JPS6238414B2 - - Google Patents

Abstract

PURPOSE:To provide a copper alloy wire for connecting a semiconductor element which eliminates the need for using noble metals and to assure inexpensive and reliable connection by incorporating a trace amt. of >=1 kinds of elements among Ga, Ge, In, Au, Ni, Li,Sb and Si into high-purity Cu as a raw material. CONSTITUTION:The above-described copper alloy wire is formed by incorporating 0.001-0.1wt% >=1 kinds of elements among Ga, Ge, In, Au, Ni, Li, Sb and Bi into Cu of 99.99wt% purity as the raw material. This invention is embodied by heating the copper alloy wire 2 exposed at the top end from a capillary 1 to form a ball 3 as shown in the figure, then press welding the same, by for example, ultrasonic bonding, onto the Al electrode 5 on a silicon semiconductor chip 4, thereby connecting the chip. Since the trace elements are added to the alloy wire in addition to Cu in this invention, the strength in the copper alloy wire part 2a in proximity to the ball 3 is increased. The loop wire is therefore capable of maintaining the preferable state without lying too much as shown by a virtual line 9 even after the connection to an outside lead frame 8.

Description

[Detailed description of the invention]

<Field of the Invention> This invention relates to a semiconductor device wiring method used to connect electrodes on a semiconductor chip to an external lead frame after the semiconductor chip is mounted on a stem when assembling semiconductor devices such as ICs, LSIs, and transistors. Regarding metal wire for use. <Background of the Invention> Conventionally, fine metal wires containing gold as a main component have been used to connect semiconductor chips to external lead frames. However, gold wire had the disadvantage of being extremely expensive. In addition, in some cases, aluminum alloy wires are used to avoid the use of expensive gold wires, that is, to move away from precious metals. However, aluminum alloy wires have various drawbacks as described in detail below. First, there was a problem that the workability into thin wires was considerably inferior to that of gold. Second, when connecting by forming a ball at the tip, the shape of the ball is unstable. This is because an oxide film tends to form on the surface of aluminum, which is strong and causes instability. Thirdly, the strength was low, and the bonding strength or loop wire formation condition was not good. Fourth
Another disadvantage is that it tends to react with the capillary used for crimping the electrodes on the semiconductor chip, and the tip of the capillary often becomes clogged. Semiconductor devices are required to have reliability on the order of ppm, but when aluminum alloy wire is used for wiring, it has various drawbacks as mentioned above, so it is difficult to obtain semiconductor devices with reliability on the order of ppm. I couldn't help it. The inventor of the present application aimed to effectively eliminate the drawbacks of both the gold wire and the aluminum alloy wire described above, that is, to obtain an inexpensive and highly reliable copper alloy wire for connecting semiconductor devices. Various experiments were repeated using inexpensive copper. More specifically, the inventor of the present application has developed a tough pitch copper wire,
The experiment was repeated using oxygen-free copper wire or copper alloy wire based on these. However, when connecting these copper wires and copper alloy wires to aluminum electrodes on silicon semiconductor devices, it is difficult to connect them to aluminum electrodes on silicon semiconductor devices using thermocompression bonding methods such as wedge bonding or nail head bonding, ultrasonic bonding methods, or a method that uses a combination of these methods. However, it was found that it was difficult to obtain a sufficiently stable and reliable connection. Because copper wire and copper alloy wire are relatively hard compared to aluminum, the pressure required for crimping often damages semiconductor elements. Therefore, until now, copper wires and copper alloy wires have rarely been put into practical use as metal wires for connecting semiconductor elements. <Summary of the Invention> Therefore, an object of the present invention is to provide a metal wire for connecting semiconductors, which is free from precious metals, is inexpensive, and can connect with excellent reliability. The inventor of the present application has diligently studied the above-mentioned problems and repeated experiments, and found that using copper with a purity of 99.995% by weight or more as a material, Ga, In, Au, Ni, Li, etc.
It has been found that a metal wire for connecting semiconductor devices that can achieve the above-mentioned purpose can be obtained by forming a thin wire by containing 0.001 to 0.1% by weight of one or more elements selected from the group consisting of Bi and Bi. The reason why we set the bonding wire to be 99.995% by weight or more is to make the deformation behavior of the bonding wire similar to that of gold wire, and to obtain a sufficiently stable and highly reliable connection without damaging the silicon semiconductor element during crimping. It's for a reason. It is known that if it is less than 99.995% by weight, silicon semiconductor devices are likely to be damaged. In this invention, using such high purity copper as a material,
Furthermore, "one or more elements selected from the group consisting of Ga, In, Au, Ni, Li, and Bi" is "0.001~
A material containing 0.1% by weight is used. The reason for adding these elements is that while maintaining the above deformability, the first ball bonding part becomes too soft due to heating during ball formation, leading to deterioration of bonding strength, and secondly, the loop wire is too flat. This is to prevent undesirable conditions. It should be noted that each of the above elements has the effect of improving the ball forming ability, but does not impair the deformability (that is, the softness that allows the silicon chip to be crimped without damaging it). In carrying out this invention, as shown in a schematic front view in FIG. 1, a copper alloy wire 2 whose tip is exposed from a capillary 1 is heated to form a ball 3,
