JP3565425B2 - Method for producing silicon nitride-based powder and method for producing silicon nitride-based sintered body - Google Patents

Description

Ｉ_{β（１０１）} ：β型Ｓｉ３Ｎ_４の（１０１）面回折ヒ゜−ク強度，
Ｉ_{β（２１０）} ：β型Ｓｉ３Ｎ_４の（２１０）面回折ヒ゜−ク強度，
Ｉ_{α（１０２）} ：α型Ｓｉ３Ｎ_４の（１０２）面回折ヒ゜−ク強度，
Ｉ_{α（２１０）} ：α型Ｓｉ_３Ｎ_４の（２１０）面回折ヒ゜−ク強度。
また、得られた窒化ケイ素質粉末の平均粒子径および平均アスペクト比は、ＳＥＭ観察にて観察倍率×２０００倍で得られたＳＥＭ写真を用い、２００μｍ×５００μｍ視野面積内にある計５００個の窒化ケイ素質粒子を無作為に選定して画像解析装置により最小径と最大径を測定し、その平均値を求めて評価した。次に得られた窒化ケイ素質焼結体から、直径１０ｍｍ×厚さ３ｍｍの熱伝導率および密度測定用の試験片、ならびに縦３ｍｍ×横４ｍｍ×長さ４０ｍｍの曲げ試験片を採取した。密度はマイクロメ−タにより寸法を測定し、また重量を測定し、算出した。熱伝導率はレーザーフラッシュ法により常温での比熱および熱拡散率を測定し熱伝導率を算出した。３点曲げ強度は常温にてＪＩＳ Ｒ１６０６に準拠して測定を行った。以上の製造条件の概略および評価結果を、表１，２の試料Ｎｏ．１〜１１に示す。
【００３０】
（比較例１）
表１に記載の製造条件とした以外は実施例１と同様にしてβ分率の異なる窒化ケイ素質粉末を作製した。次いで得られた窒化ケイ素質粉末を用いて窒化ケイ素質焼結体を作製し、評価した。以上の製造条件の概略および評価結果を、表１，２の試料Ｎｏ．３１〜４１に示す。
【００３１】
【表１】

【００３２】
【表２】

【００３３】
表１および表２の試料Ｎｏ．１〜１１から、以下の知見が得られた。
成長核として添加する窒化ケイ素質粉末のβ分率が３０％以上、不純物としての酸素含有量が０．５ｗｔ％以下，Ｆｅ含有量が１００ｐｐｍ以下、およびＡｌ含有量が１００ｐｐｍ以下であり、平均粒子径が０．２〜１０μｍ、アスペクト比が１０以下、およびβ化率が３０％以上の前記窒化ケイ素質粉末の配合量を１〜５０ｗｔ％とし得られた窒化ケイ素質焼結体は、常温における熱伝導率が１００ｗ／（ｍ・Ｋ）以上になり、かつ常温における３点曲げ強度が６００ＭＰａ以上になる。従来技術による窒化ケイ素質焼結体の熱伝導率４０ ｗ／（ｍ・Ｋ）程度であり、熱伝導率を飛躍的に高めることができた。また、焼結助剤として、Ｍｇを酸化マグネシウム（ＭｇＯ）換算し、Ｙ，Ｌａ，Ｃｅ，Ｄｙ，ＧｄおよびＹｂを酸化物（ＲＥ_ｘＯ_ｙ）換算して、それら酸化物換算含有量の合計が０．６〜７．０ｗｔ％であり、かつ（ＭｇＯ／ＲＥ_ｘＯ_ｙ）（重量比）が１〜７０のものは熱伝導率が１００ｗ／（ｍ・Ｋ） 以上でかつ曲げ強度が６００ＭＰａ以上を得られた。
【００３４】
これに対し、表１，２の比較例１の試料Ｎｏ．３１〜４１から以下の知見が得られた。
Ｎｏ．３１では、窒化ケイ素質粒子のβ分率が３０％未満では曲げ強度が顕著に低下し５００ＭＰａ程度になる。
またＮｏ．３２では、窒化ケイ素質粉末中に不可避に含有する酸素量が０．５ｗｔ超では熱伝導率が７０ ｗ／（ｍ・Ｋ）以下に劣化する。
またＮｏ．３３およびＮｏ．３４では、窒化ケイ素質粉末中に含有する不純物のＦｅおよびＡｌの含有量がそれぞれ１００ｐｐｍを超えると熱伝導率が６５ ｗ／（ｍ・Ｋ）以下に低下する。
またＮｏ．３５およびＮｏ．３６では、窒化ケイ素質粉末の平均粒子径が０．２μｍ未満では熱伝導率は６０ ｗ／（ｍ・Ｋ）以下に低下し、１０μｍより大きい場合には緻密な焼結体が得られず熱伝導率は６０ ｗ／（ｍ・Ｋ）以下になり曲げ強度は６００ＭＰａ以下に低下する。
またＮｏ．３７では、窒化ケイ素質粉末のアスペクト比が１０以上では、緻密な焼結体が得られず、曲げ強度は６００ＭＰａ以下に低下した。
またＮｏ．３８およびＮｏ．３９では、窒化ケイ素質粉末の添加量が１．０ｗｔ％未満では曲げ強度は６００ＭＰａ以下に低下し、５０ｗｔ％より大きい場合には熱伝導率は７０ ｗ／（ｍ・Ｋ）以下に低下した。
またＮｏ．４０およびＮｏ．４１では、焼結助剤成分が０．６ｗｔ％未満では焼結体の密度が低下し、このために熱伝導率および曲げ強度は著しく低下した。また焼結助剤成分が７．０ｗｔ％を超えると焼成過程で充分なガラス相が生成するので焼結体の緻密化は達成されたが、その反面、低熱伝導相である粒界相の増加により熱伝導率は６０ ｗ／（ｍ・Ｋ）以下に低下した。
【００３５】
（実施例２）
実施例１で作製したβ化率が３０％以上の窒化ケイ素質粉末に３ｗｔ％ＭｇＯ、１ｗｔ％Ｙ_２Ｏ_３の焼結助剤を添加した混合粉末を作製した。次いで、アミン系の分散剤を２ｗｔ％添加したトルエン・ブタノール溶液を満たしたボールミルの樹脂製ポット中に作製した混合粉末および粉砕媒体の窒化ケイ素製ボールを投入し、４８時間湿式混合した。次いで、前記ポット中の混合粉末１００重量部に対しポリビニル系の有機バインダーを１５重量部および可塑剤（ジメチルフタレ−ト）を５重量部添加し、次いで４８時間湿式混合しシート成形用スラリーを得た。この成形用スラリーを調整後、ドクターブレード法によりグリーンシート成形した。次いで、成形したグリーンシートを空気中４００〜６００℃で２〜５時間加熱することにより、予め添加し有機バインダー成分を十分に脱脂（除去）した。次いで脱脂体を０．９ＭＰａ（９気圧）の窒素雰囲気中で１８５０℃×５時間の焼成を行い、次いで同窒素雰囲気中で１９００℃×２４時間の熱処理を行い、その後室温に冷却した、得られた窒化ケイ素質焼結体シートに機械加工を施し縦５０ｍｍ×横５０ｍｍ×厚さ０．６ｍｍの半導体装置用の基板を製造した。この窒化ケイ素質焼結体製基板を用いて図２に示す回路基板を作製した。図２において、回路基板１は作製した前記縦５０ｍｍ×横５０ｍｍ×厚さ０．６ｍｍの寸法の窒化ケイ素質焼結体製基板２の表面に銅製回路板３を設け、前記基板２の裏面に銅板４をろう材５により接合して構成されている。この回路基板１に対し、３点曲げ強度の評価および耐熱サイクル試験を行った。その結果、曲げ強度が６００ＭＰａ以上と大きく、回路基板１の実装工程における締め付け割れおよびはんだ付け工程時の熱応力に起因するクラックの発生する頻度がほぼ見られなくなり、回路基板を使用した半導体装置の製造歩留まりを大幅に改善できることが実証された。また、耐熱サイクル試験は、−４０℃での冷却を２０分、室温での保持を１０分および１８０℃における加熱を２０分とする昇温／降温サイクルを１サイクルとし、これを繰り返し付与し、基板部にクラック等が発生するまでのサイクル数を測定した。その結果、１０００サイクル経過後においても窒化ケイ素質焼結体製基板２の割れや銅製回路板２の剥離はなく、優れた耐久性と信頼性を兼備することが確認された。また、１０００サイクル経過後においても耐電圧特性の低下は発生しなかった。
