Al connecting material

Abstract

Provided is an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength. The Al connecting material contains 3.0 mass% to 12.0 mass% (inclusive) of Si, and contains 5 mass ppm to 800 mass ppm (inclusive) of at least one of Sr, Eu and Na in total, and the average value of 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 (cross-section in the central axis direction including the central axis) of the Al connecting material is 0.25 to 0.65 (inclusive).

Description

Technical Field

[0001] The present invention relates to an Al connection material. Background Art

[0002] In a semiconductor device, electrodes formed on a semiconductor chip and electrodes on a lead frame or a substrate are connected by a bonding wire (wire material) or a bonding tape (strip material). In a power semiconductor device, a bonding wire or a bonding tape mainly made of aluminum (Al) is used. The wire diameter of the Al bonding wire is mainly in the range of 100 μm to 600 μm, and the width of the Al bonding tape is mainly in the range of 100 μm to 3000 μm, and the thickness is in the range of 50 μm to 600 μm. Herein, the Al bonding wire or the Al bonding tape is collectively referred to as an Al connection material.

[0003] In a power semiconductor device, silicon (Si) is mostly used as a material of the semiconductor chip, and an Al—Si alloy or an Al—Cu alloy is mostly used as a material of the electrodes formed on the semiconductor chip. In addition, a power semiconductor device using an Al connection material is mostly used for high-power equipment such as an air conditioner or a solar power generation system, or a semiconductor device for a vehicle.

[0004] Regarding a bonding method of the Al connection material, both a first bonding with an electrode on a semiconductor chip and a second bonding with an electrode on a lead frame or a substrate are performed by wedge bonding. The so-called wedge bonding is a method of solid-phase diffusion bonding in which ultrasonic vibration and load are applied to the Al connection material via a metal fixture (implement) to break the surface oxide film of the Al connection material and the electrode material to expose a newly generated surface. This connection method is characterized by connecting in a solid state without melting the connection material, and is a bonding technique different from a welding technique for melting a connection material.

[0005] Compared with a general power semiconductor device, a next-generation power semiconductor device is required to operate stably for a long time. The power semiconductor device repeats the on and off of current and operates. When current is supplied to a Si-based semiconductor chip through the Al connection material, the temperature of the first bonding portion rises. On the other hand, when the supply of current is stopped, the temperature of the first bonding portion decreases. In this way, when the power semiconductor operates, the temperature of the first bonding portion repeatedly rises and falls. Thus, in the first bonding portion, a thermal stress caused by the thermal expansion difference between the Al connection material and the semiconductor chip is repeatedly applied. In the case of using a connection material composed of only high-purity Al, the thermal stress causes the Al connection material to break in a relatively short time, and it is difficult to satisfy the performance required for the next-generation power semiconductor device. Therefore, in the next-generation power semiconductor, it is required to improve the life of the bonding portion (hereinafter, referred to as "temperature cycle reliability") accompanying the temperature rise and fall of the first bonding portion.

[0006] Regarding the requirements for temperature cycle reliability, an Al bonding material mainly aimed at improving mechanical strength has been proposed. As a method for improving the mechanical properties of the Al bonding material, 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 that contains 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. In this patent document, the effect of high-strength improvement based on solid solution strengthening of Mg or Si or the effect of suppressing cracks based on precipitated magnesium silicide (Mg2Si) is disclosed, and the reduction in the bonding strength of the first joint portion in a cold temperature cycle test in the temperature range of 70°C to 120°C is delayed.

[0008] Patent Document 2 discloses a bonding wire characterized by containing 0.01 to 0.2 mass% of iron (Fe), containing 1 to 20 mass ppm of silicon (Si), and the remaining part being composed of an alloy of Al with a purity of 99.997 mass% or more, with a solid solution amount of Fe being 0.01 to 0.06%, a precipitation amount of Fe being 7 times or less the solid solution amount of Fe, and a fine structure with an average crystal grain size of 6 to 12 μm. In this patent document, it is disclosed that the intermetallic compound particles of Fe and Al are uniformly dispersed in Al to improve the mechanical strength of the matrix, and further the recrystallized grains are refined, thereby suppressing the reduction in the bonding strength of the first joint portion in a thermal shock test in the temperature range of -50°C to 200°C.

[0009] Patent Document 3 discloses a bonding wire formed by melting an Al-Si alloy containing 0.1 to 5 mass% of silicon (Si) and the remaining part being composed of Al and impurities, and ejecting and rapidly cooling it to form a thin wire. In this patent document, it is disclosed that the molten Al-Si alloy is rapidly cooled to make Si finely and uniformly dispersed, thereby improving the mechanical strength.

[0010] Prior art documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Laid-Open No. 2014-131010

[0013] Patent Document 2: Japanese Patent Laid-Open No. 2014-129578

[0014] Patent Document 3: Japanese Patent Laid-Open No. 59-57440 Summary of the invention

[0015] Technical problem to be solved by the invention

[0016] As described above, compared with general power semiconductor devices, the next-generation power semiconductor devices are required to be able to withstand longer-term use. When the power semiconductor device operates, the temperature of the first joint repeatedly rises and falls. As a result, since the Al bonding material has a larger coefficient of linear expansion than the semiconductor chip, thermal stress caused by the difference in the coefficients of linear expansion of the two is generated at the first joint, and there is a case where the Al bonding material is eventually fatigued and damaged. As one of the tests for accelerating the evaluation of the life (temperature cycle reliability) of the joint accompanying the temperature rise and fall of the first joint, there is a temperature cycle test. The Al bonding material used in the next-generation power semiconductors is required to exhibit excellent temperature cycle reliability in the temperature cycle test. However, in the case of using an Al bonding material strengthened by adding Si or the like as disclosed in Patent Documents 1 to 3, in the temperature cycle test assumed for use in the next-generation power semiconductor device, the following technical problems have been confirmed: Cracks develop relatively rapidly in the Al alloy electrode having a lower strength than the Al bonding material, and it is difficult to stably obtain good temperature cycle reliability.

[0017] In the conventional temperature cycle test (hereinafter referred to as "TCT"), a commercially available test device is used, and the test can be easily performed. However, since the temperature change rate in TCT is relatively slow, there is a concern that there will be a deviation from the relatively fast temperature change rate during the operation of the power semiconductor device. Therefore, recently, in order to approach the actual use conditions, a high-speed temperature cycle test (hereinafter also referred to as "high-speed TCT") with an accelerated temperature change rate has been studied. Different from the conventional TCT in which the temperature change rate is about 10°C / min, for example, in high-speed TCT, the temperature changes at a high speed of about 200°C / min, for example. Regarding the reliability evaluation of the joint of the Al bonding material, even for an Al bonding material whose reliability does not decrease in the conventional TCT evaluation, when evaluated by high-speed TCT, there are cases where the joint strength is low and the joint life is reduced. Therefore, an Al bonding material is required that exhibits good joint reliability and excellent temperature cycle reliability even in a more severe test approaching the actual use conditions, i.e., high-speed TCT. Hereinafter, the temperature cycle reliability in high-speed TCT is sometimes referred to as "high-speed temperature cycle reliability".

[0018] In addition, during bonding, if bonding defects such as peeling of the Al bonding material from the electrode occur, it may lead to defective product conditions or a decrease in manufacturing yield. Therefore, good bonding strength is required at each bonding part. In this regard, when ultrasonic vibration or load is strongly applied to obtain good bonding strength at the first bonding part, the semiconductor chip may be damaged. Especially in the case of using an Al bonding material strengthened by adding Si or the like, its hardness makes it easy to damage the semiconductor chip during the first bonding. When the ultrasonic vibration or load is adjusted to reduce such damage, its high deformation resistance or instability in the deformation direction may result in an inability to stably ensure the bonding area, etc., and sometimes sufficient bonding strength of the first bonding part (hereinafter sometimes simply referred to as "first bonding strength") cannot be obtained. These problems during the initial bonding of the first bonding part further cause a decrease in temperature cycle reliability or instability, thus becoming an obstacle to the application of Al bonding materials strengthened by adding Si or the like.

[0019] An object of the present invention is to provide an Al bonding material that satisfies excellent temperature cycle reliability and good first bonding strength.

