JP2004288912A

JP2004288912A - Semiconductor heat dissipation substrate and its manufacturing method

Info

Publication number: JP2004288912A
Application number: JP2003079894A
Authority: JP
Inventors: Tomoyuki Sugiyama; 知之杉山; Masahiro Omachi; 正弘大町
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 2003-03-24
Filing date: 2003-03-24
Publication date: 2004-10-14

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lid-type heat dissipation substrate which has a high coefficient of thermal conductivity and a high coefficient of thermal expansion. <P>SOLUTION: The lid-type heat dissipation substrate is an Al-SiC-based one, and it is made of a composite material which contains SiC of 50-80 wt.%, as well as silicon and Al, and has such a shape that has the bottom within a rectangular frame. An inner surface in the bottom has a flatness of 0.5 μm or below per 1mm in the diagonal direction. A method of manufacturing the lid-type heat dissipation substrate comprises a process of molding the composite material containing SiC of 50-80 wt.%, silicon, and Al into the shape of a lid, a process of sintering the molding at a temperature not higher than the melting point of Al, and a process of hot-forging of the sintered material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、半導体装置に有用な放熱基板、特に主成分がＳｉＣ、珪素とＡｌを含む複合材料で構成された放熱基板、その製造方法、及びそれを用いたパッケージ、半導体装置に関する。
【０００２】
【従来の技術】
半導体素子は年々高性能化、高機能化が進み、それに応じて半導体素子を搭載するパッケージの形態もいろいろに変遷してきている。このうち、入出力端子数の増大に対応する図４に示すパッケージ構造が用いられるようになった。この構造では、半導体素子４と半導体パッケージ１０の接合をフリップチップ実装（ＦｌｉｐＣｈｉｐ）を使った方式で行っているのが特徴である。この構造のものでは板状の放熱基板５と、それを支えるスティフナー（Ｓｔｉｆｆｎｅｒ）６といわれる枠状の金属部材が使用される。放熱基板等のパッケージ用部材には、軽量で優れた熱伝導性を有するとともに、形状の多様化に対応可能なものが要求される。最近熱伝導性に優れ、軽量な炭化珪素（以下ＳｉＣという）と、アルミニウム（以下Ａｌという）を組み合わせた複合材（以下この複合材をＡｌ−ＳｉＣという）が注目されている。
【０００３】
特許文献１には、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Ａｌ−ＳｉＣ系複合材料が開示されている。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％以上の窒素を含み、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。そして、非酸化性雰囲気においてさらに再圧縮したり、再圧縮後にさらに加熱処理をすることができることが開示されている。これらの目的は、寸法精度の向上と、残存した気孔を除去し緻密化を図ることにある。
【０００４】
特許文献２は、常圧焼結法とＨＩＰ法とを組み合わせた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する。次に、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Ａｌ−ＳｉＣ系複合材料が得られている。また、焼結後さらに熱間鍛造することも開示されている。熱間鍛造の目的は、熱伝導率が高く、かつ熱膨張係数が１０×１０^−６／Ｋ以下のものを得ることにある。
【０００５】
【特許文献１】
特開平１０−３３５５３８号公報
第２頁、第１２頁、第２２欄、６−１０行
【特許文献２】
特開平１１−３１０８４３号公報
第２頁、表３
【０００６】
【発明が解決しようとする課題】
半導体素子の性能向上により、半導体素子からの発熱量が増大している。半導体素子からの放熱は、例えば図４に示されているように、半導体素子４上に塗布された樹脂２を介して放熱基板５に伝えられる。放熱基板５に塗布された樹脂は、熱伝導率が放熱基板の１／１０〜１／２０程度とかなり低いので、樹脂２の厚さを薄くすることが必要である。図４で使用している単純な板状の放熱基板５、スティフナー６と半導体パッケージ１０で構成された半導体装置では、スティフナー６の両側の２箇所を樹脂２により接合するので高さを精度良く維持することが難しい。しかしながらリッド型放熱基板を用いると、接合箇所が１箇所になるので、より精度の出しやすい構造でありリッド型の形状の場合が有利となる。
【０００７】
しかしながら図１に示すようなリッド型放熱基板１を粉末冶金法によって製造する場合、内底面１３の平面度及びリッド深さのバラツキすなわち内底面１３からリッド足部９の高さのバラツキを精密に制御することが困難である。これは、リッド型放熱基板１のリッド足部９と底部８で厚さが異なるので、金型へ粉末を供給するときに各部の厚さに比例した粉末を供給するのが難しく、厚さの異なる境界などに歪やいわゆる引けが発生し寸法精度が悪い。すなわちＡｌ−ＳｉＣ系の複合材料を用いて内底面１３の平面度が対角方向の１ｍｍあたり０．５μｍ以下のリッド型放熱基板を製造するには、研削又は切削加工が必須の工程であった。
【０００８】
したがって、放熱基板として満足のいく価格性能比を持った製品は開示されていなかった。また、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価格性能比を満足する製品を得ることは困難であった。そこで本発明は、切削加工や研削加工をすることなく、安価で高い寸法精度を維持したＡｌ−ＳｉＣ系のリッド型放熱基板を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明では上記の課題を、まずリッド足部の密度を底部の密度より低くした焼結体であっても、次の熱間鍛造により底部からリッド足部に物質移動を起こして密度を均一化し、平面度を高めるという画期的手法を用いて解決したものである。
【００１０】
本発明は、Ａｌ−ＳｉＣ系の半導体放熱基板に関するもので、半導体放熱基板は、ＳｉＣを５０〜８０質量％、珪素とＡｌを含む複合材料で構成され、矩形枠内に底部を有する形状のリッド型放熱基板であり、底部の内底面の平面度が対角方向の１ｍｍあたり０．５μｍ以下である半導体放熱基板である。ここでいう平面度は、まず定盤上に置かれたリッド型放熱基板の内底面の対角線に沿って表面粗さ計で高さ方向の変位量を測定する。次に、その測定チャート上において開始点と終了点を直線で結び、その直線から最も離れた点までの距離を、測定した長さで割った値である。測定長さは、内底面の対角長さの半分以上とするのが望ましい。
【００１１】
そして本発明の方法は、ＳｉＣを５０〜８０質量％、珪素とＡｌを含む複合材料をリッド型に成形する成形工程と、その成形体をＡｌの融点以下の温度で焼結する焼結工程と、焼結体を熱間鍛造する熱間鍛造工程を含む半導体放熱基板の製造方法である。このような方法を採用することで、切削加工や研削加工が不要になり価格性能比の高い半導体放熱基板を提供することができる。そして、熱間鍛造の雰囲気は大気中が望ましい。
【００１２】
