Al bonding wire or al bonding ribbon

Abstract

The present invention provides an Al bonding wire or an Al bonding ribbon, which is capable of securing good bonding strength even if used for a power semiconductor that has a thin structure or a high-density element structure in which an element is arranged directly below an electrode. This Al bonding wire or the Al bonding ribbon contains Si in an amount of 3.0 mass% to 20.0 mass% inclusive. In a region observed by X-ray CT analysis, the ratio (Vs / Vc × 100 (%)) of Vs to Vc is 0.02% to 4.00% inclusive, where Vs is the total volume of voids that each have a sphere equivalent diameter of 1 μm or more and less than 10 μm and Vc is the total volume of the measurement region. If Ns is the number of Si phases that each have a circle equivalent diameter of 0.5 μm to 0.8 μm inclusive 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 that each have a circle equivalent diameter of 0.5 μm or more in the L cross-section, the ratio (Ns / Nc × 100 (%)) of Ns to Nc is 30% to 95% inclusive.

Description

Al bonding wire or Al bonding ribbon

[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.

[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 primarily use bonding wires or bonding ribbons made of aluminum (Al). The wire diameter of Al bonding wires is typically in the range of 100 μm to 600 μm, while Al bonding ribbons typically have widths in the range of 100 μm to 3000 μm and thicknesses 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. Furthermore, 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: first, with an electrode on a semiconductor chip, and second, with an electrode on a lead frame or substrate. Both methods use wedge bonding. Wedge bonding 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 connection method is characterized by connecting in a solid state without melting the connecting material, and is a joining technique that differs from welding techniques that 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 using a connecting material made solely of high-purity Al, the Al bonding wire or Al bonding ribbon breaks due to thermal stress in a relatively short period of time, making it difficult to meet the performance requirements of 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, an Al bonding wire that focuses on improving mechanical strength has been proposed. As a method for improving the mechanical properties of the Al bonding wire, a method of adding a specific element to Al has been proposed.

[0007] Patent Document 1 discloses a bonding wire made of an Al alloy containing at least magnesium (Mg) and silicon (Si), and the total content of Mg and Si is 0.03 mass % or more and 0.3 mass % or less. This patent document describes the effect of increasing strength by solid solution strengthening of Mg and Si, and the effect of precipitated magnesium silicide (Mg ２ It is disclosed that the crack propagation suppression effect of Si) delays the decrease in the bond strength of the first bonded portion in a cold temperature cycle test in the temperature range of 70°C to 120°C.

[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 bonding wire has a fine structure with an average crystal grain size of 6 to 12 μm. This patent document 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 mechanical strength is improved by rapidly cooling the molten Al-Si alloy to finely and uniformly disperse the Si.

[0010] JP 2014-131010 A JP 2014-129578 A JP 59-57440 A

[0011] As described 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 ultimately leads 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 life (temperature cycle reliability) of the 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 have been developed for power semiconductors, in which elements such as diodes are located directly below the electrodes to be bonded. 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 or loads. Furthermore, it is predicted that the use of highly heat-resistant silicon carbide (SiC) will increase in next-generation power elements, replacing the previously mainstream silicon (Si). Connections for SiC power semiconductors require even more stringent temperature cycle testing than currently required. 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 semiconductor damage increases even further.

[0013] As described above, there are concerns that the development of highly reliable Al bonding wires or Al bonding ribbons for power semiconductors, which have improved temperature cycle reliability, may increase the risk of damage to the semiconductors. 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 wires or ribbons, there are concerns that their hardness can reduce the bond strength during the first bonding stage, that bonding with increased load and ultrasonic output can lead to unstable deformation, and that damage to the elements and cracks can occur. While temporary measures such as adjusting the ultrasonic vibration or load can be taken 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 performed to evaluate the bond strength of the first bond, measure shear fracture strength from the lateral direction. Because shear tests primarily break the bonding wire or bonding ribbon, the apparent shear strength of high-strength bonding wires or ribbons is often evaluated as high due to the influence of material strength. In other words, even if the apparent shear strength of high-strength materials is high at the first bond, 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.

