JPH05302199A - Method for controlling composition of copper plating bath in copper plating using insoluble anode - Google Patents

Abstract

PURPOSE:To control the composition of a copper plating bath by equalizing the electrolytic current in a copper ion replenishing tank to that in a plating bath. CONSTITUTION:Copper ion and hydroxide ion are supplied from a copper ion replenishing tank 1 to a copper plating bath 2 in copper plating using an insoluble electrode. The tank 1 is separated by a thin membrane impermeable to copper ion and permselective to hydroxide ion. One compartment of the tank 1 is filled with a copper plating soln., a copper metallic electrode 7 is dipped in the compartment, and electrolysis is carried out between the positive electrode 7 and a negative counter electrode to generate copper ion from the electrode 7. In this case, the electrolytic current in the tank 1 is equalized to that in the plating bath. Consequently, the composition of the copper plating bath is controlled by replenishing a plating bath contg. copper ion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the composition of a copper plating bath by replenishing the copper plating bath with a plating solution containing copper ions in an electrolytic copper plating method using an insoluble anode.

[0002]

2. Description of the Related Art As a copper electroplating method, a method using a soluble anode as an anode and a method using an insoluble anode are known. However, in the case of the soluble anode method using metallic copper as the anode, since the supply of copper ions to the plating bath is performed by the dissolution of the anode metallic copper by the electrolytic reaction on the anode surface, when performing the plating treatment continuously, Since the metal copper is consumed by the melting, it was necessary to periodically replenish and renew the metal copper. In addition, since the shape of the electrode changes with time, the distance between the object to be plated and the anode changes, and the current distribution in the plating tank changes. There was a problem that I could not.

On the other hand, when the insoluble anode is used, the amount of plating adhered does not vary, and highly accurate plating can be performed.
It is necessary to supply copper ions from other than the anode into the plating bath. Generally, as shown in FIG. 3, the copper ion replenishment tank 1 is provided and the plating solution is circulated between the insoluble anode 8 and the plating bath 2 in which the material to be plated 9 is placed, and the replenishment is performed. As a replenishment method, JP-A-56-75590 discloses a method of replenishing copper ions into the plating solution by using cuprous oxide and hydrogen peroxide in combination into the plating solution. However, in such a method, the copper unit price of copper ion supply is higher than that of metallic copper, and in order to keep the plating bath composition constant during the continuous plating treatment, analysis of bath components such as copper ion and pH and chemical There are drawbacks such as the need for weighing and addition, the fact that when undissolved cuprous oxide enters the plating bath, cuprous oxide accumulates on the insoluble anode and causes the plating current to fluctuate, or is involved in plating. there were.

[0004]

In copper plating, when a wire or plate is continuously plated, a plating method using an insoluble anode is effective for obtaining a stable and constant plating thickness over a long period of time. However, in such a plating method, metal ions essentially consumed by the plating must be continuously replenished.

Therefore, an object of the present invention is to use a plating solution having a high copper unit price for supplying copper ions without changing the plating solution composition suitable for plating or conditions such as bath temperature, and further to obtain a plating solution. Another object of the present invention is to provide a method for replenishing copper ions inexpensively and easily without adding a third component, and a method for easily and accurately controlling copper ion concentration and liquid pH.

[0006]

[Means for Solving the Problems] In order to achieve such an object, the inventors of the present invention diligently studied a method of supplying copper ions into a plating bath and a method of controlling the composition of the bath in a copper plating method using an insoluble anode. As a result, it was found that the above object can be achieved by using a replenishment tank having a diaphragm that selectively passes hydroxide ions without passing copper ions as a copper ion replenishment tank under predetermined conditions. The present invention has been completed.

That is, the present invention relates to a method for controlling the composition of a copper plating bath in a copper plating method using an insoluble electrode by supplying copper ions and hydroxide ions from a copper ion replenishing tank. , One side of the copper ion replenishing tank separated by a diaphragm that selectively permeates hydroxide ions without permeating copper ions is filled with a copper plating solution and a copper metal electrode is immersed therein, and the other Is filled with an alkaline aqueous solution and the counter electrode is immersed therein, and the copper metal electrode is electrolyzed so that the counter electrode becomes positive and the counter electrode becomes negative, whereby copper ions are produced from the copper metal electrode. By controlling the electrolytic current in the copper ion replenishing tank and the electrolytic current in the plating bath to be equal,
It is characterized in that the concentration of copper ions and hydroxide ions to be replenished is kept constant.

