JPH05226405A - Semiconductor device - Google Patents

Abstract

(57) [Abstract] [Purpose] When an external lead is bonded to a bonding pad formed on a substrate of a semiconductor chip via an insulating film by ultrasonic bonding, peeling of the interface between the underlying insulating film and the pad is prevented. To prevent. [Structure] The vicinity of the outer periphery of a conventional bonding pad is covered with a uniform protective film and strongly bound.
Slits with a large aspect ratio that can generate voids when depositing a protective film are placed near the outer periphery of the pad, weakening the restraining force, facilitating pad deformation during ultrasonic bonding, and absorbing ultrasonic shock. Then, the interface between the base insulating film and the pad is protected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device in which a bonding pad is provided on a chip for connecting an external lead. (Adhesion at the interface between the underlying oxide film and the bonding pad metal)
And a bonding pad structure for improving

[0002]

2. Description of the Related Art In order to electrically connect a bonding pad of a semiconductor chip and an external lead wire of a package or the like, thermocompression bonding and ultrasonic bonding techniques are usually used. In particular, when an aluminum (hereinafter simply referred to as Al or aluminum) wire is used as the lead wire material and Al is used as the pad material, good bonding cannot be achieved by the thermocompression bonding method, and therefore bonding with strong ultrasonic waves is applied. Press the head against the Al wire on the Al pad and press Al-Al
Join between.

FIG. 10 is an example of a partial sectional view of a semiconductor chip including a conventional bonding pad. A silicon oxide film (SiO 2 film) formed by the CVD method is formed on the silicon substrate 1.
₂ film) 2 and a boron phosphosilicate glass (hereinafter abbreviated as BPSG) film 3 having a high concentration of impurities added thereto. Then B
An aluminum alloy (Al-Si-Cu) film 5 is deposited on the PSG film, and the aluminum alloy film is patterned by a lithography technique to obtain a metal wiring film including the bonding pad 5. Next, as a protective film, a phosphosilicate glass (hereinafter abbreviated as PSG) film 6 and a silicon nitride (hereinafter abbreviated as Si N)
A film 8 is deposited on the entire surface, and for bonding, a part of the protective film is removed to obtain an opening surface 9. The bonding pad 5 having such a structure has a structure in which the side wall and the upper surface of the outer peripheral edge of the pad are covered with the protective films 6 and 8. Therefore, when ultrasonic waves with Al wires pressed against the opening surface 9 of the pad, the ultrasonic shock is concentrated at the interface between the bonding pad 5 and the underlying BPSG film 3, causing interface peeling,
This may cause the underlying oxide film to break (crack).

In order to improve the reliability of the wiring film made of an aluminum alloy, a laminated wiring structure may be used in which a titanium-based barrier metal is laid under the aluminum alloy wiring film. Have a similar structure,
The barrier metal comes into contact with the underlying oxide film. Since the adhesive strength between the barrier metal and the underlying oxide film is weaker than the adhesive strength between the aluminum alloy single layer wiring and the underlying oxide film, the probability of peeling is high, which is a serious problem.

[0005]

When electrically connecting the chip and the external lead, the external lead, for example, Al wire is bonded to the bonding pad of the aluminum alloy film on the chip by ultrasonic bonding. In the prior art, the impact of ultrasonic waves at the time of bonding may cause the peeling of the interface between the bonding pad and the underlying oxide film or the destruction of the underlying oxide film. In particular, in order to improve the reliability of the wiring, a laminated wiring structure in which a barrier metal is laid under the aluminum alloy wiring is often used, but the above-mentioned peeling phenomenon becomes more remarkable in the laminated wiring structure in which the barrier metal is laid, which causes a serious problem. Is becoming

The present invention has been made to solve the above-mentioned problems, and the ultrasonic power applied at the time of wire bonding is released to a position other than the interface between the pad and the underlying oxide film to protect the interface. Thus, it is an object of the present invention to provide a semiconductor device having a pad structure capable of maintaining good adhesion without peeling or the like.