[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 a region 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 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, wherein, in a region observed by X-ray CT (Computed Topography) analysis, when Vs is the total volume of voids having a sphere-equivalent diameter of 1 μm or more and less than 10 μm and Vc is the total volume of the measurement region, the ratio of Vs to Vc [Vs / Vc × 100(%)] is 0.02% or more and 4.00% or less, and when 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 direction of the central axis including the central axis) and Nc is the number of Si phases having a circle-equivalent diameter of 0.5 μm or more in the L cross section, the ratio of Ns to Nc [Ns / Nc × 100(%)] is 30% or more and 95% or less. <2> The Al bonding wire or Al bonding ribbon according to <1>, wherein, in an area observed by X-ray CT analysis, the total number of voids having a sphere-equivalent diameter of 1 μm or more and less than 7 μm is Ps, and the total number of voids having a sphere-equivalent diameter of 1 μm or more is Pc, and the ratio of Ps to Pc [Ps / Pc × 100 (%)] is 60% or more and 98% or less. <3> The Al bonding wire or Al bonding ribbon according to <1> or <2>, further containing one or more of Sr, Na, Dy, and B in a total amount of 10 ppm by mass or more and 800 ppm by mass or less. <4> The Al bonding wire or Al bonding ribbon according to any one of <1> to <3>, further containing one or more of Ni, Ti, Fe, and Cu in a total amount of 100 ppm by mass or more and 1500 ppm by mass or less. <5> The Al bonding wire or Al bonding ribbon according to any one of <1> to <4>, 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. <6> The Al bonding wire or Al bonding ribbon according to any one of <1> to <5>, wherein the circle equivalent diameter and the number of Si phases are values ​​measured using a SEM-EDS-EBSD device.<7> The Al bonding wire or Al bonding ribbon according to any one of <1> to <6>, which is for use in a semiconductor device. <8> A semiconductor device including the Al bonding wire or Al bonding ribbon according to any one of <1> to <7>.

[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.

[0019] FIG. 1 is a schematic diagram for explaining the measurement target surface (inspection surface) when measuring the small diameter ratio of the Si phase for an Al bonding wire. The measurement target surface is a cross section (L cross section) in the central axis direction including the central axis of the Al bonding wire. FIG. 2 is a schematic diagram for explaining the measurement target surface (inspection surface) when measuring the small diameter ratio of the Si phase for an Al bonding ribbon. The measurement target surface is a cross section (L cross section) in the central axis direction including the central axis of the Al bonding ribbon. FIG. 3 is an example of a brightness histogram created when determining the brightness threshold of voids or external space and substances in X-ray CT analysis. FIG. 4 is an example of a graph showing the number distribution of circle equivalent diameters of Si phases in an L cross section.

[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, wherein 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 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 "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 central axis direction 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 the 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 bonded portion, if the bonding wire or ribbon breaks internally during a shear test, it is difficult to accurately evaluate the bondability of high-strength materials. In this regard, a method for evaluating bond strength while suppressing 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) of a tensile test is effective. The factors governing the apparent shear strength of a first bonded portion 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 yield strength of the wire or ribbon 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 have found that the bond condition can be more accurately evaluated by using the shear strength ratio (SH / PS) normalized by 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 elements 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% to 20.0 mass% 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 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 the Al bonding wire and the cross section (L cross section) in the central axis direction including the central axis are as shown in FIG. 1. FIG. 1 shows the case of 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 central axis direction including the central axis and perpendicular to the width W direction (FIG. 2). Specifically, the central axis of the Al bonding ribbon and the cross section (L cross section) in the central axis direction including the central axis are as shown in FIG. 2. When cross-section processing is performed 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 wire or ribbon, and that the voids are mainly formed around the Si phase. 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 inhibited from deforming, whereas the Al phase surrounding the Si phase easily undergoes plastic deformation, which is thought to result in the formation of voids at the end of the Si phase. Furthermore, the small size of the voids and the low total volume ratio of the small voids are thought to be advantageous in mitigating compressive deformation due to the application of a 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 effect of mitigating the propagation of compressive stress and ultrasonic vibrations can be utilized, 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 mitigated, thereby promoting metal bonding at the bonded interface.

