JP3673366B2 - Semiconductor element - Google Patents

Semiconductor element Download PDF

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Publication number
JP3673366B2
JP3673366B2 JP11320497A JP11320497A JP3673366B2 JP 3673366 B2 JP3673366 B2 JP 3673366B2 JP 11320497 A JP11320497 A JP 11320497A JP 11320497 A JP11320497 A JP 11320497A JP 3673366 B2 JP3673366 B2 JP 3673366B2
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semiconductor element
weight
gold alloy
ball
gold
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JPH10303239A (en
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智裕 宇野
宏平 巽
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Nippon Steel Corp
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Nippon Steel Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は、半導体素子上の電極と金合金細線との接合部信頼性に優れた半導体素子に関するものである。
【０００２】
【従来の技術】
現在半導体素子上の電極と外部リードとの間を接合するボンディング線としては、金合金細線が主として使用されている。金合金細線の接合技術としては超音波併用熱圧着方式が一般的である。金細線先端をアーク入熱で加熱溶融し、表面張力によりボールを形成させた後に、１５０〜３００℃の範囲内で加熱した半導体素子の電極上にこのボール部を圧着接合せしめた後に、さらに外部リード側との接続を超音波圧着する方法である。トランジスタやＩＣなどの半導体素子として使用するためには、前記の金合金細線によるボンディングの後に、Ｓｉチップ、ボンディングワイヤ、およびＳｉチップが取り付けられた部分のリードフレームを、これらを保護する目的で熱硬化エポキシ樹脂で封止する。
【０００３】
半導体素子の高集積化、薄型化の傾向により、金合金細線が満足すべき特性も多様化しており、例えば、高密度配線および狭ピッチに対応するため、金合金細線の長尺化、細線化あるいは高ループ化、さらに半導体素子の薄型化を可能にすべく低ループ化などが要求されている。上記の長尺化、細線化、ループ高さの調整に対応するため、数種の合金化元素を添加した金細線の開発が進められ、例えば特開昭６１−２９６７３１号公報や特開昭６１−１７２３４３号公報などが開示されている。
【０００４】
ところで、最近、半導体素子が使用される環境条件がますます厳しくなっており、例えば自動車のエンジンルーム内で使用される半導体素子では高温あるいは高湿などの環境で使用される場合もある。また半導体素子の高密度実装により使用時に発生する熱が無視できなくなっている。金細線を用いた場合、高温環境下におけるアルミ電極との接合部の長期信頼性の低下などが問題視されている。
【０００５】
耐熱性が要求される環境条件で使用される半導体素子においては、従来、ボンディングワイヤとしてはアルミ合金細線を使用し、セラッミックスパッケージした半導体素子が利用されていた。アルミ合金細線では、半導体素子上の電極との接合部において同種金属の接合により、高信頼性が得られる利点がある。しかし、樹脂封止と比較してセラッミックスパッケージは高価であり、またアルミ合金細線では大気中で正常なボール形成が困難であることから接合方法としてウェッジ接合法が一般的であり、金合金細線に比べて生産性が低下する。
【０００６】
コスト、生産性などの理由から、アルミ合金細線の使用は特定の半導体素子に限定されており、今後とも高速性、生産性、作業性などに優れている、金合金細線によるボンディング方式が主流であると考えれる。金細線とアルミ電極との接合において、高温環境における高い接合信頼性を有する金合金細線を用いた半導体素子が関連する事業分野から望まれている。
【０００７】
【発明が解決しようとする課題】
従来の金細線を用いた場合、半導体素子上のアルミ電極との接合部の長期信頼性の低下が問題視されていた。電極部材であるアルミと金が相互拡散して金属間化合物の生成やボイドの発生による接合部で剥離や電気的導通不良などが生じることが問題として指摘されている。
【０００８】
金合金細線とアルミ電極との接合部の信頼性に関して検討した結果、樹脂封止され接合部における金属間化合物層の腐食が信頼性に及ぼす影響が大きいことが確認された。接合界面近傍に成長した金とアルミの金属間化合物が封止樹脂中に含有成分と反応することにより、接合部の電気抵抗が増加し、腐食が顕著な場合は電気的導通不良などが生じる。信頼性向上を目的として接合部における拡散挙動をコントロールするためには、金細線の合金元素の添加が有効となる。
【０００９】
ここで腐食反応に関与している封止樹脂成分は、臭素およびアンチモンであり、これらは難燃剤として封止樹脂の必須成分である。これらの難燃剤を低減すると、樹脂の高温保管性が低下することが問題となる。
