JP4885117B2 - Bonding wires for semiconductor devices - Google Patents

Bonding wires for semiconductor devices Download PDF

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Publication number
JP4885117B2
JP4885117B2 JP2007312240A JP2007312240A JP4885117B2 JP 4885117 B2 JP4885117 B2 JP 4885117B2 JP 2007312240 A JP2007312240 A JP 2007312240A JP 2007312240 A JP2007312240 A JP 2007312240A JP 4885117 B2 JP4885117 B2 JP 4885117B2
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Japan
Prior art keywords
wire
bonding
skin layer
core material
ball
Prior art date
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Application number
JP2007312240A
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Japanese (ja)
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JP2009140942A (en
Inventor
智裕 宇野
圭一 木村
隆 山田
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
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Application filed by Nippon Steel Materials Co Ltd, Nippon Micrometal Corp filed Critical Nippon Steel Materials Co Ltd
Priority to JP2007312240A priority Critical patent/JP4885117B2/en
Publication of JP2009140942A publication Critical patent/JP2009140942A/en
Application granted granted Critical
Publication of JP4885117B2 publication Critical patent/JP4885117B2/en
Active legal-status Critical Current
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  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Wire Bonding (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high performance bonding wire excellent in shape of ball joint, stabilization of size, stability of loop shape, and the like, and applicable even to semiconductor mounting technologies for thin line, narrow pitch, long span, three-dimensional mounting, or the like. <P>SOLUTION: A bonding wire for semiconductor device consists of a core material comprising a conductive metal, and a skin layer formed on the core material and principally comprising a metal different from that of the core material, wherein the metal of the skin layer is face-centered cubic crystal and the proportion of longitudinal crystal orientation &lt;hkl&gt; in the crystal surface on the surface of the skin layer, which is occupied by &lt;111&gt; and &lt;100&gt;, is less than 50%. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

本発明は、半導体素子上の電極と、回路配線基板(リードフレーム、基板、テープ等)の配線とを接続するために利用される半導体装置用ボンディングワイヤに関するものである。   The present invention relates to a bonding wire for a semiconductor device used for connecting an electrode on a semiconductor element and wiring of a circuit wiring board (lead frame, substrate, tape, etc.).

現在、半導体素子上の電極と、外部端子との間を接合するボンディングワイヤとして、線径20〜50μm程度の細線(ボンディングワイヤ)が主として使用されている。ボンディングワイヤの接合には超音波併用熱圧着方式が一般的であり、汎用ボンディング装置、ボンディングワイヤをその内部に通して接続に用いるキャピラリ冶具等が用いられる。ボンディングのワイヤ先端をアーク入熱で加熱溶融し、表面張力によりボールを形成させた後に、150〜300℃の範囲内で加熱した半導体素子の電極上に、このボール部を圧着接合せしめ、その後で、直接ボンディングワイヤを外部リード側に超音波圧着により接合させる。   Currently, fine wires (bonding wires) having a wire diameter of about 20 to 50 μm are mainly used as bonding wires for bonding electrodes on semiconductor elements and external terminals. Bonding wires are generally joined by ultrasonic thermocompression bonding, and a general-purpose bonding apparatus, a capillary jig used for connection through the bonding wire, or the like is used. After the wire tip of the bonding was heated and melted by arc heat input to form a ball by surface tension, this ball part was crimped and bonded onto the electrode of the semiconductor element heated within the range of 150 to 300 ° C, and then The bonding wire is directly bonded to the external lead side by ultrasonic pressure bonding.

近年、半導体実装の構造・材料・接続技術等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、ポリイミドテープ等を使用するBGA(Ball Grid Array)、CSP(Chip Scale Packaging)等の新しい形態が実用化され、ループ性、接合性、量産使用性等をより向上したボンディングワイヤが求められている。   In recent years, the structure, materials, connection technology, etc. of semiconductor packaging have been diversified rapidly. For example, in addition to the QFP (Quad Flat Packaging) that uses the current lead frame, the packaging structure uses a substrate, polyimide tape, etc. New forms such as BGA (Ball Grid Array) and CSP (Chip Scale Packaging) have been put into practical use, and bonding wires with improved loop characteristics, bonding properties, mass production usability, etc. have been demanded.

隣接するボンディングワイヤの間隔が狭くなる狭ピッチ化が進行している。これに対応するボンディングワイヤへの要求として、細線化、高強度化、ループ制御、接合性の向上などが求められる。半導体実装の高密度化によりループ形状は複雑化している。ループ形状の分類として、ループ高さ、ボンディングのワイヤ長さ（スパン）が指標となる。最新の半導体では、一つのパッケージ内部に、高ループと低ループ、短いスパンと長いスパンなど、相反するループ形成を混載させるケースが増えている。それを１種類のボンディングワイヤで実現するには、厳しいボンディングワイヤの材料設計が必要となる。   Narrow pitches are being made to reduce the spacing between adjacent bonding wires. As a request for a bonding wire corresponding to this, thinning, high strength, loop control, improvement in bonding property, etc. are required. The loop shape has become complicated due to the high density of semiconductor packaging. As loop shape classification, loop height and bonding wire length (span) are used as indices. In the latest semiconductors, there are an increasing number of cases in which conflicting loop formations such as a high loop and a low loop, a short span and a long span are mixedly mounted in one package. In order to achieve this with a single type of bonding wire, strict material design of the bonding wire is required.

ボンディングワイヤの素材は、これまで高純度4N系(純度>99.99mass%)の金が主に用いられている。高強度化、高接合などの特性を向上するため、微量の合金元素を調整することが行われている。最近では、接合部の信頼性を向上する目的などで、添加元素濃度を1%以下まで増加させた純度2N（純度＞99%）の金合金ワイヤも実用化されている。金に添加する合金元素の種類、濃度を調整することで、高強度化、信頼性の制御など可能である。一方で、合金化により、接合性が低下したり、電気抵抗が増加するなどの弊害が生じる場合もあり、ボンディングワイヤに要求される多様な特性を総合的に満足することは難しい。   Conventionally, gold of high purity 4N type (purity> 99.99 mass%) has been mainly used as a material for the bonding wire. In order to improve characteristics such as high strength and high bonding, a small amount of alloy elements are adjusted. Recently, a gold alloy wire having a purity of 2N (purity> 99%) with an additive element concentration increased to 1% or less has been put into practical use for the purpose of improving the reliability of the joint. By adjusting the type and concentration of the alloy element added to gold, it is possible to increase the strength and control the reliability. On the other hand, the alloying may cause adverse effects such as a decrease in bondability and an increase in electrical resistance, and it is difficult to comprehensively satisfy various characteristics required for bonding wires.

また、金は高価であるため、材料費が安価である他種金属が所望されており、材料費が安価で、電気伝導性に優れた、銅を素材とするボンディングワイヤが開発されている。しかし、銅のボンディングワイヤでは、ボンディングのワイヤ表面の酸化により接合強度が低下することや、樹脂封止されたときのワイヤ表面の腐食等が起こり易いことが問題となる。これらが銅のボンディングワイヤの実用化が進まない原因ともなっている。   Further, since gold is expensive, other types of metals having a low material cost are desired, and a bonding wire made of copper having a low material cost and excellent electrical conductivity has been developed. However, the problem with copper bonding wires is that the bonding strength decreases due to oxidation of the bonding wire surface, and that the wire surface is easily corroded when sealed with resin. These are also the reasons why the practical application of copper bonding wires has not progressed.

これまでに実用化されたボンディングワイヤは全て単層構造であることを特徴とする。素材が金、銅など変わっても、内部に合金元素を均一に含有しており、ボンディングのワイヤ断面でみるとワイヤ単層構造であった。ワイヤ表面に薄い自然酸化膜、表面保護のための有機膜などが形成されている場合もあるが、これらも最表面の極薄い領域（〜数原子層レベル）に限られる。   All the bonding wires put to practical use so far have a single-layer structure. Even if the material is changed, such as gold or copper, the alloy element is uniformly contained inside, and the wire cross section of the bonding wire has a single layer structure. In some cases, a thin natural oxide film, an organic film for surface protection, or the like is formed on the surface of the wire, but these are also limited to an extremely thin region (up to several atomic layers) on the outermost surface.

ボンディングワイヤに要求される多様なニーズに応えるため、ワイヤ表面に別の金属を被覆した多層構造のボンディングワイヤが提案されている。   In order to respond to various needs required for bonding wires, a bonding wire having a multilayer structure in which another metal is coated on the wire surface has been proposed.

銅ボンディングワイヤの表面酸化を防ぐ方法として、特許文献1には、金、銀、白金、パラジウム、ニッケル、コバルト、クロム、チタン等の貴金属や耐食性金属で銅を被覆したボンディングワイヤが提案されている。また、ボール形成性、メッキ液の劣化防止等の点から、特許文献2には、銅を主成分とする芯材、該芯材上に形成された銅以外の金属からなる異種金属層、及び該異種金属層の上に形成され、銅よりも高融点の耐酸化性金属からなる被覆層の構造をしたボンディングワイヤが提案されている。特許文献3には、銅を主成分とする芯材と、該芯材の上に芯材と成分又は組成の一方または両方の異なる金属と銅を含有する外皮層を有し、その外皮層の厚さが0.001〜0.02μmの薄膜であるボンディングワイヤが提案されている。   As a method for preventing surface oxidation of a copper bonding wire, Patent Document 1 proposes a bonding wire in which copper is coated with a noble metal such as gold, silver, platinum, palladium, nickel, cobalt, chromium, titanium, or a corrosion-resistant metal. . In addition, from the viewpoints of ball formability, prevention of deterioration of the plating solution, and the like, Patent Document 2 describes a core material mainly composed of copper, a dissimilar metal layer made of a metal other than copper formed on the core material, and There has been proposed a bonding wire formed on the dissimilar metal layer and having a coating layer structure made of an oxidation-resistant metal having a melting point higher than that of copper. Patent Document 3 has a core material containing copper as a main component, and an outer skin layer containing copper and a metal different from one or both of the core material and its component or composition on the core material. A bonding wire which is a thin film having a thickness of 0.001 to 0.02 μm has been proposed.

また、金ボンディングワイヤでも、多層構造が多く提案されている。例えば、特許文献4には、高純度Au又はAu合金からなる芯線の外周面に高純度Pd又はPd合金からなる被覆材を被覆したボンディングワイヤが提案されている。特許文献5には、高純度Au又はAu合金からなる芯線の外周面に高純度Pt又はPt合金からなる被覆材を被覆したボンディングワイヤが提案されている。特許文献6には、高純度Au又はAu合金からなる芯線の外周面に高純度Ag又はAg合金からなる被覆材を被覆したボンディングワイヤが提案されている。   Also, many multi-layer structures have been proposed for gold bonding wires. For example, Patent Document 4 proposes a bonding wire in which the outer peripheral surface of a core wire made of high-purity Au or Au alloy is covered with a coating material made of high-purity Pd or Pd alloy. Patent Document 5 proposes a bonding wire in which the outer peripheral surface of a core wire made of high-purity Au or Au alloy is covered with a coating material made of high-purity Pt or Pt alloy. Patent Document 6 proposes a bonding wire in which the outer peripheral surface of a core wire made of high-purity Au or Au alloy is coated with a coating material made of high-purity Ag or Ag alloy.

量産で使用されるワイヤ特性として、ボンディング工程におけるループ制御が安定しており、接合性も向上しており、樹脂封止工程でワイヤ変形を抑制すること、接続部の長期信頼性等の、総合的な特性を満足することで、最先端の狭ピッチ、３次元配線などの高密度実装に対応できることが望まれている。   As a wire characteristic used in mass production, the loop control in the bonding process is stable, the bondability is improved, wire deformation is suppressed in the resin sealing process, long-term reliability of the connection part, etc. It is desired that high-density mounting such as state-of-the-art narrow-pitch, three-dimensional wiring can be achieved by satisfying general characteristics.

ボール接合に関連して、ボール形成時に真球性の良好な初期ボールを形成し、そのボールを電極上に接合したボール接合部の形状が真円に近いことが重要となる。接合部で十分な接合強度も求められる。また、接合温度の低温化、ボンディングワイヤの細線化等に対応するためにも、回路配線基板上の配線部にボンディングワイヤをウェッジ接続した部位での接合強度、引張り強度等も必要である。初期ボールまたはボール接合部の形状の安定性の追及、低温での接合性の向上などにより、半導体製造工程の不良発生率をppmオーダで管理する厳しい要求に適応できなくては実用化に至らない。   In connection with ball bonding, it is important that an initial ball having good sphericity is formed at the time of ball formation, and the shape of the ball bonding portion where the ball is bonded onto the electrode is close to a perfect circle. Sufficient joint strength is also required at the joint. Further, in order to cope with a decrease in the bonding temperature, a thinning of the bonding wire, and the like, a bonding strength, a tensile strength, and the like at a portion where the bonding wire is wedge-connected to the wiring portion on the circuit wiring board are also required. By pursuing the stability of the shape of the initial ball or ball joint, improving the bondability at low temperatures, etc., it will not be put into practical use unless it can adapt to the strict requirement of managing the defect rate in the semiconductor manufacturing process in ppm order. .

こうした半導体向けの多層構造のボンディングワイヤは、実用化の期待は大きいものの、これまで実用化されていなかった。多層構造による表面改質、高付加価値などが期待される一方で、ワイヤ製造の生産性、品質、またボンディング工程での歩留まり、性能安定性、さらに半導体使用時の長期信頼性などが総合的に満足されなくてはならない。
特開昭62-97360号公報 特開2004-64033号公報 特開2007-12776号公報 特開平4-79236号公報 特開平4-79240号公報 特開平4-79242号公報 Although such a bonding wire having a multilayer structure for semiconductors is expected to be put into practical use, it has not been put into practical use so far. While multi-layered surface modification and high added value are expected, overall productivity and quality of wire manufacturing, yield in bonding process, performance stability, and long-term reliability when using semiconductors are comprehensive. It must be satisfied.
JP-A 62-97360 JP 2004-64033 A JP 2007-12776 Japanese Unexamined Patent Publication No. 4-79236 Japanese Patent Laid-Open No. 4-79240 JP-A-4-79242

従来の単層構造のボンディングワイヤ(以下、単層ワイヤと記す)では、引張り強度、接合部の強度、信頼性などを改善するのに、合金化元素の添加が有効であるが、特性向上には限界が懸念されている。多層構造をしたボンディングワイヤ（以下、複層ワイヤと記す）では、単層ワイヤよりもさらに特性を向上して付加価値を高めることが期待される。高機能化をもたらす複層ワイヤとして、例えば、銅ボンディングワイヤの表面酸化を防ぐために、ワイヤ表面に貴金属や耐酸化性の金属を被覆することが可能である。金ボンディングワイヤでも、ワイヤ表面に強度の高い金属または合金を被覆することで、樹脂流れを低減する効果が期待される。   In conventional bonding wires with a single layer structure (hereinafter referred to as single layer wires), the addition of alloying elements is effective in improving the tensile strength, joint strength, reliability, etc. There are concerns about the limits. A bonding wire having a multilayer structure (hereinafter referred to as a multi-layer wire) is expected to further improve the characteristics and increase added value as compared with a single-layer wire. For example, in order to prevent the surface of a copper bonding wire from being oxidized, it is possible to coat the surface of the wire with a noble metal or an oxidation-resistant metal as a multi-layered wire that provides high functionality. Even a gold bonding wire is expected to have an effect of reducing the resin flow by coating the surface of the wire with a high-strength metal or alloy.

しかし、半導体実装の高密度化、小型化、薄型化等のニーズを考慮して、本発明者らが評価したところ、複層ワイヤでは、後述するような実用上の問題が多く残されていることが判明した。   However, the present inventors have evaluated the semiconductor packaging in consideration of needs for higher density, smaller size, thinner thickness, etc., and as a result, there are many practical problems that will be described later in multilayer wires. It has been found.

