JP7361566B2 - Semiconductor device and its manufacturing method - Google Patents

Description

The present invention relates to a semiconductor device having bonding pads and a method for manufacturing the same.

A conventional semiconductor device having bonding pads will be described. Semiconductor devices are provided with bonding pads for supplying a power supply voltage or ground potential to a semiconductor integrated circuit and for exchanging data with the outside. FIG. 11 is a cross-sectional view showing a bonding pad of a conventional semiconductor device.

A first metal film 51 is provided on an insulating film 53 provided on the surface of the semiconductor substrate 50. A second metal film 52 is provided directly on the first metal film 51 . The protective film 54 covers the second metal film 52 and has an opening above the bonding pad. The protective film 54 covers the second metal film 52 except for the opening of the protective film 54 . Therefore, the opening in the protective film 54 defines the area used as a bonding pad.

Here, regarding Young's modulus, which is a physical property of the first metal film 51 and the second metal film, the Young's modulus of the first metal film 51 is higher than that of the second metal film 52. With such a structure, the first metal film 51 with a high Young's modulus is provided as a lower layer of the bonding pad, so the resistance around the bonding pad against stress generated by the impact of wire bonding is increased (for example, see Patent Document 1). ).

Japanese Patent Application Publication No. 2009-027098

However, in the technique described in Patent Document 1, the upper surface and side surfaces of the second metal film 52 are distorted due to the stress generated by the impact of wire bonding, and the protective film 54 covering the bonding pad is cracked. was there.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a semiconductor device that can prevent cracks from forming in the protective film 54 covering the bonding pads.

The present invention uses the following means to solve the above problems.
First, a semiconductor device having a bonding pad,
a semiconductor substrate;
an insulating film provided on the surface of the semiconductor substrate;
a first metal film provided on the insulating film;
a second metal film covering the top and side surfaces of the first metal film;
a protective film having an opening above the second metal film and covering the second metal film and the insulating film other than the opening;
The semiconductor device is characterized in that the Young's modulus of the second metal film is higher than the Young's modulus of the first metal film.

Further, a method for manufacturing a semiconductor device having a bonding pad, the method comprising:
a step of forming an insulating film on a semiconductor substrate;
forming a first metal film on the insulating film;
forming a second metal film having a higher Young's modulus than the first metal film so as to cover the top and side surfaces of the first metal film;
forming a protective film to cover the second metal film and the insulating film;
forming an opening in the protective film on the second metal film;
A method for manufacturing a semiconductor device is used.

By using the above means, distortion (deformation) of the first metal film that occurs during wire bonding can be prevented. This makes it possible to prevent cracks from forming in the protective film covering the bonding pads.

1 is a cross-sectional view of a semiconductor device according to a first embodiment of the present invention. FIG. 3 is a cross-sectional view showing distortion of a film due to wire bonding. FIG. 7 is a plan view and a cross-sectional view of a semiconductor device according to a second embodiment of the present invention. FIG. 3 is a cross-sectional view of a semiconductor device according to a third embodiment of the present invention. FIG. 1 is a diagram showing a manufacturing process of a semiconductor device according to a first embodiment of the present invention. FIG. 6 is a diagram following FIG. 5 illustrating the manufacturing process of the semiconductor device according to the first embodiment of the present invention. FIG. 7 is a diagram following FIG. 6 illustrating the manufacturing process of the semiconductor device according to the first embodiment of the present invention. FIG. 7 is a diagram showing a manufacturing process of a semiconductor device according to a third embodiment of the present invention. 9 is a diagram showing a manufacturing process of a semiconductor device according to a third embodiment of the present invention following FIG. 8. FIG. FIG. 9 is a diagram showing a manufacturing process of a semiconductor device according to a third embodiment of the present invention, following FIG. 9 . FIG. 2 is a cross-sectional view showing a conventional semiconductor device.

Embodiments of the present invention will be described below with reference to the drawings.
First, the structure of a semiconductor device having bonding pads 30 will be described. FIG. 1 is a cross-sectional view of a semiconductor device according to a first embodiment of the invention.

