Cubic boron nitride sintered body and heat sink using the same

Abstract

The present invention relates to a cubic boron nitride sintered body, comprising 90.0% to 99.5% by mass of cubic boron nitride and 0.5% to 10.0% by mass of silicon, wherein the total content of the cubic boron nitride and silicon is 94.0% to 100% by mass.

Description

Technical Field

[0001] This invention relates to a cubic boron nitride sintered body and a heat sink using the same. Prior Technology

[0002] As an environmental issue, the demand for solar and wind power generation, electric vehicles, and other technologies is constantly expanding in order to reduce greenhouse gas emissions. These systems utilize power semiconductors. The materials used in power semiconductors are shifting from the currently mainstream silicon (Si) to higher-performance silicon carbide (SiC) or gallium nitride (GaN). These power semiconductors employ heat sinks to facilitate heat dissipation.

[0003] Cubic boron nitride (hereinafter, also denoted as cBN) has a thermal conductivity second only to diamond. Furthermore, cubic boron nitride has a coefficient of thermal expansion close to that of power semiconductors, thus making it an insulating material. Therefore, cubic boron nitride is suitable as a material for heat sinks. Summary of the Invention

[0004] This invention relates to a cubic boron nitride sintered body, comprising 90.0% to 99.5% by mass of cubic boron nitride and 0.5% to 10.0% by mass of silicon, and... The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0005] The present invention is a heat sink using the above-mentioned cubic boron nitride sintered body. Implementation

[0006] [The problem that this invention aims to solve] Previously, when cubic boron nitride was applied to heat sinks, a cubic boron nitride sintered body was used. This cubic boron nitride sintering system was formed by sintering cubic boron nitride particles using a bonding material. However, the bonding material became a major cause of the decrease in thermal conductivity.

[0007] Therefore, the object of the present invention is to provide a cubic boron nitride sintered body with high thermal conductivity and a coefficient of thermal expansion close to that of a power semiconductor; and a heat sink with high thermal conductivity and a coefficient of thermal expansion close to that of a power semiconductor.

[0008] [Effects of the Invention] According to the present invention, a cubic boron nitride sintered body having high thermal conductivity and a coefficient of thermal expansion close to that of a power semiconductor can be provided; and a heat sink having high thermal conductivity and a coefficient of thermal expansion close to that of a power semiconductor can be provided.

[0009] [Description of Embodiments of the Invention] First, the embodiments of the present invention will be described. (1) This invention relates to a cubic boron nitride sintered body, comprising 90.0% to 99.5% by mass of cubic boron nitride and 0.5% to 10.0% by mass of silicon, and The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0010] According to the present invention, a cubic boron nitride sintered body having high thermal conductivity and a coefficient of thermal expansion close to that of a power semiconductor can be provided.

[0011] (2) Preferably, the cubic boron nitride sintered body contains carbon, and The carbon content is between 0.10% and 5.00% by mass. This improves the thermal conductivity of the cubic boron nitride sintered body and allows its coefficient of thermal expansion to approach that of power semiconductors.

[0012] (3) Preferably, at least a portion of the carbon is diamond. This improves the thermal conductivity of the cubic boron nitride sintered body and allows the coefficient of thermal expansion to approach that of power semiconductors.

[0013] (4) Preferably, the above-mentioned cubic boron nitride sintered body contains aluminum, and The aluminum content is between 0.01% and 5.00% by mass. This improves the thermal conductivity of the cubic boron nitride sintered body.

[0014] (5) Preferably, the above-mentioned cubic boron nitride sintered body contains a plurality of grains comprising cubic boron nitride. The median grain size d50 of the aforementioned grains is greater than 1.0 μm. This improves the thermal conductivity of the cubic boron nitride sintered body.

[0015] (6) Preferably, the thermal conductivity of the cubic boron nitride sintered body is 300 W / mK or higher. Thus, the cubic boron nitride sintered body has high thermal conductivity.

[0016] (7) Preferably, the coefficient of thermal expansion of the cubic boron nitride sintered body is 4.0 × 10⁻⁶ / K or more and 6.0 × 10⁻⁶ / K or less. Thereby, the cubic boron nitride sintered body has a coefficient of thermal expansion close to that of a power semiconductor.

[0017] (8) Preferably, the dislocation density of the cubic boron nitride is 1×10¹⁶ / m² or less. This improves the thermal conductivity of the cubic boron nitride sintered body.

[0018] (9) Preferably, the above-mentioned dislocation density is calculated using the modified Williamson-Hall method and the modified Warren-Averbach method.

[0019] (10) Preferably, the above-mentioned misalignment density is measured using radioactive light as an X-ray source.

[0020] (11) The present invention relates to a heat sink using the above-described cubic boron nitride sintered body. According to the present invention, a heat sink having high thermal conductivity and a coefficient of thermal expansion close to that of a power semiconductor can be provided.

[0021] [Details of the embodiments of the present invention] The following describes specific examples of the cubic boron nitride sintered body and heat sink of the present invention.

[0022] In this specification, the expression "A~B" refers to the upper and lower limits of the range (i.e., above A and below B). When A does not specify a unit but only B specifies a unit, the unit of A is the same as the unit of B.

[0023] In this specification, power semiconductors refer to semiconductors made of silicon carbide (SiC) or gallium nitride (GaN). The coefficient of thermal expansion of SiC is 4.0~5.0×10⁻⁶ / K, and that of GaN is 5.5~6.0×10⁻⁶ / K. Therefore, in this specification, the coefficient of thermal expansion of power semiconductors refers to 4.0~6.0×10⁻⁶ / K.

[0024] [Implementation Method 1: Cubic Boron Nitride Sintered Body] One embodiment of the present invention (hereinafter also referred to as "this embodiment") is a cubic boron nitride sintered body, comprising 90.0% to 99.5% by mass of cubic boron nitride and 0.5% to 10.0% by mass of silicon, and The total content of the cubic boron nitride and the silicon is more than 94.0% by mass and less than 100% by mass.

[0025] The cubic boron nitride sintered body of this embodiment can have high thermal conductivity and a coefficient of thermal expansion close to that of power semiconductors. The reason for this is speculated to be as described in (i) to (iv) below.

[0026] (i) The cubic boron nitride sintered body of this embodiment contains 90.0% to 99.5% by mass of cubic boron nitride with high thermal conductivity. Therefore, the cubic boron nitride sintered body can have high thermal conductivity.

