JP2011077254A - Bonding wire for semiconductor - Google Patents

Bonding wire for semiconductor Download PDF

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Publication number
JP2011077254A
JP2011077254A JP2009226464A JP2009226464A JP2011077254A JP 2011077254 A JP2011077254 A JP 2011077254A JP 2009226464 A JP2009226464 A JP 2009226464A JP 2009226464 A JP2009226464 A JP 2009226464A JP 2011077254 A JP2011077254 A JP 2011077254A
Authority
JP
Japan
Prior art keywords
wire
palladium
copper
gold
bonding
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP2009226464A
Other languages
Japanese (ja)
Other versions
JP4637256B1 (en
Inventor
Shinichi Terajima
晋一 寺嶋
Tomohiro Uno
智裕 宇野
Takashi Yamada
隆 山田
Daizo Oda
大造 小田
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nippon Micrometal Corp
Nippon Steel Chemical and Materials Co Ltd
Original Assignee
Nippon Steel Materials Co Ltd
Nippon Micrometal Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to JP2009226464A priority Critical patent/JP4637256B1/en
Application filed by Nippon Steel Materials Co Ltd, Nippon Micrometal Corp filed Critical Nippon Steel Materials Co Ltd
Priority to SG2012004065A priority patent/SG178063A1/en
Priority to PCT/JP2010/062082 priority patent/WO2011013527A1/en
Priority to MYPI2012000003A priority patent/MY164643A/en
Priority to CN201080019191.6A priority patent/CN102422404B/en
Priority to CN201510431505.8A priority patent/CN105023902B/en
Priority to EP10804273.0A priority patent/EP2461358B1/en
Priority to KR1020107028435A priority patent/KR101707244B1/en
Priority to US13/384,819 priority patent/US8742258B2/en
Application granted granted Critical
Publication of JP4637256B1 publication Critical patent/JP4637256B1/en
Publication of JP2011077254A publication Critical patent/JP2011077254A/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Abstract

<P>PROBLEM TO BE SOLVED: To provide a bonding wire for semiconductor which secures a favorable wedge bonding property even if bonding is applied on palladium-plated lead frames and has excellent oxidation resistance, and in which copper or a copper alloy is used as a core wire. <P>SOLUTION: The bonding wire is characterized by comprising a core wire that comprises copper or a copper alloy, a coating layer that is arranged on the surface of the core wire, has a thickness of 10 to 200 nm and contains palladium, and an alloy layer that is arranged on the surface of the coating layer, has a thickness of 3 to 80 nm and contains gold and palladium where a concentration of the gold in the alloy layer containing gold and palladium is 15 to 75 vol.%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は、半導体素子上の電極と外部接続端子を接続するために使用される半導体用ボンディングワイヤーに関するものである。   The present invention relates to a semiconductor bonding wire used for connecting an electrode on a semiconductor element and an external connection terminal.

現在、半導体素子上の電極と外部接続端子との間を接続する半導体用ボンディングワイヤー（以下、「ボンディングワイヤー」という）としては、線径１５−５０μｍ程度で、材質は高純度４Ｎ（４−Ｎｉｎｅ、純度が９９．９９質量％以上）の金（Ａｕ）であるボンディングワイヤー（金ボンディングワイヤー）が主として使用されている。金ボンディングワイヤーを半導体素子であるシリコンチップ上の電極に接合させるには、超音波併用熱圧着方式のボールボンディングを行うことが一般的である。つまり、汎用ボンディング装置を用い、前記ボンディングワイヤーをキャピラリと呼ばれる治具の内部に通して、ワイヤー先端をアーク入熱で加熱溶融し、表面張力によりボール部を形成させた後に、１５０〜３００℃の範囲内で加熱した前記電極上に、加熱溶融して形成されたボール部を圧着接合せしめる手法である。   At present, as a semiconductor bonding wire (hereinafter referred to as “bonding wire”) for connecting between an electrode on a semiconductor element and an external connection terminal, the wire diameter is about 15-50 μm, and the material is high purity 4N (4-Nine). Bonding wire (gold bonding wire) which is gold (Au) having a purity of 99.99% by mass or more is mainly used. In order to bond a gold bonding wire to an electrode on a silicon chip that is a semiconductor element, it is common to perform ball bonding by a thermocompression bonding method using ultrasonic waves. That is, using a general-purpose bonding apparatus, the bonding wire is passed through a jig called a capillary, the wire tip is heated and melted by arc heat input, and a ball portion is formed by surface tension. This is a technique in which a ball portion formed by heating and melting is pressure-bonded onto the electrode heated within the range.

一方、金ボンディングワイヤーをリードやランド等の外部接続端子に接続する場合には、前述のようなボール部を形成することなく、金ボンディングワイヤーを直接電極に接合する、いわゆるウェッジボンディングを行うことが一般的である。近年、半導体実装の構造・材料・接続技術などは急速に多様化しており、例えば、実装構造では、現行のリードフレームを使用したＱＦＰ（Ｑｕａｄ Ｆｌａｔ Ｐａｃｋａｇｉｎｇ）に加え、基板やポリイミドテープなどを使用するＢＧＡ（Ｂａｌｌ Ｇｒｉｄ Ａｒｒａｙ）、ＣＳＰ（Ｃｈｉｐ Ｓｃａｌｅ Ｐａｃｋａｇｉｎｇ）などの新しい実装形態が実用化され、外部接続端子も多様化している。そのため、ウェッジボンディング特性は、従来以上に重要視されつつある。   On the other hand, when connecting a gold bonding wire to an external connection terminal such as a lead or a land, so-called wedge bonding can be performed by directly bonding the gold bonding wire to the electrode without forming the ball portion as described above. It is common. In recent years, the structure, materials, connection technology, etc. of semiconductor mounting have been diversified rapidly. For example, in the mounting structure, in addition to QFP (Quad Flat Packaging) using the current lead frame, a substrate, polyimide tape, etc. are used. New mounting forms such as BGA (Ball Grid Array) and CSP (Chip Scale Packaging) have been put into practical use, and external connection terminals are also diversified. For this reason, wedge bonding characteristics are becoming more important than ever.

ところで、昨今の資源価格の高騰に伴い、金ボンディングワイヤーの原料となる金の価格も急騰しており、金に代わる低コストなワイヤー素材として、銅（Ｃｕ）が検討されている。しかしながら、金と比べて銅は酸化されやすいことから、単純な銅ボンディングワイヤーでは長期の保管が難しく、ウェッジボンディング特性も良好ではない。また、このような単純な銅ボンディングワイヤーの先端にボール部を形成する際には、ボール部が酸化しないように、還元雰囲気にしなければならない。具体的には、窒素（Ｎ２）に4体積%程度の水素（Ｈ２）を混在させたガスを用いて、ボール部周辺を還元雰囲気とすることが一般的であるのであるが、それでも金ボンディングワイヤーを用いたような良好なボールボンディングを行うことは難しい。これらの理由から、銅ボンディングワイヤーの利用は、一般的なＬＳＩ分野にまだ広まっていない。 By the way, with the recent increase in resource prices, the price of gold as a raw material for gold bonding wires has also increased rapidly, and copper (Cu) has been studied as a low-cost wire material that can replace gold. However, since copper is more easily oxidized than gold, it is difficult to store for a long time with a simple copper bonding wire, and the wedge bonding characteristics are not good. Moreover, when forming a ball part at the tip of such a simple copper bonding wire, a reducing atmosphere must be provided so that the ball part is not oxidized. Specifically, it is common to use a gas in which about 4% by volume of hydrogen (H 2 ) is mixed with nitrogen (N 2 ) to create a reducing atmosphere around the ball part. It is difficult to perform good ball bonding using a bonding wire. For these reasons, the use of copper bonding wires has not yet spread to the general LSI field.

そこで、銅ボンディングワイヤーの酸化という課題を解決するため、銅ワイヤーの表面に貴金属、具体的には金（Ａｕ）を被覆した銅ボンディングワイヤーが提案されている。例えば、特許文献１では、銅ワイヤーに金を被覆した具体例は示されていないが、ボンディングワイヤーの内部金属としてアルミニウム（Ａｌ）、銅、鉄（Ｆｅ）、鉄とニッケルの合金（ＦｅＮｉ）等の非純貴金属が挙げられ、前記ボンディングワイヤーの表面被覆金属として水分、塩分、アルカリ等に対する耐食性のある金属、例えば、金や銀とすることが開示されている。特許文献２では、銅又はスズを含んだ銅合金を芯線とし、その上に金めっきしたボンディングワイヤーが開示され、破断強度が向上すると記載されている。また、特許文献３では、銅ワイヤーに金を被覆した具体例は示されていないが、銅系ワイヤーに金、銀を含む貴金属を被覆した銅ボンディングワイヤーが例示されており、銅系ワイヤーに被覆を施せば、耐腐食性が一層向上すると記載されている。特許文献４では、アルミニウム（Ａｌ）や銅ワイヤーに、金や銀等の貴金属をメッキしたボンディングワイヤーが開示され、銅ボンディングワイヤーの場合には、前記メッキによって耐食性及び熱酸化の問題が解消され、リードフレームとの接合性も金ボンディングワイヤーと同様の信頼性が得られるとされている。特許文献５では、高純度銅極細線の表面に、貴金属あるいは耐食性金属を被覆した銅ボンディングワイヤーが開示され、前記被覆する貴金属の１つとして金が使用されている。このように構成することで、銅ボンディングワイヤーの表面酸化（具体的には、大気中に１０日間放置後の表面酸化の有無である。）が抑制できるとしている。また、前記銅極細線の直径としては１５〜８０μｍとし、前記被覆する被膜は１０ｎｍ〜１μｍの平均層厚であるとしている（実施例では、２５μｍ直径のワイヤーで、０．１μｍの平均層厚の被膜である。）。特許文献６では、銅芯線の外周を金で被覆することが開示されており、アルミニウムから成る電極への接合性が向上すると記載されている。特許文献７では、塑性変形しない芯材と、芯材よりも軟らかく塑性変形する外周材とから成る複合導体が開示されて、芯材として金が、外周材として銅合金が一例として示されており、導線と回路との間の接続強度を高める効果があるとされている。特許文献８では、銅合金の外側を金もしくは金合金で覆うことが開示されており、半導体素子を樹脂封止する際にボンディングワイヤー同士が接触する不良事故を防げることが示されている。特許文献９では、無酸素銅ワイヤーから成る線材の表面に純金めっきをすることが開示されており、高周波伝送に優れた信号導通率の高いボンディングワイヤーが示されている。特許文献１０では、銅を主成分とする芯材の上に銅以外の金属から成る異種金属層を介して銅よりも高融点の耐酸化性金属から成る被覆層を有するボンディングワイヤーが開示されており、真球のボール部を安定的に形成でき、更に被覆層と芯材との間の密着性に優れる特性が示されている。   Therefore, in order to solve the problem of oxidation of the copper bonding wire, a copper bonding wire in which the surface of the copper wire is coated with a noble metal, specifically, gold (Au) has been proposed. For example, Patent Document 1 does not show a specific example in which a copper wire is coated with gold, but the inner metal of the bonding wire is aluminum (Al), copper, iron (Fe), an alloy of iron and nickel (FeNi), or the like. It is disclosed that the surface metal of the bonding wire is a metal having corrosion resistance against moisture, salt, alkali, etc., for example, gold or silver. Patent Document 2 discloses a bonding wire in which a copper alloy containing copper or tin is used as a core wire and gold is plated thereon, and it is described that the breaking strength is improved. Patent Document 3 does not show a specific example in which a copper wire is coated with gold. However, a copper bonding wire in which a copper-based wire is coated with a noble metal including gold and silver is exemplified, and the copper-based wire is coated. It is described that the corrosion resistance is further improved by applying. Patent Document 4 discloses a bonding wire in which a noble metal such as gold or silver is plated on aluminum (Al) or a copper wire. In the case of a copper bonding wire, the problem of corrosion resistance and thermal oxidation is eliminated by the plating. The bondability with the lead frame is said to be as reliable as the gold bonding wire. In patent document 5, the copper bonding wire which coat | covered the noble metal or the corrosion-resistant metal was disclosed on the surface of the high purity copper extra fine wire, and gold is used as one of the said noble metals to coat | cover. By configuring in this way, the surface oxidation of the copper bonding wire (specifically, the presence or absence of surface oxidation after being left in the atmosphere for 10 days) can be suppressed. In addition, the diameter of the copper fine wire is 15 to 80 μm, and the coating film to be coated has an average layer thickness of 10 nm to 1 μm (in the example, a wire having a diameter of 25 μm and an average layer thickness of 0.1 μm). It is a coating.) Patent Document 6 discloses that the outer periphery of a copper core wire is covered with gold, and describes that the bonding property to an electrode made of aluminum is improved. In Patent Document 7, a composite conductor composed of a core material that is not plastically deformed and an outer peripheral material that is softer than the core material is disclosed. Gold is used as the core material, and a copper alloy is shown as an example of the outer peripheral material. It is said that there is an effect of increasing the connection strength between the conductor and the circuit. Patent Document 8 discloses that the outer side of a copper alloy is covered with gold or a gold alloy, and it is shown that a defective accident in which bonding wires come into contact with each other when a semiconductor element is resin-sealed can be prevented. Patent Document 9 discloses that pure gold plating is performed on the surface of a wire made of an oxygen-free copper wire, and shows a bonding wire with high signal conductivity that is excellent in high-frequency transmission. Patent Document 10 discloses a bonding wire having a coating layer made of an oxidation-resistant metal having a melting point higher than that of copper via a dissimilar metal layer made of a metal other than copper on a core material mainly composed of copper. In addition, it is possible to stably form a true sphere ball portion and to exhibit excellent properties of adhesion between the coating layer and the core material.