【００１０】
本発明は、金合金細線と半導体素子上のアルミ電極部とのボール接合部がエポキシ樹脂で封止された状態において、化合物の腐食にともなう接合強度の低下および電気抵抗の増加を低減することにより、高温保管性に優れた半導体素子を提供することを目的としている。
【００１１】
【課題を解決するための手段】
本発明者等は前述した観点から、高温下での接合信頼性を向上させる半導体素子について研究を行った結果、封止樹脂中に、臭素およびアンチモンを適量添加することにより、難燃効果を高め、さらに金合金細線中にはＭｎ元素の添加、さらにＭｎ元素とＰｄ元素を併用させることで、樹脂封止した接合部において金属間化合物層の腐食を著しく低減させる効果があることが見出した。ここでＭｎとＰｄの両者を組み合わせることによる複合効果により、耐食性が高まる。
【００１２】
さらに、金合金細線中にＰｔ，Ａｇ，Ｃｕの添加により接合直後の接合強度を高めることを確認し、また、Ｃａ，Ｂｅ，Ｉｎ，希土類元素の添加することは圧着ボール径の異方性を低減するため、高密度実装に有効であることを見出した。
【００１３】
すなわち、本発明は上記知見に基づくものであって、以下の構成を要旨とする。
（１） 金合金細線と電極膜との接合部を樹脂で封止する構造の半導体素子において、封止樹脂は臭素またはアンチモンの少なくとも１種を総計で０．１〜１５重量％、Ｐｄを０．００５〜１．０重量％の範囲で含有するエポキシ樹脂であり、電極材はアルミまたはアルミ合金であり、金合金細線はＭｎを０．００５〜０．５重量％の範囲で含有する金合金細線であることを特徴とする、耐熱性に優れた半導体素子。
【００１４】
（２） 前記（１）項に記載の構造の半導体素子において、金合金細線がＭｎを０．００５〜０．５重量％、Ｐｄを０．００５〜１．０重量％、さらにＰｔ，Ａｇ，Ｃｕの少なくとも１種を総計で０．０１〜２．０重量％の範囲で含有する金合金細線であることを特徴とする半導体素子。
【００１５】
（３） 前記（１）または（２）項に記載の半導体素子において、金合金細線において、さらにＣａ，Ｂｅ，Ｉｎ，希土類元素の少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有する金合金細線を使用して接続した半導体素子。
【００１６】
【発明の実施の形態】
以下に、本発明に係わる半導体素子の構成についてさらに説明する。
封止樹脂が高温で使用されると部材の変質および分解することにより、信頼性が低下することになる。何らかの原因で発火した際にも燃焼を抑えることが不可欠であり、通常の樹脂中には難燃材として、臭素およびアンチモンが含有される。こららの含有量が多いほど、難燃効果は高まるものの、高温環境で分解したそれらのガス成分が悪影響を及ぼす原因となる。例えば、金ボール部とアルミ電極との接合部に成長した金／アルミの金属間化合物が、封止樹脂中のガス成分と容易に腐食反応することが問題となる。従って、臭素およびアンチモンの含有量を増加して、且つ、上記の化合物の腐食を抑制できれば、難燃効果と耐腐食性を併せ持つ、耐熱性を向上させた半導体素子となる。
【００１７】
難燃性を高めるためには、封止樹脂中に臭素およびアンチモンの少なくとも一方は含有することが不可欠である。ここで臭素とアンチモンの含有量が総計として、０．１〜１５重量％であることが望ましい。この理由として、０．１重量％未満では封止難燃効果がえられず、１５重量％以上含有すると、本発明に係わる金合金細線を使用しても、化合物の腐食を抑制することは困難であるためである。さらに好ましくは、臭素の含有量は０．１〜１０％、アンチモンの含有量は０．２〜６％であることが望ましい。これは、臭素とアンチモンの両者を併用することにより、より高い難燃効果が得られ、その適量が上記範囲であるためである。
【００１８】
従来の金合金細線を使用する半導体素子では、金／アルミ接合部の腐食の問題から、通常の封止樹脂中の臭素およびアンチモンの含有量には上限があり、臭素では３％およびアンチモンでは２％程度である。本発明に係わる金合金細線を使用すると、臭素およびアンチモンの含有量を従来より増加させても信頼性を損なうことなく、難燃性を高めることができる。また、大半の半導体素子の使用において、封止樹脂のガラス転移温度より約３０度高い温度までが一つの目安となることがあるが、本発明に係わる半導体素子では、ガラス転移温度より６０度高い温度まで使用することが可能となり、高温環境での実用性が向上する。例えば、自動車のエンジン周辺の高温環境で使用される半導体素子では、実用範囲が拡がることが期待される。
【００１９】
金細線中にＭｎ添加における化合物相の腐食を抑える効果は、化合物相の内部にまで腐食が進行することを抑制しており、長時間加熱においての電気抵抗の増加を抑えることに有効である。
ＭｎとＰｄを併用添加することにより腐食抑制効果を著しく高めることができ、Ｍｎ単独添加あるいはＰｄ単独添加に比べて接合信頼性を一段と向上することができる。Ｍｎに加えてＰｄも併用添加することにより、腐食の初期段階において化合物相と金の界面近傍でのボイドの生成を抑えて、接合強度の低下を抑制することができる。
【００２０】
Ｍｎの含有量を０．００５〜０．５重量％の範囲において接合信頼性が向上することを確認した。Ｍｎの含有量が０．００５重量％未満では接合部における金属間化合物の腐食を抑制する効果が小さく、一方を０．５重量％を超えるとワイヤ先端に形成したボール部の真球度が低下して、扁平な形状が発生するという理由に基づくものであると共に、半導体素子上の電極間距離の短ピッチ化に対応するために好ましい小径ボールの作製が困難となるという理由に基づくものである。
【００２１】
