JPH045842A - Bonding pad - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bonding pad formed on a semiconductor device.

[Conventional technology]

Bonding pads formed on semiconductor devices are conventionally formed on a semiconductor substrate constituting the semiconductor device as one minute metal plate, and the outer periphery is covered with an insulating film such as a passivation film. There is. Bonding pads formed in compound semiconductor devices are often formed on the surface of a compound semiconductor substrate, and in this case, the first layer wiring metal patterned on the surface of the compound semiconductor substrate can be used as it is as a bonding pad. many.

FIG. 4 shows a conventional bonding pad formed on a semiconductor device having multilayer wiring. In the illustrated semiconductor device, a first layer wiring metal 2 is patterned on the surface of a semiconductor substrate 1, and the first layer wiring metal 2 is covered with an insulating film 3.

A second layer wiring metal is patterned on the upper surface of the insulating film 3, and a bonding pad 5 having a substantially square shape is formed by the second layer wiring metal. The bonding pad 5 is electrically connected to the first layer wiring metal 2 by a via metal 6 passing through the insulating film, and the outer periphery of the surface thereof is covered with a passivation film 7 together with the surrounding insulating film 3. It has a curved structure.

[Problem to be solved by the invention]

When bonding wires such as gold wires are connected to conventional bonding pads as described above by hot pressing or ultrasonic hot pressing, the bottom surface of the bonding pad is connected to the top surface of the semiconductor substrate or the bottom surface of the bonding pad. Since the contact force (adhesion force) on the upper surface of the insulating film is not sufficient, there is a problem in that the bonding pad is easily peeled off from the semiconductor device due to the tension applied to the wire during wire bonding, and such peeling occurs frequently.

Therefore, in view of the above-mentioned circumstances, an object of the present invention is to provide a bonding pad that is difficult to peel off from a semiconductor device.

[Means to solve the problem]

In order to achieve the above object, the bonding pad according to the present invention includes a first metal layer and a second metal layer, which are spaced apart from each other and arranged approximately parallel to a semiconductor substrate constituting a semiconductor device; The extent to which the first and second metal layers are bonded to each other and the connection between the first metal layer and the second metal layer can be maintained against the tension transmitted from the bonding wire during wire bonding. The first and second metal layers each have an outer circumference that protrudes laterally from the joint with the connection metal part, and The second metal layer has a structure in which its outer periphery is covered with an insulating film that covers the periphery thereof.

[Effect]

With this configuration, the thickness of the bonding pad is thicker than that of the conventional bonding pad, and its shear strength is improved. Further, the insulating film covering the outer periphery of the first and second metal layers presses the first and second metal layers toward the semiconductor device side 4-1, respectively, against the external force that tries to peel off the bonding pad. It works like this.

The present invention was completed based on the findings described below obtained through the following experiments.

That is, as shown in FIG.
In the case where the bonding pad 15 is formed on the top and the bonding wire 18 is connected (bonding) with the outer periphery of the bonding pad 15 covered with the passivation film 17 (see figure (a)), The frequency of peeling of the bonding pad 15 was compared between cases where wire bonding was performed without covering (see (b) and (C) in the same figure).

Furthermore, the bonding pad 15 is connected to the passivation film 1.
The experiments conducted with the bonding wire 18 not covered by the pad 15 were conducted in two cases: one in which the bonding wire 18 protruded from the pad 15 (see FIG. A comparison was also made with the case in which it did not occur (see figure (c)).

As a result of the experiment, pad 1 in the state shown in FIG.
5 had the highest peeling frequency, as shown in Figures (C) and (A).
The frequency of peeling of the pad 15 decreased in this order. From this result, we were able to obtain the following knowledge. In other words, the same figure (
Comparing the experimental results in b) and the experimental results in figure (c), the frequency of peeling in case of figure (c) was less than 1/10 of that in figure (b). When the wire 18 comes off the center of the pad 1-5 and hangs on the end of the pad 1-5 as shown in FIG.
The stress acting between pad 15 and semiconductor substrate 11 causes
It concentrates on the edges of the film, and peeling easily occurs from there. Therefore, in order to reduce the frequency of occurrence of peeling, it is desirable to prevent the wire 18 from touching the end of the pad 15. Further, when the bonding pads in which delamination occurred in the experiments shown in FIGS. 6(b) and 7(c) were examined, there were no pads in which the pad 15 was partially torn off and delaminated, and in all cases, the entire pad had delaminated. From this, it was found that the adhesive strength between the semiconductor substrate 11 and the bonding pad 15 was smaller than the shear strength of the bonding pad itself. Furthermore, when the outer circumferential portion of the pad 15 is covered with the passivation film 17 (see FIG. 3(a)),
Even if the wire 18 is bonded to a position shifted from the center of the pad 15, the passivation film 1 covering the outer periphery
7 prevents the wire 18 from coming into contact with the end of the pad 15. As a result, the wire 18 is connected to the pad in a state substantially similar to that shown in FIG. Even if the precision is poor, the frequency of peeling of the pad 15 can be reduced.In addition, the passivation film 17 covering the outer periphery of the pad 15
The pad 15 is attached to the substrate 1 against the external force that tries to peel off the pad 15.
It also plays the role of holding down against 1. As a result, the frequency of occurrence of peeling in the case of FIG. 5(a) was lower than that in the case of FIG. 2(c).

