Bonding wire for semiconductor devices

Abstract

Provided is a novel Cu bonding wire that produces a good FAB shape and also has good bonding properties in a 2nd junction, and that furthermore produces good bonding reliability in a harsh high-temperature environment. This bonding wire for a semiconductor device is characterized by including a core comprising Cu or a Cu alloy and a coating layer containing an electroconductive metal other than Cu formed on the surface of the core, the coating layer having a region having Ni as a main component on the core side in the thickness direction of the coating layer, and having a region including Au and Ni on the wire surface side, the thickness of the coating layer being 10-130 nm, the ratio CAu / CNi of the concentration CAu (mass%) of Au and the concentration CNi (mass%) of Ni with respect to the wire overall being 0.02-0.7, the concentration of Au in the surface of the wire being 10-90 at%, and at least one of conditions (i) and (ii) being satisfied.　(i): The concentration of In with respect to the wire overall is 1-100 mass ppm. (ii): The concentration of Ag with respect to the wire overall is 1-500 mass ppm.

Description

[Technical Field]

[0001] The present invention relates to a bonding wire for a semiconductor device, and further to a semiconductor device including the bonding wire. [Background technology]

[0002] In semiconductor devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or substrate using bonding wires. The bonding wire is typically connected using ultrasonic thermocompression bonding, using a general-purpose bonding device or a capillary jig through which the bonding wire is passed for connection. The connection process is completed by first bonding to an electrode on the semiconductor chip, then forming a loop, and then second bonding of the wire to an external electrode on the lead frame or substrate. The first bonding involves heating and melting the tip of the wire with arc heat input, forming a free air ball (FAB; hereinafter simply referred to as a "ball" or "FAB") due to surface tension, and then crimping the ball to the electrode on the semiconductor chip (hereinafter referred to as "ball bonding"). The second bonding involves crimping the wire to the external electrode by applying ultrasonic waves and a load (hereinafter referred to as "wedge bonding") without forming a ball.

[0003] Until now, gold (Au) has been the mainstream material for bonding wire, but copper (Cu) is increasingly replacing it, primarily for LSI applications (e.g., Patent Documents 1 to 3). Furthermore, with the recent widespread use of electric and hybrid vehicles, it is expected that Cu, which has high thermal conductivity and fusing current, will be used in automotive devices and also in power devices (power semiconductor devices) used in high-power equipment such as air conditioners and solar power generation systems. Cu is therefore expected to be a highly efficient and reliable alternative.

[0004] Cu has the disadvantage of being more susceptible to oxidation than Au, and as a method of preventing the surface oxidation of Cu bonding wire, a structure in which the surface of the Cu core material is coated with metal such as Pd or Ni has been proposed (Patent Document 4).In addition, a Pd-coated Cu bonding wire has also been proposed in which the surface of the Cu core material is coated with Pd and further Pd or Pt is added to the Cu core material, thereby improving the bonding reliability of the first bonding portion (Patent Document 5). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Unexamined Patent Publication No. 61-48543 [Patent Document 2] Special Publication No. 2018-503743 [Patent Document 3] International Publication No. 2017 / 221770 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-167020 [Patent Document 5] International Publication No. 2017 / 013796 Summary of the Invention [Problem to be solved by the invention]

[0006] Automotive devices and power devices tend to be exposed to higher temperatures during operation than general electronic devices, and the bonding wires used are required to exhibit good bonding reliability even in harsh high-temperature environments.

[0007] The inventors conducted an evaluation based on the characteristics required for in-vehicle devices, etc., and found that with a conventional Cu bonding wire having a Pd coating layer, galvanic corrosion occurs in high-temperature environments, and sufficient bonding reliability may not be obtained at the second bonded portion. On the other hand, with bare Cu bonding wire without a Pd coating layer, although galvanic corrosion does not occur, the FAB shape is poor, and the crimped shape of the first bonded portion is inferior, which not only is insufficient for the narrow-pitch connection required for high-density mounting, but also may not be sufficient for the first bonded portion in high-temperature environments.

[0008] We investigated Cu-based bonding wires that achieve good FAB shapes and have little deterioration in bonding reliability even in the harsh high-temperature environments required for automotive devices, and found that Ni-coated Cu bonding wires, which have a Cu core surface coated with Ni, exhibited fairly good results in terms of FAB shapes and bonding reliability in high-temperature environments. However, with Ni-coated Cu bonding wires, there were cases where sufficient bondability was not obtained at the second bond (bondability of the second bond immediately after bonding).

[0009] As described above, it is desirable to develop a Cu-based bonding wire that provides a good FAB shape, has good bondability at the second bond, and exhibits good bond reliability in high-temperature environments. In this regard, the characteristics required for in-vehicle devices and the like are becoming increasingly stringent, and there is a need to ensure operation at higher temperatures. When evaluating the bond reliability of a bonding wire in a high-temperature environment, a high-temperature storage life test (HTSL) is often performed in which the wire is exposed to an environment at a temperature of 175°C, assuming a harsh high-temperature environment. However, the present inventors performed HTSL at a temperature of 200°C, assuming an even harsher high-temperature environment. As a result, they found that even bonding wires that exhibit good bond reliability at both the first and second bonded portions at a temperature of 175°C tend to lose bond reliability at a temperature of 200°C, especially at the second bonded portion. It was also confirmed that this tendency becomes more pronounced as the wire diameter of the bonding wire increases.

[0010] The present invention provides a novel Cu bonding wire that provides a good FAB shape, good bondability at the second bond, and good bonding reliability at both the first and second bond even in harsh high-temperature environments. [Means for solving the problem]

[0011] As a result of extensive research into the above problems, the present inventors have found that the above problems can be solved by providing the following configuration, and have completed the present invention.

[0012] That is, the present invention includes the following. [1] A bonding wire for a semiconductor device, comprising a core material made of Cu or a Cu alloy and a coating layer containing a conductive metal other than Cu formed on the surface of the core material, the coating layer has, in a thickness direction of the coating layer, a region containing Ni as a main component on the core material side and a region containing Au and Ni on the wire surface side; The thickness of the coating layer is 10 nm or more and 130 nm or less, Au concentration in the entire wire, C Au (mass%) and Ni concentration C Ni (mass%) ratio C Au / C Ni is between 0.02 and 0.7, the concentration of Au on the surface of the wire is 10 atomic % or more and 90 atomic % or less; A bonding wire for a semiconductor device that satisfies at least one of the following conditions (i) and (ii): (i) The concentration of In in the entire wire is 1 mass ppm or more and 100 mass ppm or less (ii) The Ag concentration in the entire wire is 1 mass ppm or more and 500 mass ppm or less [2] The bonding wire according to [1], wherein the concentration of Au on the surface of the wire is measured by Auger electron spectroscopy (AES) under the following conditions: <Conditions> The center of the wire width is positioned at the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface. [3] The bonding wire according to [1] or [2], wherein the coating layer further contains Pd as a conductive metal other than Cu. [4] Total concentration of Ni, Au, and Pd in ​​the whole wire, C M (mass%) and Ni concentration C Ni (mass%) ratio C Ni / C M The bonding wire according to any one of [1] to [3], wherein the value of the bonding wire resistance is 0.5 or more. [5] The bonding wire according to any one of [1] to [4], wherein the maximum concentration of Ni in the concentration profile in the depth direction of the wire is 80 atomic % or more. [6] A bonding wire according to [5], wherein the concentration profile in the depth direction of the wire is obtained by measuring by Auger electron spectroscopy (AES) under the following conditions while digging in the depth direction from the surface of the wire by Ar sputtering. <Conditions> The center of the wire width is positioned at the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface. [7] When a free air ball (FAB) is formed using a wire, the crystal orientation of the cross section perpendicular to the bonding direction of the FAB is measured, and the angle difference with respect to the bonding direction is 15 degrees or less. <100> The bonding wire according to any one of [1] to [6], wherein the proportion of crystal orientation is 30% or more. [8] The angle difference with respect to the crimping direction is 15 degrees or less. <100> The bonding wire according to [7], wherein the proportion of crystal orientation is 50% or more. [9] The bonding wire according to any one of [1] to [8], wherein the coating layer has a thickness of 18 nm or more.

[10] A bonding wire according to any one of [1] to [9], which contains one or more elements (hereinafter referred to as "first additional elements") selected from the group consisting of B, P and Mg, and the total concentration of the first additional elements in the entire wire is 1 mass ppm or more and 100 mass ppm or less.

[11] A bonding wire according to any one of [1] to

[10] , which contains one or more elements (hereinafter referred to as "second additional elements") selected from the group consisting of Se, Te, As and Sb, and the total concentration of the second additional elements in the entire wire is 1 mass ppm or more and 100 mass ppm or less.

[12] A bonding wire according to any one of [1] to

[11] , which contains one or more elements (hereinafter referred to as "third additional elements") selected from the group consisting of Ga and Ge, and the total concentration of the third additional elements relative to the entire wire is 0.011 mass% or more and 1.5 mass% or less.