放熱基板に含有されるＳｉＣは５０〜８０質量％である。ＳｉＣの含有量が５０質量％より少ない場合は、鍛造時に大気中で焼結体の温度を上げた際にＡｌ合金の強度が低くなり、熱間鍛造時の製品取り扱いが難しくなる。また、ＳｉＣの含有量が８０質量％より大きい場合は、成形体を焼結する際、Ａｌ合金の成分量が少なくなり過ぎ、焼結することが難しいからである。また、この範囲にあれば、半導体放熱基板の熱膨張係数を１３×１０^−６／Ｋ以下の範囲に保つことができる。
【００１３】
半導体放熱基板の表面は、熱間鍛造されたままであることが望ましい。一般的に、Ａｌの焼結体は色むらを生じ易く、焼結体や熱間鍛造したものは、その表面をバレル処理や軽くブラスト処理されるのが通常である。従ってここでいう熱間鍛造されたままとは、研削や切削をしない状態を意味し、バレル処理や軽くブラスト処理されるものを含む意味である。本発明においても、熱間鍛造品の角部のバリを取り、丸くする目的と上記の色むらを除去するためにバレル処理や軽いブラスト処理することが望ましい。このとき内底面の角などには色むらなどが残り、バレル処理やブラスト処理したことがわかる。
【００１４】
本発明の半導体基板および半導体の製造方法は、珪素を焼結体の０．０５〜１質量％含有していることが望ましい。Ａｌの中に溶融した珪素は、ＳｉＣとＡｌの濡れ性を高める働きと、溶湯の粘度を下げる働きがある。珪素の含有量が１質量％を越えると珪素分がＡｌと反応し、Ａｌ−Ｓｉ合金となり、融点が下がり、溶融金属の粘度が低くなる。その結果、熱間鍛造するときに焼結体を予備加熱するが、そのときにＡｌ−Ｓｉの溶湯が製品からにじみ出たり、また形状を保ちにくくなるとともに、熱間鍛造時に溶湯が金型から漏れる可能性がある。逆に、０．０５質量％未満の場合は、ＳｉＣとＡｌの濡れ性が不足し、また粘度が高くなり熱間鍛造に時間がかかる。
【００１５】
ＳｉＣの平均粒経が、４〜５０μｍの範囲にあることが望ましい。ＳｉＣは、焼結体の骨格をなすので成形や熱間鍛造のときの支えになる。熱間鍛造する前に予備加熱するとき、形状を維持できるのは実にこのＳｉＣの働きによるものである。ＳｉＣの平均粒度が５０μｍを越えると、熱間鍛造のときにＳｉＣが割れて製品の熱伝導率が下がる原因となる。また、４μｍ未満の場合は、成形体強度が不足する。
【００１６】
さらに本発明では、リッド深さｄがｄ_０±５０μｍの範囲にあることが望ましい。ただしｄ_０はリッド深さの平均値を示す。±５０μｍの範囲を超えると、パッケージや半導体装置に組み上げたとき、接合用の樹脂の厚さが厚くなり放熱性が悪くなる。
【００１７】
本発明のリッド型放熱基板は、放熱基板の内底面の対角長さＬ３が３０ｍｍ以上であることが好ましい。リッドの対角線長さＬ３によりリッドの大きさを定めたもので、細長い矩形から正方形まで各種のものを包含する。
【００１８】
図２を参照して、リッド深さｄと底部の厚さｔの和（ｄ＋ｔ）ｍｍを基板の上面７の面積（Ｌ１ｍｍ×Ｌ２ｍｍ）で割った値、（ｄ＋ｔ）／（Ｌ１×Ｌ２）の値が０．０００１〜０．００４ｍｍ^−１の間にあることが望ましい。この数値の意味は、例えば基板の上面の面積が５０ｍｍ×５０ｍｍのとき、厚さが０．２５ｍｍから１０ｍｍの間が望ましいという意味である。さらに望ましい値は、底部の厚さｔが１〜４ｍｍ、リッドの深さｄが０．３〜０．９ｍｍの範囲である。
【００１９】
本発明の方法において熱間鍛造は、大気中で温度は６５０〜８００℃の範囲が望ましい。６５０℃未満では、Ａｌ合金の粘度が低い。一方、８００℃を越えると、製品内のＡｌの粘度が低くなり過ぎ、製品からＡｌが溶出しやすくなり、また金型にくっつきやすくなる。
【００２０】
本発明は、さらに前述したリッド型放熱基板を搭載したパッケージを提供するものである。また、本発明は、前述のリッド型放熱基板を搭載した、高い価格性能比を有する半導体装置を提供するものである。
【００２１】
【発明の実施の形態】
本発明のリッド型放熱基板は、矩形枠の中の底に枠の高さより薄い板状体をはめ込んだいわゆる蓋の形状をしている。この発明では、枠のことをリッド足部、板状体のことを底部と呼んでいる。本発明の途中で得られる図１、図２に示すような焼結体は、焼結体のリッド足部９の密度を低くし、それ以外の底部８の密度を高くした多孔質の焼結体である。この焼結体は、余肉の逃げ場所を多孔質部に備えている。従って、熱間鍛造により物質移動を起こしリッド足部９と底部８の密度を均一にした後にゆがみが発生せず、機械加工や研削加工が不要な製品となる。なお、本発明においてリッド足部９とは、足部底面１１から基板の上面７に至る部分のことである。
【００２２】
本発明のリッド型放熱基板は、放熱基板の内底面の対角長さＬ３が３０ｍｍ以上、足の幅Ｗ１、Ｗ２は１〜１０ｍｍが好ましい。リッドの大きさを内底面の対角線長さＬ３により規定した。また本発明では成形用金型や鍛造用金型を用いるので、各部の角部は金型の角部に対応して約０．５ｍｍのアールや０．５ｍｍの面取りをしてある。
【００２３】
本発明のリッド型放熱基板は以下のようにして製造される。まず、主成分としてＳｉＣ、珪素とＡｌを含む混合粉末を調製する。次に、図３（Ａ）に示す断面形状の金型に粉末２４を入れる。このとき、粉末はスプレードライヤーにより造粒されているので、金型の中に粉末を充填した時点では、金型の空間に均等に供給される。次に、上杵２１を下方に、また下杵２３を上方に動かして粉末２４を臼２２の中で圧縮して図３（Ｂ）の状態にする。このとき、リッド足部９と底部８の圧縮率が異なるので、成形密度の差が生じる。技術的に言えば、臼２２と上杵２１、下杵２３を成形時に適切に動かすことで成形体自体のリッド足部９と底部８の密度差を小さくすることはできる。しかしながら、設備的に複雑となると共に、調整にも熟練度を必要とする。本発明はこのような課題を、熱間鍛造法を導入することで解決した。
【００２４】
リッド深さｄがｄ_０±５０μｍの範囲にあることが望ましいとする具体的な理由を図面を用いて説明する。図１に示すように、半導体素子４を半田ボール３により半導体パッケージ１０に接合し、さらにリッド型放熱基板１を樹脂２により半導体素子４に接合する。樹脂の熱伝導率は、放熱基板の１／１０〜１／２０程度とかなり低いので、樹脂の厚さを極力薄くする必要がある。そのためには、リッド深さｄのバラツキを５０μｍ以下とすることが望ましい。また、リッド深さは、リッド型放熱基板を定盤の上に置き、ダイヤルゲージを用いて内底面１３から足部底面１１までの高さを測定して求める。内底面の反りの影響を極力減らすため、足部底面１１の測定点直下の内底面１３との高さの違いをリッド深さとするのが好ましい。
【００２５】
また、調製した粉末の嵩密度のコントロールが大切である。嵩密度は、０．９〜１．３ｇ／ｃｍ^３が適している。嵩密度を０．９ｇ／ｃｍ^３未満に調製することは難しい。また、嵩密度を１．３ｇ／ｃｍ^３より大きくしたときには、成形時に粉末の移動が起こりにくく、底部は固まっているのにリッド足部は固まらず所望の成形体を得ることが出来ない。この得られた成形体を、窒素ガスを９９％以上含む非酸化性雰囲気中で、Ａｌの融点以下の温度範囲で常圧焼結し、焼結体を得る。
【００２６】
本発明の方法において、熱間鍛造の温度は６５０〜８００℃の範囲が望ましい。熱間鍛造の際、金型と製品はくっつき易いので金型にくっつき防止剤を塗布することが望ましい。本発明では、水にカーボンを浮遊させたものをスプレーで適量塗布し、水分を蒸発させる方法が最適と判断した。その他の方法としては窒化ホウ素を塗布する方法、また予め製品に窒化チタンを塗布しておく方法等がある。これらの表面付着物は後工程の表面処理工程で簡単に除去できる。
【００２７】
以上のように本発明の複合材料は、ＳｉＣを５０〜８０質量％含み、内底面の平面度が対角方向の１ｍｍあたり０．５μｍ以下である製品を安価に大量に製作することが可能となる。このような複合材料からなる半導体放熱基板は優れた熱伝導率と熱膨張率を有するので、パッケージや半導体装置に用いられる半導体素子やその周辺部材との整合性が良い。
【００２８】
（実施例１）
平均粒径１０μｍのＳｉＣ粒子と平均粒径５０μｍの溶湯噴射（アトマイズ）によるＳｉを０．５質量％含むＡｌ合金粉末を用意した。これらの粉末を、表１の原料配合組成で混合した。この混合粉末と１質量％のポリビニルアルコールを混合しさらに水を加え、スラリ−を製作した。このスラリーを窒素雰囲気のスプレードライヤーにて乾燥し、混合粉末を製作した。このときの粉末の嵩密度を測定したところ、各粉末とも０．９５〜１．０５ｇ／ｃｍ^３の嵩密度であった。
【００２９】
この調製した粉末を用いて図２の形状の成形体を製作した。このようにして得られた成形体の、底部８とリッド足部９の密度を測定し、その差を求めて表１の密度差の欄に記載した。約１５〜２０％リッド足部の密度が低かった。図２の放熱基板の幅Ｌ１と長さＬ２が４０ｍｍで、内底面の対角長さＬ３が４０ｍｍ、リッド側面１２の厚さ（ｄ＋ｔ）が３．０ｍｍ、ｔが２．３ｍｍ、Ｗ１とＷ２が５．９ｍｍである。この成形体を窒素雰囲気のベルト炉にて６４５℃まで昇温し、３０分間キープして焼結し、次に降温し、焼結体を製作した。
【００３０】
【表１】

