Al connection material

Abstract

The present invention provides an Al connection material that achieves excellent temperature cycle reliability and a good first bonding strength. Provided is an Al connection material comprising 3.0-12.0 mass% Si, wherein: when the crystal orientation of an Al phase in an L cross-section of the Al connection material is measured, the total of the orientation ratios of the <110> crystal orientation and the <111> crystal orientation for which the angle difference with respect to the center axis direction is not more than 15° is 20-70%, given that, when the total of said orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation for which is angle difference with respect to the center axis direction is not more than 15° is not less than 5%; and when the crystal orientation of the Si phase in the L cross-section of the Al connection material is measured, the orientation ratio of the <110> crystal orientation and the <111> crystal orientation for which the angle difference with respect to the center axis direction is not more than 15° is 20-70%.

Description

Al connecting material

[0001] The present invention relates to an Al connecting material.

[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 and 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. Power semiconductor devices using Al interconnects 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 connecting materials: first joining with electrodes on a semiconductor chip, and second joining with electrodes on a lead frame or substrate, both of which use wedge joining. Wedge joining is a method in which ultrasonic vibrations and loads are applied to the Al connecting material via a metal jig (tool), destroying the surface oxide films on the Al connecting material and the electrode material to expose new surfaces and perform solid-state diffusion bonding. This joining method is characterized by connecting the connecting material in a solid state without melting it, 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 connecting material, 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 connecting material and the semiconductor chip. When using a connecting material made solely of high-purity Al, the Al connecting material breaks down in a relatively short time due to thermal stress, making it difficult to achieve the performance required for next-generation power semiconductor devices. Therefore, next-generation power semiconductors are required to improve the junction life (hereinafter also referred to as "temperature cycle reliability") associated with temperature rise and fall of the first junction.

[0006] In response to the demand for temperature cycle reliability, 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 joint repeatedly rises and falls. As a result, because the Al connecting material has a higher linear expansion coefficient than the semiconductor chip, thermal stress occurs at the first joint due to the difference in linear expansion coefficients between the two materials, which can ultimately lead to fatigue failure of the Al connecting material. A temperature cycle test is one type of accelerated evaluation test for the life (temperature cycle reliability) of such a first joint as a result of temperature rise and fall. Al connecting materials used in next-generation power semiconductors are required to exhibit excellent temperature cycle reliability in a temperature cycle test. However, when using Al connecting materials strengthened by the addition of Si or other additives, as disclosed in Patent Documents 1 to 3, in temperature cycle tests intended for use in next-generation power semiconductor devices, cracks propagate relatively rapidly in Al alloy electrodes that are weaker than the Al connecting material, making it difficult to consistently achieve good temperature cycle reliability.

[0012] Furthermore, if bonding defects, such as peeling of the Al connecting material from the electrode, occur during bonding, this can lead to product defects and reduced manufacturing yields, so it is necessary to obtain good bonding strength at each joint. In this regard, applying strong ultrasonic vibrations or loads to the first joint in order to obtain good bonding strength can damage the semiconductor chip. In particular, when using an Al connecting material whose strength has been increased by adding Si or the like, its hardness makes it easy to damage the semiconductor chip during the first bonding. Adjusting the ultrasonic vibrations or load to reduce such damage can sometimes result in insufficient bonding strength at the first joint (hereinafter simply referred to as "first bonding strength") due to its high deformation resistance and unstable deformation direction, making it difficult to stably secure the bonding area. These problems during the initial bonding of the first joint ultimately lead to reduced and unstable temperature cycle reliability, thereby hindering the practical use of Al connecting materials whose strength has been increased by adding Si or the like.

[0013] An object of the present invention is to provide an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength.

[0014] As a result of intensive research into the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by an Al connecting material containing 3.0 mass% or more and 12.0 mass% or less of Si, in which the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Al phase in the L-section (a cross section in the central axis direction including the central axis) of the Al connecting material and the orientation ratio of the <110> crystal orientation of the Si phase in the L-section are within a specific range.Based on this finding, the inventors have conducted further research and completed the present invention.

[0015] That is, the present invention includes the following: <1> An Al connecting material containing 3.0 mass % or more and 12.0 mass % or less of Si, wherein, when the crystal orientation of the Al phase is measured in an L-section of the Al connecting material (a cross section in the central axis direction including the central axis), the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis, is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation, which has an angular difference of 15° or less with respect to the central axis, is 5% or more, and when the crystal orientation of the Si phase is measured in the L-section of the Al connecting material, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis, is 20% or more and 70% or less. <2> The Al connection material according to <1>, wherein the crystal orientation of the Al phase in the L cross section has an orientation ratio of 5% to 40% of the <110> crystal orientation, which has an angular difference of 15° or less with respect to the central axis direction. <3> The Al connection material according to <1> or <2>, wherein the average diameter of the Al phase in the L cross section is 5 μm to 40 μm. <4> The Al connection material according to any one of <1> to <3>, wherein the average ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is 0.2 to 0.70. <5> The Al connection material according to any one of <1> to <4>, further containing one or more of Sr, Ca, Eu, and Sb in a total amount of 10 ppm to 800 ppm by mass. <6> The Al connecting material according to any one of <1> to <5>, further containing at least one of Ni, Mg, Fe, and In in a total amount of 10 ppm by mass to 500 ppm by mass. <7> The Al connecting material according to any one of <1> to <6>, wherein the total concentration of other elements in the Al connecting material is 0.5 mass% or less.

[0016] According to the present invention, it is possible to provide an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength.

[0017] Fig. 1 is a schematic diagram for explaining the measurement surface (inspection surface) when measuring the crystal orientation, average diameter, and shape of the Al phase and Si phase of an Al connecting material. The measurement surface is a cross section (L cross section) in the central axis direction including the central axis of the Al connecting material. Fig. 2 is a schematic diagram for explaining the short side length (e) and long side length (f) of the Si phase in the L cross section. Fig. 3 is a schematic diagram for explaining a hollow defect in the first joint.

[0018] 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.

[0019] [Al connecting material] The Al connecting material of the present invention is an Al connecting material containing 3.0 mass% or more and 12.0 mass% or less of Si, characterized in that, when the crystal orientation of the Al phase is measured in an L-section of the Al connecting material (a cross section in the central axis direction including the central axis), the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction, is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation, which has an angular difference of 15° or less with respect to the central axis direction, is 5% or more, and when the crystal orientation of the Si phase is measured in an L-section of the Al connecting material, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction, is 20% or more and 70% or less.

[0020] As mentioned above, in the temperature cycle test, when a connecting material made only of high-purity Al was used, cracks propagated relatively quickly within the connecting material, making it difficult to obtain good temperature cycle reliability. On the other hand, when an Al connecting material strengthened by the addition of Si or the like was used, cracks propagated within the Al alloy electrode, which has relatively low strength, making it difficult to obtain the temperature cycle reliability required for next-generation power semiconductor devices. Furthermore, when an Al connecting material strengthened by the addition of Si or the like was used, the semiconductor chip was easily damaged during the first bonding step, and adjusting the ultrasonic vibration or load to reduce such damage sometimes resulted in insufficient first bonding strength.

[0021] As a result of intensive research to solve the above problems, the inventors have found that an Al connecting material containing 3.0 mass% to 12.0 mass% Si, in which the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Al phase in the L-section and the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Si phase in the L-section are within specific ranges, can improve temperature cycle reliability and can also improve first bond strength. Such an Al connecting material of the present invention significantly contributes to realizing the temperature cycle reliability required for next-generation power semiconductor devices and realizing good first bond strength.

