Al bonding wire

Abstract

Provided is a novel Al-Mg alloy-based Al bonding wire that has excellent wire drawing and wedge bonding characteristics, as well as excellent reliability at high temperature and high humidity. This Al bonding wire is characterized by containing 0.10-2.0 mass% of Mg, 5-500 mass ppm in total of one or more elements (also referred to as "first group elements") selected from the group consisting of Ga, Ge, Ta, and Ag, and 5-500 mass ppm of Ni, wherein the balance includes Al.

Description

Al bonding wire

[0001] The present invention relates to an Al bonding wire.

[0002] In semiconductor devices, electrodes formed on a semiconductor chip are connected to electrodes on a lead frame or a substrate by bonding wires. The bonding wire connection process is completed by first bonding to an electrode on the semiconductor chip, then forming a loop, and then second bonding the wire portion to an external electrode on the lead frame or substrate. Gold (Au), copper (Cu), or aluminum (Al) is used as the material for the bonding wire depending on the type and function of the semiconductor device. For Au and Cu bonding wires, ball bonding is used for the first bonding and wedge bonding is used for the second bonding. For Al bonding wires, wedge bonding is usually used for both the first and second bonding. Ball bonding refers to a technique in which the tip of the wire is heated and melted by arc heat input, forming a free air ball (FAB) due to surface tension, and then crimping and bonding the ball portion to an electrode on the semiconductor chip. Wedge bonding refers to a technique in which the wire is crimped and bonded to an electrode without forming a ball.

[0003] Thick Al bonding wires (mainly with a wire diameter of over 100 μm) used as connecting materials for semiconductor devices use high-purity Al of 4N to 5N. On the other hand, thin Al bonding wires (mainly with a wire diameter of 100 μm or less) require higher strength than thick Al bonding wires to prevent breakage during wire drawing and wedge bonding. Therefore, Al-Si alloys strengthened by the addition of silicon (Si) have traditionally been used. For example, Patent Document 1 discloses a bonding wire formed by melting an Al-Si alloy containing 0.1 to 5 mass% silicon (Si), the remainder being Al and impurities, and then spray-quenching the melted Al-Si alloy to form it into a thin wire. This patent document discloses that mechanical strength is improved by quenching the molten Al-Si alloy to finely and uniformly disperse the Si.

[0004] Japanese Patent Application Publication No. 59-57440

[0005] In conventional Al-Si alloy-based Al bonding wires, the amount of Si added to ensure a certain level of strength tends to lead to the formation of crystallized particles during casting, and also to the formation of precipitates during subsequent heat treatment. Therefore, there is a problem that these crystallized particles and precipitates cause stress concentration during wire drawing, which can easily lead to wire breakage. Furthermore, the presence of these crystallized particles and precipitates on the wire surface can have a negative effect on bonding, reducing wedge bondability. To solve these problems, it is necessary to uniformly disperse the crystallized particles and precipitates, which requires heat treatment (solution treatment), which tends to increase energy consumption and costs during manufacturing.

[0006] In this regard, by using magnesium (Mg) instead of Si as an alloying element, strength can be increased by solid solution strengthening (for example, Light Metals, Vol. 38, No. 8 (1988), pp. 496-512), and the effects of crystallized substances and precipitates such as those caused by the addition of Si can be eliminated. However, when a thin Al bonding wire is manufactured using an Al-Mg alloy to which Mg is added alone, a repeated yield phenomenon specific to Al-Mg alloys occurs, making the stress applied to the wire during processing unstable. When the wire diameter is thinned to about 30 μm, the frequency of wire breakage tends to increase, and there is room for improvement in wiredrawability.

[0007] In recent years, bonding wires have been required to have good reliability in high-temperature, high-humidity environments. However, in the case of Al bonding wires that have been strengthened by adding Mg, corrosion progresses in high-temperature, high-humidity environments, and there have been cases where reliability in high-temperature, high-humidity environments (hereinafter also referred to as "high-temperature, high-humidity reliability") has not been sufficiently obtained.

[0008] An object of the present invention is to provide a novel Al-Mg alloy-based Al bonding wire that has good wiredrawability and wedge bondability, and also has good high-temperature, high-humidity reliability.

