JP3764629B2 - Semiconductor device with wire wedge-bonded - Google Patents

Semiconductor device with wire wedge-bonded Download PDF

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Publication number
JP3764629B2
JP3764629B2 JP2000120333A JP2000120333A JP3764629B2 JP 3764629 B2 JP3764629 B2 JP 3764629B2 JP 2000120333 A JP2000120333 A JP 2000120333A JP 2000120333 A JP2000120333 A JP 2000120333A JP 3764629 B2 JP3764629 B2 JP 3764629B2
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Japan
Prior art keywords
wire
bonding
wedge
electrode film
gold
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Expired - Fee Related
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JP2000120333A
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Japanese (ja)
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JP2001308133A (en
Inventor
智裕 宇野
晋一 寺嶋
宏平 巽
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Nippon Steel Corp
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Nippon Steel Corp
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    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/20—Parameters
    • H01L2924/207—Diameter ranges
    • H01L2924/20754—Diameter ranges larger or equal to 40 microns less than 50 microns

Abstract

PROBLEM TO BE SOLVED: To ensure a bondability and a long-term reliability superior in the wedge bond of a gold wire with an electrode film suited for narrowing the pitch of electrodes. SOLUTION: For wedge-bonding a gold alloy boding wire 1 onto an electrode film 3, the relation of the minimum value D of a wire compression bond thickness at its bond zone to the electrode film thickness (t) is set for 4t+2<=D (&mu;m). For wedge-bonding the bonding wire 1 onto a metal bump 2 formed on the electrode film 3, the height H of the bump 2 is set for 2t+2<=H<=6t+50 (&mu;m).

Description

【０００１】
【発明の属する技術分野】
本発明は、金ボンディングワイヤを用いて、半導体素子上の電極と外部端子とを電気的に接続する半導体装置に関する。
【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を接合するボンディングワイヤとしては、線径２０−５０μｍ程度の金ボンディングワイヤ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樹脂封止する。
【０００３】
半導体素子上の電極膜に用いられる材質は、現在、ＡｌまたはＡｌ合金が主流である。最近、半導体素子の高集積化が進むに従い、ＣｕまたはＣｕ合金の電極膜が使用されて始めており、またＣｕの酸化防止などを目的として、表面にＡｌ層またはＡｕ層が形成されたＣｕまたはＣｕ合金の電極膜も実用化されている。
【０００４】
半導体素子の高集積化、高密度化の傾向により、金ボンディングワイヤの狭ピッチ接合が必要となっており、近年、金ボンディングワイヤの高強度細線化、狭ピッチ接合技術などが進歩してきている。しかし、狭ピッチ化が進むに従い、隣接するボール接合部の接触、あるいはキャピラリ冶具の先端形状の加工限界などの制約が問題となる。
【０００５】
従来のボール接合よりも狭ピッチに好適な接合として、ボール部を介さないで直接ワイヤを電極に接合するウェッジ接合がある。この接合では、ボールを形成しないため熱影響部がなくループ曲がりが低く抑えられるなど、狭ピッチ接合の点で有利となる。しかし、ウェッジ接合法では超音波印加の方向性の制約などにより、生産性が低下することなどの問題があり、金ワイヤによるウェッジ接合はほとんど実用化されておらず、現在でも金ワイヤではボール接合が主流である。
【０００６】
アルミ合金細線によるウェッジ接合は、セラッミックスパッケージされる半導体素子に利用されている。アルミ合金細線では、半導体素子上のアルミ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、アルミ合金細線を樹脂封止する半導体素子に使用すると、外部から侵入した水分などによりアルミ合金細線が腐食することが問題となるので、アルミ合金細線は樹脂封止パッケージへの適用は困難である。従って、アルミ合金細線の用途は限定され、しかも線径は１００−５００μｍ程度の太径で使用される場合がほとんどである。
【０００７】
従来のウェッジ接合は、ボール接合に比して生産性が低いことが問題とされてきたが、ボンディング装置の性能向上などにより、ウェッジ接合でもボール接合に匹敵する生産性が期待される。
【０００８】
今後、半導体実装の主流である樹脂封止パッケージにおいて、狭ピッチ化に適した、金合金細線をウェッジ接合する半導体装置が所望されている。
【０００９】
【発明が解決しようとする課題】
金ワイヤのウェッジ接合法は、接続材料が金とアルミである点に関しては金ワイヤのボール接合法と類似しており、また、ワイヤを電極上に直接接合する点では、アルミ合金細線のウェッジ接合法と類似する。しかしながら、従来のボール接合技術およびアルミ合金細線の接合技術を用いただけでは、金ワイヤのウェッジ接合において接合性および信頼性を確保することは困難であり、具体的な問題について下述する。
