JP3593206B2 - Gold alloy fine wires and bumps for bumps - Google Patents

Gold alloy fine wires and bumps for bumps Download PDF

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Publication number
JP3593206B2
JP3593206B2 JP08288896A JP8288896A JP3593206B2 JP 3593206 B2 JP3593206 B2 JP 3593206B2 JP 08288896 A JP08288896 A JP 08288896A JP 8288896 A JP8288896 A JP 8288896A JP 3593206 B2 JP3593206 B2 JP 3593206B2
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Prior art keywords
gold
wire
weight
bumps
gold alloy
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JP08288896A
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JPH09272930A (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外部リードを接続するためのバンプ（金属突起）を形成するために使用される金バンプ用金合金細線およびこれを用いて形成されるスタッドバンプに関する。
【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の接合としてはワイヤボンディング方式が主として使用されている。最近、ＩＣチップの小型化、薄型化の要求に対し、ワイヤ方式では限界が指摘されており、ワイヤレスボンディング方式の採用が進んでいる。
【０００３】
ＴＡＢ（Ｔａｐｅ Ａｕｔｏｍａｔｅｄ Ｂｏｎｄｉｎｇ）方式では、ポリイミド樹脂テープとその上に接着した銅箔回路により形成され、ＴＡＢのリード部とＩＣチップの電極部との接合は、バンプと呼ばれる金属突起物を介して接合される。このバンプとしては、ＬＳＩチップの電極部にメッキ法により形成した金バンプが主に用いられている。メッキのために電極部上にバリヤ層の形成などを要するなど、バンプ形成工程が煩雑で高コストであることに加えて、バンプ形成したウエハの入手が困難であるなどの問題が指摘されている。
【０００４】
また他のワイヤレス方式であるフリップチップ方式では、ＬＳＩチップをフェースダウンで回路基板に接続するため、接続エリアがＬＳＩチップの面積ですみ、実装の高密度化に適した方法であるが、この方法においても、電極部ではバンプを介した接続が主流である。
【０００５】
ワイヤ方式において信頼性が確認されている金合金細線によってバンプを形成するスタッドバンプ方式が提案されており、概略を図１に示している。これは、通常のワイヤボンディングと同様に、キャピラリ３の穴に通した金線１の先端に放電によりボールを形成し、このボールをキャピラリを介してチップ７上の電極パッド６に超音波併用の熱圧着法により接合した後に、キャピラリの上昇時にクランパでワイヤを挟んで強制的にネック部４で破断することにより、バンプ５を形成するものである。
このスタッドバンプ法の利点としては、実績のあるワイヤ方式を基本としており、高速性に優れており、製造コストも安価であること、さらに現有プロセスで稼働しているボンディング装置で対応が可能であることなどが挙げられる。
【０００６】
電極との接続に用いられるバンプにおいては、ＬＳＩチップと接続基板の間隔および接合強度に及ぼす影響が大きいことから、バンプ高さを一定に保つことは重要である。特にワイヤによるバンプ形成においては、バンプ直上の破断部高さを如何に低くするかが課題となる。しかし従来のワイヤボンディングに使用されている金合金細線を用いると、接合したボール部の直上のワイヤ破断長さが長く、さらに破断箇所も定まらないことから高さのばらつきも大きいことが問題となる。バンプ高さの低い良好なスタッド金合金バンプを形成するためのスタッドバンプ用の金合金細線に関連しては、例えば特願平７−６６５９１号などに記載されている。
【０００７】
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の環境で使用される場合がある。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。
【０００８】
コスト、生産性などの理由から、信頼性の高いセラミックスパッケージよりも、安価な樹脂封止による半導体装置が所望されている。スタッドバンプにより接合される半導体装置においても、実装形態として樹脂封止での使用が増えてきている。バンプと電極との接合部に加わる外部ストレスなどはボンディングワイヤと比較しても問題となり、また高密度実装への対応として接合部が微小することに伴い、発熱による接合部の経時変化も懸念されるため、接合信頼性の観点からの厳しい管理が必要となる。
【０００９】
【発明が解決しようとする課題】
上述したように、スタッドバンプにおいては接合信頼性の課題がより問題となる可能性が高いにも拘わらず、破断長さの低減を目的とした従来の金細線の場合の素材選定が主であり、接合信頼性の向上という観点からの材料開発はほとんど行われていなかった。
従来の金細線では、半導体素子上のアルミ電極との長期信頼性の低下が問題視される。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ためである。
【００１０】
本発明者等が、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、樹脂封止された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するハロゲン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。
本発明は、樹脂封止された状態でのアルミ電極との接合部において高い接合信頼性を有する金バンプおよび、その金スタッドバンプを容易に作製することができる金合金細線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、ネック部の破断箇所を短く抑えられるスタッドバンプ形成に好適な金合金細線を開発すべく研究を行った結果、
（ａ）Ｍｎを０．００５〜０．８重量％の範囲で添加させることで、樹脂封止した接合部において長期信頼性が向上していることを見出した。さらに、Ｍｎの適量添加では、バンプの破断長さを低減にも効果がある。また、Ｍｎ元素の単独添加でなく、さらに下記の第一群、第二群、第三群の元素を共存せしめることにより、以下の知見を見出した。
