JP3673368B2 - Gold-silver alloy fine wire for semiconductor devices - Google Patents

Gold-silver alloy fine wire for semiconductor devices Download PDF

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Publication number
JP3673368B2
JP3673368B2 JP13411497A JP13411497A JP3673368B2 JP 3673368 B2 JP3673368 B2 JP 3673368B2 JP 13411497 A JP13411497 A JP 13411497A JP 13411497 A JP13411497 A JP 13411497A JP 3673368 B2 JP3673368 B2 JP 3673368B2
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Prior art keywords
gold
weight
range
wire
silver alloy
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JP13411497A
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JPH10326803A (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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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C5/00—Alloys based on noble metals
    • C22C5/02—Alloys based on gold
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    • H01L2224/04—Structure, shape, material or disposition of the bonding areas prior to the connecting process
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    • H01L2224/0554—External layer
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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に利用される接合部信頼性に優れた金合金細線に関するものである。
【０００２】
【従来の技術】
ＩＣ，ＬＳＩなどの半導体素子上の内部配線と、インナーリード部との電気的導通を得る接続法として、線径２０〜５０μｍの細線を用いたボンディングワイヤ法が主流である。この細線の材料としては、現在は金とアルミニウムが使用されている。アルミ細線ではアルミ電極部との同種材料の接続が得られるため信頼性が高いことが長所であり、金細線の長所として、金は化学的に安定あることが挙げられる。金細線はアルミ電極との接続に用いるボール接合において、大気中でのワイヤの溶融時の酸化の心配がなく、真球で清浄なボールが容易に得られる。アルミ電極とのボール接合でも、超音波を併用した熱圧着により良好な接合性が得られており、高速接合、量産性に優れている。これに対し、アルミは大気中で溶融すると容易に酸化するため、ボール接続には適用できず、ボールを形成しない接続法に用いられている。この接続法は使用時の量産性が落ちることから、アルミ細線の使用は、高価でも高信頼性が要求されるようなセラミックパッケージなどに限定されている。このような理由からも、ＬＳＩの大半を占める樹脂封止する半導体では、金細線が広く用いられている。
【０００３】
半導体市場では、機能性を高めることに加えて、激しい価格競争が行われ、構成部材の材料コストの削減などが切望されている。金細線では、原材料である金が高価であり、金細線の製造法の改善での低コスト化が期待できない。そこで素材コストの低減を目的として、これまでも、金に代替可能な素材として銅、銀、パラジウムの細線などが検討された。しかし、ボール形成性、接合性、信頼性、樹脂との腐食の問題など、課題が残されており、実用化には至っていないのが現状である。このような現況のもと、高密度実装にも適用できる特性を具備しており、且つ低コスト化できる半導体素子用金細線が市場から切望されている。
【０００４】
金細線のほとんど全ては、特性発現のために添加する不純物の総量を０．０１％以下におさえた、純度が９９．９９％（４Ｎ：フォーナイン）の高純度細線が用いられているのが現状であり、高機能化した半導体の開発が進む中でも、成分範囲には大きな変動はみられていない。最近では、不純物総量として１％程度含有する合金細線の検討もされているが、大幅な低コスト化のメリットを重視した場合の、１０％以上の合金化を達成した金合金細線が使用された実例はみられない。
【０００５】
金中に％オーダー以上の高濃度添加させることが可能な元素として、金と全率固溶するＡｇ，Ｐｔ，Ｐｄ，Ｃｕなどが考えられる。しかし合金化に伴う問題も多く、低コスト化のために高濃度含有させた半導体用金合金細線として、実用化できるものは限られる。例えば、Ｐｔ，Ｐｄ，Ｃｕは高濃度含有することにより、５％程度の上限を目安として濃度が限られる。それ以上含有すると、ワイヤの強度増加によるワイヤ接合時の変形不良、またはボール部の硬度増加による接合時の半導体素子への損傷などが問題となるためである。
【０００６】
Ａｇの高濃度添加では、特開昭５５−１５８６４２号公報において、低コスト化と硫化による細線表面の変色などを考慮して、Ａｇの添加範囲として２０〜５０重量％が開示されている。また特開昭５６−１３７４０号公報および特開昭５６−１９６２８号公報においては、Ａｇ添加により高温での機械的強さ、特に破断強さに優れ、且つ接合部の引張強さに優れていることを考慮して、Ａｇの添加範囲として１９〜５９重量％と他元素群Ｐｄ，Ｐｔ，Ｒｈ，Ｉｒ，Ｏｓ，Ｒｕを０．０００３〜０．１重量％と併用することについて開示されており、また特開昭５６−１９６２８号公報においては、同様の効果を得るためのＡｇの添加範囲として１９〜５９重量％と、他元素群Ｂｅ，Ｃａ，Ｃｏ，Ｆｅ，Ｎｉを０．０００３〜０．１重量％と併用することについて開示されている。
【０００７】
Ａｇに関して、高濃度含有しても、細線の強度上昇も問題のないレベルであり、大気中でのボール溶融時の酸化も抑えられ、ボール部の硬化は軽減されていることが確認され、低コスト化を達成するための高濃度含有としてＡｇ添加は有望である。ただし、実際の量産に用いられる半導体素子用細線としては、Ａｇを高濃度に含有した金銀合金細線は用いられていない。
【０００８】
【発明が解決しょうとする課題】
金細線を低コスト化するための有力な候補として期待される、高濃度の銀を含有する金銀合金細線では、ボール接合において、ボール形状、表面性状、接合性などにおいて良好な特性を有すること、狭ピッチ接続において隣接ワイヤと接触することのないループ形状および機械的特性を有することなどが重要となる。さらに、本発明者らは種々の実用化を研究することにより、銀の高濃度添加において最大の課題として、半導体素子上のアルミ電極との接合部において、長時間加熱したときの接合強度の低下が問題となることを見出した。すなわち、Ａｇを含有する金合金細線をアルミ電極に接合後に高温保管すると、接合強度が低下したり、さらに加熱したのみで剥離にまでいたるものが発生する。こうした金ボール部とアルミ電極との接合信頼性の著しい低下は、現有品である４Ｎ系の高純度金細線では認められない。