【００１０】
ウェッジ接合ではワイヤを直接接合するため、ワイヤ径の１．４〜２．５倍のボール部を接合するボール接合法と比べて接合面積が減少することなどの理由から、ボール接合の場合のような良好な金属接合を得ることが難しい。金合金細線のウェッジ接合でも、荷重を高めれば接合強度を増加することはできるものの、ワイヤも過剰に変形させてしまうため、ワイヤ断面積の減少および過大な加工に伴ないワイヤ強度を著しく低下させることが問題となる。特に、接合部近傍の最弱部では、ループ形成時あるいは使用時にワイヤ破断に至る不良が発生してしまう。一方、アルミ合金細線によるウェッジ接合では、こうした接合部近傍での破断はほとんど問題とならない。その理由として、アルミ／アルミの同種金属接合のため接合強度が得やすいこと、また現行のアルミ合金細線は金ワイヤの数十倍の太径であるため金ワイヤと比較して変形挙動が異なることなどが挙げられる。つまり、太径のアルミ合金細線では、ワイヤ断面積の減少も非常に少ないため、接合部近傍でのワイヤ強度も十分確保することができる。
【００１１】
しかしながら、金ワイヤのウェッジ接合では狭ピッチ接合への対応が求められており、荷重、超音波振動などの接合条件だけの改善では、高速ボンディング時の量産性を高め、接合強度を確保することが困難である。一方、金ワイヤの変形量を減らすと、接合強度の低下をもたらす。これは、従来のボール接合に比べてウェッジ接合では、接合面積を高めるのが困難であり、破断を起こさないための変形許容量に制限があるなどの要因が関連している。先述したように、こうした問題はアルミ合金細線では問題とならず、金ワイヤのウェッジ接合に特有の問題と考えられる。金ワイヤのウェッジ接合では、ワイヤ破断を起こさないで、しかも接合強度を確保することが課題となる。
【００１２】
また、半導体装置の高周波化により動作時の発熱量が増大し、また半導体の使用環境は自動車のエンジン周辺などのように高温に曝されることなどから、接合部の長期信頼性に関する要求が高まっている。金ボール部と電極膜の接合部では、長期信頼性は良好であった。しかしながら、金ワイヤと電極膜とのウェッジ接合部では、長時間加熱されると接合強度が低下することが問題となる。この高温加熱における接合強度の低下は、接合不良の原因であり、金ワイヤのウェッジ接合の実用化を制約する一因となっていた。
【００１３】
こうしたＡｕワイヤのウェッジ接合に関する問題は、アルミ電極膜に限られたことでなく、電極材質がＣｕまたはＣｕ合金、またＡｌ層またはＡｕ層を上層とするＣｕまたはＣｕ合金の電極膜の場合にも、Ａｕワイヤをウェッジ接合した場合に接合性および長期信頼性が低下する問題が懸念されている。
【００１４】
本発明は、金ワイヤと電極膜とのウェッジ接合部において、接合性および長期信頼性に優れた半導体装置を提供することを目的とする。
【００１５】
【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、金ワイヤと電極膜とのウェッジ接合部における接合性および長期信頼性の支配要因について調査した結果、各接合部位の形態、厚さ、寸法、硬さなどが接合性および長期信頼性に密接に関係していることを見出した。
【００１６】
すなわち、本発明は以下の構成を要旨とする。
（１） アルミまたはアルミ合金の電極膜、ＣｕまたはＣｕ合金の電極膜、Ａｌ層またはＡｕ層を上層とするＣｕまたはＣｕ合金の電極膜の上に金合金ボンディングワイヤがウェッジ接合され、その接合部においてワイヤ圧着厚さの最小値Ｄと電極膜厚ｔの関係が、４ｔ＋２≦Ｄ（μｍ）であることを特徴とする半導体装置。
（２） さらにワイヤのビッカース硬度Ｈｗと電極膜のビッカース硬度Ｈｐの関係がＨｐ＋５≦Ｈｗ≦２Ｈｐ＋２０であることを特徴とする上記（１）に記載の半導体装置。
【００１７】
【発明の実施の形態】
以下に、本発明に係わる半導体装置およびワイヤなどの構成についてさらに説明する。
【００１８】
本発明者らは、金ワイヤを電極上に接合するという点ではボール接合法とウェッジ接合法は類似しているものの、接合プロセス、キャピラリ冶具、接合部形態、寸法などの相違により、両者は接合性、長期信頼性が異なることを明らかにした。先述したように、金ワイヤのウェッジ接合法では、ボール接合に比べて長期信頼性および接合性が低下することが問題であり、本発明者らは鋭意研究した結果、長期信頼性および接合性を向上させるためのワイヤ、電極膜など各部位の構造（形態、厚さ、寸法、硬さ）について初めて見出した。具体的な接合構造と長期信頼性および接合性との関係について下述する。
【００１９】
金ワイヤとアルミ電極膜との接合部が高温に曝されると、接合界面ではＡｕ−Ａｌ化合物相が成長し、この化合物相の成長が接合性および長期信頼性と関連しており、従来のＡｕワイヤのボール接合では、良好な接合性および長期信頼性を比較的容易に確保できることが知られていた。本発明者らはウェッジ接合部の拡散挙動を詳細に調査した結果、ボール接合とウェッジ接合では、Ａｕの厚みなどの供給量の差異により、化合物相の成長挙動が異なることを見出した。
【００２０】
金ボールを用いた接合部では、金ボール部の厚さはアルミ電極膜厚よりも十分厚いため、拡散が進行して接合部直下のアルミ電極膜中におけるＡｌ層が消失する。その後も、金ボール部にはＡｕが十分に存在しているのでＡｕ原子の供給が継続されるため、化合物相はよりＡｕ−ｒｉｃｈな相（主にＡｕ4Ａｌ相）へと変化する。
【００２１】
それに比して、ウェッジ接合では、ワイヤの圧着厚さがボール接合と比して小さいため、原子の拡散が十分進行すると、接合部でのアルミ電極のＡｌと金ワイヤ部のＡｕともに拡散に消費されてしまう。その後はＡｕ原子が供給されなくなるため、ウェッジ接合部で成長する化合物相は、ボール接合の場合と比べてＡｌ−ｒｉｃｈな相（例えばＡｕ2Ａｌ、ＡｕＡｌ2相）となる。こうしたボール接合とは異なる化合物相が成長することが、ウェッジ接合において長期信頼性を低下させている原因であることを明らかにした。
【００２２】
こうした機構を踏まえて、ウェッジ接合での長期信頼性および接合性を向上する方策を検討したところ、電極膜に対する金ワイヤ圧着部の相対的な厚さを制御することが有効であることを見出した。ここで図１にウェッジ接合部位を水平方向からみた図を示す。図１では、線径Ｗの金ワイヤ１が、厚さｔの電極膜上にウェッジ接合され、その接合部においてワイヤ圧着厚さの最小値がＤであることを示している。
【００２３】
金ワイヤのウェッジ接合では、図１に示すように、ワイヤ圧着厚さの最小値Ｄと電極膜厚ｔの関係が、４ｔ＋２≦Ｄ（μｍ）であれば、接合直下のアルミ膜中のＡｌ層が消失するまでＡｕの拡散が進行しても、金ワイヤ部位が拡散供給源として機能することにより、加熱後の接合強度の低下が抑えられ、高い信頼性を確保できる。
【００２４】
上記のようなウェッジ接合を行うためには、従来のアルミ合金細線のウェッジ接合における接合技術および冶具などをそのまま適用して、金ワイヤを電極膜上に接合するだけでは、上記のワイヤ圧着厚さと電極膜厚の関係を満足させることはできない。上記のワイヤ圧着厚さを得るためには、例えば、金ワイヤへの合金化元素の添加あるいは、製造における伸線、熱処理などの組合せにより金ワイヤを硬化させたり、また、アルミ膜の合金化、スパッタ製法の適正化により、接合時におけるアルミ電極膜の変形を抑えることなどが有効である。その他、接合時の荷重、超音波振動を調整したり、ワイヤに接するキャピラリ先端の寸法、曲率などの選定により、ワイヤ圧着厚さを適正化することが可能である。
