WO2017014169A1 - Silicon nitride sintered body - Google Patents

Silicon nitride sintered body Download PDF

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WO2017014169A1
WO2017014169A1 PCT/JP2016/070928 JP2016070928W WO2017014169A1 WO 2017014169 A1 WO2017014169 A1 WO 2017014169A1 JP 2016070928 W JP2016070928 W JP 2016070928W WO 2017014169 A1 WO2017014169 A1 WO 2017014169A1
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silicon nitride
sintered body
nitride sintered
less
crystal
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PCT/JP2016/070928
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French (fr)
Japanese (ja)
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由佳 葛城
英章 粟田
秀行 大国
貴志 関谷
宮永　美紀
小野木　伯薫
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住友電気工業株式会社
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Priority to JP2017529868A priority Critical patent/JPWO2017014169A1/en
Publication of WO2017014169A1 publication Critical patent/WO2017014169A1/en

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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/03—Use of materials for the substrate

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  • Patent Document 1 Japanese Patent Application Laid-Open No. 2009-280494
  • Patent Document 1 has a low productivity because it requires a slow cooling rate of 100 ° C./hour or less after sintering in order to obtain high thermal conductivity. There was a problem.
  • a silicon nitride ceramic substrate having higher thermal conductivity has been desired.
  • the content of various impurity metal elements other than silicon, yttrium, and magnesium can be 0.5% by mass or less.
  • Such a silicon nitride sintered body has a high thermal conductivity.
  • the area ratio of the grain boundary phase which is a portion other than the silicon nitride crystal particles to the silicon nitride crystal particles in an arbitrarily specified cross section of the silicon nitride sintered body is 10% or less. be able to.
  • Such a silicon nitride sintered body has a high thermal conductivity.
  • SEM scanning electron microscope
  • EBSD electron beam backscatter diffraction
  • each extracted Si 3 N 4 crystal particle is approximated to an ellipse, and its short axis particle size and long axis particle size are calculated.
  • the aspect ratio is calculated by dividing the major axis particle size by the minor axis particle size.
  • the aspect ratio which is the ratio of the major axis grain size to the minor axis grain size of Si 3 N 4 crystal grains, is 2.0 or more and 7.7 or less, preferably 2.5 or more, more preferably 3.0 or more.
  • 7.5 or less is preferable, and 7.0 or less is more preferable, which means that an average value for five Si 3 N 4 crystal grains is included in this range.
  • the sintering of the Si 3 N 4 crystal particles is performed by dissolving the ⁇ -Si 3 N 4 crystal phase and the ⁇ -Si 3 N 4 crystal phase in the sintering aid liquid phase, and ⁇ - It proceeds by reprecipitation as a Si 3 N 4 crystal phase. Therefore, ⁇ -Si 3 N 4 crystalline phase the Si 3 N 4 powder of raw material, the core during the re-precipitation of the ⁇ -Si 3 N 4 crystal phase from the sintering aid liquid phase.
  • the ⁇ crystal phase ratio in the raw silicon nitride powder and the abundance ratio of the ⁇ -Si 3 N 4 crystal phase that becomes the nucleus when the ⁇ -Si 3 N 4 crystal phase is reprecipitated from the liquid phase of the sintering aid are the same.
  • the ratio I Y2 / I Y20 of the strength I Y2 is preferably 0 or more and 3.0 or less from the viewpoint of high thermal conductivity.
  • the Y 20 N 4 Si 12 O 48 crystal phase and the Y 2 Si 3 N 3 O 4 crystal phase are generated to trap solid solution oxygen in the Si 3 N 4 crystal particles.
  • the Si 3 N 4 powder is not particularly limited, but the minor axis particle size is 1.7 ⁇ m or more and 10.5 ⁇ m or less, and the aspect ratio which is the ratio of the major axis particle size to the minor axis particle size is 2.0 or more.
  • Si (NH) 2 ) 2 silicon diimide
  • Si (NH 2 ) 4 silicon tetraamide
  • Si 2 N 2 NH silicon nitrogen imide
  • a mixed powder of an imide decomposition powder obtained by thermally decomposing an imide compound and a direct nitriding powder is preferable.
  • the raw material slurry having a volume of 0.25 to 0.5 times the volume of the ball mill mixing container to be used is filled.
  • the raw slurry is homogenized by mixing for 30 minutes or more.
  • ultrasonic mixing the raw material slurry is homogenized by mixing for 10 minutes or more. The presence or absence of granulation does not matter.
  • the molding pressure is preferably 0.5 tf / cm 2 (weight ton / cm 2 ) or more, more preferably 0.8 tf / cm 2 or more, from the viewpoint of forming a high-density molded body.
  • a silicon nitride sintered body of the present embodiment even if the holding time at the maximum temperature during sintering is not increased, if the holding time is 4 hours or more, 30 hours or less, more preferably Even if it is 17 hours or less, a silicon nitride sintered body having a thermal conductivity of 95 W ⁇ m ⁇ 1 ⁇ K ⁇ 1 or more can be obtained.
  • the mass part of each raw material is the total of silicon nitride (Si 3 N 4 ) powder, yttrium oxide (Y 2 O 3 ) powder, and magnesium oxide (MgO) powder, which are all inorganic raw material powders used as raw materials.
  • Si 3 N 4 silicon nitride
  • Y 2 O 3 yttrium oxide
  • MgO magnesium oxide
  • the identification of the Si 3 N 4 crystal particles was carried out by X-ray diffraction as a powder X-ray diffraction database of ICDD PDF-4 + 2014 No. 26191 and no. 79798, respectively.
  • X-ray diffraction was performed using a Cu-K ⁇ ray excited at 45 kV and 40 mA, scanning by the ⁇ -2 ⁇ method, a step width of 0.03 °, and an integration time of 1 second.
  • the analysis of O utilized the inert gas melting-non-dispersion type infrared absorption (NDIR) method by EMGA650W made from HORIBA.
  • NDIR inert gas melting-non-dispersion type infrared absorption
  • the sintered substrate was pulverized with an agate mortar and pestle.
  • 0.03 g of pretreated powder is put in a carbon crucible, and CO gas and / or CO 2 gas generated when the temperature is raised to 1600 ° C. at a high frequency of 20 ⁇ 2 MHz exists above the background level. Therefore, qualitative analysis was performed, and quantitative analysis was performed from the amount of gas generated.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Ceramic Products (AREA)

Abstract

A silicon nitride sintered body that contains silicon nitride, yttrium, magnesium and oxygen, wherein: the plurality of silicon nitride crystal grains contained in the silicon nitride sintered body have a minor axis particle diameter of 1.7-10.5μm, inclusive; and the aspect ratio, which is the ratio of the major axis particle diameter to the minor axis particle diameter, is 2.0-7.7, inclusive. As a result, the present invention provides a silicon nitride sintered body that exhibits high thermal conductivity and is favorable for use as a semiconductor device substrate or the like.

Description

窒化ケイ素焼結体Sintered silicon nitride
　本発明は、半導体デバイスの基板などに好適に用いることができる高い熱伝導率を有する窒化ケイ素焼結体に関する。 The present invention relates to a silicon nitride sintered body having high thermal conductivity that can be suitably used for a substrate of a semiconductor device.
　特開２００９－２８０４９４号公報（特許文献１）は、パワーモジュールのリーク電流の発生を抑制し、大電力化、大容量化した場合でも絶縁性、動作の信頼性を大幅に向上させることのできるパワーモジュールとして、厚さ１．５ｍｍ以下の窒化ケイ素焼結体表面に、幅が１μｍ以上のマイクロクラックがなく、幅が１μｍ未満のサブミクロンクラックが単位面積１００μｍ2当りに０～２個である窒化ケイ素焼結体から成り、温度２５℃、湿度７０％の条件で上記窒化ケイ素焼結体の表裏間に１．５ｋＶ－１００Ｈｚの交流電圧を印加したときの電流リーク値が４２０ｎＡ以下であり、熱伝導率が５０Ｗ・ｍ-1・Ｋ-1以上、３点曲げ強度が５００ＭＰａ以上、残留炭素含有量が５００ｐｐｍ以下である窒化ケイ素セラミックス基板に金属回路板を設けるとともに半導体素子を搭載して成るパワーモジュールであり、上記窒化ケイ素セラミックス基板はＭｇをＭｇＯに換算して０．５～３．０質量％含有するパワーモジュールを開示する。 Japanese Patent Laid-Open No. 2009-280494 (Patent Document 1) suppresses generation of a leakage current of a power module, and can greatly improve insulation and operational reliability even when power is increased and capacity is increased. As a power module, there are no microcracks having a width of 1 μm or more on the surface of a silicon nitride sintered body having a thickness of 1.5 mm or less, and 0 to 2 submicron cracks having a width of less than 1 μm per 100 μm 2 unit area. The current leakage value is 420 nA or less when an alternating voltage of 1.5 kV-100 Hz is applied between the front and back surfaces of the silicon nitride sintered body, comprising a silicon nitride sintered body at a temperature of 25 ° C. and a humidity of 70%. thermal conductivity 50W · m -1 · K -1 or more, three-point bending strength of more than 500 MPa, the metal times the silicon nitride ceramic substrate residual carbon content is 500ppm or less A power module formed by mounting a semiconductor element provided with a plate, the silicon nitride ceramic substrate discloses a power module contains 0.5 to 3.0 mass% in terms of Mg to MgO.
特開２００９－２８０４９４号公報JP 2009-280494 A
　特開２００９－２８０４９４号公報（特許文献１）に開示されるパワーモジュールは、高い熱伝導率を得るために、焼結後に毎時１００℃以下という遅い冷却速度を必要とするため、生産性が低いという問題点があった。また、さらに高い熱伝導率を有する窒化ケイ素セラミックス基板が要望されていた。 The power module disclosed in Japanese Patent Application Laid-Open No. 2009-280494 (Patent Document 1) has a low productivity because it requires a slow cooling rate of 100 ° C./hour or less after sintering in order to obtain high thermal conductivity. There was a problem. In addition, a silicon nitride ceramic substrate having higher thermal conductivity has been desired.
　そこで、半導体デバイスの基板などに好適に用いることができる、高い熱伝導率を有する窒化ケイ素焼結体を提供することを目的とする。 Therefore, an object is to provide a silicon nitride sintered body having high thermal conductivity that can be suitably used for a substrate of a semiconductor device.
　本発明のある態様にかかる窒化ケイ素焼結体は、窒化ケイ素、イットリウム、マグネシウムおよび酸素を含む窒化ケイ素焼結体であり、窒化ケイ素焼結体に含まれる複数の窒化ケイ素結晶粒子は、短軸粒径が１．７μｍ以上１０．５μｍ以下であり、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である。 The silicon nitride sintered body according to an aspect of the present invention is a silicon nitride sintered body containing silicon nitride, yttrium, magnesium and oxygen, and the plurality of silicon nitride crystal particles contained in the silicon nitride sintered body have short axes. The particle size is 1.7 μm or more and 10.5 μm or less, and the aspect ratio, which is the ratio of the long axis particle size to the short axis particle size, is 2.0 or more and 7.7 or less.
　上記によれば、半導体デバイスの基板などに好適に用いることができる、高い熱伝導率を有する窒化ケイ素焼結体を提供できる。 According to the above, it is possible to provide a silicon nitride sintered body having high thermal conductivity that can be suitably used for a substrate of a semiconductor device.
　［本発明の実施形態の説明］
　本発明のある実施形態にかかる窒化ケイ素焼結体は、窒化ケイ素、イットリウム、マグネシウムおよび酸素を含む窒化ケイ素焼結体であり、窒化ケイ素焼結体に含まれる複数の窒化ケイ素結晶粒子は、短軸粒径が１．７μｍ以上１０．５μｍ以下であり、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である。本実施形態の窒化ケイ素焼結体は、高い熱伝導率を有する。 [Description of Embodiment of the Present Invention]
A silicon nitride sintered body according to an embodiment of the present invention is a silicon nitride sintered body containing silicon nitride, yttrium, magnesium, and oxygen, and the plurality of silicon nitride crystal particles included in the silicon nitride sintered body are short. The axial particle size is 1.7 μm or more and 10.5 μm or less, and the aspect ratio, which is the ratio of the long axis particle size to the short axis particle size, is 2.0 or more and 7.7 or less. The silicon nitride sintered body of the present embodiment has a high thermal conductivity.
　本実施形態の窒化ケイ素焼結体は、複数の窒化ケイ素結晶粒子と、窒化ケイ素結晶粒子以外の部分である粒界相と、を含み、粒界相は、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相、あるいは、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相およびＹ2Ｓｉ3Ｎ3Ｏ4結晶相、を含み、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークの強度に対するＹ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークの強度の比を０以上３．０以下とすることができる。かかる窒化ケイ素焼結体は、高い熱伝導率を有する。 The silicon nitride sintered body of the present embodiment includes a plurality of silicon nitride crystal particles and a grain boundary phase that is a portion other than the silicon nitride crystal particles, and the grain boundary phase includes Y 20 N 4 Si 12 O 48 crystals. Phase, or a Y 20 N 4 Si 12 O 48 crystal phase and a Y 2 Si 3 N 3 O 4 crystal phase, and the X-ray diffraction caused by the (112) plane of the Y 20 N 4 Si 12 O 48 crystal phase The ratio of the intensity of the X-ray diffraction peak due to the (211) plane of the Y 2 Si 3 N 3 O 4 crystal phase to the intensity of the peak can be 0 or more and 3.0 or less. Such a silicon nitride sintered body has a high thermal conductivity.
　本実施形態の窒化ケイ素焼結体において、ケイ素、イットリウムおよびマグネシウム以外の各種の不純物金属元素の含有率を各々０．５質量％以下とすることができる。かかる窒化ケイ素焼結体は、高い熱伝導率を有する。 In the silicon nitride sintered body of the present embodiment, the content of various impurity metal elements other than silicon, yttrium, and magnesium can be 0.5% by mass or less. Such a silicon nitride sintered body has a high thermal conductivity.
　本実施形態の窒化ケイ素焼結体において、酸化マグネシウム結晶相を存在しないようにすることができる。かかる窒化ケイ素焼結体は、高い相対密度および高い熱伝導率を有する。 In the silicon nitride sintered body of this embodiment, it is possible to prevent the magnesium oxide crystal phase from being present. Such a silicon nitride sintered body has a high relative density and a high thermal conductivity.
　本実施形態の窒化ケイ素焼結体において、熱伝導率を９５Ｗ・ｍ-1・Ｋ-1以上とすることができる。かかる窒化ケイ素焼結体は、高い熱伝導率を有する。 In the silicon nitride sintered body of the present embodiment, the thermal conductivity can be 95 W · m −1 · K −1 or more. Such a silicon nitride sintered body has a high thermal conductivity.
