Al wiring material

Abstract

Provided is a novel Al wiring material that exhibits good high-temperature reliability while suppressing an increase in strength at room temperature. The Al wiring material is characterized by containing at least one selected from the group consisting of Er, Yb, and Gd, wherein: when the total content of said at least one is x1 (mass%), 0.001≤x1≤0.6; and the remainder contains Al.

Description

Technical Field

[0001] The present invention relates to an Al wiring material. Furthermore, it relates to a semiconductor device including the Al wiring material.

Background Art

[0002] In linear materials used for electrical connection and / or mechanical connection in industrial equipment and electronic components, with the demand for the electrification of automobiles, the use of aluminum (Al) is increasing due to its lower weight and cost compared to conventional copper (Cu). For Al wires (circular) and Al bars (flat, elliptical) used in industrial equipment such as transport equipment and robots, mechanical properties such as breaking strength and elongation, as well as electrical conductivity and thermal conductivity, are required according to the usage purpose.

[0003] In a semiconductor device, the electrodes formed on a semiconductor chip are connected to the electrodes on a lead frame or a circuit board (also simply referred to as "substrate") by bonding wires or bonding ribbons. In a power semiconductor device, Al is mainly used as the material. For example, Patent Document 1 shows an example of using a 300 μmφ Al bonding wire in a power semiconductor module. In a power semiconductor device using an Al bonding wire or an Al bonding ribbon, as the bonding method, wedge bonding is used for both the first connection to the electrode on the semiconductor chip and the second connection to the electrode on the lead frame or the substrate.

[0004] The above-mentioned Al wires, Al bars, Al bonding wires, Al bonding ribbons, etc. are collectively referred to as Al wiring materials hereinafter.

[0005] Power semiconductor devices using aluminum (A) wiring are often used in high-power equipment such as air conditioners and solar power generation systems, as well as in automotive semiconductor devices. In these semiconductor devices, the connection points between the wiring and connected components are exposed to temperatures exceeding 120°C during device operation. Furthermore, rapid switching of high voltage creates a harsh environment with repeated temperature increases and decreases. When using a material consisting solely of high-purity aluminum as the wiring material, the wiring material tends to soften easily in the operating temperature environment, making it difficult to use in high-temperature environments.

[0006] Al wiring materials made from materials to which specific elements have been added have been proposed. For example, Patent Document 2 discloses an Al bonding wire in which mechanical strength is improved by adding 0.05 to 1% by weight of scandium (Sc) to Al and precipitation hardening, and Patent Document 3 discloses an Al bonding wire in which 0.15 to 0.5% by mass of Sc has been added to Al and forced into solid solution, and which is precipitation hardened by aging heat treatment after connection. Patent Document 4 discloses that an Al wiring material containing one or more of nickel (Ni), silicon (Si), and phosphorus (P) in a total amount of 800 ppm by mass or less exhibits good bonding strength and weather resistance. Patent Document 5 discloses an Al bonding wire containing 0.01 to 0.2 mass% iron (Fe) and 1 to 20 mass ppm Si, wherein the solid solution amount of Fe is 0.01 to 0.06 mass%, the amount of Fe precipitated is 7 times or less the solid solution amount, and the average crystal grain size is 6 to 12 μm, and it is stated that the wire exhibits good bonding reliability. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-314038 [Patent Document 2] Special Publication No. 2016-511529 [Patent Document 3] Japanese Patent Publication No. 2014-47417 [Patent Document 4] Japanese Patent Publication No. 2016-152316 [Patent Document 5] Japanese Patent Publication No. 2014-129578 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] With the increasing sophistication and expanding application range of industrial equipment and electronic components, the demands on aluminum (Al) wiring materials are becoming more stringent. Al wiring materials used in industrial equipment such as conveying equipment and robots are required to withstand high temperatures and repeated bending deformation. Recently, in automotive applications, the strength of the wires deteriorates during use in high-temperature environments, leading to deformation abnormalities and cracks, which can eventually result in wire breakage. Therefore, suppressing the decrease in strength of Al wiring materials in high-temperature environments and improving high-temperature reliability is a challenge. However, simply increasing the strength of the wiring material is insufficient to achieve sufficient high-temperature reliability, and there are concerns that this may also reduce workability and jointability during installation and use.

[0009] Furthermore, in Al wiring materials used in electronic components such as semiconductors, the expanding applications of power devices for automobiles require improved initial bonding performance and high-temperature reliability of the bonding area. There are two connections for Al wiring materials in semiconductors: a connection to electrodes on the semiconductor chip (hereinafter referred to as the "first connection") and a connection to external electrodes on the lead frame or substrate (hereinafter referred to as the "second connection"). In power devices, shock thermal stress occurs due to temperature changes during operation (hereinafter referred to as "thermal shock"), which can damage the first connection area, where the Al wiring material connects to the electrodes on the semiconductor chip. Specifically, cracks may occur at the interface of the connection area due to the difference in thermal expansion coefficients between the Al wiring material and the connected component (hereinafter referred to as "bond cracks"). Cracks may also occur in the loop rise portion near the connection area due to bending stress caused by the expansion and contraction of the Al wiring material itself (hereinafter referred to as "heel cracks"). Corrosion in the operating environment of the equipment causes these bond cracks and heel cracks to propagate, ultimately leading to delamination of the Al wiring connections and compromising the high-temperature reliability of the connections. In this regard, one method is to add other elements to the Al wiring to suppress grain coarsening and increase strength. However, with such a method, as the content of other elements in the Al wiring increases, breaks and scratches may occur during the manufacturing of the Al wiring, reducing yield, or the connected components may be damaged when connecting the Al wiring (hereinafter referred to as "chip damage").

