JPH0450741B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a semiconductor device in which an electrode of a semiconductor element and an external lead are connected by a copper bonding wire, and particularly relates to a semiconductor device in which an electrode of a semiconductor element and an external lead are connected by a copper bonding wire. The present invention relates to semiconductor devices to be connected.

[Conventional technology]

Conventionally, in general-purpose semiconductor devices that have been widely used, electrodes on a semiconductor element and lead frames are connected by ball bonding of gold wire. In other words, ball bonding involves forming a ball at the tip of a wire using hydrogen flame or short-circuit discharge.
This method connects the ball by pressing it onto the electrode. Gold wire easily forms a ball with a shape close to a perfect sphere even in the air, and also has high bonding strength with electrodes. However, this gold wire belongs to the expensive category among precious metals, and in recent years, the number of multi-pin products having a large number of input and output pins has been increasing. Therefore, 1
The amount of gold wire used for each element has tended to increase, creating a manufacturing cost problem.
From the above background, attempts are being made in various places to apply inexpensive copper wires in place of gold wires.

A semiconductor device using copper wire is described, for example, in Japanese Patent Application Laid-Open No. 124959/1983. Connections with copper wires are also made by ball bonding. That is, the ball is formed by short-circuit discharge, and the connection is made by applying ultrasonic waves to the electrodes. FIG. 3 shows a sectional view of a resin-sealed semiconductor device using a conventional copper wire. In FIG. 3, reference numeral 11 is a copper wire;
12 is an electrode, 13 is a pellet, 14 is a lead frame, and 15 is a resin. Its structure is such that one end of a copper wire 11 is ball-bonded to an electrode 12 (aluminum or Al-Si alloy film) on a pellet 13, and the other end of the wire is a lead frame 14 (Fe-42% Ni) plated with silver or copper. alloy or copper alloy) and is entirely covered with resin 15.

However, the above-mentioned conventional technology did not take into consideration the reliability of the joint between the wire and the electrode.

The problem with the above conventional technology is that the reliability of the joint between the wire and the electrode is low. That is, the bonded portion easily peels off during high temperature storage and temperature cycle tests. FIG. 4 is a graph showing the incidence of connection failures (%, vertical axis) in a conventional temperature cycle test (-55° C. to 150° C.) of a semiconductor device in relation to the number of cycles (horizontal axis). This graph shows that conventional semiconductor devices tend to fail in a relatively short period of time.

Further, FIG. 5 is a graph showing the failure rate (%, vertical axis) in a high temperature storage test of a conventional semiconductor device at 200° C. in relation to the storage time (time, horizontal axis). In this case as well, it can be seen that conventional semiconductor devices tend to fail in a short period of time. Semiconductor devices using gold wires do not fail in any of the above tests.

Next, we will discuss the results of investigating the cause of the disconnection failure. FIG. 6 is a schematic cross-sectional view of a junction between a ball and an electrode of a semiconductor device in which a disconnection failure occurred in a temperature cycle test. A scanning electron micrograph shows that the bonding interface between the copper ball and the electrode has peeled off as shown in FIG. It was also confirmed that the failure in the high-temperature storage test was due to peeling of the bonding interface between the ball and the electrode.

[Problem that the invention seeks to solve]

As described above, conventional semiconductor devices have had problems with the reliability of the junction between the ball and the electrode.

An object of the present invention is to improve the reliability of the junction and provide a semiconductor device using a more reliable copper wire.

[Means for solving problems]

To summarize the present invention, the present invention relates to a semiconductor device, and in a semiconductor device in which an electrode of a semiconductor element and a lead are connected and led out by a copper bonding wire, a copper bonding wire is formed at the bonding interface between the wire and the electrode.
It is characterized by the formation of an aluminum-based intermetallic compound.

When copper wires are applied, bonding of the wires to the electrodes is by ultrasound. In this case, since the ball and the electrode film are rubbed against each other by ultrasonic waves, the oxide film on both is removed and a new surface is exposed.
This is the mechanism by which the new surfaces of the two are joined together. However, in conventional semiconductor devices, since the copper balls are very hard, the area of the resulting new surfaces of both is small. In other words, the electrode film protrudes outside the ball before a sufficient area of the new surface is exposed. Therefore, the bond between the ball and the electrode is weak. Furthermore, the periphery of the joint is not sufficiently joined. Therefore, when a temperature cycle and high temperature storage test are performed in this state, the joint part easily peels off due to the stress applied to the joint part.

In order to solve the above problems, the present invention is to form a copper-aluminum intermetallic compound at the interface between the ball and the electrode film.

That is, the present invention forms an intermetallic compound layer at the bonding interface by holding the wire at an appropriate temperature during bonding to the electrode or by heat-treating the wire after bonding.

When the intermetallic compound layer is formed, the ball and the electrode film are in close contact with each other, and the joint is strengthened.

On the other hand, copper-aluminum intermetallic compounds mainly have three types: θ, η ₂ , and γ ₂ phases. In this,
It is the θ phase (Al ₂ Cu) that contributes to the strengthening of the joint. Figures 7 and 8 are graphs showing the incidence of disconnection defects in the temperature cycle and 200°C high temperature storage test of a semiconductor device in which the above three types of intermetallic compound phases are formed at the bonding interface between the ball and the electrode. be. In other words, Figure 7 is a graph showing the relationship between the number of cycles (horizontal axis) and defective rate (%, vertical axis), and Figure 8 is a graph showing the relationship between the number of cycles (horizontal axis) and defect rate (%, vertical axis), and Figure 8 is the graph showing the relationship between leaving time (time, horizontal axis) and defective rate (%, vertical axis).
It is a graph showing the relationship between In each graph, a indicates the θ phase, b indicates the η ₂ phase, and c indicates the γ ₂ phase. The number tested was 50. It can be seen that the semiconductor devices in which the η ₂ and γ ₂ phases are formed each have defects, but those in the θ phase do not. This is because the θ phase is softer and more tough than other phases.