（ｂ）Ｃｕ，Ｐｄ，Ｐｔ（第一群）の少なくとも１種を総計で０．００５〜５重量％の範囲での添加は、Ｍｎ添加と併用することにより、金属間化合物層の成長を抑制する効果が高まり、接合信頼性が高まるものである。
（ｃ）Ｓｃ，Ｇａ，Ａｌ（第二群）の少なくとも１種を総計で０．０００５〜０．０５重量％の範囲での添加は、Ｍｎ添加の併用することにより、金合金細線をアルミニウム電極上への接合性を高める効果が得られることを確認した。
（ｄ）Ｃａ，Ｂｅ，Ｌａ，Ｃｅ，Ｙ（第三群）の少なくとも１種を総計で０．０００２〜０．０３重量％の範囲での添加は、Ｍｎ添加と併用することにより、ボール形成時の熱影響による再結晶領域を短く抑えることにより、ネック部の破断長さを安定して短く抑えられることを確認した。
【００１２】
すなわち、本発明は上記知見に基づくものであって、金合金細線および、その金合金細線を用いて、アルミニウムまたはアルミニウム合金の電極部の上に接合して樹脂封止されている半導体装置として、以下の構成を要旨とする。
（１）Ｍｎを０．００５〜０．８重量％、およびＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０７〜５重量％の範囲で含有し、残部を金の不可避不純物からなる金合金バンプおよびバンプ用金合金細線。
（２）Ｍｎを０．００５〜０．８重量％、およびＳｃ，Ｇａ，Ａｌの少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有した金合金バンプおよびバンプ用金合金細線。
（３）Ｍｎを０．００５〜０．８重量％、およびＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．００５〜５重量％、さらにＳｃ，Ｇａ，Ａｌの少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有した金合金バンプおよびバンプ用金合金細線。
（４）Ｍｎを０．００５〜０．８重量％、およびＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０６〜５重量％、さらにＣａ，Ｂｅ，Ｌａ，Ｃｅ，Ｙの少なくとも１種を総計で０．０００２〜０．０３重量％の範囲で含有した金合金バンプおよびバンプ用金合金細線。
（５）Ｍｎを０．００５〜０．８重量％、およびＳｃ，Ｇａ，Ａｌの少なくとも１種を総計で０．０００５〜０．０５重量％ 、さらにＣａ，Ｂｅ，Ｌａ，Ｃｅ，Ｙの少なくとも１種を総計で０．０００２〜０．０３重量％の範囲で含有した金合金バンプおよびバンプ用金合金細線。
【００１３】
【発明の実施の態様】
以下に、金合金バンプおよび、バンプ作製に用いる金合金細線に関する本発明の構成についてさらに説明する。本発明で使用する高純度金とは、純度が少なくとも９９．９９５重量％以上の金を含有し、残部を不可避不純物からなるものである。
【００１４】
金ワイヤ接合部が高温環境に曝されると、接合界面において金とアルミの相互拡散に伴い数種の金属間化合物が成長し、この金／アルミニウム化合物の中で特定の化合物相（Ａｕ４ Ａｌ相）が封止樹脂中のハロゲン元素と容易に反応して、接合部における電気抵抗を増加させる原因となる。
【００１５】
金中にＭｎを添加すると、Ｍｎ元素が金中を拡散によりＡｕ／Ａｌ界面近傍に濃化偏析して腐食される化合物相の成長を抑制するものであり、高温放置した接合部の電気抵抗の上昇を抑制する。Ｍｎの含有量を０．００５〜０．８重量％と定めたのは、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０．８重量％を超えるとワイヤ先端に形成したボール部表面に酸化膜が形成されたと思われる、接合直後の接合強度の低下が認められるという理由に基づくものである。
【００１６】
さらにスタッドバンプとしての使用性能をより高めることに重点を置いたとき、好ましくは、Ｍｎの含有量が０．０２〜０．８重量％の範囲内であることがより望ましい。これは、０．０２重量％以上では、ネック部における再結晶抑制する効果があるため、破断長さの低減効果が高められているためである。
【００１７】
Ｍｎの添加に加えて、Ｃｕ，Ｐｄ，Ｐｔ（第一群）の少なくとも１種を総計で０．００５〜５重量％の範囲で含有することにより、金／アルミニウムの化合物層全体の成長速度を抑制する効果が高まることが判明した。Ｃｕ，Ｐｄ，Ｐｔのみの添加でも成長速度を遅くする効果はあるものの、化合物相（Ａｕ４ Ａｌ相）の成長を積極的に抑えることは困難である。Ｍｎの添加と併用することにより、腐食反応の抑制効果が高まるものである。第一元素群の含有量を上記範囲と定めたのは、０．００５重量％未満では接合部における信頼性向上の効果が小さく、一方５重量％を超えるとボール部の硬度および強度が高くなるため、接合時にアルミニウム電極の直下のシリコン基板にクラックなどの損傷を与えるという理由に基づくものである。
【００１８】
また、Ｍｎの添加に加えて、Ｓｃ，Ｇａ，Ａｌ（第二群）の少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で添加は、金合金細線とアルミニウム電極との連続接合性を高めることが判明した。前述した接合時の損傷を懸念して、接合荷重または超音波振動を低く設定すると、接合直後に十分な強度を確保することが難しくなるが、第二元素群をＭｎの添加と併用することにより、連続接合時の不良発生はなく、接合強度を高めることができるものである。詳細な機構については判明していないが、初期の化合物成長の促進または、接合性の低下をもたらす可能性のあるワイヤ表面でのＭｎの酸化の抑制などが考えられる。第二元素群の含有量を上記範囲と定めたのは、０．０００５重量％未満では接合性を高める効果が小さく、一方０．０５重量％を超えると、かえって接合強度の低下をもたらすという理由に基づくものである。
【００１９】
バンプ作製の破断長さを支配している要因として、ボール形成時の熱影響を受けた再結晶領域の長さが重要である。高純度金の細線ではネック部の熱影響部長さが長いため、ワイヤ破断長さのばらつきの原因となることが懸念される。これには、Ｃａ，Ｂｅ，Ｌａ，Ｃｅ，Ｙ（第三群）の少なくとも１種を総計で０．０００２〜０．０３重量％の範囲で含有させることにより、ネック部の破断長さを安定して短く抑えられる。熱影響端の部位では第三元素群の添加によりその再結晶を抑制することにより、強度低減した部位をボール部近傍のみに限定させ、常にボール部直上での破断を助長して、破断残り長さを低減する。ここで含有量を上記範囲としたのは、０．０００２重量％未満ではネック部破断の促進効果が小さく、一方０．０３重量％を超えると、ボール部の真球度が低下するため、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。
【００２０】
Ｍｎの添加および、第一、二元素群の共存により、接合後で且つ樹脂封止しない状態で半導体装置が高温維持されたときに、接合強度が顕著に上昇し、半導体装置の高温保管における信頼性の向上効果が高めることができる。これは、Ｍｎの単独添加の場合の接合部では、化合物層が厚く成長したときに化合物層と金細線の界面近傍に小さなボイド（空隙）が観察されたが、さらに第一、二元素群の併用添加させることによりそれらの欠陥の発生も抑えられていることが原因であると思われる。
