JP2770575B2 - Semiconductor device bonding method and semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device bonding method for connecting a chip electrode of a semiconductor device to an external lead, and a semiconductor device manufactured by the bonding method.

[0002]

2. Description of the Related Art As is well known, in assembling a semiconductor device in which a semiconductor element such as an IC chip is incorporated, a gold wire is used as a bonding wire (hereinafter referred to as a wire) for connecting the semiconductor element and an external lead. , Aluminum wires, and copper wires for some of them. Among these wires, gold wire has been used for a long time because it has advantages such as excellent corrosion resistance, and the amount of wire made of gold or gold alloy is still overwhelmingly greater than other wires even today. Many.

When such a wire is bonded to an aluminum bonding pad (hereinafter, referred to as a pad) on a semiconductor element, the tip of the wire passed through a capillary is melted using an electric torch or the like. A ball bonding method is used in which a spherical portion (ball) is formed at the tip portion, and the spherical portion is bonded to the pad by ultrasonic pressure bonding.

The wire having one end joined to the pad in this manner is pulled up by the capillary, extended to an external lead while drawing a gentle curve, pressed by the external lead, and again subjected to ultrasonic thermocompression bonding. Joined. The wire whose both ends are joined to the pad and the external lead of the semiconductor device is pulled up again by the capillary, and the pulled up portion is clamped and cut to complete one bonding. Next, a spherical portion is formed at the tip of the newly formed wire by cutting in the same manner as described above, and bonding is performed by repeating the same steps as above.

In recent years, automation and speeding up of bonding machines have been advanced in order to reduce the assembly cost of semiconductor devices, and accordingly, wires and wires that can withstand such bonding work and do not cause flow during resin molding are used. A wire that does not bend or break even with various heat histories and vibrations in a semiconductor device assembly process has been required. Further, with the diversification of use environments of semiconductor devices, demands for highly reliable wires that do not cause troubles such as disconnection even in a bad environment such as high temperature and high pressure are increasing.

[0006] To meet these requirements, La
There have been proposed wires made of a gold alloy to which various elements such as Al, Be, and Ce are added at a very small ratio of about several ppm by weight.

[0007]

It has been recognized that some of such conventionally proposed wires have high room-temperature strength and high-temperature strength, or have a high loop in addition to them. Have been. However, there has been no satisfactory solution to the deterioration of the joint between the wire and the pad under a high temperature, which is the most problematic in such a wire. For this reason, poor connection between the wire and the pad occurs due to the deterioration of the junction, which makes it difficult to exhibit stable performance, resulting in shortening the life of the semiconductor device.

Further, the semiconductor device after resin molding is subjected to various temperature changes under the above-mentioned bad environment. However, due to the difference in thermal expansion coefficient between the molded resin and the silicon constituting the semiconductor element. It is known that such a temperature change causes a force in the shearing direction to act on the joint between the wire and the pad. However, the temperature difference that changes with the recent diversification of the usage environment of the semiconductor device as described above has become extremely large, and accordingly, a great amount of shearing force has also acted on the junction. And this has come to cause a problem that the wire is peeled off from the pad in combination with the deterioration of the bonding portion.

Further, when the wire is bonded to the pad by the ball bonding method, the aluminum constituting the pad melted by the ultrasonic thermocompression is pressed by the spherical portion formed at the tip of the wire to bond the wire to the pad. A so-called rejection phenomenon that runs off the surface may occur. When such rejection occurs, aluminum of the pad is not effectively used for bonding with the wire, which is a factor that further deteriorates the bonding property between the two.

Furthermore, in a state where the wire mainly composed of gold and the pad made of aluminum are joined and the gold and aluminum are in contact with each other, Au ₂ Al, Au _{5 is formed on} the joint surface of the two at high temperature. It is known that a layer of an intermetallic compound of gold and aluminum such as Al ₂ and Au ₄ Al grows. However, these intermetallic compound layers do not promote the bonding between the wire and the pad unless growth is performed at all, but have the property that cracks and cavities are liable to occur and the brittleness is increased. For this reason, as described above, if the semiconductor device is exposed to a high temperature and the layer of the intermetallic compound grows too much, the wire may be peeled off from the bonding surface with the pad.

As described above, the above-mentioned conventionally proposed wires do not solve these problems.
It has been difficult to say that the requirements for the wire described above are still sufficiently satisfied.

[0012] The present invention solves the above-mentioned problems, and it is possible to form a wire having little deterioration in a high-temperature environment and having sufficient strength against a shear force generated by a temperature change. The purpose is to provide.

