Silicon nitride sintered body

Abstract

A silicon nitride sintered body according to the present invention is characterized in that the crystal lattice strain of silicon nitride crystal grains constituting the silicon nitride sintered body is less than 0.003.　The present invention makes it possible to provide a silicon nitride sintered body with which it is possible to form a silicon nitride circuit board having excellent temperature cycle characteristics and high reliability.

Description

Silicon nitride sintered body

[0001] The present invention relates to a silicon nitride sintered body.

[0002] Silicon nitride sintered bodies have attracted attention as ceramic materials in various industrial fields due to their excellent properties such as high thermal conductivity, high insulation properties, and high strength. For example, they are used as circuit boards (silicon nitride circuit boards) for power modules for automobiles and semiconductors.

[0003] Silicon nitride circuit boards are manufactured, for example, by bonding a metal plate (such as a copper plate) to a silicon nitride substrate and then etching the metal plate to form the silicon nitride circuit board. Semiconductor elements are then mounted on the silicon nitride circuit board for use. For example, Patent Document 1 describes an invention relating to a silicon nitride circuit board, which is a circuit board with excellent temperature cycle characteristics, characterized by having a metal clad material with a thickness of 1 mm or more bonded to at least one surface of the silicon nitride substrate, and describes mounting multiple semiconductor elements on the silicon nitride circuit board.

[0004] Japanese Patent Application Laid-Open No. 2003-168770

[0005] In recent years, the increasing density and power output of electronic devices and semiconductor devices has created a demand for highly reliable silicon nitride circuit substrates with excellent temperature cycle characteristics. Temperature cycle characteristics are an index of a sample's durability when the sample is repeatedly subjected to temperature changes from low to high and then back to low.

[0006] On the other hand, conventional silicon nitride circuit boards have the problem that the surface of the silicon nitride board may be partially destroyed when subjected to repeated temperature changes, and there is room for improvement in terms of reliability. Therefore, the present invention aims to provide a silicon nitride sintered body that can be used to form silicon nitride circuit boards with better temperature cycle characteristics than conventional ones.

[0007] The present inventors have conducted extensive research to achieve the above object, and as a result, have focused on the crystal lattice distortion of silicon nitride sintered bodies, which had not previously been investigated, and have found that the above problems can be solved by using a silicon nitride sintered body having a crystal lattice distortion of less than 0.003, thereby completing the present invention.

[0008] The gist of the present invention is the following [1] to [4]. [1] A silicon nitride sintered body, characterized in that the crystal lattice distortion of the silicon nitride crystal grains constituting the silicon nitride sintered body is less than 0.003. [2] The silicon nitride sintered body according to the above [1], wherein the silicon nitride crystal grains have a dissolved oxygen concentration of less than 500 ppm. [3] The silicon nitride sintered body according to the above [1] or [2], wherein the silicon nitride crystal grains have an average particle size of 1 to 15 μm. [4] The silicon nitride sintered body according to any of the above [1] to [3], which is a heat dissipation substrate.

[0009] According to the present invention, it is possible to provide a silicon nitride sintered body that has excellent temperature cycle characteristics and can be used to form a highly reliable silicon nitride circuit board.

[0010] 1 is a diagram for explaining vacancies in a silicon nitride crystal lattice, 2 is a diagram for explaining vacancy cluster defects in a silicon nitride crystal lattice, and 3 is an example of a TEM dark-field image of a silicon nitride particle containing a helical dislocation.

[0011] [Silicon nitride sintered body] The silicon nitride sintered body of the present invention will be described in detail below.

[0012] <Crystal lattice distortion> In the silicon nitride sintered body of the present invention, the crystal lattice distortion of the silicon nitride crystal grains constituting the silicon nitride sintered body is less than 0.003. When the crystal lattice distortion is less than 0.003, the temperature cycle characteristics of a silicon nitride circuit board manufactured using the silicon nitride sintered body are improved. From the viewpoint of further improving the temperature cycle characteristics, the crystal lattice distortion of the silicon nitride crystal grains is preferably 0.002 or less, more preferably 0.001 or less. The lower limit of the crystal lattice distortion of the silicon nitride crystal grains is not particularly limited, but is ideally 0. The crystal lattice distortion of the silicon nitride crystal grains can be measured by X-ray diffraction. Details of the measurement method will be explained in the examples.

