Al bonding wire or Al bonding ribbon

Abstract

An Al bonding wire or Al bonding ribbon that can ensure good bonding strength even when used in power semiconductors with a thin structure or a high-density element structure in which elements are arranged directly under electrodes is provided. The Al bonding wire or Al bonding ribbon contains 3.0 to 20.0 mass% Si, and in an area observed by X-ray CT analysis, when Vs is the total volume of voids with a sphere-equivalent diameter of 1 μm to less than 10 μm and Vc is the total volume of the measurement area, the ratio of Vs to Vc [Vs / Vc × 100(%)] is 0.02 to 4.00%, and when Ns is the number of Si phases with a circle-equivalent diameter of 0.5 μm to 0.8 μm in an L-section (a cross section along the central axis including the central axis) and Nc is the number of Si phases with a circle-equivalent diameter of 0.5 μm or more in the L-section, the ratio of Ns to Nc [Ns / Nc × 100(%)] is 30 to 95%.

Description

[Technical Field]

[0001] The present invention relates to an Al bonding wire or an Al bonding ribbon, and further to a semiconductor device obtained using the Al bonding wire or the Al bonding ribbon. [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 (wire material) or bonding ribbons (strip material). Power semiconductor devices mainly use bonding wires or bonding ribbons made of aluminum (Al). The wire diameter of Al bonding wires is mainly in the range of 100 μm to 600 μm, while the width of Al bonding ribbons is mainly in the range of 100 μm to 3000 μm and the thickness is mainly in the range of 50 μm to 600 μm. Here, Al bonding wires and Al bonding ribbons are collectively referred to as Al connecting materials.

[0003] In power semiconductor devices, silicon (Si) is often used as the material for the semiconductor chip, and Al-Si alloys or Al-Cu alloys are often used as the materials for the electrodes formed on the semiconductor chip. Power semiconductor devices using Al bonding wire or Al bonding ribbon are often used in high-power equipment such as air conditioners and solar power generation systems, as well as in-vehicle semiconductor devices.

[0004] There are two methods for joining Al bonding wire or Al bonding ribbon: the first bonding with an electrode on a semiconductor chip, and the second bonding with an electrode on a lead frame or substrate, both of which use wedge joining. Wedge joining is a method in which ultrasonic vibration and load are applied to the Al bonding wire or Al bonding ribbon via a metal jig (tool), destroying the surface oxide film between the Al bonding wire or Al bonding ribbon and the electrode material, exposing a new surface and performing solid-state diffusion bonding. This joining method is characterized by connecting in a solid state without melting the connecting material, and is different from welding techniques, which melt the connecting material.

[0005] Next-generation power semiconductor devices are required to operate stably for longer periods of time than general-purpose power semiconductor devices. Power semiconductor devices operate by repeatedly turning current on and off. When current is supplied to a Si semiconductor chip through an Al bonding wire or Al bonding ribbon, the temperature of the first junction rises. On the other hand, when the current supply is stopped, the temperature of the first junction drops. Thus, the first junction repeatedly rises and falls in temperature during power semiconductor operation. This repeatedly applies thermal stress to the first junction due to the difference in thermal expansion between the Al bonding wire or Al bonding ribbon and the semiconductor chip. When a connecting material made solely of high-purity Al is used, the Al bonding wire or Al bonding ribbon breaks down due to thermal stress in a relatively short period of time, making it difficult to achieve the performance required for next-generation power semiconductor devices. Therefore, next-generation power semiconductors are required to improve the junction life (hereinafter also referred to as "temperature cycle reliability") associated with temperature rise and fall of the first junction.

[0006] In response to the demand for temperature cycle reliability, Al bonding wires have been proposed that focus on improving mechanical strength. Adding specific elements to Al has been proposed as a method for improving the mechanical properties of Al bonding wires.

[0007] Patent Document 1 discloses a bonding wire made of an Al alloy containing at least magnesium (Mg) and silicon (Si), with the total content of Mg and Si being 0.03% by mass or more and 0.3% by mass or less. This patent document discloses that the decrease in bonding strength of the first bonded portion in a cold-temperature cycle test in the temperature range of 70°C to 120°C is delayed due to the effect of increasing strength through solid solution strengthening of Mg and Si and the effect of suppressing crack propagation due to precipitated magnesium silicide (MgSi).

[0008] Patent Document 2 discloses a bonding wire made of an alloy containing 0.01 to 0.2 mass% iron (Fe), 1 to 20 mass ppm silicon (Si), and the remainder being Al with a purity of 99.997 mass% or more, wherein the amount of Fe in solid solution is 0.01 to 0.06%, the amount of Fe precipitated is 7 times or less the amount of Fe in solid solution, and the wire has a fine structure with an average crystal grain size of 6 to 12 μm. This patent document also discloses that by uniformly dispersing intermetallic compound particles of Fe and Al in Al to improve the mechanical strength of the matrix and further refining the recrystallized grains, it is possible to suppress a decrease in the bonding strength of the first bonded portion in a thermal shock test in a temperature range of -50°C to 200°C.

[0009] Patent Document 3 discloses a bonding wire obtained by melting an Al-Si alloy containing 0.1 to 5 mass % silicon (Si) with the remainder being Al and impurities, and then forming the melted Al-Si alloy into a thin wire by rapid cooling. This patent document discloses that the mechanical strength is improved by rapidly cooling the molten Al-Si alloy to finely and uniformly disperse the Si. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-131010 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-129578 [Patent Document 3] Japanese Patent Application Publication No. 59-57440 Summary of the Invention [Problem to be solved by the invention]

[0011] As mentioned above, next-generation power semiconductor devices are required to withstand longer periods of use than general-purpose power semiconductor devices. During operation of a power semiconductor device, the temperature of the first bonded portion repeatedly rises and falls. As a result, because the Al bonding wire or Al bonding ribbon has a larger linear expansion coefficient than the semiconductor chip, thermal stress occurs at the first bonded portion due to the difference in linear expansion coefficients between the two, which can ultimately lead to fatigue failure of the Al bonding wire or Al bonding ribbon. A temperature cycle test is one type of accelerated evaluation test for the lifespan (temperature cycle reliability) of such a first bonded portion as it rises and falls in temperature. The Al bonding wire or Al bonding ribbon used in next-generation power semiconductors is required to exhibit excellent temperature cycle reliability in a temperature cycle test.

[0012] High-density element structures, in which elements such as diodes are located directly below the electrodes to be bonded, have been developed for power semiconductors. In such high-density element structures, there is a risk of damaging the elements directly below the electrodes when bonding wires or ribbons using ultrasonic waves and pressure. Furthermore, it is predicted that silicon carbide (SiC), which has high heat resistance, will increasingly be used in next-generation power elements to replace silicon (Si), which has been the mainstream until now. Connections for SiC power semiconductors will require even more stringent temperature cycle tests than currently available. Demand for thinner SiC substrates is expected to increase in order to reduce the substrate resistance of SiC semiconductors and improve energy conversion efficiency, as well as to reduce the amount of expensive material used. When bonding wires or ribbons using thin substrates, the risk of damaging the semiconductor increases even more.

[0013] As mentioned above, there are concerns about the increased risk of damage to semiconductors when developing high-reliability Al bonding wire or Al bonding ribbon for power semiconductors, which have improved temperature cycle reliability. As a result of improving temperature cycle reliability, the materials used have become stronger and have finer crystal grains. In particular, when using Al alloys strengthened by the addition of Si or other additives as bonding wire or ribbon, concerns exist regarding reduced bond strength during the first bonding stage due to their hardness, unstable deformation due to increased bonding load and ultrasonic output, damage to the device, and cracking. While temporary measures such as adjusting the ultrasonic vibration or load are possible to reduce such damage, these measures result in insufficient bonding and reduced temperature cycle reliability.

[0014] On the other hand, shear tests, which are commonly used to evaluate the bond strength of the first bond, measure shear fracture strength from the lateral direction. Because shear tests primarily break at the bonding wire or bonding ribbon, the apparent shear strength of high-strength bonding wires or ribbons is often overestimated due to the material strength. In other words, even if the apparent shear strength of the first bond is high for high-strength materials, the metal bond with the electrode at the bond interface may be insufficient, resulting in reduced temperature cycle reliability. Therefore, rather than relying solely on the shear strength value of the first bond, a bond evaluation that more appropriately reflects the interface condition, etc., is required, and material design suitable for high-reliability Al alloys for power semiconductors based on this standard is required.

[0015] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an Al bonding wire or Al bonding ribbon that can ensure good bonding strength even when used in power semiconductors having a thin structure or a high-density element structure in which elements are arranged directly under the electrodes. [Means for solving the problem]

[0016] As a result of intensive research into the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by an Al bonding wire or Al bonding ribbon containing 3.0 mass% or more and 20.0 mass% or less of Si, in which, in an area observed by X-ray CT analysis, the ratio of the total volume of voids having a sphere-equivalent diameter of 1 μm or more and less than 10 μm, and the ratio of the number of Si phases having a circle-equivalent diameter of 0.5 μm or more and 0.8 μm or less in an L-section (a cross section in the central axis direction including the central axis) are within a specific range.Based on this finding, the inventors further researched and completed the present invention.

