JP4305986B2

JP4305986B2 - Method for producing silicon carbide composite material

Info

Publication number: JP4305986B2
Application number: JP36930098A
Authority: JP
Inventors: 千尋河合; 伸一山形; 彰福井; 義信武田
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1998-12-25
Filing date: 1998-12-25
Publication date: 2009-07-29
Anticipated expiration: 2018-12-25
Also published as: JP2000192182A

Description

【０００１】
【発明の属する技術分野】
本発明は、各種装置・機器に用いられる放熱基板、特に半導体装置の放熱基板に用いられる高い熱伝導性を有する炭化珪素系複合材料およびそれを用いた半導体装置に関する。
【０００２】
【従来の技術】
近年半導体装置の高速演算・高集積化に対する市場の要求は急速に高まりつつある。それとともに、同装置の半導体素子搭載用放熱基板には、同素子から発生する熱をより一層効率良く逃がすため、その熱伝導率のより一層の向上が求められてきた。さらに同素子ならびに同基板に隣接配置された同装置内の他の部材(周辺部材)との間の熱歪みをより一層小さくするために、より一層それらに近い熱膨張係数を有するものであることも求められてきた。具体的には、半導体素子として通常用いられるＳｉ、ＧａＡｓの熱膨張係数がそれぞれ４．２×１０^-6／℃、６．５×１０^-6／℃であり、半導体装置の外囲器材として通常用いられるアルミナセラミックスのそれが６．５×１０^-6／℃程度であることから、同基板の熱膨張係数はこれらの値に近いことが望まれる。
【０００３】
また近年のエレクトロニクス機器の応用範囲の著しい拡張にともない、半導体装置の使用範囲はより一層多様化しつつある。その中で、高出力の交流変換機器・周波数変換機器等のいわゆる半導体パワーデバイス機器への利用が増えつつある。これらのデバイスでは、半導体素子からの発熱が半導体メモリーやマイクロプロセッサーに比べ数倍から数十倍(通常例えば数十Ｗ)にも及ぶ。このためこれらの機器に使われる放熱基板は、その熱伝導率を格段に向上させるとともに、その熱膨張係数の周辺部材のそれとの整合性を高めることが重要である。一方半導体メモリーやマイクロプロセッサーのように、実用時に以上述べたパワーデバイスほど大きな発熱を伴わない機器もある。このような機器は、多量に製造されるためにパワーデバイス機器以上に安価なものが要求される。したがってこれに用いられる放熱基板は、上記ほど高い放熱性は必要としないが、安価なものが要求される。このように機器の出力容量やその実用機能レベルによって基板に要求される放熱性のレベルも千差万別である。またそれぞれの機器での基板周辺の構造によって、基板に要求される熱膨張係数の整合性の度合いもまちまちである。
【０００４】
パワーデバイスの場合、通常の基本構造は、例えば以下のようになっている。まずＳｉ半導体素子を第一の放熱基板である高熱伝導性の窒化アルミニウム(以下単にＡｌＮとも言う)セラミック基板上に載せる。次いでその第一の放熱基板の下に銅等のより高熱伝導性の金属からなる第二の放熱基板を配置する。さらにこの第二の基板の下に、これを水冷または空冷可能な放熱機構を配置する。以上のような構造によって外部に遅滞なく熱を逃がす。したがって複雑な放熱構造とならざるを得ない。この構造においては、第一の放熱基板であるＡｌＮセラミックスに１７０Ｗ／ｍ・Ｋ程度のものを用いるとすると、第二の放熱基板は、この第一の基板から伝達された熱をその下の放熱機構に遅滞なく逃がす必要がある。このため第二の基板としては、室温で少なくとも２００Ｗ／ｍ・Ｋ以上の高い熱伝導率と第一の基板との熱膨張係数の整合のため、１０×１０^-6／℃以下、特に８×１０^-6／℃以下の低い熱膨張係数を有するものが要求される。
【０００５】
特にパワーデバイスの内でも実用時の発熱量の大きなものでは、放熱基板自体の温度も１００℃以上に昇温することがあるため、このような温度での高い熱伝導率を要求される場合もある。したがって、このような温度下でも１５０Ｗ／ｍ・Ｋ以上の熱伝導率のものが要求される。またその容量が大きくなればなるほどＳｉ半導体素子のサイズも大きくなる。それ故それを搭載する放熱基板も大きくせざるを得ない。例えばパソコン用の基板が高々２０〜４０ｍｍ角程度のであるのに対し、容量の大きなパワーデバイスでは、２００ｍｍ角を越えるものも求められつつある。このような大きな基板では、実装時のその寸法精度のみならず高温でその精度の低下しないことが要求されている。すなわち高温で基板に反りや変形が生じると、上記した基板の下に配置される放熱機構(ラジエターやフィン等)との界面に隙間ができ放熱効率が落ちる。また最悪の場合半導体素子が破壊する場合もある。それ故高温での放熱基板の優れた熱伝導性の確保は、重要な課題である。
【０００６】
また以上述べた各種機器に用いられる放熱基板には、従来より例えばＣｕ−Ｗ系やＣｕ−Ｍｏ系の複合合金からなるものが用いられてきた。これらの基板は、原料が高価なためにコスト高となる。さらに重量が大きくなるという問題があった。そこで、最近は安価で軽量な材料として各種のアルミニウム(以下単にＡｌとも言う)複合合金が注目されるようになってきた。中でもＡｌと炭化珪素(以下単にＳｉＣとも言う)を主成分とするＡｌ−ＳｉＣ系複合合金は、それらの原料が比較的安価であり、軽量かつ高熱伝導性である。なお通常市販されている純粋なＡｌ、ＳｉＣ単体の密度は、それぞれ２．７ｇ／ｃｍ³程度、３．２ｇ／ｃｍ³程度、熱伝導率は、それぞれ２４０Ｗ／ｍ・Ｋ程度、２００〜３００Ｗ／ｍ・Ｋ程度までであるが、さらにその純度や欠陥濃度を調整すれば、その熱伝導率のレベルはさらに向上するものと思われる。そのため、特に注目されている材料である。また純粋なＳｉＣ単体、Ａｌ単体の熱膨張係数はそれぞれ４．２×１０^-6／℃程度、２４×１０^-6／℃程度であり、それらを複合化することによって、その熱膨張係数が広い範囲で制御可能となる。したがってこの点でも有利である。
【０００７】
かかるＡｌ−ＳｉＣ系複合合金およびその製造方法については、(１)特開平１−５０１４８９号公報、(２)特開平２−３４３７２９号公報、(３)特開昭６１−２２２６６８号公報および(４)特開平９−１５７７７３号公報に開示されている。(１)は、ＳｉＣとＡｌの混合物中のＡｌを溶融させて鋳造法によって固化する方法に関するものである。(２)、(３)は、いずれもＳｉＣ多孔体の空隙にＡｌを溶浸する方法に関するものである。この内(３)は、加圧下でＡｌを溶浸する、いわゆる加圧溶浸法に関するものである。また(４)は、ＳｉＣとＡｌの混合粉末の成形体かまたはそれをホットプレスしたものを型内に配置し、これを真空中、Ａｌの融点以上の温度で液相焼結する方法に関するものである。
【０００８】
本発明者等は、特願平９−１３６１６４号にて、(５)液相焼結法によって得られ、その熱伝導率が１８０Ｗ／ｍ・Ｋ以上のアルミニウム−炭化珪素系複合材料を提示している。この複合材料は、例えば１０〜７０重量％の粒子状ＳｉＣ粉末とＡｌ粉末との混合粉末を成形した後、９９体積％の窒素を含み、酸素濃度が２００ｐｐｍ以下、露点が−２０℃以下の非酸化性雰囲気中、６００〜７５０℃で焼結する工程によって得られる。また本発明者等は、特願平９−９３４６７号にて、(６)その熱膨張係数が１８×１０^-6／℃以下、その熱伝導率が２３０Ｗ／ｍ・Ｋ以上であり、焼結後の寸法が実用寸法に近い、いわゆるネットシェイプなアルミニウム−炭化珪素系複合材料も提示している。さらに本発明者等は、特願平１０−４１４４７号にて、(７)常圧焼結法とＨＩＰ法とを組み合わせた同複合材料の製造方法を提案している。それによれば、例えば粒子状ＳｉＣを１０〜７０重量％混合したＡｌ−ＳｉＣ系混合粉末の成形体を、窒素ガスを９９％以上含む非酸化性雰囲気中、６００℃以上、Ａｌの溶融温度以下の温度範囲で常圧焼結し、その後金属容器に封入して７００℃以上の温度でＨＩＰすることによって、均質でその熱伝導率が２００Ｗ／ｍ・Ｋ以上のアルミニウム−炭化珪素系複合材料が得られている。
【０００９】
さらに(８)特開平９−１５７７７３号公報には、Ａｌ粉末とＳｉＣ粉末との混合物をホットプレスし、成形と焼結とを同時に行う方法が開示されている。その方法は、Ａｌ１０〜８０体積％、残部ＳｉＣの混合粉末を成形し、Ａｌの溶融点以上の温度下５００ｋｇ／ｃｍ²以上の圧力でホットプレスするものである。この方法によって１５０〜２８０Ｗ／ｍ・Ｋの熱伝導率のアルミニウム−炭化珪素系複合材料が得られている。
【００１０】
また主成分金属をアルミニウムから銅に置き換えた銅−炭化珪素系の複合材料については、その文献は少ないが、本発明者等の知見によれば、この複合材料は、アルミニウムを銅(以下単にＣｕとも言う)に置き換えれば、以上述べた製造方法とほぼ同様の方法によって得られる。なお純粋なＣｕ単体の密度は８．９ｇ／ｃｍ³程度、その熱伝導率は３９５Ｗ／ｍ・Ｋ程度、その熱膨張係数は１７×１０^-6／℃程度である。したがって、アルミニウム系のものに比べ得られる複合材料の密度は大きくなるので、軽量化による効果は小さい。その一方で銅はその熱伝導率がアルミニウムのそれに比べ約６０％大きく、またその熱膨張係数がアルミニウムのそれに比べ約４０％小さい。このためアルミニウム系のものに比べ高い熱伝導率で低い熱膨張係数が必要な基板材料の製造には有利な材料である。なお銅はアルミニウムに比べ溶融温度がかなり高く重量も嵩むので、アルミニウム系に比べ製造コスト面でいくぶん不利である。
【００１１】
【発明が解決しようとする課題】
以上述べたような複合材料を半導体装置用の比較的高い放熱量の基板として使用するためには、以下に述べる解決すべきいくつかの課題が残っている。先ず上記(１)に記載の方法では、Ａｌ溶湯を鋳型に流し込み、ＳｉＣ粒子を分散させて固化する鋳造法を用いる。したがってＡｌとＳｉＣの密度差により冷却時に成形体中のＳｉＣ粒子の偏析が生じ、固化体の組成が不均一になり易い。このため固化体の表面がＡｌまたはＡｌ合金からなる被覆層(以下この層をＡｌ被覆層とも言う)により覆われるのは避けられない。そのためこの表面と内部および内部での組成の偏析によって、熱応力による反り等の変形は避けられない。また上記（２）および（３）の方法では、通常第一成分の融液とＳｉＣ粒子との濡れ性を確保するとともに、第一成分の溶浸不足による引け巣を防ぐため、外周部にあえて過剰の第一成分の溶出層を溶出させるのは避けられない。それ故溶浸後の仕上げ加工に手間がかかる。また（３）の加圧溶浸法は、その設備費用が高い。上記（４）および（８）のホットプレスによる方法では、融点以上の第一成分がその加圧によって型外に染み出し、複合材料の組成にばらつきが生じ易い。またその事前のセッティングや事後の取り出し等にかなりの手間がかかる。（６）の溶出を抑制する手段の場合や（７）のＨＩＰを併用する場合でも、同様にその事前事後の準備・整理に手間が要る。以上の品質上・生産上の問題に加えて、同基板の周辺部材が熱膨張係数の比較的小さいものである場合には、これら部材とのその整合性も配慮する必要がある。その熱膨張係数を小さくするためには、どうしてもＳｉＣの量を多くせざるを得ない。このためその熱伝導性を犠牲にする必要があった。
【００１２】
以上詳述したように、従来のＡｌ−ＳｉＣ系の複合材料の製造には品質上・生産上のいくつかの課題をかかえている。したがってＡｌ−ＳｉＣ系の複合材料は、高い放熱性を要求される基板の一つとして、その性能面で最近有望視されているにもかかわらず、従来から行われてきた鋳造法、溶浸法、焼結法、ホットプレス法やそれらを組み合わせたいずれの方法でも、満足のゆく本来の性能レベルのものは得られていない。その理由の一つとして以下のことが考えられる。すなわちＡｌとＳｉＣの間の濡れ性を改善するためやＡｌ融液のＳｉＣ粒子間への自発的な浸透を促したり、空孔の発生を抑えるためにＡｌ中にＳｉ等の従成分を添加したり、またはこれらの従成分を不純物として含むＡｌを用いたりする場合が多々あった。このためこれらの従成分の介在によって複合材料の熱伝導率の低下は避けられなかった。特にＳｉＣ自体がＡｌに匹敵するか、またはそれを凌ぐ高い熱伝導率を有しながら、従来のＡｌ−ＳｉＣ系の複合材料では、その量の多い組成域での熱伝導性が低い。このため本発明者等は、既に特願平１０−２６００３号公報にて、特にパワーデバイスに用いられるＡｌ−ＳｉＣ系およびＣｕ−ＳｉＣ系の放熱基板材料を提案した。これによって高熱伝導の要求課題はほぼ克服できる見通しを得た。その手段は、例えば比較的純度の高いＳｉＣ粉末および第一成分の混合物を、特に高い成形圧力によって第一成分粒子の表面に存在する酸化物や吸着成分からなる被膜を破断し、その後の鍛造によって加圧固化する。成形時に表面被膜を破ることによって、その後の加熱で溶融した第一成分がＳｉＣ粒子と直接触れるため双方の濡れが促進される。さらに熱間で加圧鍛造することによって、双方の密着が確実に達成される。このような手順によって、ＳｉＣ量が多くても従来に無い高い熱伝導性を付与することができる。
【００１３】
ところで一般には、溶融したアルミニウム（Ａｌ）は、下記式（１）で示される化学反応をしつつＳｉＣ粒子の表面を濡らす。
４Ａｌ＋３ＳｉＣ→Ａｌ₄Ｃ₃＋３Ｓｉ（１）
しかし上述のように、Ａｌ原料の表面はその酸化物層と吸着成分とからなる被膜に覆われている。通常この皮膜は、主に化学式がＡｌ₂Ｏ₃のアルミナまたは化学式がＣｕ₂Ｏ、ＣｕＯの酸化銅からなり、さらに水分やＯＨ基が吸着している。成形時にこの表面被膜を破断しておかないと、その後の焼成によって同皮膜が成長して厚い酸化物の膜となり、ＳｉＣ粒子との濡れ性を低下させる。一方同皮膜を破断しておくと、上述のように、第一成分の粒子表面の破断部に露呈したＡｌやＣｕを主成分とする金属が、ＳｉＣ粒子表面を濡らし易い。このため以上詳述した各種のいずれの方法でも、鋳造法を除き、ＳｉＣ粉末やこれと第一成分粉末との混合粉末を成形する際、通常は４ｔｏｎ／ｃｍ²以上の高い圧力を負荷する必要があるからである。このように硬質のＳｉＣ粒子を含む粉末を高い圧力で成形すると、その圧力が高いほど成形型の摩耗がより一層激しくなる。さらに成形型の寸法精度を維持するのが難しくなる。その結果成形コストの上昇を招くという問題がある。また上記した鍛造法での固化は、高速の圧力が負荷される。したがって、この型もまた同様の問題がある。