[0020] Technical means for solving technical problems

[0021] The inventors of the present invention conducted in-depth research on the above technical problems and finally found that: in an Al bonding material containing 3.0 mass% or more and 12.0 mass% or less of Si, and containing one or more of Sr, Eu, and Na in a total amount of 5 mass ppm or more and 800 mass ppm or less, an Al bonding material in which the average value of 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 (the cross-section in the central axis direction including the central axis) of the Al bonding material is within a specific range can solve the above technical problems. Based on this understanding, further repeated research was carried out to complete the present invention.

[0022] That is, the present invention includes the following content.

[0023] <1>

[0024] An Al bonding material, which is an Al bonding material containing 3.0 mass% or more and 12.0 mass% or less of Si, and containing one or more of Sr, Eu, and Na in a total amount of 5 mass ppm or more and 800 mass ppm or less,

[0025] The average value of 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 (the cross-section in the central axis direction including the central axis) of the Al bonding material is 0.25 or more and 0.65 or less.

[0026] <2>

[0027] The Al bonding material according to <1>,

[0028] The average value of the ratio (c / d) of the short side length c to the long side length d of the Al phase in the L cross-section is 0.25 or more and 0.7 or less.

[0029] <3>

[0030] The Al connecting material according to <1> or <2>,

[0031] The average diameter of the Al phase in the L cross-section is 5 μm or more and 40 μm or less.

[0032] <4>

[0033] The Al connecting material according to any one of <1> to <3>,

[0034] It further contains one or more of Fe, Mg, Mn, Ga, and Ge in a total amount of 5 mass ppm or more and 700 mass ppm or less.

[0035] Advantages of the Invention

[0036] According to the present invention, an Al connecting material that satisfies excellent temperature cycle reliability and good first bonding strength can be provided. Description of the Drawings

[0037] Figure 1 It is a schematic diagram for explaining the measurement object surface (inspection surface) when measuring the shape (shape ratio (e / f), shape ratio (c / d)), and average diameter of the Si phase and Al phase for the Al connecting material. The measurement object surface is a cross-section (L cross-section) in the central axis direction of the Al connecting material including the central axis.

[0038] Figure 2 It 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.

[0039] Figure 3 It is a schematic diagram for explaining the short side length (c) and long side length (d) of the Al phase in the L cross-section. Detailed Description of the Invention

[0040] Hereinafter, the present invention will be described in detail in conjunction with its preferred embodiments. In the description, the drawings may be referred to at times, but each drawing only schematically shows the shape, size, and configuration of the constituent elements to the extent that the invention can be understood. The present invention is not limited to the following embodiments and illustrative examples, and can be arbitrarily changed and implemented without departing from the scope of protection of the present invention and its equivalent scope.

[0041] [Al Connecting Material]

[0042] The Al bonding material of the present invention is an Al bonding material containing 3.0% by mass or more and 12.0% by mass or less of Si, and containing any one or more of Sr, Eu, and Na in a total amount of 5 mass ppm or more and 800 mass ppm or less (hereinafter also referred to as "the first element group"), and is characterized in that

[0043] In the L cross-section (the cross-section in the central axis direction including the central axis) of the Al bonding material, the average value of the ratio (e / f) of the short side length e to the long side length f of the Si phase is 0.25 or more and 0.65 or less.

[0044] As described above, in the temperature cycle test (TCT), when using a bonding material composed only of high-purity Al, cracks develop at a relatively fast rate inside the bonding material, and it is difficult to obtain good temperature cycle reliability. On the other hand, it has also been confirmed that: when using an Al bonding material strengthened by adding Si or the like, since cracks occur in the Al alloy electrode with relatively low strength, it is difficult to obtain the temperature cycle reliability required for next-generation power semiconductor devices. That is, it has been confirmed that: in a high-speed temperature cycle test (high-speed TCT) with an accelerated temperature change rate close to actual use conditions, even for an Al bonding material whose reliability does not decrease during evaluation in a conventional TCT, there are cases where the bonding strength decreases and the bonding life shortens. And when using an Al bonding material strengthened by adding Si or the like, it is easy to damage the semiconductor chip during the first bonding. When adjusting the ultrasonic vibration or load to reduce this damage, there are cases where sufficient first bonding strength cannot be obtained.

[0045] The inventors of the present invention have conducted in-depth research to solve the above technical problems and finally found that: an Al bonding material containing 3.0% by mass or more and 12.0% by mass or less of Si, and containing any one or more of the first element group in a total amount of 5 mass ppm or more and 800 mass ppm or less, and having an average value of 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 of 0.25 or more and 0.65 or less can improve the temperature cycle reliability and also improve the first bonding strength. The Al bonding material of the present invention significantly contributes to achieving the temperature cycle reliability required in next-generation power semiconductor devices and achieving good first bonding strength.

[0046] The Al bonding material of the present invention contains 3.0 mass% or more and 12.0 mass% or less of Si, and is composed of an Al phase in which Si is dissolved in Al and an Si phase formed by crystallization or precipitation of Si. Here, in the Al phase, other additive elements may also be dissolved in addition to Si. In addition, the Si phase is a general term for Si crystallized products and Si precipitated products. The so-called Si crystallized products are formed from the solution during solidification and are as large as about 1 to 20 μm in size. In contrast, the so-called Si precipitated products are formed from the solid state and are as small as about 0.1 to several μm in size.

[0047] In addition, in the present invention, the L cross-section of the Al bonding material, that is, the cross-section in the central axis direction of the Al bonding material including the central axis, is as described in the reference in the column of “(Method for measuring the shapes of the Si phase and the Al phase)” described later. Figure 1 as described.

[0048] Regarding the reasons why the Al bonding material of the present invention can bring excellent temperature cycle reliability and good first bonding strength, it is inferred as follows.

[0049] Regarding the temperature cycle reliability, for the Al bonding material containing Si at a high concentration, the Si phase crystallized during solidification has a smaller coefficient of thermal expansion than the Al wire, which helps to reduce the difference in the coefficient of linear expansion between the Al bonding material and the semiconductor chip, and further can reduce the generated thermal stress. Therefore, the bonding reliability in the normal TCT can be improved. However, in the high-speed TCT with a fast temperature change rate, intense thermal fatigue occurs, and it is sometimes difficult to meet the strict reliability requirements only by adding Si. Specifically, in the Al bonding material containing Si at a high concentration, the Si phase coarsens into plate-like or columnar shapes, and its distribution tends to be locally present. However, when regions with a large amount of Si and regions with a shortage of Si coexist, strain concentration under high-speed TCT is likely to occur, resulting in a reduction in the bonding life. In response to this, it is considered that by adding the first element group in a specified amount, the Si phase in the Al bonding material is refined, and the effect of making it distribute substantially uniformly throughout the Al bonding material is obtained. It is inferred that the uniform distribution of the Si phase will relieve the stress concentration under high-speed TCT and improve the life.

[0050] In addition, regarding the first bonding strength, as described above, it is considered that by adding the first element group in a specified amount, the Si phase in the Al bonding material is refined, and the effect of making it distribute substantially uniformly throughout the Al bonding material is obtained. Through the uniform distribution of the Si phase, when ultrasonic vibration and load are applied, the deformation of the Al bonding material in the direction perpendicular to the ultrasonic vibration can be stabilized. And it is considered that by controlling the shape (ratio (e / f)) of the Si phase, the close contact in the central axis direction of the interface between the Si phase and the Al phase can be improved, the interface sliding when ultrasonic vibration and load are applied can be controlled, and the effect of improving the bonding strength can be obtained.

[0051] It is inferred that by simultaneously achieving uniform distribution of the Si phase and controlling the shape of the Si phase brought about by the first element group, it is possible to simultaneously promote plastic deformation in the direction perpendicular to and parallel to the central axis of the Al bonding material, improve the bonding strength, and improve the bonding reliability in high-speed TCT due to the dispersion of thermal fatigue at the joint.

