Aluminum alloy bonding wire

Abstract

To provide an aluminum bonding wire that satisfies excellent temperature cycle reliability and good first bonding properties.SOLUTION: An aluminum bonding wire contains 3.0% or more and 10.0% or less of Si. The average diameter of an Si phase in a cross-section (L-section) of an aluminum alloy bonding wire in the central axis direction including a wire central axis is 0.8 μm or more and 5.5 μm or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In semiconductor devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or a substrate by a bonding wire. In power semiconductor devices, bonding wires made of aluminum (Al) are mainly used, and their wire diameters are mainly in the range of Φ300μm to Φ600μm. In power semiconductor devices, silicon (Si) is often used as the material for the semiconductor chip, and an Al-Si alloy or an Al-Cu alloy is often used as the material for the electrodes formed on the semiconductor chip. In addition, power semiconductor devices using Al bonding wires are often used as high-power devices such as air conditioners and solar power generation systems, and as semiconductor devices for vehicles.

[0003] There are two methods for bonding Al bonding wire: the first bonding with an electrode on a semiconductor chip, and the second bonding with an electrode on a lead frame or a substrate. Both methods use wedge bonding. Wedge bonding is a method in which ultrasonic waves and a load are applied to the Al bonding wire through a metal jig to break the surface oxide film of the bonding wire material and the electrode material, exposing the new surface, and performing solid-phase diffusion bonding. If a bonding failure occurs during bonding, such as the Al bonding wire peeling off from the electrode, it will lead to product defects and reduced manufacturing yield, so it is necessary to obtain good bonding strength at each bonding part. If strong ultrasonic waves or loads are applied to the first bonding part to obtain good bonding strength, the semiconductor chip may be damaged. Therefore, in addition to obtaining good bonding strength, it is necessary to suppress damage to the semiconductor chip in the first bonding.

[0004] Next-generation power semiconductor devices are required to operate stably for a long period of time compared to general-purpose power semiconductor devices. Power semiconductor devices operate by repeatedly turning current on and off. When current is supplied to a Si semiconductor chip through an Al bonding wire, the temperature of the first junction rises. On the other hand, when the current supply is stopped, the temperature of the first junction drops. In this way, the first junction repeatedly rises and falls in temperature during operation of the power semiconductor. As a result, thermal stress caused by the difference in thermal expansion between the Al bonding wire and the semiconductor chip is repeatedly applied to the first junction. When a material made only of high-purity Al is used as the Al bonding wire, the Al bonding wire breaks in a relatively short time due to thermal stress, making it difficult to satisfy the performance required for next-generation power semiconductor devices. Therefore, in next-generation power semiconductors, it is required to improve the junction life (hereinafter also referred to as "temperature cycle reliability") associated with the rise and fall of the temperature of the first junction.

[0005] In response to the demand for temperature cycle reliability, Al bonding wires that focus on improving mechanical strength have been proposed. As a method for improving the mechanical properties of Al bonding wires, a method of adding specific elements to Al has been proposed.

[0006] Patent Document 1 discloses a bonding wire made of an Al alloy containing at least magnesium (Mg) and silicon (Si) and having a total content of Mg and Si of 0.03% by mass to 0.3% by mass. This patent document discloses that the decrease in the bonding strength of the first bonding part in a thermal cycle test in the temperature range of 70°C to 120°C is delayed due to the effect of increasing the strength by solid solution strengthening of Mg and Si and the effect of suppressing crack growth by precipitated magnesium silicide (Mg2Si).

[0007] Patent Document 2 discloses a bonding wire made of an alloy containing 0.01-0.2 mass% iron (Fe), 1-20 mass ppm silicon (Si), and the remainder being Al with a purity of 99.997 mass% or more, in which the amount of Fe in solid solution is 0.01-0.06%, the amount of Fe precipitated is 7 times or less the amount of Fe in solid solution, and the wire has a fine structure with an average crystal grain size of 6-12 μm. This patent document discloses that the mechanical strength of the matrix is ​​improved by uniformly dispersing intermetallic compound particles of Fe and Al in Al, and the recrystallized grains are further refined, thereby suppressing a decrease in the bonding strength of the 1st bonding portion in a thermal shock test in a temperature range of -50°C to 200°C.

[0008] 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 extruding and quenching the melted Al-Si alloy to form it into a thin wire. This patent document discloses that mechanical strength is improved by quenching the molten Al-Si alloy to finely and uniformly disperse Si. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2014-131010 A [Patent Document 2] JP 2014-129578 A [Patent Document 3] Japanese Patent Application Publication No. 59-57440 Summary of the Invention [Problem to be solved by the invention]

[0010] The Al bonding wire used in next-generation power semiconductor devices is required to have high temperature cycle reliability at the first bonded part so that it can withstand long-term use, and to provide good bondability at the first bonded part.

[0011] Next-generation power semiconductor devices are required to withstand longer use than general-purpose power semiconductor devices. As described above, the temperature of the first junction rises and falls repeatedly during operation of the power semiconductor device. As a result, since the Al bonding wire has a larger linear expansion coefficient than the semiconductor chip, thermal stress occurs in the first junction due to the difference in linear expansion coefficient between the two, and there is a problem that the Al bonding wire eventually breaks down due to fatigue. The temperature cycle test is one of the tests for accelerating evaluation of the life (temperature cycle reliability) of the junction due to the rise and fall of the temperature of the first junction. The Al bonding wire used in the next-generation power semiconductor is required to have excellent temperature cycle reliability in the temperature cycle test. However, when the high-strength Al bonding wire disclosed in Patent Documents 1 to 3 is used, in the temperature cycle test assuming use in the next-generation power semiconductor device, it was confirmed that there is a problem that cracks progress at a relatively high speed in the Al alloy electrode, which has a lower strength than the Al bonding wire, and it is difficult to stably obtain good temperature cycle reliability.

[0012] That is, although there have been some reports on the effectiveness of Al bonding wire, which has been strengthened by adding other elements to Al, in terms of temperature cycle reliability, the effect has been insufficient.

[0013] An object of the present invention is to provide an Al bonding wire that satisfies excellent temperature cycle reliability and good first bondability. [Means for solving the problem]

[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 alloy bonding wire containing 3.0 mass% or more and 10.0 mass% or less of Si, wherein the average diameter of the Si phase in a cross section (L cross section) in the central axis direction including the central axis of the Al alloy bonding wire is 0.8 to 5.5 μm. Based on this finding, the inventors have further researched and completed the present invention.

