JP2007123597A - Bonding wire for semiconductor devices - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper bonding wire for semiconductor devices which is excellent in ball bonding properties, wedge bonding properties, loop controllability, chip damage etc. for a semiconductor etc. with a large diameter for use in a power IC, and a semiconductor etc. for which a low cost is top priority. <P>SOLUTION: The bonding wire for a semiconductor devices has a core material which makes more than one kind among silver, gold, palladium, platinum, and aluminum serve as a major component, and a skin layer on the core material which makes a conductive metal having the composition different from that of the core material serve as a major component. The thickness of the skin layer is in the range of 0.001-0.09 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bonding wire for a semiconductor device used for connecting an electrode on a semiconductor element and a wiring of a circuit wiring board (lead frame, substrate, tape).

  Currently, fine wires (bonding wires) having a wire diameter of about 20 to 50 μm are mainly used as bonding wires for bonding between electrodes on semiconductor elements and external terminals. Bonding wires are generally joined by ultrasonic thermocompression bonding, and a general-purpose bonding apparatus, a capillary jig used for connecting the wires through the inside, or the like is used. After the wire tip is heated and melted by arc heat input and a ball is formed by surface tension, this ball portion is pressure bonded onto the electrode of the semiconductor element heated within the range of 150 to 300 ° C., and then directly The wire is bonded to the external lead side by ultrasonic pressure bonding.

  In recent years, the structure, materials, connection technology, etc. of semiconductor mounting have been diversified rapidly. For example, in the mounting structure, in addition to QFP (Quad Flat Packaging) using the current lead frame, a substrate, polyimide tape, etc. are used. New forms such as BGA (Ball Grid Array) and CSP (Chip Scale Packaging) have been put into practical use, and there is a demand for bonding wires with improved loop characteristics, bondability, mass production usability, and the like. In such wire connection technology, in addition to the current mainstream ball / wedge joints, wedge / wedge joints suitable for narrow pitches join the wires directly at two locations, so it is necessary to improve the jointability of fine wires. It is done.

  The materials to which bonding wires are bonded are diversified, and in addition to conventional Al alloys, Cu suitable for finer wiring has been put to practical use as wiring and electrode materials on silicon substrates. In addition, Ag plating, Pd plating, etc. are applied on the lead frame, and Cu wiring is applied on the resin substrate, tape, etc., and noble metal elements such as gold and alloys thereof are formed thereon. In many cases, a film is applied. It is required to improve the bondability of the wire and the reliability of the joint according to these various joining partners.

  In the demand from the wire bonding technology, it is important to form a ball having good sphericity when forming the ball and obtain a sufficient bonding strength at the bonding portion between the ball portion and the electrode. Further, in order to cope with a decrease in the bonding temperature, thinning of the wire, etc., it is necessary to have a bonding strength, a tensile strength, and the like at a portion where the wire is wedge-connected to the wiring portion on the circuit wiring board.

  In the resin sealing process in which high-viscosity thermosetting epoxy resin is injected at high speed, the wire deforms and comes into contact with the adjacent wire, and further, while narrow pitch, long wire, and thinning are progressing, It is required to suppress even a little wire deformation during resin sealing. Although the deformation can be controlled to some extent by increasing the wire strength, it is difficult to put it to practical use unless problems such as loop control becomes difficult and the strength at the time of bonding decreases.

  As a wire characteristic that satisfies these requirements, loop control in the bonding process is easy, and bondability to the electrode and lead parts has also been improved, suppressing excessive wire deformation in the resin sealing process after bonding. It is desirable to satisfy comprehensive characteristics such as

  As a material of the bonding wire, high purity 4N-based (purity> 99.99 mass%) gold is mainly used for a semiconductor sealed with an epoxy resin that is most frequently used. There is a desire for bonding wires of other types of metals that have low material costs.

  Silver, palladium, platinum, aluminum, etc. are promising materials that have some features such as material cost, electrical conductivity, bondability, and long-term reliability. Regarding the advantages of each material, silver is inexpensive and can be melted in the air, palladium can be easily strengthened, platinum can delay the diffusion of the bonding interface and improve bonding reliability, and aluminum can be used as a frame. For example, the joint strength of the same-type metal joint is improved. However, the reason why the practical use of bonding wires made of these materials has not progressed is the problem of oxidation / corrosion of the wire surface, oxidation during ball formation, reduction of bonding strength, and corrosion of the wire surface when resin-sealed. Is likely to occur. Aluminum wires have been used for a long time in ceramic packages, large diameter applications, etc., but their usage such as wedge / wedge bonding is limited.

  In another method for achieving high strength, a bonding wire (hereinafter referred to as a two-layer bonding wire) made of a metal having a different core portion and outer peripheral portion has been proposed. For example, in Patent Document 1, a silver core is covered with gold. Patent Document 2 discloses a wire in which the core portion is a conductive metal and the surface is gold-plated, and Patent Document 3 discloses a wire having a platinum / platinum alloy core and a silver / silver alloy outer periphery thereof. ing. These are difficult to obtain with a wire (hereinafter referred to as a single-layer bonding wire) composed of a single member in which all general-purpose products fall within the category by combining different metals in the core and the outer periphery. It is expected that the above characteristics will be satisfied comprehensively.

JP-A-4-79241 JP 59-155161 A JP-A-4-79246

  Multi-layer structure with wire surface coated with dissimilar metals for the purpose of increasing the practicality of silver, gold, palladium, platinum, and aluminum bonding wires with the aim of suppressing wire surface oxidation, increasing bonding strength, and suppressing wire deformation Is possible.

  However, such a two-layer bonding wire in which the core wire and its outer peripheral portion are made of different metals has not been put into practical use so far, and practical examples evaluated in actual semiconductors have hardly been reported. It is. The reason for this is that it is difficult to manufacture, control quality, etc. with metals with different cores and outer peripheries, and it is difficult to comprehensively satisfy many wire requirements even if specific characteristics are improved. It is mentioned.

  The present inventors have evaluated the semiconductor packaging in consideration of needs such as high density, downsizing, and thinning. As a result, a conventional two-layer wire having a structure in which the surface of the core material is covered with an outer peripheral portion (hereinafter, conventional) It was found that there are many practical problems that will be described later.