【００２５】
さらに、ワイヤと電極膜の硬さがウェッジ接合での接合性と密接に関係することを見出した。つまり、ウェッジ接合での接合性を高めるためには、ワイヤおよび電極膜それぞれのビッカース硬さＨｗ、Ｈｐの関係がＨｐ＋５≦Ｈｗ≦２Ｈｐ＋２０であると好ましい。これは、金ワイヤの硬さがこの範囲であれば、ウェッジ接合時に荷重、超音波を印加してワイヤをある程度変形させることにより、アルミ電極表面の酸化膜を破壊して良好な金属接合が得られ、さらに加熱後の信頼性も高められるためである。ここでの接合性として、ワイヤ破断強度の低下を抑えつつ接合強度を確保する必要があり、それを判定する基準として、ワイヤ自身の破断強度に対するウェッジ接合部近傍での破断強度の割合Ｒが１／４以上であることが望ましいことを見出した。ワイヤ硬さＨｗと電極膜の硬さＨｐの関係が上記範囲内であれば、この割合Ｒを１／４以上にできるため、良好な接合性が得られるが、Ｈｗ＜Ｈｐ＋５となると金ワイヤがアルミ電極と比して軟らかいため主にワイヤが変形し、Ａｌ酸化膜の破壊が十分進まず接合強度を高めるのが困難であり、またＨｗ＞２Ｈｐ＋２０となると、金ワイヤがアルミ電極と比して過剰に硬くなり接合時に電極下のチップに損傷を与えてしまう。
【００２６】
材料の硬さを調整して上記の関係を満足する手法は幾つかあるが、例えば、後述するウェッジ接合に好適なワイヤを使用したり、またアルミ電極膜の成膜法、合金化、アニール処理などが有効である。一例として、２０〜３０μｍに伸線した金合金ワイヤを用い、アルミ合金（Ａｌ−Ｓｉ、Ａｌ−Ｃｕ、Ａｌ−Ｓｉ−Ｃｕ）膜上にその金合金ワイヤをウェッジ接合することにより、ワイヤ硬さと電極膜の硬さの関係を本発明の範囲内にすることができる。さらに、硬さの関係はＨｐ＋１０≦Ｈｗ≦２Ｈｐ＋５であることがより好ましい。これは、この範囲であれば、低温でも接合強度をより高めることができ、また接合時の衝撃荷重を特に制御することなくチップ損傷も軽減できるためである。
【００２７】
また、上述した、本発明のワイヤ圧着厚さと電極膜厚さの関係および、ワイヤと電極膜のビッカース硬さの関係は、Ａｕワイヤとアルミ電極膜とのウェッジ接合の場合に特に有効であるが、これは電極材質がアルミまたはアルミ合金に限られたことでなく、ＣｕまたはＣｕ合金の電極膜、またＡｌ層またはＡｕ層を上層とするＣｕまたはＣｕ合金の電極膜の場合にも、接合性および長期信頼性を向上する効果が得られることを見出した。つまり、ＡｕワイヤとＣｕ電極との接合では、アルミ電極膜の場合と比較して、接合界面に成長する化合物相の種類、成長速度などに相違が生じるものの、Ｃｕ電極とのウェッジ接合部において接合性および長期信頼性が低下することでは、アルミ電極膜の場合と共通している。Ｃｕ電極へのウェッジ接合における接合性および長期信頼性を向上するために、前述したワイヤと電極膜との厚さの関係（４ｔ＋２≦Ｄ（μｍ））、ビッカース硬さの関係（Ｈｐ＋５≦Ｈｗ≦２Ｈｐ＋２０）を満足することが有効である。
【００３７】
ウェッジ接合における接合性、接合信頼性を向上するために、ワイヤ、電極材の厚さ、硬度、寸法などについて、本発明に係わる関係を実現する手段として、特に、ワイヤの機械的特性、表面性状を調整することが有効であることを見出した。電極材などの材質を変更すると、配線工程、電気的性能なども影響を受けるため、それらを評価し、適正化することまで検討しなくてはならない場合が多いのに対して、ワイヤの材質の変更は比較的容易であり、しかも接合性、接合信頼性を向上する効果も大きい。
【００３８】
すなわち、引張破断強度Ｆ（ＭＰａ）が８０〜４００ＭＰａで、破断伸びＣ（％）が１〜９％であり、さらに強度Ｆと伸びＣの関係が１５０≦Ｆ・Ｃ≦２５００の範囲であり、純度が９９質量％の金である金合金ワイヤを用いると、良好なウェッジ接合が得られる。
【００３９】
ワイヤの引張破断強度Ｆ（ＭＰａ）と破断伸びＣ（％）との積が一定の関係を満足することにより、ウェッジ接合における接合性、接合信頼性を高めることができ、その強度Ｆと伸びＣの関係としては、１５０≦Ｆ・Ｃ≦２５００の範囲であることが望ましいことを見出した。これは、Ｆ・Ｃ＜１５０であれば、ウェッジ接合時にワイヤが過剰に変形して、接合信頼性が低下することが問題であり、Ｆ・Ｃ＞２５００であれば、ワイヤが接合強度を高めることが困難なためである。
【００４０】
さらに、ウェッジ接合性だけでなく、ワイヤのループ形成、樹脂封止時のワイヤ変形などの要求特性を十分満足するためには、Ｆ・Ｃの積を上記の範囲とすることに加えて、引張破断強度Ｆが８０〜４００ＭＰａであり、破断伸びＣが１〜９％の範囲であることが必要である。これは、強度Ｆが８０ＭＰａ未満であれば、ループが下方に垂れる問題が発生し、Ｆが４００ＭＰａを超えるとウェッジ接合時にチップに損傷を与えたり、ループ形状を制御することが困難となり、ループ高さのバラツキが大きくなることが問題となるためである。また、破断伸びＣが１％未満であれば、ウェッジ接合部での強度を確保すること困難であり、Ｃが９％を超えると、ループ形成されたワイヤの直線性が低下することが問題である。
【００４１】
ワイヤの素材は純度９９％以上を有する金合金ワイヤである。つまり、本発明での金合金ワイヤとは、純度１％以下の添加元素を含有するワイヤおよび、純度が９９．９９％以上であり、残りを不可避不純物とする高純度金ワイヤも含まれる。例えば、Ｃａ、Ｂｅ、Ｃｕ、Ａｇ、Ｐｔ、Ｐｄなどから１種類以上の元素を総計で０．０００１−１％の範囲で含有し、残部がＡｕであり、それをダイス伸線により２０〜３０μｍに伸線した金合金ワイヤを用いれば、良好なウェッジ接合特性が得られる。
【００４２】
また、ワイヤを電極に直接接続するウェッジ接合では、上述した、ワイヤの機械的特性に加えて、ワイヤの表面性状も重要であり、ワイヤ表面から１０ｎｍの深さまでの平均酸素濃度が１０ａｔ％以下であることが、ウェッジ接合性の向上には有効であることを見出した。これは、１０ｎｍの深さまでの平均酸素濃度が１０ａｔ％を超えると、接合時に接合強度を低下させる原因となり、また、その酸素濃度が高い表層部を破壊させて良好な接合を得るには、超音波振動を高める必要があり、これに伴い、チップへの損傷、ワイヤの直線性の低下などの問題が発生するためである。ワイヤ表面の平均酸素濃度は、例えばオージェ分光法にて測定できる。
【００４３】
以上のことから、ワイヤの引張破断強度Ｆ（ＭＰａ）が８０〜４００ＭＰａで、破断伸びＣ（％）が１〜９％であり、さらに強度Ｆと伸びＣの関係が１５０≦Ｆ・Ｃ≦２５００の範囲であり、ワイヤ表面から１０ｎｍの深さまでの平均酸素濃度が１０ａｔ％以下とすることにより、ウェッジ接合部の接合性、接合信頼性を向上することができ、さらに良好なループ形状が得られ、樹脂封止時のワイヤ変形も抑制することができ、狭ピッチ接合に適応できることを確認した。こうした性能を有する金ワイヤを得るためには、金中の元素添加、あるいはワイヤ伸線加工技術および熱処理条件の適正化などが有効であることを確認した。
【００４４】
金ワイヤを電極上にウェッジ接合する手法としては、これまで中心的に述べた、ボール部を形成しないで接続するウェッジ−ウェッジ接合法の他に、電極側にボール部を接合する通常のボール接合とは異なり、ワイヤを電極側にウェッジ接合する方法や、チップ同士の電極間をボール−ウェッジ接合する方法もある。こうした電極側にワイヤをウェッジ接合することは、接合面積を縮小できるため狭ピッチ接続には有利であり、また、複数のチップを接続する場合にも活用できる。前述した、ウェッジ接合における接合性および信頼性の低下は、電極側にワイヤをウェッジ接合する手法に共通する問題である。従って、本発明に係わる半導体装置および、それに用いられる金合金ワイヤは、電極側にワイヤをウェッジ接合する方法であれば、ウェッジ−ウェッジ接合、ボール−ウェッジ接合の両手法に適用されるものである。