しかしながら、上述のように銅ワイヤーの表面に金を被覆した銅ボンディングワイヤーでは、銅の表面酸化（特に、保管中の酸化の進行）を抑制できるが、ボンディングする際にワイヤー先端に形成するボール部が真球とならずにいびつとなることが多く、当該銅ボンディングワイヤーの実用化を妨げている。これは、ワイヤー先端を加熱溶融しようとアークによって入熱が与えられる際、銅は比熱が大きい（380 J/kg・K）ため溶融させにくいのに対し、金は比熱が小さい（128 J/kg・K）ことでわずかな入熱でも溶融可能であり、その結果、銅と金の複層構造体では金が優先的に溶融してしまうことが関係していると思われる。   However, the copper bonding wire with the copper wire coated with gold as described above can suppress the surface oxidation of copper (particularly the progress of oxidation during storage), but the ball part formed at the wire tip during bonding In many cases, the sphere does not become a true sphere and becomes distorted, which impedes the practical application of the copper bonding wire. This is because when heat is applied by an arc to heat and melt the wire tip, copper has a large specific heat (380 J / kg · K) and is difficult to melt, whereas gold has a small specific heat (128 J / kg).・ K) can be melted even with a slight heat input, and as a result, it seems to be related to the fact that gold is preferentially melted in a multilayer structure of copper and gold.

一方、金を被覆する代わりに、銅ワイヤーの表面に別な貴金属、具体的にはパラジウム（Ｐｄ）を被覆することも考えられる。実際に、特許文献３〜５には、被覆層には金以外の貴金属としてパラジウムも例示されている。前記文献では、パラジウムの優勢性は示されていないが、本発明者らは、パラジウムの比熱は金よりも高い（244 J/kg・K）ので、パラジウムを被覆すると、上述の金のように銅ワイヤーが溶融してボール部が形成する前に被覆層が溶融して真球状のボール部を形成できないという問題を解決できるものと考えている。即ち、銅ワイヤーの表面にパラジウムを被覆することで、銅の酸化防止とボール部の真球性確保というふたつの課題を同時に解決できると考えられる。特許文献１１では、芯線と被覆層（外周部）の２層ボンディングワイヤーにおいて芯線と被覆層との間に拡散層を設けて被覆層の密着性等を改善することが開示されているが、芯線に銅を、被覆層にパラジウムを使用する例が示されている。このようなパラジウムを被覆した銅ボンディングワイヤーでは、銅ボンディングワイヤーの酸化が抑制されているため、ワイヤーの長期保管やウェッジボンディング特性に優れるのみならず、ワイヤー先端にボール部を形成する際にボール部が酸化するという懸念が大幅に改善されている。よって、危険なガスである水素を使わずに、純窒素ガスを用いてボール部周辺を窒素雰囲気としただけでも、真球のボール部が形成できる。   On the other hand, instead of coating gold, it is conceivable to coat the surface of the copper wire with another noble metal, specifically palladium (Pd). Actually, in Patent Documents 3 to 5, palladium is exemplified as a noble metal other than gold in the coating layer. Although the above document does not show the predominance of palladium, the present inventors show that the specific heat of palladium is higher than that of gold (244 J / kg · K). It is considered that the problem that the spherical layer cannot be formed by melting the coating layer before the copper wire is melted to form the ball part is considered. That is, it is considered that the two problems of preventing oxidation of copper and ensuring the sphericity of the ball part can be solved simultaneously by coating the surface of the copper wire with palladium. Patent Document 11 discloses that in a two-layer bonding wire of a core wire and a coating layer (outer peripheral portion), a diffusion layer is provided between the core wire and the coating layer to improve adhesion of the coating layer. In this example, copper is used for the coating layer and palladium is used for the coating layer. In such a copper bonding wire coated with palladium, oxidation of the copper bonding wire is suppressed, so that not only is the wire long-term storage and wedge bonding characteristics excellent, but also the ball portion is formed when the ball portion is formed at the wire tip. Concern about oxidation is greatly improved. Therefore, a true ball portion can be formed by using pure nitrogen gas without using hydrogen, which is a dangerous gas, and simply forming a nitrogen atmosphere around the ball portion.

特開昭５７−１２５４３号公報JP 57-12543 A 特開昭５９−１５５１６１号公報JP 59-155161 A 特開昭５９−１８１０４０号公報JP 59-181040 A 特開昭６１−２８５７４３号公報JP-A 61-285743 特開昭６２−９７３６０号公報JP-A-62-97360 特開昭６３−４６７３８号公報JP 63-46738 A 特開平３−３２０３３号公報JP-A-3-32033 特開平４−２０６６４６号公報JP-A-4-206646 特開２００３−５９９６３号公報JP 2003-59963 A 特開２００４−６７４０号公報JP 2004-6740 A 再公表ＷＯ２００２−２３６１８Republished WO2002-23618

前述のように、銅ボンディングワイヤーの表面にパラジウムを被覆することで、金ボンディングワイヤーに比べて安価なボンディングワイヤーとして実用可能になってきたが、最近の半導体実装における構造・材料・接続技術などの急速な変化や多様化に必ずしも対応できないという問題が顕在化してきた。   As mentioned above, the surface of the copper bonding wire is covered with palladium, making it practical as a cheaper bonding wire compared to gold bonding wires. The problem of not always being able to cope with rapid changes and diversification has become apparent.

例えば、これまでのリードフレームの表面は銀めっきされているのが一般的であったのに対して、最近ではパラジウムめっきされたリードフレームの使用が進みつつある。これは、従来の銀めっきされたリードフレーム（以下、「銀めっきリードフレーム」という）では、リードフレームをマザーボード等の基板に半田付けする前に、半田との濡れ性を少しでも高める目的で、リードの先端にあらかじめ薄く半田をめっきする工程（半田めっき工程）があり、高コストとなっていたので、銀よりも半田に対して高い濡れ性を確保できるパラジウムを銀の代わりにリードフレーム上にめっきすることで、該半田めっき工程を省略し、低コストとするものである。   For example, the surface of a lead frame so far is generally silver-plated, but recently, a lead frame plated with palladium has been used. This is because the conventional silver-plated lead frame (hereinafter referred to as “silver-plated lead frame”) is intended to increase the wettability with solder before soldering the lead frame to a substrate such as a mother board. Since there was a process to solder thinly on the tip of the lead in advance (solder plating process), it was expensive, so palladium that can secure higher wettability to solder than silver was put on the lead frame instead of silver By plating, the solder plating step is omitted and the cost is reduced.

発明者らは、銅ワイヤーの表面にパラジウムを被覆した銅ボンディングワイヤーの場合、これまでの銀めっきリードフレームでは顕在化していなかったが、パラジウムめっきされたリードフレームに対するウェッジ接合性が不充分となるケースが多くなるという新たな問題があることを明らかにした。更に、発明者らは、前記問題について詳細に検討したところ、該銅ボンディングワイヤーの最表面はパラジウムであるため、パラジウムめっきされたリードフレームに対するウェッジ接合ではパラジウム同士が接触する。そうすると、パラジウムの硬度（パラジウムのモース硬度４．７５、銅のモース硬度３．０）が高いためにパラジウムが変形し難しいので、よってパラジウム表面の酸化皮膜層の破壊が不充分となることが、上記問題の原因であることを見出した。更に、ワイヤー最表面のパラジウムとリードフレーム上のパラジウムとの間で生じる拡散が遅いことで、両パラジウム層の間に充分な拡散層が形成されないことも上記問題の原因であることを見出した。   In the case of a copper bonding wire in which the surface of the copper wire is coated with palladium, the inventors have not made it obvious in the conventional silver-plated lead frame, but the wedge bondability to the palladium-plated lead frame becomes insufficient. Clarified that there is a new problem of increasing cases. Furthermore, the inventors have studied the above-mentioned problem in detail, and since the outermost surface of the copper bonding wire is palladium, palladium contacts with each other in wedge bonding to a lead frame plated with palladium. Then, since the hardness of palladium (palladium Mohs hardness 4.75, copper Mohs hardness 3.0) is high, palladium is difficult to be deformed, and therefore the destruction of the oxide film layer on the palladium surface is insufficient. We found that it was the cause of the above problem. Furthermore, it has been found that the above-mentioned problem is caused by the fact that the diffusion that occurs between the palladium on the outermost surface of the wire and the palladium on the lead frame is slow, so that a sufficient diffusion layer is not formed between the two palladium layers.

銅ボンディングワイヤーの酸化を防止するためには、銅ワイヤーの表面に、銅よりも酸化しにくい貴な金属を被覆することが考えられる。一般に、銅よりも貴な金属として銀、白金、金が知られているが、その内の金は、前記のようにボール部の形成性に難がある。そこで、銅ワイヤーの表面に別な貴金属、具体的には銀や白金を被覆することも考えられる。しかしながら、発明者らは、銅ワイヤーの表面に銀を被覆した銅ボンディングワイヤーでは、銅ボンディングワイヤーの保管中に、周辺の雰囲気中に微量に含有される硫黄によって銅ボンディングワイヤーの表面が汚染され、保管期間が長くなるにつれ、ウェッジボンディング特性が低下するという問題を見出した。これは、銀が硫化し易い性質を有する元素であることに起因する。一方、白金は極めて高価な材料であることから、銅ワイヤーの表面に白金を被覆した銅ボンディングワイヤーの工業的な利用は難しいと思われる。   In order to prevent oxidation of the copper bonding wire, it is conceivable to coat the surface of the copper wire with a noble metal that is less likely to oxidize than copper. In general, silver, platinum, and gold are known as noble metals than copper, but gold has difficulty in forming the ball portion as described above. Therefore, it is conceivable to coat the surface of the copper wire with another noble metal, specifically, silver or platinum. However, in the copper bonding wire in which the surface of the copper wire is coated with silver, the inventors contaminated the surface of the copper bonding wire with sulfur contained in a small amount in the surrounding atmosphere during storage of the copper bonding wire. It has been found that the wedge bonding characteristics deteriorate as the storage period becomes longer. This is due to the fact that silver is an element having the property of being easily sulfided. On the other hand, since platinum is an extremely expensive material, it is considered difficult to industrially use a copper bonding wire in which the surface of the copper wire is coated with platinum.