  Conventionally, when a ball is formed at the tip of a two-layer wire, there is a problem that a flat ball deviated from a true sphere is formed, or an unmelted wire remains in the ball. If such an abnormal ball portion is bonded onto the electrode, it may cause problems such as displacement of the bonding position and chip damage.

  Conventionally, when complex loop control or the like is performed with a two-layer wire, problems such as separation at the interface between the outer peripheral portion and the core material and unstable loop shape depending on the wiring direction of the wire occur. In particular, in a narrow pitch connection, there is a concern that adjacent wires may cause an electrical short.

  In order to promote the practical application of multi-layered wires, it is well adapted to thick wires with a diameter of 50 μm or more, which are not often used with gold wires for power IC applications, while fine wires with a diameter of 20 μm or less for high-density connections. In terms of characteristics, it is necessary to adapt to stricter requirements than the improvement of thick line bonding, small pitch small ball bonding, low temperature bonding, reverse bonding of multilayer chip connection, and the like.

  Therefore, in the present invention, the problems of the prior art as described above are solved, the ball section formability and bondability are improved, the loop controllability is good, the joint strength of wedge connection is increased, and the industrial productivity is improved. Another object of the present invention is to provide a bonding wire for a semiconductor device having a multilayer structure that can be secured.

(1) Bonding having a core material mainly composed of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer mainly composed of a conductive metal different from the main component element on the outside of the core material. A bonding wire for a semiconductor device, wherein the thickness of the outer skin layer is in the range of 0.001 to 0.09 μm.
(2) Bonding having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component and an outer skin layer containing a conductive metal different from the main component as the main component on the outside of the core. A bonding wire for a semiconductor device, wherein the outer skin layer contains a total concentration of additive elements in a range of 0.0001 to 0.02 mol% and a thickness in a range of 0.001 to 0.09 μm.
(3) Thickness of a core material composed mainly of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer composed mainly of a conductive metal different from the main component element on the outside of the core material Is a bonding wire having a range of 0.001 to 0.09 μm, and the total concentration of the conductive metal in the entire wire is in the range of 0.002 to 1.0 mol%.
(4) A conductive metal concentration gradient region is provided in the wire radial direction in the vicinity of the boundary between the outer skin layer and the core material, and the thickness of the concentration gradient region is in the range of 0.001 to 0.09 μm. (1) -The bonding wire for semiconductor devices in any one of (3).
(5) In the middle of the outer skin layer and the core material, the conductive metal concentration gradient region in the wire radial direction, and the main constituent elements constituting the core material and the conductive metal constituting the outer skin layer. The bonding wire for a semiconductor device according to any one of (1) to (3), which has at least one intermetallic compound layer containing one or more of each.
(6) Bonding having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component and an outer skin layer containing a conductive metal different from the main component as the main component on the outside of the core. A bonding wire for a semiconductor device, wherein a thickness of a region having a conductive metal concentration of 40 mol% or more in the outer skin layer is 0.001 to 0.08 μm.
(7) A bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component and an outer skin layer containing a conductive metal different from the main component on the outside of the core. In the outer skin layer, the maximum concentration of the conductive metal has a concentration gradient of the conductive metal in the wire radial direction in the range of 50 to 100 mol%, and the thickness of the concentration gradient region is 0.001 to 0.001. A bonding wire for a semiconductor device having a range of 0.08 μm.
(8) Bonding having a core material mainly composed of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer mainly composed of a conductive metal different from the main component element on the outside of the core material. For a semiconductor device according to any one of (4) to (7), wherein a thickness of a region having a constant conductive metal concentration in the wire radial direction in the vicinity of the surface of the outer skin layer is 0.07 μm or less. Bonding wire.
(9) The bonding wire for a semiconductor device according to any one of (1) to (8), wherein the conductive metal constituting the outer skin layer is at least one selected from gold, palladium, platinum, silver, or aluminum. .
(10) The bonding wire for a semiconductor device according to any one of (1) to (8), wherein the conductive metal and the main component elements are concentrated on the surface of the outer skin layer.
(11) The core material contains one or more additive elements selected from Ba, Ca, Sr, Be, Ge, Sn, In or rare earth elements, and the concentration of the additive elements in the entire wire is 0. The bonding wire for a semiconductor device according to any one of (1) to (8), which is in the range of 0001 to 0.03 mass%.

  The bonding wire for a semiconductor device of the present invention has an excellent ball bondability, wire bondability, etc., and a good loop forming property, a multilayer structure suitable for narrow pitch thinning and power IC use. A bonding wire for a semiconductor device can be provided.

  The present invention provides a bonding material having a core material composed mainly of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer composed mainly of a conductive metal different from the main component element on the outside of the core material. A bonding wire characterized in that the outer skin layer is thin. Further improvements include keeping the total concentration of additive elements in the skin layer low, keeping the total concentration of conductive metals in the entire wire low, having a concentration gradient region between the skin layer and the core, It is also effective to optimize the concentration distribution of the conductive metal in the skin layer. With these bonding wires, the ball section formability and bondability are improved, loop controllability is good, the bonding strength of the wedge connection is increased, and the bonding wire has a multilayer structure with excellent industrial productivity. Can do.

  By using an element in which the main component element of the core material is different from the conductive metal of the outer skin layer, it is possible to increase the added value such as increasing the strength and preventing oxidation compared to the single-layer wire, but in the actual bonding process, there is no ball. It was confirmed that defects such as stable formation, chip damage during ball bonding, and variations in loop shape often occur. In addition to conventional general-purpose needs, new mounting needs such as thick wire connection, small pitch small ball bonding, low temperature bonding, reverse bonding of multilayer chip connection, and further improvement of mass production adaptability such as expansion of manufacturing margin We have found that the control of the thickness of the outer skin layer is effective by developing a wire that can be used.