[0022] The Al connecting material of the present invention contains 3.0 mass% to 12.0 mass% Si and is composed of an Al phase in which Si is dissolved 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 particles and Si precipitates. Si crystallized particles are formed from the melt during solidification and are coarse with sizes of about 1 to 20 μm, while Si precipitates are formed from the solid state and are small with sizes of about 0.1 to several μm.

[0023] In the present invention, the L-section of the Al connecting material, i.e., the cross section in the central axis direction including the central axis of the Al connecting material, is as will be explained later in the section "(Method for measuring the orientation ratio of the crystal orientations of the Al phase and the Si phase)" with reference to Figure 1.

[0024] The reason why the Al connecting material of the present invention can provide excellent temperature cycle reliability and good first bonding strength is presumed to be as follows.

[0025] First, with regard to temperature cycle reliability, the Si phase has a smaller linear expansion coefficient than Al, which contributes to reducing the difference in linear expansion coefficient between the Al connecting material and the semiconductor chip, thereby reducing thermal stress. It is also believed that the particulate Si phase can suppress the growth of cracks that occur at the bonding interface into the Al connecting material. Furthermore, when the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Al phase is in the range of 20% to 70% (wherein, when the total orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation with an angle difference of 15° or less with respect to the central axis is 5% or more), the yield strength in the central axis direction during temperature cycle testing is increased and slip deformation is reduced. Furthermore, when the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Si phase is in the range of 20% to 70%. It is also believed that the stress concentration around the Si phase is reduced.

[0026] Regarding the first bonding strength, it is believed that by setting the orientation ratio of the crystal orientations of the Al phase and the Si phase within the range of the present invention, the deformation of the Al phase and the rotation of the crystal lattice near the bonding interface when ultrasonic vibration and load are applied are controlled, thereby improving the bonding strength. That is, when the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Al phase is in the range of 20% to 70% (however, when the total orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation having an angle difference of 15° or less with respect to the central axis direction is 5% or more), the deformation of the Al connecting material in the direction perpendicular to the central axis is promoted, thereby improving the adhesion of the bonding interface. Furthermore, when the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Si phase is in the range of 20% to 70%, the effect of controlling the deformation of the Al connecting material in the central axis direction is obtained. It is believed that by simultaneously controlling the crystal orientation of the Al phase and the crystal orientation of the Si phase, deformation of the Al connecting material is promoted in both directions perpendicular to the central axis and in the direction of the central axis, thereby enhancing the effect of destroying the oxide film at the bonding interface and promoting metal bonding.

[0027] As described above, it is presumed that the Al connecting material of the present invention can provide excellent temperature cycle reliability and good first bond strength as described above, as a result of appropriately controlling the factors that contribute to improving temperature cycle reliability and first bond strength.

[0028] -Si Concentration- A Si concentration in the range of 3.0% by mass or more and 12.0% by mass or less reduces thermal distortion at the joint and helps improve temperature cycle characteristics. If the Si concentration is less than 3.0% by mass, the improvement effect is small, while if it exceeds 12.0% by mass, problems such as a decrease in initial joint strength due to hardening and damage to the semiconductor chip occur. From the viewpoint of obtaining good temperature cycle reliability, the Si concentration in the Al connecting material of the present invention is 3.0% by mass or more, preferably 4.0% by mass or more, more preferably 4.2% by mass or more, 4.4% by mass or more, 4.5% by mass or more, 4.6% by mass or more, 4.8% by mass or more, or 5.0% by mass or more. On the other hand, if the hardness of the Al connecting material is excessive, damage to the semiconductor chip is likely to occur during the first joining under commonly used ultrasonic vibration and load joining conditions. From the viewpoint of obtaining good bonding strength when performing the first bonding under general bonding conditions, the Si concentration in the Al connecting material of the present invention is 12.0 mass% or less, preferably 11.5 mass% or less or 11.0 mass% or less, and more 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.

[0029] 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 connecting material of the present invention. If elements derived from atmospheric contaminants such as oxygen or carbon are adsorbed on the surface of the Al connecting material, it is effective to wash the surface with an acid or alkali according to the adsorbed substance before analysis.

[0030] -Crystal orientation of Al phase in L cross section- When the crystal orientation of the Al phase in the L cross section of an Al connecting material is measured from the viewpoint of obtaining excellent temperature cycle reliability and good first bond strength, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction (hereinafter also referred to as the "total <111> + <110> ratio of the Al phase") is 20% or more, preferably 22% or more, 24% or more, 25% or more, or more than 25%, more preferably 26% or more or 28% or more, even more preferably 30% or more, and even more preferably 35% or more, 40% or more, 42% or more, 44% or more, or 45% or more. When a detailed investigation was conducted on an embodiment in which the <111> + <110> total ratio of the Al phase was low, it was confirmed that the effect of improving temperature cycle reliability and first bond strength could be obtained even when the total ratio was in the range of 20% or more but less than 30%. However, it has been confirmed that it is important that when the total ratio of <111> + <110> of the Al phase is 25% or less, the ratio of the <110> crystal orientation with an angular difference of 15° or less with respect to the central axis direction is 5% or more. From the viewpoint of obtaining excellent temperature cycle reliability and good first bonding strength, the upper limit of the total ratio of <111> + <110> of the Al phase is 70% or less, preferably 65% ​​or less, more preferably 60% or less, and even more preferably 58% or less, 56% or less, or 55% or less.

[0031] From the viewpoint of obtaining even better first joint strength and suppressing hollows in the first joint (a phenomenon in which a portion where the metal bond is insufficient is formed in the joint region between the Al connecting material and the electrode), when the crystal orientation of the Al phase in the L cross section of the Al connecting material is measured, the orientation ratio of the <110> crystal orientation, which has an angle difference of 15° or less with respect to the central axis direction (hereinafter also referred to as the "<110> ratio of the Al phase"), is preferably in the range of 5% to 40%. That is, with regard to the crystal orientation of the Al phase, satisfying the above condition that the total ratio of the <111> + <110> of the Al phase is in the range of 20% to 70%, and having the <110> ratio of the Al phase be in the range of 5% to 40%, a high effect of suppressing hollows in the first joint and improving the first joint strength is obtained. The reason why the above effect is obtained when the <110> ratio of the Al phase is in this range is presumed to be as follows. That is, when the <110> ratio of the Al phase is within this range, it is believed that deformation of the Al connecting material in the ultrasonic vibration direction can be promoted, and thus the first bond strength can be further improved. Furthermore, since hollow holes often occur in the ultrasonic vibration direction, it is believed that promoting deformation of the Al connecting material in the ultrasonic vibration direction as described above also suppresses hollow holes. From the viewpoint of obtaining even better first bond strength and suppressing hollow holes in the first bonded portion, the <110> ratio of the Al phase is more preferably 10% or more, even more preferably 12% or more, 14% or more, or 15% or more. Furthermore, the upper limit of the <110> ratio of the Al phase is more preferably 38% or less, 36% or less, or 35% or less.

[0032] To measure the orientation ratio of the Al phase crystal orientation in the L-section of an Al connecting material, a method can be used that combines information on the Al and Si concentrations obtained by SEM-EDS with information on the crystal orientation obtained by electron backscatter diffraction (EBSD). Specifically, in the measurement area where the L-section of the Al connecting material 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 FE-SEM. Specifically, it is preferable to use the Chi Scan function, which is a function of the OIM Data Collection or OIM Analysis software (both manufactured by TSL Solutions) provided with the FE-SEM. Then, for the area identified as Al phase, the orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Al phase, as well as their total, can be calculated using the analysis software provided with the instrument. To calculate the orientation ratio, a partial ratio is used, which is calculated as a population of the area of ​​only the crystal orientations that could be identified based on a certain reliability within the measurement area. The area ratios of the <111> crystal orientation and the <110> crystal orientation are defined as the orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation, respectively. Therefore, in one embodiment, the orientation ratio of the crystal orientation of the Al phase in the L-section of the Al connection material of the present invention is calculated by the following steps (1) to (3). (1) In the measurement area where the L-section of the Al connection material is used as the inspection surface, 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 from the EDS measurement results of Si, Al and Si can be separated and identified. The crystal orientation can be analyzed using the crystal information of Al and Si from the material file. (3) The crystal orientation of the region identified as the Al phase is analyzed, and the orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation of the Al phase are calculated.

