JPH03174731A - Bump electrode for integrated circuit and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce the risk of damage to the base and chip during the mounting of the chip by employing a stepped bump structure, in which each bump electrode protruding from the chip surface of a semiconductor integrated circuit includes a base and a tip, coaxial with the base, having a cross section half that of the base. CONSTITUTION:Small bump electrodes 10 are provided on a chip 1. Each bump electrode has a stepped structure, which includes a base 11 and a tip 12 that is smaller than, and coaxial with, the base 11. The tip 12 has loss than half the cross section of the base 11. These bump electrodes are pressed against wiring conductors 32 of a printed-circuit board 30, or they are bonded using shrink curing resin. At first, the tip must be pressed to bring all the bump electrodes into contact with the corresponding conductors 32. The required pressure to be applied is relatively small because the small-area tips 12 can easily be deformed. Therefore, it is possible to eliminate damage to the base and chip during the mounting of the chip.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to bump electrodes that protrude from a chip of an integrated circuit device for external connection.

[Conventional technology]

With the recent progress in high-integration technology, the number of circuits built into a single integrated circuit device has increased, and the number of connection points with the outside has also tended to increase accordingly. Therefore, flip chips equipped with bump electrodes as external connection points are increasingly being used.

In the flip chip of such a highly integrated integrated circuit device, dozens to hundreds of small bump electrodes, each several tens of micrometers in size, are arranged at a narrow arrangement pitch of several tens of micrometers along the periphery of a small chip of several millimeters square. It is arranged to a certain extent.

FIG. 3 is an enlarged view of a conventional small bump electrode, and FIG. 4 is an enlarged view of a flip chip equipped with the same mounted on a wiring board.

In FIG. 3, a wiring film 3 is disposed on an oxide film 2 covering the surface of a chip 1 of an integrated circuit device, and a protective film 4 is further placed thereon to protect the ends of the wiring film 3. Bump electrodes IO are provided in the windows opened in the membrane 4. Gold or copper is mainly used as the metal for this small bump electrode 10, and is grown by electrolytic plating on the lower base film 5a and upper base film 5b that are in conductive contact with the wiring film 3 within the window. . Such a conventional small bump electrode 10 has a size of, for example, 30 μm square or diameter and a height of 20 μm, but since it is grown by electrolytic plating, the tip is larger than the base, for example, 40 to 50 μm, as shown in the figure. It is usually formed in a swollen, dew-like shape.

FIG. 4 shows a state in which the chip 1 having such a bump electrode 10 is mounted on a wiring board 30 in a so-called face-down manner. During this mounting, the hang electrode 10 is connected directly to the wiring conductor 32 disposed on the insulating substrate 31 made of ceramic or the like of the wiring board 30 as in this example, or to a similar bump electrode protruding thereon. or joined. As the connection means in this case, a means of so-called pressure contact under heating and pressure, a means of surrounding the connection part with an infrared curable resin and making use of the shrinkage force of the resin upon curing, etc., are employed.

[Problem to be solved by the invention]

However, since the height of the bump electrodes, which protrude from the chip of an integrated circuit device by several tens or hundreds, inevitably varies by at least ±10%, the above-mentioned differences occur when mounting on a wiring board, etc. Regardless of which connection method is used, it is necessary to apply a pressure force of, for example, about 30 g per bump electrode to compensate for variations in the height of the bump electrode. There are problems that can easily lead to damage.

In Figure 4, the bump electrode with a height larger than the average is numbered 10.
The bump electrode 10 is deformed considerably by the above-mentioned pressing force as shown in the figure in order to ensure the connection with the wiring conductor 32 of the normal height. At the same time,
Wiring film 3 at the location indicated by a small circle in FIG. Damage may occur on the surface of the oxide film 2 or the chip 1 due to the pressure P, causing troubles such as the bump electrode 10 coming off or cracks or damage occurring in the protective film 4, resulting in deterioration of the characteristics of the integrated circuit. It happens.

