JP3871094B2 - Bonding wire and manufacturing method thereof - Google Patents

Bonding wire and manufacturing method thereof Download PDF

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Publication number
JP3871094B2
JP3871094B2 JP08064498A JP8064498A JP3871094B2 JP 3871094 B2 JP3871094 B2 JP 3871094B2 JP 08064498 A JP08064498 A JP 08064498A JP 8064498 A JP8064498 A JP 8064498A JP 3871094 B2 JP3871094 B2 JP 3871094B2
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Prior art keywords
wire
bonding wire
weight
manufacturing
strength
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JPH11284009A (en
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雅夫 内藤
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Sumitomo Metal Mining Co Ltd
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Sumitomo Metal Mining Co Ltd
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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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    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
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    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
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    • H01L2224/45001—Core members of the connector
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  • Materials Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Crucibles And Fluidized-Bed Furnaces (AREA)
  • Wire Bonding (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は、半導体素子上のチップ電極と外部リードとを電気的に接続するためなどに用いられるボンディングワイヤーとその製造方法に関する。
【０００２】
【従来の技術】
トランジスタ、ＩＣ、ＬＳＩなどの半導体素子上のチップ電極と外部リードとを電気的に接続するためには、耐食性、接合性に優れた直径１５〜１００μｍのボンディングワイヤーが用いられてきた。
【０００３】
これらボンディングワイヤーは、金と添加元素の原料を高純度黒鉛坩堝に入れ、真空もしくは不活性ガス雰囲気中で溶解、鋳造し、得られた鋳塊を適宜歪み除去のため熱処理を施しながら溝ロール圧延、ダイス線引きを順次行い、最終直径のワイヤーとし、更に熱処理して所定の伸び率に調整後、スプールに巻き取って製品となる。
【０００４】
【発明が解決しようとする課題】
しかし、上記製造方法では、添加元素の組成がほぼ同一でもロット内やロット間で強度がばらついていた。この強度のばらつきは、製造工程内の品質管理を困難にするばかりか、半導体素子上のチップ電極と外部リードとを接続したワイヤーの形状のばらつきも招き、突発的な歩留まり低下等の問題を生じていた。
【０００５】
そこで本発明は、製品間の強度のばらつきをおさえたボンディングワイヤー及びその製造方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
発明者は、Ａｕ中にＣが極微量存在してもワイヤー強度の向上は望めないが、Ｃの含有量が増大するとともにワイヤー強度のバラツキも増大することを解明し、本発明に至った。
【０００７】
即ち、上記目的を解決するための本発明のボンディングワイヤーは、Ｂｅ、Ｍｇ、Ｃａ、Ｇｅ、Ｓｎ、Ｉｎ、Ｐｂ、Ｐｄ、Ｐｔ、Ｃｕ、Ａｇ、Ｙを含む希土類元素の内の１種以上を１〜１００重量ｐｐｍ含み、Ｃの含有量が１重量ｐｐｍ未満であり、残部がＡｕ及び不可避不純物からなることを特徴とする。
【０００８】