[0009] As a result of intensive research into the above-mentioned problems, the inventors discovered that the above-mentioned problems can be solved by an Al bonding wire having the following configuration, and through further research based on this finding, they completed the present invention.

[0010] That is, the present invention includes the following: <1> An Al bonding wire containing 0.10 to 2.0 mass% Mg, one or more elements selected from the group consisting of Ga, Ge, Ta, and Ag (hereinafter referred to as "first group elements") in a total amount of 5 to 500 mass ppm, 5 to 500 mass ppm Ni, and the balance including Al. <2> The Al bonding wire according to <1>, having a Si content of 100 mass ppm or less. <3> The Al bonding wire according to <1> or <2>, having a wire diameter of 15 to 100 μm.

[0011] According to the present invention, it is possible to provide a novel Al-Mg alloy-based Al bonding wire that has good wiredrawability and wedge bondability, and also has good high-temperature, high-humidity reliability.

[0012] The present invention will be described in detail below with reference to preferred embodiments thereof. The present invention is not limited to the following description, and each component can be appropriately modified within the scope of the present invention.

[0013] [Al Bonding Wire] The Al bonding wire of the present invention (hereinafter also referred to as "Al wire of the present invention" or "Al wire") contains 0.10 to 2.0 mass% Mg, a total of 5 to 500 mass ppm of one or more elements selected from the group consisting of Ga, Ge, Ta, and Ag (hereinafter referred to as "first group elements"), 5 to 500 mass ppm of Ni, and the balance being Al.

[0014] By adding 0.10 to 2.0 mass% Mg, the strength of the Al wire can be increased by solid solution strengthening. This eliminates the effects of crystallized deposits and precipitates, as occurs with conventional Si addition, and can achieve good wedge bondability. Furthermore, the inventors have discovered that adding specific amounts of specific first-group elements and Ni in addition to Mg can suppress the occurrence of wire breakage during wire drawing and the occurrence and progression of corrosion in high-temperature, high-humidity environments, which can be problems with Al-Mg alloy-based Al wires. Thus, the present invention significantly contributes to the practical application of Al-Mg alloy-based Al bonding wires.

[0015] - Mg Concentration - In order to obtain an Al wire that exhibits good wiredrawability, wedge bondability, and good high-temperature, high-humidity reliability in a combination of a first group element described below and Ni, the Mg concentration in the Al wire of the present invention is 0.10 to 2.0 mass%. In order to achieve an Al wire that exhibits even better wiredrawability and wedge bondability, as well as better high-temperature, high-humidity reliability, even when producing a thin Al wire, the Mg concentration in the Al wire is preferably 0.20 mass% or more, more preferably 0.30 mass% or more, and even more preferably 0.40 mass% or more, 0.50 mass% or more, 0.60 mass% or more, 0.80 mass% or more, or 1.0 mass% or more. It has been confirmed that, provided that the concentrations of the first group elements described below and the Ni concentration are within the ranges of the present invention, an Mg concentration of 0.40 mass% or more (more preferably 0.50 mass% or more) can realize an Al wire that exhibits even better wiredrawability, wedge bondability, and high-temperature, high-humidity reliability.

[0016] From the viewpoint of being able to achieve Al wire that exhibits better wiredrawability and wedge bondability as well as better high-temperature, high-humidity reliability even when manufacturing a thin Al wire, and from the viewpoint of suppressing an increase in resistivity and obtaining good conductivity, the upper limit of the Mg concentration in the Al wire is preferably 1.9 mass% or less, 1.8 mass% or less, 1.7 mass% or less, 1.6 mass% or less, or 1.5 mass% or less.

[0017] - Concentration of First Group Elements (Ga, Ge, Ta, Ag) - From the viewpoint of providing an Al wire that exhibits good wiredrawability, wedge bondability, and good high-temperature, high-humidity reliability in a combination of the above-mentioned Mg and the later-described Ni, the Al wire of the present invention contains a first group element, that is, one or more elements selected from the group consisting of Ga, Ge, Ta, and Ag, and the total concentration of the first group elements is 5 to 500 ppm by mass.

