Al bonding wire for semiconductor devices

Abstract

Provided is an Al bonding wire for semiconductor devices that offers good service life under high temperatures and high humidity in the high-temperature, high-humidity environments required for next-generation vehicle-mounted power devices. The present invention is an Al bonding wire for semiconductor devices including a total of 3-500 mass ppm of one or more of Pd and Pt, wherein a <100> crystal orientation with an angular difference of 15 degrees or less with respect to the wire axis direction constitutes a proportion of 30-90% of crystal orientations when the crystal orientation of a cross section that includes the wire axis of the bonding wire and is parallel to the wire axis direction is measured.

Description

[Technical Field]

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

[0002] In power devices installed in electric vehicles, hybrid vehicles, industrial equipment, etc., bonding wire is used as the wiring material responsible for the electrical connection between semiconductor elements and external substrates. Aluminum (Al) is the main material used for bonding wires used in power devices due to the requirements for excellent bonding with electrodes on semiconductor elements and external substrates, electrical conductivity, and low cost. Al bonding wire is required to have mechanical properties such as breaking strength and elongation, as well as thermal conductivity, depending on the intended use.

[0003] In power devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or substrate by bonding wires. Aluminum (Al) bonding wires are mainly used in power devices. In addition, in power devices using Al bonding wires, wedge bonding is used as the bonding method for both the first connection with the electrode on the semiconductor chip and the second connection with the electrode on the lead frame or substrate.

[0004] When an Al bonding wire is made of a material consisting solely of high-purity Al, corrosion of the Al bonding wire progresses in a short period of time in the high-temperature, high-humidity environment during device operation, impairing electrical connection, making it difficult to use in such environments. As a method for extending the lifespan in high-temperature, high-humidity environments (hereinafter also referred to as "high-temperature, high-humidity life"), Al bonding wires made of a material containing specific elements added to Al have been proposed. For example, Patent Document 1 describes a bonding wire containing Al with at least one of Pd and Pt in the range of 0.001 to 0.08%, and Patent Document 2 describes a bonding wire containing at least one of Rh and Pd in ​​the range of 10 to 200 mass ppm in total. It is disclosed that these bonding wires exhibit good high-temperature, high-humidity lifespans in an accelerated evaluation test called the Pressure Cooker Test (PCT) at a temperature of 121°C and a relative humidity of 100%.

[0005] Regarding the heat treatment conditions when manufacturing Al bonding wire, Patent Document 1 does not disclose the heat treatment conditions, but Patent Document 2 discloses that heat treatment is performed as necessary at a wire diameter before reaching the final wire diameter, and that heat treatment is performed for 1 hour at a temperature range of 200 to 300°C at the final wire diameter. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 61-032444 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-224283 Summary of the Invention [Problem to be solved by the invention]

[0007] Bonding wires used in power devices are required to satisfy basic properties such as wedge bondability, electrical conductivity, and heat resistance, as well as to achieve a good life under high temperature and high humidity conditions.

[0008] In recent years, the demand for high-temperature, high-humidity life has become increasingly stringent for Al bonding wires used in cutting-edge power devices. In particular, Al bonding wires used in next-generation automotive power devices are expected to require improved high-temperature, high-humidity life in an accelerated evaluation test called HAST (Highly Accelerated Stress Test) under accelerated evaluation conditions of 150°C and 85% RH (relative humidity), which are designed to operate in higher temperature environments. In response to the increasing demand for high-temperature, high-humidity life in the future, the inventors performed an unbiased HAST (hereinafter also referred to as uHAST) test under accelerated evaluation conditions of 150°C and 85% RH, in which no bias voltage is applied to the bonded portion. For example, when using Al bonding wires made of Al with a purity of 99.99% by mass or higher, the high-temperature, high-humidity life significantly decreased in less than 2000 hours, failing to meet the performance requirements for next-generation automotive power devices. This is because corrosion progresses throughout the bonding wire, and aluminum oxides and aluminum hydroxides, which have higher electrical resistance than aluminum, are produced as corrosion products, causing the electrical resistance of the bonding wire to increase. uHAST tests at a higher temperature than PCT, accelerating the rate at which the corrosion products mentioned above are formed. Since uHAST is required to have a high-temperature, high-humidity lifespan that is at least twice that of PCT, there is expected to be a demand for improved high-temperature, high-humidity lifespan in uHAST, taking into account operation in higher temperature environments.