また、上記本発明のボンディングワイヤーの製造方法は、不純物が０．１重量％未満のＢｅＯ、ＭｇＯ、または、ＴｈＯ2製坩堝を用いて溶解鋳造することを特徴とする。
【０００９】
【発明の実施の形態】
前記のように、Ａｕ中にＣが極微量存在してもワイヤー強度の向上は望めないが、Ｃの含有量が増大するとともにワイヤー強度のバラツキも増大する。その原因は未だ完全には把握されていないが、Ｃａ、Ｂｅなどの他の添加元素と炭化物を形成する等が考えられている。
【００１０】
従って、極力Ｃの含有量をおさえることが望ましいが、１重量ｐｐｍ未満であれぱ実用上問題はない。本発明においては、Ｃの含有量を１重量ｐｐｍ未満とする。
【００１１】
一方、従来の溶解鋳造による金ワイヤー製造方法では、費用及び成型の容易さなどの点から専ら高純度黒鉛堆蝸が用いられてきた。ところがＡｕはＣを極少量ではあるが固溶することができるため、坩堝中のＣがＡｕ合金を汚染してＡｕ中にＣが数重量ｐｐｍ程度含有されるのを常としていた。このため、Ａｕ中のＣの含有量を滅らすためには、従来の溶解鋳造で用いる坩堝の材質を変更する必要がある。
【００１２】
溶解鋳造中でのＡｕ中のＣによる汚染を防ぐためには、坩堝の材質としてＢｅＯ、ＭｇＯ、ＣａＯ、ＴｈＯ ２ が適している。ただし、これらの坩堝中の不純物が０．１重量％以上あるとその不純物によってＡｕの汚染が生じ、ワイヤー強度のばらつきを生じさせる要因となるので、坩堝中の不純物は、０．１重量％未満とする必要がある。なお不純物中のＣの含育量には特に配慮することはいうまでもない。
【００１３】
Ｂｅ、Ｍｇ、Ｃａ、Ｇｅ、Ｓｎ、Ｉｎ、Ｐｂ、Ｐｄ、Ｐｔ、Ｃｕ、Ａｇ、Ｙを含む希土類元素等の１〜１００重量ｐｐｍの添加は、ワイヤーの強度や耐熱性を向上させる効果がある。これら添加元素の添加量は１重量ｐｐｍ未満では効果が十分でなく、また、１００重量ｐｐｍを超えると効果が飽和するだけでなく、ワイヤーが脆化して伸線加工中に断線を起こしやすくなる。
【００１４】
【実施例】
以下に本発明を実施例によってより詳細に説明する。Ｂｅ、Ｃａ、Ｌａ、Ｇｅ、Ｐｔを添加元素とした金合金の溶解鋳造を、不純物が０．１重量％未満のＭｇＯ製坩堝を用いて行った。原料のＡｕは、純度９９，９９９ｗｔ％以上の電解金とし、実施例（No.１〜４）の各組成を３ロットずつ作製した。各組成を表１に示す。組成分析は、Ｃを除いてＩＣＰ分光分析で行い、Ｃについては全炭素燃焼法（高周波加熱／赤外吸光法）を用いた。
【００１５】
【表１】

Figure 0003871094
【００１６】
これらの鋳塊の内、組成分析用の試料を除いて適宜歪み取りのための熱処理を施しながら溝ロール圧延、ダイス線引きを順次行い、最終線径３０μｍのボンディングワイヤーとした。最後に大気雰囲気中で連統焼鈍して、伸び率が約６％となるように調整した。
【００１７】
得られたボンディングワイヤーについて、ワイヤー強度を測定した。強度は、溶解鋳造方法ごとに３ロット各２０点の常温で測定し、各ロットごとの平均値と標準偏差σを表２に示す。
【００１８】
【表２】
Figure 0003871094
【００１９】
次に、各ポンデイングワイヤーを用いて、高速自動ボンダーによりチップ電極と外部リード間のボンディングを行い、ボンディング後のワイヤー形状の指標であるループ高さをそれぞれ５０点測定し、平均値と標準偏差σを算出した。ここで「ループ高さ」は、チップ電極と外部リード間をボンディングされたワイヤー形状の、チップ表面からワイヤーループの最高点までの垂直距離とし、結果を表３に示す。
【００２０】
【表３】
Figure 0003871094
【００２１】
表１に示すように、Ｎｏ．１〜４の各組成で本発明の実施例となるＭｇＯ製坩堝で溶解鋳造した鋳塊のＣ濃度は、検出限界以下だった。この鋳塊を３０μｍのポンディングワイヤーにした強度は、表２に示されるように、ロット内の標準偏差が小さく、さらに平均値のロット間の差も小さかった。また表３に示されるように、どの組成もルーブ高さの各ロツト間の平均値のパラツキやロット内の標準偏差が小さく、ポンディング後のワイヤー形状が安定していた。
【００２２】
また、比較例として、高純度黒鉛製坩堝を用いて実施例と同様の金合金を溶解鋳造し、金合金線を作成した（No.５〜８）。結果を実施例と同様に表１〜表３に示す。
【００２３】
比較例では添加元素の含有量については実施例とほとんど差はないが、Ｃの濃度が高く、３〜４重量ｐｐｍ検出された。また、強度は実施例と比較してロット内の標準偏差も、平均値のロット間の差も大きかった。ループ高さも実施例と比較して、ロット間のばらつきやロット内の標準偏差が大きかった。
【００２４】
【発明の効果】
本発明により、製品間の強度のばらつきをおさえたボンディングワイヤー及びその製造方法を提供することができた。本発明のボンディングワイヤーは、製品間の強度バラツキが小さいことから、ポンディング後のワイヤー形状の安定性が増し、工業上極めて有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bonding wire used for electrically connecting a chip electrode on a semiconductor element and an external lead and a manufacturing method thereof.