[0010] Thus, aluminum wiring materials are required to suppress the increase in strength at room temperature, maintain and improve deformation and bonding workability, while also improving high-temperature reliability.

[0011] On the other hand, it is known that adding Sc to Al wiring material improves high-temperature reliability (Patent Documents 2 and 3). However, this technology is also affected by the increase in strength at room temperature, and because Sc is expensive, the material cost is high. Furthermore, in order to improve high-temperature reliability by utilizing Sc precipitation, it is necessary to control conditions such as supplemental heat treatment during manufacturing or after connection within a narrow range, which is an obstacle to practical application.

[0012] Regarding heat treatment during the manufacturing of wiring materials or supplemental heat treatment after connection, if performance improvements can be achieved through low-temperature or short-duration processing, it will be possible to improve the productivity of wiring materials, minimize thermal impact on connected components, and comprehensively satisfy a wide range of performance requirements.

[0013] The present invention aims to provide a novel Al wiring material that suppresses the increase in strength at room temperature while exhibiting good high-temperature reliability. [Means for solving the problem]

[0014] As a result of diligent research into the above-mentioned problems, the inventors of this invention discovered that the above-mentioned problems can be solved by an Al wiring material having the following configuration, and based on this finding, they completed the present invention through further research. In other words, the present invention includes the following: [1] When one or more elements selected from the group consisting of Er, Yb, and Gd are present, and the total amount of these elements is x1 [mass%], The value is 0.001 ≤ x1 ≤ 0.6, and the remainder is Al, which is Al wiring material. [2] Furthermore, when one or more selected from the group consisting of Sc and Zr are included, and the total content of these is x2 [mass%], The Al wiring material described in [1], where 0.005 ≤ x² ≤ 0.6. [3] Furthermore, when the material contains one or more selected from the group consisting of Si, Fe, Ni, Ce, Y, and Zn, and the total amount of these is x3 [mass%], Al wiring material as described in [1] or [2], wherein 0.001 ≤ x3 ≤ 1. [4] Bonding wire, which is an Al wiring material as described in any of [1] to [3]. A semiconductor device containing Al wiring material as described in any of [5][1]~[4]. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a novel Al wiring material that suppresses an increase in room temperature strength and exhibits good high-temperature reliability. Such a novel Al wiring material has its increase in room temperature strength suppressed, which can improve workability and productivity during installation and connection to a device. Regarding heat treatment during wiring material production or supplementary heat treatment after connection, it can maintain and improve strength during use in a high-temperature environment and exhibit good high-temperature reliability through low-temperature or short-time treatment, or without requiring such heat treatment.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail in accordance with its preferred embodiments.

[0017] [Al Wiring Material] The Al wiring material of the present invention contains one or more selected from the group consisting of Er, Yb, and Gd, and when the total content thereof is x1 [mass%], it is characterized by satisfying 0.001 ≦ x1 ≦ 0.6.

[0018] By adding a small amount of one or more (hereinafter, also referred to as "Group 1 elements") selected from the group consisting of Er, Yb, and Gd to the Al wiring material, the high-temperature reliability of the Al wiring material can be enhanced, and moreover, an increase in the room temperature strength of the Al wiring material can be suppressed to improve the work performance of deformation and bonding. Regarding such high-temperature reliability, it can be confirmed by the strength of the Al wiring material after high-temperature heating being maintained or increased compared to before heating. Regarding room temperature strength, it can be confirmed by suppressing an increase in the hardness of the Al wiring material, suppressing damage to the connected member (such as a semiconductor chip) during connection, and having good initial bonding properties.

[0019] As an example of the characteristic evaluation of the Al wiring material added with Group 1 elements, the breaking strength when heated at a high temperature of 300 to 500 °C for a long time can be increased. As an effect achieved during use in a harsh high-temperature environment, for example, even after heating at 350 °C for 4 hours, deterioration of the breaking strength of the Al wiring material is suppressed, and rather, the breaking strength increases.

[0020] We found that by finishing Al alloys containing Group 1 elements into wire rods, the improvement in high-temperature reliability due to the addition of these elements is greater than the improvement obtained with bulk materials, plates, and other components. It is thought that the precipitation and solid solution state of Er, Yb, and Gd within the Al alloy have a favorable effect on high-temperature reliability by utilizing the formation of texture during wire drawing and the progression of recrystallization phenomena due to heat treatment such as heating and cooling of fine wires.

[0021] Characteristics of Er, Yb, and Gd include their rapid atomic diffusion rates within Al and low maximum solid solubility (maximum solid solubility) within Al. These factors are thought to promote precipitation during heating, which is advantageous for improving high-temperature reliability. In other words, the addition of Er, Yb, and Gd allows for the efficient formation of precipitate nuclei even with small amounts of additive, and the rapid precipitation rate suggests that strength can be improved even with low-temperature, short-duration heat treatment.

[0022] By heating an Al alloy containing Group 1 elements, stable precipitates such as Al3Er, Al3Yb, and Al3Gd, which are intermetallic compounds between Group 1 elements and Al, can be formed. These precipitates exhibit good cohesion with Al at their interfaces, which suppresses dislocation and grain boundary movement, thus significantly enhancing strength, hardness, and ductility in high-temperature environments.

[0023] Adding Group 1 elements increases the efficiency of precipitate formation, making it easier to control the size and density of the precipitates. As a result, compared to conventional methods such as adding Sc, it is possible to improve strength even with low-temperature, short-duration heat treatment, and the additive effect of increasing strength in high-temperature environments is significantly higher, thus greatly contributing to improved high-temperature strength. The fact that these particularly remarkable functions can be achieved with relatively inexpensive materials is also a practical advantage.