【００３６】
以上記述の通り、本発明の窒化ケイ素質粉末の製造方法は、凝集したり表面に酸化物が付着することがなく、粉砕ならびに酸処理工程などの面倒で手間の掛かる工程を必要としないので生産性に優れています。また本発明の窒化ケイ素質焼結体の製造方法によれば、窒化ケイ素質焼結体が本来有する高強度/高靭性に加えて高い熱伝導率を具備させることができるので、半導体素子用基板として用いた場合に半導体素子の作動に伴う繰り返しの熱サイクルによって基板にクラックが発生することが少なく、耐熱衝撃性ならびに耐熱サイクル性を著しく向上することができる。
【図面の簡単な説明】
【図１】本発明の代表的な窒化ケイ素質粉末を走査型電子顕微鏡により撮影した写真である。
【図２】本発明の回路基板の要部断面図を示す。
【符号の説明】
１ 回路基板、 ２ 基板、 ３ 銅製回路板、 ４ 銅板、 ５ ろう材。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a high strength and high thermal conductivity suitable as a member for electronic components such as a substrate for a semiconductor or a heat sink for a heating element, or a member for a general machine tool, a member for a molten metal, or a structural member such as a member for a heat engine. Rich silicon nitride sintered bodyofProduction methodas well asThe present invention relates to a method for producing a silicon nitride powder suitable for the production.
[0002]
[Prior art]
Silicon nitride sintered bodies have excellent heat resistance, low thermal expansion properties, thermal shock resistance, and corrosion resistance to metals, in addition to mechanical properties such as high-temperature strength properties and wear resistance. It is used for various structural members such as members, members for engines, mechanical members for steelmaking, and melting members of molten metal. In addition, it is used as an electrical insulating material by utilizing high insulating properties.
[0003]
2. Description of the Related Art In recent years, with the development of semiconductor elements having a large amount of heat, such as high-frequency transistors and power ICs, the demand for ceramic substrates having a high thermal conductivity in order to obtain good heat dissipation characteristics in addition to electrical insulation has been increasing. Although an aluminum nitride substrate is used as such a ceramic substrate, there is a problem that mechanical strength, fracture toughness, and the like are low, and cracks are generated by fastening in a process of assembling the substrate unit. Further, in a circuit board in which a Si semiconductor element is mounted on an aluminum nitride substrate, since the thermal expansion difference between Si and the aluminum nitride substrate is large, cracks and cracks occur in the aluminum nitride substrate due to thermal cycling, and mounting reliability is reduced. There's a problem.
