JP4301617B2

JP4301617B2 - Method for manufacturing aluminum nitride sintered body for DBC circuit board and method for manufacturing DBC circuit board

Info

Publication number: JP4301617B2
Application number: JP37127598A
Authority: JP
Inventors: 通泰小松
Original assignee: Toshiba Corp; Toshiba Materials Co Ltd
Current assignee: Toshiba Corp; Toshiba Materials Co Ltd
Priority date: 1998-12-25
Filing date: 1998-12-25
Publication date: 2009-07-22
Anticipated expiration: 2018-12-25
Also published as: JP2000191376A

Description

【０００１】
【発明の属する技術分野】
本発明は、半導体基板等に使用されるＤＢＣ回路基板用窒化アルミニウム焼結体の製造方法およびＤＢＣ回路基板の製造方法に係り、特に窒化アルミニウム特有の高熱伝導性を損うことなく、強度ならびに破壊靭性値を共に大幅に改善し、放熱性に優れたＤＢＣ回路基板用窒化アルミニウム焼結体の製造方法およびＤＢＣ回路基板の製造方法に関する。
【０００２】
【従来の技術】
従来の金属材料と比較して強度、耐熱性、耐食性、耐摩耗性、軽量性などの諸特性に優れたセラミックス焼結体が、半導体基板、電子機器材料、エンジン用部材、高速切削工具用材料、ノズル、ベアリングなど、従来の金属材料では対応できない苛酷な温度、応力、摩耗条件下で使用される機械部品、機能部品、構造材や装飾品材料として広く利用されている。
【０００３】
特に窒化アルミニウム（ＡｌＮ）焼結体は高熱伝導性を有する絶縁体であり、シリコン（Ｓｉ）に近い熱膨張係数を有することから高集積化した半導体装置の放熱板や基板として、その用途を拡大している。
【０００４】
従来上記窒化アルミニウム焼結体は一般的に下記の製造方法によって量産されている。すなわち、窒化アルミニウム原料粉末に焼結助剤と、有機バインダと、必要に応じて各種添加剤や溶媒、分散剤とを添加して原料混合体を調製し、得られた原料混合体をドクターブレード法や泥漿鋳込み法（スリップキャスティング法）によって成形し、薄板状ないしシート状の成形体としたり、原料混合体をプレス成形して厚板状ないし大型の成形体を形成する。次に得られた成形体は、空気または窒素ガス雰囲気において加熱され脱脂処理され、有機バインダとして使用された炭化水素成分等が成形体から排除脱脂される。そして脱脂された成形体は窒素ガス雰囲気等で高温度に加熱され緻密化焼結されて窒化アルミニウム焼結体が形成される。
【０００５】
上記製造方法において、原料ＡｌＮ粉末として平均粒径が０．５μｍ以下程度の超微細な原料粉末を使用する場合は、ＡｌＮ粉末単独でもかなりの緻密な焼結体が得られる。しかしながら、原料粉末表面等に付着した多量の酸素等の不純物が焼結時に、ＡｌＮ結晶格子中に固溶したり、格子振動の伝播を妨げるＡｌ−Ｏ−Ｎ化合物等の複合酸化物を生成する結果、焼結助剤を使用しないＡｌＮ焼結体の熱伝導率は比較的に低かった。
【０００６】
一方原料粉末として平均粒径１μｍ以上のＡｌＮ粉末を使用する場合は、その原料粉末単独では焼結性が良好でないため、ホットプレス法以外には助剤無添加では緻密な焼結体を得ることが困難であり、量産性が低い欠点があった。そこで常圧焼結法によって効率的に焼結体を製造しようとする場合には、焼結体の緻密化およびＡｌＮ原料粉末中の不純物酸素がＡｌＮ結晶粒子内へ固溶することを防止するために、焼結助剤として、酸化イットウリム（Ｙ₂Ｏ₃）などの希土類酸化物や酸化カルシウムなどのアルカリ土類金属酸化物等を添加することが一般に行なわれている。
【０００７】
これらの焼結助剤は、ＡｌＮ原料粉末に含まれる不純物酸素やＡｌ₂Ｏ₃と反応して液相を形成し、焼結体の緻密化を達成するとともに、この不純物酸素を粒界相として固定し、高熱伝導率化も達成するものと考えられている。
【０００８】
【発明が解決しようとする課題】
しかしながら上記従来の製造方法においては、本来、ＡｌＮと液相化合物との濡れ性が低く、また液相自体が偏析し易い性質を有することから、焼結後に液相が凝固する際に、液相はＡｌＮ粒子の間隙部に偏在するように残留し、凝固して粗大で脆弱な粒界相を形成する傾向がある。また、結晶粒の粒成長が進行し易く、さらに焼結体の結晶組織に平均粒径が５〜１０μｍと粗大な結晶粒が形成され易く、また微小な気孔が消滅せずに結晶粒内に残存し、焼結体の緻密化を阻害し、最終的に３点曲げ強度が３５０〜４００ＭＰａ程度の低強度であり、また破壊靭性値が２．８ＭＰａ・ｍ^1/2以下という低靭性の窒化アルミニウム焼結体しか得られない問題点があった。
【０００９】
上記問題点を解決するために、粒径が均一で細かい窒化アルミニウム原料粉末を使用して可及的に微細な結晶組織を有するＡｌＮ焼結体を形成したり、各種添加物を添加して焼結性を高める工夫も試行されている。例えばＷ成分等を含有させることにより、焼結性を改善して高強度のＡｌＮ焼結体を得る方法も本願発明者らが発案した。しかしながら、Ｗ成分を含有させることにより、結晶組織が微細で均一化されるため、焼結体の強度は改善される反面、破壊靭性値は逆に低下してしまうことも判明した。したがって、強度および靭性値が共に優れた半導体基板用のＡｌＮ焼結体を得ることは困難であった。
【００１０】
近年、半導体素子の高集積化、高出力化に伴って増加する発熱量に対応するために、高熱伝導性（高放熱性）を有する上記窒化アルミニウム材料が普及しつつあり、その放熱性については大体満足する結果が得られている。しかしながら上記のように構造部材としての強度ならびに靭性値が不足するため、例えば窒化アルミニウム焼結体で形成した半導体基板を実装ボードに装着する際に作用する僅かな曲げ応力や取扱時に作用する衝撃力によって半導体基板が損傷し易く、半導体回路基板の製造歩留りが大幅に低下してしまう問題点があった。
【００１１】
また、焼結体を適正に焼結できる温度幅が狭く、その適正温度幅を超えると焼結体表面に液相の凝集偏析が顕著になる欠点がある。この欠点は、ＣｕＯと酸素との共晶化合物を介して銅回路板等を基板表面に直接的に接合するＤＢＣ（銅直接接合）法で回路基板を製造する際に悪影響を及ぼす。すなわち、銅回路形成工程において重要な前工程である基板の表面酸化熱処理において、酸化膜が均一に形成されず、ＤＢＣ法による回路基板の製造歩留りを低下させる要因のひとつとなっている。