The above-mentioned diaphragm may be either an inorganic material or an organic material as long as it selectively permeates hydroxide ions without permeating copper ions. For example, an alumina sintered material, an ion exchange membrane or the like is used. be able to. Since the permeation rate of hydroxide ions varies depending on the diaphragm used, the concentration of the alkaline aqueous solution put into one side of the copper ion replenishment tank needs to be changed correspondingly. For example, when the volume ratio of the alkaline aqueous solution and the copper plating solution is 1:10, the alumina sintered material is used as a diaphragm and the pH of the plating bath is
In order to maintain the pH value at an appropriate value (pH 8 to 9), it is preferable to set the initial concentration of the alkaline aqueous solution within the range of 260 to 340 g / l. Further, in order to maintain the pH of the plating bath at an appropriate value by using an anion ion exchange membrane, it is preferable to set the initial concentration of the alkaline aqueous solution within the range of 10 to 65 g / l.

In the present invention, in order to prevent the plating solution from coagulating and precipitating due to the reaction of the plating solution with the permeating alkaline solution on the diaphragm surface of the separation tank containing the plating solution in the copper ion supply tank, It is preferable to stir the solution in the vicinity of the diaphragm surface of the separation tank containing the plating solution so that the electrolysis is performed within a range in which the current density on the diaphragm surface does not exceed a certain value.

In the present invention, the concentration of copper ions is made constant by equalizing the electrolytic current in the copper ion replenishing tank with the electrolytic current in the plating bath. As shown in FIG. 1, a method of electrically connecting a copper ion supply tank and a plating bath in series, and as another method, an electrolytic power supply is installed in each of the copper ion supply tank and the plating bath to supply copper ions. There is a method of controlling the current value of the bath to be the same as the current value of the plating bath.

On the other hand, the pH of the plating solution in the plating bath is such that hydroxide ions consumed in the insoluble anode in the plating bath are generated by electrolysis in a separation tank containing an alkaline solution of a predetermined concentration in advance. Is transferred to the plating bath from the separation tank to replenish and stabilize it. Here, the method of transferring hydroxide ions from the separation tank containing the alkaline aqueous solution to the separation tank containing the copper plating solution is mainly 2
One is a method of transferring all the hydroxide ions generated by electrolysis using the electroosmosis of hydroxide ions or the natural permeation phenomenon of an alkaline aqueous solution through the diaphragm, and specifically, the diaphragm. Is a method using the above-mentioned ion exchange membrane or a sintered material of an inorganic compound. For example, when a copper pyrophosphate plating solution at 50 ° C. is used as the plating solution and an alumina sintered material is used as the diaphragm, and the current density of the current passing through the diaphragm is 1 A / dm ² , electrolysis is performed at 300 g / l.
It is possible to stably replenish copper ions to the plating bath without changing the pH by adding the potassium hydroxide aqueous solution having the concentration of 3 to the separation tank.

In another method, in the diaphragm electrolysis method, the surface of the alkaline aqueous solution in the separation tank is located higher than the surface of the plating solution due to osmotic pressure. By utilizing this phenomenon, the surface of the alkaline aqueous solution becomes higher than a certain value. At this point, a solution is provided in which the solution in the separation tank containing the alkaline aqueous solution overflows into the separation tank containing the plating solution and is transferred. For example, in FIG.
As shown in (3), by providing a hole and a pipe 13 on the upper part of the diaphragm, it is possible to assist the migration of the alkaline aqueous solution.

[0013]

[Function] In the plating method using an insoluble anode, the reaction in the plating bath is performed by the following formula (2) on the cathode surface of the material to be plated and the reduction of copper ions represented by the following formula (1). Oxidation of the indicated hydroxide ions occurs.

[0014]

[Formula 1] Cu ²⁺ + 2e ⁻ → Cu (1) 2OH ⁻ → H ₂ O + 1 / 2O ₂ + 2e ⁻ (2)

That is, in the plating method using an insoluble anode, since copper ions and hydroxide ions in the plating solution are consumed, copper ions and hydroxide ions are continuously replenished for continuous plating treatment. There is a need to.

The control method of the composition of the copper plating solution in the present invention is carried out by applying positive electricity to the copper electrode immersed in the plating solution in one of the separation tanks of the copper ion replenishment tank by the reaction represented by the following formula (3). By supplying a copper ion in the plating solution without electroplating the counter electrode by interposing a film that does not permeate the copper ion between the counter electrode and the counter electrode, the supply to the plating bath is replenished. It makes it possible.