【００３１】
次に得られた焼結体は、熱間鍛造機を用いて成形体と同じ形状となるように熱間鍛造した。熱間鍛造の条件は、圧力を８ｔｏｎ／ｃｍ^２（７８４ＭＰａ）、保持時間を５秒間とし、温度を表１に示した。
【００３２】
得られたリッド型放熱基板をバレル処理したのち、各試料の密度、熱伝導率、熱膨張率、内底面の平面度を測定し、表２に示した。リッド深さｄのバラツキは、標準偏差をσとしたとき３σで評価し表２に示した。本発明のＳｉＣ量の範囲内では、内底面の平面度が１ｍｍあたり０．５μｍ以下となる片面に凹形状を有する目的とする製品を製作できた。各試料の密度、熱伝導率、熱膨張率、内底面平面度および３σは、いずれも良好な値であった。尚、密度については、各試料共に５個を測定した平均値である。
【００３３】
【表２】

【００３４】
これらのリッド型放熱基板を、半導体パッケージに接合された半導体素子の上に樹脂で接合し半導体装置を作製した。その放熱特性は表２の測定結果から予想されるとおり優れていて、近年高性能化が著しい半導体素子の能力を十分発揮できる半導体装置を得ることができた。また、スティフナーを用いたものと比較すると、高い精度を実現しているため、高歩留まりで、実用的な信頼性を有する半導体装置を得ることができた。すなわち、価格性能比の極めて高い、半導体装置を実現することが可能となった。
【００３５】
（実施例２）
平均粒径３０μｍのＳｉＣ粒子と平均粒径２０μｍ市販のＡｌ粉末および市販の珪素粉末を用意した。これらの粉末を表３の質量ベースの各試料組成比率にて、混合した。この混合粉末を転造流動層に投入し、１０質量％ポリビニルアルコール水溶液を投入質量として全体の１質量％となるまで、スプレーにて流動層中の粉末に塗布することにより、調製した混合材料を製作した。このときの粉末の嵩密度を測定したところ、各粉末とも１．０５〜１．２０ｇ／ｃｍ^３の嵩密度であった。この調製した粉末を用いて実施例１と同様に成型体を製作した。このようにして得られた成形体の、底部と足部の密度を測定し、その差を求めて表３の密度差の欄に記載した。約１５〜２０％足部の密度が低かった。
【００３６】
この成形体を窒素雰囲気のベルト炉にて６４５℃まで昇温し、３０分キープしたのち、降温し、焼結体を製作した。得られた焼結体は、実施例１と同様に大気中で熱間鍛造された。熱間鍛造の条件は、圧力が８ｔｏｎ／ｃｍ^２（７８４ＭＰａ）、保持時間を５秒とし、温度を表３に示した。
【００３７】
【表３】

【００３８】
以上の結果から以下のことが判る。本発明のＳｉＣ量の範囲内では、内底面の平面度が１ｍｍあたり０．５μｍ以下となる所望の製品を製作できる。又、得られた製品の内底面の平面度およびリッド深さｄを測定し実施例１と同様に標準偏差σを求めた。表４に示すように、各試料の密度、熱伝導率、熱膨張率、内底面平面度および３σは、いずれも良好な値であった。尚、密度については、各試料共に５個を測定した平均値である。
【００３９】
【表４】