[0033] 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 connecting material, it is preferable to compare it at about 30%. A supplementary explanation of the procedure for adjusting this Tolerance is provided 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 in the EDS map, which displays the Si element concentration in EDS analysis in two dimensions.

[0034] In the present invention, the orientation ratios of the <111> crystal orientation and the <110> crystal orientation of the Al phase in the L cross section were determined as the average values ​​of the orientation ratios 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 connection material to be measured at intervals of 50 cm or more along the central axis of the Al connection material and provide them for measurement. Furthermore, in the present invention, the measurement area for crystal orientation using the EBSD method has a length in the direction of the central axis of the Al connection material of 300 μm or more and less than 800 μm, and it is desirable that the entire Al connection material be included in the direction perpendicular to the central axis of the Al connection material. However, if the size is large and it is difficult to measure the entire Al connection material, the measurement area can be adjusted to a range of less than 600 μm.

[0035] -Crystal orientation of Si phase in L cross section- When the crystal orientation of the Si phase in the L cross section of the Al connecting material is measured from the viewpoint of obtaining excellent temperature cycle reliability and good first bond strength, the total ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction (hereinafter also referred to as the "total ratio of the <111> + <110> of the Si phase") is 20% or more, preferably 25% or more, more preferably 26% or more, 28% or more, or 30% or more. From the viewpoint of obtaining excellent temperature cycle reliability and good first bond strength, the total ratio of the <111> + <110> of the Si phase is 70% or less, preferably 65% ​​or less, more preferably 60% or less, and even more preferably 58% or less, 56% or less, 55% or less, 54% or less, 52% or less, or 50% or less.

[0036] To measure the orientation ratio of the Si phase's crystal orientation in the L-section of an Al connecting material, a technique can be used that combines information on the Al and Si concentrations obtained by SEM-EDS with information on the crystal orientation obtained by EBSD, similar to the measurement of the orientation ratio of the Al phase's crystal orientation. The detailed procedure can be the same as that described above in relation to the measurement of the orientation ratio of the Al phase's crystal orientation. That is, for the region identified as the Si phase, the orientation ratio of the <111> crystal orientation and the <110> crystal orientation of the Si phase, as well as their total, can be calculated using the analysis software provided with the device. To calculate the orientation ratio, a partial ratio is used, calculated as a population of the area of ​​only the crystal orientations that can be identified with a certain level of reliability within the measurement area. Therefore, in one embodiment, the orientation ratio of the Si phase's crystal orientation in the L-section of an Al connecting material of the present invention is calculated using the following procedures (1) to (3). (1) In the measurement area where the L-section of the Al connection material is used as the inspection surface, 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 from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) The crystal orientation is analyzed for the area identified as the Si phase, and the orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation of the Si phase are calculated.

[0037] In the present invention, the orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation of the Si phase in the L cross section were the average values ​​of the orientation ratios obtained by measuring at least three locations. The tolerance setting range, the method for obtaining the measurement sample, and the measurement area of ​​the crystal orientation by the EBSD method in the above step (2) are the same as those described above for the measurement of the orientation ratio of the crystal orientation of the Al phase.

[0038] - Average Diameter of Al Phase in L Cross Section - In the Al connecting material of the present invention, the average diameter of the Al phase in the L cross section is preferably 5 μm or more and 40 μm or less.

[0039] The second bonding is often performed on a material harder than Al, such as a Cu substrate. Furthermore, the ultrasonic vibration and load conditions during the second bonding are set higher than those during the first bonding. This can lead to unstable deformation of Al connecting materials strengthened by the addition of Si or other additives during the second bonding. The inventors discovered that the variation in bonding strength during the second bonding can be reduced by setting the average diameter of the Al phase in the L cross section to 5 μm or more and 40 μm or less. This is thought to be due to the synergistic effect of the following: The effect of promoting the deformation of the Al connecting material due to ultrasonic vibration is achieved by containing Si at a predetermined concentration and controlling the crystal orientation ratio of the Al phase and the Si phase within a predetermined range; and the effect of uniforming the deformation of the Al connecting material in both directions parallel and perpendicular to the central axis of the Al connecting material is achieved by setting the average diameter of the Al phase to 5 μm or more and 40 μm or less.

[0040] From the viewpoint of further reducing the variation in the bonding strength in the second bonding and realizing a better stability of the bonding strength, the average diameter of the Al phase in the L cross section of the Al connecting material of the present invention is more preferably 10 μm or more, more preferably 12 μm or more, 14 μm or more, or 15 μm or more. Moreover, the upper limit of the average diameter of the Al phase in the L cross section is more preferably 35 μm or less, more preferably 30 μm or less, and even more preferably 28 μm or less, 26 μm or less, or 25 μm or less.

[0041] A method for measuring the average diameter of the Al phase in the L-section of an Al connecting material will now be described. Similar to the measurement of the orientation ratio of the crystal orientation described above, the measurement of the average diameter of the Al phase in the L-section can be performed by combining information on the Al and Si concentrations obtained by SEM-EDS with information on the crystal orientation obtained by EBSD. The detailed procedure may be the same as that described above in relation to the measurement of the orientation ratio of the crystal orientation. That is, the crystal orientation of the region identified as Al phase can be analyzed using the analysis software provided with the device. If the orientation difference between measurement points is 15° or more, it is determined to be a grain boundary, and the circle-equivalent diameter is calculated. The average circle-equivalent diameter of each Al phase is defined as the average diameter of the Al phase. In the process of determining the average diameter of the Al phase, regions where the crystal orientation could not be measured or where the crystal orientation analysis reliability was low were excluded from the calculation. Therefore, in one embodiment, the average diameter of the Al phase in the L-section of the Al connecting material of the present invention is calculated using the following steps (1) to (3). (1) Using the L-section of the Al connecting material as the inspection surface, the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Using the Chi Scan function, Al and Si are separated and extracted. Specifically, by setting a tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) The crystal orientation of the region identified as Al phase is analyzed, and 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 of each crystal grain is calculated. The circle-equivalent diameters of each crystal grain are then averaged to calculate the average diameter of the Al phase. Here, for the average calculation, the average value calculated by area averaging, which can be selected in the software provided with the device, is used. By using the average value calculated by area averaging, it is possible to accurately measure and determine whether the conditions related to the average diameter of the Al phase, which are suitable for improving the stability of the joint strength in the second joint, are met. The average area is calculated by averaging the values ​​obtained by multiplying the ratio of each particle area to the total particle area, and is calculated automatically by the software.

[0042] In the present invention, when calculating the average diameter of the Al phase in the L cross section, only Al phases having a diameter (circle equivalent diameter) of 0.5 μm or more are considered, which makes it possible to accurately determine whether the requirement for the average diameter of the Al phase in the L cross section, which is suitable for improving the stability of the joining strength in the second joining, is met.

[0043] When measuring the average diameter of the Al phase in the L cross section, the setting range of the tolerance in the procedure (2) above, the method of obtaining the sample for measurement, and the measurement area of ​​the crystal orientation by the EBSD method are as described above in relation to the measurement of the orientation ratio of the crystal orientation of the Al phase.