[0052] - Si Concentration -

[0053] The Si concentration is in the range of 3.0 mass% or more and 12.0 mass% or less, which helps to reduce the thermal stress at the joint and improve the temperature cycle characteristics. If it is less than 3.0 mass%, the improvement effect is negligible. If it is higher than 12.0 mass%, problems such as a decrease in the initial bonding strength due to hardening and damage to the semiconductor chip will occur. From the viewpoint of obtaining good temperature cycle reliability even in high-speed TCT with an accelerated temperature change rate close to actual use conditions, the concentration of Si in the Al bonding material of the present invention is 3.0 mass% or more, preferably 3.5 mass% or more, more preferably 3.6 mass% or more, 3.8 mass% or more, 4.0 mass% or more, 4.2 mass% or more, 4.4 mass% or more, 4.5 mass% or more, 4.6 mass% or more, 4.8 mass% or more, or 5.0 mass% or more. On the other hand, when the hardness of the Al bonding material is too high, damage to the semiconductor chip is likely to occur during the first bonding under the bonding conditions of ultrasonic vibration and load commonly used. From the viewpoint of obtaining good bonding strength during the first bonding under normal bonding conditions, the Si concentration in the Al bonding material of the present invention is 12.0 mass% or less, preferably 11.5 mass% or less or 11.0 mass% or less, 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.

[0054] For the concentration analysis of the elements contained in the Al bonding material of the present invention, for example, an ICP (Inductively Coupled Plasma) emission spectroscopic analysis device or an ICP mass analysis device can be used. When elements such as oxygen or carbon from atmospheric contaminants are adsorbed on the surface of the Al bonding material, it is effective to perform cleaning with an acid or a base according to the adsorbed substance before analysis.

[0055] - Concentration of the First Element Group -

[0056] From the viewpoint of achieving good temperature cycle reliability and good first bonding strength even in high-speed TCT, the total concentration of the first element group in the Al bonding material of the present invention is 5 mass ppm or more, preferably 10 mass ppm or more, more preferably 20 mass ppm or more, 30 mass ppm or more, 40 mass ppm or more, or 50 mass ppm or more, still more preferably 60 mass ppm or more, 80 mass ppm or more, or 100 mass ppm or more, and the upper limit is 800 mass ppm or less, preferably 750 mass ppm or less, or 700 mass ppm or less, more preferably 650 mass ppm or less, or 600 mass ppm or less, still more preferably 580 mass ppm or less, 560 mass ppm or less, or 550 mass ppm or less. When the total concentration of the first element group is within the above preferred range, it is also beneficial from the viewpoints of suppressing damage to the semiconductor chip and easily achieving good first bonding strength.

[0057] - Shape of Si phase in L cross-section -

[0058] It has been found that: in an Al bonding material containing Si and the first element group at a specified concentration, when the average value of the ratio (e / f) of the short side length e to the long side length f of the Si phase in its L cross-section is in the range of 0.25 or more and 0.65 or less, good temperature cycle reliability and good first bonding strength can be obtained even in high-speed TCT.

[0059] The value of this ratio (e / f) is an index indicating flatness. Refer to Figure 2 for further explanation. Figure 2 is a diagram schematically showing the Si phase in the L cross-section of the Al bonding material, showing that the central axis direction of the Al bonding material corresponds to Figure 2 the horizontal direction (left - right direction), and the direction perpendicular to the central axis corresponds to Figure 2 the vertical direction (up - down direction). Regarding the Si phase in the L cross-section, the above "short side length e" corresponds to Figure 2 the dimension shown by reference numeral e in Figure 2 . In addition, regarding the Si phase in the L cross-section, the above "long side length f" corresponds to

[0060] It should be noted that, regarding obtaining good temperature cycle reliability and good first bonding strength in high-speed TCT, 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 for the shape ratio (e / f) of all Si phases to be in the range of 0.25 or more and 0.65 or less. For example, Si phases with a shape ratio (e / f) less than 0.25 may be included, and Si phases with a shape ratio (e / f) higher than 0.65 may also be included.

[0061] From the viewpoint of obtaining better temperature cycle reliability and better first bonding strength in high-speed TCT, the average value of the shape ratio (e / f) of the Si phase in the L cross-section of the Al bonding material of the present invention is more preferably 0.3 or more, even more preferably 0.32 or more, 0.34 or more, or 0.35 or more, and its upper limit is more preferably 0.6 or less, even more preferably 0.58 or less, 0.56 or less, or 0.55 or less.

[0062] In the measurement of the average value of the shape ratio (e / f) of the Si phase in the L cross-section of the Al bonding material, a method combining the information on the Al concentration and Si concentration obtained by SEM-EDS and the information on the crystal orientation obtained by EBSD can be adopted. Specifically, in the measurement area where the L cross-section of the Al bonding material is used as the inspection surface, the concentration measurement of Al and Si using EDS and the crystal orientation analysis using EBSD are carried out simultaneously. Then, using the analysis software attached to the device, the Al phase and Si phase are separated and extracted from the measurement results of EDS. Specifically, it is preferable to use the chemical-assisted scanning (ChiScan) function of the functions of the analysis software OIM DataCollection or OIM Anaysis (both manufactured by TSLSolution) attached to the FE-SEM device. And for the area determined to be the Si phase, the crystal orientation can be analyzed by using the analysis software attached to the device. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary, and the ratio (e / f) is calculated. The average value of the shape ratio (e / f) of each Si phase is defined as the average value of the shape ratio (e / f) of the Si phase. In the process of obtaining the shape ratio (e / f) of the Si phase, the parts where the crystal orientation cannot be measured or the parts where the reliability of the orientation analysis is low although it can be measured are excluded from the calculation. Therefore, in one embodiment, the average value of the shape ratio (e / f) of the Si phase in the L cross-section of the Al bonding material of the present invention is calculated through the following steps (1) to (3).

[0063] (1) Using the L cross-section of the Al bonding material as the inspection surface, simultaneously perform the concentration measurement of Al and Si using EDS and the crystal orientation measurement using EBSD.

[0064] (2) Use the Chi scan function to separate and extract Al and Si. Specifically, according to the measurement results of the EDS of Si, set the tolerance equivalent to the threshold value of Si, so that Al and Si can be separated and identified. Using the crystal information of Al and Si from the material file, the crystal orientation can be analyzed.

[0065] (3) Regarding the region determined to be the Si phase, analyze the crystal orientation. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary, and the shape ratio (e / f) of each grain is obtained. The average value of the shape ratios (e / f) of each grain is calculated, and the average value of the shape ratio (e / f) of the Si phase is calculated. Here, the average value of the shape ratio (e / f) of the Si phase adopts the value of the Grain Shape Aspect Ratio of the analysis software (hereinafter referred to as "Grain Shape Aspect Ratio"). This value is obtained by averaging the Grain Shape Aspect Ratios of each grain. In addition, regarding the calculation method of the Grain Shape Aspect Ratio, 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 a grain is obtained. In addition, for the average calculation, the area average that can be selected by the software attached to the device is adopted. By adopting the average value obtained by the area average, 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, which is preferable for obtaining good temperature cycle reliability and good first bonding strength in high-speed TCT, are satisfied. In the calculation of the area average, it is calculated based on the average value obtained by multiplying the proportion of the area of each particle in the area of all particles by the area value of each particle, and is automatically calculated by the software.

[0066] In the step (2) above, the setting of the tolerance (%) can be selected in the range of 20 - 40%, and in the standard analysis of the L section of the Al connection material, it is preferably compared at about 30%. Supplementary description is made for this step of adjusting the tolerance. It is preferably selected or confirmed the tolerance value in such a way that it is equivalent to the shape and size of the Si phase identified from the EDS map of the Si element concentration displayed two-dimensionally in the Chi scan function.

[0067] In the present invention, the average value of the shape ratio (e / f) of the Si phase is set to the average value of each value obtained by measuring at three or more locations. When selecting the measurement region, from the viewpoint of ensuring the objectivity of the measurement data, it is preferable to obtain a measurement sample from the Al connection material to be measured at intervals of 50 cm or more in the central axis direction of the Al connection material for measurement. Further, in the present invention, the length of the Al connection material in the central axis direction of the measurement region of the crystal orientation based on the EBSD method is 300 μm or more and less than 800 μm, and it is expected that the entire Al connection material enters in the direction perpendicular to the central axis of the Al connection material. However, in the case where the size is large and it is difficult to measure the whole, it can be adjusted within a range of less than 600 μm.