[0013] The reason why the temperature cycle characteristics of the silicon nitride sintered body are improved by reducing the crystal lattice distortion of the silicon nitride crystal grains is presumed to be as follows. The crystal lattice distortion of the silicon nitride sintered body is related to vacancies formed by dissolved oxygen. The silicon nitride crystals (Si ３ N ４ It is known that silicon nitride contains dissolved oxygen due to the type of raw material and manufacturing method. When oxygen atoms (O) displace and dissolve with nitrogen atoms (N) that make up silicon nitride crystals, silicon atom (Si) vacancies are generated to ensure electrical neutrality. For example, Figure 1 shows a diagram of a silicon nitride crystal lattice in which four oxygen atoms replace four nitrogen atoms, leaving one silicon atom missing and creating a vacancy.

[0014] When the amount of dissolved oxygen in a silicon nitride sintered body is about the same, it is thought that the number of vacancies that will be generated will also be about the same. However, it is thought that the durability of the substrate will differ depending on whether the vacancies are individually dispersed or whether several vacancies are aggregated to form vacancy cluster defects.

[0015] For example, the left and right diagrams in Figure 2 each show a schematic representation of a silicon nitride crystal lattice with the same number of vacancies (five). The left diagram shows five vacancies dispersed throughout. On the other hand, the right diagram shows several vacancies clustered together to form a vacancy cluster defect, as indicated by A. Such vacancy cluster defects are thought to be the cause of etch pits and voids on the surface of a silicon nitride substrate that are generated by etching when forming a circuit pattern. If a temperature cycle test is performed with defects such as etch pits and voids present, the silicon nitride substrate will be partially destroyed, originating from the defects. In other words, by reducing the number of vacancy cluster defects, it is thought that destruction of the silicon nitride substrate caused by the vacancy cluster defects is suppressed, and the temperature cycle characteristics are improved.

[0016] Since the crystal lattice is distorted near vacancy cluster defects, the fewer the vacancy cluster defects, the smaller the crystal lattice distortion. Therefore, it is believed that the smaller the crystal lattice distortion, the better the temperature cycle characteristics of the silicon nitride sintered body of the present invention when it is used to form a silicon nitride circuit board.

[0017] The presence or absence of vacancy cluster defects in a silicon nitride sintered body can be confirmed by observation with a transmission electron microscope (TEM). That is, vacancy cluster defects are observed by TEM as, for example, dislocation loops or helical dislocations. For example, Figure 3 shows an example of a TEM dark-field image of a silicon nitride particle containing a helical dislocation. A helical dislocation is observed as a helical white line inside the silicon nitride particle in the center of Figure 3.

[0018] The method for adjusting the value of the crystal lattice distortion is not particularly limited, but it can be adjusted, for example, by the conditions under which the silicon nitride sintered body is produced, particularly the cooling conditions after firing.

[0019] <Solute Oxygen> The solute oxygen concentration of the silicon nitride crystal particles constituting the silicon nitride sintered body of the present invention is not particularly limited, but is, for example, 2500 ppm or less. A solute oxygen concentration of 2500 ppm or less can increase the thermal conductivity of the silicon nitride sintered body. On the other hand, the solute oxygen concentration of the silicon nitride crystal particles constituting the silicon nitride sintered body is preferably as low as possible from the viewpoint of improving thermal conductivity, but in practical terms, it is 100 ppm or more. When the solute oxygen concentration is low, there are fewer vacancies in Si atoms, resulting in higher thermal conductivity. When vacancies are generated, they become scattering sources for lattice vibrations (phonons), causing a decrease in thermal conductivity. Therefore, generally, the lower the amount of solute oxygen in the silicon nitride sintered body, the fewer phonon scattering sources there are, and the higher the thermal conductivity tends to be. From this perspective, the solute oxygen concentration of the silicon nitride crystal particles constituting the silicon nitride sintered body of the present invention is preferably less than 500 ppm, more preferably 450 ppm or less, and even more preferably 400 ppm or less. By reducing the crystal lattice distortion and the dissolved oxygen concentration as described above, the silicon nitride sintered body of the present invention has improved temperature cycle characteristics and good heat dissipation properties, making it possible to provide a silicon nitride sintered body with extremely excellent physical properties.

[0020] In the present invention, the solute oxygen concentration refers to the concentration of oxygen dissolved inside the silicon nitride sintered body (internal oxygen), and does not include adsorbed oxygen (external oxygen) inevitably present on the surface of the sintered body. The solute oxygen concentration can be adjusted by various raw materials used to produce the silicon nitride powder, the type and amount of sintering aid used in producing the sintered body, sintering conditions, etc. The solute oxygen concentration can be measured by the method described in the Examples.