[0009] It is difficult to improve the high-temperature, high-humidity life of uHAST solely through the effects of added elements. For example, even the Al bonding wires containing one or more precious metal elements disclosed in the aforementioned Patent Documents 1 and 2 do not provide a sufficient high-temperature, high-humidity life in uHAST, and the high-temperature, high-humidity life required for next-generation automotive power devices cannot be obtained.

[0010] An object of the present invention is to provide an Al bonding wire that exhibits a good high-temperature, high-humidity life in the high-temperature, high-humidity environment required for next-generation automotive power devices. [Means for solving the problem]

[0011] As a result of extensive research into the above-mentioned problems, the inventors have found that a wire containing at least one of Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm 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 is <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.

[0012] That is, the present invention includes the following. [1] An Al bonding wire for semiconductor devices containing one or more of Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm, and when the crystal orientation of a cross section of the bonding wire that includes the wire axis and is parallel to the wire axis direction is measured, the angle 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], having a tensile strength of 25 MPa or more and 85 MPa or less. [3] An Al bonding wire for a semiconductor device according to [1] or [2], further containing one or more of Si, Au, and Ag in a total amount of 3 mass ppm or more and 10,000 mass ppm 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 Mg in a total amount of 3 mass ppm or more and 700 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]

[0013] According to the present invention, it is possible to provide an Al bonding wire that exhibits a good high-temperature, high-humidity life in the high-temperature, high-humidity environment required for next-generation automotive power devices.

[0014] The present invention can further improve properties such as loop straightness when a long-span loop is formed and shear strength of the wedge joint. [Brief explanation of the drawings]

[0015] [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

[0016] 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.

[0017] [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 Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm, and when the crystal orientation of a cross section of the bonding wire that includes the wire axis and is parallel to the wire axis direction 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.

[0018] As mentioned above, Al bonding wires used in cutting-edge power devices, especially next-generation automotive power devices, are expected to require improved high-temperature, high-humidity life in an accelerated evaluation test called uHAST, which is conducted under accelerated evaluation conditions of 150°C and 85% RH, taking into account operation in higher-temperature environments. It has been difficult to improve the high-temperature, high-humidity life in uHAST solely through the effects of added elements. It has been confirmed that the life of Al bonding wires is more strongly affected by temperature in high-humidity environments. For example, accelerated evaluation tests in high-temperature environments include PCT, which is conducted at a temperature of 121°C and 100% RH. However, even Al bonding wires containing one or more precious metal elements that are said to exhibit good high-temperature, high-humidity life in PCT sometimes exhibited insufficient high-temperature, high-humidity life in uHAST, which is conducted in a higher-temperature environment than PCT.

[0019] In contrast, the present inventors have discovered a method for producing a wire having a cross section parallel to the wire axis direction, in which the cross section contains at least one of Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm, and the angle difference with respect to the wire axis direction is 15 degrees or less. <100> We found that Al bonding wire with a crystal orientation ratio of 30% to 90% exhibits good high-temperature, high-humidity life even in uHAST, and more specifically, that it can suppress wire corrosion and maintain good electrical connection even after 2000 hours in uHAST. <100> We confirmed that the synergistic effect of controlling the orientation ratio of the crystal orientation and adding Pd and Pt elements is more effective in suppressing corrosion at higher temperatures. For example, controlling the crystal orientation is effective in suppressing corrosion in environments above 140°C. Furthermore, the above-mentioned effect is sufficient not only in unbiased-HAST, in which no bias voltage is applied to the joint, but also in biased-HAST, in which a bias voltage is applied to the joint. Here, the wire axis refers to the axis passing through the center of the wire and parallel to the longitudinal direction of the wire. Thus, the Al bonding wire for semiconductor devices of the present invention (hereinafter simply referred to as "bonding wire" or "wire") can exhibit good high-temperature, high-humidity life even in the high-temperature, high-humidity environments required for cutting-edge power devices, particularly next-generation automotive power devices, and significantly contributes to improving the high-temperature, high-humidity resistance of power devices.

