Al wiring material

Abstract

Provided is a novel aluminum wiring material that brings good high-temperature reliability and has good workability and bondability during installation and connection to a device. The aluminum wiring material is characterized by: containing Mg and Si; when the content of Mg is x1a [mass%] and the content of Si is x1b [mass%], 0.05 ≤ x1a ≤ 2.5, 0.02 ≤ x1b ≤ 1, and 0.1 ≤ (x1a + x1b) ≤ 3 being satisfied; further containing one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y; when the total content thereof is x2 [mass%], 0.001 ≤ x2 ≤ 0.5 being satisfied; and the remainder including Al.

Description

[Technical Field]

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

[0002] As a wire-shaped material used for electrical and / or mechanical connections in industrial equipment and electronic components, the use of aluminum (Al) is increasing due to its lighter weight and lower cost than conventional copper (Cu) in line with the demand for computerization in automobiles. The Al wire (round) and Al strip (flat and oval) used in industrial equipment such as transport equipment and robots require mechanical properties such as breaking strength and elongation, as well as electrical conductivity and thermal conductivity, depending on the intended use.

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

[0004] The above-mentioned Al wire, Al strip, Al bonding wire, Al bonding ribbon, etc. are hereinafter collectively referred to as Al wiring material.

[0005] Power semiconductor devices using Al wiring materials are often used in high-power equipment such as air conditioners and solar power generation systems, as well as in-vehicle semiconductor devices. In these semiconductor devices, the connection between the wiring material and the connected components is exposed to high temperatures of 140°C or higher during device operation. Rapid on / off switching of high voltage creates a harsh environment where the temperature repeatedly rises and falls. When materials made solely of high-purity Al are used as wiring materials, they tend to soften in the temperature environment during device operation, making them difficult to use in high-temperature environments.

[0006] Al wiring materials made of Al with specific elements added have been proposed. For example, Patent Document 2 discloses an Al bonding wire with improved mechanical strength by adding 0.05 to 1 wt% of scandium (Sc) to Al to cause precipitation hardening. Patent Document 3 discloses an Al bonding wire with forced solid solution of 0.15 to 0.5 wt% of Sc added to Al, which is precipitation hardened by aging heat treatment after connection. Patent Document 4 discloses that an Al wiring material containing 800 wt% or less of one or more of nickel (Ni), silicon (Si), and phosphorus (P) in total exhibits good bonding strength and weather resistance. Patent Document 5 discloses that an Al wiring material with a total content of magnesium (Mg) and Si of 0.03 wt% to 0.3 wt% improves the reliability of the connection. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-314038 [Patent Document 2] Special Publication No. 2016-511529 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-47417 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-152316 [Patent Document 5] Patent No. 6272674 Summary of the Invention [Problem to be solved by the invention]

[0008] As industrial equipment and electronic components become more functional and their range of applications expands, the requirements for aluminum wiring materials are becoming more stringent. Aluminum wiring materials used in industrial equipment such as transport equipment and robots must be able to withstand high-temperature environments and repeated bending deformation. Recently, in automotive applications, wire strength has deteriorated during use in high-temperature environments, resulting in abnormal deformation and cracks, which can lead to wire breakage if they progress. Therefore, the challenge is to prevent the strength degradation of aluminum wiring materials in high-temperature environments and improve their high-temperature reliability. However, simply increasing the strength of the wiring material is not enough to achieve sufficient high-temperature reliability, and there are concerns that it may also reduce workability and bondability during installation and use.

[0009] Furthermore, with the expansion of applications in automotive power devices, aluminum wiring materials used in electronic components such as semiconductors are required to improve both the initial bondability and the high-temperature reliability of the joints. In semiconductors, aluminum wiring materials are connected at two locations: to electrodes on the semiconductor chip (hereinafter referred to as the "first connection") and to external electrodes on the lead frame or substrate (hereinafter referred to as the "second connection"). In power devices, temperature changes during operation can cause thermal shocks (hereinafter referred to as "thermal shock"), which can damage the first connection between the aluminum wiring material and the electrodes on the semiconductor chip. Specifically, cracks can occur at the connection interface due to differences in the thermal expansion coefficients between the aluminum wiring material and the connected components (hereinafter referred to as "bond cracks"). Bending stress due to the expansion and contraction of the aluminum wiring material itself can also cause cracks in the rising portion of the loop near the connection (hereinafter referred to as "heel cracks"). Corrosion in the operating environment of the equipment can cause these bond cracks and heel cracks to propagate, ultimately leading to delamination of the connection between the Al wiring material and the Al wiring, impairing the high-temperature reliability of the connection. One method for accelerating thermal shock evaluation is the power cycle test, which involves repeated on / off voltage cycling, resulting in rapid heating and cooling. If this thermal shock reduces or worsens the bond strength of the connection with the connected component, cracks can propagate near the connection interface, leading to delamination and other problems. Adding other elements to the Al wiring material can be considered to suppress grain coarsening and increase strength. However, as the content of other elements in the Al wiring material increases, this method can lead to breaks and scratches during the manufacturing process, reducing yields, or even damage to the connected component when connecting the Al wiring material (hereinafter referred to as "chip damage").

[0010] Furthermore, it is becoming increasingly difficult to achieve or improve the reliability of connections over long periods of time in high-temperature environments, which is required for high-temperature power devices such as SiC. For example, regarding durability in power cycle tests, under harsh conditions exceeding 10,000 cycles, defects such as bond cracks occur in the connections of Al wiring materials, which is an obstacle to the practical application of power devices.