[13] A semiconductor device including the bonding wire according to any one of [1] to

[12] . [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a novel Cu bonding wire that not only produces a good FAB shape, but also has good bondability at the second bond, and further provides good bonding reliability at both the first and second bond even in harsh high-temperature environments. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram for explaining the position and dimensions of the measurement surface when performing composition analysis by AES. [Figure 2] FIG. 2 is a schematic diagram for explaining a cross section perpendicular to the pressure bonding direction of the FAB. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below with reference to preferred embodiments. While the description may refer to drawings, each drawing merely shows the shape, size, and arrangement of components to the extent that the invention can be understood. The present invention is not limited to the following embodiments and examples, and can be modified and implemented as desired within the scope of the claims and their equivalents.

[0016] [Bonding wire for semiconductor devices] The bonding wire for a semiconductor device of the present invention (hereinafter also referred to simply as "the wire of the present invention" or "the wire") is a core material made of Cu or a Cu alloy; a coating layer formed on the surface of the core material and containing a conductive metal other than Cu; the coating layer has, in a thickness direction of the coating layer, a region containing Ni as a main component on the core material side and a region containing Au and Ni on the wire surface side; The thickness of the coating layer is 10 nm or more and 130 nm or less, Au concentration in the entire wire, C Au (mass%) and Ni concentration C Ni (mass%) ratio C Au / C Niis between 0.02 and 0.7, the concentration of Au on the surface of the wire is 10 atomic % or more and 90 atomic % or less; The concentration of at least one of In and Ag in the entire wire is 1 mass ppm or more.

[0017] As mentioned above, bonding wires used in automotive devices and power devices are required to exhibit good bonding reliability in harsh high-temperature environments. For example, bonding wires used in automotive devices are required to have bonding reliability in high-temperature environments exceeding 150°C. The present inventors conducted evaluations based on the characteristics required for automotive devices and the like, and found that with conventional Cu bonding wires having a Pd coating layer, galvanic corrosion occurs in high-temperature environments, and sufficient bonding reliability may not be obtained at the second bonding portion. Furthermore, with bare Cu bonding wires without a Pd coating layer, although galvanic corrosion does not occur, the fabrication block shape is poor, which in turn results in an inferior crimped shape at the first bonding portion, and is insufficient for the narrow-pitch connection required for high-density mounting. Furthermore, sufficient bonding reliability may not be obtained at the first bonding portion in high-temperature environments.

[0018] We investigated Cu-based bonding wires that achieve good FAB shapes and minimize deterioration in bonding reliability even in the harsh high-temperature environments required for automotive devices, and found that Ni-coated Cu bonding wires, which have a Cu core surface coated with Ni, exhibited relatively good results in terms of FAB shapes and bonding reliability in high-temperature environments. However, with Ni-coated Cu bonding wires, the bondability at the second bond (the bondability of the second bond immediately after bonding) was sometimes insufficient. Furthermore, when bonding was performed using Ni-coated Cu bonding wires, wire shavings accumulated inside the capillary jig, causing clogging (hereinafter, this phenomenon is also referred to as "capillary clogging"), which sometimes hindered continuous bonding.

[0019] The characteristics required for automotive devices and power devices are becoming increasingly stringent, and there is a need to ensure operation at higher temperatures. When evaluating the bonding reliability of bonding wires in high-temperature environments, HTSL is often performed, in which the wire is exposed to an environment at a temperature of 175°C, assuming a harsh high-temperature environment. However, the present inventors performed HTSL at a temperature of 200°C, assuming an even harsher high-temperature environment. As a result, they found that even bonding wires that exhibit good bonding reliability at both the first and second bonding portions at a temperature of 175°C tend to lose bonding reliability at a temperature of 200°C, especially at the second bonding portion. They also confirmed that this tendency becomes more pronounced as the wire diameter of the bonding wire increases.

[0020] In contrast, a bonding wire for a semiconductor device includes a core material made of Cu or a Cu alloy and a coating layer containing a conductive metal other than Cu formed on the surface of the core material, the coating layer having a region containing Ni as a main component on the core material side in the thickness direction of the coating layer and a region containing Au and Ni on the wire surface side, the thickness of the coating layer is 10 nm or more and 130 nm or less, and the concentration C of Au in the entire wire is Au (mass%) and Ni concentration C Ni (mass%) ratio C Au / C Ni The inventors have discovered that a bonding wire having a ρ of 0.02 or more and 0.7 or less, an Au concentration of 10 atomic % or more and 90 atomic % or less on the wire surface, and an In or Ag concentration of 1 mass ppm or more in the entire wire, results in a good FAB shape and good bondability at the second bond. Furthermore, regardless of the wire diameter, the present inventors have found that good bond reliability is achieved at both the first and second bonded portions, even in a severe high-temperature environment such as 200°C. Furthermore, such a wire can suppress capillary clogging during continuous bonding, thereby maintaining good productivity of semiconductor devices. Thus, the present invention significantly contributes to the practical application and promotion of Cu bonding wire in automotive devices and the like.

[0021] <Core material made of Cu or Cu alloy> The wire of the present invention includes a core material made of Cu or Cu alloy (hereinafter, also simply referred to as "Cu core material").

[0022] The Cu core material is not particularly limited as long as it is made of Cu or Cu alloy, and a known Cu core material constituting a conventional Pd-coated Cu wire known as a bonding wire for semiconductor devices may be used.

[0023] In the present invention, the concentration of Cu in the Cu core material can be, for example, 97 atomic% or more, 97.5 atomic% or more, 98 atomic% or more, 98.5 atomic% or more, 99 atomic% or more, 99.5 atomic% or more, 99.8 atomic% or more, 99.9 atomic% or more, 99.98 atomic% or more, or 99.99 atomic% or more at the center (axial core part) of the Cu core material.

[0024] From the viewpoint of improving the bonding reliability in a high-temperature environment, particularly from the viewpoint of realizing a bonding wire that exhibits good bonding reliability of the 2nd bonding part in a severe high-temperature environment regardless of the wire diameter, it is preferable that the Cu core material contains In and / or Ag such that the concentration of at least one of In and Ag with respect to the entire wire is 1 mass ppm or more. The preferred ranges of the concentrations of In and Ag with respect to the entire wire are as described later.

[0025] The Cu core material may also contain, for example, one or more dopants selected from the following-described first additive element, second additive element, and third additive element. The preferred contents of these dopants are as described later.

[0026] In one embodiment, the Cu core material consists of Cu and inevitable impurities. In another embodiment, the Cu core material consists of Cu, at least one of In and Ag, and inevitable impurities. In still another embodiment, the Cu core material consists of Cu, one or more elements selected from the first additive element, the second additive element, and the third additive element described below, and inevitable impurities. In still another embodiment, the Cu core material consists of Cu, at least one of In and Ag, one or more elements selected from the first additive element, the second additive element, and the third additive element described below, and inevitable impurities. The term "inevitable impurities" for the Cu core material includes elements constituting a coating layer containing a conductive metal other than Cu described below.

[0027] <Coating layer containing a conductive metal other than Cu> The wire of the present invention includes a coating layer (hereinafter also simply referred to as "coating layer") containing a conductive metal other than Cu formed on the surface of the Cu core material. Although a suitable composition of the coating layer will be described later, in the wire of the present invention, it is preferable that the concentration of the conductive metal other than Cu in the coating layer is 50 atomic% or more.

[0028] In order to provide a good FAB shape, good bonding property at the second joint, and further good bonding reliability in a high-temperature environment, it is important that the coating layer in the wire of the present invention satisfies all of the following conditions (1) to (4). (1) In the thickness direction of the coating layer, it has a region mainly composed of Ni on the core material side and a region containing Au and Ni on the wire surface side (2) The thickness of the coating layer is 10 nm or more and 130 nm or less (3) The ratio C of the concentration C of Au Au (mass%) to the concentration C of Ni Ni (mass%) in the whole wire is such that Au and Ni are contained so that C Au / C Ni is 0.02 or more and 0.7 or less (4) Au is contained so that the concentration of Au on the surface of the wire is 10 atomic% or more and 90 atomic% or less

[0029] ​​​​-Condition (1)- Condition (1) relates to the coating layer having, in the thickness direction of the coating layer, a region containing Ni as a main component on the core material side and a region containing Au and Ni on the wire surface side.

[0030] In combination with conditions (2) to (4), the wire of the present invention includes a coating layer that satisfies condition (1), which provides a good FAB shape and good bonding reliability in high-temperature environments, while also providing excellent bondability at the second bond. Furthermore, the inclusion of a coating layer that satisfies condition (1) can prevent capillary clogging during continuous bonding, thereby maintaining good productivity for semiconductor devices.

[0031] In condition (1), the coating layer has a region containing Ni as the main component on the core material side in the thickness direction of the coating layer. In the present invention, the "region containing Ni as the main component" in the coating layer means a region in which the concentration of Ni is 50 atomic % or more. As will be described later, the coating layer may contain Au on the wire surface side as a conductive metal other than Cu, in addition to Ni, and may also contain a conductive metal such as Pd. However, from the viewpoint of achieving a good FAB shape and good bonding reliability in a high-temperature environment, particularly bonding reliability of the first bonding portion, it is preferable that the total concentration C of Ni, Au, and Pd in ​​the entire wire be 50 atomic % or more. M (mass%) and Ni concentration C Ni (mass%) ratio C Ni / C M The coating layer preferably contains Ni so that the ratio C is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more or 0.8 or more. Ni / C M The upper limit of the ratio C is not particularly limited as long as it satisfies the conditions (2) to (4), and can be, for example, 0.995 or less or 0.99 or less. Ni / C M is the Ni concentration C of the entire wire measured by the method described in [Measurement of element content] below. Ni (mass%) was measured in the same way as the total concentration C of Ni, Au, and Pd. M It can be calculated by dividing by the mass %.