[0044] - Shape of Si phase in L cross section - When the bond strength of multiple wires was evaluated in a temperature cycle test, it was confirmed that multiple bonds did not deteriorate simultaneously, but that there was variation in the time to failure (lifespan) when the bond strength decreased. To achieve the temperature cycle reliability required for next-generation power semiconductor devices, it is necessary to not only manage the lifespan based on the average bond strength in the temperature cycle test, but also to control the variation in bond strength.

[0045] The inventors have been studying an Al connecting material containing 3.0% by mass or more and 12.0% by mass or less of Si, and in which the total ratio of the <111> + <110> Al phase in the L cross section and the total ratio of the <111> + <110> Si phase in the L cross section are within a specific range. They have found that the shape of the Si phase in the L cross section affects the variability of bonding strength in a temperature cycle test. Specifically, they have found that when the average ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is in the range of 0.2 to 0.70, not only is the effect of suppressing deterioration of bonding strength after a temperature cycle test, but also the variability of bonding strength is reduced. The value of this ratio (e / f) is an index of flatness. This will be further explained with reference to FIG. 2 . FIG. 2 is a schematic diagram showing the Si phase in the L cross section of an Al connecting material, with the central axis direction of the Al connecting material corresponding to the horizontal direction (left-right direction) in FIG. 2 and the direction perpendicular to the central axis corresponding to the vertical direction (up-down direction) in FIG. 2. For the Si phase in the L cross section, the above-mentioned "short side length e" corresponds to the dimension indicated by the symbol e in FIG. 2. Also, for the Si phase in the L cross section, the above-mentioned "long side length f" corresponds to the dimension indicated by the symbol f in FIG. 2. Hereinafter, the ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is also referred to as the "shape ratio (e / f) of the Si phase." The value of the shape ratio (e / f) of the Si phase can be determined using the Grain Shape Aspect Ratio in the analysis software provided with the apparatus.

[0046] The reason why the variation in bonding strength in a temperature cycle test can be reduced by controlling the average value of the shape ratio (e / f) of the Si phase in the Al connecting material of the present invention is presumed to be as follows: The reason why the bonding strength decreases in a temperature cycle test is that cracks propagate along the central axis of the Al connecting material or at the bonding interface within the Al connecting material or in a direction close to that. Here, due to plastic processing by wiredrawing, the Si phase tends to be aligned so that the direction of its long side length f is the central axis of the Al connecting material or in a direction close to that. When the average value of the shape ratio (e / f) of the Si phase is in the range of 0.2 to 0.70, the Si phase takes on a shape such as an ellipse or a column, which acts to relieve thermal stress in the central axis direction of the Al connecting material, and thus is thought to be able to suppress crack propagation along the central axis of the Al connecting material or in a direction close to that. In order to reduce the variation in bonding strength in the temperature cycle test, it is sufficient that the average value of the shape ratio (e / f) of the Si phase in the L cross section is within the above-mentioned preferred range, and it is not necessary that the shape ratio (e / f) of all the Si phases be in the range of 0.2 to 0.70. For example, the Si phase may contain an Si phase having an shape ratio (e / f) of less than 0.2, or may contain an Si phase having an shape ratio (e / f) of more than 0.70.

[0047] From the viewpoint of reducing the variation in bonding strength in a temperature cycle test and achieving better temperature cycle reliability required for next-generation power semiconductor devices, the average value of the shape ratio (e / f) of the Si phase in the L cross section of the Al connecting material of the present invention is more preferably 0.25 or more. From the viewpoint of achieving even better temperature cycle reliability, the upper limit of the average value of the shape ratio (e / f) of the Si phase is more preferably 0.6 or less.

[0048] A method for measuring the shape ratio (e / f) of the Si phase in the L-section of an Al connecting material will be described. First, as with the above-mentioned crystal orientation measurement and Al phase average diameter measurement, a method can be used that combines information on the Al and Si concentrations obtained by SEM-EDS with information on the crystal orientation obtained by EBSD. The detailed procedure may be the same as that described above in relation to the measurement of the crystal orientation ratio. That is, the crystal orientation of the region identified as the Si phase can be analyzed using the analysis software provided with the device. If the orientation difference between measurement points is 15° or more, it is determined to be a grain boundary, and the shape ratio (e / f) is calculated. The average value of the shape ratios (e / f) of each Si phase is defined as the average value of the Si phase shape ratio (e / f). In the process of determining the Si phase shape ratio (e / f), parts where the crystal orientation could not be measured or where the crystal orientation could be measured but the reliability of the orientation analysis was low were excluded from the calculation. Therefore, in one embodiment, the average value of the shape ratio (e / f) of the Si phase in the L-section of the Al connecting material of the present invention is calculated using the following steps (1) to (3). (1) Using the L-section of the Al connecting material as the inspection surface, the Al and Si concentrations are measured using EDS and the crystal orientation is measured using EBSD simultaneously. (2) Using the Chi Scan function, Al and Si are separated and extracted. Specifically, by setting a tolerance equivalent to the Si threshold from the Si EDS measurement results, Al and Si can be separated and identified. The crystal orientation can be analyzed using the Al and Si crystal information from the material file. (3) For the region identified as the Si phase, the crystal orientation is analyzed, and if the orientation difference between the measurement points is 15° or more, it is determined to be a grain boundary, and the shape ratio (e / f) of each crystal grain is calculated. The shape ratios (e / f) of each crystal grain are averaged to calculate the average shape ratio (e / f) of the Si phase. Here, the average value of the shape ratio (e / f) of the Si phase is calculated using the numerical value of the grain shape aspect ratio (hereinafter referred to as the "grain shape aspect ratio") of the analysis software. This value is the average value obtained by calculating the grain aspect ratio of each crystal grain.The grain shape aspect ratio is calculated by determining the ratio (e / f) of the short side length (e) (Grain Shape Minor Axis) to the long side length (f) (Grain Shape Major Axis) of one crystal grain. The average value calculated by area averaging, which can be selected in the software provided with the device, is used. By using the average value calculated by area averaging, it is possible to accurately measure and determine whether the conditions related to the average value of the shape ratio (e / f) of the Si phase are met, which is suitable for reducing the variation in bonding strength in temperature cycle tests and further achieving the temperature cycle reliability required for next-generation power semiconductor devices.

[0049] When measuring the average value of the shape ratio (e / f) of the Si phase in the L cross section, the setting range of Tolerance in the procedure (2) above and the measurement area of ​​the crystal orientation by the EBSD method are as described above for the measurement of the orientation ratio of the crystal orientation of the Al phase.

[0050] In addition to the above, there are several other methods for measuring the average diameter of the Al phase and the shape ratio (e / f) of the Si phase, including binarization processing from an observed image of the L cross section. However, in the present invention, a method is used in which the information on the Al concentration and Si concentration obtained by SEM-EDS is combined with the information on the crystal orientation obtained by EBSD, as described above, for reasons such as the fact that the present invention is equipped with many measurement functions and can determine multiple characteristics such as the above-mentioned crystal orientation, the average diameter of the Al phase, and the shape ratio (e / f) of the Si phase in a single measurement, that automatic analysis is possible, and that measurement is easy using widely used equipment and analysis techniques.

[0051] -Addition of Sr, Ca, Eu, and Sb- The Al connecting material of the present invention may further contain one or more of Sr, Ca, Eu, and Sb (hereinafter also referred to as the "first element group") in a total amount of 10 ppm by mass or more and 800 ppm by mass or less.

[0052] Furthermore, by containing a total of 10 mass ppm to 800 mass ppm of one or more of Sr, Ca, Eu, and Sb, the frequency of wire breakage during wiredrawing of an Al connecting material can be reduced. Al alloys containing a high concentration of Si at 3.0 mass% to 12.0 mass% tend to have an increased frequency of wire breakage during the wiredrawing process. One possible cause of this is thought to be that particles of the Si phase 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 orientation ratio of the crystal orientations of the Al phase and the Si phase in the L cross section, enhances the effect of alleviating stress concentration during wiredrawing.