【０００９】
そこで本発明は、Ａｇ元素を高濃度に含有する金銀合金細線において、使用時の発熱および高温使用環境などにも耐えうるために、大気、樹脂封止された状態で高温保管された時の、アルミ電極との接合信頼性、特に高温の長期信頼性を改善することを目的とする。
【００１０】
【課題を解決するための手段】
本発明者らは、金中にＡｇを数％オーダー以上の高濃度含有させた金銀合金細線において、Ａｇ濃度域においてある限定された範囲においてのみ接合信頼性が非常に優れていることを見出した。その適性濃度域よりずれた場合として、下限値未満および上限値を超える範囲のいずれにおいても、高温保管後の接合強度の低下による不良が発生していることが確認された。すなわち、ある限定された濃度域でのみ、優れた接合信頼性が得られるものである。
さらに、接合性およびループ形状という観点の改善を考慮して、金と銀の合金細線において、第３元素添加を検討した結果、適正範囲の含有量とすることが良好であることを確認した。
【００１１】
すなわち、本発明は上記知見に基づくものであって、以下の各項に記載した構成を要旨とする。
（１）Ａｇを１１〜１８．５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半導体素子用金銀合金細線。
（２）Ａｇを１１〜１８．５重量％の範囲で含有し、さらにＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％（但し、Ｃｕは０．３〜４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半導体素子用金銀合金細線。
（３）Ａｇを１１〜１８．５重量％の範囲で含有し、さらにＣａ，Ｃｅ，Ｙ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半導体素子用金銀合金細線。
（４）Ａｇを１１〜１８．５重量％の範囲で含有し、さらにＭｎ，Ｃｒの少なくとも１種を総計で０．０１〜０．２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半導体素子用金銀合金細線。
【００１２】
（５）Ａｇを１１〜１８．５重量％の範囲で含有し、Ｃｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％の範囲で含有し、さらにＩｎを必須成分とし、Ｃａ，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半導体素子用金銀合金細線。
（６）Ａｇを１１〜１８．５重量％の範囲で含有し、Ｍｎ，Ｃｒの少なくとも１種を総計で０．０１〜０．２重量％の範囲で含有し、Ｃｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％の範囲で含有し、さらにＣａ，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半導体素子用金銀合金細線。
（７）上記（１）乃至（６）のそれぞれに記載の細線を用い、アルミまたはアルミ合金である配線電極部とを接続した半導体素子。
【００１３】
【発明の実施の形態】
以下に、金銀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。
従来の金細線ではアルミ電極との接合部において、大気中での高温保管によって金／アルミの化合物は成長するが、実用上の大きな問題は発生していない。加速加熱試験の一例として、大気中で２００℃の高温で１０００時間の加熱試験を行っても、接合強度の低下は認められない。
【００１４】
しかし、金中に高濃度のＡｇが含有した金銀合金細線では、アルミ電極との接合部において、高温保管後に接合強度が低下するという、問題が発生した。これは、通常の金細線ではみられない現象であり、金中に高濃度含有するＡｇの影響により、接合部においての金属間化合物相の成長が変化して、通常の金細線とは異なる金属間化合物相が成長したためである。信頼性低下が著しい一例として、％オーダーの高濃度のＡｇを含有する金合金細線では、２００℃で１０時間加熱した接合強度が、加熱前の１／３程度まで低下しているものも観察された。
【００１５】
本発明者らの研究において、接合信頼性に関しては、Ａｇ濃度の増加に対して単調に変化するのではなく、ある一定濃度域に限ってのみ、信頼性が優れていることを初めて見出した。このＡｇの適性な濃度域としては、１１〜１８．５重量％の範囲である。これは、Ａｇの含有量が１１重量％未満および１８．５重量％を超える範囲であれば、加熱後のアルミ電極との接合信頼性が著しく低下するためである。すなわち、Ａｇの濃度域が上記範囲内でのみ、優れた実用性能を発現するものであり、しかも低コスト化としての大きな効果も期待される。
【００１６】
上記の金銀合金細線を製造する上において、伸線工程の途中に加熱処理を施すことにより、最終線径での熱処理（調質焼鈍）をした状態で、強度の増加に加えて伸びも向上することが可能であり、ループ形状におけるばらつきが低減することができる。
【００１７】
また、最終線径での調質焼鈍を施した後に、細線表面に銀の安定な酸化膜を形成させておくことにより、細線の接着性および、大気中に放置している間の経時変化などを抑制できる。これは、大気中でのさらなる酸化の進行を抑えること、また金中の銀と大気中に含まれる微量な硫化ガスとの反応を抑制できるためである。
【００１８】
さらに上記のＡｇを高濃度に有する半導体素子用金銀合金細線において、接合信頼性を損なわないで、使用性能を高める効果が得られることを見出した。
【００１９】
本発明の金銀の合金細線に、さらにＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％（但し、Ｃｕは０．３〜４重量％）の範囲で含有させることにより、アルミ電極との接続直後の接合強度が高まることができる。その効果は、上記の元素を高純度の金のみに添加するよりも、Ａｇと併用して含有させることにより、より高められる。Ｃｕ，Ｐｄ，Ｐｔの含有量を上記範囲と定めたのは、０．０１重量％未満であれば上記効果は小さく、４重量％を超えるとボール部が硬化するため接合時に半導体素子に損傷を与えることが懸念され、それを回避するために接合時の変形を軽減すると接合強度がむしろ低下するという理由に基づくものである。
【００２０】
金中に多量の銀が含有すると、伸線時の強度が増加することに関連して、製造工程において伸線加工による硬化が進むため、伸線時の断線不良や加工ぐせが発生したり、さらに半導体素子とリード部とを結線した後にも、金銀合金細線のループ形成時に曲がり変形が増えることが懸念される。本発明の金銀合金細線に、さらにＣａ，Ｃｅ，Ｙの少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有すると、伸線時の断線不良が低下し、ループ形成時の曲がり変形が低下するため、隣接する細線ピッチが狭い高密度接合に好適な金銀合金細線が得られる。その効果は、上記の元素を高純度の金のみに添加するよりも、Ａｇと併用して含有させることにおいて、高い効果が得られる。
Ｃａ，Ｃｅ，Ｙの含有量を上記範囲と定めたのは、０．０００５重量％未満であれば上記効果は小さく、０．０５重量％を超えると伸線後に熱処理を施しても伸線時の加工ぐせを低減することが困難になり、ワイヤのループ形成時の曲がり変形が増加するためである。
