JP3562042B2

JP3562042B2 - Ceramic substrate and method of manufacturing the same

Info

Publication number: JP3562042B2
Application number: JP17904995A
Authority: JP
Inventors: 浩平下田; 博彦仲田
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1995-07-14
Filing date: 1995-07-14
Publication date: 2004-09-08
Anticipated expiration: 2015-07-14
Also published as: JPH0925186A

Description

【０００１】
【産業上の利用分野】
本発明は、ＩＣの回路基板やパッケージをはじめとする電子デバイス等に使用されるセラミックス基板、特に高い熱伝導率を有し、放熱性に優れた窒化アルミニウムからなるセラミックス基板、及びその製造方法に関する。
【０００２】
【従来の技術】
窒化アルミニウム（ＡｌＮ）の熱伝導率は、理論値としては３２０Ｗ／ｍ・Ｋであり、この値は金属アルミニウムの１．５倍に相当する。この高い熱伝導率に加えて、窒化アルミニウムは高い絶縁性と機械的強度を備え、金属導体と容易に接合できるといった優れた特性を有するため、ＩＣの回路基板やパッケージ材料として注目を集めている。
【０００３】
一般に、窒化アルミニウムを回路基板やパッケージとして用いる場合、窒化アルミニウム基板の表面を研磨加工した上で、その基板表面にメタライズ層又はめっき層等の金属化層を形成することが必要である。又、この金属化層を介して窒化アルミニウム基板上に表面平滑性に優れたポリイミド層を形成し、そのポリイミド層上に微細配線を形成して回路基板とすることも行われている。
【０００４】
【発明が解決しようとする課題】
ところが、窒化アルミニウム基板表面に形成した金属化層には欠けや膨れ等が発生しやすく、金属化層の層厚が薄くなると欠けや膨れの発生が増大する傾向にあり、特に層厚が２０μｍ以下においてその傾向が顕著になるという欠点があった。同様に、この金属化層の上に設けるポリイミド層においても、欠けが発生したり、ポリイミド層形成時に発泡が生じるという問題があった。
【０００５】
これらの欠陥の発生は、窒化アルミニウム基板に存在する空孔が原因ではないかと考えられている。即ち、窒化アルミニウム基板は本質的に粉末を焼結して得た焼結体であるため、一般的に直径２０〜５０μｍ程度の球形状の空孔の存在が避けられず、基板表面に存在する空孔の上で金属化層やポリイミド層に欠けや膨れ等の欠陥が発生するとされている。
【０００６】
そこで従来は、金属化層やポリイミド層を厚くすることにより、その欠けや膨れ等の欠陥の発生を低減させる方法が採られていた。しかし、金属化層の層厚が厚くなると、回路配線を微細化させる場合に配線間の絶縁を十分確保することができなくなる。このため、金属化層を厚くすることには限界があり、特に線幅１００μｍ以下のような微細配線を形成する場合は、配線間の絶縁確保のため層厚の薄い金属化層が求められ、中でも層厚２０μｍ以下の金属化層ではその欠けや膨れの発生が大きな問題となっていた。
【０００７】
また、ポリイミド層についても層厚が厚くなると欠け等の欠陥が発生しやすいので、層厚を３００μｍ以上とすることにより微細配線形成時の欠けや膨れ等を低減することが行われている。しかし、この方法では、回路配線の電気特性には優れるものの、熱伝導性に劣るポリイミド層が極めて厚くなるため、回路基板の放熱性の低下を招くという問題があった。
【０００８】
このように、従来の窒化アルミニウム基板においては、その表面上に形成する金属化層やポリイミド層に欠けや膨れ等の欠陥が発生しやすく、これらの欠陥をなくすため金属化層やポリイミド層の厚さを厚くすれば、回路配線の微細化に支障を来したり、放熱性を低下させるといった問題があった。
【０００９】
本発明は、かかる従来の事情に鑑み、表面に形成する金属化層やポリイミド層に欠けや膨れ等の欠陥が発生せず、特に微細配線の形成に適した窒化アルミニウム基板及びその製造方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
上記目的を達成するため、本発明が提供する窒化アルミニウム基板は、周期律表の２Ａ族、３Ａ族元素の化合物の少なくとも１種を当該元素換算で０．１〜１５重量％含有し、非球形状の空孔を含む窒化アルミニウム基板であって、研磨加工を施した表面に現れている前記空孔の深さに対する長さの比が５．０以上で且つ深さが１０μｍ以下であることを特徴とする。
【００１１】
また、本発明によるセラミックス基板の製造方法は、周期律表の２Ａ族、３Ａ族元素の化合物の少なくとも１種を当該元素換算で０．１〜１５重量％含有する窒化アルミニウム焼結体を、１ｋｇ／ｃｍ^２以上の圧力で１軸方向に加圧しながら１３００℃以上の温度にて熱処理した後、研磨加工面を前記加圧軸とほぼ直角方向にして表面研磨加工することを特徴とする。
【００１２】
【作用】
窒化アルミニウム焼結体は、本質的に粉末を焼結して得られるので、一般的に直径２０〜５０μｍ程度の球形状の空孔の存在が避けられない。この空孔は焼結体内部に存在していても、表面研磨加工を施した基板においては表面に現れてくる。本発明者らは、特にこの表面に現れた空孔の形状が、表面上に形成される金属化層やポリイミド層の欠けや膨れ等の欠陥の発生に影響を及ぼすことを突き止めた。
【００１３】
即ち、研磨加工を施した基板表面に現れる空孔の形状について詳細に検討した結果、表面に現れている空孔の長さＬｍと深さＴｍの比と、微細配線形成時の不良発生率との間に相関関係が存在することを見いだした。具体的には、表面に現れている空孔の形状が非球形状に偏平になり、その表面からの深さＴｍに対する表面上での長さＬｍの比Ｌｍ／Ｔｍが５．０以上になると、金属化層等の欠けや膨れがなくなり、微細配線の不良発生率が低減する。ここで、非球形状の空孔の長さ（Ｌｍ）とは、基板表面に現れている空孔の最も長い部分における長さを言う。
【００１４】
更に、より安定した微細配線の形状について検討を重ねた結果、基板表面に現れている非球形状空孔の深さＴｍがある一定レベル以上に深くなると、微細配線の断線等の発生頻度が急激に高くなることが判った。その深さＴｍのレベルは配線の種類や厚さ等にもよるが、概ね１２〜２０μｍ程度である。特に、表面に現れている非球形状空孔の深さＴｍが１０μｍ以下であると、微細配線の形成に特に優れていることが判った。
【００１５】
尚、金属化層等の欠けや膨れをなくすためには、基板表面に現れている全ての空孔が、上記の特徴を備えた非球形状空孔であることが必要である。この非球形状空孔の長さＬｍは、微動測定ステージを備えた倍率１００〜１０００倍の金属顕微鏡等による目視測定若しくは写真測定により求めることができる。又、この非球形状空孔の深さＴｍは、同じく倍率１００〜１０００倍の金属顕微鏡等を用いて、光学的測定法として一般的に知られている焦点深度法により求めることができる。尚、本発明では便宜上任意の視野を選んで行うものとする。以上により求めたＬｍ及びＴｍの結果から、表面に現れた空孔の深さに対する長さの比Ｌｍ／Ｔｍを算術的に求めることができる。
【００１６】
セラミックス基板の研磨加工を施した表面の微細な凹凸も、上記した空孔の形状ほどではないが、微細配線の形成に影響を与える。セラミックス基板表面の表面粗さＲａ（ＪＩＳＢ０６０１に基づいて測定）が０．２μｍを越えると、金属化層の膨れなどによる微細配線の不良発生率が増加しやすい。
【００１７】
表面の研磨加工により上記のような表面平滑性に優れた窒化アルミニウム基板を得るためには、ＡｌＮ結晶粒の平均結晶粒径が１５μｍ以下であることが好ましい。ＡｌＮ結晶粒の平均結晶粒径は、基板の破面における各粒子の最大寸法を走査型電子顕微鏡（ＳＥＭ）の２次平面上で観測し、３０個以上の粒子の算術平均として求める。
【００１８】
一般に窒化アルミニウム焼結体中の空孔は等方性を有する球形状であり、特異方向に歪んだ形状の空孔は存在しない。特に、本発明のごとく、表面に現れた空孔の深さに対する長さの比Ｌｍ／Ｔｍが５．０以上という一方向に大きく歪んだ非球形状の空孔を有する窒化アルミニウム焼結体は、従来知られておらず、空孔形状の制御を考慮した製法でなければ製造することができない。