【００４０】
【発明の効果】
本発明は、Ａｌ−ＳｉＣ系の焼結体を熱間鍛造することにより、内底面の平面度が高く、リッド深さのバラツキが小さいリッド型放熱基板を提供する。上記のように寸法精度の高いリッド型放熱基板を半導体素子に樹脂接合するとき、樹脂層の厚さを薄くすることができる。接合に用いる樹脂は、熱伝導率が小さいのでこれを薄くすることにより、放熱効率を高めることができる。その上、本発明のリッド型放熱基板は、研削や切削しないので安価な放熱基板を提供できる。
【図面の簡単な説明】
【図１】図１は、本発明に係るリッド型放熱基板を用いた半導体装置の断面図である。
【図２】図２は、本発明に係るリッド型放熱基板を示し、（Ａ）はその底面図、（Ｂ）は（Ａ）のＡ−Ａ断面図である。
【図３】図３は、本発明に係るリッド型放熱基板を作製するための金型の動きを説明するための断面図で、図３（Ａ）は、粉末を供給した状態を示し、図３（Ｂ）は、成形した状態を示す断面図である。
【図４】従来の放熱基板であって、スティフナーを有する半導体装置の断面図である。
【符号の説明】
１リッド型放熱基板
２樹脂
３半田ボール
４半導体素子
５放熱基板
６スティフナー
７基板の上面
８底部
９リッド足部
１０半導体パッケージ
１１足部底面
１２リッド側面
１３内底面
２１上杵
２２臼
２３下杵
２４粉末
Ｌ１、Ｌ２放熱基板の幅と長さ
Ｌ３内底面の対角長さ。
Ｗ１、Ｗ２足の幅
ｄリッド深さ
ｔ底部の厚さ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat radiation substrate useful for a semiconductor device, particularly to a heat radiation substrate composed mainly of a composite material containing SiC and silicon and Al, a method of manufacturing the same, a package using the same, and a semiconductor device.
[0002]
[Prior art]
The performance and functionality of semiconductor elements have been increasing year by year, and accordingly, the form of packages on which semiconductor elements are mounted has changed in various ways. Among them, the package structure shown in FIG. 4 corresponding to the increase in the number of input / output terminals has come to be used. This structure is characterized in that the semiconductor element 4 and the semiconductor package 10 are joined by a method using flip chip mounting (Flip Chip). In this structure, a plate-shaped heat dissipation board 5 and a frame-shaped metal member called a stiffener 6 for supporting the board are used. A package member such as a heat radiating substrate is required to be lightweight and have excellent thermal conductivity and be able to cope with diversification of shapes. Recently, a composite material (hereinafter, this composite material is referred to as Al-SiC), which combines light weight silicon carbide (hereinafter, referred to as SiC) and aluminum (hereinafter, referred to as Al), which has excellent thermal conductivity, has attracted attention.
[0003]
Patent Literature 1 discloses an Al—SiC-based composite material obtained by a liquid phase sintering method and having a thermal conductivity of 180 W / (m · K) or more. This composite material contains, for example, a mixed powder of 10 to 70% by weight of particulate SiC powder and Al powder, and then contains 99% or more of nitrogen, has an oxygen concentration of 200 ppm or less, and has a dew point of -20 ° C or less. It is obtained by a step of sintering at 600 to 750 ° C. in an oxidizing atmosphere. It is disclosed that recompression can be further performed in a non-oxidizing atmosphere, and further heat treatment can be performed after recompression. The purpose of these is to improve the dimensional accuracy and to remove the remaining pores to achieve densification.
[0004]
Patent Literature 2 proposes a method of manufacturing a composite material by combining a normal pressure sintering method and a HIP method. According to this, for example, a compact of an Al-SiC-based mixed powder in which 10 to 70% by weight of particulate SiC is mixed is placed in a non-oxidizing atmosphere containing 99% or more of nitrogen gas at a temperature of 600 ° C or more and a melting temperature of Al or less. Normal pressure sintering in the temperature range. Next, by being sealed in a metal container and subjected to HIP at a temperature of 700 ° C. or higher, an Al—SiC composite material having a uniform thermal conductivity of 200 W / (m · K) or higher is obtained. It also discloses that hot forging is performed after sintering. The purpose of hot forging is to obtain a material having a high thermal conductivity and a coefficient of thermal expansion of 10 × 10 ⁻⁶ / K or less.
[0005]
[Patent Document 1]
JP-A-10-335538, page 2, page 12, column 22, line 6-10
JP-A-11-310843, page 2, Table 3
[0006]
[Problems to be solved by the invention]
As the performance of semiconductor elements has improved, the amount of heat generated from the semiconductor elements has increased. The heat radiation from the semiconductor element is transmitted to the heat radiation substrate 5 via the resin 2 applied on the semiconductor element 4, as shown in FIG. 4, for example. Since the thermal conductivity of the resin applied to the heat radiating substrate 5 is considerably low, about 1/10 to 1/20 of the heat radiating substrate, it is necessary to reduce the thickness of the resin 2. In the semiconductor device composed of a simple plate-shaped heat radiation substrate 5, a stiffener 6, and a semiconductor package 10 used in FIG. 4, the height is accurately maintained because two places on both sides of the stiffener 6 are joined by the resin 2. Difficult to do. However, if a lid-type heat dissipation board is used, the number of joining points is one, so that the structure is more easily provided with accuracy, and the case of a lid-type shape is advantageous.
[0007]
However, when the lid-type heat dissipation board 1 as shown in FIG. 1 is manufactured by powder metallurgy, variations in the flatness of the inner bottom surface 13 and variations in the lid depth, that is, variations in the height of the lid foot 9 from the inner bottom surface 13 are precisely determined. Difficult to control. This is because it is difficult to supply powder in proportion to the thickness of each part when supplying powder to the mold because the thickness is different between the lid feet 9 and the bottom 8 of the lid-type heat dissipation board 1. Distortion or so-called shrinkage occurs at different boundaries and the like, resulting in poor dimensional accuracy. That is, in order to manufacture a lid-type heat dissipation substrate in which the flatness of the inner bottom surface 13 is 0.5 μm or less per 1 mm in a diagonal direction using an Al—SiC-based composite material, grinding or cutting is an essential step. .
[0008]
Therefore, a product having a satisfactory price-performance ratio as a heat dissipation board has not been disclosed. Further, it has been difficult to obtain a product satisfying the price-performance ratio by any of the conventional casting method, infiltration method, sintering method, hot pressing method and a combination thereof. Therefore, an object of the present invention is to provide an Al-SiC-based lid-type heat radiation substrate that is inexpensive and maintains high dimensional accuracy without cutting or grinding.
[0009]
[Means for Solving the Problems]
In the present invention, the above problem is solved.First, even in a sintered body in which the density of the lid foot is lower than the density of the bottom, mass transfer from the bottom to the foot of the lid is performed by the next hot forging to make the density uniform. The problem is solved using a revolutionary method of increasing the flatness.