【００２１】
またＭｎ添加および、第一、三元素群の共存により、伸線加工による金細線の作製において、伸線強度が上昇することが判明しており、極細線の作製が容易となり、狭ピッチなどの高密度実装に対応した微小バンプの形成に好適である。従来の金合金細線においても線径が２０μｍ以下の極細を作製すると、伸線時に強度不足により断線が発生する確率が増える。Ｍｎ添加では強度の上昇はあまり望めず、第一元素群を添加すると強度はある程度増加することは判ったが、さらに第三元素群も併用添加することにより、著しく破断強度が増加することが確認された。また生産性への効用としては、伸線工程での高速化においての断線の低減にも有効であることが挙げられる。
【００２２】
さらにＭｎ添加および、第二、三元素群の共存により、接合直後の接合強度の増加が促進され、実用面では接合時の加熱温度の低温化もはかることが可能となる。これは、第三元素群の添加による細線の強度の適度の上昇が、接合時にアルミニウム電極上の酸化膜の破壊を促進するように作用して、上述した第二元素群の接合性の向上効果をより一層高めていると推察される。
【００２３】
【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、表１および表２に示す化学成分の金合金を溶解炉で溶解鋳造し、その鋳塊を圧延および伸線により、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を調整した。
ワイヤボンディングに使用される高速自動ボンダーを使用して、アーク放電によりワイヤ先端に作製した金合金ボールを走査型電子顕微鏡で観察し、ボール形状が異常なもの、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△印で示した。さらにボール接合部の損傷に関しては、王水などを使用して金細線およびアルミニウム電極などを溶解し、接合部直下のシリコン基板の表面におけるクラックなどの損傷を走査型電子顕微鏡で観察した。５０本以上の電極部を観察し、クラックなどの損傷が２カ所以上認められるものを×印にて示した。ボール形成が良好であり、且つ基板への損傷が認められないものを○印にて評価した。
【００２４】
バンプ形成としては、高速自動ボンダーにより、前述の金ボールをシリコンチップ上に配線している膜厚の１μｍの高純度アルミ電極膜上に超音波併用熱圧着法により接合した後に、上方でワイヤを強制的に引張ることにより、ワイヤをネック部で破断させることにより作製した。そのネック部における破断部長さを、１００個のバンプについて測定したバンプ高さで評価した。
【００２５】
バンプの接合強度については、アルミ電極の３μｍ上方で冶具を平行移動させて剪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。さらに、バンプ接合後の半導体装置を樹脂封止しない状態で、窒素ガス中において２００度で２００時間加熱処理した後に、５０本のシェアテストの平均値により接合強度の変化を評価した。
【００２６】
伸線工程における破断程度は、所定成分に調整した金合金の鋳塊２ｋｇを、線径５００μｍから最終線経２０μｍの金合金細線に到るまで伸線する工程において、断線回数を調査し、０回のものを◎で、１〜５回を○、５回を超えるものを△で示した。
【００２７】
金ボールをアルミニウム電極に接合した半導体装置を樹脂封止しない状態で、窒素ガス中において２００度で２００時間加熱処理した後に、５０本のシェアテストの平均値により接合強度の変化を評価した。さらに、同一の熱処理を施した半導体装置を用いて、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ニウムの金属間化合物層中を観察した。ボイドなどの欠陥が接合界面全体に認められる場合は△印で、ボイドが局所的にのみ発生している場合を○印で、観察されない場合を◎印で表記した。
【００２８】
接合部における腐食調査としては、金細線を接合した半導体装置を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３００時間加熱処理した後に、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ニウム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％以下では腐食の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。
【００２９】
表１において、実施例１〜４は本発明の第１請求項記載に係わるものであり、実施例５〜６は第２項、実施例７〜８は第３項、実施例９〜１３は第４請求項、実施例１４は第５請求項記載に係わる金合金細線の結果である。表２は比較例である。
【００３０】
本発明に係わるＭｎ添加では、比較例１，３，４などと比較すると接合部の腐食が明らかに抑えられていた。Ｍｎ含有に加えて、第一元素群のＣｕ，Ｐｄ，Ｐｔの併用している実施例１〜４では化合物層の腐食がほとんど認められず、信頼性がさらに向上しており、また、第一元素群と第二元素群が共存している実施例７〜８では、腐食の抑制に加えてボイドの発生も抑えられていることが判明した。しかし、Ｍｎ濃度が０．８重量％以上含まれている比較例２，５，１０などでは、ボール部先端での引け巣の発生およびシェア強度の低下していること、また比較例６，７ではＣｕ，Ｐｄ，Ｐｔの含有量が５重量％以上であり、ボール接合時のシリコン基板への損傷が認められた。
【００３１】
Ｍｎ含有に加えて、第二元素群のＳｃ，Ｇａ，Ａｌを適量含有する実施例５〜６では、接合直後のシェア強度が５０ｇｆ以上が確保されていること、さらに、第二元素群と第三元素群が共存している実施例１４では、両者とも含有しない場合と比較して、シェア強度が２０ｇｆ程度増加していることが確認された。
【００３２】
第一元素群と第三元素群が共存している実施例９〜１３では、２０μｍ径の細線までの伸線工程において断線が認められず、生産性が向上することが可能であることが確認できた。
【００３３】
【表１】

Figure 0003593206
【００３４】
【表２】
Figure 0003593206
【００３５】
【表３】
Figure 0003593206
【００３６】
【表４】
Figure 0003593206
【００３７】
【表５】
Figure 0003593206
【００３８】
【表６】
Figure 0003593206
【００３９】
【発明の効果】
以上説明したように、本発明に係わる金バンプ合金細線を使用して、アルミニウム電極部との接合部において高い長期信頼性を有するバンプを容易に形成することが可能である、半導体の高密度実装に適したワイヤレスボンディングに対応する金バンプ用金合金細線を提供するものである。
【図面の簡単な説明】
【図１】スタッドバンプ形成法についての説明図である。
【符号の説明】
１ 金合金細線
２ クランパ