  That is, a bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element and an outer skin layer mainly containing a conductive metal different from the main component element on the outer side of the core material. And it is a bonding wire whose thickness of an outer skin layer is the range of 0.001-0.09 micrometer. If the thickness of the outer skin layer is in the above range, the effect of greatly improving the sphericity of the ball part, the bonding shape of the press-bonded ball part, etc. is obtained, and the loop controllability such as low loop and long span is excellent, In addition, it is possible to sufficiently secure the effect of enhancing the wire bondability, the wire strength, and the like, which are expected for a multilayer structure. In addition, productivity problems when the plating thickness is large can be solved. Here, if the thickness of the outer skin layer is thick, functions such as surface protection and bonding buffering are expected, but if it exceeds 0.09 μm, the ball formability is drastically reduced and the concentricity of the wire cross section is based on mass production. In addition, if it is less than 0.001 μm, the effect of improving the wire strength, bondability and the like cannot be obtained compared to a single-layer wire, and the film thickness is accurately controlled because it is too thin. This is because it becomes difficult. Preferably, when the thickness of the outer skin layer is in the range of 0.002 to 0.07 μm, variation in ball diameter can be reduced, which is advantageous for forming a small ball. More preferably, if it is in the range of 0.005 to 0.05 μm, it is possible to sufficiently improve the stability during wire production, and a large diameter for power IC use with a wire diameter of 50 to 100 μm and a wire diameter of 15 to 20 μm. It can cover a wide range of mounting needs such as narrow pitch thin wires. Even more preferably, in the range of 0.008 to 0.03 μm, the effect of improving the surface irregularities and reducing the eccentric balls is enhanced by stabilizing the dissolution and solidification of the balls. These various relationships between the film thickness of the outer skin layer and the usage characteristics are similarly applied to bonding wires having an outer skin layer and a core material configured as described later.

  Here, the main component is a main element that constitutes a member such as an outer skin layer or a core material. As a guide, the concentration is 30 mol% or more. If it is above this concentration, it will dominate most of the properties of the member, so it is distinguished from additive elements.

  If the main component of the core material is one of silver, gold, palladium, and platinum, balls can be easily formed even by arc discharge in the atmosphere. If aluminum is used, bonding to the aluminum electrode on the substrate is possible. There are advantages such as reliability and low material cost. Moreover, even an alloy containing two or more of silver, gold, palladium, platinum, and aluminum is effective in increasing tensile strength and reducing material costs.

  In order to effectively bring out the characteristics of the wire having the structure of the outer skin layer and the core material according to the present invention, when the core material is silver, gold, palladium, or platinum, the ball / Wedge bonding is advantageous, and in the case of aluminum, wedge / wedge bonding is advantageous because ball formation in the atmosphere is difficult.

  The conductive metal of the outer skin layer is premised on being different from the main component element of the core material, but the candidate element is preferably one or more selected from gold, palladium, platinum, silver or aluminum. Among them, gold, palladium, platinum, and silver have sufficient conductivity and can be used for high-frequency semiconductor devices. In addition, gold has advantages in that it has many achievements in adhesion to the sealing resin, bondability to electrodes, etc., and quality control is easy. Silver is advantageous in that it is relatively inexpensive, has little surface oxidation, and provides good bonding properties with silver plating frequently used on the surface of the frame. Palladium and platinum have the effect of stabilizing the ball shape. With aluminum, high bondability with an aluminum electrode can be obtained.

  Specific examples of the combination of the main elements of the outer skin layer / core material are excellent in the high temperature reliability of the joint portion with the aluminum electrode if each is a gold / silver system, gold / aluminum system, platinum / aluminum If it is a system, surface oxidation can be suppressed. If it is a palladium / silver system, the ball shape is stable and good. If it is a silver / platinum system, the bondability with the silver plating on the lead is improved. Features can be used.

  The boundary between the outer skin layer and the core material is an area where the total concentration of the conductive metals constituting the outer skin layer is 10 mol% or more. This is based on the fact that the effect of improving the characteristics can be expected from the structure of the outer skin layer of the present invention, and the concentration of the conductive metal often changes continuously. Therefore, the concentration of the conductive metal was set to 10 mol% or more. Preferably, in the region of 15 mol% or more, quantitative analysis is simple due to improved measurement accuracy, so quality assurance and the like are relatively easy and mass production adaptability is high.

  The composition of the outer skin layer is also important. The core material is composed of a core material mainly composed of one or more of silver, gold, palladium, platinum, and aluminum and the outer skin layer mainly composed of a conductive metal different from the main component element. A bonding wire having a total concentration of additive elements of 0.02 mol% or less and a thickness in the range of 0.001 to 0.09 μm. Further improvement can be made and the replacement life of the capillary can be increased. This is because if the total concentration of the additive elements in the outer skin layer is less than 0.0001 mol%, the effect of improving the bondability and the capillary exchange life cannot be obtained, and it is below the lower limit of analysis of the trace elements contained in the thin outer skin layer. Because. Also, if it exceeds 0.02 mol%, the additive element delays the diffusion at the interface of the wedge bonding, thereby lowering the low-temperature bonding property and causing the surface of the outer skin layer to harden or oxidize. This is because there is a concern that the inner wall, tip, etc. of the capillary may become dirty or worn inside. In addition, the lower the total concentration of the additive elements in the outer skin layer, the higher the electrical conductivity, and it can be applied to high frequency ICs such as kigahertz. Here, the additive element of the outer skin layer has a slightly different effect depending on the conductive metal, but among the elements that are relatively easy to use, rare earth elements (Ce, La, Eu, Pr, Nd), Cu, Be, Ca, Cr, By containing Mn, Ni and the like in a total concentration range of 0.02 mol% or less, it is effective for increasing the wire strength and controlling the wire deformation.

  A core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element, and an outer skin layer containing a conductive metal as a main component different from the main component element on the outer side of the core material has a thickness of 0.001 Bonding wire having a range of ˜0.09 μm, and a bonding wire having a total concentration of conductive metal occupying the entire wire in the range of 0.002 to 1.0 mol%, while improving wedge bondability, Curing of the ball portion can be suppressed or the bonding strength can be increased. It has been found that the hardness and bondability of the ball portion formed by melting the wire are mainly influenced by the concentration of the conductive metal in the outer skin layer. If the total concentration of the conductive metal occupying the entire wire is in the above range, there are sufficient effects such as suppressing the sweep of the aluminum electrode film during ball bonding to increase the bonding strength and reducing chip damage directly under the ball. can get. By keeping the conductive metal concentration in the entire wire low, even if the conductive metal contained in the outer skin layer is dissolved in the ball, the degree of curing can be suppressed and chip damage can be reduced. . Here, when the outer skin layer having a thickness of less than 0.002 mol% and having the above thickness is formed, there is a concern that the protective function may be deteriorated because the outer skin layer is damaged by the strict loop control and the core material is exposed. . On the other hand, when the electrode is an Al thin film, low-k dielectric film / Cu wiring, etc., if it exceeds 1.0 mol%, damage to the chip or low-k film directly below the ball, reduction in bonding strength, etc. will be problematic. Because. Preferably, if the total concentration of the conductive metal in the entire wire is in the range of 0.003 to 0.6 mol%, the effect of reducing damage is further improved.

