Silicon nitride sintered body and electronic component mounting substrate

Abstract

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

Description

Technical Field

[0001] The present invention relates to a silicon nitride sintered body and a method for 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 is 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 ratio 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, and a silicon nitride sintered body substrate having isotropic fracture toughness in both directions is obtained. C2

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 the 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 such that the fracture toughness value K C1 in a direction perpendicular to the thickness direction and the fracture toughness value K C2 in the thickness direction are such that 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 such that in a cross-sectional photograph taken of a cross-section obtained by cutting the substrate perpendicular to the plane, there are 10 or more β-type silicon nitride particles having a major axis of 50 μm or more in a region of 200,000 μm 2 .

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

[0013] A further form of the silicon nitride sintered body of the present invention is more preferably such 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 method for manufacturing a silicon nitride sintered body, in which the silicon nitride (Si 3 N 4 ) is 85 to 95 mol%, the rare earth oxide (RE 2 O 3 ) is 1 to 3 mol%, and the 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 forming step of forming the mixed powder 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 for a predetermined time in a nitrogen atmosphere to produce a silicon nitride sintered body.

[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 formed body is produced by a sheet forming 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 formed 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, 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 plate thickness direction of the substrate.

Brief Description of the Drawings

[0020]

Figure 1

[0021]

Figure 2

[0022]

Figure 3

[0023]

Figure 4

[0024]

Figure 5

[0025]

Figure 6

[0026]

Figure 7

[0027]

Figure 8

[0028]

Figure 9

[0029]

Figure 10

[0030]

Figure 11

[0031]

Figure 12

Mode for Carrying Out 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 oxides, 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 as to preferentially orient β-type silicon nitride 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 ) (Equation 1) ρ 0 = ΣI 0 (hk0) / ΣI 0 (hkl) (Equation 2) ρ = ΣI(hk0) / ΣI(hkl) (Equation 3) ρ 0 is calculated using the diffraction intensity I 0 in the range of 2θ from 20 degrees to 65 degrees of the X-ray diffraction spectrum of the non-oriented sample, and the sum of the total diffraction intensities ΣI 0 The sum of the diffraction intensities ΣI 0 of the (hk0) plane with respect to ΣI(hkl) of all diffraction intensities is obtained by Equation 2 as the ratio of (hk0). Here, the diffraction intensity I 0 is calculated from the X-ray diffraction spectrum of the reference sample (a non-oriented sample having the same composition as the target sample). Also, ρ is calculated using the diffraction intensity I in the range of 2θ from 20 degrees to 65 degrees of the X-ray diffraction spectrum of the silicon nitride sintered body sample, and is obtained by Equation 3 as the ratio of the sum of the diffraction intensities ΣI(hk0) of the (hk0) plane to the sum of all diffraction intensities ΣI(hkl). Note that h, k, and l are integers and represent the plane indices. If the crystal orientation of the obtained sample is random, the difference between ρ and ρ 0 is small, and according to Equation 1, f(hk0) approaches a value close to zero. If f(hk0) is a negative value (ρ < ρ 0 ), it means that the obtained sample has a lower degree of orientation of the (hk0) plane than the non-oriented sample. That is, when the Lotgering factor f(hk0) of the obtained sample takes a negative value, it is shown that the (00l) plane (i.e., the long axis) of the β-type silicon nitride particles is strongly oriented in the plate thickness direction.

[0037] Also, as another index indicating the degree of orientation of the β-type silicon nitride particles in the substrate of the silicon nitride sintered body of the present embodiment, the intensity I 101 of the X-ray diffraction peak of the (101) plane of the β-type silicon nitride of the silicon nitride sintered body, and the intensity I 210 of the X-ray diffraction peak of the (210) plane of the β-type silicon nitride, and the intensity ratio I 101 / I 210include. In the silicon nitride sintered body of the present 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 the present 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 axes of the β-type silicon nitride particles are 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 the present embodiment, in the cross-sectional photograph taken of the 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 the present embodiment contains a relatively large number of coarse particles having a long axis of 50 μm or more, and the long axes of the β-type silicon nitride are preferentially oriented in the thickness direction of the substrate.

[0041] And, in the silicon nitride sintered body of the present 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 the present embodiment is densified to a relative density of 98% or more. And, in the silicon nitride sintered body of the present embodiment, the value K of the fracture toughness in the first direction parallel to the substrate plane C1is 5.5MPa m 1 / 2 or more, and the fracture toughness value K C2 is 5.5MPa 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 Compared to K C1 / K C2 is 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 method for producing the silicon nitride sintered body is a reaction sintering method in which silicon powder is used as a starting material instead of silicon nitride powder, and the molded silicon powder is heated in a nitrogen atmosphere to simultaneously perform nitridation and densification. In general, the reaction sintering method improves the thermal conductivity of the sintered body because of the high purity of the raw material, but it is said that the raw material adjustment and sintering conditions for densification are difficult. In addition, in a general reaction sintering method, silicon powder is converted into rod-shaped β-type silicon nitride particles, so it is difficult to control the orientation in the plate thickness direction, and it is known that the orientation is likely to become random.

[0044] According to this embodiment, the method for producing a silicon nitride sintered body mainly includes 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 molar ratio of the silicon nitride sintered body is 85-95 mol % of silicon nitride, 1-3 mol % of rare earth oxide, and 4-12 mol % of magnesium silicon nitride, a forming step of slurrying 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 densifying 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] Prepare silicon powder as the starting material. Grind the silicon powder, organic solvent, and dispersant using 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 is adjusted, mix rare earth oxide powder and silicon nitride magnesium powder as sintering aids 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 using a ball mill, and then add a binder, plasticizer, and 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 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 fine silicon powder increases, and aggregation is likely to occur, resulting in poor fillability. 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, so the drying shrinkage becomes large and fine bubbles are likely 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 of 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, and is a value calculated from the weight ratio of the raw material inorganic content.