３ キャピラリ
４ ネック部（ワイヤ破断部位）
５ バンプ
６ アルミ電極
７ シリコンチップ
８ ネック部長さ
９ バンプ高さ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gold alloy fine wire for a gold bump used to form a bump (metal projection) for connecting an electrode on a semiconductor element to an external lead, and a stud bump formed using the same.
[0002]
[Prior art]
At present, wire bonding is mainly used for bonding between electrodes on a semiconductor element and external leads. In recent years, the demand for smaller and thinner IC chips has been pointed out by the wire method, and the use of a wireless bonding method has been promoted.
[0003]
In the TAB (Tape Automated Bonding) method, the lead portion of the TAB and the electrode portion of the IC chip are joined by a metal protrusion called a bump, which is formed by a polyimide resin tape and a copper foil circuit adhered thereon. Is done. As the bump, a gold bump formed by plating on an electrode portion of an LSI chip is mainly used. In addition to the complexity and high cost of the bump formation process, such as the need to form a barrier layer on the electrode portion for plating, it has been pointed out that it is difficult to obtain a bumped wafer. .
[0004]
In the flip-chip method, which is another wireless method, the LSI chip is connected face-down to the circuit board, so the connection area is limited to the area of the LSI chip, and this method is suitable for high-density mounting. Also, in the electrode part, connection via a bump is mainstream.
[0005]
A stud bump method in which a bump is formed by a gold alloy fine wire whose reliability has been confirmed in the wire method has been proposed, and is schematically shown in FIG. In this method, a ball is formed at the tip of the gold wire 1 passing through the hole of the capillary 3 by electric discharge, and the ball is applied to the electrode pad 6 on the chip 7 through the capillary, as in the case of ordinary wire bonding. After joining by the thermocompression bonding method, the bump 5 is formed by forcibly breaking the wire at the neck portion 4 with the clamper sandwiching the wire when the capillary rises.
The advantages of this stud bump method are that it is based on the proven wire method, has high speed, is inexpensive to manufacture, and can be handled by the bonding equipment that is operating in the existing process And the like.
[0006]
It is important to keep the bump height constant since the bumps used for connection to the electrodes have a large effect on the distance between the LSI chip and the connection substrate and the bonding strength. In particular, in forming a bump using a wire, the problem is how to reduce the height of the broken portion immediately above the bump. However, when the gold alloy thin wire used in the conventional wire bonding is used, the wire breaking length immediately above the bonded ball portion is long, and the breaking point is not determined. . A gold alloy thin wire for a stud bump for forming a good stud gold alloy bump having a low bump height is described in, for example, Japanese Patent Application No. 7-66591.
