Method for storage of a metal ion supply source in a plating equipment

Abstract

To avoid change in plating performance, even where operation of the plating equipment is interrupted, the properties of the plating solution need to be preserved. For plating equipment having an insoluble anode, add a reservoir (7) for storing a replacement solution to the tank (4) having a metal ion supply source (copper ball (5)) and, upon termination of the plating operation, the entire plating solution is discharged from the tank (4) containing the metal ion supply source, while the solution for replacement is transferred from the reservoir (7) to the empty tank having a metal ion supply source, and immediately prior to the resumption of the plating operation transfer the solution for replacement back to the reservoir (7) and return the plating solution to the tank (4) containing the metal ion supply source.

Description

DETAILED DESCRIPTION OF INVENTION

1. Background to Invention

The present invention relates to effective storage of a copper supply source, for example, in a copper plating equipment.

2. Prior Art Technology

It has been widely known that a brightener, which is an additive designed to promote a plating reaction and to provide glossiness to plating, for example, 4,5-dithiaoctane-1,8-disulfonic acid [(SCH₂CH₂CH₂SO₃H)₂], continues to be decomposed where a copper anode exists even after the electrical plating operation has ceased (For example, J. Electroanal. Chem., 338 (1992), 166-177).

Also, as discussed on pages 69-75 of Advanced Metallization Conference (1999) by A. Thies, H. Meyer, J. Helneder, M. Schwerd and T. Gebhart, a copper dissolver (dissolving tank) is to be annexed to plating equipment in order to supply copper ions where an insoluble anode is used in copper plating. This copper dissolving unit is designed to allow copper ions to be dissolved from an inserted copper ball in proportion to the amount of copper deposition on the substrate, which is a cathode reaction. Where the cathode reaction is:
Cu²⁺+2e⁻→Cu⁰  (1)
The anode reaction is:
Fe²⁺→Fe³⁺+e⁻  (2)
Also, copper ions are supplied in the copper dissolver according to the following reaction:
Cu⁰+2Fe²⁺→Cu²⁺+2Fe²⁺  (3)
Problem to be Resolved by Invention

In a system employing an insoluble anode like this, copper ions are usually supplied from a copper ball housed in a copper dissolver. In an actual copper dissolver, the possibility exists that a brightener is decomposed because of the existence of a copper ball even while the plating equipment is deactivated, as discussed in the literature reference mentioned above (J. Electroanal. Chem.). Therefore, when the plating equipment is activated again, the solution contained in the copper dissolver enters the plating reactor (reaction tank), making it impossible to carry out plating under the same conditions that existed prior to inactivating the plating equipment.

A similar phenomenon also occurs in a system having a soluble anode. It has been reported that it becomes difficult to achieve the same plating performance that existed prior to inactivating the plating equipment when the operation of the plating equipment is restarted (J. Electroanal. Chem., 338 (1992), 167-177). Furthermore, dissolved substances generated while the plating equipment remains inactive act as impurities and exert an adverse effect on the plating surface.

Thus, it is an object of the present invention to prevent deterioration (change in quality) of a plating solution and changes in plating performance even in those situations where the operation of the plating equipment is interrupted.

Means to Resolve the Problem

According to the present invention, the above-described problem is resolved by providing a reservoir designed to store a solution that does not deteriorate a metal ion supply source as a “solution for replacement” and by replacing at least part of the plating solution for said “solution for replacement” during the period when the plating operation is interrupted.

In the case of plating equipment having an insoluble anode, a tank having a metal ion supply source is provided with said reservoir, upon completion of the plating operation, the entire plating solution is discharged from the tank containing a metal ion supply source, the replacement solution is transferred from the reservoir into the emptied tank having the metal ion supply source, and when the plating operation is restarted, the replacement solution is returned into the reservoir and the plating solution is thereafter returned into the tank containing the metal ion supply source.

For plating equipment having a soluble anode, the plating tank is provided with the reservoir and a plating solution storage tank, upon completion of the plating operation, the plating solution is transferred from the plating tank into the plating solution storage tank, and then the replacement solution is transferred from the reservoir into the emptied plating tank and, when the plating operation is restarted, the replacement solution is returned into to the reservoir and the plating solution is thereafter returned into the plating tank.