[0032] Regarding condition (1), whether the coating layer has a region containing Ni as the main component on the core side in the thickness direction of the coating layer and a region containing Au and Ni on the wire surface side can be confirmed by performing composition analysis using Auger electron spectroscopy (AES) while digging from the wire surface in the depth direction (toward the center of the wire) using Ar sputtering. Specifically, after 1) performing composition analysis of the wire surface, 2) sputtering with Ar and 3) repeating composition analysis of the surface after sputtering can obtain the concentration change of each element in the depth direction (center) from the wire surface (so-called depth concentration profile), and confirmation can be made from this concentration profile. In the present invention, the unit of depth in the depth direction concentration profile is SiO2 equivalent.

[0033] When performing 1) compositional analysis of the wire surface and 3) compositional analysis of the surface after sputtering, the position and dimensions of the measurement surface are determined as follows. In the following, the width of the measurement surface refers to the dimension of the measurement surface in the direction perpendicular to the wire axis (direction of the wire thickness), and the length of the measurement surface refers to the dimension of the measurement surface in the direction of the wire axis (direction of the wire length). This will be further explained with reference to Figure 1. Figure 1 is a schematic plan view of a wire 1, in which the direction of the wire axis (direction of the wire length) corresponds to the vertical direction (up and down direction) in Figure 1, and the direction perpendicular to the wire axis (direction of the wire thickness) corresponds to the horizontal direction (left and right direction) in Figure 1. Figure 1 shows a measurement surface 2 in relation to the wire 1, and the width of the measurement surface 2 is the dimension w of the measurement surface in the direction perpendicular to the wire axis. a and the length of the measurement surface 2 is the dimension l of the measurement surface in the direction of the wire axis. a is.

[0034] In the present invention, the wire is positioned so that the center of its width in the direction perpendicular to the wire axis is the center of the width of the measurement surface, and the measurement surface is determined so that the width of the measurement surface is 5% to 15% of the wire diameter. The length of the measurement surface is set to be 5 times the width of the measurement surface. In Figure 1, the width of the wire is indicated by the symbol W, and the center of the wire width is indicated by the dashed line X. Therefore, the measurement surface 2 is positioned so that the center of its width coincides with the dashed line X, which is the center of the wire width, and the width w of the measurement surface is determined so that the center of its width coincides with the dashed line X, which is the center of the wire width. a is determined so that it is 5% to 15% of the wire diameter (same value as the wire width W), that is, 0.05W to 0.15W. In addition, the length l of the measurement surface a is, l a =5w a By determining the position and dimensions of the measurement surface as described above, it is possible to obtain a good FAB shape and to accurately confirm the presence of a region in the coating layer that is mainly composed of Ni or a region that contains Au and Ni, which are suitable for obtaining good bondability at the second bond.

[0035] In the present invention, the coating layer has, in the thickness direction of the coating layer, a region mainly composed of Ni on the core material side and a region containing Au and Ni on the wire surface side, based on the results of measurements taken under the conditions described in the section below titled "Analysis of coating layer thickness by Auger electron spectroscopy (AES)."

[0036] The trends of the depth concentration profile obtained for a wire according to one embodiment of the present invention are described below. A region containing Au and Ni exists from the wire surface to a certain depth. In this region, the Au concentration tends to decrease and the Ni concentration tends to increase from the wire surface toward the depth. Further in the depth direction, the Ni concentration reaches a maximum, followed by a decrease in the Ni concentration and an increase in the Cu concentration. The Ni concentration may exhibit a maximum concentration at a certain depth (d1) or may exhibit a maximum concentration over a certain depth range (d1-d2). By focusing on the increase or decrease in the Au and Ni concentrations in such a concentration profile, it is possible to determine the presence and location of regions containing both Au and Ni or regions primarily composed of Ni. Furthermore, by focusing on the increase or decrease in the Au and Ni concentrations in such a concentration profile, the maximum Au and Ni concentrations can be determined from the positions where these concentrations are maximum. To determine the maximum concentration of Au or Ni in the coating layer, it is preferable to obtain concentration profiles for multiple measurement surfaces (n≧3) spaced 1 mm or more apart along the wire axis and use the arithmetic mean value. The preferred range for the maximum Ni concentration will be described later, but when the maximum Ni concentration is 50 mass% or more, it can be said that the above-mentioned "region containing Ni as the main component" exists.

[0037] In a preferred embodiment, the position showing the maximum concentration of Au in the concentration profile in the depth direction of the wire is closer to the surface of the wire than the position showing the maximum concentration of Ni.

[0038] In combination with conditions (2) to (4), from the viewpoint of realizing even better bonding reliability in high-temperature environments, particularly bonding reliability of the first bonding portion, the maximum concentration of Ni in the concentration profile in the depth direction of the wire is preferably 80 atomic % or more, more preferably 85 atomic % or more, and even more preferably 90 atomic % or more, more than 90 atomic %, 92 atomic % or more, 94 atomic % or more, or 95 atomic % or more. The upper limit of the maximum concentration of Ni in the coating layer is not particularly limited and may be, for example, 100 mass %.

[0039] -Condition (2)- Condition (2) relates to the thickness of the coating layer.

[0040] In combination with conditions (1), (3), and (4), the wire of the present invention includes a coating layer that satisfies condition (2), thereby achieving a good FAB shape and good bonding reliability in high-temperature environments.

[0041] Regarding condition (2), the thickness of the coating layer (the calculation method will be described later) is 10 nm or more, preferably 12 nm or more, more preferably 14 nm or more, even more preferably 15 nm or more, even more preferably 16 nm or more, and particularly preferably 18 nm or more or 20 nm or more, from the viewpoint of realizing a good FAB shape and good bonding reliability, particularly bonding reliability of the first bonded portion. A coating layer thickness of 18 nm or more is particularly preferable because it can realize not only a good FAB shape but also a particularly good bonded shape of the first bonded portion, and it is also easy to further improve the bonding reliability of the first bonded portion. Therefore, in a preferred embodiment, the thickness of the coating layer is 18 nm or more. Note that a coating layer thickness of less than 10 nm tends to cause eccentricity during FAB formation, deteriorating the FAB shape and the bonded shape of the first bonded portion. Furthermore, from the viewpoint of realizing a good FAB shape, the upper limit of the thickness of the coating layer is 130 nm or less, and preferably 125 nm or less, 120 nm or less, 115 nm or less, 110 nm or less, 105 nm or less, 100 nm or less, 95 nm or less, or 90 nm or less. If the thickness of the coating layer exceeds 130 nm, deformation or poor melting may occur during FAB formation, deteriorating the FAB shape and the compression shape of the first bonded portion.

[0042] The thickness of the coating layer under condition (2) can be determined from the concentration profile in the depth direction. First, the boundary between the Cu core material and the coating layer is determined based on the Cu concentration. The boundary is determined to be the position where the Cu concentration is 50 atomic %, and the region where the Cu concentration is 50 atomic % or more is the Cu core material, and the region where the Cu concentration is less than 50 atomic % is the coating layer. In the present invention, the boundary between the Cu core material and the coating layer does not necessarily have to be a grain boundary. The thickness of the coating layer can be determined by checking the concentration profile from the wire surface toward the wire center and calculating the distance from the wire surface to the depth position where the concentration of the core material, Cu, first reaches 50 atomic %. In the present invention, when determining the thickness of the coating layer from the concentration profile in the depth direction, the unit of depth is SiO2 equivalent. In addition, it is preferable to obtain concentration profiles for multiple measurement surfaces (n≧3) spaced 1 mm or more apart in the wire axial direction and use the arithmetic average value.

[0043] -Condition (3)- Condition (3) is the concentration of Au in the entire wire, C Au (mass%) and Ni concentration C Ni (mass%) ratio C Au / C Ni Regarding the range of.

[0044] In combination with conditions (1), (2), and (4), the wire of the present invention includes a coating layer that satisfies condition (3), which provides good bonding reliability in high-temperature environments, a good FAB shape, and good bondability at the second bond. Furthermore, the inclusion of a coating layer that satisfies condition (3) can prevent capillary clogging during continuous bonding, thereby maintaining good productivity of semiconductor devices.

[0045] Regarding condition (3), the ratio C Au / C Ni From the viewpoint of realizing good bondability at the second bonded portion and suppressing clogging of the capillary during continuous bonding, the ratio C is 0.02 or more, preferably 0.04 or more, more preferably 0.05 or more, 0.06 or more, 0.08 or more, or 0.1 or more.Au / C Ni If the ratio C is less than 0.02, the bondability at the second bonding portion tends to deteriorate, and the frequency of capillary clogging during successive bonding tends to increase. Au / C Ni The upper limit of the ratio C is 0.7 or less, preferably 0.65 or less, more preferably 0.6 or less, 0.55 or less, 0.5 or less, 0.48 or less, 0.46 or less, or 0.45 or less, from the viewpoint of providing a good FAB shape and realizing a good crimped shape of the first bonded portion. Au / C Ni If the value exceeds 0.7, eccentricity occurs during the formation of the FAB, which deteriorates the shape of the FAB and also tends to deteriorate the crimped shape of the first bonded portion.