[0020] The reason why the bonding wire of the present invention can provide a good high-temperature, high-humidity life in uHAST is presumed to be as follows. First, it is thought that the cause of the impaired high-temperature, high-humidity life is corrosion caused by the formation of Al oxides and Al hydroxides on the bonding wire surface in a high-temperature, high-humidity environment. The formation of Al oxides and Al hydroxides is presumed to be due to a chemical reaction between Al and H2O. Although the detailed mechanism is unknown, the bonding wire of the present invention contains a predetermined amount of one or more of Pd and Pt, and further, the amount of Al in a cross section parallel to the wire axis direction is presumed to be 0.01%. <100> It is presumed that the specified ratio of crystal orientations worked synergistically to suppress corrosion in uHAST.

[0021] From the viewpoint of obtaining a good high-temperature, high-humidity life, the total concentration of one or more of Pd and Pt in the bonding wire of the present invention is 3 mass ppm or more, more preferably 5 mass ppm or more, and even more preferably 10 mass ppm or more, 12 mass ppm or more, 14 mass ppm or more, 15 mass ppm or more, 16 mass ppm or more, 18 mass ppm or more, or 20 mass ppm or more. Furthermore, when Pd and Pt are added in combination, a better high-temperature, high-humidity life is obtained than when Pd or Pt is added alone. On the other hand, if the Pd and Pt content is excessive, the ultrasonic and load conditions for obtaining a good bonding state tend to become narrower (hereinafter, also referred to as "deteriorated wedge bondability"). This is thought to be due to the fact that if the Pd and Pt content is excessively high, the wire becomes excessively hard, and the amount of wire deformation during wedge bonding is insufficient under commonly used ultrasonic and load conditions. The requirement for wedge bondability is difficult to satisfy, especially for next-generation automotive power devices. This is because the wedge bondability required for conventional power devices may not be sufficient to satisfy the basic properties, such as heat resistance, required for next-generation automotive power devices. Therefore, the total concentration of one or more of Pd and Pt is 500 ppm by mass or less, preferably less than 500 ppm by mass or 450 ppm by mass or less, and 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.

[0022] 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.

[0023] From the viewpoint of obtaining a good life under high temperature and high humidity, the crystal orientation of the cross section parallel to the wire axis direction including the wire axis of the bonding wire is measured, and the angle difference with respect to the wire axis direction is 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> If the orientation ratio of the crystal orientation is less than 30%, sufficient high-temperature, high-humidity life tends not to be obtained in uHAST. <100> It is thought that the reason for this is that the effect of reducing corrosion susceptibility due to the chemical reaction between Al and H2O was not sufficiently obtained when the orientation ratio of the crystal orientation was low. <100> It was found that if the orientation ratio of the crystal orientation is too high, the wedge bondability tends to decrease. <100> It is believed that if the orientation ratio of the crystal orientation is too high, the amount of wire deformation during wedge bonding will be insufficient. <100> The orientation ratio of the crystal orientation is 90% or less, preferably less than 90% or 88% or less, more preferably 86% or less, 85% or less, 84% or less, 82% or less, or 80% or less.

[0024] 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.

[0025] 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.

[0026] 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 obtain measurement samples from the bonding wire to be measured at intervals of 1 m or more along the wire axis direction and provide them for measurement, in order to ensure the objectivity of the measurement data. In the present invention, the measurement area for the crystal orientation using the EBSD method is set to a length along the wire axis of 300 μm or more and less than 600 μm, and a length perpendicular to the wire axis that covers the entire wire.