[0011] In Al wiring materials containing other elements, performance is improved by utilizing solid solution and precipitation, and heat treatment is performed during the manufacturing of the Al wiring material and after the Al wiring material is connected. In order to improve the high-temperature reliability, heat treatment must be performed at a higher temperature or for a longer time than conventional Al wiring material products. This can lead to problems such as deterioration of bondability, reduced productivity, increased manufacturing costs, and thermal effects on the components to which the Al wiring material is connected (e.g., substrates and peripheral components). Therefore, there is a demand for Al wiring materials that can improve high-temperature reliability even when heat treated at a lower temperature or for a shorter time.

[0012] Technologies for improving the high-temperature reliability of Al wiring materials have been investigated. For example, it is known that Al wiring materials containing Mg and Si improve high-temperature reliability (Patent Documents 4 and 5). However, the improvement effect is small and has not been put to practical use. In rigorous power cycle tests, improvement may be observed within a short number of cycles, but as the number of cycles increases, defects such as cracks occur in the connection. Furthermore, Al wiring materials containing Sc are also known to improve high-temperature reliability (Patent Documents 2 and 3). However, to improve high-temperature reliability, heat treatment during manufacturing must be performed at high temperatures, and there are problems such as the narrow range of appropriate heat treatment conditions and difficulty in controlling them. Furthermore, when heat treatment is performed after connection, heat treatment at high temperatures for a relatively long time is required, which hinders practical use.

[0013] If the reliability and bondability of the connection can be improved by low-temperature or short-time heat treatment during wiring material manufacturing or after connection, the quality and reliability when used in high-temperature environments can be improved, contributing to improved functionality, quality, and reliability of automotive electronic components, power semiconductor devices, etc.

[0014] An object of the present invention is to provide a novel Al wiring material that has good high-temperature reliability and also has good workability and bondability when being installed and connected to a device. [Means for solving the problem]

[0015] As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using an Al wiring material having the following composition. Based on this finding, further research has led to the completion of the present invention. That is, the present invention includes the following. [1] When Mg and Si are contained, and the Mg content is x1a [mass%] and the Si content is x1b [mass%], 0.05≦x1a≦2.5, 0.02≦x1b≦1, 0.1≦(x1a+x1b)≦3 and further containing one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y, and when the total content thereof is x2 [mass%], 0.001≦x2≦0.5 and the remainder is an Al wiring material containing Al. [2] When the material further contains one or more elements selected from the group consisting of Zr, Fe, Ni, Mn, Cu, and Zn, and the total content of these elements is x3 [mass%], 0.01≦x3≦0.5 The Al wiring material according to [1], [3] The Al wiring material according to [1] or [2], which is a bonding wire. [4] A semiconductor device comprising the Al wiring material according to any one of [1] to [3]. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a novel Al wiring material that provides good high-temperature reliability and also has good workability and bondability when installed and connected to a device. Such a novel Al wiring material can improve workability and bondability when installed and connected to a device, and can exhibit good high-temperature reliability by low-temperature or short-time heat treatment during wiring material production or heat treatment after connection, or without the need for such heat treatment. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below based on preferred embodiments thereof.

[0018] [Al wiring material] The Al wiring material of the present invention contains Mg and Si, and is characterized in that, when the Mg content is x1a [mass%] and the Si content is x1b [mass%], the following relationships are satisfied: 0.05≦x1a≦2.5, 0.02≦x1b≦1, and 0.1≦(x1a+x1b)≦3. The Al wiring material of the present invention further contains one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y, and, when the total content of these elements is x2 [mass%], the following relationship is satisfied: 0.001≦x2≦0.5.

[0019] By including Mg and Si (hereinafter also referred to as "first group elements") in an Al wiring material, and further including one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y (hereinafter also referred to as "second group elements"), the high-temperature reliability of the Al wiring material can be improved, even when heat treatment during manufacturing or after connection is performed at a low temperature or for a short time. Room-temperature characteristics, such as ease of installation and connection to connected components and bondability, can also be improved. By simultaneously satisfying both high-temperature reliability and room-temperature characteristics, high-temperature reliability can be improved and promoted when used in high-power electronic devices such as automotive electronic components and power semiconductor devices. Furthermore, when the Al wiring material is connected to a connected component (e.g., an Al electrode) at room temperature, the unbonded area, where the metal bond is insufficient, can be reduced at the connection interface, resulting in increased bond strength and reduced connection peeling during mass production. Furthermore, the high-temperature reliability of connections can be improved during repeated thermal cycles of high and low temperatures during high-power operation of electronic devices. For example, in a power cycle test, which is an accelerated test for evaluating high-temperature reliability, it is possible to suppress a decrease in bonding strength and to suppress the occurrence of cracks in the connection portion.

[0020] The inclusion of Mg and Si suppresses the progression of recovery and recrystallization in high-temperature environments, even when the heat treatment temperature during manufacturing or after connection of the Al wiring material is low, due to the formation of solid solutions within the Al and Mg-Si compounds. Furthermore, the inclusion of one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y maintains the recrystallization suppression effect at higher temperatures or for longer periods, achieving excellent high-temperature reliability. Even under harsh conditions of over 10,000 cycles, power cycle tests using high voltages can suppress the occurrence of cracks due to coarsening of recrystallized grains at the connection points of the Al wiring material, thereby maintaining high bonding strength. Furthermore, optimizing the types and amounts of Group 1 and Group 2 elements can also increase bonding strength in high-temperature environments.