[0024] The first group elements, Er, Yb, and Gd, can similarly achieve the above-mentioned additive effects. Furthermore, by utilizing the characteristics of each element, optimization can be performed to meet specific requirements. For example, with Er, the Al-Er system is eutectic, making it relatively easy to maintain the supersaturated solid solution state necessary for precipitation, and solid solution strengthening can also be utilized to promote high strength. With Yb, it is the only face-centered cubic element among the first group elements, and its diffusion rate within Al is the fastest, which is advantageous for shortening the heating time for precipitation. Gd tends to suppress the increase in strength in the solid solution state, making it more suitable for applications where workability at room temperature is prioritized, such as improving the deformation and bonding performance of Al wiring materials.

[0025] Depending on the application and required characteristics, one or more elements from Group 1 can be selected and used accordingly. For example, combining Er and Yb is advantageous in reducing the content and accelerating the precipitation rate, while combining Er and Gd is advantageous in simultaneously improving deformation and bonding workability at room temperature and maintaining and improving strength when used in high-temperature environments. The combinations of Group 1 elements are not limited to these; Yb and Gd may be combined, or all three elements may be combined.

[0026] The Al wiring material of the present invention contains, as a first group element, one or more elements selected from the group consisting of Er, Yb, and Gd in a total amount in the range of 0.001 to 0.6 mass%. That is, when the total amount of first group elements in the Al wiring material is x1 [mass%], the condition 0.001 ≤ x1 ≤ 0.6 is satisfied.

[0027] From the viewpoint of increasing strength when used in high-temperature environments and obtaining an Al wiring material with good high-temperature reliability, the total content of the first group elements in the Al wiring material, i.e., x1, is 0.001 mass% or more, preferably 0.002 mass% or more, 0.003 mass% or more, or 0.005 mass% or more, more preferably 0.01 mass% or more, 0.02 mass% or more, 0.03 mass% or more, 0.05 mass% or more, 0.07 mass% or more, 0.09 mass% or more, or 0.1 mass% or more. It has been confirmed that when x1 is 0.01 mass% or more, an Al wiring material with even better high-temperature reliability can be realized.

[0028] The total content of Group 1 elements in the Al wiring material, i.e., the upper limit of x1, is 0.6 mass% or less, preferably 0.55 mass% or less, and more preferably 0.5 mass% or less, from the viewpoint of obtaining an Al wiring material with good deformation and bonding workability while suppressing an increase in strength at room temperature. It has been confirmed that when x1 is 0.5 mass% or less, an Al wiring material with even better workability at room temperature can be realized.

[0029] Therefore, in a preferred embodiment, the total content of the first group elements in the Al wiring material, i.e., x1, satisfies 0.001 ≤ x1 ≤ 0.6, and more preferably 0.01 ≤ x1 ≤ 0.5.

[0030] -Sc, Zr (Group 2 elements)- The Al wiring material of the present invention may further contain one or more elements selected from the group consisting of Sc and Zr.

[0031] By including one or more elements selected from the group consisting of Sc and Zr (also called "group 2 elements") in addition to group 1 elements, it is possible to suppress the increase in strength at room temperature, maintain workability at room temperature such as deformation and joining, while further increasing the strength when used in high-temperature environments, thereby realizing an Al wiring material with even better high-temperature reliability. As an example of this effect, Al wiring materials with a composite addition of group 2 elements and group 1 elements can improve strength in higher temperature ranges, and further improve the high-temperature reliability of connection parts in thermal histories that repeatedly go between high and low temperatures during high-power operation of electronic equipment.

[0032] The following are examples of characterization evaluations of Al wiring materials with a combination of Group 2 and Group 1 elements. In the first example, as an effect achieved when used in harsh high-temperature environments, for example, even after heating to a high temperature of 400°C, the degradation of the breaking strength of the Al wiring material was suppressed, and in fact, the breaking strength was increased. This indicates the possibility of achieving superior reliability even at temperatures more than 50°C higher than when only Group 1 elements are added.

[0033] In the second example, in Al wiring materials with a composite addition of Group 2 and Group 1 elements, the high-temperature reliability of the connection to the connected component is further improved. In particular, high bonding strength can be maintained even against thermal shock caused by repeated temperature increases and decreases, resulting in a long lifespan. Here, one method for accelerating thermal shock evaluation is the power cycle test. This test involves repeated rapid heating and cooling by repeatedly switching the voltage ON / OFF. If the bonding strength of the connection to the connected component decreases or worsens due to this thermal shock, problems such as crack propagation and delamination near the connection interface can occur. By suppressing the phenomenon of grain growth and coarsening inside the wiring material, which is a problem in conventional Al wiring materials, in response to thermal strain generated at the connection of the Al wiring material due to rapid heating and cooling, it is possible to improve the high-temperature reliability of the connection. Regarding this high-temperature reliability of the connection, it has been confirmed that improvement can be achieved even with the addition of Group 1 elements alone, but a more significant improvement can be obtained by further adding Group 2 elements in a composite manner.

[0034] By adding the first group of elements and the second group of elements in combination, in addition to the solid solution of the elements, precipitates of intermetallic compounds composed of one or two of the second group of elements, the first group of elements, and Al are formed. It is considered that this precipitate can achieve the above remarkable effect in suppressing the grain boundary movement and grain coarsening of the wiring material and the connection part in a high-temperature environment. Ternary intermetallic compounds are typical. For example, Al3(Er, Sc), Al3(Yb, Sc), Al3(Er, Zr), Al3(Gd, Zr), etc. can be cited. In addition, binary precipitates are also formed in part. For example, Al3Er, Al3Sc, etc. can be cited. Regarding the notation of the composition such as Al3(Er, Sc), it can also be expressed as Al3(Er x ,Sc 1-x )(where x satisfies 0 < x < 1), but in this specification, the simple notation Al3(Er, Sc) is used. Also, the composition of the precipitate is not limited to the above.