一方、Ｐｄの単独添加では化合物相の成長速度を抑制させることを確認したが、腐食の抑制効果は必ずしも十分ではなく、特に化合物の広範囲に腐食が進む段階に相当するような長時間加熱おいて、腐食を遅らせる効果を得るためにはＰｄ添加量を約１重量％を超える範囲が必要となる。しかしＰｄの高濃度含有によりボール部の形状が扁平になったり、ボール部の硬化により接合時にシリコン基板に損傷を与えることが問題視される。Ｐｄ添加量を少量にするとボール形状は問題ないが、長時間加熱した接合部において化合物が十分成長した後では腐食抑制の効果は小さいことが問題となる。Ｍｎ添加を併用することにより、Ｐｄ単独では抑制が困難であった電気抵抗の上昇も抑えられ、少量のＰｄでも腐食進行を抑える効果を非常に高めることができる。これらの理由から、腐食の進行を短時間および長時間にわたり抑えるためには、ＭｎとＰｄの併用が有効である。
【００２２】
Ｍｎの含有量を０．００５〜０．５重量％、Ｐｄを０．００５〜１．０重量％の範囲において接合信頼性が向上することを確認した。Ｍｎ含有量が上記範囲は、上述した理由に基づくものであり、この範囲内で信頼性を向上する効果が十分得られる。またＰｄの含有量が０．００５重量％では上述したＭｎとの併用効果が非常に小さく、１．０重量％を超えるとボール部が硬化してシリコン基板にダメージを与えたり、ボール表面に酸化膜が形成されて、アルミ電極との接合性が低下するという理由に基づくものである。
【００２３】
Ａｕボール部とアルミ電極との接合性として、ボンディング直後の接合強度は重要であり、小ボール化に伴い接合強度を確保することか困難になることがある。Ａｌ表面の酸化膜が強固なときなどに、ＭｎとＰｄの添加した金ワイヤの小ボール接合において、ボンディング直後の接合強度を向上させることが課題となる場合があり、Ｐｔ，Ａｇ，Ｃｕの少なくとも１種をさらに添加することにより、接合界面における化合物成長を促進して、接合強度を高めることができる。
Ｐｔ，Ａｇ，Ｃｕの含有量を０．０１〜２．０重量％の範囲としたのは、０．０１重量％未満では接合強度を高める効果が十分でなく、２．０重量％を超えるとボールの真球性が低下するため、小ボールの形成および接合に悪影響を及ぼすためである。
【００２４】
狭ピッチ接続においては、圧着したボールの形状に異方性があれば、隣接するボールの接触などが問題となることがある。ボールの圧着後の形状を上部から観察して真円からずれる異方性が大きくなると、狭ピッチ接続において、隣接するボールの接触などが問題となることがある。上記の第一群元素あるいは第二群元素の添加によりボール硬度は高くなることから、接合面積を確保することを重視した場合に、接合時の荷重および超音波振動を高める必要がある。その場合に、圧着ボールの形状の異方性が問題となることがある。
【００２５】
そこでＣａ，Ｂｅ，Ｉｎ，希土類元素の少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有することにより、ボール変形時の異方性を低減することができ、さらに接合強度も高めることができる。Ｃａ，Ｂｅ，Ｉｎ，希土類元素の添加により、ボール部の結晶粒が微細化する傾向にあり、変形時の異方性の抑制にも有効に作用しているものと思われる。Ｃａ，Ｂｅ，Ｉｎ，希土類元素の含有量を上記範囲と定めた理由は、０．０００５重量％以下であれば十分な効果が得られないこと、０．０５重量％を超えるとボール先端に引け巣が発生して接合性が低下するためである。
【００２６】
【実施例】
以下、実施例について説明する。
金純度が約９９．９９５重量％以上の電解金を用いて、前述の各添加元素群を含有する母合金を個別に高周波真空溶解炉で溶解鋳造して母合金を溶製した。
このようにして得られた各添加元素の母合金の所定量と金純度が約９９．９９５重量％以上の電解金とにより、表１に示す化学成分の金合金を高周波真空溶解炉で溶解鋳造し、その鋳塊を圧延した後に常温で伸線加工を行い、必要に応じて金合金細線の中間焼鈍工程を加え、さらに伸線工程を続け、最終線径が２５μｍの金合金細線とした後に、大気中で連続焼鈍して伸び値が約４％になるように調整した。
【００２７】
高速自動ボンダーを使用して電気トーチによるアーク放電により作製した金合金ボールの形状を走査型電子顕微鏡で観察し、真球性が悪く形状が扁平なもの、ボール先端部において収縮孔の発生が認められるもの等半導体素子上の電極に良好な接合ができないものを×印、良好なものを○印にて評価した。
【００２８】
ボール変形の異方性に関しては、Ａｕボール部をＡｌ電極上に超音波併用の熱圧着方式により接合し、ボール部５０個の圧着径を超音波印加と垂直方向（Ｄｘ）および平行方向（Ｄｙ）の２方向で測定し、ＤｘとＤｙの比率により評価した。Ｄｙ／Ｄｘの値が１．０に近いほど真円を保ちながら変形していることになるため、Ｄｙ／Ｄｘの平均値が０．９８〜１．０２の範囲であれば異方性がほとんどないため◎印、異方性は問題ないレベルである０．９５〜０．９８または１．０２〜１．０５の範囲であれば○印、０．９５未満あるいは１．０５を超える範囲であれば狭ピッチ接続では注意を要することがあるため△印で表記した。
【００２９】
Ａｕボール部の接合強度については、高速自動ボンディングワイヤ後にリードフレームと測定する半導体素子を冶具で固定した後に、アルミ電極の３μｍ上方で冶具を平行移動させて煎断破断を読みとるシェアテスト法で測定し、５０本の破断荷重の平均値を測定した。
【００３０】
金合金細線の先端に形成したボールをアルミ電極に接合し、さらにエポキシ樹脂で封止した後に、窒素ガス中において２００度で２５０時間加熱処理した半導体素子を用いて、ボール接合部の中心を通る断面まで垂直研磨し、接合界面に成長した金とアルミの金属間化合物層の腐食を観察した。金属間化合物層は灰色を呈し、腐食が進行した化合物層は褐色になり容易に識別可能であることを利用して、ボール接合部における金属間化合物の腐食の進行を調べた。