[0027] - Wire tensile strength - Bonding wires used in power devices are required to have good loop straightness when long-span loops are formed. For example, when using Al bonding wire made from Al with a purity of 99.99% or more by mass, the wire bends perpendicular to the line connecting the wire bond, i.e., the first bond with the electrode on the semiconductor chip, and the second bond with the electrode on the lead frame or substrate, when a long-span loop is formed, and the required performance cannot be met.

[0028] The inventors have discovered a method for producing a wire having a cross section parallel to the wire axis direction, the cross section including the wire axis being angled 15 degrees or less with respect to the wire axis direction. <100> In the course of further investigation into Al bonding wire with a crystal orientation ratio of 30% or more and 90% or less, it was discovered that the straightness of the loop when a long-span loop is formed can be improved by having the wire have a tensile strength of 25 MPa or more and 85 MPa or less.

[0029] The reason why the tensile strength of the bonding wire of the present invention is 25 MPa or more and 85 MPa or less improves the straightness of the loop when a long-span loop is formed is presumed to be as follows: That is, the effect of increasing the yield stress in the wire axial direction by containing a predetermined amount of one or more of Pd and Pt is enhanced in a cross section parallel to the wire axial direction. <100> It is presumed that this is because controlling the orientation ratio of the crystal orientation within a predetermined range has the effect of reducing the variation in mechanical strength in the wire axial direction, and controlling the tensile strength of the wire within a predetermined range has the effect of increasing the yield stress in the wire axial direction, and these effects act synergistically.

[0030] From the viewpoint of improving the straightness of a long-span loop when it is formed, the tensile strength of the bonding wire of the present invention is preferably 25 MPa or more, more preferably 26 MPa or more or 28 MPa or more, and even more preferably 30 MPa or more, 32 MPa or more, 34 MPa or more, 36 MPa or more, 38 MPa or more, or 40 MPa or more. If the tensile strength of the bonding wire of the present invention is less than 25 MPa, the straightness of the long-span loop when it is formed tends to be insufficient. This is thought to be due to the wire becoming excessively soft. On the other hand, if the tensile strength of the wire is too high, the wedge bondability tends to decrease. This is thought to be due to the wire becoming excessively hard, resulting in insufficient wire deformation during wedge bonding. Therefore, the tensile strength of the wire is preferably 85 MPa or less, more preferably 84 MPa or less, 82 MPa or less, 80 MPa or less, 78 MPa or less, 76 MPa or less, or 75 MPa or less.

[0031] The tensile strength of the bonding wire can be measured using a tensile test. A commercially available tensile tester (TENSILON RTF-1225 manufactured by A&D) can be used for the tensile test. Measurements can be performed with a gauge length of 100 mm, a pulling speed of 10 mm / min, and a load cell rated load of 250 N. In the present invention, tensile strength refers to the maximum stress in the tensile test.

[0032] -Si, Au, Ag- The bonding wire of the present invention may further contain one or more of Si, Au, and Ag in a total amount of 3 mass ppm to 10,000 mass ppm, thereby achieving even better high-temperature, high-humidity life.

[0033] Regarding the reason why the high temperature, high humidity life is further improved by further containing one or more of Si, Au, and Ag in a total amount of 3 mass ppm to 10,000 mass ppm in the bonding wire of the present invention, it is thought that the catalytic action is exerted by adding one or more of Si, Au, and Ag in the presence of Pd and Pt, i.e., by adding Pd, Pt, and one or more of Si, Au, and Ag in combination.

[0034] From the viewpoint of achieving even better high-temperature, high-humidity life, the total concentration of one or more of Si, Au, and Ag contained in the bonding wire of the present invention is preferably 3 mass ppm or more, more preferably 5 mass ppm or more, and even more preferably 6 mass ppm or more, 8 mass ppm or more, 10 mass ppm or more, 12 mass ppm or more, 14 mass ppm or more, or 15 mass ppm or more. In addition, the total concentration of one or more of Si, Au, and Ag is preferably 1000 mass ppm or less, more preferably less than 1000 mass ppm, 950 mass ppm or less, 900 mass ppm or less, 850 mass ppm or less, 800 mass ppm or less, 750 mass ppm or less, 700 mass ppm or less, 650 mass ppm or less, or 600 mass ppm or less. It has been found that by further containing one or more of Si, Au, and Ag in the preferred ranges described above, the bonding wire of the present invention can suppress corrosion of the wire and maintain good electrical connection even after 3000 hours in uHAST.