[0035] Regarding the element distribution of the ternary precipitate, a composite structure (core-shell structure) composed of different elements in the interior (core) and the outer shell (shell) also effectively acts on the improvement of the high-temperature characteristics. For the Al wiring material with the combined addition of the first group of elements and the second group of elements, it has been confirmed by TEM analysis of the precipitate, etc. that the first group of elements tend to concentrate mainly in the interior of the precipitate and the second group of elements tend to concentrate in the outer shell. For example, in the ternary precipitate of Al-Er-Sc, the structure in which Er is concentrated in the interior and Sc is concentrated in the outer shell, and in the ternary precipitate of Al-Yb-Zr, the structure in which Yb is concentrated in the interior and Zr is concentrated in the outer shell tends to be formed. This is considered to be due to the fact that the first group of elements with a high diffusion rate aggregate quickly to form a core precipitate with Al, and the second group of elements precipitate around it to form a shell with it as the nucleus. As a method for analyzing the composition of the precipitate, composition analysis (EDS analysis) of a transmission electron microscope (TEM) can be used.

[0036] One advantage of this core-shell structure is that even in high temperature ranges where the core, composed of Group 1 elements and Al, becomes coarser, the shell suppresses precipitate growth, thus maintaining fine precipitates. This results in a remarkable effect of maintaining the reliability of Al wiring materials even at considerably high temperatures. This is also the reason why the above particularly remarkable effect is achieved when Group 1 and Group 2 elements are combined in the additive. Regarding the formation of precipitates in core-shell structures, it is difficult to stably distribute them within the sample in large components such as bulk materials, but we have found that it is relatively easy to uniformly distribute core-shell structure precipitates in Al wiring materials, which are two-dimensional wires. In other words, Al wiring materials with combined additives of Group 1 and Group 2 elements are advantageous for mass production as products with improved high-temperature characteristics. As a method for analyzing the structure and composition of such precipitates, methods such as the 3-dimensional atom probe (3DAP) method can be used. The structure can be analyzed by the concentration distribution of elements within the precipitates.

[0037] Compound additives, which involve simultaneously adding multiple elements such as Group 1 and Group 2 elements (and Group 3 elements described later), offer economic advantages. They allow for a reduction in the content of expensive Sc, and enable the satisfaction of requirements with smaller amounts of Group 2 elements. As a result, the amount of Group 1 elements used is also reduced, lowering raw material costs. Furthermore, regarding heat treatment conditions for improving high-temperature reliability, compound additives allow for the formation of precipitates at lower temperatures and in shorter times, thus improving productivity.

[0038] The Al wiring material of the present invention preferably contains one or more elements selected from the group consisting of Sc and Zr as Group 2 elements in a total amount of 0.005 to 0.6 mass%. That is, when the total amount of Group 2 elements in the Al wiring material is x2 [mass%], it is preferable that 0.005 ≤ x2 ≤ 0.6 is satisfied.

[0039] From the viewpoint of further increasing the strength when used in high-temperature environments and obtaining an Al wiring material with even better high-temperature reliability, the total content of the second group elements in the Al wiring material, i.e., x2, is preferably 0.005 mass% or more, more preferably 0.006 mass% or more, 0.008 mass% or more, or 0.009 mass% or more, and even more preferably 0.01 mass% or more, 0.02 mass% or more, 0.03 mass% or more, 0.05 mass% or more, or 0.1 mass% or more. It has been confirmed that when x2 is 0.01 mass% or more, an Al wiring material with particularly good high-temperature reliability can be realized.

[0040] The upper limit of the total content of Group 2 elements in the Al wiring material, i.e., x2, is preferably 0.6 mass% or less, more preferably 0.55 mass% or less, and even more preferably 0.5 mass% or less, from the viewpoint of obtaining an Al wiring material with good working performance at room temperature, such as deformation and joining, while suppressing an increase in strength at room temperature. It has been confirmed that when x2 is 0.5 mass% or less, an Al wiring material with even better working performance at room temperature can be realized. In the Al wiring material of the present invention to which Group 1 elements are added, the content of Group 2 elements can be suppressed, and x2 may be as low as 0.45 mass% or less, 0.4 mass% or less, 0.35 mass% or less, 0.3 mass% or less, 0.25 mass% or less, 0.2 mass% or less, 0.15 mass% or less, or less than 0.15 mass%.

[0041] Therefore, in one preferred embodiment, the total content of the second group elements in the Al wiring material, i.e., x2, satisfies 0.005 ≤ x2 ≤ 0.6, and more preferably 0.01 ≤ x2 ≤ 0.5.

[0042] -Si, Fe, Ni, Ce, Y, Zn (group 3 elements)- The Al wiring material of the present invention may further contain one or more elements selected from the group consisting of Si, Fe, Ni, Ce, Y, and Zn.

[0043] By including one or more elements selected from the group consisting of Si, Fe, Ni, Ce, Y, and Zn (also called "group 3 elements") in addition to group 1 elements, high-temperature reliability can be improved in the second connection, which is the connection between the Al wiring material and the lead frame or external electrodes on the substrate, or the bending deformability of the Al wiring material at high temperatures can be improved. By compounding group 3 elements and group 1 elements, a greater effect can be obtained in suppressing the deterioration of bonding strength even in high-temperature environments of 200°C or higher in the second connection with external electrodes made of materials that have a higher melting point and are harder than Al, compared to when group 1 elements are added alone.