[0004]
Therefore, although the thermal conductivity is inferior to the aluminum nitride substrate, the thermal expansion coefficient is close to that of Si, and a substrate made of a high thermal conductive silicon nitride sintered body having excellent mechanical strength, fracture toughness and thermal fatigue resistance has attracted attention. The proposal has been made.
[0005]
For example, Japanese Unexamined Patent Publication No. Hei 4-175268 discloses that silicon and aluminum are substantially composed of silicon nitride, each containing 3.5% by weight or less of Al and oxygen as impurities, and having a density of 3.15Mg / m3 (3.15g). / Cm3) or more, and a silicon nitride sintered body having a thermal conductivity of 40 w / (m · K) or more.
[0006]
Japanese Patent Application Laid-Open No. 9-30866 discloses that 85-99% by weight of β-type silicon nitride grains are composed of a grain boundary phase of oxide or oxynitride, and Mg, Ca, 0.5 to 10% by weight of at least one element selected from Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er and Yb, Silicon nitride having an Al element content of 1% by weight or less, a porosity of 5% or less, and a proportion of β-type silicon nitride particles having a minor axis diameter of 5 μm or more of 10 to 60% by volume. An elementary sintered body is described.
[0007]
Also, in the proceedings of the Annual Meeting of the Ceramic Society of Japan 1996, 1G11 and 1G12, and JP-A-10-194842, columnar silicon nitride particles or whiskers are added to raw material powder in advance, and a doctor blade method or an extrusion molding method is used. After obtaining a molded body in which these particles are two-dimensionally oriented by using sintering, the sintered body is sintered to impart anisotropy to heat conduction to increase thermal conductivity in a specific direction. Is described.
[0008]
Improve the thermal conductivity of silicon nitride or improve the balance between flexural strength and fracture toughness.FineAs a method for producing a β powder used for constructing a structure, a silicon nitride raw material powder is mixed with a predetermined amount of Y.₂O₃And SiO₂And sintering the mixture in a non-oxidizing atmosphere such as nitrogen. Ceram. Soc. Japan. , 101 [9] 1078-80 (1993).
[0009]
Further, as a method for improving the β fraction of silicon nitride powder, a specific surface area of 1 m²/ G or more, SiO₂Japanese Patent Application Laid-Open No. Hei 6-263410 describes a method of heat treating a silicon nitride raw material powder containing 2 to 5% by weight of oxygen in a non-oxidizing atmosphere such as nitrogen.
[0010]
[Problems to be solved by the invention]
In the above-mentioned Japanese Patent Application Laid-Open No. 4-175268, a thermal conductivity of 40 W / (m · K) or more is obtained. However, a material having a higher thermal conductivity and excellent mechanical strength is desired. In the methods described in JP-A-9-30866 and JP-A-10-194842, a seed crystal or a whisker serving as a growth nucleus is used to obtain large columnar particles in a silicon nitride sintered body. And firing in a nitrogen atmosphere of 2000 ° C. or more and 10.1 MPa (100 atm) or more is indispensable. Therefore, special high-temperature and high-pressure equipment such as a hot press or HIP is required, resulting in an increase in cost. Also, since the molding process for obtaining a molded body in which silicon nitride particles are oriented is complicated,sexIs significantly reduced.
[0011]
In addition, the aforementioned J.I. Ceram. Soc. Japan, 101 [9] 1078-80 (1993) describes a method of using Y as a slag.₂O₃Quantity and SiO₂Because of the large amount, the resulting treated powder is strongly agglomerated and must be crushed in a mortar or the like. Also removes oxides adhering to the particle surfaceofAnd a classification process for adjusting the particle size are required, which complicates the process. Further, there is a problem that the used auxiliary component is dissolved in the obtained processed powder.
[0012]
Further, the method described in the above-mentioned Japanese Patent Application Laid-Open No. 6-263410 makes it possible to industrially and inexpensively produce a silicon nitride powder having a β fraction of 95% or more. According to this, as a technique for improving the β fraction, SiO 2 is used.₂Contains 2 to 5% by weight of oxygen as conversion and has a specific surface area of 1 m²/ G or more of silicon nitride-based powderConversionHeat treatment at a temperature of 1500 ° C. or more in a neutral atmosphere. The amount of oxygen contained in the silicon nitride-based powder used in the present invention is determined as SiO₂The reason why the content is defined as 2 to 5 wt% in terms of conversion is that if the value is less than 2 wt%, the effect of increasing the β fraction of the silicon nitride powder is small, and the β fraction tends to vary. On the other hand, if the value exceeds 5 wt%, SiO₂And the powder characteristics of the silicon nitride powder deteriorate. As for the particle size, the specific surface area is 1 m in order to perform the treatment of the present invention uniformly and in a short time.²/ G or more is preferred. However, in the example, although a processing powder having a β fraction of 95% or more was obtained, in order to complete the processing at a low temperature and in a short time, SiO powder was used.₂Since the silicon nitride raw material powder having an oxygen content of 2 to 5 wt% in conversion is used, the oxygen content of each of the obtained powders is 1.2 wt% or more. Further, in order to adjust the oxygen amount of the raw material powder to a predetermined amount, SiO₂There are drawbacks such as adding powder or heat treatment in an oxygen atmosphere. Furthermore, since the silicon nitride-based powder obtained by the method of the present invention is agglomerated by heat treatment, the use thereof requires a step of pulverizing using, for example, a ball mill or a roll crusher. is there.