【００１９】
そこで、本発明方法では、この非球形状の空孔を有する窒化アルミニウム焼結体からなる基板を得るため、塑性変形を助長する副成分を含有した窒化アルミニウム焼結体に１軸方向の加圧熱処理を加えることにより、焼結体中の球形状空孔を加圧軸方向に圧し潰して非球形状に変形させる。
【００２０】
まず、そのための窒化アルミニウム焼結体は、上記副成分として周期律表の２Ａ族、３Ａ族元素の化合物の少なくとも１種をその元素換算で０．１〜１５重量％含有する必要がある。その理由は、窒化アルミニウムは共有結合が強く、且つ六方晶型の結晶形態となるため、熱処理を行っても限られた条件下でしか粒界滑り、塑性変形が生じず、目的とする一方向に歪んだ非球形状の空孔を有する焼結体が得られないためである。
【００２１】
そこで、窒化アルミニウム焼結体に周期律表の２Ａ族、３Ａ族元素の化合物の少なくとも１種を含有させることにより、これらの副成分の化合物が粒界に存在して、加圧熱処理時にＡｌＮ結晶の粒界滑りを促進し、その結果十分な変形能が付与され、目的とする深さに対する長さの比Ｌｍ／Ｔｍが５．０以上という一方向に大きく歪んだ非球形状の空孔を有する焼結体が得られる。焼結体中に存在してかかる作用を果す化合物としては酸化物、例えばＹ_２Ｏ_３、ＹＡＧ（３Ｙ_２Ｏ_３・５Ａｌ_２Ｏ_３）、ＹＡＬ（Ｙ_２Ｏ_３・Ａｌ_２Ｏ_３）、ＹＡＭ（２Ｙ_２Ｏ_３・Ａｌ_２Ｏ_３）、３ＣａＯ・Ａｌ_２Ｏ_３、ＣａＯ・Ａｌ_２Ｏ_３等のほか、窒化物ＹＮ、酸窒化物Ｙ−Ａｌ−Ｏ−Ｎ等がある。
【００２２】
上記副成分の含有量が元素換算で０．１重量％未満では粒界滑りの効果が不十分となり、逆に１５重量％を越えると窒化アルミニウム焼結体の熱伝導率の低下が顕著となるため、共に好ましくない。又、窒化アルミニウム焼結体中の炭素量が多い場合にも加圧熱処理時の粒界滑りが困難となりやすいため、炭素含有量は０．０５重量％以下であることが好ましい。
【００２３】
上記副成分を含む窒化アルミニウム焼結体は、副成分の化合物粉末又はこれらの液状体を原料粉末に混合し、通常のごとく焼結することにより製造される。この加圧熱処理前の窒化アルミニウム焼結体の平均結晶粒径は１５μｍ以下であることが好ましい。平均粒径が１５μｍより大きくなると、加圧熱処理時の粒界滑りと塑性変形が生じにくく、目的とする非球形状の空孔を得ることが難しくなるからである。又、加圧熱処理前の焼結体の密度は、相対密度９０％以上であることが好ましい。
【００２４】
上記の副成分を含む窒化アルミニウム焼結体は、次に加圧熱処理が施される。加圧熱処理における加圧力は１ｋｇ／ｃｍ^２以上とし、一方向に圧し潰された形状の空孔を得るため１軸方向に加圧する。加圧力が１ｋｇ／ｃｍ^２未満では、目的の非球形状の空孔を得るために長時間を必要とし、経済性の低下を招く。又、加圧力が１０００ｋｇ／ｃｍ^２を越えると、加圧設備のコスト上昇を招くので好ましくない。
【００２５】
又、加圧熱処理の温度が１３００℃未満では、焼結体の塑性変形能が不十分であるため空孔が圧し潰されず、目的の非球形状の空孔を得ることができない。従って、加圧熱処理の温度は１３００℃以上とするが、大気雰囲気の場合は１５００℃を越えると酸化による変質が生じやすく、その他のガス雰囲気の場合は２１００℃を越えるとＡｌＮの分解が始まるので好ましくない。尚、加圧熱処理の雰囲気としては、真空、大気、その他の窒素、水素、アルゴン等のガス雰囲気を用いることができ、大気やガス雰囲気の場合は加圧雰囲気でも良い。
【００２６】
加圧熱処理の後、非球形状に圧し潰された空孔を有する窒化アルミニウム焼結体を、研磨加工面が前記加圧軸とほぼ直角方向になるように面方向に制御を行いながら、表面研磨加工する。研磨加工面の直角度は±１０°以内とすることが好ましい。又、研磨加工は、固定砥石を用いる研磨加工のほか、遊離砥粒を用いる研磨加工等を用いることもでき、研磨砥粒の粒度は＃１０００以上が好ましく、＃２０００以上が更に好ましい。
【００２７】
この研磨加工によって、得られるセラミックス基板の表面に非球形状空孔が現れ、その表面における空孔の深さＴｍに対する長さの比Ｌｍの比Ｌｍ／Ｔｍが、５．０以上という一方向に大きく歪んだ非球形状の空孔が得られる。尚、得られるＡｌＮセラミックス基板は緻密で、相対密度が９０％以上であることが好ましく、特に相対密度が９９．５％以上であることが更に好ましい。
【００２８】
このような本発明のＡｌＮセラミックス基板を用いることにより、その表面上に、層厚２０μｍ以下という薄さでも欠けや膨れ等の欠陥の発生しない金属化層を形成したセラミックス回路基板が得られる。その結果、従来のＡｌＮセラミックス基板では困難であった線幅１００μｍ以下のような微細で、且つ絶縁性に優れる配線を備えた回路基板の提供が可能となった。ここで、金属化層の層厚とは、メタライズ層の他にめっき層も含めた合計の厚さをいい、半田層やロウ材層の厚さは含まないものとする。又、金属化層は、このセラミックス基板上に直接形成する方法及び／又はグレーズ層を介してセラミックス基板上に形成する方法のいずれで形成したものであっても良い。
【００２９】
更に、このＡｌＮセラミックス基板の上に、層厚２０μｍ以下の金属化層を介して、層厚２５０μｍ以下のポリイミド層を形成したセラミックス回路基板を得ることもできる。これにより、基板の放熱性を損なうことなく、表面平滑性に優れたポリイミド回路基板を作成することが可能となる。この場合、金属化層としては、銅、クロム、チタンから選択された２層以上の積層構造が好ましく、特にチタン／クロムの２層構造、又はチタン／クロム／銅／クロムの４層構造が好適に用いられる。
【００３０】
【実施例】
実施例１
ＡｌＮ粉末にＹ_２Ｏ_３粉末とＣａＯ粉末を添加して窒素雰囲気中にて常圧焼結することにより、３Ｙ_２Ｏ_３・５Ａｌ_２Ｏ_３及びＣａＯ・Ａｌ_２Ｏ_３を形成し、副成分元素としてＹとＣａを含有するＡｌＮ焼結体を製造した。この焼結体中の副成分元素の含有量は、ＩＣＰ（誘導結合型プラズマ発光分光）分析法により求めた結果、Ｙが２．４重量％及びＣａが０．３重量％であった。又、この焼結体中の炭素含有量は、ＬＥＣＯ法により求めた結果、０．０３重量％であった。この焼結体の見掛け密度をアルキメデス法により測定し、相対密度を求めた結果、９９．７％であった。更に、焼結体破面の各結晶粒の最大寸法を走査型電子顕微鏡（ＳＥＭ）により測定し、結晶粒３０個について求めた平均粒径は３．８μｍであった。
【００３１】
このＡｌＮ焼結体を、下記表１に示す温度と加圧力の条件下に、窒素ガス雰囲気中において１軸加圧しつつ１時間の加圧熱処理を行った。この加圧熱処理後、研磨加工面が１軸加圧の加圧軸方向と直角方向となるように面方向の制御を行いながら、＃１２００のダイヤモンド砥石を用いた粗研磨、＃２０００のダイヤモンド砥石を用いた中研磨、及びダイヤモンド遊離砥粒を用いた仕上げ研磨を順次実施した。
【００３２】
その結果、得られた基板の表面粗さはＲａで０．０３μｍであった。又、得られた各基板表面に現れている全ての空孔について、微動測定ステージを備えた金属顕微鏡を用いて、最大長さ方向の長さＬｍ及び表面からの深さＴｍをそれぞれ測定し、深さに対する長さの比Ｌｍ／Ｔｍを求め、試料ごとに表１にＬｍ／Ｔｍについては全空孔の最小値を及び深さＴｍについては全空孔の最大値を示した。
【００３３】
一方、８０重量％Ｗ、１０重量％Ｍｏ、５重量％Ａｌ_２Ｏ_３、５重量％ＣａＯ、０．１重量％Ｎｉ、及びバインダー成分としてエチルセルロース、希釈剤成分として酢酸ブチルカルビトールを、３本ロールにて混練し、メタライズペーストを作製した。このペーストを、上記の各基板表面にスクリーン印刷により線幅７０μｍ幅で塗布し、窒素雰囲気中にて１５５０℃で焼成した。このメタライズ層上に、電解法にて厚さ２μｍのＮｉめっき層と０．５μｍのＡｕめっき層を順次形成し、回路基板とした。メタライズ層とめっき層との金属化層の合計層厚は、断面研磨法により測定したところ３２〜３５μｍであった。
【００３４】
得られた各加圧熱処理条件ごとの試料について、配線抵抗を４端子法により測定した。これから、目標抵抗値の±１０％以内の配線抵抗規格値に対する配線２０本での配線抵抗の工程能力指数（Ｃｐ）を求め、その結果を表１に併せて示した。
【００３５】
【表１】