【００４５】
【実施例】
以下、実施例について説明する。
ワイヤには、高純度金ワイヤ（純度＞９９．９９％）または、Ｃａ、Ｂｅ、Ｃｕ、Ａｇ、Ｐｔ、Ｐｄなどから１種類以上の元素を総計で０．０００１−１％の範囲で含有する金合金ワイヤを用い、その線径Ｗは１５〜３０μｍとした。ワイヤの強度または硬度を調整するために、ワイヤ製造工程において、伸線ダイス減面率（２〜１５％）、伸線速度（１０〜６００ｍ／ｍｉｎ）および、最終段階での熱処理温度（２００〜７００℃）などを選定した。シリコン基板上の電極材質には、純Ａｌ、Ａｌ合金（Ａｌ−１％Ｓｉ、Ａｌ−０．５％Ｃｕ）、純Ｃｕ、またＡｌ層またはＡｕ層を上層（０．１μｍ）とする純Ｃｕ膜などを使用し、電極膜の厚さｔは０．５〜４μｍとした。市販の自動ウェッジボンダーを使用して、電極上にワイヤを接合した。
【００４７】
ワイヤの引張破断強度および伸び率は、長さ１０ｃｍのワイヤ５本の引張試験を実施し、その平均値により求めた。ワイヤの硬度測定は、ビッカース硬度測定法に基づいて、２９ｍＮの荷重で測定し、５点の平均値を求めた。ワイヤ表面の酸素濃度の測定は、オージェ分光装置を用い、ワイヤ表面をスパッタしながら、１０ｎｍの深さの平均値を求めた。
【００４８】
ワイヤ接合部の強度評価としては、プル試験法を用いた。このプル試験法は、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固定した状態で、ボンディング後の金合金細線をフックで上方に引張り、そのときの破断強度を４０本測定し、プル強度の平均値および標準偏差を評価した。その際、電極との接合性を評価するために、フックを掛けて上方引張する箇所を、中央部よりも電極に近いところで試験した。
【００４９】
長期信頼性の評価として、金ワイヤを電極にウェッジ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１８５℃で３００時間加熱した後に、４０本のプル強度を測定した。金ワイヤのウェッジ接合した半導体装置が用いられる使用温度での寿命評価として、１８５℃３００時間の加熱試験は十分と考えられ、この加熱により強度が低下しない場合には、接合部の長期信頼性は良好であると判断できる。
【００５０】
金合金細線のループ形成時のワイヤ曲がりは、ワイヤ長さが約５ｍｍとなるようボンディングを行った後に、半導体素子とほぼ垂直上方向からワイヤを投影機を用いて観察し、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５０本測定した平均値で示した。
【００５１】
接合時のチップ損傷を調べるため、ボンディングした素子を王水中に数分間つけて、金ワイヤおよび電極などを溶解した後に、２００個の接合箇所を光学顕微鏡およびＳＥＭで観察した。光顕観察でもクラックが観察された場合は損傷が大きいとして×印、光顕では損傷は観察されないが、２０００倍程度の倍率で微小な傷または穴が認められるものは○印、光顕およびＳＥＭ観察において損傷が認められない場合は◎印で示した。
【００５３】
【表１】

Figure 0003764629
【００５４】
【表２】
Figure 0003764629
【００５５】
表１において、ワイヤを電極膜上にウェッジ接合に関した実施例１〜１０は、ワイヤ圧着厚さと電極膜厚の関係を第１の発明である４ｔ＋２≦Ｄ（μｍ）の条件範囲とし、また実施例１〜８は、ワイヤと電極膜の硬度の関係を第２の発明であるＨｐ＋５≦Ｈｗ≦２Ｈｐ＋２０の条件範囲に調整したものである。
【００５６】
また表２の比較例１〜９は、ワイヤ圧着厚さと電極膜厚の関係が第１の発明に該当しない例であり、そのなかでも比較例６〜９は、ワイヤと電極膜の硬度の関係が第２の発明の範囲にも該当しない例について、それぞれ比較として示した。
【００５７】
本発明例１〜１０では、ワイヤ圧着厚さの最小値Ｄと電極膜厚ｔの関係が、４ｔ＋２≦Ｄ（μｍ）の関係を満足しており、加熱後でもプル強度は高い値を維持しているのに対し、４ｔ＋２＞Ｄ（μｍ）の関係となっている比較例１〜５では、加熱後のプル強度は明らかに低下していた。
【００５８】
本発明例１〜８では、ワイヤおよび電極膜のビッカース硬度であるＨｗ、Ｈｐの関係がＨｐ＋５≦Ｈｗ≦２Ｈｐ＋２０の範囲であるため、接合直後のワイヤ単位面積当りのプル強度が９８ｍＮ以上の十分高いことが確認された。それに対し、Ｈｐ＋５＞Ｈｗである比較例６、８では初期のプル強度が低くなり、またＨｗ＞２Ｈｐ＋２０である比較例７、９では接合時のチップ損傷が観察された。また、本発明例９，１０は、厚さの関係は４ｔ＋２≦Ｄ（μｍ）を満足するものの、硬度の関係では第２の発明の条件範囲を満足しない例であり、Ｈｐ＋５＞Ｈｗである本発明例９ではプル強度が若干低くなり、Ｈｗ＞２Ｈｐ＋２０である本発明例１０では、少数の電極部の下部にチップ損傷が観察された。さらに、本発明例１〜５は、Ｈｐ＋１０≦Ｈｗ≦２Ｈｐ＋５の関係を満足するため、接合性は特に優れており、チップ損傷も全くみとめられなかった。本発明例７では、Ｈｐ＋５≦Ｈｗ≦２Ｈｐ＋２０の範囲であるものの、Ｈｗ＜Ｈｐ＋１０となることから、チップ表面のＳＥＭ観察により微小な傷が確認されたが、問題のないレベルと判断される。
【００６４】
本発明例１〜１０では、ワイヤの特性をみれば第３の発明に係わる特性を有しており、具体的には、引張破断強度Ｆが８０〜４００ＭＰａで、破断伸びＣが１〜９％であり、さらに強度Ｆと伸びＣの関係が１５０≦Ｆ・Ｃ≦２５００の範囲であった。一方、比較例２、３、７、８、９では、強度Ｆ、伸びＣ、Ｆ・Ｃ、酸素濃度の少なくとも一つ以上の特性が、本発明の範囲を満足しない場合であり、例えば、比較例７ではＦ＞４００ＭＰａであり、また比較例９ではＦ・Ｃ＞２５００であるため、電極下にチップ損傷を与えたり、また比較例８では、平均酸素濃度が１０ａｔ％を超えており、接合強度が低いことが確認された。ワイヤ表面から１０ｎｍの深さまでの平均酸素濃度が１０ａｔ％を超える比較例８では、プル強度が大きく減少しており、ウェッジ接合部における接合性が低下していることが確認された。
【００６５】
【発明の効果】
以上説明したように、本発明においては、金ワイヤと電極膜とのウェッジ接合部において、ワイヤと電極膜の厚さの関係または、硬さの関係を適正化することにより、従来のボール接合よりも狭ピッチ接合に優れ、しかも高い長期信頼性を有する、半導体装置を提供するものである。
【図面の簡単な説明】
【図１】 金ワイヤの電極上へのウェッジ接合部を、水平方向から見た図を示す。
【符号の説明】
１：金合金ワイヤ
２：金属バンプ
３：電極膜
４：シリコン基板
Ｗ：ワイヤ径
Ｄ：ワイヤ圧着厚さの最小値
ｔ：電極の膜厚[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device that electrically connects an electrode on a semiconductor element and an external terminal using a gold bonding wire.
