JP2000340595A - Gold bump and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain sufficient bond strength between a gold bump and an base barrier metal, adjust the surface state of the gold bump over an range and moreover obtain sufficient bond strength with an external lead. SOLUTION: A barrier metal 9, such as Ti, TiW or the like, is formed on an electrode pad 8 (A). As a first stage, gold with a large particle diameter is grown at a higher gold plating solution temperature of about 65 deg.C or higher by using a resist 10 as a mask (B). Consequently, a bond between a gold bump and a base metal 9 thereunder is improved. Furthermore, gold is grown to a small particle diameter by making the plating temperature to about 55 deg.C or lower (C). Then, bondability with an external lead is also improved by flattening the surface state of the gold bump 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gold bump provided on an electronic component such as a semiconductor chip and a method for forming the gold bump, and more particularly to an electrolytic gold plating method.

[0002]

2. Description of the Related Art In order to take out signals from an electrode pad made of an aluminum alloy or the like formed on a semiconductor chip, it must be connected to a lead electrode pad. In such a case, a protruding gold bump is conventionally formed on the electrode pad. In most cases, the gold bump is generally formed by a gold plating method. Hereinafter, a conventional gold plating method will be described.

[0003] Gold plating for forming gold bumps on a semiconductor chip is usually performed using a dedicated gold plating apparatus. There are two types of gold plating apparatuses called “jet type” and “dip type”. Here, a gold plating method using a general jet type gold plating apparatus will be described.

FIG. 2 is a sectional view showing an example of a jet gold plating apparatus. In FIG. 2, 1 is a semiconductor wafer to be plated with gold, 2 is a gold plating cup, 3 is a gold plating solution,
Reference numeral 4 denotes a cathode electrode, 5 denotes an anode electrode, 6 denotes a power source, and 7 denotes a jet pump for forming a flow of the gold plating solution 3 toward the semiconductor wafer 1.

Next, a procedure for gold plating using this apparatus will be described. First, the semiconductor wafer 1 to be plated is placed on the cathode electrode 4 with the surface to be plated facing downward.
After an electrode pad is formed on the surface of the semiconductor wafer 1 to be plated, Ti, TiW, Pd, Au, or the like is applied to the entire surface of the semiconductor wafer as a barrier metal interposed between the electrode pad and the gold bump. The resist is applied except for the portion where the crystal is grown. That is, the resist portion where the gold bump is to be formed is left open.

Thereafter, when the gold plating solution 3 is jetted from the lower portion of the gold plating cup 2 toward the surface of the semiconductor wafer 1 to be plated by the jet pump 7, the jetted gold plating solution 3 hits the semiconductor wafer 1 to be plated. Gold starts plating. Although not shown in FIG. 2, the central portion of the anode electrode 5 is opened concentrically so that the jetted gold plating solution passes through the anode electrode 5. Usually, a solution in which components such as sulfurous acid, sulfuric acid, and thallium are dissolved is used as the gold plating solution 3 used for electrolytic gold plating. When gold plating is performed, the temperature of the gold plating solution 3 is constantly raised to, for example, about 60 ° C. during plating. After that, the cathode electrode 4 and the anode electrode 5
, A current is supplied via the gold plating solution 3. that time,
Gold ions in the gold plating solution 3 are collected on the semiconductor wafer 1 to be plated, which is charged by the current from the cathode electrode 4, and gold plating becomes possible, and gold bumps are formed.

[0007]

However, when the gold bump is formed by the plating method using the gold plating apparatus, the bonding strength between the gold bump and the underlying barrier metal may not be sufficient. On the other hand, adjustment of the surface condition of the gold bump relating to the bonding strength between the gold bump and the external lead, for example, adjustment of the surface condition of the gold bump to a flat surface or a surface having large irregularities, could not be performed widely. For the reasons described above, the bonding strength at each part of the gold bump tends to be incomplete in the conventional plating method.

In view of the above problems, the present invention can provide a sufficient bonding strength between the gold bump and the underlying barrier metal, can adjust the surface condition of the gold bump over a wide range, and has a sufficient bonding strength with the external lead. It is an object to provide a gold bump and a method for forming the same.