[0017] That is, the present invention includes the following. <1> An Al bonding wire or Al bonding ribbon containing 3.0 mass% or more and 20.0 mass% or less of Si, In the region observed by X-ray CT (Computed Topography) analysis, when the total volume of voids having a sphere-equivalent diameter of 1 μm or more and less than 10 μm is Vs and the total volume of the measurement region is Vc, the ratio of Vs to Vc [Vs / Vc × 100 (%)] is 0.02% or more and 4.00% or less, An Al bonding wire or Al bonding ribbon in which the ratio of Ns to Nc [Ns / Nc × 100 (%)] is 30% or more and 95% or less, where Ns is the number of Si phases with a circle equivalent diameter of 0.5 μm or more and 0.8 μm or less in an L cross section (a cross section along the central axis including the central axis) and Nc is the number of Si phases with a circle equivalent diameter of 0.5 μm or more in an L cross section. <2> In the area observed by X-ray CT analysis, when the total number of voids with a sphere-equivalent diameter of 1 μm or more and less than 7 μm is defined as Ps and the total number of voids with a sphere-equivalent diameter of 1 μm or more is defined as Pc, the ratio of Ps to Pc [Ps / Pc×100(%)] is 60% or more and 98% or less. <1> The Al bonding wire or Al bonding ribbon according to claim 1. <3> Further, it contains one or more of Sr, Na, Dy, and B in a total amount of 10 mass ppm or more and 800 mass ppm or less. <1> or <2> The Al bonding wire or Al bonding ribbon according to claim 1. <4> Furthermore, it contains one or more of Ni, Ti, Fe, and Cu in a total amount of 100 mass ppm or more and 1500 mass ppm or less. <1> ~ <3> The Al bonding wire or Al bonding ribbon according to any one of the above. <5> The total concentration of elements other than Al, Si, Sr, Na, Dy, B, Ni, Ti, Fe, and Cu in the Al bonding wire or Al bonding ribbon is 0.5 mass% or less. <1> ~ <4> The Al bonding wire or Al bonding ribbon according to any one of the above. <6> The circle equivalent diameter and the number of Si phases are values ​​measured using a SEM-EDS-EBSD device. <1> ~ <5> The Al bonding wire or Al bonding ribbon according to any one of the above. <7> for semiconductor device, <1> ~ <6> The Al bonding wire or Al bonding ribbon according to any one of the above. <8> <1> ~ <7> A semiconductor device comprising the Al bonding wire or Al bonding ribbon according to any one of the above. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an Al bonding wire or Al bonding ribbon that can ensure good bonding strength even when used in a power semiconductor having a thin structure or a high-density element structure in which elements are placed directly under the electrode, and a semiconductor device obtained using the Al bonding wire or Al bonding ribbon. [Brief explanation of the drawings]

[0019] [Figure 1]1 is a schematic diagram illustrating a measurement surface (inspection surface) when measuring the small diameter ratio of the Si phase in an Al bonding wire. The measurement surface is a cross section (L cross section) in the central axis direction including the central axis of the Al bonding wire. [Figure 2] 2 is a schematic diagram illustrating the measurement surface (inspection surface) when measuring the small diameter ratio of the Si phase in an Al bonding ribbon. The measurement surface is a cross section (L cross section) in the central axis direction including the central axis of the Al bonding ribbon. [Figure 3] FIG. 3 shows an example of a brightness histogram created when determining the brightness thresholds for voids or external spaces and materials in X-ray CT analysis. [Figure 4] FIG. 4 is an example of a graph showing the number distribution of the circle-equivalent diameter of the Si phase in the L cross section. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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 of the present invention and their equivalents.

[0021] [Al bonding wire or Al bonding ribbon] The Al bonding wire or Al bonding ribbon of the present invention is an Al bonding wire or Al bonding ribbon containing 3.0 mass% or more and 20.0 mass% or less of Si, In the region observed by X-ray CT (Computed Topography) analysis, when the total volume of voids having a sphere-equivalent diameter of 1 μm or more and less than 10 μm is Vs and the total volume of the measurement region is Vc, the ratio of Vs to Vc [Vs / Vc×100(%)] (hereinafter also referred to as the "microvoid volume ratio") is 0.02% or more and 4.00% or less, When the number of Si phases having a circle-equivalent diameter of 0.5 μm or more and 0.8 μm or less in an L cross section (a cross section in the direction of the central axis including the central axis) is defined as Ns, and the number of Si phases having a circle-equivalent diameter of 0.5 μm or more in an L cross section is defined as Nc, the ratio of Ns to Nc [Ns / Nc × 100 (%)] is 30% or more and 95% or less.

[0022] As mentioned above, when evaluating the bondability of a first bond, it is difficult to accurately evaluate the bondability of high-strength materials if the bonding wire or ribbon breaks internally during a shear test. In this regard, a method for evaluating bond strength while minimizing the influence of material strength is to determine the shear strength as a value normalized by the material strength. After investigating the relationship between material strength and bondability, the inventors found that calculating the ratio (SH / PS, hereinafter referred to as the "shear strength multiplier") obtained by dividing the shear strength (SH) by the 0.2% proof stress (PS) in a tensile test is effective. The factors governing the apparent shear strength of a first bond can be divided into net bond strength and the deformation resistance of the wire or ribbon. The latter, deformation resistance, correlates with the yield strength at which the wire or ribbon yields and begins plastic deformation during a shear test. Therefore, in order to evaluate net bond strength, we devised a method to exclude the influence of the wire or ribbon's yield strength from the apparent shear strength. As the yield strength, a 0.2% proof stress, which is the strength value when the elongation rate in a tensile test is 0.2%, is used.

[0023] That is, the inventors discovered that the bond condition can be more accurately evaluated by using the shear strength ratio (SH / PS) normalized by the 0.2% proof stress (PS). A high shear strength ratio indicates that a good bond has been obtained at the bond interface. Using the shear strength ratio (SH / PS) as an index, a wire or ribbon with a high shear strength ratio can achieve both good bond strength and reduced bond damage, and can also exhibit excellent temperature cycle reliability, making it suitable for bonding power semiconductors with a thin structure or where elements are located directly under the electrodes.

[0024] As a result of further intensive research to solve the above problems, the inventors have found that Al-Si alloy wire or ribbon containing a high concentration of Si contains tiny voids, and that controlling the volume of these voids and further controlling the number distribution of the circle equivalent diameter of the Si phase are important for increasing the shear strength ratio and obtaining good initial bonding, and that the Al bonding wire or Al bonding ribbon also has excellent temperature cycle reliability and bonding shape.

[0025] The Al bonding wire or Al bonding ribbon of the present invention contains 3.0 mass% or more and 20.0 mass% or less of Si, and has an Al phase in which Si is solid-solved in Al, and a Si phase formed by crystallization or precipitation of Si. Here, the Al phase may contain other additive elements in addition to Si as a solid solution. The Si phase is a general term for Si crystallized deposits and Si precipitates. Si crystallized deposits are formed from the melt during solidification and are coarse, measuring approximately 1 to 25 μm in size, while Si precipitates are formed from the solid state and are small, measuring approximately 0.1 to several μm in size. The Si phase has a smaller linear expansion coefficient than Al, which contributes to reducing the difference in the linear expansion coefficient between the Al bonding wire or Al bonding ribbon and the semiconductor chip, thereby reducing thermal stress and improving temperature cycle reliability.

[0026] In the present invention, "wire" and "ribbon" are not classified by shape, but by their manufacturing method. That is, "wire" refers to a "connecting material manufactured by wire drawing using a die," and "ribbon" refers to a "connecting material manufactured by a rolling process." A "wire" typically has a circular cross-sectional shape, and a "ribbon" typically has a rectangular or nearly rectangular cross-sectional shape.

[0027] That is, the central axis of an Al bonding wire and a cross section (L cross section) in the direction of the central axis including the central axis are as shown in FIG. 1. FIG. 1 shows an Al bonding wire having a circular cross section, but in the case of an Al bonding ribbon having a rectangular or approximately rectangular cross section with a width W and a thickness T, the central axis refers to the axis passing through the center of the width W and the center of the thickness T, and the L cross section refers to a cross section in the direction of the central axis including the central axis and perpendicular to the width W direction (FIG. 2). Specifically, the central axis of an Al bonding ribbon and a cross section (L cross section) in the direction of the central axis including the central axis are as shown in FIG. 2. When processing the cross section to expose the L cross section of the Al bonding wire, there may be a deviation from the central axis of the Al bonding wire. In this case, if the length of the L cross section in the direction perpendicular to the central axis is 90% or more of the wire diameter of the Al bonding wire, it can be considered to be a cross section including the central axis.

[0028] The reason why the Al bonding wire or Al bonding ribbon of the present invention exhibits excellent shear strength magnification is presumed to be as follows.

[0029] The inventors have found that voids on the order of several μm in size exist in Al-Si alloy wires or ribbons, and that the voids are mainly formed around the Si phases. This is thought to be because the voids are formed inside during the wiredrawing process of the Al-Si alloy wire or the rolling process of the Al-Si alloy ribbon. During the wiredrawing or rolling process, the hard Si phase is suppressed from deformation, while the Al phase surrounding the Si phase easily undergoes plastic deformation, which is thought to result in the voids being formed at the end of the Si phase. Furthermore, the small size of the voids and the low total volume ratio of these small voids are thought to be advantageous in mitigating compressive deformation due to the application of load during joining and locally dispersing ultrasonic vibrations to achieve uniform deformation.

[0030] In the present invention, the interrelationship between the volume fraction of microvoids and the number distribution of the circle-equivalent diameter of the Si phase further enhances the effect of improving the bonded interface and increases the shear strength ratio. By setting the microvoid volume fraction [Vs / Vc × 100 (%)] in the range of 0.02% to 4.00%, the propagation of compressive stress and ultrasonic vibration is alleviated, thereby reducing the occurrence of cracks under the bonded portion. Furthermore, by simultaneously satisfying the number distribution of Si phases with small circle-equivalent diameters, it is believed that the concentration of local strain near the bonded interface can be alleviated, thereby promoting metal bonding at the bonded interface.

[0031] There are concerns that stress and strain may concentrate around Si phases with large equivalent circle diameters, and that cracks may originate from the Si phases. By using Si phases with small equivalent circle diameters, it is thought that stress concentration and strain near the bonding interface can be reduced relatively uniformly. Therefore, by controlling the distribution of the number of Si phases with small equivalent circle diameters relative to the total number of Si phases, the shear strength ratio can be increased.