[0031] There is a concern that stress and strain may concentrate around Si phases with large equivalent circle diameters, or that cracks may originate from the Si phases. By utilizing Si phases with small equivalent circle diameters, it is believed 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 to improve the shear strength ratio and reduce thermal distortion of the joint, 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 the 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. However, 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 obtaining good temperature cycle reliability, the Si concentration in the Al bonding wire or Al bonding ribbon of the present invention is 3.0 mass% or more, preferably 3.5 mass% or more, more preferably 4.0 mass% or more, and even more preferably 4.2 mass% or more, 4.4 mass% or more, 4.5 mass% or more, 4.6 mass% or more, 4.8 mass% or more, or 5.0 mass% or more. In addition, from the viewpoint of improving the shear strength ratio while effectively suppressing defects such as a decrease in initial bond 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 a region observed by X-ray CT (Computed Tomography) 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, by controlling the ratio of Vs to Vc [Vs / Vc × 100 (%)] within an appropriate range and by controlling the distribution of the circle-equivalent diameter of the Si phase, which will be described later, within an appropriate range, it is possible to promote metal bonding at the bonding interface, and as a result, it is possible to increase the shear strength magnification and improve 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 and less than 10 μm contributes to improved bondability. The lower limit was set to 1 μm, taking into consideration that a sphere-equivalent diameter of voids 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 voids is set to 10 μm, comprehensively considering that a sufficient improvement effect can be obtained by setting the upper limit to less than 10 μm, and that this is advantageous for production by wire drawing or rolling.

[0036] The reason why the shear strength factor is improved 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, it is possible to prevent the Si phase from inhibiting its effect of reducing thermal expansion. 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 in which elements are arranged directly under 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 magnification, 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 minor 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 minor 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 having a circle-equivalent diameter of 0.5 μm or more and 0.8 μm or less is important is considered as follows. Specifically, Si phases having a circle-equivalent diameter of 0.5 μm or more have a sufficiently large volume, and therefore can sufficiently reduce thermal expansion. Furthermore, from the viewpoint of the analytical accuracy of current EDS and EBSD analysis devices, it is appropriate to target Si phases having a circle-equivalent diameter of 0.5 μm or more. On the other hand, Si phases having a circle-equivalent diameter of 0.8 μm or less sufficiently uniformly distribute 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 considered as follows. Specifically, by setting the small diameter ratio of the Si phase to 30% or more, an increase in the proportion of Si phases having a coarse circle-equivalent diameter can be suppressed, and the transmission of ultrasonic vibrations is less likely to be impeded, 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, and to reduce 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 bonded interface. Therefore, the ratio of the number of Si phase particles affects the shear strength ratio. On the other hand, the effect of coarse particles is overestimated by the particle area, making it difficult to accurately evaluate the correlation with the shear strength ratio.

