JPH02236295A - Electroplating method - Google Patents

Abstract

PURPOSE:To improve the wettability of a member to be plated and to obviate the generation of defective bumps by evacuating the inside of a plating cell where the above-mentioned member and an anode plate are disposed to face each other to a vacuum, then immersing the member into a plating liquid supplied into the cell and starting an electroplating. CONSTITUTION:The member 12 to be plated is constituted by forming a plating substrate metal 2 on a substrate 1 and forming a resist film 3 provided with apertures 4 thereon in the In bump plating. The above-mentioned member 12 to be used as cathode and the anode plate 13 consisting of In are disposed to face each other in the plating cell 11 and the inside of the cell 11 is evacuated to a vacuum. The plating liquid 5 is in succession introduced from a plating liquid tank 16 to immerse the member 2 and the anode plate 13 in the above- mentioned liquid 5. Then, the liquid 5 intrudes into the apertures 4 of the resist film 3 of the member 12 and comes into sufficient contact with the plating substrate metal 2. A current is thereafter impressed from a plating power source 18, by which the In plating bumps 6 having no plating defects are formed without allowing bubbles to remain in the apertures 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electroplating method for forming a plating film on a plate-shaped member to be plated.

[Conventional technology]

Bumps made of soft metal such as indium have conventionally been used in semiconductor chips for photoelectric conversion and silicon IC semiconductor chips for signal processing. A hybrid infrared image sensor is known in which poles are formed and the poles are placed facing each other and bonded under heat. The bump electrodes are typically made of a soft metal such as indium, and are arranged in, for example, 64 x 64 with a diameter of 25 microns, a height of 10 microns, and a pitch of 50 microns. In addition, the formation method is to form a resist film with an opening on the plating base metal film, then plating and growing a bump electrode only in the opening using the plating base metal film as a cathode, and then plating the unnecessary resist film and plating. This is to remove the underlying metal film.

[Problem to be solved by the invention]

However, in such conventional plating film formation for bump electrodes, the resist film 3 formed on the plating base metal 2 of the substrate 1 is hydrophobic, as shown in FIG. If it does not dry out sufficiently, air bubbles 7 remain in the opening, which tends to cause plating defects. Naturally, areas with poor plating will result in pixel defects, which will impair the performance of the image sensor.

In particular, the height of the bump to be formed is large; the resist film thickness becomes large. Furthermore, as the element becomes finer, the opening diameter becomes smaller, so plating defects due to poor wettability become more noticeable.

Furthermore, although the addition of a surface-active material improves wettability to some extent, it leads to the introduction of impurities into the plating film, which increases the hardness of the plated bumps and impairs thermocompression bondability. b1 cannot be applied to

In this way, the occurrence of poor pump plating formation has been an obstacle to increasing the size and miniaturization of pixels in sensors.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electroplating method that solves the above-mentioned drawbacks, improves wettability, and eliminates the occurrence of defective bumps.

[Means to solve the problem]

In order to achieve the above object, in the electroplating method according to the present invention, a plating tank in which a member to be plated and an anode plate are disposed facing each other is evacuated, and then a plating solution supplied into the tank is evacuated. After immersing the member to be plated in the solution, electroplating is started. Furthermore, evacuation can be continued even during electroplating.

[Effect]

The member to be plated has a resist film formed with openings, but in the electroplating method of the present invention, when the plating solution is supplied to the member in a vacuum, the resist openings are free of air, etc. No gas remains and no bubbles remain. Therefore, the plating solution comes into sufficient contact with the plating base metal in the opening, and wettability can be improved without the need for any surface active material, so that good bumps with no defects can be formed.

〔Example〕

Next, an embodiment in which the present invention is applied to In pump plating will be described with reference to the drawings.

Figures 1 (a) to (c) are diagrams showing the process of forming In bumps using the electroplating method of the present invention, and Figure 2 shows an example of the plating equipment used to carry out this process. FIG. As shown in FIG. 1(a), the plated member on which a plating film is to be formed is a plated base metal 2 formed on a flat substrate 1, and a resist film 3 on which an opening 4 is formed. is formed as a mask.

In FIG. 2, first, valves 17a, 17b, 1 are installed in the piping connecting the plating tank 11 and the plating solution tank 16.
7c and 17d are closed, a plating solution is placed in a plating solution tank 16, and a member to be plated 12, which serves as a cathode, and an anode plate 13 made of indium are placed inside the plating tank 11, facing each other. Next, the vacuum pump 15 or the valve 17e of the pipe communicating with the atmosphere is switched to evacuate the inside of the plating tank II by the vacuum pump 15. The plating tank 11 is a closed container that can maintain a vacuum. Subsequently, the valves 17a and 17c are opened, the agate solution 5 is introduced from the plating solution tank 16 by the solution pump 14, and the member to be plated 12 and the anode plate 13 are immersed in the plating solution 5. Here, as shown in Figure 1(b), the plating solution 5
enters the opening 4 of the resist film 3 of the member to be plated and sufficiently contacts the plating base metal. After this, plating power supply 1
By applying current from 8, In plated bumps 6 are formed as shown in FIG. 1(c).

After filling the plating tank l1 with the plating solution 5, normally it would be sufficient to switch the valve 17e to introduce atmospheric air, but since the vacuum is continued during plating, the control of the tank pump becomes complicated. However, it can also effectively remove air bubbles generated during plating.

After plating is completed, valves 17a and 17c are closed, and valves 17b and 17c are closed.
By opening 17d and returning the plating liquid to the plating liquid tank l6 using the liquid feed pump 14, the next member to be plated can be replaced. In the method of the present invention, as shown in FIG. 3, no bubbles remain and no punb plating defects occur.

It should be noted that the above embodiment is merely an example, and it goes without saying that it can be similarly applied to bump materials other than indium.

〔Effect of the invention〕

As explained above, according to the present invention, no air bubbles remain in the opening where the bump plating is formed, and therefore, a bump without plating defects can be formed.

[Brief explanation of drawings]

Figures 1 (a) to (c) are enlarged views of a member to be plated to explain the process of forming In bumps using the electroplating method of the present invention, and Figure 2 is an enlarged view of a plated member used to carry out the process. FIG. 3 is a partial cross-sectional view showing an example of the device, and is a diagram showing the shape of an In bump formed by a conventional method. 1... Substrate 2... Plating base metal 3.
...Resist film 4...Opening 5...Plating solution 6...In plating bump 7...Bubble
11... Plating tank 12... Member to be plated 13... Anode plate 14... Liquid feed pump 15
...Vacuum pump 16-...Plating liquid tank 17a
, 17b, 17c, 17d, 17e-Valve 18...Plating power supply patent applicant NEC Corporation

Claims (2)

[Claims] (1) After evacuating the plating tank in which the member to be plated and the anode plate are placed facing each other, and then immersing the member to be plated in the plating solution supplied into the tank, electroplating is started. An electroplating method characterized by: (2) The electroplating method according to claim 1, characterized in that vacuum evacuation is continued even during electroplating.