[0027] (ii) In the cubic boron nitride sintered body of this embodiment, the total content of cubic boron nitride (thermal expansion coefficient: approximately 3.0~4.0×10⁻⁶ / K) and silicon (thermal expansion coefficient: approximately 4.0×10⁻⁶ / K), which have a thermal expansion coefficient close to that of power semiconductors, is 94.0% by mass and less than 100% by mass. Therefore, this cubic boron nitride sintered body can have a thermal expansion coefficient close to that of power semiconductors.

[0028] (iii) In this embodiment, a portion of the silicon in the cubic boron nitride sintered body reacts with the carbon in the cubic boron nitride to form silicon carbide (SiC). Since silicon carbide is a material with excellent oxidation resistance, if silicon carbide is present between or near the cubic boron nitride particles, oxygen, as an unavoidable impurity, will not enter between the cubic boron nitride particles, thus suppressing the formation of oxides that hinder the bonding between the cubic boron nitride particles. Therefore, the bonding force between the cubic boron nitride particles is improved, and the cubic boron nitride sintered body can have high thermal conductivity. Furthermore, the coefficient of thermal expansion of silicon carbide is the same as or similar to that of power semiconductors. Therefore, this cubic boron nitride sintered body can have a coefficient of thermal expansion close to that of power semiconductors. Moreover, as long as this effect is observed, the cubic boron nitride sintered body of this embodiment may or may not contain silicon carbide.

[0029] (iv) In a cubic boron nitride sintered body, when oxygen, as an unavoidable impurity, is present on the surface of cubic boron nitride particles, i.e., between the cubic boron nitride particles, there is a tendency for the bonding force between the cubic boron nitride particles to decrease. In this embodiment, a portion of the silicon contained in the cubic boron nitride combines with this oxygen to form silicon oxide (SiO2). In this case, the oxygen present on the surface of the cubic boron nitride particles, i.e. between the cubic boron nitride particles, is reduced, the decrease in the bonding force between the cubic boron nitride particles is suppressed, and the thermal conductivity of the cubic boron nitride sintered body is improved. Furthermore, as long as this effect is exhibited, the cubic boron nitride sintered body of this embodiment may or may not contain silicon oxide.

[0030] <Composition> The cubic boron nitride sintered body of this embodiment comprises 90.0% to 99.5% by mass of cubic boron nitride and 0.5% to 10.0% by mass of silicon, wherein the total content of the cubic boron nitride and the silicon is 94.0% to 100% by mass. The cubic boron nitride sintered body of this embodiment may contain unavoidable impurities arising from the raw materials used, manufacturing conditions, etc. The content (by mass%) of unavoidable impurities in the cubic boron nitride sintered body is preferably 0% to 1% by mass, and more preferably 0% to 0.1% by mass. The cubic boron nitride sintered body of this embodiment may contain cubic boron nitride particles, silicon, and unavoidable impurities. The cubic boron nitride sintered body of this embodiment may contain cubic boron nitride particles, silicon, carbon, and unavoidable impurities. The cubic boron nitride sintered body of this embodiment may contain cubic boron nitride particles, silicon, aluminum, and unavoidable impurities.

[0031] <Content of cubic boron nitride> The lower limit of the cubic boron nitride content in the cubic boron nitride sintered body is 90.0% by mass or more, preferably 91.0% by mass or more, more preferably 92.0% by mass or more, and even more preferably 93.0% by mass or more. The upper limit of the cubic boron nitride content in the cubic boron nitride sintered body is 99.5% by mass or less, preferably 99.0% by mass or less, more preferably 98.0% by mass or less, and even more preferably 97.0% by mass or less. The cubic boron nitride content in the cubic boron nitride sintered body is 90.0% by mass or more and 99.5% by mass or less, preferably 91.0% by mass or more and 99.0% by mass or less, more preferably 92.0% by mass or more and 98.0% by mass or less, and even more preferably 93.0% by mass or more and 97.0% by mass or less.

[0032] The content (mass%) of cubic boron nitride in the cubic boron nitride sintered body was determined using methods (A1) to (F1) below. The following methods can be performed using an energy dispersive X-ray analyzer (EDX) attached to a scanning electron microscope (SEM) (JSM-7800F (trade name) manufactured by Nippon Electron Ltd.) (OXFORD X-MAX80 EDS (Energy Dispersive Spectroscopy) system) (hereinafter also referred to as "SEM-EDX").

[0033] (A1) A sample containing a cross-section of a cubic boron nitride sintered body is prepared by cutting at any position on the cubic boron nitride sintered body. The cross-section is prepared using a focused ion beam device or a cross-section polishing device, etc.

[0034] (B1) The cross-section was observed using SEM at 5000x magnification to obtain a reflectance electron image. In the reflectance electron image, the black areas represent the regions where cubic boron nitride is present. The gray and white areas represent the regions where components other than cubic boron nitride (silicon, carbon, aluminum, unavoidable impurities, etc.) are present. The presence of cubic boron nitride in the black areas and components other than cubic boron nitride in the gray and white areas of the reflectance electron image can be confirmed by elemental analysis of the same observation areas of the cubic boron nitride sintered body using SEM-EDX.

[0035] (C1) Next, the reflected electron image was binarized using image analysis software (WinROOF of Mitani Corporation). During binarization, when the reflected electron image was captured, the image contrast value was divided into 256 (low contrast: 0, high contrast: 255), and the contrast value of the region containing cubic boron nitride, as specified above, was set to be below 30. This allows the region containing cubic boron nitride to be extracted.

[0036] (D1) A measurement region of 12 μm × 9 μm is set in the binarized image. The area ratio of the region containing cubic boron nitride in this measurement region is calculated. By treating the calculated area ratio as a volume percentage, the cubic boron nitride content (volume percentage) of the cubic boron nitride sintered body can be determined. If the threshold setting in the above binarization process is performed, the cubic boron nitride content of the cubic boron nitride sintered body will not differ as long as the same field of view is measured.

[0037] (E1) Using Archimedes' principle, the density ρ1 of the cubic boron nitride sintered body described above was determined. The density ρ1 of the cubic boron nitride sintered body is expressed by the following formula. ρ 1=M×(ρ 0-d) / (AB)+d In the above formula, ρ1 is the density of the cubic boron nitride sintered body (g / cm3), A is the weight in air (g), B is the weight in liquid (g), ρ0 is the density of the liquid (g / cm3), and d is the density of air (0.001 g / cm3).