[0013]

Here, the inventors of the present invention added various elements such as Ca, Si, etc. in addition to the above-mentioned La, Be, Ce and the like to various kinds of high-purity gold. Form the wire,
This wire was bonded to an aluminum pad, and studies on the bondability between the two were repeated. As a result, a spherical portion was formed at the tip of the wire by a ball bonding method by adding these elements to a specific combination and adding high amount of gold to high-purity gold compared to the conventional one to form a wire. At this time, they have come to the knowledge that a minute concave portion is formed at the tip of the spherical portion.

The present invention has been made based on such knowledge, and a method of bonding a semiconductor device according to the first aspect of the present invention is a method of bonding a semiconductor device by bonding a bonding wire made of a thin metal wire to a bonding pad of a semiconductor element. In the bonding method of the apparatus, the tip of the bonding wire is heated to form a spherical portion, and a concave portion is formed at the protruding end of the spherical portion, and the spherical portion is pressed against the bonding pad of the semiconductor element and is bonded to the bonding pad. The method is characterized in that the bonding wire is joined while forming a projection engaging with the recess.

According to a second aspect of the present invention, there is provided a semiconductor device in which a bonding wire made of a thin metal wire is bonded to a bonding pad of a semiconductor element. The semiconductor device was bonded to a bonding pad, and a bonding portion between the bonding wire and the bonding pad was formed with a concave portion on the bonding wire side, and a convex portion engaging with the concave portion was formed on the bonding pad side. It is characterized by the following.

[0016]

According to the present invention, when the tip of the wire is heated by the above-described ball bonding method to form a spherical portion,
At the same time, a minute concave portion is formed at the tip of the spherical portion. Then, by pressing the spherical portion formed with the concave portion to the pad, the spherical portion of the wire is pressed against the pad while being crushed, while the aluminum constituting the semi-dissolved pad by the heat of ultrasonic waves is spherical. By being pressed by the portion, the portion facing the concave portion enters the concave portion to form a convex portion that engages with the concave portion.

By forming the concave and convex portions which engage with each other at the joint between the wire and the pad, the joint area between the wire and the pad increases, so that the joint strength at the joint between the two can be improved. be able to. Accordingly, even if the semiconductor device is held at a high temperature for a long time, the time until the wire is peeled off from the pad can be extended as compared with the related art.

Further, when the concave portion and the convex portion are engaged with each other, the wire and the pad are engaged with each other in a direction of shearing the joint between the wire and the pad. The strength is significantly improved.

On the other hand, the aluminum of the pad enters the recess formed in the spherical portion at the tip of the wire,
Negative pressure is generated in the aluminum in a semi-molten state by the heat of the ultrasonic wave. Since the negative pressure and the pressing by the pressing of the spherical portion cancel each other, it is possible to suppress the rejection of aluminum at the time of wire pressing which occurs in the conventional pressing only state.

[0020]

Embodiments of the present invention will be described below.

In the present embodiment, an ingot is prepared by adding 40 wt.ppm La and 50 wt.ppm Si to 99.999% high-purity gold, and the ingot is drawn to a diameter of 25 μm. Was manufactured. Then, this gold alloy thin wire is subjected to a heat treatment so that the elongation at break at room temperature is 4%.
%, And a wire was manufactured. The wire was bonded to an aluminum pad of a semiconductor element by the above-described ball bonding method. This is referred to as Example 1.

In the same manner as in Embodiment 1, 99.99
9% gold, 30wt.ppm La and 40wt.ppm Ca added wire, 20wt.ppm Be and 20wt.ppm Si and 20wt.%
A wire to which wt.ppm of Ce was added and a wire to which 20 wt.ppm of La, 20 wt.ppm of Be and 30 wt.ppm of Si were added were bonded to an aluminum pad of a semiconductor device. These are Examples 2, 3 and 4, respectively.

Further, as a comparative example to these comparative examples, 99.999% of gold was added to 7 w
A wire to which t · ppm La and 3 wt · ppm Be were added, and a wire to which 4 wt · ppm La, 2 wt · ppm Be and 4 wt · ppm Ce were added, and bonded to an aluminum pad. These are referred to as Comparative Examples 1 and 2, respectively.

Table 1 shows the compositions of the additional elements added to the wires used in Examples 1 to 4 and Comparative Examples 1 and 2.

[0025]

[Table 1]

The bonding conditions at this time are as shown in Table 2.