Furthermore, as mentioned above, the conventional bump electrode 1o is exposed and has low strength at the base, so if the tip touches or hits an object and an external force is applied in the shearing direction shown by S in FIG. 3, it will come off relatively easily. There is a problem in that it is easy to be damaged, so it must be handled with care not only during mounting but also during transportation.

In addition, when soldering the bump electrode 10 by thermocompression bonding,
Due to variations in the height of the bump electrode 10 and the height with respect to the wiring conductor 32, problems occur such that the bump electrode 1o and the wiring conductor 32 do not come into contact with each other, or bridges with adjacent bump electrodes occur due to excess solder dripping. Shasui.

The present invention solves this problem and reduces the risk of damage to the bump electrode itself or the chip body when pressure is applied during mounting of a chip in an integrated circuit device, or ensures the connection between the bump electrode and the wiring conductor. The purpose is to

[Means to solve the problem]

According to the present invention, the metal bump electrodes protruding from the chip surface of an integrated circuit device are formed into a stepped structure consisting of a concentrically stacked base and a tip, so that the area of the tip is equal to the area of the base. This can be achieved by forming it to one-half or less.

The base and tip of the bump electrode described above are preferably grown by electrolytic plating while being restrained within the plating openings using separate photoresist films as masks.

[Effect]

The present invention focuses on the fact that the problem with conventional bump electrodes is caused by their dewy shape.The present invention provides bump electrodes with a stepped structure consisting of a base and a tip to facilitate growth by electrolytic plating. By making the area of the bump electrode less than half of the area of the base, when a large pressing force is applied to a specific bump electrode during chip mounting, only the tip of the bump electrode is deformed, preventing deformation of the base and the area below it. This prevents damage to the chip surface. Moreover, all the bump electrodes are reliably connected to the wiring conductors.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
The figure shows the state when a chip 1 of an integrated circuit device equipped with a bump electrode according to the present invention is mounted face-down on wiring and a substrate 30, and FIG. 2 shows the procedure for making this bump electrode 10 on the chip 1. For illustrative purposes, Figures 3 and 4
Parts corresponding to those in the figure are given the same reference numerals.

In FIG. 1, a bump electrode 10 according to the present invention protruding from a tip l is a small bump electrode made of, for example, gold, and is made up of a base 11 and a tip 12 that is concentric with the base and has a smaller area. For example, the base portion 11 is 20 μm square or in diameter, the tip portion 12 is 10 μm square or in diameter, and the overall height is about 10 μm. In the hang electrode 10 according to the present invention, the tip portion 12
The area ratio of the M part 11 to the M part 11 is set to be 1/2 or less, and the lower limit is usually set to 1/6 or more, but in order to easily deform the tip part 12 during mounting, the Practically speaking, it is desirable to use a trowel to reduce the amount by about 1/2.

Even in the bump electrode 10 according to the present invention, there is a variation in height of at least ±10%, so this is
When connecting to the wiring conductors 32, etc. of chip 1 by pressure contact or by using shrinkable hardening resin as described above, first apply pressure as in the past to connect all the bump electrodes 10 of chip 1 as shown in the figure. It is necessary to reliably contact the corresponding wiring conductor 32, but in the case of the present invention, the small-area tip portion 12 of the bump electrode 10 can be easily deformed, so the pressing force for this purpose may be lower than in the conventional case. For example, in this embodiment, the amount may be 10 to 15 g per bump electrode film.

Even with such a reduced pressing force, the tip 12 of the bump electrode 10, which has a large height inside the chip 1, is easily deformed as shown by the reference numeral 12a in the figure, but the base 11 and the tip 12, which have a smaller area, are easily deformed. No deformation occurs at the root of the attachment. In order to cause deformation to occur in the tip 12 as much as possible, it is desirable to make the area smaller and its height larger than the base 11. From experience, it is known that the height of the base 11 and the tip 12 should be increased. It is most desirable to set the ratio to around 3 near.

Next, an example of how to fabricate such a bump electrode with a stepped structure on a chip will be described with reference to FIG. 2.