【００３６】
上記の結果から、空孔の深さに対する長さの比Ｌｍ／Ｔｍが５．０以上の範囲において、配線抵抗の工程能力指数が高いことが判る。尚、比較のため、別途平均粒径が１７μｍであること以外は前記と同様のＡｌＮ焼結体を、上記試料１と同様に加圧熱処理及び研磨加工したものについて同様に評価したところ、配線抵抗の工程能力指数（Ｃｐ）は１．１０となり、試料１に比べてＣｐが低下する傾向が認められた。
【００３７】
実施例２
３ｋｇ／ｃｍ^２の加圧窒素ガス雰囲気中にて焼結し、副成分元素としてＹとＣａを含有する平均粒径９．２μｍのＡｌＮ焼結体を製造した。実施例１と同様に求めた焼結体中の副成分元素の含有量はＹが０．９重量％及びＣａが０．０２重量％であり、炭素含有量は０．０２重量％であった。又、この焼結体の相対密度は９９．３％であった。
【００３８】
このＡｌＮ焼結体を、７５体積％窒素−２５体積％水素の混合ガス雰囲気中において、１００ｋｇ／ｃｍ^２の加圧力を１軸方向に加えながら１８００℃で３時間の加圧熱処理を行った。その後、種々の加工方法により、研磨加工面が上記加圧軸方向と直角になるように面方向の制御を行いつつ研磨加工を施した。得られた各基板について、表面粗さＲａを求め、実施例１と同様に測定した空孔の長さＬｍと深さＴｍから求めたＬｍ／Ｔｍの最小値及びＴｍの最大値と共に、表２に示した。
【００３９】
更に、各基板について実施例１と同様に金属化層を形成し、回路基板とした。メタライズ層とめっき層の金属化層の合計層厚は３２〜３５μｍであった。得られた各試料について、配線抵抗を４端子法により測定し、実施例１と同様に配線抵抗の工程能力指数（Ｃｐ）を求め、その結果を表２に併せて示した。
【００４０】
【表２】