As shown in FIG. 1, bonding pads 30 are provided on the insulating film 13 provided on the surface of the semiconductor substrate 10. The bonding pad 30 is composed of a first metal film 11 and a second metal film 12. The first metal film 11 is provided on an insulating film 13, and a second metal film is provided to cover the top and side surfaces of the first metal film 11. 12 are provided. Further, a protective film 14 having an opening 15 is provided on the second metal film 12 and the insulating film 13. That is, the protective film 14 covers the second metal film 12 and the insulating film 13 except for the opening 15 . The area not covered by the protective film 14 becomes the pad portion 16. Here, the first metal film 11 is formed of, for example, an aluminum film alone or an aluminum alloy film. The second metal film 12 is a laminated film of a barrier metal film 12x and a bonding stabilizing film 12y, and the barrier metal film 12x is in contact with the first metal film 11. A nickel film, a tungsten film, a titanium film, a palladium film, or the like is used as the barrier metal film 12x, and a gold (Au) film is used as the bonding stabilizing film 12y. The Young's modulus of aluminum (Al) is about 70 GPa, the Young's modulus of nickel (Ni) is about 200 GPa, the Young's modulus of tungsten (W) is about 400 GPa, the Young's modulus of titanium (Ti) is about 110 GPa, and the Young's modulus of palladium (Pd). The Young's modulus of is about 120 GPa. In such a configuration, at least the Young's modulus of the barrier metal film 12x constituting the second metal film 12 is higher than the Young's modulus of the first metal film 11. For reference, the Young's modulus of gold (Au) is approximately 80 GPa, which is higher than the Young's modulus of aluminum (Al) constituting the first metal film 11.

Referring to FIG. 2, distortion of a film forming a bonding pad when wire bonding is performed on the bonding pad will be described. FIG. 2(a) is a cross-sectional view showing film distortion due to wire bonding at the bonding pad of a conventional semiconductor device, and FIG. 2(b) is a cross-sectional view showing film distortion at the bonding pad of the semiconductor device according to the first embodiment of the present invention. 2 shows a cross-sectional view showing the distortion of the film due to

As shown in FIG. 2A, when wire bonding is performed on a conventional bonding pad, the portion where the wire ball portion 17 contacts the bonding pad, that is, the second metal film 52 is exposed from the opening of the protective film 54. A recess 55 is formed in the central region of the bonding pad, thereby causing a partial movement of the second metal film 12 from the central region of the bonding pad to the peripheral region of the bonding pad. Due to the partial movement of the second metal film 52 in the direction indicated by the arrow, a convex strain 56 is generated on the upper surface and side surfaces of the peripheral area of the bonding pad, and the protective film 14 in contact with the strain 56 is cracked and the protective film 54 is damaged accordingly. Peeling will occur. Cracking or peeling of the protective film 54 may facilitate moisture intrusion into the interior of the semiconductor device, which may reduce the reliability of the semiconductor device.

On the other hand, as shown in FIG. 2B, in the bonding pad 30 of the semiconductor device according to the first embodiment of the present invention, the upper surface and side surfaces of the first metal film 11 have a Young's modulus lower than that of the first metal film 11. It is covered with a high second metal film 12. Therefore, even if wire bonding is performed on the bonding pad 30, the second metal film 12 is provided in the central region of the bonding pad 30 where the wire ball portion 17 contacts, and a recess is difficult to be formed in this region. Furthermore, since the second metal film 12 has a structure that covers from the central region to the upper surface and side surfaces of the peripheral region, even if excessive stress is applied to the central region, the first metal film 11 and the second metal film 12 in the peripheral region Less likely to cause distortion. Therefore, it is possible to prevent the protective film 14 in contact with the protective film 14 from cracking and the resulting peeling of the protective film 14, thereby realizing a highly reliable semiconductor device 1.

FIG. 3 is a plan view and a cross-sectional view of a semiconductor device according to a second embodiment of the invention. As shown in the plan view of FIG. 3A, the difference from the first embodiment is that the first metal film 11 has a checkered sea-island structure. The sea-island structure has a rectangular island region 21 made of the first metal film 11 and a sea region 22 where the first metal film 11 is absent and the underlying insulating film 13 is exposed, and adjacent island regions 21 are located at the apex of each rectangle. The structure is such that they are connected at the edges and separated from each other at the edges.