[0038] (F1) Based on the measured cubic boron nitride content q (volume %), density ρ2 (g / cm3, specifically 3.45 g / cm3), and density ρ1 (g / cm3) of the cubic boron nitride sintered body, the cubic boron nitride content (mass %) of the cubic boron nitride sintered body is calculated. The cubic boron nitride content (mass %) of the cubic boron nitride sintered body is expressed by the following formula. The content (mass%) of cubic boron nitride in the sintered cubic boron nitride body = q × ρ² / ρ¹

[0039] <Silicone content>

[0040] The silicon content of the cubic boron nitride sintered body is 0.5% by mass to 10.0% by mass. This allows the cubic boron nitride sintered body to possess a coefficient of thermal expansion close to that of power semiconductors. Furthermore, the increased bonding force between cBN particles results in high thermal conductivity in the cubic boron nitride sintered body.

[0041] In cubic boron nitride sintered bodies, silicon can exist either as elemental silicon or as silicon compounds formed by the reaction of silicon with other elements contained in the cubic boron nitride sintered body. In the case of elemental silicon, elements such as boron can still be present in elemental form within silicon. Examples of such silicon compounds include silicon boride (SiB₆), silicon nitride (SiN), silicon oxide (SiO₂), and silicon carbide (SiC). Furthermore, due to the high cost of silicon as a raw material, it was not previously used in cubic boron nitride sintered bodies at a content of more than 0.5% by mass.

[0042] The silicon content of the cubic boron nitride sintered body in this embodiment is at least 0.5% by mass, preferably at least 1.0% by mass, more preferably at least 2.0% by mass, and even more preferably at least 3.0% by mass. The silicon content of the cubic boron nitride sintered body is at least 10.0% by mass, preferably at least 9.0% by mass, more preferably at least 8.0% by mass, and even more preferably at least 7.0% by mass. The silicon content of the cubic boron nitride sintered body is at least 0.5% by mass and at least 10.0% by mass, preferably at least 1.0% by mass and at least 9.0% by mass, more preferably at least 2.0% by mass and at least 8.0% by mass, and even more preferably at least 3.0% by mass and at least 7.0% by mass.

[0043] The silicon content of the cubic boron nitride sintered body was determined using an electron probe microanalyzer (EPMA). The measuring equipment and conditions are shown below. Equipment: JXA-8530F manufactured by Nippon Electronics Co., Ltd. Measurement conditions: accelerating voltage 15 kV

[0044] <Carbon content> The cubic boron nitride sintered body of this embodiment preferably contains carbon, with a carbon content of 0.10% by mass to 5.00% by mass. A portion of the carbon in the cubic boron nitride sintered body reacts with silicon to form silicon carbide (SiC). Since silicon carbide is a material with excellent oxidation resistance, if silicon carbide is present between or near the cubic boron nitride particles, oxygen, as an unavoidable impurity, will not enter between the cubic boron nitride particles, thus suppressing the formation of oxides that hinder the bonding between the cubic boron nitride particles. If the cubic boron nitride sintered body contains carbon within the above-mentioned range, the bonding force between the cubic boron nitride particles is improved, and the cubic boron nitride sintered body can have high thermal conductivity. Furthermore, the coefficient of thermal expansion of SiC is the same as or similar to that of power semiconductors. Therefore, this cubic boron nitride sintered body can have a coefficient of thermal expansion close to that of power semiconductors.

[0045] The lower limit of the carbon content in the cubic boron nitride sintered body is preferably 0.10% by mass or more, more preferably 1.00% by mass or more, and even more preferably 2.00% by mass or more. The upper limit of the carbon content in the cubic boron nitride sintered body is preferably 5.00% by mass or less, more preferably 4.50% by mass or less, and even more preferably 4.00% by mass or less. The carbon content in the cubic boron nitride sintered body is preferably 0.10% by mass or more and 5.00% by mass or less, more preferably 1.00% by mass or more and 4.50% by mass or less, and even more preferably 2.00% by mass or more and 4.00% by mass or less.

[0046] Preferably, at least a portion of the aforementioned carbon is diamond. This improves the thermal conductivity of the cubic boron nitride sintered body and allows its coefficient of thermal expansion to approach that of power semiconductors. The aforementioned carbon may be partially or entirely composed of diamond.

[0047] In the cubic boron nitride of this embodiment, the median diameter d50 (hereinafter also referred to as "diameter d50") of the diamond is preferably 1.0 μm or more. This improves the thermal conductivity of the cubic boron nitride sintered body. In this specification, the median diameter d50 refers to the diameter at which the cumulative frequency of a number of diamonds reaches 50%.

[0048] The lower limit of the circumferential diameter d50 of the aforementioned diamond is preferably 1.0 μm or more, preferably 2.0 μm or more, preferably 3.0 μm or more, preferably 5.0 μm or more, preferably 7.0 μm or more, and preferably 8.0 μm or more. The larger the circumferential diameter d50 of the aforementioned diamond, the higher the thermal conductivity; therefore, there is no particular limitation, but from a manufacturing point of view, it can be set to 100 μm or less. The circumferential diameter d50 of the aforementioned diamond is preferably 1.0 μm or more and 100 μm or less, preferably 2.0 μm or more and 100 μm or less, preferably 3.0 μm or more and 100 μm or less, preferably 5.0 μm or more and 100 μm or less, preferably 7.0 μm or more and 100 μm or less, and preferably 8.0 μm or more and 100 μm or less.

[0049] In this specification, the d50 of the diamond equivalent diameter contained in cubic boron nitride is determined by the following procedure.

[0050] Using the same method (A1) to (C1) as the method for determining the content (mass%) of cubic boron nitride in the cubic boron nitride sintered body described above, a binarized image of the cubic boron nitride sintered body was obtained.

[0051] A measurement field of 12 μm × 9 μm was set in the binarized image. With the grain boundaries of the diamond observed within this measurement field of view separated, the distribution of the diamond's circular equivalent diameter was measured using the aforementioned image processing software. Five measurement fields were arbitrarily set.

[0052] Based on the above distribution of the diamond's equivalent diameter, the total number of diamonds within the measurement field of view is used as the denominator to calculate the d50 of the diamond's equivalent diameter. The d50 of the diamond's equivalent diameter is calculated for each of the five measurement fields, and their average value is then determined. This average value corresponds to the d50 of the diamond's equivalent diameter contained in cubic boron nitride.