  Although it is not easy to measure the thickness of the outer skin layer on the order of 0.001 μm and manage the mass production, the measurement of the total concentration of the conductive metal in the entire wire uses an existing analysis method such as ICP analysis. Thus, measurement can be performed relatively easily and with high accuracy, and production variations can be managed. Further, since the measurement of the total concentration is used in combination with the thickness measurement, the measurement error of the thickness of the outer skin layer can be suppressed to a low level. Therefore, the total concentration is a very effective index for practical use.

  It is also effective to have a concentration gradient in the outer skin layer. That is, by having a conductive metal concentration gradient in the wire radial direction between the outer skin layer and the core material, the adhesion between the core material and the outer skin layer is improved compared to the case where the conductive metal concentration distribution is uniform. And the improvement of the wedge bondability of a wire can be improved simultaneously. In a specific configuration example, a core material mainly composed of one or more of silver, gold, palladium, platinum, and aluminum, and an outer skin layer mainly composed of a conductive metal different from the main component element are formed of the core material. A bonding wire provided outside, wherein the concentration gradient region has a thickness in the range of 0.001 to 0.09 μm, and a conductive metal concentration gradient in the wire radial direction between the outer skin layer and the core material. Bonding wires having regions are preferred. With regard to the effect of adhesion, a stable loop shape can be obtained even by loop control that combines the bending, bending, straight line and the like of the wire in a complicated manner. This is because if the thickness of the concentration gradient region is less than 0.001 μm, it is difficult to manage the thickness variation at the time of manufacture, and if it exceeds 0.09 μm, there is a concern about deterioration of electrical characteristics due to high frequency applications, thinning, and the like. Preferably, if it is 0.05 μm or less, the loop shape can be stabilized even with a short span of 1 mm or less while increasing the strength of the wedge joint.

  The concentration gradient in the outer skin layer is desirably such that the degree of concentration change in the depth direction is 10 mol% or more per 1 μm. If this change is exceeded, the above-described improvement effect can be expected, and the results of good reproducibility can be obtained in terms of the accuracy of quantitative analysis. Preferably, if it is 10 mol% or more per 0.01 μm, even if the thickness of the outer skin layer is as thin as less than 0.01 μm, a high effect of satisfying both an increase in wire strength and an improvement in bonding strength can be obtained.

  The region of the conductive metal concentration gradient is not necessarily uniform and may be partial. In the case of having a plurality of conductive metals, if at least one of the conductive metals has a concentration gradient, characteristics such as bondability and loop control can be improved. For example, one type of conductive metal has a significant concentration gradient, and another type of conductive metal exists mainly on the outermost surface, and the concentration gradient is small, so that conflicting performance such as bonding properties and anti-oxidation is improved. Is also possible.

  If the concentration gradient tends to decrease in the depth direction from the surface, it is advantageous for improving the adhesion between the outer skin layer and the core material. With respect to the method of forming this concentration gradient, if the layer is formed by diffusion, there are advantages such as low possibility of defects such as local peeling and cracking, and easy formation of continuous concentration changes, etc. This is because there are many.

  From the viewpoint of productivity and quality stability, it is preferable that the concentration gradient is continuously changed. That is, the degree of the gradient of the concentration gradient does not necessarily have to be constant within the outer skin layer and may change continuously.

  In addition to the concentration gradient, it is also effective for the outer skin layer to contain an intermetallic compound phase mainly composed of main component elements and conductive metals. That is, in the middle of the outer skin layer and the core material, the conductive metal concentration gradient region in the wire radial direction and the conductive metal constituting the outer skin layer and the main component element constituting the core material are each one kind. By having at least one intermetallic compound layer contained above, in addition to improving the wedge bondability, the mechanical properties such as the strength and elastic modulus of the wire are increased, and the linearity of the loop is improved. This is effective for suppressing wire flow. Preferably, the thickness of the intermetallic compound layer is in the range of 0.001 to 0.03 μm. Here, when the thickness is less than 0.001 μm, the effect of increasing the wire strength is small, and when it exceeds 0.03 μm, the loop controllability is lowered.

  A bonding wire having a core material composed mainly of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer composed mainly of a conductive metal different from the main component element on the outside of the core material. In the case of a bonding wire having a conductive metal concentration of 40 mol% or more in the outer skin layer and having a thickness of 0.001 to 0.08 μm, the neck breaking strength in the pull test is improved while improving the wedge bondability. Effective for climbing. The neck portion usually decreases in strength due to the heat effect during ball formation. On the other hand, a conductive metal layer having a relatively high concentration of 40 mol% or more acts as a supply source for diffusing the conductive metal into the wire in the process of thermal influence, thereby increasing the strength of the neck portion. Conceivable. As a basis for the concentration and thickness, if the concentration is in the region of 40 mol% or more, the above-described diffusion supply action can be sufficiently expected, and if the thickness is less than 0.001 μm, these improvement effects are small. If the thickness exceeds 0.08 μm, chip damage, reduction of bonding strength, and the like become problems.

  A bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element and an outer skin layer containing a conductive metal different from the main component element on the outer side of the core material, In the skin layer, a bonding wire in which the maximum concentration of the conductive metal is in the range of 50 to 100 mol% and the thickness of the region having the conductive metal concentration gradient in the wire radial direction is in the range of 0.001 to 0.08 μm. If it exists, in addition to the improvement of wedge bondability, high effects such as suppressing anisotropic deformation when the ball is ultrasonically bonded and improving the roundness of the ball bond can be obtained. This is because by suppressing the conductive metal concentration in the outer skin layer to a low level, arc discharge can be concentrated on the tip of the wire, and melting can be performed almost in parallel with the outer skin layer and the core material, thereby suppressing unmelted parts. This is probably because the solidified structure is also made uniform. The reason for the concentration and thickness is that if the copper concentration on the outermost surface is 50 mol% or more, arc discharge and melting behavior are stabilized. Moreover, if the thickness of the region having the concentration gradient of the conductive metal is 0.001 μm, the above-described effects are enhanced, and if it exceeds 0.08 μm, the wedge bondability at a low temperature of less than 200 ° C. is deteriorated. It is to do. More preferably, even in the concentration gradient region in addition to the outermost surface, the effect in ball formation and bonding can be further enhanced by always setting the conductive metal concentration to 40 mol% or less.