【００４１】
上記の結果から、回路基板の配線抵抗の工程能力指数（Ｃｐ）は、空孔の比Ｌｍ／Ｔｍ及び深さＴｍがほぼ一定の条件下では表面粗さＲａに依存し、Ｒａが０．２μｍを越える領域では配線抵抗の工程能力指数（Ｃｐ）が低くなる傾向にあることが判る。
【００４２】
実施例３
平均粒径１．１μｍのＡｌＮ粉末に平均粒径０．６μｍのＹ_２Ｏ_３粉末を下記表３に示す割合（Ｙ元素に換算）で添加し、更に有機バインダーとしてポリメタクリレート１０重量％を加え、ボールミルを用いて粉砕混合した後、ドクターブレード法により５０ｍｍ×５０ｍｍ×０．６ｍｍのシート成形体とした。この各シート成形体を、窒素ガス雰囲気中において脱脂後、常圧窒素ガス雰囲気中にて１８００℃で焼結した。得られた各ＡｌＮ焼結体の炭素含有量はいずれも０．０２〜０．０３重量％であり、また各焼結体について求めた相対密度を表３に示した。
【００４３】
得られた各ＡｌＮ焼結体を、窒素ガス雰囲気中において、３００ｋｇ／ｃｍ^２の加圧力を１軸方向に加えながら１７００℃で１時間の加圧熱処理を行った。その後、実施例１と同様に表面を研磨加工し、基板の表面粗さＲａを全て０．０５μｍとした。各基板について、実施例１と同様に測定した空孔の長さＬｍと深さＴｍから求めたＬｍ／Ｔｍの最小値及びＴｍの最大値を表３に併せて示した。
【００４４】
更に、各基板について、その表面にＴｉを０．１μｍ、Ｐｔを０．１５μｍ、及びＡｕを１．０μｍの厚さに順次コーティングし、線幅１０μｍのメタライズ層を形成し、回路基板を作製した。この金属化層の合計の層厚は１．１２〜１．１７μｍであった。得られた各試料について、配線抵抗を４端子法により測定し、実施例１と同様に配線抵抗の工程能力指数（Ｃｐ）を求め、その結果を表３に併せて示した。
【００４５】
【表３】

（注）表中の＊を付した試料は比較例である。尚、試料２４は金属化層に膨れが発生したため配線形成ができなかった。
【００４６】
上記の結果から、周期律表の２Ａ族、３Ａ族元素が０．１〜１５重量％含まれるＡｌＮ焼結体を用いることにより、１軸方向の加圧熱処理で非球形状の空孔を形成でき、従って工程能力指数（Ｃｐ）の高い配線抵抗が得られることが判る。尚、比較のため、同一条件で焼結したＹ含有量０．１重量％で炭素含有量０．０６重量％のＡｌＮ焼結体について同様の加圧熱処理を行ったところ、研磨加工した表面の空孔の深さに対する長さの比Ｌｍ／Ｔｍは５．１であった。
【００４７】
実施例４
０．５ｋｇ／ｃｍ^２の減圧窒素雰囲気中にて焼結し、副成分元素としてＹｂを含有する平均粒径０．８μｍのＡｌＮ焼結体を製造した。実施例１と同様に求めた焼結体中の副成分元素Ｙｂの含有量は５．５重量％であった。又、この焼結体の炭素含有量は０．０２重量％であり、相対密度は９９．８％であった。
【００４８】
このＡｌＮ焼結体を、アルゴンガス雰囲気中において、下記表４に示す温度条件で１００ｋｇ／ｃｍ^２の加圧力で１軸方向に加圧しながら１分間の加圧熱処理を行った。その後、実施例１と同様に研磨加工面の面方向を制御しながら研磨加工を施し、得られた各基板の表面粗さＲａを０．０７μｍとした。又、得られた各基板について、実施例１と同様に測定した空孔の長さＬｍと深さＴｍから求めたＬｍ／Ｔｍの最小値及びＴｍの最大値を表４に示した。
【００４９】
更に、各基板について実施例３と同様に金属化層を形成し、回路基板とした。得られた各試料について、配線抵抗を４端子法により測定し、実施例１と同様に配線抵抗の工程能力指数（Ｃｐ）を求め、その結果を表４に併せて示した。加圧熱処理の温度が１３００℃未満では、目的とするＬｍ／Ｔｍが５μｍ以上でＴｍが１０μｍ以下の非球形状空孔が得られず、工程能力指数（Ｃｐ）が低下することが判る。
【００５０】
【表４】

【００５１】
実施例５
実施例４で作製した各ＡｌＮ基板上に、ＴｉとＣｒの金属化層を順次形成し、金属化層の合計の層厚を１５μｍとした。更に、この金属化層の上に、ポリイミド前駆体をスピンコート法により塗布し、窒素ガス雰囲気中にて４５０℃で熱処理してポリイミド層を形成した。得られた各ポリイミド層の層厚はいずれも３０μｍであった。
【００５２】
各試料について、２０倍の実態顕微鏡によりポリイミド層の状態を評価し、その結果を表５に示した。その結果から明らかなように、本発明の加圧熱処理の温度範囲において、膨れや欠け等の欠陥の発生のないポリイミド層を形成することができる。
【００５３】
【表５】

【００５４】
実施例６
実施例４で作製した各ＡｌＮ基板上に、Ｔｉ、Ｃｒ、Ｃｕ、Ｃｒの金属化層を順次形成し、金属化層の合計の層厚を３５μｍとした。更に、この金属化層の上に、ポリイミド前駆体をスピンコート法により塗布し、窒素ガス雰囲気中にて４５０℃で熱処理してポリイミド層を形成した。得られた各ポリイミド層の層厚はいずれも７０μｍであった。
【００５５】
各試料について、２０倍の実態顕微鏡によりポリイミド層の状態を評価し、その結果を表６に示した。その結果から明らかなように、本発明の加圧熱処理の温度範囲において、膨れや欠け等の欠陥の発生のないポリイミド層を形成することができる。
【００５６】
【表６】

