Al bonding wire for semiconductor devices

Abstract

The present invention provides an Al bonding wire for semiconductor devices, which makes it possible to stably provide satisfactory bonding strength at a 2nd bonding part. Provided is an Al bonding wire for semiconductor devices, which contains at least one element selected from Sc, Zr and Mg in a total amount of 0.01% by mass or more and less than 0.8% by mass, and has a property such that, when the crystal orientation of a cross-section that includes a wire axis of the bonding wire and is parallel to the direction of the wire axis is measured, the orientation ratio of <100> crystal orientation having an angle difference relative to the direction of the wire axis of 15 degrees or less is 30% to 90% inclusive.

Description

[Technical Field]

[0001] The present invention relates to an Al bonding wire for a semiconductor device. [Background technology]

[0002] In semiconductor devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or a substrate by bonding wires. In power semiconductor devices, bonding wires made mainly of aluminum (Al) are used, and for example, Patent Document 1 shows an example in which an Al bonding wire with a diameter of 300 μm is used in a power semiconductor module. Power semiconductor devices using Al bonding wires are often used in high-power equipment such as air conditioners and solar power generation systems, and in-vehicle semiconductor devices.

[0003] Wedge bonding is used as a bonding method for Al bonding wire, both for the first bonding with electrodes on a semiconductor chip and for the second bonding with electrodes on a lead frame or substrate. Wedge bonding is a solid-state diffusion bonding method in which ultrasonic waves and a load are applied to the bonding wire via a metal jig to break the surface oxide films on the bonding wire material and electrode material, exposing new surfaces. In cutting-edge power semiconductor devices, the number of bonding wires is increasing as the rated current increases. Since bonding defects, such as peeling of the bonding wire from the electrode during bonding, can lead to product defects and reduced manufacturing yields, it is necessary to achieve stable, high-strength bonding at each bond. To address this requirement, when using a material consisting solely of high-purity Al as the bonding wire, the softness of the bonding wire sometimes prevents sufficient destruction of the surface oxide films on the bonding wire and substrate material during the second bonding step, making it difficult to achieve stable, high-strength bonding.

[0004] Bonding wires made of Al with specific elements added have been proposed. Patent Document 2 discloses that Al bonding wires containing 800 weight ppm or less of one or more of nickel (Ni), silicon (Si), and phosphorus (P) in total exhibit good bonding strength. Patent Document 3 discloses a bonding wire in which mechanical strength is improved by adding 0.05 to 1 weight % of scandium (Sc) to Al to utilize precipitation strengthening. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-314038 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-152316 [Patent Document 3] Special Publication No. 2016-511529 Summary of the Invention [Problem to be solved by the invention]

[0006] Al bonding wire used in power semiconductor devices is required to have good electrical conductivity to allow current to flow efficiently, high long-term reliability at the joint to withstand long-term use, and good bondability at the first joint, while also providing stable, good bond strength at the second joint.

[0007] In the second bonding step, Cu substrates, Al substrates, and Al alloy substrates with a Ni film formed on their surfaces are used as the substrates to be bonded. Among these substrates, Al alloy substrates with a Ni film formed on their surfaces are particularly popular. Substrates with an Al alloy substrate with a Ni film formed on its surface have a strong Ni oxide film formed on the Ni surface. When bonding such substrates with a bonding wire made solely of high-purity Al, sufficient bonding strength cannot be obtained at some joints, resulting in bonding defects such as peeling of the Al bonding wire from the substrate during bonding. Therefore, there is a need for the development of an Al bonding wire that can stably provide good bonding strength to Al alloy substrates with a Ni film formed on their surfaces.

[0008] As mentioned above, there have been several reports of Al bonding wires that have been strengthened by adding other elements to Al, but it has been difficult to consistently obtain good bonding strength at the second bonding point simply by adding other elements.

[0009] An object of the present invention is to provide an Al bonding wire for a semiconductor device that stably provides good bonding strength at the second bonded portion. [Means for solving the problem]

[0010] As a result of intensive research into the above-mentioned problems, the inventors have found that a wire containing at least one of Sc, Zr, and Mg in a total amount of 0.01 mass % or more but less than 0.8 mass % and having an angle difference of 15 degrees or less with respect to the wire axis direction in a cross section parallel to the wire axis direction. <100> The inventors discovered that an Al bonding wire having a crystal orientation ratio within a specific range can solve the above-mentioned problems, and further research based on this finding led to the completion of the present invention.