金属間化合物の腐食進行としては、ボール接合部の研磨断面において腐食領域長さ（ｂ）が金属間化合物層成長の長さ（ａ）に占める割合で評価したものであり、腐食部が占める割合（ａ／ｂ）を３０個のボール接合部で平均した値が、５％以下では腐食が抑制が顕著であると判断して○印、４０％以上で腐食が顕著なものは×印、その中間である５％〜４０％のものは△印で表記した。
【００３１】
加熱後の接合強度の低下に関しては、樹脂封止した状態で２００度で２００時間した後に、樹脂を開封してから、シェアテスト法により２０個のボール接合部のシェア強度を測定して、加熱前の接合強度の６割以下にまで低下している場合には△印、８割以上の高い値であれば◎印、６割から８割の範囲であれば○印で表示した。
【００３２】
表１は、本発明構成成分で製造した半導体素子において、主として金合金細線の評価結果を示し、表２には本発明構成を外れる半導体素子においての評価結果を示した。
表１において、実施例１〜６は第１請求項に係わるものであり、実施例７〜１２は第２請求項に係わるものであり、実施例１３〜３０は第３請求項に関する結果である。
【００３３】
ＭｎとＰｄの適量添加した実施例１〜６においては、接合部における化合物層の腐食抑制効果はさらに向上し、初期における強度の低下も認められなかった。一方、比較例１，２ではＰｄ添加は本発明範囲であるがＭｎ含有量が０．００５重量％未満であるため、腐食抑制効果は小さく、接合強度も低下している。またＰｄ添加量の多い比較例３，４ではボール形状が不良となり電極との接合性が悪く、初期における強度も低い。
【００３４】
実施例７〜１２では接合直後に測定したシェア強度は６５ｇｆ以上であり、Ｐｔ，Ａｇ，Ｃｕの適量添加により１５ｇｆ以上も増加していることが確認された。
【００３５】
ボール部の圧着径の異方性に関しては、本実験の材料成分および接合条件においては５％以下であり通常の実装では問題のないレベルであるが、Ｃａ，Ｂｅ，Ｉｎ，希土類元素を適量添加している実施例１３〜３０では、異方性が２％以下の低い値にまで向上しており、狭ピッチ接続に好適である。
【００３６】
実施例に示したエポキシ樹脂では、臭素、アンチモンの含有量が本発明の範囲内であり、接合部における腐食は抑制されており、且つ、難燃性も確保されていることが確認された。比較例６では、臭素、アンチモンの含有量が１５％を超えると、接合部において腐食反応が観察された。
【００３７】
本実験では、素子上の配線材料として純アルミを用いて実験したが、最近の半導体素子で一般的に使用されているＳｉおよびＣｕなどを含有するアルミ合金を用いても、本発明の金合金細線は高い耐食性を保持している。
【００３８】
【表１】

Figure 0003673366
【００３９】
【表２】
Figure 0003673366
【００４０】
【発明の効果】
以上、本発明に係わる半導体素子を構成する金合金細線とアルミ電極部の接合部と、さらに封止用樹脂を用いることにより、接合部における腐食反応を抑制し、さらに難燃性を高めることにより、高温環境において高い信頼性を有する半導体素子を提供するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor element having excellent joint reliability between an electrode on a semiconductor element and a gold alloy fine wire.
[0002]
[Prior art]
Currently, gold alloy fine wires are mainly used as bonding wires for joining electrodes on semiconductor elements and external leads. As a gold alloy thin wire joining technique, an ultrasonic combined thermocompression bonding method is generally used. After the tip of the gold wire is heated and melted by arc heat input to form a ball by surface tension, this ball portion is bonded to the electrode of the semiconductor element heated within the range of 150 to 300 ° C. In this method, the connection with the lead side is subjected to ultrasonic pressure bonding. In order to use it as a semiconductor element such as a transistor or an IC, after bonding with the gold alloy thin wire, the Si chip, the bonding wire, and the lead frame where the Si chip is attached are heated for the purpose of protecting them. Seal with cured epoxy resin.