【００５７】
【発明の効果】
本発明によれば、表面に形成する金属化層やポリイミド層に欠けや膨れ等の欠陥が発生せず、従来のＡｌＮセラミックス基板では対応できなかった特に金属化層の薄い微細回路配線の形成に対応することができ、高集積化・小型化が求められているエレクトロニクス材料として好適な窒化アルミニウム基板を提供することができる。[0001]
[Industrial applications]
The present invention relates to a ceramic substrate used for an electronic device such as a circuit board of an IC or a package, particularly a ceramic substrate made of aluminum nitride having high thermal conductivity and excellent heat dissipation, and a method of manufacturing the same. .
[0002]
[Prior art]
The thermal conductivity of aluminum nitride (AlN) is theoretically 320 W / m · K, which is 1.5 times that of metallic aluminum. In addition to this high thermal conductivity, aluminum nitride has high insulating properties and mechanical strength, and has excellent properties such as easy bonding with metal conductors. .
[0003]
Generally, when aluminum nitride is used for a circuit board or a package, it is necessary to polish the surface of the aluminum nitride substrate and then form a metallized layer such as a metallized layer or a plated layer on the surface of the substrate. Also, a polyimide layer having excellent surface smoothness is formed on an aluminum nitride substrate via the metallized layer, and fine wiring is formed on the polyimide layer to form a circuit board.
[0004]
[Problems to be solved by the invention]
However, the metallized layer formed on the surface of the aluminum nitride substrate tends to be chipped or swelled, and the chipping or swelling tends to increase when the thickness of the metallized layer is reduced, especially when the layer thickness is 20 μm or less. However, there is a defect that the tendency becomes remarkable. Similarly, the polyimide layer provided on the metallized layer also has a problem that chipping occurs and foaming occurs when the polyimide layer is formed.
[0005]
It is considered that the generation of these defects is caused by vacancies existing in the aluminum nitride substrate. That is, since the aluminum nitride substrate is essentially a sintered body obtained by sintering powder, the existence of spherical holes having a diameter of about 20 to 50 μm is generally unavoidable and is present on the substrate surface. It is said that defects such as chipping and swelling occur in the metallization layer and the polyimide layer on the holes.
[0006]
Therefore, conventionally, a method has been adopted in which the occurrence of defects such as chipping and swelling is reduced by increasing the thickness of the metallized layer or the polyimide layer. However, when the thickness of the metallization layer is increased, sufficient insulation between the wirings cannot be ensured when miniaturizing circuit wirings. For this reason, there is a limit in increasing the thickness of the metallization layer. Particularly, when a fine wiring having a line width of 100 μm or less is formed, a thin metallization layer is required to secure insulation between the wirings. Above all, in a metallized layer having a thickness of 20 μm or less, the occurrence of chipping or swelling has been a serious problem.
[0007]
Also, when the polyimide layer is too thick, defects such as chipping are likely to occur. Therefore, chipping and swelling during the formation of fine wiring are reduced by setting the layer thickness to 300 μm or more. However, this method has a problem in that although the electrical characteristics of the circuit wiring are excellent, the polyimide layer having poor thermal conductivity becomes extremely thick, which causes a decrease in the heat dissipation of the circuit board.
[0008]
As described above, in the conventional aluminum nitride substrate, defects such as chipping and swelling are liable to occur in the metallized layer and the polyimide layer formed on the surface thereof, and the thickness of the metallized layer and the polyimide layer is reduced to eliminate these defects. If the thickness is increased, there is a problem that the miniaturization of the circuit wiring is hindered and the heat radiation property is reduced.
[0009]
In view of such conventional circumstances, the present invention provides an aluminum nitride substrate which is free from defects such as chipping and swelling in a metallized layer or a polyimide layer formed on the surface and is particularly suitable for forming fine wiring, and a method for manufacturing the same. The purpose is to do.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an aluminum nitride substrate provided by the present invention contains at least one compound of Group 2A and 3A elements of the periodic table in an amount of 0.1 to 15% by weight in terms of the element, An aluminum nitride substrate containing holes having a shape, wherein a ratio of a length to a depth of the holes appearing on the polished surface is not less than 5.0 and not more than 10 μm. Features.
[0011]
Further, the method for producing a ceramic substrate according to the present invention is characterized in that 1 kg of an aluminum nitride sintered body containing 0.1 to 15% by weight, in terms of the element, of at least one compound of Group 2A and Group 3A elements of the periodic table. After performing a heat treatment at a temperature of 1300 ° C. or more while applying pressure in a uniaxial direction at a pressure of / cm ² or more, the surface is polished with the polished surface substantially perpendicular to the pressure axis.
[0012]
[Action]
Since an aluminum nitride sintered body is essentially obtained by sintering powder, the existence of generally spherical holes having a diameter of about 20 to 50 μm cannot be avoided. Even if these pores exist inside the sintered body, they appear on the surface of the substrate subjected to the surface polishing. The present inventors have found out that the shape of the pores appearing on the surface particularly affects the occurrence of defects such as chipping and swelling of the metallized layer and the polyimide layer formed on the surface.
[0013]
That is, as a result of detailed examination of the shape of the holes appearing on the surface of the polished substrate, the ratio of the length Lm to the depth Tm of the holes appearing on the surface, the defect occurrence rate when forming fine wiring, and Found that a correlation exists. Specifically, when the shape of the pores appearing on the surface becomes non-spherical and flat, and the ratio Lm / Tm of the length Lm on the surface to the depth Tm from the surface becomes 5.0 or more. In addition, chipping and swelling of the metallized layer and the like are eliminated, and the defect occurrence rate of fine wiring is reduced. Here, the length (Lm) of the non-spherical hole refers to the length of the longest portion of the hole appearing on the substrate surface.
[0014]
Furthermore, as a result of repeated studies on more stable fine wiring shapes, when the depth Tm of the non-spherical voids appearing on the substrate surface becomes deeper than a certain level, the frequency of disconnection of the fine wirings increases rapidly. It turned out to be higher. The level of the depth Tm is generally about 12 to 20 μm, although it depends on the type and thickness of the wiring. In particular, it has been found that when the depth Tm of the non-spherical holes appearing on the surface is 10 μm or less, the formation of fine wiring is particularly excellent.
[0015]
Note that in order to eliminate chipping or swelling of the metallized layer or the like, it is necessary that all holes appearing on the substrate surface are non-spherical holes having the above characteristics. The length Lm of the non-spherical hole can be determined by visual or photographic measurement using a metal microscope with a magnification of 100 to 1000 equipped with a fine movement measurement stage. Further, the depth Tm of the non-spherical holes can be obtained by a depth of focus method generally known as an optical measurement method using a metal microscope or the like having a magnification of 100 to 1000 times. In the present invention, an arbitrary field of view is selected for convenience. From the results of Lm and Tm determined as described above, the ratio Lm / Tm of the length to the depth of the holes appearing on the surface can be arithmetically determined.
[0016]
The fine irregularities on the polished surface of the ceramic substrate also affect the formation of fine wiring, though not as much as the above-described hole shape. When the surface roughness Ra of the ceramic substrate surface (measured based on JIS B0601) exceeds 0.2 μm, the incidence of defective fine wiring due to swelling of the metallized layer and the like tends to increase.
[0017]
In order to obtain an aluminum nitride substrate having excellent surface smoothness as described above by polishing the surface, the average crystal grain size of AlN crystal grains is preferably 15 μm or less. The average crystal grain size of the AlN crystal grains is obtained as an arithmetic average of 30 or more grains by observing the maximum dimension of each grain on the fracture surface of the substrate on a secondary plane of a scanning electron microscope (SEM).
[0018]
Generally, the pores in the aluminum nitride sintered body have a spherical shape with isotropic properties, and there are no pores distorted in a specific direction. In particular, as in the present invention, an aluminum nitride sintered body having non-spherical voids greatly distorted in one direction, in which the ratio Lm / Tm of length to the depth of voids appearing on the surface is 5.0 or more, However, it is not conventionally known, and it cannot be manufactured unless the manufacturing method takes into account the control of the hole shape.
[0019]
Therefore, in the method of the present invention, in order to obtain a substrate made of an aluminum nitride sintered body having non-spherical holes, the aluminum nitride sintered body containing an auxiliary component that promotes plastic deformation is uniaxially pressed. By applying the heat treatment, the spherical holes in the sintered body are crushed and crushed in the direction of the pressure axis to deform into a non-spherical shape.
[0020]
First, the aluminum nitride sintered body for that purpose needs to contain at least one compound of Group 2A and Group 3A elements of the periodic table as the above subcomponent in an amount of 0.1 to 15% by weight in terms of the element. The reason is that aluminum nitride has a strong covalent bond and has a hexagonal crystal form, so that even under heat treatment, grain boundary sliding and plastic deformation do not occur under limited conditions, and the desired unidirectional This is because it is not possible to obtain a sintered body having non-spherical holes that are distorted.
[0021]
Therefore, by making the aluminum nitride sintered body contain at least one compound of elements of the 2A group and 3A group elements of the periodic table, the compounds of these subcomponents are present at the grain boundaries, and the AlN crystal during the heat treatment under pressure. Promotes intergranular slippage, and as a result, a sufficient deformability is imparted, and a non-spherical hole largely distorted in one direction such that the ratio of length to target depth Lm / Tm is 5.0 or more is formed. Is obtained. Oxide as a compound which performs the function of such present in the sintered body, for example, _{_{_{_{Y 2 O 3, YAG (3Y}}}} 2 O 3 · 5Al 2 O 3), YAL (Y 2 O 3 · Al 2 O 3), _{_{_{_{YAM (2Y 2 O 3 · Al}}}} 2 O 3), 3CaO · Al 2 O 3, CaO · Al 2 O 3 other such, there is a nitride YN, oxynitride Y-Al-O-N and the like.
[0022]
If the content of the subcomponent is less than 0.1% by weight in terms of element, the effect of grain boundary sliding becomes insufficient, and if it exceeds 15% by weight, the thermal conductivity of the aluminum nitride sintered body is significantly reduced. Therefore, both are not preferred. Further, even when the amount of carbon in the aluminum nitride sintered body is large, the grain boundary slip during the heat treatment under pressure tends to be difficult, so that the carbon content is preferably 0.05% by weight or less.
[0023]
The aluminum nitride sintered body containing the subcomponent is manufactured by mixing a compound powder of the subcomponent or a liquid thereof with a raw material powder and sintering as usual. The average crystal grain size of the aluminum nitride sintered body before the pressure heat treatment is preferably 15 μm or less. If the average particle size is larger than 15 μm, grain boundary slip and plastic deformation during the heat treatment under pressure hardly occur, and it becomes difficult to obtain the desired non-spherical pore. Further, the density of the sintered body before the pressure heat treatment is preferably 90% or more relative density.
[0024]
The aluminum nitride sintered body containing the above subcomponents is then subjected to a pressure heat treatment. The pressing force in the pressure heat treatment is set to 1 kg / cm ² or more, and pressure is applied in one axial direction to obtain crushed holes in one direction. When the applied pressure is less than 1 kg / cm ^2, it takes a long time to obtain the desired non-spherical holes, which leads to a decrease in economic efficiency. On the other hand, if the pressing force exceeds 1000 kg / cm ² , the cost of the pressurizing equipment increases, which is not preferable.
[0025]
On the other hand, if the temperature of the heat treatment under pressure is lower than 1300 ° C., the plastic deformability of the sintered body is insufficient, so that the pores are not crushed and the desired non-spherical pores cannot be obtained. Therefore, the temperature of the pressurized heat treatment is set to 1300 ° C. or higher. However, in the case of an air atmosphere, if the temperature exceeds 1500 ° C., deterioration due to oxidation is apt to occur. Not preferred. In addition, as an atmosphere of the pressurized heat treatment, vacuum, air, and other gas atmospheres such as nitrogen, hydrogen, and argon can be used. In the case of an air or gas atmosphere, a pressurized atmosphere may be used.
[0026]
After the pressure heat treatment, the surface of the aluminum nitride sintered body having holes crushed into a non-spherical shape is controlled so that the polished surface is substantially perpendicular to the pressure axis, and the surface is controlled. Polishing. The perpendicularity of the polished surface is preferably within ± 10 °. The polishing may be performed using a fixed grindstone, or may be performed using free abrasive grains. The grain size of the abrasive grains is preferably # 1000 or more, more preferably # 2000 or more.
[0027]
By this polishing, non-spherical holes appear on the surface of the obtained ceramic substrate, and the ratio Lm / Tm of the length ratio Lm to the depth Tm of the holes on the surface is in one direction of 5.0 or more. Largely distorted non-spherical holes are obtained. The obtained AlN ceramic substrate is dense and preferably has a relative density of 90% or more, and more preferably has a relative density of 99.5% or more.
[0028]
By using such an AlN ceramic substrate of the present invention, it is possible to obtain a ceramic circuit substrate having a metallized layer on its surface which is free from defects such as chipping or swelling, even if it is as thin as 20 μm or less. As a result, it has become possible to provide a circuit board having fine wiring having a line width of 100 μm or less and having excellent insulation properties, which has been difficult with a conventional AlN ceramics substrate. Here, the thickness of the metallized layer refers to the total thickness including the plating layer in addition to the metallized layer, and does not include the thickness of the solder layer or the brazing material layer. Further, the metallized layer may be formed by any of a method of directly forming on the ceramic substrate and / or a method of forming on the ceramic substrate via a glaze layer.
[0029]
Furthermore, a ceramic circuit board can be obtained in which a polyimide layer having a layer thickness of 250 μm or less is formed on the AlN ceramic substrate via a metallized layer having a layer thickness of 20 μm or less. This makes it possible to produce a polyimide circuit board having excellent surface smoothness without impairing the heat dissipation of the board. In this case, as the metallized layer, a laminated structure of two or more layers selected from copper, chromium, and titanium is preferable, and a two-layer structure of titanium / chromium or a four-layer structure of titanium / chromium / copper / chromium is particularly preferable. Used for
[0030]
【Example】
Example 1
By adding Y ₂ O ₃ powder and CaO powder to AlN powder and sintering them under normal pressure in a nitrogen atmosphere, 3Y ₂ O ₃ .5Al ₂ O ₃ and CaO.Al ₂ O ₃ are formed, and subcomponents are formed. An AlN sintered body containing Y and Ca as elements was manufactured. The content of the subcomponent elements in this sintered body was determined by ICP (inductively coupled plasma emission spectroscopy), and as a result, Y was 2.4% by weight and Ca was 0.3% by weight. Further, the carbon content in this sintered body was 0.03% by weight as a result of being determined by the LECO method. The apparent density of this sintered body was measured by the Archimedes method, and the relative density was determined to be 99.7%. Further, the maximum dimension of each crystal grain on the fracture surface of the sintered body was measured by a scanning electron microscope (SEM), and the average grain size obtained for 30 crystal grains was 3.8 μm.
[0031]
This AlN sintered body was subjected to a pressure heat treatment for one hour while being uniaxially pressed in a nitrogen gas atmosphere under the conditions of temperature and pressure shown in Table 1 below. After this pressure heat treatment, rough polishing using a # 1200 diamond grindstone, and # 2000 diamond grindstone while controlling the surface direction so that the polished surface is perpendicular to the direction of the uniaxial pressing axis. , And finish polishing using diamond free abrasive grains were sequentially performed.
[0032]
As a result, the surface roughness of the obtained substrate was 0.03 μm in Ra. Further, for all the holes appearing on each of the obtained substrate surfaces, the length Lm in the maximum length direction and the depth Tm from the surface were measured using a metal microscope equipped with a fine movement measurement stage, respectively. The ratio Lm / Tm of the length to the depth was determined, and Table 1 shows the minimum value of all holes for Lm / Tm and the maximum value of all holes for depth Tm in Table 1 for each sample.
[0033]
On the other hand, 80 wt% W, 10 wt% Mo, 5 wt% Al ₂ O ₃ , 5 wt% CaO, 0.1 wt% Ni, ethyl cellulose as a binder component, and butyl carbitol acetate as a diluent component were mixed in three pieces. It was kneaded with a roll to produce a metallized paste. This paste was applied on the surface of each of the above substrates by screen printing with a line width of 70 μm and baked at 1550 ° C. in a nitrogen atmosphere. On this metallized layer, a Ni plating layer having a thickness of 2 μm and an Au plating layer having a thickness of 0.5 μm were sequentially formed by an electrolytic method to obtain a circuit board. The total layer thickness of the metallized layer including the metallized layer and the plated layer was 32 to 35 μm as measured by a cross-sectional polishing method.
[0034]
The wiring resistance was measured by a four-terminal method for the samples obtained under the respective pressure heat treatment conditions. From this, the process capability index (Cp) of the wiring resistance of 20 wirings with respect to the wiring resistance standard value within ± 10% of the target resistance value was obtained, and the results are also shown in Table 1.
[0035]
[Table 1]