複層ワイヤのボール接合部の不具合の代表例として、花弁現象と芯ずれ現象がある。花弁現象とは、ボール接合部の外周近傍が花弁状に凹凸変形を起こして、真円性からずれるものであり、小さい電極上に接合するときにボールがはみ出たり、接合強度の低下を誘発したりする不良の原因となる。芯ずれ現象とは、初期ボールがワイヤ軸に対し非対称に形成される現象であり、そのずれ程度が激しければゴルフクラブ状となる場合もある。芯ずれした初期ボールを接合したときに、ボール接合部がワイヤ軸からずれて変形することによる形状不良を偏芯と呼ぶ。すなわち偏芯の原因として、初期ボールの芯ずれが関係している場合が多い。偏芯が発生すると、狭ピッチ接続では隣接するボールと接触するショート不良を起こすことが問題となる。これら複層ワイヤにおける花弁現象と芯ずれ現象の発生頻度は単層ワイヤより増える傾向であり、生産性の低下をもたらす一因であるため、ワイヤボンディング工程の管理基準を厳しくする必要がある。   As typical examples of defects in the ball joint portion of the multilayer wire, there are a petal phenomenon and a misalignment phenomenon. The petal phenomenon is a phenomenon in which the vicinity of the outer periphery of the ball joint part is deformed in a petal shape and deviates from roundness, and when joining on a small electrode, the ball protrudes or the joint strength is reduced. Cause failure. The misalignment phenomenon is a phenomenon in which the initial ball is formed asymmetrically with respect to the wire axis, and if the deviation is severe, it may be a golf club shape. When a misaligned initial ball is joined, a defective shape due to the ball joint being deformed by being displaced from the wire axis is called eccentricity. That is, the cause of eccentricity is often related to the misalignment of the initial ball. When eccentricity occurs, a short-circuit failure that comes into contact with an adjacent ball becomes a problem in a narrow pitch connection. The frequency of occurrence of the petal phenomenon and the misalignment phenomenon in these multi-layer wires tends to increase more than that of single-layer wires, and this is one factor that causes a reduction in productivity. Therefore, it is necessary to tighten the management standards of the wire bonding process.

特に最近の狭ピッチ接続に複層ワイヤを用いると、芯ずれおよび偏芯の発生頻度が上昇したり、また、ずれ程度が著しい強芯ずれ現象が発生する場合がある。強芯ずれ現象は、発生頻度は低いが、不良に直結する場合もあり、実用上の大きな障害となる。単層ワイヤでの芯ずれ不良は、ボンディング装置の汚れ、キャピラリ冶具の取付け不具合などが原因である場合が多く、ワイヤ材質に起因する芯ずれ不良の頻度は低かった。複層ワイヤでの芯ずれ不良は、単層ワイヤの場合に比べて、発生頻度で数十倍となる場合もあり、ずれの程度も1.5倍程度も増加する場合なども確認されている。これは、ボール形成の各プロセスと関連している。例えば理想的な真円のボール接合部を形成するには、ワイヤ先端に生じたアーク放電がボンディングワイヤに均一に広がることで軸対称なボールを形成し、そのボールを電極上で等方的に変形させることなどが必要である。単層ワイヤでは通常では容易に達成できるのに対して、複層ワイヤのボール接合では、全ての要素を同時に満足することが困難であると考えられる。   In particular, when a multilayer wire is used for the recent narrow pitch connection, the frequency of occurrence of misalignment and eccentricity may increase, or a strong misalignment phenomenon with a significant degree of misalignment may occur. Although the occurrence of the strong misalignment phenomenon is low, it may be directly connected to a defect, which is a large practical obstacle. The misalignment failure with a single-layer wire is often caused by contamination of the bonding apparatus, a mounting failure of the capillary jig, and the like, and the frequency of misalignment due to the wire material was low. The misalignment failure in the multi-layer wire has been confirmed to be several tens of times the frequency of occurrence as compared to the single-layer wire, and the degree of misalignment is also increased by about 1.5 times. This is associated with each process of ball formation. For example, in order to form an ideal perfect ball joint, an arc discharge generated at the tip of the wire spreads uniformly on the bonding wire to form an axisymmetric ball, and the ball isotropically formed on the electrode. It is necessary to deform. While it is usually easy to achieve with a single-layer wire, it is considered difficult to satisfy all the elements at the same time in ball bonding of a multi-layer wire.

複層ワイヤの芯ずれの程度がひどい場合には、隣接するボール接合部と接触する危険性が高まる。この目安として、ワイヤ軸からボール最外周までの距離を比較すると、正常なボール変形より、偏芯レベルが最大で1.5倍程度まで変形する場合もある。このままでは狭ピッチ接続には不利である。接合条件で対応する手段として、ボール形成時のサイズを小さくすることも可能であるが、これにより接合強度を低下させるため、改善は困難である。   When the misalignment of the multilayer wire is severe, the risk of contact with adjacent ball joints increases. As a guideline, when the distance from the wire axis to the outermost circumference of the ball is compared, there is a case where the eccentric level is deformed up to about 1.5 times from the normal ball deformation. This is disadvantageous for narrow pitch connection. Although it is possible to reduce the size at the time of ball formation as a means to cope with the bonding conditions, this reduces the bonding strength, so that improvement is difficult.

芯ずれまたは偏芯したボールでは、接合のときの荷重、超音波振動がボールに均一に伝わらないため、ボンディングワイヤと電極との接合界面の拡散および金属間化合物の形成が不均一となる可能性が高い。これは、連続ボンディング時に接合部での剥離が生じる不良を誘発したり、初期の接合強度を低下させることが問題となる。さらに、半導体使用時の長期信頼性を低下させる原因ともなる。こうした接合強度、信頼性の観点からも、芯ずれおよび偏芯を低減できなければ、複層ワイヤの実用範囲が限定されることが懸念される。   In a misaligned or eccentric ball, the bonding load and ultrasonic vibrations are not uniformly transmitted to the ball, so the bonding interface between the bonding wire and electrode may diffuse and the formation of intermetallic compounds may be non-uniform. Is expensive. This causes problems such as inducing defects that cause peeling at the joint during continuous bonding, and lowering the initial bonding strength. In addition, long-term reliability when using semiconductors is also a cause. From the viewpoint of such bonding strength and reliability, if the misalignment and eccentricity cannot be reduced, there is a concern that the practical range of the multilayer wire is limited.

ウエッジ接合におけるボンディングワイヤの捲れまたは部分剥離などの不良も、複層ワイヤの実用化では問題となる。リード電極上にワイヤを接続するウエッジ接合では、接合後にボンディングワイヤを上方に引き上げ接合部で破断させること（テイルカット）が行われるが、その際に、接合の端部からワイヤが捲れたり剥離が生じることで、接合強度の低下、ボール径のばらつきなどの不良を起こすことが懸念される。複層ワイヤでは、表皮層と芯材はお互いに材質が異なるため、それぞれが接合にどのように影響するかにより、捲れや剥離が増加する場合がある。   Defects such as bending or partial peeling of the bonding wire in wedge bonding also become a problem in the practical application of multilayer wires. In wedge bonding in which a wire is connected to a lead electrode, the bonding wire is pulled up after the bonding and broken at the bonded portion (tail cut). At that time, the wire is bent or peeled off from the end of the bonding. As a result, there is a concern that defects such as a decrease in bonding strength and a variation in ball diameter may occur. In the multi-layer wire, the skin layer and the core material are different from each other, so that the twisting and peeling may increase depending on how each affects the bonding.

複層ワイヤでループ形成したときの不具合として、ループの直線性が低下して、ボンディングワイヤの倒れ、垂れ、曲がりなどの不具合が生じる場合がある。このループの直線性が低下することで、製造歩留まりを低下させることが問題となる。   As a problem when a loop is formed with a multi-layer wire, the linearity of the loop may be reduced, and problems such as a falling, drooping, or bending of the bonding wire may occur. As the linearity of the loop is lowered, there is a problem that the manufacturing yield is lowered.

複層銅ワイヤでは、単層銅ワイヤより酸化を遅らせる効果が期待できるが、その効果は、表皮層またはワイヤ表面近傍における組成、構造、厚さなどにより大きく異なる。複層銅ワイヤの構造の適正化が重要となる。金ワイヤと同等の作業性を確保するには、例えば、２ヶ月程度の大気保管の後でも、ウェッジ接合性、ループ形状などが劣化しないことが保障される必要がある。これは、単層銅ワイヤの保管寿命に比べれば数十倍の寿命向上が必要であり、銅を主体とする材料においては相当厳しい条件が求められることになる。   The multilayer copper wire can be expected to have an effect of delaying oxidation compared to the single-layer copper wire, but the effect varies greatly depending on the composition, structure, thickness, etc. in the skin layer or near the wire surface. It is important to optimize the structure of the multilayer copper wire. In order to ensure workability equivalent to that of a gold wire, it is necessary to ensure that, for example, the wedge bondability and the loop shape do not deteriorate even after storage in the atmosphere for about two months. This requires an improvement in the life of several tens of times compared with the shelf life of the single-layer copper wire, and considerably strict conditions are required for materials mainly composed of copper.

本発明では、上述するような従来技術の問題を解決して、従来の基本性能に加えて、ボール形成の芯ずれを抑制して、ボール接合形状を改善し、ループ形状、直線性を安定化させるなどの性能向上を図った半導体装置用ボンディングワイヤを提供することを目的とする。   The present invention solves the above-mentioned problems of the prior art, improves the ball joint shape, stabilizes the loop shape and linearity in addition to the conventional basic performance, suppresses the misalignment of the ball formation. An object of the present invention is to provide a bonding wire for a semiconductor device in which performance is improved.

本発明者らが、上記ボール形成の芯ずれ、ボール接合形状不良等の問題を解決するために複層構造のボンディングワイヤを検討した結果、特定の表皮層であって前記表皮層の組織を制御することが有効であることを見出した。   As a result of studying a bonding wire having a multilayer structure in order to solve the problems such as misalignment of the ball formation and defective ball joint shape, the present inventors have controlled the structure of the skin layer in a specific skin layer. I found it effective.

本発明は前記知見の基づいてなされたものであり、以下の構成の要旨とする。   This invention is made | formed based on the said knowledge, and makes it the summary of the following structures.

本発明の請求項１に係るボンディングワイヤは、導電性金属からなる芯材と、前記芯材の上に芯材とは異なる金属を主成分とする表皮層を有する半導体装置用ボンディングワイヤであって、前記表皮層の金属が面心立方晶であって、前記表皮層の表面の結晶面における長手方向の結晶方位<hkl>のうち、<111>と<100>の占める割合が、ともに50%未満であることを特徴とする。   A bonding wire according to claim 1 of the present invention is a bonding wire for a semiconductor device having a core material made of a conductive metal, and a skin layer mainly composed of a metal different from the core material on the core material. The skin layer metal is a face-centered cubic crystal, and the proportion of <111> and <100> in the longitudinal crystal orientation <hkl> in the crystal plane of the surface of the skin layer is 50% It is characterized by being less than.

本発明の請求項２に係るボンディングワイヤは、請求項１において、前記表皮層の表面におけるワイヤ長手方向の結晶方位が<111>または<100>である結晶粒の面積が、ワイヤ表面の総面積に対する割合として、ともに35%以下であることを特徴とする。   The bonding wire according to a second aspect of the present invention is the bonding wire according to the first aspect, wherein the crystal grain area in which the crystal orientation in the wire longitudinal direction is <111> or <100> on the surface of the skin layer is the total area of the wire surface. Both are characterized by being 35% or less.

本発明の請求項３に係るボンディングワイヤは、請求項１又は２において、前記表皮層の表面におけるワイヤ長手方向の結晶方位が<111>または<100>である結晶粒の面積の総計が、ワイヤ表面の総面積に対する割合として、50%以下であることを特徴とする。   The bonding wire according to a third aspect of the present invention is the bonding wire according to the first or second aspect, wherein the total area of crystal grains having a crystal orientation of <111> or <100> in the wire longitudinal direction on the surface of the skin layer is It is characterized by being 50% or less as a percentage of the total surface area.

本発明の請求項４に係るボンディングワイヤは、請求項１又は２において、前記芯材の断面の結晶面におけるワイヤ長手方向の結晶方位<hkl>のうち、<111>と<100>との占める割合の総計が30%以上であることを特徴とする。   A bonding wire according to a fourth aspect of the present invention is the bonding wire according to the first or second aspect, wherein <111> and <100> occupy the crystal orientation <hkl> in the wire longitudinal direction in the crystal plane of the cross section of the core material The total percentage is 30% or more.

本発明の請求項５に係るボンディングワイヤは、請求項１〜４のうちいずれか１項において、前記表皮層の表面における、円周方向の結晶粒サイズの平均が2μm以下であることを特徴とする。   The bonding wire according to a fifth aspect of the present invention is characterized in that, in any one of the first to fourth aspects, an average crystal grain size in the circumferential direction on the surface of the skin layer is 2 μm or less. To do.

本発明の請求項６に係るボンディングワイヤは、請求項１〜５のうちいずれか１項において、前記表皮層を構成する主成分がPd、Pt、Ruの少なくとも１種であることを特徴とする。   A bonding wire according to a sixth aspect of the present invention is characterized in that, in any one of the first to fifth aspects, the main component constituting the skin layer is at least one of Pd, Pt, and Ru. .

本発明の請求項７に係るボンディングワイヤは、請求項１〜６のうちいずれか１項において、前記芯材を構成する主成分がCu、Auの少なくとも１種であることを特徴とする。   The bonding wire according to a seventh aspect of the present invention is characterized in that, in any one of the first to sixth aspects, the main component constituting the core material is at least one of Cu and Au.

本発明の請求項８に係るボンディングワイヤは、請求項１〜７のうちいずれか１項において、前記表皮層と前記芯材の間に、前記表皮層及び前記芯材を構成する主成分とは異なる成分からなる中間金属層を有することを特徴とする。   The bonding wire according to an eighth aspect of the present invention is the bonding wire according to any one of the first to seventh aspects, wherein the main component constituting the outer skin layer and the core material is between the outer skin layer and the core material. It has an intermediate metal layer made of different components.

本発明の半導体装置用ボンディングワイヤにより、ボール形成の芯ずれ不良、またはボール接合部の偏芯不良を改善できる。また、ループの直線性、ループ高さの安定性を向上できる。また、ボンディングワイヤの接合形状の安定化を促進できる。その結果、細線化、狭ピッチ化、ロングスパン化、三次元実装など最新の半導体実装技術にも適応する、高機能のボンディングワイヤを提供することが可能となる。   With the bonding wire for a semiconductor device of the present invention, it is possible to improve the misalignment of ball formation or the eccentricity of the ball joint. In addition, the linearity of the loop and the stability of the loop height can be improved. In addition, stabilization of the bonding shape of the bonding wire can be promoted. As a result, it is possible to provide a high-performance bonding wire that can be adapted to the latest semiconductor mounting technologies such as thinning, narrowing, long span, and three-dimensional mounting.

半導体装置用ボンディングワイヤ（以下、ボンディングワイヤという）について、導電性金属からなる芯材と、該芯材の上に芯材とは異なる面心立方晶の金属を主成分とする表皮層で構成されたものを検討した結果、ボンディングワイヤの表面近傍に導電性金属を含有することにより、ウェッジ接合強度の向上など期待できる反面、ボール形成での芯ずれ不良の発生、ボール接合部の偏芯不良の発生、ボールサイズのばらつきなどが問題となることを確認した。   A bonding wire for a semiconductor device (hereinafter referred to as a bonding wire) is composed of a core material made of a conductive metal and a skin layer mainly composed of a face-centered cubic crystal metal different from the core material on the core material. As a result of the investigation, the inclusion of a conductive metal near the surface of the bonding wire can be expected to improve the wedge bonding strength, but the occurrence of misalignment in ball formation and the eccentricity of the ball bonding part It was confirmed that the occurrence and variation in ball size became a problem.