[0011] That is, the present invention includes the following. [1] An Al bonding wire for semiconductor devices containing one or more of Sc, Zr, and Mg in total at 0.01 mass% or more but less than 0.8 mass%, wherein the crystal orientation of a cross section parallel to the wire axis direction including the wire axis of the bonding wire is measured, and the angular difference with respect to the wire axis direction is 15 degrees or less. <100> An Al bonding wire for semiconductor devices, having a crystal orientation ratio of 30% or more and 90% or less. [2] The Al bonding wire for a semiconductor device according to [1], further containing one or more of Pd and Pt in a total amount of 3 mass ppm or more and 500 mass ppm or less. [3] The Al bonding wire for a semiconductor device according to [1] or [2], further containing Ni in an amount of 3 ppm by mass or more and 100 ppm by mass or less. [4] The Al bonding wire for a semiconductor device according to any one of [1] to [3], further containing at least one of Fe and Si in a total amount of 3 mass ppm or more and 750 mass ppm or less. [5] The Al bonding wire for a semiconductor device according to any one of [1] to [4], wherein the Al content is 98 mass % or more. [6] The Al bonding wire for a semiconductor device according to any one of [1] to [5], wherein the remainder consists of Al and inevitable impurities. [7] A semiconductor device comprising the Al bonding wire for a semiconductor device according to any one of [1] to [6]. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an Al bonding wire for a semiconductor device that stably provides good bonding strength at the second bonded portion. [Brief explanation of the drawings]

[0013] [Figure 1] Figure 1 shows the Al bonding wire. <100> FIG. 2 is a schematic diagram for explaining a measurement target surface (inspection surface) when measuring the orientation ratio of crystal orientations. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below with reference to preferred embodiments thereof. However, the present invention is not limited to the following embodiments and examples, and can be implemented with any modifications within the scope of the claims of the present invention and their equivalents.

[0015] [Al bonding wire for semiconductor devices] The Al bonding wire for semiconductor device of the present invention is an Al bonding wire for semiconductor device containing one or more of Sc, Zr, and Mg in total at 0.01 mass % or more but less than 0.8 mass %, and when the crystal orientation of a cross section parallel to the wire axis direction including the wire axis of the bonding wire is measured, the angular difference with respect to the wire axis direction is 15 degrees or less. <100> It is characterized in that the orientation ratio of the crystal orientation is 30% or more and 90% or less.

[0016] As mentioned above, when bonding wire made only of high-purity Al to a substrate with a strong oxide film formed on the surface, such as a substrate with Ni formed on the surface of an Al alloy, in the second bonding step, sufficient bonding strength cannot be obtained at some joints, resulting in variations in bonding strength and problems such as bonding defects such as the Al bonding wire peeling off from the substrate during bonding. Although several reports have been made on Al bonding wires that have been strengthened by adding other elements to Al, it has been difficult to solve these problems simply by adding other elements.

[0017] As a result of extensive research by the inventors to solve the above problems, it was found that a wire containing at least one of Sc, Zr, and Mg in a total amount of 0.01 mass % or more but less than 0.8 mass % and having an angle difference of 15 degrees or less with respect to the wire axis direction in a cross section parallel to the wire axis direction. <100> It has been discovered that an Al bonding wire with a crystal orientation ratio of 30% to 90% can improve the bonding strength at the second bond while reducing its variability. The Al bonding wire for semiconductor devices (hereinafter simply referred to as "bonding wire" or "wire") of the present invention significantly contributes to achieving the bonding strength and stability of the second bond required for cutting-edge power semiconductor devices.

[0018] The reason why the bonding wire of the present invention can stably provide good bonding strength at the second bonded portion is presumed to be as follows: By containing at least 0.01 mass % of one or more of Sc, Zr, and Mg in total, the wire becomes hard and its mechanical strength increases. Such improved mechanical strength makes it possible and accelerates the destruction of the oxide film on the wire surface and electrode surface in the second bonding step. On the other hand, in a cross section parallel to the wire axial direction of the bonding wire, the angle difference with respect to the wire axial direction is 15 degrees or less. <100> By controlling the orientation ratio of the crystal orientation to 30% or more, the influence of variations in mechanical strength in the longitudinal direction of the wire due to variations in crystal orientation tends to be alleviated. In the bonding wire of the present invention, the effect of improving the mechanical strength and the effect of alleviating the influence of variations in mechanical strength in the longitudinal direction of the wire can act synergistically, so it is presumed that good bonding strength can be stably achieved at the second bonded portion.