[0002]
[Prior art]
Currently, gold bonding wires having a wire diameter of about 20 to 50 μm are mainly used as bonding wires for bonding between 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, the 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 ultrasonically bonded. 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 resin.
[0003]
Currently, Al or Al alloy is mainly used as the material for the electrode film on the semiconductor element. Recently, as semiconductor devices have been highly integrated, Cu or Cu alloy electrode films have begun to be used, and Cu or Cu layers with an Al layer or Au layer formed on the surface for the purpose of preventing oxidation of Cu or the like. Alloy electrode films have also been put into practical use.
[0004]
Due to the trend toward higher integration and higher density of semiconductor elements, narrow pitch bonding of gold bonding wires is required, and in recent years, high strength thinning of gold bonding wires, narrow pitch bonding technology, and the like have advanced. However, as the pitch becomes narrower, restrictions such as contact between adjacent ball joints or processing limits of the tip shape of the capillary jig become a problem.
[0005]
As a bonding suitable for a narrower pitch than the conventional ball bonding, there is a wedge bonding in which a wire is directly bonded to an electrode without using a ball portion. This joining is advantageous in terms of narrow pitch joining because no ball is formed and there is no heat affected zone and loop bending is kept low. However, the wedge bonding method has problems such as reduced productivity due to restrictions on the direction of application of ultrasonic waves. Wedge bonding with gold wires has hardly been put to practical use. Is the mainstream.
[0006]
Wedge bonding using an aluminum alloy fine wire is used for a semiconductor device to be 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 portion with the aluminum electrode on the semiconductor element. However, when aluminum alloy fine wires are used for semiconductor devices that are resin-sealed, it becomes a problem that the aluminum alloy fine wires corrode due to moisture entering from the outside. is there. Therefore, the use of the aluminum alloy fine wire is limited, and the wire diameter is almost always used with a large diameter of about 100 to 500 μm.
[0007]
Conventional wedge bonding has been considered to have a low productivity as compared to ball bonding, but due to improved performance of the bonding apparatus, productivity equivalent to ball bonding is also expected in wedge bonding.
[0008]
In the future, there is a demand for a semiconductor device that wedge-bonds a gold alloy thin wire suitable for narrowing the pitch in a resin-sealed package that is the mainstream of semiconductor mounting.
[0009]
[Problems to be solved by the invention]
The gold wire wedge bonding method is similar to the gold wire ball bonding method in that the connection material is gold and aluminum, and in that the wire is directly bonded onto the electrode, the wedge bonding of the aluminum alloy thin wire is performed. Similar to legal. However, it is difficult to ensure the bondability and reliability in the wedge bonding of gold wires only by using the conventional ball bonding technology and aluminum alloy fine wire bonding technology, and specific problems will be described below.
[0010]
In wedge bonding, since the wire is directly bonded, the bonding area is reduced as compared with the ball bonding method in which the ball portion of 1.4 to 2.5 times the wire diameter is bonded, as in the case of ball bonding. It is difficult to obtain a good metal joint. Even in the case of wedge bonding of gold alloy thin wires, if the load is increased, the bonding strength can be increased, but the wire is also deformed excessively, so the wire cross-sectional area is reduced and the wire strength is significantly reduced due to excessive processing. Is a problem. In particular, in the weakest part in the vicinity of the joint, a defect that leads to wire breakage occurs during loop formation or use. On the other hand, in wedge bonding using an aluminum alloy fine wire, breakage in the vicinity of such a joint hardly causes a problem. The reason for this is that it is easy to obtain joint strength because of the same kind of aluminum / aluminum metal joint, and the deformation behavior differs from that of gold wire because the current aluminum alloy wire is tens of times thicker than gold wire. Etc. That is, with a large-diameter aluminum alloy thin wire, the wire cross-sectional area decreases very little, so that sufficient wire strength in the vicinity of the joint can be ensured.
[0011]
However, gold wire wedge bonding is required to support narrow pitch bonding, and improving only the bonding conditions such as load and ultrasonic vibration can increase mass productivity during high-speed bonding and ensure bonding strength. Have difficulty. On the other hand, when the deformation amount of the gold wire is reduced, the bonding strength is lowered. This is due to factors such as the fact that it is difficult to increase the bonding area in wedge bonding as compared to conventional ball bonding, and that there is a limit to the amount of deformation that can be prevented from breaking. As described above, such a problem is not a problem with an aluminum alloy fine wire, but is considered to be a problem peculiar to wedge bonding of a gold wire. In wedge bonding of gold wires, there is a problem of ensuring bonding strength without causing wire breakage.
[0012]
In addition, the higher the frequency of semiconductor devices, the greater the amount of heat generated during operation, and the environment in which semiconductors are used is exposed to high temperatures, such as in the vicinity of automobile engines. ing. Long-term reliability was good at the joint between the gold ball portion and the electrode film. However, in the wedge joint portion between the gold wire and the electrode film, there is a problem that the joint strength is lowered when heated for a long time. This decrease in bonding strength due to high-temperature heating is a cause of bonding failure and has been a factor that restricts the practical application of gold wire wedge bonding.
[0013]
The problem related to wedge bonding of Au wires is not limited to the aluminum electrode film, but the electrode material is Cu. Or In the case of a Cu alloy or an electrode film of Cu or Cu alloy with an Al layer or Au layer as an upper layer, there is a concern that the bondability and long-term reliability are lowered when the Au wire is wedge-bonded.