[0015] That is, the present invention includes the following. [1] An Al alloy bonding wire containing 3.0 mass% or more and 10.0 mass% or less of Si, wherein the average diameter of the Si phase in a cross section (L cross section) in the central axis direction including the central axis of the Al alloy bonding wire is 0.8 μm or more and 5.5 μm or less. [2] The Al alloy bonding wire according to [1], wherein the average ratio (a / b) of the length (a) of the Si phase in the L cross section in the direction of the central axis of the wire to the length (b) in the direction perpendicular to the central axis of the wire is 1.3 or more and 3.2 or less. [3] The Al alloy bonding wire according to [1] or [2], wherein the average diameter of the α phase in the L cross section is 5 μm or more and 50 μm or less. [4] In the results of measuring the crystal orientation of the Si phase in the L cross section, the crystal orientation in the direction of the wire central axis has an angle difference of 15° or less with respect to the wire central axis. <110> The Al alloy bonding wire according to any one of [1] to [3], wherein the orientation ratio is 30% or more and 80% or less. [5] The Al alloy bonding wire according to any one of [1] to [4], further containing at least one of Ni, Pd and Pt in a total amount of 3 ppm by mass or more and 150 ppm by mass or less. [6] The aluminum alloy bonding wire according to any one of [1] to [5], wherein the remainder is aluminum and inevitable impurities. [7] A semiconductor device comprising the Al alloy bonding wire according to any one of [1] to [6]. Effect of the Invention

[0016] According to the present invention, it is possible to provide an Al alloy bonding wire that satisfies excellent temperature cycle reliability and good first bondability. [Brief description of the drawings]

[0017] [Figure 1]1 is a schematic diagram for explaining a measurement surface (inspection surface) when measuring the average diameter and crystal orientation of the Si phase of an Al alloy bonding wire. The measurement surface is a cross section (L cross section) in the central axis direction including the wire central axis of the Al alloy bonding wire. [Diagram 2] FIG. 2 is a schematic diagram for explaining the length (a) of the Si phase in the L cross section along the central axis of the wire and the length (b) in the direction perpendicular to the central axis of the wire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention will be described in detail below with reference to preferred embodiments. However, the present invention is not limited to the following embodiments and examples, and can be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

[0019] [Al alloy bonding wire] The Al alloy bonding wire of the present invention (hereinafter simply referred to as "the wire of the present invention" or "wire") is an Al alloy bonding wire containing 3.0 mass% to 10.0 mass% Si, and is characterized in that the average diameter of the Si phase in a cross section (L cross section) in the central axis direction including the wire central axis of the wire is 0.8 μm to 5.5 μm. In the present invention, the wire central axis of the Al alloy bonding wire and the cross section (L cross section) in the central axis direction including the wire central axis of the wire are as described below in the section "(Method of measuring the average diameter of the Si phase and the shape of the Si phase)" with reference to FIG. 1.

[0020] In the temperature cycle test, when a bonding wire made only of high-purity Al was used, cracks propagated relatively quickly inside the bonding wire, making it difficult to obtain good temperature cycle reliability. On the other hand, when an Al bonding wire with added elements and increased strength was used, cracks propagated inside the Al alloy electrode, which has a relatively low strength, making it difficult to obtain the temperature cycle reliability required for next-generation power semiconductor devices.

[0021] As a result of intensive research to solve the above problems, the inventors have found that an Al alloy bonding wire containing 3.0 mass% to 10.0 mass% Si and having an average diameter of the Si phase in the L cross section of 0.8 μm to 5.5 μm can improve temperature cycle reliability. Such a wire of the present invention significantly contributes to realizing the temperature cycle reliability required for next-generation power semiconductor devices. The wire of the present invention has a hypoeutectic composition containing 3.0 mass% to 10.0 mass% Si, and is composed of an α phase in which Si is solid-dissolved in Al and a Si phase.

[0022] The reason why the wire of the present invention can provide good temperature cycle reliability is presumed to be as follows. First, since the Si phase has a smaller linear expansion coefficient than Al, by containing Si at 3.0 mass% or more and 10.0 mass% or less, the linear expansion coefficient of the Al alloy bonding wire is reduced, and the thermal stress generated during the temperature cycle test is reduced. Furthermore, by controlling the average diameter of the Si phase in the L cross section of the Al alloy bonding wire to 0.8 μm or more, the strength of the α phase due to the precipitation strengthening of the Si phase can be suppressed. This provides the effect of preventing cracks from progressing in the Al alloy electrode during the temperature cycle test. Furthermore, by controlling the average diameter of the Si phase in the L cross section of the Al alloy bonding wire to a range of 0.8 μm or more and 5.5 μm or less, when the tip of the crack that has progressed during the temperature cycle test reaches the hard Si phase, the effect of suppressing further crack progression can be fully obtained. As described above, it is believed that the wire of the present invention can exhibit good reliability by appropriately controlling multiple factors that contribute to improving the temperature cycle reliability.

[0023] In the temperature cycle test, from the viewpoint of obtaining good temperature cycle reliability, the concentration of Si in the Al alloy bonding wire of the present invention is 3.0 mass% or more, preferably 4.0 mass% or more, more preferably 4.2 mass% or more, 4.4 mass% or more, 4.5 mass% or more, 4.6 mass% or more, or 4.8 mass% or more. On the other hand, if the hardness of the Al alloy bonding wire is excessive, damage to the semiconductor chip is likely to occur during 1st bonding under commonly used ultrasonic and load bonding conditions. From the viewpoint of obtaining good bonding strength when performing 1st bonding under general bonding conditions, the Si concentration in the Al alloy bonding wire of the present invention is 10 mass% or less, preferably 8.0 mass% or less or 7.0 mass% or less, more preferably 6.8 mass% or less, 6.6 mass% or less, or 6.5 mass% or less.

[0024] In the temperature cycle test, from the viewpoint of obtaining good temperature cycle reliability, the average diameter of the Si phase in the L cross section of the wire of the present invention is 0.8 μm or more, preferably 1.2 μm or more or 1.4 μm or more, more preferably 1.5 μm or more, 1.6 μm or more, or 1.8 μm or more. On the other hand, if the Si phase becomes too coarse, the number density of the Si phase decreases, and it becomes difficult to stably obtain the crack propagation suppression effect by the Si phase. Therefore, from the viewpoint of stably obtaining good temperature cycle reliability, the average diameter of the Si phase in the L cross section of the wire of the present invention is 5.5 μm or less, preferably 5.0 μm or less or 4.5 μm or less, more preferably 4.0 μm or less.

[0025] For example, an ICP (Inductively Coupled Plasma) emission spectrometer or an ICP mass spectrometer can be used to analyze the concentration of elements contained in the wire of the present invention. If elements derived from atmospheric contaminants such as oxygen or carbon are adsorbed on the surface of the wire, it is effective to wash the wire with an acid or alkali according to the adsorbed substance before analysis.