[0053] From the viewpoint of reducing the frequency of wire breakage during wire drawing, the total concentration of the first element group in the Al connecting material 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.

[0054] - Addition of Ni, Mg, Fe, and In - The Al connecting material of the present invention may further contain one or more of Ni, Mg, Fe, and In (hereinafter also referred to as the "second element group") in a total amount of 10 ppm by mass or more and 500 ppm by mass or less.

[0055] Furthermore, by containing at least one of Ni, Mg, Fe, and In in a total amount of 10 mass ppm to 500 mass ppm, scratches and abrasions on the surface of the Al connecting material can be suppressed, resulting in a smooth surface. Al alloys containing Si at a high concentration of 3.0 mass% to 12.0 mass% can harden the surface and cause the Si phase and Al oxide present on the surface to fall off, resulting in scratches and abrasions on the surface during wiredrawing, resulting in an Al connecting material with large surface irregularities. It is believed that the addition of the second element group stabilizes the Al oxide on the surface of the Al connecting material, refines the structure of the Al crystal grains, and hardens them, thereby reducing scratches and abrasions during wiredrawing. It is believed that controlling the orientation ratio of the crystal orientations of the Al phase and the Si phase in the L-section and adding the second element group can enhance the effect of suppressing scratches and abrasions on the surface of the Al connecting material and forming a smooth surface.

[0056] From the viewpoint of forming an Al connecting material 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 connecting material of the present invention is more preferably 20 mass ppm or more, even more preferably 30 mass ppm or more, 40 mass ppm or more, or 50 mass ppm or more, and the upper limit is preferably 450 mass ppm or less, more preferably 440 mass ppm or less, 420 mass ppm or less, or 400 mass ppm or less.

[0057] When manufacturing the Al connecting material of the present invention, it is preferable to use Al with a purity of 4N (Al: 99.99% by mass or more) as the aluminum raw material, and it is even more preferable to use Al with a purity of 5N (Al: 99.999% by mass or more) or more, which has a lower amount of impurities.

[0058] The Al connecting material 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"), as long as the effects of the present invention are not impaired. The total concentration of the other elements in the Al connecting material is not particularly limited, as long as the effects of the present invention are not impaired. The total concentration of the other elements may be, for example, 0.5 mass% or less, 0.4 mass% or less, 0.3 mass% or less, 0.2 mass% or less, 0.15 mass% or less, 0.1 mass% or less, 0.08 mass% or less, 0.06 mass% or less, 0.05 mass% or less, 0.04 mass% or less, 0.03 mass% or less, 0.025 mass% or less, 0.02 mass% or less, 0.018 mass% or less, 0.016 mass% or less, 0.015 mass% or less, 0.014 mass% or less, 0.012 mass% or less, or 0.01 mass% or less. The lower limit of the total concentration of the other elements is not particularly limited, and may be 0 mass%. In one embodiment, the remainder of the Al connecting material of the present invention consists of Al and other elements. Therefore, in a preferred embodiment, the Al connecting material of the present invention consists of Al, Si, and other elements. In another preferred embodiment, the Al connecting material 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 connecting material 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 connecting material 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.

[0059] In one embodiment, the balance of the Al connecting material of the present invention consists of Al and inevitable impurities. Therefore, in a preferred embodiment, the Al connecting material of the present invention consists of Al, Si, and inevitable impurities. In another preferred embodiment, the Al connecting material 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 connecting material 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 connecting material 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.

[0060] In a preferred embodiment, the Al connecting material of the present invention does not have a coating containing a metal other than Al as a main component on the outer periphery of the Al connecting material. Here, the term "coating containing a metal other than Al as a main component" refers to a coating in which the content of a metal other than Al is 50 mass % or more.

[0061] The Al connecting material of the present invention may be an Al bonding wire or an Al bonding ribbon. When the Al connecting material of the present invention is an Al bonding wire, its wire diameter is not particularly limited and may be, for example, in the range of 100 to 600 μm. When the Al connecting material of the present invention is an Al bonding ribbon, the dimensions (W×T) of its rectangular or approximately rectangular cross section are not particularly limited and, for example, W may be 100 to 3000 μm and T may be 50 to 600 μm.

[0062] The Al connecting material of the present invention can provide excellent temperature cycle reliability and good first bond strength, and therefore can be suitably used as an Al connecting material for semiconductor devices, particularly for power semiconductor devices.

[0063] -Method of Manufacturing Al Connecting Material- An example of a method of manufacturing an Al connecting material of the present invention will be described below, focusing on the manufacture of an Al bonding wire having a wire diameter of 200 to 400 μm.

[0064] The Al and alloying elements used as raw materials preferably have high purity. The purity of Al is preferably 99.99% by mass or more, with the remainder consisting of inevitable impurities. The purity of Si, the first element group, and the second element group used as alloying elements is preferably 99.9% by mass or more, with the remainder consisting of inevitable impurities. The Al alloy used for bonding wire can be produced by loading the Al raw material and the alloying element raw materials into a graphite or alumina crucible processed to obtain a cylindrical ingot and melting them using an electric furnace or high-frequency heating furnace. The diameter of the cylindrical ingot is preferably Φ6 mm or more and less than 8 mm, taking into account the workability in subsequent processing steps. The atmosphere in the furnace during melting is preferably an inert or reducing atmosphere to prevent excessive oxidation of Al and other elements constituting the wire. The maximum temperature of the molten metal during melting is preferably in the range of 800°C or more and less than 1050°C, taking into account 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. The cooling method after melting can be water cooling, furnace cooling, air cooling, or the like.

[0065] The cylindrical ingot obtained by melting is subjected to a solution treatment in which it is heated at a high temperature, and then repeatedly subjected to wire drawing using a die to produce a wire of the desired wire diameter. The wire after wire drawing can be used as an Al alloy bonding wire by performing a final heat treatment using an electric furnace.

[0066] In order to control the crystal orientation of the Si phase and the crystal orientation of the Al phase in the L cross section, 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 the wiredrawing process, it is effective to use a lubricant to ensure lubrication at the contact interface between the wire and the die.

[0067] An example of manufacturing conditions for controlling the total ratio of <111> + <110> of the Al phase in the L cross section to within a range of 20% to 70% and for controlling the total ratio of <111> + <110> of the Si phase in the L cross section to within a range of 20% to 70% is shown below.

[0068] In order to adjust the crystal orientation of the Si phase, it is effective to subject the ingot to a two-stage heat treatment and to control the area reduction rate during wire drawing.

[0069] The solution treatment temperature is effectively set to 400°C or higher but lower than 550°C for 1 hour or higher but lower than 6 hours. After the solution treatment, it is effective to perform a homogenization treatment at 250°C or higher but lower than 350°C for 2 hours or higher but lower than 6 hours. This promotes the division and growth of the Si phase that crystallizes during the solidification process, thereby promoting the orientation of the <111> and <110> crystals in the Si phase.

[0070] Regarding the wire drawing conditions, it is effective to set the wire area reduction rate per die used during wire drawing to be in the range of 10% or more and less than 20%. Here, if the wire area reduction rate per die is P1, P1 is expressed by the following formula.

[0071] P1 = {(R ２ ２ -R １ ２ ) / R ２ ２}×100 where R ２ is the diameter of the wire before processing (mm), R １ represents the diameter (mm) of the wire after processing.

[0072] By adjusting the wire area reduction rate within the above range, the entire wire is significantly deformed during die processing, increasing processing strain even within the wire, and the Si phase is aligned along the central axis of the wire while simultaneously adjusting the processing strain within the Si phase. By performing a subsequent heat treatment in this wiredrawing state, it is possible to increase the orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have high atomic density, and also to increase the orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have high elastic modulus, in the Si phase.