[0014]
An object of the present invention is to provide a semiconductor device excellent in bondability and long-term reliability at a wedge bond portion between a gold wire and an electrode film.
[0015]
[Means for Solving the Problems]
From the viewpoints described above, the present inventors have investigated the governing factors of the bondability and long-term reliability in the wedge joint portion between the gold wire and the electrode film, and as a result, the form, thickness, size, hardness, etc. of each joint portion are as follows. Closely related to bondability and long-term reliability And I found it.
[0016]
That is, the gist of the present invention is as follows.
(1) Aluminum Or Aluminum alloy Electrode film , Cu Or Cu alloy Electrode film Al layer or Au layer Or Cu alloy electrode film of A semiconductor device characterized in that a gold alloy bonding wire is wedge-bonded thereon, and the relationship between the minimum value D of the wire crimping thickness and the electrode film thickness t is 4t + 2 ≦ D (μm) at the bonded portion.
(2) The semiconductor device according to (1), wherein the relationship between the Vickers hardness Hw of the wire and the Vickers hardness Hp of the electrode film is Hp + 5 ≦ Hw ≦ 2Hp + 20.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the semiconductor device and the wire according to the present invention will be further described.
[0018]
The inventors of the present invention are similar to the ball bonding method and the wedge bonding method in that the gold wire is bonded onto the electrode. However, due to differences in the bonding process, capillary jig, bonding portion shape, dimensions, etc., the two are bonded. The long-term reliability was clarified. As described above, in the gold wire wedge bonding method, there is a problem that long-term reliability and bondability are deteriorated compared to ball bonding. Wire to improve, electrode Membrane etc. For the first time, the structure (form, thickness, size, hardness) of each part was found. The relationship between the specific joint structure, long-term reliability and bondability is described below.
[0019]
When the joint between the gold wire and the aluminum electrode film is exposed to a high temperature, an Au-Al compound phase grows at the joint interface, and the growth of this compound phase is related to bondability and long-term reliability. It has been known that good bonding properties and long-term reliability can be relatively easily ensured in ball bonding of Au wires. As a result of examining the diffusion behavior of the wedge joint in detail, the present inventors have found that the growth behavior of the compound phase differs between the ball joint and the wedge joint due to the difference in the supply amount such as the thickness of Au.
[0020]
In the joint portion using gold balls, the gold ball portion is sufficiently thicker than the aluminum electrode film thickness, so that diffusion proceeds and the Al layer in the aluminum electrode film immediately below the joint portion disappears. After that, since Au is sufficiently present in the gold ball portion, the supply of Au atoms is continued, so that the compound phase is a more Au-rich phase (mainly Au-rich). Four Al phase).
[0021]
In contrast, in wedge bonding, the wire crimping thickness is smaller than in ball bonding, so if the diffusion of atoms sufficiently proceeds, both the aluminum of the aluminum electrode and the gold of the gold wire are consumed for diffusion. Will be. After that, since Au atoms are not supplied, the compound phase grown at the wedge bonding portion is an Al-rich phase (for example, Au-phase) compared to the case of ball bonding. 2 Al, AuAl 2 Phase). It has been clarified that the growth of a compound phase different from such ball bonding is the cause of lowering long-term reliability in wedge bonding.
[0022]
Based on these mechanisms, we examined measures to improve long-term reliability and bondability in wedge bonding, and found that it was effective to control the relative thickness of the gold wire crimping part to the electrode film. . Here, FIG. 1 shows a view of the wedge joint portion seen from the horizontal direction. FIG. 1 shows that a gold wire 1 having a wire diameter W is wedge-bonded onto an electrode film having a thickness t, and the minimum value of the wire crimping thickness is D at the bonded portion.
[0023]
In wedge bonding of gold wires, as shown in FIG. 1, if the relationship between the minimum value D of wire crimping thickness and the electrode film thickness t is 4t + 2 ≦ D (μm), the Al layer in the aluminum film directly under the bonding Even if the diffusion of Au proceeds until disappearance, the gold wire portion functions as a diffusion supply source, so that a decrease in bonding strength after heating can be suppressed and high reliability can be ensured.
[0024]
In order to perform the wedge bonding as described above, it is possible to apply the bonding technique and jigs in the conventional aluminum alloy fine wire wedge bonding as they are, and simply bond the gold wire onto the electrode film. The relationship of electrode film thickness cannot be satisfied. In order to obtain the above wire crimping thickness, for example, the addition of an alloying element to the gold wire, or the gold wire is cured by a combination of wire drawing and heat treatment in production, or alloying of an aluminum film, It is effective to suppress the deformation of the aluminum electrode film during bonding by optimizing the sputtering method. In addition, it is possible to optimize the wire crimping thickness by adjusting the load at the time of bonding, ultrasonic vibration, and selecting the dimensions and curvature of the capillary tip in contact with the wire.
[0025]
Furthermore, it has been found that the hardness of the wire and the electrode film is closely related to the bondability in wedge bonding. That is, in order to improve the bondability in wedge bonding, the relationship between the Vickers hardness Hw and Hp of the wire and the electrode film is preferably Hp + 5 ≦ Hw ≦ 2Hp + 20. If the hardness of the gold wire is within this range, a good metal joint can be obtained by destroying the oxide film on the surface of the aluminum electrode by applying a load and ultrasonic waves during wedge joining to deform the wire to some extent. This is because the reliability after heating is further improved. As the bondability here, it is necessary to ensure the bond strength while suppressing the decrease in the wire break strength, and as a criterion for judging this, the ratio R of the break strength in the vicinity of the wedge joint to the break strength of the wire itself is 1. / 4 or more was found desirable. If the relationship between the wire hardness Hw and the electrode film hardness Hp is within the above range, this ratio R can be made ¼ or more, so that good bondability can be obtained, but when Hw <Hp + 5, the gold wire The wire is mainly deformed because it is softer than the aluminum electrode, and the breakdown of the Al oxide film does not progress sufficiently and it is difficult to increase the bonding strength. When Hw> 2Hp + 20, the gold wire is smaller than the aluminum electrode. It becomes excessively hard and damages the chip under the electrode during bonding.
[0026]
There are several methods that satisfy the above relationship by adjusting the hardness of the material. For example, a wire suitable for wedge bonding, which will be described later, is used, or an aluminum electrode film is formed, alloyed, or annealed. Etc. are effective. As an example, by using a gold alloy wire drawn to 20 to 30 μm and wedge bonding the gold alloy wire onto an aluminum alloy (Al—Si, Al—Cu, Al—Si—Cu) film, The hardness relationship of the electrode film can be within the scope of the present invention. Further, the hardness relationship is more preferably Hp + 10 ≦ Hw ≦ 2Hp + 5. This is because, within this range, the bonding strength can be further increased even at low temperatures, and chip damage can be reduced without particularly controlling the impact load during bonding.