【００２１】
本発明の金銀の合金細線に、Ｃｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％の範囲で含有させ、さらにＩｎを必須成分とし、Ｃａ，Ｉｎ、希土類元素の少なくとも１種を総計で０．０００５〜０．０５重量％の範囲で含有させると、樹脂封止工程における金銀合金細線の変形量が低減することが判明した。これは、高温強度が増加することと関連するものである。上記の元素添加による樹脂封止時の変形量の低減する効果については、Ａｇと併用して含有させることにおいて、より高い効果が得られる。ここで、各元素群の含有量を上記範囲と定めたのは、前述した理由に基づくものである。
【００２２】
本発明の金銀の合金細線に、さらにＭｎ，Ｃｒの少なくとも１種を総計で０．０１〜０．２重量％の範囲で含有すると、樹脂封止された接合部においての信頼性が向上する。従来の金細線を用いて、樹脂封止後に加熱されると、接合部に成長した金属間化合物相が樹脂成分と腐食反応を起こして、電気抵抗の増加および接合強度の低下を引き起こす。金銀の合金細線においても同様の現象が起こるが、Ｍｎ，Ｃｒを含有することにより、その腐食反応が抑制される。ここで、含有量を上記範囲と定めたのは、０．０１重量％未満では上記効果は小さく、０．２重量％を超えると、真球で清浄なボール部を得ることが困難となるためである。
【００２３】
【実施例】
以下、実施例について説明する。
金純度は約９９．９９５重量％以上の電解金を、Ａｇ純度は９９．９５％以上の高純度のものを用いた。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。
【００２４】
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、連続焼鈍して伸び値が４％程度になるように調整した。
得られた金合金細線について、半導体素子用途のボンディング性を中心とした使用性能などを調べた結果を表１に併記した。
【００２５】
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銀合金ボールを１０本採取し、走査型電子顕微鏡で観察した。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、形状が真球で表面も清浄である良好なボールについて○印で示した。
【００２６】
ボール接合部の接合強度については、アルミ電極の２μｍ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、４０本の破断荷重の平均値を測定した。さらに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℃で２００時間加熱処理した後に、４０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。
【００２７】
金銀合金細線のループ形成時のワイヤ曲がりは、ワイヤ両端の接合距離（スパン）が４．５mmとなるようボンディングしたワイヤを半導体素子とほぼ垂直上方向から観察し、ワイヤ中心部からワイヤの両端接合部を結ぶ直線と、ワイヤの曲がりが最大の部分との垂線の距離を、投影機を用いて５０本測定した平均値で示した。
【００２８】
樹脂封止後のワイヤ流れの測定に関しては、ワイヤのスパンとして４．５mmが得られるようボンディングした半導体素子が搭載されたリードフレームを、モールディング装置を用いてエポキシ樹脂で封止した後に、軟Ｘ線非破壊検査装置を用いて樹脂封止した半導体素子内部をＸ線投影し、前述したワイヤ曲がりと同等の手順によりワイヤ流れが最大の部分の流れ量を４０本測定し、その平均値をワイヤのスパン長さで除算した値（百分率）を封止後のワイヤ流れと定義した。
【００２９】
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℃で２００時間加熱処理した後に、ボール接合部を垂直研磨し、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。
【００３０】
表１（表１−１，表１−２）において、実施例１〜３は本発明の請求項第１項記載に係わるものであり、実施例４〜１０は第２項、実施例１１〜１８は第３項、実施例１９〜２３は第４請求項、実施例２４，２５は第５項、実施例２６，２７は第６請求項記載に係わる金銀合金細線の結果である。
【００３１】
また表２の実施例ｂ１〜ｂ２６は、Ａｇの含有量が請求項第１項の範囲であることから本発明に関わるものであるが、Ａｇ以外の元素添加量が請求項第２項から第４請求項に記載されている適性な含有量からはずれる金合金細線について、比較として示したものである。実施例ｂ１〜ｂ８は請求項第２項に対する比較、実施例ｂ９〜ｂ２０は第３項、実施例ｂ２１〜ｂ２６は第４項に対する比較として示した。
【００３２】
表３はＡｇの含有量が本発明を外れる比較例であり、加熱後の接合強度では、比較例１の高純度金では低下しなかったが、比較例２，３ではＡｇ濃度が１１重量％未満であり、比較例４，５ではＡｇ濃度が１８．５重量％超であり、いずれも、加熱後に接合強度が低下していた。それに対し、単独添加したＡｇ濃度が本発明の成分範囲である実施例１〜３では、接合強度の低下は認められず、非常に良好であった。
【００３３】
実施例１〜３の金銀合金細線の伸線工程の途中において、線径１００μｍの時に加熱処理を施しておくと、線径が２５μｍでの連続焼鈍後の引張伸びが２割以上向上し、ループ形状のばらつきも低減していた。
【００３４】
さらに、実施例１〜３のいずれの細線とも、線径である２５μｍでの調質熱処理において、温度が５５０℃では、表面に銀の酸化膜が形成されており、大気中に５ヶ月放置した後も、細線表面の変色は認められず、５００本のリード端子との接合性テストでも不良はみられなかった。それに対し、３００℃の低温で調質熱処理した上記の細線では、表面の部分的に赤色部分が認められ、接着性において２本で接着不良が認められた。
【００３５】
Ａｇの適性量の含有に加えて、Ｃｕ，Ｐｄ，Ｐｔを０．０１〜４重量％（但し、Ｃｕは０．３〜４重量％）の範囲で含有する実施例４〜１０では、接合直後の接合強度が６０ｇｆ以上と高い値を示しており、例えば含有量が上記範囲をはずれる実施例ｂ１〜ｂ８などと比較しても、２割以上の向上が確認された。
【００３６】
Ａｇの適性量の含有に加えて、Ｃａ，Ｃｅ，Ｙの含有量が０．０００５〜０．２重量％の範囲である実施例１１〜１８では、ループ形成時のワイヤ曲がり量が２０μｍ以下であり、すなわち金細線の直径よりも小さく抑えられているのに対し、例えば含有量が上記範囲をはずれる実施例ｂ９〜ｂ２０ではワイヤ曲がり量が３５μｍ以上であることと比較しても、４割以上低減している。
【００３７】
Ａｇの適性量の含有に加えて、Ｍｎ，Ｃｒの含有量が０．０１〜０．２重量％の範囲である実施例１９〜２３では、樹脂封止後に加熱した接合においても化合物の腐食が抑制されていることが確認された。一方、Ｍｎ，Ｃｒの含有量が０．２重量％を超えると、ゴール部の形状が真球からずれて扁平であった。
【００３８】
Ｃｕ，Ｐｄ，Ｐｔの元素群と、Ｉｎを必須成分とし、Ｃａ，Ｉｎ，希土類元素の元素群とを、本発明の請求項第５項に記載の範囲で含有する実施例２４，２５では、樹脂封止時のワイヤ流れ率が２％以下であり、他の金合金細線における流れ率が４％以上の結果と比較しても、半分以下にまでに低く抑えられていることが確認された。
【００３９】
【表１】

Figure 0003673368
【００４０】
【表２】
Figure 0003673368
