JPH045843A - Bonding pad - Google Patents

Abstract

PURPOSE:To improve a shearing strength, and to eliminate peeling of a metal layer from a semiconductor device by providing a coupling metal for coupling upper and lower metal layers, and covering the outer peripheries of the upper and lower layers with insulating films. CONSTITUTION:Bonding pads 26 are formed of first and second metal layers 22, 23, and a coupling metal 25 for coupling the layer 22 to the layer 23 on a semiconductor substrate 21. The layer 22 is covered with an interlayer insulating film 28 together with the substrate 21 therearound and a metal interconnection pattern 27 except the part bonded to the metal 25. Accordingly, the layer 22 is pressed to the substrate 21 by the film 28 covering the outer periphery. The layer 23 is covered with a passivation film 30 together with the film 28 at the outer periphery. Therefore, the layer 23 is pressed to the substrate 21 by the film 30 covering the outer periphery.

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
It is formed as a single minute metal plate on a semiconductor substrate constituting a semiconductor device, and has a structure in which the outer periphery is covered with an insulating film such as a passivation film. Bonding pads formed in compound semiconductor devices are often formed on the surface of a compound semiconductor substrate, and in this case, compound '1! .

The first layer wiring metal patterned on the surface of the conductor substrate is often used as it is as a bonding pad.

FIG. 5 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 an approximately 11-sided planar 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 3, and the outer periphery of the surface thereof is covered with a passivation film 7 together with the surrounding insulating film 3. It has become.

[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 adhesive strength (adhesion strength) 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 the bonding operation, 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 metal layer is covered with an insulating film surrounding the first metal layer except for the joints with the connection metal parts, and the second
The outer periphery of the metal layer is covered with an insulating film surrounding the metal layer.

[Effect]

With this configuration, the thickness of the bonding pad is substantially thicker than in the prior art, improving its shear strength. Furthermore, the insulating films covering the first and second metal layers act to press the first and second metal layers toward the semiconductor device, respectively, against external forces that tend to peel off the bonding pads.

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

That is, as shown in FIG. 6, when the bonding pad 15 is formed on the semiconductor substrate 11 and the bonding wire 18 is connected (bonded) with the outer periphery of the bonding pad 15 covered with the passivation film 17. Compare the frequency at which the bonding pad 15 peels off (see (a) in the same figure) and when wire bonding is performed without covering it with the passivation film 17 (see (b) and (c) in the same figure). did.

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 deviates from the center of the pad 15 and hangs on the end of the pad 15 as shown in FIG.
The stress acting between the pad 15 and the semiconductor substrate 11 is concentrated at the end of the pad 15, and peeling easily occurs there. Therefore, in order to reduce the frequency of peeling, it is desirable to prevent the wire 18 from touching the end of the pad 15. In addition, when we examined the bonding pads that had peeled off in the experiments shown in Figures (b) and (c), we found that pad 1
None of the pads were partially torn and peeled off, but the entire pad was peeled off in all of them. 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, the outer periphery of the pad 15 is covered with the passivation film 1.
7 (see figure (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 and peripheral portion
7 prevents the wire 18 from contacting 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 bonding position accuracy is poor, the frequency of peeling of the pad 15 can be reduced. Also, pad 1
The passivation film 17 covering the outer periphery of the pad 15
The pad 15 is removed from the substrate 11 by resisting the external force that tries to peel it off.
It also plays a role in suppressing the situation. As a result,
The frequency of occurrence of peeling in the case of FIG. 3(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 4.

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 plurality of connecting metal parts 25 that interconnect these parts.

The first metal layer 22 constituting the lower layer part 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, Q, 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 μm, and the electron beams formed on the semiconductor substrate 21 via the metal wiring pattern 27 are patterned. connected to the circuit. The first metal layer 22 is covered with an interlayer insulating film 28 along with the surrounding surface of the semiconductor substrate 21 and the metal wiring pattern 27, except for the joint portion with the connecting metal portion 25. Therefore, the first metal layer 22 is pressed against the semiconductor substrate 21 by the interlayer insulating film 28 covering it.

FIG. 2 shows the planar shape and arrangement of the plurality of connecting metal parts 25. As shown in FIG.
They are formed on the metal layer 22 to be spaced apart from each other. The connecting metal portion 25 can be formed in the same manner as via metal.

In this embodiment, the connecting metal portion 25 is formed in a region other than the outer peripheral portion of the first metal layer 22. Therefore, the first metal layer 22 has an overhang portion that overhangs laterally from the region where the plurality of connecting metal portions 25 are formed.