[0017]

[Number 2] ^{Cu → Cu 2+ + 2e - (} 3)

On the counter surface in the separation tank containing the alkaline aqueous solution, hydroxide ions are generated by electrolysis of water represented by the following formula (4).

[0019]

[Equation 3] 2H ₂ O + 2e ⁻ → 2OH ⁻ + H ₂ (4)

The reason why the pH of the plating solution can be controlled in the method of the present invention is as follows. That is,
As shown in FIG. 2, there are cations other than hydroxide ions and copper ions as the components that permeate the inside of the membrane. However, when a membrane that selectively permeates only hydroxide ions is used, an alkaline aqueous solution was introduced. All of the hydroxide ions represented by the above formula (4) generated in the separation tank permeate the diaphragm as an electrically conductive medium and move into the plating solution to replenish the consumption of the hydroxide ions represented by the above formula (2). Therefore, the pH of the replenishment plating solution is stable.

When cations other than copper ions permeate the diaphragm as the conductive medium in the diaphragm, all the hydroxide ions represented by the above formula (4) are contained in the diaphragm. However, since the alkali concentration in one of the separation tanks is higher than that in the separation tank containing the plating solution, the alkaline aqueous solution in the separation tank moves to the plating tank due to natural permeation. The pH can be stabilized. Further, for example, even when the migration amount of the alkaline aqueous solution due to natural permeation due to electrolysis conditions is temporarily small, a shortage of the migration amount of the alkaline aqueous solution is accumulated in the separation tank containing the alkaline aqueous solution, Since the natural permeation rate increases as the alkali concentration increases, the plating solution becomes stable at a certain pH as a result.

As a preferred example of the present invention, the upper limit of the diaphragm current density is set and the plating solution is agitated in the vicinity of the diaphragm surface of the separation tank containing the plating solution because the production of mud-like products is suppressed. This is because. That is, when the diaphragm current density is high and the plating solution agitation on the diaphragm surface is weak, the pH on the diaphragm surface rises and copper hydroxide is produced, which precipitates and solidifies on the diaphragm surface, and the electrolytic voltage rises and the plating solution composition increases. Is to change.

[0023]

EXAMPLES Next, the present invention will be described in detail with reference to its examples. As shown in Fig. 1, the inside of the copper ion supply tank 1 is separated into two parts by the diaphragm 3, and the metal copper electrode specified in JIS H 2121-1961 for copper ion supply is provided in the separation tank 5 on one side. 7 and a counter electrode 6 in the separation tank 4 on the other side.

A plating bath 2 provided with an insoluble anode 8 and an electrode 9 to be plated is provided adjacent to the copper ion replenishing tank 1, and the plating solution is circulated between the replenishing tank 1 and the plating bath 2. I tried to tighten it.

Next, an aqueous solution of potassium hydroxide having a predetermined concentration shown in Table 1 is placed in the separation tank 5 and the other separation tank 4 is placed.
Copper pyrophosphate, potassium pyrophosphate and pyrophosphate were dissolved in water to give a copper ion concentration of 22 g / l, and (pyrophosphate ion concentration) / (copper ion concentration) value of 7.3 and p.
A copper pyrophosphate plating solution adjusted to have an H value of 8.3 was added, and the inside of the tank was heated to 50 ° C. In FIG. 1, 10 is a blower for stirring the plating solution on the diaphragm surface, 11 is an auxiliary tank for circulating the solution between the replenishing tank and the plating bath, and 12 is a pump for circulating the plating solution. Each one is shown.

As shown in FIG. 1, insoluble in the copper metal electrode 7
Make the anode 8 positive and the counter electrode 6 and the plated electrode 9 negative.
Electrical wiring is performed on the copper electrode and the current density of the copper electrode is 2A
/ Dm ², Counter current density 2 to 4 A / dm²Electrolysis experiment at
It was. As a conventional example, batch processing without replenishing copper ions
In addition, a plating experiment using an insoluble anode 8 was also performed.
It was

In this experiment, as the type of the diaphragm, a sintered material of alumina was used in Example 1, and an ion exchange membrane (anion exchange membrane) was used in Example 2. Also, with each example
A 1400 cc copper pyrophosphate plating solution and a 120 cc aqueous solution of potassium hydroxide were placed in each separation tank, and an electrolysis experiment was continuously performed at a diaphragm area of 100 cm ² with a plating current and a copper ion supply electrolytic current of 1 A.