【００１２】
本発明は上記の問題点を解決するためになされたものであり、ＡｌＮ焼結体の結晶粒の大きさおよび微構造を適正に制御し焼結体組織を微細化するとともに、粒界相と結晶粒との結合強化を図って焼結体の強度ならびに破壊靭性値の向上を図り、放熱特性を損うことなく機械的強度を高め、さらに適正に焼結できる温度範囲を拡げることができ、また焼結体表面における液相の凝集偏析を大幅に抑制することが可能なＡｌＮ焼結体およびその製造方法を提供することを目的とする。
【００１３】
【課題を解決するための手段】
本願発明者は上記目的を達成するため、窒化アルミニウム原料粉末の合成方法，ＡｌＮ原料粉末の粒度分布，原料窒化アルミニウム粉末に添加する焼結助剤や添加物の種類や添加量を種々変えて、それらが焼結体や焼結体の表面の液相状態，結晶組織の微構造，強度特性や破壊靭性値および伝熱特性に及ぼす影響について実験検討を進めた。
【００１４】
その結果、所定のＡｌＮ原料粉末に焼結助剤の他に添加剤としてのＳｉ成分と、炭化ボロン（Ｂ₄Ｃ）と、ＨｆおよびＺｒの少なくとも１一方とを複合的に微量添加し、その混合体を成形焼結したときに、平均結晶粒径が３〜４．５μｍと微細であり、かつ上記炭化ボロンが粒界相とＡｌＮ結晶粒との結合度を改善するとともに均一に分散した焼結体組織が得られ、強度特性および破壊靭性値が共に優れたＡｌＮ焼結体が得られた。また、焼結体表面に液相の凝集偏析が発生せず、適正に焼結できる温度範囲が大幅に拡大したＡｌＮ焼結体が得られた。本発明は上記知見に基づいて完成されたものである。
【００１５】
すなわち本発明に係る窒化アルミニウム焼結体は、周期律表IIIa族元素，Ｃａ，Ｓｒ，Ｂａから選択される少なくとも１種の元素の酸化物を１〜１０重量％と、炭化ボロンを０．２〜２．０重量％と、ＳｉＯ_２，Ｓｉ_３Ｎ_４，ＳｉＣ，Ｓｉ_２Ｎ_２Ｏ，β−サイアロン，α−サイアロンおよびポリタイプの窒化アルミニウム（Ａｌ−Ｓｉ−Ｏ−Ｎ）から選択された少なくとも１種のけい素化合物として含有されるをＳｉ成分換算で０．２重量％以下と、ＨｆおよびＺｒの少なくとも１種を酸化物換算で０．１〜２重量％と、残部を構成する窒化アルミニウムとから成る窒化アルミニウム焼結体であって、破壊靭性値が３ＭＰａ・ｍ ^１／２以上であり、３点曲げ強度が４５０ＭＰａ以上であり、熱伝導率が１３０Ｗ／ｍ・Ｋ以上であり、窒化アルミニウム結晶粒の平均結晶粒径が３〜４．５μｍであり、上記窒化アルミニウム焼結体の表面に酸化膜を具備していることを特徴とする。
さらにＴｉ，Ｆｅ，Ｎｉ，Ｃｒ，Ｃｏ，Ｌｉ，Ｍｇから選択される少なくとも１種の金属元素を酸化物換算で０．０５〜０．５重量％含有させるとよい。さらに焼結体の平均結晶粒径が２〜４．５μｍであるとよい。そして上記組成から成り、かつ広い結晶粒径分布を有するＡｌＮ焼結体は、熱伝導率が１３０Ｗ／ｍ・Ｋ以上であり、また３点曲げ強度が４５０ＭＰａであり、破壊靭性値が３．０ＭＰａ・ｍ^１／２以上となる。さらに、焼結体を適正に焼結できる温度範囲は±２０〜±３０℃程度拡大される。
【００１６】
また本発明に係るＤＢＣ回路基板用窒化アルミニウム焼結体の製造方法は、窒化アルミニウム原料粉末に、周期律表IIIa族元素，Ｃａ，Ｓｒ，Ｂａから選択される少なくとも１種の元素の酸化物を１〜１０重量％と、炭化ボロン（Ｂ_４Ｃ）を０．２〜２．０重量％と、ＳｉＯ_２，Ｓｉ_３Ｎ_４，ＳｉＣ，Ｓｉ_２Ｎ_２Ｏ，β−サイアロン，α−サイアロンおよびポリタイプの窒化アルミニウム（Ａｌ−Ｓｉ−Ｏ−Ｎ）から選択された少なくとも１種のけい素化合物をＳｉ成分換算で０．２重量％以下と、ＨｆおよびＺｒの少なくとも１種を酸化物換算で０．１〜２重量％とを添加した混合粉末を成形する工程と、得られた成形体を非酸化性雰囲気中で１６５０〜１９００℃の温度域で焼結することにより、表面の液相の凝集偏析が抑制され均一な表面を有し、破壊靭性値が３ＭＰａ・ｍ^１／２以上であり、３点曲げ強度が４５０ＭＰａ以上であり、熱伝導率が１３０Ｗ／ｍ・Ｋ以上であり、窒化アルミニウム結晶粒の平均結晶粒径が３〜４．５μｍである窒化アルミニウム焼結体を得る工程と、得られた焼結体を酸化熱処理することにより焼結体表面に均一な酸化膜を形成する工程とを具備することを特徴とする。
【００１７】
本発明方法において使用され、焼結体の主成分となる窒化アルミニウム（ＡｌＮ）原料粉末としては、焼結性および熱伝導性を考慮して不純物酸素含有量が１．５重量％以下に抑制され、平均粒径が０．５〜２μｍ程度、好ましくは１．５μｍ以下の微細なＡｌＮ原料粉末を使用する。
【００１８】
周期律表IIIa族元素，Ｃａ，Ｓｒ，Ｂａの酸化物は、焼結助剤として作用し、ＡｌＮ焼結体を緻密化するために、ＡｌＮ原料粉末に対して１〜１０重量％の範囲で添加される。上記焼結助剤の具体例としては希土類元素（Ｙ，Ｓｃ，Ｃｅ，Ｄｙなど）の酸化物、窒化物、アルカリ土類金属（Ｃａ）の酸化物、もしくは焼結操作によりこれらの化合物となる物質が使用され、特に酸化イットリウム（Ｙ₂Ｏ₃）、酸化セリウム（ＣｅＯ）や酸化カルシウム（ＣａＯ）が好ましい。上記焼結助剤の添加量が１重量％未満の場合は、焼結性の改善効果が充分に発揮されず、焼結体が緻密化されず低強度の焼結体が形成されたり、ＡｌＮ結晶中に酸素が固溶し、高い熱伝導率を有する焼結体が形成できない。
【００１９】
一方添加量が１０重量％を超える過量となると、焼結助剤としての効果は飽和状態に達して無意味となるばかりでなく、却って焼結して得られるＡｌＮ焼結体の熱伝導率が低下する一方、粒界相が焼結体中に多量に残存したり、熱処理により除去される粒界相の体積が大きいため、焼結体中に空孔が残ったりして収縮率が増大し、変形を生じ易くなる。
【００２０】
Ｓｉ成分は、焼結性を向上させるとともに焼結温度を低下させる効果を有するが、特に上記焼結助剤と複合添加することにより、焼結体の粒成長を抑止することができ、微細なＡｌＮ結晶組織を形成し、焼結体の構造強度を高めるために添加される。上記Ｓｉ成分としては、ＳｉＯ₂，Ｓｉ₃Ｎ₄，ＳｉＣ，Ｓｉ₂Ｎ₂Ｏ，β−サイアロン，α−サイアロンおよびポリタイプの窒化アルミニウム（Ａｌ−Ｓｉ−Ｏ−Ｎ）等のけい素化合物を使用することが望ましい。このけい素化合物の含有量はＳｉ成分として０．２重量％以下の範囲に調整される。しかしながら、Ｓｉ成分の含有量が０．０１重量％未満の場合は、粒成長の抑止効果が不充分となり、粗大な結晶組織となり、高強度のＡｌＮ焼結体が得られない。一方、含有量が０．２重量％を超える過量となると、焼結体の熱伝導率が低下するとともに、曲げ強度が低下する場合もある。
【００２１】
また炭化ボロン（Ｂ₄Ｃ）はＡｌＮ焼結体の粒界相と結晶粒との結合度を高めるとともに、焼結体組織内に均一に分散してクラックの伝播を阻止する作用を発揮しＡｌＮ焼結体の破壊靭性値をさらに向上させる効果を有し、このＢ₄Ｃの含有量は０．２〜２重量％の範囲に調整される。Ｂ₄Ｃの含有量が０．２重量％未満の場合には、上記靭性改善効果が不充分となる一方、含有量が２重量％を超える過量となると、焼結体の熱伝導率が低下してしまう。