[0041] - Microvoid number ratio - In addition to controlling the microvoid volume ratio [Vs / Vc × 100(%)] described above, when 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, by making the ratio of Ps to Pc [Ps / Pc × 100(%)] (hereinafter referred to as the "microvoid number ratio") 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 the number of microvoids with a sphere-equivalent diameter of 1 μm or more but less than 7 μm, ultrasonic vibration propagation and the effect of uniforming strain near the bonding interface can be enhanced. Because large voids have little improvement effect, controlling the void volume fraction while increasing the microvoid ratio, which is the ratio of the number of microvoids to the total number of voids, promotes deformation of the first bond and promotes increased shear strength. This makes it possible to adjust the load and ultrasonic output, thereby improving the effect of reducing 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") is also advantageous for 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 having a sphere-equivalent diameter in the range of 1 μm or more but 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 provides a sufficiently large effect of alleviating distortion, and that a void size of less than 7 μm provides a sufficiently large improvement effect. The reason why the microvoid number ratio [Ps / Pc × 100 (%)] is preferably 60% or more but less than 98% is thought to be as follows: A microvoid number ratio of 60% or more can sufficiently obtain the effect of alleviating distortion due to the voids, thereby sufficiently obtaining 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 by X-ray CT- In the present invention, the microvoid volume ratio [Vs / Vc x 100 (%)] and the microvoid number ratio [Ps / Pc x 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 illustrates an analytical method for measuring voids in an Al bonding wire with a wire diameter of 300 μm. The analytical conditions are not limited to these, and appropriate analytical conditions can be selected depending on the device and sample. As an X-ray CT device, for example, a 3D X-ray microscope "Xradia 520 Versa" (manufactured by ZEISS) can be used. 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. Under the above conditions, it has been confirmed that transmission images with a transmittance of 30% to 70% can be obtained. To observe minute voids, the pixel size is set to approximately 0.7 μm / pixel, allowing the measurement of an area of ​​approximately 700 μm x 700 μm x 700 μm. The sample is fixed at a length of approximately 10 mm, and X-rays are transmitted through the sample at a rotation angle of 360 degrees around the axis of the sample to measure CT projection images. After CT projection images at all angles are obtained, reconstruction processing such as center shift processing can be performed to obtain three-dimensional 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 area is selected and removed from the image data area. This allows image data containing only voids in material within the measurement area of ​​the sample to be identified. Next, by similar processing, 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, and in the case of the Al bonding wire or Al bonding ribbon of the present invention, this includes Al, Si, the first element group, the second element group, and other elements, as well as their alloys, oxides, intermetallic compounds, etc. 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 the material thus obtained are analyzed. The calculation methods for the microvoid volume ratio and the microvoid number ratio are specifically described below. Using image analysis software, 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) are calculated. The total volume Vc of the measurement area is calculated by adding Vg and Vm (Vc = Vg + Vm). Then, the microvoid volume ratio [Vs / Vc × 100 (%)], which is the ratio of Vs to Vc, is calculated. Furthermore, using image analysis software, 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 are calculated. 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 method for calculating the small diameter ratio- A method for measuring the circle-equivalent diameter of the Si phase in the L cross section of an Al bonding wire or Al bonding ribbon will be described. The circle-equivalent diameter of the Si phase in the L cross section can be measured using an SEM-EDS-EBSD device. Specifically, a method can be used in which information on the Al concentration and Si concentration obtained by SEM-EDS (scanning electron microscope-energy dispersive X-ray spectroscopy) is combined 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 phase and Si phase are separated and extracted from the EDS measurement results using the analysis software provided with the device. 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) provided with the 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 provided with 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, the calculation is performed excluding portions where the crystal orientation cannot be measured or portions where the crystal orientation can be measured but the reliability of the orientation analysis is low. 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 cross 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) The Chi Scan function is used to separate and extract Al and Si.Specifically, by setting a tolerance equivalent to the Si threshold value based on 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) The crystal orientation of the region identified as the Si phase 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 the 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. Considering the analytical accuracy of current ESD and EBSD analysis equipment, fine particles less than 0.5 μm are excluded. The number of Si phases, Ns, with a circle-equivalent diameter in the range of 0.5 μm to 0.8 μm is also tallied. The ratio of Ns to Nc [Ns / Nc × 100 (%)] (the small diameter ratio of the Si phase) is then calculated.

[0049] In the above procedure (2), the Tolerance (%) setting can be selected in the range of 20 to 40%, and in a standard analysis of the L cross section of an Al bonding wire or Al bonding ribbon, it is preferable to compare it at about 30%. The procedure for adjusting this Tolerance is explained below. 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 from 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 the average (arithmetic mean) of the orientation ratio values ​​obtained by measuring 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 central axis direction of the Al bonding wire or Al bonding ribbon of 300 μm or more and 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 large and it is difficult 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 section having a width of 0.1 μm, and the vertical axis shows the number of particles. The range of 0.5 μm or more and 0.8 μm or less is shown by a double-headed arrow, and the particle number ratio [Ns / Nc × 100 (%)] in this section is 50%. It has been confirmed that this Al bonding wire exhibits excellent shear strength magnification.

[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 amount 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 believed 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, 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. In addition, 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, 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. In addition, 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 B 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 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, 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 "second element group"). The total concentration of the second element group may be 0 mass ppm, preferably 1 mass ppm or more or 3 mass ppm or more, more preferably 5 mass ppm or more or 8 mass ppm or more, even more preferably 10 mass ppm or more or 30 mass ppm or more, particularly preferably 50 mass ppm or more, 80 mass ppm or more, or 100 mass ppm 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 abrasion 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 Si phases and Al oxides present on the surface to fall off, resulting in scratches and abrasion 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 abrasion 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. In addition, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon having 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. In addition, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon having 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 abrasion 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 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. In addition, from the viewpoint of suppressing the occurrence of scratches and scraping on the surface and forming an Al bonding wire or Al bonding ribbon having a smooth surface, the Cu 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 Cu 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 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 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 inevitable impurities. Therefore, in a preferred embodiment, the Al bonding wire or Al bonding ribbon of the present invention consists of Al, Si, and inevitable 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 inevitable 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 inevitable 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 inevitable 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, the term "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 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 of its rectangular or approximately rectangular cross section (width W x thickness T) 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 of 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 in the casting process for melting and solidifying the Al alloy used for Al bonding wire. In continuous casting, a molten liquid containing dissolved Al raw material and alloying element raw materials is poured into a water-cooled mold, while a cast material (ingot) is continuously drawn from below the mold. The atmosphere in the furnace during melting is preferably an inert atmosphere or a 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 to 15 mm. Furthermore, after solution treatment in which the ingot is heated at high temperature, wire drawing using a die is repeatedly performed to produce wire of the desired diameter. The wire after wire drawing can be used as Al bonding wire by performing final heat treatment in an electric furnace. In this hot extrusion process, it is necessary to process a sample in a high-temperature state. Examples of methods that can be used include a method in which a sample heated in a furnace is removed and extruded, or a method in which extrusion is performed while the device or jig is heated.