[0068] - Shape of Al phase in L-section -

[0069] In the Al connection material of the present invention, it is preferable that the average value of the ratio (c / d) of the short side length c to the long side length d of the Al phase in its L-section is in the range of 0.25 or more and 0.7 or less.

[0070] Regarding the Al connection material containing a high concentration of Si, wire breakage sometimes occurs during the wire drawing process of the Al connection material, resulting in a decrease in the manufacturing yield. As the cause of the wire breakage, it is considered that the traction force during the wire drawing process increases, causing the fracture of the Al phase, uneven work hardening, the progress of local deformation of the Al phase, and shrinkage and fracture.

[0071] In the process of studying the Al connection material, the inventors of the present invention found that the shape of the Al phase in the L-section affects the occurrence frequency of wire breakage during processing. Among them, for any Al connection material containing 3.0 mass% or more and 12.0 mass% or less of Si and containing any one or more of the first element groups with a total of 5 mass ppm or more and 800 mass ppm or less, the average value of the shape ratio (e / f) of the Si phase in its L-section is 0.25 or more and 0.65 or less. Specifically, it was found that: by setting the average value of the ratio (c / d) of the short side length c to the long side length d of the Al phase in the L-section to be in the range of 0.25 or more and 0.7 or less, the occurrence frequency of wire breakage during processing is reduced.

[0072] The value of this ratio (c / d) is an index indicating flatness. Refer to Figure 3 For further explanation. Figure 3 It is a diagram schematically showing the Al phase in the L-section of the Al connection material, showing that the central axis direction of the Al connection material corresponds to Figure 3 the horizontal direction (left - right direction), and the direction perpendicular to the central axis corresponds to Figure 3 the vertical direction (up - down direction). Regarding the Al phase in the L-section, the above "short side length c" corresponds to Figure 3The size indicated by the reference symbol c in the figure. In addition, regarding the Al phase in the L cross section, the above-mentioned "long side length d" is equivalent to Figure 3 The dimension shown by the reference symbol d in the figure. Hereinafter, the ratio (c / d) of the short side length c to the long side length d of the Al phase in the L cross section is referred to as the "shape ratio (c / d) of the Al phase". The value of the shape ratio (c / d) of the Al phase can be obtained by the analysis software attached to the device using the grain shape aspect ratio (Grain Shape Aspect Ratio).

[0073] In the Al connecting material of the present invention, the reason why the frequency of wire breakage during processing can be reduced by controlling the average value of the shape ratio (c / d) of the Al phase is inferred as follows. It is believed that when the average value of the shape ratio (c / d) of the Al phase in the L section is controlled within the above range, the pressure and tension applied to the Al connecting material during processing play a role in making the deformation of the grains uniform. Since the Si phase is hard and hardly contributes to plastic deformation, it is believed that the shape of the Al phase is effective in improving the wire breakage defect.

[0074] It should be noted that, in order to reduce the frequency of wire breakage during processing, the average value of the shape ratio (c / d) of the Al phase in the L cross section is sufficient to be in the above preferred range, and it is not necessary to make the shape ratio (c / d) of all Al phases in the range of 0.25 to 0.7. For example, an Al phase having a shape ratio (c / d) of less than 0.25 may be included, and an Al phase having a shape ratio (c / d) of more than 0.7 may be included.

[0075] From the viewpoint of further reducing the frequency of wire breakage during processing, the average value of the shape ratio (c / d) of the Al phase in the L cross-section of the Al connecting material of the present invention is preferably greater than 0.3, more preferably greater than 0.32, greater than 0.34 or greater than 0.35, and the upper limit is more preferably less than 0.65, more preferably less than 0.64, less than 0.62 or less than 0.6.

[0076] In the determination of the average value of the shape ratio (c / d) of the Al phase in the L cross section of the Al connecting material, similarly to the determination of the average value of the shape ratio (e / f) of the Si phase, a method of combining the information of the Al concentration and Si concentration obtained by SEM-EDS with the information of the crystal orientation obtained by EBSD can be adopted. Therefore, in one embodiment, the average value of the shape ratio (c / d) of the Al phase in the L cross section of the Al connecting material of the present invention is calculated by the following steps (1) to (3).

[0077] (1) Using the L-section of the Al connecting material as the inspection surface, the concentrations of Al and Si were measured using EDS and the crystal orientation was measured using EBSD at the same time.

[0078] (2) Use the Chi scanning function to separate and extract Al and Si. Specifically, according to the measurement results of the EDS of Si, set the tolerance equivalent to the threshold value of Si, so that Al and Si can be separated and identified. Using the crystal information of Al and Si from the material file, the crystal orientation can be analyzed.

[0079] (3) For the region determined to be the Al phase, analyze the crystal orientation. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary. Obtain the shape ratio (c / d) of each grain, and calculate the average value of the shape ratios (c / d) of each grain to calculate the average value of the shape ratio (c / d) of the Al phase. Here, regarding the average value of the shape ratio (c / d) of the Al phase, similar to the case of calculating the average value of the shape ratio (e / f) of the Si phase, use the value of Grain Shape AspectRatio (grain shape aspect ratio) of the analysis software. In addition, for the average calculation, similar to the case of calculating the average value of the shape ratio (e / f) of the Si phase, adopt the average value obtained by area averaging that can be selected by the software attached to the device. By adopting the average value obtained by area averaging, it is possible to accurately measure and determine whether the conditions related to the average value of the shape ratio (c / d) of the Al phase, which is preferably obtained to achieve good temperature cycle reliability and good first bonding strength even in high-speed TCT, are satisfied.

[0080] When measuring the average value of the shape ratio (c / d) of the Al phase in the L cross-section, the setting range of the tolerance in the above step (2), the method for obtaining the measurement sample, or the measurement region of the crystal orientation based on the EBSD method is the same as that described above for the measurement of the average value of the shape ratio (e / f) of the Si phase.

[0081] -Average diameter of the Al phase in the L cross-section-

[0082] The Al bonding material of the present invention preferably has an average diameter of the Al phase in its L cross-section of 5 μm or more and 40 μm or less.

[0083] In many cases, the second object to be joined uses a harder material than Al, such as a Cu substrate, and the conditions of ultrasonic vibration or load during the second joining are set higher than those during the first joining, which will have an impact. During the second joining of the Al joining material strengthened by adding Si or the like, the deformation is likely to become unstable. In this regard, the inventors of the present invention have found that by setting the average diameter of the Al phase in the L cross-section to be in the range of 5 μm or more and 40 μm or less, the deviation of the joining strength during the second joining can be reduced. The reason is considered to be that the following effects act synergistically: the effect of promoting the deformation of the Al joining material by ultrasonic vibration by containing Si and the first element group at a specified concentration and controlling the average value of the shape ratio (e / f) of the Si phase within a specified range; and the effect of making the deformation of the Al joining material uniform in both directions parallel and perpendicular to the central axis of the Al joining material by setting the average diameter of the Al phase to be 5 μm or more and 40 μm or less.

[0084] From the viewpoint of further reducing the deviation of the joining strength during the second joining and achieving better stability of the joining strength, the average diameter of the Al phase in the L cross-section of the Al joining material of the present invention is more preferably 10 μm or more, and even more preferably 12 μm or more, 14 μm or more, or 15 μm or more. In addition, the upper limit of the average diameter of the Al phase in the L cross-section is more preferably 35 μm or less, and even more preferably 30 μm or less, and further preferably 28 μm or less, 26 μm or less, or 25 μm or less.

[0085] A method for measuring the average diameter of the Al phase in the L cross-section of the Al joining material will be described. For the measurement of the average diameter of the Al phase in the L cross-section, similar to the measurement of the average value of the shape ratio (e / f) of the Si phase or the average value of the shape ratio (c / d) of the Al phase described above, a method of combining the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD can be adopted. The detailed steps can be the same as those described above for the measurement of the average value of the shape ratio (c / d) of the Al phase associated with. That is, for the region determined to be the Al phase, the crystal orientation can be analyzed by using the analysis software attached to the device. If the orientation difference between the measurement points is 15° or more, it is determined as a crystal grain boundary, and the equivalent circle diameter is calculated. The average value of the equivalent circle diameters of each Al phase is defined as the average diameter of the Al phase. In the process of obtaining the average diameter of the Al phase, the parts where the crystal orientation cannot be measured or the parts where the reliability of the orientation analysis is low although it can be measured are excluded from the calculation. Therefore, in one embodiment, the average diameter of the Al phase in the L cross-section of the Al joining material of the present invention is calculated by the following steps (1) to (3).