  A bonding wire having a core material composed mainly of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer composed mainly of a conductive metal different from the main component element on the outside of the core material. If the bonding wire has a constant thickness of the conductive metal in the wire radial direction in the vicinity of the surface of the outer skin layer and has a thickness of 0.07 μm or less, a high effect of increasing the adhesion strength of wedge bonding can be obtained. For the constant concentration region, it is desirable that the average value is 60 mol% or more and the concentration difference is suppressed to 5% or less in the range of 0.001 μm or more. The reason for this thickness is that if the thickness exceeds 0.07 μm, deformation during ball formation tends to occur. Preferably, if the thickness is 0.05 μm or less, the sag failure of the wedge joint is improved. With regard to the effects, adhesion with the electrode film that is the bonding partner is increased by promoting diffusion in a region where the conductive metal concentration is constant in heat application during bonding, local heating by ultrasonic vibration, and the like. it is conceivable that.

  The core material contains one or more additive elements selected from Ba, Ca, Sr, Be, Ge, Sn, In or rare earth elements, and the concentration of the additive elements in the entire wire is 0.0001 to 0.03 in total By being in the range of mass%, the additive element in the core material synergizes with the conductive metal at the time of ball formation, and has the effect of further improving the roundness at the time of ball deformation. Regarding such an additive effect, it can be seen that the effect is enhanced when the outer skin layer and the additive element are used in combination, compared with the case where the outer skin layer is not formed and the conventional single layer wire is added. It was issued. If the concentration of the additive element is less than 0.0001% by mass, the above-described improvement effect is small, and if it exceeds 0.03% by mass, a shrinkage nest is generated at the tip of the ball and the ball shape becomes unstable. This is because it is difficult to improve the shape and bonding strength of the ball even if the outer skin layer is thinned.

  Regarding the distribution of elements on the surface of the outer skin layer described so far, if the conductive metal and the main component elements are bonding wires with concentrated concentration, in addition to improving wedge bondability, good sphericity in forming small balls It is advantageous to form a simple ball. For example, for general-purpose gold wire, there are many problems in mass production. Furthermore, it is difficult to realize with a general-purpose gold wire, such as a narrow pitch of 50 μm or less, and small ball bonding with a crimped ball diameter of 2.3 times or less of the wire diameter. Can also be supported. The structure of concentration unevenness may be a microscopically distributed region where the concentration of the conductive metal or the main component element is distributed in an island shape, or there may be an amorphous high concentration region. The degree of density deviation is desirably a density difference of 10% or more, and the magnitude is desirably a density distribution in the range of 0.002 to 1 μm. Since the ball stabilization due to the concentration deviation is highly effective when the outer skin layer is thick, any bonding wire having a relatively thin outer skin layer structure according to the present invention described above is sufficient. It was confirmed that the effect was obtained. The mechanism of ball stabilization is not clear, but there are concerns about the phenomenon that the electron emission of arc discharge spreads over a wide area of the outer skin layer, which is feared to occur in the outer skin layer and the multilayer wire of the core material. It is expected that the arc discharge is more concentrated in a certain region at the tip of the wire due to the concentration of the component elements.

  For the concentration analysis of the wire, a method of analyzing the wire surface while digging in the depth direction by sputtering or the like, or a line analysis or a point analysis at the wire cross section is effective. The former is effective when the outer skin layer is thin, but if it is thick, it takes too much measurement time. The analysis of the latter cross section is effective when the outer skin layer is thick, and the advantage is that the concentration distribution over the entire cross section and the reproducibility confirmation in several places are relatively easy. When the outer 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 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. . EPMA, EDX, Auger spectroscopic analysis, a transmission electron microscope (TEM), etc. can be utilized in the analysis apparatus used for these concentration analyses. 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 addition, in order to indirectly grasp the thickness of the outer skin layer, it is relatively easy to measure the total concentration of conductive metals in the entire wire by ICP analysis and convert it to a film thickness. It is a technique. However, since information such as the concentration distribution of the outer skin layer cannot be obtained, for example, the thickness is converted on the assumption that the conductive metal concentration of the outer skin layer is constant. The measurement result of the content concentration is not used alone, but can be used in combination with the thickness measurement, so that the measurement error of the thickness of the outer skin layer can be kept low.

  In producing the wire of the present invention, a step of forming the core material and the outer skin layer, a concentration gradient of the main component elements in the outer skin layer, and a heat treatment step exposed to the outermost surface are required.

  Examples of methods for forming the outer skin layer on the surface of the core include plating, vapor deposition, and melting. As the plating method, either electrolytic plating or electroless plating can be used. Electrolytic plating called strike plating or flash plating has a high plating speed and good adhesion to the substrate. 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, reduction type plating is used after substitutional plating. It is effective to apply stepwise. The electroless method is simple and easy to use, but requires more time than the electrolysis method.

  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.

  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 in the latter film formation and wire drawing, it is advantageous to improve 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 wire in an electrolytic plating solution on a wire having a target wire diameter, or a thick wire in an electrolytic or electroless plating bath After forming the film by dipping, a method of drawing the wire to reach the final diameter is possible.

  A diffusion heat treatment by heating is effective as a step of using the outer skin layer and the core material formed by the above-described method and exposing the concentration gradient of the main component elements in the outer skin layer and the main component elements on the outermost surface. This is a heat treatment for promoting mutual diffusion between the main component element and the conductive metal at the interface between the outer skin layer and the core material. The method of performing heat treatment while continuously sweeping the wire is excellent in productivity and quality stability. However, the distribution of the main component elements on the surface and inside of the outer skin layer cannot be controlled simply by heating the wire. Even if the processing strain relief annealing used in normal wire manufacturing is applied as it is, loop control becomes unstable due to a decrease in the adhesion between the outer skin layer and the core material, and wire scraps accumulate inside the capillary and clog. In addition, it is difficult to completely solve problems such as occurrence of oxidization and oxidation of main component elements exposed on the surface to decrease bonding strength. Therefore, it is important to control the temperature, speed, time, etc. of the heat treatment.