[0021] <Average particle size> The average particle size of the silicon nitride crystal particles constituting the silicon nitride sintered body of the present invention is not particularly limited, but is preferably 1 to 15 μm, more preferably 3 to 12 μm, and even more preferably 5 to 10 μm. If the average particle size of the silicon nitride crystal particles is equal to or greater than these lower limits, the thermal conductivity of the sintered body tends to be high. If the average particle size of the silicon nitride crystal particles is equal to or less than these upper limits, the mechanical strength of the sintered body tends to be high.

[0022] The average particle size of silicon nitride crystal grains in a silicon nitride sintered body is a weighted average particle size based on a volumetric distribution, and is measured as follows: A cross section of the silicon nitride sintered body is observed with a scanning electron microscope (SEM), and images of 300 or more particles are analyzed with an image analyzer to determine the equivalent circle diameter of each particle. The weighted average particle size is then calculated based on the volumetric distribution of the equivalent circle diameters.

[0023] <Thermal Conductivity> The thermal conductivity of the silicon nitride sintered body of the present invention is preferably 85 W / (m·K) or more, more preferably 90 W / (m·K) or more, from the viewpoint of improving heat dissipation when used as a heat dissipation substrate. The higher the thermal conductivity, the better, but it is, for example, 150 W / (m·K) or less, and in practical use, 100 W / (m·K) or less. The thermal conductivity can be measured by a laser flash method.

[0024] [Method for Producing Sintered Silicon Nitride] The sintered silicon nitride of the present invention can be obtained by firing silicon nitride powder, preferably by firing a mixed raw material containing silicon nitride powder and a sintering aid.

[0025] (Silicon nitride powder) The average particle size of the silicon nitride powder contained in the mixed raw material is not particularly limited, but from the viewpoint of setting the average particle size of silicon nitride crystal particles in the silicon nitride sintered body in the desired range described above, it is preferably 0.5 to 3 μm, more preferably 0.5 to 2 μm. The average particle size of the silicon nitride powder can be measured using a laser diffraction / scattering particle size distribution analyzer, and a volume frequency distribution curve is obtained with the horizontal axis representing particle size (μm) and the vertical axis representing volume frequency. The average particle size of the silicon nitride powder means the particle size (D50) at which the cumulative curve of the measured volume-based particle size distribution reaches 50%.

[0026] Silicon nitride powder can be produced by known methods. Examples of methods for producing silicon nitride powder include a reduction-nitridation method in which silica powder is used as a raw material and nitrogen gas is passed through in the presence of carbon powder to produce silicon nitride, a direct nitridation method in which silicon powder is reacted with nitrogen at high temperatures, and an imide decomposition method in which silicon halide is reacted with ammonia. Silicon nitride powder can also be produced by combustion synthesis, a direct nitridation method that utilizes self-combustion. Combustion synthesis allows for stable production of silicon nitride powder without incurring energy costs.

[0027] The combustion synthesis method uses silicon powder as a raw material, forcibly ignites a portion of the raw material powder under a nitrogen atmosphere, and synthesizes silicon nitride by self-heating of the raw material compound. The combustion synthesis method is a known method, and reference can be made to, for example, JP 2000-264608 A and WO 2019 / 167879 A.

[0028] (Sintering Aid) It is preferable to use a metal oxide as the sintering aid. By using a metal oxide as the sintering aid, the sintering of the silicon nitride powder is facilitated, and a denser and stronger sintered body is more likely to be obtained. As the metal oxide, yttria (Y ２ O ３ ), ceria (CeO), magnesia (MgO), etc. Among these, yttria is preferable. One type of metal oxide may be used alone, or two or more types may be used in combination.

[0029] As the sintering aid, it is preferable to use an oxygen-free compound together with the metal oxide. By using an oxygen-free compound as the sintering aid, it is possible to reduce the dissolved oxygen derived from the sintering aid. As a result, it is possible to obtain a silicon nitride sintered body with high thermal conductivity. Examples of the oxygen-free compound include carbonitride-based compounds containing rare earth elements and carbonitride-based compounds containing magnesium element. It is preferable to use a carbonitride-based compound containing magnesium element as the oxygen-free compound, and it is preferable to use both a carbonitride-based compound containing rare earth element and a carbonitride-based compound containing magnesium element.