[0044] External electrodes on lead frames and substrates are not particularly limited, but examples include Cu-based alloys and Fe-based alloys coated with Ni, Ag, or Pd. In the second connection, the size and thickness of the external electrodes are relatively large, making it easier to ensure reliability compared to the first connection on the chip side. Nevertheless, under harsh operating conditions, problems arise such as voids and cracks forming at the connection interface due to high temperature environments or heat generation during operation when high voltage is applied. In the future, as Al wiring materials become thinner, high-temperature reliability of the connection part with the external electrode will become a problem. This is because the connected material is hard and has a high melting point, so deformation of the Al wiring material mainly occurs during connection, making it difficult to obtain a metallic bond at the connection interface, and the diffusion rate at the interface is slow.

[0045] Third-group elements, Si, Fe, Ni, Ce, Y, and Zn, exist in greater quantities in solid solution within Al than first-group elements. Therefore, they can contribute to further improvement of high-temperature reliability by influencing solid solution strengthening or the processing / recrystallization structure. Combining the solid solution of third-group elements with the precipitation of first-group elements exposes a newly formed metal surface at the connection point with a hard connected member, promoting interdiffusion. Furthermore, heat treatment of Al wiring material forms ternary alloy precipitates composed of Al, third-group elements, and first-group elements, promoting uniform deformation of the Al wiring material during ultrasonic connection. This synergistic effect of solid solution and precipitation, along with the formation of ternary intermetallic compounds, is expected to improve high-temperature reliability at the connection point with the external electrode. Examples of ternary intermetallic compound compositions include, but are not limited to, Al3(Er,Si), Al3(Yb,Si), Al3(Er,Ni), and Al3(Gd,Si).

[0046] The Al wiring material of the present invention preferably contains, as a third group element, one or more elements selected from the group consisting of Si, Fe, Ni, Ce, Y, and Zn in a total amount in the range of 0.001 to 1 mass%. That is, when the total content of the third group element in the Al wiring material is x3 [mass%], it is preferable that 0.001 ≤ x2 ≤ 1 is satisfied.

[0047] From the viewpoint of obtaining an Al wiring material with good high-temperature reliability at the second connection point, the total content of the third group elements in the Al wiring material, i.e., x3, is preferably 0.001 mass% or more, more preferably 0.002 mass% or more, even more preferably 0.003 mass% or more, 0.005 mass% or more, 0.006 mass% or more, 0.008 mass% or more, 0.009 mass% or more, or 0.01 mass% or more. It has been confirmed that when x3 is 0.003 mass% or more, an Al wiring material with particularly good high-temperature reliability at the second connection point can be realized.

[0048] The upper limit of the total content of the third group elements in the Al wiring material, i.e., x3, is preferably 1% by mass or less, more preferably 0.9% by mass or less, and even more preferably 0.8% by mass or less, from the viewpoint of obtaining an Al wiring material with good working performance at room temperature, such as deformation and bonding, while suppressing an increase in strength at room temperature. It has been confirmed that when x3 is 0.8% by mass or less, an Al wiring material with even better working performance at room temperature can be realized.

[0049] Therefore, in a preferred embodiment, the total content of the third group elements in the Al wiring material, i.e., x3, satisfies 0.001 ≤ x3 ≤ 1, and more preferably 0.003 ≤ x3 ≤ 0.8.

[0050] The remainder of the Al wiring material of the present invention contains Al. Industrially pure Al with a purity of 4N (Al: 99.99% by mass or higher) can be used as the aluminum raw material when manufacturing the Al wiring material. It is even more preferable to use aluminum with a purity of 5N (Al: 99.999% by mass or higher) or higher, which has a lower impurity content. The remainder of the Al wiring material of the present invention may contain elements other than Al, as long as it does not hinder the effects of the present invention. The Al content in the remainder of the Al wiring material of the present invention is not particularly limited as long as it does not hinder the effects of the present invention, but is preferably 98% by mass or higher, 98.5% by mass or higher, 99% by mass or higher, 99.5% by mass or higher, 99.6% by mass or higher, 99.7% by mass or higher, 99.8% by mass or higher, or 99.9% by mass or higher. In a preferred embodiment, the remainder of the Al wiring material of the present invention consists of Al and unavoidable impurities.

[0051] The content of Group 1 elements, Group 2 elements, Group 3 elements, etc. in the Al wiring material can be measured by the method described in [Measurement of Elemental Content] below.

[0052] The Al wiring material of the present invention may or may not have a coating on its outer periphery composed mainly of elements other than Al. In one preferred embodiment, the Al wiring material of the present invention does not have a coating on its outer periphery composed mainly of metals other than Al. Here, "coating composed mainly of metals other than Al" refers to a coating in which the content of metals other than Al is 50% by mass or more.

[0053] The Al wiring material of the present invention exhibits suppressed increases in strength at room temperature, improving workability and productivity during installation and connection to equipment. Furthermore, regarding heat treatment during manufacturing or supplemental heat treatment after connection, it can maintain and improve strength in high-temperature environments and exhibit good high-temperature reliability through low-temperature or short-time treatment, or even without the need for such heat treatment. Therefore, the Al wiring material of the present invention can be used in a wide range of applications where both room-temperature workability and high-temperature reliability are required when connecting to components. For example, it can be suitably used for connecting components in industrial equipment such as conveying equipment and robots (Al wiring material for industrial equipment), and it can also be suitably used for connecting components in various semiconductor devices, including power semiconductor devices (Al wiring material for semiconductor devices).