このように、銅ワイヤーの表面に単純に貴金属（金、パラジウム、銀、白金）を被覆しても、パラジウムめっきされたリードフレーム上での良好なウェッジ接合性、耐酸化性並びに耐硫化性を同時に満足することは難しい。   In this way, even if the surface of the copper wire is simply coated with a noble metal (gold, palladium, silver, platinum), good wedge bondability, oxidation resistance and sulfidation resistance on a palladium-plated lead frame can be obtained. It is difficult to be satisfied at the same time.

また、モーター等の大電流を流すパワーデバイスに用いられるボンディングワイヤーは、芯線の線径が２００μｍ程度必要であるが、この場合、線径が大きいので、ウェッジ接合およびボール接合において特に不具合は生じない。これに対し、芯線の線径が１５−５０μｍ程度であるＬＳＩ用のボンディングワイヤーの場合、線径が小さいのでワイヤー表面の汚れや傷、あるいはボール形状などが接合性に悪影響を与えてしまうという問題がある。したがって、芯線の線径が１５−５０μｍ程度であるＬＳＩ用のボンディングワイヤーでは、ウェッジ接合性とボール部の真球性が特に重要となる。   In addition, the bonding wire used for a power device that passes a large current, such as a motor, requires a core wire diameter of about 200 μm, but in this case, since the wire diameter is large, there is no particular problem in wedge bonding and ball bonding. . On the other hand, in the case of an LSI bonding wire having a core wire diameter of about 15-50 μm, the wire diameter is so small that dirt or scratches on the surface of the wire or the ball shape adversely affects the bondability. There is. Therefore, in the bonding wire for LSI whose core wire diameter is about 15-50 μm, wedge bondability and sphericity of the ball portion are particularly important.

本発明は、上記問題点に鑑みてなされたものであり、その目的とするところは、パラジウムめっきされたリードフレームであっても良好なウェッジ接合性を確保でき、耐酸化性と耐硫化性の両方に優れた、銅又は銅合金を芯線とする半導体素子用ボンディングワイヤーを提供することを目的とする。   The present invention has been made in view of the above problems, and the object of the present invention is to ensure good wedge bondability even with a palladium-plated lead frame, and to have oxidation resistance and sulfidation resistance. An object of the present invention is to provide a bonding wire for a semiconductor element having copper or a copper alloy as a core wire, excellent in both.

前述した目的を達成するための本発明の要旨は次の通りである。   The gist of the present invention for achieving the above-described object is as follows.

請求項１に係る半導体用ボンディングワイヤーは、銅又は銅合金から成る芯線と、該芯線の表面に、10〜200nmの厚さを有するパラジウムを含む被覆層と、該被覆層の表面に、3〜80nmの厚さを有する金とパラジウムとを含む合金層とを有し、前記合金層中の金の濃度が15体積%以上75体積%以下であることを特徴とする。   The bonding wire for a semiconductor according to claim 1 is a core wire made of copper or a copper alloy, a coating layer containing palladium having a thickness of 10 to 200 nm on the surface of the core wire, and 3 to It has an alloy layer containing gold and palladium having a thickness of 80 nm, and the concentration of gold in the alloy layer is 15 volume% or more and 75 volume% or less.

請求項２に係る半導体用ボンディングワイヤーは、前記合金層の表面結晶粒の内、<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積が、40%以上100%以下であることを特徴とする。   The bonding wire for a semiconductor according to claim 2 has an area of a crystal grain in which the inclination of the <111> crystal orientation with respect to the drawing direction is 15 degrees or less among the surface crystal grains of the alloy layer is 40% or more and 100% or less It is characterized by being.

請求項３に係る半導体用ボンディングワイヤーは、前記ボンディングワイヤーの表面のマイヤー硬度が、0.2〜2.0GPaの範囲であることを特徴とする。   The bonding wire for semiconductor according to claim 3 is characterized in that the Mayer hardness of the surface of the bonding wire is in a range of 0.2 to 2.0 GPa.

請求項４に係る半導体用ボンディングワイヤーは、前記合金層中の金の濃度が、40体積%以上75体積%以下であることを特徴とする。   The bonding wire for a semiconductor according to claim 4 is characterized in that the gold concentration in the alloy layer is 40% by volume or more and 75% by volume or less.

請求項５に係る半導体用ボンディングワイヤーは、前記芯線が、B、P、Seの内の少なくとも1種を総計で5〜300質量ppm含有することを特徴とする。   The bonding wire for semiconductor according to claim 5 is characterized in that the core wire contains 5 to 300 mass ppm in total of at least one of B, P, and Se.

本発明によれば、パラジウムめっきされたリードフレームであっても良好なウェッジ接合性を確保でき、耐酸化性と耐硫化性の両方に優れた、銅又は銅合金を芯線とする安価な半導体素子用ボンディングワイヤーを提供できる。   According to the present invention, even a palladium-plated lead frame can ensure good wedge bondability and is excellent in both oxidation resistance and sulfidation resistance. Bonding wire can be provided.

以下に、本発明のボンディングワイヤーの構成について更に説明する。尚、以下の説明において、特に断りの無い限り、「％」は「体積％」を意味する。また、組成は複数個所を分析した際に得られた金属のみの数値の平均値であり、炭素は自然混入物（不可避不純物）としては存在するが、以下で述べる組成には含めないものとする。   Below, the structure of the bonding wire of this invention is further demonstrated. In the following description, “%” means “volume%” unless otherwise specified. In addition, the composition is an average value of only the metal values obtained when analyzing a plurality of locations, and carbon exists as a natural contaminant (inevitable impurity) but is not included in the composition described below. .

パラジウムめっきされたリードフレーム（以下、「パラジウムめっきリードフレーム」という）上での良好なウェッジ接合性と耐酸化性の両者を確保し、かつ、銅又は銅合金を芯線とする安価なボンディングワイヤーを提供するには、銅又は銅合金から成る芯線の表面に特定の厚みのパラジウムを含む被覆層を形成し、更に、該被覆層の表面を特定の厚みで特定の組成の金とパラジウムを含む合金としたボンディングワイヤーが有効であることを、本発明者らは見出した。   An inexpensive bonding wire that secures both good wedge-bonding and oxidation resistance on a palladium-plated lead frame (hereinafter referred to as “palladium-plated lead frame”) and uses copper or copper alloy as the core wire. To provide, an alloy containing gold and palladium having a specific thickness on the surface of the coating layer formed on a surface of a core wire made of copper or a copper alloy, and further comprising a coating layer containing a specific thickness of palladium. The present inventors have found that the bonding wire is effective.

まず、銅又は銅合金から成る芯線の表面に、適切な厚みのパラジウムを含む被覆層を有する構成について説明する。前述のように銅又は銅合金は酸化されやすいため、銅又は銅合金からなるボンディングワイヤーでは長期保管やウェッジボンディング特性が劣るものの、銅又は銅合金からなる芯線の表面にパラジウムを含む被覆層を形成しておけば、銅の酸化が抑制されることで、前述の長期保管やウェッジボンディング特性に優れるのみならず、ボンディングワイヤーの先端にボール部を形成する際にボール部が酸化する懸念が大幅に改善されることになる。これは、前記被覆層に、銅に比べて酸化し難い（即ち、酸化物生成熱△H0が大きい）パラジウムを含むので前記効果が得られるのである。そのため、危険なガスである水素と窒素との混合ガスを使用せずに、純窒素ガスを用いてボール部周辺を窒素雰囲気としただけでも、真球のボール部が形成できる。このような効果を得るためには、該被覆層の厚みは10〜200nmである必要があり、10nm未満であれば酸化抑制効果が不充分となる。該被覆層の厚みが200nmを超えると、ボール部の表面に直径数μｍの大きさの気泡が生じることが多く、好ましくない。ここで、パラジウムを含む被覆層におけるパラジウム以外に含まれる元素は、パラジウムの不可避不純物と芯線やボンディングワイヤーの最表面を構成する元素である。また、該被覆層のパラジウムの含有量は、50%以上であれば充分な酸化抑制効果が得られる。但し、該被覆層に含まれるパラジウム以外の元素として、後述する最表面を構成する金を含まないか、若しくは金を含む場合には金濃度が１５％未満であることが好ましい。該被覆層の金の濃度が１５％以上になると、上述のような金被覆ワイヤーの問題（ボール部が真球とならずにいびつとなる不良）が現れるからである。 First, the structure which has the coating layer containing palladium of appropriate thickness on the surface of the core wire which consists of copper or a copper alloy is demonstrated. As mentioned above, copper or copper alloy is easily oxidized, so long as the bonding wire made of copper or copper alloy is inferior in long-term storage and wedge bonding characteristics, a coating layer containing palladium is formed on the surface of the core wire made of copper or copper alloy. If this is done, the copper oxidation is suppressed, which not only improves the long-term storage and wedge bonding characteristics described above, but also greatly increases the concern that the ball part will oxidize when the ball part is formed at the tip of the bonding wire. It will be improved. This is because the coating layer contains palladium that is not easily oxidized compared to copper (that is, the oxide generation heat ΔH 0 is large), and thus the above-described effect can be obtained. Therefore, a true ball portion can be formed by using pure nitrogen gas and making the surrounding of the ball portion a nitrogen atmosphere without using a gas mixture of hydrogen and nitrogen, which is a dangerous gas. In order to obtain such an effect, the thickness of the coating layer needs to be 10 to 200 nm, and if it is less than 10 nm, the oxidation suppressing effect is insufficient. When the thickness of the coating layer exceeds 200 nm, bubbles with a diameter of several μm are often generated on the surface of the ball part, which is not preferable. Here, the element contained other than palladium in the coating layer containing palladium is an element that constitutes the inevitable impurity of palladium and the outermost surface of the core wire or bonding wire. Further, if the content of palladium in the coating layer is 50% or more, a sufficient oxidation suppressing effect can be obtained. However, as an element other than palladium contained in the coating layer, gold constituting the outermost surface described later is not included, or when gold is included, the gold concentration is preferably less than 15%. This is because, when the gold concentration of the coating layer is 15% or more, the above-described problem of the gold-coated wire (the defect that the ball portion does not become a true sphere but becomes distorted) appears.