【００１４】
【課題を解決するための手段】
本発明の目的は、以上述べてきたいくつかの課題も考慮し、特にこの成形および焼結のコスト上昇を最少限に抑え、安価に炭化珪素系複合材料を提供することである。このため本発明の製造方法では、成形時には高い圧力を負荷しない。その代わり焼結加熱前に成形体を熱処理し、上記した第一成分粒子表面の皮膜の厚みを予め薄くする。これによって焼結時の高い圧力負荷の必要も無くなる。ただし、その結果焼結後第一・第二両成分間の濡れは改善されるが、第一成分の溶融相内に小さな空孔が残るのは避けられない。すなわち本発明の方法で提供される複合材料は、アルミニウムまたは銅を主成分とする金属を第一成分とし、炭化珪素を主成分とする粒子を第二成分とするものであり、１０〜２０％の空孔率のものである。またその熱伝導率は、１７０Ｗ／ｍ・Ｋ以上のものである。また本発明には、炭化珪素粒子の量が、５０〜８０重量％の範囲のものが含まれる。また本発明の複合材料には、炭化珪素粒子が、酸素含有量１重量％以下、鉄を含む成分の含有量が鉄元素に換算して０．０１重量％以下、アルミニウムを含む成分の含有量がアルミニウム元素に換算して０．０１重量％以下の高純度であり、かつ低欠陥であるものも含まれる。さらに本発明には、上記の炭化珪素系複合材料を用いた半導体装置も含まれる。
【００１５】
本発明の複合材料の製造方法は、アルミニウムまたは銅を主成分とする金属からなる第一成分と、炭化珪素粉末を主成分とする第二成分とからなる原料を準備する工程と、同原料を混合して混合物とする工程と、同混合物を成形し成形体とする工程と、同成形体をアルミニウムまたは銅を主成分とする金属の融点未満の温度下、雰囲気圧力１×１０^−３Ｔｏｒｒ以下の真空中で加熱し、熱処理体とする工程と、該熱処理体をアルミニウムまたは銅を主成分とする金属の融点以上の温度で焼結し、焼結体とする工程とを含む。なおこの熱処理体とする工程の雰囲気圧力が、１×１０^−４Ｔｏｒｒ以下であれば、より好ましい。
【００１６】
さらに原料である炭化珪素粉末は、酸素量が１重量％以下、鉄を含む成分の量が鉄元素に換算して０．０１重量％以下、アルミニウムを含む成分の量がアルミニウム元素に換算して０．０１重量％以下の純度の高い粉末を用いる方法もある。その場合、例えば通常の炭化珪素粉末を不活性ガス雰囲気中１６００〜２４００℃の温度範囲で加熱する予備加熱処理をする方法や通常の炭化珪素粉末をフッ酸、硝酸または塩酸の内の少なくとも１種の酸を含む水溶液中に浸漬する予備酸処理をする方法が挙げられる。また予備酸処理後予備加熱処理をする方法もある。
【００１７】
【発明の実施の形態】
本発明によって提供される炭化珪素系複合材料には、大別するとアルミニウムを主成分とする金属からなる第一成分と炭化珪素を主成分とする第二成分とを含む複合材料（以下Ａｌ−ＳｉＣ系複合材料、単にＡｌ−ＳｉＣ系またはＡｌ系とも言う）と、銅を主成分とする金属からなる第一成分と炭化珪素を主成分とする第二成分とを含む複合材料（以下Ｃｕ−ＳｉＣ系複合材料、単にＣｕ−ＳｉＣ系またはＣｕ系とも言う）とがある。本発明は、これらの材料に着目し、放熱基板(ヒートシンク)、特に半導体装置用の放熱基板の熱伝導性とともに、その生産性を、特にＳｉＣ量が５０重量％以上の組成領域で、向上させるためになされたものである。
【００１８】
本発明の複合材料は、前述のようにその空孔率が１０〜２０％であり、その熱伝導率が１７０Ｗ／ｍ・Ｋ以上のものである。空孔率をこの範囲としたのは、その下限未満とするためには、後述のように製造時の粉末成形圧力を上げる必要があり、これによって成形型の摩耗が大きくなるからである。その結果成形体の成形寸法のばらつきを抑えるため、成形型の交換頻度が増し、成形コストが上昇するからである。また空孔率が上限を越えると、熱伝導率が急激に低下するからである。
【００１９】
本発明の複合材料の炭化珪素結晶粒子は、純度が高くかつ低欠陥であるのが望ましい。例えばその炭化珪素粒子が、酸素含有量１重量％以下、鉄を含む成分の含有量が鉄元素に換算して０．０１重量％以下、アルミニウムを含む成分の含有量がアルミニウム元素に換算して０．０１重量％以下の高純度であり、かつ低欠陥であるものがある。このような材料は、以下に述べるように予め純度の高いＳｉＣ粉末原料を準備することによって得られる。これらの例示した不純物の上限値は、その量をこの値以下にコントロールすることによって、上記のような空孔率であっても、より優れた熱伝導性のものが得られるからである。
【００２０】
本発明の複合材料の製造方法は、前述のように、第一成分と第二成分との混合物を含む成形体をアルミニウムまたは銅を主成分とする金属の融点未満の温度下、雰囲気圧力１×１０^-3Ｔｏｒｒ以下の真空中で加熱し、熱処理体とする工程と、同熱処理体をアルミニウムまたは銅を主成分とする金属の融点以上の温度で焼結し、焼結体とする工程とを含むことに特徴がある。なおこの熱処理体とする工程の雰囲気圧力が、１×１０^-4Ｔｏｒｒ以下であれば、より好ましい。また上記混合物中の炭化珪素粉末の量は、通常は５０〜８０重量％の範囲とする。下限未満では本発明の成形コストの低減効果が小さく、上限を越えるとＳｉＣ量が多くなり過ぎて、成形体密度の確保が難しくなるからである。
【００２１】
また本発明では、成形体を焼結する前に上記のように予め真空雰囲気中で熱処理する。これによって、既に述べたように、第一成分粒子の表面に形成された酸化物層上に吸着した水分やＯＨ基を主体とする成分の被膜を予め除去する。もし熱処理をせずこの皮膜を残留させると、その後の焼結時の加熱によって酸化物層の厚みが増大し、ＳｉＣ粒子との濡れ性を低下させる。その状態を模式的に図１に示す。同図の上の図が熱処理をしない場合である。この場合焼結後第一成分粒子１の表面の膜２がより厚い酸化物層となり、ＳｉＣ粒子３との界面が濡れず殆どの部分が密着していない。密着していない界面部分は空孔となり、同部分では熱抵抗が大きくなる。一方下の図が熱処理をした場合である。この場合第一成分粒子１の表面の膜２がほとんど除かれ、焼結後ＳｉＣ粒子３との界面がほぼ濡れて密着している。界面部分には空孔が殆ど残らない。なお成形体中のＳｉＣ粒子の骨格は堅牢であるとともに、機械的に圧力がかからないためにその隙間は縮まらない。このため第一成分が溶融してもその隙間を完全に埋めることはできない。したがって同骨格中に内在する隙間には空孔が残る。
【００２２】
加熱時の真空雰囲気の圧力は、１×１０^-3Ｔｏｒｒ以下とする。これを越えると吸着した水分やＯＨ基を主体とする成分の除去が不十分となり、その結果最終的な複合材料において空孔率が増加し、その熱伝導率が急激に低下するため好ましくない。また加熱温度は第一成分の金属の融点未満とする。融点以上の温度では第一成分の金属と吸着成分が反応してそれぞれの酸化物を形成し、同金属表面の酸化層の厚みが増加し、ＳｉＣ粒子との濡れ性が急激に低下するからである。ただし融点未満であれば、その温度は高いほど望ましい。その下限は、通常第一成分がＡｌを主成分とするものの場合は３００℃以上、Ｃｕを主成分とするものの場合は６００℃以上とする。なお加熱時間は、雰囲気圧力や温度にもよるが、通常は１０分程度で効果が現れ、長いほどその効果は上がる。この熱処理後の焼結は、非酸化性雰囲気中、第一成分の金属の融点以上の温度下で行う。窒素が望ましい。この場合、常圧下でも加圧下でもよい。
【００２３】
以下本発明の複合材料の熱伝導率のレベルを向上させる手段について述べる。本発明の材料は、上述のように空孔を含むものである。このためそれによる熱伝導性の低下は避けられない。それ故以下に述べるように構成する両成分の内部や界面の熱抵抗を下げる必要がある。したがって、原料粒子に高純度のものを選んだり、予めキャリア濃度の高いＳｉＣ原料粉末を調製したりする。
【００２４】
その第一は、酸素、陽イオン不純物、特に鉄やアルミニウムを含む不純物の少ない炭化珪素原料粉末を使うことである。これによって、得られる炭化珪素結晶粒子中の不純物や欠陥の量を少なくすることができる。その結果複合材料の熱伝導率のレベルを上げることができる。特に結晶粒子中の酸素含有量が１重量％以下、鉄を含む成分の含有量が鉄元素に換算して０．０１重量％以下、アルミニウムを含む成分の含有量がアルミニウム元素に換算して０．０１重量％以下の高純度の炭化珪素粉末を使い、同程度の不純物量・欠陥量の炭化珪素結晶粒子であるのが望ましい。酸素量や鉄・アルミニウムを含む不純物量がこの量を越えると、熱伝導率が大きく低下することがある。なお前述のように、この不純物レベルの炭化珪素粉末は、炭化珪素粉末を不活性ガス雰囲気中１６００〜２４００℃の温度範囲で加熱する予備加熱処理の工程を経ても得られる。この場合雰囲気ガス中には、ＳｉＣ粒子中に固溶して同結晶内に格子欠陥を作り易い窒素や炭素成分が共存しないことが重要である。雰囲気ガスの圧力は高い方が望ましく、例えば高圧下ＨＩＰ(熱間静水圧成形)処理を行っても良い。温度が１６００℃未満では、同熱処理での欠陥低減の効果が小さくなり易い。また２４００℃を越えるとＳｉＣが昇華・分解し易くなり、収率が低下する場合がある。
【００２５】
さらにこのような粉末は、炭化珪素粉末をフッ酸、硝酸または塩酸の内の少なくとも１種の酸を含む水溶液中に浸漬することによっても得られる。この処理によって、粉末中の粒子表面に存在する陽イオン不純物、鉄(Ｆｅ)、クロミウム(Ｃｒ)、バナジウム(Ｖ)、ニッケル(Ｎｉ)等の遷移金属を含む不純物、とりわけ鉄(Ｆｅ)や酸素、炭素を溶解除去することができる。これによって、ＳｉＣ結晶粒子中でのフォノン散乱の原因となる不純物の量が少なくなり、得られる複合材料の熱伝導性は向上する。すなわちこれらの成分は、高温下で粒子表面から同内部に拡散し、欠陥を形成し熱伝導率の低下を招き易いからである。この予備酸処理後予備加熱処理をすることによって、さらに高純度かつ低欠陥のＳｉＣ粉末が得られる。
【００２６】
またＳｉＣ結晶中のキャリヤ濃度もその熱拡散率に影響するものと考えられる。一般にＳｉＣは、過剰電子を持つｎ型半導体や過剰空格子を持つｐ型半導体になりうる材料である。したがって、これらの過剰な電子や空格子(キャリヤ)濃度が増加すると、それがＳｉＣ結晶粒子中のフォノンを散乱させる一因となる。このためＳｉＣの熱伝導性が低下するものと考えられる。ＳｉＣには、６Ｈ、４Ｈ、３Ｃ、１５Ｒ等の結晶型の異なる多形が存在する。前述のように、これらの中でも熱伝導性の高いのは、６Ｈまたは４Ｈ型であるが、特に６Ｈ型のＳｉＣは、ｎ型半導体であり、結晶内の不純物の量が同程度のレベルであれば、他の結晶型のものに比べてキャリヤ濃度が低い。それ故本発明の炭化珪素系複合材料に用いるＳｉＣ原料は、６Ｈ型のものが望ましい。そのキャリヤ濃度は、１×１０¹⁹個／ｃｍ³以下であるのが望ましい。なお本発明の炭化珪素系複合材料の製造に供するＳｉＣ原料は、全量この６Ｈ型であるのが望ましいが、他の結晶型のものが一部混在しても構わない。
【００２７】
なおＳｉＣ粒子の表面に存在する前記不純物の量は、酸抽出法によって確認できる。その手順は、ＳｉＣ粉末を１００℃に保持された硝酸とフッ酸からなる混酸水溶液中に約２時間浸漬し同表面に存在する不純物を溶出した後、その溶出物をＩＰＣ発光分光分析法によって定量する。またＳｉＣ粒子の内部に存在する不純物の量も確認したい場合には、加圧酸分解法によって不純物を溶出する。この場合は、ＳｉＣ粉末を１９０〜２３０℃に保持された硝酸とフッ酸からなる混酸水溶液中に約４０時間浸漬する。これによってＳｉＣ粒子の表面のみならず内部の不純物も抽出できるので、同様にその溶出物をＩＰＣ発光分光分析法によって定量する。ＳｉＣ粒子の積層欠陥の量は、対象とするＳｉＣ粒子を透過型電子顕微鏡で直接観察することによって確認できる。また複合化後の炭化珪素系複合材料中のＳｉＣ粒子の不純物や積層欠陥の量を確認する場合には、まず第一成分を酸等で分離除去後、残留したＳｉＣ粒子を同様な手順で分析・評価する。なおＳｉＣ粒子のキャリヤ濃度の確認は困難であるが、同粒子の集合体である粉末であれば、ラマン分光分析によって確認できる。
【００２８】
アルミニウムまたは銅を主成分とする第一成分の原料は、市販のものを用いればよい。なお本発明で用いる第一成分の原料の使用形態は、塊状・粉末状他のいかなる形態であってもよいが、通常は粉末状のものを用いる。原料粉末内に介在する不純物種としては、特にアルミニウムに固溶し易い遷移金属元素、特に８ａ族元素を含む成分は、可能な限り少ないのが望ましい。したがって、市販のアルミニウム合金粉末を用いる場合には、これらの合金を作るための成分の少ないものを選ぶのが望ましい。
【００２９】
以上述べたように、本発明で使用する原料は、第二成分のＳｉＣ粉末として可能な限り高純度かつ低欠陥のものを用い、第一成分のアルミニウムや銅を主成分とする原料も高純度のものを用いるのが望ましい。原料の混合方法は、原料の形態・性状に合わせ原料純度が低下しない方法であれば、既存の方法でよい。また混合物は、その成形性を高めるために、例えば顆粒状に造粒してその嵩を下げるのが好ましい。混合物の成形法については、通常のいかなる方法であってもよい。
【００３０】
【実施例】
（実施例１）原料として、いずれもその平均粒径が５０μｍで、表１に記載の各種予備処理を行ったＳｉＣ原料粉末と、表２に記載のＡｌ系原料および表３に記載のＣｕ系原料とを準備した。ラマン分光分析によって確認したＳｉＣ原料粉末のキャリヤ濃度は、いずれのものも１×１０¹⁷個／ｃｍ³程度であった。なお表１の予備処理欄に「なし」と記述のものは、該当する予備処理をしていないものである。予備酸処理は、表に記載の濃度・温度の酸水溶液中に記載の時間浸漬後、純水で洗浄する過程を３回繰り返し、それを温風乾燥する手順によって行った。したがって、例えば原料Ｓ２の場合は、原料Ｓ１のＳｉＣ粉末をまず室温の濃度１０％のフッ酸水溶液に３０分間浸漬し、その後純水で洗浄し、この一連の操作を３回繰り返した後、温風によって脱水・乾燥した。また予備加熱処理は、粉末を炭化珪素質のケースに装入し、ヒーターがタングステン製の炉にセットし、アルゴンガス雰囲気中、記載の同ガス圧力下・記載の温度で１時間保持する方法で行った。同表に記載の各ＳｉＣ粉末中の不純物量は、前記した条件の加圧酸分解法によって同粉末から不純物含有成分を溶解抽出し、その抽出物をＩＰＣ発光分光法によって分析して得た値であり、粒子表面のみでなくその内部も含めた粒子全体に存在する量である。表１にはＦｅ(鉄)以外の本発明で言う陽イオン元素(遷移金属元素)の量は記載されていないが、それら個々の量は、いずれの番号の原料においても高々５００ｐｐｍであった。またC(炭素)の量は、いずれの番号の原料においても高々５００ｐｐｍであった。
【００３１】
【表１】