It is desirable that said replacement solution is a plating solution containing no brightener that undergoes a decomposition reaction while the plating operation is being interrupted. In the case of copper plating, 3-(benzothiazoryl-2-thio) propylsulfonic acid and its sodium salt, 3-mercaptopropane-1-sulfonic acid and its sodium salt, ethylenedithiodipropylsulfonic acid and its sodium salt, bis-(p-sulfophenyl)-disulfide and its disodium salt, etc. may be used as said brightener. Specific examples of the replacement solution suitable for plating with copper include a solution containing copper sulphate and sulfuric acid, a solution containing copper sulphate, sulfuric acid and chlorine, and a sulfuric acid solution.

PREFERRED EMBODIMENTS OF INVENTION

The present invention will be described below in greater detail based on representative examples thereof.

EXAMPLE 1

FIG. 1 shows an embodiment in which this invention is applied to plating equipment having an insoluble anode. A copper dissolver 4, which is annexed to a plating tank (not shown in the figure) which is the main unit of the plating equipment, is provided with copper balls 5. The copper dissolver 4 and the plating tank, which is not shown in the figure, are mutually connected via pipes 2, 3 and each of them is filled with a copper plating solution. The composition of the copper plating solution comprises, for example, copper ions at a concentration of 35 g/liter, sulfuric acid at a concentration of 180 g/liter, iron ions at a concentration of 12 g/liter and chlorine ions at a concentration of 50 mg/liter. The copper plating solution also contains additives, such as brightener, leveler, etc. This copper plating solution is referred to hereinbelow as a “real plating solution” in order to distinguish the copper plating solution from the replacement plating solution.

In addition to the copper dissolver 4, there is also provided a reservoir for the replacement solution 7. These two tanks are mutually connected via a pipe equipped with a pump 6. The pump 6 is so structured to enable a reversed rotation. The replacement plating solution is stored in the reservoir 7 for the replacement solution. The replacement plating solution is a solution (“base plating solution”) that does not contain additives, such as a brightener. The replacement plating solution, however, may contain additives, provided that they are substances that undergo no dissolution under the effect of copper balls and cause no deterioration of the copper surface. In the event that a base plating solution containing no additives is used, it is expected to be able to reduce absorption of the additives onto the copper surface and to suppress emission from the copper surface into the plating solution during plating restarting. Furthermore, it is also possible to use a plating solution containing neither brightener nor iron ions, or to use a sulfuric acid solution with a concentration similar to that of the sulfuric acid in the real plating solution, so no copper sulphate be contained.

In order to operate the plating equipment, valves 15, 16 in the pipes 2, 3 are opened and the real plating solution circulates between the plating tank and the copper dissolver 4. In this process, the pump 6 must be inactivated so that the replacement plating solution within the reservoir 7 is not supplied to the copper dissolver 4.

Once the plating operation is completed and the equipment is stopped, the valves 15, 16 in the pipes 2, 3 are closed, and the real plating solution within the copper dissolver 4 is discharged to the plating tank or another tank via the pipe 1 so that only the copper balls are left in the copper dissolver 4. The pump 6 is thereafter operated to introduce the replacement plating solution into the copper dissolver 4 from which the real plating solution has been discharged. The replacement plating solution is thus introduced in order to prevent any deterioration to the copper ball surface, such as dying out or oxidization, and to preserve the pre-existing properties until restarting the plating operation.

To restart operation of the plating equipment, the replacement plating solution in the copper dissolver 4 is discharged into the reservoir 7 and only the copper balls are left in the copper dissolver; then the valves 15, 16 are opened to introduce the real plating solution from the plating tank via the pipe 3, and plating operation is started.

EXAMPLE 2

FIG. 2 shows an embodiment in which this invention is applied to plating equipment having a soluble anode. The shown structure basically comprises a plating tank 10 equipped with a cathode (substrate) 11 and a soluble anode (phosphorous copper anode) 12, a reservoir 14 for replacement plating solution and a plating solution storage tank (not shown in the figure). The plating tank 10 and the reservoir 14 for replacement plating solution are mutually connected via a pipe equipped with a pump 13, and the plating tank 10 and the storage tank can be connected to each other via a pipe 15. The pump 13 is also structured in such a way to enable reversed rotation. The composition of the copper plating solution contained in the plating tank 10 is the same plating solution as that shown in Example 1 above, except that it does not contain iron ions, and the content of additives is also the same. A printed circuit board or semiconductor wafer can be used as a substrate of the cathode 11; however, it is not limited to them.