　本実施形態の窒化ケイ素焼結体において、窒化ケイ素焼結体の任意に特定される断面における窒化ケイ素結晶粒子に対する窒化ケイ素結晶粒子以外の部分である粒界相の面積比率を１０％以下とすることができる。かかる窒化ケイ素焼結体は、高い熱伝導率を有する。 In the silicon nitride sintered body of the present embodiment, the area ratio of the grain boundary phase which is a portion other than the silicon nitride crystal particles to the silicon nitride crystal particles in an arbitrarily specified cross section of the silicon nitride sintered body is 10% or less. be able to. Such a silicon nitride sintered body has a high thermal conductivity.
　［本発明の実施形態の詳細］
　（窒化ケイ素焼結体）
　本実施形態の窒化ケイ素焼結体は、窒化ケイ素（Ｓｉ3Ｎ4）、イットリウム（Ｙ）、マグネシウム（Ｍｇ）および酸素（Ｏ）を含む窒化ケイ素焼結体であり、窒化ケイ素焼結体に含まれる複数の窒化ケイ素（Ｓｉ3Ｎ4）結晶粒子は、短軸粒径が１．７μｍ以上１０．５μｍ以下であり、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である。本実施形態の窒化ケイ素焼結体は、高い熱伝導率を有する。 [Details of the embodiment of the present invention]
(Silicon nitride sintered body)
The silicon nitride sintered body of the present embodiment is a silicon nitride sintered body containing silicon nitride (Si 3 N 4 ), yttrium (Y), magnesium (Mg), and oxygen (O). The plurality of silicon nitride (Si 3 N 4 ) crystal particles contained have a minor axis particle size of 1.7 μm or more and 10.5 μm or less, and an aspect ratio which is a ratio of the major axis particle size to the minor axis particle size is 2. 0 or more and 7.7 or less. The silicon nitride sintered body of the present embodiment has a high thermal conductivity.
　本実施形態の窒化ケイ素焼結体は、Ｓｉ3Ｎ4、Ｙ、ＭｇおよびＯを含む。Ｓｉ3Ｎ4の結晶粒子の焼結の進行すなわち緻密化と粒子成長は、初期の焼結助剤の液相化による毛管凝集に引き続き、Ｓｉ3Ｎ4結晶粒子であるα－Ｓｉ3Ｎ4結晶相およびβ－Ｓｉ3Ｎ4結晶相のＹおよびＭｇを含む焼結助剤液相への溶解、および焼結助剤液相からのβ－Ｓｉ3Ｎ4結晶相としての再析出により進行する。かかる再析出の際に不純物がＳｉ3Ｎ4結晶粒子中に残留すると、得られる窒化ケイ素焼結体の熱伝導率が低下する。Ｙは、固溶酸素をトラップすることから、Ｓｉ3Ｎ4結晶粒子への酸素（Ｏ）の固溶を抑えることができるため、β－Ｓｉ3Ｎ4結晶相の結晶構造が乱されない。また、Ｙは、β－Ｓｉ3Ｎ4結晶相中に固溶しないため、β－Ｓｉ3Ｎ4結晶相の結晶構造が乱されない。結晶構造の乱れは、熱の伝導を阻害することから、熱伝導率を高めるためには望ましくない。このため、Ｙを含む焼結助剤は、熱伝導率向上に有効である。Ｍｇは、Ｓｉ3Ｎ4結晶粒子の表面に形成されるＳｉＯxのような酸化物またはＳｉＯＮのような酸窒化物の融点を下げるため、Ｓｉ3Ｎ4結晶粒子の液相焼結には必須の元素である。 The silicon nitride sintered body of the present embodiment contains Si 3 N 4 , Y, Mg and O. The progress of sintering of Si 3 N 4 crystal particles, that is, densification and particle growth, followed by capillary aggregation due to the liquid phase formation of the initial sintering aid, followed by α-Si 3 N 4 which is Si 3 N 4 crystal particles. Progression by dissolution of the crystal phase and β-Si 3 N 4 crystal phase in the sintering aid liquid phase containing Y and Mg, and reprecipitation from the sintering aid liquid phase as β-Si 3 N 4 crystal phase To do. If impurities remain in the Si 3 N 4 crystal particles during the reprecipitation, the thermal conductivity of the obtained silicon nitride sintered body is lowered. Since Y traps solid solution oxygen, the solid solution of oxygen (O) in the Si 3 N 4 crystal particles can be suppressed, so that the crystal structure of the β-Si 3 N 4 crystal phase is not disturbed. Further, Y may, for β-Si 3 N 4 is not a solid solution in the crystal phase, the crystal structure of β-Si 3 N 4 crystal phase is not disturbed. The disorder of the crystal structure inhibits heat conduction and is not desirable for increasing the thermal conductivity. For this reason, the sintering aid containing Y is effective in improving the thermal conductivity. Mg is, Si 3 N 4 for lowering the melting point of the oxide or oxynitride such as SiON, such as SiO x formed on the surface of the crystal grains, Si 3 N 4 essential for liquid phase sintering of the crystal grains Elements.
　上記のＳｉ3Ｎ4、ＹおよびＭｇは、原料とする窒化ケイ素（Ｓｉ3Ｎ4）粉末、酸化イットリウム（Ｙ2Ｏ3）粉末および酸化マグネシウム（ＭｇＯ）粉末にそれぞれ含まれるものであり、これらの混合粉末を、成形・脱脂後、焼結するために存在する。ここで、原料とする全ての無機原料粉末を１００質量部としたとき、たとえば、Ｓｉ3Ｎ4粉末は８７．６質量部以上９８．５質量部以下であり、Ｙ2Ｏ3粉末は１．０質量部以上１０．４質量部以下であり、ＭｇＯ粉末は０．５質量部以上２．０質量部以下である。 The above Si 3 N 4 , Y and Mg are contained in the silicon nitride (Si 3 N 4 ) powder, yttrium oxide (Y 2 O 3 ) powder and magnesium oxide (MgO) powder as raw materials, respectively. Is present for sintering after molding and degreasing. Here, when all the inorganic raw material powders used as raw materials are 100 parts by mass, for example, the Si 3 N 4 powder is 87.6 parts by mass or more and 98.5 parts by mass or less, and the Y 2 O 3 powder is 1. It is 0 to 10.4 parts by mass, and the MgO powder is 0.5 to 2.0 parts by mass.
　本実施形態の窒化ケイ素焼結体において、全体の質量を１００質量％としたとき、Ｙの含有率は、好ましくは０．５質量％以上１０．４質量％以下である。ここで、Ｙの含有率は、より好ましくは０．６質量％以上、さらに好ましくは２．２質量％以上である。また、Ｙの含有率は、より好ましくは４．０質量％以下、さらに好ましくは２．６質量％以下である。Ｍｇの含有率は、好ましくは０．０５質量％以上０．７質量％以下である。ここで、Ｍｇの含有率は、より好ましくは０．０７質量％以上、さらに好ましくは０．１５質量％以上である。また、Ｍｇの含有率は、より好ましくは０．５質量％以下、さらに好ましくは０．２４質量％以下である。Ｏの含有率は、好ましくは０．３質量％以上２．０質量％以下である。ここで、Ｏの含有率は、より好ましくは０．５質量％以上、さらに好ましくは０．８質量％以上である。また、Ｏの含有率は、より好ましくは１．５質量％以下、さらに好ましくは１．１質量％以下である。 In the silicon nitride sintered body of the present embodiment, when the total mass is 100% by mass, the Y content is preferably 0.5% by mass or more and 10.4% by mass or less. Here, the content of Y is more preferably 0.6% by mass or more, and further preferably 2.2% by mass or more. The Y content is more preferably 4.0% by mass or less, and even more preferably 2.6% by mass or less. The Mg content is preferably 0.05% by mass or more and 0.7% by mass or less. Here, the Mg content is more preferably 0.07% by mass or more, and still more preferably 0.15% by mass or more. The Mg content is more preferably 0.5% by mass or less, and still more preferably 0.24% by mass or less. The content of O is preferably 0.3% by mass or more and 2.0% by mass or less. Here, the O content is more preferably 0.5% by mass or more, and still more preferably 0.8% by mass or more. The O content is more preferably 1.5% by mass or less, and still more preferably 1.1% by mass or less.
　ここで、Ｙの含有率が０．５質量％未満、Ｍｇの含有率が０．０５質量％未満、またはＯの含有率が０．３質量％未満であるとき、焼結助剤として作用するこれらの元素の含有率が足りないため、焼結が進まないことから焼結体として十分な相対密度が得られにくい傾向がある。Ｙの含有率が１０．４質量％より多い、Ｍｇの含有率が０．７質量％より多い、またはＯの含有率が２．０質量％より多いとき、熱伝導率が低い粒界相の量が多くなるため、焼結体の熱伝導率が低くなる傾向がある。 Here, when the Y content is less than 0.5 mass%, the Mg content is less than 0.05 mass%, or the O content is less than 0.3 mass%, it acts as a sintering aid. Since the content of these elements is insufficient, sintering does not proceed, so that it is difficult to obtain a relative density sufficient as a sintered body. When the Y content is more than 10.4% by mass, the Mg content is more than 0.7% by mass, or the O content is more than 2.0% by mass, the thermal conductivity is low. Since the amount increases, the thermal conductivity of the sintered body tends to decrease.
　Ｓｉ3Ｎ4の定性分析には、ＰＡＮａｌｙｔｉｃａｌ社製Ｘ’Ｐｅｒｔ　ＰＲＯまたは同等の装置によるＸ線回折の後、およびＲｉｇａｋｕ社製統合粉末Ｘ線解析ソフトウェアのＰＤＸＬ２または同等のソフトウェアを利用する。かかるＳｉ3Ｎ4の定性分析の際は、表面の大きさが５００μｍ×５００μｍ以上の焼結体を用いる。ここで、Ｓｉ3Ｎ4は、α－Ｓｉ3Ｎ4結晶相およびβ－Ｓｉ3Ｎ4結晶相の少なくともいずれかの結晶型であると考えられるため、粉末Ｘ線回折データベースとして国際回折データセンターによる粉末回折データファイルであるＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．２６１９１およびＮｏ．７９７９８のそれぞれを利用していずれの結晶型かを同定する。Ｘ線回折は、４５ｋＶ、４０ｍＡで励起したＣｕ－Ｋα線を利用し、θ－２θ法による走査、０．０３°のステップ幅、１秒の積算時間で行なう。 For qualitative analysis of Si 3 N 4 , after X-ray diffraction using X'Pert PRO (manufactured by PANalytical) or equivalent, and PDXL2 (integrated powder X-ray analysis software (Rigaku) or equivalent software) are used. In the qualitative analysis of Si 3 N 4, a sintered body having a surface size of 500 μm × 500 μm or more is used. Here, since Si 3 N 4 is considered to be at least one of an α-Si 3 N 4 crystal phase and a β-Si 3 N 4 crystal phase, an international diffraction data center is used as a powder X-ray diffraction database. No. of ICDD PDF-4 + 2014 which is a powder diffraction data file by 26191 and no. Each of 79798 is used to identify which crystal type. X-ray diffraction is performed using a Cu-Kα ray excited at 45 kV and 40 mA, scanning by the θ-2θ method, a step width of 0.03 °, and an integration time of 1 second.
　ＹおよびＭｇの定性分析および定量分析には、ＳＨＩＭＡＤＺＵ社製ＩＣＰＳ－８１００または同等の装置による誘導結合プラズマ－発光分光分析（ＩＣＰ－ＡＥＳ）を利用する。かかるＩＣＰ－ＡＥＳの際の手順を以下に例示する。前処理として、焼結体をメノウ製の乳鉢と乳棒によって粉砕する。ＹおよびＭｇの分析においては、前処理粉末の溶液を霧状にしてＡｒプラズマに導入することにより励起された元素が基底状態に戻る際に放出される光の波長から定性分析を行ない、その光の強度から定量分析を行なう。これにより、焼結体中に存在するＹおよびＭｇの質量％が定量される。前処理粉末の溶液は、０．１ｇの前処理粉末を、２ｇの炭酸カルシウムおよび０．５ｇの酸化ホウ素からなるアルカリ溶媒とともに、白金ルツボ中に投入して１０００℃で溶融し、その溶融体を２０ｍｌの３５質量％の塩酸および２０ｍｌのイオン交換水からなる酸性溶液内にて６０℃で回収した後に、イオン交換水で２００ｍｌまで希釈することにより作製する。 For the qualitative analysis and quantitative analysis of Y and Mg, inductively coupled plasma-emission spectroscopic analysis (ICP-AES) using ICPS-8100 manufactured by SHIMADZU or an equivalent apparatus is used. The procedure for such ICP-AES is exemplified below. As a pretreatment, the sintered body is pulverized with an agate mortar and pestle. In the analysis of Y and Mg, a qualitative analysis is performed from the wavelength of the light emitted when the excited element returns to the ground state by introducing the solution of the pretreatment powder into a mist and introducing it into Ar plasma. Quantitative analysis from the intensity of Thereby, the mass% of Y and Mg present in the sintered body is quantified. The pretreated powder solution was prepared by pouring 0.1 g of the pretreated powder into a platinum crucible together with 2 g of calcium carbonate and 0.5 g of boron oxide in a platinum crucible and melting the melt. It is prepared by collecting at 60 ° C. in an acidic solution consisting of 20 ml of 35% by mass hydrochloric acid and 20 ml of ion exchange water, and then diluting to 200 ml with ion exchange water.
　Ｏの定性分析および定量分析には、ＨＯＲＩＢＡ社製ＥＭＧＡ６５０Ｗまたは同等の装置による不活性ガス融解－非分散型赤外線吸収（ＮＤＩＲ）法を利用する。かかる不活性ガス融解－ＮＤＩＲ法による分析の際の手順を以下に例示する。前処理として、焼結体をメノウ製の乳鉢と乳棒によって粉砕する。Ｏの分析においては、０．０３ｇの前処理粉末をカーボンルツボに入れ、高周波にて１６００℃まで昇温した際に発生したＣＯガスおよび／またはＣＯ2ガスがバックグラウンドレベル以上存在することから定性分析を行ない、それらのガスの発生量から定量分析を行なう。これにより、焼結体中に存在するＯの質量％が定量される。 For the qualitative analysis and quantitative analysis of O, an inert gas melting-non-dispersive infrared absorption (NDIR) method using EMGA650W manufactured by HORIBA or an equivalent apparatus is used. The procedure for the analysis by the inert gas melting-NDIR method is exemplified below. As a pretreatment, the sintered body is pulverized with an agate mortar and pestle. In the analysis of O, 0.03 g of pretreated powder is placed in a carbon crucible and the CO gas and / or CO 2 gas generated when the temperature is raised to 1600 ° C. at a high frequency is present because it is above the background level. Analysis is performed, and quantitative analysis is performed from the amount of gas generated. Thereby, the mass% of O present in the sintered body is quantified.