[0032] -Si concentration- A Si concentration in the range of 3.0% by mass or more and 20.0% by mass or less helps improve the shear strength ratio and reduce thermal distortion at the bonded portion, thereby improving temperature cycle reliability. Specifically, a Si concentration of 3.0% by mass or more can significantly improve temperature cycle reliability. Furthermore, with advances and optimization of equipment and conditions used in the manufacture and bonding of wires, etc., higher Si concentrations have become tolerable while suppressing defects such as wire breakage during processing, deterioration of surface properties, reduction in initial bond strength due to hardening, and damage to semiconductor chips. A Si concentration of 20.0% by mass or less can effectively suppress these defects while improving the shear strength ratio. From the viewpoint of achieving good temperature cycle reliability, the Si concentration in the Al bonding wire or Al bonding ribbon of the present invention is 3.0% by mass or more, preferably 3.5% by mass or more, more preferably 4.0% by mass or more, and even more preferably 4.2% by mass or more, 4.4% by mass or more, 4.5% by mass or more, 4.6% by mass or more, 4.8% by mass or more, or 5.0% by mass or more. In addition, from the viewpoint of improving the shear strength ratio while effectively suppressing defects such as a decrease in initial bonding strength due to hardening and damage to the semiconductor chip, the Si concentration in the Al bonding wire or Al bonding ribbon of the present invention is 20.0 mass% or less, preferably 19.0 mass% or less, 18.0 mass% or less, 17.0 mass% or less, 16.0 mass% or less, 15.0 mass% or less, 14.5 mass% or less, 14.0 mass% or less, 13.5 mass% or less, 13.0 mass% or less, or 12.5 mass% or less. Furthermore, if the hardness of the Al bonding wire or Al bonding ribbon is high, damage to the semiconductor chip is more likely to occur during the first bonding depending on the bonding conditions of ultrasonic vibration and load. From the viewpoint of obtaining good bonding strength under a wider range of bonding conditions, the Si concentration in the Al bonding wire or Al bonding ribbon of the present invention is more preferably 12.0 mass% or less, even more preferably 11.5 mass% or less or 11.0 mass% or less, and particularly preferably 10.8 mass% or less, 10.6 mass% or less, 10.5 mass% or less, 10.4 mass% or less, 10.2 mass% or less, or 10.0 mass% or less.

[0033] For example, an ICP (Inductively Coupled Plasma) optical emission spectrometer or an ICP mass spectrometer can be used to analyze the concentration of elements contained in the Al bonding wire or Al bonding ribbon of the present invention. If elements derived from atmospheric contaminants such as oxygen or carbon are adsorbed on the surface of the Al bonding wire or Al bonding ribbon, it is effective to clean the surface with an acid or alkali depending on the adsorbed substance before analysis.

[0034] -Microvoid volume ratio- In the region observed by X-ray CT (Computed Tomography) analysis, the total volume of voids with a sphere-equivalent diameter of 1 μm or more but less than 10 μm is defined as Vs, and the total volume of the measurement region is defined as Vc. By controlling the ratio of Vs to Vc [Vs / Vc × 100 (%)] within an appropriate range and also controlling the distribution of the circle-equivalent diameter of the Si phase (described below) within an appropriate range, it is possible to promote metal bonding at the bonding interface, thereby increasing the shear strength ratio and improving the reliability of temperature cycle tests.

[0035] The inventors have confirmed that a relatively small volume of voids with a sphere-equivalent diameter in the range of 1 μm or more but less than 10 μm contributes to improved bondability. The lower limit of the sphere-equivalent diameter of the voids was set to 1 μm, taking into consideration that a sphere-equivalent diameter of 1 μm or more provides a sufficient effect of alleviating strain, and that the spatial resolution of X-ray CT analysis is limited. The upper limit of the sphere-equivalent diameter of the voids was set to 10 μm, comprehensively considering that a sphere-equivalent diameter of less than 10 μm provides a sufficient improvement effect, and that it is advantageous for production by wire drawing or rolling.

[0036] The reason why the shear strength factor improves when the microvoid volume ratio [Vs / Vc × 100 (%)] is 0.02% or more and 4.00% or less is thought to be as follows. By setting the microvoid volume ratio to 0.02% or more, the effect of the voids in alleviating strain can be sufficiently increased, thereby sufficiently achieving the effect of increasing the shear strength factor. On the other hand, regarding the upper limit, by setting the microvoid volume ratio to 4.00% or less, the effect of the Si phase in reducing thermal expansion can be prevented from being hindered. In other words, by controlling the microvoid volume ratio to the range of 0.02% or more and 4.00% or less, it can be applied to the bonding of thin power semiconductors or power semiconductors with elements placed directly under the electrodes.

[0037] From the viewpoint of further improving the shear strength ratio, the lower limit of the microvoid volume ratio [Vs / Vc × 100 (%)] of the Al bonding wire or Al bonding ribbon is 0.02% or more, preferably 0.03% or more or 0.05% or more, more preferably 0.08% or more or 0.10% or more, even more preferably 0.20% or more or 0.30% or more, particularly preferably 0.50% or more, 0.80% or more or 1.00% or more. From the viewpoint of further improving the shear strength ratio, the upper limit of the microvoid volume ratio [Vs / Vc × 100 (%)] of the Al bonding wire or Al bonding ribbon is 4.00% or less, preferably 3.80% or less or 3.60% or less, more preferably 3.40% or less or 3.20% or less, even more preferably 3.00% or less, 2.80% or less or 2.60% or less, particularly preferably 2.40% or less, 2.20% or less or 2.00% or less.

[0038] -Distribution of circle equivalent diameter of Si phase in L cross section- From the viewpoint of further improving the shear strength ratio, when the number of Si phases having a circle-equivalent diameter of 0.5 μm or more and 0.8 μm or less in the L cross section of the Al bonding wire or Al bonding ribbon is Ns, and the number of Si phases having a circle-equivalent diameter of 0.5 μm or more in the L cross section is Nc, the ratio of Ns to Nc [Ns / Nc × 100(%)] (hereinafter also referred to as the "small diameter ratio of Si phases") is 30% or more and 95% or less. The lower limit of the small diameter ratio of Si phases [Ns / Nc × 100(%)] is preferably 32% or more, 35% or more, 38% or more, 40% or more, 42% or more, or 45% or more, more preferably 48% or more, even more preferably 50% or more or 52% or more, and particularly preferably 55% or more or 60% or more. The upper limit of the small diameter ratio of the Si phase [Ns / Nc × 100(%)] is preferably 92% or less, 90% or less, 88% or less, or 85% or less, more preferably 82% or less, or 80% or less, even more preferably 78% or less, or 75% or less, and particularly preferably 72% or less, or 70% or less. In one embodiment, the small diameter ratio of the Si phase [Ns / Nc × 100(%)] is preferably 40% or more and 90% or less.

[0039] The reason why the proportion of Si phases with equivalent circle diameters of 0.5 μm to 0.8 μm is important is believed to be as follows: Si phases with equivalent circle diameters of 0.5 μm or more have a sufficiently large volume, which allows them to sufficiently reduce thermal expansion. Furthermore, from the perspective of the analytical accuracy of current EDS and EBSD analysis equipment, it is appropriate to target Si phases with equivalent circle diameters of 0.5 μm or more. On the other hand, Si phases with equivalent circle diameters of 0.8 μm or less ensure sufficient uniformity of stress and strain near the bonding interface due to the Si phase. Furthermore, the reason why the small diameter ratio of the Si phase [Ns / Nc × 100 (%)] in the range of 30% to 95% can further improve the shear strength ratio is believed to be as follows: By setting the small diameter ratio of the Si phase to 30% or more, an increase in the proportion of Si phases with coarse equivalent circle diameters can be suppressed, which reduces the interference with ultrasonic vibration transmission, thereby strengthening the metal bonding at the interface. On the other hand, by setting the small diameter ratio of the Si phase to 95% or less, it is possible to prevent the resistance to plastic deformation from increasing due to fine Si, thereby reducing the risk of damaging the element directly below the electrode.

[0040] Here, each Si phase is formed in a particle shape, and it has been confirmed that the number of Si phase particles has a large effect on the strain at the bonding interface. Therefore, the ratio of the number of Si phase particles affects the shear strength multiplier. On the other hand, the effect of coarse particles is overestimated by particle area, making it difficult to accurately evaluate the correlation with the shear strength multiplier.

[0041] -Micro void number ratio- In addition to controlling the microvoid volume ratio [Vs / Vc × 100(%)] described above, when the total number of voids in the region observed by X-ray CT analysis that have a sphere-equivalent diameter of 1 μm or more and less than 7 μm is defined as Ps, and the total number of voids that have a sphere-equivalent diameter of 1 μm or more is defined as Pc, by keeping the ratio of Ps to Pc [Ps / Pc × 100(%)] (hereinafter referred to as the "microvoid number ratio") at 60% or more and 98% or less, it is possible to enhance the effects of achieving both an increase in shear strength magnification and a reduction in chip damage directly below the bond.

[0042] By properly controlling the microvoid ratio [Ps / Pc × 100 (%)], which is the ratio of microvoids with a sphere-equivalent diameter of 1 μm or more but less than 7 μm, ultrasonic vibration propagation and strain uniformity near the bonding interface can be improved. Because large voids have little effect on the improvement, controlling the void volume fraction while increasing the microvoid ratio (the ratio of microvoids to the total number of voids) promotes deformation in the first bond and increases the shear strength ratio. This allows for adjustment of the load and ultrasonic output, resulting in improved reduction of chip damage directly below the bond. For example, using bonding conditions in which the ultrasonic output is initially high and gradually decreases (hereinafter referred to as "graded bonding conditions") can also be advantageous in reducing damage to semiconductors during bonding. The synergistic effect of simultaneously controlling the microvoid ratio and the Si small diameter ratio can expand the margin of bonding conditions for thin power semiconductors or power semiconductors with elements located directly below the electrodes, and good bonding can be achieved even under graded bonding conditions.

[0043] The reason why the number of microvoids with a sphere-equivalent diameter in the range of 1 μm or more and less than 7 μm is important is that statistical analysis of experimental data has confirmed that a void size of 1 μm or more as described above has a sufficiently large effect of alleviating distortion, and that a void size of less than 7 μm has a sufficiently large improvement effect. The reason why the microvoid number ratio [Ps / Pc × 100 (%)] is preferable is as follows: A microvoid number ratio of 60% or more can fully achieve the distortion alleviation effect of the voids, thereby fully achieving the effect of increasing the shear strength ratio under the gradient joining conditions. On the other hand, a microvoid number ratio of 98% or less makes industrial production relatively easy.

[0044] From the viewpoint of further increasing the shear strength magnification under the inclined joining conditions, the lower limit of the microvoid number ratio [Ps / Pc×100(%)] is 60% or more, preferably 62% or less, more preferably 64% or less, even more preferably 66% or less, and particularly preferably 68% or less or 70% or less. From the viewpoint of further increasing the shear strength magnification under the inclined joining conditions, the upper limit of the microvoid number ratio [Ps / Pc×100(%)] is 98% or less, preferably 96% or less, more preferably 94% or less or 92% or less, even more preferably 90% or less or 88% or less, and particularly preferably 86% or less or 84% or less.