[0013]
The present invention has been made in view of the above-described conventional problems, and does not require a costly firing method such as high-temperature / high-pressure firing at 2,000 ° C. or higher and 10.1 MPa (100 atm) or higher, and disintegrates the aggregated powder. Provided is a high thermal conductivity type silicon nitride sintered body which has excellent mechanical strength, does not have anisotropy in the direction of heat conduction, and has improved thermal conductivity as compared with the prior art.AlthoughAn object of the present invention is to provide a silicon nitride powder having a high thermal conductivity and a high strength by defining a β fraction, an oxygen content, an impurity amount, a mixing ratio with an α-type silicon nitride powder, and the like. Base sintered bodyofIt is to provide a manufacturing method. Another object of the present invention is to provide a method for producing a silicon nitride powder used for developing high strength and high thermal conductivity.
[0014]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present inventors stably specify 100 W / (%) by defining powder characteristics such as a β fraction, an oxygen content, an impurity and a mixing ratio with an α powder of a silicon nitride powder to be used. It has been discovered that a silicon nitride sintered body having a thermal conductivity of at least m · K) and a sufficient bending strength can be obtained. Further, it is effective to improve the sinterability by using a sintering aid as an MgO group and to contain a specific amount of at least one element selected from rare earth elements (RE) containing La, Y and Yb. Discovered and led to the present invention.
[0015]
The silicon nitride-based powder of the present invention is, for example, a metal silicon direct nitridation method, using a silicon nitride-based powder as a raw material by a silica reduction method or a silicon imide decomposition method, in nitrogen or a mixed atmosphere of nitrogen / hydrogen at 1400 ° C to 1950 ° C It can be manufactured by heat treatment for 5 to 20 hours. In order to achieve high β fraction and low oxygen, heat treatment conditions are 1800 ° C ~ 19FiveMore preferably, the temperature is 0 ° C. × 5 to 20 hours. Note that the heat treatment at 1800 ° C. or more is preferably performed in a nitrogen or nitrogen / hydrogen atmosphere of 1.0 MPa (10 atm) or more to avoid decomposition of silicon nitride. In order to reduce the oxygen content after the heat treatment to less than 0.5 wt%, the initial oxygen content is set to SiO2.₂It is preferable that the content be less than 2 wt% in terms of amount. In order to minimize the amount of impurities such as Fe and Al, it is more preferable to use a high-purity raw material silicon nitride powder by an imide decomposition method. The container used for filling the raw material powder may be made of carbon or BN. However, if a carbon heater and a heat treatment furnace with a carbon insulating material specification are used, BN is used to suppress the action of an excessive CO reducing atmosphere. Is preferred.
[0016]
Since the silicon nitride powder of the present invention uses a raw material powder having a low oxygen content, SiO 2 acting as an auxiliary agent is used.₂Since the phase transition from α-type silicon nitride powder to β-type silicon nitride powder is through the gas phase, it has a low oxygen content as a result, there is no aggregation even after heat treatment, and pulverization and surface There is no need for an acid treatment step for oxide removal. Also, Y₂O₃Is not used as a sintering aid for particle growth, so that solid solution of these aid components in the silicon nitride powder can be avoided. That is, the present inventionDepends on manufacturing methodSilicon nitride powder,It is characterized by being a columnar particle having a β fraction of 30 to 100%, an oxygen content of less than 0.5 wt%, an average particle diameter of 0.2 to 10 μm, and an aspect ratio of 10 or less. Further, the Fe content and the Al content are each 100 ppm or less.
[0017]
Further, in the method for producing a silicon nitride sintered body of the present invention, the β fraction is 30 to 100%.so,Oxygen content is 0.5wt%, Fe content and Al content respectively 100 ppm Less than,Average particle size is 0.2 to 10 μmIn the range ofAspect ratio of 10 or lessColumnar particlesIsβ type1 to 50 parts by weight of silicon nitride-based powder and 0.2 to 4 μm in average particle diameterIn rangeα-type silicon nitride powder 99 to 50 parts by weight,Mg and at least one element selected from rare earth elements (RE) containing La, Y and Yb are respectively converted into magnesium oxide (MgO) and an oxide of a rare earth element compound (RE). _x O _y ), And the sum of the oxide equivalent contents is 0.6 ~ 7 wt% and (MgO / RE _x O _y ) Is 1 to 70 Sintering aid, and an organic binder are blended, and a molded body obtained from these is blended. 1650 ~ 1900 In ° CIt is characterized by sintering. When the β-fraction of the silicon nitride powder is less than 30%, although it has an effect as a growth nucleus, it partially acts as a nucleus, so that abnormal grain growth occurs, and the microstructure of the finally obtained silicon nitride sintered body is reduced. Large particles cannot be uniformly dispersed in the tissue, and the flexural strength decreases. Therefore, the β fraction of the silicon nitride powder is desirably 30% or more. If the average particle diameter of the silicon nitride powder is less than 0.2 μm, a silicon nitride sintered body having a microstructure in which columnar particles are uniformly developed cannot be obtained as described above, and the thermal conductivity and the bending strength may be increased. Is difficult. If the average particle diameter of the silicon nitride powder is larger than 10 μm, densification of the silicon nitride of the sintered body is hindered. Therefore, the average particle diameter of the silicon nitride powder is preferably 0.2 to 10 μm. On the other hand, when the aspect ratio is more than 10, the densification of the silicon nitride-based sintered body is hindered, and as a result, the three-point bending strength at room temperature becomes less than 600 MPa. Therefore, the aspect ratio of the silicon nitride powder is set to 10 or less.Columnar particlesIt is preferable that