When the plating equipment is to be operated, the pump 13 is stopped so that the base replacement plating solution in the reservoir 14 is not transferred to the plating tank 10. When the equipment is stopped for completion of the plating operation, the real copper plating solution in the plating tank 10 is discharged into the storage tank via the pipe 15 so that the plating tank 10 is emptied. The pump 13 is then operated and the base replacement plating solution is introduced into the emptied plating tank 10, from which the real plating solution has been discharged. Through the introduction of the base replacement plating solution, it become possible to prevent the deterioration of surface conditions, including drying out of the black film formed on the anode surface, thereby preserving the properties until restarting the plating operation.

To restart operation of the plating equipment, the base replacement plating solution within the plating tank 10 is discharged into the reservoir 14 to empty the plating tank 10, then the real plating solution is then introduced from the storage tank via the pipe 1.

In either of said examples, objects to be plated are not limited to printed circuit boards or semiconductor wafers.

Effect of Invention

In accordance with the present invention, it is possible to prevent a change in plating performance after interruption to the plating operation, as a reservoir for storing a replacement plating solution that does not deteriorate a metal ion supply source is installed and at least part of the plating solution is replaced for said replacement plating solution during the interruption of the plating operation.

• • by installing a reservoir to the tank having a metal ion supply source, in the case of plating equipment having an insoluble anode, or by installing a reservoir and a plating solution storage tank to the plating tank, in the case of plating equipment having a soluble anode, it becomes possible to prevent the surface of the anode or other metal ion supply source from deteriorating during the plating operation and also to prevent a possible change in plating properties caused by decomposition of a brightener contained in the plating solution.

Brief Description Of Drawings

[FIG. 1]

This figure outlines the major components when this invention is applied to plating equipment having an insoluble anode.

• • [FIG. 2]

This figure outlines the major components when this invention is applied to plating equipment having a soluble anode.

Key To Drawings

• 4: copper dissolver
• 5: copper ball
• 6, 13: pump with ability for reserved rotation.
• 7, 14: reservoir for replacement solution
• 10: plating tank
• 11: cathode
• 12: anode

Claims

1. A method for preventing deterioration of a plating solution when the operation of the plating equipment is interrupted, comprising the steps of providing a reservoir containing a solution causing no deterioration of the metal ion supply source as a replacement solution, and replacing at least part of the plating solution with said replacement solution when the plating operation is stopped.

2. The method for preventing deterioration of a plating solution according to claim 1, wherein in the plating equipment having an insoluble anode, a tank containing the metal ion supply source is provided with said reservoir, upon completion of the plating operation the entire plating solution is discharged from the tank containing the metal ion supply source, the replacement solution is transferred from the reservoir into the emptied tank containing the metal ion supply source, and when the plating operation is restarted, the replacement solution is returned into the reservoir and the plating solution is thereafter returned into the tank containing the metal ion supply source.

3. The method for preventing deterioration of a plating solution according to claim 1, wherein in the plating equipment having a soluble anode, a plating tank is provided with said reservoir and a plating solution storage tank, upon completion of the plating operation the plating solution is transferred from the plating tank into the plating solution storage tank and the replacement solution is transferred from the reservoir into the emptied plating tank, and when the plating operation is restarted, the replacement solution is returned into the reservoir and the plating solution is thereafter returned into the plating tank.

4. The method for preventing deterioration of a plating solution according to any of claims 1-3, wherein said replacement solution is a plating solution containing no brightener that undergoes a decomposing reaction when the plating operation is stopped.

5. The method for preventing deterioration of a plating solution according to any of claims 1-4, wherein said plating is copper plating.

6. The method for preventing deterioration of a plating solution according to claim 4, wherein said replacement solution is a sulfuric acid solution.