[0073] In order to adjust the crystal orientation of the Al phase, it is effective to combine the control of the area reduction rate in the wire drawing process and the final heat treatment conditions.

[0074] Specifically, by adjusting the die area reduction rate within the range of 10% or more and less than 20%, the processing strain can be controlled and the ratio of the <111> crystal orientation to the <110> crystal orientation formed as the processing texture can be promoted. For example, as the area reduction rate increases, the processing strain increases and the ratio of the <111> crystal orientation to the <110> crystal orientation tends to increase.

[0075] 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 24 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 in addition to the formation of the above-mentioned deformation texture, it becomes easy to control the orientation of the crystal orientation. For example, adjusting the final heat treatment temperature or time tends to increase the orientation ratio of the densely packed <111> crystal orientation and the <110> crystal orientation.

[0076] In order to control the average diameter of the Al phase in the L cross section to a range of 5 μm or more and 40 μm or less, it is effective to adjust the temperature and time of the heat treatment at the final wire diameter to control the growth of crystal grains due to recrystallization of the Al phase.

[0077] It is effective to control the temperature range of the final heat treatment to be equal to or higher than 250° C. and lower than 340° C., and the time range to be equal to or higher than 5 hours and lower than 24 hours. By performing the homogenization treatment at a relatively low temperature, the amount of solid solution of Si contained in the Al phase can be adjusted, which makes it easy to adjust the recrystallization temperature of the Al phase in the final heat treatment, and the size of the Al phase can be controlled within the target range.

[0078] Furthermore, if an intermediate heat treatment is performed as needed, it becomes easier to adjust the conditions for the final heat treatment. Intermediate heat treatment is a heat treatment performed during the process of processing from an ingot to the final wire diameter. It is effective to set the temperature range of the intermediate heat treatment to 250°C or higher and lower than 400°C, and the time period to 30 minutes or higher and lower than 3 hours. It is effective to perform the intermediate heat treatment at a wire diameter that is 2.5 to 4.0 times the final wire diameter. By performing the intermediate heat treatment, it is possible to reduce the processing strain of the Al phase and promote recrystallization, and by first adjusting the Al phase, it becomes easier to adjust the grain size of the Al phase in the subsequent final heat treatment. For example, if the intermediate heat treatment temperature is increased, the diameter of the Al phase tends to decrease.

[0079] In order to adjust the shape (shape ratio (e / f)) of the Si phase in the L cross section, it is effective to control the above-mentioned two-stage heat treatment and final heat treatment.

[0080] The temperature range of the solution treatment of the ingot is 400°C or higher but lower than 550°C for 1 hour or higher but lower than 6 hours, and the subsequent homogenization treatment is preferably 250°C or higher but lower than 350°C for 2 hours or higher but lower than 6 hours. The solution treatment causes the division and growth of the Si phase crystallized during the solidification process, and the homogenization treatment causes solid solution and precipitation of Si at the interface of the Si phase, making it possible to control the shape of the Si phase. For example, when solution treatment is performed at a high temperature, the shape ratio (e / f) of the Si phase tends to decrease.

[0081] As mentioned above, the above is an example of the production of Al bonding wire, which is a wire material, as a representative example of an Al connecting material. The same procedure can also be used to produce 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 producing Al bonding ribbon by rolling, the die area reduction rate can be adjusted by replacing it with the rolling reduction rate.

[0082] [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 connecting material of the present invention. As described above, wedge bonding is used for both the first bonding with the electrodes on the semiconductor chip and the second bonding with the electrodes on the lead frame or substrate.

[0083] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, and an Al connecting material for electrically connecting the circuit board and the semiconductor chip, and is characterized in that the Al connecting material is the Al connecting material of the present invention.

[0084] 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.

[0085] 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.

[0086] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0087] (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, Ca, Eu, Sb), and the second element group (Ni, Mg, Fe, In) had a purity of 99.99% by mass or more, with the remainder consisting of inevitable impurities. The Al alloy used for the Al connecting material was produced by loading the Al raw material and the alloying element raw materials into an alumina crucible and melting them using a high-frequency heating furnace. The atmosphere in the furnace during melting was an Ar atmosphere, and the maximum temperature of the molten metal during melting was 800°C or higher but lower than 1050°C. The cooling method after melting was air cooling (cooling in air) or water cooling (cooling in water).

[0088] A cylindrical ingot with a diameter of 6 mm was obtained by melting, and the ingot was subjected to solution treatment and homogenization treatment. After that, wire drawing using a die and intermediate heat treatment were performed to produce an Al connecting material (Al bonding wire) with a diameter of 300 μm. The temperature range of the solution treatment was 500 ° C or higher and lower than 550 ° C, and the time was 2 hours or higher and lower than 4 hours. After the solution treatment, a homogenization treatment was performed continuously during cooling. The temperature range of the homogenization treatment was 250 ° C or higher and lower than 350 ° C, and the time was 2 hours or higher and lower than 5 hours. The cooling method after the homogenization treatment was air cooling in the atmosphere.

[0089] A commercially available lubricant was used during wire drawing, and the wire area reduction rate per die during wire drawing was 12.5% ​​or more and less than 16.0%. The temperature range of the final heat treatment was 250°C or more and less than 360°C, and the time of the final heat treatment was 2 hours or more and less than 24 hours.

[0090] In some examples, the wire was drawn using a die with a die angle of 14° or more and less than 18°.

[0091] (Method for measuring element content) The concentration analysis of elements contained in the Al connecting material was performed using an ICP-OES ("PS3520UVDDII" manufactured by Hitachi High-Tech Science Corporation) or an ICP-MS ("Agilent 7700x ICP-MS" manufactured by Agilent Technologies, Inc.) as an analytical device.

[0092] (Method for measuring the orientation ratio of the crystal orientations of the Al phase and the Si phase) The L-section (a cross section in the central axis direction including the central axis) of the Al connecting material was used as the inspection surface, and the crystal orientations of the Al phase and the Si phase were measured. In the present invention, the central axis of the Al connecting material and the cross section in the central axis direction including the central axis (L-section) are as shown in FIG. 1. FIG. 1 shows a case where the Al connecting material is an Al bonding wire having a circular cross-sectional shape. However, if the Al connecting material is an Al bonding ribbon having a rectangular or approximately rectangular cross-sectional shape 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-section refers to a cross section in the central axis direction including the central axis and in the direction of the thickness T. When processing the cross section to expose the L-section of the Al connecting material, there may be a deviation from the central axis of the Al connecting material. In this case, if the length in the direction perpendicular to the central axis of the L-section is 90% or more of the wire diameter of the Al connecting material (thickness T in the case of a ribbon), it can be considered to be a cross section including the central axis.

[0093] The measurements were performed using an FE-SEM (SU-70 manufactured by Hitachi High-Technologies Corporation), and analysis software APEX (for data collection), OIM Data Collection (for ChiScan), and OIM Analysis (for data analysis) manufactured by TSL Solutions. Three measurement areas were randomly selected at intervals of 50 cm or more along the central axis of the Al connecting material, and measurements were performed on the three areas. The measurement area was determined so that it was 300 μm or more and less than 800 μm in the direction of the central axis of the Al connecting material, and the entire Al connecting material was included in the direction perpendicular to the central axis. The main conditions for EDS and EBSD measurements were an acceleration voltage of 15 kV, a measurement magnification of 350x, a scan speed of 30 to 120 points / second, and a measurement interval in the range of 0.1 to 0.3 μm. Here, a fast scan speed can shorten the measurement time, but there is a concern that the EDS measurement accuracy will decrease. It is desirable to select an appropriate scan speed within the above range.