【００２２】
Ｈｆ成分およびＺｒ成分は、焼結性をさらに向上させると共に焼結体表面に発生し易い液相の凝集偏析を抑制し、適正に焼結できる温度範囲を拡大する効果を有する。上記成分としては酸化物，炭化物，窒化物，珪化物，硼化物等の化合物を使用することが望ましい。このＨｆ化合物およびＺｒ化合物は酸化物換算で０．１〜２重量％の範囲で添加される。添加量が０．１重量％未満の場合は上記改善効果が不十分となる一方、添加量が２重量％を超えると過量となると、他の不純物と同様にＡｌＮ焼結体の熱伝導率を低下させる。
【００２３】
Ｔｉ，Ｆｅ，Ｎｉ，Ｃｒ，Ｃｏ，Ｌｉ，Ｍｇの酸化物は、焼結温度を下げて焼結性を向上させる一方、焼結体を着色して不透明な焼結体を形成する等、ＡｌＮ焼結体の特性を改善するために有効であり、酸化物換算で０．０５〜０．５重量％の範囲で添加してもよい。添加量が０．０５重量％未満の場合は、上記特性改善効果が不充分となる一方、添加量が０．５重量％を超える過量となると、他の不純物と同様にＡｌＮ焼結体の熱伝導率を低下させる。
【００２４】
また上記各種添加物以外の不純物陽イオンはＡｌＮ焼結体の熱伝導を阻害する化合物を形成し易いため、ＡｌＮ焼結体中の含有量は０．２重量％以下とする。
【００２５】
上記ＡｌＮ原料粉末、各種焼結助剤，Ｓｉ成分用Ｓｉ化合物，Ｂ₄ＣおよびＨｆ，Ｚｒ化合物は、例えばボールミル等の粉砕混合機に投入され、所定時間混合されることによって原料混合体となる。次に得られた原料混合体を所定形状の金型に充填し加圧成形して成形体が形成される。このとき予め原料混合体にパラフィン、ステアリン酸等の有機バインダを５〜１０重量％添加しておくことにより、成形操作を円滑に実施することができる。
【００２６】
成形法としては、汎用の金型プレス法、泥漿鋳込み法、静水圧プレス法、押出し成形法あるいはドクターブレード法のようなシート成形法などが適用できる。
【００２７】
上記成形操作に引き続いて、成形体を空気中で温度４００〜５５０℃に加熱したり、または非酸化性雰囲気中、例えば窒素ガス雰囲気中で温度４００〜８００℃に加熱して、予め添加していた有機バインダを充分に脱脂除去する。
【００２８】
次に脱脂処理された複数のシート状の成形体は、例えばセラミックス焼結粉から成るしき粉を介して焼成炉内において多段に積層され、この配置状態で複数の成形体は一括して所定温度で焼結される。焼結操作は、窒素ガスなどの非酸化性雰囲気で成形体を温度１６５０〜１９００℃で２〜６時間程度加熱して実施される。特にＳｉ成分と、ＨｆおよびＺｒの少なくとも１種とを添加することにより、１７００〜１７８０℃程度と従来より低い温度で焼結することが可能となる。焼結雰囲気は、ＡｌＮと反応しない非酸化性雰囲気あればよいが、通常は窒素ガス、または窒素ガスを含む還元性雰囲気で行う。還元性ガスとしてはＨ₂ガス、ＣＯガスを使用してもよい。なお、焼結は真空（僅かな還元雰囲気を含む）、減圧、加圧および常圧を含む雰囲気で行ってもよい。焼結温度が１６５０℃未満と低温状態で焼成すると、原料粉末の粒径、含有酸素量によって異なるが、緻密化が困難であり、強度および熱伝導性などの特性に難点が生じ易い一方、１９００℃より高温度で焼成すると、焼成炉内におけるＡｌＮ自体の蒸気圧が高くなり緻密化が困難になるとともに熱伝導率が急激に低下するおそれがあるため、焼結温度は上記範囲に設定される。
【００２９】
そして上記ＡｌＮ原料粉末に焼結助剤，Ｂ₄Ｃ，Ｓｉ成分およびＨｆ，Ｚｒ成分を添加した所定の組成を有する原料混合体を成形、脱脂、焼結することにより、平均結晶粒径が３〜４．５μｍ程度と微細であり、かつ粒界相とＡｌＮ結晶粒との結合度が改善されるとともに、Ｂ₄Ｃ粒子が均一に分散した結晶組織を有し、熱伝導率が１３０Ｗ／ｍ・Ｋ以上であり、かつ曲げ強度が４５０ＭＰａ以上，破壊靭性値が３．０ＭＰａ・ｍ^1/2以上である高強度で高靭性のＡｌＮ焼結体が得られる。また、より広い焼結温度範囲において、焼結体表面における液相の凝集偏析が少ないＡｌＮ焼結体が得られる。
【００３０】
上記構成に係る窒化アルミニウム焼結体およびその製造方法によれば、周期律表IIIa族元素，Ｃａ，Ｓｒ，Ｂａの酸化物から成る焼結助剤とともに所定量のＳｉ成分とＢ₄Ｃと、ＨｆおよびＺｒの少なくとも１種とを複合添加してＡｌＮ焼結体としているため、Ｓｉ成分によって結晶粒の大きさが適正に制御された結晶組織が得られる。またＢ₄Ｃによって粒界相とＡｌＮ結晶粒との結合度が改善され、かつＢ₄Ｃ粒子が均一に分散した微構造を有する結晶組織が得られる。したがって、クラックの伝播が効果的に阻止され強度特性および破壊靭性値が共に優れた窒化アルミニウム焼結体が得られる。また、Ｈｆ成分やＺｒ成分を添加しているため、焼結体表面における液相の凝集偏析が効果的に抑制され、均一な表面を有する焼結体が得られる。したがって、ＤＢＣ法で回路基板を製造する際に重要な前工程である基板の酸化熱処理工程において酸化膜が均一に形成されるため、高品質の回路基板が得られる。
【００３１】
【発明の実施の形態】
次に下記の実施例を参照して本発明に係る窒化アルミニウム焼結体をより具体的に説明する。
【００３２】
実施例１〜５０
還元窒化合成法によって製造され、不純物として酸素を０．８重量％含有し、平均粒径１μｍの窒化アルミニウム原料粉末に対して、表１および表２に示すようにＳｉ成分，Ｂ₄Ｃ，Ｈｆ化合物，Ｚｒ化合物および焼結助剤としてのＹ₂Ｏ₃，ＴｉＯ₂，Ｆｅ₂Ｏ₃，ＮｉＯ，Ｃｒ₂Ｏ₃，ＣｏＯ，Ｌｉ₂Ｏ，ＭｇＯ，ＳｉＯ₂，Ｓｉ₃Ｎ₄，ＳｉＣ，Ｓｉ₂Ｎ₂Ｏ，α−サイアロン，β−サイアロン，ポリタイプＡｌＮ等をそれぞれ所定量ずつ添加し、エチルアルコールを溶媒としてボールミルで４８時間混合して原料混合体を調製した。次にこの原料混合体に有機バインダとしてのパラフィンを７．５重量％添加して造粒粉を調製した。
【００３３】
次に得られた造粒粉をプレス成形機の成形用金型内に充填して1000kg／cm²の加圧力にて一軸方向に圧縮成形して、縦５０mm×横５０mm×厚さ５mmの角板状成形体を多数調製した。引き続き各成形体を空気中で４５０℃で１時間加熱して脱脂処理した。
【００３４】
次に脱脂処理した各成形体をＡｌＮ製焼成容器内に収容し、焼成炉において表１および表２に示す焼成温度１７００〜１８２０℃で４時間緻密化焼結を実施し、その後冷却速度２００℃／hrで冷却してそれぞれ実施例１〜５０に係るＡｌＮ焼結体を製造した。
【００３５】
比較例１
一方、表２に示すように、Ｓｉ成分，Ｂ₄Ｃ，Ｈｆ成分およびＺｒ成分を全く添加せず、従来の焼結助剤のみを添加し１８００℃で焼結した以外は実施例１と同一条件で原料調整、成形、脱脂、焼結処理して同一寸法を有する比較例１に係るＡｌＮ焼結体を製造した。