[0045] -Analysis of voids using X-ray CT- In the present invention, the microvoid volume ratio [Vs / Vc × 100 (%)] and the microvoid number ratio [Ps / Pc × 100 (%)] are measured using X-ray CT analysis. X-ray CT analysis technology is excellent for non-destructively observing voids in materials, and by performing three-dimensional image analysis based on the data, microvoids in metals can be observed with high precision. The following describes an example of an analysis method for measuring voids in an Al bonding wire with a wire diameter of 300 μm. The analysis conditions are not limited to these, and appropriate analysis conditions can be selected depending on the device and sample. For example, a 3D X-ray microscope "Xradia 520 Versa" (manufactured by ZEISS) can be used as an X-ray CT device. The main measurement conditions for X-ray CT are as follows: X-ray voltage 40 kV, X-ray output 3 W, wavelength limiting filter LE1, and magnification lens 4x. It has been confirmed that under these conditions, a transmission image with a transmittance of 30% to 70% can be obtained. To observe minute voids, the pixel size is set to approximately 0.7 μm, allowing the measurement field of view to be approximately 700 μm x 700 μm x 700 μm. The sample is fixed at a length of approximately 10 mm, and CT projection images can be measured by passing X-rays through it at a rotation angle of 360 degrees around the sample axis. After CT projection images are obtained at all angles, reconstruction processing such as center shifting can be performed to obtain 3D image data.

[0046] Next, the 3D image data is analyzed using image analysis software. Avizo Inspection can be used as the image analysis software. Specifically, a brightness histogram (Figure 3) is created using the measurement data. The brightness value at the midpoint of two peak positions corresponding to voids or external space and material is set as a threshold. Image data areas showing brightness lower than the threshold are identified as voids or external space (the environment surrounding the sample). Next, for the identified voids and external space, the external space areas are selected and removed from the image data area. This allows image data containing only voids in the material within the measurement area of ​​the sample to be identified. Next, using a similar process, image data with brightness higher than the threshold is identified as image data related to material. This "material" refers to something that has mass and volume. In the case of the Al bonding wire or Al bonding ribbon of the present invention, this includes Al, Si, element group 1, element group 2, and other elements, as well as their alloys, oxides, and intermetallic compounds. Furthermore, in the X-ray CT analysis of the present invention, pixels showing brightness higher than the above threshold are considered to contain material.

[0047] The image data of the voids and material thus obtained are analyzed. The calculation methods for the microvoid volume ratio and microvoid number ratio are described below. Image analysis software is used to calculate the total volume Vs of voids with a sphere-equivalent diameter of 1 μm or more but less than 10 μm, the total volume of voids of all sizes (Vg), and the volume of material (Vm). The total volume Vc of the measurement area is calculated by adding Vg and Vm (Vc = Vg + Vm). The microvoid volume ratio [Vs / Vc × 100(%)], which is the ratio of Vs to Vc, is then calculated. Furthermore, image analysis software is used to calculate the total number Ps of voids with a sphere-equivalent diameter of 1 μm or more but less than 7 μm, and the total number Pc of voids with a sphere-equivalent diameter of 1 μm or more. The microvoid number ratio is calculated as the ratio Ps to Pc [Ps / Pc × 100(%)].

[0048] -Method for measuring the circle equivalent diameter of the Si phase and calculating the small diameter ratio- This paper describes a method for measuring the circle-equivalent diameter of the Si phase in the L-section of an Al bonding wire or Al bonding ribbon. The circle-equivalent diameter of the Si phase in the L-section can be measured using a SEM-EDS-EBSD instrument. Specifically, this method combines information on the Al and Si concentrations obtained by SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) with information on the crystal orientation obtained by electron backscatter diffraction (EBSD). More specifically, in the measurement area where the L-section of the Al bonding wire or Al bonding ribbon is used as the inspection surface, Al and Si concentration measurements are performed using EDS, and crystal orientation analysis is performed using EBSD simultaneously. Next, the Al and Si phases are separated and extracted from the EDS measurement results using the analysis software provided with the instrument. Specifically, it is preferable to use the Chi Scan function, which is a function of the analysis software OIM Data Collection or OIM Analysis (both manufactured by TSL Solutions) attached to an FE-SEM (Field Emission-Scanning Electron Microscope) device. Then, for the region identified as the Si phase, the crystal orientation can be analyzed using the analysis software attached to the device. If the orientation difference between the measurement points is 15° or more, it is determined to be a grain boundary and the circle equivalent diameter is calculated. In the process of calculating the small diameter ratio of the Si phase, parts where the crystal orientation cannot be measured or parts where the crystal orientation can be measured but the reliability of the orientation analysis is low are excluded from the calculation. Therefore, in one embodiment, the small diameter ratio of the Si phase in the L cross section of the Al bonding wire or Al bonding ribbon of the present invention is calculated by the following steps (1) to (3). (1) The L-section of the Al bonding wire or Al bonding ribbon is used as the inspection surface, and the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Use the Chi Scan function to separate and extract Al and Si. Specifically, by setting a tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information in the material file. (3) For the areas identified as Si phase, the crystal orientation is analyzed, and if the misorientation between measurement points is 15° or more, it is determined to be a grain boundary, and the circle-equivalent diameter of each crystal grain is calculated. The number of crystal grains identified as Si phase is tallied to determine the total number of Si phase particles, Nc. Here, Si phases with a circle-equivalent diameter of 0.5 μm or more are targeted. Taking into account the analytical accuracy of current ESD and EBSD analysis equipment, fine particles less than 0.5 μm are excluded. In addition, the number of Si phases, Ns, with a circle-equivalent diameter in the range of 0.5 μm to 0.8 μm is tallied. Then, the ratio of Ns to Nc [Ns / Nc × 100 (%)] (the small diameter ratio of Si phases) is calculated.

[0049] In step (2) above, the Tolerance (%) setting can be selected in the range of 20 to 40%, and for standard analysis of the L cross section of Al bonding wire or Al bonding ribbon, it is preferable to compare at approximately 30%. Here is a supplementary explanation of the procedure for adjusting this Tolerance. It is preferable to select or confirm the Tolerance value so that the shape and size of the Si phase extracted and identified by the Chi Scan function are equivalent to those identified in the EDS map, which displays the Si element concentration in EDS analysis in two dimensions.

[0050] In the present invention, the small diameter ratio of the Si phase is defined as the average (arithmetic mean) of the orientation ratio values ​​obtained by measuring at three or more locations. When selecting the measurement area, in order to ensure the objectivity of the measurement data, it is preferable to obtain measurement samples from the Al bonding wire or Al bonding ribbon to be measured at intervals of 50 cm or more along the central axis of the Al bonding wire or Al bonding ribbon and provide them for measurement. Furthermore, in the present invention, the measurement area for crystal orientation using the EBSD method has a length in the direction of the central axis of the Al bonding wire or Al bonding ribbon of 300 μm or more but less than 800 μm, and it is desirable that the entire Al bonding wire or Al bonding ribbon is included in the direction perpendicular to the central axis of the Al bonding wire or Al bonding ribbon. However, if the size is too large to measure the entire area, it can be adjusted to a range of less than 600 μm.

[0051] An example of the measurement results is shown in Figure 4. The horizontal axis shows the circle equivalent diameter of the Si phase, with each interval having a width of 0.1 μm, and the vertical axis shows the number of particles. The range of 0.5 μm to 0.8 μm is shown with a double-headed arrow, and the particle number ratio in this interval [Ns / Nc × 100 (%)] is 50%. It has been confirmed that this Al bonding wire exhibits excellent shear strength multiplier.

[0052] -Addition of Sr, Na, Dy, and B- The Al bonding wire or Al bonding ribbon of the present invention may further contain one or more of Sr, Na, Dy, and B (hereinafter also referred to as the "first element group"). The total concentration of the first element group may be 0 ppm by mass, preferably 1 ppm by mass or more, more preferably 3 ppm by mass or more, even more preferably 5 ppm by mass or more, and particularly preferably 8 ppm by mass or more or 10 ppm by mass or more. The upper limit of the total concentration of the first element group is preferably 10,000 ppm by mass or less or 8,000 ppm by mass or less, more preferably 5,000 ppm by mass or less or 3,000 ppm by mass or less, even more preferably 2,000 ppm by mass or less or 1,000 ppm by mass or less, and particularly preferably 900 ppm by mass or less or 800 ppm by mass or less. In one embodiment, the total concentration of the first element group is preferably 10 ppm by mass or more and 800 ppm by mass or less.

[0053] By further containing at least one of Sr, Na, Dy, and B in a total content of 10 mass ppm to 800 mass ppm, the frequency of wire breakage during wiredrawing of the Al bonding wire or Al bonding ribbon can be reduced. Al alloys containing a high concentration of Si at 3.0 mass% to 20.0 mass% tend to have a higher frequency of wire breakage during the wiredrawing process. This is thought to be due in part to the fact that Si phase particles crystallized during solidification cause stress concentration during wiredrawing, inducing wire breakage. It is presumed that the addition of the first element group can uniformly distribute the particulate Si phase and inhibit the growth and coarsening of the Si phase, thereby alleviating stress concentration during wiredrawing and reducing wire breakage. It is thought that the addition of the first element group, along with controlling the microvoid volume ratio of the Si phase and the small diameter ratio of the Si phase, enhances the effect of alleviating stress concentration during wiredrawing.

[0054] From the viewpoint of reducing the frequency of wire breakage during wire drawing, the total concentration of the first element group in the Al bonding wire or Al bonding ribbon of the present invention is more preferably 20 ppm by mass or more, even more preferably 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more, and the upper limit is preferably 750 ppm by mass or less, more preferably 740 ppm by mass or less, 720 ppm by mass or less, or 700 ppm by mass or less, even more preferably 680 ppm by mass or less, 650 ppm by mass or less, 620 ppm by mass or less, or 600 ppm by mass or less, and particularly preferably 580 ppm by mass or less, 550 ppm by mass or less, 520 ppm by mass or less, or 500 ppm by mass or less.