[0030] Examples of carbonitride compounds containing rare earth elements include Y ２ Si ４ N ６ C, Yb ２ Si ４ N ６ C, Ce ２ Si ４ N ６ Among these, Y is preferred from the viewpoint of easily obtaining a silicon nitride sintered body having a high thermal conductivity. ２ Si ４ N ６ C, Yb ２ Si ４ N ６ C is preferred, and Y ２ Si ４ N ６ C is more preferable. Examples of carbonitride compounds containing magnesium include MgSi ４ N ６ Examples include C.

[0031] When an oxygen-free compound is used as a sintering aid, the content of the oxygen-free compound in the mixed raw material is preferably 1 to 15 parts by mass, more preferably 3 to 12 parts by mass, and even more preferably 6 to 10 parts by mass, per 100 parts by mass of silicon nitride powder. By adjusting the content of the oxygen-free compound as a sintering aid within the above range, it becomes easier to adjust the dissolved oxygen concentration low while allowing sintering to proceed.

[0032] The content of the sintering aid in the mixed raw material (total content of all sintering aids) is preferably 5 to 20 parts by mass, more preferably 6 to 18 parts by mass, and even more preferably 8 to 15 parts by mass, per 100 parts by mass of silicon nitride powder. By adjusting the content of the sintering aid within the above range, it becomes easier to adjust the dissolved oxygen concentration low while allowing sintering to proceed.

[0033] (Firing conditions) The silicon nitride sintered body of the present invention can be obtained by firing a mixed powder containing the silicon nitride powder and sintering aid described above. The mixed powder can be formed into a compact by press molding, and then fired in a firing furnace or the like. The press molding is typically uniaxial press molding, but a method in which uniaxial press molding is followed by CIP (cold isostatic pressing) molding is preferably used.

[0034] The firing temperature (firing temperature) can be, for example, 1500 to 1900°C. The maximum firing temperature is preferably 1700 to 1800°C, more preferably 1750 to 1800°C. Setting the firing temperature at such a high level promotes grain growth, making it easier to obtain a silicon nitride sintered body with high toughness. The holding time at the maximum temperature may be, for example, about 3 to 20 hours. As described above, the material is held at the maximum temperature for a certain period of time and then cooled. The cooling rate from the maximum temperature to 1000°C is preferably 0.1 to 5°C / min, more preferably 0.1 to 3°C / min. Setting the cooling rate at a slower rate in this way makes it easier to reduce the crystal lattice strain in the silicon nitride sintered body, promote grain growth, and make it easier to obtain a silicon nitride sintered body with high toughness. The conditions for cooling from 1000°C to near room temperature (e.g., 25°C) do not significantly affect the magnitude of crystal lattice strain, so they can be set appropriately.

[0035] Furthermore, it is preferable to perform cooling under increased pressure (furnace pressure); specifically, the pressure during cooling is preferably 120 to 1000 kPa, more preferably 150 to 800 kPa, and even more preferably 180 to 600 kPa. By adjusting the pressure during cooling within the above range, the effect of adiabatic compression is also added, making it easier to reduce the crystal lattice distortion of the silicon nitride sintered body. From the perspective of reducing the crystal lattice distortion of the silicon nitride sintered body, it is particularly preferable to adjust both the cooling rate from the maximum temperature to 1000°C and the pressure during cooling within the above ranges.

[0036] The firing is preferably carried out in an inert gas atmosphere, such as a nitrogen atmosphere or an argon atmosphere, with a nitrogen atmosphere being preferred.

[0037] The silicon nitride sintered body of the present invention can be suitably used as a variety of heat dissipation substrates. Furthermore, since the silicon nitride sintered body of the present invention has small crystal lattice distortion, it can be used to form a silicon nitride circuit board with excellent temperature cycle characteristics.

[0038] EXAMPLES The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0039] [Measurement Methods] Various physical properties in the examples and comparative examples were measured by the following methods.

