JPH0562982A - Manufacture of bump electrode - Google Patents

Abstract

PURPOSE:To enable the surface of a resin film to be cleaned after a bump electrode is built in an integrated circuit device where the resin film is made to serve as an outermost protective film. CONSTITUTION:A bump electrode metal 8 is made to grow through electroplating making a metal base film 6 in contact with a resin film 5 serve as a plating electrode, the metal base film is removed from the resin film 5 by etching, the resin film is slightly dry-etched not only to clean its surface but also to remove etching residue 6a of the base film left unremoved by etching carried out in a preceding process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protruding electrode for external connection to an integrated circuit device in which a resin film such as a polyimide resin is used as a protective film for the outermost shell in addition to a normal protective film such as silicon nitride. A manufacturing method for incorporating a bump electrode.

[0002]

2. Description of the Related Art As is well known, a bump electrode is a metal projection electrode projecting from an integrated circuit device chip for external connection, and a so-called flip chip incorporating the bump electrode is not housed in a package. The cost of the integrated circuit device itself can be reduced by mounting the device in a chip state on a wiring board, and the space and labor required for the mounting can be significantly saved. It has been widely adopted in mass-produced products.

In such an integrated circuit device mounted on a chip, there is a higher risk that the characteristics are deteriorated by being directly exposed to the outside air during use, as compared with the case where the integrated circuit device is mounted in a package and then mounted. Strictly apply a protective film such as silicon nitride, which has an excellent ability to block the outside air, to the surface of the embedded side, and project bump electrodes at the windows that are opened at the relevant points at a height suitable for connection with the mounting partner. .. Since this protruding height requires at least several tens of μm, it is customary to selectively grow the metal for the bump electrode only at the required place by the electrolytic plating method. Since it is necessary, a thin metal base film is deposited on the protective film, and using this as a plating electrode film, the metal for bump electrodes is electrolytically plated, and then the portions between the bump electrodes in the base film are removed by etching. Is. Hereinafter, this procedure will be briefly described with reference to FIG.

FIG. 2 shows an enlarged cross section of a portion of the integrated circuit device wafer 10 in which the bump electrodes 20 are incorporated. An aluminum wiring film 3 connected to an integrated circuit is provided on an insulating film 2 such as silicon oxide which covers the semiconductor substrate of the wafer 10 and the semiconductor region 1 which is an epitaxial layer thereon, and the above-mentioned nitriding film which covers the wiring film 3 is formed. A bump electrode 20 connected to the wiring film 3 is projected in the window opened in the protective film 4 made of silicon or the like. This bump electrode 20
In order to grow the metal 8 of FIG. 3 by electrolytic plating, a lower layer 6 of titanium or the like and an upper layer 7 of copper or the like are usually entirely coated with a two-layered lower layer, and the upper layer 7 is protected by a protective film. Pattern a slightly larger size than the 4th window.

Next, a window for exposing the upper base film 7 only is opened by attaching a photoresist mask film M shown by a thin line in the drawing, and the lower base film 6 is used as a plating electrode film in the window of the mask film M. A metal 8 is grown to a desired height on the upper base film 7 by electroplating. Further, the mask film M is first removed, and then the portion of the lower base film 6 indicated by a thin line in the drawing is removed by chemical etching or the like using the metal 8 and the upper base film 7 as a mask to connect the metal 8 to each other. There is no independent bump electrode 20. Although the residue 6a tends to remain after the etching of the lower base film 6, the surface of the protective film 4 is cleaned by removing the residue 6a by means such as immersion in an ultrasonic bath.

[0006]

It is usual that the integrated circuit device incorporating the bump electrode by the above-described conventional method can maintain stable characteristics over a long use period after mounting. Depending on the conditions during use, it is necessary to coat the resin film for the protective film of the outermost shell in addition to the above-mentioned protective film of silicon nitride to enhance the barrier property against the outside air.
However, since the properties of the resin film are considerably different from those of the silicon nitride film, the conventional method described above has a problem that the cleaning of the surface thereof tends to be insufficient.

That is, a silicon nitride film as a protective film has features that it has a dense structure and very low air permeability, but it has the drawback of being hard and slightly brittle, so that the pressure and temperature applied during flip-chip mounting or during use will be applied. There is a possibility that defects such as minute cracks may occur due to the heat cycle and the external air barrier property may be deteriorated. On the other hand, a resin film using a polyimide resin or the like is much more tough under the temperature and pressure conditions during mounting and in use, and when combined with a silicon nitride film, it is very advantageous in preventing the occurrence of defects that lower the outside air barrier property. , When removing the plating electrode base film by etching after the bump electrode is protruded, removal of minute residues and surface cleaning are likely to be incomplete, which increases the leakage current of the integrated circuit device and lowers the withstand voltage. Or problems occur.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a bump electrode manufacturing method capable of highly cleaning the surface of a resin film after incorporating the bump electrode into an integrated circuit device using a resin film as the outermost shell protective film.