FIG. 3(b) is a cross-sectional view taken along line AA in FIG. 3(a). A bonding pad 30 is provided on the insulating film 13 provided on the surface of the semiconductor substrate 10. The bonding pad 30 is composed of a first metal film 11 and a second metal film 12. The first metal film 11 is provided on an insulating film 13, and a second metal film is provided to cover the top and side surfaces of the first metal film 11. 12 are provided. Further, a protective film 14 having an opening 15 is provided on the second metal film 12 and the insulating film 13. That is, the protective film 14 covers the second metal film 12 and the insulating film 13 except for the opening 15 .

The adjacent island regions 21 are made of the second metal film 12, and a sea region 22 is provided between them. The second metal film 12 is densely embedded in the recessed portion of the sea region 22 . Assuming that the second metal film 12 is deposited uniformly on the surface of the first metal film 11, the width d1 of the sea region, that is, the width by which adjacent island regions 21 are separated, is twice the film thickness of the second metal film 12. By making the length shorter than that, the sea region 22 can be completely buried with the second metal film 12. With such a structure, two layers of the second metal film 12 having a high Young's modulus are sandwiched between adjacent island regions 21, thereby forming a stronger strain prevention layer. This makes it possible to prevent the protective film 14 from cracking and the resulting peeling of the protective film 14, making it possible to realize a highly reliable semiconductor device 1.

In the example shown in FIG. 3B, the sea region 22 is completely buried only with the barrier metal film 12x of the second metal film 12, and the barrier metal film 12x is covered with the bonding stabilizing film 12y. Although not shown, if the barrier metal film 12x is thinner than the example shown in FIG. 3(b), the sea region 22 will be buried in the barrier metal film 12x and the bonding stabilizing film 12y.

FIG. 4 is a cross-sectional view of a semiconductor device according to a third embodiment of the present invention. A bonding pad 30 is provided on the insulating film 13 provided on the surface of the semiconductor substrate 10. The bonding pad 30 is composed of a first metal film 11 and a second metal film 12. The first metal film 11 is provided on an insulating film 13, and a second metal film is provided to cover the top and side surfaces of the first metal film 11. 12 are provided. Further, a protective film 14 having an opening 15 is provided on the second metal film 12 and the insulating film 13. That is, the protective film 14 covers the second metal film 12 and the insulating film 13 except for the opening 15 .

The difference from the first embodiment is that the upper edge 11a of the first metal film 11 is rounded. Since the upper surface and side surfaces of the first metal film 11 are covered with the second metal film 12, the upper edge 12a of the second metal film 12 also has a round shape reflecting the base. By forming the bonding pad 30 into a round shape, there is no region having an acute angle or a right angle in cross section, and damage to the protective film 14 in contact with the region is further reduced. With such a structure, it is also possible to avoid cracks in the protective film 14 due to the difference in expansion coefficients between the bonding pad 30 and the protective film 14.

Although not shown, the same effect can be obtained by making the upper edge 11a of the first metal film 11 and the upper edge 12a of the second metal film 12 chamfered in place of the round shape of the third embodiment of the present invention. is obtained.

Note that the round shape of the third embodiment of the present invention can be applied not only to the semiconductor device of the first embodiment but also to the semiconductor device of the second embodiment.
5 to 7 are diagrams showing a method for manufacturing a semiconductor device according to the first embodiment of the present invention.

First, as shown in FIG. 5, an insulating film 13 is formed on the surface of the semiconductor substrate 10, and an aluminum film (Al) or an aluminum alloy film (for example, Al-Si, Al-Si-Cu) is formed on the surface of the insulating film 13. , Al--Cu) having a low Young's modulus is formed, and then etched using a predetermined resist pattern to form the first metal film 11.