【００３２】
【表２】

【００３３】
【表３】

【００３４】
第二成分として表１に記載の各ＳｉＣ原料粉末、第一成分として表２に記載のＡｌ系原料粉末Ａ１１または表３に記載のＣｕ系原料粉末Ｃ１１を選び、それぞれの組合わせで本発明の熱処理を含む方法によって、ＳｉＣを７０重量％含む炭化珪素系複合材料試片をそれぞれ作製した。表４の原料欄に作製した３８種類の原料の組み合わせを示す。まず表１に記載の各ＳｉＣ原料粉末７０重量％と、残部３０重量％が上記Ａ１１またはＣ１１の原料粉末となるように秤取し、バインダーとしてパラフィンを３重量％添加し、エタノール中３時間混合した。得られたスラリーを噴霧乾燥して造粒粉末とした。これを乾式粉末成形プレスによって、超硬内張りダイス鋼製型により、表４の成形圧力欄に記載の成形圧力（ただし表の数値はｔｏｎ／ｃｍ²単位）で直径１００ｍｍで、厚みはほぼ１０ｍｍ程度に成形した。その後、これらをニクロム線ヒーター炉内に配置し、窒素気流中４００℃でバインダーを除去し成形体とした。これらの各成形体をニクロム線ヒーターの真空炉内に装入し、表４の熱処理欄に記載の窒素分圧Ｐｎ(ただし表の数値は１０^-4Ｔｏｒｒ単位）、温度条件下で、いずれも２０分間熱処理を行った。次いでこの熱処理体を炭化珪素製の保持容器に入れ、同表の焼結欄に記載の温度範囲、窒素気流中にて、いずれも２時間焼結した。焼結体の最終厚みは、いずれの試料もほぼ１０ｍｍであった。その後試料を研削加工仕上げした。成形圧力の成形型の摩耗速度に及ぼす影響については、試料５および試料１２〜１４、さらに同じ組成粉末を用いた５ｔｏｎ／ｃｍ²の場合も追加して、成形数１０００個および５０００個での成形型の内径寸法を内径マイクロメーターによって確認し、その摩耗状況を調べた。その結果を表５に示す。表５の数値は内径の増量である。当初寸法が１００ｍｍであるので、同数値はそれに対する％単位の増加率を示すことになる。
【００３５】
各試料の実測した単重と体積から計算した見かけ密度と、主成分の密度とその組成比率から複合則によって計算した理論密度とからその空孔率を、またレーザーフラッシュ法によって鍛造体の径方向の熱伝導率を、差動トランス式熱膨張係数測定装置によってその熱膨張係数を、さらに前記した加圧酸分解法と発光分光分析の組み合わせによってそのＳｉＣ結晶粒子中の不純物量を、それぞれ求めた。これらの結果も併せて表４に示す。なお別途予備加熱処理の雰囲気ガスを窒素または炭素を含むガスに切り換えて行ったＳｉＣ原料粉末Ｓ１を用いて、表４と同様の第一成分との組成・組み合わせ、同様の成形・焼結の手順で作製した焼結体は、その熱伝導率が事前の酸処理を行った場合、Ａｌ−ＳｉＣ系で表４の試料９程度、Ｃｕ−ＳｉＣ系で表４の試料２８程度であり、予備酸処理を行わなかったものでは、これより低下してＡｌ−ＳｉＣ系で１７０Ｗ／ｍ・Ｋ程度、Ｃｕ−ＳｉＣ系で２００Ｗ／ｍ・Ｋ程度であり、予備加熱処理の効果は小さくなった。
【００３６】
【表４】

【００３７】
【表５】

【００３８】
以上の結果より以下のことが分かる。（１）通常より低い成形圧力（４ｔｏｎ/ｃｍ²未満）で成形し、それを第一成分の融点未満の温度、１０^-3Ｔｏｒｒ以下の雰囲気圧力下で熱処理を行わずに、常圧下で焼結すると、空孔率は２０％を越える。その結果焼結体の熱伝導率は、Ａｌ−ＳｉＣ系では１７０Ｗ／ｍ・Ｋ未満、Ｃｕ−ＳｉＣ系では１９０Ｗ／ｍ・Ｋ未満となる。一方同熱処理を行ったものは、空孔率が２０％以下となり、その結果焼結体の熱伝導率は、Ａｌ−ＳｉＣ系では１７０Ｗ／ｍ・Ｋ以上、Ｃｕ−ＳｉＣ系では１９０Ｗ／ｍ・Ｋ以上となる。また特に熱処理の雰囲気圧力を１０^-4Ｔｏｒｒ以下にすることによって、さらに熱伝導性は向上する。この理由は以下のように考えられる。減圧下での熱処理によって、第一成分表面の酸化物や付着成分からなる被膜がほぼ除かれる。これによって炭化珪素と第一成分融液との界面の濡れが改善される。その結果双方界面の密着度が増し、そこでの熱抵抗が減少したことによるものと思われる。また（２）成形圧力を上げると、焼結体の空孔率は下がり熱伝導性は向上する。しかしその一方で成形型の内径の摩耗量は大きくなる。特に成形圧力が４ｔｏｎ/ｃｍ²以上になると、急激に摩耗量が大きくなる。さらに（３）ＳｉＣ粉末を事前に予備加熱または予備酸処理したものは、しないものに比べ熱伝導性が改善される。
【００３９】
（実施例２）表１のＳ３のＳｉＣ粉末、表２のＡ１１、Ａ１２のアルミニウム粉末および表３のＣ１１、Ｃ１２の銅粉末を用いて、実施例１とほぼ同じ方法によって、表６に記載のＳｉＣ量のＡｌ−ＳｉＣ系およびＣｕ−ＳｉＣ系焼結体を作成した。なお造粒粉末の成形、熱処理および焼結の各条件は、Ａｌ−ＳｉＣ系では試料１３に、Ｃｕ−ＳｉＣ系では試料３２のそれに合わせた。得られた試料を実施例１と同様の項目で評価をした。その結果を表６に併せて示す。
【００４０】
【表６】