[0019] From the viewpoint of sufficiently destroying the oxide film on the wire surface and the electrode surface in the second bonding step and obtaining good bonding strength, the total concentration of one or more of Sc, Zr, and Mg in the bonding wire of the present invention is 0.01 mass% or more, preferably 0.02 mass% or more, more preferably 0.04 mass% or more or 0.05 mass% or more, and even more preferably 0.06 mass% or more, 0.08 mass% or more, 0.1 mass% or more, 0.12 mass% or more, 0.14 mass% or more, or 0.15 mass% or more. On the other hand, if the hardness of the bonding wire is excessive, the amount of wire deformation during the second bonding under commonly used ultrasonic and load conditions becomes insufficient, making it difficult to obtain good bonding strength. From the viewpoint of obtaining good bonding strength when performing second bonding under general conditions, the total concentration of one or more of Sc, Zr, and Mg in the bonding wire of the present invention is less than 0.8 mass%, preferably 0.79 mass% or less, more preferably 0.78 mass% or less, 0.76 mass% or less, or 0.75 mass% or less, and even more preferably 0.7 mass% or less, 0.65 mass% or less, 0.6 mass% or less, 0.55 mass% or less, or 0.5 mass% or less.

[0020] An ICP (Inductively Coupled Plasma) optical emission spectrometer or an ICP mass spectrometer can be used to analyze the concentration of elements contained in bonding wire. If elements derived from atmospheric contaminants such as oxygen or carbon are adsorbed on the surface of the bonding wire, it is effective to clean the wire with acid or alkali before analysis.

[0021] From the perspective of reducing the influence of anisotropy in mechanical properties due to crystal orientation and reducing the variation in the amount of wire deformation during the second bonding to improve the stability of bonding strength, the crystal orientation of the cross section parallel to the wire axis direction including the wire axis of the bonding wire was measured and the angular difference with respect to the wire axis direction was 15 degrees or less. <100> The orientation ratio of the crystal orientation is 30% or more, preferably 40% or more, more preferably 50% or more, and even more preferably 55% or more or 60% or more. <100> It was found that if the orientation ratio of the crystal orientation is too high, the bonding strength at the second bonding portion tends to be insufficient. <100> The orientation ratio of the crystal orientation is 90% or less, preferably 88% or less, more preferably 86% or less, 85% or less, 84% or less, 82% or less, or 80% or less.

[0022] A method for measuring the crystal orientation of a cross section parallel to the wire axis direction and including the wire axis of a bonding wire in the present invention will be described. Electron backscattered diffraction (EBSD) can be used to measure the crystal orientation. The device used for the EBSD method is composed of a scanning electron microscope and a detector attached to it. The EBSD method is a technique in which the diffraction pattern of reflected electrons generated when a sample is irradiated with an electron beam is projected onto a detector, and the diffraction pattern is analyzed to determine the crystal orientation at each measurement point. Dedicated software (such as OIM analysis by TSL Solutions, Inc.) can be used to analyze data obtained by the EBSD method. The cross section including the wire axis and parallel to the wire axis direction (cross section parallel to the longitudinal direction of the bonding wire) is used as the inspection surface, and the orientation ratio of a specific crystal orientation can be calculated by using the analysis software provided with the device. In the present invention, the wire axis of the bonding wire and the cross section including the wire axis and parallel to the wire axis direction refer to the "( <100> This is as explained in the section "Measurement of the orientation ratio of crystal orientations" with reference to Figure 1.

[0023] In the present invention, <100> The orientation ratio of the crystal orientation is calculated by taking the measurement area as the population. <100> The orientation ratio is defined as the area ratio of the crystal orientation. In calculating the orientation ratio, the area of ​​only the crystal orientations that could be identified based on a certain reliability within the measurement area was calculated as the population. <100> The area ratio of the crystal orientation is <100> In the process of calculating the orientation ratio, areas where the crystal orientation could not be measured, or areas where the orientation analysis was unreliable even if it could be measured, were excluded from the calculation.