[0078] In order to control the microvoid volume ratio [Vs / Vc×100(%)], the microvoid number ratio [Ps / Pc×100(%)], and the 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 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 ratio of voids with a sphere-equivalent diameter of 1 μm or more but less than 10 μm, it is advantageous to adjust the frequency of void generation and growth around the Si phase, which is the main cause of void generation. Processing the solidified casting by hot extrusion, or increasing the wiredrawing speed in the wiredrawing process after intermediate annealing, are effective in controlling the frequency of void generation and size by utilizing the difference in processing deformability between the Al phase and the Si phase. Furthermore, by performing air or water cooling in the cooling process after heat treatments such as solution treatment, intermediate annealing, and final diameter heating, it is effective in efficiently utilizing the difference in thermal expansion between the Al phase and the Si phase to control the frequency of void generation and size. Air cooling can be used to reduce the void volume, and water cooling can be used to increase the 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 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 20 m / min or more and less than 50 m / min. By increasing the wiredrawing speed while processing strain is reduced by 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 process in which the coarse Si phase formed by the eutectic reaction is broken down and reduced in size during the solution treatment. Intermediate annealing is carried out twice and final diameter annealing is carried out once, at a temperature in the range of 250 to 350°C for a period of 1 to 12 hours, and cooling is carried out by air-cooling for each step. The wire diameter in which intermediate annealing is carried out is preferably approximately 1 / 3 and 2 / 3 of the wire diameter at the start of wiredrawing.

[0083] <Control of Microvoid Ratio> Controlling the microvoid ratio can be achieved using manufacturing conditions similar to those used for controlling the void volume ratio described above. Furthermore, adjusting the thermal history of the solidification process and processing conditions such as hot extrusion and thin-wire processing is effective for controlling the ratio of voids with a spherical equivalent diameter of 1 μm or more and 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 of the hot extrusion process effectively controls the frequency of microvoid generation.

[0084] <Control of the Small Diameter Ratio of the Si Phase> Optimizing the intermediate heat treatment conditions and the final heat treatment conditions as a set is effective in controlling the small diameter ratio of the Si phase. Specifically, if the temperature of the intermediate heat treatment for the wire diameter (final) closest to the final wire diameter is Tm (°C) and the temperature of the final heat treatment for the final wire diameter is Tc (°C), the intermediate heat treatment temperature Tm being 50°C or more higher than the final heat treatment temperature Tc makes it easy to adjust the small diameter ratio of the Si phase to 30% or more and 95% or less. Specifically, by increasing the intermediate heat treatment temperature, the Si dissolved in the Al phase can be homogenized, and by lowering the temperature of the final heat treatment step, the concentration of Si dissolved in the Al phase can be reduced. Combining these temperatures can increase the number of fine Si phases and increase the small diameter ratio of the Si phase. Among multiple intermediate heat treatments, adjusting the temperature of the final intermediate heat treatment is more effective, and it is thought that this can promote an increase in the number of fine Si phases by utilizing dislocations and the like increased in the subsequent processing steps.

[0085] Regarding the final heat treatment conditions, it is effective to adjust the temperature range to 200°C or higher and lower than 360°C, and the time range to 2 hours or higher and lower than 20 hours. The final heat treatment promotes recovery and recrystallization of the Al phase, and at the same time, the amount of Si dissolved in the Al phase changes depending on the heat treatment temperature, thereby changing the recrystallization temperature. By adjusting the progress of recrystallization by 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 for a short time, the small diameter ratio of the Si phase tends to increase.