【００４１】
【表３】
Figure 0003673368
【００４２】
【表４】
Figure 0003673368
【００４３】
【発明の効果】
以上説明したように、本発明においては、高濃度の銀を適性範囲で含有させて、材料費の低減と、優れた接合信頼性を向上させた金銀合金細線を提供するものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gold alloy fine wire having excellent joint reliability used for connecting an electrode on a semiconductor element and an external lead.
[0002]
[Prior art]
As a connection method for obtaining electrical continuity between an internal wiring on a semiconductor element such as IC or LSI and an inner lead portion, a bonding wire method using a thin wire having a wire diameter of 20 to 50 μm is mainly used. Currently, gold and aluminum are used as the material for the fine wires. An aluminum thin wire has the advantage of being highly reliable because the same kind of material can be connected to the aluminum electrode portion, and an advantage of the gold thin wire is that the gold is chemically stable. In the ball bonding used for the connection with the aluminum electrode, the gold thin wire does not have to worry about oxidation when the wire is melted in the atmosphere, and a true and clean ball can be easily obtained. Even in ball bonding with an aluminum electrode, good bonding properties are obtained by thermocompression bonding using ultrasonic waves, and high-speed bonding and mass productivity are excellent. On the other hand, aluminum is easily oxidized when melted in the atmosphere, so it cannot be applied to ball connection and is used in a connection method in which a ball is not formed. Since this connection method reduces mass productivity during use, the use of aluminum thin wires is limited to ceramic packages that require high reliability even though they are expensive. For these reasons as well, gold thin wires are widely used in resin-sealed semiconductors that occupy most of LSIs.
[0003]
In the semiconductor market, in addition to enhancing functionality, fierce price competition is taking place, and there is an urgent need to reduce material costs for components. In the gold fine wire, the raw material gold is expensive, and it is not expected to reduce the cost by improving the production method of the gold fine wire. Therefore, for the purpose of reducing material costs, copper, silver, and palladium fine wires have been studied as materials that can be substituted for gold. However, there are still problems such as ball formability, bondability, reliability, and problems of corrosion with resin, and the present situation is that they have not been put into practical use. Under such circumstances, there is a strong demand from the market for a semiconductor element gold wire that has characteristics that can be applied to high-density mounting and that can reduce costs.
[0004]
Almost all of the gold thin wires are high purity thin wires with a purity of 99.99% (4N: Four Nine), in which the total amount of impurities added for the expression of properties is 0.01% or less. While the present situation is progressing with the development of highly functional semiconductors, the component range has not changed significantly. Recently, a thin alloy wire containing about 1% of the total amount of impurities has also been studied, but a gold alloy thin wire that has achieved alloying of 10% or more when emphasizing the merit of significant cost reduction has been used. There are no examples.