そこで、狭ピッチ接続、３次元接続などの新たなニーズへの対応、小さい電極による生産性の向上などにも対応できる複層構造のボンディングワイヤを検討した結果、特定の表皮層であって前記表皮層の組織を制御することが有効であることを見出した。特に、これまでほとんど知られていなかった複層ワイヤの表面の集合組織とワイヤボンディングの使用性能の関係に着目することで、特定の結晶方位を制御することにより、ボール形成性、接合性、ループ制御性などの総合的な改善が可能であることを初めて確認した。更に効果的には、表皮層と芯材の組織の組合せなどの制御が有効であることを見出した。   Therefore, as a result of studying a bonding wire having a multi-layer structure that can respond to new needs such as narrow pitch connection, three-dimensional connection, and improvement of productivity by using a small electrode, It has been found that it is effective to control the layer structure. In particular, by controlling the specific crystal orientation by focusing on the relationship between the surface texture of multi-layered wire and the use performance of wire bonding, which has been hardly known so far, ball formability, bondability, loop It was confirmed for the first time that comprehensive improvements such as controllability were possible. Further, it has been found that the control of the combination of the structure of the skin layer and the core material is effective.

即ち、導電性金属からなる芯材と、前記芯材の上に芯材とは異なる面心立方晶の金属を主成分とする表皮層を有するボンディングワイヤであって、表皮層の表面の結晶面における長手方向の結晶方位<hkl>のうち、<111>と<100>の占める割合がそれぞれ50%未満であるボンディングワイヤであることが望ましい。前記ボンディングワイヤであれば、ボール接合部の芯ずれ不良を抑制する高い効果が得られる。   That is, a bonding wire having a core material made of a conductive metal and a skin layer mainly composed of a face-centered cubic metal different from the core material on the core material, the crystal plane of the surface of the skin layer In the longitudinal crystal orientation <hkl>, the proportion of <111> and <100> is preferably less than 50%. If it is the said bonding wire, the high effect which suppresses the misalignment defect of a ball joint part will be acquired.

表皮層を構成する成分が面心立方晶の金属であれば、加工時の降伏降下もなく、加工性も良好であり、伸線加工、ループ制御などの複雑な加工、曲げなどに順応しやすい。面心立方晶の金属で形成、観察される結晶方位では、例えば、<111>、<100>、<110>、<210>、<211>、<221>、<113>、<320>などが知られている。   If the component of the skin layer is a face-centered cubic metal, there is no yield drop during processing, good workability, and easy adaptation to complicated processing such as wire drawing and loop control, bending, etc. . For crystal orientations formed and observed with face-centered cubic metals, for example, <111>, <100>, <110>, <210>, <211>, <221>, <113>, <320>, etc. It has been known.

本発明者らは芯ずれを抑制する方策を検討した結果、1)ウェッジ接合の後にワイヤ切断するテイルカット工程でワイヤ破断部の長さ、形状などが安定していること、2)ワイヤ先端に生じたアーク放電がボンディングワイヤに均一に広がること、3)溶融された初期ボールが凝固する際にボンディングワイヤに軸対称を維持すること、4)そのボールを電極上に接合する際にボールが等方的に変形して真円を維持すること、などが同時に満足されることが重要であることを見出した。その改善手段の一つとして、ワイヤ長手方向の結晶方位<hkl>のうち、<111>と<100>の占める割合がそれぞれ50%未満であることが有効である。面心立方晶の金属の<111>及び<100>方位は、加工や熱処理の過程で起こる配向の代表的な結晶方位であり、これらの方位の割合が多い表皮層では、組成としては均一であっても組織としては不均一、即ち、特定の方位が発達した部分が不均一に分布する。このような不均一な組織表面では、同じ組成であっても結晶面によって仕事関数（化学ポテンシャル）が異なるので、例えば、ワイヤ先端の表面に組織的不均一があると、アーク放電がボンディングワイヤに均一に広がらないということが起こる。したがって、これらの方位の割合を抑えることで、テイルカット長さ、アーク放電、初期ボール部の凝固組織、超音波印加によるボール変形などをバランスよく制御できると考えられる。ここで該比率が50%以上では、芯ずれのレベルの激しい不良が突発的に発生し、例えばゴルフクラブ状の不良ボールなどが発生する場合が多いためである。好ましくは、該比率がそれぞれ40%以下であれば、ゴルフクラブ状などの著しい芯ずれを抑制し、さらに平均的な芯ずれの発生率を低減する効果も高められる。より好ましくは、30%以下であれば芯ずれを抑制する効果がさらに高まり、例えば、小さい電極への接合でもはみ出しを抑制できる。   As a result of investigating measures for suppressing misalignment, the present inventors have found that 1) the length and shape of the wire breakage portion are stable in the tail cutting process of cutting the wire after wedge bonding, and 2) the wire tip. The generated arc discharge spreads evenly on the bonding wire, 3) maintains the axial symmetry of the bonding wire when the molten initial ball solidifies, 4) the ball is bonded to the electrode, etc. It has been found that it is important to simultaneously satisfy such conditions as isotropic deformation and maintaining a perfect circle. As one of the improvement means, it is effective that the proportion of <111> and <100> in the crystal orientation <hkl> in the longitudinal direction of the wire is less than 50%. The <111> and <100> orientations of face-centered cubic metals are typical crystal orientations that occur during processing and heat treatment, and the composition of the skin layer with a high proportion of these orientations is uniform. Even in such a case, the structure is non-uniform, that is, the portion where a specific orientation is developed is non-uniformly distributed. Since the work function (chemical potential) differs depending on the crystal plane even with the same composition on such a non-uniform structure surface, for example, if there is a structure non-uniformity on the surface of the wire tip, arc discharge will occur on the bonding wire. It happens that it doesn't spread evenly. Therefore, it can be considered that by controlling the ratio of these orientations, tail cut length, arc discharge, solidified structure of the initial ball portion, ball deformation due to application of ultrasonic waves, and the like can be controlled in a balanced manner. Here, when the ratio is 50% or more, a severe defect with a misalignment level occurs suddenly, and for example, a golf club-like defective ball is often generated. Preferably, when the ratio is 40% or less, significant misalignment such as a golf club shape is suppressed, and further, the effect of reducing the average misalignment occurrence rate is enhanced. More preferably, if it is 30% or less, the effect of suppressing misalignment is further enhanced, and for example, protrusion can be suppressed even when joining to a small electrode.

複層ワイヤでは表層と芯材が異なる成分で構成されているため、ワイヤ表面を被覆している表層の組織を分離して制御することが比較的容易である。この表面組織の制御による特性改善効果も高い。こうした点では、従来の単層ワイヤの組織制御とは異なる。単層ワイヤでは、ワイヤ全体の集合組織および結晶方位を管理することはできるが、表面近傍だけワイヤ内部と分離して組織制御することは難しい。因って、複層ワイヤの表層の組織制御には、複層ワイヤ独自の考え方が求められ、単層ワイヤのワイヤ断面における集合組織および結晶方位の管理を当てはめることはできない。   In the multilayer wire, the surface layer and the core material are composed of different components, so that it is relatively easy to separate and control the surface layer structure covering the wire surface. The effect of improving the characteristics by controlling the surface texture is also high. In this respect, it differs from conventional single layer wire tissue control. With a single-layer wire, the texture and crystal orientation of the entire wire can be managed, but it is difficult to control the structure separately from the inside of the wire only in the vicinity of the surface. Therefore, the structure control of the surface layer of the multilayer wire requires a unique idea of the multilayer wire, and cannot manage the texture and crystal orientation in the wire cross section of the single layer wire.

ある結晶方位の配向率の表示法には、母集団の選定により２通りある。一つは、ワイヤ表面の測定面積に対する各結晶方位<hkl>が占める比率（以下、<hkl>面積比率とよぶ）、又は、測定エリアのなかで結晶方位が識別できる結晶粒または領域を母集団とした各結晶方位<hkl>の比率（以下、<hkl>方位比率とよぶ）である。これまでの説明では、測定できる結晶方位を基準とした方位比率で表示できた。今後狭ピッチ化に適応するため細線化が進めば、表面積の影響がますます増すことで、結晶方位の及ぼす効果をボンディングワイヤの表面を基準とした面積比率で整理する方が、実用の効果をより正確に把握することが可能となる。   There are two ways to display the orientation rate of a certain crystal orientation, depending on the selection of the population. One is the ratio of the crystal orientation <hkl> to the measurement area of the wire surface (hereinafter referred to as <hkl> area ratio), or the population of crystal grains or regions that can identify the crystal orientation in the measurement area. The ratio of each crystal orientation <hkl> (hereinafter referred to as <hkl> orientation ratio). In the explanation so far, it has been possible to display the orientation ratio based on the crystal orientation that can be measured. As thinning progresses to adapt to narrower pitches in the future, the effect of the surface area will increase, and the effect of crystal orientation will be more effectively organized by the area ratio based on the surface of the bonding wire. It becomes possible to grasp more accurately.

具体的には、表皮層の表面の結晶面における長手方向の結晶方位<hkl>のうち、<111>と<100>の占める割合（方位比率）がそれぞれ50%未満である複層構造のボンディングワイヤであって、さらに表皮層の表面におけるワイヤ長手方向の結晶方位が<111>または<100>である結晶粒の面積の、ワイヤ表面の面積に対する割合（面積比率）であって、前記割合（面積比率）がともに35%以下であることが望ましい。これにより、テイルカット形状、ボール凝固時の軸対称性、ボールの高速圧縮変形などを総合的に安定化させ、線径22μm以下に細線化されたボンディングワイヤでもボール接合部の偏芯不良を低減することができる。線径22μm以下の細いボンディングワイヤでは、伸線加工歪みの増大などにより、測定が難しい結晶方位の領域が増加すること等で、測定できる結晶方位のうちの、<111>と<100>の比率（方位比率）だけでは、ボール接合部の形状を正確に把握することが難しい場合も多い。そこで表皮層の表面における<111>の面積比率を併せて適正化することで、細線でも良好な特性が得られる。該面積比が35%以下である理由は、<111>と<100>の方位比率がそれぞれ50%未満であっても、<111>と<100>の面積比率がそれぞれ35%を超えると、線径22μm以下のボンディングワイヤを用いた接続において、ボール接合部の偏芯不良が増えるためである。好ましくは、該面積比率が25%以下であれば、線径18μm以下の細線を接続しても、接合部の偏芯を低減できる。さらに好ましくは、該面積比率が12%以下であれば、線径15μm以下の細線での接合部の偏芯を抑制する効果がさらに高められるため、電極間隔が40μm以下の狭ピッチ接続にも有利となる。好ましくは、該面積比率の下限値として1%以上であれば、伸線、熱処理などのワイヤ製造が容易となる。   Specifically, bonding of a multilayer structure in which <111> and <100> account for less than 50% of the longitudinal crystal orientation <hkl> in the crystal plane of the surface of the skin layer, respectively (orientation ratio). The ratio of the area of the crystal grains in which the crystal orientation in the longitudinal direction of the wire on the surface of the skin layer is <111> or <100> to the area of the wire surface (area ratio), The area ratio is preferably 35% or less. As a result, tail-cut shape, axial symmetry when solidifying the ball, high-speed compression deformation of the ball, etc. are comprehensively stabilized, and even the bonding wire thinned to a wire diameter of 22 μm or less reduces the eccentricity of the ball joint. can do. For thin bonding wires with a wire diameter of 22 μm or less, the ratio of <111> to <100> of the crystal orientations that can be measured due to an increase in the region of crystal orientations that are difficult to measure due to increased strain on wire drawing, etc. In many cases, it is difficult to accurately grasp the shape of the ball joint portion only by (orientation ratio). Thus, by optimizing the area ratio of <111> on the surface of the skin layer, good characteristics can be obtained even with fine wires. The reason why the area ratio is 35% or less is that, even if the orientation ratio of <111> and <100> is less than 50%, respectively, the area ratio of <111> and <100> exceeds 35%, This is because in the connection using a bonding wire having a wire diameter of 22 μm or less, the eccentricity failure of the ball joint portion increases. Preferably, when the area ratio is 25% or less, even if a thin wire having a wire diameter of 18 μm or less is connected, the eccentricity of the joint can be reduced. More preferably, if the area ratio is 12% or less, the effect of suppressing the eccentricity of the joint portion with a thin wire having a wire diameter of 15 μm or less can be further enhanced, which is advantageous for narrow pitch connection with an electrode interval of 40 μm or less. It becomes. Preferably, when the lower limit of the area ratio is 1% or more, wire production such as wire drawing and heat treatment becomes easy.

表皮層の表面における長手方向<hkl>のうち、<111>と<100>の方位比率が、ともに50%未満である複層構造のボンディングワイヤであって、さらに<111>または<100>である結晶粒の面積の総計がワイヤ表面の面積に対する割合（面積比率）が50%以下であれば、ウエッジ接合におけるボンディングワイヤの捲れまたは部分剥離などの不良を抑制することで、高速接続、低温接合などにおける量産歩留りを向上することができる。ボンディングワイヤの捲れまたは部分剥離を誘発する要因として、ウエッジ接合の変形形状、接合界面での接着力、テイルカット時のワイヤ破断力（テイルカット強さ）などが関与していると考えられる。例えば、テイルカット強さが接着力よりも高くなるほど、捲れ現象が増える傾向となる。<111>と<100>それぞれの方位の具体的な関与は必ずしも明確でないが、これらの方位が増えるほど、結晶粒の配向分布に局所的な偏りが生じる傾向にあることにより、ウエッジ接合での変形形状が不均一となったり、ワイヤ表面硬さの局部変動によりテイルカット強さが不安定になることなどが、ワイヤ捲れ、部分剥離などを発生させていると考えられる。言い換えれば、こうした変形形状、接着力、テイルカット強さなどを安定化させるには、<111>、<100>をトータルで低く抑えることが有効である。前記方位比率及び前記面積比率が50%以下であれば、ウエッジ接合におけるワイヤ捲れを低減する高い効果が得られる。例えば、線径25μmの細線を用い、接合温度が200℃程度の一般的な接合条件で上記効果を確認している。好ましくは、25%以下であれば、160℃以下の低温接合でも、ワイヤ捲れを低減する効果がさらに促進できる。好ましくは、該面積比率の下限値として1%以上であれば、伸線、熱処理などのワイヤ製造が容易となる。   A multi-layered bonding wire in which the orientation ratio of <111> and <100> in the longitudinal direction <hkl> on the surface of the skin layer is less than 50%, and further <111> or <100> If the total area of a crystal grain is 50% or less of the wire surface area (area ratio), high-speed connection and low-temperature bonding can be achieved by suppressing defects such as bending or partial peeling of the bonding wire in wedge bonding. The mass production yield can be improved. It is considered that factors that induce bending or partial peeling of the bonding wire are related to the deformed shape of the wedge bonding, the adhesive strength at the bonding interface, the wire breaking force (tail cut strength) during tail cutting, and the like. For example, as the tail cut strength becomes higher than the adhesive strength, the dripping phenomenon tends to increase. The specific involvement of the <111> and <100> orientations is not always clear, but as these orientations increase, local deviations in the orientation distribution of crystal grains tend to occur, which It is considered that the deformation shape becomes non-uniform or the tail cut strength becomes unstable due to local fluctuations in the wire surface hardness, etc., causing wire bending and partial peeling. In other words, it is effective to keep <111> and <100> low in order to stabilize such deformed shape, adhesive strength, tail cut strength, and the like. When the azimuth ratio and the area ratio are 50% or less, a high effect of reducing wire bending in wedge bonding can be obtained. For example, the above-mentioned effect has been confirmed under general joining conditions using a thin wire having a wire diameter of 25 μm and a joining temperature of about 200 ° C. Preferably, if it is 25% or less, the effect of reducing wire bending can be further promoted even at low-temperature bonding at 160 ° C. or less. Preferably, when the lower limit of the area ratio is 1% or more, wire production such as wire drawing and heat treatment becomes easy.