[0021] Although the factors that produce these improvements are not entirely clear, it is thought that low-temperature heat treatment causes the formation of Mg-Si compounds, precipitates, and intermediate phases, with elements such as Sc, Er, Yb, Gd, Ce, and Y gathering around these products, or that these elements react with Al to form precipitates (Al3Sc, Al3Er, Al3Yb, etc.).The combined action of these added elements is thought to suppress the movement of dislocations and grain boundaries within the Al wiring material in high-temperature environments, thereby maintaining or increasing strength, or to suppress the grain growth of recrystallization and thereby refine the crystal grains.

[0022] The Al wiring material of the present invention, which contains both first-group and second-group elements, is also superior in that it can improve bondability when connected to a connected component. Specifically, this Al wiring material can increase the effective bond area ratio R, which corresponds to the proportion of the area where a metal bond is achieved at the connection interface. As a result, even under conditions of low load and low ultrasonic vibration during connection, it can improve bond strength, which is effective in reducing damage to chips. While bondability can be roughly evaluated by bond strength using a shear measurement method, evaluating the R value is effective for more accurately assessing the actual state of the connection interface. Here, the effective bond area ratio R is calculated as the ratio of the area where a metal bond is achieved (M2) to the bond area (M1) (M2 / M1). For example, the effective bond area ratio R at the connection between the Al wiring material and an electrode on a semiconductor chip can be calculated using the following procedure. First, a shear test is performed on the connection, and the resulting broken connected electrode is observed using an optical microscope or SEM. Image analysis was then used to determine the bonded area M1 and the area of ​​the unbonded portion M3, where the electrode was deformed during bonding but a metallic bond was not achieved, and the area where a metallic bond was achieved M2 (= M1 - M3) was calculated. The R value can be calculated as the ratio of M2 to M1 (M2 / M1), and the specific formula for this calculation is R = M2 / M1 = (M1 - M3) / M1. It was discovered that the higher the R value, the better the bondability and the more effective it is in improving high-temperature reliability.

[0023] Although the inclusion of Mg and Si (first group elements) alone may maintain reliability in high-temperature environments for a short time, the problem is that reliability actually decreases over time. Furthermore, the inclusion of Sc, Er, Yb, Gd, Ce, and Y (second group elements) alone requires high-temperature heat treatment to improve high-temperature reliability, which can lead to a problem of reduced bonding strength of the Al wiring material. Furthermore, when heat treatment is performed after connecting the Al wiring material, a relatively high temperature and long time are required, which raises concerns about the impact on surrounding materials, as mentioned above.

[0024] In contrast, we have confirmed that the coexistence of group 1 and group 2 elements significantly improves high-temperature reliability and bondability, even when lowering the heat treatment temperature during manufacturing of Al wiring materials or the heat treatment temperature after connection. For example, we compare high-temperature reliability when the mounting heat treatment after connection is performed at a low temperature. Using power semiconductors bonded to Al electrodes, we performed mounting heat treatment at low temperatures and short times, i.e., at 200–300°C for 10 minutes to 2 hours, followed by a power cycle test. Al wiring materials containing both group 1 and group 2 elements maintained high bond strength up to 50,000 and 100,000 cycles, demonstrating favorable results. On the other hand, Al wiring materials containing only group 1 elements sometimes exhibited good strength up to 50,000 cycles, but showed a significant decrease in strength at 100,000 cycles. Al wiring materials containing only group 2 elements showed a decrease in strength at 50,000 cycles.

[0025] The second group elements Sc, Er, Yb, Gd, Ce, and Y can achieve the same effects. Furthermore, by utilizing the characteristics of each element, optimization can be tailored to meet specific requirements. For example, Sc can increase strength in high-temperature environments, thereby maintaining or even increasing joint strength even when the connection is exposed to harsh high-temperature environments during device operation or in operating environments where high voltages are rapidly switched on and off. Er can improve high-temperature reliability even when the heat treatment temperatures during the manufacturing of Al wiring materials or after connection are low. Yb has a fast diffusion rate within Al, which is advantageous for shortening the heat treatment time for precipitation strengthening. Gd has a strong tendency to reduce the hardness of Al wiring materials, thereby increasing their deformability at room temperature and improving initial bondability. Ce and Y promote work hardening of the wire near the bond interface, thereby stabilizing the shape and size of the wire bond. Adding multiple elements is also effective. For example, coexisting Sc and Ce or Sc and Yb can reduce their content and increase precipitation efficiency. The coexistence of Sc and Er can further reduce the heat treatment temperature. The combinations of the second group elements are not limited to these, and may include combinations of Sc and Gd, Sc and Y, Er and Yb, Er and Gd, Yb and Gd, Yb and Ce, or Ce and Y, or a combination of three of these elements, or a combination of all four elements.

[0026] The Al wiring material of the present invention contains Mg and Si as first group elements, with the Mg content being 0.05 to 2.5 mass%, the Si content being 0.02 to 1 mass%, and the total content of Mg and Si being 0.1 to 3 mass%. That is, when the Mg content in the Al wiring material is x1a [mass%] and the Si content is x1b [mass%], 0.05≦x1a≦2.5, 0.02≦x1b≦1, and 0.1≦(x1a+x1b)≦3 Meet the following.