[0018] From the viewpoint of achieving an Al wire that exhibits better wiredrawability and wedge bondability as well as better high-temperature, high-humidity reliability even when producing a thin Al wire, the total concentration of the first group elements in the Al wire is preferably 10 ppm by mass or more, more preferably 20 ppm by mass or more, 30 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more, even more preferably 60 ppm by mass or more or 80 ppm by mass or more, and still more preferably 100 ppm by mass or more, more than 100 ppm by mass, 120 ppm by mass or more, 140 ppm by mass or more, 160 ppm by mass or more, 180 ppm by mass or more, or 200 ppm by mass or more. It has been confirmed that, provided that the above-mentioned Mg concentration and the below-described Ni concentration are within the ranges of the present invention, when the total concentration of the first group elements is 100 ppm by mass or more (more preferably more than 100 ppm by mass), an Al wire having even better wiredrawability, wedge bondability, and high-temperature / high-humidity reliability can be realized.

[0019] From the viewpoint of being able to achieve an Al wire that exhibits better wiredrawability and wedge bondability as well as better high-temperature, high-humidity reliability even when manufacturing a thin Al wire, and from the viewpoint of suppressing an increase in resistivity and obtaining good conductivity, the upper limit of the total concentration of the first group elements in the Al wire is preferably 480 ppm by mass or less, more preferably 460 ppm by mass or less, still more preferably 450 ppm by mass or less, 440 ppm by mass or less, 420 ppm by mass or less, or 400 ppm by mass or less.

[0020] When Ag is contained as a first group element, the concentration of Ag in the Al wire of the present invention may be determined so as to satisfy the above-mentioned total concentration in relation to the other first group elements. For example, the concentration of Ag in the Al wire of the present invention may be 380 mass ppm or less, 360 mass ppm or less, 350 mass ppm or less, 340 mass ppm or less, 320 mass ppm or less, 300 mass ppm or less, 280 mass ppm or less, etc. The concentrations of the other first group elements (Ga, Ge, Ta) may also be the same as above.

[0021] -Ni Concentration- In the above combination of Mg and the first group element, from the viewpoint of obtaining an Al wire exhibiting good wiredrawability, wedge bondability, and good high-temperature, high-humidity reliability, the Al wire of the present invention contains Ni, and the concentration thereof is 5 to 500 ppm by mass.

[0022] From the viewpoint of achieving an Al wire that exhibits better wiredrawability and wedge bondability as well as better high-temperature, high-humidity reliability even when producing a thin Al wire, the Ni concentration in the Al wire is preferably 10 ppm by mass or more, more preferably 20 ppm by mass or more, 30 ppm by mass or more, or 40 ppm by mass or more, and even more preferably 50 ppm by mass or more, 60 ppm by mass or more, 80 ppm by mass or more, or 100 ppm by mass or more. It has been confirmed that, provided that the Mg concentration and the total concentration of the first group elements are within the ranges of the present invention, when the Ni concentration is 50 ppm by mass or more, an Al wire that exhibits better wiredrawability, wedge bondability, and high-temperature, high-humidity reliability can be achieved.

[0023] From the viewpoint of achieving an Al wire that exhibits better wiredrawability and wedge bondability as well as better high-temperature, high-humidity reliability even when producing a thin Al wire, the upper limit of the Ni concentration in the Al wire is preferably 480 ppm by mass or less, more preferably 460 ppm by mass or less, and even more preferably 450 ppm by mass or less, 440 ppm by mass or less, 420 ppm by mass or less, or 400 ppm by mass or less. In this regard, if the Ni concentration exceeds 500 ppm by mass, Ni crystallization at grain boundaries tends to occur significantly, and wiredrawability tends to deteriorate. The Ni concentration may be, for example, 380 ppm by mass or less, 360 ppm by mass or less, 350 ppm by mass or less, 340 ppm by mass or less, 320 ppm by mass or less, 300 ppm by mass or less, or 280 ppm by mass or less.