[0026] A method for measuring the diameter of the Si phase in the L cross section of the wire of the present invention will be described. As a method for measuring the diameter of the Si phase in the L cross section, for example, a method using a backscattered electron image by a field emission scanning electron microscope (FE-SEM) can be mentioned. A specific measurement method will be described below. First, a backscattered electron image of the L cross section of the wire is obtained using an FE-SEM. In the backscattered electron image, the α phase and the Si phase are observed with different contrasts, and the Si phase is extracted by a binarization process using this contrast. In the binarization process, the brightness value of the backscattered electron image of the obtained L cross section is normalized to a range of 0 to 1, and a threshold value is determined in a range of 0.45 to 0.95 for binarization. At this time, the threshold value is appropriately determined so that the Si phase and the α phase can be distinguished. Note that the L cross section may have foreign matter or scratches attached during sample preparation, and may be observed with a contrast close to that of the Si phase. In order to distinguish between these foreign objects and scratches and the Si phase and to eliminate the influence of the foreign objects and scratches, it is effective to measure the Si concentration using an energy dispersive X-ray spectrometer (EDS: Energy Dispersive X-ray Spectrometer) attached to the FE-SEM to identify the Si phase. In this way, the Si phase is identified based on the Si concentration information as necessary, and then the Si phase is extracted by binarization processing based on the backscattered electron image. Then, the circle equivalent diameter is calculated for each extracted Si phase using image analysis software (Esprit manufactured by Bruker, etc.). In the present invention, the circle equivalent diameter is defined as the diameter of the Si phase, and the arithmetic average value of the diameters of each Si phase is defined as the average diameter. Therefore, in one embodiment, the average diameter of the Si phase in the L cross section of the wire of the present invention is calculated by the following steps (1) to (3). (1) A backscattered electron image of the L cross section of the wire is obtained using an FE-SEM. (2) The Si phase is extracted by binarization processing that utilizes the contrast of the acquired backscattered electron image. (3) Image analysis is performed on each extracted Si phase to determine the circle equivalent diameter, and the average diameter of the Si phase is calculated by arithmetic averaging. As described above, in the above (2), the Si phase may be identified by measuring the Si concentration using EDS in order to set a threshold value and, if necessary, to distinguish the Si phase from foreign matter or scratches.

[0027] In the present invention, only Si phases having a diameter of 0.5 μm or more are considered when calculating the average diameter of the Si phases, which allows accurate judgment of whether the requirements for the average diameter of the Si phases suitable for satisfying the temperature cycle reliability required for next-generation power semiconductor devices are met.

[0028] In the present invention, the measurement region for the average diameter of the Si phase was determined so that the length in the wire central axis direction was 100 μm or more and less than 400 μm, and the entire wire was included in the direction perpendicular to the wire central axis.

[0029] - Shape of the Si phase - As a method for evaluating the life of the first junction of a power semiconductor device with increasing and decreasing temperature, a test in which temperature is increased and decreased repeatedly in a shorter time than in a temperature cycle test (hereinafter also referred to as a "high-speed temperature cycle test") is sometimes used. It is desirable that next-generation power semiconductor devices can obtain a superior junction life (hereinafter also referred to as "high-speed temperature cycle reliability") in a high-speed temperature cycle test compared to conventional power semiconductor devices.

[0030] In the course of investigating an Al alloy bonding wire containing 3.0% by mass or more and 10.0% by mass or less of Si and having an average diameter of the Si phase in the L cross section of 0.8 μm or more and 5.5 μm or less, the inventors have found that the shape of the Si phase in the L cross section also affects the high-speed temperature cycle reliability. In detail, the inventors have found that the high-speed temperature cycle reliability can be improved by setting the average value of the ratio (a / b) of the length (a) of the Si phase in the L cross section in the wire central axis direction to the length (b) in the direction perpendicular to the wire central axis of 1.3 to 3.2. Further explanation will be given with reference to FIG. 2. FIG. 2 is a schematic diagram showing the Si phase in the L cross section of the wire, in which the wire central axis direction corresponds to the horizontal direction (left-right direction) of FIG. 2, and the direction perpendicular to the wire central axis corresponds to the vertical direction (up-down direction) of FIG. 2. Regarding the Si phase in the L cross section, the above-mentioned "length (a) in the wire central axis direction" refers to the maximum dimension of the Si phase in the wire central axis direction, which corresponds to the dimension indicated by the symbol a in FIG. 2. Moreover, for the Si phase in the L cross section, the above-mentioned "length (b) in the direction perpendicular to the central axis of the wire" refers to the maximum dimension of the Si phase in the direction perpendicular to the central axis of the wire, and corresponds to the dimension indicated by the symbol b in Fig. 2. Hereinafter, the ratio (a / b) of the length (a) of the Si phase in the L cross section in the direction of the central axis of the wire to the length (b) in the direction perpendicular to the central axis of the wire will also be simply referred to as the "ratio (a / b) of the Si phase in the L cross section."

[0031] Regarding the reason why the high-speed temperature cycle reliability is improved by controlling the average value of the ratio (a / b) of the Si phase in the L cross-section in the wire of the present invention, it is speculated as follows. During the high-speed temperature cycle test, cracks progress inside the Al alloy bonding wire and lead to fracture. The cracks tend to progress along the wire central axis direction or a direction close to it, and it is considered effective to reduce the thermal stress in the wire central axis direction. That is, by controlling the shape of the Si phase so that the length of the Si phase in the wire central axis direction in the L cross-section is greater than or equal to a certain value compared to the length in the direction perpendicular to the wire central axis, the linear expansion coefficient in the wire central axis direction can be reduced. As a result, it is considered that the thermal stress in the wire central axis direction applied to the Al alloy bonding wire can be reduced. Specifically, in addition to containing 3.0 mass% or more and 10.0 mass% or less of Si and the average diameter of the Si phase in the L cross-section being 0.8 μm or more and 5.5 μm or less, by further controlling the average value of the ratio (a / b) of the Si phase in the L cross-section to be 1.3 or more and 3.2 or less, it is considered that the effect of reducing the thermal stress that causes fatigue fracture of the Al alloy bonding wire is synergistically enhanced. In the high-speed temperature cycle test, since the time exposed to high temperature is shorter compared to the temperature cycle test, recovery and recrystallization are less likely to occur, and plastic strain that serves as the driving force for crack progress is likely to accumulate. Since the amount of plastic strain introduced into the Al alloy wire during the high-speed temperature cycle test decreases as the thermal stress decreases, it is estimated that the above-described shape control of the Si phase contributed to the improvement of the high-speed temperature cycle reliability. In achieving the effect of improving the high-speed temperature cycle reliability, it is sufficient that the average value of the ratio (a / b) of the Si phase in the L cross-section is within the above-mentioned suitable range, and it is not necessary for the ratio (a / b) of all Si phases to be in the range of 1.3 or more and 3.2 or less. For example, it may contain Si phases with a ratio (a / b) of less than 1.3, such as Si phases where a < b or a = b, or it may contain Si phases with a ratio (a / b) of more than 3.2.

[0032] From the viewpoint of reducing thermal stress in the wire central axis direction generated during high-speed temperature cycle testing and improving high-speed temperature cycle reliability, the average value of the ratio (a / b) of the Si phase in the L cross section of the wire of the present invention is more preferably 1.4 or more. On the other hand, if the average value of the ratio (a / b) is too large, the end of the Si phase becomes acute, and cracks are likely to occur along the interface between the end of the Si phase and the α phase, so that the effect of improving the high-speed temperature cycle reliability cannot be obtained. Therefore, the average value of the ratio (a / b) of the Si phase in the L cross section of the wire of the present invention is preferably 3.2 or less, more preferably 2.8 or less.