[0035] -Fe, Mg- The bonding wire of the present invention may further contain one or more of Fe and Mg in a total amount of 3 ppm by mass to 700 ppm by mass, which can further improve the shear strength of the wedge bonded portion.

[0036] In the bonding wire of the present invention, the reason why the shear strength of the wedge bond is improved by further containing a predetermined amount of one or more of Fe and Mg is thought to be because the yield stress in the axial direction of the wire is increased mainly by solid solution strengthening.

[0037] From the viewpoint of improving the shear strength of the wedge bond, the total concentration of one or more of Fe and Mg 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 6 mass ppm or more, 8 mass ppm or more, 10 mass ppm or more, 12 mass ppm or more, 14 mass ppm or more, or 15 mass ppm or more. In addition, the total concentration of one or more of Fe and Mg is preferably 700 mass ppm or less, more preferably less than 700 mass ppm, 650 mass ppm or less, 600 mass ppm or less, 550 mass ppm or less, 500 mass ppm or less, 450 mass ppm or less, or 400 mass ppm or less.

[0038] 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.

[0039] 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.

[0040] The bonding wire of the present invention satisfies basic properties such as wedge bondability, electrical conductivity, and heat resistance, and can provide a good high-temperature, high-humidity life in the high-temperature, high-humidity environment required for next-generation automotive power devices. Therefore, the bonding wire of the present invention can be suitably used as an Al bonding wire for semiconductor devices, particularly power semiconductor devices (especially for automotive power semiconductor devices).

[0041] The diameter of the bonding wire of the present invention is not particularly limited, and may be, for example, 50 to 600 μm.

[0042] (Bonding wire manufacturing method) The method for manufacturing the Al wiring material of the present invention is not particularly limited, and may be manufactured using known processing methods such as extrusion, swaging, wire drawing, and rolling. When the wire diameter becomes thin to a certain extent, it is preferable to perform wire drawing using a diamond die. Cold processing, in which wire drawing is performed at room temperature, requires a relatively simple configuration, such as a manufacturing device, and is excellent in workability. Furthermore, when the resistance during wire drawing is reduced to increase productivity, hot processing, in which the wire is heated and drawn, may be used.

[0043] Pure metals of Al and each additive element are weighed as starting materials so that the content of each additive element falls within a specific range, and then mixed and melted and solidified to produce an ingot. Alternatively, a master alloy containing a high concentration of the additive element may be used as the raw material for each additive element. The melting process for producing this ingot can be performed using a batch or continuous casting method. The diameter of the cylindrical ingot is preferably φ8 mm or less (e.g., φ3 mm to 8 mm) in consideration of workability in subsequent processing steps.

[0044] The obtained cylindrical ingot can be subjected to wire drawing or the like to produce a wire of a predetermined diameter. It is preferable to perform a refining heat treatment at a wire diameter before reaching the final wire diameter (hereinafter referred to as an "intermediate wire diameter") or at the final wire diameter. The refining heat treatment can remove processing strain and cause recrystallization. Conditions for the refining heat treatment include, for example, heating at a temperature range of 300°C to 600°C for 1 second to less than 600 seconds.

[0045] 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 carry out, for example, heat treatment at an intermediate wire diameter (hereinafter also referred to as "intermediate heat treatment").

[0046] 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 an intermediate wire diameter in a temperature range of 300°C to 550°C. It is effective to set the heat treatment time to 1 second or more and less than 600 seconds. It is effective to perform the intermediate heat treatment once at wire diameters 1.3 to 2.0 times and once at wire diameters 2.3 to 4.0 times the final wire diameter. The heat treatment atmosphere is preferably an inert atmosphere such as an Ar gas atmosphere to prevent oxidation.