[0027]
In addition, the above-described relationship between the wire crimping thickness and the electrode film thickness and the relationship between the wire and the Vickers hardness of the electrode film are particularly effective in the case of wedge bonding between the Au wire and the aluminum electrode film. This is an electrode material made of aluminum Or Not limited to aluminum alloys, but Cu Or Cu alloy Electrode film It has also been found that the effect of improving the bondability and long-term reliability can be obtained also in the case of an electrode film of Cu or Cu alloy having an Al layer or Au layer as an upper layer. In other words, the bonding between the Au wire and the Cu electrode is different in the type of compound phase growing at the bonding interface, the growth rate, etc., compared with the case of the aluminum electrode film, but bonding at the wedge bonding portion with the Cu electrode. The deterioration of the reliability and long-term reliability is common to the case of the aluminum electrode film. In order to improve the bondability and long-term reliability in wedge bonding to a Cu electrode, the relationship between the thickness of the wire and the electrode film (4t + 2 ≦ D (μm)) and the relationship between the Vickers hardness (Hp + 5 ≦ Hw ≦ It is effective to satisfy 2Hp + 20).
[0037]
Wires and electrodes to improve bondability and bonding reliability in wedge bonding Material It has been found that it is particularly effective to adjust the mechanical properties and surface properties of the wire as means for realizing the relationship according to the present invention with respect to thickness, hardness, dimensions, and the like. electrode Materials If the material of the wire is changed, the wiring process, electrical performance, etc. will also be affected, so there are many cases where it is necessary to evaluate and optimize them, while changing the wire material is a comparison. In addition, the effect of improving the joining property and the joining reliability is great.
[0038]
That is, the tensile breaking strength F (MPa) is 80 to 400 MPa, the breaking elongation C (%) is 1 to 9%, and the relationship between the strength F and the elongation C is in the range of 150 ≦ F · C ≦ 2500, When a gold alloy wire having a purity of 99% by mass is used, good wedge bonding can be obtained.
[0039]
By satisfying a certain relationship between the product of the tensile breaking strength F (MPa) and breaking elongation C (%) of the wire, the bondability and bonding reliability in wedge bonding can be improved, and the strength F and elongation C As for the relationship, it has been found that it is desirable that the range is 150 ≦ F · C ≦ 2500. This is a problem that if F · C <150, the wire is excessively deformed at the time of wedge bonding and the bonding reliability is lowered, and if F · C> 2500, the wire increases the bonding strength. This is because it is difficult.
[0040]
Furthermore, in order to fully satisfy not only the wedge bondability but also the required characteristics such as wire loop formation and wire deformation during resin sealing, in addition to making the product of F and C within the above range, tensile It is necessary that the breaking strength F is 80 to 400 MPa and the breaking elongation C is in the range of 1 to 9%. This is because if the strength F is less than 80 MPa, the loop hangs downward, and if F exceeds 400 MPa, it becomes difficult to damage the tip during wedge bonding or control the loop shape. This is because a large variation in the thickness becomes a problem. Further, if the elongation at break C is less than 1%, it is difficult to ensure the strength at the wedge joint, and if C exceeds 9%, the linearity of the loop-formed wire decreases. is there.
[0041]
The material of the wire is a gold alloy wire having a purity of 99% or more. That is, the gold alloy wire in the present invention includes a wire containing an additive element having a purity of 1% or less and a high-purity gold wire having a purity of 99.99% or more and the remainder being an inevitable impurity. For example, one or more elements from Ca, Be, Cu, Ag, Pt, Pd, etc. are contained in the total range of 0.0001-1%, the balance is Au, and it is 20-30 μm by die drawing. If a gold alloy wire drawn in a wire is used, good wedge bonding characteristics can be obtained.
[0042]
Also, wire Extremely In wedge bonding for direct connection, in addition to the above-described mechanical properties of the wire, the surface properties of the wire are also important. The average oxygen concentration from the wire surface to a depth of 10 nm is 10 at% or less. It was found to be effective for improving the sex. This is because when the average oxygen concentration up to a depth of 10 nm exceeds 10 at%, it causes a decrease in bonding strength at the time of bonding, and in order to obtain a good bonding by destroying the surface layer part having a high oxygen concentration, This is because it is necessary to increase the sonic vibration, and this causes problems such as damage to the chip and deterioration of the linearity of the wire. The average oxygen concentration on the wire surface can be measured, for example, by Auger spectroscopy.
[0043]
From the above, the tensile breaking strength F (MPa) of the wire is 80 to 400 MPa, the breaking elongation C (%) is 1 to 9%, and the relationship between the strength F and the elongation C is 150 ≦ F · C ≦ 2500. When the average oxygen concentration from the wire surface to the depth of 10 nm is 10 at% or less, the bondability and bonding reliability of the wedge bonded portion can be improved, and a better loop shape can be obtained. It was also confirmed that wire deformation during resin sealing can be suppressed and that it can be applied to narrow pitch bonding. In order to obtain a gold wire having such performance, it was confirmed that the addition of elements in gold or the optimization of wire drawing technology and heat treatment conditions were effective.
[0044]
In addition to the wedge-wedge bonding method in which the gold wire is wedge-bonded onto the electrode, which has been mainly described so far, the ball portion is bonded to the electrode side. Unlike the method, there are a method in which the wire is wedge-bonded to the electrode side, and a method in which the electrodes between the chips are ball-wedge bonded. Wedge bonding of the wire to the electrode side is advantageous for narrow pitch connection because the bonding area can be reduced, and can also be used for connecting a plurality of chips. The above-described deterioration in the bondability and reliability in wedge bonding is a problem common to the technique of wedge bonding a wire to the electrode side. Therefore, the semiconductor device according to the present invention and the gold alloy wire used therein are applicable to both the wedge-wedge bonding and the ball-wedge bonding methods as long as the wire is wedge-bonded to the electrode side. .
[0045]
【Example】
Examples will be described below.
The wire contains a high-purity gold wire (purity> 99.99%) or one or more elements from Ca, Be, Cu, Ag, Pt, Pd, etc. in a total range of 0.0001-1%. A gold alloy wire was used, and its wire diameter W was 15 to 30 μm. In order to adjust the strength or hardness of the wire, in the wire manufacturing process, the drawing die reduction (2 to 15%), the drawing speed (10 to 600 m / min), and the final heat treatment temperature (200 to 700 ° C.). The electrode material on the silicon substrate is pure Al, Al alloy (Al-1% Si, Al-0.5% Cu), pure Cu, or pure Cu with an Al layer or Au layer as the upper layer (0.1 μm). A film or the like was used, and the thickness t of the electrode film was set to 0.5 to 4 μm. A commercially available automatic wedge bonder was used to bond the wires onto the electrodes.
[0047]
The tensile breaking strength and elongation of the wire were obtained by carrying out a tensile test of five wires having a length of 10 cm and calculating the average value. Wai Ya's The hardness was measured with a load of 29 mN based on the Vickers hardness measurement method, and an average value of 5 points was obtained. The oxygen concentration on the wire surface was measured by using an Auger spectroscope to obtain an average value of a depth of 10 nm while sputtering the wire surface.