[0007]
2. Description of the Related Art Recently, environmental conditions in which semiconductor devices are used have become increasingly severe. For example, a semiconductor device used in an engine room of an automobile may be used in a high-temperature or high-humidity environment. Further, heat generated during use cannot be ignored due to the high-density mounting of semiconductor elements. When a gold wire is used, there is a problem that a long-term reliability of a joint with an aluminum electrode in a high-temperature environment is reduced.
[0008]
For reasons such as cost and productivity, there is a demand for a semiconductor device that uses inexpensive resin sealing rather than a highly reliable ceramic package. Also in semiconductor devices joined by stud bumps, the use of resin sealing as a mounting form is increasing. External stress applied to the joint between the bump and the electrode is a problem compared to the bonding wire, and there is a concern that the joint may change over time due to heat generation due to the miniaturization of the joint in response to high-density mounting. Therefore, strict control is required from the viewpoint of joining reliability.
[0009]
[Problems to be solved by the invention]
As described above, in the case of stud bumps, although the problem of bonding reliability is more likely to be a problem, the selection of a material in the case of a conventional gold wire for the purpose of reducing the breaking length is mainly performed. Material development from the viewpoint of improving joint reliability has hardly been performed.
In the conventional gold wire, there is a problem that the long-term reliability with the aluminum electrode on the semiconductor element is deteriorated. This is because aluminum and gold, which are electrode members, interdiffuse, and peeling and poor electrical conduction occur at the joint due to generation of intermetallic compounds and generation of voids.
[0010]
The present inventors have studied the reliability of the joint between the gold alloy thin wire and the aluminum electrode, and as a result, it has been confirmed that the corrosion of the intermetallic compound layer at the resin-sealed joint has a large effect on the reliability. Was. The intermetallic compound of gold and aluminum grown near the joint interface reacts with the halogen component contained in the sealing resin, thereby increasing the electric resistance of the joint. If corrosion is remarkable, poor electrical conduction will occur. .
An object of the present invention is to provide a gold bump having high bonding reliability at a bonding portion with an aluminum electrode in a resin-sealed state, and a gold alloy thin wire from which the gold stud bump can be easily manufactured. And
[0011]
[Means for Solving the Problems]
From the above-mentioned viewpoint, the present inventors have studied to improve the bonding reliability under high temperature and to develop a gold alloy thin wire suitable for forming a stud bump capable of suppressing a broken portion of a neck portion short.
(A) It has been found that by adding Mn in the range of 0.005 to 0.8% by weight, long-term reliability is improved in a resin-sealed joint. Further, the addition of an appropriate amount of Mn is also effective in reducing the breaking length of the bump. In addition, the following findings were found by coexisting the following first group, second group, and third group elements instead of adding Mn element alone.
(B) Addition of at least one of Cu, Pd, and Pt (first group) in a total range of 0.005 to 5% by weight suppresses the growth of the intermetallic compound layer by being used together with Mn addition. The effect is improved, and the bonding reliability is improved.
(C) The addition of at least one of Sc , Ga, and Al (second group) in a total range of 0.0005 to 0.05% by weight is performed by using Mn in combination with the gold alloy thin wire to form an aluminum electrode. It was confirmed that the effect of increasing the upward bonding property was obtained.
(D) Addition of at least one of Ca, Be, La, Ce, and Y (third group) in a total amount of 0.0002 to 0.03% by weight is used in combination with Mn addition to form a ball. It has been confirmed that the breaking length of the neck portion can be stably suppressed to be short by suppressing the recrystallization region caused by the heat effect at the time to be short.
[0012]
That is, the present invention is based on the above-described findings, and as a semiconductor device that is resin-sealed by using a gold alloy thin wire and the gold alloy thin wire to be bonded onto an electrode portion of aluminum or an aluminum alloy. The following configuration is the gist.
(1) Gold containing 0.005 to 0.8% by weight of Mn and at least one of Cu, Pd, and Pt in a total range of 0.07 to 5% by weight , with the balance being inevitable impurities of gold Alloy bumps and fine gold alloy wires for bumps.
(2) A gold alloy bump and a bump gold alloy containing 0.005 to 0.8% by weight of Mn and a total of 0.0005 to 0.05% by weight of at least one of Sc, Ga and Al. Thin line.
(3) 0.005 to 0.8% by weight of Mn, 0.005 to 5% by weight in total of at least one of Cu, Pd, and Pt, and 0 in total of at least one of Sc, Ga, and Al. Gold alloy bumps and gold alloy thin wires for bumps contained in the range of 0.0005 to 0.05% by weight.
(4) 0.005 to 0.8% by weight of Mn, and 0.06 to 5% by weight in total of at least one of Cu, Pd and Pt, and at least one of Ca, Be, La, Ce and Y And gold alloy thin wires for bumps containing a total of 0.0002 to 0.03% by weight.