[0007]

A semiconductor device according to claim 1 of the present invention is a semiconductor device having a bonding pad of a metal coating formed on the chip for connecting a semiconductor chip and an external lead line. , A slit formed by cutting out the outer peripheral edge of the bonding pad (see, for example, FIG.
The bonding pad is provided with at least one of the reference numeral 50a) and a slit that does not cut out the outer peripheral edge of the bonding pad (for example, reference numeral 50b in FIG. 6) provided near the pad outer peripheral portion. ..

The semiconductor device according to claim 2 of the present invention is characterized in that a ratio of a depth of the slit and a distance between side walls of the slit which face each other, that is, an aspect ratio is 0.5 or more. It is a semiconductor device.

[0009]

[Function] When ultrasonically bonding an Al lead wire to a bonding pad, it has been found that if the outer peripheral edge of the pad is not covered with a protective film, the peeling of the interface between the pad and the underlying oxide film is significantly reduced. did. That is, there is a significant difference in the transmission of the external force to the underlying interface between the case where the outer peripheral side wall and the outer peripheral upper surface of the bonding pad are covered with the protective film and constrained, and the case where the outer peripheral side wall and the upper surface of the bonding pad are not constrained without the protective film.
In the latter case, peeling or the like is extremely reduced. This is probably because the pad metal is easily deformed in the latter case when ultrasonic waves are applied, and the ultrasonic energy is absorbed by this deformation, and the ultrasonic shock applied to the interface between the pad and the underlying oxide film is significantly reduced. Be done.

Therefore, according to the present invention, a large number of slits are provided in the peripheral portion of the pad, and a void (void) is generated at the slit step portion when the protective film is deposited, thereby weakening the binding force of the protective film to the peripheral portion of the pad. , The pad metal is deformed when the ultrasonic wave is applied in the subsequent wire bonding,
The energy of ultrasonic impact is attenuated, and the adhesiveness at the interface between the pad and the underlying oxide film is maintained.

As described above, in the present invention, the slit is provided in the vicinity of the outer peripheral portion of the pad (outer peripheral area covered with the protective film).
The shape needs to have a void in the slit step portion when the protective film is deposited. The present invention according to claim 2 is
It is an embodiment example of the shape of the slit for generating a void in the slit step portion at the time of depositing the protective film. That is, according to the trial result, the aspect ratio (depth / depth /
If the bottom shortest length) is 0.5 or more, the probability of void occurrence is extremely high.

[0012]

The present invention will be described in more detail based on the following examples. 1 to 3 show a first embodiment of the present invention,
It is a figure in the case of providing a slit which notched the outer peripheral edge of a bonding pad. 1 and 2 are views for explaining the formation of the structure of the bonding pad according to the present invention.
FIG. 3 is a cross-sectional view taken along line A ′ (see FIG. 3), and FIG. 3 is a plan view of the bonding pad.

In FIG. 1, CVD is performed on the Si substrate 11.
To form a SiO ₂ film 12 with a thickness of 300 nm, followed by BPS.
The G film 13 is deposited to a thickness of 700 nm. At this time, B
The PSG film 13 is formed by the high temperature melt process (900 to 950).
In order to improve the flatness due to (° C.), for example, a structure containing several% boron (B) and phosphorus (P) is used.

Next, a barrier metal 14 containing titanium (Ti) is formed to a thickness of about 10 by magnetron sputtering.
After 0 nm deposition, heat treatment at 600 ° C is performed. Subsequently, an aluminum alloy (Al-Si-Cu) film 15 is deposited by sputtering similarly to a thickness of about 800 nm.

After that, the aluminum alloy film and the barrier metal are patterned by the photo-etching method to form the bonding pad 1.
A metal wiring pattern including 5 is formed. FIG. 3 is a plan view of the patterned bonding pad 15.
In the vicinity of the outer peripheral portion of the bonding pad 15, slits 50a which are formed by cutting out the outer peripheral edge of the pad are formed on three sides of the pad. The slit 50a has a width m = about 1 μm and a depth n =
It has a shape with an aspect ratio of 0.9 in a cubic space of about 2 μm and depth d (see FIG. 1) = about 0.9 μm.