[0040] <Crystal lattice distortion> (i) Preparation of measurement sample One side of the surface of a plate-shaped silicon nitride sintered body (thickness about 0.3 mm) is mechanically polished until the thickness is about 0.2 mm, and used as a sample for X-ray diffraction measurement.However, during mechanical polishing, in order to suppress and remove the generation of polishing damage layer, CMP (chemical mechanical polishing) slurry is used together with diamond slurry.The type of CMP slurry is not particularly limited, but in this embodiment, alkali-based colloidal silica (particle size 50 nm) slurry is used.(ii) Measurement The sample for X-ray diffraction measurement prepared as above is calculated by X-ray diffraction (XRD) using CuKα radiation according to the following procedure. From the X-ray diffraction pattern obtained by scanning the X-ray detector in 0.02° increments over the 2θ range of 15 to 80°, the integral widths of the (101), (110), (200), (201), and (210) planes of the β phase were calculated, and the integral widths were substituted into the Williamson-Hall equation of the following formula 2. The integral width is the value obtained by dividing the area obtained by subtracting the area of ​​the peak background from the area of ​​the peak waveform obtained by X-ray diffraction by the peak height. The following formula 2 was plotted with "2 sin θ / λ" on the X axis and "β cos θ / λ" on the Y axis, and the crystal lattice distortion (η) was calculated from the slope of the straight line obtained by the least squares method. βcosθ / λ=η×(2sinθ / λ)+(1 / Dc) (2) (β: integral width (rad), θ: Bragg angle (rad), η: crystal lattice strain, λ: X-ray wavelength, Dc: crystallite size (nm))

[0041] <Presence or absence of vacancy aggregate defects> (i) Preparation of transmission electron microscope (TEM) observation sample For the plate-shaped silicon nitride sintered body (thickness approximately 0.3 mm) produced in each example and comparative example, both surfaces were mechanically polished until the thickness was approximately 0.1 mm, and then 6 keV argon ions were irradiated until perforations were formed using an ion slicer "EM-09100IS" manufactured by JEOL Ltd., to prepare a TEM observation sample. (ii) TEM observation Using a transmission electron microscope "JEM-2100" manufactured by JEOL Ltd., 10 visual fields were observed at an acceleration voltage of 200 kV and an observation magnification of 2000 times. If dislocation loops or helical dislocations were observed in at least one of the 10 visual fields, it was evaluated as "there are particles containing dislocation loops and helical dislocations." If dislocation loops or helical dislocations were not observed in any of the 10 visual fields, it was evaluated as "there are no particles containing dislocation loops or helical dislocations."

[0042] <Solute oxygen concentration> The solute oxygen concentration of silicon nitride crystal grains constituting the silicon nitride sintered body was measured by secondary ion mass spectrometry (SIMS). The secondary ion mass spectrometer used was a "PHI ADEPT-1010" manufactured by ULVAC-PHI, Inc. The primary ions were Cs ＋ Use Cs ＋ The beam was focused to about 50 nm and irradiated onto the surface of the sample to generate secondary ions. The generated secondary ions were measured using a mass spectrometer to determine the dissolved oxygen concentration. The dissolved oxygen concentration was determined as follows: ３０ To Si １６ The relative sensitivity factor (RSF) of a standard sample implanted with O ions was determined.

[0043] In addition, since adsorbed oxygen exists on the sample surface, when quantifying the dissolved oxygen concentration by SIMS, the amount of dissolved oxygen in the sample excluding the adsorbed oxygen is １６ O / ３０ The Si intensity ratio is calculated. As a method for calculating the dissolved oxygen concentration in a sample by removing the influence of adsorbed oxygen, the method described in JP 2018-24548 A can be referred to.

[0044] <Average Particle Diameter of Silicon Nitride Crystal Particles> (i) Preparation of Scanning Electron Microscope (SEM) Observation Samples The cross sections of the plate-shaped silicon nitride sintered bodies produced in each Example and Comparative Example were mechanically polished to a mirror finish to prepare SEM observation samples. (ii) SEM Observation Using a JEOL Ltd. scanning electron microscope "JCM-7000," 5 fields of view per sample were observed at an acceleration voltage of 15 kV and an observation magnification of 5000x, and particle images of 300 or more silicon nitride crystal particles were obtained. The 300 or more particle images were analyzed using an image analyzer attached to the SEM device, and the area-equivalent circle diameter of each particle was determined. Then, a weighted average particle diameter based on the volume-based distribution of the area-equivalent circle diameters was calculated. The weighted average particle diameter based on the volume-based distribution can be calculated using the following formula: Weighted average particle diameter based on volume-based distribution = Σ(area-equivalent circle diameter^4) / Σ(area-equivalent circle diameter^3)