[0033] A method for measuring the length (a) of the Si phase in the wire central axis direction and the length (b) in the direction perpendicular to the wire central axis in the L cross section of the wire of the present invention will be described. First, as in the above-mentioned method for measuring the diameter of the Si phase in the L cross section of the wire, a backscattered electron image of the L cross section is obtained by FE-SEM, and the Si phase is extracted by binarization processing using the contrast of the obtained backscattered electron image. Here, as described above for the method for measuring the diameter of the Si phase, the guideline for setting the threshold value for the binarization processing and, if necessary, the Si phase may be identified by measuring the Si concentration using EDS in order to distinguish the Si phase from foreign matter or scratches are also as described above for the method for measuring the diameter of the Si phase. Next, the length (a) in the wire central axis direction and the length (b) in the direction perpendicular to the wire central axis are calculated for each extracted Si phase using image analysis software (Esprit manufactured by Bruker, etc.). The average value of the ratio (a / b) of the Si phase in the L cross section is the arithmetic average value of the ratio (a / b) values ​​calculated for each Si phase. Therefore, in one embodiment, the average value of the ratio (a / b) of the Si phase in the L cross section of the wire of the present invention is calculated by the following steps (1) to (3). (1) A backscattered electron image of the L cross section of the wire is obtained using an FE-SEM. (2) The Si phase is extracted by binarization processing that utilizes the contrast of the acquired backscattered electron image. (3) For each extracted Si phase, image analysis is performed to measure the length (a) in the direction of the central axis of the wire and the length (b) in the direction perpendicular to the central axis of the wire to obtain the ratio (a / b). These are then arithmetically averaged to calculate the average ratio (a / b) of the Si phase.

[0034] In the present invention, when calculating the ratio (a / b) of the Si phase in the L cross section, only Si phases having a diameter (equivalent circle diameter) of 0.5 μm or more are considered. This makes it possible to accurately determine whether the requirement related to the ratio (a / b) of the Si phase in the L cross section, which is suitable for improving the high-speed temperature cycle reliability, is met.

[0035] In addition, when measuring the length (a) of the Si phase in the L cross section along the wire's central axis and the length (b) perpendicular to the wire's central axis, the measurement area was determined so that the length along the wire's central axis was 100 μm or more and less than 400 μm, and the entire wire was included in the direction perpendicular to the wire's central axis.

[0036] -Average diameter of α phase- In the wire of the present invention, the average diameter of the α phase in the L cross section is preferably 5 μm or more and 50 μm or less.

[0037] The present inventors have found that by setting the average diameter of the α phase in the L cross section to a range of 5 μm to 50 μm, the variation in the bonding strength in the 2nd bond can be reduced. This is believed to be because the effect of promoting uniform deformation of the wire by containing a predetermined concentration of Si and controlling the average diameter of the Si phase in the L cross section to a predetermined range and the effect of reducing the variation in the mechanical strength in the direction perpendicular to the central axis of the wire by setting the average diameter of the α phase in the L cross section to a range of 5 μm to 50 μm work synergistically.

[0038] From the viewpoint of further reducing the variation in the bonding strength in the 2nd bonding and realizing a better stability of the bonding strength, the average diameter of the α phase in the L cross section of the wire of the present invention is more preferably 10 μm or more, even more preferably 12 μm or more, 14 μm or more, or 15 μm or more. Also, the upper limit of the average diameter of the α phase in the L cross section is more preferably 45 μm or less, even more preferably 40 μm or less, 38 μm or less, 36 μm or less, or 35 μm or less.

[0039] A method for measuring the diameter of the α phase in the L cross section of the wire of the present invention will be described. The diameter of the α phase in the L cross section can be measured by combining information on the Al concentration obtained by SEM-EDS and information on the crystal orientation obtained by electron backscattered diffraction (EBSD). In detail, the L cross section of the wire is used as the inspection surface, and the concentration measurement of Al and Si using EDS and the crystal orientation analysis using EBSD are performed simultaneously. Then, for the region identified as the α phase from the EDS measurement result, 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 to be a grain boundary and the circle equivalent diameter is calculated. The arithmetic mean value of the circle equivalent diameter of each α phase is defined as the average diameter of the α phase. In the process of calculating the diameter of the α phase, the parts where the crystal orientation cannot be measured or the parts where the crystal orientation can be measured but the reliability of the orientation analysis is low are excluded from the calculation. Therefore, in one embodiment, the average diameter of the α phase in the L cross section of the wire of the present invention is calculated by the following steps (1) to (3). (1) The L-section of the wire is used as the inspection surface, and the Al and Si concentrations are measured using EDS and the crystal orientation is analyzed using EBSD simultaneously. (2) For the regions identified as α-phase from the EDS measurement results, 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 circle equivalent diameter of each crystal grain is calculated. (3) The average diameter of the α phase is calculated by arithmetically averaging the equivalent circle diameters of each crystal grain.

[0040] In the present invention, when calculating the average diameter of the α phase in the L cross section, only α phases having a diameter (equivalent circle diameter) of 0.5 μm or more are considered. This makes it possible to accurately determine whether the requirement related to the average diameter of the α phase in the L cross section, which is suitable for improving the stability of the joint strength in the 2nd joint, is met.

[0041] In addition, when measuring the average diameter of the α phase in the L cross section, the measurement region was determined to have a length in the wire central axis direction of 100 μm or more and less than 400 μm, and the entire wire was included in the direction perpendicular to the wire central axis.

[0042] -Crystal orientation of the Si phase- In the wire of the present invention, the crystal orientation of the Si phase in the L cross section is measured, and among the crystal orientations in the direction of the central axis of the wire, the crystal orientation has an angle difference of 15° or less with respect to the central axis of the wire. <110> It is preferable that the orientation ratio of the crystal orientation is 30% or more and 80% or less. <110> The orientation ratio of the Si phase in the L cross section is <110> It is also called the "azimuth ratio".

[0043] Crystal orientation of the Si phase in the L section <110> The inventors have found that the loop straightness is improved by controlling the orientation ratio of the Si phase in the L cross section to 30% or more and 80% or less. The reason for this is that the effect of promoting uniform deformation of the wire by controlling the average diameter of the Si phase in the L cross section to a predetermined range and the effect of controlling the crystal orientation of the Si phase in the L cross section to 30% or more are obtained. <110> This is believed to be because the effect of reducing the variation in mechanical strength in the central axis direction of the wire is synergistically achieved by setting the orientation ratio of 30% to 80%.

[0044] In order to further improve the straightness of the loop, the crystal orientation of the Si phase in the L cross section of the wire of the present invention is <110> The orientation ratio of the Si phase in the L cross section is more preferably 35% or more, and further preferably 40% or more, 45% or more, or 50% or more. <110> If the orientation ratio exceeds 80%, the effect of improving the loop straightness tends not to be obtained. <110> The upper limit of the orientation ratio is preferably 80% or less, more preferably 78% or less, 76% or less, or 75% or less.

[0045] Crystal orientation of the Si phase in the L section of the wire of the present invention <110> When measuring the orientation ratio, a method can be used that combines the information on the Al and Si concentrations obtained by SEM-EDS and the information on the crystal orientation obtained by EBSD. In detail, the L-section of the wire is used as the inspection surface, and the Al and Si concentrations are measured using EDS and the crystal orientation is analyzed using EBSD at the same time. Next, for the area identified as the Si phase from the EDS measurement results, the crystal orientation of the Si phase is analyzed using the analysis software provided with the device. <110> The orientation ratio can be calculated by using the area of ​​the crystal orientations that can be identified based on a certain degree of reliability within the measurement area as the population. <110> The area ratio of the crystal orientation <110> In the process of calculating the orientation ratio, the calculation was performed excluding the parts where the crystal orientation could not be measured, or the parts where the crystal orientation could be measured but the reliability of the orientation analysis was low. Therefore, in one embodiment, the crystal orientation of the Si phase in the L cross section of the wire of the present invention is <110> The orientation ratio is calculated by the following steps (1) and (2). (1) The L-section of the wire is used as the inspection surface, and the Al and Si concentrations are measured using EDS and the crystal orientation is analyzed using EBSD simultaneously. (2) The crystal orientation of the region identified as the Si phase from the EDS measurement results was analyzed, and the crystal orientation of the Si phase was <110> Calculate the azimuth ratio of .