[0046] The ratio C under condition (3) Au / C Ni is the concentration of Au in the entire wire measured by the method described in [Measurement of element content] below. Au (mass%), and the Ni concentration C Ni It can be calculated by dividing by the mass %.

[0047] -Condition (4)- Condition (4) relates to the concentration of Au on the surface of the wire.

[0048] In combination with conditions (1) to (3), the wire of the present invention includes a coating layer that satisfies condition (4), thereby achieving a good FAB shape and good bondability at the second bond. Furthermore, the inclusion of a coating layer that satisfies condition (4) can prevent capillary clogging during continuous bonding, thereby maintaining good productivity of semiconductor devices. Regarding condition (4), from the viewpoint of realizing good bondability at the second bonded portion and suppressing capillary clogging during continuous bonding, the concentration of Au at the surface of the wire of the present invention is 10 atomic % or more, preferably 15 atomic % or more, more preferably 20 atomic % or more, even more preferably 25 atomic % or more, and still more preferably 30 atomic % or more, 32 atomic % or more, 34 atomic % or more, 35 atomic % or more, 36 atomic % or more, 38 atomic % or more, or 40 atomic % or more. If the concentration of Au at the wire surface is less than 10 atomic %, the bondability at the second bonded portion tends to deteriorate, and the frequency of capillary clogging during continuous bonding also tends to increase. The upper limit of the Au concentration on the wire surface is 90 atomic % or less, preferably 85 atomic % or less, and more preferably 80 atomic % or less, 78 atomic % or less, 76 atomic % or less, 75 atomic % or less, 74 atomic % or less, 72 atomic % or less, or 70 atomic % or less, from the viewpoint of realizing a good FAB shape and a good compression shape of the first bonded portion. If the Au concentration on the wire surface exceeds 90 atomic %, eccentricity occurs during FAB formation, deteriorating the FAB shape and the compression shape of the first bonded portion, which tends to deteriorate.

[0049] The concentration of Au on the wire surface under condition (4) can be determined by analyzing the composition of the wire surface using Auger electron spectroscopy (AES), with the wire surface as the measurement surface. Here, gas components such as carbon (C), sulfur (S), oxygen (O), and nitrogen (N), as well as nonmetallic elements, are not taken into account when determining the concentration of Au on the surface.

[0050] The composition analysis of the wire surface can be performed under the same conditions as those described in 1) Composition Analysis of the Wire Surface, which was explained in relation to the method for obtaining a concentration profile in the depth direction. That is, when performing composition analysis of the wire surface by Auger electron spectroscopy (AES), the position and dimensions of the measurement surface are determined as follows:

[0051] The wire is positioned so that the center of its width in the direction perpendicular to the wire axis is the center of the width of the measurement surface, and the measurement surface is determined so that the width of the measurement surface is 5% to 15% of the wire diameter. The length of the measurement surface is set to be 5 times the width of the measurement surface. By determining the position and dimensions of the measurement surface as described above, the Au concentration on the wire surface can be measured with high accuracy, which is suitable for improving the FAB shape and the bondability at the second bond. In addition, it is preferable to perform measurements on multiple locations (n≧3) of the measurement surface spaced 1 mm or more apart along the wire axis and use the arithmetic average value.

[0052] The Au concentration on the wire surface under the above condition (4) is based on the results of measurements performed under the conditions described in the section "Analysis of Wire Surface Composition by Auger Electron Spectroscopy (AES)" below.

[0053] The coating layer may contain, for example, one or more dopants selected from the first additional element, the second additional element, and the third additional element described below. The preferred contents of these dopants are as described below.

[0054] The coating layer may also contain Pd as a conductive metal other than Cu. For example, the Pd concentration C Pd (mass%) and Ni concentration C Ni (mass%) ratio C Pd / C Ni The coating layer may contain Pd in ​​an amount such that the ratio C is 0.8 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.12 or less, 0.11 or less, 0.1 or less, 0.08 or less, 0.06 or less, or 0.05 or less. When the coating layer contains Pd, the ratio C Pd / C Ni The lower limit of is not particularly limited, and can be, for example, 0.0001 or more, 0.0005 or more, or 0.001 or more.

[0055] In one embodiment, the coating layer is made of Ni and Au; and unavoidable impurities. In another embodiment, the coating layer is made of Ni and Au; at least one of In and Ag; and unavoidable impurities. In yet another embodiment, the coating layer is made of Ni and Au; one or more elements selected from Pd, the first additional element, the second additional element, and the third additional element described below; and unavoidable impurities. In yet another embodiment, the coating layer is made of Ni and Au; at least one of In and Ag; Pd, one or more elements selected from the first additional element, the second additional element, and the third additional element described below; and unavoidable impurities. Note that the term "unavoidable impurities" used in reference to the coating layer also encompasses the elements that make up the Cu core material described above.

[0056] The wire of the present invention is characterized by containing at least one of In and Ag. By including a coating layer that satisfies all of the above conditions (1) to (4) and containing at least one of In and Ag in an amount of 1 mass ppm or more relative to the entire wire, the wire of the present invention can achieve a good FAB shape, good bondability at the second bonded portion, and good bond reliability at both the first bonded portion and the second bonded portion in a high-temperature environment.

[0057] Therefore, the wire of the present invention includes a coating layer that satisfies all of the above conditions (1) to (4), and also satisfies at least one of the following conditions (i) and (ii): (i) The concentration of In in the entire wire is 1 mass ppm or more (ii) The concentration of Ag in the entire wire is 1 mass ppm or more

[0058] -Condition (i)- Condition (i) relates to the concentration of In in the entire wire. Regarding condition (i), from the viewpoint of improving bonding reliability in high-temperature environments, particularly from the viewpoint of realizing a bonding wire that exhibits good bonding reliability at the second bond in harsh high-temperature environments regardless of the wire diameter, the concentration of In in the entire wire is 1 mass ppm or more, preferably 2 mass ppm or more, 3 mass ppm or more, 4 mass ppm or more, or 5 mass ppm or more, more preferably 6 mass ppm or more, 8 mass ppm or more, or 10 mass ppm or more, even more preferably 20 mass ppm or more, 30 mass ppm or more, or 40 mass ppm or more, and even more preferably 50 mass ppm or more. In particular, an In concentration of 50 mass ppm or more in the entire wire is preferable because it is easy to realize a bonding wire that exhibits good bonding reliability at the second bond in harsh high-temperature environments regardless of the wire diameter. The upper limit of the In concentration in the entire wire may be set to, for example, 100 ppm by mass or less, 95 ppm by mass or less, 90 ppm by mass or less, taking into consideration costs, etc., because an increase in the In concentration above this level will limit the effect of improving the bonding reliability of the second bonded portion in high-temperature environments. Therefore, in one embodiment, when the wire of the present invention satisfies condition (i), the In concentration in the entire wire is 1 ppm by mass or more and 100 ppm by mass or less.

[0059] -Condition (ii)- Condition (ii) relates to the concentration of Ag in the entire wire. Regarding condition (ii), from the viewpoint of improving bonding reliability in high-temperature environments, particularly from the viewpoint of realizing a bonding wire that exhibits good bonding reliability of the second bond in a harsh high-temperature environment regardless of the wire diameter, the concentration of Ag in the entire wire is 1 mass ppm or more, preferably 2 mass ppm or more, 3 mass ppm or more, 4 mass ppm or more, or 5 mass ppm or more, more preferably 10 mass ppm or more, 20 mass ppm or more, 30 mass ppm or more, 40 mass ppm or more, or 50 mass ppm or more, even more preferably 60 mass ppm or more, 80 mass ppm or more, and even more preferably 100 mass ppm or more. In particular, when the concentration of Ag in the entire wire is 100 mass ppm or more, it is preferable because it is easy to realize a bonding wire that exhibits good bonding reliability of the second bond in a harsh high-temperature environment regardless of the wire diameter. The upper limit of the Ag concentration in the entire wire may be set to, for example, 500 ppm by mass or less, 480 ppm by mass or less, 460 ppm by mass or less, 450 ppm by mass or less, taking into consideration costs, etc., because an increase in the Ag concentration above this level will limit the effect of improving the bonding reliability of the second bonded portion in high-temperature environments. Therefore, in one embodiment, when the wire of the present invention satisfies condition (ii), the Ag concentration in the entire wire is 1 ppm by mass or more and 500 ppm by mass or less.

[0060] When neither condition (i) nor (ii) is satisfied, i.e., when the concentration of both In and Ag in the entire wire is less than 1 mass ppm, the bonding reliability of the second bonded portion tends to be impaired in a severe high-temperature environment such as 200° C. As mentioned above, this tendency becomes more pronounced as the wire diameter of the bonding wire increases.