　本実施形態の窒化ケイ素焼結体は、焼結体中のＳｉ3Ｎ4結晶粒子の短軸粒径が１．７μｍ以上１０．５μｍ以下であり、Ｓｉ3Ｎ4結晶粒子の短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である。かかる窒化ケイ素焼結体は、高い熱伝導率を有することができる。窒化ケイ素焼結体の熱伝導率をより高くする観点から、焼結体中のＳｉ3Ｎ4結晶粒子の短軸粒径は、１．８μｍ以上が好ましく、２．２μｍ以上がより好ましい。また、窒化ケイ素焼結体の熱伝導率をより高くする観点から、Ｓｉ3Ｎ4結晶粒子の短軸粒径に対する長軸粒径の比であるアスペクト比は、２．５以上が好ましく、３．０以上がより好ましく、また、７．５以下が好ましく、７．０以下がより好ましい。 In the silicon nitride sintered body of the present embodiment, the short axis particle size of the Si 3 N 4 crystal particles in the sintered body is 1.7 μm or more and 10.5 μm or less, and the short axis particle size of the Si 3 N 4 crystal particles is The aspect ratio, which is the ratio of the major axis particle size to the, is 2.0 or more and 7.7 or less. Such a silicon nitride sintered body can have a high thermal conductivity. From the viewpoint of further increasing the thermal conductivity of the silicon nitride sintered body, the minor axis particle size of the Si 3 N 4 crystal particles in the sintered body is preferably 1.8 μm or more, and more preferably 2.2 μm or more. In addition, from the viewpoint of increasing the thermal conductivity of the silicon nitride sintered body, the aspect ratio, which is the ratio of the major axis grain size to the minor axis grain size of the Si 3 N 4 crystal particles, is preferably 2.5 or more. 0.0 or more is more preferable, 7.5 or less is preferable, and 7.0 or less is more preferable.
　Ｓｉ3Ｎ4結晶粒子の短軸粒径およびアスペクト比（短軸粒径に対する長軸粒径の比）の解析には、ＳＥＭ（走査型電子顕微鏡）－ＥＢＳＤ（電子線後方散乱回折）測定を利用する。ＳＥＭ観察にはＣａｒｌ　Ｚｅｉｓｓ社製ＳＵＰＲＡ　３５　ＶＰまたは同等装置を利用し、電子後方散乱回折にはＴＳＬソリューションズ社製ＯＩＭ５．２または同等装置を利用する。 SEM (scanning electron microscope) -EBSD (electron beam backscatter diffraction) measurement is used to analyze the minor axis diameter and aspect ratio (ratio of major axis diameter to minor axis diameter) of Si 3 N 4 crystal particles. Use. For SEM observation, SUPRA 35 VP manufactured by Carl Zeiss or an equivalent device is used, and for electron backscatter diffraction, OIM5.2 manufactured by TSL Solutions or an equivalent device is used.
　ＳＥＭ－ＥＢＳＤ測定の手順を以下に例示する。前処理として、平面研削盤を利用してダイヤモンド砥石（アライドマテリアル社製ダイヤモンド研削砥石＃４００）を用いて、焼結体の表面から５００μｍ以上の深さまで研削後、ケメット社製ラップ加工機を利用して仕上げ加工する。まず、銅定盤と粒径が３μｍのダイヤモンド砥石とを用いて焼結体をその表面から１０μｍ以上の深さまで研磨し、次に、錫定盤と粒径が０．５μｍのダイヤモンド砥石とを用いて焼結体をその研削後の表面から３μｍ以上の深さまで研磨する。この際、仕上げ加工における両研磨とも、回転数５０ｒｐｍ、荷重０．２ＭＰａの条件で行なう。表面加工は、上記と同等の加工でも構わない。 The SEM-EBSD measurement procedure is illustrated below. As pre-processing, after grinding to a depth of 500 μm or more from the surface of the sintered body using a diamond grindstone (Diamond grindstone # 400 made by Allied Material) using a surface grinder, use a lapping machine made by Kemet And finish processing. First, the sintered body is polished from its surface to a depth of 10 μm or more using a copper surface plate and a diamond grindstone having a particle size of 3 μm. Next, a tin surface plate and a diamond grindstone having a particle size of 0.5 μm are polished. The sintered body is polished to a depth of 3 μm or more from the ground surface. At this time, both polishings in the finishing process are performed under conditions of a rotation speed of 50 rpm and a load of 0.2 MPa. The surface processing may be processing equivalent to the above.
　ＥＢＳＤ測定は、測定面積３０μｍ×１００μｍとし、測定条件は例えば加速電圧１５ｋＶ、ワーキングディスタンス１５ｍｍ、ステップサイズ０．１μｍ、ビニング８×８、積算時間０．０１秒で行なう。これにより、ＩＱ（イメージクオリティ）マップを取得する。取得されたＩＱマップ画像（視野面積３０μｍ×１００μｍ）の内、最も面積が大きいＳｉ3Ｎ4結晶粒子から５番目に面積が大きいＳｉ3Ｎ4結晶粒子までを抽出し、当該５個のＳｉ3Ｎ4結晶粒子をＩｍａｇｅＪソフトウェア（Ｗａｙｎｅ　Ｒａｓｂａｎｄ氏開発のオープンソース。以下同じ。）および同等ソフトウェアによって、短軸粒径、長軸粒径およびアスペクト比を算出する。ＩｍａｇｅＪソフトウェアにおいては、抽出された各Ｓｉ3Ｎ4結晶粒子を楕円形に近似して、その短軸粒径および長軸粒径を算出する。長軸粒径を短軸粒径で除することによりアスペクト比を算出する。表１～３に記載の短軸粒径の範囲は、５個のＳｉ3Ｎ4結晶粒子についての最小値と最大値の範囲である。また、表１～３に記載のアスペクト比は、５個のＳｉ3Ｎ4結晶粒子についての平均値である。本実施形態の窒化ケイ素焼結体中のＳｉ3Ｎ4結晶粒子の短軸粒径は、１．７μｍ以上１０．５μｍ以下であり、１．８μｍ以上が好ましく、２．２μｍ以上がより好ましいとは、５個のＳｉ3Ｎ4結晶粒子についての最小値と最大値とがこの範囲に含まれることを意味している。また、Ｓｉ3Ｎ4結晶粒子の短軸粒径に対する長軸粒径の比であるアスペクト比は、２．０以上７．７以下であり、２．５以上が好ましく、３．０以上がより好ましく、また、７．５以下が好ましく、７．０以下がより好ましいとは、５個のＳｉ3Ｎ4結晶粒子についての平均値がこの範囲に含まれることを意味している。 The EBSD measurement is performed with a measurement area of 30 μm × 100 μm, and measurement conditions are, for example, an acceleration voltage of 15 kV, a working distance of 15 mm, a step size of 0.1 μm, a binning of 8 × 8, and an integration time of 0.01 seconds. Thereby, an IQ (image quality) map is acquired. Of the obtained IQ map image (field area 30 [mu] m × 100 [mu] m), most area from a large Si 3 N 4 crystal grains to the fifth area is large Si 3 N 4 crystal grains extracts, the five Si 3 The N 4 crystal grains are calculated by ImageJ software (open source developed by Wayne Rasband, the same applies hereinafter) and equivalent software, and the minor axis grain size, major axis grain size and aspect ratio are calculated. In the ImageJ software, each extracted Si 3 N 4 crystal particle is approximated to an ellipse, and its short axis particle size and long axis particle size are calculated. The aspect ratio is calculated by dividing the major axis particle size by the minor axis particle size. The range of the short axis particle size described in Tables 1 to 3 is the range of the minimum value and the maximum value for the five Si 3 N 4 crystal particles. The aspect ratios listed in Tables 1 to 3 are average values for five Si 3 N 4 crystal grains. The short axis particle size of the Si 3 N 4 crystal particles in the silicon nitride sintered body of the present embodiment is 1.7 μm or more and 10.5 μm or less, preferably 1.8 μm or more, and more preferably 2.2 μm or more. Means that the minimum value and the maximum value of the five Si 3 N 4 crystal grains are included in this range. The aspect ratio, which is the ratio of the major axis grain size to the minor axis grain size of Si 3 N 4 crystal grains, is 2.0 or more and 7.7 or less, preferably 2.5 or more, more preferably 3.0 or more. Preferably, 7.5 or less is preferable, and 7.0 or less is more preferable, which means that an average value for five Si 3 N 4 crystal grains is included in this range.
　焼結体中の複数（具体的には、上記で抽出される５個）のＳｉ3Ｎ4結晶粒子の短軸粒径の最小が１．７μｍ未満であるとき、Ｓｉ3Ｎ4結晶粒子の粒子成長が不十分であることから、原料であるＳｉ3Ｎ4粒子中の不純物の除去が不十分であるため、焼結体の熱伝導率を高くすることが難しい。複数のＳｉ3Ｎ4結晶粒子の短軸粒径の最大が１０．５μｍより大きいとき、高熱伝導を得るために長時間の焼結時間が必要となることから生産性が低下するとともに、焼結体の熱伝導率が低下する傾向がある。また、アスペクト比が７．７より大きいとき、焼結密度が十分に上がらずに、熱伝導率が低下する傾向がある。アスペクト比が２．０より小さいとき、焼結体の熱伝導率を高くすることが難しい。 When the minimum minor axis diameter of a plurality of (specifically, five extracted above) Si 3 N 4 crystal particles in the sintered body is less than 1.7 μm, the Si 3 N 4 crystal particles Since the particle growth is insufficient, it is difficult to increase the thermal conductivity of the sintered body because the impurities in the raw material Si 3 N 4 particles are not sufficiently removed. When the maximum minor axis diameter of the plurality of Si 3 N 4 crystal particles is larger than 10.5 μm, a long sintering time is required to obtain high thermal conductivity, and productivity is lowered and sintering is performed. The thermal conductivity of the body tends to decrease. On the other hand, when the aspect ratio is larger than 7.7, the sintered density does not sufficiently increase and the thermal conductivity tends to decrease. When the aspect ratio is less than 2.0, it is difficult to increase the thermal conductivity of the sintered body.
　また、本実施形態の窒化ケイ素焼結体の製造に用いられる原料の窒化ケイ素（Ｓｉ3Ｎ4）粉末は、β結晶相率（α－Ｓｉ3Ｎ4結晶相およびβ－Ｓｉ3Ｎ4結晶相の合計に対するβ－Ｓｉ3Ｎ4結晶相の質量百分率）が５質量％以上４０質量％以下であることが、短軸粒径が１．７μｍ以上１０．５μｍ以下で短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下であり高い熱伝導率を有する窒化ケイ素焼結体を得る観点から、好ましい。かかる観点から、β結晶相率は、より好ましくは１０質量％以上、さらに好ましくは２０質量％以上である。また、β結晶相率は、より好ましくは３５質量％以下、さらに好ましくは３２質量％以下である。ここで、β結晶相率の算出は、上記のようにＸ線回折により原料のＳｉ3Ｎ4粉末中のα－Ｓｉ3Ｎ4結晶相およびβ－Ｓｉ3Ｎ4結晶相を同定した後、ＲＩＲ（参照強度比）法を用いて行う。 The raw material silicon nitride (Si 3 N 4 ) powder used in the production of the silicon nitride sintered body of the present embodiment has a β crystal phase ratio (α-Si 3 N 4 crystal phase and β-Si 3 N 4 crystal). (Mass percentage of β-Si 3 N 4 crystal phase with respect to the total of the phases) is 5% by mass or more and 40% by mass or less. From the viewpoint of obtaining a silicon nitride sintered body having an aspect ratio, which is a ratio of axial particle diameters, of 2.0 or more and 7.7 or less and high thermal conductivity. From this viewpoint, the β crystal phase ratio is more preferably 10% by mass or more, and still more preferably 20% by mass or more. Further, the β crystal phase ratio is more preferably 35% by mass or less, and further preferably 32% by mass or less. Here, the calculation of the β crystal phase ratio is performed after identifying the α-Si 3 N 4 crystal phase and the β-Si 3 N 4 crystal phase in the raw material Si 3 N 4 powder by X-ray diffraction as described above. RIR (reference intensity ratio) method is used.
　このためには、原料のＳｉ3Ｎ4粉末には、従来構造材として使用されるイミド分解粉末だけを用いるのではなく、直接窒化粉末あるいは直接窒化粉末およびイミド分解粉末の混合粉末を用いることが好ましい。直接窒化粉末はβ結晶相率が２０質量％以上６０質量％以下であり、イミド分解粉末はβ結晶相率が１質量％以下である。このことから、原料の窒化ケイ素粉末は、直接窒化粉末とイミド分解粉末との混合比を調整することにより、そのβ結晶相率を５質量％以上４０質量％以下に調整することができる。 For this purpose, the raw material Si 3 N 4 powder should not be used only with the imide decomposition powder conventionally used as a structural material, but with direct nitriding powder or a mixed powder of direct nitriding powder and imide decomposition powder. preferable. The direct nitriding powder has a β crystal phase ratio of 20% by mass or more and 60% by mass or less, and the imide decomposition powder has a β crystal phase ratio of 1% by mass or less. From this, the silicon nitride powder of the raw material can be adjusted to have a β crystal phase ratio of 5% by mass or more and 40% by mass or less by directly adjusting the mixing ratio of the nitrided powder and the imide decomposition powder.
　Ｓｉ3Ｎ4結晶粒子の焼結は、α－Ｓｉ3Ｎ4結晶相およびβ－Ｓｉ3Ｎ4結晶相の焼結助剤液相への溶解、および焼結助剤液相からのβ－Ｓｉ3Ｎ4結晶相としての再析出により進行する。したがって、原料のＳｉ3Ｎ4粉末中のβ－Ｓｉ3Ｎ4結晶相が、焼結助剤液相からのβ－Ｓｉ3Ｎ4結晶相の再析出の際の核となる。すなわち、原料の窒化ケイ素粉末中のβ結晶相率と焼結助剤液相からのβ－Ｓｉ3Ｎ4結晶相の再析出の際の核となるβ－Ｓｉ3Ｎ4結晶相の存在率が同じになる。 The sintering of the Si 3 N 4 crystal particles is performed by dissolving the α-Si 3 N 4 crystal phase and the β-Si 3 N 4 crystal phase in the sintering aid liquid phase, and β- It proceeds by reprecipitation as a Si 3 N 4 crystal phase. Therefore, β-Si 3 N 4 crystalline phase the Si 3 N 4 powder of raw material, the core during the re-precipitation of the β-Si 3 N 4 crystal phase from the sintering aid liquid phase. That is, the β crystal phase ratio in the raw silicon nitride powder and the abundance ratio of the β-Si 3 N 4 crystal phase that becomes the nucleus when the β-Si 3 N 4 crystal phase is reprecipitated from the liquid phase of the sintering aid Are the same.