【００３６】
比較例２
また、Ｓｉ成分を全く添加せず、かつ温度１７６０℃で焼結した以外は実施例１と同一条件で処理して比較例２に係るＡｌＮ焼結体を製造した。
【００３７】
比較例３
Ｂ₄Ｃ成分を全く添加せず、かつ１７４０℃で焼結した以外は実施例１と同一条件で原料調整，成形，脱脂，焼結処理して同一寸法を有する比較例３に係るＡｌＮ焼結体を製造した。
【００３８】
比較例４
また、Ｈｆ成分を全く添加せず、かつ温度１７６０℃で焼結した以外は実施例１と同一条件で処理して比較例４に係るＡｌＮ焼結体を製造した。
【００３９】
比較例５
焼結助剤としてのＹ₂Ｏ₃を過剰量１５重量％添加し、かつ１７８０℃で焼結した以外は実施例１と同様に処理して比較例５に係るＡｌＮ焼結体を製造した。
【００４０】
比較例６
Ｂ₄Ｃを過剰量３重量％添加し、かつ１７４０℃で焼結した以外は実施例１と同様に処理して比較例６に係るＡｌＮ焼結体を製造した。
【００４１】
比較例７
ＨｆＯ₂を過剰量３重量％添加し、かつ１７４０℃で焼結した以外は実施例１と同様に処理して比較例７に係るＡｌＮ焼結体を製造した。
【００４２】
比較例８
Ｓｉ成分としてのＳｉＯ₂を過剰量０．３重量％（Ｓｉ換算）添加し、かつ１７４０℃で焼結した以外は実施例１と同様に処理して比較例８に係るＡｌＮ焼結体を製造した。
【００４３】
比較例９
焼結助剤としてＹ₂Ｏ₃に加えてＴｉＯ₂を過剰量１重量％添加し、かつ１７４０℃で焼結した以外は実施例１と同様に処理して比較例９に係るＡｌＮ焼結体を製造した。
【００４４】
こうして得られた実施例１〜５０および比較例１〜９に係る各ＡｌＮ焼結体の強度特性および放熱特性に加えて表面状態を評価するために、各試料の３点曲げ強度、破壊靭性値，熱伝導率および平均結晶粒径（Ｄ５０）を測定するとともに、表面における液相の凝集偏析の有無を観察する一方、各ＡｌＮ焼結体を酸化熱処理したときに形成された酸化膜の均一性を調査し、下記表１〜２に示す結果を得た。なお、破壊靭性値は、マイクロインデンテーション法における新原方式により測定した値である。
【００４５】
【表１】

【００４６】
【表２】

【００４７】
上記表１〜２に示す結果から明らかなように、Ｙ₂Ｏ₃，ＣａＯ等の焼結助剤に加えてＢ₄Ｃと、Ｈｆ，Ｚｒの少なくとも一方と、Ｓｉ成分とを微量ずつ複合添加した実施例１〜５０に係るＡｌＮ焼結体においては、結晶粒径がいずれも３〜４．５μｍと極めて微細であり、かつＢ₄Ｃによって粒界相とＡｌＮ結晶粒との結合度が改善されるとともに、Ｂ₄Ｃ粒子が均一に分散した結晶組織が得られ、Ｂ₄Ｃ粒子によってクラック伝播が阻止されるため、高い曲げ強度に加えて破壊靭性値および熱伝導率が共に優れていることが判明した。さらに、Ｈｆ成分やＺｒ成分を添加することにより、焼結体表面における液相の凝集偏析が効果的に抑制される。そのためＤＢＣ工程において重要な前処理である基板の酸化熱処理工程においてＡｌＮ製基板表面に酸化膜が均一に形成されることも判明した。
【００４８】
一方、Ｓｉ成分を全く添加しない比較例１および比較例２に係るＡｌＮ焼結体は、熱伝導率においては実施例１〜５０より優れているものがある反面、概して曲げ強度が低く、耐久性および取扱性において難点がある。また
Ｓｉ成分を過量に添加した比較例８の試料では、熱伝導率が不充分となり、また従来の焼結助剤としてのＹ₂Ｏ₃を過量に添加した比較例５の試料では、Ｓｉ成分を添加したにも拘らず、熱伝導率および強度が共に低下することが確認された。
【００４９】
また、Ｂ₄Ｃを全く添加しない比較例３に係るＡｌＮ焼結体は、熱伝導率においては実施例１〜５０より優れていものがある反面、概して破壊靭性値が低く、耐久性および取扱性において難点がある。
【００５０】
またＢ₄Ｃを過量に添加した比較例６に係るＡｌＮ焼結体は熱伝導率が低下することが確認された。Ｈｆ成分を全く添加しない比較例４に係るＡｌＮ焼結体は、熱伝導率，曲げ強度ならびに靭性値は実施例１〜５０と同等であるが、焼結体表面における液相の凝集偏析が中程度であり、また、酸化熱処理によるＡｌＮ焼結体製基板への酸化膜の形成が不均一になり、ＤＢＣ法による回路基板の製造時に難点があった。
【００５１】
さらにＨｆ成分を適量に添加した比較例７に係るＡｌＮ焼結体は曲げ強度ならびに靭性値は実施例１〜５０と同等であるが、熱伝導率が不十分となる。また、ＴｉＯ₂を適量に添加した比較例９に係るＡｌＮ焼結体は曲げ強度ならびに靭性値は実施例１〜５０と同等であるが、熱伝導率が不十分となる。
【００５２】
【発明の効果】
以上説明の通り本発明に係るセラミックス焼結体およびその製造方法によれば、周期律表IIIa族元素，Ｃａ，Ｓｒ，Ｂａの酸化物から成る焼結助剤とともに所定量のＳｉ成分とＢ₄ＣとＨｆおよびＺｒの少なくとも１種とを複合添加してＡｌＮ焼結体としているため、Ｓｉ成分によって結晶粒の大きさが適正に制御された結晶組織が得られる。またＢ₄Ｃによって粒界相とＡｌＮ結晶粒との結合度が改善され、かつＢ₄Ｃ粒子が均一に分散した微構造を有する結晶組織が得られる。したがって、クラックの伝播が効果的に阻止され強度特性および破壊靭性値が共に優れた窒化アルミニウム焼結体が得られる。さらに、ＨｆおよびＺｒから選択される少なくとも１種の成分を添加しているため、焼結体表面における液相の凝集偏析が効果的に抑制される。そのため、ＤＢＣ法で回路基板を製造する際に重要な前処理である酸化熱処理工程において、ＡｌＮ焼結体製基板表面に酸化膜を均一に形成することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing an aluminum nitride sintered body for a DBC circuit board and a method for manufacturing a DBC circuit board used for a semiconductor substrate and the like, and in particular, strength and destruction without impairing the high thermal conductivity unique to aluminum nitride. The present invention relates to a method for producing an aluminum nitride sintered body for a DBC circuit board and a method for producing a DBC circuit board , both of which greatly improve the toughness value and are excellent in heat dissipation.