[0053] In the applicant's measurements, as long as the d50 of the diamond circle is measured on the same sample, even if the selected location of the measurement field of view in the cubic boron nitride sintered body is changed and the calculation is repeated multiple times, the measurement results are almost identical, confirming that the measurement results will not change arbitrarily even if the measurement field of view is set arbitrarily.

[0054] <Aluminum content> The cubic boron nitride sintered body of this embodiment preferably contains aluminum, with an aluminum content of 0.01% by mass or more and 5.00% by mass or less. In the cubic boron nitride sintered body, when oxygen, as an unavoidable impurity, is present on the surface of the cubic boron nitride particles, i.e., between the cubic boron nitride particles, there is a tendency for the bonding force between the cubic boron nitride particles to decrease. If the cubic boron nitride contains aluminum, a portion of the aluminum may combine with the aforementioned oxygen to form aluminum oxide (Al₂O₃). In this case, the oxygen present on the surface of the cubic boron nitride particles, i.e., between the cubic boron nitride particles, is reduced, the decrease in the bonding force between the cubic boron nitride particles is suppressed, and the thermal conductivity of the cubic boron nitride sintered body is improved.

[0055] In cubic boron nitride sintered bodies, a portion of the aluminum reacts with the nitrogen or silicon contained within the body to form aluminum nitride (AlN) or aluminum silicon carbide (Al₄SiC₄). Since aluminum nitride or aluminum silicon carbide are highly resistant to oxidation, the presence of aluminum nitride or aluminum silicon carbide between or near cubic boron nitride particles prevents oxygen, an unavoidable impurity, from entering the spaces between the particles, thus inhibiting the formation of oxides that hinder the bonding between the particles. Therefore, the bonding strength between cubic boron nitride particles is increased, resulting in a cubic boron nitride sintered body with high thermal conductivity.

[0056] In some cases, a portion of the aluminum contained in the cubic boron nitride sintered body can react with the boron contained in the cubic boron nitride sintered body to form aluminum boride (AlB2, AlB12).

[0057] <Unavoidable Impurities> The cubic boron nitride sintered body of the present invention may contain unavoidable impurities within the scope of demonstrating the effects of the present invention. Examples of unavoidable impurities include hydrogen, oxygen, lithium (Li), sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg). The content of unavoidable impurities in the cubic boron nitride sintered body is preferably 0% by mass or more and 1% by mass or less, and more preferably 0% by mass or more and 0.1% by mass or less. The content of unavoidable impurities can be determined by secondary ion mass spectrometry (SIMS).

[0058] <The equivalent diameters of the grain circle are d50 and d90> In this embodiment of the cubic boron nitride sintered body, the cubic boron nitride sintered body contains a plurality of grains comprising cubic boron nitride, and the median grain diameter d50 (hereinafter also referred to as "d50 of the circle equivalent diameter") of the grains is preferably 1.0 μm or more. This improves the thermal conductivity of the cubic boron nitride sintered body. In this specification, the median grain diameter d50 of the circle equivalent diameter refers to the circle equivalent diameter whose frequency, based on a number basis, accumulates to 50%.

[0059] The lower limit of the circumference-equivalent diameter d50 of the aforementioned grains is preferably 1.0 μm or more, preferably 2.0 μm or more, preferably 3.0 μm or more, preferably 5.0 μm or more, preferably 7.0 μm or more, and preferably 8.0 μm or more. The larger the circumference-equivalent diameter d50 of the aforementioned grains, the higher the thermal conductivity; therefore, there is no particular limitation, but from a manufacturing point of view, it can be set to 100 μm or less. The circumference-equivalent diameter d50 of the aforementioned grains is preferably 1.0 μm or more and 100 μm or less, preferably 2.0 μm or more and 100 μm or less, preferably 3.0 μm or more and 100 μm or less, preferably 5.0 μm or more and 100 μm or less, preferably 7.0 μm or more and 100 μm or less, and preferably 8.0 μm or more and 100 μm or less.

[0060] In the cubic boron nitride sintered body of this embodiment, the cubic boron nitride preferably comprises a plurality of grains, and the d90 of the circular equivalent diameter of these grains is 1.2 μm or more. This improves the thermal conductivity of the cubic boron nitride sintered body. In this specification, the d90 of the circular equivalent diameter of the grains refers to the 90% circular equivalent diameter obtained by accumulating the frequency of a number of grains.

[0061] The lower limit of the circumference diameter (d90) of the aforementioned grains is preferably 1.2 μm or more, and more preferably 3.6 μm or more. A larger circumference diameter (d90) of the aforementioned grains results in higher thermal conductivity; therefore, there is no particular limitation, but from a manufacturing point of view, it can be set to 150 μm or less. The circumference diameter (d90) of the aforementioned grains is preferably 1.2 μm or more and 150 μm or less, more preferably 3.6 μm or more and 150 μm or less.

[0062] In this specification, the d50 and d90 of the circular equivalent diameters of the plurality of grains contained in cubic boron nitride are determined by the following procedure.

[0063] Using the same method (A1) to (C1) as the method for determining the content (mass%) of cubic boron nitride in the cubic boron nitride sintered body described above, a binarized image of the cubic boron nitride sintered body was obtained.

[0064] A measurement field of 12 μm × 9 μm was set in the binarized image. With the grain boundaries of the cubic boron nitride grains observed within this measurement field of view separated, the distribution of the circular equivalent diameter of the grains was measured using the aforementioned image processing software. Five measurement fields were arbitrarily set.

[0065] Based on the distribution of the equivalent diameter of the grains described above, the total number of grains within the measurement field of view is used as the denominator to calculate the d50 of the equivalent diameter of the grains. The d50 of the equivalent diameter of the grains is calculated in each of the five measurement fields, and their average value is then determined. This average value corresponds to the d50 of the equivalent diameter of the plurality of grains contained in cubic boron nitride.

[0066] Based on the distribution of the equivalent diameter of the grains described above, the number of all grains within the measurement field of view is used as the denominator to calculate the d90 of the equivalent diameter of the grains. The d90 of the equivalent diameter of the grains is calculated in each of the five measurement fields, and their average value is then determined. This average value corresponds to the d90 of the equivalent diameter of the plurality of grains contained in the cubic boron nitride sintered body.

[0067] In the applicant's measurements, as long as the circumference diameters d50 and d90 of the grains of the same sample are measured, even if the selected location of the measurement field of view in the cubic boron nitride sintered body is changed and the calculation is repeated multiple times, the measurement results are almost identical, confirming that the measurement results will not change arbitrarily even if the measurement field of view is set arbitrarily.