Next, as shown in FIG. 6, a laminated film including a metal film having a higher Young's modulus than the first metal film 11 is formed so as to cover the surfaces of the first metal film 11 and the insulating film 13. The laminated film is formed by successively depositing the barrier metal film 12x and the bonding stabilizing film 12y in this order. For continuous deposition, methods such as sputtering, vapor deposition, or plating are used. The barrier metal film 12x to be deposited may be a single film of nickel, tungsten, titanium, or palladium, or may be a laminated film of a plurality of these film types. If the barrier metal film 12x is a laminated film of a nickel film and a palladium film, it is preferable to form the nickel film in contact with the first metal film 11. The bonding stable film 12y in contact with the palladium film is a gold (Au) film.

After the film formation, each film is sequentially etched using a predetermined resist pattern to form the second metal film 12. During etching, over-etching caused by the microbattery can be prevented by using a buffer solution with a controlled hydrogen ion index (pH). As shown in the figure, the second metal film 12, which is a laminated film of a barrier metal film 12x and a bonding stabilizing film 12y, is formed to cover the top and side surfaces of the first metal film 11.

In the above example, the second metal film 12 is etched using a resist pattern, but a method of selectively forming the second metal film 12 at predetermined locations using a metal mask may also be used. .

Next, as shown in FIG. 7, a protective film 14 such as a plasma nitride film is formed on the surface of the second metal film 12, and then etched using a predetermined resist pattern to form a protective film 14 on the second metal film 12. An opening 15 is formed in the protective film 14 so that the second metal film 12 is exposed in the opening 15.

By using the above manufacturing method, it is possible to prevent distortion of the first metal film 11 due to stress generated during wire bonding. This can prevent cracks from forming in the protective film 14 covering the bonding pads 30, and can prevent moisture from entering through the cracks.

Furthermore, when manufacturing the semiconductor device according to the third embodiment of the present invention, the method for forming the first metal film 11 shown in FIG. 8 is used instead of the method shown in FIG.
First, as shown in FIG. 8, an insulating film 13 is formed on the surface of the semiconductor substrate 10, and then a metal film with a low Young's modulus such as aluminum or aluminum alloy is formed on the surface of the insulating film 13, and then a predetermined film is formed. The first metal film 11 is formed by etching using the resist pattern 19. When the upper edge 11a of the first metal film 11 is rounded, the over-etching time is set to be longer than usual in etching the first metal film 11, so that the edge of the resist pattern 19 disappears during etching. After that, a part of the first metal film 11 is further etched.

FIG. 8A is a cross-sectional view of the first metal film 11 being etched using the resist pattern 19 as a mask, and shows the cross-sectional shape after normal over-etching. Incidentally, the normal overetching time is 0.2 to 0.5 times the detected end point time. At this stage, although an inclined portion can be seen on the side surface of the resist pattern 19, the side surface of the first metal film 11 is formed vertically.

FIG. 8(b) is a cross-sectional view showing a state in which over-etching has been further added. The film thickness of the resist pattern 19 is greatly reduced, and the slope of the side surface is larger than that at the stage after normal over-etching. In such a resist pattern 19, the upper edge 11a of the first metal film 11 is not covered with the resist pattern 19, and a round shape is formed in the upper edge 11a. The over-etching time employed here is 1.5 to 2.5 times the normal over-etching time. Next, by removing the resist pattern 19, the first metal film 11 having a rounded upper edge 11a as shown in FIG. 8(c) is obtained.

As explained above, the over-etching time is set to 1.5 to 2.5 times longer than usual, and etching is performed until the film thickness at the ends of the resist pattern 19 disappears. The exposed upper edge 11a of the first metal film 11 can be etched to form a round shape. Note that the method for forming the round shape on the upper edge 11a of the first metal film 11 is not limited to this.

Furthermore, when the upper edge 11a of the first metal film 11 and the upper edge 12a of the second metal film 12 are to have a chamfered shape instead of a round shape, wet etching is adopted for etching the first metal film 11, and the upper edge 12a of the second metal film 12 is chamfered. By controlling the adhesion between the first metal film 11 and the resist pattern 19, a chamfered shape can be obtained.