銅又は銅合金から成る芯線の表面にパラジウムを含む被覆層を有する上述の構成のみでは、パラジウムめっきリードフレーム上で良好なウェッジ接合性を確保することはできない。この課題を解決するには、本発明者らは、更に、金とパラジウムとを含む合金層を該被覆層の表面に更に有すると良いことを見出した。該合金層は、前記被覆層の上に、更に3〜80nmの厚みを有するものである。これは、ウェッジ接合性はワイヤーの最表面から3nm程度の領域の物性値に支配されることに起因する。つまり、ワイヤーの最表面から3nmの領域が、金とパラジウムとの合金であれば、パラジウムめっきリードフレーム上にウェッジ接合させる際、ワイヤーの最表面を構成する金とパラジウムとを含む該合金中の金がパラジウムめっきリードフレーム上のパラジウムに向けて優先的に拡散し、ボンディングワイヤーとパラジウムめっきリードフレームの両者の間に合金層を形成しやすくする。そのため、パラジウムめっきリードフレームとのウェッジボンディング性が向上し、例えば、2ndピール強度が良好となるのである。これは、金とパラジウムとの間の相互拡散の方が、パラジウムの自己拡散よりも早いことに起因する。但し、該合金層の厚みが3nmに満たないと、ボンディングワイヤーの下地である被覆層が前記ウェッジボンディング性に影響してしまうので、パラジウムめっきリードフレームとのウェッジボンディング性は確保できない。前記効果を得るためには、前記金とパラジウムとを含む合金層の厚みの上限に特に制限は無いが、該厚みを80nm超とするには、後述する電解めっきであれば大電流下で、無電解めっきであれば長時間、蒸着法であれば長時間、それぞれ金めっきもしくは金蒸着した上、更に、後述する加熱工程での加熱温度を700℃超と高温にしなければならず、安定した品質を確保しがたくなるので該合金の厚みの上限を80nm以下とした。なお、合金の厚みは、上限を50nm以下とすることがより好ましい。上限を50nm以下とすると、該加熱温度を600℃〜650℃にできるからである。   Only the above-described configuration having a coating layer containing palladium on the surface of a core wire made of copper or a copper alloy cannot ensure good wedge bondability on a palladium-plated lead frame. In order to solve this problem, the present inventors have found that it is preferable to further have an alloy layer containing gold and palladium on the surface of the coating layer. The alloy layer further has a thickness of 3 to 80 nm on the coating layer. This is due to the fact that the wedge bondability is governed by the physical property values in the region of about 3 nm from the outermost surface of the wire. In other words, if the region of 3 nm from the outermost surface of the wire is an alloy of gold and palladium, when wedge-bonding on the palladium plating lead frame, the alloy containing the gold and palladium constituting the outermost surface of the wire Gold preferentially diffuses towards the palladium on the palladium plated lead frame, making it easier to form an alloy layer between both the bonding wire and the palladium plated lead frame. Therefore, the wedge bonding property with the palladium plating lead frame is improved, and for example, the 2nd peel strength is improved. This is due to the fact that interdiffusion between gold and palladium is faster than self-diffusion of palladium. However, if the thickness of the alloy layer is less than 3 nm, the covering layer, which is the base of the bonding wire, affects the wedge bonding property, so that the wedge bonding property with the palladium plated lead frame cannot be ensured. In order to obtain the effect, there is no particular limitation on the upper limit of the thickness of the alloy layer containing gold and palladium, but to make the thickness more than 80 nm, under a large current if the electrolytic plating described later, For electroless plating, long time for vapor deposition, gold plating or gold vapor deposition for a long time respectively, and further, the heating temperature in the heating process described later must be higher than 700 ° C, which is stable Since it is difficult to ensure the quality, the upper limit of the thickness of the alloy is set to 80 nm or less. The upper limit of the alloy thickness is more preferably 50 nm or less. This is because if the upper limit is 50 nm or less, the heating temperature can be set to 600 ° C to 650 ° C.

また、前記金とパラジウムとを含む合金層による上記効果を得るためには、該合金層中の金の組成（金濃度）が特定の範囲である必要がある。具体的には、前記金とパラジウムとを含む合金層中の金濃度が、15%以上75%以下であり、より好ましくは40%以上75%以下であれば前述のパラジウムめっきリードフレームとのウェッジボンディング性が更に高まるので良い。前記金濃度が15%未満では前述の効果は得られない。逆に、前記金濃度が75%を超えると、ワイヤー先端にボール部を形成する際に金とパラジウムとを含む前記合金層中の金が優先的に溶融することで、いびつなボール部が形成される危険性が増すので良くない。これは、既述のように、ワイヤー先端をアーク入熱で加熱溶融する際に、熱伝導率の低い金（317 W/m・K）では熱がこもり易く、金が優先的に溶融してしまうのに対し、熱伝導率の高い銅（401 W/m・K）では抜熱し易いことで、銅は一部分のみしか溶融しないことが関係していると思われる。それに対し、該合金層中の金濃度が75%以下であれば、ワイヤーの表面層では金とパラジウムが均質に混ざっているため、ワイヤー先端にボール部を形成する際に、金だけ優先的に溶融して、いびつなボール部が形成される危険性は無く、ボール部の真球性や寸法精度を損なうことは無い。また、前記金濃度が、15%以上40%未満であればボール部の真球性や寸法精度が更に良好となるので良い。   In addition, in order to obtain the above-described effect by the alloy layer containing gold and palladium, the gold composition (gold concentration) in the alloy layer needs to be in a specific range. Specifically, if the gold concentration in the alloy layer containing gold and palladium is 15% or more and 75% or less, more preferably 40% or more and 75% or less, the wedge with the palladium plating lead frame described above It is good because the bondability is further improved. If the gold concentration is less than 15%, the above effects cannot be obtained. Conversely, when the gold concentration exceeds 75%, the gold in the alloy layer containing gold and palladium is preferentially melted when forming the ball portion at the wire tip, thereby forming an irregular ball portion. It is not good because the risk of being increased. As described above, when the wire tip is heated and melted by arc heat input, it is easy to accumulate heat with gold (317 W / m · K) with low thermal conductivity, and gold is preferentially melted. On the other hand, copper with high thermal conductivity (401 W / m · K) is considered to be related to the fact that only a part of copper is melted because heat is easily removed. On the other hand, if the gold concentration in the alloy layer is 75% or less, gold and palladium are homogeneously mixed in the surface layer of the wire, so when forming the ball portion at the wire tip, only gold is preferential. There is no risk of melting and forming a distorted ball portion, and the sphericity and dimensional accuracy of the ball portion are not impaired. Further, if the gold concentration is 15% or more and less than 40%, the sphericity and dimensional accuracy of the ball portion may be further improved.

したがって、銅又は銅合金から成る芯線の表面に特定の厚みのパラジウムを含む被覆層を有し、該被覆層の表面に特定の厚みと特定の組成の金とパラジウムとを含む合金層を有するボンディングワイヤーでは、パラジウムめっきリードフレーム上での良好なウェッジ接合性、耐酸化性並びに耐硫化性を確保し、かつ、銅又は銅合金を芯線とする安価なボンディングワイヤーを提供することができるのである。   Therefore, bonding having a coating layer containing palladium with a specific thickness on the surface of a core wire made of copper or a copper alloy, and having an alloy layer containing gold and palladium with a specific thickness and a specific composition on the surface of the coating layer With respect to the wire, it is possible to provide an inexpensive bonding wire that ensures good wedge bondability, oxidation resistance and sulfidation resistance on a palladium-plated lead frame, and uses copper or a copper alloy as a core wire.

被覆層並びに合金層の厚さと組成の測定は、ボンディングワイヤーの表面からスパッタ法により深さ方向に掘り下げながら分析する手法や、ボンディングワイヤーの断面での線分析又は点分析する方法を用いる。ここで、合金層の厚さは、表面から深さ方向に組成分析して金の濃度が15%以上である部分の距離（深さ）である。また、被覆層の厚さは、前記合金層の厚さとなる界面から深さ方向に組成分析してパラジウムの濃度が５０％以上である部分の距離（深さ）である。これらの分析に用いる分析装置として、EPMA（電子線マイクロ分析、Electron Probe Micro Analysis）、EDX（エネルギー分散型Ｘ線分析、Energy Dispersive X-Ray Analysis）、AES（オージェ電子分光法、Auger Electron Spectroscopy）、TEM（透過型電子顕微鏡、Transmission Electron Microscope）等が利用できる。上記いずれか１つの方法で得られる厚さや組成が本発明の範囲内であれば、本発明の作用効果が得られるものである。   For the measurement of the thickness and composition of the coating layer and the alloy layer, a method of analyzing while digging in the depth direction from the surface of the bonding wire by a sputtering method, or a method of performing line analysis or point analysis on the cross section of the bonding wire is used. Here, the thickness of the alloy layer is a distance (depth) of a portion where the gold concentration is 15% or more by composition analysis in the depth direction from the surface. The thickness of the coating layer is the distance (depth) of the portion where the concentration of palladium is 50% or more by composition analysis in the depth direction from the interface that becomes the thickness of the alloy layer. EPMA (Electron Probe Micro Analysis), EDX (Energy Dispersive X-Ray Analysis), AES (Auger Electron Spectroscopy) are used as analytical equipment for these analyses. TEM (Transmission Electron Microscope) can be used. If the thickness and composition obtained by any one of the above methods are within the scope of the present invention, the effects of the present invention can be obtained.

上述のような、パラジウムめっきリードフレーム上での良好なウェッジ接合性と耐酸化性の両者を確保し、更に、後述するループ特性も満足させるためには、ワイヤー表面の結晶方位、ワイヤー表面の硬さ、又は芯線中の添加元素の種類と組成を特定の範囲としたボンディングワイヤーが有効であることを、発明者らは見出した。   In order to ensure both good wedge bondability and oxidation resistance on the palladium-plated lead frame as described above, and to satisfy the loop characteristics described later, the crystal orientation of the wire surface and the hardness of the wire surface In addition, the inventors have found that a bonding wire having a specific range of the type and composition of the additive element in the core wire is effective.

ワイヤー表面の結晶方位に関しては、前記合金層の表面結晶粒の内、<111>結晶方位の伸線方向に対する傾きが無い又は小さい方がより好ましい。具体的には、前記傾きが15度以下である結晶粒の面積を40%以上100%以下とすれば、300μm以上の高ループ高さという特殊なボンディングを行った際であっても、リーニング不良と呼ばれる、ボンディング方向と垂直な方向にループが倒れる不良が生じにくくなるので良く、より好ましくは70%以上100%以下とすれば更にその効果が高まるので更に良い。これは、該方位が<111>結晶方位もしくはその近傍であると、材料の強度や弾性率が高くなるためである。本発明者らが更に検討を重ねた結果、リーニング不良の発生率を抑制するためには、ワイヤー表面において<111>結晶方位の伸線方向に対する傾きを小さくし、該傾きが15度以下である結晶粒の面積を40%以上とすると、リーニング不良の発生率を抑制するに足る強度並びに弾性率が確保できることが判明した。しかし、該傾きが15度以下である結晶粒の面積が50%未満では、リーリング不良の発生率を抑制する効果は十分ではない。ここで、前記合金層の表面で観察される結晶粒の<111>結晶方位の伸線方向に対する傾きは、TEM観察装置中に設置した微小領域Ｘ線法あるいは電子後方散乱図形（ＥＢＳＤ、Electron Backscattered Diffraction）法等で測定できるものである。中でも、ＥＢＳＤ法は個別の結晶粒の方位を観察し、隣り合う測定点間での結晶方位の角度差を図示できるという特徴を有し、ボンディングワイヤーのような細線であっても、比較的簡便ながら精度良く結晶粒の傾きを観察できるのでより好ましい。また、該傾きが15度以下である結晶粒の面積は、微小領域Ｘ線法ではそれぞれの結晶粒における結晶方位のＸ線強度をもとに結晶方位の体積比率として求めることができ、またＥＢＳＤ法では、前記で観察した個別の結晶粒の方位から直接算出可能である。前記面積の比率を算出するには、ワイヤー表面の任意の面であって、ボンディングワイヤーの伸線方向と垂直な方向においてボンディングワイヤーの直径の少なくとも1/4の幅を、ボンディングワイヤーの伸線方向に少なくとも100μmの長さの面を観察し、その観察面積を１００として、該傾きが15度以下である結晶粒の占める面積の百分率とする。上記いずれか１つの方法で得られる厚さや組成が本発明の範囲内であれば、本発明の作用効果が得られるものである。   With respect to the crystal orientation of the wire surface, it is more preferable that the <111> crystal orientation has no or little inclination with respect to the drawing direction among the surface crystal grains of the alloy layer. Specifically, if the area of the crystal grains with the inclination of 15 degrees or less is 40% or more and 100% or less, even when special bonding with a high loop height of 300 μm or more is performed, the leaning failure It may be difficult to cause a defect that the loop collapses in a direction perpendicular to the bonding direction, and more preferably 70% or more and 100% or less, and the effect is further enhanced. This is because the strength and elastic modulus of the material increase when the orientation is the <111> crystal orientation or the vicinity thereof. As a result of further studies by the present inventors, in order to suppress the incidence of leaning defects, the inclination of the <111> crystal orientation with respect to the drawing direction on the wire surface is reduced, and the inclination is 15 degrees or less. It has been found that when the crystal grain area is 40% or more, sufficient strength and elastic modulus can be secured to suppress the occurrence rate of leaning defects. However, when the area of the crystal grains having the inclination of 15 degrees or less is less than 50%, the effect of suppressing the occurrence rate of the reeling failure is not sufficient. Here, the inclination of the <111> crystal orientation of the crystal grain observed on the surface of the alloy layer with respect to the drawing direction is determined by a micro-region X-ray method or an electron backscattered pattern (EBSD, Electron Backscattered) installed in a TEM observation apparatus. Diffraction) method or the like. Among other things, the EBSD method has the feature that the orientation of individual crystal grains can be observed and the angle difference of the crystal orientation between adjacent measurement points can be illustrated, and even a thin wire such as a bonding wire is relatively simple. However, it is more preferable because the inclination of the crystal grains can be observed with high accuracy. In addition, the area of a crystal grain having an inclination of 15 degrees or less can be obtained as a volume ratio of the crystal orientation based on the X-ray intensity of the crystal orientation in each crystal grain in the micro region X-ray method. In the method, it is possible to directly calculate from the orientation of the individual crystal grains observed as described above. In order to calculate the ratio of the area, the width of at least 1/4 of the diameter of the bonding wire in the direction perpendicular to the wire drawing direction of the bonding wire is an arbitrary surface of the wire surface, and the wire drawing direction of the bonding wire A surface having a length of at least 100 μm is observed, and the observation area is defined as 100, and the percentage of the area occupied by the crystal grains having the inclination of 15 degrees or less is defined. If the thickness and composition obtained by any one of the above methods are within the scope of the present invention, the effects of the present invention can be obtained.