[0068] The crystal grains containing cubic boron nitride can be simple cubic boron nitride without impurity elements, or they can contain unavoidable impurities in addition to cubic boron nitride, within the scope of exhibiting the effects of the present invention. The content of unavoidable impurities in the crystal grains is preferably 0% by mass or more and 0.1% by mass or less. The content of unavoidable impurities is determined by ICP emission spectroscopy (inductively coupled plasma) (measuring device: Shimadzu Corporation's "ICPS-8100" (trademark)).

[0069] Thermal conductivity The lower limit of the thermal conductivity of the cubic boron nitride sintered body in this embodiment is preferably 290 W / mK or higher, more preferably 300 W / mK or higher, and even more preferably 500 W / mK or higher. The upper limit of the thermal conductivity of the cubic boron nitride sintered body is not particularly limited; for example, it can be set to 2000 W / mK or lower. The thermal conductivity of the cubic boron nitride sintered body is preferably 290 W / mK or higher and 2000 W / mK or lower, more preferably 300 W / mK or higher and 2000 W / mK or lower, more preferably 400 W / mK or higher and 2000 W / mK or lower, and even more preferably 500 W / mK or higher and 2000 W / mK or lower.

[0070] In this specification, the thermal conductivity of the cubic boron nitride sintered body is obtained by measuring the thermal diffusivity using a xenon flash lamp laser flash method and converting the thermal diffusivity into thermal conductivity. The measurement temperature is set to 25°C. The measuring apparatus can be the "LFA467 Hyper Flash" (trademark) manufactured by NETZSCH. The following conditions (a) to (c) are used when performing the above conversion. (a) Thermal conductivity = thermal diffusivity × specific heat × density; (b) The density of cubic boron nitride is 3.45 g / cm³, and its specific heat is 0.6 J / mol; (c) The content of cubic boron nitride in the cubic boron nitride sintered body is considered to be 100% by mass.

[0071] Coefficient of thermal expansion The coefficient of thermal expansion of the cubic boron nitride sintered body in this embodiment is preferably 4.0 × 10⁻⁶ / K or higher and 6.0 × 10⁻⁶ / K or lower. Therefore, the cubic boron nitride sintered body can have a coefficient of thermal expansion close to that of power semiconductors.

[0072] The lower limit of the coefficient of thermal expansion of the cubic boron nitride sintered body in this embodiment is preferably 4.0 × 10⁻⁶ / K or higher, more preferably 4.3 × 10⁻⁶ / K or higher, and even more preferably 4.5 × 10⁻⁶ / K or higher. The upper limit of the coefficient of thermal expansion of the cubic boron nitride sintered body is preferably 6.0 × 10⁻⁶ / K or lower, more preferably 5.8 × 10⁻⁶ / K or lower, and even more preferably 5.5 × 10⁻⁶ / K or lower. The coefficient of thermal expansion of the cubic boron nitride sintered body is preferably 4.0 × 10⁻⁶ / K or higher and 6.0 × 10⁻⁶ / K or lower, preferably 4.3 × 10⁻⁶ / K or higher and 6.0 × 10⁻⁶ / K or lower, preferably 4.5 × 10⁻⁶ / K or higher and 6.0 × 10⁻⁶ / K or lower, preferably 4.0 × 10⁻⁶ / K or higher and 5.8 × 10⁻⁶ / K or lower, preferably 4.3 × 10⁻⁶ / K or higher and 5.8 × 10⁻⁶ / K or lower, preferably 4.5 × 10⁻⁶ / K or higher and 5.8 × 10⁻⁶ / K or lower, preferably 4.0 × 10⁻⁶ / K or higher and 5.5 × 10⁻⁶ / K or lower, and preferably 4.5 × 10⁻⁶ / K or higher and 5.5 × 10⁻⁶ / K or lower. -6 / K or below.

[0073] In this specification, the coefficient of thermal expansion of the cubic boron nitride sintered body was measured using a commercially available measuring instrument (NETZSCH DIL 402C (trademark)). The measurement temperature range was set to 25℃~500℃.

[0074] <Dislocation Density> In this embodiment, the dislocation density of cubic boron nitride is preferably below 1 × 10¹⁶ / m². This improves the thermal conductivity of the sintered cubic boron nitride body.

[0075] The upper limit of the dislocation density of cubic boron nitride is preferably 1×10¹⁶ / m² or less, more preferably 9×10¹⁵ / m² or less, and even more preferably 8×10¹⁵ / m² or less. The lower limit of the dislocation density of the cubic boron nitride sintered body is not particularly limited, but from a manufacturing point of view, it can be set to 1×10¹⁵ / m² or more. The dislocation density of the cubic boron nitride sintered body is preferably 1×10¹⁵ / m² or more and 1×10¹⁶ / m² or less, more preferably 1×10¹⁵ / m² or more and 9×10¹⁵ / m² or less, and even more preferably 1×10¹⁵ / m² or more and 8×10¹⁵ / m² or less.

[0076] In this specification, the dislocation density of cubic boron nitride is calculated using the following procedure. A specimen containing a sintered cubic boron nitride body is prepared. The specimen has dimensions of 2.0 mm × 2.0 mm (observation surface) and a thickness of 1.0 mm. The observation surface of the specimen is ground using a diamond grinding stone.

[0077] X-ray diffraction measurements were performed on the observation surface of the sample under the following conditions to obtain the spectral profiles of diffraction peaks from the main orientations (111), (200), (220), (311), (400), and (331) of cubic boron nitride.

[0078] (X-ray diffraction measurement conditions) X-ray source: radiation light Device requirements: Detector NaI (fluorescence cutoff achieved using a suitable ROI (Region of Interest)). Energy: 18 keV (wavelength: 0.6888 Å) Spectroscopic crystal: Si(111) Entrance slit: 5 mm wide × 0.5 mm high Light-receiving slit: Double slit (3 mm width × 0.5 mm height) Mirror: Platinum-coated mirror Angle of incidence: 2.5 mrad Scanning method: 2θ~θ scan Peaks were measured for cubic boron nitride at (111), (200), (220), (311), (400), and (331). Peaks with surface indices were excluded when the contour could not be obtained based on texture and orientation.

[0079] Measurement conditions: Set at least 9 measurement points within the half-width. Set the peak intensity to at least 2000 counts. Since the lower edge of the peak is also used for analysis, the measurement range is set to approximately 10 times the half-width.