[0086] As mentioned above, the above is an example of the manufacture of Al bonding wire, which is a wire material, as a representative example of Al bonding wire or Al bonding ribbon. The same procedure can also be used to manufacture Al bonding ribbon, which is a strip material. The temperature and time of the heat treatment can be approximately the same as those described above. Furthermore, when manufacturing Al bonding ribbon by rolling, the die area reduction rate can be adjusted by replacing it with the rolling reduction rate.

[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, a semiconductor device may be configured including a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor device described in JP 2020-150116 A.

[0090] Examples of the semiconductor device include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, aircraft, etc.), and among these, power semiconductor devices are preferred.

[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 had a purity of 4N (99.99% by mass or more), 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 more, 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 more and less than 1000°C. The cast material emerging from the mold was cooled by spraying water 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 was completed, 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 in the range of 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 10.0% or more and less than 30.0%. The wire area reduction rate was adjusted according to the wire diameter of the die. Intermediate heat treatment was performed twice, and the wire diameter for the first intermediate heat treatment relative to the wire diameter of 10 mm at the start of wire drawing was 5.5 to 7.5 mm, and the wire diameter for the second intermediate heat treatment was 1.5 to 3.0 mm. The temperature range of the intermediate heat treatment was adjusted to be 250°C or more and less than 400°C, and the time was adjusted to be 1 hour or more and less than 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 (Tm) of the second intermediate annealing 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) (manufactured by Hitachi High-Tech Science Corporation, "PS3520UVDDII") or an ICP-MS (Inductively Coupled Plasma-Mass Spectrometer) (manufactured by Agilent Technologies, Inc., "Agilent 7700x ICP-MS") as an analytical device.

[0098] (X-ray CT analysis) A 3D X-ray microscope "Xradia 520 Versa" (manufactured by ZEISS) was used. 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 image was set to a range of 30% to 70%. The size per pixel was approximately 0.7 μm / pixel, and the measurement field of view was approximately 700 μm × 700 μm × 700 μm. The sample length was approximately 10 mm, and the sample was fixed. X-rays were passed through the sample at a rotation angle of 360° around the sample axis to measure the CT projection images. In this measurement, CT projection images were acquired at intervals of 0.225° per image per 360° rotation (1601 images in total). Each CT projection image was observed with an exposure time of 30 seconds. After obtaining CT projection images at all angles, reconstruction processing such as center shift processing was performed to obtain three-dimensional image data. Furthermore, beam hardening processing was 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 (substances) exhibited high brightness, while low-density voids and external spaces exhibited low density. First, a brightness histogram was created, graphing the brightness values ​​and their frequency in each voxel of the 3D image data. The brightness value at the midpoint of two peak positions corresponding to voids or external spaces and substances was set as a threshold. Image data regions exhibiting brightness lower than the threshold were identified as voids or external spaces. Next, the identified voids and external spaces were subjected to a process of selecting and removing external space regions from the image data region. This resulted in the extraction of image data of only voids in the substance within the measurement area. Next, by similar processing, image data with brightness higher than the threshold was extracted as image data related to the substance.

[0100] The image data of the voids and the material thus obtained were analyzed. The calculation methods for the microvoid volume ratio and the microvoid number ratio will be described below. Using image analysis software, the total volume Vs of voids having a sphere-equivalent diameter of 1 μm or more and less than 10 μm, the total volume of voids of all sizes (Vg), and the volume of the material (Vm) were calculated. The total volume Vc of the measurement area was calculated by adding Vg and Vm (Vc = Vg + Vm). Then, the microvoid volume ratio [Vs / Vc × 100 (%)], which is the ratio of Vs to Vc, was calculated. Furthermore, using image analysis software, the total number Ps of voids having a sphere-equivalent diameter of 1 μm or more and less than 7 μm, and the total number Pc of voids having a sphere-equivalent diameter of 1 μm or more were calculated. 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 Si phase in the L cross section [Ns / Nc × 100 (%)] was measured using a SEM-EDS-EBSD device, and a method was used in which the information on Al concentration and Si concentration obtained by SEM-EDS was combined with the information on crystal orientation obtained by EBSD. Specifically, the measurement was performed according to the following procedures (1) to (3). (1) In the measurement area in which the L cross section of the Al bonding wire or Al bonding ribbon was used as the inspection surface, Al and Si concentration measurements were performed using EDS and crystal orientation measurements were performed using EBSD simultaneously. (2) Al and Si were separated and extracted using the Chi Scan function, which is a function of the EBSD analysis software. Specifically, Al and Si were separated and identified from the EDS measurement results of Si by setting a tolerance equivalent to the Si threshold. The crystal orientation analysis was performed using the Al and Si crystal information in the material file. Here, the tolerance condition was mainly set to 30% and adjusted as necessary. (3) The crystal orientation of the region identified as the 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 the 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 devices, 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. Then, the ratio of Ns to Nc [Ns / Nc × 100 (%)] (the small diameter ratio of the Si phase) was calculated.