[0024] In the present invention, <100> The orientation ratio of the crystal orientation was determined as the arithmetic average of the orientation ratio values ​​obtained by measuring at five or more locations. When selecting the measurement area, it is preferable to ensure the objectivity of the measurement data by, for example, obtaining measurement samples from the bonding wire to be measured at intervals of 1 m or more in the wire axial direction. In addition, in the present invention, the measurement area for the crystal orientation using the EBSD method is set so that the length in the wire axial direction is 300 μm or more and less than 600 μm, and the length in the direction perpendicular to the wire axial direction is set so that the entire wire is included.

[0025] -Addition of Pd and Pt- The manufacturing process for bonding wire involves wire drawing. During this wire drawing process, scratches can occur on the surface of the bonding wire. Scratches on the bonding wire surface occur when part of the wire surface is scraped off due to frictional forces generated at the contact interface between the wire and the die as the wire passes through the die during the wire drawing process. Scratches on the surface of Al bonding wire not only impair the appearance of the product, but can also cause a decrease in wedge bondability. Therefore, when manufacturing Al bonding wire, there is a need to reduce scratches on the wire surface and improve surface quality.

[0026] The inventors have discovered a wire containing at least one of Sc, Zr, and Mg in a total amount of 0.01 mass % or more but less than 0.8 mass %, and in a cross section parallel to the wire axis direction, which includes the wire axis, the angle difference with respect to the wire axis direction is 15 degrees or less. <100> In the course of further investigation into Al bonding wire with a crystal orientation ratio of 30% to 90%, it was discovered that by further containing one or more of Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm, scratches on the wire surface can be reduced and the wire surface properties can be improved.

[0027] The reason why scratches on the wire surface can be reduced by adding a predetermined amount of Pd and Pt to the bonding wire of the present invention is presumed to be as follows: The effect of hardening the wire surface by including a predetermined amount of one or more of Sc, Zr, and Mg is synergistically enhanced by adding a total of 3 mass ppm to 500 mass ppm of one or more of Pd and Pt, and further, the hardness of the cross section parallel to the wire axial direction is improved. <100> It is thought that an orientation ratio of 30% to 90% in terms of crystal orientation reduces the variation in mechanical strength in the longitudinal direction of the wire, which in turn reduces the variation in frictional force at the interface between the wire and the die during wiredrawing.The reason why the wire surface becomes significantly hard when it contains one or more of Sc, Zr, and Mg together with one or more of Pd and Pt is not clear, but it is thought that Sc, Zr, and Mg form precipitate phases with Pd and Pt near the wire surface, which hardens the wire through precipitation strengthening.

[0028] In order to sufficiently harden the wire surface and improve the wire surface properties in combination with one or more of Sc, Zr, and Mg, the total concentration of one or more of Pd and Pt contained in the bonding wire of the present invention is preferably 3 ppm by mass or more, more preferably 5 ppm by mass or more, and even more preferably 10 ppm by mass or more, 12 ppm by mass or more, 14 ppm by mass or more, 15 ppm by mass or more, 16 ppm by mass or more, 18 ppm by mass or more, or 20 ppm by mass or more. On the other hand, if the content of Pd and Pt is excessive, the wire surface becomes excessively hardened, the frictional force at the interface between the die and the wire increases, and the wire surface properties cannot be sufficiently improved. Therefore, the total concentration of one or more of Pd and Pt contained in the bonding wire of the present invention is preferably 500 ppm by mass or less, more preferably 450 ppm by mass or less, and even more preferably 400 ppm by mass or less, 350 ppm by mass or less, 300 ppm by mass or less, 250 ppm by mass or less, or 200 ppm by mass or less.

[0029] -Ni- The bonding wire of the present invention may further contain Ni in an amount of 3 ppm by mass or more and 100 ppm by mass or less.

[0030] Furthermore, the present inventors have found that the inclusion of 3 ppm by mass or more and 100 ppm by mass or less of Ni can further improve the stability of the bond strength at the second bonded portion. This is thought to be due to the synergistic effect of the effect of hardening the wire by including a predetermined amount of one or more of Sc, Zr, and Mg, and the effect of reducing the variation in mechanical strength in the longitudinal direction of the wire by including 3 ppm by mass or more and less than 100 ppm by mass of Ni, which refines the crystal grains constituting the wire and increases the proportion of equiaxed crystal grains.