[0045] <Evaluation of Temperature Cycle Characteristics> The plate-shaped silicon nitride sintered bodies (approximately 0.3 mm thick) produced in each Example and Comparative Example were used as silicon nitride substrates and evaluated as follows. A copper plate was bonded to each silicon nitride substrate using an active metal brazing material. Two copper plates measuring 20 mm long x 15 mm wide x 1.0 mm thick were provided on the front side of each silicon nitride substrate. Furthermore, one copper plate measuring 45 mm long x 35 mm wide x 1.0 mm thick was provided on the back side of each silicon nitride sintered body. The active metal brazing material used was composed of Ag (57 wt%), Cu (30 wt%), Sn (10 wt%), and Ti (3 wt%). An active metal brazing material paste was applied to the silicon nitride substrate to a thickness of 40 μm, and a copper plate was placed on the active metal brazing material paste. Next, the silicon nitride substrates were heated in a vacuum (1000 rpm) at 820°C. －２ The thermal bonding process was carried out at a pressure of 100 Pa or less. Copper plates were bonded to both sides of the silicon nitride substrate. The sides of the copper plates were etched to form 80° inclined surfaces. The active metal brazing material layer was allowed to protrude 40 μm from the sides of the copper plates. The temperature cycle characteristics of the obtained silicon nitride circuit substrate were evaluated. Specifically, one cycle consisted of -40°C x 30 minutes → room temperature (25°C) x 10 minutes → 200°C x 30 minutes → room temperature (25°C) x 10 minutes, and the silicon nitride substrate was examined for cracks after 4,000 cycles. The presence or absence of cracks was measured using a fluorescent flaw detection method.

[0046] The following materials were used as raw materials for producing sintered silicon nitride: <Silicon nitride powder> Silicon nitride powder: silicon nitride powder with an average particle size of 0.95 μm produced by combustion synthesis.

[0047] <Sintering aid> Metal oxide: yttria (Y ２ O ３ ) Carbonitride compounds containing rare earth elements: Y ２ Si ４ N ６ C It was prepared by thermal synthesis using the following reaction formula: 8Si ３ N ４ +6Y ２ O ３ +15C+2N ２ →6Y ２ Si ４ N ６ C+9CO ２ Carbonitride compounds containing magnesium element: MgSi ４ N ６ C was prepared by thermal synthesis using the following reaction formula: Si ３ N ４ + MgSiN ２ + C → MgSi ４ N ６ C

[0048] Example 1: 100 parts by mass of silicon nitride powder was mixed with Y as a sintering aid. ２ O ３ 3 parts by mass of Y ２ Si ４ N ６ 2 parts by mass of C, MgSi ４ N ６Six parts by mass of C were added and mixed in a planetary ball mill to obtain a mixed raw material. Next, the mixed raw material was subjected to uniaxial press molding and CIP molding to produce a molded body, which was then introduced into a sintering furnace and sintered under a nitrogen atmosphere at atmospheric pressure. The sintering was carried out under conditions of a maximum temperature of 1760°C and a holding time at the maximum temperature of 10 hours. The material was then cooled from the maximum temperature to 1000°C at a cooling rate of 0.5°C / min. The furnace pressure was set to 200 kPa. The material was then naturally cooled from 1000°C to room temperature to obtain a silicon nitride sintered body. Table 1 shows the evaluation results of the silicon nitride sintered body thus produced.

[0049] Examples 2 to 5, Comparative Examples 1 and 2 Silicon nitride sintered bodies were produced in the same manner as in Example 1, except that the firing conditions were changed as shown in Table 1. Table 1 shows the results of various evaluations of the produced silicon nitride sintered bodies.

[0050]

[0051] As shown in Table 1, the silicon nitride sintered bodies of each Example, which had a crystal lattice distortion of less than 0.003, did not develop cracks in the silicon nitride substrate after the temperature cycle test. On the other hand, the silicon nitride sintered bodies of each Comparative Example, which had a crystal lattice distortion of 0.003 or more, developed cracks in the silicon nitride substrate after the temperature cycle test. The silicon nitride sintered body of the present invention has excellent temperature cycle characteristics and can be used to form highly reliable silicon nitride circuit boards.

Claims

1. A silicon nitride sintered body, characterized in that the crystal lattice distortion of silicon nitride crystal grains constituting the silicon nitride sintered body is less than 0.

003.

2. The silicon nitride sintered body according to claim 1, wherein the silicon nitride crystal grains have a dissolved oxygen concentration of less than 500 ppm.

3. The silicon nitride sintered body according to claim 1, wherein the average particle size of the silicon nitride crystal grains is 1 to 15 μm.

4. The silicon nitride sintered body according to any one of claims 1 to 3, which is a heat dissipation substrate.

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