[0048]
The pull test method was used for strength evaluation of the wire joint. In this pull test method, the lead frame and the semiconductor element to be measured are fixed after the bonding wire, the gold alloy fine wire after bonding is pulled upward with a hook, the breaking strength at that time is measured 40 pieces, and the average pull strength is measured. Values and standard deviations were evaluated. At that time, in order to evaluate the bondability with the electrode, the portion that was hooked and pulled upward was tested at a location closer to the electrode than the center portion.
[0049]
As an evaluation of long-term reliability, a pull strength of 40 wires was measured after heating a semiconductor device in which a gold wire was wedge-bonded to an electrode without heating with resin at 185 ° C. for 300 hours. As a life evaluation at the working temperature at which a semiconductor device with a gold wire wedge bonded is used, a heating test at 185 ° C. for 300 hours is considered sufficient. If the strength does not decrease due to this heating, the long-term reliability of the bonded portion is It can be judged that it is good.
[0050]
Wire bending at the time of forming a loop of a gold alloy thin wire is performed by bonding the wire so that the wire length is about 5 mm, and then observing the wire from a direction substantially perpendicular to the semiconductor element by using a projector, and starting from the center of the wire. The average distance of 50 perpendicular lines measured between the straight line connecting the joints at both ends of the wire and the portion where the bending of the wire is maximum was shown.
[0051]
In order to examine chip damage during bonding, the bonded element was placed in aqua regia for several minutes to dissolve gold wires and electrodes, and then 200 bonding points were observed with an optical microscope and SEM. If cracks are observed even under light microscope observation, the damage is marked as x, and no damage is observed with light microscope. When is not recognized, it is indicated by ◎.
[0053]
[Table 1]
Figure 0003764629
[0054]
[Table 2]
Figure 0003764629
[0055]
In Table 1, wire is placed on the electrode film. Ye In Examples 1 to 10 relating to wedge bonding, the relationship between the wire crimping thickness and the electrode film thickness is in the condition range of 4t + 2 ≦ D (μm), which is the first invention. The relationship of the hardness of the film is adjusted to the condition range of Hp + 5 ≦ Hw ≦ 2Hp + 20 according to the second invention.
[0056]
Comparative Examples 1 to 9 in Table 2 are examples in which the relationship between the wire crimping thickness and the electrode film thickness does not correspond to the first invention, and among them, Comparative Examples 6 to 9 are the relationship between the hardness of the wire and the electrode film. Does not fall within the scope of the second invention For example About each, it showed as a comparison.
[0057]
In Invention Examples 1 to 10, the relationship between the minimum value D of the wire crimping thickness and the electrode film thickness t satisfies the relationship of 4t + 2 ≦ D (μm), and the pull strength remains high even after heating. On the other hand, in Comparative Examples 1 to 5 having a relationship of 4t + 2> D (μm), the pull strength after heating was clearly reduced.
[0058]
In the inventive examples 1 to 8, the relationship between Hw and Hp, which is the Vickers hardness of the wire and the electrode film, is in the range of Hp + 5 ≦ Hw ≦ 2Hp + 20, so that the pull strength per unit area of the wire immediately after bonding is 98 mN or more sufficiently high It was confirmed. On the other hand, in Comparative Examples 6 and 8 where Hp + 5> Hw, the initial pull strength was low, and in Comparative Examples 7 and 9 where Hw> 2Hp + 20, chip damage during bonding was observed. Invention Examples 9 and 10 are examples in which the thickness relationship satisfies 4t + 2 ≦ D (μm) but the hardness relationship does not satisfy the condition range of the second invention, and Hp + 5> Hw. In Invention Example 9, the pull strength was slightly lowered, and in Invention Example 10 where Hw> 2Hp + 20, chip damage was observed below a small number of electrode portions. Furthermore, Examples 1 to 5 of the present invention satisfy the relationship of Hp + 10 ≦ Hw ≦ 2Hp + 5, and therefore have particularly excellent bonding properties, and no chip damage was found. In Example 7 of the present invention, although Hp + 5 ≦ Hw ≦ 2Hp + 20, since Hw <Hp + 10, minute scratches were confirmed by SEM observation of the chip surface, but it is determined that there is no problem.
[0064]
Invention Examples 1 to 10 Then, if you look at the characteristics of the wire, 3 Specifically, the tensile breaking strength F is 80 to 400 MPa, the breaking elongation C is 1 to 9%, and the relationship between the strength F and the elongation C is 150 ≦ F · The range was C ≦ 2500. On the other hand, Comparative Examples 2, 3, 7, 8, and 9 are cases where at least one characteristic of strength F, elongation C, F · C, and oxygen concentration does not satisfy the scope of the present invention. In Example 7, F> 400 MPa, and in Comparative Example 9, since F · C> 2500, the tip was damaged under the electrode. In Comparative Example 8, the average oxygen concentration exceeded 10 at%. It was confirmed that the strength was low. In Comparative Example 8 in which the average oxygen concentration from the wire surface to a depth of 10 nm exceeded 10 at%, the pull strength was greatly reduced, and it was confirmed that the bondability at the wedge joint was lowered.
[0065]
【The invention's effect】
As described above, in the present invention, the thickness relationship or the hardness relationship between the wire and the electrode film is optimized at the wedge joint between the gold wire and the electrode film. Especially Accordingly, it is an object of the present invention to provide a semiconductor device that is excellent in narrow pitch bonding and has high long-term reliability as compared with conventional ball bonding.
[Brief description of the drawings]
FIG. 1 shows a view of a wedge joint on a gold wire electrode as seen from the horizontal direction.
[Explanation of symbols]
1: Gold alloy wire
2: Metal bump
3: Electrode film
4: Silicon substrate
W: Wire diameter
D: Minimum wire crimp thickness
t: film thickness of electrode

Claims (2)

アルミまたはアルミ合金の電極膜、ＣｕまたはＣｕ合金の電極膜、Ａｌ層またはＡｕ層を上層とするＣｕまたはＣｕ合金の電極膜の上に金合金ボンディングワイヤがウェッジ接合され、その接合部においてワイヤ圧着厚さの最小値Ｄと電極膜厚ｔの関係が、４ｔ＋２≦Ｄ（μｍ）であることを特徴とする半導体装置。A gold alloy bonding wire is wedge-bonded onto an electrode film of aluminum or aluminum alloy, an electrode film of Cu or Cu alloy , or an electrode film of Cu or Cu alloy with an Al layer or Au layer as an upper layer , and wire crimping is performed at the bonded portion. A semiconductor device characterized in that the relationship between the minimum thickness value D and the electrode film thickness t is 4t + 2 ≦ D (μm). さらにワイヤのビッカース硬度Ｈｗと電極膜のビッカース硬度Ｈｐの関係がＨｐ＋５≦Ｈｗ≦２Ｈｐ＋２０であることを特徴とする請求項１に記載の半導体装置。  2. The semiconductor device according to claim 1, wherein the relationship between the Vickers hardness Hw of the wire and the Vickers hardness Hp of the electrode film is Hp + 5 ≦ Hw ≦ 2Hp + 20.
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