The copper ion concentration of the plating solution in the plating bath 2,
The pH was analyzed and measured over time, and the copper ion concentration and the pH were evaluated as the composition stability of the plating solution. The obtained results are shown in Tables 1 and 2 below.

[0029]

[Table 1]

[0030]

[Table 2]

As is clear from the experimental results shown in Table 1,
In the conventional batch method, after one day, all of the copper ions are consumed and the pH of the plating bath also drops significantly, so that normal plating cannot be performed and the plating bath needs to be renewed. On the other hand, in any of the examples of the present invention, both the copper ion concentration and pH were stable for 4 days, and copper ion replenishment and pH control were sufficiently performed.

Table 2 shows the experimental results on the influence of the diaphragm current density and the plating solution stirring strength on the mud-like product formed on the diaphragm surface. In this experiment, the apparatus shown in FIG. 1 was used, and the above-mentioned copper pyrophosphate plating solution and 200 g / l were used.
Using a potassium hydroxide aqueous solution having a concentration, a predetermined diaphragm current density and plating solution stirring strength were set, and after electrolytic treatment for 24 hours, the diaphragm surface was visually inspected to determine the presence or absence of a mud-like product. The plating solution is agitated by air, and the strength is "weak" with air having a flow rate of 1 l / min per liter of plating solution, and "medium" with a flow rate of 3 l / min.
The stirring "strong" indicates a flow rate of 5 l / min. As is clear from Table 2, the stirring is "strong" and the diaphragm current density is 1.5.
By setting the range not to exceed A / dm ² , it is possible to sufficiently suppress the production of mud-like products. From this result, it can be understood that the electrolysis can be performed at a higher diaphragm current density by increasing the stirring.

[0033]

As described above, according to the present invention,
In a continuous copper plating method using an insoluble anode, by using a copper ion replenishment tank provided with a diaphragm capable of selectively permeating hydroxide ions without permeating copper ions under predetermined conditions, Copper ions can be supplied without using copper ions supplied with a high copper unit price, without changing conditions such as solution composition or bath temperature, and without adding a third component to the plating solution. The ion concentration and pH can be kept stable, which allows
The workability for controlling the plating solution is greatly improved, the productivity is improved, and the quality and productivity are improved by using the insoluble anode, and the practical effect thereof is great.

[Brief description of drawings]

FIG. 1 is a layout diagram showing liquid circulation between a copper ion replenishment tank and a plating bath used in the present invention.

FIG. 2 is a cross-sectional view of an example copper ion replenishment tank used in the present invention.

FIG. 3 is a sectional view of a plating bath used in a conventional plating method using an insoluble anode.

[Explanation of symbols]

1 Copper ion replenishment tank 2 Plating bath 3 Separation membrane 4 Separation tank containing alkaline aqueous solution 5 Separation tank containing replenishment plating solution 6 (in separation tank) Counter electrode 7 Copper metal electrode 8 Insoluble anode 9 Plated material (plated electrode) ) 10 Plating solution stirring blower 11 Plating solution circulation auxiliary tank 12 Plating solution circulation pump 13 Means (pipe) for overflowing the alkaline aqueous solution in the separation tank into the plating solution separation tank

Claims (2)

[Claims] 1. A method for controlling the composition of a copper plating bath in a copper plating method using an insoluble electrode by supplying copper ions and hydroxide ions to the copper plating bath from a copper ion replenishing tank. One side of the copper ion replenishment tank separated by a diaphragm that selectively permeates hydroxide ions without permeation is filled with a copper plating solution and a copper metal electrode is immersed therein, and the other side is alkali A copper ion is generated from the copper metal electrode by electrolyzing it so that the counter electrode is positive and the counter electrode is negative when the counter electrode is filled with an aqueous solution and is immersed therein. By controlling the electrolytic current in the replenishment tank and the electrolytic current in the plating bath to be equal, the concentration of copper ions and hydroxide ions to be replenished is kept constant. Of controlling the composition of the copper plating bath in the copper plating method. 2. The method according to claim 1, wherein an upper limit is set for the diaphragm current density, and the plating solution is stirred in the vicinity of the diaphragm surface of the separation tank containing the plating solution.