[0002]
[Prior art]
Compared to conventional metal materials, ceramic sintered bodies with excellent properties such as strength, heat resistance, corrosion resistance, wear resistance, and light weight are semiconductor substrates, electronic equipment materials, engine parts, and materials for high-speed cutting tools. It is widely used as mechanical parts, functional parts, structural materials and decorative materials used under severe temperature, stress, and wear conditions that cannot be handled by conventional metal materials such as nozzles and bearings.
[0003]
In particular, aluminum nitride (AlN) sintered body is an insulator with high thermal conductivity and has a thermal expansion coefficient close to that of silicon (Si), so its application is expanded as a heat sink and substrate for highly integrated semiconductor devices. is doing.
[0004]
Conventionally, the aluminum nitride sintered body is generally mass-produced by the following manufacturing method. That is, a raw material mixture is prepared by adding a sintering aid, an organic binder, and various additives, solvents, and dispersants as necessary to the aluminum nitride raw material powder, and the obtained raw material mixture is a doctor blade. Or a sludge casting method (slip casting method) to form a thin plate or sheet-shaped molded body, or a raw material mixture is press-molded to form a thick plate or large-sized molded body. Next, the obtained molded body is heated and degreased in an air or nitrogen gas atmosphere, and hydrocarbon components and the like used as an organic binder are removed from the molded body and degreased. The degreased molded body is heated to a high temperature in a nitrogen gas atmosphere or the like and densified and sintered to form an aluminum nitride sintered body.
[0005]
In the above manufacturing method, when an ultrafine raw material powder having an average particle size of about 0.5 μm or less is used as the raw material AlN powder, a fairly dense sintered body can be obtained even with the AlN powder alone. However, a large amount of impurities such as oxygen adhering to the surface of the raw material powder form a solid oxide in the AlN crystal lattice during sintering, or a composite oxide such as an Al—O—N compound that hinders the propagation of lattice vibration. As a result, the thermal conductivity of the AlN sintered body using no sintering aid was relatively low.
[0006]
On the other hand, when an AlN powder having an average particle size of 1 μm or more is used as a raw material powder, the raw material powder alone does not have a good sinterability. However, there is a drawback that mass productivity is low. Therefore, in order to efficiently produce a sintered body by the normal pressure sintering method, in order to prevent densification of the sintered body and impurity oxygen in the AlN raw material powder from dissolving into the AlN crystal particles. In addition, a rare earth oxide such as yttrium oxide (Y ₂ O ₃ ) or an alkaline earth metal oxide such as calcium oxide is generally added as a sintering aid.
[0007]
These sintering aids react with impurity oxygen and Al ₂ O ₃ contained in the AlN raw material powder to form a liquid phase, achieve densification of the sintered body, and use this impurity oxygen as a grain boundary phase. It is believed that they are fixed and achieve high thermal conductivity.
[0008]
[Problems to be solved by the invention]
However, in the above conventional manufacturing method, originally, the wettability between AlN and the liquid phase compound is low, and the liquid phase itself is easily segregated. Tends to remain unevenly distributed in the gaps between the AlN particles and solidify to form coarse and brittle grain boundary phases. In addition, crystal grain growth is easy to proceed, and coarse crystal grains with an average grain size of 5 to 10 μm are easily formed in the crystal structure of the sintered body, and minute pores are not lost in the crystal grains. Residual, densification of the sintered body is inhibited, and finally the three-point bending strength is a low strength of about 350 to 400 MPa, and the low toughness nitriding is a fracture toughness value of 2.8 MPa · m ^1/2 or less. There was a problem that only an aluminum sintered body could be obtained.
[0009]
In order to solve the above problems, an aluminum nitride raw material powder having a uniform and fine grain size is used to form an AlN sintered body having as fine a crystal structure as possible, or various additives are added and sintered. Attempts have also been made to improve cohesion. For example, the inventors of the present invention also devised a method for improving the sinterability and obtaining a high-strength AlN sintered body by including a W component or the like. However, it has also been found that the inclusion of the W component makes the crystal structure fine and uniform, so that the strength of the sintered body is improved, but the fracture toughness value is conversely reduced. Therefore, it has been difficult to obtain an AlN sintered body for a semiconductor substrate having both excellent strength and toughness values.
[0010]
In recent years, the above-mentioned aluminum nitride material having high thermal conductivity (high heat dissipation) is becoming widespread in order to cope with the heat generation amount that increases with higher integration and higher output of semiconductor elements. The results are generally satisfactory. However, since the strength and toughness value as a structural member is insufficient as described above, for example, slight bending stress acting when mounting a semiconductor substrate formed of an aluminum nitride sintered body on a mounting board and impact force acting when handling As a result, the semiconductor substrate is easily damaged, and the manufacturing yield of the semiconductor circuit substrate is greatly reduced.
[0011]
Further, there is a drawback that the temperature range at which the sintered body can be properly sintered is narrow, and when the appropriate temperature range is exceeded, agglomeration and segregation of the liquid phase becomes remarkable on the surface of the sintered body. This drawback has an adverse effect when a circuit board is manufactured by a DBC (copper direct bonding) method in which a copper circuit board or the like is directly bonded to the substrate surface via a eutectic compound of CuO and oxygen. That is, in the surface oxidation heat treatment of the substrate, which is an important pre-process in the copper circuit formation process, the oxide film is not formed uniformly, which is one of the factors that reduce the production yield of circuit boards by the DBC method.
[0012]
The present invention has been made in order to solve the above-mentioned problems, and appropriately controls the crystal grain size and microstructure of the AlN sintered body to refine the sintered body structure, By strengthening the bond with crystal grains and improving the strength and fracture toughness value of the sintered body, the mechanical strength can be increased without impairing the heat dissipation characteristics, and the temperature range that can be properly sintered can be expanded. It is another object of the present invention to provide an AlN sintered body capable of greatly suppressing liquid phase aggregation and segregation on the surface of the sintered body and a method for producing the same.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the inventor of the present application variously changed the synthesis method of the aluminum nitride raw material powder, the particle size distribution of the AlN raw material powder, the sintering additive and additive added to the raw aluminum nitride powder, Experimental studies were conducted on the effects of these on the sintered body and the liquid phase state of the surface of the sintered body, the microstructure of the crystal structure, strength characteristics, fracture toughness values, and heat transfer characteristics.
[0014]
As a result, in addition to the sintering aid, Si component as an additive, boron carbide (B ₄ C), and at least one of Hf and Zr are added in a small amount to a predetermined AlN raw material powder, When the mixture is formed and sintered, the average crystal grain size is as fine as 3 to 4.5 μm, and the boron carbide improves the bonding degree between the grain boundary phase and the AlN crystal grains and is uniformly dispersed. A compact structure was obtained, and an AlN sintered body excellent in both strength properties and fracture toughness values was obtained. Moreover, the liquid phase aggregation segregation did not generate | occur | produce on the sintered compact surface, and the AlN sintered compact in which the temperature range which can be sintered appropriately expanded significantly was obtained. The present invention has been completed based on the above findings.
[0015]
That is, the aluminum nitride sintered body according to the present invention comprises 1 to 10% by weight of an oxide of at least one element selected from Group IIIa elements of the periodic table, Ca, Sr, and Ba, and 0.2% of boron carbide. and 2.0 _wt%, was selected _{_{SiO 2, Si 3 N 4,}} SiC, Si 2 N 2 O, β- sialon, from α- sialon and polytypes of aluminum nitride (Al-SiO-N) Nitridation comprising at least one silicon compound, 0.2% by weight or less in terms of Si component, and 0.1-2% by weight in terms of oxide of at least one of Hf and Zr, constituting the balance in an adult Ru nitrided sintered aluminum from aluminum, and the fracture toughness value is 3 MPa ^{· m 1/2} or more, three-point bending strength of not less than 450 MPa, thermal conductivity of 130W / m · K or higher Yes, nitriding The average crystal grain size of the aluminum crystal grains is 3 to 4.5 μm, and an oxide film is provided on the surface of the aluminum nitride sintered body .