After that, as shown in FIG.
A PSG film 16 having a thickness of nm is deposited by the CVD method. At this time, the void 17 is formed in the slit 50a. Further, a SiN film 18 having a thickness of about 700 nm is deposited on the entire surface by a plasma CVD method to form a laminated protective film. After that, a resist pattern having a pad opening portion 19 having a smaller area than the pad is formed on the pad 15, the SiN film 18 is formed by the CDE method, and the PSG film 16 is formed by NH ₄ F-based wet etching. Each is etched to have a shape as shown in FIG. After this, follow the normal assembly process
Ultrasonic bonding the Si lead wire onto the bonding pad 15.

FIGS. 4 to 6 are views showing a second embodiment of the present invention in which a bonding pad is provided with a slit which does not cut out the outer peripheral edge thereof. 4 and 5 are sectional views taken along the line BB '(see FIG. 6) for explaining the formation of the bonding pad structure, and FIG. 6 is a plan view of the bonding pad. In the second embodiment, the bonding pad 25
At the time of patterning, the slit 50b which does not cut the outer peripheral edge of the pad is formed in the vicinity of the outer peripheral portion of the pad.
The slit 50b has a width w (FIG. 4) of about 1 μm, a longitudinal length l (FIG. 6) of several μm, and a depth d of FIG. 4 of about 0.9 μm.
Let m. The other parts of the bonding pad structure and formation are almost the same as those of the first embodiment, and the description thereof will be omitted. After forming such a bonding pad 25,
As in the first embodiment, the PSG film 26 having a thickness of about 400 nm is formed by C
When deposited by the VD method, a void 27 is formed inside the elongated slit.

In order to compare the effects of the conventional bonding pad shown in FIG. 10 in which the vicinity of the outer peripheral portion is restrained by a protective film and the bonding pads in the first and second embodiments of the present invention, an aluminum alloy film and a barrier are used. After the Al-Si alloy lead is wedge-bonded to the bonding pad having a laminated structure with metal using ultrasonic waves, a tensile test (Peeling test) is performed.
Was done. With respect to each of about 500 pads, about 30% of peeling defects occurred in the conventional pad structure, whereas in the case of the present invention, the defective rate was 0%.

This is because the outer peripheral side wall and the upper surface of the conventional pad are uniformly adhered and restrained to the protective film.
This is because the pad outer peripheral portion of the present invention is adhered to the protective film via the slit including the void, so that the binding force of the protective film is significantly reduced. That is, in ultrasonic wire bonding, the interface between the pad and the lead wire is frictionally deformed by ultrasonic vibration and a fresh surface is exposed for bonding, but in the pad structure of the present invention, this ultrasonic vibration causes , The thin protective film on the side wall of the pad crushes,
Deformation of the pad metal becomes easy, and the ultrasonic energy is absorbed by the deformation, and the ultrasonic shock to peel off the pad metal and the underlying oxide film is not applied, and the adhesion at this interface is maintained. It is inferred that it will fall.

FIG. 7 is a cross-sectional view for explaining a process in which a void is generated at the outer peripheral portion of the bonding pad during deposition of the protective film. In the figure, CVDSi 2 O 3 is formed on the semiconductor substrate 31.
_{The two} films 32, the BPSG film 33, and the aluminum alloy film (bonding pad) 35 are laminated, and the aluminum alloy film 35 includes
Similar to the second embodiment, the width w and the thickness d are not notched at the outer peripheral edge.
Slit 51 is provided. A PSG film 36 is deposited as a protective film on this laminated film by the CVD method.
As long as the thickness of the protective film 36 is relatively small and the minimum distance x between the deposited films in the slit is larger than 0, no void is generated in the protective film. It can be considered that a void occurs when the thickness of the protective film 36 increases and x = 0. x = 0 is used as an evaluation criterion of whether or not a void is generated, the aspect ratio d / w of the slit and the thickness of the protective film 36 are changed,
The conditions under which voids are generated were investigated. According to the trial results, voids were observed in the slits having an aspect ratio of more than 0.5.