(5) 0.005 to 0.8% by weight of Mn , 0.0005 to 0.05% by weight in total of at least one of Sc, Ga and Al, and at least one of Ca, Be, La, Ce and Y A gold alloy bump and a gold alloy thin wire for a bump containing one kind in a total amount of 0.0002 to 0.03% by weight .
[0013]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, the configuration of the present invention relating to the gold alloy bump and the gold alloy fine wire used for producing the bump will be further described. The high-purity gold used in the present invention contains gold having a purity of at least 99.995% by weight or more, with the balance being unavoidable impurities.
[0014]
When the gold wire joint is exposed to a high temperature environment, several kinds of intermetallic compounds grow at the joint interface with the mutual diffusion of gold and aluminum, and a specific compound phase (Au 4 Al) among the gold / aluminum compounds is grown. Phase) easily reacts with the halogen element in the sealing resin, causing an increase in electrical resistance at the joint.
[0015]
When Mn is added to gold, the Mn element diffuses in the gold to concentrate and segregate in the vicinity of the Au / Al interface, thereby suppressing the growth of a compound phase that is corroded. Suppress the rise. The reason that the Mn content is determined to be 0.005 to 0.8% by weight is that when the Mn content is less than 0.005% by weight, the effect of suppressing corrosion of the intermetallic compound at the joint is small. When the content exceeds 8% by weight, it is considered that an oxide film is formed on the surface of the ball portion formed at the tip of the wire, and the bonding strength is reduced immediately after the bonding.
[0016]
Further, when emphasis is placed on enhancing the performance of use as a stud bump, it is more preferable that the Mn content is in the range of 0.02 to 0.8% by weight. This is because at 0.02% by weight or more, there is an effect of suppressing recrystallization in the neck portion, and thus the effect of reducing the fracture length is enhanced.
[0017]
By adding at least one of Cu, Pd, and Pt (first group) in a total range of 0.005 to 5% by weight in addition to the addition of Mn, the growth rate of the entire gold / aluminum compound layer can be reduced. It has been found that the effect of suppressing increases. Although the addition of only Cu, Pd, and Pt has the effect of reducing the growth rate, it is difficult to actively suppress the growth of the compound phase (Au 4 Al phase). When used in combination with the addition of Mn, the effect of suppressing the corrosion reaction is enhanced. When the content of the first element group is set to the above range, the effect of improving the reliability at the joint portion is small when the content is less than 0.005% by weight, while the hardness and strength of the ball portion are increased when the content exceeds 5% by weight. Therefore, it is based on the reason that the silicon substrate immediately below the aluminum electrode is damaged at the time of bonding, such as a crack.
[0018]
In addition to the addition of Mn, S c, Ga, Al added in an amount of 0.0005 to 0.05 wt% of at least one in the total (second group), the gold alloy thin wire and the aluminum electrode It has been found that the continuous bondability is improved. If the bonding load or ultrasonic vibration is set low with concern for the damage at the time of the above-described bonding, it becomes difficult to secure sufficient strength immediately after the bonding, but by using the second element group together with the addition of Mn, In addition, there is no failure at the time of continuous joining, and the joining strength can be increased. Although the detailed mechanism has not been elucidated, it is considered that promotion of initial compound growth or suppression of oxidation of Mn on the wire surface, which may cause a decrease in bondability, are considered. The reason why the content of the second element group is set to the above range is that the effect of enhancing the bonding property is small when the content is less than 0.0005% by weight, whereas the content of the second element group is more than 0.05% by weight, but rather lowers the bonding strength. It is based on.
[0019]
As a factor governing the breaking length of the bump fabrication, the length of the recrystallized region affected by heat during ball formation is important. Since the length of the heat-affected zone of the neck portion is long in a high-purity gold thin wire, there is a concern that it may cause variation in the wire break length. To this end, the break length of the neck portion is stabilized by containing at least one of Ca, Be, La, Ce, and Y (third group) in a total range of 0.0002 to 0.03% by weight. And keep it short. At the heat-affected end part, the recrystallization is suppressed by the addition of the third element group, so that the part where the strength has been reduced is limited only to the vicinity of the ball part, and the fracture immediately above the ball part is always promoted, and the remaining fracture length To reduce When the content is set to the above range, the effect of promoting the breakage of the neck portion is small when the content is less than 0.0002% by weight, while the sphericity of the ball portion is reduced when the content exceeds 0.03% by weight. This is based on the reason that it is difficult to produce a preferable small-diameter ball in order to cope with a short pitch between electrodes on the element .
[0020]
Due to the addition of Mn and the coexistence of the first and second elements, when the semiconductor device is maintained at a high temperature after the bonding and without resin sealing, the bonding strength is significantly increased, and the reliability of the semiconductor device in high-temperature storage is high. The effect of improving the properties can be enhanced. This is because at the junction where Mn was added alone, small voids (voids) were observed near the interface between the compound layer and the gold wire when the compound layer grew thickly. It is considered that the generation of those defects is suppressed by adding them together.
[0021]
In addition, it has been found that the addition of Mn and the coexistence of the first and the three element groups increase the drawing strength in the production of gold wires by wire drawing, making the production of extra-fine wires easier and reducing the pitch, etc. It is suitable for forming minute bumps corresponding to high-density mounting. When a conventional gold alloy thin wire is made ultrafine with a wire diameter of 20 μm or less, the probability of occurrence of disconnection due to insufficient strength at the time of drawing is increased. With Mn addition, the increase in strength was not so much expected, and it was found that the strength increased to some extent when the first element group was added. However, it was confirmed that the addition of the third element group also significantly increased the breaking strength. Was done. In addition, as an effect on productivity, it is effective to reduce disconnection in a high-speed drawing process.