[0036]
From the above results, it can be seen that the process capability index of the wiring resistance is high when the ratio Lm / Tm of the length to the depth of the hole is 5.0 or more. For comparison, the same AlN sintered body as described above except that the average particle diameter was 17 μm was evaluated similarly under pressure heat treatment and polishing in the same manner as in Sample 1 above. Has a process capability index (Cp) of 1.10, which is lower than that of Sample 1.
[0037]
Example 2
Sintering was performed in a pressurized nitrogen gas atmosphere of 3 kg / cm ² to produce an AlN sintered body containing Y and Ca as accessory component elements and having an average particle size of 9.2 μm. The content of the subcomponent element in the sintered body determined in the same manner as in Example 1 was 0.9% by weight of Y and 0.02% by weight of Ca, and the carbon content was 0.02% by weight. . The relative density of this sintered body was 99.3%.
[0038]
This AlN sintered body was subjected to a pressure heat treatment at 1800 ° C. for 3 hours in a mixed gas atmosphere of 75% by volume of nitrogen and 25% by volume of hydrogen while applying a pressure of 100 kg / cm ² in one axis direction. Thereafter, polishing was performed by various processing methods while controlling the surface direction so that the polished surface was perpendicular to the pressure axis direction. For each of the obtained substrates, the surface roughness Ra was determined, and together with the minimum value of Lm / Tm and the maximum value of Tm determined from the length Lm and the depth Tm of the hole measured in the same manner as in Example 1, Table 2 was used. It was shown to.
[0039]
Further, a metallized layer was formed on each substrate in the same manner as in Example 1 to obtain a circuit substrate. The total thickness of the metallized layer and the metallized layer of the plating layer was 32 to 35 μm. For each of the obtained samples, the wiring resistance was measured by the four-terminal method, and the process capability index (Cp) of the wiring resistance was obtained in the same manner as in Example 1. The results are also shown in Table 2.
[0040]
[Table 2]