[0010]
TECHNICAL FIELD The present invention relates to an Al—SiC-based semiconductor heat dissipation substrate, and the semiconductor heat dissipation substrate is made of a composite material containing 50 to 80% by mass of SiC and silicon and Al, and has a rectangular frame with a bottom having a bottom. This is a semiconductor heat radiating substrate, wherein the flatness of the inner bottom surface at the bottom is 0.5 μm or less per 1 mm in a diagonal direction. The flatness is measured by measuring a displacement in a height direction by a surface roughness meter along a diagonal line of an inner bottom surface of a lid-type heat radiation board placed on a surface plate. Next, on the measurement chart, the start point and the end point are connected by a straight line, and the distance from the straight line to the farthest point is divided by the measured length. It is desirable that the measurement length be at least half the diagonal length of the inner bottom surface.
[0011]
The method of the present invention includes a molding step of molding a composite material containing 50 to 80% by mass of SiC and silicon and Al into a lid mold, and a sintering step of sintering the molded body at a temperature equal to or lower than the melting point of Al. And a method for manufacturing a semiconductor heat dissipation substrate including a hot forging step of hot forging a sintered body. By adopting such a method, a cutting and grinding process is not required, and a semiconductor heat dissipation substrate having a high price-performance ratio can be provided. The atmosphere of the hot forging is desirably in the air.
[0012]
SiC contained in the heat dissipation substrate is 50 to 80% by mass. When the content of SiC is less than 50% by mass, the strength of the Al alloy is reduced when the temperature of the sintered body is increased in the atmosphere during forging, and it becomes difficult to handle products during hot forging. Further, when the content of SiC is more than 80% by mass, the component amount of the Al alloy is too small when the molded body is sintered, and it is difficult to perform sintering. In addition, if it is in this range, the coefficient of thermal expansion of the semiconductor heat dissipation substrate can be kept in a range of 13 × 10 ⁻⁶ / K or less.
[0013]
It is desirable that the surface of the semiconductor heat dissipation board be kept hot forged. In general, a sintered Al body is likely to cause color unevenness, and the surface of a sintered body or a hot forged one is usually subjected to barrel processing or light blast processing. Therefore, the term “hot forged” as used herein means a state in which grinding or cutting is not performed, and includes a state in which barrel processing or light blasting is performed. In the present invention as well, it is desirable to remove the burrs at the corners of the hot forged product, and to perform barrel treatment or light blast treatment for the purpose of rounding and removing the color unevenness. At this time, color unevenness and the like remain at the corners of the inner bottom surface, indicating that barrel processing and blast processing have been performed.
[0014]
The semiconductor substrate and the method of manufacturing a semiconductor according to the present invention desirably contain silicon in an amount of 0.05 to 1% by mass of the sintered body. Silicon melted in Al has a function of increasing the wettability of SiC and Al and a function of lowering the viscosity of the molten metal. If the silicon content exceeds 1% by mass, the silicon component reacts with Al to form an Al-Si alloy, the melting point decreases, and the viscosity of the molten metal decreases. As a result, the sintered body is preheated at the time of hot forging, and at that time, the molten Al-Si oozes out of the product, and it is difficult to maintain the shape, and the molten metal leaks from the mold at the time of hot forging. there is a possibility. On the other hand, when the content is less than 0.05% by mass, the wettability of SiC and Al becomes insufficient, and the viscosity becomes high, so that hot forging takes time.
[0015]
It is desirable that the average particle size of SiC is in the range of 4 to 50 μm. Since SiC forms the skeleton of the sintered body, it serves as a support during molding and hot forging. It is actually the function of SiC that the shape can be maintained when preheating is performed before hot forging. If the average particle size of the SiC exceeds 50 μm, the SiC is cracked during hot forging, which causes a reduction in the thermal conductivity of the product. On the other hand, if it is less than 4 μm, the strength of the compact is insufficient.
[0016]
Further, in the present invention, it is desirable that the lid depth d is in the range of d ₀ ± 50 μm. However d ₀ denotes the average value of the lid depth. When the thickness exceeds the range of ± 50 μm, when assembled into a package or a semiconductor device, the thickness of the joining resin becomes large, and the heat dissipation becomes poor.
[0017]
In the lid-type heat dissipation board of the present invention, the diagonal length L3 of the inner bottom surface of the heat dissipation board is preferably 30 mm or more. The size of the lid is determined by the diagonal length L3 of the lid, and includes various types from an elongated rectangle to a square.
[0018]
Referring to FIG. 2, a value obtained by dividing the sum (d + t) mm of lid depth d and bottom thickness t by the area (L1 mm × L2 mm) of upper surface 7 of the substrate, (d + t) / (L1 × L2) Desirably, the value is between 0.0001 and 0.004 mm ^-1 . The meaning of this numerical value means that, for example, when the area of the upper surface of the substrate is 50 mm × 50 mm, the thickness is desirably between 0.25 mm and 10 mm. More desirable values are such that the thickness t of the bottom portion is 1 to 4 mm and the depth d of the lid is 0.3 to 0.9 mm.
[0019]
In the hot forging in the method of the present invention, the temperature is preferably in the range of 650 to 800C in the atmosphere. Below 650 ° C., the viscosity of the Al alloy is low. On the other hand, if the temperature exceeds 800 ° C., the viscosity of Al in the product becomes too low, so that Al is easily eluted from the product and sticks to the mold.
[0020]
The present invention further provides a package on which the above-mentioned lid type heat dissipation board is mounted. Another object of the present invention is to provide a semiconductor device having the above-described lid-type heat dissipation substrate and having a high price-performance ratio.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