[0046] In the present invention, the crystal orientation of the Si phase in the L cross section <110> The orientation ratio was determined as the arithmetic average of the orientation ratio values ​​obtained by measuring three or more locations. In selecting the measurement area, it is preferable to obtain measurement samples from the bonding wire to be measured at intervals of 1 m or more in the wire central axis direction and provide them for measurement, from the viewpoint of ensuring the objectivity of the measurement data. In the present invention, the measurement area of ​​the crystal orientation by the EBSD method is determined so that the length in the wire central axis direction is 100 μm or more and less than 400 μm, and the entire wire is included in the direction perpendicular to the wire central axis.

[0047] -Addition of Ni, Pd, and Pt- The wire of the present invention may further contain at least one of Ni, Pd and Pt in a total amount of 3 ppm by mass or more and 150 ppm by mass or less.

[0048] Furthermore, the present inventors have found that the corrosion resistance in a high-temperature, high-humidity environment can be improved by including at least one of Ni, Pd, and Pt in a total amount of 3 ppm by mass to 150 ppm by mass. Although the reason for this is unclear, it is believed that the effect of improving the corrosion resistance in a high-temperature, high-humidity environment by including a specific concentration of Si is synergistically enhanced by including at least one of Ni, Pd, and Pt in a total amount of 3 ppm by mass to 150 ppm by mass.

[0049] From the viewpoint of improving corrosion resistance in a high-temperature and high-humidity environment, the total concentration of Ni, Pd, and Pt in the wire of the present invention is preferably 3 ppm by mass or more, more preferably 5 ppm by mass or more, 6 ppm by mass or more, 8 ppm by mass or more, or 10 ppm by mass or more, and the upper limit is preferably 150 ppm by mass or less, more preferably 145 ppm by mass or less, or 140 ppm by mass or less.

[0050] As the aluminum raw material for manufacturing the wire of the present invention, it is preferable to use Al with a purity of 4N (Al: 99.99% by mass or more), and more preferable to use Al with a low impurity content of 5N (Al: 99.999% by mass or more). The remainder of the wire of the present invention may contain elements other than Al, as long as the effect of the present invention is not impaired. In the wire of the present invention, the content of Al is not particularly limited as long as the effect of the present invention is not impaired, but is preferably 90% by mass or more, more preferably 92% by mass or more, 92.5% by mass or more, or 93% by mass or more, and even more preferably 93.5% by mass or more, 94% by mass or more, 94.5% by mass or more, 94.6% by mass or more, 94.8% by mass or more, or 95% by mass or more. In one embodiment, the remainder of the wire of the present invention consists of Al and inevitable impurities. Therefore, in a preferred embodiment, the wire of the present invention consists of Al, Si, and inevitable impurities. In another preferred embodiment, the wire of the present invention consists of Al, Si, one or more of Ni, Pd, and Pt, and inevitable impurities.

[0051] In a preferred embodiment, the wire of the present invention does not have a coating mainly composed of a metal other than Al on the outer periphery of the wire. Here, the term "coating mainly composed of a metal other than Al" refers to a coating containing 50 mass % or more of a metal other than Al.

[0052] The wire of the present invention satisfies both good temperature cycle reliability and good bondability at the 1st bonded portion, and also provides good high-speed temperature cycle reliability, good bond strength at the 2nd bonded portion, loop straightness, and high corrosion resistance in a high-temperature, high-humidity environment. Therefore, the bonding wire of the present invention can be suitably used as an Al alloy bonding wire for semiconductor devices, particularly as an Al alloy bonding wire for power semiconductor devices.

[0053] The wire diameter of the wire of the present invention is not particularly limited and may be appropriately determined depending on the specific purpose, but may be preferably 50 μm or more, 60 μm or more, 80 μm or more, 100 μm or more, 120 μm or more, 140 μm or more, 150 μm or more, etc. The upper limit of the wire diameter is not particularly limited and may be, for example, 600 μm or less, 550 μm or less, 500 μm or less, etc.

[0054] (Manufacturing method of Al alloy bonding wire) An example of a method for manufacturing an Al alloy bonding wire of the present invention will be described. The Al and alloying elements used as raw materials preferably have a high purity. The purity of Al is preferably 99.99% by mass or more, with the remainder being composed of inevitable impurities. The purity of Si, Ni, Pd, and Pt used as alloying elements is preferably 99.9% by mass or more, with the remainder being composed of inevitable impurities. The Al alloy used for the bonding wire can be produced by loading the Al raw material and the raw material of the alloying elements into a graphite or alumina crucible processed to obtain a cylindrical ingot, and melting it using an electric furnace or a high-frequency heating furnace. The diameter of the cylindrical ingot is preferably Φ6 mm or more and less than 8 mm, taking into consideration the workability in the subsequent processing steps. The atmosphere in the furnace during melting is preferably an inert atmosphere or a 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 700 ° C or more and less than 1050 ° C to prevent the incorporation of impurity elements from the crucible into the molten metal while ensuring the fluidity of the molten metal. The cooling method after melting can be water cooling, furnace cooling, air cooling, or the like.

[0055] The cylindrical ingot obtained by melting is subjected to homogenization treatment, and then wire drawing using a die and intermediate heat treatment are repeated to produce wire of the desired diameter. The wire after wire drawing can be used as Al alloy bonding wire by performing final heat treatment in an electric furnace.

[0056] In order to control the average diameter of the Si phase in the L cross section to the range of 0.8 μm to 5.5 μm, it is effective to control the manufacturing conditions such as the homogenization treatment conditions, wire drawing conditions, intermediate heat treatment conditions, and final heat treatment conditions. During the wire drawing process, it is effective to use a lubricant to ensure lubrication at the contact interface between the wire and the die. Below, an example of the manufacturing conditions for controlling the average diameter of the Si phase in the L cross section to the range of 0.8 μm to 5.5 μm is shown.

[0057] It is effective to set the temperature range of homogenization to 500°C or higher and lower than 560°C, and the time to 3 hours or higher and lower than 5 hours. This homogenization treatment can reduce the variation in the concentration of Si contained in the α phase that crystallizes during the solidification process, and by growing fine Si phases to soften the wire, it is possible to control the deformation behavior of the Si phase during the subsequent wiredrawing process. The diameter of the Si phase can then be controlled by repeating wiredrawing and intermediate heat treatment. When wiredrawing is performed, the Si phase deforms in the direction of the central axis of the wire, and some of the Si phase breaks and becomes fine. On the other hand, when intermediate heat treatment is performed, the Si phase grows. Therefore, in order to control the Si phase to the desired diameter, it is important to optimize the wiredrawing conditions, the temperature and time of intermediate heat treatment, the number of times intermediate heat treatment is performed, and the wire diameter. Regarding wiredrawing conditions, it is effective to set the wire area reduction rate per die used during wiredrawing to a range of 10.5% or higher and lower than 12.5%. Here, if the wire area reduction rate per die is P1, P1 is expressed by the following formula.