[0086] (1) Take the L cross-section of the Al bonding material as the inspection surface, and simultaneously measure the concentrations of Al and Si using EDS and measure the crystal orientation using EBSD.

[0087] (2) Use the Chi scan function to separate and extract Al and Si. Specifically, according to the measurement results of EDS of Si, set the tolerance equivalent to the threshold value of Si, so that Al and Si can be separated and identified. Using the crystal information of Al and Si from the material file, the crystal orientation can be analyzed.

[0088] (3) For the area determined to be the Al phase, analyze the crystal orientation. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary, and the equivalent circle diameter of each grain is obtained. Then, the equivalent circle diameters of each grain are averaged to calculate the average diameter of the Al phase. In addition, for the average calculation, the average value obtained by area averaging that can be selected by the software attached to the device is used. By using the average value obtained by area averaging, it is possible to accurately measure and determine whether the conditions related to the average diameter of the Al phase, which is preferable for reducing the bonding strength deviation in the second bonding and obtaining good bonding strength stability, are satisfied.

[0089] In the present invention, when calculating the average diameter of the Al phase in the L cross-section, only the Al phase with a diameter (equivalent circle diameter) of 0.5 μm or more is targeted. Thereby, it is possible to accurately judge whether the elements related to the average diameter of the Al phase in the L cross-section, which is preferable for improving the bonding strength stability in the second bonding, are satisfied.

[0090] When measuring the average diameter of the Al phase in the L cross-section, the setting range of the tolerance in the step (2) above, the method for obtaining the measurement sample, and the measurement area of the crystal orientation based on the EBSD method are the same as those described above for the measurement of the average value of the shape ratio (e / f) of the Si phase.

[0091] It should be noted that among the methods for measuring the shape ratio (e / f) of the Si phase, the shape ratio (c / d) of the Al phase, and the average diameter of the Al phase, in addition to the above, there are several methods including the binarization process of the observation image of the L cross-section. However, in the present invention, due to the reasons such as having multiple measurement functions, being able to automatically analyze by obtaining the above-mentioned multiple characteristics of the shape ratio (e / f) of the Si phase, the shape ratio (c / d) of the Al phase, and the average diameter of the Al phase in one measurement, being a popular device and analysis technology, and being easy to measure, as described above, the method of combining the information of the Al concentration and Si concentration obtained by SEM-EDS with the information of the crystal orientation obtained by EBSD is adopted.

[0092] - Add Fe, Mg, Mn, Ga, Ge -

[0093] The Al bonding material of the present invention may also contain one or more of Fe, Mg, Mn, Ga, and Ge in a total amount of 5 mass ppm or more and 700 mass ppm or less (hereinafter also referred to as the "second element group").

[0094] Moreover, by containing one or more of Fe, Mg, Mn, Ga, and Ge in a total amount of 5 mass ppm or more and 700 mass ppm or less, the occurrence of damage and scraping on the surface of the Al bonding material can be suppressed, and a smooth surface can be formed. Regarding an Al alloy containing Si at a high concentration of 3.0 mass% or more and 12.0 mass% or less, due to surface hardening, the exfoliation of Si phases and Al oxides present on the surface, etc., damage and scraping occur on the surface during wire drawing processing, and sometimes it belongs to an Al bonding material with large surface irregularities. It is inferred that by adding the second element group, the stabilization of Al oxides on the surface of the Al bonding material, the reduction of friction between the Al bonding material and the die, etc. are promoted, and thus the damage and scraping during wire drawing processing can be reduced. It is considered that by adding the second element group in combination with the first element group, the occurrence of damage and scraping on the surface of the Al bonding material can be suppressed, and the effect of forming a smooth surface can be improved.

[0095] From the viewpoint of suppressing the occurrence of surface damage and scraping and forming an Al bonding material with a smooth surface, the total concentration of the second element group in the Al bonding material of the present invention is more preferably 10 mass ppm or more, still more preferably 20 mass ppm or more, 30 mass ppm or more, 40 mass ppm or more, or 50 mass ppm or more. From the viewpoint of suppressing damage to the semiconductor chip and easily achieving good first bonding strength, its upper limit is more preferably 650 mass ppm or less, still more preferably 640 mass ppm or less, 620 mass ppm or less, or 600 mass ppm or less.

[0096] As the aluminum raw material when manufacturing the Al bonding material of the present invention, Al with a purity of 4N (Al: 99.99 mass% or more) is preferably used, and Al of 5N (Al: 99.999 mass% or more) or more with less impurity content is more preferably used.

[0097] Within the scope that does not hinder the effects of the present invention, the Al bonding 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"). The total concentration of other elements in the Al bonding material is not particularly limited within the scope that does not hinder the effects of the present invention. For example, the total concentration of these other elements may also be 0.5% by mass or less, 0.4% by mass or less, 0.3% by mass or less, 0.2% by mass or less, 0.15% by mass or less, 0.1% by mass or less, 0.08% by mass or less, 0.06% by mass or less, 0.05% by mass or less, 0.04% by mass or less, 0.03% by mass or less, 0.025% by mass or less, 0.02% by mass or less, 0.018% by mass or less, 0.016% by mass or less, 0.015% by mass or less, 0.014% by mass or less, 0.012% by mass or less, or 0.01% by mass or less. The lower limit of the total concentration of other elements is not particularly limited and may also be 0% by mass.

[0098] In one embodiment, the remaining portion of the Al bonding material of the present invention consists of Al and unavoidable impurities. Therefore, in a preferred embodiment, the Al bonding material of the present invention consists of Al, Si, and unavoidable impurities. In yet another preferred embodiment, the Al bonding material of the present invention consists of Al, Si, any one or more of the first element group, and unavoidable impurities. In another preferred embodiment, the Al bonding material of the present invention consists of Al, Si, any one or more of the second element group, and unavoidable impurities. In another preferred embodiment, the Al bonding material of the present invention consists of Al, Si, any one or more of the first element group, any one or more of the second element group, and unavoidable impurities.

[0099] In a preferred embodiment, the Al bonding material of the present invention does not have a coating mainly composed of a metal other than Al on the outer periphery of the Al bonding material. Herein, the so-called "coating mainly composed of a metal other than Al" refers to a coating in which the content of a metal other than Al is 50% by mass or more.

[0100] The Al bonding material of the present invention may be an Al bonding wire or an Al bonding tape. When the Al bonding material of the present invention is an Al bonding wire, its wire diameter is not particularly limited, and for example, it may be in the range of 100 to 600 μm. When the Al bonding material of the present invention is an Al bonding tape, the dimensions (W×T) of its rectangular or substantially rectangular cross-section are not particularly limited. For example, W may be 100 to 3000 μm, and T may also be 50 to 600 μm.

[0101] The Al bonding material of the present invention can satisfy excellent temperature cycle reliability and good first bonding strength. Therefore, the Al bonding material of the present invention can be preferably used as an Al bonding material for semiconductor devices, particularly as an Al bonding material for power semiconductor devices.

[0102] - Manufacturing method of Al bonding material -

[0103] An example of the manufacturing method of the Al bonding material of the present invention will be described. Hereinafter, an example of the manufacturing of an Al bonding wire with a wire diameter of 200 to 400 μm will be described.