[0002]
[Prior art]
In order to electrically connect a chip electrode on a semiconductor element such as a transistor, IC, or LSI and an external lead, a bonding wire having a diameter of 15 to 100 μm having excellent corrosion resistance and bondability has been used.
[0003]
These bonding wires are rolled into a high-purity graphite crucible with the raw materials for gold and additive elements, melted and cast in a vacuum or inert gas atmosphere, and the resulting ingot is subjected to groove roll rolling while being subjected to heat treatment to remove distortion as appropriate. Then, the wire is drawn sequentially to obtain a wire having a final diameter, further heat-treated to adjust to a predetermined elongation rate, and then wound on a spool to obtain a product.
[0004]
[Problems to be solved by the invention]
However, in the above manufacturing method, the strength varies among lots or between lots even if the composition of the additive elements is almost the same. This variation in strength not only makes quality control in the manufacturing process difficult, but also causes variations in the shape of the wire connecting the chip electrode on the semiconductor element and the external lead, causing problems such as a sudden drop in yield. It was.
[0005]
Then, an object of this invention is to provide the bonding wire which suppressed the dispersion | variation in the intensity | strength between products, and its manufacturing method.
[0006]
[Means for Solving the Problems]
The inventor cannot improve the wire strength even if a very small amount of C is present in Au, but elucidates that the content of C increases and the variation in wire strength also increases, leading to the present invention.
[0007]
That is, the bonding wire of the present invention for solving the above-described object is one or more of rare earth elements including Be, Mg, Ca, Ge, Sn, In, Pb, Pd, Pt, Cu, Ag, and Y. It contains 1 to 100 ppm by weight, the C content is less than 1 ppm by weight, and the balance consists of Au and inevitable impurities .
[0008]
Moreover, the manufacturing method of the bonding wire of the present invention is characterized by melting and casting using a BeO, MgO, or ThO 2 crucible having an impurity of less than 0.1% by weight.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As described above, even if a very small amount of C is present in Au, improvement in wire strength cannot be expected, but as the C content increases, variation in wire strength also increases. Although the cause has not been completely grasped yet, formation of carbides with other additive elements such as Ca and Be is considered.
[0010]
Therefore, it is desirable to suppress the content of C as much as possible, but there is no practical problem if it is less than 1 ppm by weight. In the present invention, the C content is less than 1 ppm by weight.
[0011]
On the other hand, in the conventional gold wire manufacturing method by melt casting, high-purity graphite deposits have been used exclusively from the viewpoints of cost and ease of molding. However, since Au can dissolve C in a very small amount, it is usual that C in the crucible contaminates the Au alloy so that about several ppm by weight of C is contained in Au. For this reason, in order to destroy the content of C in Au, it is necessary to change the material of the crucible used in the conventional melting and casting.
[0012]
In order to prevent contamination by C in Au during melt casting, BeO, MgO, CaO and ThO 2 are suitable as the crucible material. However, if the impurities in these crucibles are 0.1% by weight or more, the impurities cause Au contamination and cause variations in wire strength. Therefore, the impurities in the crucible are less than 0.1% by weight. It is necessary to. Needless to say, special consideration is given to the amount of C contained in the impurities.
[0013]
Addition of 1 to 100 ppm by weight of rare earth elements including Be, Mg, Ca, Ge, Sn, In, Pb, Pd, Pt, Cu, Ag, and Y has an effect of improving the strength and heat resistance of the wire. . If the added amount of these additive elements is less than 1 ppm by weight, the effect is not sufficient, and if it exceeds 100 ppm by weight, not only the effect is saturated, but also the wire becomes brittle and breaks easily during wire drawing.