[0027] To improve the strength when used in high-temperature environments and obtain an Al wiring material with good high-temperature reliability, the Mg content in the Al wiring material, i.e., x1a, is 0.05% by mass or more, preferably 0.06% by mass or more, 0.08% by mass or more, or 0.09% by mass or more, and more preferably 0.1% by mass or more, 0.15% by mass or more, 0.2% by mass or more, 0.25% by mass or more, or 0.3% by mass or more. It has been confirmed that, provided that the values ​​of x1b, (x1a + x1b), and x2 are within the ranges of the present invention, when x1a is 0.1% by mass or more, an Al wiring material with even better high-temperature properties can be obtained.

[0028] The upper limit of the Mg content in the Al wiring material, i.e., x1a, is 2.5% by mass or less, preferably 2.4%, 2.3%, 2.2%, or 2.1% by mass or less, and more preferably 2%, 1.9%, 1.8%, 1.6%, or 1.5% by mass or less, from the viewpoint of obtaining an Al wiring material with good room-temperature properties such as ease of installation and connection to a connected member and bondability. It has been confirmed that, provided that the values ​​of x1b, (x1a + x1b), and x2 are within the ranges of the present invention, when x1a is 2% by mass or less, an Al wiring material with a high effective bonding area ratio and even better room-temperature properties can be obtained.

[0029] Therefore, in a preferred embodiment, the content of Mg in the Al wiring material, that is, x1a, satisfies 0.05≦x1a≦2.5, and more preferably 0.1≦x1a≦2.

[0030] To improve the strength when used in high-temperature environments and obtain an Al wiring material with good high-temperature reliability, the Si content in the Al wiring material, i.e., x1b, is 0.02% by mass or more, preferably 0.03% by mass or more or 0.04% by mass or more, and more preferably 0.05% by mass or more, 0.06% by mass or more, 0.08% by mass or more, or 0.1% by mass or more. It has been confirmed that, provided that the values ​​of x1a, (x1a + x1b), and x2 are within the ranges of the present invention, when x1b is 0.05% by mass or more, an Al wiring material with even better high-temperature properties can be obtained.

[0031] The upper limit of the Si content in the Al wiring material, i.e., x1b, is 1% by mass or less, preferably 0.95%, 0.9%, or 0.85% by mass or less, and more preferably 0.8%, 0.75%, 0.7%, 0.65%, or 0.6% by mass or less, from the viewpoint of obtaining an Al wiring material with good room-temperature properties such as ease of installation and connection to a connected member and bondability. It has been confirmed that, provided that the values ​​of x1a, (x1a + x1b), and x2 are within the ranges of the present invention, when x1b is 0.8% by mass or less, an Al wiring material with a high effective bonding area ratio and even better room-temperature properties can be obtained.

[0032] Therefore, in a preferred embodiment, the content of Si in the Al wiring material, that is, x1b, satisfies 0.02≦x1b≦1, and more preferably 0.05≦x1b≦0.8.

[0033] To improve the strength when used in high-temperature environments and obtain an Al wiring material with good high-temperature reliability, the total content of Mg and Si in the Al wiring material, i.e., (x1a + x1b), is 0.1% by mass or more, preferably 0.12% by mass or more, 0.14% by mass or more, 0.16% by mass or more, or 0.18% by mass or more, and more preferably 0.2% by mass or more, 0.25% by mass or more, 0.3% by mass or more, 0.35% by mass or more, or 0.4% by mass or more. It has been confirmed that, provided that the values ​​of x1a, x1b, and x2 are within the ranges of the present invention, when (x1a + x1b) is 0.2% by mass or more, an Al wiring material with even better high-temperature properties can be obtained.

[0034] The upper limit of the total content of Mg and Si in the Al wiring material, i.e., (x1a + x1b), is 3% by mass or less, preferably 2.9%, 2.8%, 2.7%, or 2.6% by mass or less, and more preferably 2.5%, 2.4%, 2.3%, 2.2%, 2.1%, or 2% by mass or less, from the viewpoint of obtaining an Al wiring material with good room-temperature properties such as workability and bondability when installing and connecting to a connected member. It has been confirmed that, provided that the values ​​of x1a, x1b, and x2 are within the ranges of the present invention, when (x1a + x1b) is 2.5% by mass or less, an Al wiring material with a high effective bonding area ratio and even better room-temperature properties can be obtained.

[0035] Therefore, in a preferred embodiment, the total content of Mg and Si in the Al wiring material, i.e., (x1a+x1b), satisfies 0.1≦(x1a+x1b)≦3, and more preferably 0.2≦(x1a+x1b)≦2.5.

[0036] The Al wiring material of the present invention contains, as a second group element, one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y in a total amount of 0.001 to 0.5 mass %. That is, when the total content of the second group elements in the Al wiring material is x2 [mass %], the relationship 0.001≦x2≦0.5 is satisfied.

[0037] To improve the strength when used in high-temperature environments and obtain an Al wiring material with good high-temperature reliability, the total content of the second group elements in the Al wiring material, i.e., x2, is 0.001% by mass or more, preferably 0.002% by mass or more, 0.003% by mass or more, or 0.004% by mass or more, and more preferably 0.005% by mass or more, 0.006% by mass or more, 0.008% by mass or more, 0.01% by mass or more, 0.015% by mass or more, 0.02% by mass or more, 0.025% by mass or more, or 0.03% by mass or more. It has been confirmed that, provided that the values ​​of x1a, x1b, and (x1a + x1b) are within the ranges of the present invention, an Al wiring material with even better high-temperature properties can be obtained when x2 is 0.005% by mass or more.

