that the specific surface area of the silicon powder is 5.0 m 2 / g or more and the D 99.9 iameter is adjusted to 9.5 μm or less. Here, in the particle size distribution curve with the horizontal axis being the particle diameter (μm) and the vertical axis being the frequency (%), the D 50 iameter (median diameter) is the particle diameter at a frequency of 50%, and the D 99.9 iameter is the particle diameter at a frequency of 99.9% (corresponding to the mode of the distribution). Once the particle size of the silicon powder has been adjusted, mix rare earth oxide powder and silicon nitride magnesium powder as a sintering aid to produce a mixed powder. The specific surface area of the silicon nitride magnesium powder is preferably 9.0 m 2 / g or more. Here, in terms of molar ratio, 85 - 95 mol% of silicon in terms of silicon nitride after complete nitridation of silicon, 1 - 3 mol% of rare earth oxide, and 4 - 12 mol% of silicon nitride magnesium are mixed. Thoroughly mix this mixed powder with a ball mill, and then add a binder, a plasticizer, and an organic solvent to make a slurry.

[0046] Next, degas the slurry under vacuum and adjust its viscosity. Set the proportion of the organic solvent contained in the degassed slurry to 35 wt% or less, and set the viscosity of the slurry to 15000 - 25000 cps. Then, produce a sheet-shaped molded body using a doctor blade or the like.

[0047] The molded body is produced so that the inorganic filling rate is 47% or more. To make the inorganic filling rate of the molded body 47% or more, it is preferable to adjust the grinding particle size so that the specific surface area of the silicon powder is 9.0 m 2 / g or less (that is, within the range of 5.0 - 9.0 m 2 / g), and set the proportion of the organic solvent after degassing to 35 wt% or less. When the specific surface area of the silicon powder is 9.0 m 2When it is larger than / g, the proportion of particulate silicon powder increases, and agglomeration is likely to occur, resulting in poor filling properties. Also, when the proportion of the organic solvent contained in the slurry after defoaming exceeds 35 wt%, the amount of the organic solvent volatilized during sheet forming increases, leading to large drying shrinkage and making it easy for fine bubbles to occur in the formed body. The method for measuring the inorganic filling rate is as follows. The sheet formed body used for the measurement was one with the remaining organic solvent being 0.1 wt% or less. The volume and weight of the sheet formed body were measured, and the green density ρ g (g / cm 3 ) was measured. Then, the sheet formed body used for the measurement was subjected to a debinding treatment in the air at 500 °C for 3 h. The organic content ratio Pi (%) was obtained by measuring the weight after the debinding treatment, and the inorganic filling rate Fi (%) was calculated by the following formula 4. Fi = ρ g × (1 - Pi / 100) / ρ th × 100 (Formula 4) Here, ρ th is the theoretical density at the time of mill compounding, which is a value calculated from the weight ratio of the raw material inorganic components.

[0048] Next, the produced sheet-shaped formed body was subjected to debinding in a dry air atmosphere at about 500 to 800 °C. Then, it was heated in a vacuum to about 1000 °C (the first temperature) in the furnace, and then the atmosphere was changed to a nitrogen pressurized atmosphere, and the temperature was raised from about 1000 °C to about 1350 °C (the second temperature). At this time, in the nitrogen pressurized atmosphere, the temperature can be raised gradually (for example, 1 °C / min) from the first temperature to the second temperature to nitride the formed body. Then, the inside of the furnace is set to a higher pressure nitrogen pressurized atmosphere, and the temperature is raised from the second temperature to the third temperature to about 1750 to 2000 °C (preferably 1900 °C). After the temperature rise, the nitrided formed body is sintered by holding the temperature at the third temperature for a long time (for example, about 8 hours), and the densification of the formed body is sufficiently performed to produce a silicon nitride sintered body.