[0055] When the Al bonding wire or Al bonding ribbon of the present invention contains one or more elements from the first element group, it may contain one element from the first element group, two elements from the first element group, three elements from the first element group, or all four elements from the first element group. Also, when the Al bonding wire or Al bonding ribbon of the present invention contains one or more elements from the first element group, it may contain Sr, Na, Dy, or B.

[0056] When the Al bonding wire or Al bonding ribbon of the present invention contains Sr from the first element group, the Sr concentration may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, or 8 ppm by mass or more. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wire drawing, the Sr concentration is more preferably 10 ppm by mass or more, and even more preferably 20 ppm by mass or more, 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more. The upper limit of the Sr concentration is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, 3,000 ppm by mass or less, 2,000 ppm by mass or less, 1,000 ppm by mass or less, or 900 ppm by mass or less. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wiredrawing, the Sr concentration is more preferably 800 ppm by mass or less, even more preferably 750 ppm by mass or less, 740 ppm by mass or less, 720 ppm by mass or less, 700 ppm by mass or less, 680 ppm by mass or less, 650 ppm by mass or less, 620 ppm by mass or less, 600 ppm by mass or less, 580 ppm by mass or less, 550 ppm by mass or less, 520 ppm by mass or less, or 500 ppm by mass or less.

[0057] When the Al bonding wire or Al bonding ribbon of the present invention contains Na in the first element group, the Na concentration may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, or 8 ppm by mass or more. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wire drawing, the Na concentration is more preferably 10 ppm by mass or more, even more preferably 20 ppm by mass or more, 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more. The upper limit of the Na concentration is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, 3,000 ppm by mass or less, 2,000 ppm by mass or less, 1,000 ppm by mass or less, or 900 ppm by mass or less. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wiredrawing, the Na concentration is more preferably 800 ppm by mass or less, even more preferably 750 ppm by mass or less, 740 ppm by mass or less, 720 ppm by mass or less, 700 ppm by mass or less, 680 ppm by mass or less, 650 ppm by mass or less, 620 ppm by mass or less, 600 ppm by mass or less, 580 ppm by mass or less, 550 ppm by mass or less, 520 ppm by mass or less, or 500 ppm by mass or less.

[0058] When the Al bonding wire or Al bonding ribbon of the present invention contains Dy from the first element group, the Dy concentration may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, or 8 ppm by mass or more. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wire drawing, the Dy concentration is more preferably 10 ppm by mass or more, even more preferably 20 ppm by mass or more, 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more. The upper limit of the Dy concentration is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, 3,000 ppm by mass or less, 2,000 ppm by mass or less, 1,000 ppm by mass or less, or 900 ppm by mass or less. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wiredrawing, the Dy concentration is more preferably 800 ppm by mass or less, even more preferably 750 ppm by mass or less, 740 ppm by mass or less, 720 ppm by mass or less, 700 ppm by mass or less, 680 ppm by mass or less, 650 ppm by mass or less, 620 ppm by mass or less, 600 ppm by mass or less, 580 ppm by mass or less, 550 ppm by mass or less, 520 ppm by mass or less, or 500 ppm by mass or less.

[0059] When the Al bonding wire or Al bonding ribbon of the present invention contains B from the first element group, the concentration of B may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, or 8 ppm by mass or more. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wire drawing, the concentration of B is more preferably 10 ppm by mass or more, even more preferably 20 ppm by mass or more, 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more. The upper limit of the concentration of B is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, 3,000 ppm by mass or less, 2,000 ppm by mass or less, 1,000 ppm by mass or less, or 900 ppm by mass or less. Furthermore, from the viewpoint of reducing the frequency of wire breakage during wiredrawing, the concentration of B is more preferably 800 ppm by mass or less, still more preferably 750 ppm by mass or less, 740 ppm by mass or less, 720 ppm by mass or less, 700 ppm by mass or less, 680 ppm by mass or less, 650 ppm by mass or less, 620 ppm by mass or less, 600 ppm by mass or less, 580 ppm by mass or less, 550 ppm by mass or less, 520 ppm by mass or less, or 500 ppm by mass or less.

[0060] -Addition of Ni, Ti, Fe, and Cu- The Al bonding wire or Al bonding ribbon of the present invention may further contain one or more of Ni, Ti, Fe, and Cu (hereinafter also referred to as the "second element group"). The total concentration of the second element group may be 0 ppm by mass, preferably 1 ppm by mass or more or 3 ppm by mass or more, more preferably 5 ppm by mass or more or 8 ppm by mass or more, even more preferably 10 ppm by mass or more or 30 ppm by mass or more, particularly preferably 50 ppm by mass or more, 80 ppm by mass or more, or 100 ppm by mass or more. The upper limit of the total concentration of the second element group is preferably 10,000 ppm by mass or less, more preferably 8,000 ppm by mass or less, even more preferably 5,000 ppm by mass or less, particularly preferably 3,000 ppm by mass or less, 2,000 ppm by mass or less, 1,800 ppm by mass or less, 1,600 ppm by mass or less, or 1,500 ppm by mass or less. In one embodiment, the total concentration of the second element group is preferably 100 ppm by mass or more and 1,500 ppm by mass or less.

[0061] The Al bonding wire or Al bonding ribbon of the present invention further contains one or more of Ni, Ti, Fe, and Cu in a total amount of 100 ppm by mass to 1500 ppm by mass, thereby suppressing scratches and abrasions on the surface of the Al bonding wire or Al bonding ribbon and forming a smooth surface. Al alloys containing Si at a high concentration of 3.0% by mass to 20.0% by mass may harden the surface and cause the Si phase and Al oxide present on the surface to fall off, resulting in scratches and abrasions on the surface during wiredrawing, resulting in an Al bonding wire or Al bonding ribbon with large surface irregularities. It is presumed that the addition of the second element group stabilizes the Al oxide on the surface of the Al bonding wire or Al bonding ribbon, refines the structure of the Al crystal grains, and hardens them, thereby reducing scratches and abrasions during wiredrawing. It is believed that by controlling the microvoid volume ratio of the Si phase and the small diameter ratio of the Si phase, as well as adding the second element group, the occurrence of scratches and abrasions on the surface of the Al bonding wire or Al bonding ribbon can be suppressed, thereby enhancing the effect of forming a smooth surface.

[0062] From the viewpoint of forming an Al bonding wire or Al bonding ribbon having a smooth surface by suppressing the occurrence of scratches and abrasions on the surface, the total concentration of the second element group in the Al bonding wire or Al bonding ribbon of the present invention is more preferably 150 mass ppm or more, even more preferably 200 mass ppm or more, 250 mass ppm or more, or 300 mass ppm or more, and the upper limit is more preferably 1200 mass ppm or less, even more preferably 1000 mass ppm or less, 900 mass ppm or less, or 800 mass ppm or less, and particularly preferably 700 mass ppm or less, 600 mass ppm or less, or 500 mass ppm or less.

[0063] When the Al bonding wire or Al bonding ribbon of the present invention contains one or more elements from the second element group, it may contain one element from the second element group, two elements from the second element group, three elements from the second element group, or all four elements from the second element group. Also, when the Al bonding wire or Al bonding ribbon of the present invention contains one or more elements from the second element group, it may contain Ni, Ti, Fe, or Cu.

[0064] When the Al bonding wire or Al bonding ribbon of the present invention contains Ni from the second element group, the Ni concentration may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 30 ppm by mass or more, 50 ppm by mass or more, or 80 ppm by mass or more. Furthermore, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Ni concentration is more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, 200 ppm by mass or more, 250 ppm by mass or more, or 300 ppm by mass. The upper limit of the Ni concentration is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, or 3,000 ppm by mass or less. Furthermore, from the viewpoint of suppressing the occurrence of scratches and abrasions on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Ni concentration is more preferably 2000 mass ppm or less, even more preferably 1800 mass ppm or less, 1600 mass ppm or less, 1500 mass ppm or less, 1200 mass ppm or less, 1000 mass ppm or less, 900 mass ppm or less, 800 mass ppm or less, 700 mass ppm or less, 600 mass ppm or less, or 500 mass ppm or less.

[0065] When the Al bonding wire or Al bonding ribbon of the present invention contains Ti from the second element group, the Ti concentration may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 30 ppm by mass or more, 50 ppm by mass or more, or 80 ppm by mass or more. Furthermore, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Ti concentration is more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, 200 ppm by mass or more, 250 ppm by mass or more, or 300 ppm by mass. The upper limit of the Ti concentration is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, or 3,000 ppm by mass or less. Furthermore, from the viewpoint of suppressing the occurrence of scratches and abrasions on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Ti concentration is more preferably 2000 mass ppm or less, even more preferably 1800 mass ppm or less, 1600 mass ppm or less, 1500 mass ppm or less, 1200 mass ppm or less, 1000 mass ppm or less, 900 mass ppm or less, 800 mass ppm or less, 700 mass ppm or less, 600 mass ppm or less, or 500 mass ppm or less.

[0066] When the Al bonding wire or Al bonding ribbon of the present invention contains Fe from the second element group, the Fe concentration may be 0 ppm by mass, preferably 1 ppm by mass or more, 3 ppm by mass or more, 5 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 30 ppm by mass or more, 50 ppm by mass or more, or 80 ppm by mass or more. Furthermore, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Fe concentration is more preferably 100 ppm by mass or more, even more preferably 150 ppm by mass or more, 200 ppm by mass or more, 250 ppm by mass or more, or 300 ppm by mass. The upper limit of the Fe concentration is preferably 10,000 ppm by mass or less, 8,000 ppm by mass or less, 5,000 ppm by mass or less, or 3,000 ppm by mass or less. Furthermore, from the viewpoint of suppressing the occurrence of scratches and abrasions on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Fe concentration is more preferably 2000 mass ppm or less, even more preferably 1800 mass ppm or less, 1600 mass ppm or less, 1500 mass ppm or less, 1200 mass ppm or less, 1000 mass ppm or less, 900 mass ppm or less, 800 mass ppm or less, 700 mass ppm or less, 600 mass ppm or less, or 500 mass ppm or less.