ワイヤー表面の硬さに関しては、前記ワイヤー表面のマイヤー硬度を0.2〜2.0GPaの範囲とすると、80μmクラスのループ高さという低ループボンディング時であっても、ネックダメージと呼ばれる不良の発生が抑制されるので更に良い。   Regarding the hardness of the wire surface, if the Meyer hardness of the wire surface is in the range of 0.2 to 2.0 GPa, the occurrence of defects called neck damage is suppressed even during low loop bonding with a loop height of 80 μm class. So even better.

このネックダメージは、ボール部と母線部との境界領域（ネック部）における損傷を指し、極端に低いループ高さでループを形成する際に、ネック部に過度な負担がかかることで生じる不良である。昨今のフラッシュメモリー等の薄型電子機器では、メモリーの容量を少しでも大容量化するために、薄いシリコンチップを複数枚搭載した薄型デバイスを使用しているのであるが、このような薄型デバイスでは必然的にループ高さを低くせざるを得ないため、従来、前記ネックダメージが発生し易くなっていた。   This neck damage refers to damage in the boundary area (neck part) between the ball part and the busbar part. It is a defect that occurs when an excessive load is applied to the neck part when forming a loop with an extremely low loop height. is there. In recent thin electronic devices such as flash memory, thin devices with multiple thin silicon chips are used in order to increase the capacity of the memory as much as possible. Therefore, the neck damage has been apt to occur conventionally because the loop height has to be lowered.

本発明者らは、上記ネックダメージの発生には、ワイヤー表面の硬度が密接に関係していることを明らかにし、該硬度を低くすれば、低ループボンディング時にネックに過度の負荷が与えられても、表面が塑性変形でき、ネックダメージを抑制できることを見出した。具体的には、前記ボンディングワイヤーの表面のマイヤー硬度を2.0GPa以下とすれば、上記効果が十分得られる。但し、前記ボンディングワイヤーの表面のマイヤー硬度が2.0GPaを超える場合、通常の金合金並みの硬度となってしまい、低ループボンディング時にネックに過度の負荷が与えられると、表面層が充分には塑性変形し難くなり、前記効果が十分得られない。一方、前記ボンディングワイヤーの表面のマイヤー硬度が0.2GPa未満の場合では、硬度が小さすぎるのでボンディングワイヤーの取り扱い過程でワイヤー表面に容易に傷が入り易くなり、取り扱い方法によっては多くの表面傷が生じる場合がある。ここで、マイヤー硬度とは、鋼球あるいは超硬合金球の圧子を用いて計測する硬さのことで、圧子で試験面にくぼみをつけたときの荷重を、永久くぼみの直径の投影面積で除した値を指し、その値は応力の次元を有する。ナノインデンション法と呼ばれる物質表面の解析手法を用いると、1nm程度の深さにおけるマイヤー硬度も測定可能であるので、本発明のマイヤー硬度値の確認には、ナノインデンション法を用いるのが好ましい。また、ボンディングワイヤーの表面のマイヤー硬度は、合金層及び被覆層を有するボンディングワイヤーの最表面をナノインデンション法で測定して得られるものである。尚、0.2〜2.0GPaのマイヤー硬度は、おおむね50〜570Hvのビッカース硬度に相当する。   The present inventors have revealed that the occurrence of the neck damage is closely related to the hardness of the wire surface, and if the hardness is lowered, an excessive load is applied to the neck during low-loop bonding. It was also found that the surface can be plastically deformed and neck damage can be suppressed. Specifically, if the Meyer hardness of the surface of the bonding wire is 2.0 GPa or less, the above effect can be sufficiently obtained. However, if the Meyer hardness of the surface of the bonding wire exceeds 2.0 GPa, the hardness will be the same as that of a normal gold alloy, and if an excessive load is applied to the neck during low-loop bonding, the surface layer will be sufficiently plastic. It becomes difficult to deform, and the above effect cannot be obtained sufficiently. On the other hand, if the Meyer hardness of the surface of the bonding wire is less than 0.2 GPa, the hardness is too small and the wire surface is easily damaged in the handling process of the bonding wire, and many surface scratches occur depending on the handling method. There is a case. Here, Meyer's hardness is the hardness measured using a steel ball or cemented carbide ball indenter. The load when the test surface is indented with the indenter is the projected area of the diameter of the permanent indentation. The value has a dimension of stress. Since the Mayer hardness at a depth of about 1 nm can be measured using a material surface analysis method called the nanoindentation method, it is preferable to use the nanoindentation method for confirming the Meyer hardness value of the present invention. . The Mayer hardness of the surface of the bonding wire is obtained by measuring the outermost surface of the bonding wire having the alloy layer and the coating layer by the nanoindentation method. A Meyer hardness of 0.2 to 2.0 GPa corresponds to a Vickers hardness of about 50 to 570 Hv.

芯線中の添加元素の種類と組成に関し、本発明に係る伸線は、銅又は銅合金からなるものであるが、前記芯線には、本発明の作用効果を損なわない範囲で種々の添加元素を添加してもよい。該芯線に添加できる元素の例としては、Ca、B、P、Al、Ag、Se等が挙げられる。これらの添加元素の中で、B、P、Seの内の少なくとも1種を含むのがより好ましい。該添加元素が総計で5〜300質量ppm含有すると、ボンディングワイヤーの強度がより向上する。その結果、例えば、ループ長さが5mmを超える長尺ループのボンディングをした際でもループの直進性が確保できるようになる。これは、該添加元素が芯線における銅結晶粒内での固溶強化あるいは結晶粒界の強化に寄与するためと思われる。但し、5質量ppmを下回る添加では上記強度の更なる向上という効果が十分得られない。一方、300質量ppmを超える添加は、ボール部をより硬化するようになるので、ボールボンディング時にチップを損傷する危険性が高まり好ましくない場合がある。芯線中の成分含有量を分析するには、ボンディングワイヤーを切断し、その断面部からスパッタ等により深さ方向に掘り下げながら分析する手法や、該断面での線分析又は点分析する手法を用いる。これらの分析に用いる分析装置として、EPMA、EDX、AES、TEM等が利用できる。また、平均的な組成の分析には、表面部から段階的に酸等の薬液でボンディングワイヤーを溶解していき、その溶液中に含まれる濃度から溶解した部位の組成を求める手法を用いることができる。上記いずれか１つの方法で得られる厚さや組成が本発明の範囲内であれば、本発明の作用効果が得られるものである。   Regarding the kind and composition of the additive element in the core wire, the wire drawing according to the present invention is made of copper or a copper alloy, but various additive elements are added to the core wire as long as the effects of the present invention are not impaired. It may be added. Examples of elements that can be added to the core wire include Ca, B, P, Al, Ag, Se, and the like. Among these additive elements, it is more preferable to include at least one of B, P, and Se. When the additive elements are contained in a total amount of 5 to 300 ppm by mass, the strength of the bonding wire is further improved. As a result, for example, even when a long loop having a loop length exceeding 5 mm is bonded, the straightness of the loop can be ensured. This is presumably because the additive element contributes to solid solution strengthening or grain boundary strengthening in the copper crystal grains in the core wire. However, if the addition is less than 5 ppm by mass, the effect of further improving the above strength cannot be obtained sufficiently. On the other hand, addition of more than 300 ppm by mass causes the ball part to be hardened more, which increases the risk of damaging the chip during ball bonding and may be undesirable. In order to analyze the component content in the core wire, a technique of cutting the bonding wire and analyzing it by digging it in the depth direction by sputtering or the like, or a technique of performing line analysis or point analysis on the cross section is used. EPMA, EDX, AES, TEM, etc. can be used as an analyzer used for these analyses. In addition, for the analysis of the average composition, it is necessary to use a technique in which the bonding wire is dissolved stepwise from the surface with a chemical solution such as an acid and the composition of the dissolved portion is determined from the concentration contained in the solution. it can. If the thickness and composition obtained by any one of the above methods are within the scope of the present invention, the effects of the present invention can be obtained.

以上、本発明の好適な例を述べたが、本発明は適宜変形が可能である。例えば、前記芯線と前記被覆層との間には拡散層が形成されていても良い。例えば、パラジウムを含有する領域が前記被覆層と連続して、前記パラジウムや芯線を構成する銅が拡散してパラジウムを５０％未満含有する拡散層である。このような拡散層が存在することにより、ボンディングワイヤーは、被覆層と芯線との密着性を向上することができる。   The preferred examples of the present invention have been described above, but the present invention can be modified as appropriate. For example, a diffusion layer may be formed between the core wire and the coating layer. For example, the palladium-containing region is a diffusion layer containing less than 50% palladium by diffusing the palladium and copper constituting the core wire continuously with the coating layer. Due to the presence of such a diffusion layer, the bonding wire can improve the adhesion between the coating layer and the core wire.

以下、本発明のボンディングワイヤーの製造方法について一例を説明する。   Hereinafter, an example is demonstrated about the manufacturing method of the bonding wire of this invention.