[0047] 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 by recrystallization during the intermediate heat treatment or the heat treatment process at the final wire diameter. 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 important to perform the intermediate heat treatment at a predetermined wire diameter to control the growth of crystal grains. Furthermore, 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, heat treatment temperature, and heat treatment time, and the wire manufactured through the final heat treatment process has a high crystal grain growth rate. <100> It is believed that the orientation ratio of the crystal orientations can be controlled within the desired range.

[0048] [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.

[0049] 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.

[0050] 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.

[0051] Examples of the semiconductor device include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, aircraft, etc.), and in particular, power semiconductor devices, especially power semiconductor devices for automobiles, are preferred. [Example]

[0052] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0053] (sample) First, the manufacturing method of the samples will be described. The raw material Al used had a purity of 4N (99.99% by mass or more), with the remainder consisting of inevitable impurities. Pd, Pt, Si, Au, Ag, Fe, and Mg were used with 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 material to be alloyed into an alumina crucible with an inner diameter of 40 mm or more and less than 70 mm, and melting them using a high-frequency melting furnace. The atmosphere inside the furnace during melting was an Ar atmosphere, and the maximum temperature reached during melting was in the range of 1050°C or more and less than 1300°C. Note that a batch-type high-frequency melting furnace was used for the melting process to produce this ingot. Air cooling was used after melting. If organic matter or the like was attached to the surface of the melted ingot, it was polished, degreased, and pickled as necessary.

[0054] A cylindrical ingot with a diameter of 3 mm to 8 mm was obtained by melting, and the ingot was subjected to wire drawing using a die to produce a wire with a diameter of 300 μm. A commercially available lubricant was used during the wire drawing to ensure lubrication at the contact interface between the wire and the die. The area reduction rate per die during the wire drawing was 10% to less than 15%. Here, the area reduction rate is the ratio, expressed as a percentage, of the cross-sectional area of ​​the wire reduced by the wire drawing to the cross-sectional area of ​​the wire before the wire drawing. The wire feed speed during the wire drawing was 10 m / min to less than 300 m / min. The intermediate heat treatment at the intermediate wire diameter and the final heat treatment at the final wire diameter were performed under the conditions described below.

[0055] The intermediate heat treatment was performed while continuously sweeping the wire. The atmosphere during the intermediate heat treatment was Ar gas. The heat treatment temperature was 300°C or higher and 550°C or lower, and the heat treatment time was 1 second or higher and less than 600 seconds. The intermediate heat treatment was performed once for wire diameters 1.3 to 2.0 times and 2.3 to 4.0 times the final wire diameter.

[0056] The wire after wire drawing was subjected to a final heat treatment so that the final tensile strength would be 25 MPa or more and 85 MPa or less, and the breaking elongation would be 15% or more and less than 25%. The final heat treatment was performed while continuously sweeping the wire. The atmosphere during the final heat treatment was an Ar gas atmosphere. The heat treatment temperature for the final heat treatment was 400°C or more and 600°C or less, and the heat treatment time was 1 second or more and less than 600 seconds.

[0057] In producing the wires of Comparative Examples 7 to 11, the intermediate heat treatment temperature was 250°C and the heat treatment time was 5 seconds. The intermediate heat treatment was performed once for each of wire diameters of 500 μm and 900 μm. The final heat treatment temperature was less than 400°C and the heat treatment time was less than 1 second. In producing the wire of Comparative Example 12, the intermediate heat treatment temperature was 350°C and the heat treatment time was 8 seconds. The intermediate heat treatment was performed once for each of wire diameters of 450 μm and 1100 μm. The final heat treatment temperature was 450°C and the heat treatment time was 4 seconds. In producing the wires of Examples 39 to 44, the intermediate heat treatment temperature was 570°C and the heat treatment time was 400 seconds. The intermediate heat treatment was performed once for each of wire diameters of 600 μm and 1000 μm. The final heat treatment temperature was 600°C or higher and the heat treatment time was 600 seconds or higher.

[0058] (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.