[0049] By going through the steps described above, it is possible to produce a silicon nitride sintered body in which β-type silicon nitride particles are preferentially oriented in the thickness direction of the substrate. That is, in the manufacturing method, by using magnesium silicon nitride and minimizing the addition amount of yttrium oxide (that is, setting the rare earth oxide to 1 to 3 mol %), the amount of oxygen in the green compact is suppressed, and it can be considered that the reducibility in the nitriding process and the densification process is increased. When the reducibility is increased in this way, the silicon oxide film on the surface of the silicon powder is reduced, and SiO(g) volatilizes in the plate thickness direction. Furthermore, the reduction reaction of SiO(g) + CO(g) → Si(g) + CO 2 (g) is promoted, and the generated Si(g) is 3Si(g) + 2N 2 (g) → β-Si 3 N 4 in the reaction process in the pores, and it is considered that β-Si 3 N 4 precipitates in the plate thickness direction. Furthermore, when the heat treatment temperature increases, a silicon nitride substrate in which β-type silicon nitride particles are preferentially oriented in the plate thickness direction is obtained with the β-Si 3 N 4 precipitated in the plate thickness direction in the pores as nuclei. And, it is considered that the thermal conductivity increases due to the elongation of β-type silicon nitride particles in the plate thickness direction, and the heat dissipation property as an insulating substrate is improved.

[0050] Note that the steps described above are merely examples and do not limit the present invention. For example, the forming method of the slurry is not limited to the doctor blade method, and the slurry may be pressure-formed into a sheet green compact by an extrusion forming method, a casting forming method, or the like.

Examples

[0051] Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

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

[0053] Silicon powder having predetermined powder characteristics and sintering aid powder were prepared. An appropriate amount of silicon powder was put into a ball mill, and the silicon powder, organic solvent, and dispersant were pulverized in the ball mill until the specific surface area and D 99.9 iameter values of the silicon powder reached predetermined values. Here, the blending composition ratios in each sample, as well as the D 99.9 iameter, D 50 iameter, and specific surface area values of the silicon powder are as shown in Table 1. When the particle size adjustment of the silicon powder was completed, a sintering aid was added and mixed in the 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 to adjust the viscosity. The ratio of the organic solvent contained in the degassed slurry was set to 35 wt% or less, and the viscosity of the slurry was set to 15000 - 25000 cps. The viscosity of the slurry was measured by a TVC-7 type viscometer manufactured by Toki Sangyo Co., Ltd. Specifically, the spindle was rotated in the slurry, and the viscosity was calculated from the resistance force. Then, a sheet-shaped molded body was produced using a doctor blade with a forming speed of 200 mm / min or more. Next, the inorganic filling rate Fi (%) of the sheet-shaped molded body of each sample was measured. BN as a mold release material was spray-coated on the surface of the produced sheet-shaped molded body, and a laminate of 20 sheets in one block was prepared. The laminate was debound at 500 °C in dry air, then put into a furnace, heated to about 1000 °C in a vacuum, and heated from 0.2 MPa nitrogen pressurized atmosphere to about 1350 °C at a rate of 1 °C / min. Then, the nitrogen pressurized atmosphere was set to 0.9 MPa, heated from about 1350 °C to about 1900 °C, and sintered at about 1900 °C for about 8 hours. After sintering, 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 dimensions of 190 mm × 140 mm.

[0054] For each of the samples of Examples 1 to 20 and Comparative Examples 1 to 8 prepared, the crystal phase of each sample was identified by X-ray diffraction measurement, and by analyzing the X-ray diffraction pattern, the integrated intensity of each diffraction peak, the Lotgering factor f(hk0), and the intensity ratio I 101 / I 210 were derived. Also, for each sample, β-silicon nitride particles in the vertical cut cross-section were observed, and the number of coarse particles having a major axis of 50 μm or more and the number of coarse particles having an inclination angle of 45 degrees or less with respect to the normal of the substrate surface were derived in a region of 200,000 μm 2 . Furthermore, for each sample, the relative density, the arithmetic mean height Sa, the thermal conductivity (W / mK), and the fracture toughness (MPa·m 1 / 2 ) were measured. Various measurements were carried out under the following conditions.