[0038] The upper limit of the total content of the second group elements in the Al wiring material, i.e., x2, is 0.5% by mass or less, preferably 0.48% by mass or less or 0.46% by mass or less, and more preferably 0.45% by mass or less, 0.44% by mass or less, 0.42% by mass or less, 0.4% by mass or less, 0.38% by mass or less, 0.36% by mass or less, 0.35% by mass or less, 0.34% by mass or less, 0.32% by mass or less, or 0.3% by mass or less, from the viewpoint of obtaining an Al wiring material with good room-temperature properties, such as workability and bondability when installing and connecting to a connected member. It has been confirmed that, provided that the values ​​of x1a, x1b, and (x1a + x1b) are within the ranges of the present invention, when x2 is 0.35% by mass or less, an Al wiring material with a high effective bonding area ratio and even better room-temperature properties can be obtained.

[0039] Therefore, in a preferred embodiment, the total content of the second group elements in the Al wiring material, that is, x2, satisfies 0.001≦x2≦0.5, and more preferably 0.005≦x2≦0.35.

[0040] -Zr, Fe, Ni, Mn, Cu, 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 Zr, Fe, Ni, Mn, Cu, and Zn.

[0041] By including one or more elements selected from the group consisting of Zr, Fe, Ni, Mn, Cu, and Zn (also referred to as "third group elements") in addition to the first and second group elements, the strength when used in high-temperature environments can be increased, even if the heat treatment during manufacturing of the Al wiring material is performed at a lower temperature or for a shorter time, resulting in an Al wiring material with good high-temperature reliability. By shortening the heat treatment time, productivity during manufacturing of the Al wiring material can be improved and continuous operation is possible. Another significant effect is that even if the mounting heat treatment performed after connecting the Al wiring material is performed at a lower temperature and for a shorter time, or even if no mounting heat treatment is performed at all, an Al wiring material with good high-temperature reliability can be achieved. This reduces the burden on the mounting process due to the mounting heat treatment and reduces the thermal history of the connected components and surrounding components, resulting in further improved high-temperature reliability.

[0042] Regarding the heat treatment conditions during the manufacture of Al wiring materials, the treatment time can be shortened to 1 second to 10 minutes at a temperature range of 400 to 600°C. Furthermore, regarding the conditions for the mounting heat treatment, which is performed after connecting the Al wiring materials, the treatment time can also be shortened to 10 to 30 minutes at a low temperature range of 175 to 250°C. For example, when mounting heat treatment is performed at a low temperature of 175°C after connection, it has been confirmed that a short heat treatment time of approximately 20 minutes can suppress the decrease in bond strength in power cycle tests and achieve good high-temperature reliability. Furthermore, depending on the mounting structure and materials such as electrodes and substrates, good high-temperature reliability can be achieved even without mounting heat treatment.

[0043] The synergistic effect achieved by adding the third group elements Zr, Fe, Ni, Mn, Cu, and Zn in addition to the first and second group elements is thought to be due to the promotion of the formation of the aforementioned Mg-Si intermediate phase and the precipitation of intermetallic compounds, as well as the promotion of the diffusion of the second group elements Sc, Er, Yb, Gd, Ce, and Y to promote the formation of fine precipitates (Al3Sc, Al3Er, Al3Yb, Al3Gd, etc.), thereby suppressing the coarsening of crystal grains at high temperatures.

[0044] The Al wiring material of the present invention preferably contains one or more third group elements selected from the group consisting of Zr, Fe, Ni, Mn, Cu, and Zn in a total amount of 0.01 to 0.5 mass %. That is, when the total content of the third group elements in the Al wiring material is x3 [mass %], it is preferable that the relationship 0.01≦x3≦0.5 is satisfied.

[0045] To obtain an Al wiring material that has high strength and good high-temperature reliability when used in high-temperature environments, even when heat treatment during production or after connection is performed at a low temperature or for a short time, the total content of Group 3 elements in the Al wiring material, i.e., x3, is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, 0.03% by mass or more, or 0.04% by mass or more, and even more preferably 0.05% by mass or more, 0.06% by mass or more, 0.08% by mass or more, or 0.1% by mass or more. It has been confirmed that, provided that the values ​​of x1a, x1b, (x1a + x1b), and x2 are within the ranges of the present invention, when x3 is 0.05% by mass or more, an Al wiring material with good high-temperature properties can be obtained, even when heat treatment during production or after connection is performed at a lower temperature or for a shorter time.

[0046] The upper limit of the total content of Group 3 elements in the Al wiring material, i.e., x3, is preferably 0.5% by mass or less, more preferably 0.45% by mass or less, and even more preferably 0.4% by mass or less, 0.38% by mass or less, 0.36% by mass or less, 0.35% by mass or less, 0.34% by mass or less, 0.32% by mass or less, or 0.3% by mass or less, from the viewpoint of obtaining an Al wiring material with good room-temperature properties such as workability and bondability when installing and connecting to a connected member. It has been confirmed that, provided that the values ​​of x1a, x1b, (x1a + x1b), and x2 are within the ranges of the present invention, when x3 is 0.4% by mass or less, an Al wiring material with a high effective bonding area ratio and even better room-temperature properties can be obtained.

[0047] Therefore, in a preferred embodiment, the total content of the third group elements in the Al wiring material, that is, x3, satisfies 0.01≦x3≦0.5, and more preferably 0.05≦x3≦0.4.