[0022]
Furthermore M n added pressure and, by a second, coexistence of the three element group, the increase in the bonding strength immediately after bonding is promoted, it is possible to achieve even lower temperatures of the heating temperature during joining is practical use. This is because the moderate increase in the strength of the fine wire due to the addition of the third element group acts to promote the destruction of the oxide film on the aluminum electrode at the time of bonding, and the above-described effect of improving the bondability of the second element group. Is estimated to be even higher.
[0023]
【Example】
Hereinafter, examples will be described.
Using electrolytic gold having a gold purity of about 99.995% by weight or more, gold alloys having the chemical components shown in Tables 1 and 2 were melt-cast in a melting furnace, and the ingot was rolled and drawn to obtain a final wire diameter. Was formed into a thin gold alloy wire having a thickness of 25 μm, and then continuously annealed in the air to adjust the elongation.
Using a high-speed automatic bonder used for wire bonding, observe the gold alloy ball produced at the wire tip by arc discharge with a scanning electron microscope, and if the ball shape is abnormal, shrinkage holes are generated at the ball tip. Those that cannot be satisfactorily joined to the electrodes on the semiconductor element, such as those observed, are indicated by a triangle. Furthermore, regarding the damage of the ball joint, the gold wire and the aluminum electrode were dissolved using aqua regia and the like, and damage such as cracks on the surface of the silicon substrate immediately below the joint was observed with a scanning electron microscope. Observation was made on 50 or more electrode portions, and those having damages such as cracks at two or more locations were indicated by crosses. Those with good ball formation and no damage to the substrate were evaluated with a circle.
[0024]
The bumps were formed by using a high-speed automatic bonder to bond the above-mentioned gold balls on a high-purity aluminum electrode film with a thickness of 1 μm, which is wired on a silicon chip, by thermocompression combined with ultrasonic waves. It was made by forcibly pulling to break the wire at the neck. The length of the broken portion at the neck was evaluated by the bump height measured for 100 bumps.
[0025]
The bonding strength of the bump was measured by a shear test method in which a jig was moved in parallel 3 m above the aluminum electrode and a shear fracture was read, and an average value of 50 fracture loads was measured. Furthermore, after the semiconductor device after the bump bonding was not heat-sealed with resin in a nitrogen gas at 200 ° C. for 200 hours, a change in bonding strength was evaluated by an average value of 50 shear tests.
[0026]
The degree of breakage in the wire drawing step was determined by examining the number of wire breaks in the step of drawing 2 kg of a gold alloy ingot adjusted to a predetermined component from a wire diameter of 500 μm to a gold alloy fine wire having a final wire diameter of 20 μm.回 indicates the number of times, ○ indicates 1 to 5 times, and △ indicates more than 5 times.
[0027]
After the semiconductor device in which the gold balls were bonded to the aluminum electrodes was not heat-sealed with resin in a nitrogen gas at 200 ° C. for 200 hours, a change in bonding strength was evaluated by an average value of 50 shear tests. Further, the semiconductor device subjected to the same heat treatment was vertically polished to a cross section passing through the center of the ball joint, and the inside of the intermetallic compound layer of gold and aluminum grown at the joint interface was observed. When a defect such as a void is observed on the entire bonding interface, the symbol is marked with a triangle, when a void is generated only locally, is marked with a circle, and when it is not observed, the symbol is marked with a circle.
[0028]
As for the corrosion investigation at the joint, the semiconductor device to which the gold wire was joined was sealed with an epoxy resin, heated at 200 ° C. for 300 hours in nitrogen gas, and then vertically polished to a cross section passing through the center of the ball joint. Then, corrosion of the intermetallic compound layer of gold and aluminum grown at the joint interface was observed. The progress of the corrosion of the intermetallic compound at the ball joint was examined using the fact that the intermetallic compound layer was gray and the compound layer where corrosion had proceeded turned brown and could be easily identified. The progress of corrosion of the intermetallic compound was evaluated by the ratio of the length of the corroded region (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 corroded portion When the value of (a / b) averaged over 30 ball joints is 5% or less, it is judged that the suppression of corrosion is remarkable. Those having an intermediate value of 5% to 40% were marked with a circle.
[0029]
In Table 1, Examples 1-4 are those according to the first claim, wherein the present invention, the second term in Example 5-6, the third term Examples 7-8, Example 9-1 3 the fourth aspect, the embodiment 14 is the result of the gold alloy fine wire according to a fifth請 Motomeko described. Table 2 is a comparative example.
[0030]
With the addition of Mn according to the present invention, the corrosion of the joint was clearly suppressed as compared with Comparative Examples 1, 3, and 4. In Examples 1 to 4 in which Cu, Pd, and Pt of the first element group were used in addition to the Mn content, the corrosion of the compound layer was hardly observed, and the reliability was further improved. In Examples 7 and 8 in which the element group and the second element group coexist, it was found that the generation of voids was suppressed in addition to the suppression of corrosion. However, in Comparative Examples 2, 5, and 10 in which the Mn concentration was 0.8% by weight or more, shrinkage porosity was generated at the tip of the ball portion and the shear strength was reduced. In the test, the content of Cu, Pd, and Pt was 5% by weight or more, and damage to the silicon substrate during ball bonding was observed.