[0027]

[Table 2]

At the time of this bonding, as shown in FIG. 1, the distal end of the wire 2 passed through the capillary 1 is melted using an electric torch or the like, so that a spherical portion 3 having an average diameter of about 70 μm is formed at the distal end. Is formed. Here, in the wires of Examples 1 to 4, at the same time as the formation of the spherical portion 3, the protruding end of the spherical portion 3 has a diameter of about 15 .mu.
A hemispherical hole-shaped recess 4 having a depth of about 5 μm is formed.

Then, the capillary 1 is moved to bring the wire 2 on which the spherical portion 3 is formed to a position facing the aluminum pad 6 of the semiconductor element 5 as shown in FIG. 2, and as shown in FIG. The capillary 1 is lowered to press the spherical portion 3 against the pad 6, and the wire 2 is bonded to the pad 6 by ultrasonic thermocompression bonding.

At the time of this bonding, the pad 6 is made of aluminum constituting the pad 6 by heat generated by ultrasonic waves.
Alternatively, the aluminum constituting the semiconductor element is slightly mixed into the aluminum to form Al-1% Si, which is in a semi-molten state. And pad 6 in such a state
When the spherical portion 3 of the wire 2 is pressed into the recess, the semi-molten aluminum or Al-1% Si or the like enters the concave portion 4 formed at the protruding end of the spherical portion 3, whereby the pad 6 enters the concave portion 4. A projection 7 having an engaging shape is formed.
The spherical portion 3 pressed to the pad 6 in this manner is the capillary 1
Further, the lower end of the wire 2 is flattened so as to cover the upper surface of the pad 6 as shown in FIG. 4, and one end of the wire 2 and the pad 6 of the semiconductor element 5 are joined.

Next, the wire 2 is pulled up by the capillary 1 and extended onto the external lead while forming a loose loop, and is again subjected to ultrasonic thermocompression bonding to be joined to the external lead. The wire 2 having both ends joined to the pad 6 of the semiconductor device and the external lead is pulled up again by the capillary 1, and the pulled up portion is clamped and cut to complete one bonding. Next, when the spherical portion 3 is formed at the tip of the newly formed wire 2 by cutting in the same manner as described above, the concave portion 4 is formed at the tip of the spherical portion 3 at the same time. Is repeatedly performed.

As described above, according to the first to fourth embodiments, the concave portion 4 and the convex portion 7 that are engaged with each other are formed at the joint portion between the wire 2 and the pad 6. The joint area increases, and therefore, the joint strength at the joint between the two can be improved. As a result, the deterioration of the joint between the wire 2 and the pad 6 is suppressed, and the intermetallic compound between the gold constituting the wire 2 and the aluminum constituting the pad 6 is held at a high temperature for a long time. , The time required for the wire 2 to peel off from the pad 6 can be extended. Therefore, with the recent diversification of the use environment of the semiconductor device, even in the use under a high temperature, occurrence of poor connection between the semiconductor element and the external lead can be prevented, and the life of the semiconductor device can be extended. .

When the concave portion 4 of the wire 2 and the convex portion 7 of the pad 6 are engaged with each other, the wire 2 and the pad 6 are engaged with each other in a direction in which the joint between them is sheared. Therefore, the strength against the force acting in this direction is significantly improved. Accordingly, even when a force in the shear direction acts on the joint between the wire 2 and the pad 6 due to the difference in the coefficient of thermal expansion between the resin molded and the silicon of the semiconductor element due to the rapid temperature change in the severe use environment described above. In addition, peeling of the wire 2 from the pad 6 can be prevented. For this reason, the occurrence of connection failure of the semiconductor device can be more effectively prevented in combination with the improvement of the bonding strength, and the life of the device can be further extended.

On the other hand, in the comparative examples 1 and 2, when the wire 12 and the pad 16 are joined, the pad 16 as shown in FIG.
Of aluminum constituting aluminum oxide 8 occurred. Such rejection of aluminum becomes a factor that hinders the bondability between the wire and the pad because aluminum constituting the pad is not effectively used.

On the other hand, in the first to fourth embodiments, the aluminum of the pad 6 enters into the concave portion 4 formed in the spherical portion 3 at the time of bonding with the pad 6, so that the aluminum is semi-dissolved by the heat of the ultrasonic wave. A state in which a negative pressure is generated in the aluminum thus obtained. Then, since the negative pressure and the pressing by the compression of the spherical portion 3 cancel each other, it is possible to prevent the rejection of aluminum when the wire 2 is compressed. Therefore, pad 6
All of the aluminum is effectively used for bonding with the wire 2, and the bonding between the wire 2 and the pad 6 can be further enhanced.