Next, as shown in a schematic front view in FIG. 2, it can be connected to an electrode 5 made of aluminum on the silicon semiconductor chip 4 by pressure bonding, for example, by ultrasonic bonding. In addition, in FIG. 2, 6 indicates a die bonding part, 7 indicates a stem, and 8 indicates an external lead frame. Note that the imaginary line 9 in FIG. 2 indicates an unfavorable state of the shape of the loop wire after connection with the external lead frame 8, that is, a state in which the loop wire is too bent. This situation often occurred when aluminum alloy wire was used. In this invention, since trace elements are added in addition to copper as described above, the strength of the copper alloy wire portion 2a near the ball 3 in FIG. 1 is increased. Therefore, the external lead frame 8
Even after connecting with the loop wire, the loop wire does not fall too much as shown by the imaginary line 9, and can maintain a favorable state. Note that the connection of conventional metal wires for connecting semiconductor devices made of gold wires was usually performed in the atmosphere, but in the case of the copper alloy wire of the present invention, it is possible to It is carried out under a gas atmosphere. This is to prevent an oxide film from forming on the surface of the copper wire. <Effects of the Invention> As described above, the present invention uses 99.995% by weight or more of copper as a material and adds Ga, In, Au, etc. to the copper.
Since it uses a material containing 0.001 to 0.1% by weight of one or more elements selected from the group consisting of Ni, Li, and Bi, it is free of precious metals.
It can be used as an inexpensive metal wire for connecting semiconductor elements. In addition, since it uses such high-purity copper, it can form stable balls in a reducing atmosphere based on its oxide film characteristics and surface tension, and it is also more durable than aluminum wire. It is also possible to form a relatively small ball by using the same method, thereby making it possible to connect to a smaller electrode. Furthermore, since it has relatively high strength compared to aluminum, the condition of the loop wire can be made more preferable. Furthermore, as mentioned above, since it is mainly composed of high-purity copper, it has high deformability and therefore there is no risk of damaging the silicon semiconductor element. (Also, it has excellent processability into ultra-fine wires. Also, since it has copper as its main component, it has excellent bonding properties with electrode materials such as aluminum or silver, so it can be used with aluminum electrodes and silver-plated electrodes.) It is also possible to increase the connection strength with a mated external lead frame or a non-metallic copper alloy external lead frame). Furthermore, if copper or copper alloy is used for the external lead frame, it can be connected to the external lead frame without plating, making it possible to further eliminate precious metals, which has great benefits in industry. It can be seen that it brings about benefits. It should be pointed out that this invention can be used for bonding wires for various elements such as ICs, LSIs, and transistors, and is particularly suitable for ball bonding, which has excellent productivity. <Description of Examples> As an example of the present invention, re-electrolyzed copper with a purity of 99.998% by weight and high-purity copper obtained by a zone melting method with a purity of 99.999% by weight or more were used as materials, as shown in Table 1. A copper alloy was prepared by mixing various elements with a purity of 99.7% by weight or higher and processing it into a fine wire. As shown in Table 1, these were designated as Invention Examples 1 to 8, respectively. In addition, as conventional examples, conventional example 1 is prepared by preparing a known aluminum thin wire, and conventional example 2 is an alloy wire made by mixing high purity aluminum with 1.0% by weight of Si having a purity of 99.7% by weight or more. did. Further, as Comparative Examples 1 and 2, copper alloy wires were prepared using copper with a purity of 99.95% by weight as a material and adding Ga and In at 0.08% and 0.05% by weight, respectively. In addition, the material is copper with a purity of 99.999% by weight, 0.5% by weight of Ni and 2.0% by weight.
Copper alloy wires made by adding % by weight of Au were prepared as Comparative Examples 3 and 4. Note that all the thin wires used in this example have a diameter of 25μ.
It is m. Using the above-mentioned Examples 1 to 8 of the present invention, Conventional Examples 1 and 2, and Comparative Examples 1 to 4, a ball was formed at the tip of the capillary by an electric arc in an argon gas atmosphere, and an aluminum ball was formed on the silicon semiconductor element. Connections were made between the electrodes and a phosphor bronze external lead frame with various platings. Table 2 shows the evaluation of this connection result. The measurement means and criteria for each evaluation are shown in Table 3. Regarding wire drawability, the diameter is from 100μm to 25mm.
During the wire drawing process to μm, the length that could be drawn per wire breakage was measured and expressed as a ratio when Conventional Example 1 was taken as 1.0. Furthermore, the connection strength was determined by measuring the lateral shear strength at the joint between the copper alloy wire 2 for connecting semiconductor elements and the aluminum electrode wire 5 shown in FIG. As is clear from Table 2, in Inventive Examples 1 to 8, in terms of ball forming ability, loop wire condition, element damage, wire drawability, connection strength, and connectivity with an external lead frame, It can be seen that it shows good performance.

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【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic front view showing a ball forming state when carrying out the present invention. FIG. 2 is a schematic front view showing an example of a connected state of the copper alloy wire for connecting semiconductor elements according to the present invention. 2 shows a copper alloy wire for connecting semiconductor elements.

Claims (1)

[Claims] 1 Cu with a purity of 99.9995% by weight or more is used as a material, and one or more elements selected from the group consisting of Ga, In, Au, Ni, Li, and Bi are added to the Cu from 0.001 to 0.001%.
Copper alloy wire for connecting semiconductor devices, containing 0.1% by weight.