[0061] Regarding the conditions (i) and (ii), the preferred ranges of the In and Ag concentrations are as described above. In a more preferred embodiment, the wire of the present invention satisfies at least one of the following conditions (i) and (ii): (i) The concentration of In in the entire wire is 1 mass ppm or more and 100 mass ppm or more. (ii) The concentration of Ag in the entire wire is 1 mass ppm or more and 500 mass ppm or more.

[0062] In addition, when at least one of conditions (i) and (ii) is satisfied, the total concentration of In and Ag in the entire wire is, from the viewpoint of being able to further enjoy the effects of the present invention, 1 ppm by mass or more, preferably 2 ppm by mass or more, 3 ppm by mass or more, 4 ppm by mass or more, or 5 ppm by mass or more, more preferably 6 ppm by mass or more, 8 ppm by mass or more, or 10 ppm by mass or more, even more preferably 20 ppm by mass or more, 30 ppm by mass or more, or 40 ppm by mass or more, still more preferably 50 ppm by mass or more, 60 ppm by mass or more, or 70 ppm by mass or more, and the upper limit is preferably 600 ppm by mass or less, more preferably 550 ppm by mass or less, and even more preferably 500 ppm by mass or less.

[0063] In the wire of the present invention, In and Ag may be contained in either the Cu core material or the coating layer, or may be contained in both. From the viewpoint of improving bonding reliability in high-temperature environments, particularly from the viewpoint of realizing a bonding wire that exhibits good bonding reliability of the second bond portion in harsh high-temperature environments regardless of the wire diameter, it is preferable that In and Ag are contained in the Cu core material.

[0064] The wire of the present invention may further contain one or more elements ("first additional elements") selected from the group consisting of B, P, and Mg. When the wire of the present invention contains the first additional element, the total concentration of the first additional element in the entire wire is preferably 1 ppm by mass or more. This makes it possible to realize a bonding wire that provides a better crimped shape at the first bonded portion. The total concentration of the first additional element in the entire wire is more preferably 2 ppm by mass or more, and even more preferably 3 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 15 ppm by mass or more, or 20 ppm by mass or more. From the viewpoint of suppressing hardening of the wire and reducing chip damage during the first bonding, the total concentration of the first additional element is preferably 100 ppm by mass or less, and more preferably 90 ppm by mass or less, 80 ppm by mass or less, 70 ppm by mass or less, 60 ppm by mass or less, or 50 ppm by mass or less. Therefore, in a preferred embodiment, the wire of the present invention contains a first additional element, and the total concentration of the first additional element in the entire wire is 1 ppm by mass or more and 100 ppm by mass or less.

[0065] When the wire of the present invention contains the first additional element, the first additional element may be contained in either the Cu core material or the coating layer, or may be contained in both. From the viewpoint of realizing a bonding wire that provides a better crimped shape of the first bonded portion, it is preferable that the first additional element be contained in the Cu core material.

[0066] The wire of the present invention may further contain one or more elements ("second additional elements") selected from the group consisting of Se, Te, As, and Sb. When the wire of the present invention contains the second additional elements, the total concentration of the second additional elements relative to the entire wire is preferably 1 mass ppm or more. This can improve the bonding reliability of the first bonded portion in high-temperature environments. The total concentration of the second additional elements relative to the entire wire is more preferably 2 mass ppm or more, and even more preferably 3 mass ppm or more, 5 mass ppm or more, 8 mass ppm or more, 10 mass ppm or more, 15 mass ppm or more, or 20 mass ppm or more. From the viewpoint of realizing a good FAB shape and a good crimped shape of the first bonded portion, the total concentration of the second additional elements is preferably 100 mass ppm or less, and more preferably 90 mass ppm or less, 80 mass ppm or less, 70 mass ppm or less, 60 mass ppm or less, or 50 mass ppm or less. Therefore, in a preferred embodiment, the wire of the present invention contains a second additional element, and the total concentration of the second additional element in the entire wire is 1 ppm by mass or more and 100 ppm by mass or less.

[0067] When the wire of the present invention contains a second additive element, the second additive element may be contained in either the Cu core material or the coating layer, or may be contained in both. From the viewpoint of further improving the bonding reliability of the first bonded portion in a high-temperature environment, it is preferable that the second additive element be contained in the coating layer. When the coating layer contains the second additive element, the second additive element may be contained in a region containing Au and Ni on the wire surface side, or in a region mainly composed of Ni on the core material side. Furthermore, when the coating layer contains Pd, the second additive element may be contained together with the Pd.

[0068] The wire of the present invention may further contain one or more elements ("third additional elements") selected from the group consisting of Ga and Ge. When the wire of the present invention contains the third additional element, the total concentration of the third additional element relative to the entire wire is preferably 0.011 mass% or more. This further improves the bonding reliability of the first bonded portion in high-temperature environments. The total concentration of the third additional element relative to the entire wire is more preferably 0.015 mass% or more, and even more preferably 0.02 mass% or more, 0.025 mass% or more, 0.03 mass% or more, 0.031 mass% or more, 0.035 mass% or more, 0.04 mass% or more, 0.05 mass% or more, 0.07 mass% or more, 0.09 mass% or more, 0.1 mass% or more, 0.12 mass% or more, 0.14 mass% or more, 0.15 mass% or more, or 0.2 mass% or more. From the viewpoints of realizing a good FAB shape, realizing a good crimped shape of the first bonded portion, and realizing good second bondability, the total concentration of the third additional element is preferably 1.5 mass% or less, and more preferably 1.4 mass% or less, 1.3 mass% or less, or 1.2 mass% or less. Therefore, in a preferred embodiment, the wire of the present invention contains the third additional element, and the total concentration of the third additional element relative to the entire wire is 0.011 mass% or more and 1.5 mass% or less.

[0069] When the wire of the present invention contains a third additional element, the third additional element may be contained in either the Cu core material or the coating layer, or may be contained in both.

[0070] The contents of In, Ag, the first additional element, the second additional element, and the third additional element in the wire can be measured by the method described later in [Measurement of element contents].

[0071] In the wire of the present invention, the total concentration of Cu, Ni, Au, and Pd can be, for example, 98.4 mass % or more, 98.5 mass % or more, 98.6 mass % or more, or 98.7 mass % or more.

[0072] -Other favorable conditions- Further conditions that the wire of the present invention should preferably satisfy will be described below.

[0073] When a fabricated assembly (FAB) is formed using the wire of the present invention, the crystal orientation of a cross section of the fabricated assembly perpendicular to the bonding direction is measured, and the difference in angle with respect to the bonding direction is 15 degrees or less. <100> It is preferable that the proportion of crystal orientation is 30% or more, which makes it possible to achieve an exceptionally good crimped shape of the first bonded portion.

[0074] As mentioned above, the connection process using a bonding wire is completed by first bonding to an electrode on a semiconductor chip, then forming a loop, and then second bonding of the wire portion to an external electrode on a lead frame or substrate. In the first bonding, the tip of the wire is heated and melted by arc heat input, and a fabricated ball (FAB) is formed by surface tension, and then the FAB is pressure-bonded (ball-bonded) to the electrode on the semiconductor chip. The inventors measured the crystal orientation of a cross section perpendicular to the pressure-bonding direction of the FAB, and found that the angle difference with respect to the pressure-bonding direction was 15 degrees or less. <100> The ratio of crystal orientation (hereinafter simply referred to as "FAB cross section") <100> It has been discovered that wires with a crystal orientation ratio (also called the "ratio of crystal orientations") of 30% or more can achieve an exceptionally good crimped shape at the first joint.

[0075] In order to achieve a better crimp shape for the first joint, <100> A wire having a crystal orientation ratio of more preferably 35% or more, even more preferably 40% or more, even more preferably 45% or more, particularly preferably 50% or more, 55% or more, or 60% or more is preferred. <100> A wire with a crystal orientation ratio of 50% or more can achieve an exceptionally good crimped shape of the first bonded portion. <100> The proportion of crystal orientation is 30% or more, and more preferably 50% or more. <100> The upper limit of the proportion of the crystal orientation is not particularly limited, and may be, for example, 100%, or 99.5% or less, 99% or less, or 98% or less.

[0076] Referring to FIG. 2, a cross section perpendicular to the crimp bonding direction of the FAB will be described. FIG. 2 shows a schematic diagram of the process in which the tip of wire 1 is heated and melted by arc heat input, forming FAB 10 through surface tension. The formed FAB 10 is crimped to an electrode (not shown) on a semiconductor chip. In FIG. 2, the crimp bonding direction of FAB 10 is the direction indicated by arrow Z (the vertical direction in FIG. 2). The cross section perpendicular to the crimp bonding direction Z is the cross section exposed by cutting the FAB along dotted line AA perpendicular to the Z direction. Here, dotted line AA, which serves as the reference for cross sectioning, is set at the position where the diameter of the exposed cross section is maximum, i.e., the position where the diameter of the exposed cross section is D when the diameter of the FAB is D. During the cross sectioning process, it is possible for the line AA to deviate from the target and the diameter of the exposed cross section to be smaller than D. However, as long as the diameter of the exposed cross section is 0.9D or greater, the effect of this deviation on the crystal orientation ratio is negligibly small and is therefore acceptable.