　このため、原料のＳｉ3Ｎ4粉末のβ結晶相率が５質量％より小さいと、再析出の核となるβ－Ｓｉ3Ｎ4結晶相の粒子が少なくなり、かかる少量の粒子のβ－Ｓｉ3Ｎ4結晶相が一方向に優先的に成長（異常粒子成長）するため、アスペクト比が大きくなり過ぎるとともに、焼結体の熱伝導率を高くすることが難しい。原料のＳｉ3Ｎ4粉末のβ結晶相率が４０質量％より大きいと、再析出の核となるβ－Ｓｉ3Ｎ4結晶相の粒子が多くなり、かかる多量の粒子のβ－Ｓｉ3Ｎ4結晶相が同時に成長するため、粒子成長が不十分となるため、アスペクト比が小さくなり過ぎるとともに、焼結体の熱伝導率を高くすることが難しい。 For this reason, if the β crystal phase ratio of the raw material Si 3 N 4 powder is less than 5% by mass, the β-Si 3 N 4 crystal phase particles that become the core of reprecipitation are reduced, and the β- Since the Si 3 N 4 crystal phase preferentially grows in one direction (abnormal particle growth), the aspect ratio becomes too large and it is difficult to increase the thermal conductivity of the sintered body. When the β crystal phase ratio of the raw material Si 3 N 4 powder is larger than 40% by mass, the number of β-Si 3 N 4 crystal phase particles that become the core of reprecipitation increases, and a large amount of β-Si 3 N Since the four crystal phases grow at the same time, the grain growth becomes insufficient, so that the aspect ratio becomes too small and it is difficult to increase the thermal conductivity of the sintered body.
　そこで、原料のＳｉ3Ｎ4粉末のβ結晶相率を調整することにより、Ｓｉ3Ｎ4結晶粒子を均一粒子成長させ、高い熱伝導率を示すアスペクト比のＳｉ3Ｎ4結晶粒子を増やすことで、高い熱伝導率を有する窒化ケイ素焼結体が得られる。また、β－Ｓｉ3Ｎ4結晶相が異常粒子成長よりも均一粒子成長を優先的に起させるために、焼結温度を高めかつ冷却速度を高くすることにより、比較的低温で起こりうるβ－Ｓｉ3Ｎ4結晶相の異常粒成長を抑制している。ここで、比較的低温で起こりうるβ－Ｓｉ3Ｎ4結晶相の異常粒成長を抑制する観点から、焼結後の冷却における冷却速度は、１００℃／ｍｉｎ以上が好ましく、１２０℃／ｍｉｎ以上がより好ましい。このように、アスペクト比が大きくなりすぎることを防ぎ、Ｓｉ3Ｎ4結晶粒子の短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下とすることができる。 Therefore, by adjusting the β crystal phase ratio of the raw material Si 3 N 4 powder, Si 3 N 4 crystal particles are grown uniformly and the number of aspect ratio Si 3 N 4 crystal particles showing high thermal conductivity is increased. Thus, a silicon nitride sintered body having high thermal conductivity can be obtained. In addition, since the β-Si 3 N 4 crystal phase causes uniform particle growth preferentially over abnormal particle growth, by increasing the sintering temperature and increasing the cooling rate, β- Abnormal grain growth of the Si 3 N 4 crystal phase is suppressed. Here, from the viewpoint of suppressing abnormal grain growth of the β-Si 3 N 4 crystal phase that can occur at a relatively low temperature, the cooling rate in cooling after sintering is preferably 100 ° C./min or more, and 120 ° C./min or more. Is more preferable. Thus, the aspect ratio is prevented from becoming too large, and the aspect ratio, which is the ratio of the major axis grain size to the minor axis grain size of the Si 3 N 4 crystal grains, can be set to 2.0 or more and 7.7 or less. .
　ここで結晶成長の核となるβ－Ｓｉ3Ｎ4結晶相の粒子は、Ｙによる不純物酸素除去の効果が発揮されない。しかし、不純物の少ない核を用いることができれば、高い熱伝導率を有する示すＳｉ3Ｎ4結晶粒子が得られる。そこで、不純物である酸素、炭素、および金属元素が従来よりも少ない高純度のβ－Ｓｉ3Ｎ4結晶相を含む直接窒化粉末を原料として用いることは、高い熱伝導率を有する窒化ケイ素焼結体が得られやすい観点から、好ましい。 Here, the β-Si 3 N 4 crystal phase particles serving as the nucleus of crystal growth do not exhibit the effect of removing impurity oxygen by Y. However, if nuclei with few impurities can be used, Si 3 N 4 crystal particles having high thermal conductivity can be obtained. Therefore, the use of direct nitrided powder containing β-Si 3 N 4 crystal phase of high purity β-Si 3 N 4 as a raw material, which has less oxygen, carbon and metal elements as impurities, makes silicon nitride sintered with high thermal conductivity. It is preferable from the viewpoint of easily obtaining a body.
　原料のＳｉ3Ｎ4粉末の定量分析には、ＰＡＮａｌｙｔｉｃａｌ社製Ｘ’Ｐｅｒｔ　ＰＲＯまたは同等の装置によるＸ線回折後、Ｒｉｇａｋｕ社製統合粉末Ｘ線解析ソフトウェアのＰＤＸＬ２または同等のソフトウェアを利用する。α－Ｓｉ3Ｎ4結晶相およびβ－Ｓｉ3Ｎ4結晶相の同定には、粉末Ｘ線回折データベースとしてＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．２６１９１およびＮｏ．７９７９８をそれぞれ利用し、ＲＩＲ（参照強度比）法により定量化する。Ｘ線回折は、４５ｋＶ、４０ｍＡで励起したＣｕ－Ｋα線を利用し、θ－２θ法による走査、０．０３°のステップ幅、１秒の積算時間で行なう。 For quantitative analysis of the raw material Si 3 N 4 powder, X'Pert PRO made by PANalytical or X-ray diffraction by an equivalent apparatus, and then PDXL2 of integrated powder X-ray analysis software made by Rigaku or equivalent software is used. For identification of the α-Si 3 N 4 crystal phase and the β-Si 3 N 4 crystal phase, ICDD PDF-4 + 2014 No. 1 was used as a powder X-ray diffraction database. 26191 and no. 79798, respectively, and quantified by RIR (reference intensity ratio) method. X-ray diffraction is performed using a Cu-Kα ray excited at 45 kV and 40 mA, scanning by the θ-2θ method, a step width of 0.03 °, and an integration time of 1 second.
　本実施形態の窒化ケイ素焼結体は、複数の窒化ケイ素（Ｓｉ3Ｎ4）結晶粒子と、Ｓｉ3Ｎ4結晶粒子以外の部分である粒界相と、を含むことが好ましい。粒界相は、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相、あるいは、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相およびＹ2Ｓｉ3Ｎ3Ｏ4結晶相、を含むことが高い熱伝導率を有する観点から好ましい。Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークの強度ＩY20に対するＹ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークの強度ＩY2の比ＩY2／ＩY20が０以上３．０以下であることが高い熱伝導率を有する観点から好ましい。Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相およびＹ2Ｓｉ3Ｎ3Ｏ4結晶相は、Ｓｉ3Ｎ4結晶粒子中の固溶酸素をトラップするために生成させる。Ｓｉ3Ｎ4結晶粒子中に固溶している酸素（Ｏ）は焼結体の熱伝導率を低減する原因となるが、焼結助剤として酸化イットリウム（Ｙ2Ｏ3）を添加すると、ＯはＳｉ3Ｎ4結晶粒子中よりもＹ20Ｎ4Ｓｉ12Ｏ48やＹ2Ｓｉ3Ｎ3Ｏ4のような酸窒化物の結晶相として粒界相中に存在する方が安定になるため、焼結体の熱伝導率を低減する原因となるＳｉ3Ｎ4結晶粒子中の固溶酸素の量の低減が可能となる。特に、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相は１つのＹ原子がトラップするＯ原子の個数が多いため、焼結体の熱伝導率の低減の要因の１つである粒界相の量を増やすことなく、Ｓｉ3Ｎ4結晶粒子中の固溶酸素の量を低減することができる。 The silicon nitride sintered body of the present embodiment preferably includes a plurality of silicon nitride (Si 3 N 4 ) crystal particles and a grain boundary phase that is a portion other than the Si 3 N 4 crystal particles. The grain boundary phase includes a Y 20 N 4 Si 12 O 48 crystal phase, or a Y 20 N 4 Si 12 O 48 crystal phase and a Y 2 Si 3 N 3 O 4 crystal phase, and has high thermal conductivity. It is preferable from the viewpoint. Intensity of X-ray diffraction peak due to (112) plane of Y 20 N 4 Si 12 O 48 crystal phase I X-ray diffraction peak due to (211) plane of Y 2 Si 3 N 3 O 4 crystal phase with respect to Y20 The ratio I Y2 / I Y20 of the strength I Y2 is preferably 0 or more and 3.0 or less from the viewpoint of high thermal conductivity. The Y 20 N 4 Si 12 O 48 crystal phase and the Y 2 Si 3 N 3 O 4 crystal phase are generated to trap solid solution oxygen in the Si 3 N 4 crystal particles. Oxygen (O) dissolved in the Si 3 N 4 crystal particles causes a reduction in the thermal conductivity of the sintered body, but when yttrium oxide (Y 2 O 3 ) is added as a sintering aid, O is more stable when present in the grain boundary phase as an oxynitride crystal phase such as Y 20 N 4 Si 12 O 48 or Y 2 Si 3 N 3 O 4 than in Si 3 N 4 crystal grains. Therefore, it is possible to reduce the amount of dissolved oxygen in the Si 3 N 4 crystal particles that causes the thermal conductivity of the sintered body to be reduced. In particular, since the Y 20 N 4 Si 12 O 48 crystal phase has a large number of O atoms trapped by one Y atom, the amount of grain boundary phase, which is one of the factors for reducing the thermal conductivity of the sintered body, is reduced. Without increasing, the amount of dissolved oxygen in the Si 3 N 4 crystal particles can be reduced.
　窒化ケイ素焼結体中のＹ20Ｎ4Ｓｉ12Ｏ48結晶相とＹ2Ｓｉ3Ｎ3Ｏ4結晶相との存在比は、粒界相の量を増やすことなくＳｉ3Ｎ4結晶粒子中の固溶酸素の量を低減することにより、高い熱伝導率を有する窒化ケイ素焼結体を得る観点から、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークの強度ＩY20に対するＹ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークの強度ＩY2の比ＩY2／ＩY20は０以上３．０以下が好ましい。かかる観点から、比ＩY2／ＩY20は、０．１以上がより好ましく、０．５以上がさらに好ましく、また、２．５以下がより好ましく、２．０がさらに好ましい。 The abundance ratio of the Y 20 N 4 Si 12 O 48 crystal phase and the Y 2 Si 3 N 3 O 4 crystal phase in the silicon nitride sintered body is not increased in the Si 3 N 4 crystal grains without increasing the amount of the grain boundary phase. From the viewpoint of obtaining a silicon nitride sintered body having a high thermal conductivity by reducing the amount of dissolved oxygen, an X-ray diffraction peak caused by the (112) plane of the Y 20 N 4 Si1 2 O 48 crystal phase the ratio I Y2 / I Y20 of Y 2 Si 3 N 3 O 4 intensity of X-ray diffraction peak due to (211) plane of the crystal phase I Y2 with respect to the intensity I Y20 of 0 to 3.0 is preferred. From this viewpoint, the ratio I Y2 / I Y20 is more preferably 0.1 or more, further preferably 0.5 or more, more preferably 2.5 or less, and further preferably 2.0.
　Ｘ線回折には、ＰＡＮａｌｙｔｉｃａｌ社製Ｘ’Ｐｅｒｔ　ＰＲＯまたは同等装置を使用し、Ｘ線は励起条件が４５ｋＶで４０ｍＡのＣｕ－Ｋα線を、走査はθ－２θ法を利用する。ステップ幅は０．０３°、積算時間は１秒である。Ｘ線回折ピークの解析には、Ｒｉｇａｋｕ社製統合粉末Ｘ線解析ソフトウェアのＰＤＸＬ２または同等のソフトウェアを使用する。Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークとは、２θが３０～３３°の間の低角側に存在するピークを指し、粉末Ｘ線回折データベースとしてＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．００－０３０－１４６２を用いて同定される。Ｙ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークとは、２θが３０～３３°の間の高角側に存在するピークを指し、国際回折データセンターによる粉末回折データファイルであるＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．０１－０７６－０７２４を用いて同定される。 For X-ray diffraction, X'Pert PRO manufactured by PANalytical or an equivalent apparatus is used. For X-rays, a 40-mA Cu-Kα ray under an excitation condition of 45 kV is used, and for scanning, a θ-2θ method is used. The step width is 0.03 ° and the integration time is 1 second. For the analysis of the X-ray diffraction peak, PDXL2 of the integrated powder X-ray analysis software manufactured by Rigaku or equivalent software is used. The X-ray diffraction peak attributed to the (112) plane of the Y 20 N 4 Si 12 O 48 crystal phase refers to a peak existing on the low angle side where 2θ is between 30 and 33 °. As a powder X-ray diffraction database ICDD PDF-4 + 2014 No. Identified using 00-030-1462. The X-ray diffraction peak attributed to the (211) plane of the Y 2 Si 3 N 3 O 4 crystal phase refers to the peak existing on the high angle side between 2θ and 30 to 33 °. Powder diffraction by the International Diffraction Data Center No. of ICDD PDF-4 + 2014 which is a data file. Identified using 01-076-0724.
　上記のＹ20Ｎ4Ｓｉ12Ｏ48結晶相の存在率を高くするため、本実施形態の窒化ケイ素焼結体の製造においては、１９５０℃以上という高温にて焼結を行った後に、焼結温度から１０００℃まで１００℃／ｍｉｎ以上の冷却速度で急速に冷却するのが好ましい。１９５０℃以上という高温での焼結によりＹの拡散速度が速まるため、より効果的にＹ20Ｎ4Ｓｉ12Ｏ48結晶相が形成され、かつ、１００℃／ｍｉｎ以上の冷却速度で急速に冷却することによりＹ20Ｎ4Ｓｉ12Ｏ48結晶相からＹ2Ｓｉ3Ｎ3Ｏ4結晶相への変態が抑制される。すなわち、ＯのＹ20Ｎ4Ｓｉ12Ｏ48結晶相からの排出を抑制するとともに、粒界相からＳｉ3Ｎ4結晶粒子へのＯの再固溶を抑制させることができる。冷却速度は、より好ましくは１２０℃／ｍｉｎ以上である。 In order to increase the abundance ratio of the Y 20 N 4 Si 12 O 48 crystal phase, in the production of the silicon nitride sintered body of this embodiment, sintering is performed after sintering at a high temperature of 1950 ° C. or higher. It is preferable to rapidly cool from the temperature to 1000 ° C. at a cooling rate of 100 ° C./min or more. Since the diffusion rate of Y is increased by sintering at a high temperature of 1950 ° C. or higher, the Y 20 N 4 Si 12 O 48 crystal phase is more effectively formed and rapidly cooled at a cooling rate of 100 ° C./min or higher. By doing so, the transformation from the Y 20 N 4 Si 12 O 48 crystal phase to the Y 2 Si 3 N 3 O 4 crystal phase is suppressed. That is, it is possible to suppress the discharge of O from the Y 20 N 4 Si 12 O 48 crystal phase and to suppress the re-solution of O from the grain boundary phase to the Si 3 N 4 crystal particle. The cooling rate is more preferably 120 ° C./min or more.