【００４１】
以上の結果より、本発明の製造方法によれば、比較的低い成形圧力で成形し常圧下で焼結した場合、１０％以上の空孔はあるものの、ＳｉＣ量の広い範囲にわたって高い熱伝導性の炭化珪素系複合材料が得られることが分かる。
【００４２】
（実施例３）以上述べた実施例の試料番号３、５、１５、２２、２４、３４、４８および５９のものと同じ方法で得た炭化珪素系複合材料を、それぞれ５０個ずつ長さ２００ｍｍ、幅２００ｍｍ、厚み３ｍｍの形状の基材に仕上げ加工した。これを図２に模式的に示すようなパワーモジュールに放熱基板として実装して、各実装段階も含めて温度サイクル試験を行った。図２において、４は本発明の上記複合材料からなる第二の放熱基板、５は同基板上に配置され、その上面に(図示しないが)銅回路が形成されたセラミックスからなる電気絶縁性の第一の基板、６はＳｉ半導体素子、７は第二の放熱基板の下に配置された放熱構造体である。なおこのジャケットは、本実施例では水冷ジャケットであるが、他に空冷のフィン等もある。なお同図には半導体素子周辺の配線等については省略してある。本実施例では、Ｓｉ半導体素子を第一のセラミックス製基板を介して６個搭載したモジュールとした。
【００４３】
実装に先立ち第二の基板に直接第一の基板を半田付けできないため、第二の基板の主面に予め平均厚み１０μｍの無電解ニッケルメッキ層と平均厚み５μｍの電解ニッケルメッキ層を形成した。この内各４個の試片は、ニッケルメッキ上に直径５ｍｍの半球状のＡｇ−Ｓｎ系半田によって直径１ｍｍの銅線をメッキ面に垂直な方向に取り付けた。この試片の基板本体を治具に固定して銅線を掴みメッキ面に垂直な方向に引っ張り、基板へのメッキ層の密着強度を確認した。その結果いずれの基板のメッキ層も１ｋｇ／ｍｍ²以上の引っ張り力でも剥がれなかった。またメッキ層が形成された別の試片の内から１０個を抜き取って、−６０℃で３０分保持、１５０℃で３０分保持の昇降温を１０００サイクル繰り返すヒートサイクル試験を実施し、試験後上記と同様の密着強度を確認したところ、いずれの試片もメッキの密着性で上記レベルを満足する結果が得られた。以上の結果より本発明の複合材料からなる基板へのメッキの密着性は、実用上問題の無いレベルであることが判明した。
【００４４】
次に第二の基板上に搭載するセラミックス製の第一の基板として、熱伝導率が１５０Ｗ／ｍ・Ｋ、熱膨張係数が４．５×１０^-6／℃、３点曲げ強度４５０ＭＰａの窒化アルミニウムセラミックス製の基板Ａおよび熱伝導率が１２０Ｗ／ｍ・Ｋ、熱膨張係数が３．７×１０^-6／℃、３点曲げ強度１３００ＭＰａの窒化珪素セラミックス製の基板Ｂの二種の銅回路を形成した第一の基板を、それぞれ１８個ずつ準備した。これらの基板の形状は、いずれも長さ９０ｍｍ、幅６０ｍｍ、厚み１ｍｍとした。これらの基板を第二の基板の２００ｍｍ角の主面上に２行３列で等間隔に配置し、同基板のニッケルメッキ層を形成した面上にＡｇ−Ｓｎ系半田によって固定した。次にこのアッセンブリーの第二の基板の裏面側と水冷ジャケットとを、その接触面にシリコンオイルコンパウンドを塗布介在させてボルト閉め固定した。なおこの場合の第一の基板の取り付け穴は、予め素材段階でその四隅に開けておいた下穴部に炭酸ガスレーザーを照射して、それを直径３ｍｍまで拡げる方法によって形成した。この加工は他のセラミックス材やＣｕ−Ｗ、Ｃｕ−Ｍｏを対象とした場合に比べ、高精度かつ高速で行うことができた。この傾向は特に熱伝導率が高くなればなるほど顕著であった。
【００４５】
これらの各試片の中から第一の基板がＡとＢの物を各１５個ずつ選び、上記と同じ単サイクル条件で２０００サイクルのヒートサイクル試験を行い、その１００サイクル毎のモジュールの出力の変化を確認した。その結果、全てのモジュールが、実用上問題が無いとされる１０００サイクルまで、その出力の低下は観測されなかった。ただし、第一の基板の材質種を問わず１０００サイクルを越えた１１００サイクル以降の確認で、第二の基板に熱伝導率が２００Ｗ／ｍ・Ｋ以下の５、１５および４８の板を用いたもので、ヒートサイクルによるモジュールの若干の出力低下が、１５個中２個観測された。この出力の低下した試料では、第一・第二の両基板の半田付けされた接合界面の第一の基板側に微細な亀裂の発生が認められた。以上述べたもの以外には２０００サイクル終了までこのような異常は無かった。
【００４６】
以上の結果より、本発明の炭化珪素系複合材料からなる第一の基板を用いたパワーモジュールは、実用上問題の無いレベルのものとなることが分かる。なお別途熱伝導率が１７０Ｗ／ｍ・Ｋ以上の試料を、この種のモジュールに比べ低出力・低熱(サイクル)負荷の高容量のパーソナルコンピューター等の半導体素子搭載装置に放熱基板として実装・評価も行ったが、その信頼性・実用性能上何ら問題は無かった。
【００４７】
【発明の効果】
以上詳述したように、本発明の炭化珪素系複合材料は、通常より低い成形圧力で成形し、それを真空下第一成分の融点未満の温度で熱処理を行い、常圧下で焼結する。すなわち成形時や焼結時に通常の機械的負荷を加えない。例えば焼結時には、緻密化のためのホットプレス・鍛造等の高圧力をかけない。したがって、ＳｉＣ粉末を用いても成形型・焼結型の寿命が長くなる。それ故従来のものに比べ安価に製造できる。本発明の材料は、１０％以上の空孔率があり、緻密なものに比べその熱伝導率は低い。しかしながら上記熱処理によって、第二成分粒子と第一成分との濡れ性が大幅に改善され、その結果従来のものに比べ空孔率は高いにもかかわらず、両成分界面で密着性が高く優れた熱伝導性の材料が提供できる。なおＳｉＣ原料粒子を予め予備加熱・予備酸処理し純化することによって、さらにその熱伝導性を高めることができる。本発明によれば、ＳｉＣ量の広い範囲にわたって１７０Ｗ／ｍ・Ｋ以上の熱伝導率のものが得られ、各種半導体装置用の放熱基板に有用である。特に２００Ｗ／ｍ・Ｋ以上のものは、パワーモジュールのように高容量の半導体装置にも用いることができる。
【図面の簡単な説明】
【図１】本発明の炭化珪素系複合材料での熱処理の効果を説明する模式図である。
【図２】本発明の材料を基板に用いた半導体装置(パワーモジュール)を模式的に示す図である。
【符号の説明】
１．第一成分粒子
２．第一成分粒子表面の酸化物等の皮膜
３．第二成分粒子
４．炭化珪素系複合材料からなる第一基板
５．第二基板
６．半導体素子
７．放熱構造体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon carbide based composite material having high thermal conductivity and a semiconductor device using the same, which are used for a heat dissipation substrate used in various apparatuses and devices, particularly a heat dissipation substrate of a semiconductor device.
[0002]
[Prior art]
In recent years, market demands for high-speed computation and high integration of semiconductor devices are increasing rapidly. At the same time, the heat dissipation substrate for mounting a semiconductor element of the apparatus has been required to further improve its thermal conductivity in order to release the heat generated from the element more efficiently. Furthermore, in order to further reduce the thermal strain between the same element and other members (peripheral members) in the same device adjacent to the same board, the thermal expansion coefficient is closer to those. Has also been sought. Specifically, Si usually used as the semiconductor element, the thermal expansion coefficient of GaAs are each ^{^{4.2 × 10 -6 /℃,6.5×10 -6 / ℃}} , usually as an envelope material of a semiconductor device Since the alumina ceramic used is about 6.5 × 10 ⁻⁶ / ° C., it is desirable that the thermal expansion coefficient of the substrate is close to these values.
[0003]
In addition, with the remarkable expansion of the application range of electronic devices in recent years, the range of use of semiconductor devices is further diversifying. Among them, the use for so-called semiconductor power device devices such as high output AC conversion devices and frequency conversion devices is increasing. In these devices, the heat generated from the semiconductor element ranges from several times to several tens of times (usually, for example, several tens of watts) compared to a semiconductor memory or a microprocessor. For this reason, it is important for the heat dissipation substrate used in these devices to significantly improve the thermal conductivity and to increase the consistency of the thermal expansion coefficient with that of the peripheral member. On the other hand, there are devices such as semiconductor memories and microprocessors that do not generate as much heat as the power devices described above in practical use. Such devices are required to be cheaper than power device devices because they are manufactured in large quantities. Therefore, the heat dissipation board used for this does not require the high heat dissipation as described above, but is required to be inexpensive. As described above, the level of heat dissipation required for the substrate depends on the output capacity of the device and the level of its practical function. Further, the degree of consistency of the thermal expansion coefficient required for the substrate varies depending on the structure around the substrate in each device.
[0004]
In the case of a power device, the normal basic structure is as follows, for example. First, a Si semiconductor element is placed on a high thermal conductivity aluminum nitride (hereinafter also simply referred to as AlN) ceramic substrate as a first heat dissipation substrate. Next, a second heat dissipation substrate made of a metal having a higher thermal conductivity such as copper is disposed under the first heat dissipation substrate. Further, a heat dissipation mechanism capable of water cooling or air cooling is disposed under the second substrate. With the above structure, heat is released to the outside without delay. Therefore, it must be a complicated heat dissipation structure. In this structure, if an AlN ceramic of about 170 W / m · K is used as the first heat radiating substrate, the second heat radiating substrate radiates the heat transferred from the first substrate. It is necessary to escape to the mechanism without delay. For this reason, the second substrate has a high thermal conductivity of at least 200 W / m · K at room temperature and a thermal expansion coefficient matching with the first substrate of 10 × 10 ⁻⁶ / ° C. or less, particularly 8 ×. Those having a low coefficient of thermal expansion of 10 ⁻⁶ / ° C. or less are required.
[0005]
In particular, power devices that generate a large amount of heat during practical use may raise the temperature of the heat dissipation board itself to 100 ° C. or higher. Therefore, high thermal conductivity at such temperatures may be required. is there. Accordingly, a material having a thermal conductivity of 150 W / m · K or more is required even at such a temperature. Further, the larger the capacitance, the larger the size of the Si semiconductor element. Therefore, the heat dissipation board on which it is mounted must be enlarged. For example, while a substrate for a personal computer is at most about 20 to 40 mm square, a power device having a large capacity is demanded to exceed 200 mm square. In such a large substrate, it is required that not only the dimensional accuracy at the time of mounting but also the accuracy does not decrease at a high temperature. That is, when the substrate is warped or deformed at a high temperature, a gap is formed at the interface with the heat dissipation mechanism (radiator, fin, etc.) disposed under the substrate, and the heat dissipation efficiency is lowered. In the worst case, the semiconductor element may be destroyed. Therefore, ensuring the excellent thermal conductivity of the heat dissipation board at high temperatures is an important issue.
[0006]
Conventionally, for example, Cu—W or Cu—Mo based composite alloys have been used as heat dissipation substrates used in various devices described above. These substrates are expensive because the raw materials are expensive. Furthermore, there was a problem that the weight increased. Therefore, various aluminum (hereinafter, also simply referred to as Al) composite alloys have recently attracted attention as inexpensive and lightweight materials. Among them, Al—SiC based composite alloys mainly composed of Al and silicon carbide (hereinafter also simply referred to as SiC) are relatively inexpensive, light weight, and high thermal conductivity. The densities of pure Al and SiC, which are usually commercially available, are about 2.7 g / cm ^{3 and} about 3.2 g / cm ³ , respectively, and the thermal conductivities are about 240 W / m · K and 200 to 300 W / each, respectively. Although it is up to about m · K, if the purity and defect concentration are further adjusted, the level of thermal conductivity is expected to be further improved. Therefore, it is a material that attracts particular attention. The thermal expansion coefficients of pure SiC and Al are about 4.2 × 10 ⁻⁶ / ° C. and 24 × 10 ⁻⁶ / ° C., respectively, and by combining them, the thermal expansion coefficient is wide. Control is possible within a range. Therefore, this point is also advantageous.
[0007]
Such Al—SiC based composite alloys and methods for producing the same are described in (1) JP-A-1-501489, (2) JP-A-2-343729, (3) JP-A-61-222668 and (4). This is disclosed in JP-A-9-157773. (1) relates to a method in which Al in a mixture of SiC and Al is melted and solidified by a casting method. Both (2) and (3) relate to a method of infiltrating Al into the voids of the SiC porous body. Of these, (3) relates to a so-called pressure infiltration method in which Al is infiltrated under pressure. Also, (4) relates to a method of placing a compact of SiC and Al powder or a hot-pressed one in a mold and performing liquid phase sintering in vacuum at a temperature equal to or higher than the melting point of Al. It is.
[0008]
The present inventors, in Japanese Patent Application No. 9-136164, presented an aluminum-silicon carbide composite material obtained by (5) liquid phase sintering method and having a thermal conductivity of 180 W / m · K or more. ing. For example, this composite material is formed by molding a mixed powder of 10 to 70% by weight of particulate SiC powder and Al powder, and then containing 99% by volume of nitrogen, an oxygen concentration of 200 ppm or less, and a dew point of −20 ° C. or less. It is obtained by a process of sintering at 600 to 750 ° C. in an oxidizing atmosphere. In addition, the present inventors, in Japanese Patent Application No. 9-93467, (6) have a thermal expansion coefficient of 18 × 10 ⁻⁶ / ° C. or less, a thermal conductivity of 230 W / m · K or more, and sintering. A so-called net-shaped aluminum-silicon carbide based composite material whose later dimensions are close to practical dimensions is also presented. Furthermore, the present inventors have proposed a method for producing the composite material by combining (7) the normal pressure sintering method and the HIP method in Japanese Patent Application No. 10-41447. According to this, for example, a molded body of Al-SiC mixed powder in which particulate SiC is mixed in an amount of 10 to 70% by weight, in a non-oxidizing atmosphere containing 99% or more of nitrogen gas, is 600 ° C or higher and below the melting temperature of Al. Sintered at normal pressure in the temperature range, then sealed in a metal container and HIPed at a temperature of 700 ° C. or higher to obtain a homogeneous aluminum-silicon carbide based composite material having a thermal conductivity of 200 W / m · K or higher. It has been.
[0009]
Further, (8) Japanese Patent Application Laid-Open No. 9-157773 discloses a method in which a mixture of Al powder and SiC powder is hot-pressed to perform molding and sintering simultaneously. In this method, a mixed powder of 10 to 80% by volume of Al and the remaining SiC is formed and hot pressed at a pressure equal to or higher than the melting point of Al and at a pressure of 500 kg / cm ² or higher. By this method, an aluminum-silicon carbide based composite material having a thermal conductivity of 150 to 280 W / m · K is obtained.
[0010]