[0005]
Ag, Pt, Pd, Cu, etc., which are solid-dissolved with gold, can be considered as elements that can be added to gold at a high concentration of the order of% or more. However, there are many problems associated with alloying, and those that can be put into practical use are limited as gold alloy thin wires for semiconductors containing a high concentration for cost reduction. For example, the concentration of Pt, Pd, and Cu is limited with the upper limit of about 5% as a guideline due to the high concentration. If it is contained more than that, there will be problems such as deformation failure at the time of wire bonding due to an increase in the strength of the wire, or damage to the semiconductor element at the time of bonding due to an increase in the hardness of the ball part.
[0006]
In the case of high concentration addition of Ag, JP-A-55-158642 discloses 20 to 50% by weight as the addition range of Ag in consideration of cost reduction and discoloration of the surface of fine wires due to sulfurization. In JP-A-56-13740 and JP-A-56-19628, addition of Ag is excellent in mechanical strength at high temperatures, particularly in breaking strength, and in tensile strength in the joint. In view of the above, it is disclosed that the addition range of Ag is 19 to 59% by weight and the other element groups Pd, Pt, Rh, Ir, Os, and Ru are used in combination with 0.0003 to 0.1% by weight. In JP-A-56-19628, the addition range of Ag for obtaining the same effect is 19 to 59% by weight, and other element groups Be, Ca, Co, Fe, and Ni are 0.0003 to 0%. Disclosed in combination with 1% by weight.
[0007]
As for Ag, even if it is contained at a high concentration, it is confirmed that the strength of the fine wire is not increased and there is no problem, oxidation at the time of ball melting in the atmosphere is suppressed, and the curing of the ball portion is reduced. Addition of Ag is promising as a high concentration content for achieving cost reduction. However, as a thin wire for a semiconductor element used for actual mass production, a gold-silver alloy thin wire containing Ag at a high concentration is not used.
[0008]
[Problems to be solved by the invention]
A gold-silver alloy thin wire containing a high concentration of silver, which is expected as a promising candidate for reducing the cost of gold thin wires, has good characteristics in ball shape, surface properties, bondability, etc. It is important to have a loop shape and mechanical properties that do not contact adjacent wires in a narrow pitch connection. In addition, the present inventors have studied various practical applications, and the greatest problem with high-concentration addition of silver is the reduction in bonding strength when heated for a long time at the junction with the aluminum electrode on the semiconductor element. Was found to be a problem. That is, when a gold alloy thin wire containing Ag is stored at a high temperature after being bonded to an aluminum electrode, the bonding strength is reduced, or even when it is further heated, peeling occurs. Such a significant decrease in the bonding reliability between the gold ball portion and the aluminum electrode is not observed in the existing 4N high-purity gold thin wire.
[0009]
Therefore, the present invention is a gold-silver alloy fine wire containing Ag element at a high concentration, so that it can withstand heat generation during use and high-temperature use environment, etc., when it is stored at high temperature in the atmosphere, resin-sealed state, The purpose is to improve the bonding reliability with the aluminum electrode, particularly the long-term reliability at high temperatures.
[0010]
[Means for Solving the Problems]
The present inventors have found that, in a gold-silver alloy fine wire containing a high concentration of several percent or more of Ag in gold, the bonding reliability is very excellent only in a limited range in the Ag concentration range. . As a case where the concentration deviated from the appropriate concentration range, it was confirmed that defects occurred due to a decrease in bonding strength after high-temperature storage, both in the range below the lower limit and above the upper limit. That is, excellent bonding reliability can be obtained only in a limited concentration range.
Furthermore, considering the improvement of the viewpoint of bondability and loop shape, as a result of examining the addition of the third element in the gold and silver alloy fine wire, it was confirmed that the content in the proper range was satisfactory.
[0011]
That is, this invention is based on the said knowledge, Comprising: The structure described in each following item makes it a summary.
(1) A gold-silver alloy fine wire for a semiconductor element, containing Ag in a range of 11 to 18.5% by weight, and the balance consisting of gold and inevitable impurities.
(2) Ag is contained in the range of 11 to 18.5% by weight, and at least one of Cu, Pd, and Pt is 0.01 to 4% by weight in total (provided that Cu is 0.3 to 4% by weight) ) , And the balance consists of gold and unavoidable impurities, and is a gold-silver alloy fine wire for semiconductor elements.
(3) Ag is contained in a range of 11 to 18.5% by weight , and at least one of Ca, Ce, and Y is contained in a total range of 0.0005 to 0.05% by weight, with the balance being gold and A gold-silver alloy fine wire for semiconductor elements, characterized by comprising inevitable impurities.
(4) Ag is contained in a range of 11 to 18.5% by weight, and at least one of Mn and Cr is contained in a total range of 0.01 to 0.2% by weight, with the balance being gold and inevitable impurities. A gold-silver alloy fine wire for a semiconductor element, comprising:
[0012]
(5) Ag is contained in a range of 11 to 18.5% by weight, at least one of Cu, Pd, and Pt is contained in a total range of 0.01 to 4% by weight, and In is an essential component. A gold-silver alloy fine wire for a semiconductor device, containing at least one of Ca, In, and rare earth elements in a total amount of 0.0005 to 0.05% by weight, and the balance consisting of gold and inevitable impurities.
(6) Ag is contained in a range of 11 to 18.5% by weight, at least one of Mn and Cr is contained in a total range of 0.01 to 0.2% by weight, and at least Cu, Pd, Pt 1 type in total in the range of 0.01 to 4% by weight, further containing at least one of Ca, In and rare earth elements in total in the range of 0.0005 to 0.05% by weight, with the balance being gold And a gold-silver alloy fine wire for a semiconductor element, characterized by comprising inevitable impurities.