Further, at least one metal element selected from Ti, Fe, Ni, Cr, Co, Li, and Mg is preferably contained in an amount of 0.05 to 0.5% by weight in terms of oxide. Further, the average crystal grain size of the sintered body is preferably 2 to 4.5 μm. An AlN sintered body having the above composition and having a wide crystal grain size distribution has a thermal conductivity of 130 W / m · K or more, a three-point bending strength of 450 MPa, and a fracture toughness value of 3.0 MPa. -M ^1/2 or more. Furthermore, the temperature range in which the sintered body can be appropriately sintered is expanded by about ± 20 to ± 30 ° C.
[0016]
In the method for producing an aluminum nitride sintered body for a DBC circuit board according to the present invention, an oxide of at least one element selected from Group IIIa elements of the periodic table, Ca, Sr, and Ba is added to the aluminum nitride raw material powder. 1 to 10% by weight, boron carbide (B ₄ C) 0.2 to 2.0% by weight, SiO ₂ , Si ₃ N ₄ , SiC, Si ₂ N ₂ O, β-sialon, α-sialon and At least one silicon compound selected from polytype aluminum nitride (Al—Si—O—N) is 0.2 wt% or less in terms of Si component, and at least one of Hf and Zr is in terms of oxide. a step of forming a mixed powder prepared by adding a 0.1 to 2 wt%, by sintering at a temperature range of 1,650-1900 ° C. the resultant green body in a non-oxidizing atmosphere, the surface of the liquid phase Aggregation segregation is suppressed Has one surface, fracture toughness is at 3 MPa ^{· m 1/2} or more, three-point bending strength of not less than 450 MPa, and a thermal conductivity of 130W / m · K or more, the average aluminum nitride crystal grains And a step of obtaining an aluminum nitride sintered body having a crystal grain size of 3 to 4.5 μm and a step of forming a uniform oxide film on the surface of the sintered body by subjecting the obtained sintered body to an oxidation heat treatment. It is characterized by that.
[0017]
The aluminum nitride (AlN) raw material powder used in the method of the present invention and serving as the main component of the sintered body has an impurity oxygen content of 1.5% by weight or less in consideration of sinterability and thermal conductivity. A fine AlN raw material powder having an average particle size of about 0.5 to 2 μm, preferably 1.5 μm or less is used.
[0018]
The group IIIa element of the periodic table, Ca, Sr, and Ba oxides act as a sintering aid, and in order to densify the AlN sintered body, in the range of 1 to 10% by weight with respect to the AlN raw material powder. Added. Specific examples of the sintering aid include oxides of rare earth elements (Y, Sc, Ce, Dy, etc.), nitrides, oxides of alkaline earth metals (Ca), or these compounds by a sintering operation. Substances are used, and yttrium oxide (Y ₂ O ₃ ), cerium oxide (CeO) and calcium oxide (CaO) are particularly preferable. When the additive amount of the sintering aid is less than 1% by weight, the effect of improving the sinterability is not sufficiently exhibited, the sintered body is not densified and a low strength sintered body is formed, or AlN Oxygen is dissolved in the crystal, and a sintered body having high thermal conductivity cannot be formed.
[0019]
On the other hand, when the added amount exceeds 10% by weight, not only the effect as a sintering aid reaches a saturated state and becomes meaningless, but also the thermal conductivity of the AlN sintered body obtained by sintering is increased. On the other hand, the grain boundary phase remains in the sintered body in a large amount or the volume of the grain boundary phase removed by the heat treatment is large, so that voids remain in the sintered body and the shrinkage rate increases. , Deformation is likely to occur.
[0020]
The Si component has the effect of improving the sinterability and lowering the sintering temperature. In particular, by adding it in combination with the above-mentioned sintering aid, the grain growth of the sintered body can be suppressed and the fineness can be reduced. It is added to form an AlN crystal structure and increase the structural strength of the sintered body. Examples of the Si component include silicon compounds such as SiO ₂ , Si ₃ N ₄ , SiC, Si ₂ N ₂ O, β-sialon, α-sialon, and polytype aluminum nitride (Al—Si—O—N). It is desirable to use it. The content of the silicon compound is adjusted to a range of 0.2% by weight or less as the Si component. However, when the content of the Si component is less than 0.01% by weight, the effect of suppressing grain growth becomes insufficient, resulting in a coarse crystal structure and a high-strength AlN sintered body cannot be obtained. On the other hand, when the content exceeds 0.2% by weight, the thermal conductivity of the sintered body is lowered and the bending strength may be lowered.
[0021]
Boron carbide (B ₄ C) enhances the degree of bonding between the grain boundary phase and crystal grains of the AlN sintered body, and evenly disperses in the sintered body structure to prevent the propagation of cracks. This has the effect of further improving the fracture toughness value of the sintered body, and the B ₄ C content is adjusted to a range of 0.2 to 2% by weight. When the content of B ₄ C is less than 0.2% by weight, the effect of improving the toughness is insufficient. On the other hand, when the content exceeds 2% by weight, the thermal conductivity of the sintered body decreases. Resulting in.
[0022]
The Hf component and the Zr component have the effect of further improving the sinterability and suppressing the aggregation and segregation of the liquid phase that is likely to occur on the surface of the sintered body, thereby expanding the temperature range in which proper sintering can be performed. As the above components, it is desirable to use compounds such as oxides, carbides, nitrides, silicides and borides. The Hf compound and Zr compound are added in the range of 0.1 to 2% by weight in terms of oxide. When the addition amount is less than 0.1% by weight, the above improvement effect is insufficient. On the other hand, when the addition amount exceeds 2% by weight, the excess becomes excessive, and the thermal conductivity of the AlN sintered body is reduced as in other impurities. Reduce.
[0023]
The oxides of Ti, Fe, Ni, Cr, Co, Li, and Mg improve the sinterability by lowering the sintering temperature, while coloring the sintered body to form an opaque sintered body. It is effective for improving the properties of the sintered body and may be added in the range of 0.05 to 0.5% by weight in terms of oxide. When the added amount is less than 0.05% by weight, the above-mentioned property improvement effect is insufficient. On the other hand, when the added amount exceeds 0.5% by weight, the heat of the AlN sintered body is the same as other impurities. Reduce conductivity.
[0024]
Further, impurity cations other than the above-mentioned various additives easily form a compound that hinders the heat conduction of the AlN sintered body, so the content in the AlN sintered body is 0.2% by weight or less.
[0025]
The AlN raw material powder, various sintering aids, Si compound for Si component, B ₄ C and Hf, Zr compound are put into a pulverizing mixer such as a ball mill and mixed for a predetermined time to become a raw material mixture. . Next, the obtained raw material mixture is filled in a mold having a predetermined shape, and pressure-molded to form a molded body. At this time, by previously adding 5 to 10% by weight of an organic binder such as paraffin and stearic acid to the raw material mixture, the molding operation can be carried out smoothly.
[0026]
As a molding method, a general-purpose die press method, a slurry casting method, a hydrostatic pressure press method, an extrusion molding method or a sheet molding method such as a doctor blade method can be applied.
[0027]
Subsequent to the above molding operation, the molded body is heated in air to a temperature of 400 to 550 ° C., or heated in a non-oxidizing atmosphere, for example, a nitrogen gas atmosphere to a temperature of 400 to 800 ° C., and added in advance. Thoroughly degrease and remove the organic binder.