[0048] The balance 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 more) can be used as the aluminum raw material when producing the Al wiring material. It is more preferable to use aluminum with a purity of 5N (Al: 99.999% by mass or more), which has a lower impurity content. The balance of the Al wiring material of the present invention may contain elements other than Al, as long as the effects of the present invention are not impaired. The Al content of the balance of the Al wiring material of the present invention is not particularly limited as long as the effects of the present invention are not impaired, but is preferably 98% by mass or more, 98.5% by mass or more, 99% by mass or more, 99.5% by mass or more, 99.6% by mass or more, 99.7% by mass or more, 99.8% by mass or more, or 99.9% by mass or more. In a preferred embodiment, the balance of the Al wiring material of the present invention consists of Al and inevitable impurities.

[0049] The contents of the first group elements, second group elements, third group elements, etc. in the Al wiring material can be measured by the method described later in [Measurement of element contents].

[0050] The Al wiring material of the present invention may or may not have a coating mainly composed of an element other than Al on its outer periphery. In a preferred embodiment, the Al wiring material of the present invention does not have a coating mainly composed of a metal other than Al on its outer periphery. 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.

[0051] The Al wiring material of the present invention maintains or improves its strength and exhibits good high-temperature reliability when used in high-temperature environments, and can also improve room-temperature properties such as ease of installation and connection to equipment and bondability, without the need for low-temperature or short-time heat treatment during wiring material production or post-connection heat treatment. Therefore, the Al wiring material of the present invention can be used in a wide range of applications requiring both high-temperature reliability and room-temperature properties when connecting to connected components. For example, the Al wiring material of the present invention can be suitably used for connecting to connected components in industrial equipment such as transport equipment and robots (Al wiring material for industrial equipment), and can also be suitably used for connecting to connected components in various semiconductor devices, including power semiconductor devices (Al wiring material for semiconductor devices).

[0052] The Al wiring material of the present invention may have any dimensions depending on its specific usage. 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, and for example, w may be 500 μm to 10 mm. It may also be a stranded wire made up of multiple such Al wires. When it is an Al strip, the dimensions (w×t) of its rectangular or approximately rectangular cross section are not particularly limited, and for example, w may be 500 μm to 10 mm, and t may be 50 μm to 2 mm. 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, and for example, the diameter may be 50 to 600 μm. When it is an Al bonding ribbon, the dimensions (w×t) of its rectangular or approximately rectangular cross section are not particularly limited, and for example, w may be 100 to 3000 μm, and t may be 50 to 600 μm.

[0053] 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 small, wire drawing using a diamond die is preferable. 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 reducing resistance during wire drawing to increase productivity, hot processing, in which wire is heated and drawn, may be used.

[0054] 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, 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 to produce this ingot can be performed using either a batch or continuous casting method. Continuous casting has excellent productivity, but the batch method makes it easy to change the cooling temperature conditions for solidification. This ingot is then processed to the final dimensions to form the Al wiring material.

[0055] It is preferable to perform solution heat treatment in the ingot state, or during or after processing, to dissolve and uniformly distribute each additive element. In solution heat treatment, the additive elements are dissolved in Al at high temperatures where solid solubility is high, and then cooled to room temperature at a rapid cooling rate using water or air cooling to prevent precipitation of the dissolved elements. Solution heat treatment conditions include, for example, heating at a temperature range of 500 to 640°C for 0.5 to 20 hours, followed by cooling using water or air cooling. Heat treatment at a high temperature where solubility is high redissolves precipitates formed during solidification of the ingot, resulting in a uniform distribution of the additive elements. Using a master alloy containing a high concentration of the additive element facilitates control of the solid solution state, allowing for a shorter heating time. Alternatively, increasing the cooling rate during solidification can be used as a substitute for solution heat treatment. For example, with the continuous casting method, the solidification rate can be made faster than with the batch melting method, so it is relatively easy to dissolve the added elements in the aluminum, and it is possible to avoid carrying out solution heat treatment.

[0056] To promote precipitation in solution-heat-treated Al alloys, precipitation heat treatment may be performed. Precipitation heat treatment can be performed immediately after melting and solidification or solution heat treatment, or during or after subsequent processing. Since precipitate formation progresses, it is desirable to optimize the heat treatment conditions to obtain the desired mechanical properties.

[0057] When precipitation heat treatment is performed batchwise in a large-diameter state, the precipitation heat treatment may be performed, for example, by heating at a temperature range of 200 to 450°C for 10 minutes to 5 hours. Specific examples include 3 hours at 250°C and 30 minutes at 350°C. Alternatively, when precipitation heat treatment is performed continuously in a processed, small-diameter state, the precipitation heat treatment may be performed, for example, by heating at a temperature range of 400 to 600°C for 1 second to 5 minutes. Specific examples include heating at 400°C for 1 second to suppress the progression of precipitation, and heating at 500°C for 40 seconds to promote the formation of precipitates. For more detailed optimization of conditions, isothermal or isochronal heat treatment can be performed with reference to these heat treatment conditions, allowing for easy optimization of temperature, time, etc. For example, by producing prototype Al wiring materials isothermally heat-treated under several time conditions and measuring their mechanical properties, desired properties can be easily reproduced.

[0058] The Al wiring material may be subjected to a refining heat treatment during processing or at the final wire diameter. The refining heat treatment removes processing strain, forms a recrystallized structure, and can also form precipitates. This refining heat treatment is preferably performed continuously while the Al wiring material is continuously swept in a heating furnace. Examples of the heat treatment conditions include heating for a short time of 0.1 seconds to 2 minutes in a temperature range of 300 to 600°C. Since the refining heat treatment can also promote precipitation, the refining heat treatment can also serve as a precipitation heat treatment depending on the required degree of precipitation.