　本実施形態の窒化ケイ素焼結体は、熱伝導率を高くする観点から、ケイ素（Ｓｉ）、イットリウム（Ｙ）およびマグネシウム（Ｍｇ）以外の各種の不純物金属元素の含有率が、各々０．５質量％以下であることが好ましく、各々０．３質量％以下であることがより好ましく、各々０．１質量％以下であることがさらに好ましい。上述のとおり、Ｓｉ3Ｎ4結晶粒子への不純物金属元素の単体および／または化合物の固溶は焼結体の熱伝導率を低下させる原因となる。たとえば、Ａｌの単体および／または化合物は、Ｓｉ3Ｎ4結晶粒子に固溶しやすく、低い熱伝導率を有するサイアロン（Ｓｉ6-ZＡｌZＯZＮ8-Z、ここでＺは０から４までの有理数）を生成するため、焼結体の高熱伝導化の阻害因子となる。 In the silicon nitride sintered body of the present embodiment, the content of various impurity metal elements other than silicon (Si), yttrium (Y), and magnesium (Mg) is 0.5 from the viewpoint of increasing the thermal conductivity. The content is preferably not more than mass%, more preferably not more than 0.3 mass%, and still more preferably not more than 0.1 mass%. As described above, the solid solution of the impurity metal element and / or the compound in the Si 3 N 4 crystal particles causes a decrease in the thermal conductivity of the sintered body. For example, a simple substance and / or compound of Al is a sialon (Si 6-Z Al Z O Z N 8-Z , where Z is from 0), which is easily dissolved in Si 3 N 4 crystal particles and has a low thermal conductivity. (Rational number up to 4) is generated, which is an inhibitor of high thermal conductivity of the sintered body.
　原料粉末および焼結体中の不純物金属元素の定量分析には、ＩＣＰ（誘導結合プラズマ）を光源とする発光分光分析（ＡＥＳ）を利用する。ＩＣＰ－ＡＥＳ装置には、たとえば、ＳＨＩＭＡＤＺＵ社製ＩＣＰＳ－８１００または同等の装置を用いる。ＩＣＰ－ＡＥＳの際の手順を以下に例示する。前処理として、まず、焼結体をメノウ製の乳鉢と乳棒を使用して粉砕する。その後、０．１ｇの粉砕したその焼結体の粉末を２ｇの炭酸カルシウムおよび０．５ｇの酸化ホウ素からなるアルカリ溶媒とともに白金ルツボ中に投入して１０００℃で溶融し、その溶融体を２０ｍｌの３５質量％の塩酸および２０ｍｌのイオン交換水からなる酸性溶液内にて６０℃で回収した後に、イオン交換水にて２００ｍｌまで希釈する。このようにして得られる試料溶液を霧状にしてＡｒプラズマに導入することにより励起された金属元素が、基底状態に戻る際に放出される光を分光しその強度から定量分析を行なう。 Quantitative analysis of impurity metal elements in the raw material powder and the sintered body uses emission spectroscopic analysis (AES) using ICP (inductively coupled plasma) as a light source. As the ICP-AES device, for example, ICPS-8100 manufactured by SHIMADZU or an equivalent device is used. The procedure for ICP-AES is illustrated below. As a pretreatment, the sintered body is first pulverized using an agate mortar and pestle. Thereafter, 0.1 g of the pulverized sintered body powder was poured into a platinum crucible together with 2 g of calcium carbonate and 0.5 g of boron oxide in a platinum crucible and melted at 1000 ° C. It collect | recovers at 60 degreeC in the acidic solution which consists of 35 mass% hydrochloric acid and 20 ml ion-exchange water, Then, it dilutes to 200 ml with ion-exchange water. The sample solution thus obtained is atomized and introduced into Ar plasma, and the light emitted when the metal element excited is returned to the ground state is subjected to quantitative analysis from the intensity.
　本実施形態の窒化ケイ素焼結体は、酸化マグネシウム（ＭｇＯ）結晶相が存在しないことが好ましい。かかる窒化ケイ素焼結体は、焼結中に酸化マグネシウム（ＭｇＯ）を蒸発させることにより、熱伝導率を低くする要因の粒界相の量を低減できるため、高い熱伝導率を有することができる。 The silicon nitride sintered body according to the present embodiment preferably has no magnesium oxide (MgO) crystal phase. Such a silicon nitride sintered body can have a high thermal conductivity because the amount of grain boundary phase that causes a decrease in thermal conductivity can be reduced by evaporating magnesium oxide (MgO) during sintering. .
　窒化ケイ素焼結体中のＭｇＯ結晶相の同定のため、Ｘ線回折を行なう。Ｘ線回折には、ＰＡＮａｌｙｔｉｃａｌ社製Ｘ’Ｐｅｒｔ　ＰＲＯまたは同等の装置を使用し、Ｘ線は励起条件が４５ｋＶで４０ｍＡのＣｕ－Ｋα線を、走査はθ－２θ法を利用する。ステップ幅は０．０３°、積算時間は１秒である。Ｘ線回折ピークの解析には、Ｒｉｇａｋｕ社製統合粉末Ｘ線解析ソフトウェアのＰＤＸＬ２または同等のソフトウェアを使用する。２θが４２．５～４３．１°の間にＭｇＯの（２００）面に起因するＸ線回折ピークが、見られない場合あるいはバックグラウンドと見分けがつかない場合は、Ｓｉ3Ｎ4焼結体中にＭｇＯ結晶相が存在しないと考える。窒化ケイ素焼結体を焼結する際の焼結後の冷却速度を１００℃／ｍｉｎ以上とすることにより、ＭｇＯ結晶が結晶化しないようにすることができる。かかる観点から、冷却速度は１２０℃／ｍｉｎ以上が好ましい。 X-ray diffraction is performed to identify the MgO crystal phase in the silicon nitride sintered body. For X-ray diffraction, X'Pert PRO manufactured by PANalytical or an equivalent apparatus is used. For X-rays, 40 mA Cu-Kα ray under an excitation condition of 45 kV is used, and for scanning, θ-2θ method is used. The step width is 0.03 ° and the integration time is 1 second. For the analysis of the X-ray diffraction peak, PDXL2 of the integrated powder X-ray analysis software manufactured by Rigaku or equivalent software is used. If the X-ray diffraction peak due to the (200) plane of MgO is not seen between 2θ and 42.5 to 43.1 °, or is indistinguishable from the background, the Si 3 N 4 sintered body It is considered that there is no MgO crystal phase inside. By setting the cooling rate after sintering when sintering the silicon nitride sintered body to 100 ° C./min or more, the MgO crystal can be prevented from crystallizing. From this viewpoint, the cooling rate is preferably 120 ° C./min or more.
　本実施形態の窒化ケイ素焼結体は、熱伝導率が９５Ｗ・ｍ-1・Ｋ-1以上であることが好ましく、１００Ｗ・ｍ-1・Ｋ-1以上であることがより好ましく、１１０Ｗ・ｍ-1・Ｋ-1以上であることがさらに好ましい。かかる窒化ケイ素焼結体は、放熱特性が高く、半導体デバイスの放熱基板として有用である。Ｓｉ3Ｎ4焼結体の熱伝導率が９５Ｗ・ｍ-1・Ｋ-1未満であると、放熱基板上部の半導体デバイスが十分に放熱されないために、半導体デバイスがその耐熱温度以上となることにより破壊し、十分なデバイス特性を得ることができない。 The silicon nitride sintered body of the present embodiment preferably has a thermal conductivity of 95 W · m −1 · K −1 or more, more preferably 100 W · m −1 · K −1 or more, and 110 W · More preferably, it is m −1 · K −1 or more. Such a silicon nitride sintered body has high heat dissipation characteristics and is useful as a heat dissipation substrate for semiconductor devices. When the thermal conductivity of the Si 3 N 4 sintered body is less than 95 W · m −1 · K −1 , the semiconductor device above the heat dissipation substrate is not sufficiently dissipated, so that the semiconductor device exceeds its heat resistance temperature. It is not possible to obtain sufficient device characteristics.
　Ｓｉ3Ｎ4焼結体の熱伝導率を導出するためには、熱拡散率、比重、比熱が必要である。熱拡散率の測定には、光交流法（スキャニングレーザ加熱ＡＣ（Ａｌｔｅｒｎａｔｉｖｅ　Ｃｕｒｒｅｎｔ）法・Ａｎｇｔｒｏｍ法）またはレーザフラッシュ法を使用する。光交流法では、ＵＬＶＡＣ社製Ｌａｓｅｒ－ＰＩＴ装置または同等装置を使用する。本装置での測定手順を以下に例示する。照度が均一な周波数２．５～１０Ｈｚの帯状レーザ光を照射しつつサンプル長手方向にレーザ光を移動させることにより、試料の裏面に取り付けた一本の熱電対でＡＣ温度応答を測定し、その温度応答の振幅と位置に対する減衰率から熱拡散率を算出する。サンプル形状は、幅２．５～５ｍｍ、長さ３０ｍｍ、厚さ０．５ｍｍ以下であり、レーザ加熱面のみグラファイトスプレーにて黒体化処理を行なう。熱電対とサンプルは銀ペーストにて接着する。レーザフラッシュ法では、ＵＬＶＡＣ社製ＴＣ－７０００または同等装置を使用する。試験片の表面にレーザパルスを照射したときの試験片裏面の温度履歴曲線から熱拡散率を算出する（ＪＩＳ－Ｒ１６１１：２０１０を参照）。サンプル形状は、直径１０ｍｍ、厚さ３～６ｍｍであり、サンプル全体をグラファイトスプレーにて黒体化処理を行なう。比重測定にはアルキメデス法を使用し、比熱には０．６８Ｊ・ｇ-1・Ｋ-1を用いる。 In order to derive the thermal conductivity of the Si 3 N 4 sintered body, thermal diffusivity, specific gravity, and specific heat are required. For the measurement of the thermal diffusivity, an optical alternating current method (scanning laser heating AC (Alternative Current) method / Angtrom method) or a laser flash method is used. In the optical alternating current method, a Laser-PIT apparatus manufactured by ULVAC or an equivalent apparatus is used. The measurement procedure with this apparatus is illustrated below. The AC temperature response is measured with a single thermocouple attached to the back surface of the sample by moving the laser beam in the longitudinal direction of the sample while irradiating a band-shaped laser beam with a uniform frequency of 2.5 to 10 Hz. The thermal diffusivity is calculated from the attenuation rate with respect to the amplitude and position of the temperature response. The sample shape is 2.5 to 5 mm in width, 30 mm in length, and 0.5 mm or less in thickness. Only the laser heating surface is blackened with graphite spray. The thermocouple and the sample are bonded with silver paste. In the laser flash method, TC-7000 manufactured by ULVAC or an equivalent device is used. The thermal diffusivity is calculated from the temperature history curve on the back surface of the test piece when the surface of the test piece is irradiated with a laser pulse (see JIS-R1611: 2010). The sample has a diameter of 10 mm and a thickness of 3 to 6 mm, and the entire sample is blackened with graphite spray. The Archimedes method is used for the specific gravity measurement, and 0.68 J · g −1 · K −1 is used for the specific heat.
　本実施形態の窒化ケイ素焼結体は、窒化ケイ素焼結体の任意に特定される断面における窒化ケイ素（Ｓｉ3Ｎ4）結晶粒子に対するＳｉ3Ｎ4結晶粒子以外の部分である粒界相の面積比率が、１０％以下であることが好ましく、９％以下であることがより好ましく、６％以下であることがさらに好ましい。かかる窒化ケイ素焼結体は、Ｓｉ3Ｎ4結晶粒子に対する粒界相の面積比率が１０％以下であるため、高い熱伝導率を有することができる。 The silicon nitride sintered body of the present embodiment has a grain boundary phase which is a portion other than the Si 3 N 4 crystal particles with respect to the silicon nitride (Si 3 N 4 ) crystal particles in an arbitrarily specified cross section of the silicon nitride sintered body. The area ratio is preferably 10% or less, more preferably 9% or less, and even more preferably 6% or less. Such a silicon nitride sintered body can have high thermal conductivity because the area ratio of the grain boundary phase to the Si 3 N 4 crystal particles is 10% or less.
　窒化ケイ素焼結体は、Ｓｉ3Ｎ4結晶粒子とそれ以外の粒界相とで形成される。窒化ケイ素焼結体の任意に特定される断面におけるＳｉ3Ｎ4結晶粒子の面積Ｓ、それ以外の粒界相（かかる粒界相はＳｉ3Ｎ4結晶粒子の間に存在する）の面積ＳB、およびＳｉ3Ｎ4結晶粒子に対する粒界相の面積比率１００×ＳB／Ｓの解析には、ＳＥＭ（走査型電子顕微鏡）－ＥＢＳＤ（電子線後方散乱回折）測定を利用する。ＳＥＭ観察にはＣａｒｌ　Ｚｅｉｓｓ社製ＳＵＰＲＡ　３５　ＶＰまたは同等装置を利用し、電子後方散乱回折にはＴＳＬソリューションズ社製ＯＩＭ５．２または同等装置を利用する。 The silicon nitride sintered body is formed of Si 3 N 4 crystal grains and other grain boundary phases. The area S of Si 3 N 4 crystal grains in an arbitrarily specified cross section of the silicon nitride sintered body, and the area S of other grain boundary phases (such grain boundary phases exist between Si 3 N 4 crystal grains). SEM (scanning electron microscope) -EBSD (electron beam backscatter diffraction) measurement is used for the analysis of the area ratio 100 × S B / S of the grain boundary phase with respect to B and Si 3 N 4 crystal grains. For SEM observation, SUPRA 35 VP manufactured by Carl Zeiss or an equivalent device is used, and for electron backscatter diffraction, OIM5.2 manufactured by TSL Solutions or an equivalent device is used.
　ＳＥＭ－ＥＢＳＤ測定の手順を以下に例示する。前処理として、平面研削盤を利用してダイヤモンド砥石（アライドマテリアル社製ダイヤモンド研削砥石＃４００）を用いて、焼結体の表面から５００μｍ以上の深さまで研削後、ケメット社製ラップ加工機を利用して仕上げ加工する。まず、銅定盤と粒径が３μｍのダイヤモンド砥石とを用いて焼結体をその表面から１０μｍ以上の深さまで研磨し、次に、錫定盤と粒径が０．５μｍのダイヤモンド砥石とを用いて焼結体をその研削後の表面から３μｍ以上の深さまで研磨する。この際、仕上げ加工における両研磨とも、回転数５０ｒｐｍ、荷重０．２ＭＰａの条件で行なう。表面加工は、上記と同等の加工でも構わない。 The SEM-EBSD measurement procedure is illustrated below. As pre-processing, after grinding to a depth of 500 μm or more from the surface of the sintered body using a diamond grindstone (Diamond grindstone # 400 made by Allied Material) using a surface grinder, use a lapping machine made by Kemet And finish processing. First, the sintered body is polished from its surface to a depth of 10 μm or more using a copper surface plate and a diamond grindstone having a particle size of 3 μm. Next, a tin surface plate and a diamond grindstone having a particle size of 0.5 μm are polished. The sintered body is polished to a depth of 3 μm or more from the ground surface. At this time, both polishings in the finishing process are performed under conditions of a rotation speed of 50 rpm and a load of 0.2 MPa. The surface processing may be processing equivalent to the above.