[0018]
Of the present inventionDepends on manufacturing methodThe silicon nitride sintered body has a β fraction of 30 to 100%, an oxygen content of less than 0.5 wt%, an Fe content and an Al content of 100 ppm or less, and an average particle size of 0.2 to 10 μm, respectively. It consists of 1 to 50 parts by weight of β-type silicon nitride powder, which is a columnar particle having an aspect ratio of 10 or less, and 99 to 50 parts by weight of α-type silicon nitride powder having an average particle diameter in the range of 0.2 to 4 μm. The body contains at least one rare earth element selected from Mg and a rare earth element (RE) containing La, Y and Yb, converts Mg into magnesium oxide (MgO), and contains La, Y and Yb. At least one element selected from the elements (RE) is converted to an oxide (RE_xO_y), The sum of the oxide equivalent contents is 0.6 to 7 wt%, and (MgO / RE)_xO_y) Is from 1 to 70.AndThe thermal conductivity at room temperature is 100 to 300 W / (m · K), and the three-point bending strength is 600 to 1500 MPa. If the total content in terms of oxide is less than 0.6 wt%, the densification effect during sintering becomes insufficient and the relative density becomes less than 95%, which is not preferable. The amount of the grain boundary phase having a low thermal conductivity as a structural component becomes excessive, and the thermal conductivity of the sintered body becomes less than 100 W / (m · K). The total of these silicon nitride contents is more preferably 0.6 to 4% by weight. The silicon nitride sintered body has a thermal conductivity of 100 to 300 W / (m · K) at room temperature, a three-point bending strength of 600 to 1500 MPa at room temperature, and is rich in high strength and high thermal conductivity. The silicon nitride-based sintered body converts contained Mg into magnesium oxide (MgO), and contains at least one element selected from rare earth elements (RE) containing La, Y and Yb as oxides ( RE_xO_y), The sum of the oxide equivalent contents is 0.6 to 7 wt%, and MgO / RE_xO_yIn particular, when the weight ratio represented by is 1 to 70, high strength and high thermal conductivity are improved. (MgO / RE_xO_yIf the (weight ratio) is less than 1, the proportion of the rare earth oxide in the grain boundary phase increases, so that the liquidus temperature rises in the sintering process, and the sintering becomes difficult, and a dense sintered body cannot be obtained. (MgO / RE_xO_yIf the (weight ratio) exceeds 70, the diffusion of Mg during firing cannot be suppressed, and color unevenness occurs on the surface of the sintered body. When the MgO / RExOy (weight ratio) is in the range of 1 to 70, the preform is fired at a sintering temperature of 1650 to 1850 ° C, and then a heat treatment at 1850 to 1900 ° C is performed, whereby the high thermal conductivity becomes remarkable. A silicon nitride based sintered body exceeding 120 w / (m · K) can be obtained, which is particularly preferable. The increase in thermal conductivity by this heat treatment is due to the combined effect of the growth of silicon nitride particles and the efficient vaporization of the MgO-based grain boundary phase component out of the silicon nitride sintered body with a high vapor pressure.
[0019]
In addition, the present inventionBe involved inThe circuit board converts the contained Mg into magnesium oxide (MgO), and converts at least one element selected from the contained rare earth elements (RE) containing La, Y and Yb into an oxide (RE)._xO_y) Converted to a silicon nitride sintered body whose total oxide equivalent content is 0.6 to 7% by weight and joined to a circuit board, and which is superior in heat resistance and heat dissipation as compared with the prior art. Can be provided.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
0.5% by weight of oxygen in the silicon nitride powderLess thanThe reason is that when the silicon nitride-based powder is used as a growth nucleus to form a silicon nitride-based sintered body, the amount of oxygen dissolved in the silicon nitride-based particles constituting the silicon nitride-based sintered body is: It depends strongly on the oxygen content of the silicon nitride powder used as a growth nucleus, and the higher the oxygen content of the silicon nitride powder, the higher the amount of oxygen dissolved in the silicon nitride particles. Oxygen contained in the silicon nitride-based particles causes scattering of phonons, which are a heat-conducting medium, and lowers the thermal conductivity of the silicon nitride-based sintered body. 100 W / m. In order to express a high thermal conductivity that cannot be obtained with the conventional silicon nitride sintered body of not less than K, the oxygen content of the silicon nitride powder is set to 0.5 wt%.Less thanIt is essential to reduce the amount of oxygen in the silicon nitride sintered body finally obtained.
[0021]
When the Fe content and the Al content in the silicon nitride-based powder are more than 100 ppm, Fe or Al remarkably forms a solid solution in the silicon nitride particles. Reduce the thermal conductivity of the silicon-based sintered body. Therefore, in order to obtain a thermal conductivity of 100 W / m · K or more, it is important to control the Fe content and the Al content in the silicon nitride powder to 100 ppm or less, respectively.