[0009]

According to the present invention, there is provided a step of growing a metal of a bump electrode by electrolytic plating using a metal underlayer in contact with a resin film as a plating electrode.
The bump electrode is integrated circuit through a step of removing the base film from the resin film by etching using the metal of the bump electrode as an etching mask, and a step of dry etching the surface of the resin film in a plasma atmosphere containing oxygen. This is achieved by incorporating it in the device.

When the integrated circuit device is mounted at a temperature of 300 ° C. or higher, it is preferable to use a polyimide resin film as the resin film, and dry etching for it is performed in a pure oxygen plasma atmosphere. It is suitable. Also,
The base film for the plating electrode can be removed by dry etching, but if a titanium film is used for this base film, it can be removed from the resin film by wet etching using a dilute hydrofluoric acid solution or an ammonium-based etching solution. It is the easiest to remove and is advantageous in reducing the processing time.

[0011]

As described above, conventionally, the removal of the underlayer film for the plating electrode and the cleaning of the surface of the integrated circuit device were carried out by the same chemical etching. By performing shallow dry etching on the lower resin film, the surface of the resin film can be cleaned at the same time by removing the minute residues of the underlying film that could not be removed by the previous etching. It has succeeded in achieving higher cleanliness by chemical etching.

Therefore, according to the method of the present invention, the residue of the base film can be easily removed by the next dry etching within a short time of usually several minutes or less, even if the base film for the plating electrode is not almost completely removed by etching as in the conventional case. Can be removed to
It is possible to prevent the so-called side etching from occurring in the lower portion of the base of the bump electrode of the base film, and prevent the strength of the base from lowering as a result.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 (a) to 1 (d) are enlarged sectional views showing the main steps in the method of manufacturing a bump electrode for an integrated circuit device according to the present invention in a portion substantially corresponding to FIG. 2 of a wafer 10 of the integrated circuit device. Since the same parts as those in FIG. 2 are designated by the same reference numerals, the parts overlapping with those in the following description will be appropriately omitted.

FIG. 1 (a) shows the state of the wafer 10 before the bump electrodes are projected. Insulating film 2 covering the surface of the semiconductor region 1
After arranging the wiring film 3 made of aluminum or the like on the above, a protective film 4 made of silicon nitride or the like is formed to a film thickness of 1 to 1.5 μm by the CVD method or the like, and is formed on the upper portion of the end of the wiring film 3. Although the window is opened by the plasma etching method or the like as in FIG. 2, a resin film 5 having a film thickness of about 1.5 to 2 μm is formed by, for example, spin coating and baking polyimide resin or the like on the window. Similarly, a window is opened to expose the wiring film 3. Of course, both films 4 and 5 may be sequentially formed, and then windows may be simultaneously opened for them.

Since the bump electrode is projected in the opening of this window by electrolytic plating, the lower base film 6 and the upper base film 7 are applied as a base film having a two-layer structure also in this embodiment as in FIG. The upper base film 7 is patterned to a size for the bump electrode which is slightly larger than the window opening. For example, the lower base film 6 is a titanium film having a thickness of about 0.2 μm, and the upper base film 7 is 0.1 μm.
The copper film is about 5 μm thick. The lower base film 6 of titanium or chrome functions as a plating electrode,
The upper base film 7 also functions as a barrier film for preventing mutual diffusion between the aluminum of the wiring film 3 and the bump electrode metal, and the upper base film 7 connects the lower base film 6 to the bump electrode metal with low resistance. , Lower base film 6 and upper base film 7 in some cases
Both are used as plating electrodes.

FIG. 1 (b) shows an electrolytic plating process of the bump electrode metal 8. First, a photoresist as a mask film M for electrolytic plating is spin-coated on the entire surface of the wafer 10, and a window exposing only the upper base film 7 is opened in a size of several tens to hundreds of μm square or a diameter by a photo process. At the time of electrolytic plating, the wafer 10 is set on a plating jig as usual, and the lower base film 6 for the plating electrode is connected to a plating power source at a location not shown, and the metal 8 for bump electrode is formed.
As an example, gold is grown on the upper base film 7 in the window of the mask film M to a desired height of several tens to 100 μm as shown in the figure. Of course, the metal 8 is simultaneously grown on the surface of the wafer 10 where the bump electrodes are to be provided, and the mask film M is removed using a stripping solution after completion of this electrolytic plating.

FIG. 1C shows a step of removing the base film, in this embodiment the lower base film 6. In this step, the lower base film 6
When titanium is used, the wafer 10 is immersed in an etching solution diluted with hydrofluoric acid 50 to 100 times for a short time of about 30 to 60 seconds to perform chemical etching using the bump electrode metal 8 and the upper base film 7 as a mask. The lower base film 6 is removed by. When the lower base film 6 in contact with the resin film 5 is removed, the residue 6a tends to remain as shown in the figure than in the conventional case, but the method of the present invention can easily remove the residue 6a in the next step of FIG. 1 (d). When the upper base film 7 is also used as the plating electrode, the lower base film 6 may be removed after removing the copper with an etching solution such as ammonium persulfate. Also,
The removal of the base film in the step of FIG. 1C can be performed not only by chemical etching but also by dry etching using the bump electrode metal 8 or the like as a mask.