[0077] The crystal orientation of a cross section perpendicular to the FAB bonding direction can be measured using electron backscattered diffraction (EBSD). The equipment used for EBSD consists of a scanning electron microscope and a detector attached to it. EBSD is a technique that determines the crystal orientation at each measurement point by projecting the diffraction pattern of the backscattered electrons generated when an electron beam is irradiated onto a sample onto a detector and analyzing this diffraction pattern. Dedicated software (such as OIM analysis by TSL Solutions, Inc.) can be used to analyze data obtained by EBSD. By using the analysis software provided with the equipment and using a cross section perpendicular to the FAB bonding direction as the inspection surface, the proportion of a specific crystal orientation can be calculated.

[0078] In the present invention, in the cross section of FAB <100> The ratio of crystal orientation to the measured area <100> The area of ​​the crystal orientation is defined as a percentage. In calculating the percentage, only the crystal orientations that could be identified based on a certain reliability were used within the measurement surface, and areas where the crystal orientation could not be measured, or areas where it could be measured but the reliability of the orientation analysis was low, were not included in the measurement area and <100> The calculation was performed by excluding the area of ​​the crystal orientation. If the excluded data exceeds, for example, 20% of the total, there is a high possibility that the measurement object has been contaminated in some way, and the measurement should be performed again from the cross section. <100> The crystal orientation ratio was calculated as the arithmetic mean of the ratio values ​​obtained by measuring three or more FABs.

[0079] In the cross section of FAB <100> The inventors of the present invention speculate as follows about the reason why a wire with a crystal orientation ratio of 30% or more can achieve a particularly good crimped shape of the first bonded portion.

[0080] It is known that metals deform by sliding along a specific crystal plane or direction (the plane or direction is also called the "slip plane" or "slip direction"). The FAB formed using the wire of the present invention is mainly composed of a core material, Cu or Cu alloy, and its crystal structure is a face-centered cubic structure. When such a crystal structure is adopted, the crystal orientation of the cross section perpendicular to the crimping direction is <100> In this case, metal slippage occurs in a 45-degree direction relative to the crimped surface, causing deformation, so the FAB deforms in a 45-degree direction relative to the crimped surface and spreads radially relative to the plane parallel to the crimped surface. As a result, it is believed that the crimped shape becomes closer to a perfect circle.

[0081] In the present invention, in the cross section of FAB <100> The ratio of crystal orientations tends to be within the desired range by adjusting the thickness of the coating layer, the Ni concentration in the coating layer, and the Cu purity of the core material. For example, when the thickness of the coating layer is <100> The inventors speculate that the reason for the influence on the ratio of crystal orientation is as follows: In other words, during the melting stage, Ni in the coating layer is diffused and mixed appropriately toward the center of the FAB, and Cu or Cu alloy containing the Ni that has been diffused and mixed appropriately as a solid solution is oriented in the direction of compression bonding. <100> It is thought that the crystal orientation is oriented. When the thickness of the coating layer is within a certain range, the diffusion and mixing of Ni during melting becomes appropriate, and the orientation becomes <100> It is thought that if the coating layer is too thin, the crystal orientation is likely to be oriented, while if the coating layer is too thin, the crystal orientation is likely to be random and lacking orientation, and if the coating layer is too thick, a different crystal orientation is likely to take precedence.

[0082] The diameter of the wire of the present invention is not particularly limited and may be determined appropriately depending on the specific purpose, but is preferably 30 μm or more, 35 μm or more, 40 μm or more, etc. The upper limit of the diameter is not particularly limited and may be, for example, 80 μm or less, 70 μm or less, or 50 μm or less.

[0083] <Wire manufacturing method> An example of the method for producing a bonding wire for a semiconductor device according to the present invention will be described.

[0084] First, raw copper with high purity (4N to 6N; 99.99 to 99.9999 mass % or more) is processed into a large diameter (approximately 3 to 6 mm diameter) by continuous casting to obtain an ingot.

[0085] Methods for adding dopants such as In, Ag, and, if added, the first, second, and third additional elements, include incorporating them into the Cu core material, incorporating them into the coating layer, depositing them on the surface of the Cu core material, and depositing them on the surface of the coating layer. These methods may also be combined. The effects of the present invention can be achieved regardless of the method used. In the method for incorporating a dopant into the Cu core material, a copper alloy containing the required concentration of dopant is used as a raw material to produce the Cu core material. When adding a dopant to the raw material Cu to obtain such a copper alloy, a high-purity dopant component may be directly added to Cu, or a mother alloy containing approximately 1% of the dopant component may be used. In the method for incorporating a dopant into the coating layer, the dopant may be incorporated into the Ni, Au, or Pd plating bath (in the case of wet plating) or target material (in the case of dry plating) used to form the coating layer. In the method of depositing on the surface of a Cu core material or on the surface of a coating layer, the surface of the Cu core material or the surface of the coating layer can be used as the deposition surface, and one or more deposition processes selected from (1) application of an aqueous solution ⇒ drying ⇒ heat treatment, (2) plating method (wet type), and (3) vapor deposition method (dry type) can be carried out.

[0086] A large diameter ingot is forged, rolled, and drawn to produce a wire (hereinafter also referred to as "intermediate wire") made of Cu or a Cu alloy and having a diameter of about 0.7 to 2.0 mm.

[0087] Although electrolytic plating, electroless plating, vapor deposition, and the like can be used to form a coating layer on the surface of a Cu core material, electrolytic plating, which allows for stable control of film thickness, is industrially preferred. For example, a coating layer may be formed on the surface of an intermediate wire. Alternatively, the coating layer may be formed on the surface of the Cu core material after the intermediate wire has been drawn to a thinner wire (e.g., after drawing to the final diameter of the Cu core material). When forming a coating layer containing Pd, the coating layer may be formed using a Ni plating solution, a Pd plating solution, or a plating solution containing Ni and Pd in ​​a predetermined ratio, depending on the desired coating layer configuration. For example, a Ni layer may be formed using a Ni plating solution, and then a Pd layer or a PdNi alloy layer may be formed using a Pd plating solution or a plating solution containing Ni and Pd in ​​a predetermined ratio to form the coating layer. From the viewpoint of forming a coating layer with excellent adhesion to the Cu core material, a predetermined coating layer may be formed after strike plating of a conductive metal on the surface of the Cu core material.

[0088] The region containing Au and Ni that the coating layer has on the surface side of the wire can be formed by providing an Au layer on the surface side of the coating layer using the same method as described above.

[0089] The wire drawing process can be performed using a continuous wire drawing machine that can accommodate multiple diamond-coated dies. Heat treatment can be performed during the wire drawing process, if necessary. Heat treatment can diffuse the constituent elements between the Au layer on the wire surface and the underlying Ni layer (or Pd layer or PdNi alloy layer, if present), forming a region containing Au and Ni on the wire surface side of the coating layer. A preferred method for this is to continuously sweep the wire at a constant speed in an electric furnace at a constant furnace temperature to promote alloying, as this reliably controls the Au concentration on the wire surface within the desired range. Instead of forming a region containing Au and Ni by heat treatment after adding an Au layer on the coating layer, a method of depositing an alloy region containing Au and Ni from the beginning can also be used.

[0090] The wire of the present invention can provide a good FAB shape, good bondability at the second bonded portion, and good bond reliability at both the first and second bonded portions in a high-temperature environment. Therefore, the bonding wire of the present invention can be suitably used as a bonding wire for automotive devices and power devices.

[0091] [Method of manufacturing a semiconductor device] A semiconductor device can be manufactured by connecting electrodes on a semiconductor chip to electrodes on a lead frame or a circuit board using the bonding wire for a semiconductor device of the present invention.

[0092] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, and a bonding wire for electrically connecting the circuit board and the semiconductor chip, and the bonding wire is the wire of the present invention.

[0093] In the semiconductor device of the present invention, the circuit board and semiconductor chip are not particularly limited, and known circuit boards and semiconductor chips that can be used to configure a semiconductor device may be used. Alternatively, a lead frame may be used instead of the circuit board. For example, as in the semiconductor device described in JP 2020-150116 A, the semiconductor device may be configured to include a lead frame and a semiconductor chip mounted on the lead frame.

[0094] Examples of the semiconductor device include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, and aircraft, etc.). [Example]

[0095] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0096] (sample) First, the method for preparing the samples will be explained. The Cu used as the raw material for the Cu core material had a purity of 99.99% by mass or more (4N), with the remainder consisting of inevitable impurities. In, Ag, and, if added, the first, second, and third additional elements had a purity of 99% by mass or more, with the remainder consisting of inevitable impurities, or a master alloy in which these additional elements were blended in high concentrations with Cu was used.

[0097] The Cu alloy core material was first prepared by loading raw materials into a graphite crucible and melting them in a high-frequency furnace at 1090-1500°C in an inert atmosphere, such as N2 gas or Ar gas. Then, an ingot with a diameter of approximately 3-6 mm was produced by continuous casting. The resulting ingot was then drawn to produce an intermediate wire with a diameter of approximately 0.7-2.0 mm. The wire was then continuously drawn using a die to reduce the diameter of the wire to the diameter required for coating. A commercially available lubricant was used for the wire drawing process, and the drawing speed was 20-150 m / min. The coating layer was formed by pickling with hydrochloric acid or sulfuric acid to remove the oxide film from the wire surface. A Ni layer was then formed to cover the entire surface of the Cu alloy core material, and an Au layer was then formed on that surface. In some examples, the Ni layer was first formed, followed by a Pd layer, and then an Au layer. The Ni, Au, and Pd layers were formed using electroplating. Commercially available plating solutions were prepared as Ni plating solution, Au plating solution, and Pd plating solution, and were adjusted accordingly before use.