[0041]
From the above results, the process capability index (Cp) of the wiring resistance of the circuit board depends on the surface roughness Ra under the condition that the hole ratio Lm / Tm and the depth Tm are almost constant, and Ra is 0.2 μm It can be seen that the process capability index (Cp) of the wiring resistance tends to be lower in the region exceeding.
[0042]
Example 3
Y ₂ O ₃ powder having an average particle size of 0.6 μm was added to AlN powder having an average particle size of 1.1 μm at a ratio (converted to Y element) shown in Table 3 below, and 10% by weight of polymethacrylate was further added as an organic binder. After pulverizing and mixing using a ball mill, a 50 mm × 50 mm × 0.6 mm sheet molded body was formed by a doctor blade method. Each of the sheet compacts was degreased in a nitrogen gas atmosphere and then sintered at 1800 ° C. in a normal pressure nitrogen gas atmosphere. The carbon content of each of the obtained AlN sintered bodies was 0.02 to 0.03% by weight, and the relative density obtained for each sintered body is shown in Table 3.
[0043]
Each of the obtained AlN sintered bodies was subjected to a pressure heat treatment at 1700 ° C. for 1 hour while applying a pressing force of 300 kg / cm ^{2 in} a uniaxial direction in a nitrogen gas atmosphere. Thereafter, the surface was polished in the same manner as in Example 1, and the surface roughness Ra of the substrate was all set to 0.05 μm. Table 3 also shows the minimum value of Lm / Tm and the maximum value of Tm obtained from the length Lm and the depth Tm of the holes measured in the same manner as in Example 1 for each substrate.
[0044]
Further, with respect to each substrate, a surface thereof was sequentially coated with 0.1 μm of Ti, 0.15 μm of Pt, and 1.0 μm of Au to form a metalized layer having a line width of 10 μm, thereby producing a circuit board. . The total thickness of this metallized layer was 1.12 to 1.17 μm. For each of the obtained samples, the wiring resistance was measured by the four-terminal method, and the process capability index (Cp) of the wiring resistance was obtained in the same manner as in Example 1. The results are shown in Table 3.
[0045]
[Table 3]