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

[0103] (Method for evaluating Al bonding wire or Al bonding ribbon) The evaluation method for Al bonding wire will be described. The wire diameter of the Al bonding wire used for 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 film of Ni. 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 electrode on the semiconductor chip) and the second bonding (bonding to the 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 Magnification of the First Bonded Portion) A method for evaluating the shear strength magnification of the first bonded portion will be described. Regarding the bonding conditions, the ultrasonic output and load were set slightly higher with reference to the standard conditions for Al bonding wire, ensuring a sufficient bonding area. The shear strength was evaluated by a shear test to measure the shear strength of the first bonded portion. Ten first bonded portions were formed, and a shear test was conducted on the first bonded portions to measure the average shear strength (SH). A commercially available microshear strength tester (Nordson 4000-PLUS) was used to measure the shear strength. The shear rate was 200 μm / sec, and the height of the shear tool was 10 μm from the electrode surface. The shear strength was measured by fixing the substrate bonded with the Al bonding wire or Al bonding ribbon using a jig. Furthermore, a tensile test was conducted on five samples, and the average 0.2% proof stress (PS) was measured. The tensile tester used was an "RTF-1225" (manufactured by 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) of the tensile test was used as the shear strength magnification. If the shear strength magnification was 5.2 or more, the bonding condition was judged to be excellent and rated as "3", if it was 4.5 or more and less than 5.2, it was judged to have no practical problems and rated as "2", if it was 3.5 or more and 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 Magnification" column in the table.

[0105] (Method for Evaluating Shear Strength Magnification under Graded Bonding Conditions) Bonded samples were prepared under graded bonding conditions for power semiconductors with a thin structure or directly under the device. The graded bonding conditions were set so that the initial ultrasonic output (Wf) was high and gradually decreased over time to a slightly lower final output (Wg). The ratio of the final output to the initial output (Wg / Wf) was set to a range of 0.6 to less than 0.85. The load was kept constant. The shear strength magnification was measured in the same manner as above. A shear strength magnification of 5.0 or more was judged to be excellent under the graded bonding conditions and rated as "3." A shear strength magnification of 4.3 to less than 5.0 was judged to be acceptable for practical use and rated as "2." A shear strength magnification of 3.5 to less than 4.3 was judged to require improvement and rated as "1." A shear strength magnification of less than 3.5 was judged to be problematic for practical use and rated as "0." The evaluation results are listed in the "Shear Strength Magnification under Graded Bonding Conditions" column in the table.

[0106] (Method for Evaluating Temperature Cycle Reliability Under Graded Bonding Conditions) A commercially available thermal shock testing device was used to evaluate the temperature cycle test. In the temperature cycle test, the sample chamber was moved between a low-temperature chamber and a high-temperature chamber, repeatedly increasing and decreasing the temperature. The low-temperature chamber temperature was set to -40°C, and the high-temperature chamber temperature was set to 175°C. One cycle consisted of the test starting with the sample chamber in the high-temperature chamber, moving it to the low-temperature chamber, and then returning to the high-temperature chamber. The sample chamber spent 20 minutes in each of the low-temperature and high-temperature chambers. The samples were bonded under the graded bonding conditions described above. After 1,000 cycles, the samples were removed and subjected to a shear test on the first bond. The shear strength value of the first bond used to evaluate the temperature cycle reliability was the average shear strength of five randomly selected first bond locations. Evaluation was based on the strength ratio (F2 / F1) of the shear strength value F2 after the temperature cycle test to the shear strength value F1 before the temperature cycle test. If the strength ratio was less than 50%, it was judged to have a practical problem and was given a rating of "0", if the strength ratio was 50% or more but less than 70%, it was judged to need improvement and was given a rating of "1", if the strength ratio was 70% or more but less than 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, and "2" and "3" are passes. The evaluation results are shown in the column "Temperature cycle reliability under gradient bonding conditions" in the table.