芯材の断面におけるワイヤ長手方向の結晶方位<hkl>のうち、<111>と<100>の占める割合（方位比率）の合計が30%以上であれば、ボール接合部の外周近傍が凹凸変形する花弁不良を低減することになり、ボール接合部を真円に近づけて安定化させることができる。真円性が良好であれば接合面積の縮小に有利となり、接合工程の製造管理が容易となったり、あるいは狭ピッチ接合の生産性を向上できる。ボール部の凝固組織は、芯材の組織にも大きく反映され、芯材の結晶方位<hkl>のうち、<111>と<100>との占める割合を高くすることが有効であることを確認した。この作用効果は、通常のボールサイズの場合に、より高い効果が確認されている。例えば、初期ボール径／ワイヤ径の比率が1.9〜2.2の通常サイズのボールを接合する場合に、ボール接合部における花弁状などの形状不良を低減して、真円性を向上できる。圧縮変形、超音波印加によるボール部の変形挙動を調査した結果、ボール接合形状に関しては、表皮層の組織との相関は小さく、むしろ芯材の組織が支配的に作用することが確認された。ここで、芯材における<111>と<100>との占める割合の合計が30%未満であれば、ボールが接合時に花弁状の変形を起こす頻度が高くなり、不良となる場合がある。ボンディングワイヤの組織がボール変形に及ぼす影響は、複層ワイヤの方が顕著であり、単層ワイヤの組織の影響とは異なる場合が多い。好ましくは、芯材における<111>と<100>との占める割合の合計が50%以上であれば、小径ボールの接合形状の真円性を向上できる。例えば、初期ボール径／ワイヤ径の比率が1.5〜1.7の範囲である小径ボールを接合する場合に、ボール接合部の真円性を向上することで、電極間隔が40μm以下の狭ピッチ接続にも有利となる。   If the total ratio of <111> and <100> (orientation ratio) of the crystal orientation <hkl> in the wire longitudinal direction in the cross section of the core material is 30% or more, the vicinity of the outer periphery of the ball joint is unevenly deformed Therefore, it is possible to reduce the petal defect and to stabilize the ball joint portion close to a perfect circle. If the roundness is good, it is advantageous for reduction of the bonding area, manufacturing management of the bonding process becomes easy, or productivity of narrow pitch bonding can be improved. The solidification structure of the ball part is greatly reflected in the structure of the core material, confirming that it is effective to increase the proportion of <111> and <100> in the crystal orientation <hkl> of the core material. did. This effect has been confirmed to be higher in the case of a normal ball size. For example, when a normal ball having an initial ball diameter / wire diameter ratio of 1.9 to 2.2 is joined, a shape defect such as a petal shape at the ball joined portion can be reduced, and roundness can be improved. As a result of investigating the deformation behavior of the ball portion by compressive deformation and application of ultrasonic waves, it was confirmed that the ball bond shape had a small correlation with the structure of the skin layer, but rather the structure of the core material was dominant. Here, if the sum of the proportions of <111> and <100> in the core material is less than 30%, the frequency of the ball causing petal-like deformation at the time of joining becomes high and may become defective. The influence of the structure of the bonding wire on the ball deformation is more noticeable in the multilayer wire and is often different from the influence of the structure of the single layer wire. Preferably, if the total ratio of <111> and <100> in the core material is 50% or more, the roundness of the bonded shape of the small-diameter ball can be improved. For example, when joining small-diameter balls whose initial ball diameter / wire diameter ratio is in the range of 1.5 to 1.7, the roundness of the ball joint is improved, so that even for narrow pitch connections with an electrode spacing of 40 μm or less. It will be advantageous.

こうした芯材の組織と、前述した表皮層の組織とを組み合わせることにより相乗作用が期待でき、ループ形状の制御、ボール変形の安定化を同時に改善することが可能となる。すなわち、表皮層の表面の結晶面における長手方向の結晶方位のうち、<111>と<100>の方位比率が、ともに50%未満であり、且つ、芯材の断面におけるワイヤ長手方向の結晶方位<hkl>のうち、<111>と<100>との占める割合が30%以上である複層構造のボンディングワイヤであることが望ましい。これにより、最新ニーズである高密度実装の代表例である狭ピッチ接続での小ポール接合、あるいはBGA、CSPを用いる場合に必要となる低温接合など、厳しい接合条件でもボール接合性を高める高い効果が得られる。   A synergistic effect can be expected by combining the structure of the core material and the structure of the skin layer described above, and it becomes possible to simultaneously improve the control of the loop shape and the stabilization of the ball deformation. That is, among the longitudinal crystal orientations in the crystal plane of the surface of the skin layer, the orientation ratio of <111> and <100> is both less than 50%, and the crystal orientation in the wire longitudinal direction in the cross section of the core material It is desirable that the bonding wire has a multilayer structure in which the proportion of <111> and <100> in <hkl> is 30% or more. This makes it possible to improve ball bondability even under severe bonding conditions, such as small pole bonding with narrow pitch connections, which is a typical example of high-density mounting, which is the latest need, or low-temperature bonding required when using BGA and CSP. Is obtained.

表皮層の表面における長手方向の結晶方位<hkl>のうち、<111>と<100>の方位比率が、ともに50%未満である複層構造のボンディングワイヤであって、さらに表皮層の表面における円周方向の結晶粒サイズの平均が2μm以下であることにより、初期ボール径のバラツキを低減させて、ボール接合部のサイズも安定化させることができる。初期ボール径のバラツキを低減するには、ワイヤ先端とトーチ電極との距離（トーチ間隔）をなるべく一定にすることが望ましい。ワイヤボンディングの高速動作の過程でトーチ間隔を一定にさせる方策として、テイルカット時の破断形状、破断長さを安定化させることが有効である。表皮層の表面における結晶粒の平均サイズを小さくすることは、単層ワイヤでは効果は小さいものの、複層ワイヤでは、ワイヤ長手方向に表面の硬度、延性のばらつき、変動を抑えることができ、テイルカット時の破断形状、破断長さを安定化させることが可能である。表面の結晶粒サイズを微細化しても、<111>、<100>の方位比率が片方でも高いと、上記効果が半減することからも、表面の微細化と結晶方位制御とを両立することが有効である。ここで表面の結晶粒が2μm以下であれば、上記のボールサイズを安定化させる十分な効果が得られる。好ましくは、結晶粒の平均サイズが1μm以下であれば、初期ボール径／ワイヤ径の比率が1.8〜2.0である比較的小さい初期ボールを形成する場合でも、ボール径を安定化させる効果が高められる。さらに好ましくは、0.5μm以下であれば、初期ボール径／ワイヤ径の比率が1.5〜1.8の範囲である極小のボールでもサイズを安定化させる効果がさらに高められる。   Of the crystal orientation <hkl> in the longitudinal direction on the surface of the skin layer, the <111> and <100> orientation ratios are both less than 50% in a multi-layered bonding wire, and further on the surface of the skin layer When the average crystal grain size in the circumferential direction is 2 μm or less, variations in the initial ball diameter can be reduced and the size of the ball joint can be stabilized. In order to reduce the variation in the initial ball diameter, it is desirable to keep the distance (torch interval) between the wire tip and the torch electrode as constant as possible. As a measure for making the torch interval constant during the high-speed operation of wire bonding, it is effective to stabilize the fracture shape and the fracture length during tail cutting. Reducing the average grain size on the surface of the skin layer is less effective with single-layer wires, but with multi-layer wires, it is possible to suppress surface hardness, variation in ductility and fluctuations in the wire longitudinal direction, and tail It is possible to stabilize the fracture shape and the fracture length at the time of cutting. Even if the crystal grain size on the surface is miniaturized, if the orientation ratio of <111> and <100> is high on either side, the above effect will be halved. It is valid. Here, if the surface crystal grains are 2 μm or less, a sufficient effect of stabilizing the ball size can be obtained. Preferably, when the average size of the crystal grains is 1 μm or less, the effect of stabilizing the ball diameter is enhanced even when a relatively small initial ball having an initial ball diameter / wire diameter ratio of 1.8 to 2.0 is formed. . More preferably, if it is 0.5 μm or less, the effect of stabilizing the size can be further enhanced even with a very small ball whose initial ball diameter / wire diameter ratio is in the range of 1.5 to 1.8.

表皮層の主成分となる面心立方晶の金属とは、芯材の主成分である導電性金属とは異なる金属であり、ボンディングワイヤの接合性の改善に効果があり、ボンディングワイヤの酸化防止にも有効である金属であることが望ましい。具体的には、Pd、Pt、Ru、Rhが候補となり、さらに実用性、コストパフォーマンスなどを重視すれば、Pd、Pt、Ruの少なくとも1種の金属であることがより望ましい。ここでの主成分とは濃度が50mol%以上を有する元素のことである。Pdは、封止樹脂との密着性、電極への接合性も十分であり、品質管理も容易である等の利点がある。Ptは、ボール形状を安定化させることが比較的容易である。Ruは硬質で緻密な膜を形成し易く、材料費も比較的安価である。Rhは耐酸化性など性能は良好であるが、材料費が高価であるため、薄膜化など今後の検討が期待される。   The face-centered cubic metal that is the main component of the skin layer is a metal that is different from the conductive metal that is the main component of the core material. It is also desirable that the metal be effective. Specifically, Pd, Pt, Ru, and Rh are candidates, and if importance is placed on practicality and cost performance, at least one metal of Pd, Pt, and Ru is more desirable. The main component here is an element having a concentration of 50 mol% or more. Pd has advantages such as sufficient adhesion to the sealing resin, sufficient bonding to the electrode, and easy quality control. Pt is relatively easy to stabilize the ball shape. Ru is easy to form a hard and dense film, and the material cost is relatively low. Rh has good performance such as oxidation resistance, but the material cost is high, so future studies such as thinning are expected.

すなわち、表皮層はPd、Pt、Ruの少なくとも1種を主成分とする純金属、または導電性金属を主成分とする合金であることが好ましい。純金属であれば耐酸化性、接合性の向上などが容易である利点があり、合金であれば引張強度、弾性率の上昇により樹脂封止時のワイヤ変形を抑制する利点がある。ここでの上記純金属とは、表皮層の一部に99mol%以上の濃度を有する層が含まれるか、あるいは拡散層を除く表皮層の平均濃度が80mol%以上であることに相当する。上記合金とは、Pd、Pt、Ruの少なくとも1種の金属を50mol%以上含有するものである。   That is, the skin layer is preferably a pure metal whose main component is at least one of Pd, Pt, and Ru, or an alloy whose main component is a conductive metal. A pure metal has the advantage that oxidation resistance and bondability are easily improved, and an alloy has an advantage of suppressing wire deformation at the time of resin sealing by increasing tensile strength and elastic modulus. Here, the pure metal corresponds to a part of the skin layer including a layer having a concentration of 99 mol% or more, or an average concentration of the skin layer excluding the diffusion layer being 80 mol% or more. The alloy contains 50 mol% or more of at least one metal selected from Pd, Pt, and Ru.

芯材を構成する導電性金属は、Cu、Au、Agが候補となり、実用性を重視すれば、Cu、Auの少なくとも1種を主成分することが望ましい。Cuは、材料費が安く、電気伝導性が高く、ボール形成時にシールドガスを吹付ければ良好なボール形成も容易であるなど操作性も比較的良好である。Auは、耐酸化性が強く、ボール形成時にシールドガスなどが不要であり、接合時の変形も良好であり、接合性を確保し易いなどの利点がある。Agは、導電性が優れているが、伸線加工にやや難があり、製造技術を適正化することが必要である。一方、Cu、Auは単層ボンディングワイヤ用素材としての使用実績が多いことは利点でもある。   Cu, Au, and Ag are candidates for the conductive metal constituting the core material, and it is desirable that at least one of Cu and Au is a main component if practicality is important. Cu has a low material cost, high electrical conductivity, and a relatively good operability such as easy formation of a good ball by spraying a shielding gas when forming the ball. Au has strong oxidation resistance, does not require a shielding gas at the time of ball formation, has an advantage that deformation at the time of bonding is good, and it is easy to ensure bonding properties. Ag is excellent in electrical conductivity, but has some difficulty in wire drawing, and it is necessary to optimize the manufacturing technique. On the other hand, Cu and Au are also advantageous in that they have been used as single-layer bonding wire materials.

芯材は導電性金属を主成分とする合金であれば、ワイヤ強度の増加による細線化、または接合信頼性の向上などに有利な場合もある。Cu合金の場合には、B、Pd、Bi、Pの1種以上を5〜300pmの範囲で含有することで、ボンディングワイヤの引張り強度、弾性率の増加などにより、スパン5mm程度までのロングスパンでの直線性を向上する効果が得られる。Au合金の場合には、Be、Ca、Ni、Pd、Ptの1種以上を5〜8000pmの範囲で含有有すれば、同様の効果があり、良好な直線性を確保するのが容易となる。   If the core material is an alloy containing a conductive metal as a main component, it may be advantageous for thinning the wire by increasing the wire strength or improving the bonding reliability. In the case of Cu alloy, by containing one or more of B, Pd, Bi, and P in the range of 5 to 300 pm, a long span of up to about 5 mm due to an increase in the tensile strength and elastic modulus of the bonding wire, etc. The effect which improves the linearity in is obtained. In the case of an Au alloy, if one or more of Be, Ca, Ni, Pd, and Pt are contained in the range of 5 to 8000 pm, the same effect is obtained, and it becomes easy to ensure good linearity. .

複層ワイヤの構成では、表皮層と前記芯材の間に、前記表皮層及び前記芯材を構成する主成分とは異なる成分からなる中間金属層を有することで、前述した表皮層の結晶方位の配向を制御するのが、より有利となる。表皮層の形成では下地の結晶方位の影響を受けることがあり、芯材の結晶方位を制御するよりも、芯材の上に形成した中間金属層の結晶方位を制御する方が比較的容易であるためである。具体的には、表皮層の金属と同じ面心立方晶の金属が、中間金属層として好ましい。特に、表皮層の金属の格子定数と中間金属層の金属の格子定数が近いものが、より好ましい。   In the structure of the multilayer wire, the crystal orientation of the skin layer described above has an intermediate metal layer made of a component different from the main component constituting the skin layer and the core material between the skin layer and the core material. It is more advantageous to control the orientation of the. The formation of the skin layer may be affected by the crystal orientation of the base, and it is relatively easier to control the crystal orientation of the intermediate metal layer formed on the core material than to control the crystal orientation of the core material. Because there is. Specifically, the same face-centered cubic metal as that of the skin layer is preferable as the intermediate metal layer. In particular, it is more preferable that the metal lattice constant of the skin layer is close to the metal lattice constant of the intermediate metal layer.