[0003]
Due to the trend toward high integration and thinning of semiconductor elements, the characteristics that gold alloy thin wires can satisfy are diversifying. For example, to accommodate high-density wiring and narrow pitch, the gold alloy thin wires are made longer and thinner. Alternatively, a high loop and a low loop are required to make the semiconductor element thinner. In order to cope with the above-described lengthening, thinning, and adjustment of the loop height, development of a gold thin wire to which several kinds of alloying elements are added has been promoted, for example, Japanese Patent Laid-Open Nos. 61-296931 and 61-61. No. 172343 is disclosed.
[0004]
By the way, recently, environmental conditions in which semiconductor elements are used are becoming more and more severe. For example, semiconductor elements used in an engine room of an automobile may be used in an environment of high temperature or high humidity. Moreover, heat generated during use cannot be ignored due to high-density mounting of semiconductor elements. When gold thin wires are used, problems such as a decrease in long-term reliability of a joint portion with an aluminum electrode in a high temperature environment are regarded as problems.
[0005]
2. Description of the Related Art Conventionally, semiconductor elements that are used under environmental conditions that require heat resistance have been made of ceramic packages that use aluminum alloy fine wires as bonding wires and that are ceramic packaged. The aluminum alloy thin wire has an advantage that high reliability can be obtained by joining the same kind of metal at the joint with the electrode on the semiconductor element. However, the ceramic package is expensive compared to resin sealing, and it is difficult to form a normal ball in the air with an aluminum alloy thin wire. Productivity decreases compared to thin wires.
[0006]
For reasons such as cost and productivity, the use of aluminum alloy fine wires is limited to specific semiconductor elements. Bonding methods using gold alloy fine wires will continue to be the mainstream, which will continue to be excellent in high speed, productivity, workability, etc. It seems that there is. A semiconductor element using a gold alloy fine wire having high joining reliability in a high temperature environment is desired from the related business field in joining the gold fine wire and the aluminum electrode.
[0007]
[Problems to be solved by the invention]
In the case of using a conventional gold thin wire, there has been a problem of a decrease in long-term reliability of a joint portion with an aluminum electrode on a semiconductor element. It has been pointed out as a problem that aluminum and gold, which are electrode members, are interdiffused to cause separation and poor electrical continuity at the joint due to generation of intermetallic compounds and generation of voids.
[0008]
As a result of investigating the reliability of the joint between the gold alloy thin wire and the aluminum electrode, it was confirmed that the influence of the corrosion of the intermetallic compound layer in the joint that was sealed with resin was greatly affected. When the intermetallic compound of gold and aluminum grown in the vicinity of the bonding interface reacts with the components contained in the sealing resin, the electrical resistance of the bonded portion increases, and if the corrosion is significant, poor electrical continuity occurs. In order to control the diffusion behavior in the joint for the purpose of improving the reliability, the addition of an alloy element of a fine gold wire is effective.
[0009]
Here, the encapsulating resin components involved in the corrosion reaction are bromine and antimony, and these are essential components of the encapsulating resin as a flame retardant. When these flame retardants are reduced, there is a problem that the high temperature storage property of the resin is lowered.
[0010]
The present invention reduces a decrease in bonding strength and an increase in electrical resistance due to corrosion of a compound in a state where a ball bonding portion between a gold alloy thin wire and an aluminum electrode portion on a semiconductor element is sealed with an epoxy resin. An object of the present invention is to provide a semiconductor element excellent in high-temperature storage.
[0011]
[Means for Solving the Problems]
From the above-mentioned viewpoints, the present inventors have conducted research on semiconductor elements that improve the bonding reliability at high temperatures. As a result, by adding appropriate amounts of bromine and antimony to the sealing resin, the flame retardant effect is enhanced. Furthermore, it has been found that the addition of Mn element in the gold alloy thin wire and the combined use of Mn element and Pd element have the effect of significantly reducing the corrosion of the intermetallic compound layer in the resin-sealed joint. Here, the corrosion resistance is enhanced by the combined effect of combining both Mn and Pd.
[0012]
Furthermore, it was confirmed that the bonding strength immediately after bonding was increased by adding Pt, Ag, and Cu to the gold alloy thin wire, and that the addition of Ca, Be, In, and rare earth elements reduced the anisotropy of the pressure-bonded ball diameter. It has been found that it is effective for high-density mounting because of the reduction.
[0013]
That is, the present invention is based on the above knowledge and has the following configuration.
(1) In a semiconductor element having a structure in which a joint between a gold alloy fine wire and an electrode film is sealed with a resin, the sealing resin is 0.1 to 15% by weight in total of at least one of bromine and antimony , and Pd is 0 0.005 to 1.0% by weight of epoxy resin, electrode material is aluminum or aluminum alloy, and gold alloy thin wire is a gold alloy containing Mn in the range of 0.005 to 0.5% by weight A semiconductor element excellent in heat resistance, characterized by being a thin wire.
[0014]
( 2 ) In the semiconductor element having the structure described in the above item (1), the gold alloy fine wire has Mn of 0.005 to 0.5% by weight, Pd of 0.005 to 1.0% by weight, and further Pt, Ag, A semiconductor element comprising a gold alloy fine wire containing at least one kind of Cu in a total range of 0.01 to 2.0% by weight.