[0059] ( <100> Measurement of crystal orientation ratio a cross section including the wire axis of the bonding wire and parallel to the wire axis 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 Figure 1, i.e., the central axis of the bonding wire. Also, the cross section parallel to the wire axis direction means plane B shown in Figure 1, i.e., a cross section that includes the central axis of the bonding wire and is parallel to the wire axis direction (longitudinal direction of the wire). <100> The value of the orientation ratio of the crystal orientation was the arithmetic mean of the values ​​obtained in the five measurement areas. For the bonding wire to be measured, measurement samples were taken at intervals of 1 m or more along the wire axis direction and used for measurement. The measurement area was set so that the length in the wire axis direction was 300 μm or more and less than 600 μm, and the length in the direction perpendicular to the wire axis included the entire wire. The EBSD method was used to measure the crystal orientation. Dedicated software (such as OIM analysis by TSL Solutions Co., Ltd.) was used to analyze the data obtained by the EBSD method. The measurement results are shown in Table 1-1, Table 1-2, Table 1-3, Table 1-4 and Table 2-1. <100> The crystal orientation ratio is shown in the "Crystal orientation ratio" column.

[0060] (Measurement of tensile strength) The tensile strength of the bonding wire was measured by a tensile test. A commercially available tensile tester (TENSILON RTF-1225 manufactured by A&D) was used for the tensile test under the conditions of a gauge length of 100 mm, a tensile speed of 10 mm / min, and a load cell rated load of 250 N. The maximum stress in the tensile test was taken as the tensile strength. The arithmetic mean values ​​of the tensile strength of 10 bonding wires are shown in the "Tensile Strength" column of Tables 1-1, 1-2, 1-3, 1-4, and 2-1.

[0061] (Bonding wire evaluation method) Next, we will explain the evaluation method for the bonding wire. The diameter of the bonding wire used for the evaluation was φ300 μm. A Ni-plated Al substrate was used as the substrate. A commercially available wire bonder (REBO-7 manufactured by Ultrasonic Industries) was used to bond the bonding wire. The temperature during bonding was room temperature, and the atmosphere during bonding was air.

[0062] (Method for evaluating high temperature and humidity life) The high temperature, high humidity life evaluation method is explained below. The high temperature, high humidity life was evaluated using uHAST, an accelerated evaluation test under a high temperature, high humidity environment. The uHAST conditions were set at 150°C and 85% RH, which are higher than normal, with consideration given to operation in a higher temperature environment.

[0063] Five wires were wedge-bonded onto a substrate under typical Al wire bonding conditions. The resulting samples were then placed in a high-temperature, high-humidity furnace. The uHAST conditions were 150°C and 85% RH, with the atmosphere in the high-temperature, high-humidity furnace being air. After uHAST, the cross section of the wire loop, including the wire axis and parallel to the wire axis, was mechanically polished to reveal the presence of corrosion in the wire. A scanning electron microscope (SEM) was used to examine the presence or absence of corrosion. The observation field was 99% or more of the wire diameter and 1 mm or more in the axial direction. The presence or absence of corrosion was examined throughout the entire field of view. After 2000 hours, the entire cross section of each of the five wires was observed at 200x magnification. If even one wire showed corrosion of 10% or more in area, it was deemed unsuitable for practical use and rated "X." If all five wires showed corrosion of less than 10% in area, it was deemed acceptable for practical use and rated "O." Here, the area ratio is a value calculated by dividing the corroded area within the field of view of observation by the cross-sectional area of ​​the wire. Furthermore, if the area ratio of corrosion of all five wires was less than 10% after 3000 hours had passed, it was judged to be excellent and rated as "◎". The evaluation results are shown in the "High temperature and high humidity life" column in Tables 1-1, 1-2, 1-3, 1-4, and 2-1. × indicates failure, and ○ and ◎ indicate passing.