(7) A semiconductor element in which the thin wire described in each of (1) to (6) above is connected to a wiring electrode portion made of aluminum or an aluminum alloy.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Below, the structure of this invention regarding a gold-silver alloy fine wire is further demonstrated.
In a conventional gold wire, a gold / aluminum compound grows at a junction with an aluminum electrode by high-temperature storage in the atmosphere, but no major practical problem has occurred. As an example of the accelerated heating test, even if a heating test is performed in the atmosphere at a high temperature of 200 ° C. for 1000 hours, no decrease in bonding strength is observed.
[0014]
However, a gold-silver alloy fine wire containing a high concentration of Ag in gold has a problem in that the bonding strength is lowered after high-temperature storage at the bonded portion with the aluminum electrode. This is a phenomenon that is not seen with normal gold fine wires, and the growth of intermetallic compound phases at the joints changes due to the effect of Ag contained in gold at a high concentration, resulting in a metal different from normal gold fine wires. This is because the intermetallic phase has grown. As an example of a significant decrease in reliability, a gold alloy thin wire containing Ag with a high concentration on the order of% is observed to have a bonding strength that is reduced to about 1/3 of that before heating at 200 ° C. for 10 hours. It was.
[0015]
In the research conducted by the present inventors, it has been found for the first time that the bonding reliability does not change monotonously with an increase in Ag concentration but is excellent only in a certain concentration range. An appropriate concentration range of Ag is in the range of 11 to 18.5% by weight. This is because if the Ag content is less than 11% by weight and more than 18.5% by weight, the bonding reliability with the aluminum electrode after heating is significantly reduced. That is, excellent practical performance is exhibited only when the Ag concentration range is within the above range, and a great effect as cost reduction is also expected.
[0016]
In manufacturing the above gold-silver alloy thin wire, heat treatment is performed in the middle of the wire drawing process, so that the heat treatment (temper annealing) at the final wire diameter is performed and the elongation is improved in addition to the increase in strength. And the variation in loop shape can be reduced.
[0017]
In addition, after performing temper annealing at the final wire diameter, by forming a stable oxide film of silver on the surface of the fine wire, the adhesiveness of the fine wire and the change over time while left in the atmosphere, etc. Can be suppressed. This is because the progress of further oxidation in the atmosphere can be suppressed, and the reaction between silver in gold and a small amount of sulfur gas contained in the atmosphere can be suppressed.
[0018]
Furthermore, it discovered that the effect which improves use performance was acquired, without impairing joining reliability in the gold-silver alloy fine wire for semiconductor elements which has said Ag in high concentration.
[0019]
By containing at least one of Cu, Pd, and Pt in a total amount of 0.01 to 4% by weight (however, Cu is 0.3 to 4% by weight) in the gold-silver alloy thin wire of the present invention, The bonding strength immediately after connection with the aluminum electrode can be increased. The effect is further enhanced by containing the above elements in combination with Ag rather than adding only the high purity gold. The content of Cu, Pd, and Pt is determined to be within the above range because the effect is small if the content is less than 0.01% by weight, and if the content exceeds 4% by weight, the ball portion is cured. This is based on the reason that if the deformation at the time of joining is reduced to avoid this, the joining strength is rather lowered.
[0020]
When a large amount of silver is contained in the gold, in connection with the increase in strength at the time of wire drawing, hardening due to wire drawing progresses in the manufacturing process. Further, even after the semiconductor element and the lead portion are connected, there is a concern that bending deformation increases when the loop of the gold-silver alloy fine wire is formed. If the gold-silver alloy fine wire of the present invention further contains at least one of Ca, Ce, and Y in a total range of 0.0005 to 0.05% by weight, the disconnection failure at the time of wire drawing is reduced, and the loop is formed. Since bending deformation is reduced, a gold-silver alloy fine wire suitable for high-density joining with a narrow adjacent fine wire pitch can be obtained. The effect is higher when the above element is contained in combination with Ag than when only the high purity gold is added.
The content of Ca, Ce, Y is determined to be within the above range if the amount is less than 0.0005% by weight, the effect is small. If it exceeds 0.05% by weight, the wire is drawn even if heat treatment is performed after wire drawing. This is because it becomes difficult to reduce the processing defects of the wire, and the bending deformation at the time of wire loop formation increases.
[0021]
The gold-silver alloy thin wire of the present invention contains at least one of Cu, Pd, and Pt in a total range of 0.01 to 4% by weight, further contains In as an essential component, and contains at least one of Ca, In, and rare earth elements. It has been found that when the seeds are contained in the range of 0.0005 to 0.05% by weight in total, the deformation amount of the gold-silver alloy fine wire in the resin sealing step is reduced. This is related to an increase in high temperature strength. About the effect which reduces the deformation amount at the time of resin sealing by said element addition, a higher effect is acquired in containing together with Ag. Here, the reason why the content of each element group is defined as the above range is based on the reason described above.
[0022]
If the gold-silver alloy thin wire of the present invention further contains at least one of Mn and Cr in the range of 0.01 to 0.2% by weight in total, the reliability in the resin-sealed joint is improved. When heated after resin sealing using a conventional gold fine wire, the intermetallic compound phase grown on the joint causes a corrosion reaction with the resin component, causing an increase in electrical resistance and a decrease in joint strength. The same phenomenon occurs in the gold-silver alloy thin wire, but the corrosion reaction is suppressed by containing Mn and Cr. Here, the content is determined to be in the above range because the effect is small if it is less than 0.01% by weight, and if it exceeds 0.2% by weight, it is difficult to obtain a true and clean ball part. It is.