[0022]
The ratio between the silicon nitride powder having a β fraction of 30 to 100% and the α-type silicon nitride powder is preferably 1 to 50% by weight: 99 to 50% by weight. When the ratio of the silicon nitride-based powder having a β fraction of 30 to 100% is less than 1 wt%, although there is an effect as a growth nucleus, the number of growth nuclei acting due to a small addition amount is small, and abnormal grain growth occurs. Large particles cannot be uniformly dispersed in the microstructure, and the bending strength decreases. On the other hand, if it exceeds 50 wt%, the number of growth nuclei increases, and in the course of grain growth, particles collide with each other, thereby inhibiting growth and maintaining strength. However, the silicon nitride sintered body composed of developed columnar particles can be maintained. Cannot be obtained, and it becomes difficult to realize a high thermal conductivity as compared with the related art.
[0023]
Mg and Y are useful as sintering aids and are effective for densification of silicon nitride-based raw material powder. Since these elements have a low solid solubility in silicon nitride particles as the first microstructure component constituting the silicon nitride sintered body, the thermal conductivity of the silicon nitride particles, and thus the silicon nitride sintered body, is high. Can be kept.
[0024]
Like Y, it has a low solid solubility in silicon nitride particles and is useful as a sintering aid as an element such as La, Ce, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu. At least one rare earth element selected from the group of Among them, at least one rare earth element selected from the group consisting of La, Ce, Gd, Dy, and Yb is preferable because firing can be performed without increasing the temperature and pressure too much.
[0025]
The substrate made of the silicon nitride-based sintered body of the present invention makes use of the characteristics of high strength, high toughness and high thermal conductivity, and is used for various substrates such as a substrate for a power semiconductor or a substrate for a multi-chip module, or for a Peltier device. It is suitable for a member for electronic components such as a heat transfer plate or a heat sink for various heating elements.
[0026]
When the silicon nitride-based sintered body of the present invention is used as a substrate for a semiconductor element, the occurrence of cracks in the substrate when subjected to repeated thermal cycles accompanying the operation of the semiconductor element is suppressed, and the thermal shock resistance and the heat cycle Properties are remarkably improved, and excellent reliability is obtained. In addition, even when a semiconductor element for high output and high integration is mounted, deterioration of thermal resistance characteristics is small and excellent heat radiation characteristics are exhibited. Furthermore, the excellent mechanical properties allow not only the function as the original substrate material but also the structure itself to serve as a structural member, so that the structure of the substrate unit itself can be simplified.
[0027]
Further, the silicon nitride sintered body of the present invention can be widely used for materials requiring heat resistance properties such as thermal shock and thermal fatigue, in addition to the above-mentioned electronic component members. Structural members include various heat exchanger parts and heat engine parts, heater tubes used in the field of melting metals such as aluminum and zinc, Stokes, die-cast sleeves, propellers for molten metal agitation, ladles, thermocouple protection tubes, etc. Applicable to Further, by applying the present invention to a sink roll, a support roll, a bearing, a shaft, or the like used in a hot-dip metal plating line for aluminum, zinc, or the like, a member having high crack resistance against rapid heating and cooling can be obtained. In addition, in the field of steel or non-ferrous processing, if it is used for rolling rolls, squeeze rolls, guide rollers, drawing dies, or tool tips, it has good heat dissipation properties when it comes into contact with the work piece, so it has good thermal fatigue resistance. In addition, thermal shock resistance can be improved, whereby wear is reduced and thermal stress cracking is less likely to occur.
[0028]
Further, the present invention can be applied to a sputter target member, for example, forming an electric insulating film used for an MR head, a GMR head, or a TMR head of a magnetic recording device, and forming a wear-resistant film used for a thermal head of a thermal transfer printer. It is suitable for. The coating obtained by sputtering has essentially high thermal conductivity, a sufficiently high sputter rate, and a high electrical withstand voltage of the coating. For this reason, the electrical insulating coating for the MR head, GMR head, or TMR head formed with this sputter target has characteristics of high thermal conductivity and high withstand voltage, so that the heat generation density of the element can be increased and the insulating coating can be made thinner. Can be achieved. In addition, the wear-resistant coating for a thermal head formed with this sputter target has not only good wear resistance due to the inherent characteristics of silicon nitride but also high thermal conductivity, so that thermal resistance can be reduced. Can be enhanced.
[0029]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the examples.
(Example 1)
Oxygen content is SiO₂A BN crucible is filled with an imide decomposition silicon nitride powder having an average particle diameter of 0.2 to 2.0 μm in terms of less than 2.0 wt% in terms of conversion, and then N at normal pressure to 1.0 MPa (10 atm).₂Heat treatment was performed at 1400 ° C. to 1950 ° C. for 1 to 20 hours in an atmosphere, and then cooled to room temperature. The β fraction of the obtained silicon nitride-based powder was 90 to 100%, and the oxygen content was 0.2 to 0.4% by weight. FIG. 1 shows an SEM observation image of the obtained silicon nitride-based powder example. The powder has a β fraction of 100%, an oxygen content of 0.2 wt%, and Fe and Al contents of 50 ppm and 40 ppm, respectively. Grooves are formed in the powder in parallel to the major axis direction of the particles, which is a feature when grain growth occurs through the gas phase, and it has been demonstrated that the smaller the amount of oxygen is, the more significant it becomes. Was. Following the powder, the obtained β-type Si₃N₄5 to 30 parts by weight of a powder of silicon nitride based on α-type silicon nitride (Si) having an oxygen content of 0.3 to 1.5 wt% and an average particle diameter of 0.5 μm.₃N₄9) to 66 parts by weight of a powder, MgO powder having an average particle size of 0.2 μm as a sintering aid, and RE having an average particle size of 0.2 to 2.0 μm described in Table 1._xO_yThe powder (sintering aid) was blended, and a 2 wt% dispersant (Leogard GP) was further blended and charged into a ball mill container filled with ethanol, and then mixed. The resulting mixture is dried in vacuo and thenμ mAnd granulated through a sieve. Next, a disk-shaped molded body having a diameter of 20 mm × a thickness of 10 mm and a diameter of 100 mm × a thickness of 15 mm was obtained by CIP molding under a pressure of 3 ton with a press machine. Next, firing was performed in a nitrogen gas atmosphere at 1750 to 1900 ° C. and 0.9 MPa (9 atm) for 5 hours. The impurities of Fe and Al in the obtained silicon nitride powder were analyzed by a plasma emission spectrometry (ICP) method. The oxygen content was measured by an infrared heating absorption method. The β fraction of the obtained silicon nitride-based powder was determined from the X-ray diffraction intensity ratio using Cu-Kα ray according to the formula (1).