In addition, although there are few references on a copper-silicon carbide based composite material in which the main component metal is replaced from aluminum to copper, according to the knowledge of the present inventors, this composite material is composed of aluminum (hereinafter simply referred to as Cu). In other words, it can be obtained by substantially the same method as the manufacturing method described above. The density of pure Cu is about 8.9 g / cm ³ , its thermal conductivity is about 395 W / m · K, and its thermal expansion coefficient is about 17 × 10 ⁻⁶ / ° C. Accordingly, since the density of the composite material obtained is higher than that of aluminum-based materials, the effect of weight reduction is small. On the other hand, copper has a thermal conductivity about 60% greater than that of aluminum, and its coefficient of thermal expansion is about 40% smaller than that of aluminum. For this reason, it is an advantageous material for the production of a substrate material that requires a high thermal conductivity and a low thermal expansion coefficient as compared with an aluminum-based one. Copper is considerably disadvantageous in terms of manufacturing cost compared to aluminum because copper has a considerably higher melting temperature and weight.
[0011]
[Problems to be solved by the invention]
In order to use the composite material as described above as a substrate having a relatively high heat dissipation amount for a semiconductor device, there remain some problems to be solved as described below. First, in the method described in (1) above, a casting method is used in which molten Al is poured into a mold and SiC particles are dispersed and solidified. Therefore, due to the difference in density between Al and SiC, segregation of SiC particles in the molded body occurs during cooling, and the composition of the solidified body tends to be non-uniform. For this reason, it is inevitable that the surface of the solidified body is covered with a coating layer made of Al or an Al alloy (hereinafter, this layer is also referred to as an Al coating layer). Therefore, deformation such as warpage due to thermal stress is inevitable due to segregation of the composition on the surface and inside and inside. In the above methods (2) and (3), in order to ensure the wettability between the melt of the first component and the SiC particles, and to prevent shrinkage due to insufficient infiltration of the first component, the outer peripheral portion is dared. It is inevitable to elute the elution layer of the excess first component. Therefore, it takes time to finish after infiltration. In addition, the pressure infiltration method (3) is expensive. In the methods (4) and (8) described above by hot pressing, the first component having a melting point or higher oozes out of the mold by the pressurization, and the composition of the composite material tends to vary. In addition, it takes a lot of work to set up in advance and take out afterwards. Even in the case of means for suppressing the elution of (6) and when the HIP of (7) is used in combination, it takes time and effort to prepare and organize in advance. In addition to the above quality and production problems, when the peripheral members of the substrate have a relatively small coefficient of thermal expansion, it is necessary to consider their consistency with these members. In order to reduce the thermal expansion coefficient, the amount of SiC must be increased. For this reason, it was necessary to sacrifice the thermal conductivity.
[0012]
As described in detail above, the production of conventional Al-SiC composite materials has some problems in terms of quality and production. Therefore, Al-SiC-based composite materials are one of the substrates that require high heat dissipation, and have recently been considered promising in terms of performance. Neither the sintering method, the hot pressing method, or any combination of these methods has achieved satisfactory original performance levels. The following can be considered as one of the reasons. That is, in order to improve the wettability between Al and SiC, to promote the spontaneous penetration of Al melt between SiC particles, or to suppress the generation of vacancies, a secondary component such as Si is added to Al. In many cases, Al containing these subcomponents as impurities is used. For this reason, a decrease in the thermal conductivity of the composite material is unavoidable due to the presence of these secondary components. In particular, SiC itself has a high thermal conductivity comparable to or exceeding that of Al, but a conventional Al—SiC-based composite material has a low thermal conductivity in a large composition range. For this reason, the present inventors have already proposed Al-SiC-based and Cu-SiC-based heat dissipation substrate materials used in power devices in Japanese Patent Application No. 10-26003. As a result, it is expected that the demand for high heat conduction can be overcome. The means is, for example, by rupturing a mixture of relatively pure SiC powder and the first component, particularly a coating made of an oxide or an adsorbing component existing on the surface of the first component particle by a high molding pressure, and then forging. Solidify under pressure. By breaking the surface coating at the time of molding, the first component melted by the subsequent heating directly contacts the SiC particles, so that wetting of both is promoted. Furthermore, the close contact of both sides is reliably achieved by hot forging. By such a procedure, even if the amount of SiC is large, it is possible to impart high heat conductivity that has not been conventionally obtained.
[0013]
In general, molten aluminum (Al) wets the surface of SiC particles while performing a chemical reaction represented by the following formula (1).
4Al + 3SiC → Al ₄ C ₃ + 3Si (1)
However, as described above, the surface of the Al raw material is covered with a film composed of the oxide layer and the adsorbing component. Usually, this film is mainly composed of alumina having a chemical formula of Al ₂ O ₃ or copper oxide having chemical formulas of Cu ₂ O and CuO, and further adsorbs moisture and OH groups. If the surface film is not broken during molding, the film is grown by subsequent baking to form a thick oxide film, which reduces wettability with SiC particles. On the other hand, when the film is broken, as described above, the metal having Al or Cu as a main component exposed at the fracture portion of the particle surface of the first component tends to wet the SiC particle surface. Therefore, in any of the various methods detailed above, it is usually necessary to apply a high pressure of 4 ton / cm ² or more when molding SiC powder or mixed powder of this and the first component powder, except for the casting method. Because there is. When the powder containing hard SiC particles is molded at a high pressure in this way, the higher the pressure, the more severe the mold wear. Furthermore, it becomes difficult to maintain the dimensional accuracy of the mold. As a result, there is a problem that the molding cost is increased. Further, the solidification by the forging method described above is applied with a high-speed pressure. Therefore, this type has the same problem.
[0014]
[Means for Solving the Problems]
An object of the present invention is to provide a silicon carbide-based composite material at a low cost by taking into account some of the problems described above, and in particular minimizing the increase in molding and sintering costs. For this reason, in the manufacturing method of this invention, a high pressure is not loaded at the time of shaping | molding. Instead, the molded body is heat-treated before sintering and heating, and the thickness of the coating on the surface of the first component particles is reduced in advance. This eliminates the need for high pressure loads during sintering. However, as a result, wetting between the first and second components is improved after sintering, but it is inevitable that small voids remain in the molten phase of the first component. That is, the composite material provided by the method of the present invention has a metal containing aluminum or copper as a main component as a first component and a particle containing silicon carbide as a main component as a second component. Of the porosity. The thermal conductivity is 170 W / m · K or more. Further, the present invention includes those in which the amount of silicon carbide particles is in the range of 50 to 80% by weight. In the composite material of the present invention, the silicon carbide particles have an oxygen content of 1% by weight or less, the content of a component containing iron is 0.01% by weight or less in terms of iron element, and the content of a component containing aluminum In other words, a high purity of 0.01% by weight or less in terms of an aluminum element and a low defect are included. Furthermore, the present invention includes a semiconductor device using the silicon carbide based composite material.
[0015]
The method of producing a composite material of the present invention comprises a first component consisting of aluminum or copper from metal mainly includes the steps of preparing a raw material consisting of a second component composed mainly of silicon carbide powder, the same material A step of mixing to form a mixture, a step of forming the mixture to form a molded body, and a temperature below the melting point of a metal mainly composed of aluminum or copper, and an atmospheric pressure of 1 × 10 ⁻³ Torr or less Heating in a vacuum to form a heat-treated body, and sintering the heat-treated body at a temperature equal to or higher than the melting point of a metal mainly composed of aluminum or copper to form a sintered body. In addition, it is more preferable if the atmospheric pressure in the step of forming the heat treatment body is 1 × 10 ⁻⁴ Torr or less.
[0016]
Further, the silicon carbide powder as a raw material has an oxygen amount of 1% by weight or less, the amount of the component containing iron is 0.01% by weight or less in terms of iron element, and the amount of the component containing aluminum is converted to aluminum element. There is also a method using a powder having a high purity of 0.01% by weight or less. In that case, for example, a method of performing a preheating treatment in which normal silicon carbide powder is heated in an inert gas atmosphere at a temperature range of 1600 to 2400 ° C., or normal silicon carbide powder is at least one of hydrofluoric acid, nitric acid or hydrochloric acid. The method of carrying out the pre-acid treatment immersed in the aqueous solution containing the acid of this is mentioned. There is also a method of performing a preheating treatment after the preacid treatment.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The silicon carbide based composite material provided by the present invention is roughly divided into a composite material (hereinafter referred to as Al-SiC) containing a first component composed of a metal mainly composed of aluminum and a second component composed mainly of silicon carbide. Composite material (also referred to simply as Al—SiC or Al), and a composite material (hereinafter referred to as Cu—SiC) including a first component composed mainly of copper and a second component composed mainly of silicon carbide. Composite materials, also simply referred to as Cu-SiC or Cu). The present invention focuses on these materials and improves the productivity of the heat dissipation substrate (heat sink), in particular, the heat dissipation substrate for semiconductor devices, as well as the productivity, particularly in the composition region where the amount of SiC is 50% by weight or more. It was made for that purpose.
[0018]
As described above, the composite material of the present invention has a porosity of 10 to 20% and a thermal conductivity of 170 W / m · K or more. The reason why the porosity is within this range is that, in order to make the porosity less than the lower limit, it is necessary to increase the powder molding pressure during production as described later, which increases the wear of the molding die. As a result, in order to suppress variation in the molding dimensions of the molded body, the frequency of replacing the molding die increases, and the molding cost increases. In addition, if the porosity exceeds the upper limit, the thermal conductivity rapidly decreases.
[0019]
The silicon carbide crystal particles of the composite material of the present invention desirably have high purity and low defects. For example, the silicon carbide particles have an oxygen content of 1% by weight or less, the content of an iron-containing component is 0.01% by weight or less in terms of iron element, and the content of an aluminum-containing component is in terms of aluminum element Some have high purity of 0.01% by weight or less and low defects. Such a material can be obtained by preparing a SiC powder raw material with high purity in advance as described below. This is because the upper limit values of these exemplified impurities are controlled to the amount below this value, so that even if the porosity is as described above, more excellent thermal conductivity can be obtained.
[0020]