前記組成のボンディングワイヤーを製造するためには、高純度の銅（純度99.99％以上）、又は、これら高純度の銅と添加元素原料を出発原料として秤量した後、これを高真空下もしくは窒素やAr等の不活性雰囲気下で加熱して溶解することで銅又は銅合金のインゴットを得る。該インゴットを最終的に必要とする芯線の直径まで金属製のダイスを用いて伸線する。本発明に係るパラジウムを含む被覆層は、最終的な芯線の直径まで伸線した後に施される。パラジウムを含む被覆層を形成する手法としては、電解めっき、無電解めっき、蒸着法等が利用できるが、膜厚を安定的に制御できる電解めっきを利用するのが工業的には最も好ましい。その後、前記被覆層の表面に金とパラジウムを含む合金層を形成する。その方法はどのような方法でもよいが、前記被覆層を形成した後、更にその表面に表皮層として金膜を形成し、一定の炉内温度で電気炉中、ワイヤーを一定の速度の下で連続的に掃引することで合金化を促す方法が、確実に該合金の組成と厚みを制御できるので好ましい。前記被覆層の表面に更に金膜を形成する手法としては、電解めっき、無電解めっき、蒸着法等が利用できるが、上記の理由から電解めっきを利用するのが工業的には最も好ましい。前記合金化のための加熱時は、原料の汚染を考慮して、炉内の雰囲気を窒素やAr等の不活性雰囲気とし、更に、従来のボンディングワイヤーの加熱法とは異なり、該雰囲気中に含有される酸素濃度を5000ppm以下とする。より好ましくは、不活性ガス中に水素等の還元性ガスを少なくとも500ppm混入させると、ワイヤーの原料の汚染を防止する効果が更に高まるので良い。また、炉内の適切な温度はワイヤーの組成やワイヤーを掃引する速度によっても異なるが、おおむね210℃〜700℃の範囲とすると、安定した品質のボンディングワイヤーが得られるので良い。そして、伸線工程中にワイヤーを掃引する速度は、例えば20〜40m/min程度とすると安定した操業ができるので好ましい。   In order to manufacture a bonding wire having the above composition, high-purity copper (purity of 99.99% or more), or after weighing these high-purity copper and additive element materials as starting materials, these are weighed under high vacuum or nitrogen or An ingot of copper or copper alloy is obtained by melting under heating in an inert atmosphere such as Ar. The ingot is finally drawn using a metal die to the required core wire diameter. The coating layer containing palladium according to the present invention is applied after drawing to the final core diameter. As a method for forming the coating layer containing palladium, electrolytic plating, electroless plating, vapor deposition, or the like can be used. However, it is industrially most preferable to use electrolytic plating that can stably control the film thickness. Thereafter, an alloy layer containing gold and palladium is formed on the surface of the coating layer. Any method may be used, but after the coating layer is formed, a gold film is further formed as a skin layer on the surface, and the wire is kept at a constant speed in an electric furnace at a constant furnace temperature. A method of promoting alloying by continuously sweeping is preferable because the composition and thickness of the alloy can be reliably controlled. As a method for further forming a gold film on the surface of the coating layer, electrolytic plating, electroless plating, vapor deposition, or the like can be used. However, it is industrially most preferable to use electrolytic plating for the above reasons. At the time of heating for alloying, in consideration of contamination of raw materials, the atmosphere in the furnace is an inert atmosphere such as nitrogen or Ar, and further, unlike the conventional bonding wire heating method, The oxygen concentration contained is 5000 ppm or less. More preferably, when at least 500 ppm of a reducing gas such as hydrogen is mixed in the inert gas, the effect of preventing the contamination of the wire raw material can be further enhanced. Moreover, although the suitable temperature in a furnace changes also with the composition of a wire, and the speed which sweeps a wire, when it is set as the range of about 210 degreeC-700 degreeC, it is good because a stable quality bonding wire is obtained. The speed at which the wire is swept during the wire drawing step is preferably about 20 to 40 m / min because stable operation can be performed.

本願発明のボンディングワイヤーの製造方法において、<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積が50%以上100%以下とする製造方法は、通常の製造方法では製造することは難しく、特殊な方法で製造される。   In the manufacturing method of the bonding wire according to the present invention, the manufacturing method in which the area of the crystal grains having an inclination of <111> crystal orientation with respect to the drawing direction is 15 degrees or less is 50% or more and 100% or less is a normal manufacturing method. It is difficult to do and is manufactured in a special way.

具体的には、前記の要領でインゴットを得た後、前記インゴットにパラジウムを含む被覆層を上記と同様にして形成する。更にその上に金膜を上記と同様にして形成する。前記被覆層と金膜を形成したインゴットを、最終的な芯線の直径まで金属製のダイスを用いて伸線する際に、線径150μm以上の太さでは前記ダイスの減面率を14〜21%程度として伸線し、線径150μm未満の太さにおける伸線時は前記減面率を12〜19%程度という、通常よりも大きな減面率で伸線する。これによって、金膜上の方向性を有する集合組織（伸線方向に結晶方位が揃った集合組織）を発達させることができる。但し、大きな減面率で伸線すると断線が生じる危険性が高まることから、ボンディングワイヤーの断線を防ぐため、伸線速度は、例えば、2〜4m/minというような通常よりも低速とするのがより好ましい。本ボンディングワイヤーでも、伸線後に、前述と同様に合金化を促す熱処理を行う。伸線後に合金化を促す熱処理工程における温度が、低温であれば、<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積の割合が高まり、高温であれば、該面積の割合が低下する。この面積の低下は、該工程で、加熱して再結晶化が促進されると、前述の集合組織における方向性が失われ易くなることに起因する。具体的には、前記炉内温度が210℃〜260℃であれば、前記面積の割合が100%となり、前記炉内温度が660℃〜700℃の範囲であれば、前記面積の割合が50%程度となり、前記面積の割合は熱処理の温度で制御できる。   Specifically, after an ingot is obtained as described above, a coating layer containing palladium is formed on the ingot in the same manner as described above. Further, a gold film is formed thereon in the same manner as described above. When the ingot formed with the coating layer and the gold film is drawn to the final core wire diameter using a metal die, the area reduction rate of the die is 14 to 21 when the wire diameter is 150 μm or more. When the wire is drawn at a wire diameter of less than 150 μm, the wire is drawn at a surface reduction rate of about 12 to 19%, which is larger than usual. This makes it possible to develop a texture having a directionality on the gold film (a texture having crystal orientations aligned in the wire drawing direction). However, if the wire is drawn with a large area reduction rate, the risk of breakage increases. Therefore, in order to prevent the bonding wire from breaking, the wire drawing speed should be lower than usual, for example, 2 to 4 m / min. Is more preferable. Also in this bonding wire, after wire drawing, heat treatment for promoting alloying is performed in the same manner as described above. If the temperature in the heat treatment step that promotes alloying after wire drawing is low, the ratio of the area of the crystal grains with the inclination of the <111> crystal orientation with respect to the wire drawing direction is 15 degrees or less increases. The area ratio decreases. This reduction in area is caused by the tendency to lose the directionality in the texture described above when recrystallization is promoted by heating in this step. Specifically, if the furnace temperature is 210 ° C. to 260 ° C., the area ratio is 100%, and if the furnace temperature is in the range of 660 ° C. to 700 ° C., the area ratio is 50%. The area ratio can be controlled by the temperature of the heat treatment.

本願発明のボンディングワイヤーの製造方法において、被覆層の表面のマイヤー硬度が0.2〜2.0GPaの範囲となるボンディングワイヤーの製造方法は、通常の製造方法では製造することは難しく、特殊な方法で、ワイヤー表面の金とパラジウムとを含む合金を格別にやわらかくして製造する。具体的には、上述のいずれかの方法で目的の線径まで伸線し、前述の合金化のための熱処理工程を終えた後、更に、該ボンディングワイヤーをスプールごとにアルゴンに4%の水素が混入された雰囲気に制御された電気炉中に設置し、130〜180℃で２４〜２８時間の加熱をすることで製造できる。130℃より低温又は24時間より短時間の加熱では、金とパラジウムとを含む合金を上記硬度のように格別にやわらかくすることはできない。180℃より高温又は28時間より長時間の加熱をすると、隣り合うワイヤー間の拡散が促進され、ワイヤー同士がくっついてしまう場合があるので注意が必要である。   In the manufacturing method of the bonding wire of the present invention, the manufacturing method of the bonding wire in which the Mayer hardness of the surface of the coating layer is in the range of 0.2 to 2.0 GPa is difficult to manufacture by a normal manufacturing method, An alloy containing gold and palladium on the surface is manufactured to be exceptionally soft. Specifically, after drawing to the target wire diameter by any of the methods described above and finishing the heat treatment step for alloying, the bonding wire is further wound with 4% hydrogen in argon for each spool. It can be manufactured by installing in an electric furnace controlled in an atmosphere mixed with and heating at 130 to 180 ° C. for 24 to 28 hours. By heating at a temperature lower than 130 ° C. or shorter than 24 hours, the alloy containing gold and palladium cannot be made particularly soft as the above-mentioned hardness. Care should be taken when heating above 180 ° C or longer than 28 hours promotes diffusion between adjacent wires and may cause the wires to stick together.

以下、実施例について説明する。   Examples will be described below.

ボンディングワイヤーの原材料として、芯線に用いた銅、芯線中の添加元素としてＢ、Ｐ、Ｓｅ、Ｃａ、Ａｌ、被覆層に用いたパラジウム、表皮層に使用した金として純度が９９．９９質量％以上の素材をそれぞれ用意した。前記の銅、又は銅と添加元素原料を出発原料として秤量した後、これを高真空下で加熱して溶解することで銅又は銅合金の直径１０ｍｍ程度のインゴットを得た。その後、鍛造、圧延、伸線を行って所定の直径のワイヤーを作製した。その後、各ワイヤーの表面にパラジウムを含む被覆層を電解めっきで形成した。ここで、前記被覆層の厚さは、電解めっきの時間で制御した。更にその後、前記被覆層の表面に電気めっきで金膜を形成し、300〜800℃に保たれた炉内で該ワイヤーを30m/minの速度で連続的に掃引することで、前記被覆層の表面に金とパラジウムとの合金層を形成した。ここで、合金層の厚さは、前記金膜の目付け量、即ち、電気めっき時間で制御した。このようにして芯線の直径が２０μｍのボンディングワイヤーを得た。尚、一部の試料においては、<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積を制御するため、線径150μm以上の太さでは前記ダイスの減面率を16〜20%程度として伸線し、線径150μm未満の太さにおける伸線時は前記減面率を13〜15%程度という、通常よりも大きな減面率で伸線した。また、一部の試料においては、被覆層の表面のマイヤー硬度を制御するため、該ボンディングワイヤーをスプールごとアルゴン雰囲気に制御された電気炉中に設置し、150〜200℃で２０〜２４時間の加熱を施した。   As a raw material for the bonding wire, copper used for the core wire, B, P, Se, Ca, Al as additive elements in the core wire, palladium used for the coating layer, and gold used for the skin layer have a purity of 99.99% by mass or more. Each material was prepared. After weighing the above-mentioned copper or copper and additive element material as a starting material, this was heated and melted under high vacuum to obtain an ingot having a diameter of about 10 mm of copper or copper alloy. Thereafter, forging, rolling, and wire drawing were performed to produce a wire having a predetermined diameter. Thereafter, a coating layer containing palladium was formed on the surface of each wire by electrolytic plating. Here, the thickness of the coating layer was controlled by the time of electrolytic plating. Thereafter, a gold film is formed by electroplating on the surface of the coating layer, and the wire is continuously swept at a speed of 30 m / min in a furnace maintained at 300 to 800 ° C. An alloy layer of gold and palladium was formed on the surface. Here, the thickness of the alloy layer was controlled by the weight of the gold film, that is, the electroplating time. In this way, a bonding wire having a core wire diameter of 20 μm was obtained. In some samples, in order to control the area of the crystal grains where the inclination of the <111> crystal orientation with respect to the wire drawing direction is 15 degrees or less, the area reduction rate of the die is reduced at a wire diameter of 150 μm or more. Drawing was performed at about 16 to 20%, and at the time of drawing at a thickness of a wire diameter of less than 150 μm, the above-mentioned area reduction was about 13 to 15%, and was drawn with a larger area reduction than usual. Moreover, in some samples, in order to control the Mayer hardness of the surface of the coating layer, the bonding wire and the spool are placed in an electric furnace controlled in an argon atmosphere, and the temperature is 150 to 200 ° C. for 20 to 24 hours. Heat was applied.

できあがった該ボンディングワイヤーにおける芯線の直径、被覆層及び合金層の厚みは、ボンディングワイヤーの表面をスパッタしながらＡＥＳで分析し、また、該ボンディングワイヤーを断面研磨し、ＥＤＸで組成を分析しながら測定した。パラジウムの濃度が50%以上で、かつ、金の濃度が15%未満であった領域を被覆層とし、被覆層の表面にある金とパラジウムとを含む合金層においては金濃度が15〜75%の範囲であった領域を合金層とした。被覆層及び合金層の厚み及び組成をそれぞれ表１〜５に記載した。   The diameter of the core wire, the thickness of the coating layer and the alloy layer in the resulting bonding wire are analyzed by AES while sputtering the surface of the bonding wire, and the bonding wire is cross-polished and measured while analyzing the composition by EDX. did. A region in which the concentration of palladium is 50% or more and the concentration of gold is less than 15% is used as a coating layer, and in the alloy layer containing gold and palladium on the surface of the coating layer, the gold concentration is 15 to 75%. The region that was in the range was used as the alloy layer. The thickness and composition of the coating layer and the alloy layer are shown in Tables 1 to 5, respectively.