[0104] Al and alloy elements as raw materials are preferably those with high purity. Al is preferably a raw material with a purity of 99.99% by mass or more, and the remaining part consists of inevitable impurities. Si, the first element group, and the second element group used as alloy elements are preferably alloy elements with a purity of 99.9% by mass or more, and the remaining part consists of inevitable impurities. The Al alloy used in the bonding wire can be manufactured by the following method: in a graphite or alumina crucible processed in a manner to obtain a cylindrical ingot, load the raw materials of Al and alloy elements, and melt them using an electric furnace or a high-frequency heating furnace. Considering the workability in subsequent processing steps, the diameter of the cylindrical ingot is preferably set to be Φ6 mm or more and less than 8 mm. In order to prevent excessive oxidation of Al or other elements constituting the wire, the atmosphere in the furnace during melting is preferably set to an inert atmosphere or a reducing atmosphere. Considering that while ensuring the fluidity of the melt, it is easy to control the shape, size, etc. of the Si phase during solidification, the highest temperature reached by the melt during melting is preferably in the range of 800 °C or more and less than 1000 °C. The cooling method after melting can be water cooling, furnace cooling, air cooling, etc.

[0105] For the cylindrical ingot obtained by melting, after solution treatment by heating at a high temperature, the wire with the target wire diameter can be made by repeatedly performing wire drawing using a die. The wire after wire drawing can be used as an Al alloy bonding wire by performing final heat treatment using an electric furnace.

[0106] In order to control the shape (shape ratio (e / f), shape ratio (c / d)) of the Si phase and the Al phase in the L cross-section, and the particle size of Al, it is effective to control the heat treatment conditions such as solution treatment and final heat treatment, and the wire drawing conditions. When performing wire drawing, it is effective to use a lubricating fluid to ensure the lubricity at the contact interface between the wire and the die.

[0107] 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 wire area reduction rate during solution treatment and wire drawing.

[0108] The temperature range for solution treatment of the ingot is preferably set to 400 °C or higher and less than 550 °C, and the time is set to 1 hour or longer and less than 6 hours. Through this solution treatment, the segmentation and spheroidization of the Si phase crystallized during solidification progress, and thus the shape of the Si phase caused by subsequent wire drawing can be controlled. For example, when solution-treated at a high temperature, the shape ratio (e / f) of the Si phase tends to increase.

[0109] Regarding the wire drawing processing conditions, it is effective to set the wire area reduction rate of each die used during wire drawing to a range of 20% or more and less than 35%. Here, when the wire area reduction rate of each die is set to P1, P1 is represented by the following formula.

[0110] P1 = {(R2 2 - R1 2 ) / R2 2} × 100

[0111] In the formula, R2 represents the diameter (mm) of the wire before processing, and R1 represents the diameter (mm) of the wire after processing.

[0112] Compared with general wire drawing processing conditions, by adjusting the wire area reduction rate within the above high range (high area reduction rate), the entire wire is greatly deformed during die processing, the processing strain increases to the inside of the wire, the Si phase is arranged in the direction of the wire central axis, and at the same time, the shape of the Si phase can be adjusted. By combining the control of the conditions of the aforementioned solution treatment with the control of the wire area reduction rate during wire drawing, it becomes easy to adjust the shape ratio (e / f) of the Si phase.

[0113] In order to adjust the shape (shape ratio (c / d)) of the Al phase in the L cross-section, it is effective to control the wire feeding speed and the final heat treatment during wire drawing.

[0114] The wire feeding speed during wire drawing will be described. The wire drawing process from the ingot (wire diameter D0) obtained by melting to about half of the final wire diameter (wire diameter D) (intermediate wire diameter: D + 0.5(D0 - D)) is set as "wire drawing 1", and the wire drawing process from this intermediate wire diameter to the final wire diameter is set as "wire drawing 2". It is effective to set the wire feeding speed in wire drawing 1 to 5 m / min or more and less than 15 m / min, and the wire feeding speed in wire drawing 2 to 20 m / min or more and less than 50 m / min. By setting the wire feeding speed within the above range, it becomes easy to control the processing strain and dynamic recrystallization during wire drawing and to control the shape ratio (c / d) of the Al phase in the L cross-section of the wire within the target range. If necessary, by combining the adjustment of the wire area reduction rate in the range of 20% or more and less than 35% with the adjustment of the wire feeding speed, the shape ratio (c / d) of the Al phase can be controlled with high precision.

[0115] Regarding the conditions of the final heat treatment, a temperature range of above 250°C and less than 350°C and a time of above 2 hours and less than 24 hours are effective. Using the processing strain in the wire caused by the aforementioned wire drawing process as the driving force, the recrystallization of the Al phase is promoted, and the grain shape can be adjusted. For example, when the final heat treatment is carried out at a low temperature for a long time, the grains of the Al phase will be granulated, and the shape ratio (c / d) tends to increase.

[0116] In order to control the average diameter of the Al phase in the L cross-section within the 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 and control the grain growth caused by the recrystallization of the Al phase. The temperature range of the final heat treatment is above 250°C and less than 340°C, and it is effective to control the time within the range of 5 hours or more and less than 24 hours. By performing homogenization treatment at a relatively low temperature, the solid solution amount of Si contained in the Al phase is adjusted, so that it becomes 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.

[0117] In addition, when intermediate heat treatment is carried out as needed, the adjustment of the conditions of the above-mentioned final heat treatment becomes easy. The so-called intermediate heat treatment is a heat treatment carried out in the middle of the process from ingot processing to the final wire diameter. It is effective to set the temperature range of the intermediate heat treatment to above 250°C and less than 400°C and the time to above 30 minutes and less than 3 hours. It is effective to carry out the intermediate heat treatment at a wire diameter of 2.5 to 4.0 times the final wire diameter. By performing the intermediate heat treatment, the reduction of the processing strain of the Al phase and the progress of recrystallization can be achieved. By adjusting the Al phase once, it becomes easy to adjust the particle diameter of the Al phase in the subsequent final heat treatment. For example, when the intermediate heat treatment temperature is increased, the diameter of the Al phase tends to decrease.

[0118] [Semiconductor device]

[0119] By using the Al connection material of the present invention, a semiconductor device can be manufactured by connecting the electrodes on the semiconductor chip to the external electrodes on the lead frame or the substrate. As described above, both the first bonding to the electrodes on the semiconductor chip and the second bonding to the electrodes on the lead frame or the substrate are performed by wedge bonding.

[0120] In one embodiment, the semiconductor device of the present invention is characterized by including a circuit board, a semiconductor chip, and an Al connection material for conducting the circuit board and the semiconductor chip, and the Al connection material is the Al connection material of the present invention.

[0121] In the semiconductor device of the present invention, the circuit board and the semiconductor chip are not particularly limited, and known circuit boards and semiconductor chips that can be used to constitute the semiconductor device may be employed. Alternatively, in addition, a lead frame may be used instead of the circuit board. For example, like the semiconductor device described in Japanese Patent Laid-Open No. 2020-150116, it may be configured as a semiconductor device including a lead frame and a semiconductor chip mounted on the lead frame.

[0122] Examples of the semiconductor device include various semiconductor devices used in electrical products (such as computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and transportation means (such as motorcycles, automobiles, trains, ships, and airplanes, etc.). Among them, a semiconductor device for power use (power semiconductor device) is preferred.

[0123] [Examples]

[0124] Hereinafter, specific examples of the present invention will be shown and described in detail. However, the present invention is not limited to the examples shown below.

[0125] (Specimen)

[0126] The method for manufacturing the specimen will be described. As the raw material, Al with a purity of 4N (99.99 mass% or more) is used, and the remaining part is composed of inevitable impurities. As the alloying elements, Si, the first element group (Sr, Eu, Na), and the second element group (Fe, Mg, Mn, Ga, Ge) are alloying elements with a purity of 99.99 mass% or more, and the remaining part is composed of inevitable impurities. The Al alloy used in the Al connection material is manufactured by charging the raw materials of Al and the alloying elements into an alumina crucible and melting them using a high-frequency heating furnace. The atmosphere in the furnace during melting is set to an Ar atmosphere, and the maximum temperature reached by the molten liquid during melting is set to 800°C or more and less than 1050°C. The cooling method after melting is set to air cooling by cooling in the atmosphere or water cooling by cooling in water.

[0127] A cylindrical ingot with a diameter of Φ6 mm is obtained by melting. After solution treatment and homogenization treatment of the ingot, wire drawing using a die and intermediate heat treatment are performed to produce an Al connection material (Al bonding wire) with a diameter of Φ300 μm. The temperature range of the solution treatment is set to 400°C or more and less than 550°C, and the time is set to 1 hour or more and less than 6 hours. After the solution treatment is completed, the homogenization treatment is continuously performed during the cooling process. The temperature range of the homogenization treatment is set to 300°C or more and less than 350°C, and the time is set to 2 hours or more and less than 6 hours. The cooling method after the homogenization treatment is set to air cooling by cooling in the atmosphere.