[0098] The wire was then further drawn and processed to a final wire diameter of 50 μm. If necessary, intermediate heat treatment was performed once or twice during the drawing process at 300–700°C for 2–15 seconds. When intermediate heat treatment was performed, the wire was continuously swept while N2 gas or Ar gas was flowing. After the wire was drawn to the final diameter, the wire was continuously swept while N2 gas or Ar gas was flowing, and a thermal refining heat treatment was performed. The thermal refining heat treatment temperature was 200–600°C, the wire feed rate was 20–200 m / min, and the heat treatment time was 0.2–1.0 seconds. When the coating layer was thin or the Au concentration was low, the heat treatment temperature was lowered and the wire feed rate was faster. In the opposite cases, the heat treatment temperature was increased and the wire feed rate was slower.

[0099] (Test and evaluation methods) The test and evaluation methods are explained below.

[0100] [Composition analysis of wire surface by Auger electron spectroscopy (AES)] The Au concentration on the wire surface was determined by measuring the wire surface as the measurement surface using Auger electron spectroscopy (AES) as follows. First, the bonding wire to be measured was fixed linearly to the sample holder. Next, the wire was positioned so that the center of the wire's width in the direction perpendicular to the wire axis was the center of the width of the measurement surface, and the measurement surface was determined so that the width of the measurement surface was 5% to 15% of the wire diameter. The length of the measurement surface was set to 5 times the width of the measurement surface. Then, using an AES device (ULVAC-PHI PHI-700) at an accelerating voltage of 10 kV, the composition of the wire surface was analyzed to determine the surface Au concentration (atomic %). The composition analysis by AES was performed on three measurement surfaces spaced at least 1 mm apart along the wire axis, and the arithmetic average value was used. When determining the Au concentration on the surface, gas components such as carbon (C), sulfur (S), oxygen (O), and nitrogen (N), as well as non-metallic elements, were not taken into account.

[0101] [Coating layer thickness analysis by Auger electron spectroscopy (AES)] AES depth analysis was used to analyze the thickness of the coating layer. AES depth analysis involves alternating composition analysis and sputtering to analyze changes in composition in the depth direction, and can obtain the concentration changes of each element from the wire surface to the depth (center) (the so-called depth direction concentration profile). Specifically, after 1) analyzing the composition of the wire surface using AES, 2) sputtering with Ar and 3) analyzing the composition of the surface after sputtering were repeated to obtain a concentration profile in the depth direction. + The analysis was performed using ions at an accelerating voltage of 2 kV. In the surface composition analyses of 1) and 3), the dimensions of the measurement surface and the conditions for the AES composition analysis were the same as those described in the section "Analysis of wire surface composition by Auger electron spectroscopy (AES)" above. The concentration profile in the depth direction was acquired for three measurement surfaces spaced apart from each other by 1 mm or more in the axial direction of the wire.

[0102] -Coating layer thickness- The thickness of the coating layer was determined by checking the concentration profile in the depth direction from the wire surface toward the center of the wire and determining the distance from the wire surface to the depth where the concentration of the core material, Cu, first reached 50 atomic %. The arithmetic mean value of the values ​​obtained for the three measurement surfaces was used as the thickness of the coating layer. The depth measured by AES analysis is calculated as the product of the sputtering rate and time. Generally, the sputtering rate is measured using a standard sample of SiO2, so the depth analyzed by AES is an SiO2 equivalent value. In other words, the SiO2 equivalent value is used as the unit of thickness of the coating layer.

[0103] -Maximum concentration of Ni, etc. in the coating layer- In the obtained concentration profile in the depth direction, the increase or decrease in Ni concentration was focused on, and the maximum Ni concentration was calculated from the position where the Ni concentration was maximum. The arithmetic mean value of the values ​​obtained for the three measurement points was adopted as the maximum Ni concentration. It was confirmed that the wires of the examples had a region mainly composed of Ni on the core side, a region containing Au and Ni on the surface side of the wire, the maximum concentration of Ni was 80 atomic % or more, and the position showing the maximum Au concentration was closer to the surface than the position showing the maximum Ni concentration.For the wires of the examples in which the coating layer had a region containing Pd, it was confirmed that the position showing the maximum Pd concentration was closer to the surface than the position showing the maximum Ni concentration, and that the position showing the maximum Pd concentration was between the positions showing the maximum Au concentration and the positions showing the maximum Ni concentration.

[0104] [Measurement of element content] The contents of Au, Ni, In, Ag, Pd, the first additional element, the second additional element, and the third additional element in the wire were determined by analyzing a solution obtained by dissolving the bonding wire in strong acid using an ICP optical emission spectrometer and an ICP mass spectrometer, and were detected as the concentration of the elements contained in the entire wire. The analytical equipment used was an ICP-OES ("PS3520UVDDII" manufactured by Hitachi High-Tech Science Corporation) or an ICP-MS ("Agilent 7700x ICP-MS" manufactured by Agilent Technologies, Inc.). The total concentration C of Ni, Au, and Pd was calculated as follows: M The concentration (mass %) was calculated by adding up the concentrations of Ni, Au, and Pd.

[0105] [FAB shape] The FAB shape was evaluated by creating a FAB on a lead frame using a commercially available wire bonder and observing it with a scanning electron microscope (SEM) (number of evaluations: N = 100). The FAB was formed under conditions of a current of 30-75 mA, an EFO gap of 762 μm, and a tail length of 500 μm, while flowing N2 + 5% H2 gas at a flow rate of 0.4-0.6 L / min. The diameter of the FAB was 1.5-1.9 times the wire diameter. A perfectly spherical FAB shape was judged as good, while eccentricity, irregular shapes, or poor melting were judged as bad. Evaluation was based on the following criteria.

[0106] Evaluation criteria: ○: 5 or fewer defects △: 6 to 10 defects (no practical problems) ×: 11 or more defects

[0107] [Measurement of crystal orientation in cross section of FAB] A commercially available wire bonder was used to form the FAB under the conditions described in the above [FAB shape] section, and the crystal orientation was measured using a cross section perpendicular to the FAB compression bonding direction as the measurement surface. In the present invention, the cross section perpendicular to the FAB compression bonding direction means the cross section exposed by cutting the FAB along the dotted line AA shown in Figure 2, and the reference dotted line AA was set at the position where the diameter of the exposed cross section was maximum. The measurement was performed using the EBSD method, and the analysis software attached to the device was used to perform the above-mentioned procedure. <100> The ratio of the crystal orientation was calculated. Three FABs were measured, and the ratio values ​​were arithmetically averaged to obtain the ratio of the crystal orientation in the cross section of the FAB. <100> The ratio was determined as the ratio of crystal orientations.

[0108] [Second joint joint jointability] The bondability of the second joint was evaluated using a second joint window test, which involves determining the number of conditions under which bonding is possible out of a total of 25 second joint conditions, with the ultrasonic current during second joint set to five levels of 10 mA increments from 140 mA to 180 mA on the horizontal axis and the load during second joint set to five levels of 10 gf increments from 80 gf to 120 gf on the vertical axis.

[0109] [Table 1]

[0110] In this test, 200 wires per condition were bonded to the lead portion of a lead frame using a commercially available wire bonder for each of the examples and comparative examples. Ag-plated lead frames were used, and bonding was performed at a stage temperature of 200°C and with a flow of N2 + 5% H2 gas at 0.5 L / min. The number of conditions under which continuous bonding was possible without problems such as non-adhesion or bonder stoppage was determined, and the results were evaluated according to the following criteria.

[0111] Evaluation criteria: ◎: 24 or more conditions ○:22~23 conditions ×: 21 conditions or less

[0112] [Reliability of the first joint] The bonding reliability of the first bonding portion was evaluated by a high temperature storage life test (HTSL).

[0113] A sample for testing the bond reliability of the first bond was prepared by ball-bonding a 2.0 μm-thick Al-1.0 wt% Si-0.5 wt% Cu alloy film to an electrode on a Si substrate mounted on a standard metal frame using a commercially available wire bonder. The sample was then sealed with a commercially available thermosetting epoxy resin. The ball was formed under the conditions described in the [FAB Shape] section above. The prepared sample for bond reliability evaluation was exposed to a 200°C environment using a high-temperature incubator. The bond life of the first bond was determined by conducting a shear test on the ball bond every 500 hours, and the time until the shear strength value reached half of the initial shear strength was used. The shear strength value was the arithmetic mean value of measurements taken at 50 randomly selected locations on the ball bond. After the high-temperature storage test, the resin was removed by acid treatment to expose the ball bond, and the shear test was then performed according to the following criteria.