[0015]
( 3 ) In the semiconductor element according to ( 1 ) or ( 2 ), in the gold alloy fine wire, at least one of Ca, Be, In, and a rare earth element is added in a total amount of 0.0005 to 0.05% by weight. A semiconductor element connected using a gold alloy fine wire contained in a range.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Below, the structure of the semiconductor element concerning this invention is further demonstrated.
When the sealing resin is used at a high temperature, the reliability deteriorates due to the deterioration and decomposition of the member. It is indispensable to suppress combustion even when ignited for some reason, and bromine and antimony are contained as a flame retardant in ordinary resins. Although the flame retardancy increases as the content of these increases, those gas components decomposed in a high temperature environment cause adverse effects. For example, there is a problem that an intermetallic compound of gold / aluminum grown at a joint between a gold ball portion and an aluminum electrode easily reacts with a gas component in the sealing resin. Accordingly, if the bromine and antimony contents are increased and the corrosion of the above compounds can be suppressed, a semiconductor element having both flame retardancy and corrosion resistance and improved heat resistance can be obtained.
[0017]
In order to enhance the flame retardancy, it is essential to contain at least one of bromine and antimony in the sealing resin. Here, the total content of bromine and antimony is preferably 0.1 to 15% by weight. For this reason, if the amount is less than 0.1% by weight, the flame retardant effect of sealing cannot be obtained, and if it is contained by 15% by weight or more, it is difficult to suppress the corrosion of the compound even if the gold alloy thin wire according to the present invention is used. This is because. More preferably, the bromine content is 0.1 to 10% and the antimony content is 0.2 to 6%. This is because by using both bromine and antimony in combination, a higher flame retardant effect is obtained, and the appropriate amount is in the above range.
[0018]
In a conventional semiconductor element using a gold alloy thin wire, there is an upper limit to the bromine and antimony contents in a normal sealing resin due to the problem of corrosion of the gold / aluminum joint, and 3% for bromine and 2% for antimony. %. When the gold alloy fine wire according to the present invention is used, even if the bromine and antimony contents are increased, the flame retardancy can be enhanced without impairing the reliability. Further, in the use of most semiconductor elements, a temperature up to about 30 degrees higher than the glass transition temperature of the sealing resin may be one standard, but in the semiconductor elements according to the present invention, 60 degrees higher than the glass transition temperature. It can be used up to a temperature, and the practicality in a high temperature environment is improved. For example, a semiconductor device used in a high temperature environment around an automobile engine is expected to expand the practical range.
[0019]
The effect of suppressing the corrosion of the compound phase due to the addition of Mn in the gold fine wire suppresses the progress of the corrosion to the inside of the compound phase, and is effective in suppressing the increase of the electrical resistance in the long-time heating.
By adding Mn and Pd in combination, the corrosion inhibitory effect can be remarkably enhanced, and the bonding reliability can be further improved as compared with Mn alone or Pd alone. By adding Pd together with Mn, it is possible to suppress the formation of voids in the vicinity of the interface between the compound phase and the gold in the initial stage of corrosion, and to suppress the decrease in bonding strength.
[0020]
It was confirmed that the bonding reliability was improved when the Mn content was in the range of 0.005 to 0.5% by weight. If the Mn content is less than 0.005% by weight, the effect of suppressing the corrosion of intermetallic compounds in the joint is small, and if one exceeds 0.5% by weight, the sphericity of the ball part formed at the wire tip decreases. In addition, this is based on the reason that a flat shape occurs, and also on the reason that it is difficult to produce a preferable small-diameter ball in order to cope with the shortening of the distance between the electrodes on the semiconductor element. .
[0021]
On the other hand, it has been confirmed that the addition of Pd alone suppresses the growth rate of the compound phase. However, the effect of inhibiting corrosion is not always sufficient, and in particular, heating is performed for a long time corresponding to a stage in which corrosion progresses over a wide range of compounds. In order to obtain the effect of delaying corrosion, a range in which the amount of Pd added exceeds about 1% by weight is required. However, there is a problem that the shape of the ball portion becomes flat due to the high concentration of Pd, or the silicon substrate is damaged at the time of bonding due to the hardening of the ball portion. If the amount of Pd added is small, the ball shape is not a problem, but after the compound has sufficiently grown in the joint heated for a long time, the effect of inhibiting corrosion is a problem. By using Mn in combination, an increase in electrical resistance, which was difficult to suppress with Pd alone, can be suppressed, and the effect of suppressing the progress of corrosion can be greatly enhanced even with a small amount of Pd. For these reasons, the combined use of Mn and Pd is effective for suppressing the progress of corrosion over a short time and a long time.
[0022]
It was confirmed that the bonding reliability was improved when the Mn content was 0.005 to 0.5% by weight and the Pd was 0.005 to 1.0% by weight. The above range of the Mn content is based on the above-described reason, and the effect of improving the reliability is sufficiently obtained within this range. Further, when the Pd content is 0.005% by weight, the combined effect with Mn described above is very small. When the Pd content exceeds 1.0% by weight, the ball part is cured and damages the silicon substrate, or the ball surface is oxidized. This is based on the reason that the film is formed and the bondability with the aluminum electrode is lowered.