[0128] During wire drawing, a commercially available lubricant is used, and the wire area reduction rate for each die during wire drawing is set to be 20% or more and less than 35%. The temperature range of the final heat treatment is set to be 250°C or more and less than 350°C, and the time of the final heat treatment is set to be 2 hours or more and less than 24 hours.

[0129] In some embodiments, the wire feeding speed in wire drawing 1 is set to be 10 m / min or more and less than 15 m / min, and the wire feeding speed in wire drawing 2 is set to be 20 m / min or more and less than 40 m / min. In some embodiments, the temperature range of the intermediate heat treatment is set to be 250°C or more and less than 350°C, and the time is set to be 30 minutes or more and less than 3 hours. The number of intermediate heat treatments is set to one, and it is carried out with a wire diameter 2.5 to 4.0 times the final wire diameter.

[0130] (Method for measuring element content)

[0131] Regarding the concentration analysis of the elements contained in the Al bonding material, as an analysis device, ICP - OES ("PS3520UVDDII" manufactured by Hitachi High - Tech Science Co., Ltd.) or ICP - MS ("Agilent7700x ICP - MS" manufactured by Agilent Technologies Co., Ltd.) is used for measurement.

[0132] (Method for measuring the shape of Si phase and Al phase)

[0133] Taking the L cross - section (the cross - section in the central axis direction including the central axis) of the Al bonding material as the inspection surface, the shapes (ratio (e / f), ratio (c / d)) of the Si phase and Al phase are measured. In the present invention, the central axis of the Al bonding material and the cross - section in the central axis direction including the central axis (L cross - section) are as Figure 1 shown. Figure 1 shows the case where the Al bonding material is an Al bonding wire having a circular cross - sectional shape. However, in the case where the Al bonding material is an Al bonding tape having a rectangular or substantially rectangular cross - sectional shape with a width W and a thickness T, the central axis is the axis passing through the center of the width W and the center of the thickness T, or the L cross - section is the cross - section in the central axis direction including the central axis and the cross - section in the direction of the thickness T. When cross - section processing is performed to expose the L cross - section of the Al bonding material, it may deviate from the central axis of the Al bonding material. At this time, if the length in the direction perpendicular to the central axis of the L cross - section is 90% or more of the wire diameter of the Al bonding material (the thickness T in the case of a tape), it can be regarded as the cross - section including the central axis.

[0134] In addition, FE-SEM (SU-70 manufactured by Hitachi High-Tech Corporation) was used for measurement, and the analysis software used was APEX (for data collection), OIM Data Collection (for chemical-assisted scanning), and OIM Anaysis (for data analysis), all manufactured by TSL Solutions. Three measurement regions were randomly selected at intervals of 50 cm or more in the central axis direction of the Al bonding material, and measurements were carried out for these three regions. The measurement regions were determined in such a way that they were 300 μm or more and less than 800 μm in the central axis direction of the Al bonding material, and the entire Al bonding material entered in the direction perpendicular to the central axis. In addition, regarding the main conditions for EDS and EBSD measurements, the acceleration voltage was 15 kV, the measurement magnification was 350 times, the scanning speed was 30 to 120 points / second, and the measurement interval was in the range of 0.1 to 0.3 μm. Here, when the scanning speed is fast, the measurement time can be shortened, but it may lead to a decrease in the measurement accuracy of EDS. It is desirable to select an appropriate scanning speed within the above range.

[0135] - Shape of the Si phase -

[0136] In the measurement of the shape (shape ratio (e / f)) of the Si phase in the L cross-section of the Al bonding material, a method of combining the information on the Al concentration and Si concentration obtained by SEM-EDS with the information on the crystal orientation obtained by EBSD was adopted. Specifically, the measurement was carried out according to the following steps (1) to (3).

[0137] (1) In the measurement region where the L cross-section of the Al bonding material was used as the inspection surface, the concentration measurement of Al and Si using EDS and the crystal orientation analysis using EBSD were carried out simultaneously.

[0138] (2) Using the Chi scanning function, which is a function of the EBSD analysis software, Al and Si were separated and extracted. Specifically, by setting the tolerance equivalent to the threshold value of Si according to the EDS measurement result of Si, Al and Si were separated and identified. The crystal information of Al and Si was used from the material file for the crystal orientation analysis. Here, the tolerance condition was mainly set to 30%, and it can be adjusted as needed.

[0139] (3) For the regions determined to be the Si phase, analyze the crystal orientation. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary, and the shape ratio (e / f) of each grain is obtained. Then, the shape ratios (e / f) of each grain are 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 uses the value of Grain Shape Aspect Ratio in the analysis software ("grain shape aspect ratio"). Here, 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) to the long side length (f) (Grain Shape Major Axis) of a grain. Here, regarding the averaging calculation, the average value obtained by area averaging is used.

[0140] The average value of the shape ratio (e / f) of the Si phase is set as the average value of the values obtained for the three measurement regions through the above steps (1) to (3).

[0141] - Shape of the Al phase -

[0142] The measurement of the shape (shape ratio (c / d)) of the Al phase in the L cross-section of the Al bonding material is the same as the measurement of the shape ratio (e / f) of the Si phase. A method that combines the information on Al concentration and Si concentration obtained by SEM-EDS with the information on crystal orientation obtained by EBSD is used. Specifically, after implementing the above steps (1) and (2), the measurement is carried out according to the following step (3).

[0143] (3) For the regions determined to be the Al phase, analyze the crystal orientation. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary, and the shape ratio (c / d) of each grain is obtained. Then, the shape ratios (c / d) of each grain are averaged to calculate the average value of the shape ratio (c / d) of the Al phase. Here, the average value of the shape ratio (c / d) of the Al phase, similar to the measurement of the average value of the shape ratio (e / f) of the Si phase, uses the value of Grain Shape Aspect Ratio in the analysis software ("grain shape aspect ratio"). Regarding the averaging calculation, the average value obtained by area averaging is used.

[0144] The average value of the shape ratio (c / d) of the Al phase is set as the average value of the values obtained for the three measurement regions through the above steps (1) to (3).

[0145] (Method for measuring the average diameter of the Al phase)

[0146] Measurement of the average diameter of the Al phase in the L cross-section of the Al bonding material and measurement of the shapes of the Si and Al phases are carried out in the same way by combining the information on Al concentration and Si concentration obtained by SEM-EDS with the information on crystal orientation obtained by EBSD.

[0147] Specifically, after performing the steps of (1) and (2) above, the measurement is carried out according to the steps of (3) below.

[0148] (3) For the region determined to be the Al phase, analyze the crystal orientation. If the orientation difference between measurement points is 15° or more, it is judged as a crystal grain boundary, and the equivalent circle diameter of each grain is obtained. Then, the equivalent circle diameters of each grain are averaged to calculate the average diameter of the Al phase. Here, in the averaging calculation, the average value obtained by regional averaging is used. In addition, when calculating the average diameter of the Al phase in the L cross-section, only the Al phase with a diameter (equivalent circle diameter) of 0.5 μm or more is targeted.

[0149] The average diameter of the Al phase is set as the average value of the values obtained for three measurement regions through the steps of (1) to (3) above.

[0150] (Evaluation method for Al bonding material)

[0151] The evaluation method for the Al bonding material is described. The wire diameter of the Al bonding material (Al bonding wire) used in the evaluation is set to Φ300 μm. The semiconductor chip is a chip made of Si, and the electrodes on the semiconductor chip are electrodes formed of an alloy with a composition of Al-0.5% Cu with a thickness of 4 μm. The substrate is a substrate with Ni formed on an Al alloy with a thickness of 15 μm. A commercially available wire bonder (manufactured by Ultrasonic Industry Co., Ltd.) is used for the bonding of the Al bonding material, and both the first bonding and the second bonding are set as wedge bonding.