[0114] Evaluation criteria: ◎◎: Bonding life more than 2500 hours ◎: Bonding life is between 2000 hours and 2500 hours ○: Bonding life 1000 hours or more but less than 2000 hours ×: Bonding life less than 1000 hours

[0115] [Second joint reliability] The bonding reliability of the second bonding portion was evaluated by a high temperature storage life test (HTSL).

[0116] A sample for testing the joint reliability of the second joint was prepared by wedge-bonding the lead portion of the lead frame using a commercially available wire bonder and encapsulating it with a commercially available thermosetting epoxy resin. The lead frame was an Fe-42 atomic % Ni alloy lead frame plated with 1-3 μm Ni / Pd / Au. The prepared sample for joint reliability evaluation was exposed to a 200°C environment using a high-temperature thermostat. The second joint's joint life was determined by conducting a pull test on the wedge joint every 500 hours, and the time it took for the pull strength to reach half of the initial value. The pull strength value was the arithmetic mean of measurements taken at 50 randomly selected locations on the wedge joint. After the high-temperature storage test, the resin was removed by acid treatment to expose the wedge joint, and the pull test was then performed according to the following criteria.

[0117] Evaluation criteria: ◎: Bonding life more than 2000 hours ○: Bonding life 1000 hours or more but less than 2000 hours ×: Bonding life less than 1000 hours

[0118] [Crimp shape] The bonded shape of the first bonded portion (the crushed shape of the ball) was evaluated by forming a ball using a commercially available wire bonder under the conditions described in the "FAB Shape" section above, crimping it to an electrode made by depositing a 2.0 μm-thick film of an Al-1.0 mass % Si-0.5 mass % Cu alloy on a Si substrate, and observing it from directly above with an optical microscope (number of evaluations: N = 100). The crushed shape of the ball was judged as good if it was close to a perfect circle, and as poor if it was oval or petal-like. Evaluation was then conducted according to the following criteria.

[0119] Evaluation criteria: ◎: No defects ○: 1 to 3 defects △: 4 or 5 defects ×: 6 or more defects

[0120] [Capillary life] Continuous bonding was performed using a commercially available wire bonder, and the number of bonds was counted until the capillary became clogged and bonding became impossible. The results were evaluated according to the following criteria.

[0121] Evaluation criteria: ○: 1 million times or more ×: Less than 1 million times

[0122] [Chip damage] Chip damage was evaluated by forming a ball using a commercially available wire bonder under the conditions described in the [FAB Shape] section above, crimping it to an electrode made by depositing a 2.0 μm thick Al-1.0 mass % Si-0.5 mass % Cu alloy film on a Si substrate, then dissolving the wire and electrode in a chemical solution to expose the Si substrate, and observing the Si substrate directly below the bond with an optical microscope (evaluation number N=50). Evaluation was then performed according to the following criteria.

[0123] Evaluation criteria: ○: No cracks or bonding traces △: No cracks, but traces of bonding can be seen in some places (3 places or less) ×:Other

[0124] The evaluation results of the examples and comparative examples are shown in Tables 2 and 3.

[0125] [Table 2]

[0126] [Table 3]

[0127] All of the wires of Examples 1 to 35 included a coating layer that satisfied all of the specific conditions (1) to (4) of the present invention and contained 1 mass ppm or more of at least one of In and Ag relative to the entire wire, and were confirmed to provide a good FAB shape, good bondability at the second bonded portion, and good bond reliability at both the first and second bonded portions in a high-temperature environment at 200° C. Among these, the wires of Examples 1, 3, 4, 10, 12, 20 to 24, 26, 29 to 31, and 33 to 35, which included a coating layer that satisfied all of the specific conditions (1) to (4) of the present invention and had In and Ag contents within the preferred ranges relative to the entire wire, were confirmed to provide particularly good bond reliability at the second bonded portion in a high-temperature environment at 200° C., even when the wire diameter was relatively large at 50 μm. Additionally, it was confirmed that wires of Examples 10 to 13, 24 to 26, 32, and 33, which contained a total of 1 ppm by mass or more of the first additional element, provided a particularly good crimped shape of the first joint. It was confirmed that wires of Examples 14 to 18, 24, 26, and 32 to 35, which contained a total of 1 ppm by mass or more of the second additional element, provided a particularly good joint reliability of the first joint in a high-temperature environment. It was confirmed that wires of Examples 19 to 22, 25, 26, and 33 to 35, which contained a total of 0.011% by mass or more of the third additional element, provided a particularly good joint reliability of the first joint in a high-temperature environment. On the other hand, the wires of Comparative Examples Nos. 1 to 7 were found to have coating layers that did not satisfy at least one of the specific conditions (1) to (4) of the present invention, or to have In and Ag concentrations of less than 1 mass ppm relative to the entire wire, and to have poor FAB shape, bondability at the second joint, bond reliability at the first joint, or bond reliability at the second joint.

[0128] When a FAB is formed using wire, the crystal orientation of the cross section perpendicular to the bonding direction of the FAB is measured, and the angle difference with respect to the bonding direction is 15 degrees or less. <100> It was confirmed that a good crimped shape of the first bonded portion can be achieved when the proportion of crystal orientation is 30% or more (Examples Nos. 36 to 45). <100> It was confirmed that when the proportion of crystal orientation is 50% or more, an exceptionally excellent crimped shape of the first bonded portion can be achieved (Examples Nos. 36, 37, 39, and 44). [Explanation of symbols]

[0129] 1 Bonding wire (wire) 2 Measurement surface X Wire width center W Wire width (wire diameter) w a Measurement surface width l a Length of the measuring surface 10 FAB Z FAB crimp bonding direction

Claims

1. A bonding wire for a semiconductor device, comprising a core material made of Cu or a Cu alloy and a coating layer containing a conductive metal other than Cu formed on the surface of the core material, the coating layer has, in a thickness direction of the coating layer, a region containing Ni as a main component on the core material side and a region containing Au and Ni on the wire surface side; The thickness of the coating layer is 10 nm or more and 130 nm or less, Au concentration C for the entire wire Ａｕ (mass%) and Ni concentration C Ｎｉ Ratio C (mass%) Ａｕ / C Ｎｉ is 0.02 or more and 0.7 or less, the concentration of Au on the surface of the wire is 10 atomic % or more and 90 atomic % or less; A bonding wire for a semiconductor device that satisfies at least one of the following conditions (i) and (ii): (i) The concentration of In in the entire wire is 1 mass ppm or more and 100 mass ppm or less. (ii) The concentration of Ag in the entire wire is 1 mass ppm or more and 500 mass ppm or less.

2. 2. The bonding wire according to claim 1, wherein the concentration of Au on the surface of the wire is measured by Auger electron spectroscopy (AES) under the following conditions: <Conditions> The center of the wire width is positioned at the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface.

3. The bonding wire according to claim 1 or 2, wherein the coating layer further contains Pd as a conductive metal other than Cu.

4. Total concentration C of Ni, Au, and Pd in ​​the entire wire Ｍ (mass%) and Ni concentration C Ｎｉ Ratio C (mass%) Ｎｉ / C Ｍ The bonding wire according to any one of claims 1 to 3, wherein is 0.5 or more.

5. The bonding wire according to any one of claims 1 to 4, wherein the maximum concentration of Ni in the concentration profile in the depth direction of the wire is 80 atomic % or more.

6. The concentration profile in the depth direction of the wire is measured by Auger electron spectroscopy (AES) under the following conditions while digging in the depth direction from the surface of the wire by Ar sputtering. The bonding wire according to claim 5. <Conditions> The center of the wire width is positioned at the center of the width of the measurement surface, and the width of the measurement surface is 5% to 15% of the wire diameter, and the length of the measurement surface is 5 times the width of the measurement surface.

7. When a free air ball (FAB) is formed using the wire, the crystal orientation of a cross section perpendicular to the crimping bonding direction of the FAB is measured. The bonding wire according to any one of claims 1 to 6, wherein the proportion of <100> crystal orientations having an angle difference of 15 degrees or less with respect to the crimping bonding direction is 30% or more.

8. The bonding wire according to claim 7, wherein the proportion of <100> crystal orientations having an angle difference of 15 degrees or less with respect to the crimp bonding direction is 50% or more.

9. The bonding wire according to any one of claims 1 to 8, wherein the coating layer has a thickness of 18 nm or more.

10. The bonding wire according to any one of claims 1 to 9, comprising one or more elements (hereinafter referred to as "first additional elements") selected from the group consisting of B, P, and Mg, and having a total concentration of the first additional elements with respect to the entire wire of 1 ppm by mass or more and 100 ppm by mass or less.

11. The bonding wire according to any one of claims 1 to 10, comprising one or more elements (hereinafter referred to as "second additional elements") selected from the group consisting of Se, Te, As, and Sb, and having a total concentration of the second additional elements with respect to the entire wire of 1 ppm by mass or more and 100 ppm by mass or less.

12. The bonding wire according to any one of claims 1 to 11, comprising one or more elements (hereinafter referred to as "third additional elements") selected from the group consisting of Ga and Ge, and having a total concentration of the third additional elements with respect to the entire wire of 0.011 mass% or more and 1.5 mass% or less.

13. A semiconductor device comprising the bonding wire according to any one of claims 1 to 12.

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