[0054] The Al wiring material of the present invention may have any dimensions depending on its specific use. When the Al wiring material of the present invention is an Al wire used in industrial equipment such as conveying equipment and robots, its wire diameter is not particularly limited, for example, the diameter may be 500 μm to 10 mm. It may also be a stranded wire using multiple such Al wires. When it is an Al strip, the dimensions (w × t) of its rectangular or substantially rectangular cross-section are not particularly limited, for example, w may be 500 μm to 10 mm and t may be 50 μm to 2 mm. Furthermore, when the Al wiring material of the present invention is an Al bonding wire used in various semiconductor devices, including power semiconductor devices, its wire diameter is not particularly limited, for example, the diameter may be 50 to 600 μm. Furthermore, when it is an Al bonding ribbon, the dimensions (w × t) of its rectangular or substantially rectangular cross-section are not particularly limited, for example, w may be 100 to 3000 μm and t may be 50 to 600 μm.

[0055] 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 is relatively thin, it is preferable to perform wire drawing using a diamond die. Cold working, in which wire drawing is performed at room temperature, is easy to do as the manufacturing equipment has a relatively simple configuration and offers excellent workability. Furthermore, to reduce resistance during wire drawing and increase productivity, hot working, in which wire drawing is performed under heating, may be used.

[0056] To produce the ingot, Al and pure metals of each additive are weighed as starting materials so that the content of each additive element is within a specific range. These materials are then mixed, melted, and solidified to create the ingot. Alternatively, a master alloy containing a high concentration of each additive element may be used as the raw material for each additive element. In the melting process to produce this ingot, either a batch method or a continuous casting method can be used. The continuous casting method offers superior productivity, while the batch method allows for easy modification of the solidification and cooling temperature conditions. This ingot is then processed to its final dimensions to form the Al wiring material.

[0057] It is preferable to perform solution heat treatment to dissolve each additive element in solid solution and distribute it evenly, either in the ingot state, during processing, or after processing is complete. In solution heat treatment, the additive elements are dissolved in Al at a high temperature where the solid solubility is high, and then cooled to room temperature by increasing the cooling rate using water cooling, air cooling, etc., to suppress the precipitation of the dissolved elements. The conditions for solution heat treatment can be, for example, heating at a temperature range of 550 to 640°C for 1 to 20 hours, followed by cooling by water cooling, air cooling, etc. If the cooling rate of the ingot is fast in a batch process, it is possible to shorten the solution heat treatment time because most of the additive elements are dissolved. Alternatively, by performing heat treatment in a high temperature range where the solubility is high, precipitates generated during the solidification of the ingot can be redissolved, and a state in which the additive elements are uniformly distributed can be obtained. Therefore, solution heat treatment can be substituted by increasing the cooling rate during solidification. For example, with a continuous casting method, the solidification rate can be faster than with batch melting, making it relatively easy to solidify additive elements within the aluminum, and thus eliminating the need for solution heat treatment.

[0058] In solution-heat-treated Al alloys, it is preferable to perform a precipitation heat treatment to promote precipitation. Precipitation heat treatment can be performed immediately after solution heat treatment, or during or after subsequent processing steps. When performing precipitation heat treatment in a batch manner in the state of large diameter wires, the precipitation heat treatment may be performed by heating at a temperature range of 200 to 450°C for 10 minutes to 5 hours. Specifically, examples include low-temperature conditions of 250°C for 3 hours and high-temperature conditions of 350°C for 30 minutes. Alternatively, when performing precipitation heat treatment continuously in the state of processed small diameter wires, the precipitation heat treatment may be performed by heating at a temperature range of 400 to 600°C for 1 second to 5 minutes while the wire continuously moves inside the furnace. Specifically, examples include heating at 400°C for 5 seconds to suppress the progression of precipitation, and heating at 500°C for 1 minute to promote the formation of precipitates. The temperature and time may be determined by referring to these heat treatment conditions. If you want to optimize the conditions in more detail, you can easily optimize the temperature, time, etc., by using these heat treatment conditions as a reference and performing isothermal or isochronous heat treatment. For example, if you prototype Al wiring materials that have been isothermal treated under several time conditions and measure their mechanical properties, you can easily reproduce the desired properties.

[0059] During the processing of the Al wiring material, or at the final wire diameter, a tempering heat treatment may be applied. This tempering heat treatment removes processing stress, forms a recrystallized structure, and can also promote the growth of precipitates in conjunction with the precipitation heat treatment. This tempering heat treatment is preferably carried out continuously in a heating furnace while continuously sweeping the Al wiring material. Examples of these heat treatment conditions include heating at a temperature range of 400-600°C for a short period of time, from 0.1 seconds to 3 minutes. Since precipitation can also be promoted during the tempering heat treatment, depending on the desired degree of precipitation, the tempering heat treatment can simultaneously serve as the precipitation heat treatment.

[0060] In semiconductor devices, the connection between the Al wiring material of the present invention and the connected member is performed by wedge bonding, both for the first connection to an electrode on a semiconductor chip and for the second connection to an external electrode on a lead frame or substrate. It is preferable to perform mounting heat treatment on the semiconductor device including the Al wiring material after connection to the connected member. By performing mounting heat treatment, precipitates, which are intermetallic compounds, are formed in the Al wiring material, making it possible to further increase the strength through precipitation strengthening. In the Al wiring material of the present invention, the composition and form of the precipitates formed are as described above.

[0061] The conditions for the heat treatment during mounting are not particularly limited as long as an intermetallic compound can be formed, but for example, heating at a temperature range of 200 to 400°C for 10 to 60 minutes is preferable. The atmosphere during the heat treatment during mounting may be air, but an inert atmosphere such as nitrogen or argon may be used to suppress oxidation of the material.

[0062] The present invention also provides a method for manufacturing a semiconductor device. In one preferred embodiment, the method for manufacturing a semiconductor device according to the present invention is: (A) A step of connecting electrodes on a semiconductor chip and electrodes on a lead frame or substrate using the Al wiring material of the present invention, and (B) After connection with Al wiring material, a heat treatment process is performed. It includes.