[0009]

In order to achieve the above object, in the gold bump of the present invention, the diameter of the upper gold particle including the upper surface is smaller than the diameter of the lower gold particle including the bottom surface. It is configured. In the gold bump, it is desirable that the height of the lower portion including the bottom surface is formed to be about １ ／ or less of the height of the entire gold bump from the viewpoint of manufacturing the gold bump.

The method of forming a gold bump according to the present invention having the above-described structure includes a first step of growing a gold having a coarse particle diameter by using a plating method by setting the temperature of a plating solution to about 65 ° C. or higher;
Then, the second step of growing the gold having a particle diameter smaller than the particle diameter obtained in the first step by setting the temperature of the plating solution to about 55 ° C. or less.

In the method of forming a gold bump, a step of forming a metal film on an electrode pad formed on a substrate; and a step of partially opening the metal film to expose the surface of the metal film. Forming a resist to be formed, and using the resist as a mask, plating by using
A first step of growing gold having a coarse particle diameter at a temperature of at least 0 ° C., and then having a particle diameter smaller than the particle diameter obtained in the first step by lowering the temperature of the plating solution to about 55 ° C. or less. And a second step of growing gold.

In the second step, gold can be grown while continuously lowering the temperature of the plating solution in the first step to a temperature of about 55 ° C. or less.

According to the above-structured gold bump and the method of forming the same, it is possible to improve the bonding property between the gold bump formed by gold plating and the underlayer, particularly the barrier metal portion.
Further, the bonding property between the external lead and the gold bump can be improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional flow diagram showing a growth process by gold plating of a gold bump showing a method of forming a gold bump according to an embodiment of the present invention. In FIG. 1, reference numeral 8 denotes an electrode pad made of aluminum / copper or the like for extracting a signal to the outside. In FIG. 1, the outline is not shown, and the whole is an electrode pad. 9 is a barrier metal, 10
Is a resist, and an opening (opening 10a) is formed at a position on the electrode pad 8 where a gold bump is to be formed. 11 is a gold bump.

Here, the gold plating method of the present invention will be described with reference to the cross-sectional flow chart. First, a barrier metal 9 is provided on an electrode pad 8 on which a gold bump is to be grown (Step 2-A). This barrier metal is usually Ti
Melting point metals such as Al and TiW and alloys of high melting point metals, Pd,
A noble metal such as Au is used. Further, as a forming method, sputtering, EB vapor deposition, or the like is generally used.

Thereafter, gold plating is performed. This gold plating process is the same as that of the prior art as far as the sectional flow diagram of FIG. 1 shows. A feature of the present invention is that when performing this gold plating, the temperature of the gold plating is changed to perform the gold plating.

First, in the initial stage of gold plating, the gold plating temperature is set higher than in the conventional method, and the resist 10
Gold plating is performed halfway using
Is formed (Step B). The temperature of the gold plating solution is set around 65 ° C. The inventors of the present invention have found that when the temperature of gold plating is increased, the particle size of the growing gold crystal becomes coarse, and the resist 10
It has been found that the surface of the bump growing during the growth in the region surrounded by the circle becomes rough. When the temperature is about 65 ° C., the surface roughness is about 300 to 400 nm. In this embodiment, the temperature is about 65 ° C., but it is clear that the temperature may be higher.

Further, the present inventor has obtained the
It has been found by experiments that the bonding property between No. 1 and the underlying barrier metal 9 is good. This allows the gold bump 11
When used in a subsequent assembly process such as external lead bonding, the bonding strength of the gold bump 11 itself is increased, and an effect of increasing reliability is obtained.

Incidentally, since the growth rate of the gold to be plated is determined by the value of the current flowing to the substrate through the electrode pad 8, the growth rate of the gold is basically not affected by increasing the gold plating temperature. It is not necessary to change the plating time, even if the plating temperature is changed, in order to optimize the bonding strength. Therefore, there is also an advantage that the process can be easily managed.