[0064] (Method for evaluating loop straightness when forming a long-span loop) This section explains the evaluation method for loop straightness when forming long-span loops. The loop formation conditions were set to stricter conditions than normal loop formation conditions, with a distance between wire bonds of 30.0 mm and a loop height of 6 mm, taking into account long-span loops. Let a be the distance between wire bonds, and b be the length of the line passing through the wire axis when observing the board from directly above with an optical microscope. For the ten bonded wires, if there was even one location where the value obtained by dividing b by a (i.e., b / a) was 1.02 ≦ b / a, the result was judged as defective and marked with an "X." If there was no location where 1.02 ≦ b / a, the result was judged as good and marked with an "O." The evaluation results are shown in the "Loop Straightness" column in Tables 1-1, 1-2, 1-3, 1-4, and 2-1. An "X" indicates a failure, and an "O" indicates a pass.

[0065] (Method for evaluating the shear strength of wedge joints) The shear strength of the wedge joints was evaluated using a commercially available micro-shear strength tester. Ten wedge joints were made under typical joining conditions and the shear strength of the joints was measured. The shear strength was measured using a shear rate of 200 μm / s and a shear tool height of 10 μm from the substrate. The shear strength was measured by fixing the wire-bonded substrate in a jig. If even one of the joints had a shear strength value of less than 9 N, the joint was deemed unsatisfactory and rated "×." If all ten joints had a shear strength of 9 N or greater but less than 14 N, the joint was deemed acceptable for practical use and rated "○." Furthermore, if all ten joints had a shear strength of 14 N or greater, the joint was deemed excellent and rated "◎." The evaluation results are shown in the "Shear strength of wedge joints" column in Tables 1-1, 1-2, 1-3, 1-4 and 2-1. × indicates failure, and ○ and ◎ indicate passing.

[0066] Composition of bonding wire according to the embodiment <100> The orientation ratio (%) of the crystal orientation, the tensile strength, and the evaluation results are summarized in Tables 1-1, 1-2, 1-3, and 1-4. The composition of the bonding wire according to the comparative example is shown in Table 2-1.

[0067] [Table 1-1]

[0068] [Table 1-2]

[0069] [Table 1-3]

[0070] [Table 1-4]

[0071] [Table 2-1]

[0072] All of the bonding wires of Examples 1 to 96 contain one or more of Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm, 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 crystal orientation ratio was between 30% and 90%, and that the material exhibited good high-temperature, high-humidity life in the high-temperature, high-humidity environments required for power devices. In addition, it was confirmed that the bonding wires of Examples 1 to 38 and 45 to 96, in which the tensile strength of the wire was 25 MPa or more and 85 MPa or less, had excellent loop straightness when a long-span loop was formed. Furthermore, it was confirmed that the bonding wires of Examples 45 to 64 and 74 to 96, which contain one or more of Si, Au, and Ag in a total amount of 3 mass ppm or more and 10,000 mass ppm or less, can achieve even better high-temperature, high-humidity life in the high-temperature, high-humidity environments required for power devices. Furthermore, it was confirmed that the bonding wires of Examples 74 to 89, which contained at least one of Fe and Mg in a total amount of 3 mass ppm to 700 mass ppm, had excellent shear strength in the wedge bonded portion. On the other hand, the bonding wires of Comparative Examples Nos. 1 to 12 have a total concentration of one or more of Pd and Pt, <100> It was confirmed that the orientation ratio of the crystal orientation was outside the range of the present invention, and that corrosion progressed in the high-temperature, high-humidity environment required for power devices, making it impossible to obtain a sufficient high-temperature, high-humidity life.

Claims

1. An Al bonding wire for a semiconductor device containing one or more of Pd and Pt in a total amount of 3 mass ppm to 500 mass ppm, wherein, when the crystal orientation of a cross section of the bonding wire that includes the wire axis and is parallel to the wire axis direction 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% to 90%.

2. The Al bonding wire for a semiconductor device according to claim 1, having a tensile strength of 25 MPa or more and 85 MPa or less.

3. The Al bonding wire for a semiconductor device according to claim 1 or 2, further containing one or more of Si, Au, and Ag in a total amount of 3 ppm by mass or more and 10,000 ppm by mass or less.

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 Mg in a total amount of 3 ppm by mass or more and 700 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.

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