[0059] In a semiconductor device, 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 the second connection to an external electrode on a lead frame or substrate. After connection to the connected member, a mounting heat treatment of the semiconductor device including the Al wiring material may be performed. The mounting heat treatment forms precipitates, which are intermetallic compounds containing additive elements, in the Al wiring material, which can further increase strength through precipitation strengthening. The composition and form of the precipitates formed in the Al wiring material of the present invention are as described above.

[0060] The conditions for the mounting heat treatment are not particularly limited as long as an intermetallic compound can be formed, but it is preferable to heat for 10 to 60 minutes at a temperature range of 175 to 400° C. The mounting heat treatment may be performed in air, but may also be performed in an inert atmosphere such as nitrogen or argon to prevent oxidation of the components.

[0061] The present invention also provides a method for manufacturing a semiconductor device. In a preferred embodiment, the method for manufacturing a semiconductor device of the present invention includes the steps of: (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 connecting with Al wiring material, the process of performing mounting heat treatment Includes.

[0062] The semiconductor chip, lead frame, or substrate used in step (A) may be any known material that can be used to construct a semiconductor device, as described below. 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. In step (B), a fine precipitate phase of the intermetallic compound described above can be formed in the Al wiring material.

[0063] [Semiconductor Devices] By using the Al wiring material 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.

[0064] The semiconductor device of the present invention includes the Al wiring material of the present invention. The Al wiring material of the present invention can improve workability and bondability during installation and connection to a device, and can exhibit good high-temperature reliability by low-temperature or short-time heat treatment during wiring material production or heat treatment after connection, or without the need for such heat treatment. Therefore, a semiconductor device including the Al wiring material can achieve good operational reliability over a long period of time, even in a high-temperature operating environment, and can minimize thermal effects on connected components, thereby comprehensively satisfying many required performance requirements.

[0065] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, and an Al wiring material for electrically connecting the circuit board and the semiconductor chip, wherein the Al wiring material is the Al wiring material of the present invention. Here, the "Al wiring material of the present invention" in relation to the semiconductor device of the present invention is characterized by containing a first group element, a second group element, and optionally a third group element in the aforementioned preferred concentration ranges.

[0066] 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 precipitates separated from Al (for example, precipitates made of intermetallic compounds containing the aforementioned additive elements) as fine phases.

[0067] 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 configure a semiconductor device may be used. Alternatively, a lead frame may be used instead of the circuit board. For example, the semiconductor device may be configured to include a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor devices described in JP 2020-150116 A and JP 2002-246542 A.

[0068] Examples of semiconductor devices include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, aircraft, etc.), and among these, power semiconductor devices are preferred. [Example]

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

[0070] (sample) First, the method for preparing the samples will be described. Al with a purity of 5N (99.999% by mass or more) and Mg, Si, Sc, Er, Yb, Gd, Ce, Y, Zr, Fe, Ni, Mn, Cu, and Zn with a purity of 99.9% by mass or more were melted as raw materials to prepare Al ingots with the compositions shown in Tables 1 and 2. Next, solution heat treatment was performed at 550 to 640°C for 5 hours and then quenched (water-cooled). The ingots were extruded, swaged, and then wiredrawn. For some samples, when the wire diameter was 2 mm, precipitation heat treatment was performed at 300 to 500°C for 1 to 30 minutes. Then, die wiredrawing was performed to a final wire diameter of 300 μm, and after wiredrawing, a thermal refining heat treatment was performed for 2 seconds to obtain Al wiring materials.

[0071] [Measurement of element content] The content of added elements in the Al wiring material was measured using an ICP-OES (Hitachi High-Tech Science Corporation, "PS3520UVDDII") or an ICP-MS (Agilent Technologies, Inc., "Agilent 7700x ICP-MS") as an analytical device.

[0072] <Connection> In the semiconductor device, the electrodes of the semiconductor chip were Al-Cu pads (2 μm thick), and the external terminals were Ni-coated Cu lead frames. Both the first connection between the electrodes of the semiconductor chip and the Al wiring material and the second connection between the external terminals and the Al wiring material were wedge-bonded. For each example, a mounting heat treatment was performed under the following conditions: (1) 200°C for 30 minutes, or (2) 175°C for 30 minutes.

[0073] <Evaluation of bonding> -Joining strength- Regarding the bond strength of the Al wiring material in the semiconductor device, the initial shear strength S1 of the first connection part (before the power cycle test) was measured (number of evaluations: N = 20). If the S1 value was 9N or more, the bond strength was good and was marked as "○", if it was 7N or more but less than 9N, there was no problem in normal use but caution was required and it was marked as "△", and if it was less than 7N, the bondability was poor and it was marked as "×", and these were recorded in the "Bond Strength" column in Tables 1 and 2.

[0074] -Effective bonding area ratio- The effective bonding area ratio (R value) of the Al wiring material in the semiconductor device was determined by observing the broken connected electrode of the first connection part where the shear strength S1 was measured using an optical microscope or SEM. Image analysis was then used to measure the bonding area M1 and the unbonded area M3, where the electrode was deformed but no metallic bond was obtained, and calculate the area where a metallic bond was obtained M2 (= M1 - M3). The R value was calculated as the ratio of M2 to M1 (M2 / M1). An R value of 0.9 or greater indicates good bonding and is marked with a "Good"; an R value of 0.7 to 0.9 but less than 0.9 indicates acceptable bonding in normal use but requires caution and is marked with a "Good"; and an R value of less than 0.7 indicates poor bonding and is marked with an "Poor"; these values ​​are listed in the "Effective Bonding Area Ratio" column in Tables 1 and 2.