[0024] In the Al wire of the present invention, the total concentration of the first group elements (Ga, Ge, Ta, Ag) and Ni may be determined appropriately as long as the total concentration range of the first group elements and the concentration range of Ni are satisfied. That is, the total concentration of the first group element and Ni may be determined in the range of 10 ppm by mass or more and 1000 ppm by mass or less, and the lower limit is preferably 20 ppm by mass or more, 40 ppm by mass or more, or 50 ppm by mass or more, more preferably 60 ppm by mass or more, 80 ppm by mass or more, 100 ppm by mass or more, 120 ppm by mass or more, or 140 ppm by mass or more, even more preferably 150 ppm by mass or more, 160 ppm by mass or more, 180 ppm by mass or more, or 200 ppm by mass or more, and the upper limit is preferably 960 ppm by mass or less, more preferably 920 ppm by mass or less, even more preferably 900 ppm by mass or less, 880 ppm by mass or less, 840 ppm by mass or less, or 800 ppm by mass or less.

[0025] When Ag is contained as a first group element, the total concentration of Ag and Ni in the Al wire of the present invention may be determined so as to satisfy the above total concentration of the first group element and Ni in relation to the other first group elements. For example, the total concentration of Ag and Ni in the Al wire of the present invention may be less than 600 ppm by mass, 580 ppm by mass or less, 560 ppm by mass or less, 550 ppm by mass or less, 540 ppm by mass or less, 520 ppm by mass or less, 500 ppm by mass or less, etc. The total concentration of each of the other first group elements (Ga, Ge, Ta) and Ni may also be the same as above.

[0026] With regard to the Al wire of the present invention containing a first group element and Ni in combination with a predetermined amount of Mg, even if the total concentration of the first group element and Ni is, for example, less than 600 ppm by mass, 580 ppm by mass or less, 560 ppm by mass or less, 550 ppm by mass or less, 540 ppm by mass or less, 520 ppm by mass or less, 500 ppm by mass or less, it is possible to obtain an Al wire that exhibits good wiredrawability, wedge bondability, and good high-temperature, high-humidity reliability.

[0027] For example, an ICP (Inductively Coupled Plasma) optical emission spectrometer or an ICP mass spectrometer can be used to analyze the concentration of elements contained in the Al wire of the present invention. When elements derived from atmospheric contaminants such as oxygen and carbon are adsorbed on the surface of the Al wire, it is effective to wash the surface with an acid or alkali according to the adsorbed substance before analysis.

[0028] Other Preferred Configurations The following describes other preferred configurations that the Al bonding wire of the present invention should satisfy.

[0029] As described above, in the Al wire of the present invention, by using Mg instead of Si as an alloying element, the strength can be increased by solid solution strengthening, and the influence of crystallized substances and precipitates such as those caused by the addition of Si can be eliminated, thereby achieving good wedge bondability. Therefore, it is effective to observe the cross section of the Al wire to confirm that it has the desired structure.

[0030] Furthermore, as mentioned above, the stress applied to the Al wire during drawing or tensioning becomes unstable due to the repeated yielding phenomenon specific to Al-Mg alloys, but this effect is less likely to occur during compressive deformation. Therefore, it is also effective to check the compressive strength as a configuration that can achieve good wedge weldability.

[0031] As the aluminum raw material for producing the Al wire of the present invention, it is preferable to use Al having a purity of 4N (Al: 99.99% by mass or more), and it is more preferable to use Al having a purity of 5N (Al: 99.999% by mass or more) or more, which has a smaller amount of impurities.

[0032] The Al wire of the present invention may further contain elements other than Al, Mg, the first group element, and Ni (hereinafter also referred to as "other elements"), as long as the effects of the present invention are not impaired. The total concentration of the other elements in the Al wire is not particularly limited as long as the effects of the present invention are not impaired. The total concentration of the other elements may be, for example, 500 ppm by mass or less, 400 ppm by mass or less, 300 ppm by mass or less, 200 ppm by mass or less, 150 ppm by mass or less, or 100 ppm by mass or less. The lower limit of the total concentration of the other elements is not particularly limited, and may be 0 ppm by mass.

[0033] For example, in the Al wiring material of the present invention, the concentration (content) of Si is preferably 100 ppm by mass or less, more preferably 80 ppm by mass or less, and even more preferably 60 ppm by mass or less, 50 ppm by mass or less, 40 ppm by mass or less, 20 ppm by mass or less, or 10 ppm by mass or less. This is preferable because the effects of the present invention can be further enjoyed. The lower limit of the Si content is not particularly limited and may be 0 ppm by mass.