Note that FIG. 3D shows a state in which the pad 15 was peeled off in the experiment shown in FIG. As can be understood from this figure, the peeling in this case occurs due to simultaneous shearing of the pad 15 and peeling from the surface of the substrate 11. Therefore, when the thickness of the pad 15 was increased to increase the shear strength, the peeling of the pad was further reduced.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 is a perspective view partially showing an embodiment of a semiconductor device equipped with a bonding pad according to the present invention. In the semiconductor device shown in FIG. 1, a first metal layer 22 and a second metal layer 23 are formed substantially parallel to the surface of a semiconductor substrate 21 and separated from each other, and
formed between the metal layer 22 and the second metal layer 23,
A bonding pad 26 is constituted by a connecting metal portion 25 that interconnects these.

The first metal layer 22 constituting the lower layer of the bonding pad 26 is patterned on the surface of the semiconductor substrate 21 by photolithography or the like, and has a thickness of, for example, 0.5 μm.
The planar shape is approximately square with a side of about 50 to 100 μm. Further, the first metal layer 22 is patterned simultaneously with and in succession to a metal wiring pattern 27 having a width of about 2 μIn, and the electron beams formed on the semiconductor substrate 21 via the metal wiring pattern 27 are patterned. connected to the circuit. The outer peripheral part of the first metal layer 22 is connected to the surface of the semiconductor substrate 21 and the metal wiring pattern 2 around it.
7 and is covered with an interlayer insulating film 28. Therefore, the first metal layer 22 has an interlayer insulating film 28 covering its outer periphery.
Therefore, it is pressed against the "l'-conductor disordered plate 21."

The connecting metal portion 25 is formed on and bonded to the portion of the first metal layer 22 that is not covered by the interlayer insulating film 28 . Therefore, the outer peripheral portion of the first metal layer 22 protrudes laterally from the joint with the connecting metal portion 25. Note that the connecting metal portion 25 can be formed in the same manner as forming a via metal.

The second metal layer 23 constituting the upper layer of the bonding pad 26 is bonded to the connection metal part 25 and is patterned on the connection metal part 25 and the interlayer insulating film 28 around it. Therefore, the outer peripheral portion of the second metal layer 23 protrudes sideways from the joint with the connecting metal portion 25, similarly to the first metal layer 22. The second metal layer 23 is formed with almost the same shape and size as the first metal layer 22,
Its outer peripheral portion is covered with a passivation film 30 together with the surrounding interlayer insulating film 25 . Therefore, the second metal layer 23 is pressed toward the semiconductor substrate 21 by the passivation film 30 covering the outer periphery thereof. The portion of the second metal layer 23 not covered by the passivation film 30 is exposed and can come into contact with the bonding wire.

Note that the connection metal part 25 has a connection strength that is sufficient to maintain the connection between the first metal layer 22 and the second metal layer 23 against the tension transmitted from the bonding wire during wire bonding onto the second metal layer 23. formed to satisfy the following. The connection strength required for the connection metal part 25 varies depending on the thickness of the second metal layer 23, the thickness of the passivation film 30, etc. This can be achieved by making the bonding area of the second metal layer 23 and the second metal layer 23 at least 40% of the exposed area of the second metal layer 23, respectively.

In order to investigate the frequency of peeling of the bonding pad according to the present invention described above, the following experiment was conducted. In the experiment, the passivation film 30 was connected to the metal part 25 and the second metal layer 23.
When formed by protruding from the outer periphery of the bonding region toward the center of the second metal layer 23 by a dimension B (see FIG. 2(a)),
On the other hand, if it is formed by retracting the dimension B outward (see figure (
(See b)), and wire bonding was performed 1000 times using a thermocompression bonding method combined with ultrasonic waves.

In addition, in the experiment, a GaAs substrate was used as the semiconductor substrate 21, and Ti (100 nm) was used as the first metal layer 2:2.
/Pt (150nm) /Au (400nm)
A multilayer metal layer was formed by vacuum evaporation. Further, as the interlayer insulating film 28, a SiN film was formed with a thickness of 600 nm by plasma CVD, and as the passivation film 30, a SiN film was formed with a thickness of 500 nm. Furthermore, the second
As the metal layer 23, T1 (100nn+)/Pt (15
A multilayer metal of 0n11)/Au (700 nm) was formed by vacuum steaming each Au layer with a thickness of 750 nm as the connecting metal part 25.

As a result of this experiment, peeling occurred in 9 out of 1000 bonding pads in the structure shown in FIG. 2(b). On the other hand, no peeling occurred in the structure shown in FIG. 4(a).