[0075] -Chip damage- Chip damage in the semiconductor device was evaluated by dissolving the metal on the pad surface with acid and observing under a microscope (number of evaluations N = 50). A good case with no cracks or bonding traces was marked with "○", a case with no cracks but some bonding traces (3 or less out of 50 evaluations) was marked with "△", and all other cases were marked with "×", and these are shown in the "Chip Damage" column in Tables 1 and 2.

[0076] <Evaluation of high-temperature reliability> High-temperature reliability was evaluated using a power cycle test. In the power cycle test, semiconductor devices connected to Al wiring materials were alternately heated and cooled. Heating was performed over two seconds until the maximum temperature reached approximately 140°C, and then cooling was performed over 25 seconds until the temperature of the connection reached 30°C. This heating-cooling cycle was repeated. For semiconductor devices that underwent a 30-minute mounting heat treatment at 200°C, the above cycle was repeated both 50,000 times and 100,000 times, and evaluation was performed on these devices. For semiconductor devices that underwent a 30-minute mounting heat treatment at 175°C, the above cycle was repeated 50,000 times, and evaluation was performed on these devices.

[0077] After the power cycle test, the joint shear strength of the first connection was measured and the high-temperature reliability of the connection was evaluated. Evaluation was based on S2 / S1, which is the ratio of the shear strength S2 after the power cycle test to the initial shear strength S1 of the connection. For S2 / S1, a value of 0.9 or higher indicates excellent reliability and is marked with a "◎", a value of 0.8 or higher but less than 0.9 indicates good reliability and is marked with a "○", a value of 0.6 or higher but less than 0.8 indicates no problem with normal use but requires caution and is marked with a "△", and a value less than 0.6 indicates poor high-temperature reliability and is marked with an "×", as shown in the "High-Temperature Reliability of Connection" column in Tables 1 and 2.

[0078] Tables 1 and 2 show the manufacturing conditions and evaluation results of the Al wiring material.

[0079] [Table 1]

[0080] [Table 2]

[0081] The Al wiring materials of Examples 1 to 33 had Mg and Si contents and the total contents of Sc, Er, Yb, Gd, Ce, and Y within the range of the present invention, and exhibited good bonding properties regardless of whether heat treatment was performed during wiring material manufacturing or the temperature and time of heat treatment during wiring material manufacturing and heat treatment after connection.The high-temperature reliability (50,000 cycles) was also evaluated as ◎, showing good results. The Al wiring materials of Examples 2 to 4, 6 to 10, 12, 14 to 16, 18 to 25, 27, 28, and 30 to 33 further had Zr, Fe, Ni, Mn, Cu, and Zn contents within the preferred ranges of the present invention, and when heat treatment (mounting heat treatment) after connection was performed at a low temperature of 175°C for 30 minutes, the high-temperature reliability was evaluated as ◎, showing good results. The Al wiring materials of Comparative Examples 1 to 3 and 8 had Sc, Er, Yb, Gd, Ce and Y contents outside the lower limit of the range of the present invention, and the Al wiring materials of Comparative Examples 4, 5 and 10 to 13 had Mg and Si contents (at least one of x1a, x1b and x1a+x1b) outside the lower limit of the range of the present invention, resulting in high-temperature reliability of the connection being rated ×. The Al wiring materials of Comparative Examples 6 and 7 had Mg and Si contents (at least one of x1a, x1b and x1a+x1b) outside the upper limit of the range of the present invention, and the Al wiring material of Comparative Example 9 had Sc, Er, Yb, Gd, Ce and Y contents outside the upper limit of the range of the present invention, resulting in chip damage being rated ×. It was confirmed that the Al wiring materials according to Examples 1 to 33 exhibited better results than the comparative examples in terms of high-temperature reliability and bondability, even when no heat treatment was performed after mounting after connection.

Claims

1. When Mg and Si are contained, and the Mg content is x1a [mass%] and the Si content is x1b [mass%], 0.05≦x1a≦2.5, 0.04≦x1b≦1, 0.1≦(x1a+x1b)≦3 and further containing one or more elements selected from the group consisting of Sc, Er, Yb, Gd, Ce, and Y, and when the total content thereof is x2 [mass%], 0.001≦x2≦0.5 and the remainder is Al, An Al wiring material that is a bonding wire or a bonding ribbon.

2. When the alloy further contains one or more elements selected from the group consisting of Zr, Fe, Ni, Mn, Cu, and Zn, and the total content of the elements is x3 [mass%], 0.01≦x3≦0.5 The Al wiring material according to claim 1 ,

3. 0.06≦x3≦0.5 The Al wiring material according to claim 2 ,

4. 0.08≦x1b≦0.75 The Al wiring material according to any one of claims 1 to 3,

5. An Al wiring material described in any one of claims 1 to 4, which contains one or more elements selected from the group consisting of Er, Yb, Gd, Ce and Y.

6. When the Al wiring material is a bonding wire, the wire diameter is 50 to 600 μm, 6. The Al wiring material according to claim 1, wherein when the Al wiring material is a bonding ribbon, the length of the short side of its rectangular or approximately rectangular cross section is 50 to 600 μm.

7. The Al wiring material according to any one of claims 1 to 6, which is a bonding wire.

8. A semiconductor device comprising the Al wiring material according to any one of claims 1 to 7.

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