FIG. 9 is a graph showing the relationship between the thickness of the θ phase (μm, horizontal axis) and the failure rate (%, vertical axis) at 5000 cycles (temperature cycle test). Figure 10 also shows the thickness of the θ phase (μm, horizontal axis) and 200°C.
It is a graph showing the relationship with the failure rate (%, vertical axis) after 1000 hours of high temperature storage. Both results indicate that the thickness of the θ phase should be 0.5 μm or more.

Next, a method for forming the θ phase at the interface between the ball and the electrode will be described. The higher the heating temperature, the thicker the copper-aluminum intermetallic compound layer becomes in a shorter time. For example, when forming a θ phase with a thickness of 0.5 μm, the heating and holding time of the electrode during bonding is
It may be heated at 300℃ for 5 minutes. Furthermore, in the case of heating at 250°C, a θ phase of 0.5 μm can be formed by holding for 15 minutes. If the temperature is 400 to 500°C, it may be held for about 1 minute.

On the other hand, in the conventional case, the heating time was 10 seconds or less at 300°C, so no intermetallic compound was formed.

FIG. 11 is a schematic diagram comparing a cross section of a junction between a ball and an electrode of a conventional semiconductor device with that of the present invention. FIG. 11-1 is a schematic cross-sectional view of a conventional joint, and FIG. 11-2 is a cross-sectional view of a joint according to the present invention.
6 is a copper ball, 17 is an electrode film, 18 is a pellet,
19 means θ phase. In the conventional joint, no intermetallic compound layer is formed, and a gap is observed between the ball and the electrode. On the other hand, it can be seen that in the joint of the present invention, the ball and the electrode are in close contact with each other due to the intermetallic compound layer (θ phase).
The semiconductor device of the present invention has high reliability because the balls and electrodes are in close contact with each other as described above and the semiconductor device is in the soft and tough θ phase.

〔Example〕

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 FIG. 1 shows one of the resin-sealed semiconductor devices of the present invention.
FIG. 3 is an example cross-sectional view. In FIG. 1, the reference numeral 1 means a copper wire, 2 a pellet, 3 an electrode, 4 a θ phase, 5 a lead frame, and 6 a resin. Its structure is such that one end of a copper wire 1 with a diameter of 30 μm is connected to a pellet 2.
A lead frame 5 is ball-bonded to the upper electrode 3 (aluminum or Al-Si alloy) (theta phase 4 is formed at the bonding interface between the ball and the electrode), and the other end of the wire is plated with silver or copper.
(Fe42%Ni or copper alloy) is wedge bonded and the whole is covered with resin 6.

Example 2 FIG. 2 shows a ceramic sealed semiconductor device of the present invention. In FIG. 2, numerals 1 to 5 have the same meanings as in FIG. 1, and 7 means ceramic. The structure is similar to that of Example 1, but the sealing is done with ceramic 7.

〔Effect of the invention〕

As described above, according to the semiconductor device of the present invention, the copper wire and the electrode are in close contact with each other, and the remarkable effect of improving reliability in terms of corrosion resistance and the like can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a resin-sealed semiconductor device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a ceramic-sealed semiconductor device according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view of a conventional copper wire Fig. 4 is a graph showing the failure rate of conventional semiconductor devices in a temperature cycle test, and Fig. 5 shows the failure rate of conventional semiconductor devices in a 200°C high temperature storage test. A graph showing the incidence rate, FIG. 6 is a schematic cross-sectional view of the junction between the ball and the electrode of a conventional semiconductor device,
Figure 7 is a graph showing the failure rate in a temperature cycle test of semiconductor devices in which various intermetallic compounds are formed at the interface between the ball and the electrode. A graph showing the failure rate in a high temperature storage test of a semiconductor device formed with a compound. Figure 9 is a graph showing the relationship between the thickness of the θ phase and the failure rate in a temperature cycle test. Figure 10 is a graph showing the relationship between the θ phase thickness and the failure rate in a temperature cycle test. Graph showing the relationship between phase thickness and failure rate in high temperature storage test, No. 11
FIG. 11-1 is a schematic cross-sectional view of a junction between a ball and an electrode in each semiconductor device of the conventional semiconductor device and FIG. 11-2 of the present invention. 1 and 11... copper wire, 2, 13 and 18...
...Pellet, 3 and 12...Electrode, 4 and 19...
...θ phase, 5 and 14... Lead frame, 6 and 15... Resin, 7... Ceramic, 16... Copper ball, 17... Electrode film.

Claims (1)

[Claims] 1. A semiconductor device in which electrodes and leads of a semiconductor element are connected and led out using a copper bonding wire,
A semiconductor device characterized in that a copper-aluminum intermetallic compound is formed at a bonding interface between a wire and an electrode. 2. The semiconductor device according to claim 1, wherein the intermetallic compound is a θ phase (Al ₂ Cu). 3. The semiconductor device according to claim 2, wherein the intermetallic compound layer has a thickness of 0.5 μm or more.