[0058] P1 = {(R2 2 -R1 2 ) / R2 2}×100 In the formula, R2 represents the diameter (mm) of the wire before processing, and R1 represents the diameter (mm) of the wire after processing.

[0059] This allows the Si phase to be deformed almost uniformly throughout the wire. It is effective to set the temperature range of the intermediate heat treatment to 400°C or more and less than 440°C, and the time of the intermediate heat treatment to 1 hour or more and less than 2 hours. It is effective to perform the intermediate heat treatment twice, with the wire diameter for the first intermediate heat treatment being 2.6 to 3.0 times the final wire diameter, and the wire diameter for the second intermediate heat treatment being 1.6 to 2.0 times the final wire diameter. It is effective to set the temperature range of the final heat treatment to 250°C or more and less than 360°C, and the time of the final heat treatment being 20 hours or more and less than 24 hours. In addition, if the final heat treatment is performed without performing the intermediate heat treatment, it is not possible to simultaneously obtain the fracture elongation required for the Al alloy bonding wire and the diameter of the desired Si phase. Therefore, it is effective to set the conditions of the intermediate heat treatment to be focused on the control of the diameter of the Si phase, and the final heat treatment to be focused on the control of the fracture elongation, as described above. That is, by performing intermediate heat treatment under predetermined conditions and growing the Si phase in advance, it is possible to easily control the Si phase to a target diameter after the final heat treatment. This makes it easy to grow the Si phase and control it to a target diameter while recrystallizing the wire to ensure the breaking elongation required for the Al alloy bonding wire.

[0060] The intermediate and final heat treatments can be performed by heating in an electric furnace for a certain period of time. The atmosphere during the heat treatment is preferably an inert atmosphere or a reducing atmosphere to suppress excessive oxidation of Al and Si.

[0061] In order to control the average value of the Si phase ratio (a / b) in the L cross section of the wire to the range of 1.3 to 3.2, it is effective to control the wire feed speed during the wire drawing process according to the wire diameter to be drawn. Preferred examples of wire feed speed conditions for controlling the average value of the ratio (a / b) to the desired range are shown below.

[0062] The wiredrawing process from the ingot obtained by melting to the first intermediate heat treatment is called "wiredrawing process 1". The wiredrawing process from the first intermediate heat treatment to the second intermediate heat treatment is called "wiredrawing process 2". The wiredrawing process from the second intermediate heat treatment to the final wire diameter is called "wiredrawing process 3". It is effective to set the wire feed speed in wiredrawing process 1 to 15 m / min or more and less than 25 m / min, the wire feed speed in wiredrawing process 2 to 30 m / min or more and less than 55 m / min, and the wire feed speed in wiredrawing process 3 to 70 m / min or more and less than 90 m / min. This is thought to be because by setting the wire feed speed within a predetermined range, the stress applied in the central axis direction of the wire during wiredrawing can be controlled, and the average value of the Si phase ratio (a / b) in the L cross section of the wire can be controlled within the desired range.

[0063] In order to control the average diameter of the α phase in the L cross section of the wire to a range of 5 μm to 50 μm, it is effective to perform additional heat treatment before the final heat treatment at the final wire diameter. An example of an additional heat treatment method and its conditions for controlling the average diameter of the α phase in the L cross section to a range of 5 μm to 50 μm is shown below. For the additional heat treatment, a method of continuously sweeping the wire in a heated tubular furnace can be used. In addition, it is effective to set the temperature range of the additional heat treatment to 540 ° C or more and less than 560 ° C, and the time of the additional heat treatment to 1.5 seconds or more and less than 3.0 seconds. In order to suppress excessive oxidation of Al and Si during the heat treatment, it is preferable to reflux an inert gas in the tubular furnace. This is thought to be because, by performing the additional heat treatment before the final heat treatment under the above conditions of a higher temperature and shorter time than the final heat treatment, the growth of the Si phase can be suppressed while the α phase is recrystallized to control the diameter of the α phase to the desired range.

[0064] Crystal orientation of the Si phase in the L section of the wire <110> In order to control the orientation ratio of the Si phase in the L cross section, it is effective to control the reduction angle of the die (hereinafter, also referred to as the "die angle"). <110> In order to control the orientation ratio of the Si phase in the range of 30 to 80%, it is effective to set the die angle to between 14° and 18°. This is thought to be because the contact area between the wire and the die changes when the wire enters the die, changing the compressive stress applied to the wire surface, allowing the crystal orientation of the Si phase to be controlled in the desired range.

[0065] [Semiconductor Devices] By using the wire of the present invention to connect electrodes on a semiconductor chip to external electrodes on a lead frame or substrate, a semiconductor device can be manufactured.

[0066] In one embodiment, a semiconductor device of the present invention includes a circuit board, a semiconductor chip, and a bonding wire for electrically connecting the circuit board and the semiconductor chip, the bonding wire being the wire of the present invention.

[0067] In the semiconductor device of the present invention, the circuit board and the semiconductor chip are not particularly limited, and a known circuit board and a semiconductor chip 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, the semiconductor device may be configured to include a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor device described in JP 2020-150116 A.

[0068] Examples of the semiconductor device include various semiconductor devices used in electrical products (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. EXAMPLES

[0069] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0070] (sample) The method of preparing the samples 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, Ni, Pd, and Pt had a purity of 99.99% by mass or more, with the remainder consisting of inevitable impurities. The Al alloy used for the bonding wire was produced by loading the Al raw material and the raw materials of the alloying elements 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. The cooling method after melting was furnace cooling.

[0071] A cylindrical ingot of Φ6mm was obtained by melting, and the ingot was subjected to homogenization treatment, followed by wire drawing using a die and intermediate heat treatment to produce a wire of Φ300μm. The temperature range of the homogenization treatment was 500°C or higher and lower than 560°C, and the time was 3 hours or higher and lower than 5 hours. A commercially available lubricant was used during wire drawing, and the wire area reduction rate per die during wire drawing was 10.5% or higher and lower than 12.5%. The temperature range of the intermediate heat treatment was 400°C or higher and lower than 440°C, and the time of the intermediate heat treatment was 1 hour or higher and lower than 2 hours. The number of intermediate heat treatments was two, and the wire diameter for the first intermediate heat treatment was 2.6 to 3.0 times the final wire diameter, and the wire diameter for the second intermediate heat treatment was 1.6 to 2.0 times the final wire diameter. The temperature range of the final heat treatment was 250°C or higher and lower than 360°C, and the time of the final heat treatment was 20 hours or higher and lower than 24 hours.

[0072] In some examples, the wire feed speed in wire drawing process 1 was 15 m / min or more and less than 25 m / min, the wire feed speed in wire drawing process 2 was 30 m / min or more and less than 55 m / min, and the wire feed speed in wire drawing process 3 was 70 m / min or more and less than 90 m / min. In some examples, additional heat treatment was performed before the final heat treatment at the final wire diameter, and the additional heat treatment conditions were a temperature range of 540°C or more and less than 560°C, and a time period of 1.5 seconds or more and less than 3.0 seconds. In some examples, wire drawing was performed using a die with a die angle of 14° or more and less than 18°.