[0080] The spectral profile obtained by the above-described X-ray diffraction measurement comprises both the true extension caused by physical quantities such as the non-uniform strain of the sample and the extension generated by the device. To determine the non-uniform strain or crystallite size, the component generated by the device is removed from the measured spectral profile to obtain the true spectral profile. The true spectral profile is obtained by fitting the obtained spectral profile and the spectral profile generated by the device using a pseudo-Voigt function, and then subtracting the spectral profile generated by the device. LaB 6 is used as a standard sample for removing the diffraction extension generated by the device. Furthermore, when using radiation with high parallelism, the diffraction extension generated by the device can be considered as zero.

[0081] The error density is calculated by analyzing the obtained true spectral profiles using the modified Williamson-Hall method and the modified Warren-Averbach method. The modified Williamson-Hall method and the modified Warren-Averbach method are well-known analytical methods for determining error density of spectral profiles.

[0082] The modified Williamson-Hall method is shown in equation (I) below.

[0083] [Number 1]

[0084] (In the above formula (I), ΔK represents the half-width of the spectral profile, D represents the crystallite size, M represents the configuration parameter, b represents the Burgers vector, ρ represents the dislocation density, K represents the scattering vector, O(K 2C) represents the higher-order term of K 2C, and C represents the average value of the contrast factor). In the above formula (I), C is as shown in the following formula (II).

[0085] C=C h00[1-q(h 2k 2+h 2l 2+k 2l 2) / (h 2+k 2+l 2) 2] (II) In equation (II) above, the contrast factor C h00 for spiral dislocation and edge dislocation, and the coefficient q related to the contrast factor, are calculated using the calculation code ANIZC, with the slip system as... <110> {111}, elastic stiffness C11 is 8.44 GPa, C12 is 1.9 GPa, and C44 is 4.83 GPa. The helical misalignment of the contrast factor Ch00 is 0.203, and the edge misalignment is 0.212. The coefficient q, which is related to the contrast factor, has a helical misalignment of 1.65 and an edge misalignment of 0.58. Furthermore, the helical misalignment ratio is fixed at 0.5, and the edge misalignment ratio is fixed at 0.5.

[0086] Furthermore, the relationship between misalignment and non-uniform strain is established by using a contrast factor C, which makes the following equation (III) hold true.

[0087] <ε(L) 2>=(ρCb 2 / 4π)ln(R e / L) (III) (In the above formula (III), Re represents the effective radius of the misalignment). Based on the relationship in equation (III) above and the Warren-Averbach equation, it can be expressed as equation (IV) below, and as a modified Warren-Averbach method, the mislocation density ρ and crystallite size can be determined.

[0088] lnA(L) = lnAS(L) - (πL 2ρb 2 / 2)ln(R e / L)(K 2C) + O(K 2C) 2(IV) (In the above formula (IV), A(L) represents the Fourier series, AS(L) represents the Fourier series related to the crystallite size, and L represents the Fourier length) Details of the modified Williamson-Hall method and the modified Warren-Averbach method are described in "T. Ungar and A. Borbely, "The effect of dislocation contrast on x-ray line broadening: A new approach to line profile analysis" Appl. Phys. Lett., vol.69, no.21, p.3173, 1996." and "T. Ungar, S. Ott, P. Sanders, A. Borbely, J. Weertman, "Dislocations, grain size and planar faults in nanostructured copper determined by high resolution X-ray diffraction and a new procedure of peak profile analysis" Acta Mater., vol.46, no.10, pp.3693-3699, 1998.".

[0089] <Manufacturing Method of Cubic Boron Nitride Sintered Body> The cubic boron nitride sintered body of this embodiment can be manufactured, for example, using the following method.

[0090] Raw material preparation steps Cubic boron nitride powder and silicon powder are prepared as raw materials. The cubic boron nitride powder preferably has a cubic boron nitride content (purity) of 99% or higher. The average particle size of the cubic boron nitride powder is preferably 2~10 μm. The silicon powder preferably has a purity of 99% or higher. The average particle size of the silicon powder is preferably 1~10 μm. In this specification, the average particle size of the raw material powder refers to the median particle size d50 of the spherical equivalent diameter. This average particle size is measured using a particle size distribution measuring device (trade name: MT3300EX) manufactured by Microtrac.

[0091] Graphite powder and / or diamond powder can be prepared as carbon sources. The purity of the graphite powder is preferably 99% or higher. The average particle size of the graphite powder is preferably 1–10 μm. The purity of the diamond powder is preferably 99% or higher. The average particle size of the diamond powder is preferably 2–10 μm.

[0092] Aluminum powder can be prepared as the aluminum source. The purity of the aluminum powder is preferably above 99%. The average particle size of the aluminum powder is preferably 10~100 μm.

[0093] Mixing Steps A mixed powder is obtained by mixing cubic boron nitride powder and silicon powder. When using graphite powder and / or aluminum powder, after mixing cubic boron nitride powder and silicon powder, graphite powder and / or aluminum powder are added and mixed to obtain the mixed powder. There are no particular limitations on the mixing method, but from the viewpoint of highly efficient and homogeneous mixing, ball mill mixing, bead mill mixing, planetary mill mixing, and jet mill mixing are preferred. Each mixing method can be wet or dry.

[0094] Sintering Steps Next, the mixed powder is sealed in a molybdenum sealed chamber, and the mixed powder is heated and pressurized using a multi-anvil high-pressure generator until the temperature reaches 1600~2600℃ and the pressure reaches 5~10 GPa, thereby obtaining a cubic boron nitride sintered body.

[0095] Under the aforementioned conditions of temperature (1600~2600℃) and pressure (5~10 Gpa), the holding time is preferably 10 minutes to 30 minutes. This reduces the dislocation density of the cubic boron nitride sintered body, increases the particle size of the cubic boron nitride particles, and improves the thermal conductivity of the cubic boron nitride sintered body.

[0096] [Implementation Method 2: Radiator] The heat sink in this embodiment uses the cubic boron nitride sintered body of Embodiment 1 described above. The heat sink of this embodiment can have high thermal conductivity and a coefficient of thermal expansion close to that of power semiconductors. Therefore, this heat sink can suppress the decrease in thermal conductivity that accompanies its use, and can extend the lifespan of the semiconductor.

[0097] [Postscript 1] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon, and carbon, and The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0098] [Postscript 2] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon, and aluminum, and The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0099] [Postscript 3] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon, carbon, and aluminum, and... The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0100] [Postscript 4] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon, and unavoidable impurities. The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0101] [Postscript 5] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon, carbon, and unavoidable impurities. The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0102] [Postscript 6] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon and aluminum, and unavoidable impurities. The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less.