[0055] · X-ray diffraction measurement and its analysis Using an UltimaIV model manufactured by Rigaku Corporation, the X-ray diffraction intensity of each sample was measured by the powder X-ray diffraction method using Cu-Kα rays. For the measurement, specimens cut into 10 mm × 10 mm were used. The surface of the substrate after honing was used as the measurement surface. The measurement conditions are 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: 40 kV / 40 mA Detector: Semiconductor detector In the X-ray diffraction pattern of the substrate plane obtained by X-ray incidence on the substrate plane, the integrated intensity of the diffraction peak corresponding to the Miller index (hkl) of the β-silicon nitride particles was calculated. Based on the calculated peak intensity, the Lotgering factor f(hk0), and the intensity ratio I 101 / I 210 were derived.

[0056] · Method for observing β-silicon nitride particles in the vertical cut cross-section Individual pieces cut to 10 mm × 10 mm were used. The individual pieces were embedded in an epoxy resin, and observation of the vertical cross-section of the substrate was performed. The observation surface was prepared according to the following procedure. Planarization was carried out using #800 diamond polishing paper, and polishing was performed in the order of 15 μm, 6 μm, and 1 μm with diamond slurry until the polishing scratches generated in each previous process disappeared, and finish polishing was performed with 50 nm alumina slurry to obtain a mirror surface. After mirror finishing, plasma etching with CF 4 was performed to obtain the observation surface. Then, using a laser microscope VKX-150 manufactured by Keyence Corporation, the above observation surface was observed at an objective lens magnification of 20 times, and cross-sectional photographs were taken. Image processing of the cross-sectional photographs was performed, and in the cross-sectional photograph of an area of 200,000 μm 2 , the number of coarse particles with a major axis of 50 μm or more among the β-type silicon nitride particles, and among the coarse particles, the number of coarse particles with an inclination of 45 degrees or less with respect to the normal to the substrate surface was measured.

[0057] ·Relative density Calculated from the density of the sintered body with respect to the theoretical density obtained from the raw material mixing ratio (Equation 5). The density of the sintered body was measured by the Archimedes method using pure water. Relative density (%) = (sintered body density / theoretical density) × 100 (Equation 5)

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

[0059] ·Thermal conductivity For the measurement method of the thermal conductivity in the thickness direction of the substrate, the flash method was adopted. For the measurement, a thermal conductivity measuring device LFA467 manufactured by NETZSCH Geratebau GmbH was used. For the measurement, specimens cut into 10 mm × 10 mm from the substrate were used. For the purpose of suppressing the transmission of the flash light, sputtered films of gold were formed on both sides of the specimen, and for the purpose of uniformly absorbing the pulsed light, graphene spray was used on both sides of the specimen for blackening treatment. When calculating the thermal conductivity, a value of 0.68 J / (g·K) was used as the specific heat of the obtained sintered body.