[0031] From the viewpoint of further improving the stability of the bonding strength at the second bonded portion, the Ni concentration contained in the bonding wire of the present invention is preferably 3 mass ppm or more, more preferably 5 mass ppm or more, even more preferably 10 mass ppm or more, 15 mass ppm or more, 20 mass ppm or more, or 25 mass ppm or more. The upper limit of the Ni concentration is preferably 100 mass ppm or less, more preferably 90 mass ppm or less, even more preferably 80 mass ppm or less, 70 mass ppm or less, or 60 mass ppm or less.

[0032] -Fe, Si- The bonding wire of the present invention may further contain one or more of Fe and Si in a total amount of 3 ppm by mass or more and 750 ppm by mass or less.

[0033] In particular, when a steel sheet contains a total of 3 to 500 ppm by mass of one or more of Pd and Pt, and further contains a total of 3 to 750 ppm by mass of one or more of Fe and Si, the wire surface properties can be further improved. This is thought to be due to the synergistic effect of the effect of the wire surface being significantly hardened when one or more of Sc, Zr, and Mg are contained together with one or more of Pd and Pt, and the effect of the crystal grains on the wire surface being refined by the inclusion of a total of 3 to 750 ppm by mass of one or more of Fe and Si.

[0034] From the viewpoint of further improving the wire surface properties, the total concentration of one or more of Fe and Si contained in the bonding wire of the present invention is preferably 3 ppm by mass or more, more preferably 5 ppm by mass or more, even more preferably 6 ppm by mass or more, 8 ppm by mass or more, 10 ppm by mass or more, 12 ppm by mass or more, 14 ppm by mass or more, or 15 ppm by mass or more. On the other hand, if the content of Fe and Si is excessively high, the wire surface becomes excessively hardened, the frictional force at the interface between the die and the wire increases, and the wire surface properties cannot be sufficiently improved. Therefore, the total concentration of one or more of Fe and Si contained in the bonding wire of the present invention is preferably 750 ppm by mass or less, more preferably 700 ppm by mass or less, even more preferably 600 ppm by mass or less, 500 ppm by mass or less, 400 ppm by mass or less, 300 ppm by mass or less, 250 ppm by mass or less, or 200 ppm by mass or less.

[0035] The remainder of the bonding wire of the present invention contains Al. As the aluminum raw material for manufacturing the bonding wire, Al with a purity of 4N (Al: 99.99% by mass or more) can be used. It is more preferable to use Al with a lower impurity content of 5N (Al: 99.999% by mass or more). The remainder of the bonding wire of the present invention may contain elements other than Al, as long as the effects of the present invention are not impaired. In the bonding wire of the present invention, the Al content is not particularly limited as long as the effects of the present invention are not impaired, but is preferably 95% by mass or more, 96% by mass or more, or 97% by mass or more, more preferably 98% by mass or more, 98.5% by mass or more, 98.6% by mass or more, 98.8% by mass or more, or 99% by mass or more. In a preferred embodiment, the remainder of the bonding wire of the present invention consists of Al and inevitable impurities.

[0036] In a preferred embodiment, the bonding 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, "a coating mainly composed of a metal other than Al" refers to a coating in which the content of a metal other than Al is 50 mass % or more.

[0037] The bonding wire of the present invention satisfies requirements such as good electrical conductivity, long-term reliability of the bond, and good bondability at the first bond, and can stably provide good bond strength at the second bond. Therefore, the bonding wire of the present invention can be suitably used as an Al bonding wire for semiconductor devices, particularly for power semiconductor devices.

[0038] The diameter of the bonding wire of the present invention is not particularly limited, and may be, for example, 50 to 600 μm.