The lid-type heat radiation board of the present invention has a so-called lid shape in which a plate-like body thinner than the height of the frame is fitted into the bottom of the rectangular frame. In this invention, the frame is called a lid foot, and the plate is called a bottom. The sintered body as shown in FIGS. 1 and 2 obtained during the present invention is a porous sintered body in which the density of the lid feet 9 of the sintered body is reduced and the density of the other bottoms 8 is increased. Body. This sintered body is provided with an escape area for the excess thickness in the porous portion. Therefore, after the mass transfer is caused by hot forging and the densities of the lid foot 9 and the bottom 8 are made uniform, no distortion occurs, and a product that does not require machining or grinding is obtained. Note that, in the present invention, the lid foot 9 is a portion extending from the foot bottom surface 11 to the upper surface 7 of the substrate.
[0022]
In the lid type heat dissipation board of the present invention, the diagonal length L3 of the inner bottom surface of the heat dissipation board is preferably 30 mm or more, and the widths W1 and W2 of the feet are preferably 1 to 10 mm. The size of the lid was defined by the diagonal length L3 of the inner bottom surface. In the present invention, since a molding die or a forging die is used, the corners of each part are rounded by about 0.5 mm or chamfered by 0.5 mm corresponding to the corners of the mold.
[0023]
The lid type heat dissipation board of the present invention is manufactured as follows. First, a mixed powder containing SiC and silicon and Al as main components is prepared. Next, the powder 24 is put into a mold having a sectional shape shown in FIG. At this time, since the powder is granulated by the spray dryer, when the powder is filled in the mold, the powder is uniformly supplied to the space of the mold. Next, the upper punch 21 is moved downward, and the lower punch 23 is moved upward, so that the powder 24 is compressed in the mortar 22 to the state shown in FIG. At this time, since the compression ratios of the lid foot 9 and the bottom 8 are different, a difference in molding density occurs. Technically speaking, by appropriately moving the die 22, the upper punch 21, and the lower punch 23 during molding, the density difference between the lid foot 9 and the bottom 8 of the molded body itself can be reduced. However, the equipment becomes complicated, and the adjustment also requires skill. The present invention has solved such a problem by introducing a hot forging method.
[0024]
The specific reason that the lid depth d is desirably in the range of d ₀ ± 50 μm will be described with reference to the drawings. As shown in FIG. 1, a semiconductor element 4 is joined to a semiconductor package 10 by a solder ball 3, and a lid-type heat dissipation board 1 is joined to the semiconductor element 4 by a resin 2. Since the thermal conductivity of the resin is as low as about 1/10 to 1/20 of that of the heat dissipation board, it is necessary to reduce the thickness of the resin as much as possible. For this purpose, it is desirable that the variation in the lid depth d be 50 μm or less. The lid depth is obtained by placing the lid-type heat dissipation substrate on a surface plate and measuring the height from the inner bottom surface 13 to the foot bottom surface 11 using a dial gauge. In order to minimize the influence of the warpage of the inner bottom surface, it is preferable that the difference in height from the inner bottom surface 13 immediately below the measurement point of the foot bottom surface 11 be the lid depth.
[0025]
It is important to control the bulk density of the prepared powder. Bulk density, 0.9~1.3g / cm ³ are suitable. It is difficult to adjust the bulk density to less than 0.9 g / cm ³ . When the bulk density is larger than 1.3 g / cm ³ , the powder hardly moves during molding, and although the bottom is solidified, the lid foot is not solidified and a desired molded body cannot be obtained. The obtained compact is sintered under normal pressure in a non-oxidizing atmosphere containing 99% or more of nitrogen gas in a temperature range equal to or lower than the melting point of Al to obtain a sintered body.
[0026]
In the method of the present invention, the temperature of the hot forging is preferably in the range of 650 to 800 ° C. At the time of hot forging, the mold and the product tend to stick to each other, so it is desirable to apply an anti-sticking agent to the mold. In the present invention, it has been determined that a method in which carbon is suspended in water and applied in an appropriate amount by spraying to evaporate the water is optimal. Other methods include a method of applying boron nitride and a method of applying titanium nitride to a product in advance. These surface deposits can be easily removed in a subsequent surface treatment step.
[0027]
As described above, the composite material of the present invention is capable of mass-producing inexpensively a large number of products containing 50 to 80% by mass of SiC and having a flatness of the inner bottom surface of 0.5 μm or less per 1 mm in a diagonal direction. Become. Since the semiconductor heat dissipation substrate made of such a composite material has excellent thermal conductivity and thermal expansion coefficient, it has good compatibility with semiconductor elements used in packages and semiconductor devices and its peripheral members.
[0028]
(Example 1)
An Al alloy powder containing SiC particles having an average particle diameter of 10 μm and 0.5% by mass of Si by melt injection (atomization) having an average particle diameter of 50 μm was prepared. These powders were mixed according to the raw material composition shown in Table 1. This mixed powder and 1% by mass of polyvinyl alcohol were mixed, and water was further added to prepare a slurry. This slurry was dried with a spray dryer in a nitrogen atmosphere to produce a mixed powder. When the bulk density of the powder at this time was measured, each powder had a bulk density of 0.95 to 1.05 g / cm ³ .
[0029]
A molded body having the shape shown in FIG. 2 was manufactured using the prepared powder. The density of the bottom part 8 and the lid foot part 9 of the molded article thus obtained was measured, and the difference was determined and described in the column of density difference in Table 1. Approximately 15-20% lid foot density was low. The width L1 and length L2 of the heat dissipation board in FIG. 2 are 40 mm, the diagonal length L3 of the inner bottom surface is 40 mm, the thickness (d + t) of the lid side surface 12 is 3.0 mm, t is 2.3 mm, W1 and W2. Is 5.9 mm. The molded body was heated to 645 ° C. in a belt furnace in a nitrogen atmosphere, kept for 30 minutes for sintering, and then cooled to produce a sintered body.
[0030]
[Table 1]