[0094] -Crystal orientation of the Al phase- To measure the orientation ratio of the Al phase in the L-section of the Al connection material, a method was used that combined information on the Al and Si concentrations obtained by SEM-EDS with information on the crystal orientation obtained by EBSD. Specifically, the measurement was performed according to the following procedures (1) to (3). (1) In the measurement area where the L-section of the Al connection material was used as the inspection surface, Al and Si concentrations were measured using EDS and crystal orientation was measured using EBSD simultaneously. (2) Al and Si were separated and extracted using the Chi Scan function, a function of the EBSD analysis software. Specifically, Al and Si were separated and identified by setting a tolerance equivalent to the Si threshold from the Si EDS measurement results. Crystal orientation analysis was performed using the Al and Si crystal information from 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 Al phase was analyzed, and the orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation of the Al phase were calculated. The crystal orientations to be investigated were selected from at least three types of typical crystal orientations of Al metal: <111>, <110>, and <100>, and, if necessary, a crystal orientation with a high ratio. Here, the orientation ratio of the crystal orientations was calculated using the partial ratio.

[0095] The orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation of the Al phase were calculated as the average values ​​obtained for the three measurement regions by the above steps (1) to (3).

[0096] -Crystal orientation of Si phase- As with the measurement of the orientation ratio of the crystal orientation of the Al phase, the measurement of the orientation ratio of the crystal orientation of the Si phase in the L cross section of the Al connecting material used a method that combined information on the Al concentration and Si concentration obtained by SEM-EDS with information on the crystal orientation obtained by EBSD. In detail, after performing the above procedures (1) and (2), the measurement was performed according to the following procedure (3). (3) The crystal orientation of the region identified as the Si phase was analyzed, and the orientation ratio of the <110> crystal orientation of the Si phase and the orientation ratio of the <110> crystal orientation were calculated. The partial ratio was used for the orientation ratio of the crystal orientation.

[0097] The orientation ratio of the <111> crystal orientation and the orientation ratio of the <110> crystal orientation of the Si phase were calculated as the average values ​​obtained for the three measurement regions by the above steps (1) to (3).

[0098] (Method for Measuring the Average Diameter of Al Phase) The average diameter of the Al phase in the L-section of the Al connecting material was measured using a method that combined information on the Al concentration and Si concentration obtained by SEM-EDS with information on the crystal orientation obtained by EBSD, similar to the measurement of the orientation ratio of the crystal orientation of the Al phase. Specifically, after performing the above procedures (1) and (2), the measurement was performed according to the following procedure (3). (3) For the region identified as Al phase, the crystal orientation was analyzed, and if the orientation difference between the 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 circle-equivalent diameters of each crystal grain were then averaged to calculate the average diameter of the Al phase. Here, for the average calculation, the average value obtained by the area average, which can be selected in the software provided with the device, was used. Furthermore, when calculating the average diameter of the Al phase in the L-section, only Al phases with a diameter (circle-equivalent diameter) of 0.5 μm or more were considered.

[0099] The average diameter of the Al phase was determined as the average value of the values ​​obtained for the three measurement regions according to the above procedures (1) to (3).

[0100] (Method for measuring the shape of the Si phase) The shape (shape ratio (e / f)) of the Si phase in the L cross section of the Al connecting material was measured using a method that combines information on the Al concentration and Si concentration obtained by SEM-EDS with information on the crystal orientation obtained by EBSD, similar to the measurement of the orientation ratio of the crystal orientation of the Al phase. In detail, after performing the above procedures (1) and (2), the measurement was carried out according to the following procedure (3). (3) For the region identified as the Si phase, the crystal orientation was analyzed, and if the orientation difference between the measurement points was 15° or more, it was determined to be a grain boundary, and the shape ratio (e / f) of each crystal grain was obtained. Then, the shape ratio (e / f) of each crystal grain was averaged to calculate the average value of the shape ratio (e / f) of the Si phase. Here, the average value of the shape ratio (e / f) of the Si phase was calculated using the numerical value of the Grain Shape Aspect Ratio ("grain aspect ratio") of the analysis software. Regarding the calculation method of the grain shape aspect ratio, the software automatically calculates the ratio (e / f) of the short side length (e) (Grain Shape Minor Axis) of one crystal grain to the long side length (f) (Grain Shape Major Axis). Here, for the average calculation, the average value obtained by area averaging was used.

[0101] (Method for evaluating Al connecting material) The method for evaluating the Al connecting material will be described. The wire diameter of the Al connecting material (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 an alloy with a composition of Al-0.5% Cu, formed to a thickness of 4 μm. The substrate used was an Al alloy with a Ni film formed to a thickness of 5 μm. A commercially available wire bonder (manufactured by Ultrasonic Industries Co., Ltd.) was used to bond the Al connecting material, and wedge bonding was used for both the first bonding and the second bonding.

[0102] (Method for Evaluating Temperature Cycle Reliability) A commercially available thermal shock tester 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. The test began with the sample chamber in the high-temperature chamber, and the period from the chamber's movement to the low-temperature chamber and its return to the high-temperature chamber was defined as one cycle. The sample chamber remained in both the low-temperature and high-temperature chambers for 20 minutes. The samples used for the temperature cycle test had a structure in which a semiconductor chip was mounted on a substrate, and the electrodes on the semiconductor chip and the electrodes on the substrate were connected with an Al connecting material. After the start of the test, the samples were removed every 250 cycles and a shear test was performed on the first joint. The shear strength value of the first joint used to evaluate the temperature cycle reliability was the average shear strength of five randomly selected first joints. The number of cycles at which the shear strength dropped to 70% or less of the value before the temperature cycle test was taken as the bond life. A bond life of less than 500 cycles was judged to be problematic in practical use and rated as "0," a bond life of 500 to 750 cycles was judged to be acceptable in practical use and rated as "1," a bond life of 750 to 1000 cycles was judged to be excellent and rated as "2," and a bond life of 1000 cycles or more was judged to be particularly excellent and rated as "3." "0" is a failure, and "1," "2," and "3" are passes. The evaluation results are shown in the "Temperature Cycle Reliability" column in the table.

[0103] (Method for Evaluating Variation in Bond Strength in Temperature Cycle Test) In the above-described temperature cycle test, shear strength measurements were performed on 20 first bonded sections after 1,400 cycles. To evaluate the variation in bond strength in the temperature cycle test, the population standard deviation (σ) of shear strength was calculated. If σ was less than 30 gf, the variation in bond strength was judged to be particularly small and the stability was excellent, and the result was rated as "3." If σ was 30 gf or more but less than 50 gf, the variation in bond strength was judged to be small and the stability was excellent, and the result was rated as "2." If σ was 50 gf or more but less than 70 gf, the variation in bond strength was judged to be within the acceptable range and the stability was good, and the result was rated as "1." If σ was 70 gf or more, the variation in bond strength was judged to be large and problematic for practical use, and the result was rated as "0." In addition to the population standard deviation, if the average shear strength value decreased to 70% or less of the value before the temperature cycle test, the lifespan was judged to have been exceeded, and the result was rated as "0." "0" indicates failure, and "1," "2," and "3" indicate passing. The evaluation results are shown in the column "Temperature cycle reliability: Variation in bonding strength (1400 cycles)" in the table.

[0104] (Method for Evaluating First Bond Strength) The method for evaluating the first bond strength will be described. The first bond strength was evaluated by a shear strength test. First bond was performed at 10 locations under typical bonding conditions, and the shear strength of the first bonded portion was measured. 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 to which the Al connecting material was bonded using a jig. If the average shear strength of the 10 first bonded portions was 1400 gf or more, it was judged to be excellent and rated as "3." If it was 1200 gf or more but less than 1400 gf, it was judged to be practically acceptable and rated as "2." If it was 1000 gf or more but less than 1200 gf, it was judged to require improvement and rated as "1." If it was less than 1000 gf, it was judged to be practically problematic and rated as "0." The evaluation results are shown in the column "1st bonding strength" in the table.