In the method for producing a composite material of the present invention, as described above, a molded body containing a mixture of the first component and the second component is subjected to an atmosphere pressure of 1 × at a temperature below the melting point of a metal mainly composed of aluminum or copper. A step of heating in a vacuum of 10 ⁻³ Torr or less to form a heat treatment body, and a step of sintering the heat treatment body at a temperature equal to or higher than the melting point of a metal mainly composed of aluminum or copper to form a sintered body. It is characterized by including. In addition, it is more preferable if the atmospheric pressure in the process of forming the heat treatment body is 1 × 10 ⁻⁴ Torr or less. The amount of silicon carbide powder in the mixture is usually in the range of 50 to 80% by weight. This is because if it is less than the lower limit, the effect of reducing the molding cost of the present invention is small, and if it exceeds the upper limit, the amount of SiC is excessively increased, making it difficult to ensure the density of the molded body.
[0021]
In the present invention, the sintered body is heat-treated in advance in a vacuum atmosphere as described above before sintering. Thereby, as already described, the film of the component mainly composed of moisture and OH groups adsorbed on the oxide layer formed on the surface of the first component particle is removed in advance. If this film is left without heat treatment, the thickness of the oxide layer increases due to the subsequent heating during sintering, and the wettability with the SiC particles decreases. This state is schematically shown in FIG. The upper diagram in the figure shows a case where heat treatment is not performed. In this case, the film 2 on the surface of the first component particles 1 after sintering becomes a thicker oxide layer, and the interface with the SiC particles 3 is not wetted and most of the portions are not in close contact. The interface portion that is not in close contact becomes a void, and the thermal resistance increases at the portion. On the other hand, the lower figure shows a case where heat treatment is performed. In this case, the film 2 on the surface of the first component particles 1 is almost removed, and the interface with the SiC particles 3 after sintering is almost wet and in close contact. Almost no voids remain in the interface portion. Note that the skeleton of the SiC particles in the molded body is robust and the gap is not reduced because no mechanical pressure is applied. For this reason, even if the first component melts, the gap cannot be completely filled. Therefore, voids remain in the gaps inherent in the skeleton.
[0022]
The pressure of the vacuum atmosphere during heating is 1 × 10 ⁻³ Torr or less. Exceeding this is not preferable because the components mainly composed of adsorbed moisture and OH groups are not sufficiently removed, and as a result, the porosity of the final composite material increases and its thermal conductivity rapidly decreases. The heating temperature is lower than the melting point of the first component metal. At temperatures above the melting point, the first component metal and adsorbed component react to form their respective oxides, increasing the thickness of the oxide layer on the surface of the metal, and drastically reducing wettability with SiC particles. is there. However, if it is less than the melting point, the higher the temperature, the better. The lower limit is usually 300 ° C. or more when the first component is mainly composed of Al, and 600 ° C. or more when the first component is composed mainly of Cu. Although the heating time depends on the atmospheric pressure and temperature, the effect usually appears in about 10 minutes, and the longer the effect is. The sintering after the heat treatment is performed in a non-oxidizing atmosphere at a temperature equal to or higher than the melting point of the first component metal. Nitrogen is desirable. In this case, it may be under normal pressure or under pressure.
[0023]
The means for improving the level of thermal conductivity of the composite material of the present invention will be described below. The material of the present invention includes pores as described above. For this reason, a decrease in thermal conductivity is unavoidable. Therefore, it is necessary to reduce the thermal resistance of the inside and interface of both components configured as described below. Accordingly, high-purity raw material particles are selected, or SiC raw material powder having a high carrier concentration is prepared in advance.
[0024]
The first is to use a silicon carbide raw material powder with few impurities including oxygen and cationic impurities, particularly iron and aluminum. Thereby, the amount of impurities and defects in the obtained silicon carbide crystal particles can be reduced. As a result, the level of thermal conductivity of the composite material can be increased. In particular, the oxygen content in the crystal particles is 1% by weight or less, the content of the component containing iron is 0.01% by weight or less in terms of iron element, and the content of the component containing aluminum is 0 in terms of aluminum element. It is desirable to use high-purity silicon carbide powder of .01% by weight or less and silicon carbide crystal particles having the same amount of impurities and defects. If the amount of oxygen and the amount of impurities including iron and aluminum exceed this amount, the thermal conductivity may be greatly reduced. As described above, the silicon carbide powder at the impurity level can also be obtained through a preheating process in which the silicon carbide powder is heated in a temperature range of 1600 to 2400 ° C. in an inert gas atmosphere. In this case, it is important that the atmosphere gas does not coexist with nitrogen and carbon components that are solid-solved in the SiC particles and easily form lattice defects in the crystal. It is desirable that the pressure of the atmospheric gas is high. For example, HIP (hot isostatic pressing) treatment may be performed under high pressure. When the temperature is less than 1600 ° C., the effect of reducing defects in the heat treatment tends to be small. Moreover, when it exceeds 2400 degreeC, SiC will become easy to sublime and decompose | disassemble and a yield may fall.
[0025]
Further, such a powder can be obtained by immersing silicon carbide powder in an aqueous solution containing at least one acid selected from hydrofluoric acid, nitric acid and hydrochloric acid. By this treatment, impurities including transition metals such as cationic impurities, iron (Fe), chromium (Cr), vanadium (V), nickel (Ni), etc. present on the particle surface in the powder, particularly iron (Fe) and oxygen The carbon can be dissolved and removed. This reduces the amount of impurities that cause phonon scattering in the SiC crystal particles and improves the thermal conductivity of the resulting composite material. That is, these components are diffused from the particle surface to the inside at a high temperature to form defects and easily cause a decrease in thermal conductivity. By performing a preheating treatment after the preliminary acid treatment, a SiC powder having a higher purity and a lower defect can be obtained.
[0026]
The carrier concentration in the SiC crystal is also considered to affect the thermal diffusivity. In general, SiC is a material that can be an n-type semiconductor having excess electrons or a p-type semiconductor having excess vacancies. Therefore, when these excessive electron and vacancy (carrier) concentration increases, it contributes to the scattering of phonons in the SiC crystal particles. For this reason, it is thought that the thermal conductivity of SiC falls. SiC has polymorphs with different crystal types such as 6H, 4H, 3C, and 15R. As described above, 6H or 4H type has high thermal conductivity among these, but 6H type SiC is an n-type semiconductor, and the amount of impurities in the crystal is at the same level. For example, the carrier concentration is lower than those of other crystal types. Therefore, the SiC raw material used for the silicon carbide based composite material of the present invention is desirably 6H type. The carrier concentration is desirably 1 × 10 ¹⁹ atoms / cm ³ or less. The SiC raw material used for the production of the silicon carbide based composite material of the present invention is preferably all of this 6H type, but other crystal types may be partially mixed.
[0027]
The amount of the impurities present on the surface of the SiC particles can be confirmed by an acid extraction method. The procedure is as follows: SiC powder is immersed in a mixed acid aqueous solution composed of nitric acid and hydrofluoric acid maintained at 100 ° C. for about 2 hours to elute impurities present on the surface, and the eluate is quantified by IPC emission spectroscopy. To do. In addition, when it is desired to check the amount of impurities present inside the SiC particles, the impurities are eluted by a pressure acid decomposition method. In this case, the SiC powder is immersed in a mixed acid aqueous solution composed of nitric acid and hydrofluoric acid maintained at 190 to 230 ° C. for about 40 hours. As a result, not only the surface of the SiC particles but also impurities inside can be extracted, and the effluent is similarly quantified by IPC emission spectroscopic analysis. The amount of stacking faults in SiC particles can be confirmed by directly observing the target SiC particles with a transmission electron microscope. In addition, when confirming the amount of SiC particle impurities and stacking faults in the composite silicon carbide-based composite material, first the first component is separated and removed with an acid or the like, and the remaining SiC particles are analyzed in the same procedure. ·evaluate. Although it is difficult to confirm the carrier concentration of the SiC particles, it can be confirmed by Raman spectroscopic analysis if the powder is an aggregate of the particles.
[0028]
A commercially available material may be used as the raw material of the first component mainly composed of aluminum or copper. In addition, although the usage form of the raw material of the 1st component used by this invention may be any forms, such as a lump and a powder form, a powdery thing is used normally. As the impurity species intervening in the raw material powder, it is desirable that the number of components including a transition metal element, particularly a group 8a element, which is easily dissolved in aluminum, is as small as possible. Therefore, when using commercially available aluminum alloy powder, it is desirable to select one having a small amount of components for producing these alloys.
[0029]
As described above, the raw material used in the present invention is as high purity and low defect as possible as the second component SiC powder, and the raw material mainly composed of the first component aluminum or copper is also high purity. It is desirable to use those. The raw material mixing method may be an existing method as long as the raw material purity does not decrease in accordance with the form and properties of the raw material. In order to improve the moldability, the mixture is preferably granulated, for example, to reduce its bulk. The method for forming the mixture may be any ordinary method.
[0030]
【Example】
(Example 1) As raw materials, all have an average particle diameter of 50 μm, SiC raw material powders subjected to various pretreatments shown in Table 1, Al-based raw materials shown in Table 2, and Cu-based materials shown in Table 3 Prepared with raw materials. The carrier concentration of the SiC raw material powder confirmed by Raman spectroscopic analysis was about 1 × 10 ¹⁷ pieces / cm ³ in all cases. In addition, those described as “None” in the preliminary processing column in Table 1 are those for which no corresponding preliminary processing is performed. The preliminary acid treatment was performed by repeating the process of washing with pure water three times after immersion in an acid aqueous solution having the concentration and temperature shown in the table, followed by drying with hot air. Therefore, for example, in the case of the raw material S2, the SiC powder of the raw material S1 is first immersed in a 10% aqueous hydrofluoric acid solution at room temperature for 30 minutes and then washed with pure water. After repeating this series of operations three times, Dehydrated and dried by wind. The preheating treatment is a method in which the powder is charged into a silicon carbide case, the heater is set in a tungsten furnace, and kept in an argon gas atmosphere at the same gas pressure and at the indicated temperature for 1 hour. went. The amount of impurities in each SiC powder described in the table is a value obtained by dissolving and extracting impurities-containing components from the powder by the pressure acid decomposition method under the conditions described above, and analyzing the extract by IPC emission spectroscopy. It is an amount existing not only on the particle surface but also on the entire particle including the inside thereof. Although the amount of the cation element (transition metal element) other than Fe (iron) in the present invention is not described in Table 1, the individual amount was 500 ppm at most for any number of raw materials. The amount of C (carbon) was at most 500 ppm in any number of raw materials.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
[Table 3]