[0031]
Next, the obtained sintered body was hot forged using a hot forging machine so as to have the same shape as the compact. The conditions of the hot forging were such that the pressure was 8 ton / cm ² (784 MPa), the holding time was 5 seconds, and the temperature was shown in Table 1.
[0032]
After barrel treatment of the obtained lid-type heat dissipation substrate, the density, thermal conductivity, coefficient of thermal expansion, and flatness of the inner bottom surface of each sample were measured. The variation of the lid depth d was evaluated by 3σ when the standard deviation was σ, and is shown in Table 2. Within the range of the amount of SiC according to the present invention, a target product having a concave shape on one side with a flatness of the inner bottom surface of 0.5 μm or less per 1 mm could be produced. The density, thermal conductivity, coefficient of thermal expansion, inner bottom flatness, and 3σ of each sample were all good values. The density is an average value obtained by measuring five samples for each sample.
[0033]
[Table 2]

[0034]
These lid type heat radiating substrates were joined with a resin on a semiconductor element joined to a semiconductor package to produce a semiconductor device. The heat radiation characteristics are excellent as expected from the measurement results in Table 2, and a semiconductor device capable of sufficiently exhibiting the performance of a semiconductor element whose performance has been remarkably improved in recent years has been obtained. Further, as compared with a device using a stiffener, high accuracy is realized, and thus a semiconductor device having high yield and practical reliability can be obtained. That is, it has become possible to realize a semiconductor device having an extremely high price-performance ratio.
[0035]
(Example 2)
SiC particles having an average particle size of 30 μm, a commercially available Al powder having an average particle size of 20 μm, and a commercially available silicon powder were prepared. These powders were mixed in each sample composition ratio on a mass basis in Table 3. This mixed powder was charged into a rolling fluidized bed, and the prepared mixed material was applied by spraying to a powder in the fluidized bed by spraying until a 10% by weight aqueous solution of polyvinyl alcohol was added to 1% by weight of the whole. Made. When the bulk density of the powder at this time was measured, each powder had a bulk density of 1.05 to 1.20 g / cm ³ . A molded body was produced in the same manner as in Example 1 using the prepared powder. The density of the bottom part and the foot part of the thus obtained molded body was measured, and the difference was determined. The difference was shown in the column of density difference in Table 3. Approximately 15-20% foot density was low.
[0036]
This molded body was heated to 645 ° C. in a belt furnace in a nitrogen atmosphere, kept for 30 minutes, and then cooled to produce a sintered body. The obtained sintered body was hot forged in the air in the same manner as in Example 1. The conditions of the hot forging were such that the pressure was 8 ton / cm ² (784 MPa), the holding time was 5 seconds, and the temperature was shown in Table 3.
[0037]
[Table 3]