すなわち、前記表皮層と前記芯材の間に、前記表皮層及び前記芯材を構成する主成分とは異なる成分からなる中間金属層を有することを特徴とする複層構造のボンディングワイヤが望ましい。中間金属層を加える効果として、表皮層と芯材の密着性の向上などにより、ウェッジ接合部の接合強度の指標のひとつであるピール強度を高めることができる。ここで、ピール強度の測定には、ウェッジ接合近傍でのプル強度を測定する簡便な方法で代用できる。従って、中間金属の挿入によりピール強度を増加させることができる。ここで、中間金属層の成分は、表皮層および芯材の成分との組み合わせで選定されるべきものであり、上述のような金属成分とするのが好ましく、特に、Au、Pd、Ptがより好ましい。更に好ましくは、表皮層／芯材の主成分の組合せがPd／Cuである場合、中間金属層の主成分がAuであれば、表皮層の結晶方位の制御に有利であり、さらに表皮層／中間金属層／芯材のそれぞれの界面での密着性も比較的良好である。また、表皮層／芯材の主成分の組合せがPd／Auである場合、中間金属層の主成分がPtであれば、結晶方位の制御と表皮層の組成、膜厚の均一性に有利である。   That is, a multi-layer bonding wire characterized by having an intermediate metal layer made of a component different from the main component constituting the skin layer and the core material between the skin layer and the core material is desirable. As an effect of adding the intermediate metal layer, the peel strength, which is one of the indicators of the joint strength of the wedge joint, can be increased by improving the adhesion between the skin layer and the core material. Here, the peel strength can be measured by a simple method of measuring the pull strength in the vicinity of the wedge joint. Accordingly, the peel strength can be increased by inserting the intermediate metal. Here, the component of the intermediate metal layer is to be selected in combination with the component of the skin layer and the core material, and is preferably a metal component as described above, in particular, Au, Pd, Pt is more preferable. More preferably, when the combination of the main component of the skin layer / core material is Pd / Cu, if the main component of the intermediate metal layer is Au, it is advantageous for controlling the crystal orientation of the skin layer. Adhesion at each interface of the intermediate metal layer / core material is also relatively good. In addition, when the combination of the main component of the skin layer / core material is Pd / Au, if the main component of the intermediate metal layer is Pt, it is advantageous for the control of crystal orientation, the composition of the skin layer, and the uniformity of the film thickness. is there.

表皮層の厚さが0.005〜0.2μmの範囲であれば、前述した表皮層の結晶方位の制御にも有利であり、接合性、ループ制御などの要求特性も総合的に満足することが容易となる。厚さが0.005μm以上であれば、結晶方位を制御した表皮層の十分な効果が得られるためであり、0.2μmを超えると、ボール部の合金化による硬化が顕著となり、接合時にチップにクラックなどの損傷を与えることが問題となる場合がある。   If the thickness of the skin layer is in the range of 0.005 to 0.2 μm, it is advantageous for controlling the crystal orientation of the skin layer described above, and it is easy to comprehensively satisfy the required characteristics such as bondability and loop control. Become. If the thickness is 0.005 μm or more, a sufficient effect of the skin layer with controlled crystal orientation can be obtained. If the thickness exceeds 0.2 μm, hardening due to alloying of the ball part becomes significant and cracks occur in the chip during bonding. It may be a problem to cause damage.

好ましくは、表皮層の厚さが0.01〜0.15μmの範囲であれば、複雑なループ制御でも速度を落とすことなく、所望するループ形状を安定して形成することができる。より好ましくは、0.020〜0.1μmの範囲であれば、ボンディングワイヤの使用性能を維持しつつ、膜形成工程の処理効率を高められるなど、安定した膜質を得ることが容易である。   Preferably, when the thickness of the skin layer is in the range of 0.01 to 0.15 μm, a desired loop shape can be stably formed without reducing the speed even with complicated loop control. More preferably, if it is in the range of 0.020 to 0.1 μm, it is easy to obtain a stable film quality, such as improving the processing efficiency of the film forming process while maintaining the use performance of the bonding wire.

中間金属層の厚さが0.005〜0.2μmの範囲であれば、表皮層の結晶方位を制御するのが容易となり、また芯材との界面の密着性を向上し、複雑なループ制御にも対応できる。好ましくは、0.01〜0.1μmの範囲であれば、膜厚の均一性、再現性を確保することが容易となる。   If the thickness of the intermediate metal layer is in the range of 0.005 to 0.2 μm, it becomes easy to control the crystal orientation of the skin layer, improve the adhesion at the interface with the core material, and support complex loop control. it can. Preferably, when the thickness is in the range of 0.01 to 0.1 μm, it becomes easy to ensure uniformity of film thickness and reproducibility.

ここで、表皮層と芯材の境界は、表皮層を構成する導電性金属の検出濃度の総計が50mol%の部位とする。よって、本発明でいう表皮層とは、表皮層を構成する導電性金属の検出濃度の総計が50mol%の部位から表面であり、即ち、表皮層を構成する導電性金属の検出濃度の総計が50mol%以上の部位である。   Here, the boundary between the skin layer and the core material is a portion where the total detected concentration of the conductive metal constituting the skin layer is 50 mol%. Therefore, the skin layer referred to in the present invention is the surface from the site where the total detected concentration of the conductive metal constituting the skin layer is 50 mol%, that is, the total detected concentration of the conductive metal constituting the skin layer is It is a site of 50 mol% or more.

本発明における結晶方位は、ボンディングワイヤの長手方向に対する結晶方位の角度差が15°以内のものを含むことが好ましい。通常、ある方向の結晶方位に着目しても、個々の結晶はある程度の角度差を有しており、またサンプル準備、結晶方位の測定法などの実験法によっても若干の角度差が生じる。ここで、角度差の範囲が15°以内であれば、それぞれの結晶方位の特性を有しており、ボンディングワイヤの諸特性に及ぼす影響度も有効に活用できるためである。   The crystal orientation in the present invention preferably includes those having an angle difference of 15 ° or less with respect to the longitudinal direction of the bonding wire. Usually, even if attention is paid to a crystal orientation in a certain direction, each crystal has a certain angle difference, and a slight angle difference is also caused by an experimental method such as sample preparation or a crystal orientation measurement method. Here, if the range of the angle difference is within 15 °, it has the characteristics of each crystal orientation, and the degree of influence on the various characteristics of the bonding wire can be effectively utilized.

25μm径程度の微細線の表面の集合組織に関して、これまであまり知られておらず、特に、微細線の複層ワイヤの最表面の集合組織に関する報告例も少ない。ボンディングワイヤのように、比較的軟質で線径の細い金属線における集合組織を精度良く測定するには、高度な測定技術が必要となる。   Regarding the texture of the surface of a fine line having a diameter of about 25 μm, little is known so far, and there are few reports on the texture of the outermost surface of a multilayer wire of fine lines. In order to accurately measure a texture in a metal wire having a relatively soft and thin wire diameter such as a bonding wire, an advanced measurement technique is required.

集合組織の測定法には、測定領域を微小に絞ったり、最表面だけの情報を得るのに有利であることから、最近開発された後方電子散乱図形（Electron Back Scattering Pattern、以降EBSPという）法を用いることができる。EBSP法による集合組織の測定により、ボンディングワイヤのような細線でも、その表面または断面の集合組織を精度良く、しかも十分な再現性をもって測定できる。本測定方法により、ボンディングワイヤの微細組織に関して、サブミクロンの微細結晶粒の結晶方位、ワイヤ表面の結晶方位の分布などを、高精度に再現良く測定できる。   The texture measurement method is advantageous for narrowing down the measurement area or obtaining information only on the outermost surface, so the recently developed Back Electron Scattering Pattern (hereinafter referred to as EBSP) method. Can be used. By measuring the texture by the EBSP method, it is possible to measure the texture of the surface or cross section of a fine wire such as a bonding wire with high accuracy and sufficient reproducibility. With this measurement method, with respect to the microstructure of the bonding wire, the crystal orientation of the submicron fine crystal grains, the distribution of the crystal orientation on the wire surface, and the like can be measured with high accuracy and good reproducibility.

EBSP法では、通常、試料の凹凸、曲面が大きい場合は、結晶方位を高精度測定するのが難しい。しかしながら、測定条件を適正化すれば高精度の測定、解析が可能である。具体的には、ボンディングワイヤを平面に直線状に固定し、そのボンディングワイヤの中心近傍の平坦部をEBSP法で測定する。測定領域について、円周方向のサイズはワイヤ長手方向の中心を軸として線径の50%以下であり、長手方向のサイズは100μm以下であれば、精度に加えて測定効率を高められる。好ましくは、円周方向のサイズは線径の40%以下、長手方向のサイズは40μm以下であれば、測定時間の短縮により測定効率をさらに高められる。   In the EBSP method, it is usually difficult to measure the crystal orientation with high accuracy when the unevenness and curved surface of the sample are large. However, if measurement conditions are optimized, highly accurate measurement and analysis are possible. Specifically, the bonding wire is fixed linearly on a plane, and a flat portion near the center of the bonding wire is measured by the EBSP method. Regarding the measurement region, the size in the circumferential direction is 50% or less of the wire diameter with the center in the longitudinal direction of the wire as the axis. If the size in the longitudinal direction is 100 μm or less, the measurement efficiency can be improved in addition to accuracy. Preferably, if the size in the circumferential direction is 40% or less of the wire diameter and the size in the longitudinal direction is 40 μm or less, the measurement efficiency can be further improved by shortening the measurement time.

EBSP法で高精度の測定を行うには、１回で測定できる領域は限られるため、３箇所以上の測定を行い、ばらつきを考慮した平均情報を得ることが望ましい。測定場所は近接しないよう、円周方向に異なる領域を観察できるように、測定場所を選定することが好ましい。   In order to perform high-accuracy measurement by the EBSP method, the area that can be measured at one time is limited, so it is desirable to perform measurement at three or more locations and obtain average information in consideration of variations. It is preferable to select the measurement location so that different regions can be observed in the circumferential direction so that the measurement locations are not close to each other.

例えば、線径25μmのボンディングワイヤの測定では、平板上にワイヤ向きをなるべく変えるように固定したボンディングワイヤを用い、そのワイヤ軸を中心に円周方向に8μm、長手方向には30μmのサイズを一回の測定エリアとし、1mm以上離して3箇所の測定を行うことで、ワイヤ表面の結晶方位の平均的情報を入手することが可能である。ただし測定の領域、場所の選定はこの限りでなく、測定装置、ワイヤ状態などを考慮して適正化することが望ましい。   For example, in the measurement of a bonding wire having a wire diameter of 25 μm, a bonding wire fixed on a flat plate so as to change the direction of the wire as much as possible is used, and a size of 8 μm in the circumferential direction around the wire axis and a size of 30 μm in the longitudinal direction is unified. It is possible to obtain average information on the crystal orientation of the wire surface by measuring three locations at a distance of 1 mm or more with a measurement area of 1 time. However, the selection of the measurement region and location is not limited to this, and it is desirable to optimize the measurement device and the wire state.

また芯材の結晶方位を測定する場合は、ボンディングワイヤの長手方向の垂直断面または、長手方向と並行でワイヤ中心近傍の平行断面のどちらの測定も可能である。好ましくは、垂直断面の方が求める研磨面を容易に得られる。機械的研磨により断面を作製したときは、研磨面の残留歪みを軽減するためにエッチングにより表層を除去することが望ましい。   When measuring the crystal orientation of the core material, it is possible to measure either a vertical section in the longitudinal direction of the bonding wire or a parallel section in the vicinity of the center of the wire in parallel with the longitudinal direction. Preferably, the polishing surface required by the vertical cross section can be obtained more easily. When the cross section is produced by mechanical polishing, it is desirable to remove the surface layer by etching in order to reduce residual distortion of the polished surface.

EBSP法による測定結果の解析では、装置に装備されている解析ソフトを利用することで、上述したワイヤ表面の測定面積に対する各方位の結晶粒の面積が占める面積比、又は、測定エリアのなかで結晶方位が識別できる結晶粒または領域の総面積を母集団として各結晶方位が占める比率などを算出できる。ここで結晶方位の面積を算出する最小単位は、結晶粒または、結晶粒内の一部の微小領域でも構わない。結晶粒のサイズに関しても長手方向と円周方向での平均サイズなどを計算できる。   In the analysis of measurement results by the EBSP method, by using the analysis software installed in the device, the area ratio of the crystal grains in each orientation to the measurement area of the wire surface mentioned above, or the measurement area The ratio of each crystal orientation can be calculated using the total area of crystal grains or regions that can identify the crystal orientation as a population. Here, the minimum unit for calculating the area of the crystal orientation may be a crystal grain or a part of a minute region in the crystal grain. Regarding the size of the crystal grains, the average size in the longitudinal direction and the circumferential direction can be calculated.

本発明のボンディングワイヤを製造するに当り、芯材の表面に表皮層を形成する工程と、表皮層、拡散層、芯材などの構造を制御する加工・熱処理工程とが必要となる。   In producing the bonding wire of the present invention, a process for forming a skin layer on the surface of the core material and a processing / heat treatment process for controlling the structure of the skin layer, the diffusion layer, the core material and the like are required.

表皮層を芯材の表面に形成する方法には、メッキ法、蒸着法、溶融法等がある。メッキ法では、電解メッキ、無電解メッキ法は使い分けることが可能である。電解メッキでは、メッキ速度が速く、下地との密着性も良好である。電解メッキは１回のメッキ処理でも構わないが、フラッシュメッキと呼ばれる薄付けメッキと、その後に膜を成長させる本メッキとに区分でき、これら複数の工程に分けて行うことで、より膜質の安定化に有利である。無電解メッキに使用する溶液は、置換型と還元型とに分類され、膜が薄い場合には置換型メッキのみでも十分であるが、厚い膜を形成する場合には置換型メッキの後に還元型メッキを段階的に施すことが有効である。無電解法は装置等が簡便であり、容易であるが、電解法よりも時間を要する。   Methods for forming the skin layer on the surface of the core include plating, vapor deposition, and melting. In the plating method, electrolytic plating and electroless plating can be used properly. In electrolytic plating, the plating rate is fast and the adhesion to the substrate is good. Electrolytic plating may be performed once, but it can be divided into thin plating called flash plating and main plating that grows the film after that, and the film quality can be further stabilized by performing these steps. It is advantageous to make. Solutions used for electroless plating are classified into substitutional type and reduction type. If the film is thin, substitutional plating alone is sufficient, but when forming a thick film, the reduction type is used after substitutional plating. It is effective to apply plating step by step. The electroless method is simple and easy to use, but requires more time than the electrolysis method.

蒸着法では、スパッタ法、イオンプレーティング法、真空蒸着等の物理吸着と、プラズマCVD等の化学吸着を利用することができる。いずれも乾式であり、膜形成後の洗浄が不要であり、洗浄時の表面汚染等の心配がない。   In the vapor deposition method, physical adsorption such as sputtering, ion plating, and vacuum deposition, and chemical adsorption such as plasma CVD can be used. All of them are dry-type, and cleaning after film formation is unnecessary, and there is no concern about surface contamination during cleaning.

メッキ又は蒸着を施す段階について、狙いの線径で導電性金属の膜を形成する手法と、太径の芯材に膜形成してから、狙いの線径まで複数回伸線する手法とのどちらも有効である。前者の最終径での膜形成では、製造、品質管理等が簡便であり、後者の膜形成と伸線の組み合わせでは、膜と芯材との密着性を向上するのに有利である。それぞれの形成法の具体例として、狙いの線径の細線に、電解メッキ溶液の中にボンディングワイヤを連続的に掃引しながら膜形成する手法、あるいは、電解又は無電解のメッキ浴中に太線を浸漬して膜を形成した後に、ボンディングワイヤを伸線して最終径に到達する手法等が可能である。   Regarding the stage of plating or vapor deposition, either the method of forming a conductive metal film with a target wire diameter or the method of forming a film on a thick core material and then drawing multiple times to the target wire diameter Is also effective. In the former film formation with the final diameter, manufacturing, quality control and the like are simple, and the latter film formation and wire drawing are advantageous in improving the adhesion between the film and the core material. As a specific example of each forming method, a method of forming a film while continuously sweeping a bonding wire into an electrolytic plating solution on a thin wire having a target wire diameter, or a thick wire in an electrolytic or electroless plating bath For example, a technique of drawing the bonding wire to reach the final diameter after dipping to form a film is possible.

ここで、前述した最終線径で表皮層を形成する最終メッキ法では、成膜後には熱処理工程だけである。また、太径の芯材に膜形成する太径メッキ法では、狙いの線径までの加工工程と熱処理工程を組み合わせることが必要となる。   Here, in the final plating method in which the skin layer is formed with the final wire diameter described above, only the heat treatment step is performed after the film formation. In addition, in the large-diameter plating method in which a film is formed on a large-diameter core material, it is necessary to combine a processing step up to a target wire diameter and a heat treatment step.