When we investigated the bonding pad in which peeling occurred in the structure shown in FIG.
It was inferred that the peeling of the pad 26 occurred due to the peeling at the interface with the pad 8. Therefore, in order to prevent such peeling, the passivation film 30 is removed from the second metal layer 23 from the outer periphery of the bonding area between the connecting metal part 25 and the second metal layer 23.
It is preferable to form it so as to protrude toward the center of the area.

For comparison, the case where the passivation film 30 is not formed (see FIG. 3(a)) and the case where the connecting metal part 25 is
is formed to have the same size as the first metal layer 22 and the second metal layer 23, and the outer peripheral part of the first metal layer 22 does not protrude laterally from the joint part of the connecting metal part 25 (FIG. 3(b)). ), an experiment similar to that shown in FIG. 2 was conducted. As a result, peeling occurred in 231 out of 1000 bonding pads in the structure shown in FIG. 3(b), whereas in the structure shown in FIG.
In structure a), the frequency of peeling was reduced to 33 out of 1000. From this, when the outer peripheral part of the upper surface of the first metal layer 22 is covered with the interlayer insulating film 28, the interlayer insulating film 28 acts to press the bonding pad 26 against the semiconductor substrate 21, and the bonding pad 26
It was found that it was effective in preventing peeling.

Therefore, in order to prevent the bonding pad from peeling off, it is effective to press the bonding pad against the semiconductor substrate with an insulating film such as the passivation film 30 or the interlayer insulating film 28. As in the embodiment shown, it is preferable to press the bonding pad with an insulating film at a plurality of locations in a direction perpendicular to the surface of the semiconductor substrate.

In addition, when paying attention to the attachment strength of the bottom surface of the bonding pad, in the embodiment shown in FIGS. 1 and 2, the bottom surface of the bonding pad is 1! , is bonded to the surface of the conductive substrate. In contrast, the bottom surface of the conventional bonding pad shown in FIG. 4 is bonded to an insulating film. Metals used for bonding pads can usually achieve higher bonding strength when bonded to a semiconductor substrate than when bonded to an insulating film. In the present invention,
Even when multilayer wiring is formed on a semiconductor substrate, the bottom surface of the bonding pad can be bonded to the semiconductor substrate, resulting in higher bonding strength than conventional bonding pads in which the bottom surface is bonded to an insulating film. It is possible to obtain on its bottom surface.

Note that if the above-mentioned pressing by the insulating film can sufficiently prevent the bonding pad from peeling off (l(/J+1), there is no need to consider the bonding strength of the bottom surface of the bonding pad. The metal layer 22 may be formed on the interlayer insulation crotch of the multilayer wiring.

By the way, in the embodiment described above, the first metal layer 22
The structure is such that only the outer periphery of the metal layer 28 is covered with the living room insulating film 28, but the connecting metal part 25 connecting the first metal layer 22 and the second metal layer 23 is divided into a plurality of parts and formed at a distance from each other. However, the center portion of the upper surface of the first metal layer 22 corresponding to the gap may be covered with an interlayer insulating film along with its outer peripheral portion.

Furthermore, in the embodiment described above, the metal wiring pattern 27 is connected to the first metal layer 22, but the interlayer insulating film 2
A metal wiring pattern formed on the semiconductor substrate 8 may be connected to the second metal layer 23, thereby connecting the bonding pad 26 to an electronic circuit on the semiconductor substrate.

〔Effect of the invention〕

As explained above, according to the present invention, the thickness of the bonding pad can be made thicker than that of the conventional bonding pad, and its shear strength is improved. In addition, the insulating films covering the outer peripheries of the first and second metal layers act to press the first and second metal layers toward the semiconductor device, respectively, against external forces that try to peel off the bonding pads. do. Therefore, a bonding pad that is difficult to peel off from a semiconductor device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the bonding pad according to the present invention, FIGS. 2 and 3 are cross-sectional views of the bonding pad used in the bonding pad peeling experiment, and FIG.
The figure is a perspective view showing a conventional bonding pad, and FIG. 5 is a view showing an experiment conducted to investigate the bonding pad peeling mechanism. 21... Semiconductor substrate, 22... First metal layer, 23...
... Second metal layer, 25... Connection metal part, 26... Bonding pad, 27... Metal wiring pattern, 28
...Interlayer insulating film, 30... Passivation film.

Claims (1)

[Scope of Claims] Bonding pads formed on a semiconductor device, connected to wiring patterns on the semiconductor device, and to which bonding wires are connected, the pads being spaced apart from each other and on the surface of the semiconductor substrate constituting the semiconductor device. a first metal layer and a second metal layer that are arranged substantially parallel to each other; and a first metal layer and a second metal layer that are bonded to each other between the first and second metal layers, and that are bonded to each other to prevent tension transmitted from the bonding wire during wire bonding. a connecting metal portion that connects the first metal layer and the second metal layer to each other with a connection strength sufficient to maintain the connection between the first metal layer and the second metal layer; The layer has an outer periphery that protrudes laterally from the joint with the connecting metal part, and each of the first and second metal layers has an outer periphery covered with an insulating film that covers the periphery thereof. A bonding pad featuring