[0014]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. Melting casting of a gold alloy using Be, Ca, La, Ge, and Pt as additive elements was performed using an MgO crucible having impurities of less than 0.1% by weight. The raw material Au was electrolysis gold having a purity of 99,999 wt% or more, and three lots of each composition of the examples (No. 1 to 4) were produced. Each composition is shown in Table 1. The composition analysis was performed by ICP spectroscopic analysis except for C. For C, the all-carbon combustion method (high-frequency heating / infrared absorption method) was used.
[0015]
[Table 1]
Figure 0003871094
[0016]
Among these ingots, except for a sample for composition analysis, groove roll rolling and die drawing were sequentially performed while appropriately performing heat treatment for strain removal to obtain a bonding wire having a final wire diameter of 30 μm. Finally, continuous annealing was performed in an air atmosphere to adjust the elongation rate to about 6%.
[0017]
About the obtained bonding wire, wire strength was measured. The strength was measured at room temperature for each of the three lots for each melting casting method, and the average value and standard deviation σ for each lot are shown in Table 2.
[0018]
[Table 2]
Figure 0003871094
[0019]
Next, using each bonding wire, bonding between the chip electrode and the external lead is performed by a high-speed automatic bonder, and the loop height, which is an index of the wire shape after bonding, is measured at 50 points, and the average value and standard deviation are measured. σ was calculated. Here, “loop height” is the vertical distance from the chip surface to the highest point of the wire loop in the wire shape bonded between the chip electrode and the external lead, and the results are shown in Table 3.
[0020]
[Table 3]
Figure 0003871094
[0021]
As shown in Table 1, no. C concentration of the ingot melt-cast with the MgO crucible which becomes an Example of this invention by each composition of 1-4 was below a detection limit. As shown in Table 2, the strength of the ingot made from a 30 μm bonding wire had a small standard deviation within the lot, and a small difference between the average lots. Further, as shown in Table 3, all compositions had small variations in the average value between the lots at the lobe height and the standard deviation within the lot, and the wire shape after bonding was stable.
[0022]
In addition, as a comparative example, a gold alloy wire similar to that of the example was melted and cast using a high-purity graphite crucible to prepare gold alloy wires (Nos. 5 to 8). The results are shown in Tables 1 to 3 as in the examples.
[0023]
In the comparative example, the content of the additive element was almost the same as that of the example, but the concentration of C was high and 3 to 4 ppm by weight was detected. In addition, the intensity was larger in the standard deviation within the lot and the difference between the average lots than in the examples. The loop height was also larger in lot-to-lot variation and standard deviation in the lot than in the examples.
[0024]
【The invention's effect】
According to the present invention, it is possible to provide a bonding wire and a method for manufacturing the same that suppress variation in strength between products. Since the bonding wire of the present invention has a small strength variation between products, the stability of the wire shape after bonding is increased, which is extremely useful industrially.

Claims (2)

Ｂｅ、Ｍｇ、Ｃａ、Ｇｅ、Ｓｎ、Ｉｎ、Ｐｂ、Ｐｄ、Ｐｔ、Ｃｕ、Ａｇ、Ｙを含む希土類元素の内の１種以上を１〜１００重量ｐｐｍ含み、Ｃの含有量が１重量ｐｐｍ未満であり、残部がＡｕ及び不可避不純物からなるボンディングワイヤー。1 to 100 ppm by weight of one or more of rare earth elements including Be, Mg, Ca, Ge, Sn, In, Pb, Pd, Pt, Cu, Ag, and Y, and the C content is less than 1 ppm by weight A bonding wire in which the balance is made of Au and inevitable impurities . 不純物が０．１重量％未満のＢｅＯ、ＭｇＯ、または、ＴｈＯ２製坩堝を用いて溶解鋳造することを特徴とする請求項１に記載のボンディングワイヤーの製造方法。The method for producing a bonding wire according to claim 1, wherein the impurities are cast by using a crucible made of BeO, MgO, or ThO 2 having an impurity content of less than 0.1 wt%.
JP08064498A 1998-03-27 1998-03-27 Bonding wire and manufacturing method thereof Expired - Fee Related JP3871094B2 (en)

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