[0039] (Bonding wire manufacturing method) An example of a method for manufacturing a bonding wire according to the present invention will be described. The Al and alloying elements used as raw materials preferably have a high purity. Al preferably has a purity of 99.99% by mass or higher, with the remainder consisting of inevitable impurities. The Sc, Zr, Mg, Pd, Pt, Ni, Fe, and Si used as alloying elements preferably have a purity of 99.9% by mass or higher, with the remainder consisting of inevitable impurities. The Al alloy used for bonding wire can be produced by loading the Al raw material and alloying element raw materials into a graphite or alumina crucible processed to obtain a cylindrical ingot and melting them using an electric furnace or high-frequency heating furnace. The diameter of the cylindrical ingot is preferably less than 8 mm in consideration of workability in subsequent processing steps. The atmosphere in the furnace during melting is preferably an inert or reducing atmosphere to prevent excessive oxidation of the Al and other elements that make up the wire. The maximum temperature of the molten metal during melting is preferably in the range of 700°C or higher but less than 1080°C to prevent impurities from being mixed into the molten metal from the crucible. The cooling method after melting can be water cooling, oil cooling, furnace cooling, or the like.

[0040] The cylindrical ingot obtained by melting is subjected to wire drawing using a die to produce wire of the desired diameter. During wire drawing, it is effective to use a lubricant to ensure lubrication at the contact interface between the wire and the die. The area reduction rate per die during wire drawing is preferably in the range of 10.5% or more and less than 12.5%. Here, if the area reduction rate per die is P1, P1 can be expressed by the following formula.

[0041] 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.

[0042] The wire feed speed during wire drawing is preferably 20 m / min or more and less than 300 m / min. The wire after wire drawing is preferably subjected to a final heat treatment so that the final breaking elongation is 12% or more and less than 25%. The final heat treatment can be performed by heating for a certain period of time in a batch furnace or by continuously sweeping the wire through a tubular furnace. The atmosphere during the final heat treatment is preferably an inert atmosphere or a reducing atmosphere. The heat treatment temperature for the final heat treatment is preferably 570°C or more and less than 610°C, and the heat treatment time is preferably 0.3 seconds or more and less than 3.5 seconds.

[0043] When the crystal orientation of a cross section parallel to the wire axis direction including the wire axis of the bonding wire is measured, the angle difference with respect to the wire axis direction is 15 degrees or less. <100> In order to control the orientation ratio of the crystal orientation to 30% or more and 90% or less, it is effective to perform intermediate heat treatment at a wire diameter before reaching the final wire diameter (hereinafter referred to as "intermediate wire diameter"). <100> An example of an intermediate heat treatment method and its conditions for controlling the orientation ratio of the crystal orientation to a range of 30% to 90% is shown below.

[0044] The intermediate heat treatment can be performed by continuously sweeping the wire. When using this method, it is effective to perform the intermediate heat treatment multiple times at a temperature range of 550°C or higher and lower than 600°C at a wire diameter before reaching the final wire diameter. It is effective to perform the intermediate heat treatment once at wire diameters 1.2 to 2.0 times, 2.2 to 3.0 times, and 3.5 to 5.5 times the final wire diameter. It is effective to set the heat treatment time during the intermediate heat treatment to 0.1 seconds or higher and lower than 3.2 seconds. The intermediate heat treatment atmosphere is preferably an inert atmosphere or a reducing atmosphere.

[0045] This method is described above. <100> The reason why it is effective to control the orientation ratio of the crystal orientation to 30% or more and 90% or less will be explained below. <100> Crystal grains with a crystal orientation are formed in the process of grain growth as recrystallization occurs during the intermediate heat treatment or final heat treatment process. Therefore, it is important to control the growth of crystal grains by performing the intermediate heat treatment process at a predetermined wire diameter. Here, the growth of crystal grains is driven by the strain energy accumulated in the material due to the wire drawing process, so it is necessary to perform the process at a predetermined wire diameter. In addition, the growth rate of crystal grains increases as the heat treatment temperature increases, so it is important to control the heat treatment temperature and heat treatment time. In the present invention, the growth of crystal grains can be controlled by performing the intermediate heat treatment process at a predetermined wire diameter, and the wire manufactured through the final heat treatment process <100> It is believed that the orientation ratio of the crystal orientations can be controlled within the desired range.

[0046] [Semiconductor Devices] By using the bonding 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.

[0047] In one embodiment, the 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, and is characterized in that the bonding wire is the bonding wire of the present invention.