[0067] When the Al bonding wire or Al bonding ribbon of the present invention contains Cu from the second element group, the Cu concentration may be 0 mass ppm, preferably 1 mass ppm or more, 3 mass ppm or more, 5 mass ppm or more, 8 mass ppm or more, 10 mass ppm or more, 30 mass ppm or more, 50 mass ppm or more, or 80 mass ppm or more. Furthermore, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Cu concentration is more preferably 100 mass ppm or more, even more preferably 150 mass ppm or more, 200 mass ppm or more, 250 mass ppm or more, or 300 mass ppm. The upper limit of the Cu concentration is preferably 10,000 mass ppm or less, 8,000 mass ppm or less, 5,000 mass ppm or less, or 3,000 mass ppm or less. Furthermore, from the viewpoint of suppressing the occurrence of scratches and abrasions on the surface and forming an Al bonding wire or Al bonding ribbon with a smooth surface, the Cu concentration is more preferably 2000 mass ppm or less, even more preferably 1800 mass ppm or less, 1600 mass ppm or less, 1500 mass ppm or less, 1200 mass ppm or less, 1000 mass ppm or less, 900 mass ppm or less, 800 mass ppm or less, 700 mass ppm or less, 600 mass ppm or less, or 500 mass ppm or less.

[0068] As the aluminum raw material for manufacturing the Al bonding wire or Al bonding ribbon of the present invention, it is preferable to use Al with a purity of 4N (Al: 99.99% by mass or more), and it is even more preferable to use Al with a lower impurity content of 5N (Al: 99.999% by mass or more). In one embodiment, Al with a purity of 3N (Al: 99.9% by mass or more) may be used.

[0069] The Al bonding wire or Al bonding ribbon of the present invention may further contain elements other than Al, Si, the first element group, and the second element group (hereinafter also referred to as "other elements"). That is, "other elements" are elements other than Al, Si, Sr, Na, Dy, B, Ni, Ti, Fe, and Cu, and the Al bonding wire or Al bonding ribbon of the present invention may further contain elements other than Al, Si, Sr, Na, Dy, B, Ni, Ti, Fe, and Cu. The total concentration of other elements in the Al bonding wire or Al bonding ribbon is not particularly limited as long as it does not impair the effects of the present invention. The total concentration of the other elements may be, for example, 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.15% by mass or less, 0.1% by mass or less, 0.08% by mass or less, 0.06% by mass or less, 0.05% by mass or less, 0.04% by mass or less, 0.03% by mass or less, 0.025% by mass or less, 0.02% by mass or less, 0.018% by mass or less, 0.016% by mass or less, 0.015% by mass or less, 0.014% by mass or less, 0.012% by mass or less, or 0.01% by mass or less. The lower limit of the total concentration of the other elements is not particularly limited, and may be 0% by mass.

[0070] In one embodiment, the remainder of the Al bonding wire or Al bonding ribbon of the present invention consists of Al and other elements. Therefore, in a preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, and other elements. In another preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, one or more elements from the first element group, and other elements. In yet another preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, one or more elements from the second element group, and other elements. In yet another preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, one or more elements from the first element group, one or more elements from the second element group, and other elements.

[0071] In one embodiment, the remainder of the Al bonding wire or Al bonding ribbon of the present invention consists of Al and unavoidable impurities. Thus, in a preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, and unavoidable impurities. In another preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, one or more elements from the first element group, and unavoidable impurities. In yet another preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, one or more elements from the second element group, and unavoidable impurities. In yet another preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, one or more elements from the first element group, one or more elements from the second element group, and unavoidable impurities.

[0072] In a preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention does not have a coating mainly composed of a metal other than Al on the outer periphery of the Al bonding wire or Al bonding ribbon. Here, "a coating mainly composed of a metal other than Al" refers to a coating in which the content of a metal other than Al is 50 mass % or more.

[0073] The Al bonding wire or Al bonding ribbon of the present invention may be either an Al bonding wire or an Al bonding ribbon. When the present invention is an Al bonding wire, its wire diameter is not particularly limited and may be, for example, 50 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, 120 μm or more, 140 μm or more, 150 μm or more, 180 μm or more, or 200 μm or more. The upper limit of the wire diameter is not particularly limited and may be, for example, 600 μm or less, 550 μm or less, 500 μm or less, 450 μm or less, or 400 μm or less. In one embodiment, the wire diameter of the Al bonding wire of the present invention may be in the range of 100 to 600 μm, and preferably 200 to 400 μm. When the present invention is an Al bonding ribbon, the dimensions (width W x thickness T) of its rectangular or approximately rectangular cross section are not particularly limited, and for example, W may be 100 to 3000 μm, and T may be 50 to 600 μm.

[0074] The Al bonding wire or Al bonding ribbon of the present invention exhibits excellent shear strength magnification, and therefore can provide excellent temperature cycle reliability. Therefore, the Al bonding wire or Al bonding ribbon of the present invention can be suitably used as an Al bonding wire or Al bonding ribbon for semiconductor devices. The Al bonding wire or Al bonding ribbon of the present invention can be particularly suitably used as an Al bonding wire or Al bonding ribbon for power semiconductor devices, more suitably used as an Al bonding wire or Al bonding ribbon for SiC power semiconductor devices, and even more suitably used as an Al bonding wire or Al bonding ribbon for power semiconductor devices with a thin structure or in which an element is arranged directly under the electrode.

[0075] -Method for manufacturing Al bonding wire or Al bonding ribbon- An example of a method for manufacturing an Al bonding wire or Al bonding ribbon according to the present invention will be described below. Hereinafter, an example will be described in relation to the manufacture of an Al bonding wire.

[0076] The Al and alloying elements used as raw materials preferably have a high purity. Al preferably has a purity of 99.5% by mass or more, with the remainder consisting of inevitable impurities, more preferably a purity of 99.9% by mass or more, with the remainder consisting of inevitable impurities, and even more preferably a purity of 99.99% by mass or more, with the remainder consisting of inevitable impurities. The Si, first element group, second element group, and other elements used as alloying elements preferably have a purity of 99.9% by mass or more, with the remainder consisting of inevitable impurities, and more preferably a purity of 99.99% by mass or more, with the remainder consisting of inevitable impurities. Continuous casting can be used as a casting process for melting and solidifying the Al alloy used for Al bonding wire. In continuous casting, a molten liquid containing the Al raw material and the alloying element raw materials is poured into a water-cooled mold, while the cast material (ingot) is continuously drawn from below the mold. The atmosphere in the furnace during melting is preferably an inert or reducing atmosphere to prevent excessive oxidation of Al, Si, the first element group, the second element group, and other elements that constitute the wire or ribbon. The maximum temperature that the molten metal reaches during melting is preferably in the range of 700°C or higher and lower than 1000°C, taking into consideration factors such as ensuring the fluidity of the molten metal and making it easier to control the shape and size of the Si phase during solidification.

[0077] The ingot obtained by melting is processed by hot extrusion to a wire diameter of 5–15 mm. Furthermore, after solution treatment at high temperatures, wire can be produced with the desired diameter by repeatedly drawing the wire using a die. The drawn wire can be used as Al bonding wire after final heat treatment in an electric furnace. The hot extrusion process requires processing the sample in a high-temperature state. For example, a method in which the sample is heated in a furnace and then removed and extruded, or a method in which the extrusion is performed while the equipment or jig is heated, can be used.

[0078] To control the microvoid volume ratio [Vs / Vc x 100(%)], microvoid number ratio [Ps / Pc x 100(%)], and small diameter ratio of the Si phase, it is effective to control the heat treatment conditions such as solution treatment, homogenization treatment, and final heat treatment, as well as the wiredrawing conditions, etc. During wiredrawing, it is effective to use a lubricant to ensure lubrication at the contact interface between the wire and the die.

[0079] An example of manufacturing conditions for controlling the microvoid volume ratio [Vs / Vc × 100 (%)] to a range of 0.02% to 4.00% and for controlling the small diameter ratio of the Si phase to 30% to 95% is shown below.

[0080] <Control of microvoid volume ratio> To control the volume fraction of voids with equivalent sphere diameters of 1 μm or more but less than 10 μm, it is advantageous to adjust the frequency and growth of voids around the Si phase, which is the main cause of void generation. Hot extrusion of solidified castings and increasing the wiredrawing speed after intermediate annealing are effective ways of controlling the frequency and size of voids by taking advantage of the difference in the deformability between the Al and Si phases. Furthermore, air or water cooling after heat treatments such as solution treatment, intermediate annealing, and final diameter heating effectively utilizes the difference in thermal expansion between the Al and Si phases to effectively control the frequency and size of voids. Air cooling can be used to reduce void volume, while water cooling can be used to increase void volume.

[0081] Specific examples of manufacturing conditions are shown below. Hot extrusion preferably begins with an ingot with a wire diameter of 100 to 200 mm and is then processed to a diameter of 5 to 15 mm. The temperature is in the range of 250 to 400°C. These hot extrusion conditions are advantageous for reducing the material's deformation resistance through high-temperature processing, thereby suppressing void coarsening. Furthermore, in the wiredrawing process at a wire diameter between the wire diameter at which intermediate annealing is performed and one-third of the wire diameter at the start of wiredrawing, it is preferable to set the average wiredrawing speed to between 20 m / min and 50 m / min. By increasing the wiredrawing speed after reducing processing strain through intermediate annealing, it is possible to homogenize the strain within the sample and adjust the deformation difference between the Al phase and the Si phase, thereby adjusting the volume of small voids without excessively increasing the voids.

[0082] The solution treatment is carried out at a temperature of 450°C or higher but lower than 560°C for a period of 2 hours or higher but lower than 8 hours, and is air-cooled. This is because the shape and size of voids can be adjusted during the solution treatment, as the coarse Si phase formed by the eutectic reaction is broken down and reduced in size. Intermediate annealing is carried out twice and final diameter annealing is carried out once, at a temperature of 250 to 350°C for a period of 1 to 12 hours, and each cooling step is carried out by air-cooling. The wire diameter for intermediate annealing is preferably approximately 1 / 3 and 2 / 3 of the wire diameter at the start of wiredrawing.