The second metal layer 23 constituting the upper layer of the bonding pad 26 is bonded to the plurality of connection metal parts 25 and is patterned on the connection metal parts 25 and the interlayer insulating film 28 around the connection metal parts 25 . In the embodiment shown in FIG. 1, the second metal layer 23 is formed to have substantially the same shape and size as the first metal layer 22, and the second metal layer 23 is also similar to the first metal layer 22.
Similarly, it has an overhanging portion that overhangs laterally from the region where the plurality of connecting metal portions 25 are formed. and,
The second metal layer 23 has its outer periphery covered by the surrounding interlayer insulating film 2.
5 is covered with a passivation film 30. Therefore, the second metal layer 23 is not pressed toward the semiconductor substrate 21 by the passivation film 30 covering the outer periphery of the second metal layer 23 . An opening 30a is formed in the passivation film 30 to expose the upper surface of the second metal layer 23, and a bonding wire is connected to the exposed portion of the second metal layer 23.

Note that the plurality of connecting metal parts 25 are made of a material that can 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 connection strength. 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 is achieved by making the total bonding area of the second metal layer 23 and the second metal layer 23 at least 40% or more of the exposed area of the second metal layer 23 (opening area of the opening 30a).

Further, the connecting metal portion 25 is formed so that at least about 40% of the outer circumferential length of the opening 30a formed in the passivation film 30 is included in its bonding region. That is, at least 40% of the outer circumference is formed on the connecting metal part 25. This is to allow the second metal layer 23 to resist the shearing force that acts on the outer periphery of the opening 30a during wire bonding.

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. 3(a)),
On the other hand, if it is formed by retracting the dimension B outward (see figure (
b)) and 5,000 times and 1,000 times, respectively.
The second wire bonding was performed using a thermocompression method combined with ultrasonic waves.

In the experiment, a GaAs substrate was used as the semiconductor substrate 21, and Ti (100nIII) was used as the first metal layer 22.
) /P t (150nm) /Au (400nm
) 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 nlTl. Furthermore,
As the second metal layer 23, Tt (100 nm)/Pt (1
50 nm)/Au (700 nm), and an Au layer having a thickness of 750 nm was formed as the connecting metal part 25 by vacuum evaporation.

As a result of this experiment, peeling occurred in 7 out of 1000 bonding pads in the structure shown in FIG. 3(b). On the other hand, in the structure shown in FIG. 5(a), no peeling occurred at all among the 5,000 bonding pads. When we investigated the bonding pad in which peeling occurred in the structure shown in FIG. It was inferred that peeling had occurred. Therefore, in order to prevent such peeling, it is preferable to form the passivation film 30 so as to protrude toward the center of the second metal layer 23 from the outer periphery of the bonding region between the connecting metal part 25 and the second metal layer 23.

For comparison, a case in which no passivation film 30 is formed (see FIG. 4(a)) and a case in which a plurality of connecting metal parts 25 are not formed and a single connecting metal part 33 is formed instead.
The same experiment as in the case of FIG. 3 was conducted for the case where the metal layer was formed at the center of the first metal layer 22 and the second metal layer 23 (see FIG. 3B). As a result, in the structure shown in FIG. 4(b), 58 out of 1000 bonding pads were peeled off, whereas in the structure shown in FIG. 4(a), the peeling frequency was reduced to 17 out of 1000. From this, it was found that the interlayer insulating film 28 covering the first metal layer 22 between the plurality of connecting metal parts 25 effectively pressed down the bonding pad.

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. It is effective to cover the first metal layer 22 between the portions 25 with an interlayer insulating film 28. As in the embodiments shown in FIGS. 1 to 3, 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.

Note that with regard to the attachment strength of the bottom surface of the bonding pad, in the embodiments shown in FIGS. 1 to 3, the bottom surface of the bonding pad is bonded to the surface of the semiconductor substrate. In contrast, the bottom surface of the conventional bonding pad shown in FIG. 5 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,
It is possible to bond the bottom surface of the bonding pad to the semiconductor substrate, and it is possible to obtain bonding strength on the bottom surface that is higher than that of a conventional bonding pad in which the bottom surface is bonded to an insulating film.

Note that if the above-mentioned pressing by the insulating film can sufficiently prevent the bonding pad from peeling off, there is no need to consider the bonding strength of the bottom surface of the bonding pad. It may also be formed on the interlayer insulation crotch of the wiring.

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 the child circuit 71i 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 substantially thicker than that of the conventional bonding pad, and its shear strength is improved. Furthermore, the insulating films covering the first and second metal layers act to press the first and second metal layers toward the semiconductor device, respectively, against external forces that tend to peel off the bonding pads. 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, FIG. 2 is a view showing the arrangement of the connecting metal parts,
Figures 3 and 4 are cross-sectional views of the bonding pad used in the bonding pad peeling experiment, Figure 5 is a perspective view of a conventional bonding pad, and Figure 6 is a cross-sectional view of the bonding pad used in the bonding pad peeling experiment. FIG. 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, 3
0a...opening. Figure 3 of Bonbuishifu University and Sodo used for experiments.

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 plurality of connecting metal parts that connect the first metal layer and the second metal layer in a phase-like manner with a connection strength that is sufficient to maintain the connection between the first metal layer and the second metal layer; The second metal layer is covered with an insulating film surrounding the layer except for the joint with the connecting metal part, and the second metal layer has an outer peripheral part covered with an insulating film surrounding the second metal layer. bonding pad.