[0038]
From the above results, the following can be understood. Within the range of the amount of SiC of the present invention, a desired product in which the flatness of the inner bottom surface is 0.5 μm or less per 1 mm can be manufactured. Further, the flatness of the inner bottom surface and the lid depth d of the obtained product were measured, and the standard deviation σ was obtained in the same manner as in Example 1. As shown in Table 4, the density, thermal conductivity, thermal expansion coefficient, inner bottom flatness, and 3σ of each sample were all good values. The density is an average value obtained by measuring five samples for each sample.
[0039]
[Table 4]

[0040]
【The invention's effect】
The present invention provides a lid-type heat-dissipating substrate having a high flatness of an inner bottom surface and a small variation in a lid depth by hot forging an Al-SiC-based sintered body. When the lid-type heat dissipation board having high dimensional accuracy as described above is resin-bonded to the semiconductor element, the thickness of the resin layer can be reduced. Since the resin used for bonding has a small thermal conductivity, the heat dissipation efficiency can be increased by reducing the thickness of the resin. In addition, the lid-type heat-dissipating substrate of the present invention can provide an inexpensive heat-dissipating substrate without grinding or cutting.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a semiconductor device using a lid-type heat dissipation board according to the present invention.
FIGS. 2A and 2B show a lid-type heat dissipation board according to the present invention, wherein FIG. 2A is a bottom view thereof and FIG. 2B is a sectional view taken along line AA of FIG.
FIG. 3 is a cross-sectional view for explaining the movement of a mold for producing a lid-type heat dissipation substrate according to the present invention. FIG. 3 (A) shows a state in which powder is supplied. FIG. 3B is a cross-sectional view showing a molded state.
FIG. 4 is a cross-sectional view of a semiconductor device having a stiffener, which is a conventional heat dissipation substrate.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 lid type heat radiating substrate 2 resin 3 solder ball 4 semiconductor element 5 heat radiating substrate 6 stiffener 7 upper surface of substrate 8 bottom 9 lid foot 10 semiconductor package 11 foot bottom 12 lid side 13 inner bottom 21 upper punch 22 dies 23 lower punch 24 Powder L1, L2 Width and length of heat dissipation board L3 Diagonal length of inner bottom surface.
W1, W2 Foot width d Lid depth t Bottom thickness

Claims

In the Al-SiC based semiconductor heat radiating substrate, the semiconductor heat radiating substrate is a lid-type heat radiating substrate formed of a composite material containing 50 to 80% by mass of SiC and silicon and Al and having a bottom in a rectangular frame. Wherein the flatness of the inner bottom surface of the bottom is 0.5 μm or less per 1 mm in a diagonal direction.

The semiconductor heat dissipation board according to claim 1, wherein the surface of the semiconductor heat dissipation board is hot forged.

3. The semiconductor heat dissipation board according to claim 1, wherein said silicon is 0.05 to 1% by mass of the composite material.

The semiconductor heat dissipation substrate according to any one of claims 1 to 3, wherein the SiC has an average particle diameter of 4 to 50 m.

The semiconductor heat dissipation board according to any one of claims 1 to 4, wherein a variation range of the lid depth (d) is ± 50 µm.

The semiconductor heat dissipation board according to any one of claims 1 to 5, wherein a diagonal size L3 of an inner bottom surface of the lid is 30 mm or more.

The value obtained by dividing the sum (d + t) mm of the lid depth d and the bottom thickness t by the area of the upper surface of the substrate (L1 mm × L2 mm) is 0.0001 to 0.004 mm ^−1. 7. The semiconductor heat dissipation board according to any one of claims 6 to 6.

A forming step of forming a composite material containing 50 to 80% by mass of SiC and silicon and Al into a lid, a sintering step of sintering the formed body at a temperature equal to or lower than the melting point of Al, A method for manufacturing a semiconductor heat dissipation board, comprising a hot forging step of forging.

9. The method according to claim 8, wherein in the hot forging step, the atmosphere is in the air.

The method according to any one of claims 8 to 9, wherein in the hot forging step, a temperature of the hot forging is 650C to 800C.

A package mounted with the semiconductor heat dissipation substrate according to claim 1.

A semiconductor device on which the semiconductor heat dissipation board according to claim 1 is mounted.