[0083] <Control of the ratio of microvoids> The method for controlling the microvoid ratio can utilize manufacturing conditions similar to those used for controlling the void volume ratio described above. Furthermore, adjusting the thermal history during the solidification process and processing conditions such as hot extrusion and fine wire processing is effective for controlling the ratio of voids with a spherical equivalent diameter of 1 μm or more but less than 7 μm. Specifically, water cooling, in which water is sprayed onto the cast material removed from the mold during the cooling process of continuous casting, is effective. This water cooling during solidification increases the frequency of void generation due to the difference in thermal expansion between Al and Si, while suppressing the plate-like growth of the Si phase and breaking it into granules, thereby suppressing the formation of coarse voids. Furthermore, increasing the degree of processing (area reduction rate) per pass during the hot extrusion process is effective for adjusting the frequency of microvoid generation.

[0084] <Control of the Small-Diameter Ratio of Si Phase> Optimizing the intermediate heat treatment conditions and the final heat treatment conditions as a set is effective for controlling the small-diameter ratio of the Si phase. Specifically, assuming the temperature of the intermediate heat treatment with the wire diameter closest to the final wire diameter (final) is Tm (°C) and the temperature of the final heat treatment at the final wire diameter is Tc (°C), when the temperature Tm of the intermediate heat treatment is 50 °C or higher than the temperature Tc of the final heat treatment, it becomes easy to adjust the small-diameter ratio of the Si phase to 30% or more and less than or equal to 95%. Specifically, by increasing the temperature of the intermediate heat treatment, the Si dissolved in the Al phase can be homogenized, and by lowering the temperature of the final heat treatment step, the solid solution concentration of Si in the Al phase can be decreased. By combining these temperatures, the number of minute Si phases can be increased, and the small-diameter ratio of the Si phase can be increased. Among multiple intermediate heat treatments, adjusting the temperature of the last intermediate heat treatment is more effective, and it is considered that the number of minute Si phases can be increased by utilizing the dislocations increased in the subsequent processing steps.

[0085] Regarding the final heat treatment conditions, it is effective to adjust within the temperature range of 200 °C or higher and less than 360 °C and the time range of 2 hours or longer and less than 20 hours. When the recovery and recrystallization of the Al phase progress due to the final heat treatment, at the same time, the amount of Si dissolved in the Al phase changes depending on the heat treatment temperature, and the recrystallization temperature changes. By adjusting the progress of recrystallization due to the final heat treatment, it becomes easy to control the small-diameter ratio of the Si phase. For example, by adjusting the final heat treatment to a low temperature or a short time, the small-diameter ratio of the Si phase tends to increase.

[0086] As described above, the above is an example explained in accordance with the manufacture of an Al bonding wire as a wire material as a representative example of an Al bonding wire or an Al bonding ribbon. The Al bonding ribbon as a strip material can basically be manufactured by the same procedure. The temperature and time of the heat treatment can use conditions almost equivalent to the above. Also, when manufacturing the Al bonding ribbon by rolling, the reduction ratio of the die may be replaced with the rolling reduction ratio for adjustment.

[0087] [Semiconductor Device] A semiconductor device can be manufactured by connecting electrodes on a semiconductor chip to external electrodes on a lead frame or substrate using the Al bonding wire or Al bonding ribbon of the present invention. That is, the semiconductor device of the present invention includes the Al bonding wire or Al bonding ribbon of the present invention. As mentioned above, wedge bonding is used for both the first bonding with the electrode on the semiconductor chip and the second bonding with the electrode on the lead frame or substrate.

[0088] In one embodiment, the semiconductor device of the present invention comprises a circuit board, a semiconductor chip, and an Al bonding wire or Al bonding ribbon for electrically connecting the circuit board and the semiconductor chip, and is characterized in that the Al bonding wire or Al bonding ribbon is the Al bonding wire or Al bonding ribbon of the present invention.

[0089] 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.

[0090] Examples of semiconductor devices 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, aircraft, etc.), and among these, power semiconductor devices are preferred. [Example]

[0091] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0092] (sample) The sample preparation method will be described. The raw material Al used had a purity of 4N (99.99% by mass or higher), with the remainder consisting of inevitable impurities. The alloying elements Si, the first element group (Sr, Na, Dy, B), the second element group (Ni, Ti, Fe, Cu), and other elements (Mn, Zn) had a purity of 99.99% by mass or higher, with the remainder consisting of inevitable impurities. The Al alloy used for the Al bonding wire or Al bonding ribbon was produced by loading the Al raw material and the raw materials of the alloying elements into a melting crucible and using a continuous casting furnace to produce a cast product. The atmosphere inside the furnace during melting was an Ar atmosphere, and the maximum temperature of the molten metal during melting was 700°C or higher but lower than 1000°C. The cast material emerging from the mold was cooled by spraying water onto it and solidified.

[0093] A cylindrical ingot was obtained by melting, and hot extrusion was performed on the ingot. Next, solution treatment and homogenization treatment were performed, followed by wire drawing using a die and intermediate heat treatment to produce a Φ300 μm Al bonding wire. In addition, using the Φ300 μm Al bonding wire as the starting material, an Al bonding ribbon with a thickness of 100 μm and a width of 600 μm was produced by two-stage roll rolling. The temperature range of the solution treatment was 500 ° C or higher and lower than 560 ° C, and the time was 2 hours or higher and lower than 4 hours. After the solution treatment, a homogenization treatment was performed continuously during cooling. The temperature range of the homogenization treatment was 250 ° C or higher and lower than 350 ° C, and the time was 2 hours or higher and lower than 5 hours. The cooling method after the homogenization treatment was air cooling in the atmosphere.

[0094] Hot extrusion was performed to a wire diameter of 10 mm at a temperature ranging from 250 to 400°C. After hot extrusion to a wire diameter of 10 mm, wire drawing was performed using a die. The wire area reduction rate per die during wire drawing was between 10.0% and 30.0%. The wire area reduction rate was adjusted according to the wire diameter of the die. Intermediate heat treatment was performed twice, with the wire diameter for the first intermediate heat treatment ranging from 5.5 to 7.5 mm and the second intermediate heat treatment ranging from 1.5 to 3.0 mm relative to the starting wire diameter of 10 mm. The temperature range for intermediate heat treatment was between 250°C and 400°C, and the time was adjusted to between 1 hour and 12 hours.

[0095] The temperature range of the final heat treatment was 200°C or higher and lower than 350°C, and the time of the final heat treatment was 2 hours or higher and lower than 20 hours. The temperature of the final heat treatment (Tc) was selected in the temperature range 50 to 100°C lower than the temperature of the second intermediate annealing (Tm) described above.

[0096] In some examples, the wire was drawn using a die with a die angle of 14° or more and less than 18°.

[0097] (Method for measuring element content) The concentration analysis of elements contained in the Al bonding wire or Al bonding ribbon was performed using an ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer) ("PS3520UVDDII" manufactured by Hitachi High-Tech Science Corporation) or an ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) ("Agilent 7700x ICP-MS" manufactured by Agilent Technologies, Inc.).

[0098] (X-ray CT analysis) The X-ray microscope used was a 3D X-ray microscope "Xradia 520 Versa" (manufactured by ZEISS). The X-ray voltage was 40 kV, the X-ray output was 3 W, the wavelength-limiting filter was LE1, and the magnification lens was 4x. The transmittance of the cross-sectional images ranged from 30% to 70%. The pixel size was approximately 0.7 μm, and the measurement field of view was approximately 700 μm × 700 μm × 700 μm. The sample was fixed at a length of approximately 10 mm and rotated 360° around the sample axis to measure CT projection images. In this measurement, CT projection images were acquired at intervals of 0.225° per image over a 360° rotation angle (1601 images in total). Each CT projection image was observed with a 30-second exposure time. After obtaining CT projection images for all angles, reconstruction processing, such as center shifting, was performed to obtain 3D image data. Beam hardening was also performed as necessary.

[0099] Next, the 3D image data was analyzed using image analysis software. The image analysis software used was Avizo Inspection. The 3D image data reflected the density differences in the observation area as a 3D distribution of brightness values. Relatively high-density wire or ribbon regions (material) exhibited high brightness, while low-density voids and external space exhibited low density. First, a brightness histogram was created, which graphed the brightness values ​​and their frequency in each voxel of the 3D image data. The brightness value at the midpoint of the two peak positions corresponding to voids or external space and material was set as a threshold. Image data areas showing brightness lower than the threshold were identified as voids or external space. Next, the identified voids and external space were selected and removed from the image data area. This extracted image data of only voids within the material within the measurement area. Next, similar processing was used to extract image data with brightness higher than the threshold as image data related to material.

[0100] The image data of the voids and material thus obtained were analyzed. The calculation methods for the microvoid volume ratio and microvoid number ratio are described below. Image analysis software was used to calculate the total volume Vs of voids with a sphere-equivalent diameter of 1 μm or more but less than 10 μm, the total volume of voids of all sizes (Vg), and the volume of material (Vm). The total volume Vc of the measurement area was calculated by adding Vg and Vm (Vc = Vg + Vm). The microvoid volume ratio [Vs / Vc × 100(%)], which is the ratio of Vs to Vc, was then calculated. Image analysis software was also used to calculate the total number Ps of voids with a sphere-equivalent diameter of 1 μm or more but less than 7 μm, and the total number Pc of voids with a sphere-equivalent diameter of 1 μm or more. The microvoid number ratio was calculated as the ratio Ps to Pc [Ps / Pc × 100(%)].

[0101] (Small diameter ratio of Si phase [Ns / Nc×100(%)]) The small diameter ratio of the Si phase [Ns / Nc × 100 (%)] in the L cross section was measured using a SEM-EDS-EBSD system, combining information on the Al and Si concentrations obtained by SEM-EDS with information on the crystal orientation obtained by EBSD. In detail, the measurement was carried out according to the following steps (1) to (3). (1) In the measurement area where the L-section of the Al bonding wire or Al bonding ribbon was used as the inspection surface, the Al and Si concentrations were measured using EDS and the crystal orientation was measured using EBSD simultaneously. (2) Using the Chi Scan function of the EBSD analysis software, Al and Si were separated and extracted. Specifically, Al and Si were separated and identified by setting a tolerance equivalent to the Si threshold from the Si EDS measurement results. The Al and Si crystal information in the material file was used for crystal orientation analysis. Here, the tolerance condition was mainly set to 30%, and was adjusted as necessary. (3) The crystal orientation of the region identified as Si phase was analyzed, and if the misorientation between measurement points was 15° or more, it was determined to be a grain boundary, and the circle-equivalent diameter of each crystal grain was calculated. The number of crystal grains identified as Si phase was tallied to determine the total number of Si phase particles, Nc. Here, Si phases with a circle-equivalent diameter of 0.5 μm or more were targeted. Considering the analytical accuracy of current EDS and EBSD analysis equipment, fine particles less than 0.5 μm were excluded. Next, the number of Si phases, Ns, with a circle-equivalent diameter in the range of 0.5 μm to 0.8 μm was tallied. The ratio of Ns to Nc [Ns / Nc × 100 (%)] (the small diameter ratio of Si phases) was calculated.