[0103] [Postscript 7] The cubic boron nitride sintered body of the present invention preferably comprises 90.0% to 99.5% by mass of cubic boron nitride, 0.5% to 10.0% by mass of silicon carbide, aluminum, and unavoidable impurities. The total content of the above-mentioned cubic boron nitride and silicon is 94.0% by mass or more and 100% by mass or less. [Example]

[0104] This embodiment will be further described in detail through examples. However, this embodiment is not limited to these examples.

[0105] [Fabrication of Cubic Boron Nitride Sintered Bodies] Raw material preparation steps Cubic boron nitride powder (denoted as cBN powder in Table 1), silicon powder, graphite powder (denoted as Gr powder in Table 1), diamond powder, and aluminum powder (denoted as Al powder in Table 1) were prepared as raw materials for the cubic boron nitride sintered bodies of each sample. Graphite powder, diamond powder, and aluminum powder were used for samples in Table 1 where "Gr powder," "diamond powder," and "Al powder" were marked as "present."

[0106] The purity of the cubic boron nitride powder was 99%. The average particle size of the cubic boron nitride powder used in each sample is shown in the "d50 (μm)" column of "cBN powder" under "Raw Material Preparation Steps" in Table 1. The purity of the silicon powder was 99.9%, and the average particle size was 5 μm. The purity of the graphite powder was 99.9%, and the average particle size was 1 μm. The purity of the diamond powder was 99%, and the average particle size was 2 μm. The purity of the aluminum powder was 99.5%, and the average particle size was 30 μm.

[0107] Mixing Steps Cubic boron nitride powder and silicon powder were mixed to obtain a mixed powder. The mixing ratio of cubic boron nitride powder and silicon powder was adjusted so that the content of cubic boron nitride and silicon in the prepared cubic boron nitride sintered body became the values ​​shown in the "cBN content" and "Si content" columns of "Cubic boron nitride sintered body" in Table 2. The mixing method was ball milling.

[0108] Next, when using at least one of graphite powder, diamond powder, and aluminum powder, at least one of these powders is added to the above-mentioned mixed powder and mixed to obtain a mixed powder. The amounts of graphite powder, diamond powder, and aluminum powder added are adjusted such that the carbon content and aluminum content of the produced cubic boron nitride sintered body are the values ​​shown in the "C Content" and "Al Content" columns of "Cubic Boron Nitride Sintered Body" in Table 2. The mixing method is ball mill mixing.

[0109] Sintering Steps Next, the mixed powder was sealed in a molybdenum-made sealed chamber, and heated and pressurized using a six-directional pressurized multi-anvil high-pressure generator to obtain cubic boron nitride sintered bodies for each sample. The heating and pressurization were carried out in multiple stages, as shown in the "Sintering Steps" section of Table 1, namely "Stage 1," "Stage 2," and "Stage 3." A "-" in the "Stage 3" column of Table 1 indicates that heating and pressurization in this stage was not performed. The holding time in the final stage is shown in the "Final Stage Holding Time" column of Table 1. Here, "Final Stage Holding Time" refers to the holding time at the final pressure and temperature reached during the sintering process.

[0110] For example, regarding sample 1, in the first stage, heating and pressurization were carried out until the temperature reached 25°C and the pressure reached 10 GPa. In the second stage, heating and pressurization were carried out until the temperature reached 1600°C and the pressure reached 5.5 GPa. The sample was then held at the temperature (1600°C) and pressure (5.5 GPa) reached in the second stage for 20 minutes.

[0111] [Table 1] Table 1 Sample number Raw material preparation steps Sintering steps cBN powder Gr powder Diamond powder Al powder Phase 1 Phase 2 Phase 3 Final stage holding time temperature pressure temperature pressure temperature pressure d50(μm) Yes / No Yes / No Yes / No ℃ GPa ℃ GPa ℃ GPa minute 1 10 none none none 25 10 1600 5.5 - - 20 2 2 none none none 25 10 2000 10 - - 20 3 2 none none none 25 10 2000 10 - - 20 4 5 none none none 1000 0 1000 10 2600 10 20 5 8 have none none 25 10 2000 10 - - 20 6 2 have none none 25 10 2000 10 - - 20 7 2 none none have 25 10 2000 10 - - 20 8 2 have none have 25 10 2000 10 - - 20 9 2 have none have 25 10 2000 10 - - 20 10 10 none none none 25 10 2000 10 - - 20 11 2 none none none 25 10 2000 10 - - 20 12 2 have none have 25 10 2000 10 - - 20 13 2 have none have 25 10 2000 10 - - 20 14 2 none have none 25 10 2000 10 - - 20 15 2 none none none 25 10 2000 10 - - 20 16 2 have none have 25 10 2000 10 - - 20

[0112] [Measurement] For each sample of cubic boron nitride polycrystalline material, the content of cubic boron nitride, silicon content, carbon content, aluminum content, thermal conductivity, dislocation density of cubic boron nitride, coefficient of thermal expansion, d50 and d90 of the circular equivalent diameter of the grains containing cubic boron nitride, and flexural strength were measured.

[0113] <Content of cubic boron nitride> The content (mass%) of cubic boron nitride in the cubic boron nitride sintered body of each sample was determined. The specific determination method is as described in Example 1. The results are shown in the "cBN content" column of "cubic boron nitride sintered body" in Table 2.

[0114] <Silicon content, carbon content, aluminum content> The silicon content, carbon content, and aluminum content of the cubic boron nitride sintered body of each sample were determined. The specific determination method is as described in Example 1. The results are shown in the "Si content", "C content", and "Al content" columns of "cubic boron nitride sintered body" in Table 2.

[0115] Thermal conductivity The thermal conductivity of the cubic boron nitride sintered body for each sample was measured. The specific measurement method is as described in Example 1. The results are shown in the "Thermal Conductivity" column of "Cubic Boron Nitride Sintered Body" in Table 2. In this specification, a cubic boron nitride sintered body with a thermal conductivity of 290 W / mK or higher is considered to have a high thermal conductivity.

[0116] <Dislocation Density> The dislocation density of cubic boron nitride in the cubic boron nitride sintered body of each sample was determined. The specific determination method is as described in Example 1. The results are shown in the "Dislocation Density" column of "Cubic Boron Nitride Sintered Body" in Table 2.