[0063] The semiconductor chip, lead frame, or substrate used in step (A) may be any known one that can be used to construct a semiconductor device, as described below. Furthermore, the details and preferred embodiments of the Al wiring material of the present invention used in step (A) are as described above. In step (A), both the first connection to the electrode on the semiconductor chip and the second connection to the electrode on the lead frame or substrate may be performed by wedge bonding. Furthermore, in step (B), a fine precipitate phase of the intermetallic compound described above can be formed in the Al wiring material.

[0064] [Semiconductor device] By using the Al wiring material of the present invention, a semiconductor device can be manufactured by connecting electrodes on a semiconductor chip to external electrodes on a lead frame or substrate.

[0065] The semiconductor device of the present invention includes the Al wiring material of the present invention. The Al wiring material of the present invention has suppressed increases in strength at room temperature, which improves workability and productivity during installation and connection to the device. Furthermore, regarding heat treatment during the manufacturing of the wiring material or supplemental heat treatment after connection, it can maintain and improve strength when used in high-temperature environments and exhibit good high-temperature reliability by low-temperature or short-time treatment, or even without the need for such heat treatment.Therefore, the semiconductor device including the Al wiring material can achieve good operational reliability over a long period of time even in high-temperature operating environments, and can suppress thermal effects on connected components, thereby comprehensively satisfying many performance requirements.

[0066] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, and an Al wiring material for connecting the circuit board and the semiconductor chip, wherein the Al wiring material is the Al wiring material of the present invention. Herein, the "Al wiring material of the present invention" as used in the semiconductor device of the present invention is characterized by containing the elements of Group 1, and optionally the elements of Group 2 and Group 3, in the aforementioned preferred concentration ranges.

[0067] In the semiconductor device of the present invention, even when operated for a long time in a high-temperature environment, it is possible to maintain the precipitate separated from Al (for example, precipitates consisting of the aforementioned binary or ternary intermetallic compounds) as a fine phase.

[0068] In the semiconductor device of the present invention, the circuit board and semiconductor chip are not particularly limited, and known circuit boards and semiconductor chips that can be used to constitute a semiconductor device may be used. Alternatively, a lead frame may be used instead of a 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 described in Japanese Patent Application Publication No. 2020-150116 and Japanese Patent Application Publication No. 2002-246542.

[0069] Examples of semiconductor devices include various types of 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, and aircraft, etc.), with power semiconductor devices being particularly preferred. [Examples]

[0070] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below.

[0071] (sample) First, the method for preparing the samples will be explained. Al with a purity of 5N (99.999% by mass or higher) and Er, Yb, Gd, Sc, Zr, Si, Fe, Ni, Ce, Y, and Zn with a purity of 99.9% by mass or higher were melted to produce Al ingots with the compositions shown in Tables 1 and 2. Next, solution heat treatment was performed at a range of 550 to 640°C for 5 hours, followed by rapid cooling (water cooling). The ingots were then extruded and swaged, and then drawn. For some samples, precipitation heat treatment was performed at a range of 350 to 600°C for 1 to 60 minutes when the wire diameter was 2 mm. After that, die drawing was performed to a final wire diameter of 300 μm, and after the completion of wire drawing, tempering heat treatment was performed for a heat treatment time of 2 seconds to obtain Al wiring material.

[0072] [Measurement of elemental content] The content of additive elements in the Al wiring material was measured using either ICP-OES (Hitachi High-Tech Science Co., Ltd. "PS3520UVDDII") or ICP-MS (Agilent Technologies, Inc. "Agilent 7700x ICP-MS") as the analytical instrument.

[0073] [Mechanical properties of wire] -Changes in strength after heating- The change in wire strength after heating was evaluated by performing tensile tests before and after heat treatment, and measuring the change in wire breaking strength. Breaking strength was measured using an Instron tensile testing machine under the conditions of a gauge length of 100 mm, a tensile speed of 10 mm / min, and a load cell rated load of 1 kN. The average of five measurements was used. Heat treatment was performed on the wire under a nitrogen atmosphere at 350°C for 4 hours or at 400°C for 1 hour. The wire strength before and after heat treatment were designated as F1 and F2, respectively, and the ratio F2 / F1 was used for evaluation. For the F2 / F1 value, a value of 1.2 or higher was marked as "◎" indicating a significant improvement in the wire's high-temperature reliability, a value between 1.0 and 1.2 was marked as "○" indicating good performance in normal high-temperature environments, a value between 0.7 and 1.0 was marked as "△" indicating no problems in normal use but requiring caution in high-temperature environments, and a value below 0.7 was marked as "×" indicating poor high-temperature reliability. These values ​​are recorded in the "Strength Change After Heating" column of Tables 1 and 2.

[0074] -Hardness measurement- The Vickers hardness Hv of the longitudinal axis of the Al wiring material was measured using a micro-Vickers hardness tester. The measurement surface was a cross section parallel to the longitudinal direction (L-section) that included the longitudinal axis of the Al wiring material, and the hardness at the longitudinal axis (i.e., the center position of the Al wiring material) was measured. The average of the five measurement values ​​was adopted as the Vickers hardness of the sample. A Vickers hardness Hv in the range of 20 to less than 35 was marked as "○" because it is soft, a range of 35 to less than 45 was marked as "△", and a range of 45 or more was marked as "×" because it is hard and deformability is a concern, and these values ​​are recorded in the "Hardness Hv" column of Tables 1 and 2.