[0102] The small diameter ratio of the Si phase was determined as the average value (arithmetic mean) of the values ​​obtained for the three measurement regions by the above procedures (1) to (3).

[0103] (Evaluation method for Al bonding wire or Al bonding ribbon) The evaluation method for Al bonding wire is described below. The wire diameter of the Al bonding wire used for the evaluation was Φ300 μm. The semiconductor chip used was made of Si, and the electrodes on the semiconductor chip were made of a 4 μm thick film of an alloy with a composition of Al-0.5% Cu. The substrate used was an Al alloy with a 5 μm thick Ni film. A commercially available wire bonder (manufactured by Ultrasonic Industries Co., Ltd.) was used to bond the Al bonding wire, and wedge bonding was used for both the first bonding (bonding to the above electrodes on the semiconductor chip) and the second bonding (bonding to the above substrate). The Al bonding ribbon was bonded using a Hesse fully automatic bonder "BJ955" equipped with a ribbon bond head.

[0104] (Method for evaluating the shear strength ratio of the first joint) This section explains the evaluation method for the shear strength ratio of the first bond. The bonding conditions were based on the standard conditions for Al bonding wire, and the ultrasonic output and load were set slightly higher to ensure a sufficient bonding area. Shear strength was evaluated using a shear test to measure the shear strength of the first bond. Ten first bonded locations were subjected to shear tests on the first bonded locations, and the average shear strength (SH) was measured. Shear strength was measured using a commercially available microshear strength tester (Nordson 4000-PLUS). The shear rate was 200 μm / s, and the shear tool height was 10 μm from the electrode surface. Shear strength measurements were performed by fixing the substrate bonded with Al bonding wire or Al bonding ribbon in a jig. Tensile tests were also performed on five samples to measure the average 0.2% proof stress (PS). The tensile tester used was the RTF-1225 (A&D), and the tensile speed was 10 mm / min. The ratio (SH / PS) obtained by dividing the shear strength (SH) by the 0.2% proof stress (PS) from the tensile test was used as the shear strength multiplier. If the shear strength multiplier was 5.2 or higher, the bond was judged to be excellent and rated as "3," if it was 4.5 or higher but less than 5.2, it was judged to have no practical problems and rated as "2," if it was 3.5 or higher but less than 4.5, it was judged to require improvement and rated as "1," and if it was less than 3.5, it was judged to have practical problems and rated as "0." The evaluation results are shown in the "Shear Strength Multiplier" column in the table.

[0105] (Method for evaluating shear strength magnification under inclined joining conditions) Bonding samples were fabricated under gradient bonding conditions for thin-type or directly under-device power semiconductors. The initial ultrasonic output (Wf) was high, gradually decreasing over time to a slightly lower final output (Wg). The ratio of the final output to the initial output (Wg / Wf) was between 0.6 and 0.85. The load was constant. The shear strength ratio was measured as described above. A shear strength ratio of 5.0 or greater was considered excellent for the gradient bonding conditions and rated "3." A shear strength ratio of 4.3 to 5.0 was considered acceptable for practical use and rated "2." A shear strength ratio of 3.5 to 4.3 was considered necessary for improvement and rated "1." A shear strength ratio of less than 3.5 was considered unsuitable for practical use and rated "0." The evaluation results are listed in the "Shear strength ratio for gradient bonding conditions" column in the table.

[0106] (Method for evaluating the reliability of temperature cycles under gradient junction conditions) A commercially available thermal shock tester was used to evaluate the temperature cycle test. The temperature was repeatedly increased and decreased by moving the specimen chamber between a low-temperature chamber and a high-temperature chamber. The low-temperature chamber temperature was -40°C, and the high-temperature chamber temperature was 175°C. The test began with the specimen chamber in the high-temperature chamber, and the specimen chamber moved to the low-temperature chamber and returned to the high-temperature chamber. The specimen chamber spent 20 minutes in each chamber. The specimens were bonded under the gradient bonding conditions described above. After 1000 cycles, the specimens were removed and subjected to shear testing of the first bond. The shear strength of the first bond used to evaluate the temperature cycle reliability was the average shear strength of five randomly selected first bond locations. The strength ratio (F2 / F1) of the shear strength (F2) after the temperature cycle test to the shear strength (F1) before the temperature cycle test was used to evaluate the reliability. If the strength ratio was less than 50%, it was judged to have practical problems and was given a rating of "0", if the strength ratio was between 50% and 70%, it was judged to need improvement and was given a rating of "1", if the strength ratio was between 70% and 75%, it was judged to be excellent and was given a rating of "2", and if the strength ratio was 75% or more, it was judged to be particularly excellent and was given a rating of "3". "0" and "1" are failures, while "2" and "3" are passes. The evaluation results are shown in the "Temperature cycle reliability under gradient bonding conditions" column in the table.

[0107] (Method for evaluating wire breakage during processing) This section explains the evaluation method for wire breakage during processing. Wire drawing was performed with diameters ranging from 10 mmφ to 0.3 mmφ, and the number of wire breakages was confirmed. The wire drawing processing conditions, such as feed speed and area reduction rate, were selected from the conditions described above, and the appropriate manufacturing conditions were adjusted and changed for each wire. The drawn Al bonding wire lengths ranged from 100 to 200 m, and the number of wire breakages was calculated by converting them per 100 m. If the number of wire breakages was zero, it was judged to be good and given a rating of "3." If it was one, it was judged that it could be addressed by improving the manufacturing conditions and given a rating of "2." If it was two to four, it was judged that there was a decrease in productivity and given a rating of "1." If it was five or more, it was judged that it was difficult to use in practice and given a rating of "0." The evaluation results are shown in the "Wire breakage during processing" column in the table.

[0108] (Evaluation method for surface scratches and scrapes) The surface quality of the Al bonding wire or Al bonding ribbon was evaluated, focusing on scratches and abrasions. The Al bonding wire diameter was 0.3 mm. The Al bonding ribbon was 100 μm thick and 600 μm wide. Three measurement areas were randomly selected at intervals of at least 1 m along the central axis of the Al bonding wire or Al bonding ribbon. Three approximately 2 cm lengths were taken from each of the three areas, for a total of nine samples. The surfaces were observed using an SEM at magnifications ranging from 50 to 500x. Scratches longer than 50 μm and abrasions longer than 30 μm were considered defective. The number of scratches or abrasions was counted, and a rating of "3" was given for a good pass; one to two were considered acceptable for practical use; three to seven were considered poor for surface quality; and eight or more were considered unsuitable for practical use and rated "0." The evaluation results are listed in the "Surface Quality" column in the table.

[0109] The evaluation results of the Examples and Comparative Examples are shown in Tables 1 to 4. Examples 1 to 30 and Comparative Examples 1 to 7 in Tables 1 to 3 are results for Al bonding wires, and Examples B1 to B3 and Comparative Example B1 in Table 4 are results for Al bonding ribbons.

[0110] [Table 1]

[0111] [Table 2]

[0112] [Table 3]

[0113] [Table 4] [Explanation of symbols]

[0114] 1. Al bonding wire 10 center axis 11 L cross section 2. Al bonding ribbon 20 center axis 21 L cross section

Claims

1. An Al bonding wire or Al bonding ribbon containing 3.0 mass% or more and 20.0 mass% or less of Si, In a region observed by X-ray CT (Computed Topography) analysis, when the total volume of voids having a sphere-equivalent diameter of 1 μm or more and less than 10 μm is defined as Vs and the total volume of the measurement region is defined as Vc, the ratio of Vs to Vc [Vs / Vc×100(%)] is 0.02% or more and 4.00% or less, An Al bonding wire or Al bonding ribbon, in which the ratio of Ns to Nc [Ns / Nc x 100 (%)] is 30% or more and 95% or less, where Ns is the number of Si phases having a circle equivalent diameter of 0.5 μm or more and 0.8 μm or less in an L cross section (a cross section in the central axis direction including the central axis) and Nc is the number of Si phases having a circle equivalent diameter of 0.5 μm or more in an L cross section.

2. 2. The Al bonding wire or Al bonding ribbon according to claim 1, wherein the total number of voids having a sphere-equivalent diameter of 1 μm or more and less than 7 μm in the region observed by X-ray CT analysis is defined as Ps, and the total number of voids having a sphere-equivalent diameter of 1 μm or more is defined as Pc. The ratio of Ps to Pc [Ps / Pc×100(%)] is 60% or more and 98% or less.

3. 2. The Al bonding wire or Al bonding ribbon according to claim 1, further containing one or more of Sr, Na, Dy, and B in a total amount of 10 mass ppm or more and 800 mass ppm or less.

4. The Al bonding wire or Al bonding ribbon according to claim 1, further containing one or more of Ni, Ti, Fe, and Cu in a total amount of 100 mass ppm or more and 1500 mass ppm or less.

5. The Al bonding wire or Al bonding ribbon according to claim 3, further containing one or more of Ni, Ti, Fe, and Cu in a total amount of 100 mass ppm or more and 1500 mass ppm or less.

6. The Al bonding wire or Al bonding ribbon according to any one of claims 1 to 5, wherein the total concentration of elements other than Al, Si, Sr, Na, Dy, B, Ni, Ti, Fe, and Cu in the Al bonding wire or Al bonding ribbon is 0.5 mass% or less.

7. The Al bonding wire or Al bonding ribbon according to claim 1, wherein the circle equivalent diameter and the number of Si phases are values ​​measured using a SEM-EDS-EBSD device.

8. 2. The Al bonding wire or Al bonding ribbon according to claim 1, which is for use in a semiconductor device.

9. A semiconductor device comprising the Al bonding wire or Al bonding ribbon according to claim 1.

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