　ＥＢＳＤ測定は、測定面積３０μｍ×１００μｍとし、測定条件として例えば加速電圧１５ｋＶ、ワーキングディスタンス１５ｍｍ、ステップサイズ０．１μｍ、ビニング８×８、積算時間０．０１秒で行ない、ＩＱ（イメージクオリティ）マップを取得した。本画像を、ＩｍａｇｅＪソフトウェアにより二値化処理し、窒化ケイ素焼結体において、白色を呈する明部をＳｉ3Ｎ4結晶粒子とし、黒色を呈する暗部を粒界相として、Ｓｉ3Ｎ4結晶粒子の面積Ｓおよび粒界相の面積ＳBのそれぞれを算出し、Ｓｉ3Ｎ4結晶粒子に対する粒界相の面積比率１００×ＳB／Ｓを算出する。なお、Ｓｉ3Ｎ4結晶粒子に対する粒界相の面積比率の算出に用いるＩＱマップ画像は、解析費用の抑制の観点から、上記のＳｉ3Ｎ4結晶粒子の短軸粒径およびアスペクト比の算出に用いるＩＱマップ画像と同じであってもよい。 The EBSD measurement is performed with a measurement area of 30 μm × 100 μm and measurement conditions such as an acceleration voltage of 15 kV, a working distance of 15 mm, a step size of 0.1 μm, a binning of 8 × 8 and an integration time of 0.01 seconds, and an IQ (image quality) map. I got it. This image was binarized by ImageJ software, and in the silicon nitride sintered body, the bright portion showing white was Si 3 N 4 crystal particles, and the dark portion showing black was a grain boundary phase, and Si 3 N 4 crystal particles Of the grain boundary phase and the area S B of the grain boundary phase are calculated, and the area ratio 100 × S B / S of the grain boundary phase to the Si 3 N 4 crystal grains is calculated. Incidentally, IQ map image used to calculate the area ratio of the grain boundary phase to the Si 3 N 4 crystal grains, calculated in terms of suppression of analysis costs, the minor axis particle diameter and the aspect ratio of the the Si 3 N 4 crystal grains It may be the same as the IQ map image used for.
　（窒化ケイ素焼結体の製造方法）
　本実施形態の窒化ケイ素焼結体の製造方法は、特に制限はなく、たとえば、窒化ケイ素（Ｓｉ3Ｎ4）、イットリウム（Ｙ）、マグネシウム（Ｍｇ）および酸素（Ｏ）を含む原料を準備する原料準備工程と、原料を成形して成形体を得る成形工程と、成形体を焼結して焼結体を得る焼結工程と、を含む。本実施形態の窒化ケイ素焼結体の製造方法により、高い熱伝導率を有する窒化ケイ素焼結体が高い生産性で得られる。 (Method for producing silicon nitride sintered body)
The method for producing the silicon nitride sintered body of the present embodiment is not particularly limited, and for example, a raw material containing silicon nitride (Si 3 N 4 ), yttrium (Y), magnesium (Mg), and oxygen (O) is prepared. A raw material preparation step, a forming step of forming a raw material to obtain a formed body, and a sintering step of sintering the formed body to obtain a sintered body. By the method for producing a silicon nitride sintered body of the present embodiment, a silicon nitride sintered body having high thermal conductivity can be obtained with high productivity.
　原料準備工程は、特に制限はなく、たとえば、Ｓｉ3Ｎ4、Ｙ、ＭｇおよびＯを含む原料として、窒化ケイ素（Ｓｉ3Ｎ4）粉末、酸化イットリウム（Ｙ2Ｏ3）粉末、および酸化マグネシウム（ＭｇＯ）粉末の混合粉末を準備できる。窒化ケイ素（Ｓｉ3Ｎ4）粉末、酸化イットリウム（Ｙ2Ｏ3）粉末、および酸化マグネシウム（ＭｇＯ）粉末の混合割合は、特に制限はないが、短軸粒径が１．７μｍ以上１０．５μｍ以下、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下であり、熱伝導率が高い窒化ケイ素焼結体を得る観点から、原料とする全ての無機原料粉末を１００質量部としたとき、Ｓｉ3Ｎ4粉末が８７．６質量部以上９８．５質量部以下、Ｙ2Ｏ3粉末が１．０質量部以上１０．４質量部以下、およびＭｇＯ粉末が０．５質量部以上２．０質量部以下であることが好ましい。 The raw material preparation step is not particularly limited. For example, as a raw material containing Si 3 N 4 , Y, Mg and O, silicon nitride (Si 3 N 4 ) powder, yttrium oxide (Y 2 O 3 ) powder, and magnesium oxide A mixed powder of (MgO) powder can be prepared. The mixing ratio of the silicon nitride (Si 3 N 4 ) powder, the yttrium oxide (Y 2 O 3 ) powder, and the magnesium oxide (MgO) powder is not particularly limited, but the minor axis particle size is 1.7 μm or more and 10.5 μm. Hereinafter, from the viewpoint of obtaining a silicon nitride sintered body having an aspect ratio, which is a ratio of a major axis grain size to a minor axis grain size, of 2.0 or more and 7.7 or less and high thermal conductivity, all inorganic materials used as raw materials When the raw material powder is 100 parts by mass, the Si 3 N 4 powder is 87.6 parts by mass to 98.5 parts by mass, the Y 2 O 3 powder is 1.0 part by mass to 10.4 parts by mass, and MgO The powder is preferably 0.5 parts by mass or more and 2.0 parts by mass or less.
　ここで、Ｓｉ3Ｎ4粉末は、特に制限はないが、短軸粒径が１．７μｍ以上１０．５μｍ以下、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下であり、熱伝導率が高い窒化ケイ素焼結体を得る観点から、ケイ素単体を高温やプラズマなどの活性な雰囲気下でアンモニアや窒素などにより直接窒化することにより得られる直接窒化粉末、あるいは、ハロゲン化ケイ素とアンモニアとの反応生成物であるシリコンジイミド（Ｓｉ（ＮＨ）2）、シリコンテトラアミド（Ｓｉ（ＮＨ2）4）、シリコンニトロゲンイミド（Ｓｉ2Ｎ2ＮＨ）などのイミド系化合物を熱分解することにより得られるイミド分解粉末と直接窒化粉末との混合粉末であることが好ましい。 Here, the Si 3 N 4 powder is not particularly limited, but the minor axis particle size is 1.7 μm or more and 10.5 μm or less, and the aspect ratio which is the ratio of the major axis particle size to the minor axis particle size is 2.0 or more. Directly nitrided powder obtained by directly nitriding silicon alone with ammonia or nitrogen in an active atmosphere such as high temperature or plasma from the viewpoint of obtaining a silicon nitride sintered body having a thermal conductivity of 7.7 or less Or silicon diimide (Si (NH) 2 ), silicon tetraamide (Si (NH 2 ) 4 ), silicon nitrogen imide (Si 2 N 2 NH), which are reaction products of silicon halide and ammonia A mixed powder of an imide decomposition powder obtained by thermally decomposing an imide compound and a direct nitriding powder is preferable.
　原料は、好適な焼結体を製造する観点から、さらに、焼結助剤、有機バインダー、解膠剤・分散剤、および分散媒などを添加することができる。 From the viewpoint of producing a suitable sintered body, a sintering aid, an organic binder, a peptizer / dispersant, a dispersion medium, and the like can be further added to the raw material.
　焼結助剤としては、たとえば、酸化マグネシウム（ＭｇＯ）粉末、酸化イットリウム（Ｙ2Ｏ3）粉末などが挙げられる。有機バインダーとしては、たとえば、ポリビニルブチラール（ＰＶＢ）などが挙げられる。解膠剤・分散剤としては、たとえば、ポリカルボン酸系化合物、ポリエチレンイミン系化合物、ポリオキシエチレン誘導体などが挙げられる。分散媒としては、たとえば、エタノールなどのアルコール類、水などが挙げられる。また、上記の原料の混合方法は、特に制限はなく、たとえば、ボールミル混合、超音波混合などが挙げられる。ボールミル混合においては、鉄（Ｆｅ）などの不純物元素の混入を極力防止する観点から、窒化ケイ素製のボールおよび容器を用いる。また、使用するボールミル混合容器の体積に対して０．２５～０．５倍の体積の原料スラリーを充填する。原料スラリーは３０分以上混合することで均一化する。超音波混合においては、原料スラリーは１０分以上の混合で均一化する。造粒の有無は問わない。 Examples of the sintering aid include magnesium oxide (MgO) powder, yttrium oxide (Y 2 O 3 ) powder, and the like. Examples of the organic binder include polyvinyl butyral (PVB). Examples of the deflocculant / dispersant include polycarboxylic acid compounds, polyethyleneimine compounds, polyoxyethylene derivatives, and the like. Examples of the dispersion medium include alcohols such as ethanol, water, and the like. The mixing method of the raw materials is not particularly limited, and examples thereof include ball mill mixing and ultrasonic mixing. In ball mill mixing, balls and containers made of silicon nitride are used from the viewpoint of preventing contamination of impurity elements such as iron (Fe) as much as possible. Further, the raw material slurry having a volume of 0.25 to 0.5 times the volume of the ball mill mixing container to be used is filled. The raw slurry is homogenized by mixing for 30 minutes or more. In ultrasonic mixing, the raw material slurry is homogenized by mixing for 10 minutes or more. The presence or absence of granulation does not matter.
　成形工程における成形方法は、特に制限はなく、たとえば、一軸加圧成形法、ＣＩＰ（冷間等方加圧）法などが挙げられる。成形圧力は、高密度の成形体を形成する観点から、０．５ｔｆ／ｃｍ2（重量トン／ｃｍ2）以上が好ましく、０．８ｔｆ／ｃｍ2以上がより好ましい。 There is no restriction | limiting in particular in the shaping | molding method in a shaping | molding process, For example, the uniaxial pressure molding method, the CIP (cold isostatic pressing) method, etc. are mentioned. The molding pressure is preferably 0.5 tf / cm 2 (weight ton / cm 2 ) or more, more preferably 0.8 tf / cm 2 or more, from the viewpoint of forming a high-density molded body.
　焼結工程は、特に制限はないが、好適な焼結体を得る観点から、脱脂サブ工程、焼結サブ工程、および冷却サブ工程を含むことが好ましい。脱脂サブ工程は、特に制限はなく、たとえば、８００℃以下の大気圧大気フロー雰囲気下で、残量炭素量が１０００ｐｐｍ以下になるまで脱脂することができる。焼結サブ工程は、特に制限はなく、たとえば、窒素雰囲気下０．５ＭＰａ以上１９５０℃以上の高圧高温条件で、焼結することができる。冷却サブ工程では、特に制限はないが、短軸粒径が１．７μｍ以上１０．５μｍ以下、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下であり、熱伝導率が高い窒化ケイ素焼結体を得る観点から、１００℃／ｍｉｎ以上の冷却速度で冷却することが好ましい。１００℃／ｍｉｎ以上の冷却速度を有する冷却工程により、高い熱伝導率を有する窒化ケイ素焼結体が高い生産性で得られる。かかる観点から、冷却工程の冷却温度は１２０℃以上がより好ましい。１００℃／ｍｉｎ未満の冷却速度では、所望の短軸粒径が１．７μｍ以上１０．５μｍ以下であり、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である窒化ケイ素焼結体を得ることが難しい。 The sintering process is not particularly limited, but preferably includes a degreasing sub-process, a sintering sub-process, and a cooling sub-process from the viewpoint of obtaining a suitable sintered body. The degreasing sub-process is not particularly limited, and for example, degreasing can be performed under an atmospheric pressure atmospheric flow atmosphere of 800 ° C. or less until the remaining carbon amount is 1000 ppm or less. There is no restriction | limiting in particular in a sintering sub process, For example, it can sinter on high pressure high temperature conditions of 0.5 MPa or more and 1950 degreeC or more in nitrogen atmosphere. Although there is no particular limitation in the cooling sub-process, the minor axis particle size is 1.7 μm or more and 10.5 μm or less, and the aspect ratio that is the ratio of the major axis particle size to the minor axis particle size is 2.0 or more and 7.7 or less. In view of obtaining a silicon nitride sintered body having a high thermal conductivity, it is preferable to cool at a cooling rate of 100 ° C./min or more. By the cooling step having a cooling rate of 100 ° C./min or more, a silicon nitride sintered body having high thermal conductivity can be obtained with high productivity. From this viewpoint, the cooling temperature in the cooling step is more preferably 120 ° C. or higher. At a cooling rate of less than 100 ° C./min, the desired minor axis particle size is 1.7 μm or more and 10.5 μm or less, and the aspect ratio, which is the ratio of the major axis particle size to the minor axis particle size, is 2.0 or more and 7. It is difficult to obtain a silicon nitride sintered body of 7 or less.
　本実施形態の窒化ケイ素焼結体の製造方法によれば、焼結時の最高温度での保持時間を長くしなくても、保持時間が４時間以上であれば、３０時間以下、より好ましくは１７時間以下であっても、熱伝導率が９５Ｗ・ｍ-1・Ｋ-1以上の窒化ケイ素焼結体を得ることができる。 According to the method for producing a silicon nitride sintered body of the present embodiment, even if the holding time at the maximum temperature during sintering is not increased, if the holding time is 4 hours or more, 30 hours or less, more preferably Even if it is 17 hours or less, a silicon nitride sintered body having a thermal conductivity of 95 W · m −1 · K −1 or more can be obtained.
　１．原料の準備
　実施例１～１３および比較例１～３について、表１～３に示す種類および質量部の窒化ケイ素（Ｓｉ3Ｎ4）粉末、酸化イットリウム（Ｙ2Ｏ3）粉末、および酸化マグネシウム（ＭｇＯ）粉末、有機バインダーとして表１～３に示す質量部のＰＶＢ（ポリビニルブチラール）、分散媒として表１～３に示す質量部のエタノールの混合スラリーを準備した。さらに、実施例５～７においては、上記の混合スラリーに解膠剤・分散剤として中京油脂社製セルナＦ－２１６およびセルナＥ５０３をそれぞれ１質量部および３質量部添加した。ここで、各原料の質量部とは、原料とする全ての無機原料粉末である窒化ケイ素（Ｓｉ3Ｎ4）粉末、酸化イットリウム（Ｙ2Ｏ3）粉末、および酸化マグネシウム（ＭｇＯ）粉末の合計の質量部を１００としたときの各原料の質量部をいう。 1. Preparation of Raw Materials For Examples 1 to 13 and Comparative Examples 1 to 3, the types and parts by mass of silicon nitride (Si 3 N 4 ) powder, yttrium oxide (Y 2 O 3 ) powder, and magnesium oxide shown in Tables 1 to 3 A mixed slurry of (MgO) powder, PVB (polyvinyl butyral) in parts by mass shown in Tables 1 to 3 as an organic binder, and ethanol in parts by mass shown in Tables 1 to 3 as a dispersion medium was prepared. Further, in Examples 5 to 7, 1 part by mass and 3 parts by mass of Selna F-216 and Selna E503 manufactured by Chukyo Yushi Co., Ltd. were added to the above mixed slurry as a peptizer / dispersant, respectively. Here, the mass part of each raw material is the total of silicon nitride (Si 3 N 4 ) powder, yttrium oxide (Y 2 O 3 ) powder, and magnesium oxide (MgO) powder, which are all inorganic raw material powders used as raw materials. The mass part of each raw material when the mass part of 100 is taken as 100.