Next, as shown in FIG. 9, a laminated film including a metal film having a higher Young's modulus than the first metal film 11 is formed so as to cover the surfaces of the first metal film 11 and the insulating film 13. The laminated film is formed by successively depositing the barrier metal film 12x and the bonding stabilizing film 12y in this order. For continuous deposition, methods such as sputtering, vapor deposition, or plating are used. The barrier metal film 12x may be a single nickel film or a laminated film of a nickel film and a palladium film. In this case, it is preferable to form the nickel film so that it is in contact with the first metal film 11. The bonding stabilizing film is a gold (Au) film.

Since the first metal film 11 as the base has a round shape at the upper edge 11a, this round shape is reflected in the shape of the second metal film 12 covering the first metal film 11, and the upper edge 12a of the second metal film 12 has a round shape. A round shape is also formed.

After the film formation, each film is sequentially etched using a predetermined resist pattern to form the second metal film 12. The second metal film 12, which is a laminated film of the barrier metal film 12x and the bonding stabilizing film 12y, is formed to cover at least the top and side surfaces of the first metal film 11.

In the above example, the second metal film 12 is etched using a resist pattern, but a method of selectively forming the second metal film 12 at predetermined locations using a metal mask may also be used. .

Next, as shown in FIG. 10, a protective film 14 such as a plasma nitride film is formed on the surface of the second metal film 12, and then etched using a predetermined resist pattern to form a protective film 14 on the second metal film 12. In step, an opening 15 is formed in the protective film 14. By forming the upper edge 12a of the second metal film 12 into a round shape, damage to the protective film 14 covering it can be reduced.

By using the above manufacturing method, distortion of the first metal film 11 that occurs during wire bonding can be further prevented. This makes it possible to prevent the protective film 14 covering the bonding pad 30 from cracking and the resulting peeling of the protective film 14, thereby realizing a highly reliable semiconductor device 1.

Note that it is clear that the formation of the round shape according to the third embodiment of the present invention can be applied not only to the semiconductor device according to the first embodiment but also to the semiconductor device according to the second embodiment.

1 Semiconductor device 10 Semiconductor substrate 11 First metal film 11a Top edge 12 Second metal film 12a Top edge 12x Barrier metal film 12y Bonding stability film 13 Insulating film 14 Protective film 15 Opening 16 Pad portion 17 Wire ball portion 18 Crack 19 Resist Pattern 21 Island area 22 Sea area 30 Bonding pad d1 Width of sea area

Claims (8)

A semiconductor device having a bonding pad,
a semiconductor substrate;
an insulating film provided on the surface of the semiconductor substrate;
a first metal film formed of aluminum and having a rectangular shape in a cross-sectional view on the insulating film and having a rounded upper edge ;
a second metal film covering the top and side surfaces of the first metal film;
a protective film formed of a plasma nitride film having an opening above the second metal film and covering the second metal film and the insulating film except for the opening;
A semiconductor device, wherein a Young's modulus of the second metal film is higher than a Young's modulus of the first metal film. 2. The semiconductor device according to claim 1, wherein the first metal film is provided in a sea-island structure, and the second metal film is embedded in a sea region of the sea-island structure. 3. The semiconductor device according to claim 2, wherein the second metal film has a flat surface exposed from the opening. 2. The semiconductor device according to claim 1, wherein the second metal film is composed of a barrier metal film and a junction stabilizing film. A method for manufacturing a semiconductor device having a bonding pad, the method comprising:
a step of forming an insulating film on a semiconductor substrate;
forming a first metal film of aluminum in a rectangular shape in cross-section on the insulating film, and rounding the upper edge;
forming a second metal film having a higher Young's modulus than the first metal film so as to cover the top and side surfaces of the first metal film;
forming a protective film with a plasma nitride film so as to cover the second metal film and the insulating film;
forming an opening in the protective film on the second metal film;
A method for manufacturing a semiconductor device, comprising: 6. The semiconductor device according to claim 5, further comprising the step of forming said first metal film into a sea-island structure and embedding said second metal film in a sea region of said sea-island structure. 7. The semiconductor device according to claim 6, wherein the second metal film has a flat surface exposed from the opening. 6. The semiconductor device according to claim 5, wherein in the step of forming the second metal film, a barrier metal film and a bonding stabilizing film are formed in this order.