[0023]
【Example】
Examples will be described below.
Electrolytic gold having a gold purity of about 99.995% by weight or more and high purity having an Ag purity of 99.95% or more were used. The master alloy containing each of the additive elements described above was individually melt-cast in a high-frequency vacuum melting furnace to melt the master alloy.
[0024]
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. The film was continuously annealed to adjust the elongation value to about 4%.
Table 1 also shows the results of examining the usage performance of the obtained gold alloy thin wire, mainly focusing on bonding properties for use in semiconductor devices.
[0025]
Using a high-speed automatic bonder used for wire bonding, ten gold-silver alloy balls produced on the wire tip by arc discharge were collected and observed with a scanning electron microscope. Good balls that are not shaped like balls, or that cannot be bonded to the electrodes on the semiconductor element, such as those with shrinkage holes observed at the tip of the ball, are marked with a △ mark and have a true sphere and a clean surface. Is marked with a circle.
[0026]
The joint strength of the ball joint was measured by the shear test method in which the jig was translated 2 μm above the aluminum electrode and the shear fracture was read, and the average value of 40 fracture loads was measured. Furthermore, after the semiconductor device in which the gold ball was bonded to the aluminum electrode was not resin-sealed, it was heat-treated in nitrogen gas at 200 ° C. for 200 hours, and then the change in bonding strength was evaluated based on the average value of 40 shear tests.
[0027]
Wire bending at the time of loop formation of gold and silver alloy thin wire is observed from the upper direction of the wire almost perpendicular to the semiconductor element, and the wire bonded so that the bonding distance (span) of both ends of the wire is 4.5 mm. The distance between the perpendicular line between the straight line connecting the parts and the part where the bending of the wire is the maximum was shown as an average value of 50 measured using a projector.
[0028]
Regarding the measurement of the wire flow after resin sealing, the lead frame on which the semiconductor element bonded to obtain a wire span of 4.5 mm is sealed with epoxy resin using a molding device, and then soft X The inside of the semiconductor element sealed with resin using a non-destructive inspection apparatus is projected by X-ray, and the flow rate of 40 portions where the wire flow is maximum is measured by the same procedure as the wire bending described above. The value (percentage) divided by the span length was defined as the wire flow after sealing.
[0029]
Corrosion investigation at the joint was performed by sealing the semiconductor device joined with the gold wire with an epoxy resin and then heat-treating in nitrogen gas at 200 ° C. for 200 hours, and then polishing the ball joint vertically to grow at the joint interface. Corrosion of the intermetallic compound layer of gold and aluminum 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 the inhibition of corrosion is remarkable, and ◎ mark, and when 40% or more, the corrosion is remarkable, Δ mark Intermediate ones of 5% to 40% are indicated by ◯ marks.
[0030]
In Table 1 (Table 1-1, Table 1-2), Examples 1 to 3 relate to the description of claim 1 of the present invention, Examples 4 to 10 are the second item, Example 11 to 18 is the result of the gold-silver alloy fine wire according to the third item, Examples 19 to 23 are the fourth item, Examples 24 and 25 are the fifth item, and Examples 26 and 27 are the sixth item.
[0031]
Examples b1 to b26 in Table 2 are related to the present invention because the Ag content is within the scope of claim 1, but the element addition amount other than Ag is from claims 2 to 2. The gold alloy fine wires deviating from the appropriate content described in the 4th claim are shown for comparison. Examples b1 to b8 are shown as comparisons with respect to the second claim, Examples b9 to b20 are shown as comparisons with the third term, and Examples b21 to b26 are shown as comparisons with the fourth term.
[0032]
Table 3 is a comparative example in which the Ag content deviates from the present invention, and the bonding strength after heating did not decrease with the high-purity gold of Comparative Example 1, but in Comparative Examples 2 and 3, the Ag concentration was 11% by weight. In Comparative Examples 4 and 5, the Ag concentration was more than 18.5% by weight, and in both cases, the bonding strength decreased after heating. On the other hand, in Examples 1 to 3, in which the concentration of Ag added alone was within the component range of the present invention, no reduction in bonding strength was observed, which was very good.
[0033]
In the middle of the wire drawing process of the gold and silver alloy thin wires of Examples 1 to 3, when the heat treatment is performed when the wire diameter is 100 μm, the tensile elongation after continuous annealing at a wire diameter of 25 μm is improved by 20% or more, and the loop Variations in shape were also reduced.
[0034]
Furthermore, in any of the thin wires of Examples 1 to 3, in the tempering heat treatment at 25 μm, which is the wire diameter, a silver oxide film was formed on the surface at a temperature of 550 ° C. and left in the atmosphere for 5 months. Later, no discoloration of the surface of the fine wire was observed, and no defect was found in the bonding test with 500 lead terminals. On the other hand, in the above-mentioned thin wire subjected to the tempering heat treatment at a low temperature of 300 ° C., a red portion was partially recognized on the surface, and adhesion failure was recognized with two adhesives.
[0035]
In addition to containing an appropriate amount of Ag, in Examples 4 to 10 containing Cu, Pd and Pt in the range of 0.01 to 4 % by weight (where Cu is 0.3 to 4% by weight) , immediately after joining The bonding strength of No. 2 was as high as 60 gf or more, and for example, an improvement of 20% or more was confirmed even when compared with Examples b1 to b8 and the like whose contents deviated from the above range.