I_{β (101)} : Β-type Si3N₄(101) surface diffraction peak intensity of
I_{β (210)} : Β-type Si3N₄(210) plane diffraction peak intensity,
I_{α (102)} : Α-type Si3N₄(102) surface diffraction peak intensity of
I_{α (210)} : Α-type Si₃N₄(210) surface diffraction peak intensity.
The average particle diameter and average aspect ratio of the obtained silicon nitride-based powder were determined by using an SEM photograph obtained at an observation magnification of × 2000 by SEM observation to obtain a total of 500 nitrided particles within a visual area of 200 μm × 500 μm. The silicon particles were randomly selected, the minimum diameter and the maximum diameter were measured by an image analyzer, and the average value was obtained and evaluated. Next, from the obtained silicon nitride sintered body, a test piece having a diameter of 10 mm × thickness of 3 mm for measuring thermal conductivity and density, and a bending test piece having a length of 3 mm × 4 mm × a length of 40 mm were collected. The density was calculated by measuring the size with a micrometer and measuring the weight. The thermal conductivity was determined by measuring the specific heat and the thermal diffusivity at room temperature by a laser flash method and calculating the thermal conductivity. The three-point bending strength was measured at room temperature in accordance with JIS R1606. The outline of the above manufacturing conditions and the evaluation results are shown in Tables 1 and 2 for sample No. 1 to 11.
[0030]
(Comparative Example 1)
Silicon nitride powders having different β fractions were prepared in the same manner as in Example 1 except that the production conditions described in Table 1 were used. Next, a silicon nitride-based sintered body was prepared using the obtained silicon nitride-based powder and evaluated. The outline of the above manufacturing conditions and the evaluation results are shown in Tables 1 and 2 for sample No. 31 to 41 show.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
Table 1 and Table 2 sample No. From 1 to 11, the following findings were obtained.
The average particle size of the silicon nitride powder added as growth nuclei is such that the β fraction is 30% or more, the oxygen content as impurities is 0.5 wt% or less, the Fe content is 100 ppm or less, and the Al content is 100 ppm or less. The silicon nitride-based sintered body obtained by setting the blending amount of the silicon nitride-based powder having a diameter of 0.2 to 10 μm, an aspect ratio of 10 or less, and a β conversion ratio of 30% or more to 1 to 50 wt% at room temperature The thermal conductivity becomes 100 w / (m · K) or more, and the three-point bending strength at room temperature becomes 600 MPa or more. The thermal conductivity of the silicon nitride sintered body according to the prior art was about 40 w / (m · K), and the thermal conductivity could be dramatically increased. Further, as a sintering aid, Mg is converted to magnesium oxide (MgO), and Y, La, Ce, Dy, Gd and Yb are converted to oxides (RE_xO_y), The sum of the oxide equivalent contents is 0.6 to 7.0 wt%, and (MgO / RE)_xO_y) (Weight ratio) of 1 to 70 had a thermal conductivity of 100 w / (m · K) or more and a bending strength of 600 MPa or more.
[0034]
On the other hand, the sample Nos. The following findings were obtained from 31 to 41.
No. In the case of No. 31, when the β fraction of the silicon nitride particles is less than 30%, the bending strength is remarkably reduced to about 500 MPa.
No. In No. 32, when the amount of oxygen inevitably contained in the silicon nitride powder exceeds 0.5 wt., The thermal conductivity is reduced to 70 w / (m · K) or less.
No. 33 and No. 33. In No. 34, when the content of each of the impurities Fe and Al contained in the silicon nitride-based powder exceeds 100 ppm, the thermal conductivity decreases to 65 w / (m · K) or less.
No. 35 and No. 35. In No. 36, when the average particle diameter of the silicon nitride-based powder is less than 0.2 μm, the thermal conductivity is reduced to 60 w / (m · K) or less. The conductivity becomes 60 w / (m · K) or less, and the bending strength decreases to 600 MPa or less.
No. In No. 37, when the aspect ratio of the silicon nitride powder was 10 or more, a dense sintered body was not obtained, and the bending strength was reduced to 600 MPa or less.
No. 38 and No. 38. In No. 39, when the addition amount of the silicon nitride-based powder was less than 1.0 wt%, the bending strength was reduced to 600 MPa or less, and when it was more than 50 wt%, the thermal conductivity was reduced to 70 w / (m · K) or less.
No. 40 and No. In No. 41, when the sintering aid component was less than 0.6 wt%, the density of the sintered body was reduced, and as a result, the thermal conductivity and the bending strength were significantly reduced. When the sintering aid component exceeds 7.0 wt%, a sufficient glass phase is generated in the firing process, so that the sintered body is densified, but on the other hand, the grain boundary phase which is a low heat conductive phase increases. As a result, the thermal conductivity was reduced to 60 w / (m · K) or less.