(Note) Samples marked with * in the table are comparative examples. In Sample 24, no wiring could be formed due to swelling of the metallized layer.
[0046]
From the above results, non-spherical holes are formed by uniaxial pressing heat treatment by using an AlN sintered body containing 0.1 to 15% by weight of Group 2A and 3A elements of the periodic table. It can be seen that a wiring resistance with a high process capability index (Cp) can be obtained. For comparison, an AlN sintered body having a Y content of 0.1 wt% and a carbon content of 0.06 wt% sintered under the same conditions was subjected to the same pressure heat treatment. The ratio Lm / Tm of the length to the depth of the hole was 5.1.
[0047]
Example 4
Sintering was performed in a reduced pressure nitrogen atmosphere of 0.5 kg / cm ² to produce an AlN sintered body containing Yb as an auxiliary component element and having an average particle diameter of 0.8 μm. The content of the accessory component element Yb in the sintered body determined in the same manner as in Example 1 was 5.5% by weight. The carbon content of the sintered body was 0.02% by weight, and the relative density was 99.8%.
[0048]
The AlN sintered body was subjected to a pressure heat treatment for 1 minute in an argon gas atmosphere while being uniaxially pressed at a temperature of 100 kg / cm ² under the temperature conditions shown in Table 4 below. Thereafter, polishing was performed while controlling the surface direction of the polished surface in the same manner as in Example 1, and the surface roughness Ra of each obtained substrate was set to 0.07 μm. Table 4 shows the minimum value of Lm / Tm and the maximum value of Tm obtained from the length Lm and the depth Tm of the hole measured in the same manner as in Example 1 for each of the obtained substrates.
[0049]
Further, a metallized layer was formed on each substrate in the same manner as in Example 3 to obtain a circuit substrate. For each of the obtained samples, the wiring resistance was measured by the four-terminal method, and the process capability index (Cp) of the wiring resistance was obtained in the same manner as in Example 1. The results are also shown in Table 4. When the temperature of the pressure heat treatment is less than 1300 ° C., it is found that non-spherical pores having a target Lm / Tm of 5 μm or more and a Tm of 10 μm or less cannot be obtained, and the process capability index (Cp) decreases.
[0050]
[Table 4]

[0051]
Example 5
A metallized layer of Ti and Cr was sequentially formed on each AlN substrate manufactured in Example 4, and the total thickness of the metallized layers was set to 15 μm. Further, a polyimide precursor was applied on the metallized layer by a spin coating method, and heat-treated at 450 ° C. in a nitrogen gas atmosphere to form a polyimide layer. Each of the obtained polyimide layers had a thickness of 30 μm.
[0052]
With respect to each sample, the state of the polyimide layer was evaluated with a 20 × magnification microscope, and the results are shown in Table 5. As is clear from the results, a polyimide layer free from defects such as blisters and chips can be formed within the temperature range of the pressure heat treatment of the present invention.
[0053]
[Table 5]

[0054]
Example 6
Metallized layers of Ti, Cr, Cu, and Cr were sequentially formed on each AlN substrate manufactured in Example 4, and the total thickness of the metallized layers was 35 μm. Further, a polyimide precursor was applied on the metallized layer by a spin coating method, and heat-treated at 450 ° C. in a nitrogen gas atmosphere to form a polyimide layer. The thickness of each of the obtained polyimide layers was 70 μm.
[0055]
With respect to each sample, the state of the polyimide layer was evaluated with a 20 × magnification microscope, and the results are shown in Table 6. As is clear from the results, a polyimide layer free from defects such as blisters and chips can be formed within the temperature range of the pressure heat treatment of the present invention.
[0056]
[Table 6]

[0057]
【The invention's effect】
According to the present invention, defects such as chipping and swelling do not occur in a metallized layer or a polyimide layer formed on the surface, and particularly for the formation of fine circuit wiring having a thin metallized layer, which cannot be dealt with by a conventional AlN ceramic substrate. It is possible to provide an aluminum nitride substrate which can be used and is suitable as an electronic material for which high integration and miniaturization are required.

Claims

An aluminum nitride substrate containing at least one compound of Group 2A and 3A elements of the periodic table in an amount of 0.1 to 15% by weight in terms of the element and containing non-spherical holes. A ratio of a length to a depth of the vacancy appearing on the formed surface is not less than 5.0 and the depth is not more than 10 μm.

2. The ceramic substrate according to claim 1, wherein the polished surface has a surface roughness Ra of 0.2 μm or less. 3.

3. The ceramic substrate according to claim 1, wherein the average grain size of the aluminum nitride crystal grains is 15 μm or less.

The ceramic substrate according to any one of claims 1 to 3, wherein the relative density is 99% or more.

An aluminum nitride sintered body containing at least one compound of Group 2A and 3A elements of the periodic table in an amount of 0.1 to 15% by weight in terms of the element is applied uniaxially at a pressure of 1 kg / cm ² or more. A method for manufacturing a ceramic substrate, comprising: performing a heat treatment at a temperature of 1300 ° C. or more while applying pressure, and then performing a surface polishing process by setting a polished surface to a direction substantially perpendicular to the pressure axis.

The method for producing an aluminum nitride substrate according to claim 5, wherein the average particle diameter of aluminum nitride crystal grains contained in the aluminum nitride sintered body is 15 µm or less.

The holes appearing on the polished surface are non-spherical holes having a length to depth ratio of 5.0 or more and a depth of 10 μm or less. Item 7. The method for producing a ceramic substrate according to Item 5 or 6.