Figure (a) shows the state of the chip before the bump electrodes are formed. As usual, the chip 1 includes, for example, an n-type epitaxial layer or semiconductor region 1a, in which an integrated circuit is fabricated.
It includes a p-type junction separation layer 1b, a p-type semiconductor layer 1C, etc., and a wiring made of aluminum or the like is placed in a window formed in an oxide film 2 made of silicon dioxide or the like covering the surface thereof so as to make conductive contact with the semiconductor layer IC. A film 3 is provided, which is further covered with a protective film 4 made of silicon nitride or the like.

A bump electrode is grown by electrolytic plating in the opening made in the protective film 4 on the edge of the wiring film 3, and as is customary, a very thin base film of just under 1 μm is formed using titanium or the like on the lower side. The base film 5a and the two-side base film 5b made of palladium or copper are sequentially deposited by a spackle method or the like so as to be in conductive contact with the wiring film 3 within each opening, and only the upper base film 5b is bumped as shown in the figure. A pattern in which an electrode is to be grown is photo-etched, and the lower base film 5a is left on the entire surface to be used as a plating electrode film.

FIG. 2(b) shows the electrolytic plating process for the base 11 of the bump electrode, in which a photoresist film 21, which is usually used as a mask for electrolytic plating, is deposited to a thickness of 3 to 5 μm in this example, and the upper and lower sides are coated using a photo process. A plating opening is opened to expose the ground film 5b. Metal for the bump electrode In this example, gold electrolytic plating is performed using the lower base film 5a as the plating electrode as described above, and at this time, the metal for the base 11 is applied to the chip 1.
However, in the present invention, as shown in the figure, electrolytic plating is stopped before the growth height exceeds the thickness of the photoresist film 21, so that the base 11 is grown on the photoresist film 21 at the same time. It is grown in a shape regulated by the opening wall of the film 21, and the growth tip is prevented from becoming flared at the end.

FIG. 2(C) shows the electrolytic plating process for the tip portion 12 of the bump electrode, and in this example, the bump electrode is formed in a narrower plating opening in the upper photoresist film 22 with a thickness of 5 to 7 um. The metal for the tip portion 12 is connected to the base portion 11 and grown in a state where it is strictly regulated by the opening wall in the same manner as above.

FIG. 2(d) shows the completed state of the bump electrode 10. After removing the photoresist films 21 and 22 from the state shown in FIG. 2(C), the lower base film 5a is used as a mask and the upper base film 5b is used as a mask. Removal by chemical etching leaves the bump electrodes 10 in this completed state separated from each other.

In the bump electrode 10 formed on the chip 1 in this way, the photoresist film 2 in FIGS.
By accurately controlling the thicknesses of parts 1 and 22 and accurately opening the areas of the plating openings using the photo process, the metals for the base part 11 and the tip part 12 can be grown with accurate heights and areas, respectively. The side shape can be precisely controlled by the plating opening wall.

At this time, the concentricity of the base portion 11 and the tip portion 12 can be maintained accurately by aligning the photomasks during the photoprocessing of the photoresist films 21 and 22 with an accuracy of about 2 μm in this example. Note that the size of the base film 5a under the root of the bump electrode 10 may be slightly smaller than the base 11, but of course has a sufficiently larger area than the tip 12.

Next, another example of how to form stepped bump electrodes on a chip will be described with reference to FIG.

Figure (a) shows the state of the chip before bump electrodes are formed. The chip 1 consists of an S1 wafer or a substrate made of ceramics, glass, etc., and has an oxide film 2, such as silicon dioxide, on its surface. A wiring film 3 made of aluminum or the like is provided, and further covered with a protective film 4 made of silicon nitride or the like.

Bump electrodes are grown by electrolytic plating in the openings made in the protective film 4 on the wiring film 3.
A multilayer base film 5 as a very thin base film of a little less than .mu.m is deposited by spuck method or the like so as to be in conductive contact with the wiring film 3 within the opening.