[0048] Next, the produced sheet-shaped formed body was debound 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, nitridation of the formed body can be performed by gradually raising the temperature from the first temperature to the second temperature (for example, 1 °C / min) in the nitrogen pressurized atmosphere. Then, the inside of the furnace was set to a higher-pressure nitrogen pressurized atmosphere, and the temperature was 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 was 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 was sufficiently performed to produce a silicon nitride sintered body.

[0049] By going through the steps described above, it is possible to manufacture a silicon nitride sintered body in which β-type silicon nitride particles are preferentially oriented in the thickness direction of the substrate. That is, in the manufacturing method, by using magnesium silicon nitride and suppressing the amount of oxygen in the green body by minimizing the addition amount of yttrium oxide (that is, setting the rare earth oxide to 1 to 3 mol%), 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 by the elongation of β-type silicon nitride particles in the plate thickness direction, the thermal conductivity increases 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 body 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 ground 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. After the particle size of the silicon powder was adjusted, 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 make 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. And a sheet-shaped molded body was produced by a doctor blade with a molding 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 per block was prepared. The laminate was debound at 500 °C in dry air, then put into a furnace, heated to about 1000 °C in vacuum, and heated at a rate of 1 °C / min to about 1350 °C in a nitrogen pressurized atmosphere of 0.2 MPa. Then, a nitrogen pressurized atmosphere of 0.9 MPa was set, 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 a size of 190 mm × 140 mm.

[0054] For each of the prepared samples of Examples 1 to 20 and Comparative Examples 1 to 8, 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 section were observed, and 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 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, arithmetic mean height Sa, thermal conductivity (W / mK), and 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 powder X-ray diffraction 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 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: 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] ·Observation method for β-silicon nitride particles in the vertical cut section Individual pieces cut to 10 mm × 10 mm were used, the individual pieces were embedded in an epoxy resin, and observation of a vertical cross-section of the substrate was performed. The observation surface was prepared according to the following procedure. Planar finishing was performed using #800 diamond abrasive 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, CF 4 plasma etching was performed to obtain an 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 a cross-section photograph was taken. Image processing of the cross-section photograph was performed, and in the cross-section photograph of an area of 200,000 μm 2 , the number of coarse particles having 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 having an inclination of 45 degrees or less with respect to the normal to the substrate surface was measured.

[0057] ·Relative density It was 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 region of 500 μm × 500 μm 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 A flash method was adopted for the measurement method of the thermal conductivity in the thickness direction of the substrate. 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. Gold sputter films were formed on both sides of the specimens for the purpose of suppressing the transmission of the flash light, and graphene spray was used on both sides of the specimens for the purpose of uniformly absorbing the pulsed light, and blackening treatment was performed. 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 crack lengths c1 and c2 generated from the apex of the indentation were measured, and the fracture toughness value K C was obtained from the indentation load, the diagonal length of the indentation, the crack length, and the elastic modulus. 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 On the other hand, 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 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 in molar ratio. 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 respectively 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 process 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 with the D 99.9 iameter of the silicon powder as the starting material being 12.3 μm (larger than 9.5 μm) and the specific surface area being 4.3 m 2 / g (less than 5.0 m 2 / g). Comparative Example 5 is a sample with the specific surface area of the silicon powder as the starting material being 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. 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 body 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 their long axes aligned in the thickness direction of the substrate can be observed. 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. On the other hand, 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. Table 1 also 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-silicon nitride with a major axis of 50 μm or more, and 7 or more β-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-silicon nitride with a major axis of 50 μm or more, and 6 or fewer β-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-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 results 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-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-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-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-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-phase 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-phase 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-phase 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-phase silicon nitride particles in the thickness direction of the substrate and the coarsening of the β-phase 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 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 5.5MPa m 1 / 2 or more, and the fracture toughness value K C2 , but 5.5MPa 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 Compared to K C1 / K C2 was 0.85 to 1.2, indicating that the mechanical strength (fracture toughness) of the substrate was exerted isotropically.

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

Claims

1. A substrate containing β-type silicon nitride particles is formed, In a cross-sectional photograph taken of a cross section of a substrate cut perpendicular to the plane, ２ 1. A silicon nitride sintered body, characterized in that the region contains 10 or more β-type silicon nitride particles each having a major axis of 50 μm or more.

2. A substrate containing β-type silicon nitride particles is formed, In a cross-sectional photograph taken of a cross section of a substrate cut perpendicular to the plane, ２ 1. A silicon nitride sintered body, characterized in that the region contains seven or more β-type silicon nitride grains 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.

3. X-ray diffraction peak intensity I of the (101) plane of β-type silicon nitride １０１ and the intensity I of the X-ray diffraction peak of the (210) plane of β-type silicon nitride. ２１０ Intensity ratio I １０１ / I ２１０ 3. The silicon nitride sintered body according to claim 1, wherein the ratio of the surface area to the surface area of ​​the silicon nitride is 1.5 or more.

4. 3. 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.

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

6. 3. A substrate for mounting electronic components, comprising: the silicon nitride sintered body according to claim 1; and a metal plate brazed to a surface of the silicon nitride sintered body.

Images