[0048] In the semiconductor device of the present invention, the circuit board and semiconductor chip are not particularly limited, and any known circuit board and semiconductor chip that can be used to construct a semiconductor device may be used. Alternatively, a lead frame may be used instead of the circuit board. For example, a semiconductor device may be configured including a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor device described in Japanese Patent Laid-Open No. 2002-246542.

[0049] Examples of semiconductor devices include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, aircraft, etc.), and among these, power semiconductor devices are preferred. [Example]

[0050] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0051] (sample) First, the method for producing the samples will be explained. 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 Sc, Zr, Mg, Pd, Pt, Ni, Fe, and Si had a purity of 99.9% 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 a graphite crucible and melting them using a high-frequency heating furnace. The atmosphere inside the furnace during melting was an Ar atmosphere, and the maximum temperature of the molten metal during melting was 750°C. The cooling method after melting was furnace cooling.

[0052] A cylindrical ingot with a diameter of 6 mm was obtained by melting, and the ingot was subjected to wire drawing and intermediate heat treatment using a die to produce a wire with a diameter of 300 μm. A commercially available lubricant was used during the wire drawing. The area reduction rate per die during the wire drawing was 11.0%. The intermediate heat treatment conditions were 580°C and 0.1 seconds or more but less than 3.2 seconds. The intermediate heat treatment was performed once for wire diameters 1.2 to 2.0 times, 2.2 to 3.0 times, and 3.5 to 5.5 times the final wire diameter. The wire feed speed during the wire drawing was 25 m / min. The wire after wire drawing was subjected to a final heat treatment so that the final elongation at break was 12% or more but less than 25%. The final heat treatment was performed while the wire was continuously swept. The atmosphere during the final heat treatment was Ar. The heat treatment temperature of the final heat treatment was 570°C or higher and lower than 610°C, and the heat treatment time was 0.3 seconds or higher and lower than 3.5 seconds. When producing wires of Comparative Examples 7, 9, and 11, the intermediate heat treatment temperature was 540°C and the heat treatment time was 0.2 seconds. The intermediate heat treatment was performed once for each of wire diameters of 450 μm, 750 μm, and 1500 μm. When producing wires of Comparative Examples 8, 10, and 12, the intermediate heat treatment temperature was 620°C and the heat treatment time was 3.0 seconds. The intermediate heat treatment was performed once for each of wire diameters of 450 μm, 750 μm, and 1500 μm.

[0053] (Measurement of elemental content) The content of elements in the bonding wire was measured 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.

[0054] ( <100> Measurement of crystal orientation ratio a cross section including the wire axis of the bonding wire and parallel to the wire axis direction is used as an inspection surface; <100> The orientation ratio of the crystal orientation was measured. In the present invention, the wire axis means axis A shown in FIG. 1, that is, the central axis of the bonding wire. Also, the cross section parallel to the wire axis direction means plane B shown in FIG. 1, that is, the cross section that includes the central axis of the bonding wire and is parallel to the wire axis direction (longitudinal direction of the wire). For the measurement, the EBSD method was used, and by utilizing the analysis software attached to the device, the above-mentioned procedure was performed. <100> The orientation ratio of the crystal orientation was calculated. Five measurement areas were selected at intervals of 1 m or more along the wire axis, and the obtained orientation ratio values ​​were arithmetically averaged to obtain the <100> The orientation ratio of the crystal orientation was taken as

[0055] (Bonding wire evaluation method) The evaluation method for the bonding wire will be explained below. The diameter of the bonding wire used for the evaluation was Φ300 μm. The semiconductor element was made of Si, and the electrodes on the semiconductor element were made of a 5 μm thick film of an alloy with a composition of Al-1%Si-0.5%Cu. The substrate was made of an Al alloy with a 15 μm thick Ni film. A commercially available wire bonder (manufactured by Ultrasonic Industries Co., Ltd.) was used to bond the bonding wire.