表皮層を形成した後の加工工程では、ロール圧延、スエージング、ダイス伸線などを目的により選択、使い分ける。加工速度、圧加率またはダイス減面率などにより、加工組織、転位、結晶粒界の欠陥などを制御することは、表皮層の組織、密着性などにも影響を及ぼす。   In the processing step after forming the skin layer, roll rolling, swaging, die drawing and the like are selected and used properly. Controlling the processed structure, dislocations, defects at the grain boundaries, etc. by the processing speed, pressurization rate or die area reduction rate also affects the structure and adhesion of the skin layer.

単純にワイヤを成膜、加工及び加熱しただけでは、表皮層の表面及び内部での集合組織の結晶方位を制御できない。通常のワイヤ製造で用いられる最終線径での加工歪取り焼鈍をそのまま適用しても、表皮層と芯材との密着性の低下によりループ制御が不安定になったり、ワイヤ長手方向の表皮層の均質性、ワイヤ断面での表皮層、拡散層などの分布をコントロールすることは困難である。そこで、表皮層の成膜条件、伸線工程における減面率、速度などの加工条件、熱処理工程のタイミング、温度、速度、時間等の適正化などを総合的に組合せることで、表皮層の集合組織を安定して制御することが可能となる。   The crystallographic orientation of the texture on the surface and inside of the skin layer cannot be controlled simply by forming, processing and heating the wire. Even if the processing strain relief annealing at the final wire diameter used in normal wire manufacturing is applied as it is, loop control becomes unstable due to a decrease in adhesion between the skin layer and the core material, or the skin layer in the longitudinal direction of the wire It is difficult to control the homogeneity, the distribution of the skin layer and the diffusion layer in the wire cross section. Therefore, by comprehensively combining the skin layer deposition conditions, processing conditions such as the area reduction rate and speed in the wire drawing process, heat treatment process timing, temperature, speed and time optimization, etc. It becomes possible to control the texture stably.

ワイヤの圧延、伸線の工程では加工集合組織が形成され、熱処理工程では回復、再結晶が進行して再結晶集合組織が形成され、これらの集合組織が相互に関連して、最終的に表皮層の集合組織および結晶方位が決定する。   In the wire rolling and wire drawing process, a processed texture is formed, and in the heat treatment process, recovery and recrystallization proceed to form a recrystallized texture, and these textures are interrelated and finally the skin. The texture and crystal orientation of the layer are determined.

表層の表面での結晶方位が<111>、<100>への配向するのを抑えるためのワイヤ製法では、表層を形成した後に加工、熱処理による集合組織の変化を利用して配向を制御することが望ましい。面心立方晶の金属の加工集合組織、再結晶集合組織では、<111>、<100>への配向が高まる傾向にあることから、逆に、これらの方位を低減するには、表皮層を形成した直後の組織を有効に利用する方が有効であると考えられる。例えば成膜後の処理では、ワイヤ加工率を70%以下に抑える、あるいは、熱処理を再結晶温度以下の低温または短時間で行うこと、などの適性処理を施すことで、本願の発明に関する、表層の表面での<111>、<100>への配向を抑えることが可能となる。   In the wire manufacturing method to suppress the orientation of crystal orientation on the surface of the surface layer to <111> and <100>, the orientation should be controlled by using the texture change due to processing and heat treatment after the surface layer is formed. Is desirable. In the processing texture and recrystallization texture of face centered cubic metal, the orientation to <111> and <100> tends to increase. It is considered effective to use the tissue immediately after formation. For example, in the treatment after film formation, the surface layer relating to the invention of the present application can be obtained by performing an appropriate treatment such as suppressing the wire processing rate to 70% or less, or performing a heat treatment at a low temperature below the recrystallization temperature or in a short time. It becomes possible to suppress the orientation to <111> and <100> on the surface of the substrate.

熱処理工程では、熱処理を１回または複数回実施することが有効である。膜形成直後の焼鈍と、加工途中での焼鈍と、最終径での仕上げ焼鈍とに分類され、これらを選択、使い分けることが重要となる。どの加工段階で熱処理を行うかにより、最終の表皮層、表皮層と芯材との界面での拡散挙動などが変化する。一例では、メッキ処理後の加工途中に中間焼鈍を施し、さらにワイヤを伸線し、最終径で仕上げ焼鈍を施す工程で作製することで、中間焼鈍を施さない工程と比較して、表皮層／芯材の界面に拡散層を形成して密着性を向上するのに有利である。   In the heat treatment step, it is effective to perform the heat treatment once or a plurality of times. It is classified into annealing immediately after film formation, annealing in the middle of processing, and finish annealing at the final diameter, and it is important to select and use these properly. The final skin layer, the diffusion behavior at the interface between the skin layer and the core material, and the like change depending on the processing stage at which the heat treatment is performed. In one example, by performing intermediate annealing in the middle of processing after plating treatment, further drawing the wire, and producing by finishing annealing at the final diameter, the skin layer / It is advantageous to improve adhesion by forming a diffusion layer at the interface of the core material.

熱処理法として、ワイヤを連続的に掃引しながら熱処理を行い、しかも、一般的な熱処理である炉内温度を一定とするのでなく、炉内で温度傾斜をつけることで、本発明の特徴とする表皮層及び芯材を有するボンディングワイヤを量産することが容易となる。具体的な事例では、局所的に温度傾斜を導入する方法や、温度を炉内で変化させる方法等がある。ボンディングワイヤの表面酸化を抑制する場合には、N2やAr等の不活性ガスを炉内に流しながら加熱することも有効である。 As a heat treatment method, heat treatment is performed while continuously sweeping the wire, and the temperature in the furnace, which is a general heat treatment, is not constant, but a temperature gradient is provided in the furnace, which is a feature of the present invention. It becomes easy to mass-produce bonding wires having a skin layer and a core material. Specific examples include a method of introducing a temperature gradient locally and a method of changing the temperature in the furnace. In order to suppress the surface oxidation of the bonding wire, it is also effective to heat while flowing an inert gas such as N 2 or Ar into the furnace.

溶融法では、表皮層又は芯材のいずれかを溶融させて鋳込む手法であり、10〜100mm程度の太径で表皮層と芯材を接続した後に伸線することで生産性に優れていること、メッキ、蒸着法に比べて表皮層の合金成分設計が容易であり、強度、接合性等の特性改善も容易である等の利点がある。具体的な工程では、予め作製した芯線の周囲に、溶融した導電性金属を鋳込んで表皮層を形成する方法と、予め作製した導電性金属の中空円柱を用い、その中央部に溶融金属を鋳込むことで芯線を形成する方法に分けられる。好ましくは、後者の中空円柱の内部に芯材を鋳込む方が、表皮層中に芯材の主成分の濃度勾配等を安定形成することが容易である。ここで、予め作製した表皮層中に銅を少量含有させておけば、表皮層の表面での銅濃度の制御が容易となる。また、溶融法では、表皮層にCuを拡散させるための熱処理作業を省略することも可能であるが、表皮層内のCuの分布を調整するために熱処理を施すことで更なる特性改善も見込める。   In the melting method, either the skin layer or the core material is melted and cast, and it is excellent in productivity by drawing after connecting the skin layer and the core material with a large diameter of about 10 to 100 mm. Compared to plating and vapor deposition methods, there are advantages such that the alloy component design of the skin layer is easy, and characteristics such as strength and bondability can be easily improved. In a specific process, a melted conductive metal is cast around a core wire prepared in advance to form a skin layer, and a hollow cylinder of a conductive metal prepared in advance is used. It can be divided into methods of forming a core wire by casting. Preferably, it is easier to stably form a concentration gradient or the like of the main component of the core material in the skin layer by casting the core material inside the latter hollow cylinder. Here, if a small amount of copper is contained in the skin layer prepared in advance, the copper concentration on the surface of the skin layer can be easily controlled. Also, in the melting method, it is possible to omit the heat treatment work for diffusing Cu into the skin layer, but further improvement in characteristics can be expected by applying heat treatment to adjust the Cu distribution in the skin layer. .

さらに、こうした溶融金属を利用する場合、芯線及び表皮層のうち少なくとも一方を連続鋳造で製造することも可能である。この連続鋳造法により、上記の鋳込む方法と比して、工程が簡略化され、しかも線径を細くして生産性を向上させることも可能となる。   Further, when such a molten metal is used, at least one of the core wire and the skin layer can be manufactured by continuous casting. By this continuous casting method, the process is simplified as compared with the above casting method, and the wire diameter can be reduced to improve the productivity.

芯材の主成分が銅である複層銅ワイヤを用いてボンディングするときは、ボールを形成するときのシールドガスが必要であり、1〜10%の範囲でH2を含有するN2混合ガス、または純N2ガスを用いる。従来の単層の銅ワイヤでは、5%H2+N2に代表される混合ガスが推奨されていた。一方、複層銅ワイヤでは、安価な純N2ガスを使用しても良好な接合性が得られるため、標準ガスである5%H2+N2ガスよりも、ランニングコストを低減できる。N2ガスの純度は99.95%以上であることが望ましい。すなわち、純度が99.95%以上のN2ガスをワイヤ先端またはその周囲に吹付けながらアーク放電を生じさせてボール部を形成し、該ボール部を接合するボンディング方法であることが望ましい。 When bonding using a multilayer copper wire whose main component is copper, a shielding gas is required when forming the ball, and an N 2 mixed gas containing H 2 in the range of 1 to 10% Or pure N 2 gas. For conventional single-layer copper wires, a mixed gas typified by 5% H 2 + N 2 has been recommended. On the other hand, with a multilayer copper wire, good bondability can be obtained even if inexpensive pure N 2 gas is used, so that the running cost can be reduced as compared with the standard gas of 5% H 2 + N 2 gas. The purity of N 2 gas is desirably 99.95% or more. That is, it is desirable to use a bonding method in which an arc discharge is generated while spraying N 2 gas having a purity of 99.95% or more on or around the wire tip to form a ball portion, and the ball portion is joined.

また、表皮層と芯材との間に拡散層を形成することで密着性を向上することができる。この拡散層を制御するため、熱処理を利用することが有効である。   Moreover, adhesiveness can be improved by forming a diffusion layer between the skin layer and the core material. In order to control this diffusion layer, it is effective to use heat treatment.

表皮層、芯材などの濃度分析について、ボンディングワイヤの表面からスパッタ等により深さ方向に掘り下げていきながら分析する手法、あるいはワイヤ断面でのライン分析又は点分析する方法等が有効である。前者は、表皮層が薄い場合に有効であるが、厚くなると測定時間がかかり過ぎる。後者の断面での分析は、表皮層が厚い場合に有効であり、また、断面全体での濃度分布や、数ヶ所での再現性の確認等が比較的容易であることが利点であるが、表皮層が薄い場合には精度が低下する。ボンディングワイヤを斜め研磨して、拡散層の厚さを拡大させて測定することも可能である。断面では、ライン分析が比較的簡便であるが、分析の精度を向上したいときには、ライン分析の分析間隔を狭くしたり、界面近傍の観察したい領域に絞っての点分析を行うことも有効である。これらの濃度分析に用いる解析装置では、電子線マイクロ分析法（EPMA）、エネルギー分散型Ｘ線分析法（EDX）、オージェ分光分析法（AES）、透過型電子顕微鏡(TEM)等を利用することができる。特にAES法は、空間分解能が高いことから、最表面の薄い領域の濃度分析に有効である。また、平均的な組成の調査等には、表面部から段階的に酸等に溶解していき、その溶液中に含まれる濃度から溶解部位の組成を求めること等も可能である。本発明では、前記全ての分析手法で得られる濃度値が本発明の規定範囲を満足する必要はなく、１つの分析手法でえられる濃度値が本発明の規定範囲を満足すればその効果が得られるものである。   For concentration analysis of the skin layer, the core material, etc., a method of analyzing the surface of the bonding wire while digging in the depth direction by sputtering or the like, or a method of performing line analysis or point analysis on the wire cross section is effective. The former is effective when the skin layer is thin, but if it is thick, it takes too much measurement time. Analysis of the latter cross section is effective when the skin layer is thick, and it is advantageous that the concentration distribution over the entire cross section, reproducibility confirmation in several places, etc. are relatively easy. When the skin layer is thin, the accuracy decreases. It is also possible to measure by increasing the thickness of the diffusion layer by obliquely polishing the bonding wire. In the cross section, line analysis is relatively simple. However, if you want to improve the accuracy of the analysis, it is also effective to narrow the analysis interval of the line analysis or perform point analysis focusing on the area to be observed near the interface. . The analyzers used for concentration analysis use electron microanalysis (EPMA), energy dispersive X-ray analysis (EDX), Auger spectroscopy (AES), transmission electron microscope (TEM), etc. Can do. In particular, the AES method is effective for concentration analysis of the thinnest region because of its high spatial resolution. Further, for the investigation of the average composition, etc., it is possible to dissolve in acid or the like stepwise from the surface portion, and obtain the composition of the dissolution site from the concentration contained in the solution. In the present invention, it is not necessary that the concentration values obtained by all the analysis methods satisfy the specified range of the present invention, and if the concentration values obtained by one analysis method satisfy the specified range of the present invention, the effect can be obtained. It is what

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の原材料として、芯材に用いるCu、Au、Agは純度が約99.99質量%以上の高純度の素材を用い、表皮層または中間金属層に用いられるAu、Pt、Pd、Ru、Rhの素材には純度99.9質量%以上の原料を用意した。   Cu, Au, Ag used as the core material of the bonding wire is a high-purity material with a purity of about 99.99% by mass or more. Raw materials with a purity of 99.9% by mass or more were prepared.

ある線径まで細くしたワイヤを芯材とし、そのワイヤ表面に異なる金属の層を形成するには、電解メッキ法、無電解メッキ法、蒸着法、溶融法等を行い、熱処理を施した。最終の線径で表皮層を形成する方法と、ある線径で表皮層を形成してからさらに伸線加工により最終線径まで細くする方法とを利用した。電解メッキ液、無電解メッキ液は、半導体用途で市販されているメッキ液を使用し、蒸着はスパッタ法を用いた。線径が約15〜1500μmのワイヤを予め準備し、そのワイヤ表面に蒸着、メッキ等により被覆し、最終径の15〜50μmまで伸線して、最後に加工歪みを取り除き伸び値が5〜15%の範囲になるよう熱処理を施した。必要に応じて、線径25〜200μmまでダイス伸線した後に、拡散熱処理を施してから、さらに伸線加工を施した。伸線用ダイスの減面率は、1個のダイス当たり5〜15%の範囲で準備し、それらダイスの組み合わせにより、ワイヤ表面の加工歪みの導入などを調整した。伸線速度は20〜500m/minの間で適正化した。   In order to use a wire thinned to a certain wire diameter as a core material and form a different metal layer on the surface of the wire, an electrolytic plating method, an electroless plating method, a vapor deposition method, a melting method, or the like was performed and heat treatment was performed. A method of forming a skin layer with a final wire diameter and a method of forming a skin layer with a certain wire diameter and then further thinning to the final wire diameter by wire drawing were utilized. As the electrolytic plating solution and the electroless plating solution, a plating solution commercially available for semiconductor applications was used, and the sputtering method was used for vapor deposition. A wire having a wire diameter of about 15 to 1500 μm is prepared in advance, and the wire surface is coated by vapor deposition, plating, etc., drawn to a final diameter of 15 to 50 μm, and finally the processing strain is removed and the elongation value is 5 to 15 Heat treatment was applied so as to be in the range of%. If necessary, after wire drawing to a wire diameter of 25 to 200 μm, diffusion heat treatment was performed, and then wire drawing was further performed. The area reduction rate of the drawing dies was prepared in the range of 5 to 15% per die, and the introduction of processing strain on the wire surface was adjusted by the combination of these dies. The drawing speed was optimized between 20 and 500 m / min.