As a preferred heat treatment method, the heat treatment is performed while continuously sweeping the wire, and the temperature in the furnace is not constant, which is a general heat treatment. It becomes easy to mass-produce a wire having an outer 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 wire, it is also effective to heat while flowing an inert gas such as N ₂ or Ar into the furnace.

  In the temperature gradient method, a positive temperature gradient near the furnace inlet (temperature rises with respect to the wire sweep direction), a stable temperature range, and a negative temperature gradient near the furnace outlet (temperature falls with respect to the wire sweep direction) Etc.), it is effective to incline the temperature in a plurality of regions. This improves adhesion without causing separation between the outer skin layer and the core material in the vicinity of the furnace inlet, and promotes diffusion of the main component element and conductive metal in a stable temperature range to form a desired concentration gradient Furthermore, by suppressing excessive oxidation of the main component elements on the surface in the vicinity of the furnace outlet, it is possible to improve the bondability and loop controllability of the obtained wire. In order to obtain such an effect, it is desirable to provide a temperature gradient at the entrance / exit of 10 ° C./cm or more.

  In the method of changing the temperature, it is also effective to create a temperature distribution by dividing the furnace into a plurality of regions and performing different temperature control in each region. For example, the inside of the furnace is divided into three or more locations, temperature control is performed independently, and both ends of the furnace are set to a temperature lower than that of the central portion, so that the same improvement effect as in the case of the temperature gradient can be obtained. Moreover, in order to suppress the surface oxidation of a wire, the joint strength of a wedge-joint part can be raised by making the both ends or exit side of a furnace into low temperature with a slow oxidation rate of a main component element.

  Heat treatment with such a temperature gradient or temperature distribution is desirably performed at the final wire diameter in terms of productivity. On the other hand, by performing wire drawing after the heat treatment, the surface oxide film is removed at a low temperature. The effect of reducing wire scraping inside the capillary can be obtained by improving the bondability and further using wire drawing and strain relief annealing.

  In addition, the melting method is a method in which either the outer skin layer or the core material is melted and cast, and it is excellent in productivity by drawing after connecting the outer skin layer and the core material with a large diameter of about 1 to 50 mm. Compared to plating and vapor deposition, the alloy component design of the outer skin layer is easy, and there are advantages such as easy improvement of properties such as strength and bondability. In a specific process, a melted conductive metal is cast around a core wire prepared in advance to form an outer 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 a component element or an alloy thereof. Preferably, it is easier to stably form a concentration gradient or the like of the main component element in the outer skin layer by casting the core material inside the latter hollow cylinder. Here, if a small amount of the main component element is contained in the previously produced outer skin layer, the concentration distribution on the surface of the outer skin layer can be easily controlled. In the melting method, the heat treatment operation can be omitted, but further improvement in characteristics can be expected by performing heat treatment to adjust the concentration distribution in the outer skin layer.

  Furthermore, when using such a molten metal, it is also possible to manufacture at least one of the core wire and the outer skin layer 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.

  Examples will be described below.

  As raw materials for the bonding wires, silver, gold, palladium, platinum, and aluminum used for the core material and the outer skin layer were high-purity materials having a purity of about 99.99% by mass or more.

  In order to form a different conductive metal layer on the surface of a wire that has been thinned to a certain wire diameter, an electroplating method, electroless plating method, vapor deposition method, melting method, etc. are used to form a concentration gradient. In order to do so, heat treatment was performed. The case where the outer skin layer was formed with the final wire diameter and the method of forming the outer skin layer with a certain wire diameter and further reducing 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. The film forming conditions for controlling the film quality, film thickness, etc. were controlled by controlling the plating solution concentration, current value, time, temperature, etc. for electroplating, and the plating solution concentration, time, temperature, etc. for electroless plating. When plating on a thick rod-shaped core wire having a diameter of 1 mm or more, an outer skin layer was formed by dipping in a plating solution. Further, a wire having a diameter of about 50 to 200 μm was prepared, and the film was formed while continuously moving the wire in the plating solution or in the vapor deposition apparatus, and the wire was drawn to a final diameter of 15 to 75 μm. The diffusion heat treatment process uses two processes, the heat treatment immediately after the formation of the outer skin layer and the heat treatment at the final diameter, and optimizes the heat treatment conditions such as temperature and moving speed by forming the diffusion layer and controlling the concentration of the outer skin layer. And executed. As needed, after wire drawing to a wire diameter of 30 to 100 μm, diffusion heat treatment was performed, and then wire drawing was further performed.

  When using the melting method, a method of melting and casting the conductive metal of the outer skin layer around the core wire prepared in advance, and a metal that is the material of the core material in the center of the hollow cylinder prepared in advance A method of melting and casting the alloy was adopted. As for the diameter of the mold, the entire outer diameter including the outer skin layer portion was 10 to 20 mm, and the diameter of the core wire portion was 5 to 10 mm. It was necessary to improve the adhesion at the interface when the molten liquid was poured, and the apparatus and the melting conditions were optimized by providing a taper for some molds.

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. This temperature difference was set in the range of 30 to 200 ° C., and the temperature distribution, the wire sweep speed, etc. were optimized and adjusted so that the tensile elongation was around 4%. In the atmosphere of the heat treatment, in addition to the air, an inert gas such as N ₂ or Ar was used for the purpose of suppressing oxidation. For the heat treatment process of the comparative example, a sample was prepared in the case where the plated layer was formed after the heat treatment was applied to the drawn Cu wire, and in the case where the heat treatment was performed twice after the drawing and after the formation of the plating layer. did.

For connection of the bonding wire, 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. In order to suppress oxidation during ball melting, discharging was performed while N ₂ gas was blown onto the tip of the wire.

  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: 1 to 4 μm) or a resin substrate having an electrode structure of Au plating / Ni plating / Cu was used as a partner for wedge bonding.