[0056] (Method for evaluating the bond strength at the second bonded part) A shear test was conducted on 50 randomly selected second joints to measure the joint strength. The arithmetic mean joint strength (F) and population standard deviation (σ) were calculated. F less than 900 gf was deemed unsuitable for practical use and scored 0, while F greater than or equal to 900 gf was deemed acceptable for practical use and scored 1. The evaluation results were recorded in the "Second Joint Joint Strength (F)" column. A score of 0 was considered a failure, and a score of 1 was considered a pass. A score of 80 gf or greater was deemed unsuitable for practical use and scored 0, a score of 60 gf or greater but less than 80 gf was deemed acceptable for practical use and scored 1, a score of 50 gf or greater but less than 60 gf was deemed good and scored 2, a score of 40 gf or greater but less than 50 gf was deemed excellent and scored 3, and a score of less than 40 gf was deemed particularly excellent and scored 4. The evaluation results were recorded in the "Stability of Joint Strength (σ) at the Second Joint" column. A score of 0 was considered a failure, and a score of 1 or greater was considered a pass.

[0057] (Method for evaluating wire surface properties) Ten samples, each approximately 1 cm long, were taken from the wire at 30 cm intervals along the wire's length. The wire surfaces of the taken samples were observed using an SEM at 100x magnification to check for the presence of scratches. If three or more of the ten samples observed had scratches on the wire surface, they were judged to have a problem in practical use and given a score of 0; if two samples had scratches on the wire surface, they were judged to have no problem in practical use and given a score of 1; if one sample had scratches on the wire surface, they were judged to have excellent properties and given a score of 2; and if no scratches were found on any of the samples, they were judged to be particularly excellent and given a score of 3. The evaluation results are recorded in the "Wire surface properties" column. A score of 0 is a failure, and a score of 1 or more is a pass.

[0058] The evaluation results of the examples and comparative examples are shown in Tables 1 and 2.

[0059] [Table 1]

[0060] [Table 2]

[0061] All of the wires of Examples 1 to 61 contain one or more of Sc, Zr, and Mg in a total amount of 0.01 mass % or more but less than 0.8 mass %, and in a cross section parallel to the wire axis direction including the wire axis, the angle difference with respect to the wire axis direction is 15 degrees or less. <100> It was confirmed that the orientation ratio of the crystal orientation was between 30% and 90%, and that the bonding strength and stability of the second bonding portion were good. In addition, it was confirmed that the wires of Examples 29 to 35, 37 to 41, 43 to 50, 52 to 54, and 56 to 61, which contained at least one of Pd and Pt in a total amount of 3 to 500 ppm by mass, could reduce scratches on the wire surface and improve the wire surface properties. It was also confirmed that the wires of Examples 50 to 55 containing Ni in an amount of 3 ppm by mass or more and 100 ppm by mass or less could further improve the stability of the bonding strength at the second bonded portion. Furthermore, it was confirmed that the wires of Examples 56 to 60, which contained at least one of Fe and Si in a total amount of 3 mass ppm to 750 mass ppm, could further reduce scratches on the wire surface and further improve the wire surface properties. On the other hand, the wires of Comparative Examples Nos. 1 to 12 have a total concentration of one or more of Sc, Zr, and Mg, or <100> It was confirmed that the orientation ratio of the crystal orientation was outside the range of the present invention, and that the bonding strength at the second bonding portion could not be stabilized.

Claims

1. An Al bonding wire for a semiconductor device containing one or more of Sc, Zr, and Mg in a total amount of 0.01 mass% or more but less than 0.8 mass%, wherein, when the crystal orientation of a cross section of the bonding wire parallel to the wire axis direction including the wire axis is measured, the orientation ratio of the <100> crystal orientation, which has an angular difference of 15 degrees or less with respect to the wire axis direction, is 30% or more but 90% or less.

2. The Al bonding wire for a semiconductor device according to claim 1, further containing one or more of Pd and Pt in a total amount of 3 ppm by mass or more and 500 ppm by mass or less.

3. The Al bonding wire for a semiconductor device according to claim 1 or 2, further containing Ni in an amount of 3 ppm by mass to 100 ppm by mass.

4. The Al bonding wire for a semiconductor device according to any one of claims 1 to 3, further containing one or more of Fe and Si in a total amount of 3 ppm by mass or more and 750 ppm by mass or less.

5. The Al bonding wire for a semiconductor device according to any one of claims 1 to 4, wherein the Al content is 98 mass% or more.

6. The Al bonding wire for a semiconductor device according to any one of claims 1 to 5, wherein the remainder consists of Al and inevitable impurities.

7. A semiconductor device comprising the Al bonding wire for semiconductor device according to any one of claims 1 to 6.

Images