　Ｓｉ3Ｎ4粉末の平均粒径は０．８μｍ以上１．３μｍ以下、Ｙ2Ｏ3粉末の平均粒径は１．３μｍ以上１．８μｍ以下、ＭｇＯ粉末の平均粒径は１．０μｍ以上１．５μｍ以下であった。これらの粉末の平均粒径は、ＭｉｃｒｏｔｒａｃＢＥＬ社製マイクロトラックＭＴ３３００ＥＸを用いてレーザ回折散乱法により測定した。また、Ｓｉ3Ｎ4粉末中のβ結晶相率（体積％）を表１～３中に示した。β結晶相率は、Ｘ線回折により定量した。Ｓｉ3Ｎ4粉末中には、不純物金属元素としてのＡｌ、Ｃａ、Ｆｅ、およびＭｇがそれぞれ０．１質量％以下、不純物非金属元素としてのＯが０．５質量％以下含まれていた。 The average particle size of the Si 3 N 4 powder is 0.8 μm to 1.3 μm, the average particle size of the Y 2 O 3 powder is 1.3 μm to 1.8 μm, and the average particle size of the MgO powder is 1.0 μm to 1 μm. .5 μm or less. The average particle size of these powders was measured by a laser diffraction scattering method using Microtrac BEL Microtrac MT3300EX. Tables 1 to 3 show the β crystal phase ratio (% by volume) in the Si 3 N 4 powder. The β crystal phase ratio was quantified by X-ray diffraction. The Si 3 N 4 powder contained 0.1% by mass or less of Al, Ca, Fe, and Mg as impurity metal elements, and 0.5% by mass or less of O as an impurity nonmetallic element.
　不純物金属元素の分析は、ＩＣＰ－ＡＥＳを利用して、原料Ｓｉ3Ｎ4粉末を含む試料溶液を霧状にしてＡｒプラズマに導入することにより励起された金属元素が基底状態に戻る際に放出される光の波長から定性分析を行ない、その光の強度から定量分析を行なった。これにより、原料Ｓｉ3Ｎ4粉末中に存在するＡｌ、Ｃａ、Ｆｅ、Ｍｇの質量％が得られた。原料Ｓｉ3Ｎ4粉末の溶液は、０．１ｇの前処理粉末を、２ｇの炭酸カルシウムおよび０．５ｇの酸化ホウ素からなるアルカリ溶媒とともに、白金ルツボ中に投入して１０００℃で溶融し、その溶融体を２０ｍｌの３５質量％の塩酸および２０ｍｌのイオン交換水からなる酸性溶液内にて６０℃で回収した後に、イオン交換水にて２００ｍｌまで希釈することにより作製した。光の強度がバックグラウンドと同等であっても０．０１質量％以下とした。 The analysis of impurity metal elements uses ICP-AES and releases when the excited metal elements return to the ground state by introducing the sample solution containing the raw material Si 3 N 4 powder into a mist and introducing it into Ar plasma. Qualitative analysis was performed from the wavelength of the emitted light, and quantitative analysis was performed from the intensity of the light. Thus, Al is present in the starting material Si 3 N 4 powder, Ca, Fe, mass% of Mg was obtained. A solution of the raw material Si 3 N 4 powder was prepared by adding 0.1 g of the pretreated powder together with 2 g of calcium carbonate and 0.5 g of boron oxide into a platinum crucible and melting at 1000 ° C. The melt was collected at 60 ° C. in an acidic solution composed of 20 ml of 35% by mass hydrochloric acid and 20 ml of ion exchange water, and then diluted to 200 ml with ion exchange water. Even if the intensity of light is equivalent to the background, it was set to 0.01% by mass or less.
　原料として、Ｓｉ3Ｎ4粉末、Ｙ2Ｏ3粉末、ＭｇＯ粉末、有機バインダーであるＰＶＢ（ポリビニルブチラール）、分散媒であるエタノール、および必要な場合に解膠剤・分散剤である中京油脂社製セルナＦ－２１６およびセルナＥ５０３をそれぞれ１質量部および３質量部を、６０分間の超音波混合により均一な混合スラリーを作製した。 As raw materials, Si 3 N 4 powder, Y 2 O 3 powder, MgO powder, PVB (polyvinyl butyral) as an organic binder, ethanol as a dispersion medium, and Chukyo Yushi Co., Ltd. as a peptizer / dispersant when necessary Uniform mixed slurries were prepared by ultrasonically mixing 1 part by mass and 3 parts by mass of Celna F-216 and Celna E503, respectively, for 60 minutes.
　２．成形体の形成
　上記のようにして得られた原料の混合スラリーを、一軸加圧成形法により、表１～３に示す成形圧力で、成形した。 2. Formation of Molded Body The mixed slurry of the raw materials obtained as described above was molded at a molding pressure shown in Tables 1 to 3 by a uniaxial pressure molding method.
　３．焼結体の形成
　上記のようにして得られた成形体を、８００℃の大気圧大気フロー雰囲気下で、残量炭素量が２００ｐｐｍ（０．０２質量％）になるまで脱脂した。次いで、脱脂した成形体を、窒素雰囲気下で表１～３に示す焼結圧力、焼結温度および焼結時間で焼結した。次いで、その焼結温度から１０００℃まで表１～３に示す冷却速度で冷却した後、徐冷した。 3. Formation of Sintered Body The molded body obtained as described above was degreased under an atmospheric pressure atmospheric flow atmosphere at 800 ° C. until the amount of remaining carbon became 200 ppm (0.02 mass%). Next, the degreased molded body was sintered in a nitrogen atmosphere at the sintering pressure, sintering temperature, and sintering time shown in Tables 1 to 3. Subsequently, after cooling from the sintering temperature to 1000 ° C. at the cooling rate shown in Tables 1 to 3, it was gradually cooled.
　上記のようにして得られた焼結体について、Ｓｉ3Ｎ4結晶粒子を同定し、Ｙ、Ｍｇ、Ｏおよび不純物金属元素であるＡｌおよびＦｅの含有量を定量し、ＭｇＯ結晶相の有無を確認し、Ｓｉ3Ｎ4結晶粒子の短軸粒径およびアスペクト比（短軸粒径に対する長軸粒径の比）を解析し、断面におけるＳｉ3Ｎ4結晶粒子に対する粒界相の面積比率を解析し、熱伝導率を導出した。結果を表１～３にまとめた。 For the sintered body obtained as described above, the Si 3 N 4 crystal particles are identified, the contents of Y, Mg, O and impurity metal elements Al and Fe are quantified, and the presence or absence of the MgO crystal phase is determined. check analyzes minor axis particle diameter and an aspect ratio the Si 3 N 4 crystal grains (the ratio of the major axis diameter to the minor axis diameter), the Si 3 N 4 area ratio of the grain boundary phase to the crystal grains in the cross section Analysis was performed to derive the thermal conductivity. The results are summarized in Tables 1-3.
　ここで、Ｓｉ3Ｎ4結晶粒子の同定は、Ｘ線回折により、粉末Ｘ線回折データベースとしてＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．２６１９１およびＮｏ．７９７９８をそれぞれ利用して行なった。Ｘ線回折は、４５ｋＶ、４０ｍＡで励起したＣｕ－Ｋα線を利用し、θ－２θ法による走査、０．０３°のステップ幅、１秒の積算時間で行なった。 Here, the identification of the Si 3 N 4 crystal particles was carried out by X-ray diffraction as a powder X-ray diffraction database of ICDD PDF-4 + 2014 No. 26191 and no. 79798, respectively. X-ray diffraction was performed using a Cu-Kα ray excited at 45 kV and 40 mA, scanning by the θ-2θ method, a step width of 0.03 °, and an integration time of 1 second.
　Ｙ、Ｍｇ、ＡｌおよびＦｅの分析は、ＳＨＩＭＡＤＺＵ社製ＩＣＰＳ－８１００によるＩＣＰ－ＡＥＳを利用した。かかるＩＣＰ－ＡＥＳの際は、前処理として、焼結体をメノウ製の乳鉢と乳棒によって粉砕した。ＹおよびＭｇの分析においては、前処理粉末の溶液を霧状にしてＡｒプラズマに導入することによりで励起された元素が基底状態に戻る際に放出される光の波長から定性分析を行ない、その光の強度から定量分析を行なった。前処理粉末の溶液は、０．１ｇの前処理粉末を、２ｇの炭酸カルシウムおよび０．５ｇの酸化ホウ素からなるアルカリ溶媒とともに、白金ルツボ中に投入して１０００℃で溶融し、その溶融体を２０ｍｌの３５質量％の塩酸および２０ｍｌのイオン交換水からなる酸性溶液内にて６０℃で回収した後に、イオン交換水で２００ｍｌまで希釈することにより作製した。 The analysis of Y, Mg, Al, and Fe utilized ICP-AES by ICPS-8100 manufactured by SHIMADZU. In the case of such ICP-AES, as a pretreatment, the sintered body was pulverized with an agate mortar and pestle. In the analysis of Y and Mg, qualitative analysis is performed from the wavelength of the light emitted when the element excited by returning the ground state to the ground state by introducing the solution of the pretreatment powder into a mist and introducing it into Ar plasma. Quantitative analysis was performed from the intensity of light. The pretreated powder solution was prepared by pouring 0.1 g of the pretreated powder into a platinum crucible together with 2 g of calcium carbonate and 0.5 g of boron oxide in a platinum crucible and melting the melt. It was prepared by recovering at 60 ° C. in an acidic solution consisting of 20 ml of 35% by mass hydrochloric acid and 20 ml of ion exchanged water, and then diluting to 200 ml with ion exchanged water.
　Ｏの分析は、ＨＯＲＩＢＡ社製ＥＭＧＡ６５０Ｗによる不活性ガス融解―非分散型赤外線吸収（ＮＤＩＲ）法を利用した。かかる不活性ガス融解―ＮＤＩＲ法による分析の際は、前処理として、焼結基板をメノウ製の乳鉢と乳棒によって粉砕した。Ｏの分析においては、０．０３ｇの前処理粉末をカーボンルツボに入れ、２０±２ＭＨｚの高周波にて１６００℃まで昇温した際に発生したＣＯガスおよび／またはＣＯ2ガスがバックグラウンドレベル以上存在することから定性分析を行ない、それらのガスの発生量から定量分析を行なった。 The analysis of O utilized the inert gas melting-non-dispersion type infrared absorption (NDIR) method by EMGA650W made from HORIBA. In the analysis by the inert gas melting-NDIR method, as a pretreatment, the sintered substrate was pulverized with an agate mortar and pestle. In the analysis of O, 0.03 g of pretreated powder is put in a carbon crucible, and CO gas and / or CO 2 gas generated when the temperature is raised to 1600 ° C. at a high frequency of 20 ± 2 MHz exists above the background level. Therefore, qualitative analysis was performed, and quantitative analysis was performed from the amount of gas generated.
　ＭｇＯ結晶相の有無の確認は、Ｘ線回折により行なった。Ｘ線回折は、ＰＡＮａｌｙｔｉｃａｌ社製Ｘ’Ｐｅｒｔ　ＰＲＯを使用し、Ｘ線は励起条件が４５ｋＶで４０ｍＡのＣｕ－Ｋα線を、走査はθ－２θ法を利用した。ステップ幅は０．０３°、積算時間は１秒であった。Ｘ線回折ピークの解析には、Ｒｉｇａｋｕ社製統合粉末Ｘ線解析ソフトウェアを使用した。２θが４２．５～４３．１°の間にＭｇＯの（２００）面に起因するＸ線回折ピークが見られない場合あるいはバックグラウンドと見分けがつかない場合は、Ｓｉ3Ｎ4焼結体中にＭｇＯ結晶相が存在しないと考えた。 The presence or absence of the MgO crystal phase was confirmed by X-ray diffraction. For X-ray diffraction, X'Pert PRO manufactured by PANalytical was used. For X-ray, 40 mA Cu-Kα ray was used under an excitation condition of 45 kV, and for scanning, θ-2θ method was used. The step width was 0.03 ° and the integration time was 1 second. For analysis of X-ray diffraction peaks, integrated powder X-ray analysis software manufactured by Rigaku was used. If the X-ray diffraction peak due to the (200) plane of MgO is not observed when 2θ is between 42.5 and 43.1 °, or is indistinguishable from the background, in the Si 3 N 4 sintered body It was considered that there was no MgO crystal phase.
　Ｓｉ3Ｎ4結晶粒子の短軸粒径およびアスペクト比（短軸粒径に対する長軸粒径の比）の解析は、ＳＥＭ－ＥＢＳＤ測定を利用した。ＳＥＭ観察にはＣａｒｌ　Ｚｅｉｓｓ社製ＳＵＰＲＡ　３５　ＶＰを用い、電子後方散乱回折にはＴＳＬソリューションズ社製ＯＩＭ５．２または同等装置を利用した。ＳＥＭ－ＥＢＳＤ測定の前処理として、平面研削盤を利用してダイヤモンド砥石（アライドマテリアル社製ダイヤモンド研削砥石＃４００）を用いて、焼結体の表面から５００μｍ以上の深さまで研削後、ケメット社製ラップ加工機を利用して仕上げ加工した。まず、銅定盤と粒径が３μｍのダイヤモンド砥石とを用いて焼結体をその表面から１０μｍの深さまで研磨し、次に、錫定盤と粒径が０．５μｍのダイヤモンド砥石とを用いて焼結体をその表面から３μｍの深さまで研磨した。この際、仕上げ加工における両研磨とも、回転数５０ｒｐｍ、荷重０．２ＭＰａの条件で行なった。 SEM-EBSD measurement was used for the analysis of the minor axis grain size and aspect ratio (ratio of major axis grain size to minor axis grain size) of Si 3 N 4 crystal grains. For SEM observation, SUPER 35 VP manufactured by Carl Zeiss was used, and for electron backscatter diffraction, OIM5.2 manufactured by TSL Solutions or an equivalent apparatus was used. As a pretreatment for SEM-EBSD measurement, after grinding to a depth of 500 μm or more from the surface of the sintered body using a diamond grindstone (Diamond grindstone # 400 made by Allied Materials) using a surface grinder, manufactured by Kemet Finished using a lapping machine. First, the sintered body is polished from its surface to a depth of 10 μm using a copper surface plate and a diamond grindstone having a particle size of 3 μm. Next, a tin surface plate and a diamond grindstone having a particle size of 0.5 μm are used. The sintered body was polished from the surface to a depth of 3 μm. At this time, both polishings in the finishing process were performed under conditions of a rotation speed of 50 rpm and a load of 0.2 MPa.