Next, a photoresist film 23 is deposited, and a photomask 40 is
A photomask exposed portion 51 is obtained using the photomask transparent portion 41. The size of the photomask transparent portion 41 is determined depending on the size of the bump to be obtained (FIG. 5Q)). Subsequently, a photoresist film 24 is deposited and exposed to light Q through a photomask 42 having a photomask transparent part 43 smaller than the photomask transparent part 41, and the photomask exposed part 52 is exposed by the photomask transparent part 43. (Figure 5(C)). Next, the photoresist films 23 and 24 are simultaneously developed to form photomask patterning portions 61 and 62 (FIG. 5c)). Subsequently, electrolytic plating is performed, and the electrolytic plating is stopped before the growth height of the plating exceeds the thickness of the photoresist film 24. Thereafter, the photoresist films 23 and 24 are removed, and then the unnecessary bump underlying metal film 5 is removed to obtain the bump electrode 10 (FIG. 5(e)).

By forming the bump electrodes in this manner, the plating process can be performed only once, simplifying the process, and eliminating processes that cause many variations.

Furthermore, since the plating process is performed only once, there is no possibility that dust will adhere between the base portion 11 and the tip portion 12 of the bump electrode 10, and the reliability of the bump electrode 10 will not be impaired.

〔Effect of the invention〕

As described above, in the present invention, the bump electrodes protruding from the chip surface of an integrated circuit device are configured in a stepped structure consisting of a concentrically stacked base and a tip, and the area of the tip is half the area of the base. Since the bump electrode is formed to have a thickness of less than 1, when pressure is applied to the bump electrode during chip mounting, only the small tip of the bump electrode is easily deformed, and the inside of the chip can be easily deformed with less than half the pressure of conventional bump electrodes. While ensuring that all bump electrodes are in contact with their connection partners, it is possible to effectively prevent excessive pressure from being applied to the base of the bump electrode, especially the base of the bump electrode, and the chip surface underneath. It is possible to eliminate problems like dew bump electrodes, such as the root part coming off or chip damage during mounting.

In addition, with the bump electrode according to the present invention, even if an object accidentally touches or hits the tip during mounting or transporting the chip, there is no risk of it coming off easily unlike in the past, and the implementation of the present invention makes it easier to handle the chip. Much easier than before.

The present invention having such characteristics is particularly effective when applied to highly integrated flip chips in which a large number of small bump electrodes with a size of several tens of micrometers or less are provided. Connection reliability can also be improved.

[Brief explanation of drawings]

1 and 2 relate to the present invention, FIG. 1 is a side view illustrating a bump electrode according to the present invention in a mounted state of an integrated circuit device chip in which the bump electrode is built, and FIG. A cross-sectional view showing an example of how to create a bump electrode in each main process. Figures 3 and 4 relate to the conventional technology. Figure 3 is a cross-sectional view of a conventional bump electrode, and Figure 4 shows how it is manufactured. FIG. 5 is a side view of the integrated circuit device chip in a mounted state. FIG. 5 is a cross-sectional view showing each main step of another example of how bump electrodes are formed on the chip. In these figures,

Claims (1)

[Scope of Claims] 1) A metal bump electrode protruding from the chip surface of an integrated circuit device for external connection, which has a stepped structure consisting of a concentrically stacked base and a tip. 1. A bump electrode for an integrated circuit device, characterized in that the area of the portion is one-half or less of the area of the base. 2) A manufacturing method in which a wiring film and a protective film having an opening on the wiring film are deposited on the surface of the chip, and then a bump electrode is formed in contact with the wiring film at the opening. After forming the first photoresist film, a first exposure part with a large area is formed on the opening of the wiring film by a first exposure, and after forming a second photoresist film, a second exposure part is formed on the opening of the wiring film. forming a second exposed portion with a small area on the first exposed portion;
Developing the first and second photoresist films simultaneously,
1. A method for manufacturing a bump electrode for an integrated circuit device, which comprises forming the bump electrode by subsequent electrolytic plating. 3) A bump electrode for an integrated circuit device, wherein the bump electrode according to claim 2 has a stepped structure consisting of a base portion and a tip portion concentrically stacked.