[0028]
Next, the plurality of sheet-like compacts that have been degreased are stacked in multiple stages in a firing furnace, for example, via a powder made of ceramic sintered powder. Sintered with. The sintering operation is performed by heating the compact at a temperature of 1650 to 1900 ° C. for about 2 to 6 hours in a non-oxidizing atmosphere such as nitrogen gas. In particular, by adding the Si component and at least one of Hf and Zr, sintering can be performed at a temperature of about 1700 to 1780 ° C., which is lower than the conventional temperature. The sintering atmosphere may be a non-oxidizing atmosphere that does not react with AlN. Usually, the sintering atmosphere is nitrogen gas or a reducing atmosphere containing nitrogen gas. As the reducing gas, H ₂ gas or CO gas may be used. Sintering may be performed in an atmosphere including vacuum (including a slight reducing atmosphere), reduced pressure, increased pressure, and normal pressure. When sintered at a low temperature of less than 1650 ° C., although it varies depending on the particle size of the raw material powder and the amount of oxygen contained, it is difficult to densify, and problems such as strength and thermal conductivity tend to occur. When firing at a temperature higher than 0 ° C., the vapor pressure of AlN itself in the firing furnace becomes high and densification becomes difficult and the thermal conductivity may be drastically lowered, so the sintering temperature is set in the above range. .
[0029]
Then, a raw material mixture having a predetermined composition in which a sintering aid, B ₄ C, Si component and Hf, Zr component are added to the AlN raw material powder is molded, degreased, and sintered, so that the average crystal grain size becomes 3 It is as fine as ˜4.5 μm, the degree of bonding between the grain boundary phase and the AlN crystal grains is improved, and it has a crystal structure in which B ₄ C particles are uniformly dispersed, and the thermal conductivity is 130 W / m. A high-strength and high-toughness AlN sintered body having K or higher, a bending strength of 450 MPa or higher, and a fracture toughness value of 3.0 MPa · m ^1/2 or higher is obtained. In addition, in a wider sintering temperature range, an AlN sintered body with less liquid phase aggregation segregation on the surface of the sintered body can be obtained.
[0030]
According to the aluminum nitride sintered body and the method for producing the same according to the above configuration, a predetermined amount of Si component and B ₄ C together with a sintering aid composed of an oxide of group IIIa elements of the periodic table, Ca, Sr, Ba, Since an AlN sintered body is formed by compound addition of at least one of Hf and Zr, a crystal structure in which the size of the crystal grains is appropriately controlled by the Si component can be obtained. Also an improved degree of coupling between the grain boundary phase and the AlN crystal grains by B ₄ C, and the crystal structure is obtained having a microstructure which B ₄ C particles are uniformly dispersed. Therefore, the propagation of cracks is effectively prevented, and an aluminum nitride sintered body having excellent strength characteristics and fracture toughness values can be obtained. In addition, since the Hf component and the Zr component are added, aggregation of the liquid phase on the surface of the sintered body is effectively suppressed, and a sintered body having a uniform surface can be obtained. Therefore, since the oxide film is uniformly formed in the oxidation heat treatment step of the substrate, which is an important pre-process when manufacturing the circuit substrate by the DBC method, a high-quality circuit substrate can be obtained.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Next, the aluminum nitride sintered body according to the present invention will be described more specifically with reference to the following examples.
[0032]
Examples 1-50
As shown in Tables 1 and 2, Si components, B ₄ C, and Hf are produced for an aluminum nitride raw material powder that is manufactured by a reduction nitridation synthesis method and contains 0.8% by weight of oxygen as an impurity and has an average particle diameter of 1 μm Compounds, Zr compounds and Y ₂ O ₃ , TiO ₂ , Fe ₂ O ₃ , NiO, Cr ₂ O ₃ , CoO, Li ₂ O, MgO, SiO ₂ , Si ₃ N ₄ , SiC, Si as sintering aids Predetermined amounts of ₂ N ₂ O, α-sialon, β-sialon, polytype AlN, and the like were added and mixed in a ball mill for 48 hours using ethyl alcohol as a solvent to prepare a raw material mixture. Next, granulated powder was prepared by adding 7.5% by weight of paraffin as an organic binder to the raw material mixture.
[0033]
Next, the obtained granulated powder is filled into a molding die of a press molding machine, compression-molded in a uniaxial direction with a pressing force of 1000 kg / cm ² , and a corner of 50 mm long × 50 mm wide × 5 mm thick. A large number of plate-like molded bodies were prepared. Subsequently, each molded body was degreased by heating in air at 450 ° C. for 1 hour.
[0034]
Next, each degreased compact is housed in a firing container made of AlN, densified and sintered at a firing temperature of 1700 to 1820 ° C. shown in Tables 1 and 2 in a firing furnace for 4 hours, and then a cooling rate of 200 ° C. The AlN sintered bodies according to Examples 1 to 50 were manufactured by cooling at / hr.
[0035]
Comparative Example 1
On the other hand, as shown in Table 2, it was the same as Example 1 except that the Si component, B ₄ C, Hf component and Zr component were not added at all, and only the conventional sintering aid was added and sintered at 1800 ° C. The AlN sintered body which concerns on the comparative example 1 which has raw material adjustment, shaping | molding, degreasing | defatting, and a sintering process on condition on the same dimension was manufactured.
[0036]
Comparative Example 2
Further, an AlN sintered body according to Comparative Example 2 was manufactured by processing under the same conditions as in Example 1 except that no Si component was added and sintering was performed at a temperature of 1760 ° C.
[0037]
Comparative Example 3
AlN sintering according to Comparative Example 3 having the same dimensions by adjusting the raw material, forming, degreasing and sintering under the same conditions as in Example 1 except that no B ₄ C component was added and sintering was performed at 1740 ° C. The body was manufactured.
[0038]
Comparative Example 4
Further, an AlN sintered body according to Comparative Example 4 was manufactured by processing under the same conditions as in Example 1 except that no Hf component was added and sintering was performed at a temperature of 1760 ° C.
[0039]
Comparative Example 5
An AlN sintered body according to Comparative Example 5 was manufactured in the same manner as in Example 1 except that an excess amount of 15% by weight of Y ₂ O ₃ as a sintering aid was added and sintering was performed at 1780 ° C.
[0040]
Comparative Example 6
An AlN sintered body according to Comparative Example 6 was manufactured in the same manner as in Example 1 except that an excess amount of 3% by weight of B ₄ C was added and sintering was performed at 1740 ° C.
[0041]
Comparative Example 7
An AlN sintered body according to Comparative Example 7 was manufactured in the same manner as in Example 1 except that an excess amount of 3% by weight of HfO ₂ was added and sintered at 1740 ° C.
[0042]
Comparative Example 8
An AlN sintered body according to Comparative Example 8 was produced by treating in the same manner as in Example 1 except that an excess amount of 0.3 wt% (Si conversion) of SiO ₂ as a Si component was added and sintered at 1740 ° C. did.
[0043]
Comparative Example 9
An AlN sintered body according to Comparative Example 9 treated in the same manner as in Example 1 except that 1% by weight of TiO ₂ was added in addition to Y ₂ O ₃ as a sintering aid and sintered at 1740 ° C. Manufactured.
[0044]
In order to evaluate the surface state in addition to the strength characteristics and heat dissipation characteristics of the AlN sintered bodies according to Examples 1 to 50 and Comparative Examples 1 to 9 thus obtained, the three-point bending strength and fracture toughness value of each sample. In addition to measuring the thermal conductivity and average crystal grain size (D50) and observing the presence or absence of coagulation segregation of the liquid phase on the surface, the uniformity of the oxide film formed when each AlN sintered body was subjected to an oxidation heat treatment The results shown in Tables 1 and 2 below were obtained. The fracture toughness value is a value measured by the Shinhara method in the microindentation method.