　ＥＢＳＤ測定は、測定面積３０μｍ×１００μｍ、加速電圧１５ｋＶ、ワーキングディスタンス１５ｍｍ、ステップサイズ０．１μｍ、ビニング８×８、積算時間０．０１秒の条件で行ない、ＩＱ（イメージクオリティ）マップを取得した。取得したＩＱマップ画像（視野面積３０μｍ×１００μｍ）の内、最も面積が大きいＳｉ3Ｎ4結晶粒子から５番目に面積が大きいＳｉ3Ｎ4結晶粒子までを抽出し、当該５個のＳｉ3Ｎ4結晶粒子をＩｍａｇｅＪソフトウェアによって、短軸粒径、長軸粒径およびアスペクト比を算出した。ＩｍａｇｅＪソフトウェアにおいては、抽出された各Ｓｉ3Ｎ4結晶粒子を楕円形に近似して、その短軸粒径および長軸粒径を算出した。長軸粒径を短軸粒径で除することによりアスペクト比を算出した。ここで、表１～３の短軸粒径の範囲は、５個のＳｉ3Ｎ4結晶粒子についての最小値と最大値の範囲であった。表１～３のアスペクト比は、５個のＳｉ3Ｎ4結晶粒子についての平均値であった。 EBSD measurement was performed under the conditions of a measurement area of 30 μm × 100 μm, an acceleration voltage of 15 kV, a working distance of 15 mm, a step size of 0.1 μm, a binning of 8 × 8, and an integration time of 0.01 seconds, and an IQ (image quality) map was obtained. Of the obtained IQ map image (field area 30 [mu] m × 100 [mu] m), most area from a large Si 3 N 4 crystal grains to the fifth area is large Si 3 N 4 crystal grains extracts, the five Si 3 N The short-axis particle size, the long-axis particle size, and the aspect ratio of the four crystal particles were calculated by ImageJ software. In the ImageJ software, each extracted Si 3 N 4 crystal particle was approximated to an ellipse, and its short axis particle size and long axis particle size were calculated. The aspect ratio was calculated by dividing the major axis particle size by the minor axis particle size. Here, the range of the short axis particle size in Tables 1 to 3 was the range of the minimum value and the maximum value for the five Si 3 N 4 crystal particles. The aspect ratios in Tables 1 to 3 were average values for five Si 3 N 4 crystal grains.
　Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークの強度ＩY20に対するＹ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークの強度ＩY2の比ＩY2／ＩY20の解析には、Ｘ線回折を用いた。Ｘ線回折には、ＰＡＮａｌｙｔｉｃａｌ社製Ｘ’Ｐｅｒｔ　ＰＲＯを使用し、Ｘ線は励起条件が４５ｋＶで４０ｍＡのＣｕ－Ｋα線を、走査はθ－２θ法を利用した。ステップ幅は０．０３°、積算時間は１秒とした。Ｘ線回折ピークの解析には、Ｒｉｇａｋｕ社製統合粉末Ｘ線解析ソフトウェアのＰＤＸＬ２を使用した。Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークは、２θが３０～３３°の間の低角側に存在するピークであり、粉末Ｘ線回折データベースとして国際回折データセンターによる粉末回折データファイルであるＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．００－０３０－１４６２を用いて同定した。Ｙ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークは、２θが３０～３３°の間の高角側に存在するピークであり、国際回折データセンターによる粉末回折データファイルであるＩＣＤＤ　ＰＤＦ－４＋２０１４のＮｏ．０１－０７６－０７２４を用いて同定した。このようにして同定したＹ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークの強度ＩY20およびＹ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークの強度ＩY2からその比ＩY2／ＩY20を算出した。 Intensity of X-ray diffraction peak due to (112) plane of Y 20 N 4 Si 12 O 48 crystal phase I X-ray diffraction peak due to (211) plane of Y 2 Si 3 N 3 O 4 crystal phase with respect to Y20 X-ray diffraction was used for the analysis of the intensity I Y2 ratio I Y2 / I Y20 . For X-ray diffraction, X'Pert PRO manufactured by PANalytical was used, the X-ray was excited by an excitation condition of 45 kV and 40 mA Cu-Kα ray, and the scanning utilized the θ-2θ method. The step width was 0.03 ° and the integration time was 1 second. For the analysis of the X-ray diffraction peak, PDXL2, an integrated powder X-ray analysis software manufactured by Rigaku, was used. The X-ray diffraction peak attributed to the (112) plane of the Y 20 N 4 Si 12 O 48 crystal phase is a peak existing on the low angle side where 2θ is between 30 and 33 °. No. of ICDD PDF-4 + 2014 which is a powder diffraction data file by the diffraction data center. Identified using 00-030-1462. The X-ray diffraction peak due to the (211) plane of the Y 2 Si 3 N 3 O 4 crystal phase is a high-angle peak between 2θ between 30 and 33 °. No. of ICDD PDF-4 + 2014 which is a file. Identification was made using 01-076-0724. The intensity I Y20 of the X-ray diffraction peak due to the (112) plane of the Y 20 N 4 Si 12 O 48 crystal phase identified in this way and the (211) plane of the Y 2 Si 3 N 3 O 4 crystal phase The ratio I Y2 / I Y20 was calculated from the intensity I Y2 of the X-ray diffraction peak.
　Ｓｉ3Ｎ4焼結体の断面におけるＳｉ3Ｎ4結晶粒子に対する粒界相の面積比率の解析は、ＳＥＭ観察画像を利用した。ＳＥＭ観察にはＣａｒｌＺｅｉｓｓ社製ＳＵＰＲＡ　３５　ＶＰを利用した。解析の前処理として、平面研削機を利用して、ダイヤモンド砥石（アライドマテリアル社製ダイヤモンド研削砥石＃４００）を用いて、焼結体の表面から５００μｍ以上の深さまで研削した後、ケメット社製ラップ加工機を利用して仕上げ加工した。まず、銅定盤と粒径が３μｍのダイヤモンド砥石とを用いて焼結体をその表面から１０μｍの深さまで研磨し、次に、錫定盤と粒径が０．５μｍダイヤモンド砥石とを用いて焼結体をその表面から３μｍの深さまで研磨した。この際、仕上げ加工における両研磨とも、回転数５０ｒｐｍ、荷重０．２ＭＰａの条件で行なった。ＳＥＭには、加速電圧５ｋＶ，ワーキングディスタンス１０ｍｍを利用し、反射電子像を解析に利用した。本画像を、ＩｍａｇｅＪソフトウェアにより二値化処理し、窒化ケイ素焼結体において、白色を呈する明部をＳｉ3Ｎ4結晶粒子とし、黒色を呈する暗部を粒界相とした。 Analysis of the area ratio of the grain boundary phase to the Si 3 N 4 crystal grains in the cross section of the Si 3 N 4 sintered body utilized a SEM observation image. For SEM observation, SUPRA 35 VP manufactured by Carl Zeiss was used. As a pretreatment for the analysis, using a surface grinder, a diamond grindstone (Diamond grindstone # 400 manufactured by Allied Material Co., Ltd.) was used to grind the surface of the sintered body to a depth of 500 μm or more. Finished using a processing machine. First, the sintered body is polished from its surface to a depth of 10 μm using a copper surface plate and a diamond grindstone having a particle size of 3 μm, and then using a tin surface plate and a diamond grindstone having a particle size of 0.5 μm. The sintered body was polished from its surface to a depth of 3 μm. At this time, both polishings in the finishing process were performed under conditions of a rotation speed of 50 rpm and a load of 0.2 MPa. For SEM, an acceleration voltage of 5 kV and a working distance of 10 mm were used, and a reflected electron image was used for analysis. This image was binarized by ImageJ software, and in the silicon nitride sintered body, the bright portions exhibiting white were Si 3 N 4 crystal particles, and the dark portions exhibiting black were used as grain boundary phases.
　Ｓｉ3Ｎ4焼結体の熱伝導率の導出は、熱拡散率、比重、比熱から行なった。熱拡散率の測定は、光交流法を使用した。光交流法では、ＵＬＶＡＣ社製Ｌａｓｅｒ－ＰＩＴ装置を使用した。本装置にて、照度が均一な周波数２．５～１０Ｈｚの帯状レーザ光を照射しつつサンプル長手方向にレーザ光を移動させることにより、試料の裏面に取り付けた一本の熱電対でＡＣ温度応答を測定し、その温度応答の振幅と位置に対する減衰率から熱拡散率を算出した。サンプル形状は、幅２．５～５ｍｍ、長さ３０ｍｍ、厚さ０．５ｍｍ以下であり、レーザ加熱面のみグラファイトスプレーにて黒体化処理を行なった。熱電対とサンプルは銀ペーストにて接着した。比重測定にはアルキメデス法を使用し、比熱には０．６８Ｊ・ｇ-1・Ｋ-1を用いた。 The thermal conductivity of the Si 3 N 4 sintered body was derived from the thermal diffusivity, specific gravity, and specific heat. The measurement of thermal diffusivity used the optical alternating current method. In the optical alternating current method, a Laser-PIT apparatus manufactured by ULVAC was used. With this device, the laser beam is moved in the longitudinal direction of the sample while irradiating a band laser beam with a uniform illuminance of 2.5 to 10 Hz, so that the AC temperature response is achieved by a single thermocouple attached to the back of the sample. Was measured, and the thermal diffusivity was calculated from the attenuation rate with respect to the amplitude and position of the temperature response. The sample had a width of 2.5 to 5 mm, a length of 30 mm, and a thickness of 0.5 mm or less, and only the laser heating surface was blackened with graphite spray. The thermocouple and the sample were bonded with silver paste. The Archimedes method was used for the specific gravity measurement, and 0.68 J · g −1 · K −1 was used for the specific heat.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表１～２の実施例１～１３に示すように、窒化ケイ素、イットリウム、マグネシウムおよび酸素を含み、短軸粒径が１．７μｍ以上１０．５μｍ以下であり、短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である複数の窒化ケイ素結晶粒子を含む窒化ケイ素焼結体は、９５Ｗ・ｍ-1・Ｋ-1以上の高い熱伝導率を示した。これに対して、表３の比較例１～３に示すように、アスペクト比が２．０未満または７．７より大きい複数の窒化ケイ素結晶粒子を含む窒化ケイ素焼結体は、９５Ｗ・ｍ-1・Ｋ-1未満の低い熱伝導率を示すに留まった。 As shown in Examples 1 to 13 of Tables 1 and 2, the minor axis particle size is not less than 1.7 μm and not more than 10.5 μm, including silicon nitride, yttrium, magnesium, and oxygen. A silicon nitride sintered body including a plurality of silicon nitride crystal particles having an aspect ratio which is a ratio of diameters of 2.0 or more and 7.7 or less exhibits a high thermal conductivity of 95 W · m −1 · K −1 or more. It was. On the other hand, as shown in Comparative Examples 1 to 3 in Table 3, a silicon nitride sintered body including a plurality of silicon nitride crystal particles having an aspect ratio of less than 2.0 or greater than 7.7 is 95 W · m − It only showed a low thermal conductivity of less than 1 · K −1 .
　今回開示された実施の形態および実施例はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて請求の範囲によって示され、請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。 It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (6)

  1. 　窒化ケイ素、イットリウム、マグネシウムおよび酸素を含む窒化ケイ素焼結体であり、
    　前記窒化ケイ素焼結体に含まれる複数の窒化ケイ素結晶粒子は、短軸粒径が１．７μｍ以上１０．５μｍ以下であり、前記短軸粒径に対する長軸粒径の比であるアスペクト比が２．０以上７．７以下である、窒化ケイ素焼結体。     A silicon nitride sintered body containing silicon nitride, yttrium, magnesium and oxygen,
    The plurality of silicon nitride crystal particles included in the silicon nitride sintered body have a short axis particle size of 1.7 μm or more and 10.5 μm or less, and an aspect ratio which is a ratio of the long axis particle size to the short axis particle size. A silicon nitride sintered body that is 2.0 or more and 7.7 or less.
  2. 　前記窒化ケイ素焼結体は、複数の前記窒化ケイ素結晶粒子と、前記窒化ケイ素結晶粒子以外の部分である粒界相と、を含み、
    　前記粒界相は、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相、あるいは、Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相およびＹ2Ｓｉ3Ｎ3Ｏ4結晶相、を含み、
    　前記Ｙ20Ｎ4Ｓｉ12Ｏ48結晶相の（１１２）面に起因するＸ線回折ピークの強度に対する前記Ｙ2Ｓｉ3Ｎ3Ｏ4結晶相の（２１１）面に起因するＸ線回折ピークの強度の比が０以上３．０以下である請求項１に記載の窒化ケイ素焼結体。     The silicon nitride sintered body includes a plurality of the silicon nitride crystal particles and a grain boundary phase that is a portion other than the silicon nitride crystal particles,
    The grain boundary phase includes a Y 20 N 4 Si 12 O 48 crystal phase, or a Y 20 N 4 Si 12 O 48 crystal phase and a Y 2 Si 3 N 3 O 4 crystal phase,
    Of the X-ray diffraction peak attributed to the (211) plane of the Y 2 Si 3 N 3 O 4 crystal phase relative to the intensity of the X-ray diffraction peak attributed to the (112) plane of the Y 20 N 4 Si 12 O 48 crystal phase. The silicon nitride sintered body according to claim 1, wherein the strength ratio is 0 or more and 3.0 or less.
  3. 　ケイ素、イットリウムおよびマグネシウム以外の各種の不純物金属元素の含有率が各々０．５質量％以下である請求項１または請求項２に記載の窒化ケイ素焼結体。 The silicon nitride sintered body according to claim 1 or 2, wherein the content of various impurity metal elements other than silicon, yttrium, and magnesium is 0.5% by mass or less.
  4. 　酸化マグネシウム結晶相が存在しない請求項１から請求項３のいずれか１項に記載の窒化ケイ素焼結体。 The silicon nitride sintered body according to any one of claims 1 to 3, wherein no magnesium oxide crystal phase is present.
  5. 　熱伝導率が９５Ｗ・ｍ-1・Ｋ-1以上である請求項１から請求項４のいずれか１項に記載の窒化ケイ素焼結体。 The silicon nitride sintered body according to any one of claims 1 to 4, wherein the thermal conductivity is 95 W · m -1 · K -1 or more.
  6. 　前記窒化ケイ素焼結体の任意に特定される断面における前記窒化ケイ素結晶粒子に対する前記窒化ケイ素結晶粒子以外の部分である粒界相の面積比率が１０％以下である請求項１から請求項５のいずれか１項に記載の窒化ケイ素焼結体。 The area ratio of the grain boundary phase which is a portion other than the silicon nitride crystal particles with respect to the silicon nitride crystal particles in an arbitrarily specified cross section of the silicon nitride sintered body is 10% or less. The silicon nitride sintered body according to any one of claims.
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