[0034]
Each SiC raw material powder described in Table 1 is selected as the second component, and the Al-based raw material powder A11 described in Table 2 or the Cu-based raw material powder C11 described in Table 3 is selected as the first component. Silicon carbide composite material specimens containing 70% by weight of SiC were produced by a method including heat treatment. The combinations of 38 kinds of raw materials produced in the raw material column of Table 4 are shown. First, each SiC raw material powder described in Table 1 is weighed so that 70% by weight and the remaining 30% by weight become the above A11 or C11 raw material powder, 3% by weight of paraffin is added as a binder, and mixed in ethanol for 3 hours. did. The obtained slurry was spray-dried to obtain a granulated powder. With a dry powder molding press, with a cemented carbide die steel mold, the molding pressure listed in the molding pressure column of Table 4 (however, the numerical value in the table is in units of ton / cm ² ) is 100 mm in diameter and about 10 mm in thickness. Molded into. Then, these were arrange | positioned in a nichrome wire heater furnace, the binder was removed at 400 degreeC in nitrogen stream, and it was set as the molded object. Each of these compacts was placed in a vacuum furnace of a nichrome wire heater, and the nitrogen partial pressure Pn described in the heat treatment column of Table 4 (however, the numerical value in the table is 10 ⁻⁴ Torr unit) and temperature conditions, both Heat treatment was performed for 20 minutes. Next, this heat-treated body was put in a silicon carbide holding container, and both were sintered for 2 hours in the temperature range and nitrogen flow described in the sintering column of the same table. The final thickness of the sintered body was approximately 10 mm for all samples. The sample was then ground and finished. Regarding the influence of the molding pressure on the wear rate of the mold, Sample 5 and Samples 12 to 14, and also 5 ton / cm ² using the same composition powder were added, and molding was performed at 1000 and 5000 moldings. The inner diameter of the mold was confirmed by an inner diameter micrometer, and the wear situation was examined. The results are shown in Table 5. The numerical values in Table 5 are increases in the inner diameter. Since the initial dimension is 100 mm, the same numerical value indicates an increase rate in% unit.
[0035]
From the apparent density calculated from the measured unit weight and volume of each sample, the theoretical density calculated by the composite law from the density of the main component and its composition ratio, and the radial direction of the forged body by laser flash method The thermal expansion coefficient was measured by a differential transformer type thermal expansion coefficient measuring device, and the amount of impurities in the SiC crystal particles was determined by a combination of the above-described pressure acid decomposition method and emission spectroscopic analysis. . These results are also shown in Table 4. In addition, the composition / combination with the same first component as in Table 4 and the same molding / sintering procedure using SiC raw material powder S1 performed by switching the atmosphere gas for preheating treatment separately to a gas containing nitrogen or carbon When the thermal conductivity of the sintered body prepared in step 1 is subjected to acid treatment in advance, the Al-SiC type is about sample 9 in Table 4 and the Cu-SiC type is about sample 28 in Table 4; In the case where the treatment was not performed, the Al—SiC type was about 170 W / m · K, and the Cu—SiC type was about 200 W / m · K, and the effect of the preheating treatment was reduced.
[0036]
[Table 4]