  Regarding the loop shape stability in the bonding process, trapezoidal loops were produced with two types of general-purpose spans with a wire length of 2 mm and short spans of 0.5 mm, and 500 wires were observed with a projector, and the straight line of the wire And variations in loop height were determined. The formation of a trapezoidal loop with a short wire length of 0.5 mm requires more stringent loop control in order to avoid contact with the tip end. If the wire length is 2 mm and there are 5 or more defects such as linearity and loop height, it is determined that there is a problem and is indicated by x, the wire length is 0.5 mm and there are 2 to 4 defects, and the wire When the length is 0.5 mm and the number of defects is 5 or more, it is judged that improvement is necessary and is indicated by a Δ mark. When the wire length is 2 mm, the number of defects is 1 or less, and when the wire length is 0.5 mm, the number of defects is 2 to 4 In the case of the book, the loop shape is comparatively good, so it is indicated by a circle, and when the wire length is 0.5 mm and the number of defects is 1 or less, the loop shape is judged to be stable and is indicated by the symbol ◎. As one of the causes of defects, it is assumed that the adhesion between the interface between the core wire and the outer peripheral portion is not sufficient, characteristic variation in the cross section, and the like.

  In the evaluation of the life of the capillary, after 50,000 wires were connected, it was judged by changes in dirt, wear, etc. at the capillary tip. If the surface is clean, there is no problem in normal operation when there are a few marks, deposits, etc., and Δ marks, and when the amount and size of deposits are significant, they are marked with x marks.

  Wire flow (resin flow) during resin sealing is measured using a soft X-ray non-destructive inspection device after preparing a bonding sample with a wire length of 4 mm and sealing with a commercially available epoxy resin. The amount of flow in this part was measured, and the average value divided by the span length of the wire (percentage) was taken as the wire deformation rate at the time of sealing. If this wire deformation rate is 5% or more, it is judged as defective, and if it is 3% or more and less than 5%, improvement is necessary. Since it was judged that the wire deformation was less than 2%, the wire deformation was satisfactorily reduced.

  Since the stable formation becomes difficult when the ratio of the ball diameter to the wire diameter is small, in the evaluation of the initial ball shape, the ratio of the ball diameter / wire diameter is 1.9 to 2.2, and the normal size is 1.6. Two types of small diameter balls in the range of -1.7 were evaluated. Twenty balls before bonding were observed to determine whether the shape was a true sphere or whether the dimensional accuracy was good. If there are two or more abnormally shaped balls, the mark is bad because it is defective, and the number of irregular shapes is two or less. If there are 2 to 4 misalignments, it is judged that there is no major problem in practical use. If the misalignment is less than 1 and the dimensional accuracy is good, the ball formation is good. Indicated.

  In determining the bonded shape of the press-bonded ball portion, 500 bonded balls were observed to evaluate the roundness of the shape, dimensional accuracy, and the like. Small diameter balls having an initial ball diameter / wire diameter ratio in the range of 1.6 to 1.7 were used, and conditions were selected such that the ball crimp diameter was in the range of 2 to 3 times the wire diameter. If there are 5 or more defective ball shapes such as anisotropy and petal shape deviating 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 it is good if the Δ mark or the number of defective balls is 1 or less, it is indicated by a mark.

  Judgment of wedge bondability for bonding wires to the lead side makes bonding difficult at lower temperatures. Therefore, 1000 pieces of bonding are performed at a stage temperature of 220 ° C. and 180 ° C. The deformation shape, etc. were investigated. When there are two or more complete peels at the joint at 220 ° C, X mark, less than two at 220 ° C, and improvement when partial peel near the wire breakage occurs △ mark, there is no defect at 220 ° C, and when complete peeling at 180 ° C is 1 or less, ○ mark, no complete peeling at 180 ° C, and partial peeling is less than 3 In some cases, it is indicated by ◎.

  In order to evaluate damage to the silicon substrate immediately below the ball joint, the ball joint and the electrode film were removed with aqua regia, and then cracks, minute pit holes, etc. on the silicon substrate were observed with a light microscope, SEM, or the like. When 500 or more joints are observed and 3 or more cracks of 5 μm or more are observed, it is judged that chip damage is a problem and is represented by Δ, and 1 to 3 cracks are generated or about 1 μm. If there are two or more pit holes, chip damage is a concern, but there is no problem in practical use. Therefore, it is marked with a circle. If there are no cracks and there are one or less pit holes, Since it is good, it is indicated by ◎.

  In the evaluation of the pull strength of the neck portion directly above the ball joint, a pull test was performed using 20 samples each having a wire length of 3 mm and hooking the vicinity of the ball joint portion. If the average value is 70% or more of the breaking strength of the wire, it is judged that the pull strength is high. If it is less than 20%, there is concern about damage, so it is indicated by a triangle.

  In the shape evaluation of the wedge bonding, the wedge plating was performed on the Ag plating layer on the inner lead of the frame, and the determination was made based on the deformed shape such as breaking over or variation in the bonding shape. Observe 1000 bonding parts. If there are 5 or more variants, X mark, 3-5 marks Δ, 1-2 marks ○, less than 1 And indicated by ◎.

  Tables 1-1 to 1-4 show the bonding wire evaluation results and comparative examples according to the present invention.

  The bonding wires according to the first claim are Examples 1-30, the bonding wires according to the second claim are Examples 5, 13, 24, 28, and the bonding wires according to the third claim are Examples 1-30. The bonding wires according to the fourth claim are the first to sixth, eighth to twenty-fourth, twenty-sixth to twenty-eightth and thirty-fifth, and the bonding wire according to the fifth claim is the bonding according to the eighth, eighteenth, twenty-eighth and sixth claims The wires are Examples 2 to 4, 6 to 8, 11 to 14, 16, 18 to 21, 23 to 25, 27 to 30, and the bonding wires according to the seventh claim are Examples 2 to 4, 6 to 8, 10 -14, 16-21, 23-30, the bonding wires according to the eighth claim are Examples 2, 4, 7-9, 11, 14, 18, 20, 24-30, the bonding wires according to the ninth claim Is Examples 1 to 30 and the bonding wires according to the 10th claim are Examples 1 to 6, 8 to 11, 13, 15, 17, 18, 20, 21, 23, 14, 26, 28, 30, and 11th claim. The bonding wire according to the item corresponds to Examples 2, 5, 8, 11, 16, 20, 27, and 28.