[0152] (Evaluation method for high-speed temperature cycle reliability)

[0153] The evaluation of high-speed temperature cycle test (high-speed TCT) is carried out using a commercially available high-speed thermal shock test device. In high-speed TCT, hot air is blown onto the specimen for rapid heating. The specimen for high-speed TCT has a structure in which a semiconductor chip is mounted on a substrate, and the electrodes on the semiconductor chip and the electrodes on the substrate are connected by an Al bonding material. For the specimen placed in the specimen chamber of the high-speed thermal shock test device, the heating and cooling are repeatedly applied as one cycle to apply a thermal load. The lowest temperature during cooling is set at -50 °C, and the highest temperature during heating is set at 175 °C. The heating time including the temperature rise time is set at 20 seconds, and the cooling time including the temperature fall time is set at 40 seconds. After the start of the test, the specimen is taken out after 10,000 cycles, and the shear strength test of the first joint is carried out. The value of the shear strength of the first joint used in the high-speed temperature cycle reliability evaluation is the average of the shear strengths of 10 randomly selected first joints. The ratio (percentage) of the average shear strength after the high-speed TCT to the average shear strength before the test is defined as the strength retention rate. The higher this strength retention rate, the more excellent the reliability of the joint. If the strength retention rate is 85% or more, it is judged as excellent and represented by "3"; if it is 75% or more and less than 85%, it is judged as excellent and represented by "2"; if it is 70% or more and less than 75%, it is judged as needing improvement and represented by "1"; if it is less than 60%, there will be problems in application and it is represented by "0". The judgments of "3" and "2" are considered qualified, while "1" and "0" are considered unqualified. The evaluation results are recorded in the column of "High-speed temperature cycle reliability (10,000 times)" in the table. The requirement for temperature cycle reliability in the next-generation power semiconductor device is equivalent to 10,000 cycles.

[0154] (Evaluation method for the first joint strength)

[0155] The evaluation method for the first joint strength will be described. The first joint strength is evaluated through a shear strength test. Ten first joints are made under normal bonding conditions, and the shear strength of the first joint is measured. In the measurement of the shear strength, a commercially available micro-shear strength testing machine (4000-PLUS manufactured by Nordson) is used. The shear speed is set at 200 μm / second, and the height of the shear tool is set at 10 μm from the electrode surface. The measurement of the shear strength is carried out by fixing the substrate with the Al wiring material bonded using a jig. If the average of the shear strengths of the 10 first joints is 1600 gf or more, it is judged as excellent and evaluated as "3"; if it is 1400 gf or more and less than 1600 gf, it is judged that there are no problems in application and evaluated as "2"; if it is 1000 gf or more and less than 1400 gf, it is judged as needing improvement and evaluated as "1"; if it is less than 1000 gf, it is judged that there are problems in application and evaluated as "0". The evaluation results are recorded in the column of "First joint strength" in the table.

[0156] (Evaluation method for wire breakage during processing)

[0157] An evaluation method for wire breakage during processing will be described. From wire diameter to wire diameter Wire drawing is carried out, and the number of wire breakages is confirmed. The transfer speed, area reduction rate, etc. as the processing conditions for wire drawing are selected according to the aforementioned conditions, and appropriate manufacturing conditions are adjusted and changed for each wire. The length of the Al connection material after wire drawing is in the range of 100 to 200 m. Converted to per 100 m, the number of wire breakages is calculated. If the number of wire breakages is 0 times, it is judged as good and evaluated as "3". If it is 1 time, it is judged that it can be dealt with by improving the manufacturing conditions and evaluated as "2". If it is 2 to 4 times, the reduction in productivity is regarded as a problem and evaluated as "1". If it is 5 times or more, it is judged as difficult to be practical and evaluated as "0". The evaluation results are recorded in the column of "Wire breakage during processing" in the table.

[0158] (Evaluation method for the bonding strength stability of the second joint)

[0159] Shear strength tests are carried out on 30 randomly selected second joints to obtain the bonding strength, and the overall standard deviation (σ) is calculated. When σ is 70 gf or more, it is judged that there are problems in application and evaluated as "0". If σ is 50 gf or more and less than 70 gf, it is judged as good and evaluated as "1". If σ is 30 gf or more and less than 50 gf, it is judged as excellent and evaluated as "2". If σ is less than 30 gf, it is judged as particularly excellent and evaluated as "3". "0" is unqualified, and "1", "2", "3" are qualified. The evaluation results are recorded in the column of "Bonding strength stability of the second joint" in the table.

[0160] (Evaluation method for surface damage and scratches)

[0161] Regarding the surface shape of the Al connection material, evaluation is carried out by paying attention to damage and scratches. The wire diameter of the Al connection material is set as Three measurement areas are randomly selected at intervals of 1 m or more in the central axis direction of the Al connection material. Three samples with a length of about 2 cm are taken from each of the three areas, and a total of 9 samples are observed. The surface is observed at a magnification in the range of 50 to 500 times of SEM. Damage with a length of 50 μm or more and scratches with a length of 30 μm or more are judged as bad. The positions of the damage and scratches are counted. If it is 0 place, it is good, judged as qualified and evaluated as "3". If it is 2 places or less, it is judged that there are no problems in application and evaluated as "2". If it is 3 to 7 places, it is judged that the surface properties are bad and evaluated as "1". If it is 8 places or more, it is judged as difficult to apply and evaluated as "0". The evaluation results are recorded in the column of "Surface properties" in the table.

[0162] The evaluation results of the examples and comparative examples are shown in Tables 1 to 3.

[0163] [Table 1]

[0164]

[0165] [Table 2]

[0166]

[0167] [Table 3]

[0168]

[0169] It was confirmed that: the Al connection materials of Examples Nos. 1 to 47 all contain Si of 3.0 mass% or more and 12.0 mass% or less, and contain one or more of the first element groups (Sr, Eu, Na) with a total of 5 mass ppm or more and 800 mass ppm or less. The shape ratio (e / f) of the Si phase in the L cross-section is in the range of 0.25 or more and 0.65 or less, and shows good temperature cycle reliability and good first bonding strength in high-speed TCT.

[0170] In addition, it was also confirmed that: the Al connection materials of Examples Nos. 1 to 22, 24 to 39, and 41 to 47 with a shape ratio (c / d) of the Al phase in the L cross-section of 0.25 or more and 0.7 or less can reduce the occurrence frequency of wire breakage during processing.

[0171] It was confirmed that: the Al connection materials of Examples Nos. 1 to 8, 10 to 43, and 45 to 47 with an average diameter of the Al phase in the L cross-section of 5 μm or more and 40 μm or less are more likely to belong to better results in the bonding strength stability of the second joint.

[0172] It was further confirmed that: the Al connection materials of Examples Nos. 28 to 41 and 43 to 47 containing one or more of the second element groups (Fe, Mg, Mn, Ga, Ge) with a total of 5 mass ppm or more and 700 mass ppm or less inhibit the occurrence of surface damage and scratching and have a smooth surface.

[0173] On the other hand, it was confirmed that: for the Al connection materials of Comparative Examples Nos. 1 to 10, any one of the Si concentration, the concentration of the first element group, and the shape ratio (e / f) of the Si phase is outside the scope of the present invention, and neither temperature cycle reliability nor the first bonding strength can be obtained sufficiently.

Claims

1. An Al bonding material, which contains Si in an amount of 3.0% by mass or more and 12.0% by mass or less, and contains at least one of Sr, Eu, and Na in a total amount of 5 mass ppm or more and 800 mass ppm or less. In the L cross-section of the Al bonding material, that is, in the cross-section in the central axis direction including the central axis, the average value of the ratio e / f of the short side length e to the long side length f of the Si phase is 0.25 or more and 0.65 or less.

2. The Al bonding material according to claim 1. In the L cross-section, the average value of the ratio c / d of the short side length c to the long side length d of the Al phase is 0.25 or more and 0.7 or less.

3. The Al bonding material according to claim 1 or 2. In the L cross-section, the average diameter of the Al phase is 5 μm or more and 40 μm or less.

4. The Al bonding material according to any one of claims 1 to 3. It further contains at least one of Fe, Mg, Mn, Ga, and Ge in a total amount of 5 mass ppm or more and 700 mass ppm or less.

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