[0117] Coefficient of thermal expansion The coefficient of thermal expansion of the cubic boron nitride sintered body for each sample was determined. The specific measurement method is as described in Example 1. The results are shown in the "Coefficient of Thermal Expansion" column of "Cubic Boron Nitride Sintered Body" in Table 2. In this specification, when the coefficient of thermal expansion of the cubic boron nitride sintered body is within the range of the coefficient of thermal expansion of power semiconductors (4.0~6.0×10⁻⁶ / K), it is determined that the coefficient of thermal expansion of the cubic boron nitride sintered body is close to the coefficient of thermal expansion of power semiconductors.

[0118] <The equivalent diameters of the grain's circle, d50 and d90> The d50 and d90 of the circular equivalent diameters of the plurality of cubic boron nitride grains containing cubic boron nitride in the cubic boron nitride sintered body of each sample were measured. The specific measurement method is as described in Embodiment 1. The results are shown in the "d50" and "d90" columns of "Grains (cBN particles)" under "Cubic boron nitride sintered body" in Table 2.

[0119] [Table 2] Table 2 Sample number cubic boron nitride sintered body Grains (cBN particles) thermal conductivity Dislocation density cBN content Si content C content Al content coefficient of thermal expansion d50 d90 μm μm W / mK ×10 15 / m 2 quality% quality% quality% quality% 10 -6 / K 1 10.0 13.0 600 9.0 95.00 5.00 0 0 5.0 2 2.0 2.7 310 7.1 90.50 9.50 0 0 5.8 3 2.0 2.7 280 7.1 89.00 11.00 0 0 6.1 4 5.0 6.5 470 3.8 95.00 5.00 0 0 5.1 5 8.0 11.0 580 6.9 98.00 1.10 0.90 0 4.3 6 2.0 2.7 290 7.0 93.00 1.70 5.30 0 4.8 7 2.0 2.7 305 7.0 95.00 2.00 0 3.00 4.5 8 2.0 2.7 310 7.0 90.00 4.00 5.00 1.00 4.8 9 2.0 2.7 310 7.0 90.00 5.00 0 5.00 5.3 10 10.0 13.0 650 8.4 99.50 0.50 0 0 4.1 11 10.0 13.0 650 8.4 99.60 0.40 0 0 3.9 12 2.0 2.7 285 7.4 89.89 10.00 0.10 0.01 6.0 13 2.0 2.7 250 7.4 85.00 5.00 5.00 5.00 5.8 14 2.0 2.7 320 7.4 90.00 5.00 5.00 0 5.0 15 2.0 2.7 302 6.8 90.00 10.00 0 0 5.8 16 2.0 2.7 303 6.8 90.00 9.89 0.10 0.01 5.9

[0120] [Discussion] The cubic boron nitride sintered bodies of samples 1, 2, 4-10, and 14-16 are examples. It was confirmed that the thermal conductivity of these cubic boron nitride sintered bodies is above 290 W / mK, which is high thermal conductivity, and the coefficient of thermal expansion is 4.1~5.8×10⁻⁶ / K, which is close to the coefficient of thermal expansion of power semiconductors.

[0121] The cubic boron nitride sintered body of Sample 3 is a comparative example. The cubic boron nitride sintered body of Sample 3 has a lower thermal conductivity compared to the cubic boron nitride sintered body of the examples. This is presumably because the silicon content is relatively high at 11.00% by mass, resulting in more silicon or silicon compounds (such as SiN) present between the cubic boron nitride particles, thus reducing the bonding force between cBN particles.

[0122] The cubic boron nitride sintered body of sample 11 is a comparative example. The coefficient of thermal expansion of the cubic boron nitride sintered body of sample 11 is lower than that of the power semiconductor. It is speculated that this is because the silicon content is relatively low at 0.40% by mass.

[0123] The cubic boron nitride sintered bodies of samples 12 and 13 are comparative examples. Compared to the cubic boron nitride sintered bodies of the examples, the cubic boron nitride sintered bodies of samples 12 and 13 have lower thermal conductivity. This is presumably because the cBN content is less than 90%.

[0124] The embodiments and examples of the present invention have been described above, but it is expected from the outset that the above embodiments and examples may be appropriately combined or varied. The embodiments and examples disclosed herein should be considered illustrative in all respects and not restrictive. The scope of this invention is not defined by the above-described embodiments and examples, but by the claims, and is intended to include all modifications within the scope and meaning of the claims.

Claims

1. A cubic boron nitride sintered body comprising 90.0% to 99.5% by mass of cubic boron nitride and 0.5% to 10.0% by mass of silicon, wherein the total content of the cubic boron nitride and the silicon is 94.0% to 100% by mass, and at least a portion of the silicon exists in the form of elemental silicon.

2. The cubic boron nitride sintered body of claim 1, wherein the cubic boron nitride sintered body contains carbon, and the carbon content is 0.10% by mass or more and 5.00% by mass or less.

3. The cubic boron nitride sintered body of claim 2, wherein at least a portion of the carbon is diamond.

4. A cubic boron nitride sintered body as claimed in any of claims 1 to 3, wherein the cubic boron nitride sintered body contains aluminum, and the aluminum content is more than 0.01% by mass and less than 5.00% by mass.

5. A cubic boron nitride sintered body as claimed in any one of claims 1 to 3, wherein the cubic boron nitride sintered body contains a plurality of grains comprising cubic boron nitride, and the median grain diameter d50 of the circumference of the grains is 1.0 μm or more.

6. A cubic boron nitride sintered body as claimed in any of claims 1 to 3, wherein the thermal conductivity of the cubic boron nitride sintered body is 300 W / mK or higher.

7. A cubic boron nitride sintered body as claimed in any of claims 1 to 3, wherein the coefficient of thermal expansion of the cubic boron nitride sintered body is 4.0×10-6 / K or more and 6.0×10-6 / K or less.

8. A cubic boron nitride sintered body as claimed in any of claims 1 to 3, wherein the dislocation density of the cubic boron nitride is less than 1×10¹⁶ / m².

9. The cubic boron nitride sintered body as claimed in claim 8, wherein the dislocation density is calculated using the modified Williamson-Hall method and the modified Warren-Averbach method.

10. The cubic boron nitride sintered body as claimed in claim 8, wherein the dislocation density is measured using radioactive light as an X-ray source.

11. A heat sink using a cubic boron nitride sintered body as claimed in any one of claims 1 to 10.