  A part of the evaluation results will be described for representative examples of each claim.

  In the bonding wires of Examples 1 to 30, the thickness of the outer skin layer according to the present invention is 0.001 to 0.09 μm, so that both the ball part formability and the wedge bondability can be satisfied at the same time. confirmed. On the other hand, when the outer skin layers of Comparative Examples 3, 5, 7, and 9 are less than 0.001 μm, the problem is that the wedge bondability is poor. In Comparative Examples 1, 2, 4, 6, 8, and 10, The thickness is more than 0.09 μm, the wedge bondability is improved, and the shape is almost good even with a normal diameter ball, but the problem is that a shape defect occurs with a small diameter ball.

  In the bonding wires of Examples 5, 13, 24, and 28, the total concentration of the elements contained in the outer skin layer is 0.0001 to 0.02 mol%, and the thickness is in the range of 0.001 to 0.09 μm. It was confirmed that the capillary life was improved.

  In the bonding wires of Examples 1 to 30, the thickness of the outer skin layer is in the range of 0.001 to 0.09 μm, and the total concentration of the conductive metal in the entire wire is in the range of 0.002 to 0.8 mol%. As a result, in addition to the wedge bondability, satisfactory results were confirmed that the capillary life was good.

  The bonding wires of Examples 1 to 6, 8 to 24, 26 to 28, and 30 have a conductive metal concentration gradient region in the wire radial direction near the boundary between the outer skin layer and the core material. It was confirmed that the loop controllability was improved.

  It was confirmed that the bonding wires of Examples 8, 18 and 28 had an intermetallic compound layer in the vicinity of the boundary between the outer skin layer and the core material, thereby reducing the wire flow during resin sealing.

  In the bonding wires of Examples 2 to 4, 6 to 8, 11 to 14, 16, 18 to 21, 23 to 25, and 27 to 30, the thickness of the region where the conductive metal concentration is 40 mol% or more in the outer skin layer Was 0.001 to 0.08 μm, it was confirmed that the pull strength in the vicinity of the ball joint was improved.

  In the bonding wires of Examples 2 to 4, 6 to 8, 10 to 14, 16 to 21, 23 to 30, the maximum concentration of the conductive metal in the outer skin layer is 50 to 100 mol%, and the conductive metal in the wire radial direction It was confirmed that the pull strength in the vicinity of the ball joint portion was improved by having the concentration gradient in the range of 0.001 to 0.08 μm.

  In the bonding wires of Examples 2, 4, 7-9, 11, 14, 18, 20, 24-30, the thickness of the region where the conductive metal concentration in the wire radial direction is constant near the surface is 0.07 μm or less. It was confirmed that the low-temperature wedge bondability was further improved.

The bonding wires of Examples 2, 5, 8, 11, 16, 20, 27, and 28 have one or more additive elements whose core material is selected from Ba, Ca, Sr, Be, Ge, Sn, In, or rare earth elements. It was confirmed that the pressure-bonding shape of the small ball was improved when the additive element concentration in the entire wire was 0.0001 to 0.03% by mass.

Claims (11)

1.   A bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element and an outer skin layer mainly containing a conductive metal different from the main component element on the outer side of the core material. A bonding wire for a semiconductor device, wherein the thickness of the outer skin layer is in the range of 0.001 to 0.09 μm.
2.   A bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element and an outer skin layer mainly containing a conductive metal different from the main component element on the outer side of the core material. The outer skin layer contains a total concentration of additive elements in the range of 0.0001 to 0.02 mol%, and the thickness is in the range of 0.001 to 0.09 μm.
3.   A core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component, and an outer skin layer containing a conductive metal different from the main component as a main component, has a thickness of 0. A bonding wire for a semiconductor device, the bonding wire having a range of 001 to 0.09 μm, wherein the total concentration of the conductive metal in the entire wire is in the range of 0.002 to 1.0 mol%.
4.   2. A conductive metal concentration gradient region is provided in the wire radial direction in the vicinity of the boundary between the outer skin layer and the core material, and the thickness of the concentration gradient region is in the range of 0.001 to 0.09 μm. The bonding wire for semiconductor devices in any one of -3.
5.   The conductive metal concentration gradient region in the wire radial direction between the outer skin layer and the core material, and each of the main component elements constituting the conductive metal and the core material constituting the outer skin layer, respectively. The bonding wire for a semiconductor device according to claim 1, comprising at least one intermetallic compound layer containing the above.
6.   A bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element and an outer skin layer mainly containing a conductive metal different from the main component element on the outer side of the core material. A bonding wire for a semiconductor device, wherein a thickness of a region having a conductive metal concentration of 40 mol% or more in the outer skin layer is 0.001 to 0.08 μm.
7.   A bonding wire having a core material containing one or more of silver, gold, palladium, platinum, and aluminum as a main component element and an outer skin layer containing a conductive metal different from the main component element on the outer side of the core material, In the outer skin layer, the maximum concentration of the conductive metal is in the range of 50 to 100 mol%, and has a concentration gradient of the conductive metal in the wire radial direction, and the thickness of the concentration gradient region is 0.001 to 0.08 μm. Bonding wires for semiconductor devices that are in the range of
8.   A bonding wire having a core material composed mainly of one or more of silver, gold, palladium, platinum, and aluminum and an outer skin layer composed mainly of a conductive metal different from the main component element on the outside of the core material. The bonding wire for a semiconductor device according to any one of claims 4 to 7, wherein a thickness of a region having a constant conductive metal concentration in the wire radial direction in the vicinity of the surface of the outer skin layer is 0.07 µm or less.
9.   The bonding wire for a semiconductor device according to any one of claims 1 to 8, wherein the conductive metal constituting the outer skin layer is at least one selected from gold, palladium, platinum, silver, or aluminum.
10.   The bonding wire for a semiconductor device according to any one of claims 1 to 8, wherein the conductive metal and the main component elements are concentrated on the surface of the outer skin layer.
11.   The core material contains one or more additive elements selected from Ba, Ca, Sr, Be, Ge, Sn, In or rare earth elements, and the concentration of the additive elements in the entire wire is 0.0001-0 in total It is the range of 0.03 mass%, The bonding wire for semiconductor devices in any one of Claims 1-8.