[0060] ·Fracture toughness Using a Vickers hardness tester HV-120 manufactured by Mitutoyo Corporation, the fracture toughness of each sample was measured according to JIS-R1607. That is, mirror polishing was performed on the cross-section of the substrate cut along the thickness direction of the substrate. As shown in FIGS. 12(a) and (b), indentations having diagonal lengths a1 and a2 were formed near the center in the thickness direction of the mirror-polished surface. The diagonal lengths a1 and a2 of the resulting indentations, and the lengths c1 and c2 of the cracks generated from the apex of the indentation were measured, and the fracture toughness value K C was obtained. According to JIS-R1607, the fracture toughness value KC is obtained by the following formula. K C =0.026×E 1 / 2 ×P 1 / 2 ×a / C 3 / 2 (Equation 6) C = ((c1 / 2 + c2 / 2) / 2) / 2 (Equation 7) a = ((a1 / 2 + a2 / 2) / 2) / 2 (Equation 8) E: Elastic modulus P: Indentation load a: Half of the average of the diagonal lengths of the indentation C: Half of the average of the crack lengths In contrast, in this embodiment, the fracture toughness value K C is the fracture toughness value K C1 in the first direction (direction parallel to the substrate plane), and the fracture toughness value K C2They were evaluated separately. Specifically, the crack length occurring in the direction parallel to the substrate plane was defined as c1, and by setting C in Equation 6 to c1 / 2, K C1 was calculated. Also, the crack length occurring in the direction perpendicular to c1 (the substrate thickness direction) was defined as c2, and by setting C in Equation 6 to c2 / 2, K C2 was calculated. 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 Comparative 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. Also, FIGS. 1 to 3 exemplarily show SEM photographs of the substrate surfaces of the samples of Example 1, 5, and Comparative Example 1 taken at 2000 times magnification. FIGS. 4 to 8 exemplarily show the X-ray diffraction patterns of Example 1, 5, 12, Comparative Example 1, and 7. The Miller indices (hkl) are described for each diffraction peak of the β-type silicon nitride particles in the X-ray diffraction patterns. FIGS. 9 to 11 exemplarily show the cross-sectional photographs of Example 1, 5, and Comparative Example 1.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] Examples 1 to 20 are composed of raw material powders having a molar ratio of 85 to 95 mol% of silicon (in terms of silicon nitride), 1 to 3 mol% of rare earth oxide, and 4 to 12 mol% of magnesium silicon nitride. Here, in Examples 1 to 14, yttrium oxide (Y 2 O 3 ) was selected as the rare earth oxide (RE 2 O 3 ). In Examples 15 to 20, La 2 O 3 , Sm 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Er 2 O 3 , and Yb 2 O 3 were each selected as the rare earth oxide (RE 2 O 3 ). And the D 99.9 iameter of the silicon powder as the starting material is 8.0 to 9.5 μm (9.5 μm or less), and the specific surface area is 5.0 to 8.0 m 2 / g (5.0 m 2 / g or more and 9.0 m 2 / g or less). Also, in Examples 1 to 20, the inorganic filling rate of the molded body produced in the molding step was 47% or more. On the other hand, Comparative Examples 1 and 2 are samples using magnesium oxide as the raw material powder instead of magnesium silicon nitride. Comparative Example 3 is a sample with 3 mol% (less than 4 mol%) of magnesium silicon nitride. Comparative Example 4 is a sample in which the D 99.9 iameter of the silicon powder as the starting material is 12.3 μm (larger than 9.5 μm), and the specific surface area is 4.3 m 2 / g (less than 5.0 m 2 / g). Comparative Example 5 is a sample in which the specific surface area of the silicon powder as the starting material is 9.9 m 2 / g (larger than 9.0 m 2 / g). Comparative Example 6 is a sample with 0.9 mol% (less than 1 mol%) of yttrium oxide. Comparative Example 7 is a sample with 12.7 mol% (more than 12 mol%) of magnesium silicon nitride, and D 99.9The sample has a diameter of 10.1 μm (greater than 9.5 μm). Comparative Example 8 is a sample with 0.5 mol% (less than 4 mol%) of magnesium silicon nitride. Also, in Comparative Examples 4, 5, and 7, due to the silicon powder characteristics, the inorganic filling rate of the compact produced in the molding process was less than 47%. In Comparative Examples 1 to 3, 6, and 8, the measurement of the inorganic filling rate of the compact was omitted. However, since the silicon powder characteristics and manufacturing conditions are similar, it is presumed that the inorganic filling rate is 47% or more, similar to the examples.