[0107] (Method for Evaluating Wire Breakage During Processing) The method for evaluating wire breakage during processing will be described below. Wire drawing was performed from a wire diameter of 10 mmφ to a wire diameter of 0.3 mmφ, and the number of wire breakages was confirmed. The wire drawing processing conditions, such as the feed rate and area reduction rate, were selected from the conditions described above, and the appropriate manufacturing conditions were adjusted and changed for each wire. The length of the drawn Al bonding wire ranged from 100 to 200 m, and the number of wire breakages was calculated by converting it to per 100 m. If the number of wire breakages was 0, it was judged to be good and rated as "3." If it was 1, it was judged that it could be addressed by improving the manufacturing conditions and rated as "2." If it was 2 to 4, it was judged that there was a decrease in productivity and rated as "1." If it was 5 or more, it was judged that it was difficult to use in practice and rated as "0." The evaluation results are shown in the "Wire Breakage During Processing" column in the table.

[0108] (Method for evaluating surface scratches and abrasions) The surface quality of the Al bonding wire or Al bonding ribbon was evaluated, focusing on scratches and abrasions. The wire diameter of the Al bonding wire was 0.3 mmφ. The Al bonding ribbon was 100 μm thick and 600 μm wide. Three measurement areas were randomly selected at intervals of 1 m or more along the central axis of the Al bonding wire or Al bonding ribbon, and three pieces of approximately 2 cm length were taken from each of the three locations, for a total of nine samples. The surface was observed using an SEM at magnifications ranging from 50 to 500 times. Scratches longer than 50 μm and abrasions longer than 30 μm were judged to be defective. The number of scratches and abrasions was counted, and if there were zero, it was judged to be good and passed, rated "3." If there were one to two locations, it was judged to be acceptable for practical use, rated "2." If there were three to seven locations, it was judged to have poor surface quality, rated "1." If there were eight or more locations, it was judged to be difficult to use, rated "0." The evaluation results are shown in the "Surface properties" 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.

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[0114] REFERENCE SIGNS LIST 1 Al bonding wire 10 Central axis 11 L-section 2 Al bonding ribbon 20 Central axis 21 L-section

Claims

1. An Al bonding wire or Al bonding ribbon containing 3.0% by mass or more and 20.0% by mass or less of Si, in which, in an area 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 area is Vc, the ratio of Vs to Vc [Vs / Vc×100(%)] is 0.02% or more and 4.00% or less, and 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 central axis direction including the central axis) is Ns and the number of Si phases having a circle equivalent diameter of 0.5 μm or more in an L cross section is Nc, the ratio of Ns to Nc [Ns / Nc×100(%)] is 30% or more and 95% or less.

2. An Al bonding wire or Al bonding ribbon as described in claim 1, in which, when the total number of voids having a sphere-equivalent diameter of 1 μm or more and less than 7 μm in an area observed by X-ray CT analysis is Ps, and the total number of voids having a sphere-equivalent diameter of 1 μm or more is Pc, the ratio of Ps to Pc [Ps / Pc x 100 (%)] is 60% or more and 98% or less.

3. An Al bonding wire or Al bonding ribbon as described in claim 1 or 2, 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. An Al bonding wire or Al bonding ribbon according to any one of claims 1 to 3, further containing at least one of Ni, Ti, Fe, and Cu in a total amount of 100 ppm by mass or more and 1500 ppm by mass or less.

5. An Al bonding wire or Al bonding ribbon according to any one of claims 1 to 4, 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.

6. An Al bonding wire or Al bonding ribbon described in any one of claims 1 to 5, wherein the circle equivalent diameter and the number of Si phases are values ​​measured using a SEM-EDS-EBSD device.

7. An Al bonding wire or an Al bonding ribbon according to any one of claims 1 to 6, which is for use in a semiconductor device.

8. A semiconductor device comprising an Al bonding wire or an Al bonding ribbon according to any one of claims 1 to 7.

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