溶融法を利用する場合には、予め作製した芯線の周囲に、溶融した金属を鋳込む方法と、予め作製した中空円柱の中央部に溶融した金属を鋳込む方法とを採用した。その後、鍛造、ロール圧延、ダイス伸線等の加工と、熱処理とを行い、ワイヤを製造した。   When using the melting method, a method of casting a molten metal around a core wire prepared in advance and a method of casting a molten metal in the central portion of a hollow cylinder prepared in advance were employed. Thereafter, forging, roll rolling, die drawing, and the like, and heat treatment were performed to produce a wire.

本発明例のワイヤの熱処理について、ワイヤを連続的に掃引しながら加熱した。局所的に温度傾斜を導入する方式、温度を炉内で変化させる方式等を利用した。例えば、炉内温度を３分割して制御できるよう改造した熱処理炉を利用した。温度分布の一例では、ワイヤの挿入口から出口に向かって、高温→中温→低温、または中温→高温→低温の分布を得て、それぞれの加熱長さも管理した。温度分布と合わせて、ワイヤ掃引速度等も適正化した。熱処理の雰囲気では、酸化を抑制する目的でN2、Ar等の不活性ガスも利用した。ガス流量は、0.0002〜0.004m3/minの範囲で調整し、炉内の温度制御にも利用した。熱処理を行うタイミングとして、伸線後のワイヤに熱処理を施してから表皮層を形成する場合と、熱処理を加工前、加工途中、または表皮層を形成した直後などのうち２回以上行う場合に分類できる。 Regarding the heat treatment of the wire of the example of the present invention, the wire was heated while continuously sweeping. A method of introducing a temperature gradient locally, a method of changing the temperature in the furnace, and the like were used. For example, a heat treatment furnace modified so that the furnace temperature can be controlled by dividing into three parts was used. In an example of the temperature distribution, the distribution of high temperature → intermediate temperature → low temperature or medium temperature → high temperature → low temperature was obtained from the wire insertion port toward the outlet, and the heating length was also controlled. Along with the temperature distribution, the wire sweep speed was also optimized. In the atmosphere of heat treatment, an inert gas such as N 2 or Ar was also used for the purpose of suppressing oxidation. The gas flow rate was adjusted in the range of 0.0002 to 0.004 m 3 / min and used for temperature control in the furnace. The timing of heat treatment is classified into the case where the skin layer is formed after heat treatment is applied to the wire after drawing, and the case where heat treatment is performed twice or more before, during or immediately after the formation of the skin layer. it can.

表皮層を形成した後の圧延、伸線による加工レベルについて、成膜時のワイヤと最終線径との面積比率で算出する累積の加工率で整理できる。この加工率（％）が30％未満の場合にはR1、30％以上70％未満ではR2、70％以上95％未満ではR3、95％以上ではR4で標記した。   The processing level by rolling and wire drawing after the skin layer is formed can be organized by the cumulative processing rate calculated by the area ratio between the wire at the time of film formation and the final wire diameter. When this processing rate (%) is less than 30%, it is indicated as R1, R2 when 30% or more and less than 70%, R3 when 70% or more and less than 95%, and R4 when 95% or more.

表皮層の表面組織を制御するには、材質、組成、厚さなどの材料因子と、膜形成条件、加工・熱処理条件などプロセス因子を適正化することが必要である。実施例において、表層の表面での結晶方位を<111>、<100>への配向を抑える方策として、加工率を低減すること、初期の膜厚を厚くすること、熱処理を低温化することなどが有効である。一例として、上記加工率がR1〜R3であり、表皮層を構成する素材の再結晶温度よりも低温で熱処理することなどで、<111>、<100>への配向を抑えることが比較的容易となる。一方の比較例では、<111>または<100>への配向を高めるために、加工率を増加させたり、熱処理を高温または長時間で実施することが有効であった。   In order to control the surface texture of the skin layer, it is necessary to optimize material factors such as material, composition and thickness, and process factors such as film formation conditions and processing / heat treatment conditions. In the examples, as measures to suppress the orientation of the crystal orientation on the surface of the surface layer to <111>, <100>, reducing the processing rate, increasing the initial film thickness, lowering the heat treatment, etc. Is effective. As an example, the above processing rate is R1-R3, and it is relatively easy to suppress orientation to <111> and <100> by heat treatment at a temperature lower than the recrystallization temperature of the material constituting the skin layer. It becomes. In one comparative example, in order to increase the orientation to <111> or <100>, it was effective to increase the processing rate or to perform the heat treatment at a high temperature or for a long time.

ワイヤ表面の組織観察について、ボンディングワイヤの表層における表面のある領域において、EBSP法により結晶方位を測定した。測定試料の準備では、3〜5本のボンディングワイヤを平板上に互いにワイヤ向きをなるべく変えるように固定した。観察領域はワイヤ軸を含む四角形の領域として、サイズは円周方向に5〜10μm、長手方向に10〜50μmを一回の測定エリアとした。測定箇所は、3〜10箇所とし、お互いに0.5mm以上離して選定した。測定ポイントの間隔は0.01〜0.2μmの間隔で実施した。主に線径25μmのボンディングワイヤを用いてEBSP測定した結果で比較した。線径がさらに細い場合にも、同様の傾向が認められることが確認された。   Regarding the observation of the structure of the wire surface, the crystal orientation was measured by the EBSP method in a certain region of the surface on the surface layer of the bonding wire. In the preparation of the measurement sample, 3 to 5 bonding wires were fixed on the flat plate so as to change the wire direction as much as possible. The observation area was a square area including the wire axis, and the size was 5-10 μm in the circumferential direction and 10-50 μm in the longitudinal direction as one measurement area. The measurement locations were 3 to 10 locations, which were selected at a distance of 0.5 mm or more. The measurement point interval was 0.01 to 0.2 μm. The results of EBSP measurement using mainly bonding wires with a wire diameter of 25 μm were compared. It was confirmed that the same tendency was observed when the wire diameter was even thinner.

芯材の組織観察では、ボンディングワイヤの断面を研磨し、化学エッチングにより表面の加工歪みを低減した試料を用いて、EBSP法により結晶方位を測定した。断面は、ワイヤ長手方向に垂直の断面を主として測定したが、試料状態、再現性などを検討しながら必要に応じて、ワイヤ長手方向に平行で中心軸を通る断面でも測定を実施した。   In observing the structure of the core material, the crystal orientation was measured by the EBSP method using a sample obtained by polishing the cross section of the bonding wire and reducing the surface processing strain by chemical etching. The cross section was measured mainly with a cross section perpendicular to the longitudinal direction of the wire, but measurement was also performed on a cross section parallel to the longitudinal direction of the wire and passing through the central axis as necessary while examining the sample state and reproducibility.

EBSP測定データの解析には専用ソフト（TSL製 OIM analysisなど）を利用した。測定エリアでの結晶方位を解析し、そのうち<111>、<100>方位などの結晶粒の割合を求めた。ボンディングワイヤの長手方向を基準に方位を決定し、それぞれの結晶方位の角度差が15°以内のものまで含めた。その結晶粒の割合の算出法について、測定エリアの全体面積を母集団として算出する各方位の割合（以下、面積比率と呼ぶ）と、測定エリア内である信頼度を基準に同定できた結晶方位だけの面積を母集団として算出する各方位の割合（以下、方位比率と呼ぶ）との2種類を求めた。後者の方位比率を求める過程では、結晶方位が測定できない部位、あるいは測定できても方位解析の信頼度が低い部位などは除外して計算した。ここで、信頼度とは、解析ソフトにパラメータが用意されている場合があり、例えばConfidential Index（CI値）、Image Quality（IQ値）など数種のパラメータを利用して、試料状態、解析目的などに応じて判定基準を選定することが望ましい。   Dedicated software (such as OSL analysis from TSL) was used to analyze EBSP measurement data. The crystal orientation in the measurement area was analyzed, and the proportion of crystal grains such as <111> and <100> orientation was obtained. The orientation was determined based on the longitudinal direction of the bonding wire, and the crystal orientations were included up to 15 °. About the calculation method of the ratio of crystal grains, the ratio of each orientation that calculates the total area of the measurement area as a population (hereinafter referred to as area ratio) and the crystal orientation that can be identified based on the reliability within the measurement area Two types of ratios (hereinafter referred to as azimuth ratios) for calculating only the area as a population were obtained. In the latter process of obtaining the orientation ratio, the calculation was performed by excluding the part where the crystal orientation could not be measured, or the part where the reliability of orientation analysis was low even though it could be measured. Here, the reliability may include parameters prepared in the analysis software. For example, using several parameters such as Confidential Index (CI value) and Image Quality (IQ value), the sample state, analysis purpose, etc. It is desirable to select judgment criteria according to the above.

ワイヤ表面の膜厚測定にはAESによる深さ分析を用い、結晶粒界の濃化など元素分布の観察にはAES、EPMAなどによる面分析、線分析を行った。AESによる深さ分析では、Arイオンでスパッタしながら深さ方向に測定して、深さの単位にはSiO2換算で表示した。ボンディングワイヤ中の導電性金属濃度は、ICP分析、ICP質量分析などにより測定した。 Depth analysis by AES was used to measure the film thickness on the wire surface, and surface analysis and line analysis by AES, EPMA, etc. were performed to observe the element distribution such as concentration of grain boundaries. In depth analysis by AES, measurement was performed in the depth direction while sputtering with Ar ions, and the unit of depth was displayed in terms of SiO 2 . The conductive metal concentration in the bonding wire was measured by ICP analysis, ICP mass spectrometry and the like.

ボンディングワイヤの接続には、市販の自動ワイヤボンダーを使用して、ボール/ウェッジ接合を行った。アーク放電によりワイヤ先端にボールを作製し、それをシリコン基板上の電極膜に接合し、ワイヤ他端をリード端子上にウェッジ接合した。ボール形成時の酸化を抑制するために用いるシールドガスは、主に純N2ガスを用いた。ガス流量は、0.001〜0.01m3/minの範囲で調整した。 For connecting the bonding wires, a commercially available automatic wire bonder was used to perform ball / wedge bonding. A ball was produced at the tip of the wire by arc discharge, it was joined to the electrode film on the silicon substrate, and the other end of the wire was wedge joined to the lead terminal. The shielding gas used to suppress oxidation during ball formation was mainly pure N 2 gas. The gas flow rate was adjusted in the range of 0.001 to 0.01 m 3 / min.

接合相手は、シリコン基板上の電極膜の材料である、厚さ1μmのAl合金膜(Al-1%Si-0.5%Cu膜、Al-0.5%Cu膜)を使用した。一方、ウェッジ接合の相手には、表面にAgメッキ(厚さ:2〜4μm)したリードフレームを用いた。尚、BGA基板上のAu/Ni/Cuの電極への接合性についても、一部のワイヤ試料を用いて、前記リードフレームと同様の効果が得られることを確認している。   As a bonding partner, an Al alloy film (Al-1% Si-0.5% Cu film, Al-0.5% Cu film) having a thickness of 1 μm, which is a material of an electrode film on a silicon substrate, was used. On the other hand, a lead frame whose surface was Ag-plated (thickness: 2 to 4 μm) was used as a partner for wedge bonding. It has been confirmed that the same effect as that of the lead frame can be obtained with respect to the bonding property to the Au / Ni / Cu electrode on the BGA substrate by using some wire samples.

ボンディングされたループの直線性を評価するため、ワイヤ間隔(スパン)が2mmの通常スパン、5mmのロングスパン、7mmの超ロングスパンの３種でボンディングを行った。線径は25μmとする。30本のボンディングワイヤを投影機により上方から観察して、ボール側とウェッジ側の接合部を結ぶ直線に対し、ボンディングワイヤが最も離れている部位のずれを曲がり量として測定した。その曲がり量の平均が、線径の1本分未満であれば良好であると判断し◎印で表示し、2本分以上であれば不良であるため△印、その中間であれば、通常は問題とならないため○印で表示した。   In order to evaluate the linearity of the bonded loop, bonding was performed with three types of wire span (span): normal span of 2 mm, long span of 5 mm, and ultra-long span of 7 mm. The wire diameter is 25 μm. Thirty bonding wires were observed from above with a projector, and the deviation of the portion where the bonding wires were farthest from the straight line connecting the ball side and wedge side joints was measured as the amount of bending. If the average amount of bending is less than one wire diameter, it is judged to be good. Is not marked as a problem.

初期ボールの芯ずれ挙動の評価について、線径25μmのボンディングワイヤを用いて、ボール径／ワイヤ径の比率が、1.8〜2.5倍の範囲の初期ボールを30本採取し、光顕またはSEMで観察して、ゴルフクラブ状の著しい芯ずれと、軽度の芯ずれについてそれぞれ評価した。ゴルフクラブ状の著しい芯ずれでは、発生数が6本以上であれば不良であるため×印、2〜5本である場合には△印、1本であれば接合条件などで改善可能と判断して○印、0本であれば良好であるため◎印で表記した。一方、軽度の芯ずれについて、8本以上であれば不良であるため×印、5〜7本である場合には△印、2〜4本であれば実用上の大きな問題はないと判断して○印、1本以下であれば、芯ずれの問題はなく良好であるため◎印で表記した。   Regarding the evaluation of the misalignment behavior of the initial ball, using a bonding wire with a wire diameter of 25 μm, 30 initial balls with a ball diameter / wire diameter ratio in the range of 1.8 to 2.5 times were collected and observed with a light microscope or SEM. The golf club-shaped remarkably misalignment and the slight misalignment were evaluated. If the number of occurrences of misalignment of a golf club is 6 or more, it is bad, so it is bad. If it is 2 to 5, it is △, and if it is 1, it can be improved by joining conditions. Therefore, it is marked with ◎ because it is good if it is 0 or 0. On the other hand, for minor misalignment, if it is 8 or more, it is defective, x mark, if it is 5-7, △ mark, if it is 2-4, it is judged that there is no practical problem. If the number is 1 or less, it is good because there is no problem of misalignment, so it is marked with ◎.

ボール接合部の偏芯に関する評価では、線径が22μm、18μm、15μmそれそれでボール接合部を400本観察した。電極はみ出しの不良となる可能性が高い顕著な偏芯の発生が7本以上であれば不良であるため×印、3〜6本である場合には△印、顕著な偏芯は2本以下、且つ、電極はみ出しの可能性は低く通常は問題となることのない微小な偏芯が5〜20本の範囲であれば実用上の大きな問題はないと判断して○印、顕著な偏芯は0本、且つ、微小な偏芯が4本以下であれば、偏芯の問題はなく良好であるため◎印で表記した。   In the evaluation regarding the eccentricity of the ball joint, 400 wire joints were observed with wire diameters of 22 μm, 18 μm, and 15 μm. There is a high possibility of electrode sticking out. If there are 7 or more occurrences of significant eccentricity, it is defective. In addition, it is judged that there is no problem in practical use if the range of the minute eccentricity in the range of 5 to 20 that is not likely to cause a problem is low because the possibility of the electrode protruding is low. If the number is zero and the number of minute eccentricity is 4 or less, there is no problem of eccentricity, and it is good, so it is indicated by ◎.

初期ボールのサイズ安定性について、線径25μmのボンディングワイヤを用いて、接合ボール径／ワイヤ径の比率が、2.0以上2.3未満（通常ボール径）、1.8以上2.0未満（小ボール）、1.5以上1.8未満（極小ボール）の3水準をそれぞれ30個のボールを作製して、光学顕微鏡で測定した。初期ボール径の偏差で評価した。ボール径の偏差が1.5μｍ以上であればバラツキが問題であり×印、偏差が0.8μｍ以上1.5μｍ未満の範囲でしかも極端なサイズ異常が3本以上の場合には必要に応じて改善が望ましいから△印、偏差が0.5μｍ以上0.8μｍ未満であれば実用上は問題ないと判断して○印、偏差が0.5μｍ未満であればサイズは安定しているため◎印で表記した。   Regarding the size stability of the initial ball, using a bonding wire with a wire diameter of 25 μm, the bonding ball diameter / wire diameter ratio is 2.0 to 2.3 (normal ball diameter), 1.8 to less than 2.0 (small ball), 1.5 to 1.8 30 balls were produced for each of three levels of less than (small balls) and measured with an optical microscope. Evaluation was based on deviation of the initial ball diameter. If the deviation of the ball diameter is 1.5μm or more, the variation is a problem. × If the deviation is in the range of 0.8μm or more and less than 1.5μm, and there are 3 or more extreme size abnormalities, improvement is desirable as necessary. From Δ, the deviation is 0.5 μm or more and less than 0.8 μm, and it is judged that there is no problem in practical use, and the mark is indicated by 偏差 because the size is stable when the deviation is less than 0.5 μm.