[0067] In the SEM photographs (magnification: 2000 times) of the substrate surface of the silicon nitride sintered bodies shown in FIGS. 1 to 3, rod-shaped β-type silicon nitride particles can be confirmed. In particular, in FIGS. 1 and 2 corresponding to Examples 1 and 5, the cross-section in the short-axis direction of the β-type silicon nitride particles with the long axis arranged in the thickness direction of the substrate can be observed. Also, in the X-ray diffraction patterns of FIGS. 4 to 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 the samples of Examples 1 to 14 and Comparative Examples 1 to 8 of the silicon nitride sintered body. According to Table 1, in Examples 1 to 14, the Lotgering factor f(hk0) indicating the degree of orientation of the (hk0) plane of the β-type silicon nitride particles shows a negative value, and the intensity ratio I 101 / I 210 shows 1.5 or more. That is, it can be seen that the orientation of the 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) shows a positive value, and the intensity ratio I 101 / I 210 shows less than 1.0. Also, Table 1 shows that in Examples 1 to 14, the arithmetic mean height Sa indicating 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 area is 200,000 μm 2In the cross-sectional photograph, it was shown that there were 10 or more coarse particles of β-type silicon nitride with a major axis of 50 μm or more, and 7 or more β-type silicon nitride particles among the coarse particles with an inclination angle of 45 degrees or less with respect to the normal line of the substrate surface. On the other hand, in Comparative Examples 1 to 8, as shown in Table 1 and FIG. 11, in the cross-sectional photograph of the region 200,000 μm 2 there were 8 or fewer coarse particles of β-type silicon nitride with a major axis of 50 μm or more, and 6 or fewer β-type silicon nitride particles among the coarse particles with an inclination angle of 45 degrees or less with respect to the normal line of 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) indicating the orientation degree of the (hk0) plane of the β-type silicon nitride particles shows a negative value. In Examples 15, 16, and 20, the intensity ratio I 101 / I 210 shows 1.1 or more, and in Examples 17 to 19, the intensity ratio I 101 / I 210 shows 1.5 or more. Also, Table 2 shows that in Examples 15 to 20, the arithmetic mean height Sa indicating the roughness of the substrate surface is 0.8 μm or more. Furthermore, as shown in Table 2, according to the image analysis result of the photographed substrate cross-sectional image, in Examples 15 to 20, in the cross-sectional photograph of the region 200,000 μm 2 it was shown that there were 10 or more coarse particles of β-type silicon nitride with a major axis of 50 μm or more. Also, according to Table 2, except for Example 20 in which the rare earth oxide is Yb 2 O 3 it was shown that there were 8 or more β-type silicon nitride particles among the coarse particles with an inclination angle of 45 degrees or less with respect to the normal line of the substrate surface. In Example 20, 7 β-type silicon nitride particles with an inclination angle of 45 degrees or less were confirmed. That is, in Examples 1 to 20, it was shown that at least 7 β-type silicon nitride particles among the coarse particles had an inclination angle of 45 degrees or less with respect to the normal line of the substrate surface.

[0070] From the above results, it is presumed that in the silicon nitride sintered bodies of Examples 1 to 20, the long axes of β-type silicon nitride are preferentially oriented in the thickness direction of the substrate with respect to the samples of the comparative examples. Further, in the silicon nitride sintered bodies of Examples 1 to 20, relatively more coarse particles of β-type silicon nitride having a long axis of 50 μm or more were formed with respect to the samples of the comparative examples, and it was found that the coarse particles were preferentially arranged in the thickness direction of the substrate (within 45 degrees with respect to the normal). That is, the silicon nitride sintered body of the present invention is characterized in that crystal growth has occurred such that the β-type silicon nitride particles are coarsened in the plate thickness direction.

[0071] Table 3 shows the thermal conductivities and physical strengths 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, in the crystal structure of the silicon nitride sintered body, it can be seen that 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 value of the fracture toughness K C1 in the first direction parallel to the substrate plane was 5.5 MPa·m 1 / 2 or more, and the value of the fracture toughness 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 value of the fracture toughness K C2 in the first direction to the value of the fracture toughness K C1 / K C2 in the second direction 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 C1 / K C2 was about 0.8, and it was found that the value of the fracture toughness K C2 in the second direction perpendicular to the substrate plane was clearly larger.