[0075] <Connection> In the semiconductor device, the electrodes of the semiconductor chip were Al-Cu pads (2 μm thick), and the external terminals were made of nickel-coated Cu lead frames. Both the first connection between the semiconductor chip electrodes and the Al wiring material, and the second connection between the external terminals and the Al wiring material, were wedge joints. In some examples and comparative examples, mounting heat treatment (aging heat treatment) was performed at 300°C for 30 minutes after connection.

[0076] <Evaluation of chip damage> Chip damage in semiconductor devices was evaluated by dissolving the metal on the pad surface with acid and observing the area beneath the pad under a microscope (N=50 evaluations). Cases with no cracks or signs of bonding were marked "○", cases with no cracks but signs of bonding were observed in some areas (3 or fewer out of 50 evaluations) were marked "△", and all others were marked "×", as recorded in the "Chip Damage" column of Tables 1 and 2.

[0077] <Evaluation of high-temperature reliability> -First connection point- The high-temperature reliability of the first connection was evaluated by power cycling tests. In the power cycling tests, semiconductor devices with connected Al wiring materials were subjected to alternating heating and cooling. Two types of heating conditions were performed: medium temperature and high temperature. Under the medium temperature conditions, the connection of the Al wiring material in the semiconductor device was heated for 2 seconds until the maximum temperature reached approximately 120°C, and then cooled for 20 seconds until the temperature of the connection reached 30°C. This heating and cooling cycle was repeated 100,000 times. Under the high temperature conditions, the connection was heated for 2 seconds until the maximum temperature reached approximately 140°C, and then cooled for 25 seconds until the temperature of the connection reached 30°C. This heating and cooling cycle was repeated 100,000 times.

[0078] -Second Connection Section- The high-temperature reliability of the second connection was evaluated by a Temperature Cycle Test (TCT). The TCT is a test in which a semiconductor device with connected Al wiring is placed in a furnace of a temperature cycle test apparatus and subjected to continuous alternation between high and low temperatures. The high temperature was set to 125°C, and the low temperature to -40°C. This high-temperature / low-temperature cycle was repeated 1000 times.

[0079] The high-temperature reliability of the connection was evaluated by measuring the shear strength of the first connection after the power cycle test and the shear strength of the second connection after the temperature cycle test. The evaluation was performed using the ratio S2 / S1, which is the ratio of the shear strength S2 after the power cycle test or temperature cycle test to the initial shear strength S1 of the connection. For the S2 / S1 value, a value of 0.9 or higher was marked as "◎" indicating excellent reliability, a value of 0.8 or higher and less than 0.9 was marked as "○" indicating good reliability, a value of 0.6 or higher and less than 0.8 was marked as "△" indicating no problems in normal use but requiring caution, and a value of less than 0.6 was marked as "×" indicating poor high-temperature reliability. These values ​​were recorded in the "High-Temperature Reliability" column of Tables 1 and 2.

[0080] The manufacturing conditions and evaluation results for the Al wiring material are shown in Tables 1 and 2.

[0081] [Table 1]

[0082] [Table 2]

[0083] The Al wiring materials of Examples 1 to 40 had a total x1 content of Er, Yb, and Gd within the range of the present invention, and regardless of whether or not heat treatment was performed during wiring material manufacturing and after connection, or the temperature and duration of such treatment, the results were good in terms of strength change after heating to 350°C, chip damage, hardness, and high-temperature reliability of the first connection under medium temperature conditions. In the Al wiring materials of Examples 2, 3, 6-10, 12, 13, 15-18, 20, 21, 24-27, 29, 31, and 33-40, the Sc and Zr content was within the preferred range of the present invention, the strength change after heating to 400°C was ○ or ◎, and the high-temperature reliability of the first connection part was ○ or ◎ under both medium and high temperature conditions, indicating good results. In the Al wiring materials of Examples 2-10, 12, 14-17, 19-21, 23, 24, 26-32, 34-37, 39, and 40, the content of Si, Fe, Ni, Ce, Y, and Zn was within the preferred range of the present invention, and the high-temperature reliability of the second connection part was also good. In Comparative Examples 1-3 and 6-8, the Al wiring materials had Er, Yb, and Gd content outside the lower limit of the present invention range, and the strength change after heating at 350°C was unsatisfactory. In Comparative Examples 4 and 5, the Al wiring materials had Er, Yb, and Gd content outside the upper limit of the present invention range, and the chip damage and hardness were unsatisfactory.

Claims

1. When it contains one or more elements selected from the group consisting of Er, Yb, and Gd, and the total amount of these elements is x1 [mass%], Al wiring material having 0.001 ≤ x1 ≤ 0.6, containing at least Er or Yb, with the remainder being Al, and the Al content of the remainder being 99.5% by mass or more.

2. When it contains one or more elements selected from the group consisting of Er, Yb, and Gd, and the total amount of these elements is x1 [mass%], 0.001 ≤ x1 ≤ 0.6, Furthermore, when it contains one or more selected from the group consisting of Sc and Zr, and the total content is x² [mass%], The condition is 0.005 ≤ x² ≤ 0.6, and the remainder is Al, which is an Al wiring material.

3. Furthermore, when it contains one or more selected from the group consisting of Sc and Zr, and the total content is x² [mass%], The Al wiring material according to claim 1, wherein 0.005 ≤ x² ≤ 0.

6.

4. Al wiring material according to any one of claims 1 to 3, wherein 0.02 ≤ x1 ≤ 0.

6.

5. Furthermore, when it contains one or more elements selected from the group consisting of Si, Fe, Ni, Ce, Y, and Zn, and the total content is x3 [mass%], Al wiring material according to any one of claims 1 to 4, wherein 0.001 ≤ x3 ≤ 1.

6. A bonding wire, the Al wiring material according to any one of claims 1 to 5.

7. A semiconductor device comprising the Al wiring material described in any one of claims 1 to 6.

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