[0073] (Method of measuring element content) The concentration analysis of elements contained in the bonding wire 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.

[0074] (Method of measuring the average diameter and shape of the Si phase) The L-section of the Al alloy bonding wire was used as the inspection surface, and the average diameter and shape of the Si phase were measured. In the present invention, the wire central axis and the cross section in the wire central axis direction including the wire central axis (L-section) are as shown in FIG. 1. FE-SEM and EDS were used for the measurement, and the average diameter of the Si phase, the length of the Si phase in the wire central axis direction (a), and the length in the direction perpendicular to the wire central axis (b) were calculated using the above-mentioned procedure. The measurement area was determined to be 200 μm in the wire central axis direction, and the entire wire was included in the direction perpendicular to the wire central axis. When processing the cross section to expose the L-section of the Al alloy bonding wire, it may be shifted from the wire central axis. In this case, if the length of the L-section in the direction perpendicular to the wire central axis is 90% or more of the wire diameter, it can be considered as a cross section including the wire central axis. This is because if the length of the L-section in the perpendicular direction is 90% or more, the effect of the shift from the wire central axis on the measurement results of the average diameter of the Si phase and the shape of the Si phase is negligibly small.

[0075] (Crystal orientation of Si phase <110> (Method of measuring the orientation ratio of The L-section of the Al alloy bonding wire is used as the inspection surface, and the crystal orientation of the Si phase in the wire central axis direction is the crystal orientation that has an angle difference of 15° or less with respect to the wire central axis direction. <110> The orientation ratio of the crystal was measured. <110> To measure the orientation ratio, we used a method that combines information on the Si concentration obtained by SEM-EDS and information on the crystal orientation obtained by EBSD. In detail, we simultaneously measured the Al and Si concentrations using EDS and analyzed the crystal orientation using EBSD. Next, for the areas identified as Si phases from the EDS measurement results, we used the analysis software that came with the device to analyze the crystal orientation. <110> The orientation ratio of the Si phase was calculated. Three measurement areas were randomly selected at intervals of 1 m or more along the central axis of the wire, and the crystal orientations of the Si phase obtained from the three measurement areas were <110> The arithmetic mean value of the orientation ratio of the Si phase of the measurement sample was calculated. <110> The measurement area was determined to be 200 μm in the direction of the central axis of the wire, and the entire wire was included in the direction perpendicular to the central axis of the wire.

[0076] (Method for measuring the average diameter of the α phase) The L-section of the Al alloy bonding wire was used as the inspection surface, and the concentration of Al and Si was measured using EDS, and the crystal orientation was analyzed using EBSD at the same time. Next, for the areas identified as α-phase from the EDS measurement results, the analysis software attached to the device was used to determine that the area was a grain boundary if the orientation difference between the measurement points was 15° or more, and the circle equivalent diameter was calculated. The arithmetic mean value of the circle equivalent diameters of each α-phase was taken as the average diameter of the α-phase. The measurement area was 200 μm in the direction of the wire central axis, and the entire wire was included in the direction perpendicular to the wire central axis.

[0077] (Evaluation method for Al alloy bonding wire) The evaluation method of the Al alloy bonding wire is explained below. The wire diameter of the Al alloy bonding wire used for the evaluation was Φ300μm. 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, which was deposited to a thickness of 5μm. The substrate used was an Al alloy with a Ni film deposited to a thickness of 15μm. A commercially available wire bonder (manufactured by Ultrasonic Industries Co., Ltd.) was used to bond the Al alloy bonding wire.

[0078] (Method of 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 to repeatedly raise and lower the temperature. The temperature of the low-temperature chamber was -40°C, and that of the high-temperature chamber was 175°C. The test started with the sample chamber in the high-temperature chamber, and the test was started when the sample chamber moved to the low-temperature chamber and returned to the high-temperature chamber, which constituted one cycle. The time the sample chamber stayed in the low-temperature chamber and the high-temperature chamber was 20 minutes each. The sample 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 Al alloy bonding wires. After the start of the test, the sample was taken out every 100 cycles and a shear test was performed on the first joint. The arithmetic average value of the shear strength of the first joint at five randomly selected locations was used as the value of the shear strength of the first joint used to evaluate the temperature cycle reliability. 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 joint life. If the joint life was less than 500 cycles, it was judged to have practical problems and was rated "0", if it was between 500 and 750 cycles it was judged to have no practical problems and was rated "1", if it was between 750 and 1000 cycles it was judged to be excellent and was rated "2", and if it was 1000 cycles or more it was judged to be particularly excellent and was rated "3". "0" is a failure, while "1", "2", and "3" are passes. The evaluation results are shown in the "Temperature cycle reliability" column in the table.

[0079] (Method of evaluating reliability of high-speed temperature cycles) A commercially available high-speed thermal shock tester was used to evaluate the high-speed temperature cycle test. The samples used in the high-speed temperature cycle test were the same as those used to evaluate the temperature cycle reliability. The samples placed in the sample chamber of the high-speed thermal shock tester were repeatedly subjected to thermal loads, with heating and cooling being one cycle. The minimum temperature was -50°C and the maximum temperature was 175°C. The heating time, including the time to heat up, was 20 seconds, and the cooling time, including the time to cool down, was 40 seconds. After the start of the test, the samples were taken out every 500 cycles and a shear test was performed on the 1st joint. The arithmetic average value of the shear strength of the 1st joints at five randomly selected locations was used as the value of the shear strength of the 1st joints used to evaluate the temperature cycle reliability. 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 joint life. If the joint life was less than 4000 cycles, it was judged to have practical problems and was given a rating of "0", if the joint life was between 4000 and 6000 cycles it was judged to have no practical problems and was given a rating of "1", if the joint life was between 6000 and 8000 cycles it was judged to be excellent and was given a rating of "2", and if the joint life was 8000 cycles or more it was judged to be particularly excellent and was given a rating of "3". "0" is a failure, while "1", "2", and "3" are passes. The evaluation results are shown in the "High-speed temperature cycle reliability" column in the table.

[0080] (Method of evaluating 1st zygosity) The evaluation method of the 1st bondability is explained below. The 1st bondability was evaluated by a shear strength test. The 1st bond was performed at 10 places under general bonding conditions, and the shear strength of the 1st bond was measured. A commercially available micro shear strength tester was used to measure the shear strength. The shear speed 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 wire was bonded with a jig. If there was even one place among the 10 1st bonded places where the shear strength was less than 800 gf, it was judged to be unsatisfactory and rated as "0". If the shear strength of all 10 places was 800 gf or more but less than 1100 gf, it was judged to be practically acceptable and rated as "1". Furthermore, if there was no place among the 10 places where the shear strength was less than 800 gf and there was a place where the shear strength was 1100 gf or more, it was judged to be excellent and rated as "2". Furthermore, if the electrodes on the semiconductor chip were removed with an alkali or similar after the shear strength test and the semiconductor chip was observed under an optical microscope and cracks were found in the semiconductor chip, it was determined that there was a problem in practical use and was rated "0" even if the shear strength of the 1st bond was 800gf or more. "0" is a failure, while "1" and "2" are passes. The evaluation results are shown in the "1st bondability" column in the table.