The present invention is characterized in that a slit having a shape in which a void is generated in the protective film at the time of depositing the protective film is provided in the vicinity of the outer peripheral portion of the bonding pad. Regarding the shape and arrangement of the slit, The invention is not limited to the first and second embodiments. 8 and 9 are plan views showing another embodiment of the bonding pad having the slit. In FIG. 8, the slit 50a with the outer peripheral edge of the bonding pad cut out and the slit 50b with the outer peripheral edge not cut out are arranged with the longitudinal direction of the slit aligned with the direction of one side of the bonding pad 45. .. There is no problem even if the slits are arranged with the longitudinal direction inclined with respect to the sides of the bonding pad. FIG. 9 shows an example in which a circular slit 50c that does not cut out the outer peripheral edge of the bonding pad is provided in the vicinity of the outer peripheral portions of the two sides of the bonding pad 55. The shape and arrangement of these slits are selected in consideration of the deformation mode of the bonding pad during ultrasonic bonding.

[0022]

As described above, in the present invention, a slit having a shape for generating a void in the protective film is provided in the vicinity of the outer peripheral portion of the bonding pad, and the pad metal can be deformed during wire bonding. As a result, the applied ultrasonic power is attenuated in a portion other than the interface between the pad and the underlying oxide film, that is, in the pad, and by protecting the interface, good adhesion without peeling can be maintained. A semiconductor device having a pad structure can be provided.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a manufacturing process of a first embodiment of a semiconductor device of the present invention.

FIG. 2 is a partial cross-sectional view showing the manufacturing process following FIG.

FIG. 3 is a plan view of a bonding pad of the semiconductor device of the first embodiment.

FIG. 4 is a partial cross-sectional view showing the manufacturing process of the second embodiment of the semiconductor device of the present invention.

FIG. 5 is a partial cross-sectional view showing the manufacturing process following FIG.

FIG. 6 is a plan view of a bonding pad of a semiconductor device according to a second embodiment.

FIG. 7 is a partial cross-sectional view of a semiconductor device illustrating a void generation process.

FIG. 8 is a plan view showing a first other embodiment of the bonding pad of the semiconductor device of the present invention.

FIG. 9 is a plan view showing another second embodiment of the bonding pad of the semiconductor device of the present invention.

FIG. 10 is a partial cross-sectional view of a conventional semiconductor device during a manufacturing process.

[Explanation of symbols]

1, 11, 21, 31 Silicon semiconductor substrate _2, 12, 22, 32 CVD SiO ₂ film 3, 13, 23, 33 BPSG film 14, 24, 34 Barrier metal 5, 15, 25, 35 Al alloy bonding pad 6 , 16, 26, 36 PSG film (protective film) 17, 27 Void 8, 18, 28 Si N film (protective film) 9, 19, 29 Bonding pad opening surface 50a Slits 50b, 50c notched on the outer peripheral edge Slits without notching the outer peripheral edge d / m, d / w Ratio of the depth of the slit and the distance between the side walls of the slit facing each other (aspect ratio)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Watanabe 72 Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Higashi Shiba Horikawa-cho Factory Co., Ltd.

Claims (2)

[Claims] 1. A semiconductor device having a bonding pad of a metal coating formed on the chip for connecting a semiconductor chip and an external lead line, wherein a slit formed by cutting out an outer peripheral edge of the bonding pad and the bonding pad. A semiconductor device comprising: a bonding pad in which at least one of the slits whose outer peripheral edge is not cut is provided near the pad outer peripheral portion. 2. The semiconductor device according to claim 1, wherein the ratio of the depth of the slit and the distance between the side walls of the slit facing each other is 0.5 or more.