被覆層によるボンディングワイヤーの酸化防止効果を評価するため、湿度が85%、温度が85℃という高温高湿炉中に72時間、ボンディングワイヤーをスプールごと放置し、あえてワイヤー表面の酸化を促進するような加速試験を行った。加熱後、ボンディングワイヤーを高温高湿炉から取り出し、表面の酸化の度合いを光学顕微鏡で観察した。この時、ワイヤー表面の全面が酸化していれば×印で、ワイヤー表面が酸化していなければ○印で表１、５中の「長期保管（酸化）」の欄に表記した。   To evaluate the anti-oxidation effect of the bonding wire by the coating layer, leave the bonding wire together with the spool for 72 hours in a high-temperature and high-humidity furnace with a humidity of 85% and a temperature of 85 ° C to promote oxidation of the wire surface. Accelerated tests were conducted. After heating, the bonding wire was taken out from the high-temperature and high-humidity furnace, and the degree of surface oxidation was observed with an optical microscope. At this time, if the entire surface of the wire was oxidized, it was marked with “x”, and if the wire surface was not oxidized, it was marked with “◯” in the column of “long-term storage (oxidation)” in Tables 1 and 5.

被覆層によるボンディングワイヤーの硫化防止効果を評価するため、大気雰囲気下で温度が195℃に保たれた高温炉中に155時間、ボンディングワイヤーをスプールごと放置し、あえてワイヤー表面の硫化を促進するような加速試験を行った。前記のように大気雰囲気中に高温で放置すると、大気中に含まれる極微量の硫黄であっても硫化反応を加速できる。加熱後、ボンディングワイヤーを高温炉から取り出し、表面の硫化の度合いを市販の色彩計（ミノルタＣＲ−３００）で観察し、明度（L*）が30以下であれば硫化とみなした。この時、ワイヤー表面に硫化部が観察されれば×印で、ワイヤー表面が硫化していなければ○印で表１、５中の「長期保管（硫化）」の欄に表記した。 In order to evaluate the anti-sulfuration effect of the bonding wire by the coating layer, leave the bonding wire together with the spool for 155 hours in a high-temperature furnace maintained at 195 ° C in an air atmosphere, and dare to promote sulfidation of the wire surface. Accelerated tests were conducted. As described above, when left in an air atmosphere at a high temperature, the sulfurization reaction can be accelerated even with a very small amount of sulfur contained in the air. After heating, the bonding wire was taken out of the high temperature furnace, and the degree of sulfidation on the surface was observed with a commercially available color meter (Minolta CR-300). If the lightness (L * ) was 30 or less, it was regarded as sulfidation. At this time, if a sulfurized portion was observed on the wire surface, it was marked with “X”, and if the wire surface was not sulfided, it was marked with “◯” in the column of “long-term storage (sulfurized)” in Tables 1 and 5.

ボンディングワイヤーの接続には、市販の自動ワイヤーボンダーを使用した。ボンディングの直前にアーク放電によりボンディングワイヤーの先端にボール部を作製したが、その直径はボンディングワイヤーの直径の１．７倍となるように３４μｍとしておいた。ボール部作製時の雰囲気は窒素とした。   A commercially available automatic wire bonder was used to connect the bonding wires. A ball portion was produced at the tip of the bonding wire by arc discharge immediately before bonding, and its diameter was set to 34 μm so as to be 1.7 times the diameter of the bonding wire. Nitrogen was used as an atmosphere for producing the ball part.

ボール部の実際の直径は、各ボール部とも２０個ずつＳＥＭを用いて測定し、その最大値と最小値の差が、ボール径の平均値の１０％超であればばらつきが激しく不良であるとして×を、５％超かつ１０％以下であれば中間程度として△を、３％超かつ５％以下であれば実用上の不具合は無く良好とみなして○を、３％以下であれば極めて良好として◎を、表１、５中の「窒素中ＦＡＢ真球性」の欄に表記した。   The actual diameter of the ball part is measured with 20 SEMs for each ball part, and if the difference between the maximum value and the minimum value exceeds 10% of the average value of the ball diameter, the variation is severe and poor. If x is more than 5% and less than 10%, △ is intermediate, and if more than 3% and less than 5%, there is no practical problem and ○ is extremely less than 3%. “Excellent” is indicated in the column of “FAB sphericity in nitrogen” in Tables 1 and 5 as good.

また、ボール部をＳＥＭで観察し、その外観に気泡が見られれば、表１、５中の「窒素中ＦＡＢ気泡抑制」の欄に×印を、外観に気泡が見られなければ○印をそれぞれ表記した。   In addition, when the ball part is observed with an SEM and bubbles are observed in its appearance, an X mark is indicated in the column of “Inhibition of FAB bubbles in nitrogen” in Tables 1 and 5, and a mark is indicated if bubbles are not observed in the appearance. Represented respectively.

ボンディングワイヤーの接合の相手としては、Ｓｉチップ上に形成された厚さ１μｍのＡｌ電極と、表面が金又はパラジウムめっきリードフレームのリードをそれぞれ用いた。作製したボール部を２６０℃に加熱した前記電極とボール接合した後、ボンディングワイヤーの母線部を２６０℃に加熱した前記リードとウェッジ接合し、再びボール部を作製することで、連続的にボンディングを繰り返した。ループ長が4.9mmとなるようにした。尚、一部の試料においてはループ高さが約304.8μm（12mil）でループ長が約2mmの前記高ループボンディングを、また別な試料においてはループ長が約3mmでループ高さが76.2μm（3mil）の低ループボンディングを、更に別な試料においてはループ長が5.3mm（210mil）という長尺ボンディングをそれぞれ行った。   As bonding partners of the bonding wires, an Al electrode having a thickness of 1 μm formed on the Si chip and a lead having a gold or palladium plated lead frame on the surface were used. After the ball portion thus prepared is bonded to the electrode heated to 260 ° C., the bus wire portion of the bonding wire is wedge-bonded to the lead heated to 260 ° C., and the ball portion is formed again, thereby continuously bonding. Repeated. The loop length was set to 4.9mm. In some samples, the loop height is about 304.8 μm (12 mil) and the loop length is about 2 mm. In another sample, the loop length is about 3 mm and the loop height is 76.2 μm ( 3 mil) of low loop bonding, and another sample with long loop length of 5.3 mm (210 mil).

ボンディングワイヤーのウェッジボンディング性については、ウェッジ接合された状態のボンディングワイヤーをウェッジ接合部直上でつまみ、切断するまで上方に持ち上げ、その切断時に得られる破断荷重を読み取る、いわゆるピール強度測定法で、４０本の破断荷重（ピール強度）を測定した。ピール強度の標準偏差が5mN超であればばらつきが大きく改善が必要であるため×を、3mN超かつ5mN以下であれば実用上の大きな問題はないので○を、3mN以下であればばらつきが極めて小さく良好なので◎を、表１、５の「Ag-L/F 2nd接合」（金めっきリードフレームのリードの場合）並びに「Pd-L/F 2nd接合」（パラジウムめっきリードフレームのリードの場合）の欄に表記した。   Regarding the wedge bondability of the bonding wire, the wedge-bonded bonding wire is picked immediately above the wedge joint, lifted upward until it is cut, and the breaking load obtained at the time of cutting is read, so-called peel strength measurement method. The breaking load (peel strength) of the book was measured. If the standard deviation of the peel strength exceeds 5 mN, the variation is large and needs to be improved, so ×, and if it exceeds 3 mN and 5 mN or less, there is no practical problem. Since it is small and good, “Ag-L / F 2nd junction” (for gold-plated lead frame lead) and “Pd-L / F 2nd junction” (for palladium-plated lead frame lead) in Tables 1 and 5 It was written in the column.

前記被覆層の表面で観察される結晶粒の<111>結晶方位の伸線方向に対する傾きは、ＥＢＳＤ法で個別の結晶粒の方位を観察した上で算出した。該算出にあたっては、ボンディングワイヤーの伸線方向と垂直な方向に8μmの幅を有し、ボンディングワイヤーの伸線方向に150μmの長さを有する面を、各試料とも３視野ずつ観察した。その値を表２〜４の「<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積」欄に表記した。   The inclination of the <111> crystal orientation of the crystal grains observed on the surface of the coating layer with respect to the drawing direction was calculated after observing the orientation of the individual crystal grains by the EBSD method. In the calculation, a surface having a width of 8 μm in the direction perpendicular to the drawing direction of the bonding wire and a length of 150 μm in the drawing direction of the bonding wire was observed for each sample in three fields. The values are shown in the column of “Area of crystal grains whose inclination of <111> crystal orientation relative to the drawing direction is 15 degrees or less” in Tables 2-4.

前記の高ループボンディングをした後の、ボンディングワイヤー表面におけるリーニング不良は、各試料とも２０本のループを光学顕微鏡で観察し、1本もリーニング不良が観察されなければ極めて良好で◎◎印で、１〜２本のループのみにリーニング不良が観察された場合は良好で◎印で、３〜４本のループのみにリーニング不良が観察された場合は実用上問題の無いレベルで○印で、５本以上のループにリーニング不良が観察されれば劣悪で×印で、表２〜４の「高ループリーニング抑制」欄に表記した。   Leaning defects on the surface of the bonding wire after the high loop bonding described above are very good if each sample has 20 loops observed with an optical microscope. If a leaning defect is observed only in one or two loops, it is good and marked with ◎, and if a leaning defect is observed only in three to four loops, it is marked with ○ at a level that causes no practical problems. If a leaning defect was observed in more than one loop, it was inferior and marked with an x mark in the “High loop leaning suppression” column of Tables 2-4.

ワイヤー表面のマイヤー硬度は、ナノインデンション法によって、1nm程度の深さ精度で測定し、その値を表３〜４の「ワイヤーの表面のマイヤー硬度」欄に表記した。   The Mayer hardness of the wire surface was measured with a depth accuracy of about 1 nm by the nanoindentation method, and the value was shown in the “Meyer hardness of the wire surface” column of Tables 3-4.

前記の低ループボンディングをした後の、ネック部におけるダメージの有無は、各試料とも２０本のループを光学顕微鏡で観察し、1本もダメージが無ければ良好で◎印で、２０本中１〜２本でダメージが観察されれば問題の無いレベルで○印で、２０本中３本以上でダメージが観察されれば劣悪で×印で、表３〜４の「76.2μm(3mil)級低ループネックダメージ」欄に表記した。   The presence or absence of damage in the neck portion after the low-loop bonding described above was observed if 20 loops of each sample were observed with an optical microscope. If damage is observed with 2 pieces, it is marked with a circle with no problem level, and if damage is observed with 3 or more pieces out of 20 pieces, it is inferior and marked with x mark, “76.2 μm (3mil) class low in Table 3-4” This is shown in the “Loop Neck Damage” column.

前記の長尺ボンディングをした後のループの曲がりについては、各試料のループ２０本を投影機を用いて測定した。ここで、その平均値をループ長さで除した値をワイヤー曲がり率とし、４％未満であれば極めて良好で◎印で、４〜５％であれば実用上問題ないレベルとして○印で、５％超であれば不良と判断して×印で、表４の「5.3mm(210mil)級長尺曲がり」の欄に表記した。   Regarding the bending of the loop after the long bonding, 20 loops of each sample were measured using a projector. Here, the value obtained by dividing the average value by the loop length is the wire bending rate, and if it is less than 4%, it is very good, and if it is 4-5%, it is marked as ◯ as a practically no problem level, If it exceeds 5%, it is judged as defective, and is indicated in the column of “5.3 mm (210 mil) long bend” in Table 4 with a cross.

チップダメージの評価では、ボール接合部２０個を断面研磨し、電極に亀裂が生じていれば不良と判断して×印で、亀裂が観察されなければ良好として○印で、表４の「チップダメージ」欄に表記した。   In the evaluation of chip damage, 20 ball joints were subjected to cross-sectional polishing, and if a crack was generated in the electrode, it was judged as bad and X was marked as bad. Indicated in the "Damage" column.