[0034] In one embodiment, the balance of the Al wire of the present invention consists of Al and inevitable impurities. Therefore, in a preferred embodiment, the Al wire of the present invention consists of Al, Mg, a first group element, Ni, and inevitable impurities.

[0035] In a preferred embodiment, the Al wire of the present invention does not have a coating mainly composed of a metal on the outer periphery of the Al wire. Here, the "coating mainly composed of a metal" refers to a coating having a metal content of 50 mass % or more.

[0036] The wire diameter of the Al wire of the present invention is not particularly limited and may be determined appropriately depending on the specific purpose, but is preferably 15 μm or more, 18 μm or more, or 20 μm or more. The upper limit of the wire diameter is not particularly limited and may be, for example, 100 μm or less, 80 μm or less, 70 μm or less, or 50 μm or less. Therefore, in one embodiment, the wire diameter of the Al bonding wire of the present invention is 15 to 100 μm.

[0037] The Al wire of the present invention can provide good wiredrawability, wedge bondability, and high-temperature, high-humidity reliability. Therefore, the Al wire of the present invention can be suitably used as an Al bonding wire for semiconductor devices.

[0038] -Method for manufacturing Al wire- The method for manufacturing the Al wire of the present invention is not particularly limited, and may be manufactured using a known processing method such as extrusion, rolling, swaging, wire drawing, etc. An example of the method for manufacturing the Al wire of the present invention will be described below.

[0039] First, according to the composition of the Al bonding wire, an Al raw material (an Al raw material with a purity of 4N or higher) and an additive element raw material are weighed as starting raw materials, and then melted and mixed to obtain an ingot containing predetermined components with the remainder being Al and unavoidable impurities. Alternatively, a mother alloy containing a high concentration of the additive element may be used as the raw material for each additive element.

[0040] The resulting ingot is processed by extrusion, rolling, swaging, wire drawing, forging, etc. to obtain the final dimensions.

[0041] Tempering heat treatment may be performed during or after processing. This treatment removes processing strain and forms a recrystallized structure. This treatment is preferably performed using a batch-type heat treatment furnace when the wire diameter is large during processing, and a sweep-type heat treatment furnace when the wire diameter is final. Examples of the heat treatment conditions include heating in a temperature range of 200 to 400°C for several minutes to several hours when the wire diameter is large during processing, and heating in a temperature range of 200 to 400°C for a short time of 0.5 seconds to 2 minutes when the wire diameter is final.

[0042] [Semiconductor Device] A semiconductor device can be manufactured by connecting electrodes on a semiconductor chip to electrodes on a lead frame or a circuit board using the Al wire of the present invention.

[0043] The semiconductor device of the present invention includes the Al wire of the present invention. The Al wire of the present invention exhibits good wiredrawability and wedge bondability and good high-temperature, high-humidity reliability, and a semiconductor device including the Al wire can achieve excellent operational reliability even when exposed to a high-temperature, high-humidity environment.

[0044] In one embodiment, the semiconductor device of the present invention includes a circuit board, a semiconductor chip, and an Al wire for electrically connecting the circuit board and the semiconductor chip, wherein the Al wire is the Al wire of the present invention.

[0045] In the semiconductor device of the present invention, the circuit board and semiconductor chip are not particularly limited, and any known circuit board and semiconductor chip that can be used to construct a semiconductor device may be used. Alternatively, a lead frame may be used instead of the circuit board. For example, a semiconductor device may be configured including a lead frame and a semiconductor chip mounted on the lead frame, as in the semiconductor device described in Japanese Patent Laid-Open No. 2002-246542.

[0046] Examples of the semiconductor device include various semiconductor devices used in electrical appliances (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power generation systems, etc.) and vehicles (e.g., motorcycles, automobiles, trains, ships, aircraft, etc.).

[0047] The present invention will be specifically described below with reference to examples, although the present invention is not limited to the examples shown below.