[0035]
(Example 2)
3 wt% MgO and 1 wt% Y were added to the silicon nitride powder having a β conversion ratio of 30% or more prepared in Example 1.₂O₃A mixed powder to which the sintering aid was added was prepared. Then, the mixed powder thus produced and a silicon nitride ball as a grinding medium were put into a resin pot of a ball mill filled with a toluene / butanol solution containing 2 wt% of an amine-based dispersant, and wet-mixed for 48 hours. Next, 15 parts by weight of a polyvinyl organic binder and 5 parts by weight of a plasticizer (dimethylphthalate) were added to 100 parts by weight of the mixed powder in the pot, and then wet-mixed for 48 hours to obtain a sheet forming slurry. . After adjusting the molding slurry, green sheets were formed by a doctor blade method. Next, the formed green sheet was heated in air at 400 to 600 ° C. for 2 to 5 hours to add in advance and sufficiently degrease (remove) the organic binder component. Next, the degreased body was fired at 1850 ° C. for 5 hours in a nitrogen atmosphere of 0.9 MPa (9 atm), then heat-treated at 1900 ° C. for 24 hours in the nitrogen atmosphere, and then cooled to room temperature. The silicon nitride-based sintered body sheet was subjected to machining to produce a semiconductor device substrate having a length of 50 mm, a width of 50 mm and a thickness of 0.6 mm. A circuit board shown in FIG. 2 was produced using the silicon nitride sintered body substrate. In FIG. 2, a circuit board 1 is provided with a copper circuit board 3 on a surface of a manufactured silicon nitride-based sintered body 2 having a dimension of 50 mm × 50 mm × 0.6 mm, and a back surface of the substrate 2. A copper plate 4 is joined by a brazing material 5. This circuit board 1 was subjected to three-point bending strength evaluation and heat cycle test. As a result, the bending strength is as large as 600 MPa or more, and the frequency of occurrence of cracks due to tightening cracks in the mounting process of the circuit board 1 and thermal stress in the soldering process is hardly observed. It has been demonstrated that manufacturing yield can be significantly improved. The heat cycle test was -40.° CThe cooling / heating cycle was 20 minutes, the temperature at room temperature was 10 minutes, and the heating at 180 ° C. was 20 minutes, and the heating / cooling cycle was one cycle. This cycle was repeated until the cracks and the like occurred on the substrate portion. The number of cycles was measured. As a result, even after the lapse of 1000 cycles, there was no cracking of the silicon nitride-based sintered body substrate 2 or peeling of the copper circuit board 2, and it was confirmed that both durability and reliability were excellent. Further, even after 1000 cycles, the withstand voltage characteristics did not decrease.
[0036]
As described above, the silicon nitride powder of the present inventionProduction methodHas excellent productivity because it does not agglomerate or adhere oxides to the surface, and does not require laborious and laborious processes such as grinding and acid treatment. Further, the silicon nitride sintered body of the present inventionAccording to the manufacturing method of,Silicon nitride sintered bodyHigh thermal conductivity in addition to the inherent high strength / high toughnessBecause you canIn addition, when used as a substrate for a semiconductor element, cracks are less likely to occur in the substrate due to repeated thermal cycling accompanying the operation of the semiconductor element, and the thermal shock resistance and the thermal cycle resistance can be significantly improved.
[Brief description of the drawings]
FIG. 1 is a photograph of a representative silicon nitride powder of the present invention taken with a scanning electron microscope.
FIG. 2 is a sectional view of a main part of the circuit board of the present invention.
[Explanation of symbols]
1 circuit board, 2 boards, 3 copper circuit board, 4 copper board, 5 brazing material.

Claims (3)

The α-type silicon nitride powder raw material containing 0.02 wt% or more and less than 2.0 wt% of oxygen as calculated as SiO ₂ , having a specific surface area of 0.5 m ² / g or more and an average particle diameter of 0.2 to 2 μm is nitrogen or nitrogen. Heat treatment at a temperature of 1800 to 1950 ° C. in a non-oxidizing atmosphere of hydrogen to cause a phase transition to a β-type silicon nitride powder through a gas phase, and thereafter a β-type silicon nitride without a grinding step A method for producing a silicon nitride-based powder, wherein the method is a powder. Columnar particles having a β fraction of 30 to 100%, an oxygen content of less than 0.5 wt%, an Fe content and an Al content of 100 ppm or less, an average particle size of 0.2 to 10 μm, and an aspect ratio of 10 or less. 1 to 50 parts by weight of β-type silicon nitride powder, 99 to 50 parts by weight of α-type silicon nitride powder having an average particle size in the range of 0.2 to 4 μm, and rare earth elements containing Mg, La, Y and Yb. At least one element selected from (RE) is converted into oxides (RE _x O _y ) of magnesium oxide (MgO) and rare earth element compounds, respectively, and the total of the oxide conversion contents is 0.6 to 7 wt%. And a sintering aid having a weight ratio of (MgO / RE _x O _y ) of 1 to 70 and an organic binder are blended, and a molded product obtained therefrom is heated at 1650 to 1900 ° C. A method for producing a silicon nitride sintered body, comprising sintering. The method for producing a silicon nitride-based sintered body according to claim 2, wherein the compact is pre-fired at 1650 to 1850 ° C, and then sintered at 1850 to 1900 ° C.

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