[0081] (Method for evaluating the stability of the bond strength of the 2nd bond) Shear strength tests were conducted on 50 randomly selected second joints, and the joint strength was obtained and the population standard deviation (σ) was calculated. If σ was 80gf or more, it was judged to be problematic for practical use and rated "0", if σ was between 40gf and 80gf it was judged to be good and rated "1", and if σ was less than 40gf it was judged to be excellent and rated "2". "0" is a failure, while "1" and "2" are passes. The evaluation results are shown in the "Stability of joint strength at second joint" column in the table.

[0082] (Method of evaluating loop straightness) The evaluation method for loop straightness is explained below. The loop formation conditions were a loop length of 35.0 mm and a loop height of 8 mm. The distance between the wire bonds was X, and the length of the line passing through the center axis of the wire when observing the board from directly above with an optical microscope was Y. If the arithmetic mean value of Y divided by X (i.e., Y / X) for the 10 bonded wires was 1.04≦Y / X, it was judged as defective and rated as "0", if it was 1.02≦Y / X<1.04 it was judged as good and rated as "1", and if Y / X<1.02 it was judged as excellent and rated as "2". "0" was a failure, and "1" and "2" were passed. The evaluation results are shown in the "Loop Straightness" column in the table.

[0083] (Method of evaluating corrosion resistance in high temperature and high humidity environments) Ten Al alloy bonding wires were bonded under general bonding conditions, sealed with epoxy resin, and then left in a high-temperature, high-humidity furnace. The test conditions for the high-temperature, high-humidity test were a temperature of 130°C, a relative humidity of 85%, and the atmosphere in the high-temperature, high-humidity furnace was air. For the samples after the high-temperature, high-humidity test, the cross section of the wire loop part in the wire central axis direction including the wire central axis was exposed by mechanical polishing, and the Al alloy bonding wire was checked for corrosion every 500 hours. FE-SEM was used to check for corrosion. The observation field was 99% or more of the wire diameter, and the length in the wire central axis direction was 1mm or more. The area to check for corrosion was the entire observation field. After 2500 hours, the surfaces of the 10 wires were observed at a magnification of 200 times. If corrosion was found at a position 15 μm from the wire surface toward the wire central axis, it was judged to be problematic in practical use and rated as "0". If corrosion was not found at a position 15 μm from the wire surface toward the wire central axis for all 10 wires, it was judged to be problematic in practical use and rated as "1". Furthermore, if no corrosion was observed within 15 μm from the wire surface toward the central axis of the wire on any of the 10 wires after 3,500 hours had passed, the wire was deemed to be excellent and rated as "2." Even if the corrosion of the wire progressed in the circumferential direction of the wire, it was deemed to be satisfactory for practical use as long as no corrosion was observed within 15 μm or more from the wire surface toward the central axis of the wire. "0" is a failure, while "1" and "2" are passes. The evaluation results are shown in the "Corrosion resistance in high temperature and high humidity environments" column in the table.

[0084] The evaluation results of the examples and comparative examples are shown in Tables 1 to 5.

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3]

[0088] [Table 4]

[0089] [Table 5]

[0090] It was confirmed that all of the bonding wires of Examples 1 to 80 contained 3.0 mass% or more and 10.0 mass% or less of Si, and the average diameter of the Si phase in the L cross section was 0.8 μm or more and 5.5 μm or less, and exhibited excellent temperature cycle reliability and good 1st bondability. In addition, it was confirmed that the bonding wires of Examples 2, 3, 5-8, 10, 11, 13-22, 24, 25, 27-30, 32-38, 40-42, 44, 46, 48, 50, 51, 54, 55, 58-60, 62-64, 66-72, 74-76, and 78-80, in which the average ratio (a / b) of the length (a) of the Si phase in the L cross section along the wire's central axis to the length (b) in the direction perpendicular to the wire's central axis is 1.3 or more and 3.2 or less, exhibit better results in terms of high-speed temperature cycle reliability. Also, it was confirmed that the bonding wires of Examples 9 to 22, 31 to 48, 57 to 64, and 73 to 80, in which the average diameter of the α phase in the L cross section was 5 μm or more and 50 μm or less, exhibited better results in terms of bonding strength stability of the 2nd bonded portion. The crystal orientation of the Si phase in the L cross section was measured. <110> It was confirmed that the bonding wires of Examples 35 to 48, 61 to 64, and 77 to 80, in which the orientation ratio was 30% or more and 80% or less, exhibited better results in terms of loop straightness. Furthermore, it was confirmed that the bonding wires of Examples 17 to 22 and 43 to 48, which contain at least one of Ni, Pd, and Pt in a total amount of 3 mass ppm to 150 mass ppm, exhibit better corrosion resistance in a high-temperature, high-humidity environment. On the other hand, it was confirmed that the bonding wires of Comparative Examples 1 to 6 had at least one of the Si concentration and the average diameter of the Si phase in the L cross section outside the range of the present invention, and either the temperature cycle reliability or the 1st bondability was not sufficient.

Claims

1. An Al alloy bonding wire for semiconductor devices, containing 3.0% by mass or more and 10.0% by mass or less of Si, wherein the average diameter of the Si phase in the cross section (L section) in the direction of the wire central axis including the wire central axis of the Al alloy bonding wire for semiconductor devices is 0.8 μm or more and 5.5 μm or less.

2. The Al alloy bonding wire for semiconductor device according to claim 1, wherein the average value of the ratio (a / b) of the length of the Si phase in the wire central axis direction (a) to the length in the direction perpendicular to the wire central axis (b) in the L cross section is 1.3 or more and 3.2 or less.

3. The Al alloy bonding wire for semiconductor device according to claim 1, wherein the average diameter of the α phase in the L cross-section is 5 μm or more and 50 μm or less.

4. The Al alloy bonding wire for semiconductor device according to claim 1, wherein, as a result of measuring the crystal orientation of the Si phase in the L cross section, the ratio of crystal orientations <110>, where the angular difference with respect to the wire central axis direction is 15° or less, is 30% or more and 80% or less.

5. The Al alloy bonding wire for semiconductor devices according to claim 1, further containing one or more of Ni, Pd, and Pt in a total amount of 3 ppm by mass or more and 150 ppm by mass or less.

6. The Al alloy bonding wire for semiconductor device according to Claim 1, wherein the Al content is 90% by mass or more.

7. When the Si content is 3.0% by mass or more and 5.0% by mass or less, the Al content is 95% by mass or more, If the Si content is greater than 5.0% by mass and 7.0% by mass or less, the Al content is 93% by mass or more. If the Si content is greater than 7.0% by mass and 8.0% by mass or less, the Al content is 92% by mass or more. The Al alloy bonding wire for semiconductor devices according to claim 1, wherein the Al content is 90% by mass or more when the Si content is more than 8.0% by mass and 10.0% by mass or less.

8. A semiconductor device comprising an Al alloy bonding wire for semiconductor devices according to any one of claims 1 to 7.

Images