FIG. 1D shows a dry etching process for the resin film, which is peculiar to the method of the present invention. Dry etching of a resin which is an organic substance is preferably carried out in a plasma atmosphere in which a gas containing oxygen is used, and in the case of a polyimide resin as in this embodiment, pure oxygen is used as an etching gas.
The surface of the resin film 5 is shallowly dry-etched by a short-time treatment of about 2 to 5 minutes with high-frequency power for plasma generation of 00 to 500 W. As a result, the surface in contact with the lower base film 6 of the resin film 5 is cleaned, and the residue 6a of FIG. 1 (b) is not removed or becomes free from the surface and can be easily removed. This completes the assembly of the bump electrode 20, and thereafter, the wafer 10 may be scribed and isolated into a flip chip for chip mounting.

Regarding the removal of the residue 6a of the base film,
The dry etching process described above is more complete than the conventional immersion method in an ultrasonic bath, is easy because it does not require post-brushing, and is advantageous in that unnecessary contamination of the surface of the resin film 5 can be avoided. is there. Of course, the greatest advantage of dry etching is that invisible contamination on the surface of the resin film 5 can be removed and the surface can be cleaned. Therefore, after this step, clean nitrogen gas or the like is sprayed onto the surface to remove the ash content of the resin. It is better to just scatter.

In the flip chip in which bump electrodes are incorporated by the method of the present invention described above, the leakage current is a normal number.
It is several tens of pA per mm square chip, which is improved by about three orders of magnitude as compared with the conventional tens to hundreds of tens nA, and there is almost no decrease in the chip breakdown voltage due to the residue of the underlying film. In addition, by reinforcing the conventional protective film 4 such as silicon nitride with the resin film 5, even when a pressure of several tens to 100 g per bump electrode or a high temperature of 400 to 500 ° C. is applied to each bump electrode during flip chip mounting. It is possible to effectively prevent the generation of internal fine defects such as a protective film, and stably maintain a high barrier property against external air during a long use period after mounting.

[0021]

As described above, according to the method of the present invention, for an integrated circuit device using a resin film as the outermost shell protective film, bump electrodes are formed by electrolytic plating using a metal base film in contact with the resin film as a plating electrode. A step of growing a metal,
By incorporating the bump electrode through the step of substantially removing the base film from above the resin film by etching and the step of dry etching the surface of the resin film in a plasma atmosphere containing oxygen, the following effects can be obtained. be able to.

(A) By performing dry etching on the surface of the resin film after removing the base film to clean the surface of the resin film and also to remove minute residues of the base film,
The leakage current of the integrated circuit device can be reduced by about three orders of magnitude as compared with the conventional one, and the reduction of the chip breakdown voltage due to the residue of the underlying film can be almost eliminated. (b) The residue of the underlying film on the insulating film can be completely removed by dry etching in a short time of a few minutes or less compared with the conventional immersion method in an ultrasonic bath, and the extra labor such as conventional brushing is required. It is possible to omit and prevent unnecessary contamination of the surface of the resin film. (c) Since the residue can be easily removed by the dry etching process even if the underlying film is not completely removed by chemical etching as in the conventional case, the chemical etching time can be shortened and the residue under the base of the bump electrode of the underlying film can be reduced. It is possible to prevent side etching from occurring in the side portion and prevent the strength of the root portion from being reduced.

Further, in the integrated circuit device to which the method of the present invention is applied, since the protective film such as silicon nitride is reinforced by the resin film, even if a considerable pressure or a high temperature is applied during mounting, the protective film and the like are finely divided. Less likely to cause defects,
It is possible to stably maintain a high outside air blocking property for a long period of time throughout the usage period after mounting.

[Brief description of drawings]

FIG. 1 is an enlarged view of a portion of a wafer for an integrated circuit device where a bump electrode is provided, showing an embodiment of a method for manufacturing a bump electrode according to the present invention in each of the main steps in FIGS. 1 (a) to 1 (d). FIG.

FIG. 2 is an enlarged cross-sectional view of a part of a wafer for integrated circuit device in which bump electrodes according to the related art are incorporated.

[Explanation of symbols]

 4 Protective film such as silicon nitride 5 Resin film as outermost shell protective film of integrated circuit device 6 Base film or lower base film for plating electrode 7 Upper base film 8 Metal for bump electrode 10 Wafer for integrated circuit device 20 Bump electrode

Claims (3)

[Claims] 1. A method of incorporating a bump electrode into an integrated circuit device using a resin film as an outermost shell protective film, wherein a metal of a bump electrode is grown by electrolytic plating using a metal base film in contact with the resin film as a plating electrode. And a step of removing the base film from the resin film by etching using the metal of the bump electrode as an etching mask, and a step of dry etching the surface of the resin film in a plasma atmosphere containing oxygen. Method of manufacturing bump electrode. 2. The method for manufacturing a bump electrode according to claim 1, wherein a polyimide resin film is used as the resin film, and the dry etching of the surface is performed in a plasma atmosphere of pure oxygen. .. 3. The method for manufacturing a bump electrode according to claim 1, wherein the base film used as the plating electrode is a titanium film, and the removal from the resin film is performed by wet etching. ..