Next, Examples 1 to 4 and Comparative Example 1,
After holding the semiconductor devices bonded by the method 2 in a nitrogen atmosphere at 200 ° C. for a certain time, the semiconductor devices were taken out, the shear strength was measured, and a test was performed on the reduction in bonding strength between the wire and the pad under a high-temperature environment. The result is shown in FIG.

As can be seen from FIG. 6, Comparative Examples 1 and 2
In the semiconductor device according to the above, a decrease in bonding strength was observed 100 hours and 200 hours after the start of the test, respectively.
400 hours after the start of the test, the shear strength was 0, that is, the wire was peeled off from the pad. On the other hand, in the semiconductor devices according to Examples 1 to 4, only the semiconductor device according to Example 3 began to decrease in bonding strength 200 hours after the start of the test. Even after 500 hours from the start of the test, sufficient bonding strength was maintained except for Example 1.

As described above, in the first to fourth embodiments, even when the semiconductor device is exposed to a high-temperature environment for a long time, the time until the bonding portion between the wire and the pad is deteriorated is remarkably extended. It has been demonstrated that it has sufficient strength against the generated shear force. Then, by manufacturing a semiconductor device using the wire having such a configuration, it is possible to extend the life of the semiconductor device even in use at high temperatures due to the diversification of the usage environment of the semiconductor device in recent years. .

[0039]

As described above, according to the present invention, when a wire and a pad are joined, a spherical portion is formed at the tip of the wire, and at the same time, a concave portion is formed at the tip of the spherical portion. Is pressed onto the pad, so that the pad is also provided with a convex portion that engages with the concave portion. By joining the wire and the pad in a state where the concave portion and the convex portion are engaged with each other, the joint area of the joint portion is increased, and a strong drag is applied to the force acting on the joint portion in the shearing direction. Will be played. In addition, since the aluminum constituting the pad is prevented from being rejected, it is possible to improve the bonding property and the bonding strength between the wire and the pad.

Therefore, by bonding the semiconductor device with such a wire, it is possible to suppress the deterioration of the bonding portion between the wire and the pad even in a high temperature environment and to separate the bonding portion even by a rapid temperature change. Can be prevented, and as a result, the life of the semiconductor device can be extended.

[Brief description of the drawings]

FIG. 1 is a side view showing a spherical portion 3 at the tip of a bonding wire 2 in Examples 1 to 4.

FIG. 2 is a side view of a bonding portion of a bonding wire 2 and a bonding pad 6 in Examples 1 to 4 showing how the bonding wire 2 and the bonding pad 6 are bonded.

FIG. 3 is a side view of a bonding portion between the bonding wire 2 and a bonding pad 6 in Examples 1 to 4 showing a state of bonding between the bonding wire 2 and the bonding pad 6;

FIG. 4 is a side view of a joint between the bonding wire 2 and the bonding pad 6 according to the first to fourth embodiments, showing a state of the bonding.

FIG. 5 shows bonding wires 12 in Comparative Examples 1 and 2.
FIG. 10 is a side view of the joint portion of the two, showing a state in which aluminum constituting the bonding pad 16 has been repelled by the heat treatment.

FIG. 6 is a graph showing a change in shear strength when the semiconductor devices bonded in Examples 1 to 4 and Comparative Examples 1 and 2 are held in a high-temperature environment for a long time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capillary 2, 12 Bonding wire 3, 13 Spherical part 4 Concave part 5 Semiconductor element 6, 16 Bonding pad 7 Convex part 8 Excluding part of aluminum

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/60 301

Claims (2)

(57) [Claims] 1. A bonding method for a semiconductor device, comprising forming a semiconductor device by bonding a bonding wire made of a thin metal wire to a bonding pad of a semiconductor element.
The distal end of the bonding wire is heated to form a spherical portion, and a concave portion is formed at the protruding end of the spherical portion. The spherical portion is pressed against a bonding pad of the semiconductor element to engage the bonding pad with the concave portion. A bonding method for a semiconductor device, wherein the bonding wire is bonded while forming a projection. 2. A semiconductor device comprising a bonding wire made of a thin metal wire bonded to a bonding pad of a semiconductor element, wherein the bonding wire is connected to a bonding pad of the semiconductor element by the bonding method of the semiconductor device according to claim 1. At the joint between the bonding wire and the bonding pad, a concave portion is formed on the bonding wire side, and a convex portion engaging with the concave portion is formed on the bonding pad side. Characteristic semiconductor device.