[0105] (Method for Evaluating Holes in the First Joint) A method for evaluating defects in the first joint will now be described. After conducting the shear strength test for the first joint described above, the indentations on the fracture surface on the electrode side were observed using an optical microscope or SEM, and areas where a metal bond was not obtained within the fractured region were determined to be holes. Holes are areas where the electrodes are not bonded even when deformed, and can be distinguished from areas where the bond is metal bonded. The shear strength test was performed under the conditions described above, and the fracture surfaces of 10 first joints were observed. The ratio of the total length (K) of the holes in the bond width direction to the bond length (J) in the direction perpendicular to the central axis of the Al connecting material (the bond width direction) was calculated as the hole ratio (K / J) ( FIG. 3 ). The hole ratios were confirmed for the 10 fracture surfaces, and the maximum value was defined as the "hole defect rate." If the defect rate of hollows was less than 5%, it was judged to be good and rated as "3", if it was 5% or more but less than 15%, it was judged to be no problem in practical use and rated as "2", if it was 15% or more but less than 25%, it was judged to need improvement and rated as "1", and if it was over 25%, it was judged to be an obstacle to mass production and rated as "0". The evaluation results are shown in the column for "Hollows in 1st joint" in the table.

[0106] (Method for evaluating the bond strength stability of the second joint) A shear strength test was performed on 30 randomly selected second joints, and the bond strength was obtained and the population standard deviation (σ) was calculated. If σ was 70 gf or more, it was judged to be problematic in practice and rated as "0", if σ was 50 gf or more but less than 70 gf, it was judged to be good and rated as "1", if σ was 30 gf or more but less than 50 gf, it was judged to be excellent and rated as "2", and if σ was less than 30 gf, it was judged to be particularly excellent and rated as "3". "0" is a failure, and "1", "2", and "3" are pass. The evaluation results are shown in the "Bond strength stability of the second joint" column 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 6 mm to a wire diameter of 0.3 mm, and the number of wire breakages was confirmed. The wire drawing 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 connecting material 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 zero, it was judged to be good and rated "3." If it was one, it was judged that it could be addressed by improving the manufacturing conditions and rated "2." If it was two to four, it was judged that there was a decrease in productivity and rated "1." If it was five or more, it was judged that it was difficult to use in practice and rated "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 connecting material was evaluated, focusing on scratches and abrasions. The wire diameter of the Al connecting material was 0.3 mm. Three measurement areas were randomly selected at intervals of 1 m or more along the central axis of the Al connecting material, and three pieces of approximately 2 cm length were taken from each of the three areas, for a total of nine samples. The surface was observed at magnifications ranging from 50 to 500 times using an SEM. 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 a score of "3" was given for a good pass; a score of "2" was given for two or fewer areas for practical use; a score of "1" was given for three to seven areas for poor surface quality; and a score of "0" was given for eight or more areas for practical use. The evaluation results are shown in the "Surface Quality" column in the table.

[0109] The evaluation results of the Examples and Comparative Examples are shown in Tables 1 to 3.

[0110]

[0111]

[0112]

[0113] All of the Al connecting materials of Examples 1 to 58 contain 3.0 mass% or more and 12.0 mass% or less of Si, and the total ratio of the <111> + <110> Al phase in the L cross section is 20% or more and 70% or less (however, when the total of the orientation ratios is 25% or less, the orientation ratio of the <110> crystal orientation with an angular difference of 15° or less with respect to the central axis direction is 5% or more), and the total ratio of the <111> + <110> Si phase in the L cross section is 20% or more and 70% or less, and it was confirmed that they exhibit excellent temperature cycle reliability and good 1st joint strength. In addition, Example No. 1, in which the <110> ratio of the Al phase in the L cross section is 5% or more and 40% or less, It was confirmed that the Al connecting materials of Example Nos. 1 to 4, 6 to 13, 15, 16, 18 to 23, 25 to 32, 34 to 39, 41 to 49, 51, 52, and 54 to 58 exhibited better results in terms of first joint strength and could also suppress hollowing of the first joint. It was also confirmed that the Al connecting materials of Example Nos. 1, 3 to 23, 25 to 27, 29 to 47, 49, 50, and 52 to 58, in which the average diameter of the Al phase in the L cross section is 5 μm or more and 40 μm or less, tend to result in better results in terms of joint strength stability of the second joint. Example Nos. 1 to 4, 6 to 13, 15, 16, 18 to 23, 25 to 32, 34 to 39, 41 to 49, 51, 52, and 54 to 58, in which the average shape ratio (e / f) of the Si phase in the L cross section is 0.2 or more and 0.7 or less, tend to result in better results in terms of joint strength stability of the second joint. It was confirmed that the Al connecting materials of Examples 1, 2, 4 to 9, 11 to 21, 23 to 28, 30 to 35, and 37 to 58 tended to reduce the variation in bonding strength in a temperature cycle test. Furthermore, it was confirmed that the Al connecting materials of Examples 32 to 43 and 53 to 58, which contained a total of 10 to 800 ppm by mass of one or more elements from the first element group (Sr, Ca, Eu, Sb), could reduce the frequency of wire breakage during processing. It was confirmed that the Al connecting materials of Examples 45 to 50 and 52 to 58, which contained a total of 10 to 500 ppm by mass of one or more elements from the second element group (Ni, Mg, Fe, In), suppressed the occurrence of surface scratches and chipping and had a smooth surface.On the other hand, in the Al connecting materials of Comparative Examples 1 to 10, any of the Si concentration, the <111> + <110> total ratio of the Al phase in the L cross section (the <110> ratio of the Al phase when the total ratio is 20% or more and 25% or less), and the <111> + <110> total ratio of the Si phase in the L cross section (including the <110> ratio of the Al phase when the total ratio is 25% or less) was outside the range of the present invention, and it was confirmed that either the temperature cycle reliability or the 1st bonding strength was not sufficiently obtained.

Claims

1. An Al connecting material containing 3.0% by mass or more and 12.0% by mass or less of Si, wherein, when the crystal orientation of the Al phase in the L-section of the Al connecting material (a cross section in the central axis direction including the central axis) is measured, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction, is 20% or more and 70% or less, and when the total orientation ratio is 25% or less, the orientation ratio of the <110> crystal orientation, which has an angular difference of 15° or less with respect to the central axis direction, is 5% or more, and when the crystal orientation of the Si phase in the L-section of the Al connecting material is measured, the total orientation ratio of the <111> crystal orientation and the <110> crystal orientation, which have an angular difference of 15° or less with respect to the central axis direction, is 20% or more and 70% or less.

2. An Al connecting material as described in claim 1, in which the ratio of the <110> crystal orientation, which has an angular difference of 15° or less with respect to the central axis direction, in the crystal orientation of the Al phase in the L cross section is 5% or more and 40% or less.

3. An Al connecting material as described in claim 1 or 2, in which the average diameter of the Al phase in the L cross section is 5 μm or more and 40 μm or less.

4. An Al connecting material according to any one of claims 1 to 3, in which the average ratio (e / f) of the short side length e to the long side length f of the Si phase in the L cross section is 0.2 or more and 0.7 or less.

5. An Al connecting material according to any one of claims 1 to 4, further containing at least one of Sr, Ca, Eu and Sb in a total amount of 10 ppm by mass or more and 800 ppm by mass or less.

6. An Al connecting material according to any one of claims 1 to 5, further containing at least one of Ni, Mg, Fe and In in a total amount of 10 ppm by mass or more and 500 ppm by mass or less.

7. An Al connecting material according to any one of claims 1 to 6, in which the total concentration of other elements in the Al connecting material is 0.5 mass% or less.

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