表１の実施例１〜３６に記載のように、銅の芯線の表面に１０〜２００ｎｍの厚みのパラジウム被覆層を有し、該被覆層の表面に更に３〜８０ｎｍの厚みの金とパラジウムとの合金層を有するボンディングワイヤーでは、耐酸化性（「長期保管（酸化）」欄）、耐硫化性（「長期保管（硫化）」欄）、やボール部の真球性（「窒素中ＦＡＢ真球性」欄）を確保しつつ、かつパラジウムめっきリードフレーム上での良好なウェッジ接合性（「Pd-L/F 2nd接合」欄）が得られるものである。これらに対し、比較例１に示すように、銅ワイヤーの上に特に被覆層を設けない芯線のみでは、長期保管や2nd接合性が劣悪である。また、比較例２に示すように、銅芯線の表面の被覆層を銀とした場合は、窒素中でのボール部の真球性が大きく劣り、長期保管中に硫化の問題が生じた。また、比較例３に示すように、銅芯線の表面の被覆層を金とした場合は、窒素中でのボール部の真球性が大きく劣っている。また、比較例４〜６に示すように、銅芯線の上にパラジウムの被覆層のみを設けた場合は、パラジウムめっきリードフレーム上でのウェッジ接合性に劣っている。また、比較例７に示すように、銅芯線の上に１０〜２００ｎｍの範囲内の厚みでパラジウムの被覆層を形成しても、更にその表面上に形成した金とパラジウムとの合金層の厚みが３ｎｍより薄い場合は、パラジウムめっきリードフレーム上でのウェッジ接合性が十分ではない。また、比較例８に示すように、銅芯線の上に１０〜２００ｎｍの範囲内の厚みでパラジウムの被覆層を形成しても、更にその表面上に形成した金とパラジウムとの合金層の厚みが８０ｎｍよりも厚い場合は、安定した品質を確保しにくくなり、パラジウムめっきリードフレーム上でのウェッジ接合性（「Pd-L/F 2nd接合」欄）が劣っており、また、該合金層が酸化されることで、ボール部の真球性（「窒素中ＦＡＢ真球性」欄）が満足できるものではない。また、比較例９に示すように、銅芯線の上に１０〜２００ｎｍの範囲内の厚みでパラジウムの被覆層を形成し、更にその表面上に形成した金とパラジウムとの合金層中の金濃度が１５％よりも低い場合はパラジウムめっきリードフレーム上でのウェッジ接合性が十分ではない。また、比較例１０に示すように、銅芯線の上に１０〜２００ｎｍの範囲内の厚みでパラジウムの被覆層を形成し、更にその表面上に形成した金とパラジウムとの合金層中の金濃度が７５％を超えて高い場合は窒素中でのボール部の真球性が劣る。また、比較例１１に示すように、銅芯線の上に形成したパラジウムの被覆層の厚みが１０〜２００ｎｍの範囲を超えると、更にその表面上に形成した金とパラジウムとの合金層の厚みが３〜８０ｎｍの範囲であっても、窒素中で小径のボール部を形成すると気泡が発生する（「窒素中ＦＡＢ気泡抑制」欄）。   As described in Examples 1 to 36 of Table 1, the surface of the copper core wire has a palladium coating layer with a thickness of 10 to 200 nm, and the surface of the coating layer further has gold and palladium with a thickness of 3 to 80 nm. Bonding wires with the above alloy layers have oxidation resistance ("long-term storage (oxidation)" column), sulfidation resistance ("long-term storage (sulfurization)" column), and the spherical nature of the ball part ("FAB true in nitrogen" While maintaining the “sphericity” column), good wedge bondability on the palladium-plated lead frame (“Pd-L / F 2nd bonding” column) can be obtained. On the other hand, as shown in Comparative Example 1, long-term storage and 2nd bondability are inferior only with a core wire that is not particularly provided with a coating layer on a copper wire. Further, as shown in Comparative Example 2, when the coating layer on the surface of the copper core wire was silver, the sphericity of the ball portion in nitrogen was greatly inferior, and the problem of sulfuration occurred during long-term storage. Further, as shown in Comparative Example 3, when the coating layer on the surface of the copper core wire is gold, the sphericity of the ball portion in nitrogen is greatly inferior. Moreover, as shown in Comparative Examples 4 to 6, when only the palladium coating layer is provided on the copper core wire, the wedge bondability on the palladium plating lead frame is inferior. Moreover, as shown in Comparative Example 7, even when a palladium coating layer was formed on the copper core wire with a thickness in the range of 10 to 200 nm, the thickness of the alloy layer of gold and palladium formed on the surface of the palladium coating layer was further increased. Is thinner than 3 nm, the wedge bondability on the palladium-plated lead frame is not sufficient. Further, as shown in Comparative Example 8, even when a palladium coating layer is formed on the copper core wire with a thickness in the range of 10 to 200 nm, the thickness of the alloy layer of gold and palladium formed on the surface thereof is further increased. Is thicker than 80 nm, it becomes difficult to ensure stable quality, the wedge bondability on the palladium plated lead frame ("Pd-L / F 2nd joint" column) is inferior, and the alloy layer is Oxidation does not satisfy the sphericity of the ball part ("FAB sphericity in nitrogen" column). Moreover, as shown in Comparative Example 9, a gold coating layer was formed on the copper core wire with a thickness in the range of 10 to 200 nm, and further the gold concentration in the alloy layer of gold and palladium formed on the surface thereof. Is less than 15%, the wedge bondability on the palladium-plated lead frame is not sufficient. In addition, as shown in Comparative Example 10, a palladium coating layer was formed on a copper core wire with a thickness in the range of 10 to 200 nm, and the gold concentration in the alloy layer of gold and palladium formed on the surface thereof was further increased. Is higher than 75%, the sphericity of the ball part in nitrogen is inferior. Moreover, as shown in Comparative Example 11, when the thickness of the palladium coating layer formed on the copper core wire exceeds the range of 10 to 200 nm, the thickness of the alloy layer of gold and palladium formed on the surface is further increased. Even in the range of 3 to 80 nm, bubbles are generated when a small-diameter ball portion is formed in nitrogen ("FAB bubble suppression in nitrogen" column).

実施例１〜１８，８４、８６，８９に示すように、前記金とパラジウムとから成る合金中の金濃度が、15%以上40%未満であればボール部の真球性がより向上する（「窒素中ＦＡＢ真球性」）。   As shown in Examples 1 to 18, 84, 86, and 89, if the gold concentration in the alloy composed of gold and palladium is 15% or more and less than 40%, the sphericity of the ball portion is further improved ( “FAB sphericity in nitrogen”).

実施例１９〜３６，８５，８７，８８，９０〜９３に示すように、前記金とパラジウムとから成る合金中の金濃度が40%以上であると、ウェッジボンディング特性がより向上する（「Pd-L/F 2nd接合」欄）。   As shown in Examples 19 to 36, 85, 87, 88, 90 to 93, when the gold concentration in the alloy of gold and palladium is 40% or more, the wedge bonding characteristics are further improved (“Pd -L / F 2nd junction "column).

表２の実施例３７〜５２に示すように、前記ボンディングワイヤーの表面で観察される<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積が50%以上100%以下であると、高ループボンディングした際にリーニング不良の発生を抑制する効果が高くなり（「高ループリーニング抑制」欄）、該面積が70%以上であるとその効果が更に高まった。   As shown in Examples 37 to 52 in Table 2, the area of the crystal grains having an inclination of <111> crystal orientation with respect to the drawing direction of 15 degrees or less observed on the surface of the bonding wire is 50% or more and 100% or less When the high-loop bonding was performed, the effect of suppressing the occurrence of leaning defects was enhanced (“High-Loop Leaning Control” column), and the effect was further enhanced when the area was 70% or more.

表３の実施例５３〜５６、５９〜６２に示すように、前記ボンディングワイヤーの表面のマイヤー硬度が0.2〜2.0GPaの範囲であると、更に、低ループボンディングを行ってもネックダメージが抑制される（「７６．２μｍ（３ｍｉｌ）級低ループネックダメージ」欄）。   As shown in Examples 53 to 56 and 59 to 62 in Table 3, when the Mayer hardness of the surface of the bonding wire is in the range of 0.2 to 2.0 GPa, neck damage is suppressed even when low loop bonding is performed. ("76.2 μm (3 mil) class low loop neck damage" column).

表４の実施例６８〜７６、８０〜８３に示すように、前記芯線が、B、P、Seの内の少なくとも1種を総計で5〜300質量ppm含有する銅合金では、長尺ボンディングを行った際であってもループの曲がりが抑制される（「５．３ｍｍ（２１０ｍｉｌ）級長尺曲がり」欄）。一方、実施例７７に示すように、前記芯線に300質量ppm超の添加を行うと、チップダメージが生じた（「チップダメージ」）。   As shown in Examples 68 to 76 and 80 to 83 in Table 4, when the core wire contains a total of 5 to 300 ppm by mass of at least one of B, P, and Se, long bonding is performed. Even when it is performed, the bending of the loop is suppressed ("5.3 mm (210 mil) class long bending" column). On the other hand, as shown in Example 77, chip damage occurred when “300 ppm by mass” was added to the core wire (“chip damage”).

表５の実施例８４〜９３に示すように、前記被覆層と前記芯線の間に拡散層が生じていたり、前記芯線に含まれる銅が前記被覆層中に拡散していたりしていても、本願発明の効果が確保できた。   As shown in Examples 84 to 93 in Table 5, even if a diffusion layer is formed between the coating layer and the core wire, or copper contained in the core wire is diffused in the coating layer, The effect of the present invention can be secured.

Claims (5)

銅又は銅合金から成る芯線と、
該芯線の表面に、10〜200nmの厚さを有するパラジウムを含む被覆層と、
該被覆層の表面に、3〜80nmの厚さを有する金とパラジウムとを含む合金層と
を有し、
前記合金層中の金の濃度が15体積%以上75体積%以下であることを特徴とする半導体用ボンディングワイヤー。 A core wire made of copper or copper alloy;
On the surface of the core wire, a coating layer containing palladium having a thickness of 10 to 200 nm,
An alloy layer containing gold and palladium having a thickness of 3 to 80 nm on the surface of the coating layer;
A bonding wire for semiconductor, wherein the gold concentration in the alloy layer is 15% by volume or more and 75% by volume or less. 前記合金層の表面結晶粒の内、<111>結晶方位の伸線方向に対する傾きが15度以下である結晶粒の面積が、40%以上100%以下であることを特徴とする請求項１記載の半導体用ボンディングワイヤー。 2. The area of a crystal grain having an inclination of a <111> crystal orientation with respect to a wire drawing direction of 15 ° or less among surface crystal grains of the alloy layer is 40% or more and 100% or less. Bonding wire for semiconductor. 前記ボンディングワイヤーの表面のマイヤー硬度が、0.2〜2.0GPaの範囲であることを特徴とする請求項１又は２に記載の半導体用ボンディングワイヤー。 3. The bonding wire for a semiconductor according to claim 1, wherein a Mayer hardness of the surface of the bonding wire is in a range of 0.2 to 2.0 GPa. 前記合金層中の金の濃度が、40体積%以上75体積%以下であることを特徴とする請求項１〜３のいずれかに記載の半導体用ボンディングワイヤー。 4. The bonding wire for a semiconductor according to claim 1, wherein the gold concentration in the alloy layer is 40 vol% or more and 75 vol% or less. 前記芯線が、B、P、Seの内の少なくとも1種を総計で5〜300質量ppm含有することを特徴とする請求項１〜４のいずれかに記載の半導体用ボンディングワイヤー。 5. The bonding wire for a semiconductor according to claim 1, wherein the core wire contains at least one of B, P, and Se in a total amount of 5 to 300 ppm by mass.
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