[0048] (Sample Preparation) First, the sample preparation method will be described. The raw material for the Al bonding wire was Al, which had a purity of 99.99% by mass or more, with the remainder consisting of inevitable impurities. Mg, the first group elements (Ga, Ge, Ta, Ag), and Ni were used, with a purity of 99% by mass or more, with the remainder consisting of inevitable impurities. These raw materials were blended and melted to obtain the Al wire composition shown in Table 1, and a cylindrical ingot with a diameter of 5 to 10 mm was cast. The resulting ingot was subjected to die wire drawing until the final wire diameter was 25 μm. During processing, at the wire diameter stages of 1 mm and 300 μm, heat treatment was performed in an Ar atmosphere at a processing temperature of 200 to 400 °C for 1 hour. Furthermore, at the final wire diameter, the treatment was performed under conditions of an Ar atmosphere, a processing temperature of 200 to 400 °C, and a processing time of 1 to 2 seconds.

[0049] [Measurement of element content] The concentration analysis of elements contained in the Al wire was performed using an ICP-OES ("PS3520UVDDII" manufactured by Hitachi High-Tech Science Corporation) or an ICP-MS ("Agilent 7700x ICP-MS" manufactured by Agilent Technologies, Inc.) as an analytical device.

[0050] <Evaluation of wiredrawability> In wiredrawing from 30 μm to a final wire diameter of 25 μm, wiredrawability was evaluated based on the number of wire breakages that occurred during 100 km of wiredrawing. The results are shown in the "wiredrawability" column in Table 1, with the following criteria: "◎" if the number of wire breakages was 0 (no wire breakage), "◯" if the number of wire breakages was 1, and "×" if the number of wire breakages was 2 or more.

[0051] <Evaluation of wedge bonding properties> (1) Preparation of bonding samples In the semiconductor device, the electrodes of the semiconductor chip were Al-Cu pads, and Ag was used for the external terminals. Both the first connection between the electrodes of the semiconductor chip and the Al wire and the second connection between the external terminals and the Al wire were wedge bonded. A commercially available wire bonder, BJ820 manufactured by Hesse, was used to bond the Al wire. The temperature during bonding was room temperature, and the atmosphere during bonding was air.

[0052] (2) Evaluation of Wedge Bondability Wedge bondability was evaluated by performing wedge bonding at 20 locations under typical bonding conditions and measuring the pull strength at the center of the loop. A commercially available wire bond inspection device was used to measure the pull strength. The pull strength was measured by fixing the substrate to which the Al wire was bonded using a jig. If even one location had a pull strength value of less than 4 cN, the sample was judged to be unsatisfactory and rated "x." If all 20 locations had a pull strength value of 4 cN or more but less than 10 cN, the sample was judged to be satisfactory for practical use and rated "o." Furthermore, if all 20 locations had a pull strength of 10 cN or more, the sample was judged to be excellent and rated "◎," and this is listed in the "Wedge Bondability" column in Table 1.

[0053] <Evaluation of High-Temperature, High-Humidity Reliability> Bonding samples prepared using the same procedure as above were exposed to a high-temperature, high-humidity environment at a temperature of 121°C and a relative humidity of 100% for 24 hours, and the degree of corrosion was measured using a pressure cooker tester. The degree of corrosion was evaluated by comparing the initial pull strength with the pull strength after exposure to the high-temperature, high-humidity environment. Pull strength was measured at the center of the loop using a commercially available wire bond inspection device. The results are shown in the "High-Temperature, High-Humidity Reliability" column in Table 1, with a rating of "◎" if the pull strength after exposure was 75% or more of the initial pull strength, a rating of "◯" if it was 50% or more but less than 75%, and a rating of "×" if it was less than 50%.

[0054]

Claims

1. An Al bonding wire containing 0.10 to 2.0 mass% Mg, a total of 5 to 500 mass ppm of one or more elements selected from the group consisting of Ga, Ge, Ta, and Ag (hereinafter referred to as "first group elements"), 5 to 500 mass ppm of Ni, and the remainder being Al.

2. An Al bonding wire as described in claim 1, wherein the Si content is 100 mass ppm or less.

3. An Al bonding wire according to claim 1 or 2, having a wire diameter of 15 to 100 μm.

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