[0031]
In Examples 5 and 6 in which Sc, Ga , and Al of the second element group were contained in appropriate amounts in addition to the Mn content, the shear strength immediately after joining was 50 gf or more. In Example 14 in which the third element group coexists, it was confirmed that the shear strength was increased by about 20 gf as compared with the case where neither was contained.
[0032]
In Examples 9 to 13 in which the first element group and the third element group coexist, no disconnection was observed in the wire drawing process up to a fine wire having a diameter of 20 μm, and it was confirmed that productivity could be improved. did it.
[0033]
[Table 1]
Figure 0003593206
[0034]
[Table 2]
Figure 0003593206
[0035]
[Table 3]
Figure 0003593206
[0036]
[Table 4]
Figure 0003593206
[0037]
[Table 5]
Figure 0003593206
[0038]
[Table 6]
Figure 0003593206
[0039]
【The invention's effect】
As described above, it is possible to easily form a bump having high long-term reliability at a joint portion with an aluminum electrode portion using a gold bump alloy thin wire according to the present invention, and to achieve high-density mounting of a semiconductor. It is intended to provide a gold alloy fine wire for a gold bump which is suitable for wireless bonding.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a stud bump formation method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gold alloy thin wire 2 Clamper 3 Capillary 4 Neck (wire breakage part)
5 Bump 6 Aluminum electrode 7 Silicon chip 8 Neck length 9 Bump height

Claims (6)

Ｍｎを０．００５〜０．８重量％、およびＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０７〜５重量％の範囲で含有し、残部を金および不可避不純物からなることを特徴とする耐食性に優れたバンプ用金合金細線。Mn is contained in an amount of 0.005 to 0.8% by weight and at least one of Cu, Pd and Pt in a total range of 0.07 to 5% by weight, and the balance is made of gold and unavoidable impurities. Gold alloy fine wire for bumps with excellent corrosion resistance. Ｍｎを０．００５〜０．８重量％、およびＳｃ，Ｇａ，Ａｌの少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有し、残部を金および不可避不純物からなることを特徴とする耐食性に優れたバンプ用金合金細線。Mn and 0.005 to 0.8 wt%, and S c, Ga, contained in the range of 0.0005 to 0.05 wt% in total of at least one Al, the balance being gold and unavoidable impurities A gold alloy fine wire for bumps having excellent corrosion resistance. Ｍｎを０．００５〜０．８重量％、およびＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．００５〜５重量％、さらにＳｃ，Ｇａ，Ａｌの少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有し、残部を金および不可避不純物からなることを特徴とする耐食性に優れたバンプ用金合金細線。Mn and 0.005 to 0.8 wt%, and Cu, Pd, 0.005 to 5 wt% in total of at least one Pt, further to the S c, Ga, at least one Al in total 0. A gold alloy fine wire for bumps having excellent corrosion resistance, containing 0005 to 0.05% by weight, with the balance being gold and unavoidable impurities. Ｍｎを０．００５〜０．８重量％、およびＣｕ、Ｐｄ、Ｐｔの少なくとも１種を総計で０．０６〜５重量％、さらにＣａ，Ｂｅ，Ｌａ，Ｃｅ，Ｙの少なくとも１種を総計で０．０００２〜０．０３重量％の範囲で含有し、残部を金および不可避不純物からなることを特徴とする耐食性に優れたバンプ用金合金細線。0.005 to 0.8% by weight of Mn, at least 0.06 to 5% by weight of at least one of Cu, Pd and Pt, and at least one of at least one of Ca, Be, La, Ce and Y in total A gold alloy fine wire for bumps having excellent corrosion resistance, which is contained in the range of 0.0002 to 0.03% by weight, with the balance being gold and unavoidable impurities. Ｍｎを０．００５〜０．８重量％、およびＳｃ，Ｇａ，Ａｌの少なくとも１種を総計で０．０００５〜０．０５重量％、さらにＣａ、Ｂｅ、Ｌａ、Ｃｅ、Ｙの少なくとも１種を総計で０．０００２〜０．０３重量％の範囲で含有し、残部を金および不可避不純物からなることを特徴とする耐食性に優れたバンプ用金合金細線。Mn and 0.005 to 0.8 wt%, and S c, Ga, 0.0005 to 0.05 wt% in total of at least one Al, further Ca, Be, La, Ce, Y at least A gold alloy fine wire for bumps having excellent corrosion resistance, characterized by containing one kind in a total amount of 0.0002 to 0.03% by weight and the balance consisting of gold and unavoidable impurities. 請求項１〜５の何れかに記載の金合金細線を用いて形成したことを特徴とする金合金バンプ。Gold alloy bump, characterized in that formed using the gold alloy fine wire according to any one of claims 1-5.
JP08288896A 1996-04-04 1996-04-04 Gold alloy fine wires and bumps for bumps Expired - Fee Related JP3593206B2 (en)

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