[0036]
In Examples 11 to 18 in which the content of Ca, Ce, and Y is in the range of 0.0005 to 0.2% by weight in addition to the inclusion of an appropriate amount of Ag, the wire bending amount during loop formation is 20 μm or less. Yes, i.e., less than the diameter of the fine gold wire, for example, in Examples b9 to b20 in which the content deviates from the above range, the wire bending amount is 35 μm or more compared to 40% or more. Reduced.
[0037]
In Examples 19 to 23 in which the content of Mn and Cr is in the range of 0.01 to 0.2% by weight in addition to the inclusion of the appropriate amount of Ag, the corrosion of the compound is also caused in the bonding heated after the resin sealing. It was confirmed that it was suppressed. On the other hand, when the content of Mn and Cr exceeded 0.2% by weight, the shape of the goal portion was shifted from the true sphere and was flat.
[0038]
In Examples 24 and 25 containing an element group of Cu, Pd, and Pt, an essential component of In, and an element group of Ca, In, and a rare earth element within the scope of claim 5 of the present invention, It was confirmed that the wire flow rate during resin sealing was 2% or less, and the flow rate in other gold alloy thin wires was suppressed to less than half even when compared with the result of 4% or more. .
[0039]
[Table 1]
Figure 0003673368
[0040]
[Table 2]
Figure 0003673368
[0041]
[Table 3]
Figure 0003673368
[0042]
[Table 4]
Figure 0003673368
[0043]
【The invention's effect】
As described above, the present invention provides a gold-silver alloy fine wire that contains a high concentration of silver in an appropriate range to reduce material costs and improve excellent bonding reliability.

Claims (7)

Ａｇを１１〜１８．５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半導体素子用金銀合金細線。  A gold-silver alloy fine wire for a semiconductor element, containing Ag in a range of 11 to 18.5% by weight, and the balance consisting of gold and inevitable impurities. Ａｇを１１〜１８．５重量％の範囲で含有し、さらにＣｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％（但し、Ｃｕは０．３〜４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半導体素子用金銀合金細線。Ag is contained in a range of 11 to 18.5% by weight, and at least one of Cu, Pd and Pt is added in a range of 0.01 to 4% by weight (provided that Cu is 0.3 to 4% by weight) . A gold-silver alloy fine wire for a semiconductor element, characterized in that the remainder comprises gold and inevitable impurities. Ａｇを１１〜１８．５重量％の範囲で含有し、さらにＣａ，Ｃｅ，Ｙ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半導体素子用金銀合金細線。Ag is contained in a range of 11 to 18.5% by weight , and at least one of Ca, Ce and Y is contained in a total range of 0.0005 to 0.05% by weight, and the balance is made up of gold and inevitable impurities. A gold-silver alloy fine wire for a semiconductor device, characterized in that Ａｇを１１〜１８．５重量％の範囲で含有し、さらにＭｎ，Ｃｒの少なくとも１種を総計で０．０１〜０．２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半導体素子用金銀合金細線。  It contains Ag in a range of 11 to 18.5% by weight, further contains at least one of Mn and Cr in a total range of 0.01 to 0.2% by weight, and the balance is made of gold and inevitable impurities. Gold-silver alloy fine wire for semiconductor elements. Ａｇを１１〜１８．５重量％の範囲で含有し、Ｃｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％の範囲で含有し、さらにＩｎを必須成分とし、Ｃａ，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半導体素子用金銀合金細線。Ag is contained in a range of 11 to 18.5% by weight, at least one of Cu, Pd, and Pt is contained in a total range of 0.01 to 4% by weight, and In is an essential component. A gold-silver alloy thin wire for a semiconductor device, containing a total amount of at least one rare earth element in the range of 0.0005 to 0.05% by weight, the balance being gold and inevitable impurities. Ａｇを１１〜１８．５重量％の範囲で含有し、Ｍｎ，Ｃｒの少なくとも１種を総計で０．０１〜０．２重量％の範囲で含有し、Ｃｕ，Ｐｄ，Ｐｔの少なくとも１種を総計で０．０１〜４重量％の範囲で含有し、さらにＣａ，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半導体素子用金銀合金細線。  Ag is contained in a range of 11 to 18.5% by weight, at least one of Mn and Cr is contained in a total range of 0.01 to 0.2% by weight, and at least one of Cu, Pd and Pt is contained. Contains in total in a range of 0.01 to 4% by weight, further contains at least one of Ca, In and rare earth elements in a total range of 0.0005 to 0.05% by weight, with the balance being gold and inevitable impurities A gold-silver alloy fine wire for a semiconductor element, comprising: 請求項１乃至６のいずれか１項記載の細線を用い、アルミまたはアルミ合金である配線電極部とを接続した半導体素子。  A semiconductor element in which the thin wire according to claim 1 is connected to a wiring electrode portion made of aluminum or an aluminum alloy.
JP13411497A 1997-05-23 1997-05-23 Gold-silver alloy fine wire for semiconductor devices Expired - Fee Related JP3673368B2 (en)

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KR100801444B1 (en) 2006-05-30 2008-02-11 엠케이전자 주식회사 Au-Ag based alloy wire for a semiconductor package
JP4874922B2 (en) * 2007-01-18 2012-02-15 新日鉄マテリアルズ株式会社 Bonding wire for semiconductor mounting
JP4947670B2 (en) * 2009-12-16 2012-06-06 田中電子工業株式会社 Heat treatment method for bonding wires for semiconductor devices
CN103155129A (en) * 2011-06-10 2013-06-12 田中电子工业株式会社 High-strength, high-elongation-percentage gold alloy bonding wire
CN110029243B (en) * 2019-04-02 2020-09-25 安徽捷澳电子有限公司 Noble metal flat wire and preparation method thereof
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