Next, the remaining portions of the gold bumps 11 are grown while gradually lowering the gold plating temperature (step C).
Specifically, at the final stage of gold plating, the gold plating temperature should be about 5
Set to fall to around 5 ° C. When the plating temperature is reduced in this manner, the particle diameter of the gold crystal becomes finer in contrast to the first plating step, and the bump surface can be made relatively smooth. For example, under the above conditions, the surface roughness is about 100 to 200 nm, and the growth rate of the gold bump does not change for the above-mentioned reason. In this embodiment, the temperature is set to about 55 ° C., but may be lower than this temperature. If the temperature is lowered, gold having a smaller particle diameter can be obtained. Although the gold bump 11 is completed in this manner, the bonding strength between the external lead and the external lead can be increased because the unevenness on the uppermost surface to be bonded to the external lead is reduced.

The second plating step can be started after the first plating step is completed, and waited until the temperature of the plating solution is reduced to about 55 ° C. or less. The particle size of the crystal changes substantially discontinuously. However, as described in the above embodiment, the crystal grain size on the uppermost surface of the gold bump is reduced to the same extent even when the gold bump is formed while continuously lowering the temperature from about 65 ° C. to about 55 ° C. or less. There is no. By doing so, there is an advantage that it is not necessary to wait until the temperature decreases, and the plating time can be reduced.

As described above, when the gold bumps 11 are used in a subsequent assembly process, for example, where a COG or COF is assembled, a flat bump surface state is required. It is possible to provide bumps having irregularities that match the requirements. If a certain degree of bump surface unevenness (surface roughness) is required, it can be realized by reducing the width of decrease in the temperature of gold plating in the second stage. For example, when assembling a TAB or the like, a bump surface state having a certain degree of unevenness is required.

The gold plating step in the first stage of the present invention achieves the object if the bonding strength with the underlying barrier metal 9 is obtained. It is sufficient that the crystal particle size increases in the vicinity. Therefore, for example, as shown in FIG. 1 (step B), the thickness may be about １ ／ or less of the height of the completed gold bump. If the thickness is reduced in the first plating step, it is possible to allow sufficient time for the growth of the remaining thick gold bumps in the second step. Therefore, it becomes easy to lower the plating temperature continuously in the second stage following the first stage in the plating process to control the temperature.

[0024]

As described above, according to the gold plating method of the present invention, gold plating is performed by changing the gold plating temperature.
Particularly, the present invention is characterized in that the grain shape of gold crystals is coarsened by first increasing the gold plating temperature. With this,
The bonding property between the gold bump formed by gold plating and the underlying barrier metal portion can be improved, and the reliability of the gold bump can be improved.

Further, the present invention is characterized in that the crystal grains at the uppermost portion of the gold bump are made finer by lowering the gold plating temperature, and the surface irregularities of the gold bump formed by gold plating are reduced. It is possible to optimize the lead bonding strength.

[Brief description of the drawings]

FIG. 1 is a cross-sectional flow diagram of a growth process of a gold bump by gold plating according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of an example of a jet type gold plating apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor wafer 2 Gold plating cup 3 Gold plating solution 4 Cathode electrode 5 Anode electrode 6 Power supply 7 Jet pump 8 Electrode pad 9 Barrier metal 10 Resist 10a Opening 11 Gold bump

Claims (5)

[Claims] 1. A gold bump wherein an upper gold particle diameter including an upper surface is formed smaller than a lower gold particle diameter including a bottom surface. 2. The gold bump according to claim 1, wherein the height of the lower portion including the bottom surface is formed to be about １ ／ or less of the height of the entire gold bump. 3. A plating method, wherein the temperature of the plating solution is about 6
First to grow gold with a coarse particle size at 5 ° C or higher
And a second step of growing the gold having a particle diameter smaller than the particle diameter obtained in the first step by lowering the temperature of the plating solution to about 55 ° C. or less thereafter. Of forming gold bumps. 4. A step of forming a metal film on an electrode pad formed on a substrate, and a step of forming a resist partially open on the metal film to expose the surface of the metal film; Using the resist as a mask, a first step of growing gold having a coarse particle diameter at a plating solution temperature of about 65 ° C. or higher using a plating method, and then reducing the temperature of the plating solution to about 55 ° C. or lower. A second step of growing gold having a particle diameter smaller than the particle diameter obtained in the first step. 5. The method according to claim 1, wherein the second step is a step of growing gold while continuously lowering the temperature of the plating solution in the first step to a temperature of about 55 ° C. or less. 5. The method for forming a gold bump according to 3 or 4.