[0045]
[Table 1]

[0046]
[Table 2]

[0047]
As is clear from the results shown in Tables 1 and 2, B ₄ C, at least one of Hf and Zr, and Si component are added in small amounts in addition to the sintering aids such as Y ₂ O ₃ and CaO. In the AlN sintered bodies according to Examples 1 to 50, the crystal grain size is all very fine, 3 to 4.5 μm, and the degree of bonding between the grain boundary phase and the AlN crystal grains is improved by B ₄ C. In addition, since a crystal structure in which B ₄ C particles are uniformly dispersed is obtained and crack propagation is prevented by the B ₄ C particles, both fracture toughness value and thermal conductivity are excellent in addition to high bending strength. It has been found. Furthermore, by adding the Hf component and the Zr component, the aggregation and segregation of the liquid phase on the surface of the sintered body is effectively suppressed. For this reason, it has also been found that an oxide film is uniformly formed on the surface of the AlN substrate in the oxidation heat treatment step of the substrate, which is an important pretreatment in the DBC step.
[0048]
On the other hand, the AlN sintered bodies according to Comparative Example 1 and Comparative Example 2 to which no Si component is added are superior to Examples 1 to 50 in thermal conductivity, but generally have low bending strength and durability. And there are difficulties in handling. Further, in the sample of Comparative Example 8 in which the Si component was added in excess, the thermal conductivity was insufficient, and in the sample of Comparative Example 5 in which Y ₂ O ₃ as a conventional sintering aid was added in excess, the Si component It was confirmed that both the thermal conductivity and the strength decreased despite the addition of.
[0049]
Further, the AlN sintered body according to Comparative Example 3 to which no B ₄ C is added is superior to Examples 1 to 50 in terms of thermal conductivity, but generally has a low fracture toughness value, durability and handleability. There are difficulties.
[0050]
In addition, it was confirmed that the AlN sintered body according to Comparative Example 6 in which an excessive amount of B ₄ C was added has a reduced thermal conductivity. The AlN sintered body according to Comparative Example 4 to which no Hf component is added has the same thermal conductivity, bending strength, and toughness as those of Examples 1 to 50, but the liquid phase aggregates and segregates on the surface of the sintered body. In addition, the formation of the oxide film on the AlN sintered body substrate by the oxidation heat treatment becomes non-uniform, and there is a difficulty in manufacturing the circuit board by the DBC method.
[0051]
Furthermore, the AlN sintered body according to Comparative Example 7 to which an appropriate amount of the Hf component is added has the same bending strength and toughness as those of Examples 1 to 50, but the thermal conductivity is insufficient. Further, the AlN sintered body according to Comparative Example 9 to which TiO ₂ is added in an appropriate amount has the same bending strength and toughness as those of Examples 1 to 50, but the thermal conductivity is insufficient.
[0052]
【The invention's effect】
As described above, according to the ceramic sintered body and the manufacturing method thereof according to the present invention, a predetermined amount of Si component and B ₄ together with a sintering aid composed of Group IIIa elements of the periodic table, Ca, Sr, and Ba oxides. Since an AlN sintered body is obtained by adding C and at least one of Hf and Zr in combination, a crystal structure in which the size of the crystal grains is appropriately controlled by the Si component can be obtained. Also an improved degree of coupling between the grain boundary phase and the AlN crystal grains by B ₄ C, and the crystal structure is obtained having a microstructure which B ₄ C particles are uniformly dispersed. Therefore, the propagation of cracks is effectively prevented, and an aluminum nitride sintered body having excellent strength characteristics and fracture toughness values can be obtained. Furthermore, since at least one component selected from Hf and Zr is added, aggregation of the liquid phase on the surface of the sintered body is effectively suppressed. Therefore, an oxide film can be uniformly formed on the surface of the substrate made of an AlN sintered body in an oxidation heat treatment step that is an important pretreatment when manufacturing a circuit board by the DBC method.

Claims

窒化アルミニウム原料粉末に、周期律表IIIa族元素，Ｃａ，Ｓｒ，Ｂａから選択される少なくとも１種の元素の酸化物を１〜１０重量％と、炭化ボロンを０．２〜２．０重量％と、ＳｉＯ_２，Ｓｉ_３Ｎ_４，ＳｉＣ，Ｓｉ_２Ｎ_２Ｏ，β−サイアロン，α−サイアロンおよびポリタイプの窒化アルミニウム（Ａｌ−Ｓｉ−Ｏ−Ｎ）から選択された少なくとも１種のけい素化合物をＳｉ成分換算で０．２重量％以下と、ＨｆおよびＺｒの少なくとも１種を酸化物換算で０．１〜２重量％とを添加した混合粉末を成形する工程と、得られた成形体を非酸化性雰囲気中で１６５０〜１９００℃の温度域で焼結することにより、表面の液相の凝集偏析が抑制され均一な表面を有し、破壊靭性値が３ＭＰａ・ｍ^１／２以上であり、３点曲げ強度が４５０ＭＰａ以上であり、熱伝導率が１３０Ｗ／ｍ・Ｋ以上であり、窒化アルミニウム結晶粒の平均結晶粒径が３〜４．５μｍである窒化アルミニウム焼結体を得る工程と、得られた焼結体を酸化熱処理することにより焼結体表面に均一な酸化膜を形成する工程とを具備することを特徴とするＤＢＣ回路基板用窒化アルミニウム焼結体の製造方法。In the aluminum nitride raw material powder, 1 to 10% by weight of an oxide of at least one element selected from Group IIIa elements of the periodic table, Ca, Sr, and Ba, and 0.2 to 2.0% by weight of boron carbide. And at least one silicon selected from SiO ₂ , Si ₃ N ₄ , SiC, Si ₂ N ₂ O, β-sialon, α-sialon and polytype aluminum nitride (Al—Si—O—N) A step of molding a mixed powder in which a compound is added in an amount of 0.2% by weight or less in terms of Si component and 0.1 to 2% by weight in terms of oxide of at least one of Hf and Zr is added, and the obtained molded body Is sintered in a temperature range of 1650 to 1900 ° C. in a non-oxidizing atmosphere to suppress aggregation and segregation of the liquid phase on the surface, and has a uniform surface, and a fracture toughness value of 3 MPa · m ^1/2 or more. Yes, 3-point bending strength is 450 A step of obtaining an aluminum nitride sintered body having a MPa of not less than MPa, a thermal conductivity of not less than 130 W / m · K, and an average crystal grain size of aluminum nitride crystal grains of 3 to 4.5 μm, and the obtained sintering And a step of forming a uniform oxide film on the surface of the sintered body by subjecting the body to an oxidation heat treatment. A method for producing an aluminum nitride sintered body for a DBC circuit board .

窒化アルミニウム原料粉末に０．０５〜０．５重量％の、Ｔｉ，Ｆｅ，Ｎｉ，Ｃｒ，Ｃｏ，ＬｉおよびＭｇから選択される少なくとも１種の金属元素の酸化物を添加することを特徴とする請求項１記載のＤＢＣ回路基板用窒化アルミニウム焼結体の製造方法。0.05 to 0.5 wt% of at least one metal element oxide selected from Ti, Fe, Ni, Cr, Co, Li and Mg is added to the aluminum nitride raw material powder. The manufacturing method of the aluminum nitride sintered compact for DBC circuit boards of Claim 1 .

窒化アルミニウム原料粉末の酸素含有量が１．５重量％以下であることを特徴とする請求項１記載のＤＢＣ回路基板用窒化アルミニウム焼結体の製造方法。The process according to claim 1 DBC circuit board aluminum nitride sintered body, wherein the oxygen content of the aluminum nitride raw material powder is 1.5 wt% or less.

請求項１記載の製造方法によって製造されたＤＢＣ回路基板用窒化アルミニウム焼結体から成る基板表面に銅直接接合法（ＤＢＣ法）によって回路板を接合することを特徴とするＤＢＣ回路基板の製造方法。Method for producing a DBC circuit board, characterized by bonding the claims 1 circuit board by the manufacturing method of copper directly bonding method to the substrate surface consisting manufactured DBC circuit aluminum board nitride sintered body by (DBC method) according .