[0023]
As the bondability between the Au ball portion and the aluminum electrode, the bonding strength immediately after bonding is important, and it may become difficult to ensure the bonding strength with the reduction in the size of the ball. When the oxide film on the Al surface is strong or the like, there is a case where it is a problem to improve the bonding strength immediately after bonding in the small ball bonding of the gold wire added with Mn and Pd, and at least of Pt, Ag and Cu. By further adding one kind, the compound growth at the bonding interface can be promoted to increase the bonding strength.
The content of Pt, Ag, Cu is in the range of 0.01 to 2.0% by weight. If the content is less than 0.01% by weight, the effect of increasing the bonding strength is not sufficient. This is because the true sphericity of the ball is lowered, which adversely affects the formation and joining of small balls.
[0024]
In a narrow pitch connection, if there is anisotropy in the shape of a pressure-bonded ball, contact between adjacent balls may become a problem. When the anisotropy deviating from a perfect circle is observed when the shape of the ball after pressure bonding is observed from above, contact between adjacent balls may become a problem in narrow pitch connection. Since the ball hardness is increased by the addition of the first group element or the second group element described above, it is necessary to increase the load and ultrasonic vibration during bonding when emphasizing securing the bonding area. In that case, the anisotropy of the shape of the press-bonded ball may be a problem.
[0025]
Therefore, by containing at least one of Ca, Be, In, and rare earth elements in a total range of 0.0005 to 0.05% by weight, anisotropy during ball deformation can be reduced, and bonding strength can be further reduced. Can also be increased. The addition of Ca, Be, In, and rare earth elements tends to make the crystal grains of the ball portion finer, and it is considered that it effectively acts to suppress anisotropy during deformation. The reason why the contents of Ca, Be, In, and rare earth elements are determined to be in the above range is that a sufficient effect cannot be obtained if the content is 0.0005% by weight or less. This is because nests are generated and bonding properties are lowered.
[0026]
【Example】
Examples will be described below.
By using electrolytic gold having a gold purity of about 99.995% by weight or more, the mother alloy containing each of the additive elements described above was individually melt-cast in a high-frequency vacuum melting furnace to melt the mother alloy.
By using a predetermined amount of the master alloy of each additive element thus obtained and electrolytic gold having a gold purity of about 99.995% by weight or more, a gold alloy having chemical components shown in Table 1 is melt-cast in a high-frequency vacuum melting furnace. Then, after the ingot is rolled, wire drawing is performed at room temperature, and if necessary, an intermediate annealing step of the gold alloy thin wire is added, and further the wire drawing step is performed to obtain a gold alloy thin wire having a final wire diameter of 25 μm. Then, it was adjusted so that the elongation value was about 4% by continuous annealing in the atmosphere.
[0027]
The shape of the gold alloy ball prepared by arc discharge with an electric torch using a high-speed automatic bonder was observed with a scanning electron microscope, and the shape was flat with a poor sphericity, and a shrinkage hole was found at the tip of the ball. Those that cannot be satisfactorily bonded to the electrodes on the semiconductor element, such as those obtained, were evaluated as x, and those that were satisfactory were evaluated as ○.
[0028]
Regarding the ball deformation anisotropy, the Au ball part is joined to the Al electrode by a thermocompression bonding method using ultrasonic waves, and the crimping diameters of the 50 ball parts are set in the vertical direction (Dx) and the parallel direction (Dy). ) In two directions and evaluated by the ratio of Dx and Dy. The closer the value of Dy / Dx is to 1.0, the more the shape is deformed while maintaining a perfect circle. Therefore, if the average value of Dy / Dx is in the range of 0.98 to 1.02, the anisotropy is almost the same. ◎ mark, anisotropy is in the range of 0.95 to 0.98 or 1.02 to 1.05, which is a level with no problem, ○ mark, less than 0.95 or more than 1.05 For example, it may be necessary to pay attention to a narrow pitch connection, so it is indicated by a Δ mark.
[0029]
The bonding strength of the Au ball part is measured by the shear test method in which the lead frame and the semiconductor element to be measured are fixed with a jig after the high-speed automatic bonding wire, and then the jig is translated 3 μm above the aluminum electrode to read the breaking break. Then, an average value of 50 breaking loads was measured.
[0030]
A ball formed at the tip of a gold alloy thin wire is bonded to an aluminum electrode, sealed with an epoxy resin, and then passed through the center of the ball bonded portion using a semiconductor element heated in nitrogen gas at 200 degrees for 250 hours. The cross section was vertically polished, and the corrosion of the gold-aluminum intermetallic compound layer grown on the bonding interface was observed. The progress of the corrosion of the intermetallic compound in the ball joint was examined by utilizing the fact that the intermetallic compound layer was gray and the compound layer in which the corrosion progressed was brown and could be easily identified.