圧着ボール部の接合形状の判定では、接合されたボールを200本観察して、花弁変形を評価した。線径は25μmとする。初期ボール径／ワイヤ径の比率が2.0〜2.5の通常サイズのボールを形成する場合と、比率が1.5〜1.7の範囲である小径ボールを形成する場合の、２種類でそれぞれ評価した。真円からずれた花弁変形などの不良ボール形状が5本以上であれば不良と判定し×印、不良ボール形状が2〜4本であれば、必要に応じて改善が望ましいから△印、不良ボール形状が1本以下であれば良好であるため○印で表記した。   In determining the bonded shape of the press-bonded ball portion, 200 bonded balls were observed to evaluate the petal deformation. The wire diameter is 25 μm. Two types were evaluated: a case of forming a normal ball having an initial ball diameter / wire diameter ratio of 2.0 to 2.5, and a case of forming a small ball having a ratio of 1.5 to 1.7. If there are 5 or more defective ball shapes such as petal deformation that deviates from a perfect circle, it is judged as defective. ×, and if there are 2 to 4 defective ball shapes, improvement is desirable as necessary. Since the ball shape is good if it is 1 or less, it is indicated by a circle.

ウェッジ接合部のめくれ不良の評価について、線径25μmのボンディングワイヤを用いて、接合温度が200℃、160℃の2水準でワイヤ接続を行い、接合部のワイヤ端でのめくれを400本観察した。幅5μm以上の顕著なめくれが3個以上であれば、問題となるレベルと判定して×印、顕著なめくれが2個以下であれば、すぐに問題とならないが改善が望ましいことから△印、顕著なめくれは観察されないが、幅2μm以下程度の軽微なめくれが4〜10個の範囲であれば実用上は問題ないと判断して○印、軽微な偏芯が3本以下であれば良好であるため◎印で表記した。   Regarding the evaluation of the winding failure of the wedge joint part, using a bonding wire with a wire diameter of 25 μm, wire connection was performed at two levels of 200 ° C. and 160 ° C., and 400 turns at the wire end of the joint part were observed. . If there are 3 or more marked turns with a width of 5 μm or more, it is judged as a problem level, and if there are 2 or less noticeable turns, there is no problem immediately, but improvement is desirable. No noticeable turning is observed, but if it is in the range of 4 to 10 minor turns with a width of about 2 μm or less, it is judged that there is no problem in practical use, ○ mark, if there are 3 or less minor eccentricity Since it was good, it was marked with ◎.

表1及び2には、本発明に係わるボンディングワイヤの実施例と比較例を示す。   Tables 1 and 2 show examples of bonding wires according to the present invention and comparative examples.

第1請求項に係わるボンディングワイヤは実施例1〜30であり、第2請求項に係わるボンディングワイヤは実施例2〜21、23〜27、29、30、第3請求項に係わるボンディングワイヤは実施例3〜21、23〜30、第4請求項に係わるボンディングワイヤは実施例1〜7、10〜12、15〜17、19〜30、第5請求項に係わるボンディングワイヤは実施例1〜4、6〜12、14〜23、25〜30、第6請求項に係わるボンディングワイヤは実施例1〜17、19〜23、25〜30、第7請求項に係わるボンディングワイヤは実施例1〜24、26〜30、第8請求項に係わるボンディングワイヤは実施例26〜30に相当する。比較例1〜6では、第1請求項を満足しない場合の結果を示す。   The bonding wires according to the first claim are Examples 1 to 30, the bonding wires according to the second claim are the Examples 2 to 21, 23 to 27, 29, 30, and the bonding wires according to the third claim are performed. Examples 3 to 21, 23 to 30, and bonding wires according to the fourth claim are Examples 1 to 7, 10 to 12, 15 to 17, 19 to 30, and bonding wires according to the fifth claim are Examples 1 to 4. , 6-12, 14-23, 25-30, the bonding wires according to the sixth claim are Examples 1-17, 19-23, 25-30, and the bonding wires according to the seventh claim are Examples 1-24. , 26-30, and the bonding wires according to the eighth claim correspond to Examples 26-30. Comparative Examples 1 to 6 show results when the first claim is not satisfied.

図1には、実施例3のボンディングワイヤの表面において、EBSP測定結果の一例を示す。ワイヤ長手方向の結晶方位が<111>、<100>方位から角度差15°以内の領域を着色し、角度差が15°以上の結晶粒界を線表示した。図1における<111>と<100>面積比率の総計は37%であった。   FIG. 1 shows an example of the EBSP measurement result on the surface of the bonding wire of Example 3. Regions with an angle difference of 15 ° or less from the <111> and <100> directions in the wire longitudinal direction were colored, and crystal grain boundaries with an angle difference of 15 ° or more were displayed as lines. The total of the <111> and <100> area ratios in FIG. 1 was 37%.

それぞれの請求項の代表例について、評価結果の一部を説明する。   A part of the evaluation results will be described for representative examples of each claim.

実施例1〜30の複層構造のボンディングワイヤは、本発明に係わる、表皮層の表面における長手方向の結晶方位のうち、<111>と<100>の占める割合（<111>、<100>方位比率）がともに50%未満であることにより、初期ボール形状について、ゴルフクラブ状の強い芯ずれが抑制されていることが確認された。一方、表皮層の表面における<111>、<100>方位比率がともに50%未満である複層構造のボンディングワイヤに関する比較例1〜6では、強い芯ずれが多数確認された。好ましい事例として、<111>、<100>方位比率がともに40%以下である実施例2〜4、6、7、10、11、14〜21、24〜27、29、30では、軽度のものも含めた芯ずれの発生率が低減しており、さらに表皮層の<111>、<100>方位比率がともに30%以下である実施例4、6、10、15、17、20、21、24、27、30では、芯ずれの発生をさらに抑制する効果が確認された。   The bonding wires having a multilayer structure of Examples 1 to 30 are ratios of <111> and <100> in the longitudinal crystal orientation on the surface of the skin layer according to the present invention (<111>, <100> It was confirmed that the strong misalignment of the golf club shape was suppressed for the initial ball shape when both of the (azimuth ratio) were less than 50%. On the other hand, many strong misalignments were confirmed in Comparative Examples 1 to 6 relating to bonding wires having a multilayer structure in which the <111> and <100> orientation ratios on the surface of the skin layer were both less than 50%. As a preferable example, <111> and <100> orientation ratios are both 40% or less in Examples 2 to 4, 6, 7, 10, 11, 14 to 21, 24 to 27, 29, 30. The occurrence rate of misalignment including is further reduced, and the <111> and <100> orientation ratios of the skin layer are both 30% or less in Examples 4, 6, 10, 15, 17, 20, 21, In 24, 27 and 30, the effect of further suppressing the occurrence of misalignment was confirmed.

実施例2〜21、23〜27、29、30の複層構造のボンディングワイヤは、本発明に係わる、表皮層の表面における<111>または<100>の面積比率がともに35％以下であることにより、線径22μmでのボール接合部の偏芯不良を抑えられることが確認された。好ましくは、該面積比率が25％以下である実施例4、6〜12、14〜21、23〜27、30では、線径18μmでのボール接合部の偏芯不良を抑えられ、さらに好ましくは、該面積比率が12％以下である実施例4、8〜10、12、14、15、17、18、20、23、24、26、27では、線径15μmでの偏芯不良を抑えられることが確認された。   In the bonding wires having the multilayer structure of Examples 2 to 21, 23 to 27, 29, and 30, the area ratio of <111> or <100> on the surface of the skin layer according to the present invention is 35% or less. As a result, it was confirmed that the eccentricity failure of the ball joint portion with a wire diameter of 22 μm can be suppressed. Preferably, in Examples 4, 6-12, 14-21, 23-27, and 30 in which the area ratio is 25% or less, the eccentricity of the ball joint at a wire diameter of 18 μm can be suppressed, and more preferably In Examples 4, 8 to 10, 12, 14, 15, 17, 18, 20, 23, 24, 26, and 27 in which the area ratio is 12% or less, it is possible to suppress the eccentricity failure at the wire diameter of 15 μm. It was confirmed.

実施例3〜21、23〜30の複層構造のボンディングワイヤは、本発明に係わる、芯材の断面における<111>と<100>の面積比率の総計が50％以下であることにより、温度200℃での接続において、ウェッジ接合部のめくれ不良を低減できることを確認した。好ましくは、該面積比率が25％以下である実施例4、8〜10、12、14〜18、20、21、23〜27では、温度160℃の低温接続において、ウェッジ接合部のめくれ不良を低減できることを確認した。   The bonding wires having a multilayer structure of Examples 3 to 21 and 23 to 30 have a total temperature ratio of <111> and <100> in the cross section of the core material of 50% or less according to the present invention. In connection at 200 ° C, it was confirmed that the turning failure of the wedge joint could be reduced. Preferably, in Examples 4, 8 to 10, 12, 14 to 18, 20, 21, 23 to 27 in which the area ratio is 25% or less, the wedge joint is not turned over at a low temperature connection of 160 ° C. It was confirmed that it could be reduced.

実施例1〜7、10〜12、15〜17、19〜30の複層構造のボンディングワイヤは、本発明に係わる、芯材の断面における<111>と<100>を合計した方位比率が30％以上であることにより、通常のボール寸法で、ボール接合部の花弁不良を低減して、形状を安定化できることを確認した。好ましくは、該方位比率が50％以上である実施例3、7、10、11、19〜21、23、24、26、29、30では、厳しい接合条件である小径ボールでも、ボール接合部の真円性が向上することを確認した。   The bonding wires of the multilayer structure of Examples 1 to 7, 10 to 12, 15 to 17, and 19 to 30 have an orientation ratio of 30 in total of <111> and <100> in the cross section of the core according to the present invention. It was confirmed that the shape could be stabilized by reducing the petal defect of the ball joint portion with a normal ball size by being at least%. Preferably, in Examples 3, 7, 10, 11, 19-21, 23, 24, 26, 29, and 30 in which the orientation ratio is 50% or more, even in a small-diameter ball that is a severe joining condition, It was confirmed that the roundness was improved.

実施例1〜4、6〜12、14〜23、25〜30の複層構造のボンディングワイヤは、本発明に係わる、表皮層の表面における円周方向の結晶粒サイズの平均が2μm以下であることにより、通常ボール径での初期ボールのサイズのバラツキを低減できることを確認した。好ましくは、該結晶粒サイズが1μm以下である実施例4、8〜10、12、14、15、17、18、20、21、23、27、29では、小ボールでの初期ボールのサイズを安定化できること、より好ましくは、該結晶粒サイズが0.5μm以下である実施例9、10、12、15、17、20では、極小ボールでの初期ボールのサイズを安定化できることを確認した。   The bonding wires having a multilayer structure of Examples 1 to 4, 6 to 12, 14 to 23, and 25 to 30 have an average crystal grain size in the circumferential direction on the surface of the skin layer of 2 μm or less according to the present invention. Thus, it was confirmed that variation in the size of the initial ball at the normal ball diameter can be reduced. Preferably, in Examples 4, 8 to 10, 12, 14, 15, 17, 18, 20, 21, 23, 27, 29 in which the crystal grain size is 1 μm or less, the initial ball size in a small ball is It was confirmed that in Examples 9, 10, 12, 15, 17, and 20 in which the crystal grain size was 0.5 μm or less, the size of the initial ball with a very small ball could be stabilized.

複層構造のボンディングワイヤ（線径25μｍ）のEBSP測定結果 （ワイヤ長手方向に<111>、<100>方位に配向した領域を着色。結晶粒界を線表示）EBSP measurement result of multi-layered bonding wire (wire diameter 25μm) (colored in the <111> and <100> orientations in the longitudinal direction of the wire. The crystal grain boundaries are shown as lines)

Claims (8)

導電性金属からなる芯材と、前記芯材の上に芯材とは異なる金属を主成分とする表皮層を有する半導体装置用ボンディングワイヤであって、前記表皮層の金属が面心立方晶であって、前記表皮層の表面の結晶面における長手方向の結晶方位<hkl>のうち、<111>と<100>の占める割合が、ともに50%未満であることを特徴とする半導体装置用ボンディングワイヤ。 A bonding wire for a semiconductor device having a core material made of a conductive metal and a skin layer composed mainly of a metal different from the core material on the core material, wherein the metal of the skin layer is a face centered cubic crystal Wherein the ratio of <111> and <100> in the longitudinal crystal orientation <hkl> in the crystal plane of the surface of the skin layer is less than 50%, Wire. 前記表皮層の表面におけるワイヤ長手方向の結晶方位が<111>または<100>である結晶粒の面積が、ワイヤ表面の総面積に対する割合として、ともに35%以下であることを特徴とする請求項1に記載の半導体装置用ボンディングワイヤ。 The area of the crystal grains having a crystal orientation of <111> or <100> in the wire longitudinal direction on the surface of the skin layer is 35% or less as a percentage of the total area of the wire surface. 2. A bonding wire for a semiconductor device according to 1. 前記表皮層の表面におけるワイヤ長手方向の結晶方位が<111>または<100>である結晶粒の面積の総計が、ワイヤ表面の総面積に対する割合として、50%以下であることを特徴とする請求項1又は2に記載の半導体装置用ボンディングワイヤ。 The total area of crystal grains whose crystal orientation in the longitudinal direction of the wire on the surface of the skin layer is <111> or <100> is 50% or less as a ratio to the total area of the wire surface, Item 3. A bonding wire for a semiconductor device according to Item 1 or 2. 前記芯材の断面の結晶面におけるワイヤ長手方向の結晶方位<hkl>のうち、<111>と<100>との占める割合の総計が30%以上であることを特徴とする請求項1又は2に記載の半導体装置用ボンディングワイヤ。 3. The total proportion of <111> and <100> in the crystal orientation <hkl> in the wire longitudinal direction in the crystal plane of the cross section of the core material is 30% or more, The bonding wire for semiconductor devices as described in 2. 前記表皮層の表面における、円周方向の結晶粒サイズの平均が2μm以下であることを特徴とする請求項1〜4のうちいずれか1項に記載の半導体装置用ボンディングワイヤ。 5. The bonding wire for a semiconductor device according to claim 1, wherein an average crystal grain size in a circumferential direction on the surface of the skin layer is 2 μm or less. 前記表皮層を構成する主成分がPd、Pt、Ruの少なくとも１種であることを特徴とする請求項1〜5のうちいずれか1項に記載の半導体装置用ボンディングワイヤ。 6. The bonding wire for a semiconductor device according to claim 1, wherein a main component constituting the skin layer is at least one of Pd, Pt, and Ru. 前記芯材を構成する主成分がCu、Auの少なくとも１種であることを特徴とする請求項1〜6のいずれか1項に記載の半導体装置用ボンディングワイヤ。 7. The bonding wire for a semiconductor device according to claim 1, wherein a main component constituting the core material is at least one of Cu and Au. 前記表皮層と前記芯材の間に、前記表皮層及び前記芯材を構成する主成分とは異なる成分からなる中間金属層を有することを特徴とする請求項1〜7のうちいずれか1項に記載の半導体装置用ボンディングワイヤ。 8. The method according to claim 1, further comprising an intermediate metal layer made of a component different from a main component constituting the skin layer and the core material, between the skin layer and the core material. The bonding wire for semiconductor devices as described in 2.
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