[0037]
[Table 5]

[0038]
From the above results, the following can be understood. (1) Molding is performed at a molding pressure lower than normal (less than 4 ton / cm ² ), and is baked under normal pressure without performing heat treatment at a temperature below the melting point of the first component and at atmospheric pressure of 10 ⁻³ Torr or less. As a result, the porosity exceeds 20%. As a result, the thermal conductivity of the sintered body is less than 170 W / m · K in the Al—SiC system and less than 190 W / m · K in the Cu—SiC system. On the other hand, those subjected to the same heat treatment have a porosity of 20% or less, and as a result, the thermal conductivity of the sintered body is 170 W / m · K or more in the Al—SiC system and 190 W / m · in the Cu—SiC system. K or more. In particular, the thermal conductivity is further improved by setting the atmospheric pressure of the heat treatment to 10 ⁻⁴ Torr or less. The reason is considered as follows. By the heat treatment under reduced pressure, the coating film composed of oxides and adhering components on the surface of the first component is almost removed. This improves the wetting of the interface between silicon carbide and the first component melt. As a result, the degree of adhesion between the two interfaces is increased, and the thermal resistance is decreased there. Further, (2) when the molding pressure is increased, the porosity of the sintered body is lowered and the thermal conductivity is improved. However, on the other hand, the wear amount of the inner diameter of the mold becomes large. In particular, when the molding pressure is 4 ton / cm ² or more, the amount of wear increases rapidly. Further, (3) the heat conductivity of the SiC powder that has been preheated or pretreated with acid in advance is improved as compared with the case that the SiC powder is not.
[0039]
(Example 2) Using the SiC powder of S3 in Table 1, the aluminum powder of A11 and A12 of Table 2, and the copper powder of C11 and C12 of Table 3, by the same method as in Example 1, Al-SiC-based and Cu-SiC-based sintered bodies with SiC content were prepared. The conditions for molding, heat treatment and sintering of the granulated powder were matched to those of the sample 13 in the Al—SiC system and those of the sample 32 in the Cu—SiC system. The obtained sample was evaluated using the same items as in Example 1. The results are also shown in Table 6.
[0040]
[Table 6]

[0041]
From the above results, according to the manufacturing method of the present invention, when molded at a relatively low molding pressure and sintered under normal pressure, the thermal conductivity is high over a wide range of SiC, although there are 10% or more voids. It can be seen that a silicon carbide based composite material is obtained.
[0042]
(Example 3) 50 silicon carbide composite materials obtained by the same method as those of samples Nos. 3, 5, 15, 22, 24, 34, 48, and 59 of the examples described above, each having a length of 200 mm. The substrate was finished into a shape having a width of 200 mm and a thickness of 3 mm. This was mounted on a power module as schematically shown in FIG. 2 as a heat dissipation substrate, and a temperature cycle test was performed including each mounting stage. In FIG. 2, 4 is a second heat dissipation substrate made of the above composite material of the present invention, 5 is an electrically insulating material made of ceramics (not shown) having a copper circuit (not shown) disposed on the substrate. The first substrate, 6 is a Si semiconductor element, and 7 is a heat dissipation structure disposed under the second heat dissipation substrate. This jacket is a water-cooled jacket in this embodiment, but there are also air-cooled fins and the like. In the figure, wiring around the semiconductor element is omitted. In the present embodiment, a module in which six Si semiconductor elements are mounted via a first ceramic substrate is used.
[0043]
Since the first substrate cannot be soldered directly to the second substrate prior to mounting, an electroless nickel plating layer having an average thickness of 10 μm and an electrolytic nickel plating layer having an average thickness of 5 μm are formed in advance on the main surface of the second substrate. Each of the four specimens was formed by attaching a copper wire having a diameter of 1 mm in a direction perpendicular to the plating surface by using a hemispherical Ag-Sn solder having a diameter of 5 mm on nickel plating. The substrate body of this specimen was fixed to a jig, a copper wire was gripped and pulled in a direction perpendicular to the plating surface, and the adhesion strength of the plating layer to the substrate was confirmed. As a result, the plating layer of any substrate was not peeled off even by a tensile force of 1 kg / mm ² or more. In addition, 10 samples were taken out of another specimen on which the plating layer was formed, and a heat cycle test was repeated for 1000 cycles of holding temperature at -60 ° C for 30 minutes and holding at 150 ° C for 30 minutes, after the test. When the adhesion strength similar to the above was confirmed, all the specimens obtained the results of satisfying the above-mentioned level of plating adhesion. From the above results, it was found that the adhesion of the plating to the substrate made of the composite material of the present invention is at a level having no practical problem.
[0044]
Next, as the first ceramic substrate mounted on the second substrate, nitriding with a thermal conductivity of 150 W / m · K, a thermal expansion coefficient of 4.5 × 10 ⁻⁶ / ° C., and a three-point bending strength of 450 MPa. Two types of copper circuits: substrate A made of aluminum ceramics and substrate B made of silicon nitride ceramics having a thermal conductivity of 120 W / m · K, a thermal expansion coefficient of 3.7 × 10 ⁻⁶ / ° C., and a three-point bending strength of 1300 MPa Eighteen first substrates each having a shape formed thereon were prepared. The shapes of these substrates were 90 mm in length, 60 mm in width, and 1 mm in thickness. These substrates were arranged at equal intervals in 2 rows and 3 columns on the main surface of 200 mm square of the second substrate, and fixed with Ag-Sn solder on the surface on which the nickel plating layer was formed. Next, the back surface side of the second substrate of this assembly and the water cooling jacket were fixed by fastening a bolt with silicon oil compound applied to the contact surface. The mounting holes of the first substrate in this case were formed by a method of irradiating carbon dioxide gas lasers to pilot holes previously formed at the four corners in the raw material stage and expanding them to a diameter of 3 mm. This processing could be performed with high accuracy and high speed as compared with the case of using other ceramic materials, Cu-W, and Cu-Mo. This tendency was more remarkable as the thermal conductivity increased.
[0045]
From each of these specimens, select 15 pieces each of the first substrate of A and B, perform a heat cycle test of 2000 cycles under the same single cycle conditions as described above, and output the module output every 100 cycles. The change was confirmed. As a result, no decrease in the output was observed until 1000 cycles, in which all modules were considered to have no practical problem. However, in the confirmation after 1100 cycles exceeding 1000 cycles regardless of the material type of the first substrate, plates of 5, 15 and 48 having a thermal conductivity of 200 W / m · K or less were used for the second substrate. Therefore, a slight decrease in the output of the module due to the heat cycle was observed in 2 of 15. In the sample with the reduced output, generation of fine cracks was observed on the first substrate side of the soldered joint interface between both the first and second substrates. There was no such abnormality until the end of 2000 cycles other than those described above.
[0046]
From the above results, it can be seen that the power module using the first substrate made of the silicon carbide based composite material of the present invention has a practically no problem level. Separately, a sample with a thermal conductivity of 170 W / m · K or more can be mounted and evaluated as a heat dissipation board on a semiconductor device mounting device such as a high-capacity personal computer with a low output and low thermal (cycle) load compared to this type of module. I went there, but there was no problem in its reliability and practical performance.
[0047]
【The invention's effect】
As described above in detail, the silicon carbide based composite material of the present invention is molded at a molding pressure lower than usual, heat-treated at a temperature lower than the melting point of the first component under vacuum, and sintered under normal pressure. That is, a normal mechanical load is not applied during molding or sintering. For example, during sintering, high pressure such as hot pressing or forging for densification is not applied. Therefore, even if SiC powder is used, the service life of the mold / sinter mold is extended. Therefore, it can be manufactured at a lower cost than the conventional one. The material of the present invention has a porosity of 10% or more, and its thermal conductivity is lower than that of a dense material. However, the heat treatment significantly improves the wettability between the second component particles and the first component, and as a result, the adhesion is high and excellent at the interface between the two components, although the porosity is higher than the conventional one. A thermally conductive material can be provided. In addition, the thermal conductivity can be further improved by preliminarily purifying the SiC raw material particles by preliminary heating and preliminary acid treatment. According to the present invention, a material having a thermal conductivity of 170 W / m · K or more is obtained over a wide range of the amount of SiC, which is useful as a heat dissipation substrate for various semiconductor devices. In particular, those with 200 W / m · K or more can be used for high-capacity semiconductor devices such as power modules.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining the effect of heat treatment in a silicon carbide based composite material of the present invention.
FIG. 2 is a diagram schematically showing a semiconductor device (power module) using a material of the present invention for a substrate.
[Explanation of symbols]
1. First component particles2. 2. Coating of oxide or the like on the surface of the first component particle Second component particles4. 4. First substrate made of silicon carbide based composite material Second substrate 6. Semiconductor element 7. Heat dissipation structure

Claims

A method for producing a silicon carbide-based composite material comprising a metal having aluminum or copper as a main component as a first component and a particle having silicon carbide as a main component as a second component, the metal having aluminum or copper as a main component The amount of oxygen is 1% by weight or less, the amount of components containing iron is 0.01% by weight or less in terms of iron element, and the amount of components containing aluminum is 0. 0% in terms of aluminum element. A step of preparing a raw material comprising a second component whose main component is silicon carbide powder of not more than 01% by weight, a step of mixing the raw materials to form a mixture, and a step of forming the mixture into a molded body Heating the molded body at a temperature lower than the melting point of a metal containing aluminum or copper as a main component in a vacuum at an atmospheric pressure of 1 × 10 ⁻³ Torr or less to form a heat treated body; With copper as the main component A method for producing a silicon carbide composite material, comprising: sintering at a temperature equal to or higher than a melting point of a metal to be sintered to form a sintered body.

A method for producing a silicon carbide-based composite material comprising a metal having aluminum or copper as a main component as a first component and a particle having silicon carbide as a main component as a second component, the metal having aluminum or copper as a main component And a step of preparing a raw material comprising a first component comprising: a second component mainly composed of silicon carbide powder that has been subjected to a preheating treatment step that is heated in a temperature range of 1600 to 2400 ° C. in an inert gas atmosphere; A step of mixing the raw materials to form a mixture, a step of forming the mixture into a molded body, and a temperature below the melting point of a metal mainly composed of aluminum or copper, and an atmospheric pressure of 1 × 10 ^−３-3 Silicon carbide including a step of heating in a vacuum of Torr or less to form a heat treatment body, and a step of sintering the heat treatment body at a temperature equal to or higher than a melting point of a metal mainly composed of aluminum or copper to form a sintered body. Method for manufacturing a composite material.

A method for producing a silicon carbide-based composite material comprising a metal having aluminum or copper as a main component as a first component and a particle having silicon carbide as a main component as a second component, the metal having aluminum or copper as a main component The raw material which consists of the 1st component which consists of, and the 2nd component which has as a main component the silicon carbide powder which passed through the step of the pre-acid treatment immersed in the aqueous solution containing at least 1 sort (s) of acid of fluorine, nitric acid, or hydrochloric acid A step of mixing the raw materials to form a mixture, a step of forming the mixture into a molded body, and a temperature below the melting point of the metal mainly composed of aluminum or copper, Atmospheric pressure 1 × 10 ^−３-3 Silicon carbide including a step of heating in a vacuum of Torr or less to form a heat treatment body, and a step of sintering the heat treatment body at a temperature equal to or higher than a melting point of a metal mainly composed of aluminum or copper to form a sintered body. Method for manufacturing a composite material.

The manufacturing method of the silicon carbide-type composite material as described in any one of Claims 1-3 whose atmospheric pressure of the process made into the said heat processing body is 1 * 10 < ^-4 > Torr or less.

5. The method for producing a silicon carbide-based composite material according to claim 1 , wherein in the step of preparing the raw material, the amount of silicon carbide powder in the mixture is 50 to 80 wt%.