The progress of corrosion of the intermetallic compound is evaluated by the ratio of the corrosion area length (b) to the length of the intermetallic compound layer growth (a) in the polished cross section of the ball joint, and the ratio of the corrosion section When the average value of (a / b) at 30 ball joints is 5% or less, it is judged that corrosion is markedly suppressed. Intermediate ones of 5% to 40% are indicated by Δ.
[0031]
Regarding the decrease in bonding strength after heating, after 200 hours at 200 degrees in a resin-sealed state, the resin is opened, and then the shear strength of 20 ball joints is measured by the shear test method. When the strength was lowered to 60% or less of the previous bonding strength, it was indicated by Δ, when it was a high value of 80% or more, ◎, and when it was in the range of 60% to 80%, it was indicated by ○.
[0032]
Table 1 shows mainly the evaluation results of the gold alloy thin wires in the semiconductor elements manufactured with the constituents of the present invention, and Table 2 shows the evaluation results in the semiconductor elements that are out of the configuration of the present invention.
In Table 1, Examples 1 to 6 are related to the first claim, Examples 7 to 12 are related to the second claim, and Examples 13 to 30 are results related to the third claim. .
[0033]
In Examples 1 to 6 in which appropriate amounts of Mn and Pd were added, the effect of inhibiting the corrosion of the compound layer at the joint was further improved, and no initial decrease in strength was observed. On the other hand, in Comparative Examples 1 and 2, the addition of Pd is within the scope of the present invention, but since the Mn content is less than 0.005% by weight, the corrosion inhibiting effect is small and the bonding strength is also lowered. Further, in Comparative Examples 3 and 4 with a large amount of Pd added, the ball shape is poor, the bonding property with the electrode is poor, and the initial strength is low.
[0034]
In Examples 7 to 12 , it was confirmed that the shear strength measured immediately after joining was 65 gf or more, and increased by 15 gf or more by adding appropriate amounts of Pt, Ag, and Cu .
[0035]
Regarding the anisotropy of the crimping diameter of the ball part, it is 5% or less in the material components and bonding conditions of this experiment, which is a level that causes no problem in normal mounting, but appropriate amounts of Ca, Be, In, and rare earth elements are added. In Examples 13 to 30 , the anisotropy is improved to a low value of 2% or less, which is suitable for narrow pitch connection .
[0036]
In the epoxy resins shown in the examples, it was confirmed that the bromine and antimony contents were within the scope of the present invention, the corrosion at the joint was suppressed, and the flame retardance was ensured. In Comparative Example 6 , when the bromine and antimony contents exceeded 15%, a corrosion reaction was observed at the joint.
[0037]
In this experiment, an experiment was conducted using pure aluminum as a wiring material on the element. However, even if an aluminum alloy containing Si and Cu, which is generally used in recent semiconductor elements, is used, the gold alloy of the present invention is used. The fine wire retains high corrosion resistance.
[0038]
[Table 1]
Figure 0003673366
[0039]
[Table 2]
Figure 0003673366
[0040]
【The invention's effect】
As described above, by using the gold alloy fine wire and the aluminum electrode portion constituting the semiconductor element according to the present invention and the sealing resin, the corrosion reaction at the joint is suppressed, and the flame retardancy is further enhanced. A semiconductor device having high reliability in a high temperature environment is provided.

Claims (3)

金合金細線と電極膜との接合部を樹脂で封止する構造の半導体素子において、封止樹脂は臭素またはアンチモンの少なくとも１種を総計で０．１〜１５重量％の範囲で含有するエポキシ樹脂であり、電極材はアルミまたはアルミ合金であり、金合金細線はＭｎを０．００５〜０．５重量％、Ｐｄを０．００５〜１．０重量％の範囲で含有する金合金細線であることを特徴とする耐熱性に優れた半導体素子。In a semiconductor element having a structure in which a joint between a gold alloy fine wire and an electrode film is sealed with a resin, the sealing resin contains at least one of bromine and antimony in a total amount of 0.1 to 15% by weight. The electrode material is aluminum or an aluminum alloy, and the gold alloy thin wire is a gold alloy thin wire containing Mn in the range of 0.005 to 0.5 wt% and Pd in the range of 0.005 to 1.0 wt%. A semiconductor element having excellent heat resistance. 請求項１に記載の構造の半導体素子において、金合金細線がＭｎを０．００５〜０．５重量％、Ｐｄを０．００５〜１．０重量％、さらにＰｔ，Ａｇ，Ｃｕの少なくとも１種を総計で０．０１〜２．０重量％の範囲で含有する金合金細線であることを特徴とする半導体素子。  2. The semiconductor element having the structure according to claim 1, wherein the gold alloy fine wire is 0.005 to 0.5% by weight of Mn, 0.005 to 1.0% by weight of Pd, and at least one of Pt, Ag and Cu. A semiconductor element characterized by being a gold alloy fine wire containing a total amount of 0.01 to 2.0% by weight. 請求項１または２に記載の半導体素子において、金合金細線において、さらにＣａ，Ｂｅ，Ｉｎ，希土類元素の少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有する金合金細線を使用して接続した半導体素子。 3. The semiconductor element according to claim 1, wherein the gold alloy fine wire further contains at least one of Ca, Be, In and rare earth elements in a total range of 0.0005 to 0.05% by weight. Connected semiconductor elements using.
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