[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 value K C1 of the fracture toughness in the first direction parallel to the substrate plane was 5.5 MPa·m 1 / 2 or more, and the value K C2 of the fracture toughness 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 value K C2 of the fracture toughness in the first direction to the value K C1 of the fracture toughness in the second direction, K C2 / K

[0073] The present invention is not limited to the above-described examples, and can be implemented in various modes as long as it belongs to the technical scope of the present invention.

Claims

1. A silicon nitride sintered body, comprising a substrate containing β-type silicon nitride particles, wherein the Lotgering factor f(hk0) indicating the degree of orientation of the (hk0) plane of the β-type silicon nitride particles in the plane of the substrate is a negative value.

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

3. Fracture toughness value K perpendicular to the thickness direction Ｃ１ and fracture toughness value K in the thickness direction Ｃ２ having, where K Ｃ１ / K Ｃ２ is 0.85 or more, the silicon nitride sintered body according to claim 1.

4. In a cross-sectional photograph taken by cutting a substrate perpendicular to a plane, 200,000 μm ２ The silicon nitride sintered body according to claim 1, characterized in that, in the region of, there are contained 10 or more β-type silicon nitride particles having a major axis of 50 μm or more.

5. In a cross-sectional photograph taken by cutting a substrate perpendicularly to a plane, 200,000 μm ２ In the region of, there are contained 7 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 line of the substrate surface of 45 degrees or less, The silicon nitride sintered body according to claim 1, characterized in that.

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

7. In the silicon nitride sintered body, a mixing step of preparing a mixed powder by mixing silicon powder, rare earth oxide powder, and magnesium silicon nitride powder having a D99.9 diameter of 9.5 μm or less, a specific surface area of 5.0 m2 / g or more and 9.0 m2 / g or less so as to have a molar ratio of 85 to 95 mol% of silicon nitride, 1 to 3 mol% of rare earth oxide, and 4 to 12 mol% of magnesium silicon nitride; 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; A densification step of firing the molded body at a third temperature for a predetermined time in a nitrogen atmosphere to produce a silicon nitride sintered body. A method for manufacturing a silicon nitride sintered body, comprising the above steps.

8. The specific surface area of the magnesium silicon nitride powder is 9.0 m ２ / g or more, and the manufacturing method according to claim 7, characterized in that.

9. The manufacturing method according to claim 7, wherein the molded body is produced by a sheet molding method.

10. The manufacturing method according to claim 7, wherein the inorganic filling rate of the molded body is 47% or more.

11. The thermal conductivity in the substrate thickness direction is 100 W / mK or more, and Fracture toughness value K perpendicular to the thickness direction Ｃ１ and fracture toughness value K in the thickness direction Ｃ２ and has K Ｃ１ / K Ｃ２ The silicon nitride sintered body according to claim 1, characterized in that is 0.85 or more.

12. In a cross-sectional photograph taken by cutting a substrate perpendicularly to a plane, within a region of 200,000 μm ２ there are contained 10 or more β-type silicon nitride particles having a major axis of 50 μm or more, and In a cross-sectional photograph taken by cutting the substrate perpendicularly to the plane, 200,000 μm ２ in the region contains 7 or more β-type silicon nitride particles with 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. The silicon nitride sintered body according to any one of claims 1, 2, 3, and 11, wherein the arithmetic mean height Sa indicating the roughness of the substrate surface is 0.8 μm or more.

13. The rare earth oxide is Y ２ O ３ , La ２ O ３ , Sm ２ O ３ , Gd ２ O ３ , Dy ２ O ３ , Er ２ O ３ , and Yb ２ O ３ The manufacturing method according to claim 7, characterized in that it is selected from at least one of the group consisting of

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